meme &a changing world 

Prepared in cooperation with the Mobile Area Water and Sewer System 

Assessment of Water Quality, Benthic 

Invertebrates, and Periphyton in the 

Threemile Creek Basin, Mobile, Alabama, 

1999-2003 

Scientific Investigations Report 2004-5302 

U.S. Deparbnent of the Interior 

U.S. Geological Survey
Cover photograph. Threemile Creek downstream from Stone Street, Mobile, Alabama.
Assessment of Water Quality, Benthic 

Invertebrates, and Periphyton in the 

Threemile Creek Basin, Mobile, Alabama, 

1999–2003

By Ann K. McPherson, Amy C. Gill, and Richard S. Moreland

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the Mobile Area Water and Sewer System

Scientific Investigations Report 2004 – 5302
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2005

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

McPherson, A.K., Gill, A.C., and Moreland, R.S., 2005, Assessment of water quality, benthic invertebrates, and 

periphyton in the Threemile Creek basin, Mobile, Alabama, 1999–2003: U.S. Geological Survey Scientific Investigations 

Report 2004–5302, 153 p.
 iii

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Purpose and Scope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Previous Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Watershed Characteristics of the Threemile Creek Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

Methods of Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Water-Quality Sample Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Benthic Invertebrate and Periphyton Sample Collection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Water-Quality Data Analysis and Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

Quality-Control Methods and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Benthic Invertebrate and Periphyton Data Analysis and Review. . . . . . . . . . . . . . . . . . . . . . .21

Water-Quality Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Basic Water Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Major Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Instantaneous and Continuous Measurements of Water Properties . . . . . . . . . . . . . . . . . . .27

Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

Suspended Chlorophyll a and b . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Biochemical Oxygen Demand and Total Organic Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Fecal-Indicator Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

Organic Wastewater Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

Occurrence and Distribution of Wastewater Indicator Groups . . . . . . . . . . . . . . . . . . . .55

Organic Wastewater Compounds as Endocrine Disruptors . . . . . . . . . . . . . . . . . . . . . . .55

Antioxidants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55

Prescription and Nonprescription Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58

Steroids—Sterols and Stanols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58

Fragrances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

Detergent Metabolites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

Antimicrobials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Plasticizers/Flame Retardants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Insect Repellent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

Insecticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Herbicides and Fungicides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Polycyclic Aromatic Hydrocarbons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61

Comparison of Organic Wastewater Compounds in the Threemile Creek Basin 

to Sites Nationwide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

Benthic Invertebrates Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
iv 

Periphyton Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78

Selected References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80

Figures

1–4. Maps showing:

1. Locations of sampling sites in the Threemile Creek basin, Mobile County, 

Alabama. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Locations of stormwater outfalls, wastewater-treatment plants, sampling 

sites, and profile sites in the Threemile Creek basin, Mobile, Alabama. . . . . . . . . . . 5

 3. Delineations of the Level III and Level IV Ecoregion classifications and 

subbasin boundaries in the Threemile Creek basin, Mobile, Alabama . . . . . . . . . . 11

4. Land-use characteristics in the Threemile Creek basin, Mobile, Alabama. . . . . . . 12

5. Graph showing land use in the Threemile Creek basin, Mobile, Alabama . . . . . . . . . . . . 12

6. Piper trilinear diagram showing major ion composition of surface-water samples 

collected at six sites in the Threemile Creek basin, Mobile, Alabama, 2000–2001 . . . . . 24

7–38. Graphs showing:

7. Gage height, water temperature, specific conductance, dissolved oxygen, 

turbidity, and discharge at U.S. Geological Survey streamgaging stations 

(A) 02471013 (TM-1), (B) 0247101490 (TM-4), and (C) 02471016 (TM-5), 

August 25–September 4, 2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

8. Number of days that continuous water-quality monitors recorded 

concentrations of dissolved oxygen less than 3.0 milligrams per liter at 

three sites on Threemile Creek, Mobile, Alabama, water years 2000–2003 . . . . . . 31

9. Distribution of total nitrogen, nitrite plus nitrate, total ammonia plus organic 

nitrogen, and ammonia concentrations at sites in the Threemile Creek basin, 

Mobile, Alabama . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

10. Median concentrations of nitrite plus nitrate, ammonia, and total organic 

nitrogen at sites in the Threemile Creek Basin, Mobile, Alabama . . . . . . . . . . . . . . 34

11. Distribution of total phosphorus, dissolved phosphorus, and dissolved 

orthophosphate at sites in the Threemile Creek basin, Mobile, Alabama . . . . . . . . 35

12. Median concentrations of suspended phosphorus and dissolved phosphorus 

at sites in the Threemile Creek basin, Mobile, Alabama. . . . . . . . . . . . . . . . . . . . . . . 36

13. Distribution of dissolved inorganic nitrogen and dissolved orthophosphate 

ratios for sites in the Threemile Creek Basin, Mobile, Alabama . . . . . . . . . . . . . . . . 36

14. Concentrations of (A) enterococci, (B) Escherichia coli, and (C) fecal coliform 

concentrations in water samples collected at sites in the Threemile Creek 

basin, Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

15. Concentrations of (A) enterococci, (B) Escherichia coli, and (C) fecal coliform 

concentrations at three sites on Threemile Creek, Mobile, Alabama, 

December 13–15, 2001. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

16. Concentrations of (A) enterococci, (B) Escherichia coli, and (C) fecal coliform 

concentrations at three sites on Threemile Creek, Mobile, Alabama, 

June 24–26, 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

17. Concentrations of (A) enterococci and (B) Escherichia coli concentrations 

at three sites on Threemile Creek, Mobile, Alabama, February 26–28, 2003 . . . . . . 43
 v

18. Concentrations of (A) enterococci, (B) Escherichia coli, and (C) fecal coliform 

concentrations at three sites on Threemile Creek, Mobile, Alabama, 

September 13–16, 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

19. Relation between Escherichia coli and fecal coliform concentrations measured 

at sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003. . . . . . . . . . . . . 45

20. Frequencies of detection for selected organic wastewater compounds in water 

samples from the Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . . 47

21. Summary of organic wastewater compounds detected per sample for (A) total 

concentration (summation of 48 compounds) and (B) number of compounds 

detected. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

22. The 10 most frequently detected organic wastewater compounds at each site 

in the Threemile Creek basin, Mobile, Alabama, 2000–2003. . . . . . . . . . . . . . . . . . . . 53

23. The 10 most frequently detected organic wastewater compounds in the 

Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . . 54

24. Relation between total concentration of organic wastewater compounds and 

total phosphorus, Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . . 54

25. Summary of the types of organic wastewater compounds detected per sample 

for (A) total concentration (summation of 48 compounds) and (B) number of 

compounds detected, Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . 56

26. (A) Frequency of detection of organic wastewater compounds by general-use 

category and (B) percentage of total measured concentration of organic 

wastewater compounds by general-use category, Threemile Creek basin, Mobile, 

Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

27. Frequencies of detection of selected organic wastewater compounds in water 

samples from the the Threemile Creek basin, Mobile, Alabama, and sites 

nationwide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

28. Benthic invertebrate taxa richness at selected sites on Threemile Creek, 

Mobile, Alabama, July 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

29. Relative abundance of major benthic invertebrate taxa at selected sites on 

Threemile Creek, Mobile, Alabama, July 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

30. Average U.S. Environmental Protection Agency national tolerance values for 

benthic invertebrate communities at selected sites on Threemile Creek, 

Mobile, Alabama, July 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

31. Shannon-Weaver diversity index values for benthic invertebrate communities 

at selected sites on Threemile Creek, Mobile, Alabama, July 2000 . . . . . . . . . . . . . 69

32. Benthic chlorophyll a concentrations at selected sites in the Threemile Creek 

basin, Mobile, Alabama, September 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

33. Benthic chlorophyll a concentrations at selected sites in the Threemile Creek 

basin, Mobile, Alabama, 2000–2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

34. Periphyton ash-free dry mass at selected sites in the Threemile Creek basin, 

Mobile, Alabama, September 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

35. Periphyton ash-free dry mass at selected sites on Threemile Creek, 

Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

36. Periphyton taxa richness at selected sites in the Threemile Creek basin, 

Mobile, Alabama, 2000–2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

37. Percentage of diatom taxa richness in each saprobic class for periphyton 

community samples collected from selected sites in the Threemile Creek 

basin, Mobile, Alabama, September 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

38. Percentage of diatom biovolume in each saprobic class for periphyton 

community samples collected from selected sites in the Threemile Creek 

basin, Mobile, Alabama, September 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
vi 

Tables

1. Description of surface-water sites selected for water-quality and biological 

sampling in the Threemile Creek basin, Mobile, Alabama, 2000–2003. . . . . . . . . . . . . . . . . 5

 2. Land–use characteristics in the watersheds of sampling sites in the Threemile 

Creek basin, Mobile, Alabama . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

 3. Rainfall summary for the Mobile Regional Airport and U.S. Geological Survey 

streamgaging station 02471013 (TM-1), Mobile, Alabama . . . . . . . . . . . . . . . . . . . . . . . . . . 10

 4. Population changes (1990–2000) in the watersheds of sampling sites in the 

Threemile Creek basin, Mobile, Alabama . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

 5. Number and type of water-quality, benthic invertebrate, and periphyton samples 

collected at sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . 16

 6. Saprobic categories of diatoms and corresponding dissolved-oxygen 

concentrations and biochemical oxygen demand values . . . . . . . . . . . . . . . . . . . . . . . . . . 23

 7. Results of the Kruskal-Wallis test and the Tukey multiple-comparison test illustrating 

statistically significant (p < 0.05) differences for selected water-quality constituents 

at sites in the Threemile Creek basin, Mobile, Alabama . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

 8. Instantaneous field measurements of water-quality properties at sites in the 

Threemile Creek basin, Mobile, Alabama, 2000–2003, and corresponding 

water-quality criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

 9. Continuous measurements of water-quality properties at sites in the Threemile 

Creek basin, Mobile, Alabama, water years 2000–2003, and corresponding 

water-quality criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

10. Results of multiple-comparison tests on selected nutrients at surface-water 

sites in Threemile Creek basin, Mobile, Alabama. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

11. Ambient water-quality criteria recommendations for rivers and streams in 

Nutrient Ecoregions IX and XII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

12. Statistical summary of enterococci, Escherichia coli, and fecal coliform 

concentrations at sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . 37

13. State and Federal standards and criteria for bacteria in surface water. . . . . . . . . . . . . . 39

14. Exceedance frequencies for fecal-indicator bacteria detected at sites in the 

Threemile Creek basin, Mobile, Alabama, 2000–2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

15. Summary of organic wastewater compounds detected in water samples collected 

in the Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . 48

16. Detection frequencies and concentrations of selected organic wastewater 

compounds in water samples from the Threemile Creek basin, Mobile, 

Alabama (2000–2003) and sites nationwide (1999–2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

17. Five most abundant benthic invertebrate taxa and the respective percentages of 

total abundance for each taxa at selected sites in Threemile Creek, Mobile, 

Alabama, July 2000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

18. North Carolina biotic index values and associated water-quality conditions . . . . . . . . . 68

19. Periphyton chlorophyll a and ash-free dry mass concentrations at selected sites 

in the Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . 70

20. Mean total algal cell density and mean percentage of total algal cell density in 

major algal groups in samples from selected sites in the Threemile Creek basin, 

Mobile, Alabama, 2000–2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

21. Mean total algal biovolume and mean percentage of total algal biovolume in major 

algal groups in samples from selected sites in the Threemile Creek basin, Mobile, 

Alabama, 2000–2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
 vii

Appendix 1. Quality Control

1-1. Concentrations of nutrients, major ions, and selected organic wastewater 

compounds detected in blank samples in the Threemile Creek basin, 

Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Appendix 2. Water-Quality Samples 

2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, 

Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

2-2. Concentrations of selected organic wastewater compounds detected at sites 

in the Threemile Creek basin, Mobile, Alabama, 2000–2003 . . . . . . . . . . . . . . . . . . . . . . . 103

Appendix 3. Benthic Invertebrates and Periphyton

3-1. Benthic invertebrate taxa, percent abundance of each taxon, and total abundance 

at selected sites in Threemile Creek, Mobile, Alabama, July 2000 . . . . . . . . . . . . . . . . . 115

3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected 

sites in the Threemile Creek basin, Mobile, Alabama, 2000–2002 . . . . . . . . . . . . . . . . . . 118
viii 

Conversion Factors, Datum, and Definitions

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Volume

gallon (gal) 3.785 liter (L)

Flow rate

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

WATER-QUALITY DATA are reported in metric units, which can be converted to inch-pound 

units:

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

Area

square meter (m2) 0.0002471 acre 

square centimeter (cm2) 0.001076 square foot (ft2)

Volume

liter (L) 0.2642 gallon (gal)

Mass

gram (g) 0.03527 ounce, avoirdupois
 ix

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 x °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F - 32) / 1.8

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or 

micrograms per liter (μg/L).
x 

Abbreviations and Acronyms

cells/cm2 cells per square centimeter

col/100 mL colonies per 100 milliliters

μm3/cm2 cubic micrometer per square centimeter

g/m2 gram per square meter

μg/cm2 microgram per square centimeter

μm micrometer

mg milligram

ADCP acoustic doppler current profiler

ADEM Alabama Department of Environmental Management

AFDM ash-free dry mass

AHTN 6-acetyl-1,1,2,4,4,7-hexamethyltetraline

ANOVA analysis of variance

APEO alkylphenol polyethoxylate

BHA butylated hydroxyanisole

BHT butylated hydroxytoluene

BOD biochemical oxygen demand

BOD5 5-day biochemical oxygen demand

BU_ID biological unit identification

EPT ephemeroptera, plecoptera, and trichoptera

GIS geographic information system

HHCB 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran

IDAS Invertebrate Data Analysis System

MCL maximum contaminant level

MDL minimum detection limit

MRL minimum reporting level

MRLC multi-resolution land characteristics

NAWQA National Water-Quality Assessment Program

NP nonylphenol

NPEO nonylphenol ethoxylate

NP1EO nonylphenol monoethoxylate

NP2EO nonylphenol diethoxylate

NTU nephelometric turbidity units

NWIS National Water Information System

NWQL National Water Quality Laboratory

OPEO octylphenol ethoxylate

OP1EO octylphenol monoethyoxylate

OP2EO octylphenol diethoxylate

OWC organic wastewater compound

PAH polycyclic aromatic hydrocarbon

RBP Rapid Bioassessment Protocol

TMDL total maximum daily load

TOC total organic carbon

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

WWTP wastewater-treatment plant

WY water year
Assessment of Water Quality, Benthic Invertebrates, 

and Periphyton in the Threemile Creek Basin, 

Mobile, Alabama, 1999–2003

By Ann K. McPherson, Amy C. Gill, and Richard S. Moreland

Abstract

The U.S. Geological Survey conducted a 4-year 

investigation of water quality and aquatic-community structure 

in Threemile Creek, an urban stream that drains residential 

areas in Mobile, Alabama. Water-quality samples were 

collected between March 2000 and September 2003 at four sites 

on Threemile Creek, and between March 2000 and October 

2001 at two tributary sites that drain heavily urbanized areas in 

the watershed. Stream samples were analyzed for major ions, 

nutrients, fecal-indicator bacteria, and selected organic 

wastewater compounds. Continuous measurements of 

dissolved-oxygen concentrations, water temperature, specific 

conductance, and turbidity were recorded at three sites on 

Threemile Creek during 1999–2003. Aquatic-community 

structure was evaluated by conducting one survey of the benthic 

invertebrate community and multiple surveys of the algal 

community (periphyton). Benthic invertebrate samples were 

collected in July 2000 at four sites on Threemile Creek; 

periphyton samples were collected at four sites on Threemile 

Creek and the two tributary sites during 2000–2003. The 

occurrence and distribution of chemical constituents in the 

water column provided an initial assessment of water quality in 

the streams; the structure of the benthic invertebrate and algal 

communities provided an indication of the cumulative effects of 

water quality on the aquatic biota. Information contained in this 

report can be used by planners and resource managers in the 

evaluation of proposed total maximum daily loads and other 

restoration efforts that may be implemented on Threemile 

Creek. 

The three most upstream sites on Threemile Creek had 

similar water chemistry, characterized by a strong calciumbicarbonate component; the most downstream site on 

Threemile Creek was affected by tidal fluctuations and mixing 

from Mobile Bay and had a strong sodium-chloride component. 

The water chemistry at the tributary site on Center Street was 

characterized by a strong sodium-chloride component; the 

water chemistry at the second tributary site, Toulmins Spring 

Branch, was characterized by a strong calcium component 

without a dominant anionic species. The ratios of sodium to 

chloride at the tributary at Center Street were higher than typical 

values for seawater, indicating that sources other than seawater 

(such as leaking or overflowing sewer systems or industrial 

discharge) likely are contributors to the increased levels of 

sodium and chloride. Concentrations of fluoride and boron also 

were elevated at this site, indicating possible anthropogenic 

sources.

Dissolved-oxygen concentrations were not always within 

levels established by the Alabama Department of 

Environmental Management; continuous monitors recorded 

dissolved-oxygen concentrations that were repeatedly less than 

the minimum criterion (3.0 milligrams per liter) at the most 

downstream site on Threemile Creek. Water temperature 

exceeded the recommended criterion (32.2 degrees Celsius) at 

five of six sites in the Threemile Creek basin. The pH values 

were within established criteria (6.0–8.5) at sites on Threemile 

Creek; however, pH values ranged from 7.2 to 10.0 at the 

tributary at Center Street and from 6.6 to 9.9 at Toulmins Spring 

Branch.

Nutrient concentrations in the Threemile Creek basin 

reflect the influences of both land use and the complex 

hydrologic systems in the lower part of the basin. Nitrite-plusnitrate concentrations exceeded U.S. Environmental Protection 

Agency ecoregion nutrient criteria in 88 percent of the samples. 

In 45 percent of the samples, total phosphorus concentrations 

exceeded the U.S. Environmental Protection Agency goal of 

0.1 milligram per liter for preventing nuisance aquatic growth. 

Ratios of nitrogen to phosphorus indicate that both nutrients 

have limiting effects. 

Median concentrations of enterococci and fecal coliform 

bacteria were highest at the two tributary sites and lowest at the 

most upstream site on Threemile Creek. In general, 

concentrations of bacteria increased in a downstream direction 

on Threemile Creek. Enterococci concentrations exceeded 

the U.S. Environmental Protection Agency criterion of 

151 colonies per 100 milliliters of water in 52 percent of the
2 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

samples; Escherichia coli concentrations exceeded the 

U.S. Environmental Protection Agency criterion (576 colonies 

per 100 milliliters) in 41 percent of the samples; and fecal 

coliform concentrations exceeded the Alabama Department of 

Environmental Management criterion (4,000 colonies per 

100 milliliters) in 16 percent of the samples. Concentrations of 

bacteria at two sites on Threemile Creek were elevated during 

high flow rather than low flow, indicating nonpoint sources; 

concentrations of bacteria at the other four sites were elevated 

during low and high flow, indicating both point and nonpoint 

sources. 

Stream samples were analyzed for 48 chemical 

compounds that commonly are found in wastewater and urban 

runoff, which may indicate contamination from a human 

source—37 of these compounds were detected in at least one 

sample. Twelve of the detected compounds are known or 

suspected to be hormonally active, with the potential to disrupt 

endocrine function. Organic wastewater compounds were 

detected in each of the 63 samples collected from the Threemile 

Creek basin. Of the 48 compounds analyzed, 9 wastewaterindicator compounds were detected frequently (50-percent or 

greater detection frequency). The most frequently detected 

compounds were atrazine (herbicide), caffeine (stimulant), 

2-butoxyethanol phosphate (household cleaning agent), 

cholesterol (plant and animal steroid), diazinon (insecticide), 

bromacil (herbicide), triclosan (antimicrobial disinfectant), 

fluoranthene (polycyclic aromatic hydrocarbon), and N,Ndiethyl-m-toluamide (insect repellent commonly known as 

DEET). Steroids, detergent metabolites, plasticizer/flame 

retardants, and prescription/nonprescription drugs contributed 

almost 87 percent of the total measured concentration in all 

samples. 

Benthic invertebrate communities at all but one site on 

Threemile Creek appeared to be impaired based on taxa 

richness, numbers of Ephemeroptera/Plecoptera/Trichoptera 

taxa, and measures of community diversity. When compared to 

the North Carolina biotic index values, however, average 

national pollution-tolerance values indicate very good waterquality condition at the most upstream site and good to fair 

conditions at all other sampling sites.

Algal data indicate that organic and nutrient enrichment 

contributed to occasional nuisance algal growth in the 

Threemile Creek basin. Benthic chlorophyll a occasionally was 

found at concentrations associated with nuisance algal growth. 

Ash-free dry mass, in contrast, did not indicate nuisance algal 

growth at any of the sites, but levels neared the nuisance level 

of 50 grams per square meter at Threemile Creek near Pine 

Grove during August 2003. Taxa richness indicated more 

diverse algal communities at the main-stem sites than at the 

tributary sites, perhaps because of the difference between 

concrete and tile substrates or the colonization period. 

Nitrogen-fixing algae accounted for less than 10 percent of the 

algal biovolume from artificial substrate samples at the mainstem sites, indicating that nitrogen was not a limiting nutrient. 

Nitrogen fixing Amphithrix janthina accounted for 40 to 

45 percent of the algal community data at the tributary at Center 

Street, although water chemistry data indicate that both nitrogen 

and phosphorus were plentiful at the site. 

 Saprobic classifications of periphyton indicated that 

tributary algal communities are subjected to more organic 

enrichment than the main-stem sites. During September 2000,

β-saprobic and α-mesosaprobic diatoms were more common 

than oligosaprobic diatoms at all sites, indicating the occurrence 

of organic enrichment. At the tributary sites, however, 

oligosaprobic diatoms were not present, indicating lower 

dissolved-oxygen concentrations and higher biochemical 

oxygen demand, in contrast to measured water chemistry at the 

two sites. The discrepancy between algal and water chemistry 

data may be due to the diel cycle of dissolved-oxygen 

concentrations induced by actively photosynthesizing 

organisms. 

The results of this investigation provide a detailed survey 

of water-quality conditions in Threemile Creek for the 4-year 

period during October 1999 to September 2003. The water 

quality and aquatic-community structure in Threemile Creek 

are degraded, with degradation increasing in a downstream 

direction and most intense at the tributaries draining into 

Threemile Creek. The degree of degradation may be related to 

point and nonpoint sources of contamination originating within 

the basins. The results also have long-range watershedmanagement implications, demonstrating the association 

between urban development and stream degradation. 

Introduction

Mobile, the third most populated city in Alabama, is 

located in Mobile County in the southwestern part of the State 

(fig. 1). In 2000, the city had a population of about 200,000 and 

encompassed over 159 square miles (mi2; U.S. Census Bureau, 

2004). The opening of the Tennessee-Tombigbee Waterway in 

1985 connected the port of Mobile with the Appalachian 

coalfields and Midwest grain fields, making the city the seaport 

for the second largest river system in the Nation. In 2002, the 

port of Mobile was ranked the 17th largest port in the United 

States (U.S. Army Corps of Engineers, 2003). Major industries 

located in the Mobile area include manufacturing of paper and 

paper products, chemicals and textiles, lumber products, 

shipbuilding, and seafood processing. Over 500 oil and gas 

wells operate at inland sites, and offshore drilling tests indicate 

that extensive gas fields also lie beneath Mobile Bay and in the 

Gulf of Mexico (Mobile Area Chamber of Commerce, 2004). 

Major crops grown in Mobile County include peanuts, cotton, 

corn, hay, nursery products, pecans, potatoes, and watermelon 

(Vanderberry and Placke, 2003; Mobile Area Chamber of 

Commerce, 2004). In 2002, Mobile County ranked second in 

the State of Alabama for pecan production and seventh for milk 

production (Vanderberry and Placke, 2003). 

Threemile Creek is located entirely within the city of 

Mobile, Alabama, and extends approximately 15 miles (mi) 

upstream from its confluence with the Mobile River (fig. 1; 
Introduction 3

U.S. Army Corps of Engineers, 1985). The Alabama 

Department of Environmental Management (ADEM) has 

classified Threemile Creek as impaired due to organic 

enrichment and low dissolved-oxygen concentrations, leading 

to poor water-quality conditions (Alabama Department of 

Environmental Management, 2000a, 2002). Stream 

channelization and removal of riparian vegetation have altered 

the aquatic habitat by changing the natural flows and 

temperatures in the creek and altering streambed 

characteristics. Two segments of Threemile Creek have been 

listed on the 303(d) list of impaired waters (Alabama 

Department of Environmental Management, 2000a, 2002). 

Municipal collection system failure, highway/road/bridge 

construction, and land development have been reported by the 

ADEM as sources of contamination that degrade water quality, 

habitat, and biological communities in the 13.5-mi segment of 

Threemile Creek between its source and the Illinois Central 

Gulf Railroad bridge at Interstate 165, 1.5 mi upstream from its 

confluence with the Mobile River. In March 2000, the Alabama 

Department of Public Health issued a fish consumption 

advisory for the 0.5-mi segment of Threemile Creek upstream 

from U.S. Highway 43 advising “limited consumption” of 

striped bass and speckled trout and “no consumption” of 

Atlantic croaker because of elevated levels of chlordane in fish 

tissue.

In accordance with a 1998 judicial consent decree, the 

ADEM is required to establish total maximum daily loads 

(TMDLs) for waterbody segments in Alabama that are listed on 

the 1996 Clean Water Act Section 303(d) list of impaired 

waters. TMDLs are the maximum amounts of pollutants that a 

waterbody can assimilate without exceeding water-quality 

standards. Once the TMDL of a pollutant has been established 

for a stream of interest, the TMDL is allocated among the point 

and nonpoint dischargers to the stream. A water-quality model 

can then be developed to predict the pollutant loading effects on 

the stream by incorporating physical and chemical processes 

with the hydrodynamics associated with the stream. Such a 

water-quality model can be used as a tool to evaluate the 

effectiveness of TMDL management strategies; however, 

before the effectiveness of the proposed TMDL management 

Figure 1. Locations of sampling sites in the Threemile Creek basin, Mobile County, Alabama.
4 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

strategies or restoration efforts can be assessed, sufficient 

water-quality, aquatic-habitat, and biological community data 

are needed to define current conditions in Threemile Creek. 

The U.S. Geological Survey (USGS), in cooperation with 

the Mobile Area Water and Sewer System, conducted an 

investigation designed to characterize the hydrologic and waterquality conditions of Threemile Creek. The objectives of this 

investigation are to (1) conduct a structured scientific 

assessment of the chemical, biological, and physical properties 

characterizing water-quality and aquatic-ecosystem conditions 

in the Threemile Creek basin; (2) identify land-use activities 

that may serve as sources of contaminants; and (3) determine 

the cumulative effects of water quality on the benthic 

invertebrate and algal community health and structure. This 

report describes the water-quality and aquatic-community 

characterization of Threemile Creek, based on data collected 

during water years (WY)1 2000–2003. 

Assessing water quality at varying temporal and spatial 

scales and understanding the effects of urbanization on stream 

ecosystems is one of the priorities of the USGS National WaterQuality Assessment (NAWQA) Program. The NAWQA 

Program was designed to evaluate water-quality conditions and 

factors affecting water quality on a national and regional basis. 

The results of this study when combined with other NAWQA 

studies from across the Nation will provide local resource 

managers and interested partners with a better understanding of 

how aquatic ecosystems respond to land-use changes associated 

with urbanization and how these responses vary across a range 

of environmental settings.

Purpose and Scope

The purpose of this report is to present the results of a 

4-year study that assessed water-quality conditions based on 

water chemistry and aquatic-community structure at Threemile 

Creek, an urban stream draining parts of Mobile, Alabama. The 

natural and anthropogenic characteristics of watersheds in the 

study area are described, including the major land-use types. 

Water quality is described for a range of flow conditions, and 

the extent to which water quality is influenced by point sources 

during low flow and nonpoint sources during high flow is 

discussed for nutrients, bacteria, and organic chemicals that are 

wastewater indicators. The structures of the benthic 

invertebrate and algal communities are compared among sites 

sampled in the watersheds. During this investigation, waterquality and ecological data were examined in an upstream to 

downstream order to identify spatial differences in water 

quality on Threemile Creek. Statistical and graphical analyses 

of selected land-use, chemical, and biological data were used to 

provide a general assessment of current (2000–2003) conditions 

at the selected stream sites. 

The USGS monitored water levels, streamflow, dissolvedoxygen concentrations, specific conductance, and turbidity at 

three sites on Threemile Creek that were equipped with 

continuous water-quality monitors for a 46–49 month period. 

Stream water-quality data, including major ions, nutrients, 

selected organic wastewater compounds (OWC), and fecal 

bacteria, were collected from March 2000 through September 

2003 at various times. Water-quality samples were collected at 

four sites on Threemile Creek during the entire period; waterquality samples at the two tributaries were collected during the 

first year (March 2000–2001), with one additional sample 

collected in October 2001. Aquatic-community structure was 

evaluated by conducting one survey of the benthic invertebrate 

community (July 2000) at four sites in Threemile Creek and 

several surveys of the algal communities at six sites in the 

Threemile Creek basin (2000–2003). Information contained in 

this report can be used by planners and resource managers to 

evaluate the effectiveness of proposed TMDLs and future 

restoration efforts.

Study Area

Threemile Creek extends approximately 15 mi upstream 

from its confluence with the Mobile River to its headwaters 

(figs. 1, 2; U.S. Army Corps of Engineers, 1985). During the 

initial phase of the study (June through September 1999), a field 

reconnaissance was conducted to select representative sampling 

sites in the watersheds (figs. 1, 2; table 1). Several factors were 

considered in selecting the sites, including accessibility, stream 

hydraulics (tidal influences), and land-use characteristics in 

each watershed (table 2). Five sampling sites were identified on 

Threemile Creek (TM-1, TM-2, TM-3, TM-4, and TM-5); two 

additional sites (CEN and TSB) were selected on tributaries 

draining to Threemile Creek (figs. 1, 2). Water-quality samples 

were collected at all sites except TM-2 at varying frequencies 

during 2000–2003; benthic invertebrate samples were collected 

at TM-1, TM-2, TM-3, and TM-4 in July 2000; algal samples 

were collected at all sites except TM-5 during 2000–2003. 

Continuous monitors were installed at three of the sites (TM-1, 

TM-4, and TM-5); specific conductance, water temperature, 

and dissolved-oxygen profiles were measured at four locations 

between TM-4 and TM-5 (fig. 2). 

Although land use throughout the Threemile Creek basin 

is predominantly residential, industrial and wastewatertreatment plant (WWTP) discharges are present in the lower 

reaches of the creek between TM-4 and TM-5 (fig. 2). The 

Mobile Area Water and Sewer System supplied geographic 

information system (GIS) coverages of stormwater outfall 

locations in the Threemile Creek basin (fig. 2). Aging sewer 

lines that sometimes overflow during storms also are present in 

sections of the Threemile Creek basin. Because of flooding 

caused by low gradients and tropical storms, most of Threemile 

1 A water year is defined as the period October 1 to September 30 and is identified by the year in which the period ends.
Introduction 5

Table 1. Description of surface-water sites selected for water-quality and biological sampling in the Threemile Creek basin, Mobile, 

Alabama, 2000– 2003.

[USGS, U.S. Geological Survey; mi2, square mile; —, none]

Site 

label 

(fig. 1)

USGS station 

numbera

a

 USGS station number is based on geographic location and the downstream order of streamflow.

Station name

Site location Drainage 

area 

(mi2

)

Period of continuous record

Latitude Longitude Streamflow Water quality

TM-1 02471013 Threemile Creek at Ziegler 

Boulevard at Spring Hill

30° 42'22'' 88° 09'04'' 10.4 1999 – 2003 1999 – 2003

TM-2 0247101325 Threemile Creek near Pine Grove 30° 42'23'' 88° 07'48'' 12.0 — —

TM-3 0247101475 Threemile Creek at Fillingim 

Street at Mobile

30° 42'28'' 88° 06'04'' 17.3 — —

TM-4 0247101490 Threemile Creek at Stanton Road 

at Mobile

30° 41'48'' 88° 05'17'' 19.2 1999 – 2003 1999 – 2003

CEN 0247101495 Unnamed Tributary to Threemile 

Creek at Center Street at Mobile

30° 41'47'' 88° 04'38'' 1.078 — —

TSB 0247101550 Toulmins Spring Branch at 

Graham Avenue at Mobile

30° 43'32'' 88° 05'33'' 0.618 — —

TM-5 02471016 Threemile Creek at U.S. Highway 

43 near Prichard

30° 43'27'' 88° 03'32'' 28.1 1999 – 2003 1999 – 2003

Figure 2. Locations of stormwater outfalls, wastewater-treatment plants, sampling sites, and profile sites in the Threemile Creek basin,

Mobile, Alabama.
6 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Creek and its tributaries have undergone stream-channel 

modifications to alleviate flooding and stabilize the channels 

(Federal Emergency Management Agency, 1998). 

The most upstream site (TM-1) at USGS streamgaging 

station 02471013 (table 1) is located at Zeigler Boulevard, 

9.4 mi upstream from the Mobile River (fig. 2). This site is 

located directly downstream from Municipal Lake (fig. 2). The 

altitude at TM-1 is 

approximately 72 feet 

(ft) above the National 

Geodetic Vertical Datum 

of 1929 (NGVD 29); 

downstream from TM-1, 

a series of drop 

structures (weirs) have 

been installed to 

decrease the effects of 

flooding in residential 

and commercial areas. 

These weirs are placed at 

periodic intervals along 

the next 5 mi of 

Threemile Creek. The 

next downstream site 

(TM-2) at USGS 

streamgaging station 

0247101325 (table 1) 

was used only for 

biological sampling and 

is located approximately 

1.7 mi downstream from 

TM-1 (fig. 2). USGS 

streamgaging station 

0247101475 (TM-3) is 

located at Fillingim 

Street, approximately 4.1 mi downstream from TM-1 (5.3 mi 

upstream from the Mobile River; U.S. Army Corps of 

Engineers, 1985). The tidal cycle does not affect sites upstream 

from the last weir below Fillingim Street; however, the tidal 

cycle does affect sites downstream, including site TM-4 at 

USGS streamgaging station 0247101490 (table 1) located at 

Stanton Road, about 1.3 mi downstream from TM-3 (4.0 mi 

upstream from the Mobile River). 

Water-quality samples could not be collected safely during 

high flow at TM-4; therefore, samples were collected at TM-3 

when Threemile Creek was too deep to wade at TM-4. 

Approximately 1 mi downstream from TM-4, Threemile Creek 

flows down a straight channel through forested wetlands. The 

creek meanders throughout the wetlands and discharges into the 

constructed channel at Conception Street, 1.8 mi upstream from 

the Mobile River (fig. 2). From Conception Street, Threemile 

Creek meanders freely for 0.8 mi to site TM-5 at USGS 

streamgaging station 02471016 (table 1), located at U.S. 

Highway 43 (fig. 2). At TM-5, Threemile Creek is a wide, 

tidally influenced channel approximately 1 mi upstream from 

the Mobile River. 

Water-quality samples were collected at two tributary 

sites—Toulmins Spring Branch (TSB) and an unnamed 

tributary to Threemile Creek at Center Street (CEN). The 

unnamed tributary at Center Street flows into Threemile Creek 

3.3 mi upstream from the Mobile River and about 0.6 mi 

downstream from TM-4. Toulmins Spring Branch flows into 

Threemile Creek 1.9 mi upstream from the Mobile River and 

about 2.1 mi downstream from TM-4. The 12.8-million gallons 

per day (Mgal/d) Wright Smith, Jr., Wastewater Treatment 

Plant operated by the Mobile Area Water and Sewer System, is 

located near the confluence of Toulmins Spring Branch and 

Threemile Creek. The Carlos A. Morris Wastewater Treatment 

Plant, a 4.0-Mgal/d WWTP operated by the City of Prichard, is 

located about a mile away; discharge from this WWTP enters 

Table 2. Land-use characteristics in the watersheds of sampling sites in the Threemile Creek basin, Mobile, Alabama.

[Data from the 1992 Multi-Resolution Land Characteristics coverage (U.S. Environmental Protection Agency, 1992)]

Site 

label 

(fig. 1)

Land use, in percentage of basin

Grasses

and

agriculture

Forest

Urban land-use categories

Total 

urban 

(computed)

Wetlands Open

water Transitional Commercial,

industrial, and

transportation

Residential

TM-1 25.1 35.8 1.7 33.9 35.6 2.2 0.6 0.7

TM-2 23.6 36.3 1.8 33.3 35.1 3.9 0.5 0.6

TM-3 20.9 32.0 5.2 30.8 36.0 9.7 0.4 1.0

TM-4 20.2 30.8 5.7 33.4 39.1 8.7 0.4 0.9

CEN 7.8 22.5 1.5 68.0 69.5 0 0 0.2

TSB 9.0 12.4 6.6 71.7 78.3 0.2 0 0.1

TM-5 16.9 25.6 6.7 40.5 47.2 9.0 0.4 0.8

USGS streamgaging station 02471013, site TM-1, 

Threemile Creek at Ziegler Boulevard at Spring 

Hill and Municipal Lake
Introduction 7

Site TM-4, Threemile Creek at Stanton Road 

at Mobile

Samples were collected downstream from site CEN, 

unnamed tributary to Threemile Creek at Center Street at Mobile

Site TSB, Toulmins Spring Branch 

at Graham Avenue at Mobile
8 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Threemile Creek near Interstate 165 (fig. 2). Although the 

Threemile Creek watershed extends to the Mobile River (fig. 1), 

the Threemile Creek study area is defined as the area upstream 

from TM-5, the most downstream sampling site.

Previous Investigations

Little information has been published on the water quality 

of Threemile Creek. Every other year, the ADEM provides a 

305(b) report to Congress on the water quality of rivers, 

streams, lakes, and ground water in Alabama. In the most recent 

reports, the ADEM indicated that Threemile Creek was 

nonsupportive of its agricultural and industrial water-supply 

classification because of organic enrichment, low dissolvedoxygen concentrations, and elevated chlordane levels (Alabama 

Department of Environmental Management, 2000a, 2002). 

In May 2003, a report was prepared summarizing available 

data pertaining to water chemistry, point-source discharges, 

meteorological, and bathymetry information in the Threemile 

Creek watershed (Tetra Tech, Inc., 2003a). Another report 

presented a dynamic watershed model, a dynamic instream 

hydraulic model, and an instream kinetic water-quality model in 

support of the development of a TMDL for the impaired 

segments of Threemile Creek (Tetra Tech, Inc., 2003b). A draft 

TMDL for the impaired segments of Threemile Creek was 

presented in October 2003 (Alabama Department of 

Environmental Management and Tetra Tech, Inc., 2003). 

Numerous scientific studies have been conducted to 

investigate environmental factors that influence the streams in 

Mobile County. Maps and reports have been published 

describing the hydrology, geologic structure, stratigraphy, 

geohydrology, and lithology of the Mobile County area (Reed, 

1971; Reed and McCain, 1972; Riccio and others, 1973; Hinkle, 

1984; Mooty, 1988; Szabo and Copeland, 1988; and Moore, 

1998). Information concerning the hydrogeology, 

characteristics of major aquifers, and public supply wells in 

Mobile County and neighboring Baldwin County is 

documented in a report by Gillett and others, 2000. Detailed 

descriptions of the geographic setting in the Mobile River 

Basin, including physiography, geology, soils, climate, 

hydrology, and ecoregions, are included in a report by Johnson 

and others (2002). 

In 1991, Congress appropriated funds for the USGS to 

begin the NAWQA Program, which is an ongoing assessment 

of water-quality conditions in the Nation’s surface- and groundwater resources, and the effects of land use on these resources. 

One component of the program is to determine the effects of 

urbanization on stream-water quality and ecosystem health. 

Results of NAWQA studies for selected river basins throughout 

the United States have been summarized in national synthesis 

reports, including descriptions of the occurrence of pesticides 

(Gilliom and others, 1999; Larson and others, 1999; Hoffman 

and others, 2000; Hopkins and others, 2000) and nutrients in 

surface- and ground-water resources (Puckett, 1994; Mueller 

and others, 1995; Mueller and Helsel, 1996; Fuhrer and others, 

1999; Clark and others, 2000). Strong correlations have been 

identified between the degree of urbanization in a watershed 

and the extent of biological impairment (McMahon and 

Cuffney, 2000). The following paragraphs briefly summarize 

the complex relation between urbanization and aquaticcommunity structure.

The distribution of benthic invertebrates and algae in 

surface water is influenced by natural and human factors that 

affect water quality and habitat. Activities related to 

urbanization can modify watershed characteristics and 

influence patterns of runoff into streams. Several studies 

document the disruptive effects of urbanization on stream 

hydrology and ecology (Booth, 1990; Richards and Host, 1994; 

Finkenbine and others, 2000; Wang and others, 2000; Paul and 

Meyer, 2001). Walsh and others (2001) have shown that the 

composition of benthic invertebrate communities is a sensitive 

indicator of urban effects, and that urban density appears to be 

a key factor in the degradation of benthic invertebrate 

communities.

Urbanization can result in increased loadings of nutrients, 

pesticides, heavy metals, and other contaminants to stream 

water and bed sediment. Such contaminants can have 

substantial detrimental effects on invertebrate communities 

(Wang and others, 2000). Walsh and others (2001) studied 

urban streams with severely degraded benthic invertebrate 

communities and speculated that the transport of contaminants 

into receiving streams by stormwater drainage was a causative 

factor. 

An increase in the amount of impervious area in an urban 

environment may cause sudden changes in flow and rapid 

fluctuations of water levels, which can lead to reduced 

biodiversity. For example, increased stream velocity during 

peak flow can alter or destroy habitat that normally provides 

resources and shelter for aquatic organisms (Finkenbine and 

others, 2000). Likewise, frequent and intense flooding can 

interfere with the life-cycle activities of aquatic organisms 

(Booth, 1990). Low base flow also can be detrimental to aquatic 

communities. As urbanization increases, the amount of area 

available for ground-water recharge decreases, resulting in low 

base flow (Finkenbine and others, 2000) and subsequent 

interference with aquatic organism life cycles. 

Construction activities and removal of riparian vegetation 

adversely affect stream biota by increasing the sediment load in 

streams (Waters, 1995). As sediment in the water column settles 

to the bottom, it fills interstitial spaces and may prevent the 

attachment of primary producers, such as intolerant algal taxa, 

leading to a reduction in species richness. The negative effects 

of sediment on stream biota can persist for years (Richards and 

Host, 1994). Alternatively, removal of riparian plants can lead 

to an increase in the amount of sunlight that reaches a stream, 

thereby improving conditions for the growth of algae and 

aquatic plants. 
Watershed Characteristics of the Threemile Creek Basin 9

Acknowledgments

The authors gratefully acknowledge the contributions of 

Mark R. Dickman, hydrologist with the USGS in Tampa, 

Florida, who served as project chief for this investigation from 

1999–2003, and Susan L. Hartley, hydrologic technician with 

the USGS in Norcross, Georgia, who maintained the continuous 

water-quality monitors and organized many of the sampling 

trips. The authors also thank Brett McKinley, GIS technician 

with the Mobile Area Water and Sewer System, who assisted in 

collecting rainfall data; Jeffrey L. Corbett, Kay E. Hedrick, and 

Rebecca J. Deckard, with the USGS in Raleigh, North Carolina, 

who assisted in illustrating and editing this report; and Carolyn 

J. Oblinger, Douglas A. Harned, and Thomas F. Cuffney with 

the USGS in Raleigh, North Carolina; Kurt D. Carpenter with 

the USGS in Portland, Oregon; and Joseph F. Connell, 

hydrologist with the USGS in Knoxville, Tennessee, for their 

technical reviews and assistance during the preparation of this 

report. The authors thank all of the USGS personnel who 

assisted with fieldwork and data collection.

Watershed Characteristics of the 

Threemile Creek Basin

Mobile has a subtropical climate, with hot, humid 

summers and mild winters. Monthly mean temperatures range 

from 50.1 degrees Fahrenheit (°F) in January to 81.5 °F in July 

(Southeast Regional Climate Center, 2004a). The mean annual 

precipitation in the Mobile area for the 30-year period (1971–

2000) is 66.29 inches per year (in/yr), ranging from 45.74 in/yr 

in 2000 (table 3) to 86.58 in/yr in 1975 (Southeast Regional 

Climate Center, 2004a, 2004b). Mean monthly rainfall averages 

are fairly well distributed throughout the year (table 3; 

Southeast Regional Climate Center, 2004a). Most of the rainfall 

during the summer is from scattered afternoon and evening 

thunderstorms; during the winter and spring, rainfall tends to be 

of longer duration and associated with frontal systems. 

Snowfall is extremely rare. Tropical systems that enter the Gulf 

of Mexico and move inland in late summer and early fall can 

produce intense rainfall. October generally is the driest month 

of the year; March, July, and August generally are the wettest 

months (Southeast Regional Climate Center, 2004a). 

During the study period, recorded precipitation at the 

Mobile Regional Airport was less than the 30-year mean in 

2000 (45.74 in/yr) and 2001 (54.44 in/yr) and greater than the 

30-year mean in 2002 (72.48 in/yr) and 2003 (70.93 in/yr, 

table 3; Southeast Regional Climate Center, 2004b; National 

Weather Service Forecast Office, 2004a, 2004b). The 

differences between rainfall totals recorded at TM-1 and the 

Mobile Regional Airport illustrate how variable rainfall can be 

in the Mobile area (table 3). TM-1 is located only about 8 mi 

from the Mobile Regional Airport. 

The Threemile Creek basin is located in the East Gulf 

Coastal Plain section of the Coastal Plain physiographic 

province (Sapp and Emplaincourt, 1975; Johnson and others, 

2002). Altitudes in the Threemile Creek basin range from sea 

level at the coast to approximately 230 ft above NGVD 29 in the 

western part of the basin (U.S. Geological Survey, 1953, 1982). 

Relief is greatest in the upper reaches of Threemile Creek and 

diminishes as the creek meanders through Mobile to its 

confluence with the Mobile River. Altitude in the flood plain in 

Mobile ranges from 5 to 30 ft above NGVD 29 (Robinson and 

others, 1956); the altitude at TM-1 is approximately 72 ft above 

NGVD 29. A series of flat-topped hills rise west of the flood 

plain (Robinson and others, 1956). Geologic formations of the 

basin are predominantly the Pleistocene and Holocene Series 

overlying the Miocene Series undifferentiated (Reed, 1971). 

Major soil associations were surveyed in Mobile County 

by the U.S. Department of Agriculture, Soil Conservation 

Service (Hickman and Owens, 1980). The Urban LandSmithton-Benndale (89.3 percent) and the Dorovan-JohnstonLevy (8.0 percent) are the predominant soil associations in the 

Threemile Creek watershed (Hickman and Owens, 1980; U.S. 

Department of Agriculture, 1995). The Urban Land-SmithtonBenndale Association contains gently rolling land areas that are 

intermingled with poorly drained and well-drained soils that 

have loamy subsoils and are formed in loamy marine and fluvial 

sediments on uplands (Hickman and Owens, 1980). The 

Dorovan-Johnston-Levy Association is found predominantly in 

the lower reaches surrounding Threemile Creek and contains 

very poorly drained, mucky and loamy soils that have been 

formed in thick deposits of organic residues and alluvial 

sediments on bottomlands (Hickman and Owens, 1980). 

The Threemile Creek basin is located in the Southeastern 

Plains Level III Ecoregion and the Southern Coastal Plain Level 

III Ecoregion (fig. 3; Omernik, 1987). Ecoregions are 

characterized by their distinctive vegetative patterns, which are 

a result of soil type, climate, rainfall, and human activities. The 

principal land use in the Southeastern Plains Ecoregion is 

cropland, pasture, woodland, and forest. Woodland and forests 

are characterized by longleaf pine, with smaller areas of oakhickory-pine and southern mixed forest. The Southern Coastal 

Plain Ecoregion consists mostly of flat plains, including barrier 

islands, coastal lagoons, marshes, and swampy lowlands along 

the Gulf Coast. This ecoregion is lower in elevation, with less 

relief and wetter soils than the Southeastern Plains (Omernik, 

1987). Land cover in the Southern Coastal Plain is dominated 

by slash and loblolly pine with oak-gum-cypress forest in some 

low-lying areas. 

The six Level III Ecoregions that have been identified in 

Alabama were recently divided into 29 Level IV Ecoregions, 

illustrating the enormous ecological and biological diversity in 

the State (Griffith and others, 2001). The Threemile Creek 

watershed is located in three Level IV Ecoregions: (1) Gulf 

Coast Flatwoods, (2) Gulf Barrier Islands and Coastal Marshes, 

and (3) Southern Pine Plains and Hills (fig. 3). The Gulf Coast 

Flatwoods and the Gulf Barrier Islands and Coastal Marshes are 

subgroups of the Southern Coastal Plain Level III Ecoregion; 
Table 3. Rainfall summary for the Mobile Regional Airport and U.S. Geological Survey streamgaging station 02471013 (TM-1), Mobile, Alabama.

[—, no data]

Site label 

(fig. 1) Year

Monthly rainfall total, inches 

January February March April May June July August September October November 

Mobile Airport 2000 2.67 1.3 6.94 2.43 2.38 3.21 3.9 3.67 3.43 0.47 11.54 TM-1 2000 2.17 1.11 7.82 1.66 1.63 6.54 2.81 2.49 5.86 1.22 11.59 Mobile Airport 2001 4.08 2.7 11.04 0.88 1.52 5.99 8.55 9.49 2.59 3.53 1.24 TM-1 2001 3.87 2.25 9.24 4.87 0.98 7.85 12.59 10.28 5.94 3.26 1.30 Mobile Airport 2002 3.52 2.87 6.08 1.74 4.45 4.24 9.38 5.02 12.94 8.35 4.92 TM-1 2002 4.02 2.86 5.34 1.53 4.09 3.57 6.18 1.81 14.83 7.06 3.26 Mobile Airport 2003 0.55 5.57 4.3 3.59 9.51 20.66 9.48 5.17 1.57 3.04 3.7 TM-1 2003 0.37 5.93 4.89 3.96 8.23 18.18 8.81 7.04 1.83 — — Mean monthly 

normal Mobile Airport

1971–2000

5.75 5.1 7.2 5.06 6.1 5.01 6.54 6.2 6.01 3.25 5.41 
Watershed Characteristics of the Threemile Creek Basin 11

the Southern Pine Plains and Hills is a subgroup of the 

Southeastern Plains Level III Ecoregion (fig. 3). 

Land Use 

Land use in the study area is characterized by forested and 

agricultural land interspersed with extensive areas of 

urbanization that include mostly residential and commercial 

activities (table 2). These land uses can be sources of both pointand nonpoint-source pollution, which can affect water quality 

and habitat in the streams. Fertilizers and pesticides applied in 

residential and commercial areas can wash into streams during 

storms or infiltrate the soil and enter the ground water, which 

ultimately discharges to streams. Storm runoff from parking 

lots and roadways can contribute trace elements and organic 

compounds from diesel fuel, gasoline, motor oils, and hydraulic 

fluid. Heavily commercialized or industrialized areas can 

contribute trace metals, motor oils, polycyclic aromatic 

hydrocarbons (PAHs), solvents, bacteria, and nutrients either 

by direct discharge into the stream (point source) or by storm 

runoff (nonpoint source). Elevated levels of bacteria, ammonia, 

detergents, and by-products of human waste can enter streams 

by sewer overflows during storms, or by leaky sewer lines 

during dry or wet periods. Municipal discharges of treated 

wastewater also can be sources of bacteria, nutrients, and 

biochemical oxygen demand (BOD) to streams. 

The 1992 multi-resolution land characteristics (MRLC) 

map was used to quantify land-use characteristics in selected 

basins of Threemile Creek (figs. 4, 5; U.S. Environmental 

Protection Agency, 1992). The MRLC is a digital coverage 

(30-meter resolution) of Landsat satellite imagery of major land 

use and land. Commercial land use includes the sum of the 

commercial, industrial, and transportation categories; 

residential land use includes high- and low-intensity residential 

categories. Forested land use includes the sum of the deciduous, 

evergreen, and mixed-forest categories in the MRLC; grasses 

and agricultural is the sum of the pasture, hay, other grasses, and 

row crop categories; and wetlands is the sum of the woody 

wetlands and the emergent herbaceous wetlands. Total urban 

land use is considered to be the sum of the commercial, 

Figure 3. Delineations of the Level III and Level IV Ecoregion classifications and subbasin boundaries in the Threemile Creek basin, 

Mobile, Alabama (Omernik, 1987; Griffith and others, 2001).
12 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 4. Land-use characteristics in the Threemile Creek basin, Mobile, Alabama (U.S. Environmental Protection Agency, 1992).

Figure 5. Land use in the Threemile Creek basin, Mobile, Alabama (U.S. Environmental Protection 

Agency, 1992).
Watershed Characteristics of the Threemile Creek Basin 13

industrial, transportation, and high- and low-intensity 

residential land-use categories in the MRLC coverage (table 2). 

Urbanization accounts for about 36 percent of the land use 

in the Threemile Creek basin at TM-1 and about 47 percent of 

the land use at TM-5 (fig. 5; table 2). The two tributary basins 

(CEN and TSB) are more heavily urbanized than the Threemile 

Creek subbasins. Urbanization accounts for about 70 percent of 

the land use at CEN and about 78 percent of the land use at TSB 

(fig. 5; table 2). Residential land use represents about 95 percent 

of the urbanization at TM-1 and about 85 percent of the 

urbanization at TM-3, TM-4, and TM-5. Residential land use 

represents 98 percent of the urbanization at CEN and 92 percent 

of the urbanization at TSB (table 2). Forested land accounts for 

about 36 percent of the Threemile Creek basin at TM-1 and 

26 percent of the basin at TM-5; grasses and agricultural land 

account for about 25 percent of the basin at TM-1 and 

17 percent of the basin at TM-5. Wetlands cover about 2 percent 

of the basin at TM-1 and about 9–10 percent of the basins at 

TM-3, TM-4, and TM-5 (table 2). The percentage of grasses, 

agricultural, and forested land in the two tributary basins is less 

than in the Threemile Creek basins (table 2). 

Land use in the Threemile Creek basin varies from site to 

site; however, the differences are small and are concentrated 

within three land-use groups—agricultural, forested, and 

residential. For example, the percentage of agricultural land 

decreases in a downstream direction (25 to 17 percent), as does 

the percentage of forested land (36 to 26 percent). Conversely, 

the percentage of urban land use (primarily residential) 

increases in a downstream direction (36 to 47 percent). 

Although differences in land use can sometimes be linked to 

differences in concentrations of chemical constituents or the 

condition of the aquatic community, greater percentage 

differences in land use may be required before statistically 

significant differences in water quality or aquatic-community 

structure can be observed. 

Population density is used as an indicator of urbanization 

in a watershed. Digital coverages of population data for Mobile 

County for 1990–2000 were used to compute 

the population densities in the watersheds of the 

sampling sites (table 4). The population density 

in each of the two tributary basins (CEN and 

TSB) was 2–3 times higher throughout the 

10-year period than in the Threemile Creek 

subbasins (table 4). Of the sites on Threemile 

Creek, TM-5 had the greatest population 

density (2,525 people per square mile), and 

TM-3 had the lowest population density in 

2000 (1,965 people per square mile). From 

1990 to 2000, population density decreased at 

all sites, with the greatest reduction at TSB 

(17.8 percent) and an overall reduction of about 

9.5 percent in the Threemile Creek watershed. 

Hydrology

Streamflow in Threemile Creek is affected by several 

factors, including (1) the degree of urbanization in the 

watershed, (2) streamflow in the Mobile River, (3) tidal 

fluctuations from Mobile Bay, (4) base flow in Threemile 

Creek, and (5) precipitation in the watershed. Urbanization 

influences the hydrology of streams in several ways. As the 

amount of impervious surface area in a watershed increases, the 

amount and velocity of runoff to streams increases (Dunne and 

Leopold, 1978), causing rapid increases in water level and 

velocity in streams during storms. Urbanization often results in 

channel modification, causing higher flows during storms and 

frequent flooding. An increase in the amount of impervious 

surface area also can cause a reduction of infiltration, resulting 

in less ground-water recharge and lower base flows. Long-term 

continuous streamflow monitoring provides hydrologic data 

that can be used to determine the effects of urbanization on the 

hydrology of streams over time. 

The Mobile River is formed by the confluence of the 

Alabama and Tombigbee Rivers, about 45 mi north of 

downtown Mobile (U.S. Army Corps of Engineers, 1985). The 

Mobile River is confined to one channel for only about 

6 mi—from the confluence of the Alabama and Tombigbee 

Rivers to the division between the lower Mobile River and the 

Tensaw River (Robinson and others, 1956). At that point, the 

river enters the Tensaw swamp—a labyrinth of channels, lakes, 

and bayous extending to Mobile Bay, an estuary of the Gulf of 

Mexico. Water flows into Mobile Bay in five distinct natural 

channels; the main channel is the Mobile River. In times of low 

flow, the Alabama River is the major contributor to the Mobile 

River; in times of high flow, either the Alabama or the 

Tombigbee River can be the major contributor to the Mobile 

River. 

The Mobile River and the lower reaches of the Tombigbee 

and Alabama Rivers are affected by tidal fluctuations, except 

during periods when the streams are discharging substantial 

Table 4. Population changes (1990 –2000) in the watersheds of sampling sites in 

the Threemile Creek basin, Mobile, Alabama.

[Data from Hitt, 2003; Price, 2003; U.S. Census Bureau, 2004; mi2, square mile]

Site 

label 

(fig. 1)

Drainage 

area 

(mi2

)

Population Population, 

per square mile

Relative 

percent 

change 1990 2000 1990 2000

TM-1 10.4 23,265 22,090 2,237 2,124 -5.2

TM-2 12.0 26,477 25,169 2,206 2,097 -5.1

TM-3 17.3 35,326 33,995 2,042 1,965 -3.8

TM-4 19.2 42,124 40,457 2,194 2,106 -4.0

CEN 1.07 4,431 4,202 4,141 3,927 -5.3

TSB 0.618 3,817 3,194 6,177 5,168 -17.8

TM-5 28.1 77,887 70,941 2,772 2,525 -9.3
14 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

flood flows. Saltwater from the Gulf of Mexico enters Mobile 

Bay and the Mobile River and its tributaries, including 

Threemile Creek, as a wedge extending upstream along the 

river bottom beneath the freshwater. The extent of the tidal 

movement inland depends on such factors as stream discharge, 

tidal cycle, and shape and configuration of the stream channel 

(Reed and McCain, 1972). Specific conductance and dissolvedoxygen concentrations were measured at several sections on the 

lower reaches of Threemile Creek between TM-4 and TM-5. 

The saltwater wedge was detected at four sites between 

M.L. King Avenue and U.S. Highway 43 (TM-5, fig. 2; 

Pearman and others, 2003). 

Tides at Mobile are diurnal—only one high and one low 

tide occur during a lunar day—except at the moon’s quadrature 

(first and third quarters of the moon) when two highs and lows 

(neap tide) may occur with very little difference in vertical rise 

and fall (Robinson and others, 1956). Spring tides, which occur 

at the new and full moon, produce the greatest variations in the 

rise and fall of the tide. In coastal regions, tide levels may 

depend on additional factors, including wind, depth of water, 

and shape of the coastline (bays and estuaries). Funnel-shaped 

bays, for example, can dramatically increase tidal magnitudes. 

Tide levels in the Mobile River also depend on the water level 

(stage) in the river and the distance upstream from the river’s 

mouth.

The Threemile Creek extends approximately 15 mi 

upstream from the Mobile River (U.S. Army Corps of 

Engineers, 1985); the lower reaches of the creek are affected by 

tidal fluctuations. The tidal cycle affects the 4.4-mi segment of 

Threemile Creek between the Mobile River and the last weir 

downstream from Fillingim Street. The series of drop structures 

and weirs installed between Municipal Lake and Fillingim 

Street prevent the tide from encroaching farther upstream, 

except during extreme events. About 2 mi 

downstream from the last drop structure, 

Threemile Creek flows down a straight channel 

through forested wetlands, whereas the original 

channel meanders throughout the wetlands. 

Saltwater was measured on the channelized 

section of the creek between the profile site at 

USGS streamgaging station 0247101520, 

approximately 400 ft downstream from 

M.L. King Avenue, and TM-5 (fig. 2; Pearman 

and others, 2003). Saline water was not 

measured at TM-4, although tidal effects on 

water levels at this site were recorded throughout 

the monitoring period. 

The tidal range (amplitude) at Threemile 

Creek depends primarily on the strength of the 

tide, the stage of Threemile Creek, the stage of 

the Mobile River, the distance on Threemile 

Creek upstream from the Mobile River, and the 

lunar phase. Wind direction on the bay also can 

affect the strength of the tide. Like the Mobile 

River, the tidal effects are dampened during 

periods when Threemile Creek or the Mobile 

River is discharging substantial flood flows. The U.S. Army 

Corps of Engineers operates a streamgage (USGS station 

02471017) at the Mobile State Docks in Mobile, Alabama, 

approximately 1.0 mi from the mouth of the Mobile River 

(fig. 1). Gage height for this station is available on-line at the 

USGS National Water Information System (NWIS) Web site 

(U.S. Geological Survey, 2004). During the sampling period 

(WY 2000–2003), the mean range of the tide at the Mobile 

State Docks was 1.69 feet per day (ft/d); the mean range of the 

tide at TM-5 was 1.72 ft/d; and the mean range of the tide at 

TM-4 was 1.39 ft/d. 

In the upper reaches of Threemile Creek (TM-1), an 

increase in gage height was associated with precipitation. In the 

lower reaches of Threemile Creek, an increase in gage height 

could be associated with either precipitation or tidal effects. The 

frequency that stage exceeded certain gage heights differed 

substantially between TM-4 and TM-5. For example, gage 

height at TM-4 exceeded 4.0 ft on 27 days during the study 

period; however, gage height at TM-5 exceeded 4.0 ft only 

twice during the study period. At Threemile Creek, the 

streamgages at Stanton Road (TM-4) and U.S. Highway 43 

(TM-5) recorded the same general shape and trend for gage 

height except for the time lag between TM-4 and TM-5; 

differences in range can be attributed to differences in tidal 

effects, varying amounts of precipitation in the basin, the 

presence or absence of wetlands, and channel size. 

The hydrology of Threemile Creek is complex because of 

the degree of urbanization in the watershed, the presence of 

numerous weirs on the upper reaches of the creek, channelized 

sections of the creek, tidal fluctuations, and the presence of 

wetlands in some basins. The analysis is further complicated by 

the effects of streamflow from the Mobile River and Mobile 

Bay, which indirectly affect streamflow in Threemile Creek. 

Site TM-5, Threemile Creek at U.S. Highway 43 near Prichard
Methods of Study 15

Methods of Study

The principal factors affecting water quality are (1) natural 

conditions, such as the amount of precipitation, topographic and 

geologic features, and vegetation, and (2) human activities 

related to the use and reuse of water and the disposal of waste 

material. Causes of water-quality and aquatic-community 

degradation in urban watersheds can be difficult to identify 

because of the diversity of potential contamination sources and 

land-use activities. Industrial or municipal discharges, sewer 

overflows, runoff from parking lots, removal of riparian cover, 

and channel or flow modifications can alter stream hydrology, 

affect water quality, and influence the aquatic-community 

structure. The complicated relations among land-use activities, 

water quality, and aquatic biota in a watershed require an 

integrated approach to identify the factors that negatively affect 

a stream ecosystem.

Stream-water quality is variable over time, and organisms 

dwelling in streams respond to changes in water quality. Some 

organisms are more sensitive to certain water-quality conditions 

than others, so as water-quality conditions deteriorate, the 

assemblage of organisms in a stream becomes dominated by 

those most able to survive and flourish. Because of this, samples 

of the benthic (bottom-dwelling) organism communities in 

streams can provide useful information about stream-water 

quality. Algal biomass and community structure, benthic 

invertebrate structure, and water chemistry are environmental 

indicators that represent stream conditions at different times. 

Water samples represent water quality at the time of sample 

collection. Algal community structure and biomass typically 

reflect water-quality conditions for time periods ranging from 

several days to weeks (Porter and others, 1993) or the time 

period between major storms. Benthic invertebrates can 

integrate water-quality conditions over a span of many weeks to 

a year or more. 

Another important aspect of stream-water quality is the 

condition of the hydrologic system at the time of sampling. 

Surface-water samples were collected during a wide range of 

flow conditions. Samples collected during low-flow periods 

represent surface-water-quality conditions resulting from 

ground-water seepage, septic tank leakage, and WWTP 

discharges; samples collected during storms or elevated flow 

represent water-quality conditions associated with surface 

runoff, shallow subsurface water flow to streams, and 

resuspension of stream-bottom deposits (Wicklein, 2004). 

Elevated flow in this study is represented by samples collected 

during a storm and samples collected immediately after a storm. 

Concentrations of contaminants from nonpoint sources 

typically increase during a storm as a result of overland runoff, 

but concentrations of contaminants from point sources may 

decrease during a storm as a result of dilution. Although the 

water-quality data collected during this study generally 

represent a fair range of hydrologic conditions, the majority of 

the samples were collected during periods of low flow; not 

enough samples were collected during high flow to perform 

comparisons and analysis for sample sets representing groundwater and stormflow components of the streamflow. By 

understanding the hydrologic condition at the time of sampling 

and reviewing the data in this context, the influence of pointand nonpoint-source contributions of contaminants on water 

quality can be examined in a more subjective manner.

A combination of approaches was used to assess 

conditions on Three Mile Creek: (1) water-quality monitors 

provided a continuous record of dissolved-oxygen 

concentrations, specific conductance, turbidity, and gage height 

throughout the sampling period; (2) water-quality samples were 

collected during a range of flow conditions to examine the 

potential source(s) of contaminants; and (3) water-quality, 

algal, and benthic invertebrate data were evaluated to assess 

which sites were most affected.

Water-Quality Sample Collection 

Surface-water samples were collected from March 2000 to 

September 2003. The number of samples collected and the 

frequency of sampling varied from site to site (table 5). During 

the first year, seven samples were collected at TM-1, TM-3, 

TM-4, CEN, and TSB, and nine samples were collected at 

TM-5. Between April and August 2001, seven samples were 

collected at TM-1 and TM-4, eight samples were collected at 

TM-5, and one sample was collected at each of the two 

tributaries (CEN and TSB) in October 2001. 

During the last 2 years of data collection, water-quality 

samples were collected during four specific time periods at sites 

on Threemile Creek to obtain data to calibrate a water-quality 

model. Sampling at the two tributary sites was discontinued. 

These four time periods (December 13–14, 2001; June 24–26, 

2002; February 26–27, 2003; and September 15–16, 2003) 

represented different seasons and different flow conditions 

(storm, mixed flow, or base flow). Multiple samples (4–8) were 

collected at three sites on Threemile Creek during each of the 

four time periods. The frequency of sampling at TM-3 and 

TM-4 differed from that at TM-1 and TM-5, and the number of 

high-flow samples collected at TM-3 exceeded that at TM-4, 

TM-1, or TM-5. 

Surface-water samples were analyzed for nutrients, major 

ions, total organic carbon (TOC), 5-day biochemical oxygen 

demand (BOD5), suspended chlorophyll a, organic wastewater 

compounds (OWCs), color, turbidity, and fecal bacteria during 

a range of flow conditions. Sampling for some constituents, 

such as major ions, TOC, color, and turbidity, was limited to the 

first year; sampling for other constituents, such as BOD5, 

suspended chlorophyll a, and OWCs, was intermittent 

throughout the sampling period (table 5). OWC samples were 

shipped to the USGS National Water Quality Laboratory 

(NWQL) in Denver, Colorado, for analysis. All other samples 

were shipped to the USGS Water Quality and Research 

Laboratory in Ocala, Florida. Water-quality monitors installed 

at three sites on Threemile Creek (TM-1, TM-4, and TM-5) 

provided a continuous record of water temperature, dissolved-
16 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

oxygen concentration, specific conductance, and turbidity 

between WYs 2000 and 2003. 

Data-collection procedures conformed to standard USGS 

protocols and included equal-width increment sampling, which 

produces a composite sample that is representative of flow in a 

cross section (Wilde and others, 1999). Most water samples 

were collected by using a DH-81 sampler or a weighted bottle 

sampler (Edwards and Glysson, 1999). Storm samples were 

discrete. Instantaneous field measurements of stream discharge, 

air temperature, water temperature, pH, dissolved-oxygen 

concentration, and specific conductance were made at the time 

of sampling. A security fence located on the bridge at 

TM-4 limited access to the site because of its height; 

consequently, discharge could only be measured when 

the creek was wadeable. Continuous water-quality 

monitors in the Threemile Creek watershed recorded 

data (water temperature, dissolved-oxygen 

concentrations, specific conductance, turbidity, and 

gage height) at 15-minute intervals.

An acoustic Doppler velocity meter was mounted 

at TM-5 to collect horizontal velocities at 15-minute 

intervals. These velocity measurements and stage data 

can be used in conjunction with discharge 

measurements made with an acoustic Doppler current 

profiler (ADCP) to construct an index-velocity rating at 

a station. Numerous discharge measurements were 

made during several tidal events at TM-5 using the 

ADCP, which was mounted on a small boat; however, 

efforts to develop an index-velocity rating were 

unsuccessful because of the complex tidal currents. 

A plastic churn was used to composite the cross-section 

water subsamples, and water samples for BOD5 and unfiltered 

constituents were taken directly from the churn. Water samples 

for dissolved constituents were filtered using a 0.45-micrometer 

(μm) pore-size filter that was pre-rinsed with de-ionized water 

and native stream water. Wastewater-indicator samples were 

collected as grab samples directly from the stream in 1-liter (L) 

glass bottles. Samples were preserved and chilled immediately 

after filtration and shipped overnight to the USGS laboratories 

in Denver and Ocala. All equipment used to collect and process 

samples was cleaned with a 0.2-percent nonphosphate detergent 

Table 5. Number and type of water-quality, benthic invertebrate, and periphyton samples collected at sites in the Threemile Creek 

basin, Mobile, Alabama, 2000–20 03.

[BOD5, 5-day biochemical oxygen demand; AFDM, ash-free dry mass]

Site 

label 

(fig. 1)

Number and type of water-quality samples

Number and type of benthicinvertebrate and periphyton 

samples

 Nutrientsa

a

See appendix table 2-1. bSee appendix table 2-2. cSee appendix table 3-1. dSee table 19. eEach sample consists of three or more replicates. See 

appendix table 3-2.

Major 

ionsa

BOD5

a

Suspended 

chlorophyll a a

Enterococcia

Escherichia 

coli a

Fecal 

coliforma

Organic 

wastewater 

compoundsb

Total 

organic 

carbona

Benthic 

invertebrate 

community 

surveyc

Chlorophyll and 

AFDM 

periphytond

Periphyton 

speciese

TM-1 36 7 29 24 26 35 31 13 7 1 11 3

TM-2 0 0 0 0 0 0 0 0 0 1 8 2

TM-3 20 7 11 12 19 21 15 10 7 1 11 3

TM-4 20 7 18 18 20 19 20 11 7 1 2 1

CEN 8 7 6 8 8 8 8 8 7 0 1 1

TSB 8 7 6 8 8 8 8 8 7 0 1 1

TM-5 39 9 30 26 34 36 31 13 7 0 0 0

USGS personnel using an ADCP to make a discharge measurement at site TM-5 on 

Threemile Creek
Methods of Study 17

and rinsed with tap water, a solution of 5-percent hydrochloric 

acid, and de-ionized water. 

Wastewater-indicator compounds were analyzed from 

unfiltered samples by continuous liquid-liquid extraction with 

methylene chloride and determined by capillary-column gas 

chromatography/mass spectrometry using selection-ion 

monitoring (Brown and others, 1999; Kolpin and others 2002). 

Information in Zaugg and others (2002) provides details about 

the specific wastewater-indicator compounds analyzed and 

their uses. Nutrient concentrations were determined at the 

USGS Ocala laboratory by using methods specifically designed 

to measure low levels of certain constituents (U.S. 

Environmental Protection Agency, 1983; Fishman and 

Friedman, 1989). 

Water samples for analysis of fecal-indicator bacteria 

(enterococci, Escherichia coli (E. coli), and fecal coliform) 

were processed in the field by USGS personnel according to 

published methods (U.S. Environmental Protection Agency, 

1985, 1997). Samples were collected by using an autoclaved 

1-L polyethylene bottle or glass bottle dipped at multiple points 

across the stream. Samples were processed by membranefiltration techniques within 6 hours of collection, according to 

USGS guidelines (Myers and Wilde, 1999). Bacteria results 

were reported in units of colonies per 100 milliliters 

(col/100 mL) of water. Suspended chlorophyll a and b samples 

were collected in the same manner as fecal-indicator bacteria. 

Samples were processed through glass fiber filters, shipped on 

wet ice, and sent to the USGS Ocala laboratory for analysis. 

Suspended chlorophyll a and b samples were analyzed by using 

high-performance liquid chromatography.

Benthic Invertebrate and Periphyton Sample 

Collection 

 Benthic invertebrates are bottom-dwelling aquatic 

animals, such as insect larvae, mollusks, and worms, that 

occupy diverse functional niches in aquatic ecosystems. They 

recycle organic matter, consume smaller organisms, and are 

important components in the diet of fishes. Benthic 

invertebrates commonly are used to assess the health of aquatic 

communities because they are easy to collect and identify, 

usually abundant, and relatively sessile (Merritt and Cummins, 

1996). Benthic invertebrates typically integrate the effects of 

water quality over periods of about a year and can be more 

sensitive indicators of water quality than chemical measures. 

Benthic invertebrates were sampled during July 2000 at four 

sites (TM-1, TM-2, TM-3, and TM-4) on Threemile Creek 

(table 5). A replicate sample also was collected at site TM-4. 

Project plans called for annual invertebrate collections at these 

sites, with a replicate sample at one site per year, to help 

evaluate variance between samples. Sampling in subsequent 

years was not possible because of destruction of the emergent 

and bank vegetation and dredging of the channel for flood 

control. 

The richest instream habitat, or habitat type most likely to 

have the greatest number of distinct types (taxa) of 

invertebrates, was sampled at each site. Flow characteristics 

and substrate type, two important components of habitat, varied 

among the Threemile Creek sites. Streamflow at TM-1 consists 

of overflow (spillage) from Municipal Lake, a manmade 

impoundment of Threemile Creek located just upstream from 

this site. Invertebrate assemblages downstream from 

impoundments tend to be dominated by filtering collectors, 

such as the net spinning caddisflies. The sampled habitat at site 

TM-1 consisted of a riffle among large boulders left from 

previous road construction at the site. Riffle areas usually 

support diverse invertebrate communities because of high 

dissolved-oxygen concentrations, stable substrate, and large 

areas of available habitat; however, diversity and abundance 

can decrease with substrate larger than cobble (greater than 

10 inches; Barbour and others, 1999; Moulton and others, 

2002). The richest habitats for invertebrates at the other three 

sites (TM-2, TM-3, and TM-4) were emergent vegetation along 

the margins of the stream. Channel substrates at TM-2, TM-3, 

and TM-4 consisted of sand and gravel. The sample reach at 

TM-2 consisted of a run with steady, slow flow. The sample 

reach at TM-3 was located in a pooled area just downstream 

from a double weir located under Fillingim Street. The sample 

reach at TM-4 was located in a run with flows affected by tidal 

backwater.

Habitat differences at the sites required two different 

sampling strategies for benthic invertebrates. At TM-1, samples 

were taken from a large riffle area using a Slack sampler with a 

425-μm mesh net that narrows to a collection receptacle 

(Cuffney and others, 1993). Invertebrates were collected from 

three areas of about 0.25 square meters (m2

) each and 

composited into a single sample. At TM-2, TM-3, and TM-4, 

samples were collected by sweeping a 210-μm mesh D-frame 

net under and through vegetation. For consistency of effort, six 

30-second sweeps were made at each site and composited into 

a single sample. Simultaneous sweeps were made along the left 

and right banks, and each of the two samples was composed of 

material from six sweeps, three from each side of the stream. 

All samples were processed by placing collected material in a 

bucket, stirring to suspend the organisms, and pouring the liquid 

portion through a 425-μm sieve. Material in the sieve was 

picked through to remove large pieces of debris from the 

sample, transferred to polyethylene bottles, and preserved with 

a 10-percent buffered formalin solution. Material remaining in 

the bucket was inspected for invertebrates, which were added to 

the preserved sample. Samples were sent to the Biological Unit 

at the USGS NWQL for identification and enumeration of 

organisms, using the quantitative 300-organism count, as 

described in Moulton and others (2000). 

Periphyton are algae that are attached to the stream bottom. 

Periphyton commonly are the primary producers in streams, 

providing food for benthic invertebrates, which feed fish and 

other vertebrates. Periphyton have relatively rapid growth rates 

and can respond quickly to changes in water quality, making 

them good indicator organisms of water quality over periods of 
18 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

days or weeks (Lowe and Pan, 1996). Samples of periphyton 

were collected from six sites (TM-1, TM-2, TM-3, TM-4, CEN, 

and TSB; table 5) during the summers of 2000–2003. 

Stream periphyton samples can be collected from natural 

or in situ substrates or from artificial substrates placed in the 

stream. Artificial substrates made of glass, clay tiles, plastic, or 

other materials often are used when natural stream substrates 

differ among sites (Aloi, 1990; Porter and others, 1993). 

Periphyton communities developing on artificial substrates may 

differ substantially from communities on natural stream 

substrates because of differences in colonization time and 

substrate surface (Tuchman and Stevenson, 1980). Samples 

collected from natural substrates represent algal communities 

that have been developing over a period of months, while 

artificial substrates are often deployed for much shorter 

colonization periods (Lowe and Gale, 1980; Tuchman and 

Stevenson, 1980). According to Tuchman and Stevenson 

(1980), periphyton on clay tile substrates is less variable 

and more closely resembles natural communities than 

communities on sterilized rock substrates. Previous 

comparisons of periphyton communities have shown 

differences among various types of substrate (Lowe and 

Pan, 1996), and periphyton data should not be compared 

among multiple substrate types (Porter and others, 

1993). 

Artificial substrates made of unglazed clay tiles 

were used as uniform bases for periphyton colonization 

in the Threemile Creek basin to exclude the effects of 

multiple substrate types (concrete, boulder, and sand). 

After a colonization period of 2 to 8 weeks, material 

from a section of tile with a known surface area was 

scraped off and filtered onto a 47-millimeter (mm) 

glass-fiber filter. Filters were shipped on dry ice to 

the USGS NWQL for determination of benthic 

chlorophyll a by fluorometric methods and ash-free dry mass 

(AFDM). 

Once a year (during 2000 to 2002), all material from 

another section of the clay tiles was scraped off, preserved with 

a sufficient volume of buffered formaldehyde to obtain a final 

concentration of 3- to 5-percent buffered formalin, and shipped 

to the Philadelphia Academy of Natural Sciences for species 

identification and enumeration. Laboratory protocols 

that were used were developed in the USGS NAWQA 

Program (C. Knowles, Philadelphia Academy of Natural 

Sciences, written commun., August 2000). Periphyton 

samples from 2000 and 2001 were analyzed by using a 

600-count of diatoms and identification of all soft algae. 

In 2002, samples were analyzed by using Philadelphia 

Academy of Natural Sciences Protocol P-13-63 (Charles 

and others, 2002). Taxa richness and community 

diversity could appear to be greater for 2000–2001 

because a greater number of individual algal cells were 

counted under the laboratory method used during those 

years than in 2002. Thus, comparisons of samples from 

September 2002 are presented independently. 

Periphyton samples were collected at five sites 

(TM-1, TM-3, TM-4, CEN, and TSB) during September 

2000. Sites CEN and TSB were too shallow for the clay 

tile substrates to be submerged, so the existing concrete 

channels were sampled instead. The set of clay tiles at 

site TM-4 was lost due to high streamflows or 

vandalism, so the sample at that site and a replicate 

sample at TM-3 were collected from the natural sand substrate. 

Samples taken from existing substrates can be used to describe 

the existing periphyton communities but should not be used to 

infer differences in water quality among the sites. Another set 

of samples was collected in November 2000 and analyzed for 

benthic chlorophyll a and AFDM only. 

During 2001–2003, only sites TM-1, TM-2, and TM-3 

were sampled because they allowed the use of the uniform 

artificial substrates. Four benthic chlorophyll a and AFDM 

samples were collected during the summer of 2001, three during 

Site TM-2, Threemile Creek near Pine Grove

Site TM-3, Threemile Creek at Fillingim Street at Mobile
Methods of Study 19

the summer of 2002, and two during the summer of 2003. Tile 

exposure periods, benthic chlorophyll a, and AFDM results are 

summarized later in this report. In addition, samples were 

collected once a year (during 2000 to 2002) for enumeration of 

periphyton assemblages. Three replicate samples were 

collected at each site each year and analyzed individually to 

assess reproducibility of sample results. Data are summarized in 

appendix table 3-2. Dates of tile exposure were the same for 

benthic chlorophyll a and AFDM samples and corresponding 

identification samples. 

Water-Quality Data Analysis and Review

Methods used to interpret water-quality data in this report 

include various graphical tools and statistical methods. 

Graphical tools include the use of bar charts, which illustrate the 

speciation of certain nutrients (nitrogen and phosphorus) and 

groups of OWCs, the total concentration of OWCs, and the 

frequency of detection for other OWCs. Median concentrations 

of constituents were used when comparing constituent levels 

among sites in the Threemile Creek basin. Median 

concentrations represent the 50th percentile of the concentration 

data and are less affected than mean concentrations by the value 

of extremely high or low concentrations. Box plots are used to 

display the variability in nutrient concentrations, and elevatedflow/low-flow figures are used to illustrate the concentrations 

of fecal-indicator bacteria and the hydrologic condition at the 

time of sampling. If concentrations detected during low flow 

were consistently higher than those during elevated flow, a “P” 

was placed on the graph, indicating point sources. If the 

concentrations detected during elevated flow were consistently 

higher than those during low flow, an “NP” was placed on the 

graph, indicating nonpoint sources. If the results were mixed, a 

“B” was placed on the graph, indicating that both point and 

nonpoint sources may be contributing. Maximum concentrations and ranges of concentrations were evaluated with respect 

to flow. These data can be useful in determining the influence 

of point- and nonpoint-source contributions of contaminants on 

water quality. Statistical methods to evaluate the relation 

between discharge and concentration could not be applied at 

each site because (1) samples were collected over a limited 

range of flow, (2) discharge measurements were not made at 

every site during each sample collection (TM-4 and TM-5), and 

(3) discharge measurements at TM-5 were considered 

unreliable. 

 The USGS NWQL has implemented procedures for 

interpreting and reporting low-concentration data in waterquality samples (Childress and others, 1999). Concentrations of 

analytes that either were not detected or were not identified 

were reported as less than the minimum detection limit 

(< MDL) or less than the minimum reporting level (< MRL) and 

are considered to be nondetections. All qualitatively identified 

compounds detected less than the MRL are reported as 

estimated (Zaugg and others, 2002). Estimated concentrations 

are noted with the remark code E. The uncertainty associated 

with these estimated concentrations is greater than that 

associated with values that were detected at concentrations 

above the MRL and not estimated. The MRLs for OWCs were 

established by the NWQL. The MDL for nutrient compounds 

was established by the Ocala laboratory.

Sensitive analytical methods used in this study resulted in 

low detection limits and higher detection frequencies for many 

wastewater indicators. Comparison of detection frequencies 

among wastewater indicators can be misleading because of the 

different reporting levels associated with each of the 

wastewater indicators. For example, the pesticide diazinon has 

a reporting level of 0.5 microgram per liter (μg/L), and 

nonylphenol diethoxylate (NP2EO) has a reporting level of 

1.1 or 5.0 μg/L. Diazinon was detected more frequently than 

NP2EO in this study; however, it is unknown whether the same 

would be true if the MRL of NP2EO also were 0.5 μg/L. To 

reduce this type of bias when calculating detection frequencies, 

data sometimes are adjusted by censoring to a common 

threshold. Nonadjusted data were used when evaluating the 

frequency of detection for wastewater indicator compounds in 

the Threemile Creek basin. 

Nonparametric hypothesis tests were used to evaluate 

relations among water-quality constituents. Spearman’s rho

was used to measure the strength of association between 

constituents, including total nitrogen, total phosphorus, 

discharge, turbidity, fecal-indicator bacteria, and selected 

OWCs (SAS Institute, Inc., 1989). Spearman’s rho is the linear 

correlation coefficient computed on the ranks of the data rather 

than actual values (Helsel and Hirsch, 1992). Values of rho

range from -1.0 to 1.0, and the closer the value is to -1.0 or 1.0, 

the stronger the association between the two variables. The 

correlation coefficient, rho, is positive when both variables 

increase and negative when one variable increases as the other 

decreases. A probability statistic (p) of 0.05 means that there is 

a 95-percent probability that the correlation is statistically 

significant. For this report, significant correlation was 

determined by an absolute rho value of 0.7 or greater, provided 

that the p value was less than or equal to 0.05. All data sets with 

rho and p values within the designated ranges were verified by 

scatter plots to determine the distribution of the data. Plots that 

indicated poor distribution because of grouped data points or 

outliers were not considered in the correlation analysis. In many 

instances, correlation coefficients could not be calculated 

because of the large number of nondetection values, multiple 

detection levels, or the limited sample size. In the correlation 

analysis for nutrients, nondetection values were assumed to be 

equivalent to the detection level.

The determination that a correlation existed between 

constituents meant that the constituents varied with each other 

in a consistent pattern. This does not necessarily indicate a 

cause and effect relation (Helsel and Hirsch, 1992). Although 

statistically significant differences were found, the significance 

of the results and the power of the tests used are limited because 

of the small sample size. Thus, results should be viewed as 

preliminary and not conclusive.
20 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

The Kruskal-Wallis and the Tukey multiple-comparison 

tests were used to determine whether water-quality 

concentrations at one site were significantly different from 

concentrations at another site (SAS Institute, Inc., 1989). The 

Kruskal-Wallis test is a one-way, nonparametric analysis of 

variance (ANOVA) test that was used to determine whether 

significant differences existed among independent data 

sets—four sites on Threemile Creek (TM-1, TM-3, TM-4, 

TM-5), two sites on Threemile Creek (TM-1 and TM-5), the 

two tributary sites, and the two tributary sites with TM-4 and 

TM-5. The Tukey multiple-comparison test was then used to 

compare the differences in concentrations in an upstreamdownstream order within these data sets. The simplest 

procedures for performing nonparametric multiple comparisons 

are rank transformation tests (Helsel and Hirsch, 1992). Ranks 

were substituted for the original data, and the Tukey multiplecomparison test was performed on the ranks. Data were 

censored to the highest detection level whenever multiple 

detection levels were present. Statistical tests were not 

performed if censoring resulted in a severe (near 50 percent or 

more) loss of data (Helsel and Hirsch, 1992).

To minimize the bias that could be created from testing 

data collected under different conditions at different sites, the 

Kruskal-Wallis and Tukey multiple-comparison tests were 

applied to time periods when sampling was uniform between 

sites: (1) Threemile Creek and tributary sites—7 samples 

collected between March 13, 2000, and March 13, 2001; and 

(2) TM-1 and TM-5—36 samples collected between March 13, 

2000, and September 16, 2003. By grouping the data in this 

manner, it was possible to evaluate the differences in water 

quality among all the sites for a 1-year period (March 2000–

March 2001), and because TM-1 and TM-5 were sampled 

evenly throughout the entire sampling period, differences in 

water quality between these two sites could be evaluated for the 

entire sampling period (March 2000–September 2003). Data 

from sites TM-4, CEN, TSB, and TM-5 were examined to 

evaluate whether differences between TM-4 and TM-5 could be 

attributed to the tributaries or to other sources, including 

discharges from the WWTPs. Definitive conclusions could not 

be made in most instances because samples were not collected 

from the discharge at the WWTP, and the influx of the tide at 

TM-5 further complicated the interpretation. The significance 

of the results and the power of the tests used are limited because 

of the small sample size; therefore, the results should be viewed 

as preliminary and not conclusive.

The U.S. Environmental Protection Agency (USEPA) has 

established water-quality standards and guidelines for 

chemicals that can have adverse effects on human health, 

aquatic organisms, and wildlife. Current drinking-water 

standards, which are enforceable and apply to drinking-water 

supply systems, set maximum contaminant levels (MCLs) for 

nitrite plus nitrate at 10 milligrams per liter (mg/L), maximum 

nitrate levels at 10 mg/L, and maximum nitrite levels at 1 mg/L 

(U.S. Environmental Protection Agency, 2002a). Although the 

MCLs established by the USEPA pertain to finished drinking 

water supplied by a community water supply, these levels 

provide values for comparison with the sampled concentrations. 

The USEPA also has developed nutrient guidelines for surface 

water, which are intended to represent background concentrations of selected nutrients (U.S. Environmental Protection 

Agency, 2000a, 2000b). In order to account for regional and 

local influences, these guidelines are established for streams in 

individual ecoregions. Ecoregions are land divisions based on a 

combination of causal and integrative factors, including land 

use, land-surface forms, potential natural vegetation, and soils 

(Omernik, 1987). The ecoregion nutrient criteria are not 

intended to be enforceable standards but rather serve as 

guidelines for certain nutrient concentrations within the 

ecoregions. Concentrations of total nitrogen, total phosphorus, 

and suspended chlorophyll a were compared to recommended 

criteria developed for nutrient ecoregions IX and XII 

(U.S. Environmental Protection Agency, 2000a, 2000b). Sites 

TM-1 and TM-2 are located in nutrient ecoregion IX, and sites 

TM-3, TM-4, TM-5, CEN, and TSB are located in nutrient 

ecoregion XII (U.S. Environmental Protection Agency, 2000a, 

2000b). The USEPA also recommends that total phosphorus 

concentrations not exceed 0.10 mg/L in streams not entering 

lakes or impoundments in order to prevent nuisance aquatic 

plant growth (U.S. Environmental Protection Agency, 1986b). 

Aquatic-life criteria established by the USEPA and the 

ADEM provide for the protection of aquatic organisms for 

short-term (acute) and long-term (chronic) exposures (Alabama 

Department of Environmental Management, 2000c; U.S. 

Environmental Protection Agency, 2002c). In some instances, 

Canadian guidelines were used for comparisons when other 

criteria were not available (Canadian Council of Ministers of 

the Environment, 2001, 2002). Some compounds that are 

known to be toxic to aquatic life currently are unregulated, even 

though some are on the USEPA Toxic Substance Control Act 

Priority Testing List (U.S. Environmental Protection Agency, 

1996; Zaugg and others, 2002).

Fecal-bacteria concentrations were compared to 

established State and Federal standards and criteria. The 

USEPA has defined criteria for single-sample densities for 

enterococci and E. coli in recreational waters based on 

frequency of use and body contact (U.S. Environmental 

Protection Agency, 1986a, 2002b). For infrequent, full-body 

recreational contact, enterococci and E. coli samples should not 

exceed 151 and 576 col/100 mL, respectively. The ADEM 

continues to rely on fecal-coliform regulatory standards for 

most water-use classifications, although enterococci standards 

have been added for coastal waters (Alabama Department of 

Environmental Management, 2004). For fecal-coliform 

samples collected in streams classified for agricultural and 

industrial use, the geometric mean of at least five samples 

collected over a 30-day period should not exceed 

2,000 col/100 mL, nor should any one fecal-coliform sample 

exceed a maximum of 4,000 col/100 mL (Alabama Department 

of Environmental Management, 2000c, 2004). Exceedance 

frequencies were calculated by summing the number of 

exceedances and dividing by the total number of samples 

collected for each type of bacteria. 
Methods of Study 21

Quality-Control Methods and Results

Quality-assurance and quality-control measures were 

practiced throughout the study according to established USGS 

guidelines (Mueller and others, 1997). Laboratory and field 

blank samples were processed using water certified to contain 

undetectable concentrations of constituents to be analyzed. 

Data from blank samples were used to determine the extent of 

contamination potentially introduced during sample collection, 

processing, and analysis. Blank water used for the inorganic 

constituent sample was distilled, de-ionized water obtained 

from the USGS Ocala laboratory. Blank water used for the 

organic constituent sample was either pesticide-grade or 

volatile-organic-compound grade blank water obtained from 

the USGS NWQL. Sterile water blanks (saline or peptone 

buffer) were processed at each site to check the effectiveness of 

sterilization and processing procedures for bacterial analysis.

Blank samples were analyzed for nutrients (14 blanks), 

major ions (7 blanks), organic carbon (6 blanks), BOD5

(10 blanks), and wastewater indicators (11 field blanks; 14 

laboratory blanks; appendix table 1-1). Detections of nutrients 

in blank samples were generally at or slightly greater than the 

MDL (appendix table 1-1). Total ammonia nitrogen was the 

most frequently detected nutrient in blank samples (5 of 14 

samples); dissolved ammonia nitrogen and dissolved 

phosphorus were detected in 4 of 14 blank samples (appendix 

table 1-1). Dissolved calcium, total iron, dissolved iron, 

dissolved magnesium, total manganese, and dissolved sodium 

were detected one time each in seven blank samples; dissolved 

silica was detected in three of seven blanks. Concentrations of 

total iron, dissolved magnesium, and total manganese were 

below the MDL (appendix table 1-1). Total organic carbon was 

detected in 4 of 6 blank samples, and concentrations ranged 

from 0.3 to 0.6 mg/L (MDL < 0.01 mg/L); BOD5 was detected 

in 6 of 10 blank samples, and concentrations ranged from 0.2 to 

0.5 mg/L (MDL < 0.1 mg/L; appendix table 1-1).

The method designed by the NWQL for OWCs was under 

development during this investigation, and the final analysis of 

the associated method (lab code 8033) is pending (U.S. 

Geological Survey, 2003; S.D. Zaugg, U.S. Geological Survey, 

written commun., May 3, 2004). The method was developed in 

response to increasing concern over the effects of endocrinedisrupting chemicals in wastewater on aquatic organisms, and 

the method focuses on the determination of compounds that are 

an indicator of wastewater or that have been chosen on the basis 

of their endocrine-disrupting potential or toxicity (Zaugg and 

others, 2002). 

The method used to report OWCs is considered to be 

“information rich” (Childress and others, 1999) because 

compound identifications are determined by mass 

spectrometry; consequently, results are not censored (Zaugg 

and others, 2002). For compounds that are either at a 

concentration less than the MRL or the lowest calibration 

standard (usually 0.05 μg/L) but meet qualitative criteria, 

results are reported by using the “E” code to indicate that the 

concentration is estimated. All qualitatively identified 

compounds detected less than the MRL are reported as 

estimated, regardless of the established MRL (Zaugg and 

others, 2002). The concentrations of 16 compounds always are 

reported as estimated for one of three reasons: unacceptable 

low-biased recovery (less than 60 percent) or highly variable 

method performance (greater than 25-percent relative standard 

deviation), unstable instrument response, or reference standards 

prepared from technical mixtures (Zaugg and others, 2002). Of 

the 48 compounds examined in this study, 7 were included in 

the group of 16 compounds that are always reported as 

estimated. Six of these constituents were detected in stream 

samples (carbaryl, 17β-estradiol, nonylphenol diethoxylate 

(NP2EO total), octylphenol monoethoxylate (OP1EO), 

octylphenol diethoxylate (OP2EO), and para-nonylphenol 

total), and four were detected in blank samples (17β-estradiol, 

NP2EO total, OP1EO, and para-nonylphenol total; appendix 

table 1-1). The specific compounds included in the wastewater 

schedule and the MRLs varied among samples because of 

method refinement during the 3 years (2000–2003) that 

samples were collected and because of matrix interference.

In this study, OWC data were censored according to the 

detection level of constituents found in laboratory and field 

blanks. If a constituent was found in either a laboratory or field 

blank and also detected in a stream sample during the same 

sampling trip at the same magnitude, then the detection was not 

included. Thirteen field blanks were sent to the NWQL; results 

from two of these field blanks were eliminated from the data set 

because of problems associated with these samples at the lab 

and in the field. The NWQL analyzed 14 laboratory blanks 

associated with samples from this study. Four of 48 compounds 

were detected in the 11 field blanks collected during this study; 

16 of 48 compounds were detected in 14 laboratory blanks 

(appendix table 1-1). Only 3 of 27 detections in laboratory and 

field blanks were greater than the corresponding MRL 

associated with the sample. These low-level detections indicate 

little potential for contamination of stream-water samples, and 

few data were censored as a result of these detections. 

Benthic Invertebrate and Periphyton Data 

Analysis and Review

Benthic invertebrate data were processed through the 

USGS Invertebrate Data Analysis System (IDAS) to calculate 

commonly used metrics and measures of invertebrate 

community diversity and evenness (Cuffney, 2003). The lowest 

taxonomic level, known as the NWQL Biological Unit 

identification, or BU_ID, was used in calculations. Ambiguous 

taxa were resolved by combining all samples and distributing 

ambiguous parents proportionately among their children 

(method RC4; Cuffney, 2003). Three ambiguous parent taxa 

were resolved manually by distributing parent abundance 

among children that accounted for greater than 10 percent of the 

combined sample abundance. The metrics were then used to 

assess similarities and differences among the sample sites. 

Metrics used in this report include total taxa richness; 
22 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa 

richness; percentage dominant taxon; relative abundance of 

major taxa; and the Shannon-Weaver Diversity Index. 

Taxa richness, or total number of taxa, was used to 

describe the diversity of organisms present at each site. EPT 

taxa richness and chironomid taxa richness also were 

considered. EPT taxa richness is the number of taxa within the 

orders of Ephemeroptera (mayflies), Plecoptera (stoneflies), 

and Trichoptera (caddisflies) that generally are thought to be 

intolerant of organic enrichment and elevated trace metal 

concentrations. The chironomids, or midges, are members of 

the family Chironomidae and are considered more tolerant of 

organic enrichment than the EPT taxa. Healthy benthicinvertebrate communities have a fairly even distribution among 

Chironomidae and EPT taxa (Alabama Department of 

Environmental Management, 1996).

A stream that receives contaminants or has been altered 

from natural conditions tends to have a less diverse community 

of benthic invertebrates. Diversity is a measure combining 

richness and evenness—that is, the distribution of individuals 

among taxa. The percentage contribution of the dominant taxon 

is the percentage of total sample abundance that is contributed 

by the most abundant taxon. Large percentage contributions by 

a few taxa indicate less even invertebrate communities, which 

are indicative of less healthy streams. The abundance of a 

healthy benthic invertebrate community usually is distributed 

among several taxa. The relative abundances of major taxa were 

used to assess both evenness and diversity of benthic 

invertebrate communities. The Shannon-Weaver Diversity 

Index is a measure of the uncertainty associated with a taxon 

selected at random from the community (Peet, 1974; Cuffney, 

2003). Greater uncertainty is associated with greater diversity. 

The ADEM uses the Shannon-Weaver Diversity Index to 

indicate diversity in quantitative benthic invertebrate samples 

and to evaluate stream impairment. According to the ADEM, 

index values less than 1 indicate impairment, and values 

between 3 and 4 indicate the diversity expected in healthy 

streams (Alabama Department of Environmental Management, 

1996).

Chlorophyll a and AFDM often are used as surrogate 

measures for algal biomass. Chlorophyll a is the primary 

pigment used for photosynthesis in algal cells and accounts for 

about 0.5 to 2.0 percent of the algal biomass (Barbour and 

others, 1999). Ash-free dry mass is the mass of organic material 

in a sample, which may include fungi, bacteria, and other biota 

as well as periphyton. Algal biomass can respond to changes in 

light and nutrient availability, differences in substrate or flow 

conditions, grazing by other organisms, and the presence of 

toxins. Benthic chlorophyll a concentrations greater than 

10 micrograms per square centimeter (μg/cm2) and AFDM 

greater than 50 grams per square meter (g/m2

) may indicate 

nuisance algal growth (Barbour and others, 1999). In this report, 

benthic chlorophyll a and AFDM are used to compare standing 

crops of periphyton among sites and samples and as a screening 

tool for nuisance algal growth. 

The ratio of AFDM to chlorophyll a in milligrams per 

square meter, known as the autotrophic index, can be used to 

evaluate the amount of fungal and bacterial material included in 

AFDM measurements. Organically enriched (high BOD) 

streams commonly have higher proportions of fungi and 

bacteria and, consequently, higher autotrophic indices (Lowe 

and Pan, 1996). Organic enrichment may have occurred if the 

autotrophic index is greater than 100 (Weber, 1973). 

Periphyton community data are summarized using metrics 

much like the benthic invertebrate metrics. The abundance and 

relative abundance of certain algae types indicate whether 

nutrient enrichment, acidification, or other water-quality 

conditions exist. The metrics used for periphyton analysis were 

(1) species richness based on cell density, (2) percentage 

abundance and percentage biovolume represented by each of 

the major algal divisions found in Threemile Creek, diatoms, 

blue-green algae, green algae, cryptophyte algae, euglenoids, 

dinoflagellates, and others, and (3) percentage of taxa in each of 

the saprobic categories (van Dam and others, 1994). 

Diversity of periphyton communities was measured using 

richness and relative abundance. Algal species richness is the 

number of algal species identified in the sample and tends to 

decrease as water-quality degradation increases. The 

intermediate disturbance hypothesis predicts that taxa richness 

will increase from background conditions at an intermediate 

level of stream disturbance and then decrease as disturbance 

becomes more severe. The percentage of algal cells and the 

percentage of total biovolume represented by each division 

were used to determine the dominant algal divisions at each site. 

Differences in algal community composition could be related to 

site water quality, and overwhelming dominance of a single 

division may indicate water-quality impairment. 

The saprobic categories were used to further examine 

periphyton community response to water-quality conditions. 

The saprobic categories represent groups of diatoms that prefer 

various levels of dissolved-oxygen concentrations and BOD. 

The categories and their corresponding oxygen and BOD 

concentrations are given in table 6 (van Dam and others, 1994; 

T.F. Cuffney, U.S. Geological Survey, written commun., 2004). 

If diatoms of one saprobic category dominate the community, 

oxygen conditions favored by the dominant category are likely 

to have occurred frequently at that site during the colonization 

period. 

Water-Quality Results and Discussion

The results and discussion of water-quality sampling and 

data analysis conducted during this investigation are presented 

here. The topics discussed include analytical results related to 

basic water chemistry, major ions, instantaneous and 

continuous measurements of water properties, nutrients, 

suspended chlorophyll a and b, biochemical oxygen demand, 

total organic carbon, fecal-indicator bacteria, and OWCs at four 
Water-Quality Results and Discussion 23

sites on Threemile Creek (TM-1, TM-3, TM-4, and TM-5) and 

at two tributary sites (CEN and TSB). 

Basic Water Chemistry

The chemistry of surface water is the result of interactions 

between precipitation, ground water, rocks, and soils near the 

Earth’s surface. Dissolved and particulate constituents enter a 

stream by surface runoff, precipitation, or ground-water 

discharge. The major dissolved constituents that give water its 

characteristic chemistry are cations and anions. Cations are 

positively charged ions and include calcium, magnesium, 

sodium, and potassium. Anions are negatively charged ions and 

include bicarbonate, carbonate, sulfate, chloride, nitrate, and 

fluoride. The concentrations of these dissolved ions generally 

are reported in milligrams per liter. 

Stream-water chemistry varies with flow conditions 

because flow paths change in a watershed. Under low-flow 

conditions, stream water is predominantly ground-water 

discharge. The nature and concentration of dissolved 

constituents are dependent on the composition of the aquifers 

through which the ground water flows. During and immediately 

after a storm, stream water is a mixture of rainwater and surface 

runoff, shallow subsurface flow through the soil zone, and 

ground-water discharge. Precipitation generally produces an 

overall dilution of the major ion composition. The geochemistry 

of the ocean also can affect the water chemistry of a stream 

flowing into it. Water circulation in an estuary or tidally 

influenced stream is controlled by topography, tidal currents, 

and the volume of freshwater discharge (Drever, 1988). Stream 

water may consist of a mixture of seawater and freshwater, 

resulting in an increase in the number of sodium and chloride 

ions. Human activity can alter water chemistry by contributing 

additional ions, such as sodium and chloride from WWTP 

discharges, leaking or overflowing sewer systems, industrial 

discharge, or urban runoff. Although basic ions are not 

considered contaminants, elevated levels may indicate 

anthropogenic inputs of contaminants. 

Major Ions

Major ions account for the greatest part of the dissolved 

solids in water. A summary of the major ion concentrations at 

six sites is included in appendix table 2-1, and a Piper diagram 

is presented in figure 6 to graphically depict the ionic 

composition of the stream water sampled during this 

investigation. The Piper diagram (Piper, 1944) consists of two 

trilinear plots that indicate the cationic and anionic composition 

of the water, and a diamond-shaped plot that indicates the 

overall ionic composition of the water. Calcium-bicarbonate 

dominant water, for example, plots to the far left of center 

portion of the diamond area, and a sodium-chloride dominant 

water plots to the far right of center (fig. 6). The two triangles at 

the base of the Piper diagram illustrate a further breakdown of 

the percentages of the individual cations (left) and anions (right) 

in each water sample (fig. 6). Each vertex on the Piper plot 

represents 100 percent of a particular ion or group of ions, and 

the coordinates of a point plotted on the diagram total to 

100 percent. 

The three most upstream sites (TM-1, TM-3, and TM-4) 

on Threemile Creek exhibited similar water quality, 

characterized by a strong calcium-bicarbonate component 

(fig. 6). The water chemistry at the two tributaries, CEN and 

TSB, differed from the main-stem sites on Threemile Creek. 

The tributary site at Center Street (CEN) was characterized by 

a strong sodium-chloride component; whereas the tributary site 

at Toulmins Spring Branch (TSB) was characterized by a strong 

calcium component without a dominant anionic species—

sulfate, bicarbonate, and chloride were present at this site 

(fig. 6). The most downstream site on Threemile Creek (TM-5) 

also was characterized by a strong sodium-chloride component, 

indicative of the influx of seawater at this tidal site (fig. 6). 

The elevated levels of sodium and chloride at CEN may 

indicate leaking or overflowing sewer systems or industrial 

discharge in the basin. Seawater typically contains sodium and 

chloride levels of about 10,500 mg/L and 19,000 mg/L, 

respectively, and the ratio of sodium to chloride typically is 

0.55. The ratio of sodium to chloride at TM-5 ranged from 0.54 

to 0.60 for eight of nine samples, whereas the ratio of sodium to 

Table 6. Saprobic categories of diatoms and corresponding dissolved-oxygen concentrations and biochemical 

oxygen demand values (van Dam and others, 1994).

[O2, oxygen; >, greater than; <, less than; BOD5, 5-day biochemical oxygen demand; mg/L, milligram per liter] 

Saprobic category

oligosaprobic β-mesosaprobic α-mesosaprobic α-mesosaprobic/

polysaprobic polysaprobic

O2 saturation

(percent)

> 85 70–85 25–70 10–25 < 10

BOD5 (mg/L) < 2 2–4 4–13 13–22 > 22
24 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

chloride at CEN ranged from 0.74 to 0.80 for seven of seven 

samples. Other sources likely are contributing to the high levels 

of sodium and chloride in the CEN basin. 

Chloride is present in all natural waters, but concentrations 

generally are low (Hem, 1985). In most streams, chloride 

concentrations are lower than those of sulfate or bicarbonate. 

Exceptions occur when streams receive inflows of high-chloride 

ground water, industrial waste, or seawater. Concentrations of 

chloride at the three most upstream sites on Threemile Creek 

(TM-1, TM-3, and TM-4) ranged from 2.8 to 9.2 mg/L (TM-4; 

appendix table 2-1). Median concentrations of chloride 

increased in a downstream direction; chloride concentrations 

were less than the corresponding bicarbonate concentration in 

each of the samples. Concentrations of chloride at TSB ranged 

from 6.9 to 11 mg/L; chloride concentrations were less than the 

corresponding bicarbonate and sulfate concentrations in each of 

the samples (appendix table 2-1). Chloride concentrations at 

CEN ranged from 31 to 340 mg/L; chloride concentrations 

exceeded the bicarbonate concentrations in five of seven 

samples and sulfate concentrations in seven of seven samples. 

The highest concentration of chloride at CEN was detected 

during low flow; the lowest concentration of chloride was 

detected during elevated flow, which indicates that increased 

flows may dilute chloride concentrations, indicating point 

sources rather than nonpoint sources. Chloride concentrations at 

TM-5 ranged from 22 to 7,900 mg/L (appendix table 2-1). 

Seawater typically has a chloride concentration of about 

19,000 mg/L (Hem, 1985), but because of the mixing with 

freshwater in Threemile Creek, lower values were measured. 

The Kruskal-Wallis test and the Tukey multiplecomparison test were applied to the major ion data at six sites to 

determine if the variations in water chemistry among sites were 

statistically significant (table 7). Chloride concentrations were 

significantly higher at TM-5 than at TM-4; chloride 

concentrations at CEN and TSB were significantly higher than 

at TM-4, indicating that the tributaries may contribute to the 

higher levels of chloride found at TM-5 (table 7). The ratios of 

sodium to chloride at TM-5 indicate that the site was affected by 

seawater, whereas the ratios of sodium to chloride at CEN 

indicate that the elevated levels may have originated from 

anthropogenic sources. 

Concentrations of fluoride in most natural waters are low, 

generally less than 1.0 mg/L (Hem, 1985). Fluoride is added to 

drinking water because of its importance in preventing cavities. 

Figure 6. Piper trilinear diagram showing major ion composition of surface-water samples 

collected at six sites in the Threemile Creek basin, Mobile, Alabama, 2000–2001.
Water-Quality Results and Discussion 25

Table 7. Results of the Kruskal-Wallis test and the Tukey multiple-comparison test illustrating statistically significant (p < 0.05) 

differences for selected water-quality constituents at sites in the Threemile Creek basin, Mobile, Alabama.

[BOD5, 5-day biochemical oxygen demand; OWC, organic wastewater compound]

Site label 

(fig. 1)

Dissolved 

oxygen pH Specific conductivity

Water 

temperature Alkalinity Calcium Magnesium Potassium

One-year period (March 2000–March 2001)

TM-1 to TM-3 X X

TM-1 to TM-4 X

TM-1 to TM-5 X X X X X

TM-3 to TM-4 X

TM-3 to TM-5 X X X X X X

TM-4 to TM-5 X X X X X X

CEN to TSB X X X X X

TM-4 to CEN X X X X X X X

CEN to TM-5 X X X X X X

TM-4 to TSB X X X X X

TSB to TM-5 X X X X X X X

Three-year period (March 2000–September 2003)

TM-1 to TM-5 X X X X X X

Site label 

(fig. 1) Sodium Bicarbonate Carbonate Chloride Total organic carbon BOD5 Chlorophyll a Enterococci

One-year period (March 2000–March 2001)

TM-1 to TM-3 X

TM-1 to TM-4 X

TM-1 to TM-5 X X X X X

TM-3 to TM-4

TM-3 to TM-5 X X X X X

TM-4 to TM-5 X X X X X

CEN to TSB X X X X

TM-4 to CEN X X X X X

CEN to TM-5 X X

TM-4 to TSB X X X

TSB to TM-5 X X X

Three-year period (March 2000–September 2003)

TM-1 to TM-5 X X X X X X X

Site label 

(fig. 1)

Fecal 

coliform

Escherichia 

coli Boron Iron (dissolved)

Iron 

(total)

Manganese 

(dissolved)

Manganese 

(total)

OWC (number 

of detections)

One-year period (March 2000–March 2001)

TM-1 to TM-3

TM-1 to TM-4

TM-1 to TM-5 X X X X

TM-3 to TM-4

TM-3 to TM-5 X X X

TM-4 to TM-5 X X X

CEN to TSB X X X

TM-4 to CEN X X X X X X

CEN to TM-5 X X

TM-4 to TSB X X X

TSB to TM-5 X X X

Three-year period (March 2000–September 2003)

TM-1 to TM-5 X X X X X X

p > 0.05 No statistically significant 

differences between sites as 

determined by the Kruskal-Wallis 

test.

X p < 0.05 Statistically significant 

differences between sites as determined 

by the Tukey multiple-comparison test 

(nonparametric).

p > 0.05 No statistically significant 

differences between sites as determined 

by the Tukey multiple-comparison test 

(nonparametric).
26 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Site label 

(fig. 1)

OWC (total 

concentration)

Ammonia 

(dissolved)

Ammonia + 

organic 

nitrogen (total)

Nitrite + 

nitrate 

(dissolved)

Nitrite 

(dissolved)

Total 

nitrogen

Total 

phosphorus

One-year period (March 2000–March 2001)

TM-1 to TM-3

TM-1 to TM-4

TM-1 to TM-5 X X X X X X

TM-3 to TM-4

TM-3 to TM-5 X X X X X X

TM-4 to TM-5 X X X X X X X

CEN to TSB X X X X X X X

TM-4 to CEN X X X X X X

CEN to TM-5 X

TM-4 to TSB X X

TSB to TM-5 X X X X X

Three-year period (March 2000–September 2003)

TM-1 to TM-5 X X X X X X X

Site label 

(fig. 1)

Orthophosphate 

(dissolved)

Orthophosphate 

(total)

Phosphorus 

(dissolved)

Fluoride Silica Sulfate

One-year period (March 2000–March 2001)

TM-1 to TM-3

TM-1 to TM-4 X

TM-1 to TM-5 X X X X X

TM-3 to TM-4

TM-3 to TM-5 X X X X X

TM-4 to TM-5 X X X X X

CEN to TSB X X X X

TM-4 to CEN X X X X X X

CEN to TM-5 X X

TM-4 to TSB X X X X X

TSB to TM-5 X X X X

Three-year period (March 2000–September 2003)

TM-1 to TM-5 X X X X X

Table 7. Results of the Kruskal-Wallis test and the Tukey multiple-comparison test illustrating statistically significant (p < 0.05) 

differences for selected water-quality constituents at sites in the Threemile Creek basin, Mobile, Alabama.—Continued

[BOD5, 5-day biochemical oxygen demand; OWC, organic wastewater compound]

p > 0.05 No statistically significant 

differences between sites as 

determined by the Kruskal-Wallis 

test.

X p < 0.05 Statistically significant 

differences between sites as determined 

by the Tukey multiple-comparison test 

(nonparametric).

p > 0.05 No statistically significant 

differences between sites as determined 

by the Tukey multiple-comparison test 

(nonparametric).

Fluoride is added to drinking water by the Mobile Area Water 

and Sewer System in order to meet the USEPA, American 

Medical Association, and American Dental Association 

recommended levels (Mobile Area Water and Sewer System, 

2004). The presence of fluoride in stream water can be 

indicative of human activities, including leaking or overflowing 

sewer systems and WWTP discharges. Fluoride was not 

detected at the three upstream sites on Threemile Creek; 

however, it was detected in each of the samples at the two 

tributaries (CEN and TSB) and at TM-5. Concentrations ranged 

from 0.1 mg/L (TSB and TM-5) to 1.3 mg/L (CEN; appendix 

table 2-1). Fluoride concentrations were significantly higher at 

CEN than at TM-5 (table 7). 

Median levels of sodium and boron increased in a 

downstream direction in Threemile Creek; sodium 

concentrations ranged from 1.8 mg/L at TM-1 to 4,300 mg/L at 

TM-5, and boron concentrations ranged from 10 μg/L at TM-1 

to 1,900 μg/L at TM-5 (appendix table 2-1). Seawater typically 

has a sodium concentration of about 10,500 mg/L and a boron 

concentration of about 4,500 μg/L (Hem, 1985); thus, high 

concentrations at TM-5 indicate the presence of seawater. Boron 

compounds are used to make water softeners, soaps, and 
Water-Quality Results and Discussion 27

detergents; other uses include agricultural chemicals, pest 

controls, fire retardants, and medicines. The high range of boron 

concentrations (90–840 μg/L) at CEN may be indicative of 

leaking septic tanks or sewer lines or WWTP outflows in the 

basin. Both sodium and boron concentrations at CEN were 

highest during low flow, indicating point sources rather than 

nonpoint sources. The high concentrations of sodium at CEN 

are likely another indicator that water chemistry at this site may 

be influenced by anthropogenic sources. 

Median levels of magnesium, potassium, and sulfate also 

increased in a downstream direction in Threemile Creek. 

Concentrations of magnesium ranged from 0.6 mg/L at TM-4 to 

507 mg/L at TM-5; concentrations of potassium ranged from 

0.3 mg/L at TM-1 to 160 mg/L at TM-5; and concentrations of 

sulfate ranged from 1.9 mg/L at TM-1 to 1,300 mg/L at TM-5 

(appendix table 2-1). High levels of these constituents at TM-5 

are indicative of the presence of seawater, in which concentrations of magnesium, potassium, and sulfate typically are about 

1,350 mg/L, 390 mg/L, and 2,700 mg/L, respectively (Hem, 

1985). 

Instantaneous and Continuous Measurements 

of Water Properties 

Instantaneous field measurements of physical properties of 

water, such as pH, temperature, specific conductance, and 

dissolved-oxygen concentrations, can be used to compare 

chemical conditions in the streams at the time of sampling. 

Water quality, however, continually changes over time, and 

repeated measurements are necessary to characterize variations. 

Continuous water-quality monitors have sensors and recording 

systems that measure water-quality properties at discrete 

intervals of time. 

The ADEM criteria for pH, water temperature, dissolvedoxygen concentrations, and turbidity are based on water-use 

classification. Water-quality properties, including field 

measurements and continuous water-quality monitoring data, 

are summarized with corresponding criteria in tables 8 and 9, 

respectively. Continuous water-quality monitors in the 

Threemile Creek watershed recorded data (water temperature, 

dissolved-oxygen concentrations, specific conductance, 

Table 8. Instantaneous field measurements of water-quality properties at sites in the Threemile Creek basin, Mobile, 

Alabama, 2000–2003, and corresponding water-quality criteria.

[μS/cm, microsiemens per centimeter; °C, degrees Celsius; NTU, nephelometric turbidity unit; mg/L, milligrams per liter; <, less than or 

equal to; >, greater than or equal to]

Site label 

(fig. 1) Water year

Specific 

conductance 

(μS/cm)

Water 

temperature

(°C)

Turbidity 

(NTU)

Dissolvedoxygen 

concentration

(mg/L)

pH

Water-quality criteria for agricultural and industrial water supplya

a

Criteria established by the Alabama Department of Environmental Management (2000c).

≤ 32.2 ≤ 50b

bTurbidity should not exceed 50 NTU above background (Alabama Department of Environmental Management, 2000c).

≥ 3.0 6.0 – 8.5

Water-quality criteria for fish and wildlifea

≤ 32.2 ≤ 50b ≥ 5.0c

c

Criterion for dissolved-oxygen concentrations under extreme conditions is 4.0–5.0 mg/L (Alabama Department of Environmental 

Management, 2000c).

6.0 – 8.5

Field measurements

TM-1 2000–2003 58 – 99 15 – 31.5 2 – 130 6.8 – 9.5 6 – 7.5

TM-3 2000–2003 64 – 116 15.1 – 31.1 4 – 420 7.1 – 10.5 6.5 – 8.2

TM-4 2000–2003 63 – 126 16.8 – 33.4 3.9 – 800 5.4 – 11.5 6.1 – 7.0

CEN 2000–2001 145 – 1,230 15.2 – 34.8 0.7 – 35 8.6 – 21.5 7.2 – 10.0

TSB 2000–2001 99 – 183 15 – 35.3 5 – 39 8.9 – 15.8 6.6 – 9.9

TM-5 2000–2003 201 – 21,400 14.1 – 30 4 – 68 2.2 – 11 6.5 – 8.2
Table 9. Continuous measurements of water-quality properties at sites in the Threemile Creek basin, Mobile, Alabama, water years 2000–

water-quality criteria.[μS/cm, microsiemens per centimeter; °C, degrees Celsius; NTU, nephelometric turbidity unit; mg/L, milligrams per liter; <, less than or equal to; >, greater than or 

Site label 

(fig. 1)

Water 

year

Specific 

conductance 

(μS/cm)

Water 

temperature

(°C)

Turbidity 

(NTU)

Dissolvedoxygen 

concentration

(mg/L)

Number of days 

of good record 

for dissolved 

oxygen

Number of 

days that 

dissolved 

oxygen was 

less then 

3.0 mg/L

Water-quality criteria for agricultural and industrial water supply

aCriteria established by the Alabama Department of Environmental Management (2000c).

a

≤32.2 ≤

bTurbidity should not exceed 50 NTU above background (Alabama Department of Environmental Management, 2000c).

50b ≥ 3.0

Water-quality criteria for fish and wildlifea

≤32.2 ≤50b ≥

cCriterion for dissolved-oxygen concentrations under extreme conditions is 4.0–5.0 mg/L (Alabama Department of Environmental Management, 2000c).

5.0c

Continuous water-quality data

TM-1 2000 37 – 88 8.8 – 35.1 0 – 130 0.5 – 10.6 213 23 

2001 31 – 104 5.2 – 32.8 0 – 760 0.3 – 10.9 319 3 2002 25 – 169 5.8 – 30.3 0 – 470 0.1 – 13.3 278 47 2003 32 – 111 8.0 – 32.9 0 – 470 0.1 – 13.2 349 11 

TM-4 2000 41 – 445 7.6 – 35.2 0 – 260 0 – 11.5 115 57 

2001 48 – 309 5.3 – 32.6 0 – 650 0.2 – 12.0 224 19 2002 56 – 477 7.1 – 34.2 0 – 420 0 – 16.6 319 64 2003 40 – 202 7.8 – 31.7 0 – 580 0 – 13.5 342 110 

TM-5 2000 83 – 35,800 10.6 – 32.3 0 – 130 0 – 10.7 333 274 

2001 60 – 37,200 7.9 – 31.2 0 – 810 0 – 12.7 304 197 2002 134 – 34,700 8.9 – 31.6 0 – 290 0 – 14.6 298 176 2003 63 – 22,700 9.2 – 30.6 0 – 400 0 – 13.8 300 181 
Water-Quality Results and Discussion 29

turbidity, and gage height) at 15-minute intervals. More 

detailed information is available from continuous water-quality 

monitors in Threemile Creek in USGS annual data reports for 

Alabama (Pearman and others, 2001, 2002, 2003; Psinakis and 

others, 2004). 

Long-term continuous water-quality data were not 

available from any of the sites prior to this study. Continuous 

measurements of dissolved-oxygen concentrations, water 

temperature, and specific conductance were recorded at TM-1 

between December 1999 and September 2003, and continuous 

measurements of turbidity were recorded between May 2000 

and September 2003. Continuous measurements of dissolvedoxygen concentrations, water temperature, specific 

conductance, and turbidity were recorded at the TM-4 site 

between September 1999 and September 2003 and at the TM-5 

site between October 1999 and September 2003 (table 9; 

Pearman and others, 2001, 2002, 2003; Psinakis and others, 

2004). 

The pH of surface water generally ranges from 6.5 to 8.5. 

When pH falls below 4 or 5, possibly as a result of commercial 

or industrial discharges, urban runoff, or acid rain, the structure 

of an aquatic community can be affected. Likewise, when pH 

exceeds 9, prolonged exposure is harmful to some species of 

fish and benthic invertebrates. The pH of water determines the 

solubility and biological availability of chemical constituents, 

including nutrients and heavy metals; slight changes in pH can 

have indirect effects on a stream and the aquatic community. 

The ADEM established a pH range of 6 to 8.5 to reduce the 

effects of highly acidic or highly basic water on fish and 

wildlife (Alabama Department of Environmental Management, 

2000c). 

Field measurements of pH were made at all sites at the 

time of sampling (table 8; appendix table 2-1). In Threemile 

Creek, pH ranged from 6.0 at TM-1 to 8.2 at TM-3 and TM-5; 

in the two tributaries, pH ranged from 7.2 to 10.0 at CEN and 

from 6.6 to 9.9 at TSB (table 8; appendix table 2-1). The pH 

values at all sites on Threemile Creek were within the ADEM 

criteria established for agricultural and industrial water supply 

as well as fish and wildlife (Alabama Department of 

Environmental Management, 2000c). The higher pH values 

found at the two tributaries (CEN and TSB) may be indicative 

of contaminants from other sources. Seawater has a pH value of 

8.2; natural water with a pH value greater than 9.0 is unusual 

(Hem, 1985). High pH values often are associated with 

photosynthesis in highly productive systems, particularly in 

streams with low gradient and low velocity. In the two 

tributaries, it is assumed that some combination of 

photosynthesis and industrial discharge or sewage effluent 

(containing soap or bleach) is contributing to the high pH 

values. 

Specific conductance is an indicator of the ability of water 

to conduct an electric current and is proportional to the 

dissolved-solids concentration in the water. Many factors affect 

specific conductance in streams, including flow conditions, 

bedrock, and contributions of dissolved solids from point and 

nonpoint sources. Standards or criteria for specific conductance 

have not been established by the ADEM or the USEPA. 

Specific conductance was measured at the time of sample 

collection (table 8) and by continuous water-quality monitors at 

three sites (table 9). At site TM-1 in Threemile Creek, 

continuous measurements of specific conductance ranged from 

25 to 169 microsiemens per centimeter (μS/cm) at 25 degrees 

Celsius (°C); specific conductance ranged from 40 to 

477 μS/cm at TM-4 and from 60 to 37,200 μS/cm at TM-5 

(table 9). The higher measurements of specific conductance at 

TM-5 are attributed to the presence of seawater at this site, 

which typically has a specific conductance of about 

50,000 μS/cm (Hem, 1985). Specific conductance 

measurements ranged from 145 to 1,230 μS/cm at CEN and 

from 99 to 183 μS/cm at TSB (table 8). The higher 

measurements of specific conductance at CEN may be due to 

contaminants in the stream. The lowest specific conductance 

values recorded by field personnel in Threemile Creek were 

measured during periods of elevated flow, indicating that the 

stream water was diluted by rainwater. 

Dissolved-oxygen concentration is widely used for 

evaluating the biochemistry of streams and lakes. Dissolvedoxygen concentrations may be depleted by processes that 

consume organic matter. Actively photosynthesizing algae and 

aquatic plants can increase concentrations of dissolved oxygen 

(Hem, 1985). The ADEM has established criteria for dissolvedoxygen concentrations in streams based on water-use 

classification (Alabama Department of Environmental 

Management, 2000c). To meet the criterion for diversified 

warm-water biota, daily dissolved-oxygen concentrations 

cannot fall below 5 mg/L. Under extreme conditions resulting 

from natural causes, dissolved-oxygen concentrations ranging 

from 4.0 to 5.0 mg/L are allowed provided that the water quality 

is favorable in all other properties (Alabama Department of 

Environmental Management, 2000c). To meet the criterion for 

streams classified for agricultural and industrial use, daily 

dissolved-oxygen concentrations cannot fall below 3.0 mg/L 

(Alabama Department of Environmental Management, 2000c). 

Low concentrations are commonly found in warm waters that 

are not well mixed. Dissolved-oxygen concentrations typically 

vary in a diurnal fashion, and differences between high and low 

values can exceed 10 mg/L within a 24-hour period. For 

example, during low-flow conditions (August 25–27, 2001) at 

TM-4, peak dissolved-oxygen concentrations (8.4–9.7 mg/L) 

were recorded between 1300 and 1700 each day, and minimum 

dissolved-oxygen concentrations (0.2–0.4 mg/L) were 

recorded between 0100 and 0300 each day (fig. 7B). 

During this study, concentrations of dissolved oxygen did 

not always meet criterion established by the ADEM. The 

continuous monitors at TM-1, TM-4, and TM-5 recorded 

dissolved-oxygen concentrations that were less than the 

minimum criterion established for agricultural and industrial 

water supply (3.0 mg/L, table 9). The number of days that 

dissolved-oxygen concentrations did not meet the minimum 

criterion was greatest at TM-5 and ranged from 176 in 

WY 2002 to 274 in WY 2000 (fig. 8; table 9). In contrast, the 

number of days that dissolved-oxygen concentrations did not 
30 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 7. Gage height, water temperature, specific conductance, dissolved oxygen, turbidity, and discharge at U.S. Geological 

Survey streamgaging stations (A) 02471013 (TM-1), (B) 0247101490 (TM-4), and (C) 02471016 (TM-5), August 25 – September 4, 2001. 

(Discharge is shown for site TM-1 only.)
Water-Quality Results and Discussion 31

meet the minimum criterion at TM-1 ranged from 3 in WY 2001 

to 47 in WY 2002 (fig. 8; table 9). At the two tributaries, 

dissolved-oxygen concentrations ranged from 8.6 to 21.5 mg/L 

at CEN and from 8.9 to 15.8 mg/L at TSB (table 8). The high 

levels of dissolved oxygen at the tributaries likely indicate the 

occurrence of photosynthesis at these sites. 

Water temperature exceeded the recommended criterion 

(32.2 °C) for agricultural and industrial water supply and for 

fish and wildlife at five of six sites in the Threemile Creek basin 

(tables 8, 9). Instantaneous field measurements of water 

temperature exceeded the criterion at TM-4, CEN, and TSB 

(table 8)—all exceedances occurred during July 2000 or 

July 2001 (Pearman and others 2001, 2002, 2003; Psinakis and 

others, 2004). Continuous measurements of water temperature 

exceeded the criterion at TM-1, TM-4, and TM-5 (table 9). 

Exceedances occurred most frequently between June and 

August (Pearman and others 2001, 2002, 2003; Psinakis and 

others, 2004). Exceedances recorded by continuous monitors 

occurred most frequently at TM-1 (58) and TM-4 (57) rather 

than TM-5 (2) during the 4-year monitoring period 

(WY 2000–2003).

Turbidity, a measure of water clarity, is determined by 

measuring the degree that particles suspended in water decrease 

light penetration through the water. Particles may come from 

soil, sediment, algae, plankton, natural organic matter, or 

manmade substances. High turbidities commonly occur during 

storms when overland runoff erodes soil and carries it to the 

stream, and increased flow resuspends sediment in the 

streambed. Turbidity peaks associated with declines in specific 

conductance indicate stormwater runoff. High turbidities, 

however, also can be measured during low-flow conditions 

when certain materials or compounds are discharged from 

industrial or commercial facilities, or when algae production is 

high. Thus, high turbidities may be associated with higher-thannormal specific conductance measurements. The ADEM 

criterion requires that turbidity not exceed 50 nephelometric 

turbidity units (NTU) above background except due to natural 

origin (Alabama Department of Environmental Management, 

2000c). Background levels have not been defined by the ADEM 

for Threemile Creek; consequently, turbidity values were not 

compared to this criterion. At TM-1, turbidity ranged from 0 to 

760 NTU; at TM-4, turbidity ranged from 0 to 650 NTU; and at 

TM-5, turbidity ranged from 0 to 810 NTU (table 9). High 

turbidities were observed at all three sites and, in many cases, 

likely were the result of natural runoff (fig. 7). 

Turbidity also can be used to examine whether high-flow 

samples were collected during the first flush, when many 

contaminants may be at a maximum level. Continuous waterquality data were recorded during a 3-day period at TM-1, 

TM-4, and TM-5 (August 27–30, 2001). During this period, a 

storm produced a small increase in discharge at TM-1 (fig. 7A). 

During the storm, turbidity at TM-1 peaked (41.5 NTU) at 2045 

on August 28, yet discharge peaked (327 cubic feet per second 

[ft3/s]) at 1545 (fig. 7A), illustrating the likelihood that there 

Figure 8. Number of days that continuous water-quality monitors recorded concentrations of dissolved oxygen less 

than 3.0 milligrams per liter at three sites on Threemile Creek, Mobile, Alabama, water years 2000 – 2003.
32 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

was no first flush associated with this storm. At TM-4, turbidity 

peaked (654 NTU) at 1400 on August 28 and gage height 

increased slightly (1.11–1.33 ft) between 1230 and 1315 

because of the storm (fig. 7B). The first flush most likely 

occurred about 1400, when turbidity values were highest. At 

TM-5, turbidity increased slightly (6–24 NTU) from 1200 to 

1400 and then peaked (142 NTU) at 2200 on August 28 as the 

tide reached its lowest point—gage height showed little 

variation outside of the normal tidal fluctuation (-0.5–1.6 ft) 

except for a small increase (0.28–0.46 ft) between 1600 and 

1630, which may have been associated with rainfall or other 

discharges to the stream (fig. 7C). The hydrology at both TM-4 

and TM-5 is complex due to the tidal influences at these sites 

that tend to dampen gage-height variation caused by stormwater 

inflow. 

Nutrients 

Nutrients, chemical elements that are necessary for life, 

consist primarily of the various species of nitrogen and 

phosphorus. Nutrient concentrations in 

aquatic systems are of interest because 

excess concentrations can have 

detrimental effects on aquatic health and 

anthropogenic uses of the system. 

Eutrophication in freshwater systems is 

usually linked to high phosphorus 

concentrations and can lead to nuisance 

plant growth and algal blooms, which in 

turn can cause reduced light penetration 

and dissolved-oxygen concentrations, 

fouled water intakes, and taste and odor 

problems in drinking water. Likewise, 

excess nitrogen has been linked to 

eutrophication in coastal systems. Excess 

concentrations of nitrogen and phosphorus in streams draining 

to the northern Gulf of Mexico also have been linked to hypoxia 

in that area (Rabalais and others, 1996). 

Sources of nutrients can be natural or anthropogenic. 

Natural sources of nutrients include weathering of minerals in 

rocks and soils and biological remineralization of organic 

matter. Anthropogenic nutrient sources include fertilizers, 

manure, faulty sanitary sewers and septic tanks, and 

wastewater-treatment plant outfalls. Nutrient species measured 

for this study were total and dissolved ammonia, total and 

dissolved ammonia plus organic nitrogen, dissolved nitrite plus 

nitrate, dissolved and total orthophosphate, and dissolved and 

total phosphorus. Calculated nutrients were total nitrogen, the 

sum of total organic nitrogen plus ammonia and nitrite plus 

nitrate; total organic nitrogen, the difference in ammonia and 

total organic nitrogen plus ammonia; and suspended 

phosphorus, the difference in total phosphorus and dissolved 

phosphorus. 

Nitrogen

Nitrogen concentrations generally were lower in the 

upstream main-stem sites (TM-1, TM-3, and TM-4) and higher 

in the tributary sites (CEN and TSB) and in the downstreammost main-stem site (TM-5). Tukey’s multiple-comparison test 

was used to determine statistically significant differences 

among the water-quality sampling sites for the various 

nutrients. Because all sites were sampled on a similar schedule 

during the first year (March 2000 to March 2001), only samples 

collected during this time period were used for the test. 

Multiple-comparison test results for total nitrogen indicated 

four groups—A, AB, BC, and C (table 10). Sites with the same 

letter designation are considered to be statistically similar 

(Helsel and Hirsch, 1992). Sites with letter designation A have 

higher concentrations than those with letter designation B, 

which have higher concentrations than those with letter 

designation C. Sites can have multiple letter designations, 

meaning they are similar to other sites but the other sites are not 

necessarily similar to each other. 

Total nitrogen concentrations ranged from 0.33 to 

5.2 mg/L (appendix table 2-1; fig. 9). The highest maximum 

concentration (5.2 mg/L) was at TM-5, and the highest median 

concentration (2.5 mg/L) was at CEN (fig. 9). Median 

concentrations of total nitrogen at TM-3, TM-4, and TSB were 

lower than the ecoregion nutrient criteria; however, all samples 

at CEN and TM-5 exceeded the ecoregion nutrient criteria for 

total nitrogen (fig. 9; table 11; U.S. Environmental Protection 

Agency, 2000a, 2000b). 

Total organic nitrogen plus ammonia concentrations 

ranged from < 0.200 to 3.2 mg/L (appendix table 2-1). The 

highest maximum and median concentrations occurred at CEN 

and were 3.2 mg/L and 1.85 mg/L, respectively. Results of 

multiple-comparison tests indicate three site groupings—AB, 

B, and BC (table 10). Total organic nitrogen plus ammonia 

concentrations exceeded the ecoregion nutrient criteria for all 

samples at CEN and TM-5; the majority of the remaining 

samples at TM-3, TM-4, and TSB were below the ecoregion 

criteria (fig. 9; table 11).

Table 10. Results of multiple-comparison tests on selected nutrients at surface-water 

sites in the Threemile Creek basin, Mobile, Alabama.

Nutrients TM-1 TM-3 TM-4 CEN TSB TM-5

Total nitrogen C BC BC AB C A

Organic nitrogen plus ammonia B BC BC AB B AB

Ammonia AB B B A B AB

Nitrite-plus-nitrate nitrogen B B B B B A

Total phosphorus C C BC AB B A

Dissolved phosphorus C C C A B AB

Dissolved orthophosphate C C C AB B A
Water-Quality Results and Discussion 33

Figure 9. Distribution of total nitrogen, nitrite plus nitrate, total ammonia plus organic nitrogen, and ammonia concentrations at sites in the 

Threemile Creek basin, Mobile, Alabama.
34 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Dissolved ammonia concentrations ranged from < 0.010 to 

2.4 mg/L (appendix table 2-1). The highest maximum 

concentration (2.4 mg/L) and the highest median concentration 

(0.445 mg/L) occurred at CEN (fig. 9). Results of multiplecomparison tests indicate three site groupings—A, AB, and B 

with CEN being the only site in group A (table 10). Because 

ammonia in aerated systems usually is converted to oxidized 

forms of nitrogen, the high dissolved ammonia concentrations 

at CEN are indicative of urban influences. 

Dissolved nitrite-plus-nitrate concentrations ranged from 

< 0.02 to 3.6 mg/L (appendix table 2-1). The highest maximum 

concentration (3.6 mg/L) and median concentration (1.3 mg/L) 

of nitrite plus nitrate occurred at TM-5. Nitrite-plus-nitrate 

concentrations exceeded USEPA ecoregion nutrient criteria 

(table 11) in 88 percent of the samples. All samples at TM-3, 

TM-4, CEN, TSB, and TM-5 exceeded the ecoregion nutrient 

criteria (table 11) for nitrite plus nitrate (fig. 9); approximately 

50 percent of the samples at TM-1 exceeded the ecoregion 

nutrient criteria (table 11) for nitrite plus nitrate (fig. 9). No 

samples for nitrate exceeded the drinking-water standard of 

10 mg/L (U.S. Environmental Protection Agency, 2002a). 

Multiple-comparison tests indicated two groups for nitrite plus 

nitrate, A and B, with TM-5 being the only site in group A 

(table 10). 

Nitrite was detected infrequently and, when detected, 

concentrations were very low except at sites CEN and TM-5 

(appendix table 2-1). Nitrite concentrations ranged from 

< 0.01 mg/L to 0.15 mg/L. The highest maximum concentration 

(0.15 mg/L) and median concentration (0.07 mg/L) were at 

CEN. Because nitrite is generally unstable in oxygenated waters 

(Hem, 1985), its presence can be an indication of contamination 

from wastewater sources. The high concentrations of nitrite at 

CEN probably are a reflection of urban influences, but the 

variable influences on water quality at TM-5 make determining 

the source of nitrite difficult at TM-5.

Total organic nitrogen was the predominant species of the 

total nitrogen concentration at all sites except TM-5 and CEN. 

Excluding TM-5 and CEN, total organic nitrogen contributed 

57 to 69 percent of the total nitrogen concentration; nitrate 

contributed 20 to 35 percent of the total nitrogen concentration; 

and ammonia contributed 9 to 16 percent of the total nitrogen 

concentration (fig. 10). The median contributions of total 

organic nitrogen plus ammonia and nitrate to the total nitrogen 

concentration at TM-5 were 52 and 47 percent, respectively. 

Determining the source of increased nitrate at TM-5 would be 

difficult because of the variable influences on water quality at 

this site, including Three Mile Creek and its tributaries, the 

Mobile River, and Mobile Bay. 

Phosphorus

Phosphorus concentrations exhibited similar distribution 

patterns as nitrogen concentrations, with thr three upstream 

main-stem sites (TM-1, TM-3, and TM-4) having significantly 

Table 11. Ambient water-quality criteria recommendations for rivers and streams in Nutrient Ecoregions IX and XII (U.S. Environmental 

Protection Agency, 2000a, 2000b).

[mg/L, milligram per liter; μg/L, microgram per liter]

Ecoregion Site label 

(fig. 1)

Total Kjeldahl 

nitrogen 

(mg/L)

Nitrite plus 

nitrate 

(mg/L)

Total 

nitrogen 

(mg/L)

Total 

phosphorus 

(mg/L)

Suspended 

chlorophyll a

(μg/L)

Nutrient Ecoregion IX—Southeastern 

Temperate Forested Plains and Hills

TM-1, TM-2 0.3 0.095 0.618 0.0225 0.049

Nutrient Ecoregion XII—Southeastern 

Coastal Plain

TM-3, TM-4, CEN, 

TSB, TM-5

0.56 0.02 0.90 0.04 0.4

Figure 10. Median concentrations of nitrite plus nitrate, 

ammonia, and total organic nitrogen at sites in the Threemile 

Creek basin, Mobile, Alabama.
Water-Quality Results and Discussion 35

lower phosphorus concentrations than the tributaries (CEN and 

TSB) and downstream main-stem site (TM-5, fig. 11). Total 

phosphorus values ranged from < 0.002 to 0.831 mg/L 

(appendix table 2-1). The highest maximum concentration 

(0.831 mg/L) and median concentration (0.406 mg/L) of total 

phosphorus were at CEN (fig. 11). In 45 percent of the samples, 

total phosphorus concentrations exceeded the USEPA goal of 

0.1 mg/L for preventing nuisance aquatic growth. The majority 

of total phosphorus concentrations at TM-1, TM-3, and TM-4 

were below the ecoregion nutrient criteria (table 11) and the 

USEPA goal of 0.1 mg/L total phosphorus (fig. 11). Total 

phosphorus concentrations in all samples at CEN, TSB, and 

TM-5 exceeded both the ecoregion nutrient criteria for total 

phosphorus (table 11) and the USEPA goal of 0.1 mg/L total 

phosphorus (fig. 11; U.S. Environmental Protection Agency, 

1986b, 2000a, 2000b). 

Dissolved phosphorus concentrations ranged from < 0.002 

to 0.45 mg/L, and dissolved orthophosphate concentrations 

ranged from < 0.001 to 0.405 mg/L (appendix table 2-1). The 

highest median concentrations for dissolved phosphorus 

(0.245 mg/L) and orthophosphate (0.228 mg/L) were at CEN. 

The highest maximum concentration for dissolved phosphorus 

(0.45 mg/L) was detected at CEN, and the highest dissolved 

orthophosphate concentration (0.405 mg/L) was detected at 

TM-5. Multiple-comparison test results indicated that 

concentrations at TM-1, TM-3, and TM-4 were significantly 

less than at CEN, TSB, and TM-5 for dissolved phosphorus and 

dissolved orthophosphate (table 10; fig. 11). 

Dissolved phosphorus contributed 97 to 60 percent of the 

total phosphorus concentration, and suspended phosphorus 

contributed 3 to 40 percent of the total phosphorus 

concentration (fig. 12). The low percentage of suspended 

phosphorus at TM-4 may be because mostly base-flow samples 

were collected at this site. Because phosphorus tends to bind to 

suspended sediment and suspended-sediment concentrations 

generally are lower during base flow, the suspended phosphorus 

concentrations also are lower. Settling of suspended particles in 

the impoundment directly upstream from the sampling site may 

have caused the low suspended phosphorus values at TM-1. 

Figure 11. Distribution of total phosphorus, dissolved phosphorus, and dissolved orthophosphate at sites in the Threemile Creek 

basin, Mobile, Alabama.
36 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

The ratio of dissolved inorganic nitrogen to soluble 

reactive phosphorus provides an indication of the relative 

potential for the occurrence of nitrogen or phosphorus 

limitation (Borchardt, 1996). In aquatic systems, the 

limiting nutrient is the substance that is in shortest supply 

relative to plant demands. When the ratio of nitrogen to 

phosphorus by weight is greater than 10 to 1, phosphorus 

is considered to be the limiting nutrient; when the ratio is 

less than 5 to 1, nitrogen is considered to be the limiting 

nutrient. For nitrogen to phosphorus ratios in the ranges of 

5 to 1 and 10 to 1, the effect of each major nutrient is equal. 

In most freshwater systems, phosphorus is the limiting 

nutrient, and for most estuarine or saltwater systems, 

nitrogen is the limiting nutrient. The distribution of the 

ratios of dissolved inorganic nitrogen to dissolved 

orthophosphate indicated two distinct groups for the sites 

in the study (fig. 13). The majority of samples in the three 

upstream main-stem sites (TM-1, TM-3, and TM-4) had 

total nitrogen to phosphorus ratios greater than 10 to 1, 

indicating that phosphorus is the limiting nutrient at these 

sites. Most nitrogen to phosphorus ratios at CEN and 

TM-5 indicated equal influence of nitrogen and 

phosphorus limitation. Nitrogen to phosphorus ratios for 

all but one sample at TSB were lower than 5, indicating the 

potential for nitrogen limitation at this site. Because waterquality conditions at TM-5 are influenced by freshwater 

inputs from Threemile Creek and the Mobile River and by 

the saline inputs from Mobile Bay, it is not unexpected 

that the nitrogen to phosphorus ratio indicates equal 

influences. Water-quality conditions at the two tributary 

sites (CEN and TSB) are not influenced by Mobile Bay, and the 

nitrogen to phosphorus ratios are probably a reflection of the 

point and nonpoint nitrogen and phosphorus sources from the 

higher percentage of urban land use in these basins. 

Suspended Chlorophyll a and b

Suspended chlorophyll a was detected in 39 of 96 

(40.6 percent) water-column samples, with concentrations 

ranging from < 0.1 to 100 μg/L (appendix table 2-1). Suspended 

chlorophyll a was detected at five sites (TM-3, TM-4, CEN, 

TSB, and TM-5) but was not detected at TM-1 (appendix 

table 2-1). The highest maximum concentration of suspended 

chlorophyll a was detected at TSB (100 μg/L); the highest 

median concentrations were detected at TM-5 (24.0 μg/L), TSB 

(5.35 μg/L), and CEN (4.85 μg/L, appendix table 2-1). For 

rivers and streams in Nutrient Ecoregion XII, the USEPA 

recommends that suspended chlorophyll a not exceed 0.4 μg/L 

(table 11; U.S. Environmental Protection Agency, 2000b). 

During this study, suspended chlorophyll a exceeded this 

recommendation in 39 of 96 samples (40.6 percent) collected in 

the Threemile Creek watershed (appendix table 2-1). 

Suspended chlorophyll b was not detected in any of the samples 

(appendix table 2-1).

Figure 12. Median concentrations of suspended phosphorus and dissolved phosphorus at sites in the Threemile 

Creek basin, Mobile, Alabama.

Figure 13. Distribution of dissolved inorganic nitrogen and dissolved 

orthophosphate ratios for sites in the Threemile Creek basin, Mobile, 

Alabama.
Water-Quality Results and Discussion 37

Biochemical Oxygen Demand and Total Organic 

Carbon

Five-day biochemical oxygen demand (BOD5) is the 

amount of dissolved oxygen used by microorganisms to break 

down organic matter in water at 20 °C over a 5-day period. The 

standard BOD5 value is useful as a measure of the amount of 

oxygen that will be depleted by organic material in a stream, 

often from domestic or industrial waste. Most moderately 

contaminated streams have BOD5 values ranging between 

1 and 8 mg/L (Nemerow, 1974). Typical domestic wastewater 

can have BOD5 values ranging between 50 and 200 mg/L 

(Camp and Meserve, 1974; McGhee, 1991). In the Threemile 

Creek basin, BOD5 ranged from 0.1 mg/L (TM-1) to 8.8 mg/L 

(CEN, appendix table 2-1). The Kruskal-Wallis test and the 

Tukey multiple-comparison test were applied to the BOD5 data 

at six sites to determine if the variations in water chemistry 

among sites were statistically significant (table 7). BOD5

concentrations at TM-5 were significantly higher than at TM-1 

for WYs 2000–2003. 

Total organic carbon (TOC) represents the amount of 

carbon present in organic molecules. The average TOC 

concentration in rivers is about 7 mg/L (Thurman, 1985). TOC 

concentrations can be higher because of elevated amounts of 

organic material, such as in marshland or boggy areas, where 

average concentrations may range from 17 to 33 mg/L 

(Thurman, 1985). In contaminated rivers, TOC concentrations 

can be even higher (30 to 58 mg/L; Dojlido and Best, 1993). In 

Threemile Creek, TOC ranged from 1.9 (TM-1) to 7.9 mg/L 

(TSB, appendix table 2-1). TOC concentrations at TM-5 were 

significantly higher than TOC concentrations at TM-1, TM-3, 

and TM-4; TOC concentrations at CEN were significantly 

higher than TOC concentrations at TM-4 (table 7).

Fecal-Indicator Bacteria

Fecal-indicator bacteria are nonpathogenic bacteria that 

are useful in assessing water quality because they are 

commonly associated with the presence of waterborne 

pathogens (Myers and Wilde, 1999). The presence or absence 

of indicator organisms is used to evaluate the microbiological 

quality of water, in part, because direct techniques to analyze 

for pathogens are either quantitatively unreliable or difficult to 

perform. The most commonly used fecal-indicator bacteria 

include fecal coliform, E. coli, and enterococci. Although most 

species of fecal coliform bacteria are from the feces of humans 

and other warm-blooded animals, some species can occur 

naturally in soils. As a result, the USEPA has recommended that 

E. coli or enterococci be used instead of fecal coliform bacteria 

as an indicator of fecal contamination in waters used for 

recreation (U.S. Environmental Protection Agency, 1986a, 

2002b). This recommendation was based on studies that 

showed a strong correlation between the number of 

gastrointestinal illnesses associated with water-contact 

recreational activities and the concentrations of E. coli or 

enterococci bacteria. 

Concentrations of fecal-indicator bacteria often depend on 

hydrologic conditions prior to and during sampling. For 

example, higher concentrations occur during high flow as a 

result of nonpoint sources, such as overland runoff that carries 

high concentrations of bacteria from many different sources, 

including waste from domestic pets and wildlife, and also as a 

result of re-suspension of bacteria in the streambed. Combined 

sewer overflows and sanitary sewer overflows also contribute 

high levels of bacteria during storms. Leaking sanitary sewer 

lines, connections to sewer lines, or septic tank effluent are 

likely the sources of high levels of bacteria during low flow. 

When point-source discharges contribute fecal-indicator 

bacteria, high concentrations may be present during low flow 

(leaking sanitary sewer lines or failing septic systems) as well 

as during high flow (combined sewer overflows; Gregory and 

Frick, 2000). 

Concentrations of enterococci, E. coli, and fecal coliform 

bacteria in water samples collected from the Threemile Creek 

sites are summarized in table 12. Scatter plots, which 

differentiate between elevated-flow and low-flow samples, 

were used to display the variability in concentrations of 

enterococci, E. coli, and fecal coliform bacteria (fig. 14). The 

USEPA has defined criteria for single-sample densities of 

Table 12. Statistical summary of enterococci, Escherichia coli, and fecal coliform concentrations at sites in the Threemile 

Creek basin, Mobile, Alabama, 2000 –20 03.

[col/100 mL, colonies per 100 milliliters; <, less than]

Site 

label 

(fig. 1)

Enterococci

(col/100 mL)

Escherichia coli

(col/100 mL)

Fecal coliform

(col/100 mL)

Minimum Median Maximum Minimum Median Maximum Minimum Median Maximum

TM-1 11 48 6,000 20 71 2,400 25 100 2,400

TM-3 10 1,200 31,000 14 1,500 29,000 44 300 12,000

TM-4 10 76 47,000 47 290 21,000 83 285 17,000

CEN 110 1,300 14,000 120 2,850 26,000 38 7,000 30,000

TSB 330 2,650 93,000 20 1,060 31,000 < 10 2,550 16,000

TM-5 9 225 22,000 30 470 20,000 20 540 15,000
38 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 14. Concentrations of (A) enterococci, (B) Escherichia coli, and (C) fecal coliform concentrations in 

water samples collected at sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.

100,000

10,000

1,000

100

10

1

ENTEROCOCCI CONCENTRATIONS, IN COLONIES 

PER 100 MILLILITERS

100,000

10,000

1,000

100

10

1

ESCHERICHIA COLI CONCENTRATIONS, IN COLONIES 

PER 100 MILLILITERS

100,000

10,000

1,000

100

10

1

FECAL COLIFORM CONCENTRATIONS, IN COLONIES 

PER 100 MILLILITERS

151 col/100mL 

(USEPA)

576 col/100mL 

(USEPA)

A.

B.

C.

TM-1 TM-3 TM-4 CEN TSB TM-5

TM-1 TM-3 TM-4 CEN TSB TM-5

TM-1 TM-3 TM-4 CEN TSB TM-5

4,000 col/100mL 

(ADEM)

ELEVATED FLOW 

LOW FLOW 

BOTH POINT AND NONPOINT SOURCES 

POINT SOURCES 

NONPOINT SOURCES 

ALABAMA DEPARTMENT OF ENVIRONMENTAL 

 MANAGEMENT 

U.S. ENVIRONMENTAL PROTECTION AGENCY

B

P

NP 

ADEM 

USEPA

EXPLANATION

B NP NP NP NP B

B NP NP B NP B

B NP NP B B B
Water-Quality Results and Discussion 39

enterococci and E. coli in recreational waters based on 

frequency of use and body contact (U.S. Environmental 

Protection Agency, 1986a, 2002b). For infrequent, full-body 

recreational contact, enterococci and E. coli samples should not 

exceed 151 and 576 col/100 mL of water, respectively 

(table 13). The ADEM has defined criteria for fecal coliform 

bacteria based on water-use classification (Alabama 

Department of Environmental Management, 2000c, 2004). For 

agricultural and industrial use, the geometric mean of at least 

five samples collected over a 30-day period should not exceed 

2,000 col/100 mL, nor should any one sample exceed a 

maximum of 4,000 col/100 mL (table 13). 

E. coli concentrations in the Threemile Creek basin ranged 

from 14 to 31,000 col/100 mL (table 12). The highest 

concentration in Threemile Creek (29,000 col/100 mL) was 

detected at TM-3 during a storm in December 2001. The highest 

concentration at TSB (31,000 col/100 mL) was detected during 

elevated flow in March 2001; the two highest concentrations at 

CEN (26,000 and 24,000 col/100 mL) were detected during low 

flow in April and November 2000. Median concentrations of 

E. coli were highest at CEN, followed by TM-3, TSB, TM-5, 

TM-4, and TM-1, respectively (table 12). In general, median 

concentrations of E. coli increased in a downstream direction in 

Threemile Creek. TM-3 was sampled more frequently during 

high flow (13 of 21 samples) than other sites on Threemile 

Creek; concentrations were highest at TM-3. Storm samples 

were collected at TM-3 instead of TM-4 whenever the creek 

could not be waded at TM-4; a security fence along the bridge 

at TM-4 prevented field personnel from collecting samples 

from the bridge. 

Different patterns were observed for concentrations of 

enterococci and fecal coliform bacteria (table 12; fig. 14). 

Enterococci concentrations ranged from 9 to 93,000 col/

100 mL; fecal coliform concentrations ranged from < 10 to 

30,000 col/100 mL (table 12). Median concentrations of 

enterococci were highest at TSB, followed by CEN, TM-3, 

TM-5, TM-4, and TM-1; median concentrations of fecal 

coliform were highest at CEN, followed by TSB, TM-5, TM-3, 

TM-4, and TM-1 (table 12). For both enterococci and fecal 

coliform, median concentrations in the two tributaries were 

higher than median concentrations in Threemile Creek 

(table 12). The highest concentration of enterococci 

(93,000 col/100 mL) was detected at TSB during elevated flow 

in March 2001; the highest concentration of fecal coliform 

(30,000 col/100 mL) was detected at CEN during low flow in 

November 2000. The highest concentrations of enterococci 

(47,000 col/100 mL) and fecal coliform (17,000 col/100 mL) in 

Threemile Creek were detected at TM-4 during elevated flow in 

March 2001.

At the two tributaries, E. coli, enterococci, and fecal 

coliform concentrations exceeded 10,000 col/100 mL during 

low and high flow several times, indicating both point and 

nonpoint sources (fig. 14). In Threemile Creek, however, 

concentrations greater than 10,000 col/100 mL were detected 

almost exclusively during high flow; only one E. coli sample 

(20,000 col/100 mL) exceeded this magnitude during low flow 

at TM-5 (fig. 14). 

During the last 2 years of data collection, water-quality 

samples were collected during four specific time periods at sites 

on Threemile Creek. Sampling at the two tributary sites was 

discontinued. These four time periods targeted different seasons 

and different flow conditions on Threemile Creek: (1) storm in 

December 2001, (2) mixed flow in June 2002, (3) storm in 

February 2003, and (4) base flow in September 2003. Four to 

Table 13. State and Federal standards and criteria for bacteria in surface water.

[USEPA, U.S. Environmental Protection Agency; col/100 mL, colonies per 100 milliliters; ADEM, Alabama Department of Environmental Management]

Fecalindicator 

bacteria

USEPA 

Primary 

Drinking 

Water 

Standarda

(col/100 mL)

a

 Actual standard of the U.S. Environmental Protection Agency (2002a) is that no more than one sample per month (sampled daily) may be positive for 

total coliforms, of which fecal coliform and E. coli are a subgroup.

ADEM 

swimming and other 

whole-body water contact 

sports criterionb

(col/100 mL)

b

 Alabama Water Quality Criteria (Alabama Department of Environmental Management, 2004).

USEPA 

single sample 

infrequent 

full-body 

contact

criterionc

(col/100 mL)

c

 Single sample maximum allowable density (U.S. Environmental Protection Agency, 1986a).

ADEM 

agricultural and industrial 

water-supply criterionb

(col/100 mL)

Coastal 

waters

Noncoastal 

waters

Coastal 

waters

Noncoastal 

waters

Enterococci 0a 35d, 104e none 151c 500e none

Escherichia coli (E. coli) 0a none none 576c none none

Fecal coliform 0a none 200d

 none none 2,000d

 4,000e

d Bacterial concentration is the geometric mean of not less than five samples taken over a 30-day period at intervals not less than 24 hours (Alabama 

Department of Environmental Management, 2004).

e

 Maximum bacterial concentration not to be exceeded in any sample (Alabama Department of Environmental Management, 2004).
40 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

eight bacteria samples were collected over a 2–3 day period at 

three sites on Threemile Creek (TM-1, TM-5, and either TM-3 

or TM-4) during each of these periods. 

In December 2001, four samples were collected at TM-1, 

TM-3, and TM-5 over a 2-day period during a winter storm 

(fig. 15). Antecedent conditions consisted of light rain on 

December 10, 2001, followed by a 48-hour period without rain. 

The highest concentrations of enterococci (15,000 col/100 mL), 

E. coli (29,000 col/100 mL), and fecal coliform (12,000 col/

100 mL) occurred at TM-3 prior to peak discharge. At TM-1 

and TM-5, concentrations of fecal coliform and enterococci 

increased throughout the storm and remained elevated after 

flow began to decline (fig. 15). At TM-3, the concentrations 

peaked about the same time that the second sample was 

collected and declined thereafter, although concentrations 

remained elevated after flow began to decline (fig. 15). 

In June 2002, eight samples were collected at TM-1, 

TM-4, and TM-5 over a 3-day period representing mixed flow 

conditions (fig. 16). Antecedent conditions consisted of light 

rainfall during the preceding 48 hours. Enterococci 

concentrations were highest at TM-4 and ranged from 20 to 

3,600 col/100 mL; E. coli concentrations also were highest at 

TM-4 and ranged from 38 to 1,000 col/100 mL; and fecal 

coliform concentrations were highest at TM-5 and ranged from 

40 to 1,700 col/100 mL. Enterococci concentrations were 

higher at TM-5 than TM-4, except for one sample (fig. 16). 

Enterococci samples were not collected at TM-1. Fecal 

coliform concentrations exhibited a similar pattern and were 

consistently higher at TM-5, followed by TM-4 and TM-1 

(fig. 16). E. coli results were mixed, with highest concentrations 

recorded at both TM-4 and TM-5 (fig. 16).

In February 2003, five samples were collected at TM-1, 

TM-3, and TM-5 over a 2-day period during a winter storm 

(fig. 17). Antecedent conditions consisted of heavy rain on 

February 21–22, 2003, with streamflow conditions returning to 

normal by February 24, 2003. Enterococci concentrations 

ranged from 30 to 27,000 col/100 mL and were highest at 

TM-3; E. coli concentrations ranged from 50 to 9,000 col/

100 mL and also were highest at TM-3. Fecal coliform samples 

were not collected during this period. Initially, concentrations 

of all three types of bacteria appeared to increase or decrease 

according to flow; however, concentrations of enterococci and 

E. coli remained high even after flow had returned to normal 

conditions (fig. 17). Turbidity peaked prior to the last sample 

collected at each of the sites. 

In September 2003, five samples were collected at TM-1, 

TM-3, and TM-5 over a 2-day period during base-flow 

conditions (fig. 18). Antecedent conditions consisted of light 

rainfall on September 13, 2003, with streamflow conditions 

returning to normal by September 15, 2003. Concentrations of 

enterococci ranged from 10 to 220 col/100 mL; concentrations 

of E. coli ranged from 14 to 20,000 col/100 mL; and 

concentrations of fecal coliform ranged from 35 to 

10,000 col/100 mL. Concentrations of all three types of fecalindicator bacteria were highest at TM-5. Concentrations of 

enterococci, E. coli, and fecal coliform at TM-1 remained 

moderate throughout the sampling period and never exceeded 

200 col/100 mL; likewise, concentrations at TM-3 did not 

exceed 96 col/100 mL. Concentrations of E. coli and fecal 

coliform were consistently higher at TM-5, ranging from 580 to 

20,000 col/100 mL (E. coli) and from 780 to 10,000 (fecal 

coliform); however, concentrations of enterococci at TM-5 

ranged from 50 to 220 col/100 mL and were similar in 

magnitude to the concentrations of fecal-indicator bacteria at 

TM-1 and TM-3 (fig. 18). In general, enterococci bacteria are 

considered to be better indicators of potential waterborne 

pathogens than E. coli in marine waters (U.S. Environmental 

Protection Agency, 2002b). It is not known why the 

concentrations of E. coli and fecal coliform were so much 

higher than enterococci concentrations at TM-5 during this 

sampling period. 

In 2002, the USEPA issued a draft guidance for States in 

adopting and implementing bacteriological water-quality 

criteria to protect waters designated for recreation (U.S. 

Environmental Protection Agency, 2002b). In this document, 

the USEPA encourages States to use E. coli or enterococci as 

the basis for their water-quality criteria. The ADEM continues 

to rely on fecal-coliform regulatory standards for most wateruse classifications but has recently added enterococci criteria 

for coastal waters (Alabama Department of Environmental 

Management, 2004). To ensure consistency and continuity 

within regulatory programs, the USEPA recommends that 

States include both fecal coliform and E. coli or enterococci in 

their water-quality standards for a limited period of time, 

generally a 3-year period, while collecting data for newly 

adopted E. coli or enterococci criteria (U.S. Environmental 

Protection Agency, 2002b). 

In order to examine the relations among concentrations of 

fecal-indicator bacteria, correlations were run. Concentrations 

of enterococci, E. coli, and fecal coliform were significantly 

correlated with each other when using a large data set 

(WY 2000–2003). The strongest, most consistent correlations 

were seen between fecal coliform and E. coli concentrations 

(p = < 0.0001; rho = 0.861; fig. 19). Because E. coli is a species 

of the fecal-coliform group (Francy and others, 2000), these 

results were not unexpected. These data should be useful for the 

ADEM as the agency considers which types of fecal-indicator 

bacteria to include in water-quality criteria for the State of 

Alabama. 

Enterococci and E. coli concentrations in the study area 

were compared to the USEPA criteria (single-sample maximum 

for infrequent full-body contact; table 13), and exceedance 

frequencies were calculated (table 14). Fecal coliform 

concentrations were compared to ADEM single-sample criteria 

for streams classified for industrial and agricultural use 

(table 13). Concentrations of enterococcal bacteria at sites in 

the Threemile Creek basin exceeded the USEPA criterion 

(151 col/100 mL) in 52 percent of the samples; E. coli

concentrations exceeded the USEPA criterion (576 col/100 mL) 

in 41 percent of the samples; and fecal coliform concentrations 
Water-Quality Results and Discussion 41

151 col/100 mL (USEPA)

576 col/100 mL (USEPA)

4,000 col/100 mL (ADEM)

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0

100,000 

10,000 

1,000 

100 

10 

1

100,000 

10,000 

1,000 

100 

10 

1

100,000 

10,000 

1,000 

100 

10 

1

DISCHARGE, IN CUBIC FEET PER SECOND; 

GAGE HEIGHT, IN FEET

COLONIES PER 100 MILLILITERS

2400 1200

13

0600 1200 1800 2400

14

DECEMBER

0600 1200 1800 2400 2400

15

0600 1800

A.

B.

C.

USEPA

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

U.S. Environmental 

 Protection Agency

USEPA

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

U.S. Environmental 

 Protection Agency

ADEM

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

Alabama Department of

 Environmental Management

Figure 15. Concentrations of 

(A) enterococci, (B) Escherichia coli, and (C) fecal 

coliform concentrations at 

three sites on Threemile 

Creek, Mobile, Alabama, 

December 13–15, 2001.
42 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 16. Concentrations 

of (A) enterococci, (B) Escherichia coli, and (C) fecal 

coliform concentrations at 

three sites on Threemile 

Creek, Mobile, Alabama, 

June 24 –26, 2002.
Water-Quality Results and Discussion 43

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

U.S. Environmental Protection 

 Agency

USEPA

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

U.S. Environmental Protection 

 Agency

USEPA

151 col/100 mL (USEPA)

576 col/100 mL (USEPA)

300 

250 

200 

150 

100 

50 

0

100,000 

10,000 

1,000 

100 

10 

1

100,000 

10,000 

1,000 

100 

10 

1

300 

250 

200 

150 

100 

50 

0

DISCHARGE, IN CUBIC FEET PER SECOND; GAGE HEIGHT, MULTIPLIED BY 20, IN FEET

COLONIES PER 100 MILLILITERS

2400 1200

26

0600 1800 2400 1200

27

FEBRUARY

0600 1800 2400 1200 2400

28

0600 1800

A.

B.

Figure 17. Concentrations of (A) enterococci and (B) Escherichia coli concentrations at three sites on Threemile Creek, Mobile, 

Alabama, February 26–28, 2003.
44 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 18. Concentrations of (A) enterococci, (B) Escherichia coli, and (C) fecal coliform concentrations at three sites on Threemile Creek, Mobile, Alabama, September 13–16, 2003.

151 col/100 mL (USEPA)

USEPA

576 col/100 mL (USEPA)

4,000 col/100 mL (ADEM)

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

0

100,000 

10,000 

1,000 

100 

10 

1

100,000 

10,000 

1,000 

100 

10 

1

100,000 

10,000 

1,000 

100 

10 

1

DISCHARGE, IN CUBIC FEET PER SECOND; GAGE HEIGHT, MULTIPLIED BY 5, IN FEET

COLONIES PER 100 MILLILITERS

2400 1200

13

0600 1200 1800 2400

14

SEPTEMBER

0600 1200 1800 2400 2400

15

0600 2400 1800 1200

16

0600 1800

A.

B.

C.

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

U.S. Environmental 

 Protection Agency

USEPA

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

U.S. Environmental 

 Protection Agency

ADEM

TM-1 Discharge 

TM-3 Gage height 

TM-5 Gage height 

Sample time 

TM-1 

TM-3 

TM-5 

Alabama Department of 

 Environmental Management
Water-Quality Results and Discussion 45

Figure 19. Relation between Escherichia coli and fecal coliform concentrations measured at sites in the 

Threemile Creek basin, Mobile, Alabama, 2000–2003.

Table 14. Exceedance frequencies for fecal-indicator bacteria detected at sites in the Threemile Creek basin, Mobile, Alabama, 

2000 –20 03.

[USEPA, U.S. Environmental Protection Agency; col/100 mL, colonies per 100 milliliters; ADEM, Alabama Department of Environmental Management]

Site label 

(fig. 1)

Enterococci Escherichia coli Fecal coliform

Total 

number

 of 

samples

Samples 

exceeding 

 USEPA 

criteriona

(151 col/

100 mL)

a

 U.S. Environmental Protection Agency (1986a).

Exceedance 

frequency 

(percent)

Total 

number 

of 

samples

Samples 

exceeding 

 USEPA 

criteriona

(576 col/

100 mL)

Exceedance

frequency 

(percent)

Total 

number 

of 

samples

Samples 

exceeding 

ADEM 

criterionb

(4,000 col/

100 mL)

b

 Alabama Department of Environmental Management (2000c, 2004).

Exceedance 

frequency 

(percent)

TM-1 26 8 31 35 7 20 31 0 0

TM-3 19 11 58 21 12 57 15 5 33

TM-4 20 5 25 19 6 32 20 1 5

CEN 8 6 75 8 5 63 8 5 63

TSB 8 8 100 8 5 63 8 3 38

TM-5 34 22 65 36 17 47 31 4 13

TOTALS 115 60 52 127 52 41 111 18 16
46 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

exceeded the ADEM criterion (4,000 col/100 mL) in 16 percent 

of the samples (table 14). 

Statistically significant differences (p < 0.05) in bacteria 

concentrations were identified among sites (table 7). 

Enterococci, E. coli, and fecal coliform concentrations at TM-5 

were significantly greater than concentrations at TM-1 for the 

entire sampling period (WY 2000–2003; table 7). For the 

1-year period in WY 2000 when samples were collected at all 

sites, enterococci concentrations at TSB were significantly 

greater than TM-4, and fecal coliform concentrations at CEN 

were significantly greater than TM-4 (table 7). 

Concentrations of fecal-indicator bacteria were not well 

correlated with discharge or turbidity except at TM-3 where 

more high-flow samples were collected. At TM-3, enterococci 

concentrations also were well correlated with discharge 

(p < 0.0001; rho = 0.899) and turbidity (p < 0.0001; 

rho = 0.944). Detection of detergents, dyes, or caffeine may 

indicate human sewage as the source of fecal contamination in 

a watershed (U.S. Environmental Protection Agency, 2002b). 

Although these constituents were widely detected in the basin 

(see Organic Wastewater Compounds), concentrations of fecalindicator bacteria were not significantly correlated with 

concentrations of OWCs or with the number of wastewater 

compounds detected in a sample. The lack of correlations 

between these constituents may indicate that the sources of 

fecal contamination are different or that chemical and 

biological processes, such as survival times of indicator 

organisms and degradation of organic compounds, differ 

between these types of constituents. Other factors, including 

salinity, may affect the degradation of organic compounds or 

the survival times of indicator organisms. 

Because of the tidal nature of the lower reaches of 

Threemile Creek, it is difficult to determine whether point or 

nonpoint sources affect bacteria concentrations at some sites, in 

particular TM-5. Concentrations of bacteria at TM-1 and TM-5 

were elevated during low and high flows, indicating both point 

and nonpoint sources. Concentrations of bacteria at TM-3 and 

TM-4 were elevated during high flow rather than low flow, 

indicating nonpoint sources or possibly a reservoir of bacteria 

from a more distant source. The frequency of sampling at 

TM-3 and TM-4, however, differed from that at TM-1 and 

TM-5, and the proportion of high-flow samples collected at 

TM-3 exceeded that at TM-4, TM-1, or TM-5. 

Concentrations of bacteria at the two tributaries were 

consistently higher than at the Threemile Creek sites, indicating 

that some significant source(s) of fecal contamination is(are) in 

these basins. The flow from the tributaries to Threemile Creek 

is small, however, compared to the amount of flow in Threemile 

Creek. These ambiguities make it difficult to determine the 

source affecting Threemile Creek the most: (1) point or 

nonpoint sources along Threemile Creek, (2) contributions 

from the tributaries, (3) contributions from the Mobile River, or 

(4) contributions from Mobile Bay. It appears that a variety of 

sources are contributing to the high levels of bacterial 

contaminants in the Threemile Creek basin—probably a 

combination of point and nonpoint sources originating from 

human and other sources (animal).

Organic Wastewater Compounds

Organic wastewater compounds, referred to as OWCs or 

wastewater indicators, are chemical compounds commonly 

found in wastewater and urban runoff that can be indicative of 

contamination associated with a human source. OWCs can 

originate from a variety of natural and anthropogenic sources in 

a watershed, including wastewater-treatment facilities. 

Household chemicals, pharmaceuticals, and other consumables 

are released to the environment after passing through WWTPs 

or domestic septic systems, which often are not designed to 

remove them from the effluent. Most compounds have 

anthropogenic sources although a few compounds, such as 

cholesterol and coprostanol, also occur naturally. Comparative 

analysis of detection frequency and concentrations provides 

clues to identify the sources and origins of these compounds. 

The method used by the NWQL to identify OWCs was 

developed in response to increasing concern over the effects of 

endocrine-disrupting chemicals in wastewater on aquatic 

organisms (Zaugg and others, 2002). The method focuses on 

determining the compounds that are either an indicator of 

wastewater or that have been chosen on the basis of their 

endocrine-disrupting potential or general toxicity (Zaugg and 

others, 2002). Of the 48 compounds selected for analysis in the 

stream samples collected from the Threemile Creek basin, 

37 compounds were detected in at least one sample (fig. 20; 

table 15; appendix table 2-2). Because of the large number of 

OWCs analyzed, they have been broadly characterized into the 

following 11 groups: antioxidants, prescription and 

nonprescription drugs (17β-estradiol, caffeine, and cotinine), 

steroids (sterols and stanols), fragrances, detergent metabolites, 

antimicrobials, plasticizers/flame retardants, insect repellents, 

insecticides, herbicides and fungicides, and polycyclic aromatic 

hydrocarbons (PAHs). 

Wastewater indicators were detected in each of the 63 

samples collected from the Threemile Creek basin (appendix 

table 2-2). Of the 48 compounds analyzed in stream samples 

from the study sites, 9 OWCs were detected frequently 

(50-percent or greater detection frequency) in samples from the 

Threemile Creek basin (fig. 20). The most frequently detected 

compounds were atrazine (herbicide), caffeine (stimulant), 

2-butoxyethanol phosphate (household cleaning agent), 

cholesterol (plant and animal steroid), diazinon (insecticide), 

bromacil (herbicide), triclosan (antimicrobial disinfectant), 
Water-Quality Results and Discussion 47

ATRAZINE

CAFFEINE

2-BUTOXYETHANOL PHOSPHATE

CHOLESTEROL

DIAZINON

BROMACIL

TRICLOSAN

FLUORANTHENE

N,N-DIETHYL-m-TOLUAMIDE

NP1EO

PYRENE

TRI(2-chloroethyl)PHOSPHATE

β-SITOSTEROL

3 β-COPROSTANOL

para-NONYLPHENOL (total)

AHTN

COTININE

NP2EO

PHENANTHRENE

HHCB

PROMETON

5-METHYL-1H-BENZOTRIAZOLE

OP1EO

TRI(2-chloroisopropyl)PHOSPHATE

para-CRESOL

NAPHTHALENE

TRIPHENYL PHOSPHATE

BENZO [a] PYRENE

CARBARYL

METOLACHLOR

ACETOPHENONE

STIGMASTANOL

17 β-ESTRADIOL

2,6-DIMETHYL-NAPHTHALENE

ANTHRACENE

CHLORPYRIFOS

OP2EO

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0

FREQUENCY OF DETECTION, IN PERCENT

Figure 20. Frequencies of detection for selected organic wastewater compounds in water samples from the Threemile Creek 

basin, Mobile, Alabama, 2000–2003.
Table 15. Summary of organic wastewater compounds detected in water samples collected in the Threemile Creek basin, Mobile, Alabama, 2000–2[μg/L, micrograms per liter; BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; HHCB, 1,3,4,6,7,8hexamethyl-cyclopenta(g)-2-benzopyran; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol; OP2EO, diethoxylat

wastewater compounds; Compounds that are potential endocrine disruptors are in bold; Percent detections in bold indicate which site had the maximum concentration measured 

Compound Maximum concentration (μg/L) Number of detections Sample size Detection frequency (per

All sites TM-1 TM-3 TM-4 C

Antioxidants 2,6-di-tert-butylphenol 0 30 0 0 0 0 

2,6-di-tert-p-benzoquinone 0 30 0 0 0 0 5-methyl-1H-benzotriazole 21. 4 17 63 27 8 20 18 8BHA 0 63 0 0 0 0 BHT 0 30 0 0 0 0 para-cresol 1.4 16 63 25 0 10 0 7

Prescription and nonprescription drugs 17β−estradiol E 0.636 2 63 3 0 10 0 

Caffeine 9.8 61 63 97 92 100 100 10Cotinine E 0.469 22 63 35 23 0 18 8

Steroids (stanols and sterols) Cholesterol E 7.0 44 63 70 43 50 64 10

3β-coprostanol E 5.86 28 63 44 8 10 9 8β-sitosterol E 3.80 15 33 45 13 40 50 10Stigmastanol E 1.1 3 63 5 0 0 0 

Fragrances Acetophenone 0.236 4 63 6 0 0 0 1

AHTN E 0.42 14 33 42 25 0 0 10HHCB E 0.19 9 33 27 0 0 0 6

Detergent metabolites NP1EO E 4.91 21 43 49 30 33 22 10

NP2EO E 5.97 22 63 35 8 0 0 10OP1EO E 0.76 17 63 27 23 20 18 3OP2EO E 0.13 1 63 2 0 0 0 para-nonylphenol (total) E 3.33 27 63 43 8 30 18 10
Antimicrobials

Triclosan 0.894 36 63 57 23 40 18 10

Plasticizers/flame retardants

Triphenyl phosphate E 0.085 12 63 19 8 20 18 2Tri(2-chloroethyl)phosphate 0.31 29 63 46 31 30 55 6Tri(2-chloroisopropyl)phosphate 0.214 17 63 27 8 30 9 32-butoxyethanol phosphate 12.0 48 63 76 38 60 73 10

Insect repellents

N,N-diethyl-m-toluamide (DEET) 1.89 32 63 51 23 70 27 8

Insecticides

Carbaryl E 0.062 6 63 10 15 20 9 cis-chlordane 0 30 0 0 0 0 Chlorpyrifos 0.036 1 63 2 0 0 0 Diazinon 0.307 43 63 68 69 60 100 7Dieldrin 0 30 0 0 0 0 Lindane 0 30 0 0 0 0 Methyl parathion 0 30 0 0 0 0 

Herbicides and fungicides

Atrazine 0.64 16 16 100 100 100 100 nBromacil E 0.34 22 33 67 38 60 100 3Metolachlor E 0.3 3 33 9 0 0 0 Prometon E 0.059 9 33 27 0 0 67 10Metalaxyl 0 33 0 0 0 0 

Table 15. Summary of organic wastewater compounds detected in water samples collected in the Threemile Creek basin, Mobile, Alabama, 2000 –2[μg/L, micrograms per liter; BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; HHCB, 1,3,4,6,7,8

hexamethyl-cyclopenta(g)-2-benzopyran; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol; OP2EO, diethoxylat

wastewater compounds; Compounds that are potential endocrine disruptors are in bold; Percent detections in bold indicate which site had the maximum concentration measured 

Compound

Maximum 

concentration 

(μg/L)

Number 

of 

detections

Sample 

size

Detection frequency (per

All 

sites TM-1 TM-3 TM-4 C
Polycyclic aromatic hydrocarbons Anthracene E 0.16 1 63 2 8 0 0 

Benzo[a]pyrene E 0.15 9 63 14 8 30 9 Fluoranthene 0.287 33 63 52 23 90 55 6Naphthalene E 0.120 11 55 20 17 56 10 1-methyl-naphthalene 0 30 0 0 0 0 2-methyl-naphthalene 0 33 0 0 0 0 2,6-dimethyl-naphthalene E 0.086 1 33 3 0 0 0 Phenanthrene E 0.15 20 63 32 23 70 27 3Pyrene 0.217 30 63 48 8 80 55 6

Summary Number of OWCs detected 37 27 25 25 2

Median number of OWCs detected per sample 13 5 11 8 Number of OWCs with greatest concentration at that site 1 4 0 Median total concentration of OWCs detected per sample 2.98 0.75 1.30 2.13 2Maximum total concentration of OWCs detected per sample 56.6 7.03 4.09 3.95 5

Table 15. Summary of organic wastewater compounds detected in water samples collected in the Threemile Creek basin, Mobile, Alabama, 2000 –2[μg/L, micrograms per liter; BHA, butylated hydroxyanisole; BHT, butylated hydroxytoluene; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; HHCB, 1,3,4,6,7,8

hexamethyl-cyclopenta(g)-2-benzopyran; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol; OP2EO, diethoxylat

wastewater compounds; Compounds that are potential endocrine disruptors are in bold; Percent detections in bold indicate which site had the maximum concentration measured 

Compound Maximum concentration (μg/L) Number of detections Sample size Detection frequency (per

All sites TM-1 TM-3 TM-4 C
Water-Quality Results and Discussion 51

fluoranthene (PAH), and N,N-diethyl-m-toluamide (insect 

repellent commonly known as DEET). The frequent detection 

of several of these compounds in a national reconnaissance of 

139 streams indicates that their environmental occurrence is 

widespread (Kolpin and others, 2002). 

The median number of wastewater indicators detected in 

individual samples ranged from 5 (TM-1) to 18 (CEN, 

table 15). In Threemile Creek, the median number of detections 

was highest at TM-5 (15), followed by TM-3 (11), TM-4 (8), 

and TM-1 (5). The median number of detections at the tributary 

sites was highest at CEN (18), followed by TSB (12). The 

median of the total concentrations at each site ranged from 

0.75 μg/L (TM-1) to 20.1 μg/L (CEN). In Threemile Creek, the 

median concentration was highest at TM-5 (11.0 μg/L), 

followed by TM-4 (2.13 μg/L), TM-3 (1.30 μg/L), and TM-1 

(0.75 μg/L). At the two tributary sites, the median concentration 

was highest at CEN (20.1 μg/L), followed by TSB (4.20 μg/L). 

The number of wastewater-indicator compounds detected 

in an individual sample ranged from 2 (TM-1) to 22 (TM-5, 

fig. 21). The maximum number of wastewater indicator 

compounds detected at individual sites throughout the study 

ranged from 25 (TM-3, TM-4) to 33 (TM-5, table 15). Mixtures 

of chemicals were common, and 50 of 63 samples 

(79.4 percent) contained total concentrations of OWCs that 

exceeded 1 μg/L. The maximum total concentration was 

greatest at CEN (56.6 μg/L, fig. 21; table 15). Total 

concentrations greater than 10 μg/L also were detected at TM-5 

(25.6 μg/L) and TSB (13.2 μg/L, fig. 21; table 15). 

Concentrations were summed to illustrate the potential 

magnitude of the source—higher concentrations do not 

necessarily imply that a site is more contaminated than one with 

lower concentrations. 

In at least two major studies (Atlanta, Georgia, and Kansas 

City, Missouri), a higher number of OWCs generally was 

detected in wet-weather samples than in base-flow samples 

(Wilkison and others, 2002; Frick and Zaugg, 2003). In the 

Threemile Creek study, this was not always true. Higher 

concentrations of OWCs were detected during low flow at two 

sites (CEN and TM-5), and a greater number of compounds was 

detected during low flow, rather than high flow, at four of six 

sites (TM-1, CEN, TSB, and TM-5; fig. 21). Conversely, a 

greater number of OWCs was detected during wet weather at 

TM-3, the site that was sampled most frequently during high 

flow (fig. 21). From the Threemile Creek study, it appears that 

point-source contributions may be more significant than 

contributions from nonpoint sources at several sites; however, 

fewer wet-weather samples were collected in the Threemile 

Creek basin compared to the other two major studies, which 

limits the interpretive comparison (Wilkison and others, 2002; 

Frick and Zaugg, 2003).

The detection frequencies of the 10 most frequently 

detected OWCs at each site and the 10 most frequently detected 

OWCs in the entire watershed are illustrated in figures 22 and 

23. Compounds that were incorporated into the wastewater 

schedule midway through the sampling period, such as atrazine, 

were not included in figures 22 and 23. Caffeine was detected 

in each sample at four of six sites; 2-butoxyethanol phosphate 

was detected in each sample at three of six sites (figs. 22, 23). 

The compounds detected most frequently at CEN also 

were detected most frequently at TSB and TM-5. Seven OWCs 

(caffeine, 2-butoxyethanol phosphate, cholesterol, triclosan, 

nonylphenol monoethoxylate (NP1EO), para-nonylphenol, and 

NP2EO) were detected in each sample collected at CEN; three 

of these compounds also were detected in each sample at TSB 

(fig. 22). Of the 10 most frequently detected compounds at 

CEN, 8 OWCs were among the 10 most frequently detected 

compounds at TSB and at TM-5 (fig. 22). The 10 most 

frequently detected compounds at CEN, TSB, and TM-5 were 

found in at least 50 percent of the samples; whereas only 

2 compounds at TM-1 were detected in at least 50 percent of the 

samples (fig. 22). Five of the 10 most frequently detected 

OWCs in the Threemile Creek basin (2-butoxyethanol 

phosphate, cholesterol, triclosan, NP1EO, and tri(2-chloroethyl)phosphate) were detected more frequently at CEN and 

TM-5 than at the upstream sites on Threemile Creek (fig. 23). 

The detergent metabolites (NP1EO, NP2EO, and paranonylphenol) were detected most frequently at CEN, followed 

by TM-5 (fig. 22). PAHs, such as fluoranthene and pyrene, were 

detected most frequently at TM-3, which probably indicates 

nonpoint-source contributions (figs. 22, 23). 

Statistically significant differences in concentrations and 

number of detections of wastewater indicators among sites were 

identified. The number of OWC detections at CEN was 

significantly greater than at TM-4; the number of OWC 

detections at TM-5 was significantly greater than at TM-1 

(table 7). The total concentration of wastewater indicators at 

CEN and TSB was significantly greater than at TM-4; the total 

concentration of OWC at TM-5 was significantly greater than at 

any site on Threemile Creek (TM1, TM-3, or TM-4; table 7). 

Strong correlations were found between total phosphorus and 

the total concentration of OWC (p < 0.0001; rho = 0.744; 

fig. 24). Strong correlations also were found between the 

number of wastewater indicator compounds detected and the 

total concentrations of OWCs (p < 0.0001; rho = 0.885), and 

between caffeine concentrations and the total concentrations of 

OWCs (p < 0.0001; rho = 0.734). Correlations that were 

significant when considering the entire data set were not always 

significant at each site. 
52 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 21. Summary of organic wastewater compounds detected per sample for (A) total concentration (summation of 48 compounds) 

and (B) number of compounds detected.
Water-Quality Results and Discussion 53

Figure 22. The 10 most frequently detected organic wastewater compounds at each site in the Threemile Creek basin, 

Mobile, Alabama, 2000–2003.
54 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 23. The 10 most frequently detected organic wastewater compounds in the Threemile Creek basin, Mobile, Alabama, 2000–2003. 

0.1 1 10 100

TOTAL CONCENTRATION OF ORGANIC WASTEWATER COMPOUNDS, IN MICROGRAMS PER LITER

1 

0.1 

0.01 

0.001

TOTAL PHOSPHORUS, IN MILLIGRAMS PER LITER

TM-1 

TM-3 

TM-4 

CEN 

TSB 

TM-5

Median total concentration of OWC = 2.983 ug/L 

Median phosphorus concentration = 0.050 mg/L 

Spearman's rank sum correlation coefficient 

(rho = 0.744; p = < 0.0001; n = 62)

Figure 24. Relation between total concentration of organic wastewater compounds (OWC) and total phosphorus, 

Threemile Creek basin, Mobile, Alabama, 2000–2003.
Water-Quality Results and Discussion 55

Occurrence and Distribution of Wastewater 

Indicator Groups

The 37 detected compounds represent a wide variety of 

uses and origins, including residential, industrial, and 

agricultural sources. The OWCs were divided into 11 groups 

based on their general use and origins. Figure 25 illustrates the 

prevalence of the different groups of compounds with respect to 

each sample collected during the study period. The greatest 

concentrations of OWCs were from the following four groups: 

steroids, detergent metabolites, plasticizers/flame retardants, 

and prescription/nonprescription drugs (fig. 25A). There was 

greater diversity, however, among the compound groups 

detected in the Threemile Creek basin (fig. 25B) than illustrated 

by the concentrations shown in figure 25A. Concentrations of 

several groups of compounds, such as PAHs or herbicides, were 

low although these compounds were detected widely in the 

watershed (fig. 25). 

Two observations can be made concerning how prevalent 

the groups of compounds were in terms of the entire data set 

(63 samples). In relation to frequency of detection, 9 of 11 

groups were found in more than 50 percent of the samples 

(fig. 26A). In relation to percentage of total measured 

concentration for each group, four groups (steroids, detergent 

metabolites, plasticizer/flame retardants, and prescription/

nonprescription drugs) contributed almost 87 percent of the 

total measured concentration in all samples (fig. 26B). 

Although 79.4 percent of the samples contained total 

concentrations of OWCs exceeding 1 μg/L, only 17.9 percent of 

the samples contained concentrations of individual compounds 

that exceeded 1 μg/L (appendix table 2-2). More than 45 percent 

of the higher concentrations was derived from the steroids 

group (cholesterol, 3β-coprostanol, β-sitosterol); 35 percent 

was derived from the three detergent metabolites (paranonylphenol total, NP1EO, and NP2EO); approximately 

10 percent was derived from a plasticizer/cleaning agent 

(2-butoxyethanol phosphate); and 5.5 percent was derived from 

caffeine. 

Organic Wastewater Compounds as 

Endocrine Disruptors

An endocrine disruptor is a natural or synthetic chemical, 

that when absorbed into the body, either mimics or blocks 

hormones and disrupts the body’s normal functions. Exposure 

to endocrine disruptors can occur through direct contact with 

chemicals or through exposure to contaminated water, food, or 

air. Chemicals suspected of acting as endocrine disruptors are 

found in detergents, resins, plasticizers, insecticides, herbicides, 

fumigants, fungicides, industrial chemicals, and heavy metals. 

Of the 48 compounds included in this analysis, 19 are known or 

suspected to exhibit at least weak hormonal activity with the 

potential to disrupt endocrine function (table 15; Kolpin and 

others, 2002; S.D. Zaugg, U.S. Geological Survey, written 

commun., May 10, 2004). Twelve of these compounds were 

detected in the Threemile Creek study (appendix table 2-2) 

and can be grouped into five categories: prescription drugs 

(17β-estradiol), detergent metabolites (NP1EO, NP2EO, 

OP1EO, OP2EO, and para-nonylphenol), antimicrobials 

(triclosan), pesticides (atrazine, carbaryl, chlorpyrifos, and 

diazinon), and PAHs (benzo[a]pyrene). 

Potential endocrine disruptors were detected in 61 of 

63 samples (96.8 percent) in the Threemile Creek basin 

(fig. 21). The total concentration of potential endocrine 

disruptors detected in a single sample ranged from 0 μg/L (no 

detections) at TM-1 and TM-3 to 14.6 μg/L at CEN (fig. 21). 

The total concentration of potential endocrine disruptors 

exceeded 1 μg/L in 27 of 63 samples (42.8 percent) collected in 

the Threemile Creek basin, in 8 of 8 (100 percent) of the 

samples at CEN, and in 11 of 13 samples (84.6 percent) at 

TM-5. Median concentrations of potential endocrine disruptors 

were highest at CEN and TM-5, followed by TSB, TM-3, 

TM-4, and TM-1. The total concentration of potential endocrine 

disruptors was highest at CEN during low flow, indicating point 

sources; total concentrations at TM-5 were highest during low 

and high flow, indicating point and nonpoint sources (fig. 21). 

The number of potential endocrine disruptors detected in a 

single sample ranged from zero (TM-1, TM-3) to 7 (TM-3, 

TM-5; fig. 21); the median number of potential endocrine 

disruptors detected was greatest at CEN and TM-5 (5), followed 

by TM-4, TSB, TM-1, and TM-3 (2). 

Previous research has shown that even low-level exposure 

(< 0.001 μg/L) to select hormones can illicit deleterious effects 

in aquatic species (Kolpin and others, 2002). In addition, 

research has shown that select chemical combinations can have 

additive or synergistic toxic effects (Kolpin and others, 2002). 

Little is known about the potential interactive effects 

(synergistic or antagonistic toxicity) that can occur from 

complex mixtures of OWCs in the environment. Much is yet to 

be learned pertaining to the effects (particularly chronic effects) 

on humans, plants, and animals exposed to low-level 

concentrations of pharmaceuticals and other OWCs that were 

detected in this study.

Antioxidants

Three antioxidants—butylated hydroxyanisole (BHA), 

butylated hydroxytoluene (BHT), and 5-methyl-1Hbenzotriazole—as well as two metabolites of BHA and 

BHT— 2,6-di-tert-butylphenol and 2,6-di-tert-p-butyl 

benzoquinone—were analyzed in this study. Antioxidants 

commonly are used to delay the deterioration of food flavors 

and odors and to substantially increase the shelf life of many 

foods. Para-cresol, a common disinfectant, also is included in 

this subgroup of wastewater indicators because it is used to 

produce BHT. Para-cresol also is used in phenol-formaldehyde 

resins and in ultraviolet blockers for sunscreen and fragrances. 

BHA generally is used to keep fats from becoming rancid and 

is used widely in the food industry as a preservative. BHA is 

found in butter, lard, meats, cereals, baked goods, sweets, beer, 
56 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Figure 25. Summary of the types of organic wastewater compounds detected per sample for (A) total concentration (summation of 

48 compounds) and (B) number of compounds detected, Threemile Creek basin, Mobile, Alabama, 2000–2003.
Water-Quality Results and Discussion 57

Figure 26. (A) Frequency of detection of organic wastewater compounds by general-use category 

and (B) percentage of total measured concentration of organic wastewater compounds by generaluse category, Threemile Creek basin, Mobile, Alabama, 2000–2003.
58 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

vegetable oils, potato chips, snack foods, nuts, and flavoring 

agents; it also is found in animal feed, cosmetics, and in rubber 

and petroleum products (U.S. Department of Health and Human 

Services, 2002). BHT also prevents oxidative rancidity of fats 

and is used to preserve food odor, color, and flavor. Many 

packaging materials incorporate BHT, and it is added directly to 

shortening, cereals, and other foods containing fats and oils 

(Helmenstine, 2004). The antioxidant 5-methyl-1Hbenzotriazole is used in anti-freeze and de-icers as an anticorrosion agent (Wilkison and others, 2002). 

Of the 63 samples collected, 17 (27 percent) contained 

5-methyl-1H-benzotriazole, which was detected at each of the 

sites in the Threemile Creek basin (fig. 20; table 15; appendix 

table 2-2). This compound was most frequently detected (7 of 

8 samples; 88 percent) at CEN, where the highest concentrations also were detected (table 15; appendix table 2-2). 

Para-cresol was detected in 16 of 63 samples (25 percent) in the 

Threemile Creek basin (fig. 20; table 15; appendix table 2-2). 

Para-cresol was detected in 75 percent of the samples at the two 

tributary sites (CEN, TSB) and in 23 percent of the samples at 

TM-5; it was not detected at TM-1 or TM-4 (appendix 

table 2-2). BHA, BHT, and their metabolites were not detected 

at any site in the Threemile Creek basin (appendix table 2-2).

Prescription and Nonprescription Drugs

17β-estradiol is a naturally occurring estrogen produced in 

the human body. As a prescription drug, it is used primarily for 

hormone replacement therapy and for the prevention of 

osteoporosis and breast cancer. Intermittent exposure to 

concentrations as low as 0.12 μg/L can induce adverse 

reproductive changes in fish (Panter and others, 2000; RogersGray and others, 2000). This compound demonstrated poor or 

variable method performance, and detections were always 

qualified as estimated (E). 17β-estradiol was detected in 2 of 

63 samples in the Threemile Creek basin (E 0.636 μg/L at TM3 and E 0.314 μg/L at TSB, appendix table 2-2). 

Detection of caffeine can be an important indicator of 

wastewater contamination in surface-water samples even 

though caffeine is not persistent in the environment because of 

rapid degradation by bacteria (Zaugg and others, 2002). 

Caffeine was one of the most frequently detected wastewater 

compounds in the Threemile Creek basin. It was detected in 

61 of 63 samples (97 percent, fig. 20; table 15; appendix 

table 2-2). Caffeine is found in many substances, including 

coffee, tea, chocolate, soft drinks, and a variety of 

pharmaceutical products. A 6-ounce cup of coffee typically 

contains about 100 milligrams (mg); a 6-ounce cup of tea 

contains about 70 mg; and a 12-ounce cola contains about 

70 mg (Brain, 2003). Caffeine is found in analgesic products, 

such as Anacin (32 mg per tablet); in products used to enhance 

alertness, such as No-doz (100 mg per tablet); and in appetite 

suppressants, such as Dexatrim (200 mg per tablet; Brain, 

2003). Caffeine’s half-life varies from several hours to several 

days, but for the average nonsmoking adult, it is about 

5–7 hours (Erowid, 2003). Based on a daily per capita use rate 

of 280 mg per consumer (Barone and Roberts, 1996) and the 

most recent population figures (table 4), the average annual 

consumption of caffeine in the Threemile Creek basin is 

estimated to be about 16,000 pounds per year. Unconsumed 

coffee and soft drinks poured down drains likely contribute to 

the occurrence of caffeine in water samples. Caffeine was 

detected at each of the sites in the Threemile Creek basin 

(figs. 22, 23). The highest concentrations of caffeine were 

detected at CEN (appendix table 2-2). Median concentrations of 

the detected values were lowest at TM-1 (appendix table 2-2). 

Concentrations of caffeine were well correlated to concentrations of 2-butoxyethanol phosphate (p = 0.0149; rho = 0.810) 

at CEN. Caffeine also was well correlated to cholesterol 

concentrations (p < 0.0001; rho = 0.890) and 3β-coprostanol 

concentrations (p = 0.0014; rho = 0.787) at TM-5. 

Cotinine is a metabolic by-product that is produced by the 

body as it processes nicotine. Nicotine is found in tobacco, 

tobacco products, cigarette smoke, and smoking-cessation 

products. Exposure to nicotine can be measured by analyzing 

cotinine levels; cotinine has a 24-hour half-life in blood, saliva, 

or urine. Cotinine was detected in 22 of 63 samples (35 percent) 

and was found at five of the six sites (TM-1, TM-4, CEN, TSB, 

and TM-5) in the Threemile Creek basin (table 15; appendix 

table 2-2). The highest concentrations of this compound were 

detected at CEN (table 15; appendix table 2-2) and it was 

detected most frequently (7 of 8 samples; 88 percent) at CEN 

(fig. 22).

Steroids—Sterols and Stanols

Plant sterols (phytosterols) and plant stanols 

(phytostanols) are naturally occurring substances in fruits, 

vegetables, nuts, seeds, legumes, and other plant sources, 

including wood pulp. Plant sterols and stanols are essential 

components of plant cell membranes and are similar in structure 

to cholesterol. Cholesterol is itself a sterol; however, it is 

predominantly an animal sterol. In humans, the liver 

synthesizes cholesterol although an appreciable amount may be 

consumed through the diet. The consumption of plant sterol and 

stanols lowers cholesterol levels by inhibiting the absorption of 

dietary cholesterol. Cholesterol is microbially reduced into 

coprostanol, which is a traditional indicator of sewage 

contamination because it is produced almost exclusively in the 

digestive tract of higher mammals (humans, pigs, and cats) and 

often correlates with the presence of other sewage-derived 

pollutants, such as pathogens, toxic metals, organic compounds, 

and hormones (Zaugg and others, 2002). β-sitosterol and 

β-sitostanol (stigmastanol) are plant steroids, which are 

components of pulp-mill wastes (Mahmood-Khan and Hall, 

2003); their presence in the same sample generally indicates a 

substantial contribution from plant sterols (Zaugg and others, 

2002). β-sitostanol may be released in the environment from the 

decomposition of paper or the breakdown of grass clippings 

(Wilkison and others, 2002). β-sitosterol is the most abundant 
Water-Quality Results and Discussion 59

plant sterol in the human diet (PDRhealth, 2004) and is found 

in saw palmetto, a plant that grows abundantly in the Threemile 

Creek basin. 

Cholesterol was detected in 44 of 63 samples (70 percent) 

in the Threemile Creek basin (fig. 20; table 15). The highest 

concentrations of this compound, detected at the unnamed 

tributary at Center Street (CEN), ranged from 1.99 to 7.00 μg/L 

(appendix table 2-2). High concentrations also were detected at 

TSB (5.6 μg/L) and TM-5 (6.8 μg/L). Cholesterol was detected 

in 8 of 8 samples (100 percent) at CEN; it was detected in 85 to 

88 percent of the samples at TM-5 and TSB, respectively. In 

contrast, cholesterol was detected in 43 percent of the samples 

at the most upstream site, TM-1 (fig. 22; table 15).

Coprostanol, a traditional indicator of sewage 

contamination, was detected in 28 of 63 samples (44 percent) in 

the Threemile Creek basin (fig. 20; table 15). The highest 

concentrations of this compound were detected at the most 

downstream site on Threemile Creek (TM-5), followed by the 

tributaries CEN and TSB (appendix table 2-2). Coprostanol was 

detected in 85–88 percent of the samples at three sites—CEN, 

TSB, and TM-5 (table 15). In contrast, coprostanol was detected 

in only 8–10 percent of the samples at the upstream sites on 

Threemile Creek. 

β-sitosterol was detected in 15 of 33 samples (45 percent) 

in the Threemile Creek basin (fig. 20; table 15). The highest 

concentration of this compound was detected at the most 

downstream site on Threemile Creek (TM-5), followed by the 

tributaries CEN and TSB. β-sitosterol was detected in 3 of 3 

samples (100 percent) at CEN and in 4 of 8 samples 

(50 percent) at TM-5, but in only 1 of 8 samples (13 percent) at 

TM-1 (table 15). Stigmastanol (β-sitostanol) was detected in 

only 3 of 63 samples (5 percent) in the Threemile Creek basin 

(table 15). 

Sterols are important predictors of wastewater 

contamination (LeBlanc and others, 1992). Cholesterol, 

3β-coprostanol, and β-sitosterol showed similar distribution 

patterns, which indicate that source and fate may be similar for 

each compound. Higher detection frequencies and 

concentrations of these compounds were observed at the two 

tributaries (CEN and TSB) and at the most downstream site on 

Threemile Creek (TM-5). The concentrations of cholesterol and 

3β-coprostanol were significantly correlated at CEN 

(p = 0.0011; rho = 0.922), TSB (p = 0.0149; rho = 0.810), and 

TM-5 (p < 0.0001; rho = 0.899). Concentrations of cholesterol 

were well correlated to caffeine (p < 0.0001; rho = 0.890) at 

TM-5, and concentrations of cholesterol also were well 

correlated to fecal coliform (p = 0.0149; rho = 0.809) and 

enterococci (p = 0.0065; rho = 0.857) at TSB. 

Fragrances 

Acetophenone is used as a fragrance ingredient in soaps, 

detergents, creams, lotions, and perfumes. It also is used as a 

flavoring agent in foods, nonalcoholic beverages, and tobacco 

and as a specialty solvent for plastics and resins. Acetophenone 

was detected in 4 of 63 samples (6 percent) and was detected at 

the two tributary sites (CEN and TSB) and at TM-5 (table 15; 

appendix table 2-2). 

AHTN2 and HHCB3 belong to a group of substances used 

in fragrances that are known collectively as polycyclic musks. 

These substances are important ingredients in fragrances 

because of their fixative properties and their ability to make a 

fragrance long lasting. Musk fragrances are used as low-cost 

fragrances in soaps, perfumes, air fresheners, detergents, fabric 

softeners, and other household cleaning products. Over the last 

decade, synthetic musks have attracted the attention of 

environmental researchers because of their presence in the 

environment and the fact that they can be secreted in human 

breast milk. There also is recent evidence concerning 

bioaccumulation and potential toxicity of these substances in 

aquatic life (Franke and others, 1999; Zaugg and others, 2002). 

AHTN was detected at four sites (TM-1, CEN, TSB, TM-5) in 

14 of 33 samples (42 percent); HHCB was detected at three sites 

(CEN, TSB, and TM5) in 9 of 33 samples (27 percent, table 15). 

Concentrations of AHTN and HHCB were highest at TM-5 

(table 15; appendix table 2-2). 

Detergent Metabolites

Alkylphenol polyethoxylates (APEO) are nonionic 

surfactants that are used widely in commercial and household 

detergents in the United States. During the wastewatertreatment process, these compounds can degrade to more toxic, 

estrogenic, and lipophilic compounds (La Guardia and others, 

2001). These include para-nonylphenol (para-NP), 

nonylphenol monoethoxylate (NP1EO), nonylphenol 

diethoxylate (NP2EO), octylphenol monoethoxylate (OP1EO), 

and octylphenol diethoxylate (OP2EO). These degradation 

products are more persistent and toxic than the parent 

compounds (Wilkison and others, 2002). Alkylphenol 

ethoxylates have been used for more than 40 years as 

detergents, emulsifiers, wetting agents, and dispersing agents in 

many industries, including textile processing, pulp and paper 

processing, resins and protective coatings, steel manufacturing, 

and power generation (Canadian Council of Ministers of the 

Environment, 2001). These compounds also are a component in 

many paints, herbicides, pesticides, and cosmetics. In the 

United States, most APEO surfactants are nonylphenol 

ethoxylates (NPEO; Wilkison and others, 2002). 

2

 6-acetyl-1,1,2,4,4,7-hexamethyltetraline. 3 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran.
60 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

NP1EO was detected in 21 of 43 samples (49 percent); 

NP2EO was detected in 22 of 63 samples (35 percent); and 

para-NP was detected in 27 of 63 samples (43 percent, fig. 20; 

table 15). The highest concentrations of NP1EO, NP2EO, and 

para-NP were detected at CEN, followed by TM-5 (table 15; 

appendix table 2-2). These three compounds also were detected 

most frequently at CEN (100 percent) and TM-5 (67–85 

percent); the frequency of detection was lower at the most 

upstream sites on Threemile Creek (0–33 percent, table 15). 

OP1EO was detected in 17 of 63 samples (27 percent); OP2EO 

was detected in 1 of 63 samples (TM-5, fig. 20; table 15). The 

frequency of detection of OP1EO was slightly higher at the 

tributary sites (38 percent) than at the sites on Threemile Creek 

(18–31 percent, table 15).

These detergent metabolites are synthetic compounds that 

do not occur naturally; thus, concentrations in stream water can 

be solely attributed to human activities. All of these detergent 

metabolites are considered to be potential endocrine disruptors. 

Of the degradation products, nonylphenols (NP) are considered 

to be more toxic than NP1EO and NP2EO. In general the 

OPEOs are considered to be more toxic than the NPEOs. 

Chronic toxicity values for NP are as low as 6 μg/L in fish and 

3.9 μg/L in invertebrates (Canadian Council of Ministers of the 

Environment, 2002). Concentrations of para-NP (12 estimated 

values), NP1EO (14 estimated values), and NP2EO 

(19 estimated values) exceeded the Canadian aquatic-life 

guideline of 1 μg/L numerous times (appendix table 2-2). 

Because of the uncertainty associated with estimated values, 

however, these concentrations should not be compared directly 

to the criteria for regulatory purposes. It also is important to 

consider that these degradation products are found as complex 

mixtures in effluents and streams. The potential synergistic 

effects created from low concentrations of multiple endocrine 

disrupters have yet to be quantified. 

Antimicrobials

Triclosan is a broad-spectrum antibacterial/antimicrobial 

agent that has been in use for more than 30 years. Triclosan use 

has increased substantially in the last few years as it has been 

added to deodorants, dish soaps, laundry soaps, detergents, 

lotions, crèmes, cosmetics, toothpastes, and mouthwashes. The 

presence of triclosan in the environment is a concern for several 

reasons: (1) it may promote development of antiseptic-resistant 

bacteria strains, (2) it has been detected in human breast milk 

and blood plasma, and (3) it is a potential endocrine disruptor 

(Kolpin and others, 2002; Wilkison and others, 2002). Triclosan 

was detected in 36 of 63 samples (57 percent) in the Threemile 

Creek basin (fig. 20; table 15). Triclosan was detected in all of 

the samples at the two tributary sites (CEN and TSB) and in 

85 percent of the samples at TM-5 (figs. 22, 23; table 15); it was 

less frequently detected at the other sites on Threemile Creek 

(18–40 percent, table 15). Concentrations were highest at CEN 

and TM-5 (appendix table 2-2). Concentrations of triclosan 

were well correlated to concentrations of NP2EO (p = 0.0102; 

rho = 0.833) at CEN; triclosan concentrations also were well 

correlated to para-NP concentrations (p < 0.0001; rho = 0.876) 

at TM-5.

Plasticizers/Flame Retardants

Flame retardant compounds are used in a variety of 

products, including fabrics, carpets, and plastics. Three 

phosphate-based flame retardants (triphenyl phosphate, tri(2-

chloroethyl)phosphate, and tri(2-chlorisopropyl)phosphate) 

were analyzed by the wastewater indicator compound method. 

Triphenyl phosphate commonly is used as a flame retardant in 

certain resins for the manufacture of electrical and automobile 

components. It also is used as a plasticizer in cellulose acetate 

for photographic films and is a component of hydraulic fluids 

and lubricant oils. Tri(2-chloroethyl)phosphate is used in 

flexible foams in automobiles and furniture and in rigid foams 

used for building insulation. Tri(2-chloroisopropyl)phosphate 

is used extensively in rigid and flexible polyurethane foams as 

well as for textile finishes. One additional phosphate-based 

compound, 2-butoxyethanol phosphate, which is used as a 

plasticizer in packaging plastics and rubber gaskets and as a 

cleaning agent in floor care products, also was included in this 

OWC group.

All four of these compounds were detected at each of the 

sites in the Threemile Creek basin (table 15). Triphenyl 

phosphate was detected in 12 of 63 samples (19 percent, fig. 20; 

table 15). Occurrence of this compound was fairly evenly 

distributed between sites in the Threemile Creek basin. 

Tri(2-chloroethyl)phosphate was detected in 29 of 63 samples 

(46 percent), and tri(2-chloroisopropyl)phosphate was detected 

in 17 of 63 samples (27 percent, fig. 20; table 15). Both of these 

compounds were detected most frequently at TM-5 (table 15). 

The plasticizer and cleaning agent, 2-butoxyethanol phosphate, 

was the third most frequently detected OWC in the Threemile 

Creek basin (fig. 20) and was found in 48 of 63 samples 

(76 percent, table 15). It was detected in every sample at three 

sites (CEN, TSB, and TM-5) and was detected less frequently 

at TM-1 (38 percent), TM-3 (60 percent), and TM-4 

(73 percent, figs. 22, 23; table 15). 

Insect Repellent

DEET (N,N-diethyl-m-toluamide) is the active ingredient 

in most insect repellents that are formulated for personal use 

against mosquitoes, ticks, and other biting insects (Wilkison 

and others, 2002). DEET is designed to repel insects rather than 

kill them. DEET was developed by the U.S. Army in 1946 and 

was registered for use by the general public in 1957. Although 

DEET can be applied directly to human skin, it also can be 

applied to clothing but is removed during laundering or bathing. 

DEET can then be transported to WWTPs, where it can survive 

the treatment process and be discharged directly into receiving 

streams (Wilkison and others, 2002). DEET was the ninth most 

frequently detected wastewater compound in the Threemile 
Water-Quality Results and Discussion 61

Creek basin (fig. 20) and was detected in 32 of 63 samples 

(51 percent, table 15). DEET was most frequently detected at 

CEN, TM-3, and TM-5 (88, 70, and 62 percent, respectively) 

and was least frequently detected at TM-1 (23 percent, figs. 22, 

23; table 15). The highest concentration (1.89 μg/L) was 

detected at CEN in July 2000 (table 15; appendix table 2-2). 

Insecticides

Three of seven insecticides were detected at sites in the 

Threemile Creek basin. Diazinon was detected in 43 of 63 

samples (68 percent); carbaryl was detected in 6 of 63 samples 

(10 percent); and chlorpyrifos was detected in 1 of 63 samples 

(2 percent, table 15; fig. 20). Chlordane, dieldrin, lindane, and 

methyl parathion were not detected in any sample. Diazinon and 

carbaryl are used in urban areas to control insects on lawns and 

gardens. The maximum concentration of diazinon (0.307 μg/L) 

was found at TM-3 (table 15; appendix table 2-2). The Great 

Lakes Water Quality Agreement of 1977 established an aquatic 

life criterion of 0.08 μg/L for diazinon (International Joint 

Commission United States and Canada, 1978). This criterion 

was exceeded 18 times (including six estimated values); 

exceedances occurred at each of the surface-water sampling 

sites (appendix table 2-2). The maximum concentration of 

carbaryl (0.062 μg/L) was found at TM-3 and did not exceed the 

Canadian Water Quality Guideline of 0.2 μg/L (Canadian 

Council of Ministers of the Environment, 2002).

 Chlorpyrifos is an organophosphate insecticide used in 

gardens, in residential areas, and on a wide variety of crops to 

control insects, including the pine beetle. Chlorpyrifos also is 

used for termite control in residential and industrial settings and 

in pet shampoo. Chlorpyrifos was detected one time 

(0.036 μg/L) at TSB and did not exceed the USEPA 

recommended water-quality criteria for criterion maximum 

concentration (0.083 μg/L) or criterion minimum concentration 

(0.041 μg/L) for nonpriority pollutants (appendix table 2-2; 

U.S. Environmental Protection Agency, 2002c). The Canadian 

aquatic-life guideline of 0.0035 μg/L for the protection of 

aquatic life was exceeded (Canadian Council of Ministers of the 

Environment, 2002). 

Herbicides and Fungicides

Four herbicides (atrazine, bromacil, metolachlor, and 

prometon) were detected at sites in the Threemile Creek basin; 

the fungicide, metalaxyl, was not detected at any site. Atrazine 

is the most heavily applied herbicide in the United States 

(Majewski and Capel, 1995). It is used to control broadleaf and 

grassy weeds in corn and several other crops, and also is used as 

a nonselective herbicide on noncropped industrial lands and on 

fallow lands. Atrazine was detected in 16 of 16 samples 

(100 percent, table 15; fig. 20). The maximum concentration of 

atrazine (0.64 μg/L) did not exceed the USEPA and the ADEM 

drinking-water standard (3 μg/L) or the Canadian aquatic-life 

guideline (1.8 μg/L, Alabama Department of Environmental 

Management, 2000b; U.S. Environmental Protection Agency, 

2002a; Canadian Council of Ministers of the Environment, 

2002). Bromacil is a herbicide used for brush control along 

roads and on noncropland areas. It is especially useful against 

perennial grasses. Bromacil was detected in 22 of 33 samples 

(67 percent) at each of the sites in the basin (table 15; fig. 20). 

The maximum concentration (E 0.34 μg/L) did not exceed the 

Canadian aquatic-life guideline of 5.0 μg/L (Canadian Council 

of Ministers of the Environment, 2002). 

Metolachlor generally is applied as a preemergent 

herbicide for a variety of crops (field corn, soybeans, peanuts, 

sorghum, and cotton). Metolachlor is used to control broadleaf 

and annual grassy weeds and also is applied along highways and 

other rights-of-way and on woody ornamentals. Metolachlor 

was detected at TM-5 in 3 of 33 samples (9 percent, table 15; 

fig. 20). Concentrations did not exceed the Canadian aquaticlife guideline of 7.8 μg/L (Canadian Council of Ministers of the 

Environment, 2002). Prometon is a nonselective herbicide that 

is used to control most annual and many perennial broadleaf 

weeds and grasses. It is faster acting than simazine, but does not 

have as long a residual effect as either simazine or atrazine. 

Prometon was detected in 9 of 33 samples (27 percent, table 15; 

fig. 20). No standards or criteria are available for comparison.

The number of pesticides present in a stream may be 

important from a toxicological standpoint. Generally, the 

effects of pesticide mixtures on biota or humans are not 

included in water-quality criteria, which are most commonly 

based on single-species, single-chemical toxicity tests 

conducted under laboratory conditions (Hampson and others, 

2000). Some pesticides may become more toxic when 

combined with other toxic compounds. The synergistic effects 

created from the low concentrations of multiple pesticides have 

yet to be quantified (Hoffman and others, 2000), and the 

combined ecological effects of pesticides in streams are 

unknown.

Polycyclic Aromatic Hydrocarbons 

Polycyclic aromatic hydrocarbons (PAHs) are formed 

during combustion processes and may enter surface-water 

systems through atmospheric deposition, surface runoff, and 

soil leaching (Smith and others, 1988). Sources of PAHs 

include domestic sewage, asphalt surfaces, car tires, vehicular 

exhaust, crude oil, and petroleum (Dojlido and Best, 1993). An 

important source of PAHs is runoff from roads—PAH 

compounds come from the asphalt surfaces of the roads, car 

tires, and from the gases emitted by cars (Dojlido and Best, 

1993). Several PAHs have been identified as carcinogens or 

mutagens (Dojlido and Best, 1993). Seven of nine PAHs were 

detected in water samples from the Threemile Creek basin 

(anthracene, benzo[a]pyrene, fluoranthene, naphthalene, 

2,6-dimethyl-naphthalene, phenanthrene, and pyrene); 

1-methyl-napthalene and 2-methyl-napthalene were not 

detected in any water sample (table 15; appendix table 2-2). 
62 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

PAHs were detected at all sites but were most frequently 

detected at TM-3, which likely is due to the large number of 

samples collected at this site during periods of storm runoff 

(figs. 22, 23; appendix table 2-2). Seventy-six percent of the 

detections were estimated values; these values should not be 

compared to criteria for regulatory purposes because of 

uncertainty associated with the estimated value. Fluoranthene 

and pyrene were the most frequently detected PAHs (table 15; 

fig. 20). The maximum concentration of fluoranthene was 

0.287 μg/L (TSB)—22 water samples (including 12 estimated 

values) exceeded the Canadian guideline of 0.04 μg/L for the 

protection of aquatic life (Canadian Council of Ministers of the 

Environment, 2002). The maximum concentration of pyrene 

was 0.217 μg/L (TSB)—23 water samples (including 14 

estimated values) exceeded the Canadian guideline of 

0.025 μg/L for the protection of aquatic life (Canadian Council 

of Ministers of the Environment, 2002). The maximum 

concentration of benzo[a]pyrene was 0.15 μg/L at 

TM-5—nine water samples (including six estimated values) 

exceeded the Canadian guideline of 0.015 μg/L for the 

protection of aquatic life (Canadian Council of Ministers of the 

Environment, 2002).

Comparison of Organic Wastewater Compounds 

in the Threemile Creek Basin to Sites Nationwide

Organic wastewater data from the Threemile Creek basin 

were compared to data collected in the first nationwide 

reconnaissance of the occurrence of pharmaceuticals, 

hormones, and other OWCs in water resources (fig. 27; 

table 16). The USGS used five newly developed analytical 

methods to measure concentrations of 95 OWCs in water 

samples from 139 streams across 30 states during 1999 and 

2000 (Kolpin and others, 2002). The selection of sites in the 

nationwide reconnaissance was biased toward streams 

susceptible to contamination (downstream from intense 

urbanization and livestock production). OWCs were found in 

80 percent of the streams sampled and represented a wide range 

of residential, industrial, and agricultural origins and uses. 

Eighty-two of the 95 OWCs were found during the national 

study (Kolpin and others, 2002). Thirty-five of the OWCs 

sampled in the nationwide reconnaissance were included in the 

group of 48 OWCs discussed in the Threemile Creek study 

(fig. 27; table 16).

Sixty-three samples were collected during 2000–2003 in 

the Threemile Creek study; 85 samples were collected during 

Figure 27. Frequencies of detection of selected organic wastewater compounds in water samples from the Threemile Creek basin, Mobile, 

Alabama, and sites nationwide.
Table 16. Detection frequencies and concentrations of selected organic wastewater compounds in water samples from the Threemile Creek basin, 

Alabama (2000–2003) and sites nationwide (1999–2000).

[μg/L, micrograms per liter; MCL, maximum contaminant level; HAL, lifetime health advisory; ND, not detected; —, data not available; E, estimated; BHA, butylated hydroxya

NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol; OP2EO, diethoxylate octylphenol. Compounds that are potenti

endocrine disruptors are in bold]

Detection frequency 

(percent)

Maximum 

(μg/L)

Median of detected values 

(μg/L) MCLa

(μg/L)

(

Threemile 

Creek basin

Sites 

nationwide

Threemile 

Creek basin

Sites 

nationwide

Threemile 

Creek basin

Sites 

nationwide

2-butoxyethanol phosphate 76.2 45.9 12.0 6.7 0.51 0.51 — —2,6-di-tert-p-benzoquinone 0 9.4 ND 0.46 ND 0.13 — —2,6-di-tert-butylphenol 0 3.5 ND 0.11b ND 0.06b — —3β-coprostanol 44.4 35.3 5.86 9.8b 1.33 0.7b — —5-methyl-1H-benzotriazole 27 31.5 21.4 2.4 0.19 0.39 — —17β-estradiol 3.2 10.6 E 0.636 0.2b 0.48 0.16b — —Acetophenone 6.3 9.4 0.236 0.41 0.124 0.15 — —Anthracene 1.6 4.7 E 0.16 0.11 0.16 0.07 — —Benzo[a]pyrene 14.3 9.4 E 0.15 0.24 0.056 0.04 0.2 —BHA 0 2.4 ND 0.2b ND 0.1b — —Caffeine 96.8 70.6 9.8 5.7 0.143 0.1 — —Carbaryl 9.5 16.5 E 0.062 0.1b 0.046 0.04b — 7cis-chlordane 0 4.7 ND 0.1 ND 0.02 2 —Chlorpyrifos 1.6 15.3 0.036 0.31 0.036 0.06 — Cholesterol 69.8 55.3 E 7 10b 1.26 1b — —Cotinine 34.9 31.5 E 0.469 0.57 0.10 0.05 — —Diazinon 68.3 25.9 0.307 0.35 0.066 0.07 — Dieldrin 0 4.7 ND 0.21 ND 0.18 — —
Fluoranthene 52.4 29.4 0.287 1.2 0.055 0.04 — Lindane 0 5.9 ND 0.11 ND 0.02 0.2 0.Methyl parathion 0 1.2 ND 0.01 ND 0.01 — 2 Naphthalene 20 16.5 E 0.12 0.08 0.03 0.02 — 100 N,N-diethyl-m-toluamide 50.8 74.1 1.89 1.1 0.061 0.06 — para-nonylphenol (total) 42.9 50.6 E 3.33 40c 0.92 0.8c — NP1EO 48.8 45.9 E 4.91 20c 1.15 1c — NP2EO 34.9 36.5 E 5.97 9c 2.47 1c — OP1EO 27 43.5 E 0.76 2c 0.11 0.2c — OP2EO 1.6 23.5 E 0.13 1c 0.13 0.1c — Phenanthrene 31.7 11.8 E 0.15 0.53 0.033 0.04 — Pyrene 47.6 28.2 0.217 0.84 0.041 0.05 — Stigmastanol 4.8 5.6 E 1.1 4b 0.80 2b — Triclosan 57.1 57.6 0.894 2.3 0.098 0.14 — Tri(2-chloroethyl)phosphate 46 57.6 0.31 0.54 0.06 0.1 — Tri(2-chloroisopropyl)phosphate 27 12.9 0.214 0.16 0.077 0.1 — Triphenyl phosphate 19 14.1 E 0.085 0.22 0.054 0.04 — 

aU.S. Environmental Protection Agency, 2002a. bConcentration estimated; average recovery less than 60 percent.cConcentration estimated; reference standard prepared from a technical mixture.

Table 16. Detection frequencies and concentrations of selected organic wastewater compounds in water samples from the Threemile Creek basin, Alabama (2000–2003) and sites nationwide (1999–2000).—Continued[μg/L, micrograms per liter; MCL, maximum contaminant level; HAL, lifetime health advisory; ND, not detected; —, data not available; E, estimated; BHA, butylated hydroxya

NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol; OP2EO, diethoxylate octylphenol. Compounds that are potent

endocrine disruptors are in bold]

Detection frequency 

(percent)

Maximum 

(μg/L)

Median of detected values 

(μg/L) MCLa

(μg/L)

(

Threemile 

Creek basin

Sites 

nationwide

Threemile 

Creek basin

Sites 

nationwide

Threemile 

Creek basin

Sites 

nationwide
Benthic Invertebrates Results and Discussion 65

1999–2000 in the nationwide reconnaissance study. Samples 

for both studies were processed by the NWQL using the same 

methods; however, the specific compounds analyzed and the 

MRLs varied among samples because of method refinement 

during the 5 years (1999–2003) of sampling and because of 

matrix interference (Kolpin and others, 2002). Wastewater 

indicators were detected in each of the 63 samples collected in 

the Threemile Creek basin. Of the 35 constituents that were 

common to both studies, 28 were detected in the Threemile 

Creek basin and 35 were detected at sites nationwide (fig. 27; 

table 16). The diversity of site selection in the nationwide 

reconnaissance study likely contributed to the greater diversity 

of the detected compounds. 

The most frequently detected compounds in the Threemile 

Creek basin include caffeine, 2-butoxyethanol phosphate, 

cholesterol, diazinon, and triclosan; the most frequently 

detected compounds (using the same analytical method) in the 

national study include DEET, caffeine, triclosan, tri(2-

chloroethyl)phosphate, and cholesterol. Of the 28 compounds 

detected in the Threemile Creek basin, 14 were detected more 

frequently in the Threemile Creek basin than at sites 

nationwide—many at frequencies much greater than those seen 

nationwide. Some of the constituents were detected at similar 

frequencies, such as triclosan, detected in 57.1 percent of the 

Threemile Creek basin samples and in 57.6 percent of the sites 

nationwide. Other constituents were found in much greater 

frequencies in the Threemile Creek basin (caffeine, 

2-butoxyethanol phosphate, diazinon, fluoranthene, 

phenanthrene, and pyrene); four constituents (chlorpyrifos, 

DEET, OP1EO, and OP2EO) were detected much less 

frequently in the Threemile Creek basin than nationwide 

(fig. 27; table 16). 

Concentrations of eight OWCs (caffeine, 5-methyl-1Hbenzotriazole, anthracene, 2-butoxyethanol phosphate, 

naphthalene, DEET, tri(2-chlorisopropyl) phosphate, and 

17β-estradiol) detected in the Threemile Creek basin exceeded 

maximum concentrations detected in the nationwide 

reconnaissance (table 16; Kolpin and others, 2002). Median 

concentrations of 15 OWCs detected in the Threemile Creek 

basin exceeded median concentrations detected in the 

nationwide reconnaissance (table 16; Kolpin and others, 2002). 

Benthic Invertebrates Results and 

Discussion

Analysis of samples at selected sites in Threemile Creek 

identified 77 benthic invertebrate taxa. After ambiguous taxa 

were resolved by distributing ambiguous parent taxa among 

their children, the final data set used for analysis contained 

56 distinct taxa, which represented 6 phyla, 6 classes, and 

11 orders of invertebrates (appendix table 3-1). Taxa richness 

was highest at site TM-2 (38 taxa) and decreased downstream 

at sites TM-3 (30 taxa) and TM-4 (19 taxa) and in the replicate 

sample from TM-4 (21 taxa, fig. 28). Lowest total taxa richness 

occurred at the most upstream site, TM-1 (17 taxa). Site TM-2 

also had the highest EPT taxa richness with seven taxa present. 

Figure 28. Benthic invertebrate taxa richness at selected sites on Threemile Creek, Mobile, Alabama, July 2000.
66 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Four EPT taxa were present at site TM-1, and three at each of 

the downstream sites TM-3 and TM-4. The TM-4 replicate 

sample also contained three EPT taxa, but two of the three taxa 

found in the TM-4 replicate were not present in the regular 

sample from TM-4. At all sites, chironomid (midges) taxa 

richness was greater than EPT taxa richness. Eleven chironomid 

taxa were present at site TM-2, eight were present at site TM-3, 

and seven at all other sites.

Percentage contributions of the most dominant taxa were 

used to screen for impaired sites. An impaired community 

commonly is dominated by a few tolerant species. The five 

most abundant taxa for samples collected in the Threemile 

Creek basin and the relative percentage abundance of each are 

listed in table 17. At all sites except TM-2, the two most 

abundant taxa accounted for more than 60 percent of the total 

abundance in the samples, and when the five most abundant 

Table 17. Five most abundant benthic invertebrate taxa and the respective percentages of total abundance 

for each taxa at selected sites in Threemile Creek, Mobile, Alabama, July 2000.

Common name group Most common taxa

Relative 

abundance, 

in percent

TM-1

Caddisflies Hydropsyche rossi Flint, Voshell, and Parker/simulans Ross 48.0

Worms Prostoma sp. 18.4

Midges Cricotopus/Orthocladius sp. 12.0

Midges Thienemanniella sp. 7.91

Midges Parachironomus sp. 2.69

Total percent abundance 89.1

TM-2

Mayflies Caenis sp. 28.1

Mayflies Paracloeodes minutus (Daggy) 10.0

Mites Acari 6.46

Snails Hydrobiidae 5.15

Clams Corbicula sp. 5.06

Total percent abundance 54.8

TM-3

Worms Turbellaria 61.8

Dragonflies Gomphidae 17.6

Midges Larsia sp. 4.38

Snails Planorbella sp. 2.70

Snails Prosobranchia 1.99

Total percent abundance 88.4

TM-4

Clams Corbicula sp. 45.6

Water Striders Trepobates sp. 40.2

Midges Cryptochironomus sp. 3.12

Snails Prosobranchia 2.83

Dragonflies Erythemis simplicicollis (Say) 1.57

Total percent abundance 93.4

TM-4 replicate

Dragonflies Gomphidae 45.0

Mayflies Caenis sp. 34.6

Mosquitoes Culex sp. 6.17

Midges Ablabesmyia sp. 1.69

Clams Corbicula sp. 1.61

Worms Naididae 1.61

Total percent abundance 90.6
Benthic Invertebrates Results and Discussion 67

taxa were considered at TM-1, TM-3, and TM-4, about 

90 percent of the total abundance was included. In contrast, 

TM-2 had a more even benthic invertebrate community with the 

five most abundant taxa accounting for only about 55 percent of 

the total abundance. According to ADEM, the most abundant 

taxon usually accounts for 30 percent or less of total abundance 

in healthy streams (Alabama Department of Environmental 

Management, 1996). Site TM-2 is the only site that met this 

criterion. 

Relative abundance of the major groups of taxa in a sample 

can reveal differences in sites. The percentage of total 

abundance contained in each of 15 major taxa groups is 

illustrated in figure 29. The major taxa groups were 

(1) mosquitoes, (2) butterflies, (3) water beetles, (4) water 

striders, (5) giant water bugs, (6) dragonflies, (7) springtails, 

(8) mites, (9) midges, (10) biting midges, (11) caddisflies, 

(12) mayflies, (13) clams, (14) snails, and (15) worms. Sites 

varied greatly in group composition (figure 29; appendix 

table 3-1). Only 6 of the 15 major taxa groups were identified at 

site TM-1. Almost 50 percent of the sample at TM-1 was 

composed of hydro-psychid caddisflies, which filter particulate 

matter out of the water column for food. The worms and 

midges, two generally tolerant groups, accounted for another 

48 percent of the total abundance (fig. 29; appendix table 3-1). 

Site TM-2 had the greatest number of groups present (fig. 29). 

A generally pollution-intolerant group, the mayflies group 

(39.1 percent) was the most common (fig. 29; appendix 

table 3-1). Eleven of the groups were represented at site TM-3, 

but more than 60 percent of the sample was composed of the 

class Turbellaria, a group of flatworms containing many 

detritivores. Turbellarians commonly are found in areas with 

large amounts of decaying organic material. The two samples at 

TM-4 were very different in taxa composition, and two different 

groups dominated each sample. In the regular sample, the water 

striders composed about 40 percent, and the clams composed 

about 46 percent (fig. 29; appendix table 3-1). In contrast, the 

dragonflies (46 percent) and mayflies (36 percent) were the 

most dominant taxa in the replicate sample (fig. 29; appendix 

table 3-1). 

Average tolerance values for the communities were 

calculated on the basis of taxa richness. Tolerance values for 

taxa range from zero to 10, with zero indicating least tolerant 

and 10 indicating most tolerant to contamination. Regional 

tolerance values from USEPA’s Rapid Bioassessment Protocol 

(RBP; Appendix B; Barbour and others, 1999) were averaged to 

create national tolerance values. The national tolerance values 

were then used to calculate community tolerance values 

(fig. 30). The percentage of taxa with assigned tolerance values 

ranged from 89.5 to 94.1 percent of total taxa collected in each 

sample, indicating that the community is well represented in the 

average tolerance value. Average tolerance values at all sites 

were similar and ranged from 5.8 at site TM-1 to 6.5 at site 

TM-2 (fig. 30). 

Figure 29. Relative abundance of major benthic invertebrate taxa at selected sites on Threemile Creek, Mobile, 

Alabama, July 2000.
68 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Regional tolerance values listed in the RBP for the 

southeastern United States were developed by the North 

Carolina Department of Environmental Management for use in 

calculating a biotic index, or average tolerance value 

normalized for abundance. Table 18 summarizes relations 

between North Carolina biotic index values and stream-water 

quality (Alabama Department of Environmental Management, 

1996). If equal North Carolina biotic index and average national 

tolerance values based on taxa richness are assumed to 

represent similar water-quality conditions, then average 

national tolerance scores indicate very good water quality at 

TM-1 and good to fair water quality at all other sites. 

The Shannon-Weaver Diversity Index (also known as 

Shannon’s Diversity Index) produces a score indicating the 

diversity of a biologic community. Scores between 3 and 4 

indicate healthy streams, and scores below 1 indicate 

impairment (Alabama Department of Environmental 

Management, 1996). Site TM-2 had a score of 4.1, indicating 

high diversity (fig. 31). All other sites had scores of 1.9 to 2.5, 

indicating water quality between impaired and unimpaired. 

Based on total and EPT taxa richness, percentage of 

dominant taxa, relative contribution of major taxonomic 

groups, and the Shannon-Weaver Diversity Index, site TM-2 

appeared to support a more diverse benthic invertebrate 

community and was the least impaired sampling site on 

Threemile Creek. Site TM-1 appeared to be the least diverse, 

with a community composed predominantly of just a few major 

TM-1 TM-2 TM-3 TM-4 TM-4 Replicate

Average tolerance values based on taxa richness

Percentage of taxa with assigned tolerance values

Increasing number of 

tolerant organisms

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0

AVERAGE TOLERANCE VALUE BASED ON TAXA RICHNESS

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0

PERCENTAGE OF TAXA WITH ASSIGNED TOLERANCE VALUES

Figure 30. Average U.S. Environmental Protection Agency national tolerance values for benthic invertebrate 

communities at selected sites on Threemile Creek, Mobile, Alabama, July 2000.

Table 18. North Carolina biotic index values 

and associated water-quality conditions.

[Alabama Department of Environmental Management, 

1996]

Coastal Plain biotic 

index values

Water-quality 

conditions

0.00 – 5.46 Excellent

5.47 – 6.05 Very good

6.06 – 6.72 Good–Fair

6.73 – 7.73 Fair

7.74 – 10.00 Poor
Periphyton Results and Discussion 69

taxa groups. Average tolerance values, however, indicated that 

site TM-1 supported a slightly less tolerant benthic invertebrate 

community than the other sites. All sampling sites, except 

TM-2, appear to be affected by contamination or habitat 

alteration based on percentage of abundance contained in the 

two most dominant taxa. 

Habitat and riparian zone differences may account for 

some of the variance in invertebrate communities among sites. 

TM-1 appears to be greatly affected by the upstream 

impoundment, with an invertebrate assemblage dominated by 

the species Hydropsyche rossi, a group of filtering collector 

caddisflies that are relatively intolerant (USEPA tolerance 

score = 4.9) to pollution. The dominance of this group may 

lower the overall tolerance value for TM-1. The riparian area at 

TM-2, though previously modified for flood control, was 

largely vegetated with uncut grasses at the time of sampling and 

may have limited the flow of excess nutrients and other 

contaminants to the stream. Water-chemistry samples were not 

collected at site TM-2, so this hypothesis cannot be tested. Site 

TM-3 is adjacent to commercial and residential properties, and 

the width of the riparian zone was much less than at site TM-2. 

The influence of tides on stage and flow at site TM-4 would be 

expected to restrict the invertebrate community to only those 

organisms able to cope with large changes in flow. 

Periphyton Results and Discussion

Periphyton biomass was estimated by using benthic 

chlorophyll a concentrations and AFDM (table 19). The 

greatest chlorophyll a concentrations during September 2000 

were measured at sites TM-3 and TSB, with concentrations of 

8.1 and 6.2 μg/cm2, respectively (fig. 32). The smallest benthic 

chlorophyll a concentration measured in September 2000 was 

at TM-4 in a sand substrate sample. Benthic chlorophyll a levels 

in samples from sand and tile substrates at site TM-3 differed 

considerably, with a much smaller number of periphyton found 

on the sand substrate. During this period, benthic chlorophyll a

concentrations at all sites were below the suggested nuisance 

algal growth level of 10 μg/cm2

 (Barbour and others, 1999). 

Benthic chlorophyll a concentrations from subsequent 

sampling periods were highly variable, with two 

exceedances—TM-3 during August 2001 and TM-2 during July 

2002—of the nuisance algal growth threshold (fig. 33). Greater 

concentrations generally occurred in late summer and fall than 

in the May samples. Except for one sample collected in July 

2001, benthic chlorophyll a tended to be greater at TM-3 than 

at TM-1 (fig. 33). No other consistent trends were evident 

among sites. 

Ash-free dry mass levels did not exceed the nuisance level 

of 50 g/m2 (Biggs, 1996; Barbour and others, 1999) at any of the 

Figure 31. Shannon-Weaver diversity index values for benthic invertebrate communities at selected sites on Threemile 

Creek, Mobile, Alabama, July 2000.
Table 19. Periphyton chlorophyll a and ash-free dry mass concentrations at selected sites in the Threemile 

Creek basin, Mobile, Alabama, 2000–2003.

[μg/cm2, microgram per square centimeter; AFDM, ash-free dry mass; g/m2, gram per square meter; μg/cm2/d, microgram per 

square centimeter per day; E, estimated concentration; —, no data]

Site

label

(fig. 1)

Date Days of exposure 

for tile substrate

Chlorophyll a

(μg/cm2

)

[70957]

a

U.S. Geological Survey National Water Information System parameter code.

a

AFDM

(g/m2

)

[49954]a

Autotrophic 

index (ratio of 

AFDM to 

chlorophyll a)

Chlorophyll a

per day 

(μg/cm2

/d)

TM-1 9/12/2000 55 2.2 9 410 0.04

TM-1 9/12/2000 55 2.6 16 620 .047

TM-1 11/14/2000 35 E6.4 6.8 110 .18

TM-1 5/22/2001 28 2.1 9.9 470 .075

TM-1 7/2/2001 26 .75 5.2 690 .029

TM-1 7/16/2001 26 3.1 9.8 320 .12

TM-1 8/8/2001 28 1.4 5.8 410 .05

TM-1 5/9/2002 22 .34 30 8,800 .015

TM-1 7/17/2002 28 .97 5.2 540 .035

TM-1 9/19/2002 28 2.6 10 380 .093

TM-1 7/15/2003 43 1.0 4.7 470 .023

TM-1 8/28/2003 44 1.3 8.5 650 .03

TM-2 5/22/2001 14 0.57 2.1 370 0.041

TM-2 7/2/2001 26 .96 4.3 450 .037

TM-2 7/16/2001 26 E5.4 17 320 .21

TM-2 8/8/2001 28 2.0 5.2 260 .071

TM-2 5/9/2002 22 2.2 14 640 .1

TM-2 7/17/2002 28 12 36 300 .43

TM-2 9/19/2002 30 3.6 12 330 .12

TM-2 8/28/2003 44 .41 48 12,000 .0093

TM-3 9/13/2000 56 3.4 19 560 0.061

TM-3 9/13/2000 56 8.1 38 470 .14

TM-3 11/14/2000 35 E7.7 19 250 .22

TM-3 5/22/2001 13 2.8 28 1,000 .22

TM-3 7/2/2001 26 2.4 19 790 .092

TM-3 7/16/2001 26 1.9 8.2 430 .073

TM-3 8/7/2001 27 12 33 280 .44

TM-3 8/7/2001 27 7.9 31 390 .29

TM-3 5/9/2002 22 .89 16 1,800 .04

TM-3 7/17/2002 28 5.6 28 500 .2

TM-3 9/19/2002 30 6.9 28 410 .23

TM-3 7/15/2003 43 5.3 24 450 .12

TM-3 8/28/2003 44 5.7 28 490 .13

TM-4 9/13/2000 Existing substrate 1.4 4.6 330 —

TM-4 11/14/2000 Existing substrate E1.1 7 640 —

CEN 9/14/2000 Existing substrate 3.2 8.3 260 —

TSB 9/13/2000 Existing substrate 6.2 17 270 —

70 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003
Periphyton Results and Discussion 71

Figure 32. Benthic chlorophyll a concentrations at selected sites in the Threemile Creek basin, Mobile, Alabama, September 2000.

Figure 33. Benthic chlorophyll a concentrations at selected sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.
72 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

sites in Threemile Creek (figs. 34, 35). During September 2000, 

the tile sample at TM-3 had the greatest amount of AFDM 

(38.1 g/m2

), more than twice the amount at any of the other 

sites, including the TM-3 sand substrate sample. The sand 

sample at TM-4 contained the least AFDM. During the other 

sampling periods, site TM-3 often contained the greatest 

AFDM among the sites (table 19), indicating more 

accumulation of organic matter. Site TM-2 had the greatest 

AFDM in July 2001 (17 g/m2), July 2002 (36 g/m2), and in 

August 2003 (48 g/m2

), when AFDM approached the nuisance 

level of 50 g/m2

. Levels of AFDM at site TM-1 were relatively 

low for all samples, except May 2002 (30 g/m2

). Greater 

velocities at site TM-1 may inhibit the accumulation of algal 

cells and, therefore, reduce the amount of AFDM. 

Autotrophic index values at all sites in the Threemile 

Creek basin were greater than 100, indicating possible organic 

enrichment; the index values ranged from 110 at TM-1 to 

12,000 at TM-2 (table 19). Median index values ranged from 

260 at CEN to 485 at TM-4. These results do not agree well with 

the water-chemistry measurements, which indicated greater 

concentrations of BOD at CEN than at the other sites in the 

basin. Some of the difference may be because BOD 

measurements were made from material suspended in the water 

column, whereas AFDM was calculated from material on the 

stream substrates. Additionally, lower autotrophic indices at the 

tributaries may be caused by adequate colonization periods for 

the development of mature periphyton communities, and the 

shorter exposure times for the artificial substrates at sites 

TM-1, TM-2, and TM-3 may have limited the development of 

algal biomass. 

Periphyton taxa richness was analyzed in samples from 

four sites on Threemile Creek and the two tributary sites. 

Maximum, median, and minimum periphyton taxa richness are 

presented in figure 36. Replicate samples were similar to each 

other, indicating good reproducibility of results. In September 

2000, median taxa richness was greatest at site TM-3 (44). 

Slightly fewer taxa were found in the sand sample than in the 

clay tile substrate sample at site TM-3. Taxa richness in samples 

from the sand substrate at site TM-4 was less than that in sand 

from TM-3, perhaps because of differences in flow. Samples 

from the existing concrete stream substrates at tributary sites 

CEN and TSB had fewer algal taxa than samples from artificial 

substrates at the main-stem sites, probably because of 

differences in colonization and substrate type. Samples from 

August 2001, showed an increase in taxa richness on clay tile 

substrates from TM-1 to TM-3. In September 2002, no 

upstream to downstream pattern was noted, and median taxa 

richness ranged from 26 at site TM-3 to 43 at site TM-2.

Differences in algal growth and representation of 

dominant algal groups among sites can be evaluated using 

estimates of algal biomass. Total algal biomass can be estimated 

by using algal cell density, the number of algal cells per unit 

area, or algal biovolume, which is the total volume of algal 

cells. Cell density usually is a good indicator of algal biomass if 

algal cell sizes are similar among taxa. Algal biovolume is a 

better indicator of algal biomass when there is large variation in 

cell sizes among taxa (Stevenson, 1996). Relative biomass in 

each of the major algal groups can be used to evaluate 

community structure. 

The percentage of total cell density and total biovolume 

accounted for by the nitrogen-fixing algae and each of the major 

algal divisions are presented in tables 20 and 21, respectively. 

Mean total algal density ranged from about 165,000 cells per 

square centimeter (cells/cm2) at site TM-1 in September 2002 

to more than 4.7 million cells/cm2 at site TM-3 in September 

2000 (table 20; appendix table 3-2). Mean algal biovolume 

ranged from more than 2.3 billion cubic micrometers per square 

centimeter (μm3/cm2) at site TM-3 in September 2000 to about 

56 million μm3/cm2 at site TM-4 in September 2000 (table 21; 

appendix table 3-2). Different laboratory protocols were used 

for the 2002 samples, so percentages of relative abundance of 

the major groups were compared among 2000 and 2001 

samples, and then among 2002 samples. 

Samples collected during September 2000 indicate 

community composition differences among sites. In terms of 

cell density, blue-green algae dominated at TM-1, TM-3, and 

CEN (table 20). Diatoms and blue-green algae codominated in 

the community at TSB. Abundant growth of blue-green algae is 

a common response to phosphorus enrichment in lakes and also 

has been noted in streams (Walker, 1983; Borchardt, 1996). 

Periphyton from TM-4 was collected from sand substrate, and 

green algae were the dominant group. The formation of 

filamentous green algal colonies commonly occurs when excess 

phosphorus and nitrogen are present in streams (Borchardt, 

1996; Cuffney and others, 1997). In contrast to the sample from 

TM-4, blue-green algae were more numerous in a sand sample 

collected at site TM-3. Site TM-4 is affected by tidal backwater 

and has somewhat higher conductivities than the other sites, 

which may account for the difference in community 

composition. 

Percentage contributions by biovolume differed from 

percentages by cell density in September 2000 (table 21). Green 

algae contributed most of the biovolume in the tile sample from 

TM-3 and the sand sample from TM-4. These sites are likely to 

be affected by nutrient enrichment. The TM-3 sand sample 

biovolume was divided nearly equally among diatoms, green, 

and blue-green algae. One replicate sample each from TM-1 

and TSB was dominated by green algae, but other samples at 

those sites had a greater proportion of diatoms. Site CEN was 

dominated by blue-green algae, particularly Amphithrix 

janthina, which accounted for 40–45 percent of the total 

biovolume. The dominance of this single taxon and the presence 

of Lyngbya sp. and Oscillatoria sp., two blue-green algal genera 

known to be tolerant to organic pollution, indicate that the 

aquatic community at CEN may be stressed. 

Different groups of taxa dominated samples collected in 

subsequent years. In August 2001, green algae and blue-green 

algae accounted for the greatest percentages of cell density at 

sites TM-1 and TM-2, and blue-green algae were more common 

at TM-3 (table 20). Biovolume measurements for August 2001 

indicated that green algae accounted for the majority of the algal 

biomass (table 21). Diatoms were the most numerous algal 
Periphyton Results and Discussion 73

Figure 34. Periphyton ash-free dry mass at selected sites in the Threemile Creek basin, Mobile, Alabama, September 2000.

Figure 35. Periphyton ash-free dry mass at selected sites on Threemile Creek, Mobile, Alabama, 2000–2003.
74 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

group in samples collected during September 2002 (table 20), 

but in terms of percent biovolume, green algae and diatoms 

codominated in communities at TM-1 and TM-3, and green 

algae accounted for over 80 percent of biovolume at TM-2 

(table 21). 

Nitrogen-fixing algae can use atmospheric nitrogen 

dissolved in water to fuel growth, and these algae tend to 

dominate in low-nitrogen concentration—nitrogen 

limiting—conditions. Nitrogen-fixing algal species accounted 

for less than 10 percent of total cell density in all samples except 

one sample collected at TM-1 in August 2001 (table 20). 

Results for percentages of biovolume were more variable than 

results calculated from cell density. Except for one sample 

collected in September 2000 at TM-1, nitrogen-fixing algae 

composed less than 10 percent of the total biovolume on tile 

substrates (table 21). Sand substrates at sites TM-3 and TM-4 

had greater proportions of nitrogen-fixing algae than tile 

substrates. Nitrogen-fixing algae—represented by a single 

taxon, Amphithrix janthina—made up an average of 45 percent 

of the total biovolume in samples from CEN (table 21). Waterchemistry data from all sites indicate that nitrogen is present in 

ample amounts for algal growth. The abundance of the one 

nitrogen-fixing species at CEN probably is due to other habitat 

or water-quality conditions at that site.

Based on the absence of oligosaprobic taxa and the large 

proportion of α-mesosaprobic biovolume at TSB in September 

2000, lower dissolved-oxygen concentrations and greater BOD 

concentrations would be expected at the tributary sites, 

especially TSB, than at the main-stem sites. The percentages of 

taxa richness in each of the saprobic categories (table 6) were 

calculated for the September 2000 sample period for 

comparison among sites (fig. 37). The percentage of diatom 

taxa with assigned saprobic classifications ranged from 

52 to 86 percent. The β-mesosaprobic (dissolved-oxygen 

saturation = 70–85 percent; BOD5 = 2–4 mg/L) category 

contained the highest percentage of taxa in samples from TM-3 

and TM-4 in September 2000. These samples also had 9 to 

20 percent of their taxa classified as oligosaprobic, or intolerant 

of low dissolved oxygen and high BOD. TM-1 and tributary 

sites CEN and TSB generally had greater percentages of taxa 

classified as α-meso/polysaprobic and polysaprobic. In 

addition, there were no oligosaprobic taxa present at the two 

tributary sites. 

Percentages of sample diatom biovolume with assigned 

saprobic classifications ranged from 15 to 93 percent (fig. 38) 

and were lower in samples from tile substrates. The majority of 

the diatom biovolume was classified as β-mesosaprobic at 

TM-3, TM-4, and CEN (fig. 38). At TSB, the α-mesosaprobic 

category accounted for the greatest proportion of diatom 

biovolume. TM-1 had similar percentages of β-mesosaprobic, 

α-mesosaprobic, and α-meso/polysaprobic biovolume; taxa in 

the oligosaprobic class accounted for a slightly lower 

percentage of biovolume. Oligosaprobic taxa were absent and

β-mesosaprobic taxa represented the majority of diatom 

biovolume in August 2001 samples from TM-1 and TM-2. 

TM-3 samples, however, indicated a greater proportion of 

Figure 36. Periphyton taxa richness at selected sites in the Threemile Creek basin, Mobile, Alabama, 2000–2002.
Table 20. Mean total algal cell density and mean percentage of total algal cell density in major algal groups in samples from selected 

sites in the Threemile Creek basin, Mobile, Alabama, 2000–2002.

[Values are percent of total algal cell density per square centimeter; cells/cm2, cells per square centimeter]

September 2000

Site 

substrate

TM-1

tile

TM-3

tile

TM-3

sand

TM-4

sand

CEN

concrete

TSB

concrete

Nitrogen-fixing algae 2.43 1.89 8.19 6.13 7.33 0

Diatom 30.0 25.7 6.76 10.3 11.4 46.6

Green algae 3.89 3.09 3.47 72.3 3.09 6.47

Blue-green algae 65.1 71.1 87.8 13.9 85.5 46.8

Cryptophyte algae 0 0 .696 .312 0 0

Euglenoid algae 1.01 .0258 0 .0271 0 .159

Dinoflagellate algae 0 0 0 .0665 0 0

Unknown algal taxa 0 0 1.30 3.21 0 0

Mean total cell 

density (cells/cm2)

460,000 4,790,000 2,320,000 1,140,000 4,040,000 3,190,000

August 2001

Site 

substrate

TM-1

tile

TM-2

tile

TM-3

tile

Nitrogen-fixing algae 11.9 4.84 4.35

Diatom 5.72 1.03 17.4

Green algae 64.8 60.3 5.09

Blue-green algae 29.4 38.7 77.5

Cryptophyte algae 0 0 0

Euglenoid algae .123 0 .0295

Dinoflagellate algae 0 0 0

Unknown algal taxa 0 0 0

Mean total cell 

density (cells/cm2)

1,040,000 985,000 2,900,000

September 2002

Site 

substract

TM-1

tile

TM-2

tile

TM-3

tile

Nitrogen-fixing algae 0 2.30 1.75

Diatom 91.8 90.6 98.6

Green algae 7.65 8.89 1.41

Blue-green algae .539 .535 0

Cryptophyte algae 0 0 0

Euglenoid algae 0 0 0

Dinoflagellate algae 0 0 0

Unknown algal taxa 0 0 0

Mean total cell 

density (cells/cm2)

165,000 211,000 2,010,000

Periphyton Results and Discussion 75
Table 21. Mean total algal biovolume and mean percentage of total algal biovolume in major algal groups in samples from selected 

sites in the Threemile Creek basin, Mobile, Alabama, 2000–2002.

[Values are percent of total algal biovolume in cubic micrometers per square centimeter; μm3/cm2, cubic micrometer per square centimeter]

September 2000

Site 

substrate

TM-1

tile

TM-3

tile

TM-3

sand

TM-4

sand

CEN

existing

concrete

TSB

existing

concrete

Nitrogen-fixing algae 13.0 0.161 15.0 9.96 45.0 0

Diatom 51.8 41.2 33.5 21.6 32.5 54.3

Green algae 37.4 44.0 29.1 60.7 9.24 31.1

Blue-green algae 6.98 14.6 35.6 10.0 58.3 13.8

Cryptophyte algae 0 0 .349 .312 0 0

Euglenoid algae 3.81 .200 0 .370 0 .725

Dinoflagellate algae 0 0 0 .302 0 0

Unknown algal taxa 0 0 1.40 6.66 0 0

Mean total biovolume 

(μm3/cm2

)

166,000,000 2,330,000,000 181,000,000 56,300,000 188,000,000 1,400,000,000

August 2001

Site 

substrate

TM-1

tile

TM-2

tile

TM-3

tile

Nitrogen-fixing algae 1.49 3.43 1.47

Diatom 3.14 1.02 10.2

Green algae 94.9 97.2 88.1

Blue-green algae 1.38 1.76 1.53

Cryptophyte algae 0 0 0

Euglenoid algae .613 0 .0818

Dinoflagellate algae 0 0 0

Unknown algal taxa 0 0 0

Mean total biovolume 

(μm3/cm2

)

326,000,000 240,000,000 991,000,000

September 2002

Site 

substrate

TM-1

tile

TM-2

tile

TM-3

tile

Nitrogen-fixing algae 0 0.0179 0.921

Diatom 45.7 16.5 59.9

Green algae 54.2 83.5 40.1

Blue-green algae .0443 .0404 0

Cryptophyte algae 0 0 0

Euglenoid algae 0 0 0

Dinoflagellate algae 0 0 0

Unknown algal taxa 0 0 0

Mean total biovolume 

(μm3/cm2)

329,000,000 796,000,000 1,120,000,000

76 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003
Periphyton Results and Discussion 77

Figure 37. Percentage of diatom taxa richness in each saprobic class for periphyton community samples 

collected from selected sites in the Threemile Creek basin, Mobile, Alabama, September 2000.

Figure 38. Percentage of diatom biovolume in each saprobic class for periphyton community samples collected 

from selected sites in the Threemile Creek basin, Mobile, Alabama, September 2000.
78 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

polysaprobic organisms. In the September 2002 samples, the 

TM-1 community was dominated by a meso/polysaprobic taxa, 

and TM-2 and TM-3 taxa were more evenly distributed among 

the categories (appendix table 3-2; T.F. Cuffney, U.S. 

Geological Survey, written commun., 2004). 

The water-chemistry data somewhat agree with the 

September 2000 results of the saprobic index evaluation. 

Abundant growths of algae can cause great diel variation in 

dissolved-oxygen concentrations as a result of production 

during photosynthesis and consumption during respiration 

(Hem, 1985). If photosynthesis and respiration affect the 

dissolved-oxygen concentrations, morning concentrations 

should be much lower than afternoon concentrations. Median 

dissolved-oxygen concentrations at CEN and TSB were the 

highest in this study. All but one of the measurements of 

dissolved-oxygen concentrations at CEN and TSB were made 

in the afternoon, when oxygen production by photosynthesis 

normally peaks. Most measurements indicated that the creeks 

were supersaturated with oxygen. Dissolved-oxygen 

concentration measurements taken at CEN and TSB on 

March 13, 2001, in the morning, when dissolved-oxygen 

concentrations should be lowest were also fairly high (greater 

than 85 percent saturation), but were influenced by higher flows 

from recent rainfall. The common afternoon supersaturation at 

these sites indicates that photosynthesis affects dissolvedoxygen concentrations, and very low concentrations, though not 

observed directly, probably occur in the early morning. In 

addition, median BOD values at CEN and TSB were slightly 

higher than BOD values at the main-stem sites, though the 

Kruskal-Wallis test did not indicate that the difference was 

significant. 

Summary

The USGS conducted a 4-year investigation of water 

quality and aquatic-community structure in Threemile Creek, 

an urban stream that drains residential areas in Mobile, 

Alabama. Water-quality data were collected between March 

2000 and September 2003 at four sites on Threemile Creek 

(TM-1, TM-3, TM-4, and TM-5), and between March 2000 and 

October 2001 at two tributary sites (CEN, TSB) that drain 

heavily urbanized areas in the watershed. Stream samples were 

analyzed for major ions, nutrients, fecal-indicator bacteria, and 

selected organic wastewater constituents. Continuous 

measurements of dissolved-oxygen concentrations, water 

temperature, specific conductance, and turbidity were recorded 

at three sites on Threemile Creek during 1999–2003. Aquaticcommunity structure was evaluated by conducting one survey 

of the benthic invertebrate community and multiple surveys of 

the algal community (periphyton). Benthic invertebrate samples 

were collected in July 2000 at four sites on Threemile Creek 

(TM-1, TM-2, TM-3, and TM-4); periphyton samples were 

collected during 2000–2003 at four sites on Threemile Creek 

and the two tributary sites (TM-1, TM-2, TM-3, TM-4, CEN, 

and TSB). The occurrence and distribution of chemical 

constituents in the water column provided an initial assessment 

of water quality in the streams, and the structure of the benthic 

invertebrate and algal communities provided an indication of 

the cumulative effects of water quality on the aquatic biota. 

Water-quality data from this investigation can be used by 

planners and resource managers in the evaluation of proposed 

TMDLs and other restoration efforts that may be implemented 

on Threemile Creek. 

The three most upstream sites (TM-1, TM-3, and TM-4) 

on Threemile Creek had similar water chemistry, characterized 

by a strong calcium-bicarbonate component. The most 

downstream site on Threemile Creek (TM-5) was affected by 

tidal fluctuations and had a strong sodium-chloride component. 

The tributary site at Center Street (CEN) was characterized by 

a strong sodium-chloride component; the tributary site at 

Toulmins Spring Branch (TSB) was characterized by a strong 

calcium component without a dominant anionic species. The 

ratios of sodium to chloride at CEN were higher (0.77) than 

typical values for seawater (0.55), indicating that other sources, 

such as leaking or overflowing sewer systems or industrial 

discharge, are likely contributors to the increased levels of 

sodium and chloride at this site. Concentrations of fluoride and 

boron also were elevated at this site, indicating possible 

anthropogenic sources. 

Dissolved-oxygen concentrations were not always within 

the recommended criterion established by the ADEM. The 

continuous monitors at TM-1, TM-4, and TM-5 recorded 

dissolved-oxygen concentrations that were repeatedly less than 

the minimum criterion (3.0 mg/L) established for agricultural 

and industrial water supply. The number of days with 

exceedances ranged from 3 at TM-1 (WY 2001) to 274 at 

TM-5 (WY 2000). Water temperature exceeded the 

recommended criterion established by the ADEM (32.2 °C) for 

agricultural and industrial water supply at five of six sites in the 

Threemile Creek basin. The pH values at all sites on Threemile 

Creek were within the ADEM criterion established for 

agricultural and industrial water supply (6.0–8.5); however, pH 

ranged from 7.2 to 10.0 at CEN and from 6.6 to 9.9 at TSB. The 

higher pH measurements at the two tributaries may be 

indicative of active photosynthesis or contaminants from other 

sources, such as industrial discharge or sewage effluent. 

Nutrient concentrations generally were higher at the two 

tributary sites (CEN and TSB) and the most downstream mainstem site (TM-5); nutrient concentrations were lower at the 

upstream main-stem sites (TM-1, TM-3, and TM-4). Total 

nitrogen concentrations ranged from 0.33 to 5.2 mg/L and 

exceeded the USEPA ecoregion criterion for all samples at 

CEN and TM-5. Nitrite-plus-nitrate concentrations ranged from 

< 0.02 to 3.6 mg/L and exceeded the USEPA ecoregion criteria 

in 88 percent of the samples. All samples at TM-3, 

TM-4, CEN, TSB, and TM-5 exceeded the ecoregion nutrient 

criterion for nitrite plus nitrate; approximately 50 percent of the 

samples at TM-1 exceeded the ecoregion nutrient criterion for 
Summary 79

nitrite plus nitrate. Total ammonia plus organic nitrogen 

concentrations ranged from < 0.200 to 3.2 mg/L. Total organic 

nitrogen was the predominant species of the total nitrogen 

concentration at all sites except TM-5 and CEN. 

Total phosphorus concentrations ranged from < 0.002 to 

0.831 mg/L. In 45 percent of the samples, total phosphorus 

concentrations exceeded the USEPA goal of 0.1 mg/L for 

preventing nuisance aquatic growth. The majority of total 

phosphorus concentrations at TM-1, TM-3, and TM-4 were 

below the ecoregion nutrient criteria and the USEPA goal of 

0.1 mg/L total phosphorus; however, total phosphorus 

concentrations in all samples at CEN, TSB, and TM-5 exceeded 

both the ecoregion nutrient criterion for total phosphorus and 

the USEPA goal of 0.1 mg/L total phosphorus. Distributions of 

dissolved phosphorus and dissolved orthophosphate 

concentrations were similar and ranged from < 0.002 to 

0.45 mg/L and < 0.001 to 0.405 mg/L, respectively. 

The distribution of nitrogen to phosphorus ratios indicated 

two distinct groupings. The three most upstream main-stem 

sites (TM-1, TM-3, and TM-4) generally had nitrogen to 

phosphorus ratios of 10 to 1 or more, indicating that phosphorus 

is the limiting nutrient at these sites. Nitrogen to phosphorus 

ratios at CEN and TM-5 generally were less than 10 to 1 but 

higher than 5 to 1, indicating that nitrogen and phosphorus have 

equal influence on nutrient limitation at these sites. With the 

exception of one sample, nitrogen to phosphorus ratios at TSB 

were less than 5, indicating the potential for nitrogen limitation 

at this site. Saline waters from Mobile Bay at TM-5 may 

account for the ratio at TM-5, but the effects of urbanization 

probably account for the ratios at CEN and TSB, because these 

are freshwater systems. 

Enterococci concentrations at sites in the Threemile Creek 

watershed exceeded the USEPA criterion (151 col/100 mL) in 

52 percent of the samples; E. coli concentrations exceeded the 

USEPA criterion (576 col/100 mL) in 41 percent of the 

samples; and fecal coliform concentrations exceeded the 

ADEM criterion (4,000 col/100 mL) in 16 percent of the 

samples. Median values of enterococci and fecal coliform were 

highest at the two tributaries. Concentrations of fecal-indicator 

bacteria increased in a downstream direction in Threemile 

Creek except at TM-3, where more high-flow samples were 

collected. Concentrations of bacteria at TM-3 and TM-4 were 

elevated during high flow rather than low flow, indicating 

nonpoint sources; concentrations of bacteria at the other sites 

were elevated during low and high flow, indicating both point 

and nonpoint sources. Enterococci, E. coli, and fecal coliform 

concentrations at TM-5 were significantly greater than 

concentrations at TM-1. Concentrations of fecal-indicator 

bacteria were not well correlated with discharge or turbidity, 

except at TM-3. E. coli and fecal coliform concentrations were 

significantly correlated with each other at all sites.

Stream samples were analyzed for 48 chemical 

compounds that are commonly found in wastewater and urban 

runoff, which may indicate contamination attributed to a human 

source—37 of these compounds were detected in at least one 

sample. Organic wastewater compounds (OWCs) were detected 

in each of the 63 samples collected from the Threemile Creek 

basin. Of the 48 compounds analyzed, 9 OWCs were detected 

frequently (50-percent or greater detection frequency) in 

samples from the Threemile Creek basin. The most frequently 

detected compounds were atrazine (herbicide), caffeine 

(stimulant), 2-butoxyethanol phosphate (household cleaning 

agent), cholesterol (plant and animal steroid), diazinon 

(insecticide), bromacil (herbicide), triclosan (antimicrobial 

disinfectant), fluoranthene (PAH), and N,N-diethyl-mtoluamide (insect repellent commonly known as DEET). 

The number of OWCs detected in an individual sample 

ranged from 2 to 22; the median number of wastewater 

indicators detected per site ranged from 5 to 18. The 

concentration of OWCs detected in individual samples ranged 

from 0.15 μg/L (TM-1) to 56.6 μg/L (CEN); the median 

concentration of OWCs detected in individual samples ranged 

from 0.75 μg/L (TM-1) to 20.1 μg/L (CEN). Mixtures of 

chemicals were common, and 50 of 63 samples (79.4 percent) 

contained total concentrations of OWCs that exceeded 1 μg/L; 

only 17.9 percent of the samples contained individual 

compounds with concentrations that exceeded 1 μg/L. 

Organic wastewater compounds were grouped into 11 

categories based on their general use and origins: antioxidants, 

prescription and nonprescription drugs (17β-estradiol, caffeine, 

and cotinine), steroids (sterols and stanols), fragrances, 

detergent metabolites, antimicrobials, plasticizers/flame 

retardants, insect repellents, insecticides, herbicides and 

fungicides, and PAHs. Four groups (steroids, detergent 

metabolites, plasticizer/flame retardants, and 

prescription/nonprescription drugs) contributed almost 

87 percent of the total measured concentration of all samples, 

and 9 of 11 groups were found in more than 50 percent of the 

samples.

Although few of the OWCs measured have drinking-water 

standards or other human or ecological health criteria, there 

were exceedances of Canadian aquatic-life guidelines for NP, 

NP1EO, NP2EO, chlorpyrifos, fluoranthene, benzo[a]pyrene, 

pyrene, and diazinon. The concentrations of many of these 

compounds were estimated values, however, and should not be 

compared directly to the criteria for regulatory purposes. The 

detergent metabolites (NP1EO, NP2EO, and paranonylphenol) were detected most frequently at CEN and TM-5. 

PAHs, such as fluoranthene and pyrene, were detected most 

frequently at TM-3, indicative of nonpoint-source contributions 

and the large number of high-flow samples collected at this site. 

Higher concentrations of OWCs were detected at two sites 

(CEN and TM-5) throughout the study—concentrations were 

highest during low flow at these sites, indicating point sources. 

Greater numbers of compounds were detected during low flow 

at four of six sites. The total concentration of OWCs at TM-5 

was significantly greater than at any site on Threemile Creek 

(TM1, TM-3, or TM-4); the number of OWC detections at 

TM-5 was significantly greater than at TM-1. The total 

concentration of wastewater indicators at CEN and TSB was 
80 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

significantly greater than at TM-4; the number of OWC 

detections at CEN was significantly greater than at TM-4. 

Strong correlations were seen between the total concentration 

of OWCs and (1) total phosphorus, (2) caffeine, and (3) the 

number of wastewater indicator compounds detected. 

Nineteen of the 48 compounds analyzed are known or 

suspected to exhibit at least weak hormonal activity, with the 

potential to disrupt endocrine function—12 of these compounds 

were detected in at least one sample. Potential endocrine 

disruptors were detected in 61 of 63 samples (96.8 percent) in 

the Threemile Creek basin. The total concentration of potential 

endocrine disruptors detected in a single sample ranged from 

0 μg/L (TM-1) to 14.6 μg/L (CEN). The total concentration of 

potential endocrine disruptors exceeded 1 μg/L in about 

43 percent of the samples collected in the Threemile Creek 

basin, in all of the samples at CEN, and in about 85 percent of 

the samples at TM-5. Median concentrations of potential 

endocrine disruptors were highest at CEN and TM-5, followed 

by TSB, TM-3, TM-4, and TM-1. 

Organic wastewater data from the Threemile Creek basin 

were compared to data collected in the first nationwide 

reconnaissance of the occurrence of pharmaceuticals, 

hormones, and other OWCs in water resources. Of the 

35 constituents that were common to both studies, 28 were 

detected in the Threemile Creek basin and 35 were detected at 

sites nationwide. The most frequently detected OWCs at sites 

nationwide included DEET, caffeine, triclosan, tri(2-

chlorethyl)phosphate, and cholesterol; the most frequently 

detected OWCs in the Threemile Creek basin were caffeine, 

2-butoxyethanol phosphate, cholesterol, diazinon, and 

triclosan. Many constituents in the Threemile Creek basin were 

detected more frequently than at sites nationwide (caffeine, 

2-butoxyethanol phosphate, diazinon, fluoranthene, pyrene, and 

phenanthrene); other constituents (DEET and OP2EO) were 

detected more frequently at sites nationwide. Concentrations of 

eight OWCs (caffeine, 5-methyl-1H-benzotriazole, anthracene, 

2-butoxyethanol phosphate, naphthalene, DEET, 

tri(dichlorisopropyl) phosphate, and 17β-estradiol) in the 

Threemile Creek basin exceeded maximum concentrations 

detected in the nationwide reconnaissance. Median 

concentrations of 15 OWCs detected in the Threemile Creek 

basin exceeded median concentrations detected in the 

nationwide reconnaissance. 

In general, benthic invertebrate communities at sampled 

sites in Threemile Creek appeared to be impaired based on taxa 

richness, numbers of EPT taxa, and measures of community 

diversity. Benthic invertebrate communities appeared impaired 

at sites TM-1, TM-3, and TM-4; site TM-2 had a more diverse 

benthic invertebrate community, indicating better water quality 

than the other sites. Available tolerance values indicate very 

good water quality at TM-1 and good to fair water-quality 

conditions at all other sampling sites, with community average 

national tolerance values ranging from 5.8 at site TM-1 to 6.5 at 

TM-2.

Algal data indicate that organic and nutrient enrichment 

fueled occasional nuisance algal growth in the Threemile Creek 

basin. Benthic chlorophyll a occasionally was found at 

concentrations associated with nuisance algal growth. In 

contrast, AFDM did not indicate nuisance algal growth at any 

of the sites. Taxa richness indicated more diverse algal 

communities at the main-stem sites than at the tributary sites, 

perhaps because of the difference between concrete and tile 

substrates or colonization period. Nitrogen-fixing algae 

composed less than 10 percent of the algal biovolume from 

artificial substrate samples at the main-stem sites, indicating 

nitrogen-enriched water quality. In contrast, site CEN had an 

algal community 45 percent composed of a single species of 

nitrogen-fixing algae. Water-chemistry data indicate that 

nitrogen was not limiting at CEN, so some other water-quality 

or habitat factor must be influencing the dominance of that algal 

species. 

Measures of pollution tolerance of algae in the Threemile 

Creek basin indicated communities that are tolerant of organic 

enrichment at many of the sampling sites. The green algae, a 

generally more pollution-tolerant division, contributed most of 

the biovolume in the tile sample from site TM-3 and the sand 

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green algae contributed most of the biovolume at sites TM-1, 

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biovolume at TM-2. During September 2000, the more tolerant

β-mesosaprobic and α-mesosaprobic diatom taxa accounted for 

more of the diatom biovolume than the less tolerant 

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were not present at the tributary sites CEN and TSB, indicating 

lower dissolved-oxygen concentrations and higher BOD levels, 

in contrast to measured water chemistry at the two sites. The 

discrepancy between algal and water-chemistry data may be 

due to the diel cycle of dissolved-oxygen concentrations 

induced by actively photosynthesizing organisms. 

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86 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003
Appendixes

Appendix 1. Quality Control

Table 1-1. Concentrations of nutrients, major ions, and selected organic wastewater 

compounds detected in blank samples in the Threemile Creek basin, Mobile, 

Alabama, 2000–2003

Appendix 2. Water-Quality Samples

Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek 

basin, Mobile, Alabama, 2000–2003

Table 2-2. Concentrations of selected organic wastewater compounds detected at sites 

in the Threemile Creek basin, Mobile, Alabama, 2000–2003

Appendix 3. Benthic Invertebrates and Periphyton

Table 3-1. Benthic invertebrate taxa, percent abundance of each taxon, and total 

abundance at selected sites in Threemile Creek, Mobile, Alabama, July 2000

Table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from 

selected sites in the Threemile Creek basin, Mobile, Alabama, 2000–2002
88 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Appendix 1. Table 1-1. Concentrations of nutrients, major ions, and selected organic wastewater compounds 

detected in blank samples in the Threemile Creek basin, Mobile, Alabama, 2000–2003.

[N, nitrogen; mg/L, milligram per liter; <, less than; MDL, minimum detection limit; BOD5, 5-day biochemical oxygen demand; μg/L, 

microgram per liter; MRL, minimum reporting level; E, estimated; *, Concentrations of these compounds are always reported as estimated; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol]

Constituent

Number 

of blanks 

with no 

detection

Number 

of 

blanks

Concentration Reporting 

level

Reporting 

level 

type

Type 

of 

blank

Ammonia-plus-organic N, total as N 13 14 0.2 mg/L < 0.20 mg/L MDL Field

Ammonia, dissolved as N 10 14 0.03 mg/L < 0.01 mg/L MDL Field

Ammonia, dissolved as N 10 14 0.01 mg/L < 0.01 mg/L MDL Field

Ammonia, dissolved as N 10 14 0.01 mg/L < 0.01 mg/L MDL Field

Ammonia, dissolved as N 10 14 0.014 mg/L < 0.01 mg/L MDL Field

Ammonia, total as N 9 14 0.02 mg/L < 0.01 mg/L MDL Field

Ammonia, total as N 9 14 0.01 mg/L < 0.01 mg/L MDL Field

Ammonia, total as N 9 14 0.02 mg/L < 0.01 mg/L MDL Field

Ammonia, total as N 9 14 0.01 mg/L < 0.01 mg/L MDL Field

Ammonia, total as N 9 14 0.01 mg/L < 0.01 mg/L MDL Field

BOD5 4 10 0.2 mg/L < 0.1 mg/L MDL Field

BOD5 4 10 0.5 mg/L < 0.1 mg/L MDL Field

BOD5 4 10 0.2 mg/L < 0.1 mg/L MDL Field

BOD5 4 10 0.2 mg/L < 0.1 mg/L MDL Field

BOD5 4 10 0.2 mg/L < 0.1 mg/L MDL Field

BOD5 4 10 0.2 mg/L < 0.1 mg/L MDL Field

Calcium, dissolved 6 7 0.02 mg/L < 0.02 mg/L MDL Field

Iron, dissolved 6 7 2.4 μg/L < 2 μg/L MDL Field

Iron, total 6 7 1.7 μg/L < 2 μg/L MDL Field

Magnesium, dissolved 6 7 0.004 mg/L < 0.03g/L MDL Field

Manganese, total 6 7 0.3 μg/L < 1 μg/L MDL Field

Organic carbon, total 2 6 0.6 mg/L < 0.1 mg/L MDL Field

Organic carbon, total 2 6 0.3 mg/L < 0.1 mg/L MDL Field

Organic carbon, total 2 6 0.4 mg/L < 0.1 mg/L MDL Field

Organic carbon, total 2 6 0.6 mg/L < 0.1 mg/L MDL Field

Phosphorus, dissolved 10 14 0.003 mg/L < 0.002 mg/L MDL Field

Phosphorus, dissolved 10 14 0.004 mg/L < 0.002 mg/L MDL Field
Appendixes 89

Phosphorus, dissolved 10 14 0.002 mg/L < 0.002 mg/L MDL Field

Phosphorus, dissolved 10 14 0.003 mg/L < 0.002 mg/L MDL Field

Phosphorus, total 11 14 0.003 mg/L < 0.002 mg/L MDL Field

Phosphorus, total 11 14 0.002mg/L < 0.002 mg/L MDL Field

Phosphorus, total 11 14 0.005mg/L < 0.002 mg/L MDL Field

Silica, dissolved 4 7 0.05 mg/L < 0.01 mg/L MDL Field

Silica, dissolved 4 7 0.02 mg/L < 0.01 mg/L MDL Field

Silica, dissolved 4 7 0.09 mg/L < 0.01 mg/L MDL Field

Sodium, dissolved 6 7 0.1 mg/L < 0.1 mg/L MDL Field

2,6-di-tert-p-benzoquinone 4 5 0.096 μg/L < 0.070 μg/L MRL Lab

1-Methylnaphthalene 8 9 E 0.004 μg/L < 0.500 μg/L MRL Lab

2-Methylnaphthalene 8 9 E 0.0039 μg/L < 0.500 μg/L MRL Lab

17β-estradiol* 12 14 E 0.870 μg/L < 5.00 μg/L MRL Lab

17β−estradiol* 12 14 E 0.450 μg/L < 5.00 μg/L MRL Lab

Acetophenone 13 14 E 0.02 μg/L < 0.500 μg/L MRL Lab

Benzo[a]pyrene 13 14 E 0.370 μg/L < 0.500 μg/L MRL Lab

Cholesterol 13 14 E 0.260 μg/L < 2.00 μg/L MRL Lab

Cotinine 13 14 E 0.200 μg/L < 1.00 μg/L MRL Lab

Fluoranthene 13 14 E 0.0029 μg/L < 0.500 μg/L MRL Lab

Naphthalene 11 14 E 0.034 μg/L < 0.500 μg/L MRL Lab

Naphthalene 11 14 E 0.027 μg/L < 0.030 μg/L MRL Lab

Naphthalene 10 11 E 0.048 μg/L < 0.020 μg/L MRL Field

Naphthalene 11 14 E 0.017 μg/L < 0.020 μg/L MRL Lab

N,N-diethyl-m-toluamide 13 14 E 0.028 μg/L < 0.040 μg/L MRL Lab

N,N-diethyl-m-toluamide 10 11 E 0.031 μg/L < 0.040 μg/L MRL Field

NP2EO, total* 13 14 E 0.940 μg/L < 5.00 μg/L MRL Lab

OP1EO* 11 14 E 0.130 μg/L < 1.00 μg/L MRL Lab

OP1EO* 11 14 E 0.120 μg/L < 1.00 μg/L MRL Lab

Appendix 1. Table 1-1. Concentrations of nutrients, major ions, and selected organic wastewater compounds 

detected in blank samples in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued

[N, nitrogen; mg/L, milligram per liter; <, less than; MDL, minimum detection limit; BOD5, 5-day biochemical oxygen demand; μg/L, 

microgram per liter; MRL, minimum reporting level; E, estimated; *, Concentrations of these compounds are always reported as estimated; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol]

Constituent

Number 

of blanks 

with no 

detection

Number 

of 

blanks

Concentration Reporting 

level

Reporting 

level 

type

Type 

of 

blank
90 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

OP1EO* 11 14 E 0.160 μg/L < 1.00 μg/L MRL Lab

para-nonylphenol total* 13 14 E 0.685 μg/L < 0.500 μg/L MRL Field

Phenanthrene 13 14 E 0.0025 μg/L < 0.500 μg/L MRL Lab

Pyrene 13 14 E 0.053 μg/L < 0.500 μg/L MRL Field

Tri(2-chloroisopropyl)phosphate 13 14 E 0.064 μg/L < 0.100 μg/L MRL Lab

Tri(2-chloroethyl)phosphate 13 14 0.046 μg/L < 0.040 μg/L MRL Lab

Tributylphosphate 7 9 E 0.076 μg/L < 0.500 μg/L MRL Lab

Tributylphosphate 7 9 E 0.077 μg/L < 0.500 μg/L MRL Lab

Appendix 1. Table 1-1. Concentrations of nutrients, major ions, and selected organic wastewater compounds 

detected in blank samples in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued

[N, nitrogen; mg/L, milligram per liter; <, less than; MDL, minimum detection limit; BOD5, 5-day biochemical oxygen demand; μg/L, 

microgram per liter; MRL, minimum reporting level; E, estimated; *, Concentrations of these compounds are always reported as estimated; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxylate octylphenol]

Constituent

Number 

of blanks 

with no 

detection

Number 

of 

blanks

Concentration Reporting 

level

Reporting 

level 

type

Type 

of 

blank
Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.[NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligramed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, phooxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]

NWIS 

parameter 

code

Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-1, Threemile Creek at Ziegler Boulevard at Spring Hill, Alabama, March 2000–September 2003

00061 Discharge, ft3/s 36 287 5.1 30.4 217 21.8 11 00065 Gage height, feet 36 69.25 67.74 67.99 69.07 67.97 67.86 00095 Specific conductance, μS/cm at 25 °C 36 99 58 76 95 86 73 00400 pH 36 7.5 6 7.0 7.4 7.2 7 61028 Turbidity (field), NTU 32 130 2 16 94 13 6.4 00076 Turbidity (lab), NTU 7 24 1 5.7 24 3.4 3 00010 Water temperature, °C 36 31.5 15 23.7 31.1 27.9 26.2 00300 Dissolved oxygen, mg/L 36 9.5 6.8 7.9 9.5 8.6 7.8 00020 Air temperature, °C 22 34 15 23.4 33.6 28.0 24.4 00915 Calcium, mg/L 7 11 7 8.971 11 9.9 8.7 00925 Magnesium, mg/L 7 1.2 0.8 1.086 1.2 1.2 1.1 00935 Potassium, mg/L 7 1.2 0.3 0.857 1.2 1.1 0.9 00930 Sodium, mg/L 7 3.8 1.8 2.986 3.8 3.7 3.1 00453 Bicarbonate, mg/L 7 36 22 29 36 35 29 00452 Carbonate, mg/L 7 0 -- -- -- -- -- 00940 Chloride, mg/L 7 8.7 3.1 5.286 8.7 5.7 5.2 00950 Fluoride, mg/L 7 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 00955 Silica, mg/L 7 4.7 3 4.029 4.7 4.5 4.2 00945 Sulfate, mg/L 7 5.2 1.9 3.2 5.2 4.4 2.6 39086 Alkalinity, mg/L as CaCO3 7 30 18 24 30 28 23 00623 Nitrogen, ammonia plus organic, dissolved (mg/L as N) 36 0.86 < 0.200 0.314* *0.673 *0.400 *0.300 00625 Nitrogen, ammonia plus organic, total 

(mg/L as N)

36 1 < 0.200 0.427* *0.830 *0.500 *0.400 

00608 Ammonia, dissolved (mg/L as N) 36 0.55 0.02 0.095 0.372 0.12 0.06 00610 Ammonia, total (mg/L as N) 36 0.63 0.02 0.096 0.307 0.125 0.06 00618 Nitrate, dissolved (mg/L as N) 7 0.43 0.17 0.26 0.43 0.33 0.2 00620 Nitrate, total (mg/L as N) 9 0.33 0.14 0.216 0.33 0.265 0.19 00631 Nitrite plus nitrate, dissolved (mg/L as 

N)

36 0.45 < 0.020 0.159* *0.382 *0.235 *0.145 
NWIS parameter code Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-1, Threemile Creek at Ziegler Boulevard at Spring Hill, Alabama, March 2000–September 2003 (Continued) 00630 Nitrite plus nitrate, total (mg/L as N) 36 0.52 < 0.020 0.161* *0.384 *0.232 *0.145 

00613 Nitrite, dissolved (mg/L as N) 36 0.04 < 0.010 0.006* *0.032 *0.006 *0.002 00615 Nitrite, total (mg/L as N) 36 0.03 < 0.010 0.008* *0.030 *0.010 *0.005 00600 Total nitrogen, mg/L 20 1.4 0.34 0.679 1.378 0.817 0.73 00665 Total phosphorus, mg/L 36 0.07 < 0.002 0.016* *0.070 *0.028 *0.004 00666 Phosphorus, dissolved mg/L 36 0.02 < 0.002 0.006* *0.020 *0.010 *0.003 00671 Orthophosphate, dissolved (mg/L as P) 36 0.006 < 0.001 0.002* *0.006 *0.003 *0.002 70507 Orthophosphate, total (mg/L as P) 36 0.03 < 0.001 0.008* *0.025 *0.009 *0.006 00680 Total organic carbon, mg/L 7 3.9 1.9 2.743 3.9 3.2 2.8 00310 BOD, 5-day, mg/L 29 2.4 0.1 1.1 2.05 1.25 1.1 70953 Suspended chlorophyll a, μg/L 24 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 70954 Suspended chlorophyll b, μg/L 11 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 90909 Enterococci, colonies/100 mL 26 6,000 11 775 5,615 615 48 31633 Escherichia coli, colonies/100 mL 35 2,400 20 420 2,160 420 71 31625 Fecal coliforms, colonies/100 mL 31 2,400 25 299 1,800 370 100 01020 Boron, dissolved μg/L 7 20 10 13.6 20 15 13 01046 Iron, dissolved μg/L 7 833 299 461.9 833 529 392 01045 Iron, total μg/L 7 1600 733 1212 1600 1600 1300 01056 Manganese, dissolved μg/L 7 110 10 50.3 110 90 39 01055 Manganese, total μg/L 7 130 41 76.6 130 110 68 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued [NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS 

parameter 

code

Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-3, Threemile Creek at Fillingim Street at Mobile, Alabama, March 2000–September 2003

00061 Discharge, ft3/s 21 930 11 126 881 114 40 00065 Gage height, feet 16 10.22 7.93 8.34 10.22 8.34 8.20 00095 Specific conductance, μS/cm at 25 °C 21 116 64 92 115 101 96 00400 pH 16 8.2 6.5 7.5 8.2 7.9 7.4 61028 Turbidity (field), NTU 15 420 4 72 420 95 33 00076 Turbidity (lab), NTU 7 240 2.3 40 240 11 6.2 00010 Water temperature, °C 21 31.1 15.1 21.2 30.9 26.8 19.1 00300 Dissolved oxygen, mg/L 21 10.5 7.1 9.0 10.5 9.8 9.6 00020 Air temperature, °C 7 33 14.9 22.1 33 27.3 20 00915 Calcium, mg/L 7 16 8.5 13.071 16 15 14 00925 Magnesium, mg/L 7 1.5 0.8 1.257 1.5 1.4 1.3 00935 Potassium, mg/L 7 1.3 0.6 0.943 1.3 1.2 0.9 00930 Sodium, mg/L 7 5 2.1 3.657 5 4.3 3.8 00453 Bicarbonate, mg/L 7 50 23 41 50 49 43 00452 Carbonate, mg/L 7 0 -- -- -- -- -- 00940 Chloride, mg/L 7 6.9 3.2 5.3 6.9 6 5.8 00950 Fluoride, mg/L 7 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 00955 Silica, mg/L 7 5.2 2.5 3.786 5.2 4.7 4.2 00945 Sulfate, mg/L 7 8.8 2.9 5.243 8.8 7 4.6 39086 Alkalinity, mg/L as CaCO3 7 41 19 33 41 40 35 00623 Nitrogen, ammonia plus organic, dissolved (mg/L as N) 20 0.61 < 0.200 0.335* *0.610 *0.500 *0.260 00625 Nitrogen, ammonia plus organic, total 

(mg/L as N)

20 1.4 0.2 0.488 1.375 0.6 0.45 

00608 Ammonia, dissolved (mg/L as N) 19 0.2 0.03 0.071 0.2 0.08 0.05 00610 Ammonia, total (mg/L as N) 19 0.25 0.04 0.068 0.25 0.06 0.05 00618 Nitrate, dissolved (mg/L as N) 4 0.45 0.22 -- -- -- -- 00620 Nitrate, total (mg/L as N) 9 0.47 0.16 0.258 0.47 0.27 0.24 00631 Nitrite plus nitrate, dissolved (mg/L as 

N)

19 0.46 0.06 0.222 0.46 0.28 0.24 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued[NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS parameter code Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-3, Threemile Creek at Fillingim Street at Mobile, Alabama, March 2000–September 2003 (Continued) 00630 Nitrite plus nitrate, total (mg/L as N) 19 0.48 0.06 0.226 0.48 0.28 0.25 

00613 Nitrite, dissolved (mg/L as N) 19 0.02 < 0.010 -- 0.02 < 0.010 < 0.010 00615 Nitrite, total (mg/L as N) 19 0.02 < 0.010 0.010* *0.020 *0.010 *0.008 00600 Total nitrogen, mg/L 16 1.7 0.35 0.756 1.7 0.942 0.765 00665 Total phosphorus, mg/L 19 0.135 < 0.002 0.038* *0.135 *0.063 *0.022 00666 Phosphorus, dissolved mg/L 19 0.034 < 0.002 0.013* *0.034 *0.023 *0.009 00671 Orthophosphate, dissolved (mg/L as P) 20 0.029 < 0.001 0.007* *0.028 *0.010 *0.004 70507 Orthophosphate, total (mg/L as P) 20 0.036 < 0.001 0.012* *0.036 *0.023 *0.009 00680 Total organic carbon, mg/L 7 5.6 2.7 3.857 5.6 5.3 3.6 00310 BOD, 5-day, mg/L 11 3 0.2 1.709 3 2.5 1.3 70953 Suspended chlorophyll a, μg/L 12 6.1 < 0.100 -- 6.1 < 0.100 < 0.100 70954 Suspended chlorophyll b, μg/L 7 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 90909 Enterococci, colonies/100 mL 19 31,000 10 6,760 31,000 11,000 1,200 31633 Escherichia coli, colonies/100 mL 21 29,000 14 4,600 27,700 8,700 1,500 31625 Fecal coliforms, colonies/100 mL 15 12,000 44 3,130 12,000 5,200 300 01020 Boron, dissolved μg/L 7 28 10 20 28 23 20 01046 Iron, dissolved μg/L 7 572 258 397.6 572 432 390 01045 Iron, total μg/L 7 3300 567 1388.3 3300 1400 1300 01056 Manganese, dissolved μg/L 7 93 27 53.7 93 65 47 01055 Manganese, total μg/L 7 140 31 81.1 140 110 72 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued [NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS 

parameter 

code

Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-4, Threemile Creek at Stanton Road at Mobile, Alabama, March 2000–June 2002

00061 Discharge, ft3/s 17 52 -16 18.3 52 29.5 17 00065 Gage height, feet 20 5.62 0.21 1.30 5.45 1.73 1.20 00095 Specific conductance, μS/cm at 25 °C 20 126 63 103 126 112 103 00400 pH 20 7 6.1 6.6 7.0 6.8 6.6 61028 Turbidity (field), NTU 16 800 3.9 57 800 9.7 5.4 00076 Turbidity (lab), NTU 7 530 1.5 79 530 7.7 3.2 00010 Water temperature, °C 20 33.4 16.8 26.6 33.4 30 28 00300 Dissolved oxygen, mg/L 20 11.5 5.4 8.2 11.4 9.3 8.0 00020 Air temperature, °C 17 36 15.5 26.4 36 30.8 26.2 00915 Calcium, mg/L 7 14 7.8 11.686 14 14 12 00925 Magnesium, mg/L 7 1.6 0.6 1.343 1.6 1.5 1.5 00935 Potassium, mg/L 7 1.4 0.7 1.029 1.4 1.3 1 00930 Sodium, mg/L 7 5.3 2 4.1 5.3 4.9 4.4 00453 Bicarbonate, mg/L 7 46 23 35 46 45 33 00452 Carbonate, mg/L 7 0 -- -- -- -- -- 00940 Chloride, mg/L 7 9.2 2.8 6.214 9.2 7.1 6.5 00950 Fluoride, mg/L 7 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 00955 Silica, mg/L 7 5.9 1.8 4.171 5.9 5.3 4.6 00945 Sulfate, mg/L 7 9.3 3.6 6.086 9.3 7.2 5.6 39086 Alkalinity, mg/L as CaCO3 7 37 18 29 37 37 27 00623 Nitrogen, ammonia plus organic, dissolved (mg/L as N) 20 0.54 < 0.200 0.340* *0.538 *0.400 *0.385 00625 Nitrogen, ammonia plus organic, total 

(mg/L as N)

20 2.2 < 0.200 0.531* *2.145 *0.585 *0.450 

00608 Ammonia, dissolved (mg/L as N) 20 0.18 0.02 0.069 0.18 0.095 0.06 00610 Ammonia, total (mg/L as N) 20 0.21 < 0.010 0.074* *0.209 *0.098 *0.060 00618 Nitrate, dissolved (mg/L as N) 3 0.37 0.19 -- -- -- -- 00620 Nitrate, total (mg/L as N) 3 0.38 0.21 -- -- -- -- 00631 Nitrite plus nitrate, dissolved (mg/L as 

N)

20 0.46 < 0.020 0.136* *0.456 *0.207 *0.100 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued[NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS parameter code Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-4, Threemile Creek at Stanton Road at Mobile, Alabama, March 2000–June 2002 (Continued) 00630 Nitrite plus nitrate, total (mg/L as N) 20 0.45 < 0.020 0.138* *0.447 *0.225 *0.100 

00613 Nitrite, dissolved (mg/L as N) 20 0.02 < 0.010 -- 0.02 < 0.010 < 0.010 00615 Nitrite, total (mg/L as N) 20 0.02 < 0.010 -- 0.02 < 0.010 < 0.010 00600 Total nitrogen, mg/L 17 2.4 0.33 0.734 2.4 0.765 0.56 00665 Total phosphorus, mg/L 20 0.3 < 0.002 0.025* *0.287 *0.022 *0.004 00666 Phosphorus, dissolved mg/L 20 0.02 < 0.002 0.006* *0.020 *0.009 *0.004 00671 Orthophosphate, dissolved (mg/L as P) 20 0.007 < 0.001 0.002* *0.007 *0.003 *0.002 70507 Orthophosphate, total (mg/L as P) 20 0.02 < 0.001 0.007* *0.020 *0.008 *0.006 00680 Total organic carbon, mg/L 7 5.9 2.4 3.357 5.9 3.5 2.8 00310 BOD, 5-day, mg/L 18 4.6 0.4 1.444 4.6 1.5 1.3 70953 Suspended chlorophyll a, μg/L 18 35 < 0.100 -- 35 < 0.100 < 0.100 70954 Suspended chlorophyll b, μg/L 10 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 90909 Enterococci, colonies/100 mL 20 47,000 10 2,610 44,830 170 76 31633 Escherichia coli, colonies/100 mL 19 21,000 47 1,460 21,000 720 290 31625 Fecal coliforms, colonies/100 mL 20 17,000 83 1,200 16,200 448 285 01020 Boron, dissolved μg/L 7 23 10 19.1 23 23 20 01046 Iron, dissolved μg/L 7 650 176 322.5 650 418 304 01045 Iron, total μg/L 7 5,500 466 1,545 5,500 1,300 1,000 01056 Manganese, dissolved μg/L 7 83 24 51.3 83 65 52 01055 Manganese, total μg/L 7 230 28 80.9 230 88 67 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued [NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS 

parameter 

code

Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

CEN, Unnamed tributary to Threemile Creek at Center Street at Mobile, Alabama, March 2000–October 2001

00061 Discharge, ft3/s 8 2.90 0.180 0.778 2.90 1.33 0.315 00065 Gage height, feet 6 1.94 1.74 1.82 1.94 1.88 1.82 00095 Specific conductance, μS/cm at 25 °C 8 1,230 145 668 1,230 1,060 632 00400 pH 8 10 7.2 8.8 10 9.6 9.0 61028 Turbidity (field), NTU 4 35 0.7 -- -- -- -- 00076 Turbidity (lab), NTU 7 20 1.1 4.9 20 4.6 1.8 00010 Water temperature, °C 8 34.8 15.2 23.1 34.8 30.3 20.45 00300 Dissolved oxygen, mg/L 7 21.5 8.6 14.5 21.5 18.4 14.5 00020 Air temperature, °C 7 34 15 25.5 34 32 27.3 00915 Calcium, mg/L 7 41 23 29 41 32 29 00925 Magnesium, mg/L 7 2.6 1.7 2.086 2.6 2.4 2 00935 Potassium, mg/L 7 4.5 2.4 3.329 4.5 3.7 3.2 00930 Sodium, mg/L 7 250 25 130.429 250 240 110 00453 Bicarbonate, mg/L 7 163 36 100 163 120 118 00452 Carbonate, mg/L 7 62 0 13 62 26 1 00940 Chloride, mg/L 7 340 31 169.4 340 300 140 00950 Fluoride, mg/L 7 1.3 0.2 0.7 1.3 1.2 0.6 00955 Silica, mg/L 7 7.6 4.7 6.4 7.6 7.6 6.3 00945 Sulfate, mg/L 7 26 14 19.1 26 26 15 39086 Alkalinity, mg/L as CaCO3 7 133 78 104 133 133 97 00623 Nitrogen, ammonia plus organic, dissolved (mg/L as N) 8 2.4 0.49 1.328 2.4 1.975 1.35 00625 Nitrogen, ammonia plus organic, total 

(mg/L as N)

8 3.2 0.67 1.816 3.2 2.55 1.85 

00608 Ammonia, dissolved (mg/L as N) 8 2.4 0.03 0.621 2.4 0.72 0.445 00610 Ammonia, total (mg/L as N) 8 2.4 0.03 0.731 2.4 1.013 0.54 00618 Nitrate, dissolved (mg/L as N) 7 0.91 0.33 0.59 0.91 0.85 0.5 00620 Nitrate, total (mg/L as N) 8 0.91 0.33 0.564 0.91 0.815 0.48 00631 Nitrite plus nitrate, dissolved (mg/L as 

N)

8 1 0.38 0.64 1 0.93 0.53 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued[NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS parameter code Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

CEN, Unnamed tributary to Threemile Creek at Center Street at Mobile, Alabama, March 2000–October 2001 (Continue

00630 Nitrite plus nitrate, total (mg/L as N) 8 1 0.38 0.644 1 0.938 0.53 00613 Nitrite, dissolved (mg/L as N) 8 0.15 0.03 0.074 0.15 0.098 0.07 00615 Nitrite, total (mg/L as N) 8 0.15 0.03 0.08 0.15 0.127 0.07 00600 Total nitrogen, mg/L 7 3.4 1.1 2.271 3.4 3.1 2.5 00665 Total phosphorus, mg/L 8 0.831 0.19 0.435 0.831 0.566 0.406 00666 Phosphorus, dissolved mg/L 8 0.45 0.09 0.271 0.45 0.397 0.245 00671 Orthophosphate, dissolved (mg/L as P) 8 0.341 0.08 0.229 0.341 0.315 0.228 70507 Orthophosphate, total (mg/L as P) 8 0.457 0.13 0.308 0.457 0.402 0.323 00680 Total organic carbon, mg/L 7 7.8 3.6 5.19 7.8 6.6 4.4 00310 BOD, 5-day, mg/L 6 8.8 1.7 4.517 8.8 6.25 4.35 70953 Suspended chlorophyll a, μg/L 8 66 < 0.100 16.265* *66.000 *28.250 *4.850 70954 Suspended chlorophyll b, μg/L 7 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 90909 Enterococci, colonies/100 mL 8 14,000 110 3,690 14,000 8,100 1,300 31633 Escherichia coli, colonies/100 mL 8 26,000 120 7,740 26,000 19,350 2,850 31625 Fecal coliforms, colonies/100 mL 8 30,000 38 8,620 30,000 12,200 7,000 01020 Boron, dissolved μg/L 7 840 90 431.4 840 780 360 01046 Iron, dissolved μg/L 7 337 75 189.9 337 251 178 01045 Iron, total μg/L 7 825 240 544.6 825 723 689 01056 Manganese, dissolved μg/L 7 34 3 12.6 34 19 9 01055 Manganese, total μg/L 7 35 4 15.1 35 22 15 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued [NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS 

parameter 

code

Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TSB, Toulmins Spring Branch at Graham Avenue at Mobile, Alabama, March 2000–October 2001

00061 Discharge, ft3/s 8 6.2 0.11 1.17 6.20 1.21 0.315 00065 Gage height, feet 8 12.60 12.30 12.40 12.60 12.40 12.40 00095 Specific conductance, μS/cm at 25 °C 8 183 99 134 183 146 135 00400 pH 8 9.9 6.6 8.8 9.9 9.7 9.2 61028 Turbidity (field), NTU 3 39 5 -- -- -- -- 00076 Turbidity (lab), NTU 7 16 0.8 3.4 16 2.1 1.2 00010 Water temperature, °C 8 35.3 15 23.6 35.3 27.9 23.2 00300 Dissolved oxygen, mg/L 8 15.8 8.9 12.6 15.8 15.4 11.7 00020 Air temperature, °C 7 33.4 23.4 27.2 33.4 30 26.5 00915 Calcium, mg/L 7 21 11 16.3 21 20 16 00925 Magnesium, mg/L 7 1.6 1 1.186 1.6 1.3 1.2 00935 Potassium, mg/L 7 1.7 1.4 1.5 1.7 1.6 1.5 00930 Sodium, mg/L 7 7.2 4.5 6 7.2 7.2 6 00453 Bicarbonate, mg/L 7 49 13 27 49 43 22 00452 Carbonate, mg/L 7 9 0 2 9 6 0 00940 Chloride, mg/L 7 11 6.9 9.29 11 11 9.3 00950 Fluoride, mg/L 7 0.7 0.1 0.486 0.7 0.6 0.5 00955 Silica, mg/L 7 5.1 3.4 3.871 5.1 4.1 3.6 00945 Sulfate, mg/L 7 20 14 17 20 20 16 39086 Alkalinity, mg/L as CaCO3 7 40 12 26 40 35 26 00623 Nitrogen, ammonia plus organic, dissolved (mg/L as N) 8 1.3 0.2 0.451 1.3 0.463 0.325 00625 Nitrogen, ammonia plus organic, total 

(mg/L as N)

8 1.5 0.35 0.591 1.5 0.655 0.445 

00608 Ammonia, dissolved (mg/L as N) 8 0.22 < 0.010 0.054* *0.220 *0.070 *0.030 00610 Ammonia, total (mg/L as N) 8 0.41 0.01 0.105 0.41 0.167 0.045 00618 Nitrate, dissolved (mg/L as N) 4 0.29 0.14 -- -- -- -- 00620 Nitrate, total (mg/L as N) 3 0.3 0.13 -- -- -- -- 00631 Nitrite plus nitrate, dissolved (mg/L as 

N)

8 0.3 < 0.020 0.148* *0.300 *0.225 *0.140 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued[NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS parameter code Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TSB, Toulmins Spring Branch at Graham Avenue at Mobile, Alabama, March 2000–October 2001 (Continued) 00630 Nitrite plus nitrate, total (mg/L as N) 8 0.31 < 0.020 0.150* *0.310 *0.225 *0.140 

00613 Nitrite, dissolved (mg/L as N) 8 0.02 < 0.010 -- 0.02 0.01 < 0.010 00615 Nitrite, total (mg/L as N) 8 0.02 < 0.010 -- 0.02 0.01 < 0.010 00600 Total nitrogen, mg/L 6 1.8 0.43 0.742 1.8 0.952 0.535 00665 Total phosphorus, mg/L 8 0.232 0.128 0.185 0.232 0.215 0.193 00666 Phosphorus, dissolved mg/L 8 0.192 0.114 0.152 0.192 0.175 0.161 00671 Orthophosphate, dissolved (mg/L as P) 8 0.16 0.09 0.121 0.16 0.147 0.119 70507 Orthophosphate, total (mg/L as P) 8 0.168 0.1 0.134 0.168 0.158 0.132 00680 Total organic carbon, mg/L 7 7.9 2.7 4.386 7.9 5.7 3.7 00310 BOD, 5-day, mg/L 6 3.2 0.8 1.75 3.2 2.3 1.75 70953 Suspended chlorophyll a, μg/L 8 100 < 0.100 18.761* *100.000 *17.750 *5.350 70954 Suspended chlorophyll b, μg/L 7 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 90909 Enterococci, colonies/100 mL 8 93,000 330 17,040 93,000 24,600 2,650 31633 Escherichia coli, colonies/100 mL 8 31,000 20 7,350 31,000 16,320 1,060 31625 Fecal coliforms, colonies/100 mL 8 16,000 -- 4,710* *16,000 *7,720 *2,550 01020 Boron, dissolved μg/L 7 30 18 22 30 27 20 01046 Iron, dissolved μg/L 7 348 84 187.6 348 333 148 01045 Iron, total μg/L 7 705 89 296.1 705 519 195 01056 Manganese, dissolved μg/L 7 26 1 7.57 26 13 4 01055 Manganese, total μg/L 7 27 1 8.57 27 15 4 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued [NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS 

parameter 

code

Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-5, Threemile Creek at U.S. Highway 43 near Prichard, Alabama, March 2000–September 2003

00065 Gage height, feet 39 2.41 -0.35 1.20 2.27 1.75 1.28 00095 Specific conductance, μS/cm at 25 °C 39 21,400 201 9,340 21,300 17,500 6,460 00400 pH 34 8.2 6.5 7.1 8.0 7.4 7.1 61028 Turbidity (field), NTU 36 68 4 17 42 22 12 00076 Turbidity (lab), NTU 8 33 0.2 8.7 33 8.6 6.1 00010 Water temperature, °C 39 30 14.1 23.9 30 29.4 27.5 00300 Dissolved oxygen, mg/L 39 11 2.2 5.9 9.6 7.3 5.6 00020 Air temperature, °C 15 35.4 17.5 26.9 35.4 30 29.5 00915 Calcium, mg/L 9 170 17 74.6 170 145 41 00925 Magnesium, mg/L 9 507 2.4 185.9 507 401.5 80 00935 Potassium, mg/L 9 160 2.4 61.8 160 135 27 00930 Sodium, mg/L 9 4,300 19 1614.3 4300 3550 690 00453 Bicarbonate, mg/L 7 123 44 77 123 103 61 00452 Carbonate, mg/L 7 0 -- -- -- -- -- 00940 Chloride, mg/L 9 7,900 22 2,926.9 7,900 6,500 1,200 00950 Fluoride, mg/L 9 0.4 0.1 0.233 0.4 0.3 0.2 00955 Silica, mg/L 9 5.9 2.8 4.156 5.9 5.35 3.7 00945 Sulfate, mg/L 9 1,300 16 442.9 1300 895 200 39086 Alkalinity, mg/L as CaCO3 7 101 36 63 101 84 50 00623 Nitrogen, ammonia plus organic, dissolved (mg/L as N) 39 1.2 0.29 0.716 1.1 0.82 0.7 00625 Nitrogen, ammonia plus organic, total 

(mg/L as N)

39 1.6 0.65 1.084 1.5 1.2 1 

00608 Ammonia, dissolved (mg/L as N) 39 0.78 0.07 0.299 0.57 0.36 0.28 00610 Ammonia, total (mg/L as N) 39 0.86 0.08 0.322 0.66 0.37 0.29 00618 Nitrate, dissolved (mg/L as N) 38 3.56 0.24 1.348 2.61 1.695 1.23 00620 Nitrate, total (mg/L as N) 38 3.56 0.24 1.377 2.705 1.695 1.285 00631 Nitrite plus nitrate, dissolved (mg/L as 

N)

39 3.6 0.25 1.376 2.6 1.7 1.3 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued[NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
NWIS parameter code Water-quality constituent Sample size Maximum Minimum Mean Median 95% 75% 50% 

TM-5, Threemile Creek at U.S. Highway 43 near Prichard, Alabama, March 2000–September 2003 (Continued) 00630 Nitrite plus nitrate, total (mg/L as N) 39 3.6 0.25 1.391 2.7 1.7 1.3 

00613 Nitrite, dissolved (mg/L as N) 39 0.05 0.01 0.027 0.05 0.04 0.03 00615 Nitrite, total (mg/L as N) 39 0.06 0.01 0.028 0.05 0.04 0.03 00600 Total nitrogen, mg/L 39 5.2 1.2 2.472 4.2 2.9 2.4 00665 Total phosphorus, mg/L 39 0.53 0.136 0.301 0.503 0.38 0.272 00666 Phosphorus, dissolved mg/L 39 0.388 0.08 0.196 0.379 0.25 0.172 00671 Orthophosphate, dissolved (mg/L as P) 39 0.405 0.067 0.194 0.403 0.246 0.164 70507 Orthophosphate, total (mg/L as P) 39 0.49 0.109 0.22 0.47 0.272 0.196 00680 Total organic carbon, mg/L 7 7.8 3.8 6.257 7.8 7.6 6.2 00310 BOD, 5-day, mg/L 30 7.6 1 2.937 6.61 3.75 2.4 70953 Suspended chlorophyll a, μg/L 26 91 < 0.100 30.070* *84.700 *46.250 *24.000 70954 Suspended chlorophyll b, μg/L 13 < 0.100 < 0.100 -- < 0.100 < 0.100 < 0.100 90909 Enterococci, colonies/100 mL 34 22,000 9 2,350 16,000 1,170 225 31633 Escherichia coli, colonies/100 mL 36 20,000 30 2,000 12,350 1,580 470 31625 Fecal coliforms, colonies/100 mL 31 15,000 20 1,870 12,000 1,300 540 01020 Boron, dissolved μg/L 9 1,900 70 738.9 1,900 1,550 350 01046 Iron, dissolved μg/L 9 229 21 80.7 229 111.5 67 01045 Iron, total μg/L 9 773 319 514.2 773 724.5 407 01056 Manganese, dissolved μg/L 9 150 33 75.1 150 98 68 01055 Manganese, total μg/L 9 170 42 88.2 170 118.5 77 

Appendix 2. Table 2-1. Summary of selected constituents at sampling sites in the Threemile Creek basin, Mobile, Alabama, 2000–2003.—Continued [NWIS, National Water Information System; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter; NTU, nephelometric turbidity units; °C, Celsius; mg/L, milligram

ed; <, less than; CaCO3, calcium carbonate; *, value is estimated by using a log-probability regression to predict the values of data below the detection limit; N, nitrogen; P, pho

oxygen demand; μg/L, micrograms per liter; mL, milliliter. Site locations are shown in figure 1]
2

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydrox

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]

Site 

number 

(fig. 1)

Sample 

date

Sample 

time

1-methylnaphthalene

(μg/L)

2-methylnaphthalene

(μg/L)

2,6-Dimethylnapthalene

(μg/L)

2,6-Di-tertbutylphenol

(μg/L)

2,6-Di-tert-pbenzoquinone

(μg/L)

5-Methyl-1Hbenzotriazole

(μg/L)

A

(

TM-1 3/13/2000 1100 < 0.090 < 0.070 < 0.10 TM-1 4/25/2000 1430 < 0.090 < 0.070 < 0.10 TM-1 7/26/2000 900 < 0.080 < 0.5 < 0.10 TM-1 9/12/2000 1300 < 0.080 < 0.5 < 0.10 TM-1 11/15/2000 845 < 0.150 < 0.5 < 0.150 TM-1 2/13/2001 1720 < 0.50 < 0.50 < 0.50 < 2.0 TM-1 3/12/2001 1050 < 0.50 < 0.50 < 0.50 < 2.0 TM-1 12/14/2001 1130 < 0.50 < 0.50 < 0.50 < 2.0 TM-1 6/25/2002 600 < 0.50 < 0.50 < 0.50 < 2.0 TM-1 6/25/2002 1400 < 0.50 < 0.50 < 0.50 < 2.0 TM-1 6/25/2002 1730 < 0.50 < 0.50 < 0.50 < 2.0 TM-1 2/26/2003 1830 < 0.50 < 0.50 < 0.50 E 0.120 TM-1 9/15/03 1800 < 0.50 < 0.50 < 2.0 TM-3 3/13/2000 1500 < 0.090 < 0.070 < 0.10 TM-3 4/26/2000 1630 < 0.090 < 0.070 0.171 TM-3 7/26/2000 1330 < 0.080 < 0.5 < 0.10 TM-3 9/13/2000 1545 < 0.080 < 0.5 < 0.10 TM-3 11/13/2000 1445 < 0.150 < 0.5 E 0.143 TM-3 2/13/2001 1330 < 0.50 < 0.50 < 0.50 < 2.0 TM-3 3/12/2001 1625 < 0.50 < 0.50 < 0.50 < 2.0 TM-3 12/14/2001 245 < 0.50 < 0.50 < 0.50 < 2.0 TM-3 2/26/2003 1830 < 0.50 < 0.50 < 0.50 < 2.0 TM-3 9/15/03 1530 < 0.50 < 0.50 < 2.0 TM-4 3/15/2000 1100 < 0.090 < 0.070 < 0.10 TM-4 4/26/2000 845 < 0.090 < 0.070 0.12 TM-4 7/25/2000 1620 < 0.080 < 0.5 < 0.10 TM-4 9/13/2000 750 < 0.080 < 0.5 < 0.10 TM-4 11/13/2000 1330 < 0.150 < 0.5 E 0.124 TM-4 2/14/2001 930 < 0.50 < 0.50 < 0.50 < 2.0 TM-4 3/12/2001 1445 < 0.50 < 0.50 < 0.50 < 2.0 TM-4 6/25/2002 600 < 0.50 < 0.50 < 0.50 < 2.0 
Site number (fig. 1) Sample date Sample time 1-methyl- napthalene (μg/L) 2-methyl- napthalene (μg/L) 2,6-Dimethyl- napthalene (μg/L) 2,6-Di-tert- butylphenol (μg/L) 2,6-Di-tert-p- benzoquinone (μg/L) 5-Methyl-1H- benzotriazole (μg/L) A

(

TM-4 6/25/2002 1000 < 0.50 < 0.50 < 0.50 < 2.0 TM-4 6/25/2002 1400 < 0.50 < 0.50 < 0.50 < 2.0 TM-4 6/25/2002 1730 < 0.50 < 0.50 < 0.50 < 2.0 CEN 3/14/2000 1000 < 0.090 < 0.070 21.4 CEN 4/27/2000 1415 < 0.090 < 0.070 0.361 CEN 7/24/2000 1300 < 0.080 < 0.5 0.264 CEN 9/14/2000 1330 < 0.080 < 0.5 0.299 CEN 11/14/2000 1445 < 0.150 < 0.5 0.318 CEN 2/12/2001 1330 < 0.50 < 0.50 < 0.50 E 0.240 CEN 3/13/2001 800 < 0.50 < 0.50 < 0.50 < 2.0 CEN 10/31/2001 1345 < 0.50 < 0.50 < 0.50 E 0.590 TSB 3/14/2000 1400 < 0.090 < 0.070 < 0.10 TSB 4/26/2000 1205 < 0.090 < 0.070 0.144 TSB 7/24/2000 1500 < 0.080 < 0.5 < 0.10 TSB 9/13/2000 1030 < 0.080 < 0.5 < 0.10 TSB 11/15/2000 1400 < 0.150 < 0.5 0.164 TSB 2/12/2001 1615 < 0.50 < 0.50 < 0.50 < 2.0 TSB 3/13/2001 930 < 0.50 < 0.50 < 0.50 < 2.0 TSB 10/31/2001 1130 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 3/15/2000 100 < 0.090 < 0.070 < 0.10 TM-5 4/27/2000 915 < 0.090 < 0.070 < 0.10 TM-5 7/25/2000 1040 < 0.080 < 0.5 < 0.10 TM-5 9/14/2000 915 < 0.080 < 0.5 0.128 TM-5 11/16/2000 955 < 0.150 < 0.5 0.186 TM-5 2/13/2001 915 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 3/13/2001 1730 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 12/14/2001 1120 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 6/25/2002 600 < 0.50 < 0.50 E 0.086 E 0.60 TM-5 6/25/2002 1400 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 6/25/2002 1800 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 2/26/2003 2015 < 0.50 < 0.50 < 0.50 < 2.0 TM-5 9/15/03 1400 < 0.50 < 0.50 < 2.0 

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydrox

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]
Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alabam[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxyto

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxyl

OP2EO, diethoxylate octylphenol]

Site 

number 

(fig. 1)

Sample 

date

Sample 

time

Anthracene

(μg/L)

Atrazine

(μg/L)

Benzo[a]

pyrene

(μg/L)

β--

sitosterol

(μg/L)

BHA 

(μg/L)

BHT

(μg/L)

Bromacil

(μg/L)

Caffeine 

(μg/L)

C

TM-1 3/13/2000 1100 < 0.050 < 0.050 < 0.120 < 0.080 E 0.053 TM-1 4/25/2000 1430 < 0.050 < 0.050 < 0.120 < 0.080 0.083 TM-1 7/26/2000 900 < 0.050 < 0.050 < 0.120 < 0.080 0.091 TM-1 9/12/2000 1300 < 0.050 0.054 < 0.120 < 0.080 E 0.046 TM-1 11/15/2000 845 < 0.060 < 0.070 < 0.120 < 0.110 E 0.068 TM-1 2/13/2001 1720 < 0.50 < 0.50 < 2.0 < 5.000 E 0.120 0.69 TM-1 3/12/2001 1050 < 0.50 < 0.50 E 0.57 < 5.000 E 0.047 0.74 TM-1 12/14/2001 1130 E 0.160 < 0.50 < 2.0 < 5.000 < 0.500 < 0.500 TM-1 6/25/2002 600 < 0.50 E 0.066 < 0.50 < 2.0 < 5.000 E 0.200 E 0.077 TM-1 6/25/2002 1400 < 0.50 E 0.052 < 0.50 < 2.0 < 5.000 < 0.500 E 0.072 TM-1 6/25/2002 1730 < 0.50 E 0.030 < 0.50 < 2.0 < 5.000 < 0.500 E 0.110 TM-1 2/26/2003 1830 < 0.50 E 0.270 < 0.50 < 2.0 < 5.000 < 0.500 E 0.130 TM-1 9/15/03 1800 < 0.50 E 0.050 < 0.50 < 2.0 < 5.000 < 0.500 E 0.02 TM-3 3/13/2000 1500 < 0.050 < 0.050 < 0.120 < 0.080 0.094 TM-3 4/26/2000 1630 < 0.050 < 0.050 < 0.120 < 0.080 0.218 TM-3 7/26/2000 1330 < 0.050 < 0.050 < 0.120 < 0.080 E 0.069 TM-3 9/13/2000 1545 < 0.050 0.063 < 0.120 < 0.080 E 0.064 TM-3 11/13/2000 1445 < 0.060 < 0.070 < 0.120 < 0.110 0.169 TM-3 2/13/2001 1330 < 0.50 < 0.50 < 2.0 < 5.000 E 0.110 E 0.320 TM-3 3/12/2001 1625 < 0.50 E 0.071 E 1.0 < 5.000 E 0.150 E 0.260 TM-3 12/14/2001 245 < 0.50 E 0.054 E 1.1 < 5.000 E 0.110 E 0.160 TM-3 2/26/2003 1830 < 0.50 E 0.110 < 0.50 < 2.0 < 5.000 < 0.500 E 0.074 TM-3 9/15/03 1530 < 0.50 E 0.0470 < 0.50 < 2.0 < 5.000 < 0.500 E 0.03 TM-4 3/15/2000 1100 < 0.050 < 0.050 < 0.120 < 0.080 E 0.047 TM-4 4/26/2000 845 < 0.050 < 0.050 < 0.120 < 0.080 E 0.063 TM-4 7/25/2000 1620 < 0.050 < 0.050 < 0.120 < 0.080 E 0.044 TM-4 9/13/2000 750 < 0.050 < 0.050 < 0.120 < 0.080 E 0.067 TM-4 11/13/2000 1330 < 0.060 < 0.070 < 0.120 < 0.110 0.143 TM-4 2/14/2001 930 < 0.50 < 0.50 < 2.0 < 5.000 E 0.150 E 0.270 TM-4 3/12/2001 1445 < 0.50 E 0.056 E 1.20 < 5.000 E 0.064 E 0.260 TM-4 6/25/2002 600 < 0.50 E 0.054 < 0.50 < 2.0 < 5.000 E 0.280 E 0.290 
Site number (fig. 1) Sample date Sample time Anthracene (μg/L) Atrazine (μg/L) Benzo[a] pyrene (μg/L) β− Sitosterol (μg/L) BHA (μg/L) BHT (μg/L) Bromacil (μg/L) Caffeine (μg/L) C

TM-4 6/25/2002 1000 < 0.50 E 0.060 < 0.50 E 1.0 < 5.000 E 0.240 E 0.110 TM-4 6/25/2002 1400 < 0.50 E 0.070 < 0.50 E 0.65 < 5.000 E 0.240 E 0.120 TM-4 6/25/2002 1730 < 0.50 E 0.050 < 0.50 < 2.0 < 5.000 E 0.260 E 0.110 CEN 3/14/2000 1000 < 0.050 < 0.050 < 0.120 < 0.080 3.04 CEN 4/27/2000 1415 < 0.050 < 0.050 < 0.120 < 0.080 1.35 CEN 7/24/2000 1300 < 0.050 < 0.050 < 0.120 < 0.080 4.26 CEN 9/14/2000 1330 < 0.050 < 0.050 < 0.120 < 0.080 6.63 CEN 11/14/2000 1445 < 0.060 < 0.070 < 0.120 < 0.110 2.2 CEN 2/12/2001 1330 < 0.50 < 0.50 E 2.60 < 5.000 < 0.500 9.8 CEN 3/13/2001 800 < 0.50 < 0.50 E 1.50 < 5.000 E 0.095 0.9 CEN 10/31/2001 1345 < 0.50 < 0.50 2.2 < 5.000 < 0.500 2.6 TSB 3/14/2000 1400 < 0.050 < 0.050 < 0.120 < 0.080 0.091 TSB 4/26/2000 1205 < 0.050 < 0.050 < 0.120 < 0.080 E 0.048 TSB 7/24/2000 1500 < 0.050 < 0.050 < 0.120 < 0.080 0.336 TSB 9/13/2000 1030 < 0.050 0.06 < 0.120 < 0.080 0.163 TSB 11/15/2000 1400 < 0.060 < 0.070 < 0.120 < 0.110 0.159 TSB 2/12/2001 1615 < 0.50 < 0.50 < 2.0 < 5.000 E 0.100 E 0.100 TSB 3/13/2001 930 < 0.50 < 0.50 E 1.80 < 5.000 E 0.160 0.6 TSB 10/31/2001 1130 < 0.50 < 0.50 E 1.60 < 5.000 E 0.340 E 0.300 TM-5 3/15/2000 100 < 0.050 E 0.018 < 0.120 < 0.080 0.617 TM-5 4/27/2000 915 < 0.050 < 0.050 < 0.120 < 0.080 E 0.060 TM-5 7/25/2000 1040 < 0.050 < 0.050 < 0.120 < 0.080 0.103 TM-5 9/14/2000 915 < 0.050 < 0.050 < 0.120 < 0.080 0.127 TM-5 11/16/2000 955 < 0.060 < 0.070 < 0.120 < 0.110 0.273 TM-5 2/13/2001 915 < 0.50 < 0.50 < 2.0 < 5.000 E 0.170 0.6 TM-5 3/13/2001 1730 < 0.50 < 0.50 E 1.40 < 5.000 E 0.170 E 0.290 TM-5 12/14/2001 1120 < 0.50 E 0.052 E 1.60 < 5.000 E 0.140 0.53 TM-5 6/25/2002 600 < 0.50 E 0.042 E 0.150 E 3.80 < 5.000 E 0.230 < 0.500 TM-5 6/25/2002 1400 < 0.50 E 0.080 < 0.50 < 2.0 < 5.000 E 0.240 E 0.070 TM-5 6/25/2002 1800 < 0.50 E 0.096 < 0.50 E 0.660 < 5.000 E 0.260 E 0.097 TM-5 2/26/2003 2015 < 0.50 E 0.095 < 0.50 < 2.0 < 5.000 < 0.500 E 0.350 TM-5 9/15/03 1400 < 0.50 0.64 < 0.50 < 2.0 < 5.000 < 0.500 E 0.18 

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alabam[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxyto

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethoxyl

OP2EO, diethoxylate octylphenol]
Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]

Site 

number 

(fig. 1)

Sample 

date

Sample 

time

Chlorpyrifos 

(μg/L)

Cholesterol 

(μg/L)

3βcoprostanol 

(μg/L)

Cotinine 

(μg/L)

Diazinon 

(μg/L)

Dieldrin

(μg/L)

N,N-diethylm-toluamide

(μg/L)

es

TM-1 3/13/2000 1100 < 0.020 E 0.404 < 0.600 < 0.040 0.067 < 0.080 < 0.040 < TM-1 4/25/2000 1430 < 0.020 E 0.569 < 0.600 < 0.040 0.122 < 0.080 < 0.040 < TM-1 7/26/2000 900 < 0.020 < 1.500 < 0.600 < 0.040 0.134 < 0.080 0.069 < TM-1 9/12/2000 1300 < 0.020 < 1.500 < 0.600 E 0.013 0.096 < 0.080 0.042 < TM-1 11/15/2000 845 < 0.020 < 1.500 < 0.600 < 0.080 0.034 < 0.080 < 0.080 < TM-1 2/13/2001 1720 < 0.500 E 1.100 E 0.360 < 1.000 E 0.045 < 0.500 < TM-1 3/12/2001 1050 < 0.500 E 0.700 < 2.000 < 1.000 E 0.120 < 0.500 < TM-1 12/14/2001 1130 < 0.500 < 2.000 < 2.000 < 1.000 < 0.500 < 0.500 < TM-1 6/25/2002 600 < 0.500 < 2.000 < 2.000 E 0.100 E 0.020 < 0.500 < TM-1 6/25/2002 1400 < 0.500 < 2.000 < 2.000 E 0.120 E 0.016 < 0.500 < TM-1 6/25/2002 1730 < 0.500 E 0.610 < 2.000 < 1.000 < 0.500 < 0.500 < TM-1 2/26/2003 1830 < 0.500 E 0.870 < 2.000 < 1.000 < 0.500 < 0.500 < TM-1 9/15/03 1800 < 5.000 < 2.000 < 2.000 < 1.000 < 0.500 E 0.05 < TM-3 3/13/2000 1500 < 0.020 E 0.368 < 0.600 < 0.040 0.086 < 0.080 E 0.038 < TM-3 4/26/2000 1630 < 0.020 E 1.640 E 0.800 < 0.040 0.307 < 0.080 0.05 < TM-3 7/26/2000 1330 < 0.020 < 1.500 < 0.600 < 0.040 0.074 < 0.080 0.057 < TM-3 9/13/2000 1545 < 0.020 < 1.500 < 0.600 < 0.040 0.088 < 0.080 0.047 E TM-3 11/13/2000 1445 < 0.020 < 1.500 < 0.600 < 0.080 0.05 < 0.080 E 0.056 < TM-3 2/13/2001 1330 < 0.500 E 0.580 < 2.000 < 1.000 < 0.500 < 0.500 < TM-3 3/12/2001 1625 < 0.500 E 0.690 < 2.000 < 1.000 E 0.150 < 0.500 < TM-3 12/14/2001 245 < 0.500 E 1.000 < 2.000 < 1.000 < 0.500 E 0.064 < TM-3 2/26/2003 1830 < 0.500 < 2.000 < 2.000 < 1.000 < 0.500 < 0.500 < TM-3 9/15/03 1530 < 5.000 < 2.000 < 2.000 < 1.000 < 0.500 E 0.05 < TM-4 3/15/2000 1100 < 0.020 E 0.467 < 0.600 < 0.040 0.056 < 0.080 < 0.040 < TM-4 4/26/2000 845 < 0.020 E 0.767 < 0.600 E 0.010 0.062 < 0.080 E 0.019 < TM-4 7/25/2000 1620 < 0.020 < 1.500 < 0.600 E 0.025 0.089 < 0.080 0.056 < TM-4 9/13/2000 750 < 0.020 < 1.500 < 0.600 < 0.040 0.108 < 0.080 E 0.040 < TM-4 11/13/2000 1330 < 0.020 < 1.500 < 0.600 < 0.080 0.052 < 0.080 < 0.080 < TM-4 2/14/2001 930 < 0.500 E 0.560 < 2.000 < 1.000 E 0.034 < 0.500 < TM-4 3/12/2001 1445 < 0.500 E 1.100 E 0.400 < 1.000 E 0.290 < 0.500 < TM-4 6/25/2002 600 < 0.500 E 0.660 < 2.000 < 1.000 E 0.047 < 0.500 < 
Site number (fig. 1) Sample date Sample time Chlorpyrifos (μg/L) Cholesterol (μg/L) 3β- coprostanol (μg/L) Cotinine (μg/L) Diazinon (μg/L) Dieldrin (μg/L) N,N-diethyl- m-toluamide (μg/L) 

es

TM-4 6/25/2002 1000 < 0.500 < 2.000 < 2.000 < 1.000 E 0.047 < 0.500 < TM-4 6/25/2002 1400 < 0.500 E 0.630 < 2.000 < 1.000 E 0.050 < 0.500 < TM-4 6/25/2002 1730 < 0.500 E 0.940 < 2.000 < 1.000 E 0.038 < 0.500 < CEN 3/14/2000 1000 < 0.020 E 6.810 E 4.420 0.469 0.173 < 0.080 0.175 < CEN 4/27/2000 1415 < 0.020 E 4.860 E 3.020 0.075 0.163 < 0.080 0.086 < CEN 7/24/2000 1300 < 0.020 E 2.240 E 1.150 0.224 0.03 < 0.080 1.89 < CEN 9/14/2000 1330 < 0.020 E 1.990 < 0.600 0.19 0.067 < 0.080 0.074 < CEN 11/14/2000 1445 < 0.020 E 4.670 E 3.020 0.138 0.044 < 0.080 E 0.058 < CEN 2/12/2001 1330 < 0.500 E 7.000 E 5.400 E 0.230 < 0.500 < 0.500 < CEN 3/13/2001 800 < 0.500 E 2.500 E 1.500 < 1.000 E 0.120 E 0.064 < CEN 10/31/2001 1345 < 0.500 5.3 2.1 E 0.088 < 0.500 E 0.180 < TSB 3/14/2000 1400 < 0.020 E 1.710 E 1.090 0.053 < 0.030 < 0.080 E 0.036 < TSB 4/26/2000 1205 < 0.020 E 1.190 E 0.452 E 0.020 < 0.030 < 0.080 E 0.035 < TSB 7/24/2000 1500 < 0.020 E 1.310 E 0.465 0.204 E 0.024 < 0.080 0.432 < TSB 9/13/2000 1030 < 0.020 < 1.500 < 0.600 0.05 E 0.013 < 0.080 0.52 < TSB 11/15/2000 1400 0.036 E 1.340 E 0.864 < 0.080 < 0.030 < 0.080 < 0.080 E TSB 2/12/2001 1615 < 0.500 E 0.990 E 0.510 < 1.000 < 0.500 <0.500 < TSB 3/13/2001 930 < 0.500 E 5.600 E 4.100 < 1.000 E 0.120 <0.500 < TSB 10/31/2001 1130 < 0.500 E 1.900 E 0.850 E 0.096 < 0.500 <0.500 < TM-5 3/15/2000 100 < 0.020 E 5.210 E 5.860 0.121 < 0.030 < 0.080 0.146 < TM-5 4/27/2000 915 < 0.020 E 0.737 E 0.298 < 0.040 0.299 < 0.080 E 0.032 < TM-5 7/25/2000 1040 < 0.020 E 1.120 E 0.431 E 0.037 0.035 < 0.080 0.145 < TM-5 9/14/2000 915 < 0.020 < 1.500 < 0.600 < 0.040 0.057 < 0.080 0.067 < TM-5 11/16/2000 955 < 0.020 E 2.180 E 1.860 < 0.080 0.205 < 0.080 E 0.043 < TM-5 2/13/2001 915 < 0.500 E 6.200 E 3.900 < 1.000 E 0.066 < 0.500 < TM-5 3/13/2001 1730 < 0.500 E 3.100 E 2.000 < 1.000 E 0.140 < 0.500 < TM-5 12/14/2001 1120 < 0.500 3.4 E 1.800 < 1.000 < 0.500 E 0.076 < TM-5 6/25/2002 600 < 0.500 E 6.800 E 4.100 E 0.120 < 0.500 < 0.500 < TM-5 6/25/2002 1400 < 0.500 < 2.000 < 2.000 E 0.100 E 0.011 < 0.500 < TM-5 6/25/2002 1800 < 0.500 E 1.200 E 0.380 E 0.100 E 0.017 < 0.500 < TM-5 2/26/2003 2015 < 0.500 E 2.500 E 2.100 < 1.000 < 0.500 E 0.065 < TM-5 9/15/03 1400 < 5.000 E 1.4 E 1 < 1.000 < 0.500 E 0.12 < 

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]
Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]

Site 

number 

(fig. 1)

Sample 

date

Sample 

time

Fluoranthene

(μg/L)

HHCB

(μg/L)

Lindane

(μg/L)

Metalaxyl

(μg/L)

Methyl parathion

(μg/L)

Metolach

(μg/L)

TM-1 3/13/2000 1100 E 0.019 < 0.050 < 0.060 TM-1 4/25/2000 1430 < 0.030 < 0.050 < 0.060 TM-1 7/26/2000 900 E 0.033 < 0.050 < 0.060 TM-1 9/12/2000 1300 < 0.020 < 0.050 < 0.060 TM-1 11/15/2000 845 < 0.030 < 0.050 < 0.060 TM-1 2/13/2001 1720 < 0.50 < 0.50 < 0.500 < 0.500 TM-1 3/12/2001 1050 < 0.50 < 0.50 < 0.500 < 0.500 TM-1 12/14/2001 1130 < 0.50 < 0.50 < 0.500 < 0.500 TM-1 6/25/2002 600 < 0.50 < 0.50 < 0.500 < 0.500 TM-1 6/25/2002 1400 < 0.50 < 0.50 < 0.500 < 0.500 TM-1 6/25/2002 1730 < 0.50 < 0.50 < 0.500 < 0.500 TM-1 2/26/2003 1830 E 0.069 < 0.50 < 0.500 < 0.500 TM-1 9/15/03 1800 < 0.50 < 0.50 < 0.500 < 0.500 TM-3 3/13/2000 1500 0.059 < 0.050 < 0.060 TM-3 4/26/2000 1630 0.098 < 0.050 < 0.060 TM-3 7/26/2000 1330 E 0.055 < 0.050 < 0.060 TM-3 9/13/2000 1545 0.046 < 0.050 < 0.060 TM-3 11/13/2000 1445 E 0.029 < 0.050 < 0.060 TM-3 2/13/2001 1330 < 0.50 < 0.50 < 0.500 < 0.500 TM-3 3/12/2001 1625 E 0.160 < 0.50 < 0.500 < 0.500 TM-3 12/14/2001 245 E 0.099 < 0.50 < 0.500 < 0.500 TM-3 2/26/2003 1830 E 0.086 < 0.50 < 0.500 < 0.500 TM-3 9/15/03 1530 E 0.02 < 0.50 < 0.500 < 0.500 TM-4 3/15/2000 1100 0.038 < 0.050 < 0.060 TM-4 4/26/2000 845 E 0.043 < 0.050 < 0.060 TM-4 7/25/2000 1620 E 0.036 < 0.050 < 0.060 TM-4 9/13/2000 750 E 0.028 < 0.050 < 0.060 TM-4 11/13/2000 1330 < 0.030 < 0.050 < 0.060 TM-4 2/14/2001 930 E 0.190 < 0.50 < 0.500 < 0.500 TM-4 3/12/2001 1445 E 0.160 < 0.50 < 0.500 < 0.500 TM-4 6/25/2002 600 < 0.50 < 0.50 < 0.500 < 0.500 
Site number (fig. 1) Sample date Sample time Fluoranthene (μg/L) HHCB (μg/L) Lindane (μg/L) Metalaxyl (μg/L) Methyl parathion (μg/L) Metolach

(μg/L) 

TM-4 6/25/2002 1000 < 0.50 < 0.50 < 0.500 < 0.500 TM-4 6/25/2002 1400 < 0.50 < 0.50 < 0.500 < 0.500 TM-4 6/25/2002 1730 < 0.50 < 0.50 < 0.500 < 0.500 CEN 3/14/2000 1000 0.105 < 0.050 < 0.060 CEN 4/27/2000 1415 0.076 < 0.050 < 0.060 CEN 7/24/2000 1300 E 0.104 < 0.050 < 0.060 CEN 9/14/2000 1330 0.055 < 0.050 < 0.060 CEN 11/14/2000 1445 0.065 < 0.050 < 0.060 CEN 2/12/2001 1330 < 0.50 E 0.060 < 0.500 < 0.500 CEN 3/13/2001 800 < 0.50 E 0.048 < 0.500 < 0.500 CEN 10/31/2001 1345 < 0.50 < 0.50 < 0.500 < 0.500 TSB 3/14/2000 1400 0.038 < 0.050 < 0.060 TSB 4/26/2000 1205 < 0.030 < 0.050 < 0.060 TSB 7/24/2000 1500 E 0.030 < 0.050 < 0.060 TSB 9/13/2000 1030 0.287 < 0.050 < 0.060 TSB 11/15/2000 1400 0.047 < 0.050 < 0.060 TSB 2/12/2001 1615 < 0.50 < 0.50 < 0.500 < 0.500 TSB 3/13/2001 930 < 0.50 E 0.120 < 0.500 < 0.500 TSB 10/31/2001 1130 < 0.50 < 0.50 < 0.500 < 0.500 TM-5 3/15/2000 100 0.093 < 0.050 < 0.060 TM-5 4/27/2000 915 < 0.030 < 0.050 < 0.060 TM-5 7/25/2000 1040 E 0.040 < 0.050 < 0.060 TM-5 9/14/2000 915 E 0.029 < 0.050 < 0.060 TM-5 11/16/2000 955 < 0.030 < 0.050 < 0.060 TM-5 2/13/2001 915 E 0.069 E 0.190 < 0.500 < 0.500 TM-5 3/13/2001 1730 < 0.50 E 0.130 < 0.500 < 0.500 TM-5 12/14/2001 1120 < 0.50 E 0.130 < 0.500 < 0.500 TM-5 6/25/2002 600 E 0.210 E 0.058 < 0.500 < 0.500 TM-5 6/25/2002 1400 < 0.50 < 0.50 < 0.500 E 0.014 TM-5 6/25/2002 1800 < 0.50 < 0.50 < 0.500 E 0.020 TM-5 2/26/2003 2015 < 0.50 E 0.100 < 0.500 < 0.500 TM-5 9/15/03 1400 E 0.02 E 0.05 < 0.500 E 0.3 

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]
Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]

Site 

number 

(fig. 1)

Sample 

date

Sample 

time

paranonylphenol 

(total) 

(μg/L)

NP1EO 

(μg/L)

NP2EO 

(μg/L)

OP1EO 

(μg/L)

OP2EO 

(μg/L)

paracresol

(μg/L)

Phenanthre

(μg/L)

TM-1 3/13/2000 1100 < 0.500 < 1.0 < 1.100 < 0.100 < 0.200 < 0.030 < 0.060TM-1 4/25/2000 1430 < 0.500 < 11.0 < 1.100 < 0.100 < 0.200 < 0.030 < 0.060TM-1 7/26/2000 900 E 0.767 E 1.010 < 1.100 E 0.053 < 0.200 < 0.030 E 0.021TM-1 9/12/2000 1300 < 0.500 E 0.949 < 1.100 E 0.066 < 0.200 < 0.060 < 0.060TM-1 11/15/2000 845 < 0.700 < 1.0 < 1.100 < 0.120 < 0.200 < 0.060 < 0.050TM-1 2/13/2001 1720 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-1 3/12/2001 1050 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-1 12/14/2001 1130 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 E 0.150 TM-1 6/25/2002 600 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-1 6/25/2002 1400 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-1 6/25/2002 1730 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-1 2/26/2003 1830 < 5.000 E 0.820 E 3.700 E 0.630 < 1.000 < 1.0 E 0.051 TM-1 9/15/03 1800 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-3 3/13/2000 1500 < 0.500 < 1.0 < 1.100 < 0.100 < 0.200 < 0.030 E 0.028TM-3 4/26/2000 1630 < 0.500 < 1.10 < 1.100 < 0.100 < 0.200 < 0.030 0.067TM-3 7/26/2000 1330 E 0.706 < 1.0 < 1.100 E 0.042 < 0.200 < 0.030 E 0.035TM-3 9/13/2000 1545 E 0.864 E 1.150 < 1.100 < 0.100 < 0.200 < 0.060 E 0.023TM-3 11/13/2000 1445 E 0.272 E 0.368 < 1.100 E 0.127 < 0.200 E 0.036 < 0.050TM-3 2/13/2001 1330 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-3 3/12/2001 1625 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 E 0.092 TM-3 12/14/2001 245 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 E 0.10 TM-3 2/26/2003 1830 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-3 9/15/03 1530 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 E 0.02 TM-4 3/15/2000 1100 < 0.500 < 1.0 < 1.100 < 0.100 < 0.200 < 0.030 < 0.060TM-4 4/26/2000 845 < 0.500 < 1.10 < 1.100 < 0.100 < 0.200 < 0.030 E 0.026TM-4 7/25/2000 1620 E 0.789 E 1.020 < 1.100 E 0.076 < 0.200 < 0.030 < 0.060TM-4 9/13/2000 750 < 0.500 < 1.0 < 1.100 < 0.100 < 0.200 < 0.060 < 0.060TM-4 11/13/2000 1330 E 0.232 E 0.435 < 1.100 E 0.108 < 0.200 < 0.060 < 0.050TM-4 2/14/2001 930 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 E 0.073 TM-4 3/12/2001 1445 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 E 0.10 TM-4 6/25/2002 600 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 
Site number (fig. 1) Sample date Sample time para- nonylphenol (total) (μg/L) NP1EO (μg/L) NP2EO (μg/L) OP1EO (μg/L) OP2EO (μg/L) para- cresol (μg/L) Phenanthre

(μg/L) 

TM-4 6/25/2002 1000 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-4 6/25/2002 1400 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-4 6/25/2002 1730 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 CEN 3/14/2000 1000 E 3.330 E 4.910 E 5.340 < 0.100 < 0.200 0.112 E 0.028 CEN 4/27/2000 1415 E 1.030 E 2.460 E 2.460 < 0.100 < 0.200 0.053 < 0.060 CEN 7/24/2000 1300 E 1.150 E 1.56 E 2.990 E 0.095 < 0.200 E 0.058 E 0.027 CEN 9/14/2000 1330 E 1.220 E 1.890 E 1.460 E 0.159 < 0.200 0.241 E 0.023 CEN 11/14/2000 1445 E 0.952 E 2.610 E 5.970 E 0.268 < 0.200 0.213 < 0.050 CEN 2/12/2001 1330 E 1.200 E 2.800 < 1.000 < 1.000 1.4 < 0.50 CEN 3/13/2001 800 E 0.520 E 0.770 < 1.000 < 1.000 < 1.0 < 0.50 CEN 10/31/2001 1345 E 1.100 E 4.800 < 1.000 < 1.000 < 1.0 < 0.50 TSB 3/14/2000 1400 < 0.500 < 1.0 < 1.100 < 0.100 < 0.200 0.11 < 0.060 TSB 4/26/2000 1205 < 0.500 E 0.372 < 1.100 < 0.100 < 0.200 0.065 < 0.060 TSB 7/24/2000 1500 E 0.882 E 1.270 E 0.748 E 0.112 < 0.200 E 0.052 E 0.030 TSB 9/13/2000 1030 E 0.877 < 1.0 < 1.100 E 0.134 < 0.200 < 0.060 E 0.047 TSB 11/15/2000 1400 E 0.340 E 0.876 < 1.100 E 0.206 < 0.200 E 0.052 < 0.050 TSB 2/12/2001 1615 < 5.000 E 0.890 < 1.000 < 1.000 E 0.610 < 0.50 TSB 3/13/2001 930 < 5.000 < 5.000 < 1.000 < 1.000 E 0.160 < 0.50 TSB 10/31/2001 1130 < 5.000 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-5 3/15/2000 100 E 3.300 E 3.430 E 3.920 < 0.100 < 0.200 E 0.020 < 0.060 TM-5 4/27/2000 915 < 0.500 < 1.10 < 1.100 < 0.100 < 0.200 < 0.030 < 0.060 TM-5 7/25/2000 1040 E 0.825 E 1.070 E 1.190 E 0.071 < 0.200 < 0.030 < 0.060 TM-5 9/14/2000 915 E 0.921 E 1.210 E 1.160 E 0.082 < 0.200 < 0.060 < 0.060 TM-5 11/16/2000 955 E 1.030 E 1.280 E 2.480 E 0.149 < 0.200 E 0.032 < 0.050 TM-5 2/13/2001 915 E 2.400 E 3.200 < 1.000 < 1.000 < 1.0 < 0.50 TM-5 3/13/2001 1730 E 1.400 E 1.400 < 1.000 < 1.000 < 1.0 < 0.50 TM-5 12/14/2001 1120 E 0.840 E 2.900 < 1.000 < 1.000 < 1.0 < 0.50 TM-5 6/25/2002 600 E 1.500 E 0.510 E 1.600 < 1.000 < 1.000 E 0.140 E 0.080 TM-5 6/25/2002 1400 < 5.000 < 5.0 < 5.000 < 1.000 < 1.000 < 1.0 < 0.50 TM-5 6/25/2002 1800 < 5.000 < 5.0 E 1.400 < 1.000 < 1.000 < 1.0 < 0.50 TM-5 2/26/2003 2015 E 1.100 E 1.20 E 5.100 E 0.760 E 0.130 < 1.0 < 0.50 TM-5 9/15/03 1400 E 0.5 E 1.7 < 1.000 < 1.000 < 1.0 E 0.02 

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]
Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]

Site number 

(fig. 1)

Sample 

date Sample time Pyrene (μg/L) Stigmastanol (μg/L) Triclosan (μg/L) Tri(2-chloroethyl) phosphate (μg/L) Tri(2-chloroiso

propyl)phosphat

(μg/L) 

TM-1 3/13/2000 1100 < 0.030 < 2.0 < 0.040 < 0.040 < 0.100 TM-1 4/25/2000 1430 < 0.030 < 2.0 < 0.040 < 0.040 < 0.100 TM-1 7/26/2000 900 E 0.019 < 2.0 0.092 0.066 E 0.072 TM-1 9/12/2000 1300 < 0.030 < 2.0 < 0.040 0.052 < 0.100 TM-1 11/15/2000 845 < 0.030 < 2.0 E 0.048 < 0.040 < 0.100 TM-1 2/13/2001 1720 * < 2.0 E 0.089 E 0.071 < 0.500 TM-1 3/12/2001 1050 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-1 12/14/2001 1130 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-1 6/25/2002 600 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-1 6/25/2002 1400 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-1 6/25/2002 1730 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-1 2/26/2003 1830 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-1 9/15/03 1800 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-3 3/13/2000 1500 E 0.030 < 2.0 < 0.040 < 0.040 < 0.100 TM-3 4/26/2000 1630 0.06 < 2.0 0.079 0.044 < 0.100 TM-3 7/26/2000 1330 E 0.031 < 2.0 0.072 0.059 E 0.072 TM-3 9/13/2000 1545 0.035 < 2.0 0.064 0.058 E 0.064 TM-3 11/13/2000 1445 < 0.030 < 2.0 E 0.043 < 0.040 < 0.100 TM-3 2/13/2001 1330 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-3 3/12/2001 1625 E 0.130 < 2.0 < 1.000 < 0.500 < 0.500 TM-3 12/14/2001 245 E 0.058 < 2.0 < 1.000 < 0.500 E 0.091 TM-3 2/26/2003 1830 E 0.061 < 2.0 < 1.000 < 0.500 < 0.500 TM-3 9/15/03 1530 E 0.009 < 2.0 < 1.000 < 0.500 < 0.500 TM-4 3/15/2000 1100 E 0.020 < 2.0 < 0.040 < 0.040 < 0.100 TM-4 4/26/2000 845 E 0.026 < 2.0 < 0.040 < 0.040 < 0.100 TM-4 7/25/2000 1620 E 0.020 < 2.0 0.075 0.06 E 0.075 TM-4 9/13/2000 750 E 0.020 < 2.0 < 0.040 0.052 < 0.100 TM-4 11/13/2000 1330 < 0.030 < 2.0 E 0.033 < 0.040 < 0.100 TM-4 2/14/2001 930 E 0.130 < 2.0 < 1.000 < 0.500 < 0.500 TM-4 3/12/2001 1445 E 0.120 < 2.0 < 1.000 < 0.500 < 0.500 TM-4 6/25/2002 600 < 0.50 < 2.0 < 1.000 E 0.067 < 0.500 
Site number (fig. 1) Sample date Sample time Pyrene (μg/L) Stigmastanol (μg/L) Triclosan (μg/L) Tri(2-chloroethyl) phosphate (μg/L) Tri(2-chloroiso

propyl)phosphat

(μg/L) 

TM-4 6/25/2002 1000 < 0.50 < 2.0 < 1.000 E 0.058 < 0.500 TM-4 6/25/2002 1400 < 0.50 < 2.0 < 1.000 E 0.062 < 0.500 TM-4 6/25/2002 1730 < 0.50 < 2.0 < 1.000 E 0.057 < 0.500 CEN 3/14/2000 1000 0.063 E 0.597 0.894 0.31 < 0.100 CEN 4/27/2000 1415 0.049 < 2.0 0.221 0.064 < 0.100 CEN 7/24/2000 1300 E 0.067 < 2.0 0.18 0.138 0.181 CEN 9/14/2000 1330 0.049 < 2.0 0.214 0.211 0.214 CEN 11/14/2000 1445 0.047 < 2.0 0.346 E 0.038 < 0.100 CEN 2/12/2001 1330 < 0.50 < 2.0 E 0.280 < 0.500 < 0.500 CEN 3/13/2001 800 < 0.50 < 2.0 E 0.130 < 0.500 E 0.063 CEN 10/31/2001 1345 < 0.50 < 2.0 E 0.290 < 0.500 < 0.500 TSB 3/14/2000 1400 E 0.024 < 2.0 0.085 < 0.040 < 0.100 TSB 4/26/2000 1205 < 0.030 < 2.0 0.084 < 0.040 < 0.100 TSB 7/24/2000 1500 E 0.025 < 2.0 0.1 0.072 E 0.099 TSB 9/13/2000 1030 0.217 < 2.0 0.077 0.057 E 0.077 TSB 11/15/2000 1400 0.033 < 2.0 0.085 E 0.035 < 0.100 TSB 2/12/2001 1615 < 0.50 < 2.0 E 0.087 < 0.500 < 0.500 TSB 3/13/2001 930 < 0.50 < 2.0 E 0.200 < 0.500 < 0.500 TSB 10/31/2001 1130 < 0.50 < 2.0 E 0.110 < 0.500 < 0.500 TM-5 3/15/2000 100 0.053 E 0.801 0.5 0.123 < 0.100 TM-5 4/27/2000 915 < 0.030 < 2.0 0.046 < 0.040 < 0.100 TM-5 7/25/2000 1040 E 0.030 < 2.0 0.095 0.066 E 0.092 TM-5 9/14/2000 915 E 0.025 < 2.0 0.074 0.064 E 0.074 TM-5 11/16/2000 955 < 0.030 < 2.0 0.125 0.065 < 0.100 TM-5 2/13/2001 915 E 0.059 < 2.0 E 0.230 E 0.053 E 0.080 TM-5 3/13/2001 1730 < 0.50 < 2.0 E 0.140 < 0.500 E 0.054 TM-5 12/14/2001 1120 < 0.50 < 2.0 E 0.180 E 0.062 E 0.130 TM-5 6/25/2002 600 E 0.180 E 1.100 E 0.120 E 0.053 < 0.500 TM-5 6/25/2002 1400 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-5 6/25/2002 1800 < 0.50 < 2.0 < 1.000 < 0.500 < 0.500 TM-5 2/26/2003 2015 < 0.50 < 2.0 E 0.180 E 0.060 E 0.082 TM-5 9/15/03 1400 E 0.01 < 2.0 E 0.06 E 0.06 E 0.06 

Appendix 2. Table 2-2. Concentrations of selected organic wastewater compounds detected at sites in the Threemile Creek basin, Mobile, Alaba[μg/L, micrograms per liter; --, no data; <, less than; E, estimated; AHTN, 6-acetyl-1,1,2,4,4,7-hexamethyltetraline; BHA, butylated hydroxyanisole; BHT, butylated hydroxy

hexahydro-4,6,6,7,8,8-hexamethyl-cyclopenta(g)-2-benzopyran; *, censored; NP1EO, monoethoxylate nonylphenol; NP2EO, diethoxylate nonylphenol; OP1EO, monoethox

OP2EO, diethoxylate octylphenol]
Appendixes 115

Appendix 3. Table 3-1. Benthic invertebrate taxa, percent abundance of each taxon, and total abundance at selected sites in Threemile 

Creek, Mobile, Alabama, July 2000.

BU_ID

Sites

TM-1

(percent)

TM-2

(percent)

TM-3

(percent)

TM-4

(percent)

TM-4 replicate

(percent)

Worms: flatworms, ribbon worms, roundworms, and annelids

Turbellaria 0.907 1.96 61.8 0.945

Prostoma sp. 18.4 0.139

Nematoda 0.277 0.314 0.267

Megadrile 0.907

Naididae 0.305 1.13 0.139 0.314 1.61

Tubificidae 0.279

TOTAL 20.519 3.369 62.355 1.573 1.877

Snails (Gastropods) 

Prosobranchia 0.023 1.99 2.83 1.07

Ferrissia sp. 0.928 0.001

Hydrobiidae 5.15 0.284

Stagnicola sp. 2.81 0.567

Physella sp. 0.305 2.34 0.142

Planorbella sp. 0.023 2.70

TOTAL 0.305 11.274 5.68 2.83 1.07

Clams (Bivalves)

Corbicula sp. 1.20 5.06 0.416 45.6 1.61

Mites

Acari 6.46 0.139 0.628 0.267

Springtails

Collembola 2.52 0.139

Mayflies

Caenis sp. 0.009 28.1 1.94 34.6

Tricorythodes sp. 0.305 0.056 1.07

Centroptilum/Procloeon sp. 0.302

Paracloeodes minutus (Daggy) 10.0 0.004 0.267

Pseudocloeon sp. 0.603

TOTAL 0.314 39.061 1.94 0.004 35.937
116 Water Quality, Benthic Invertebrates, and Periphyton in the Threemile Creek Basin, Mobile, Alabama, 1999–2003

Dragonflies

Argia sp. 0.669 0.056 0.555

Enallagma sp. 1.00 0.083 0.833

Gomphidae 17.6 45.0

Erythemis simplicicollis (Say) 0.294 1.57

TOTAL 1.669 18.033 1.57 46.388

Giant water bugs

Belostoma flumineum Say 0.557

Water strider

Trepobates sp. 1.13 40.2

Veliidae 0.557

TOTAL 1.687 40.2

Caddisflies

Hydroptila sp. 1.96

Cheumatopsyche sp. 1.83

Hydropsyche rossi Flint, Voshell, 

and Parker/simulans Ross

48.0

Oecetis sp. 0.628

Orthotrichia sp. 0.692

Oxyethira sp. 4.78 0.139 0.004

TOTAL 49.83 6.74 0.831 0.632

Butterflies

Lepidoptera 0.557 0.267

Water beetles

Peltodytes sp. 2.24 0.139

Biting midges

Bezzia/Palpomyia sp. 3.09 1.73 0.329 0.535

Appendix 3. Table 3-1. Benthic invertebrate taxa, percent abundance of each taxon, and total abundance at selected sites in Threemile 

Creek, Mobile, Alabama, July 2000.—Continued

BU_ID

Sites

TM-1

(percent)

TM-2

(percent)

TM-3

(percent)

TM-4

(percent)

TM-4 replicate

(percent)
Appendixes 117

Midges

Cryptochironomus sp. 3.12

Dicrotendipes sp. 0.671 5.02 0.170 0.346 0.949

Parachironomus sp. 2.69

Paracladopelma sp. 1.52

Polypedilum sp. 1.01 1.67 0.346 1.58

Saetheria sp. 0.339

Pseudochironomus sp. 0.289

Micropsectra/Tanytarsus sp. 0.280

Tanytarsus sp. 0.289 0.170 0.280

Cricotopus/Orthocladius sp. 12.0 0.384

Cricotopus bicinctus group 1.90 0.384

Nanocladius sp. 1.56 1.10 0.346

Thienemanniella sp. 7.91

Tvetenia sp. 1.58

Clinotanypus sp. 0.910

Thienemannimyia group sp. 

(Coffman and Ferrington, 1996)

0.484

Ablabesmyia sp. 0.573 0.324 1.46 1.69

Labrundinia sp. 0.573 0.648 0.484 0.560

Larsia sp. 4.04 4.38 0.560

TOTAL 27.761 15.692 8.651 6.586 5.899

Mosquitoes

Culex sp. 6.17

Total abundance 11,100 7,180 84,900 28,000 25,100

Appendix 3. Table 3-1. Benthic invertebrate taxa, percent abundance of each taxon, and total abundance at selected sites in Threemile 

Creek, Mobile, Alabama, July 2000.—Continued

BU_ID

Sites

TM-1

(percent)

TM-2

(percent)

TM-3

(percent)

TM-4

(percent)

TM-4 replicate

(percent)
Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002. [cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer] Scientific name Algae group Percentage o

Cell density (cells/cm2) 

TM-1 9/12/2000 Subsample Identifier A Cosmarium punctulatum Bréb. Green algae 1.88% 

Stigeoclonium lubricum (Dillw.) Kütz. Green algae 3.76% Synedra ulna (Nitz.) Ehr. Diatoms 0.77% Gomphonema patrickii Kociolek & Stoermer Diatoms 3.06% Euglena sp. Euglenoids 0.88% Gomphonema parvulum (Kütz.) Kütz. Diatoms 4.34% Oscillatoria sp. 1 ANS FWA Blue-green algae 57.13% Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.68% Navicula leptostriata Jorg. Diatoms 1.62% Trachelomonas volvocina Ehr. Euglenoids 0.33% Nitzschia amphibia Grun. Diatoms 1.87% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.85% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 5.28% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.26% Hydrocoleum brebissonii Kütz. Blue-green algae 8.62% Navicula cryptocephala Kütz. Diatoms 0.43% Fragilaria crotonensis Kitton Diatoms 0.43% Navicula trivialis Lange-Bert. Diatoms 0.13% Encyonema minutum (Hilse) Mann Diatoms 0.60% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.43% Gomphonema minutum (Ag.) Ag. Diatoms 0.34% Navicula veneta Kütz. Diatoms 0.94% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.17% Achnanthes exigua var. heterovalva Krasske Diatoms 0.77% Cyclotella atomus Hust. Diatoms 0.51% Cosmarium granatum Bréb. ex Ralfs Green algae 0.44% Euastrum ciastonii Raciborski Green algae 0.44% Caloneis bacillum (Grun.) Cl. Diatoms 0.09% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.17% Scenedesmus ecornis (Ralfs) Chod. Green algae 0.88% 
Navicula minima Grun. Diatoms 0.43% Nitzschia dissipata (Kütz.) Grun. Diatoms 0.09% Navicula decussis Østr. Diatoms 0.09% Amphora pediculus (Kütz) Grun. Diatoms 0.09% Navicula seminulum Grun. Diatoms 0.09% Closterium gracile Bréb. Green algae 0.11% Achnanthes lanceolata var. frequentissima Lange-Bert. Diatoms 0.09% Nitzschia archibaldii Lange-Bertalot Diatoms 0.98% Totals (cell density and biovolume) 684,273 

TM-1 9/12/2000 Subsample Identifier B

Gomphonema patrickii Kociolek & Stoermer Diatoms 12.52% Cosmarium punctulatum Bréb. Green algae 1.29% Synedra ulna (Nitz.) Ehr. Diatoms 0.61% Euglena sp. Euglenoids 1.01% Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.86% Calothrix parientina (Näg.) Thuret Blue-green algae 12.66% Nitzschia amphibia Grun. Diatoms 3.93% Fragilaria crotonensis Kitton Diatoms 2.46% Oscillatoria sp. 1 ANS FWA Blue-green algae 44.03% Ankistrodesmus falcatus (Corda) Ralfs Green algae 0.86% Trachelomonas cylindrica Ehr. Euglenoids 0.43% Gomphonema parvulum (Kütz.) Kütz. Diatoms 2.46% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.25% Encyonema minutum (Hilse) Mann Diatoms 1.84% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 5.40% Navicula leptostriata Jorg. Diatoms 0.86% Trachelomonas volvocina Ehr. Euglenoids 0.14% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 1.11% Navicula notha Wallace Diatoms 0.98% Navicula cryptocephala Kütz. Diatoms 0.37% Achnanthes exigua var. heterovalva Krasske Diatoms 1.23% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.12% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Cymbella affinis Kütz. Diatoms 0.12% Hydrocoleum brebissonii Kütz. Blue-green algae 2.45% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.12% Caloneis bacillum (Grun.) Cl. Diatoms 0.12% Gomphonema kobayasii Kociolek & Kingston Diatoms 0.25% Cosmarium granatum Bréb. ex Ralfs Green algae 0.29% Navicula minima Grun. Diatoms 0.37% Navicula veneta Kütz. Diatoms 0.12% Cyclotella atomus Hust. Diatoms 0.12% Navicula subminuscula Mang. Diatoms 0.12% Nitzschia archibaldii Lange-Bertalot Diatoms 0.49% Totals (cell density and biovolume) 269,421 

TM-1 9/12/2000 Subsample Identifier C Gomphonema patrickii Kociolek & Stoermer Diatoms 7.24% 

Cosmarium punctulatum Bréb. Green algae 0.86% Calothrix parientina (Näg.) Thuret Blue-green algae 40.46% Synedra ulna (Nitz.) Ehr. Diatoms 0.28% Pinnularia brebissonii (Kütz.) Rabh. Diatoms 0.09% Gomphonema parvulum (Kütz.) Kütz. Diatoms 2.48% Nitzschia amphibia Grun. Diatoms 2.29% Fragilaria crotonensis Kitton Diatoms 1.38% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 5.23% Euglena sp. Euglenoids 0.24% Hydrocoleum brebissonii Kütz. Blue-green algae 13.69% Gomphonema minutum (Ag.) Ag. Diatoms 0.73% Oscillatoria sp. 1 ANS FWA Blue-green algae 16.38% Encyonema minutum (Hilse) Mann Diatoms 0.92% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.09% Navicula notha Wallace Diatoms 1.10% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.28% Achnanthes exigua var. heterovalva Krasske Diatoms 1.19% Navicula leptostriata Jorg. Diatoms 0.37% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.09% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.18% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.09% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.46% Caloneis bacillum (Grun.) Cl. Diatoms 0.18% Staurastrum alternans Bréb. Green algae 0.73% Navicula minima Grun. Diatoms 0.92% Cymbella affinis Kütz. Diatoms 0.09% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.09% Nitzschia acicularis (Kützing) Smith Diatoms 0.18% Navicula veneta Kütz. Diatoms 0.18% Navicula seminulum Grun. Diatoms 0.09% Staurastrum manfeldtii Delponte Green algae 0.12% Gomphonema kobayasii Kociolek & Kingston Diatoms 0.09% Achnanthes pusilla (Grun.) DeT. Diatoms 0.09% Nitzschia archibaldii Lange-Bertalot Diatoms 1.10% Totals (cell density and biovolume) 425,803 

TM-1 8/8/2001 Subsample Identifier A

Stigeoclonium lubricum (Dillw.) Kütz. Green algae 53.58% Cosmarium punctulatum Bréb. Green algae 0.09% Cosmarium botrytes Meneghini Green algae 0.09% Calothrix parientina (Näg.) Thuret Blue-green algae 16.88% Synedra ulna (Nitz.) Ehr. Diatoms 0.10% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 7.94% Trachelomonas volvocina Ehr. Euglenoids 0.28% Fragilaria crotonensis Kitton Diatoms 0.62% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 20.09% Frustulia rhomboides var. capitata (A. Mayer) Patr. Diatoms 0.01% Gomphonema subclavatum var. mexicanum (Grun. in V. H.) Patr. Diatoms 0.04% Encyonema prostratum (Berkeley) Kützing Diatoms 0.01% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.06% Nitzschia amphibia Grun. Diatoms 0.06% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Encyonema minutum (Hilse) Mann Diatoms 0.04% Cosmarium regnellii Wille Green algae 0.09% Totals (cell density and biovolume) 1,162,458 

TM-1 8/8/2001 Subsample Identifier B Stigeoclonium lubricum (Dillw.) Kütz. Green algae 58.66% 

Oedogonium sp. Green algae 0.34% Closterium venus Kützing Green algae 0.04% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 37.86% Fragilaria crotonensis Kitton Diatoms 0.85% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 2.00% Synedra ulna (Nitz.) Ehr. Diatoms 0.02% Gomphonema subclavatum var. mexicanum (Grun. in V. H.) Patr. Diatoms 0.03% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.07% Encyonema minutum (Hilse) Mann Diatoms 0.06% Pleurotaenium baculoides var. brevius (Skuja) Krieger Green algae 0.04% Navicula notha Wallace Diatoms 0.01% Nitzschia amphibia Grun. Diatoms 0.02% Achnanthes exigua var. heterovalva Krasske Diatoms 0.01% Totals (cell density and biovolume) 1,410,146 

TM-1 8/8/2001 Subsample Identifier C Stigeoclonium lubricum (Dillw.) Kütz. Green algae 81.26% 

Cosmarium botrytes Meneghini Green algae 0.09% Fragilaria crotonensis Kitton Diatoms 0.85% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 4.00% Trachelomonas volvocina Ehr. Euglenoids 0.09% Synedra ulna (Nitz.) Ehr. Diatoms 0.02% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 13.27% Gomphonema subclavatum var. mexicanum (Grun. in V. H.) Patr. Diatoms 0.05% Encyonema minutum (Hilse) Mann Diatoms 0.10% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.09% Navicula notha Wallace Diatoms 0.06% Eunotia bilunaris (Ehrenberg) Mills Diatoms 0.02% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Penium margaritaceum (Ehrenberg) Brébisson Green algae 0.09% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.01% Totals (cell density and biovolume) 561,144 

TM-1 9/19/2002 Subsample Identifier A

Oedogonium sp. Green algae 4.85% Synedra ulna (Nitz.) Ehr. Diatoms 8.89% Gomphonema parvulum (Kütz.) Kütz. Diatoms 45.03% Eunotia formica Ehrenberg Diatoms 0.78% Gomphonema gracile Ehr. emend. V. H. Diatoms 3.30% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 2.96% Brachysira brebissonii Ross Diatoms 0.31% Cymbella tumida (Brébisson ex Kützing) Van Heurck Diatoms 0.62% Cymbella mesiana Cholnoky Diatoms 0.62% Frustulia rhomboides var. capitata (A. Mayer) Patr. Diatoms 0.31% Encyonema minutum (Hilse) Mann Diatoms 5.46% Eunotia incisa Smith ex Gregory Diatoms 2.34% Eunotia pectinalis var. undulata (Ralfs) Rabenhorst Diatoms 0.31% Gomphonema angustatum (Kütz.) Rabh. Diatoms 2.10% Gomphonema subclavatum var. mexicanum (Grun. in V. H.) Patr. Diatoms 0.94% Fragilaria vaucheriae (Kützing) Petersen Diatoms 3.28% Eunotia implicata Nörpel, Lange-Bert. & Alles Diatoms 0.94% Cymbella gracilis (Ehr.) Kütz. Diatoms 1.72% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 10.92% Navicula notha Wallace Diatoms 1.40% Gomphonema kobayasii Kociolek & Kingston Diatoms 0.90% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.78% Achnanthes deflexa Reimer Diatoms 0.47% Scenedesmus quadricauda (Turp.) Bréb. Diatoms 0.61% Achnanthes exigua var. heterovalva Krasske Diatoms 0.16% Totals (cell density and biovolume) 155,694 

TM-1 9/19/2002 Subsample Identifier B

Closterium moniliferum Ehrenberg Green algae 1.32% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Synedra ulna (Nitz.) Ehr. Diatoms 8.15% Gomphonema parvulum (Kütz.) Kütz. Diatoms 38.05% Eunotia formica Ehrenberg Diatoms 0.57% Eunotia soleirolii (Kütz.) Rabh. Diatoms 2.00% Frustulia rhomboides var. capitata (A. Mayer) Patr. Diatoms 0.72% Encyonema silesiacum (Bleisch) Mann Diatoms 2.29% Encyonema minutum (Hilse) Mann Diatoms 7.72% Synedra acus Kützing Diatoms 0.86% Brachysira brebissonii Ross Diatoms 0.14% Gomphonema gracile Ehr. emend. V. H. Diatalgaeoms 0.92% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.86% Eunotia incisa Smith ex Gregory Diatoms 1.86% Navicula notha Wallace Diatoms 3.29% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.29% Microspora sp. Green algae 6.94% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 5.58% Gomphonema affine Kütz. Diatoms 0.31% Gomphonema aff. affine ANS NAWQA EAM Diatoms 0.31% Eunotia minor (Kützing) Grunow Diatoms 0.43% Cymbella tumida (Brébisson ex Kützing) Van Heurck Diatoms 0.14% Eunotia pectinalis var. undulata (Ralfs) Rabenhorst Diatoms 0.14% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 7.72% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.86% Scenedesmus quadricauda (Turp.) Bréb. Green algae 3.97% Navicula cryptocephala Kütz. Diatoms 0.43% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.14% Nitzschia amphibia Grun. Diatoms 0.57% Cosmarium pseudoretusum Ducellier Green algae 0.99% Gomphonema kobayasii Kociolek & Kingston Diatoms 0.46% Fragilaria vaucheriae (Kützing) Petersen Diatoms 0.29% Caloneis bacillum (Grun.) Cl. Diatoms 0.14% Gomphonema angustatum (Kütz.) Rabh. Diatoms 0.15% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Micrasterias radiosa Ralfs Green algae 0.33% Staurastrum dickiei Ralfs Green algae 0.33% Nitzschia acicularis (Kützing) Smith Diatoms 0.14% Fragilaria famelica (Kützing) Lange-Bertalot Diatoms 0.29% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.14% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 0.14% Totals (cell density and biovolume) 207,044 

TM-1 9/19/2002 Subsample Identifier C

Closterium moniliferum Ehrenberg Green algae 1.29% Synedra ulna (Nitz.) Ehr. Diatoms 10.05% Gomphonema parvulum (Kütz.) Kütz. Diatoms 37.51% Encyonema silesiacum (Bleisch) Mann Diatoms 4.87% Gomphonema gracile Ehr. emend. V. H. Diatoms 4.87% Eunotia formica Ehrenberg Diatoms 0.31% Cymbella mesiana Cholnoky Diatoms 0.94% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 1.57% Encyonema minutum (Hilse) Mann Diatoms 6.59% Synedra acus Kützing Diatoms 0.94% Gomphonema patrickii Kociolek & Stoermer Diatoms 4.39% Brachysira brebissonii Ross Diatoms 0.16% Eunotia incisa Smith ex Gregory Diatoms 2.35% Eunotia minor (Kützing) Grunow Diatoms 0.94% Frustulia rhomboides var. capitata (A. Mayer) Patr. Diatoms 0.16% Cymbella tumidula Grunow ex Schmidt Diatoms 0.31% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 5.34% Navicula notha Wallace Diatoms 2.83% Eunotia pectinalis var. undulata (Ralfs) Rabenhorst Diatoms 0.16% Navicula viridula var. linearis Hustedt Diatoms 0.31% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.94% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.16% Lyngbya sp. 1 ANS FWA Blue-green algae 1.62% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 6.12% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Gomphonema turris Ehrenberg Diatoms 0.16% Navicula cryptocephala Kütz. Diatoms 0.47% Cymbella delicatula Kützing Diatoms 0.31% Cymbella laevis Naegeli ex Kützing Diatoms 0.16% Cosmarium margaritatum (Lund) Roy & Biss. Green algae 0.97% Caloneis bacillum (Grun.) Cl. Diatoms 0.16% Scenedesmus quadricauda (Turp.) Bréb. Green algae 0.97% Navicula kotschyi Grunow Diatoms 0.16% Fragilaria vaucheriae (Kützing) Petersen Diatoms 0.16% Nitzschia amphibia Grun. Diatoms 0.16% Micrasterias radiosa Ralfs Green algae 0.32% Pediastrum tetras var. tetraodon (Corda) Rabenhorst Green algae 0.32% Navicula cincta var. rostrata Reim. Diatoms 0.16% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 0.31% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.16% Ankistrodesmus falcatus (Corda) Ralfs Green algae 0.32% Totals (cell density and biovolume) 131,594 

TM-2 8/8/2001 Subsample Identifier A Stigeoclonium lubricum (Dillw.) Kütz. Green algae 28.13% 

Unknown Chlorophyte coccoid Green algae 24.48% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 44.61% Oscillatoria princeps Vauch. Blue-green algae 2.12% Fragilaria crotonensis Kitton Diatoms 0.21% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.18% Synedra ulna (Nitz.) Ehr. Diatoms 0.01% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.23% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.00% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.01% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.00% Gomphonema rhombicum Fricke Diatoms 0.00% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.00% Cymbella affinis Kütz. Diatoms 0.00% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Fragilaria nanana Lange-Bertalot Diatoms 0.00% Placoneis elginensis (Greg.) Cox Diatoms 0.00% Nitzschia gracilis Hantz. ex Rabh. Diatoms 0.00% Nitzschia amphibia Grun. Diatoms 0.00% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.00% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.00% Navicula capitata var. hungarica (Grun.) Ross Diatoms 0.00% Achnanthes exigua var. heterovalva Krasske Diatoms 0.00% Totals (cell density and biovolume) 1,282,191 

TM-2 8/8/2001 Subsample Identifier B

Spirogyra sp. Green algae 0.28% Stigeoclonium lubricum (Dillw.) Kütz. Green algae 43.52% Unknown Chlorophyte coccoid Green algae 42.83% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 12.48% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.34% Fragilaria crotonensis Kitton Diatoms 0.20% Synedra ulna (Nitz.) Ehr. Diatoms 0.00% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.30% Placoneis clementis (Grun) Cox Diatoms 0.00% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.01% Cymbella affinis Kütz. Diatoms 0.00% Gomphonema rhombicum Fricke Diatoms 0.01% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.01% Navicula viridula var. linearis Hustedt Diatoms 0.00% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.00% Eunotia bilunaris (Ehrenberg) Mills Diatoms 0.00% Encyonema minutum (Hilse) Mann Diatoms 0.01% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.00% Fragilaria nanana Lange-Bertalot Diatoms 0.00% Nitzschia amphibia Grun. Diatoms 0.00% Achnanthes exigua var. heterovalva Krasske Diatoms 0.00% Amphora inariensis Krammer Diatoms 0.00% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Achnanthes lanceolata var. rostrata Hust. Diatoms 0.00% Totals (cell density and biovolume) 520,802 

TM-2 8/8/2001 Subsample Identifier C Unknown Chlorophyte coccoid Green algae 35.57% 

Oedogonium sp. Green algae 0.16% Stigeoclonium lubricum (Dillw.) Kütz. Green algae 5.89% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 56.80% Mougeotia sp. Green algae 0.06% Fragilaria crotonensis Kitton Diatoms 0.48% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.27% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.67% Synedra ulna (Nitz.) Ehr. Diatoms 0.00% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.02% Cymbella affinis Kütz. Diatoms 0.01% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.01% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.01% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.01% Encyonema minutum (Hilse) Mann Diatoms 0.01% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.00% Placoneis elginensis (Greg.) Cox Diatoms 0.00% Asterionella formosa Hassal Diatoms 0.00% Gomphonema rhombicum Fricke Diatoms 0.00% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.01% Fragilaria nanana Lange-Bertalot Diatoms 0.01% Nitzschia amphibia Grun. Diatoms 0.00% Achnanthes exigua var. heterovalva Krasske Diatoms 0.01% Cymbella hustedtii Krass. Diatoms 0.00% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.00% Totals (cell density and biovolume) 1,153,306 

TM-2 9/19/2002 Subsample Identifier A

Closterium moniliferum Ehrenberg Green algae 0.97% Synedra ulna (Nitz.) Ehr. Diatoms 1.33% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Brachysira brebissonii Ross Diatoms 0.74% Craticula submolesta (Hustedt) Lange-Bertalot Diatoms 0.44% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 61.42% Nitzschia palea (Kütz.) W. Sm. Diatoms 5.16% Encyonema silesiacum (Bleisch) Mann Diatoms 1.18% Gomphonema parvulum (Kütz.) Kütz. Diatoms 5.02% Eunotia formica Ehrenberg Diatoms 0.15% Navicula viridula var. linearis Hustedt Diatoms 0.88% Placoneis clementis (Grun) Cox Diatoms 0.15% Cymbella tumidula Grunow ex Schmidt Diatoms 0.59% Gomphonema gracile Ehr. emend. V. H. Diatoms 0.81% Navicula notha Wallace Diatoms 3.68% Frustulia rhomboides var. capitata (A. Mayer) Patr. Diatoms 0.15% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.44% Navicula cryptocephala Kütz. Diatoms 1.33% Eunotia pectinalis var. undulata (Ralfs) Rabenhorst Diatoms 0.15% Encyonema minutum (Hilse) Mann Diatoms 1.47% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 1.03% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.44% Achnanthidium exilis (Kützing) Round et Bukhtiyarova Diatoms 0.15% Fragilaria vaucheriae (Kützing) Petersen Diatoms 0.88% Nitzschia capitellata Hustedt Diatoms 0.44% Nitzschia amphibia Grun. Diatoms 0.88% Geissleria decussis (Hustedt) Lange-Bertalot et Metzeltin Diatoms 0.59% Gomphonema patrickii Kociolek & Stoermer Diatoms 0.49% Microspora sp. Green algae 1.62% Lyngbya sp. 1 ANS FWA Blue-green algae 0.65% Scenedesmus quadricauda (Turp.) Bréb. Green algae 2.27% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 1.03% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.74% Achnanthes minutissima var. scotica (Carter) Lange-Bertalot Diatoms 0.44% Gomphonema angustatum (Kütz.) Rabh. Diatoms 0.16% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Tabellaria flocculosa (Roth) Kütz. Diatoms 0.15% Anabaena oscillarioides Bory Blue-green algae 0.65% Cosmarium margaritatum (Lund) Roy & Biss. Green algae 0.32% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.15% Planothidium rostratum (Østrup) Lange-Bertalot Diatoms 0.15% Psammothidium subatomoides (Hustedt) Bukhtiyarova et Round Diatoms 0.15% Navicula minima Grun. Diatoms 0.29% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.15% Navicula arvensis Hust. Diatoms 0.15% Totals (cell density and biovolume) 234,068 

TM-2 9/19/2002 Subsample Identifier B Spirogyra sp. Green algae 12.39% 

Closterium moniliferum Ehrenberg Green algae 0.31% Brachysira brebissonii Ross Diatoms 1.41% Synedra ulna (Nitz.) Ehr. Diatoms 1.55% Frustulia rhomboides var. capitata (A. Mayer) Patr. Diatoms 1.97% Eunotia formica Ehrenberg Diatoms 0.56% Eunotia incisa Smith ex Gregory Diatoms 9.73% Gomphonema parvulum (Kütz.) Kütz. Diatoms 14.30% Encyonema silesiacum (Bleisch) Mann Diatoms 2.82% Cymbella turgidula Grunow Diatoms 2.54% Eunotia implicata Nörpel, Lange-Bert. & Alles Diatoms 2.82% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 1.83% Eunotia pectinalis var. undulata (Ralfs) Rabenhorst Diatoms 0.56% Nitzschia sigma (Kütz.) W. Sm. Diatoms 0.14% Gomphonema gracile Ehr. emend. V. H. Diatoms 0.95% Neidium ampliatum (Ehr.) Kramm. Diatoms 0.14% Cymbella mesiana Cholnoky Diatoms 0.42% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 21.28% Cymbella tumida (Brébisson ex Kützing) Van Heurck Diatoms 0.28% Encyonema minutum (Hilse) Mann Diatoms 3.52% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.42% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 2.26% Pinnularia gibba Ehrenberg Diatoms 0.28% Hippodonta capitata (Ehrenberg) Lange-Bertalot, Metzeltin et Witkowski Diatoms 0.14% Hippodonta lueneburgensis (Grunow) Lange-Bertalot, Metzeltin et Witkowski Diatoms 0.14% Synedra acus Kützing Diatoms 0.28% Pinnularia microstauron (Ehr.) Cl. Diatoms 0.28% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 3.66% Geissleria decussis (Hustedt) Lange-Bertalot et Metzeltin Diatoms 1.27% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.85% Gomphonema patrickii Kociolek & Stoermer Diatoms 0.95% Navicula cryptocephala Kütz. Diatoms 0.70% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.42% Achnanthidium exilis (Kützing) Round et Bukhtiyarova Diatoms 0.14% Navicula notha Wallace Diatoms 0.99% Fragilaria vaucheriae (Kützing) Petersen Diatoms 0.70% Cosmarium margaritatum (Lund) Roy & Biss. Green algae 1.55% Caloneis bacillum (Grun.) Cl. Diatoms 0.28% Cymbella naviculiformis Auerswald ex Héribaud Diatoms 0.70% Cymbella hustedtii Krass. Diatoms 0.28% Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.55% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.14% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 0.42% Planothidium rostratum (Østrup) Lange-Bertalot Diatoms 0.28% Planothidium delicatulum (Kützing) Round et Bukhtiyarova Diatoms 0.14% Euastrum ciastonii Raciborski Green algae 0.31% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.14% Staurosirella pinnata (Ehrenberg) Williams et Round Diatoms 0.14% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.28% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.42% Anabaena oscillarioides Bory Blue-green algae 0.31% Totals (cell density and biovolume) 128,796 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
TM-2 9/19/2002 Subsample Identifier C Spirogyra sp. Green algae 2.69% 

Brachysira brebissonii Ross Diatoms 1.43% Synedra ulna (Nitz.) Ehr. Diatoms 1.59% Gomphonema parvulum (Kütz.) Kütz. Diatoms 12.69% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 47.15% Eunotia incisa Smith ex Gregory Diatoms 3.98% Encyonema minutum (Hilse) Mann Diatoms 8.60% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 1.43% Cymbella mesiana Cholnoky Diatoms 0.64% Encyonema silesiacum (Bleisch) Mann Diatoms 1.11% Eunotia implicata Nörpel, Lange-Bert. & Alles Diatoms 1.75% Nupela sp. 1 ANS NEW JERSEY KCP Diatoms 0.16% Eunotia pectinalis var. undulata (Ralfs) Rabenhorst Diatoms 0.32% Gomphonema gracile Ehr. emend. V. H. Diatoms 0.67% Cymbella turgidula Grunow Diatoms 0.80% Hippodonta capitata (Ehrenberg) Lange-Bertalot, Metzeltin et Witkowski Diatoms 0.16% Navicula notha Wallace Diatoms 1.75% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.16% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.80% Pinnularia microstauron (Ehr.) Cl. Diatoms 0.16% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 2.07% Navicula cryptocephala Kütz. Diatoms 0.48% Geissleria decussis (Hustedt) Lange-Bertalot et Metzeltin Diatoms 0.64% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.16% Nitzschia amphibia Grun. Diatoms 0.80% Cymbella hustedtii Krass. Diatoms 0.64% Gomphonema patrickii Kociolek & Stoermer Diatoms 0.50% Fragilaria vaucheriae (Kützing) Petersen Diatoms 0.64% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.32% Cosmarium granatum Bréb. ex Ralfs Green algae 1.01% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 1.11% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.16% Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.68% Cymbella gracilis (Ehr.) Kütz. Diatoms 0.16% Cymbella naviculiformis Auerswald ex Héribaud Diatoms 0.32% Staurosirella pinnata (Ehrenberg) Williams et Round Diatoms 0.32% Brachysira microcephala (Grunow) CompËre Diatoms 0.16% Planothidium rostratum (Østrup) Lange-Bertalot Diatoms 0.32% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.32% Achnanthes subhudsonis var. kraeuselii (Cholnoky) Cholnoky Diatoms 0.16% Totals (cell density and biovolume) 269,452 

TM-3 9/13/2000 Subsample Identifier A

Oscillatoria princeps Vauch. Blue-green algae 15.80% Synedra ulna (Nitz.) Ehr. Diatoms 0.45% Hydrocoleum brebissonii Kütz. Blue-green algae 25.56% Gomphonema patrickii Kociolek & Stoermer Diatoms 1.41% Cymbella affinis Kütz. Diatoms 2.24% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.64% Mougeotia sp. Green algae 0.15% Melosira varians Ag. Diatoms 0.13% Oscillatoria sp. 1 ANS FWA Blue-green algae 35.79% Nitzschia palea (Kütz.) W. Sm. Diatoms 1.02% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 3.71% Eunotia soleirolii (Kütz.) Rabh. Diatoms 0.13% Fragilaria crotonensis Kitton Diatoms 0.58% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.13% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.77% Navicula notha Wallace Diatoms 1.28% Encyonema minutum (Hilse) Mann Diatoms 0.77% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.96% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.70% Nitzschia linearis (Ag. ex W. Sm.) W. Sm. Diatoms 0.06% Navicula schroeteri var. symmetrica (Patrick) Lang.-Bert. Diatoms 0.13% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Encyonopsis microcephala (Grun.) Kram. Diatoms 0.06% Diadesmis confervacea Kütz. Diatoms 0.38% Trachelomonas volvocina Ehr. Euglenoids 0.08% Nitzschia amphibia Grun. Diatoms 0.45% Navicula molestiformis Hust. Diatoms 0.70% Nitzschia fonticola Grun. Diatoms 0.70% Navicula germanii Wallace Diatoms 0.13% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.06% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.06% Navicula laevissima Kütz. Diatoms 0.06% Luticola mutica (Kutz.) Mann Diatoms 0.06% Anabaena oscillarioides Bory Blue-green algae 1.86% Achnanthes exigua var. heterovalva Krasske Diatoms 0.32% Merismopedia glauca (Ehr.) Näg. Blue-green algae 0.62% Cosmarium quadrum Lundell Green algae 0.31% Navicula decussis Østr. Diatoms 0.06% Navicula seminulum Grun. Diatoms 0.06% Navicula veneta Kütz. Diatoms 0.06% Cosmarium granatum Bréb. ex Ralfs Green algae 0.08% Navicula reichardtiana Lange-Bert. Diatoms 0.06% Achnanthes lanceolata var. frequentissima Lange-Bert. Diatoms 0.06% Navicula minima Grun. Diatoms 0.06% Navicula caterva Hohn & Hellerm. Diatoms 1.09% Nitzschia archibaldii Lange-Bertalot Diatoms 0.19% Totals (cell density and biovolume) 6,381,257 

TM-3 9/13/2000 Subsample Identifier B Oedogonium sp. Green algae 1.12% 

Synedra ulna (Nitz.) Ehr. Diatoms 0.71% Hydrocoleum brebissonii Kütz. Blue-green algae 34.79% Achnanthes lanceolata var. rostrata Hust. Diatoms 2.33% Navicula arvensis DW WHTRV 98/99 Diatoms 0.41% Gomphonema patrickii Kociolek & Stoermer Diatoms 1.32% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Cymbella affinis Kütz. Diatoms 2.94% Mougeotia sp. Green algae 0.22% Nitzschia palea (Kütz.) W. Sm. Diatoms 1.93% Eunotia soleirolii (Kütz.) Rabh. Diatoms 0.30% Melosira varians Ag. Diatoms 0.10% Onychonema filiforme (Ehr.) Roy & Biss. Green algae 6.13% Oscillatoria sp. 1 ANS FWA Blue-green algae 26.98% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.41% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 4.77% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 1.22% Navicula notha Wallace Diatoms 2.13% Gomphonema affine Kütz. Diatoms 0.20% Gomphonema aff. affine ANS NAWQA EAM Diatoms 0.20% Nitzschia amphibia Grun. Diatoms 1.22% Navicula germanii Wallace Diatoms 0.51% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.10% Encyonema minutum (Hilse) Mann Diatoms 0.71% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.10% Nitzschia fonticola Grun. Diatoms 1.22% Navicula molestiformis Hust. Diatoms 0.91% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.51% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.10% Achnanthes exigua var. heterovalva Krasske Diatoms 0.71% Fragilaria crotonensis Kitton Diatoms 0.20% Navicula minima Grun. Diatoms 1.32% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.10% Navicula cryptocephala Kütz. Diatoms 0.10% Diadesmis confervacea Kütz. Diatoms 0.10% Nitzschia liebethruthii Rabh. Diatoms 0.20% Nitzschia dissipata (Kütz.) Grun. Diatoms 0.10% Navicula decussis Østr. Diatoms 0.10% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.10% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.10% Navicula seminulum Grun. Diatoms 0.10% Pleurotaenium trabecula var. trabecula Näg. Green algae 0.11% Navicula reichardtiana Lange-Bert. Diatoms 0.10% Navicula caterva Hohn & Hellerm. Diatoms 1.12% Nitzschia archibaldii Lange-Bertalot Diatoms 1.83% Totals (cell density and biovolume) 4,179,941 

TM-3 9/13/2000 Subsample Identifier C Spirogyra sp. Green algae 0.42% 

Pinnularia maior (Kütz.) Rabh. Diatoms 0.09% Synedra ulna (Nitz.) Ehr. Diatoms 0.71% Hydrocoleum brebissonii Kütz. Blue-green algae 27.79% Gomphonema patrickii Kociolek & Stoermer Diatoms 1.96% Achnanthes lanceolata var. rostrata Hust. Diatoms 1.69% Navicula arvensis DW WHTRV 98/99 Diatoms 0.27% Cymbella affinis Kütz. Diatoms 3.03% Oscillatoria sp. 1 ANS FWA Blue-green algae 38.32% Nitzschia palea (Kütz.) W. Sm. Diatoms 1.87% Fragilaria crotonensis Kitton Diatoms 0.98% Eunotia soleirolii (Kütz.) Rabh. Diatoms 0.18% Navicula notha Wallace Diatoms 2.14% Gyrosigma nodiferum (Grun.) Reim. Diatoms 0.09% Gomphonema parvulum (Kütz.) Kütz. Diatoms 1.25% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.27% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 3.48% Nitzschia amphibia Grun. Diatoms 1.07% Navicula germanii Wallace Diatoms 0.45% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.71% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.09% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.18% Navicula schroeteri var. escambia Patr. Diatoms 0.18% Gomphonema affine Kütz. Diatoms 0.09% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Gomphonema aff. affine ANS NAWQA EAM Diatoms 0.09% Encyonema minutum (Hilse) Mann Diatoms 0.53% Navicula molestiformis Hust. Diatoms 0.98% Nitzschia fonticola Grun. Diatoms 0.71% Navicula cryptocephala Kütz. Diatoms 0.18% Navicula seminulum Grun. Diatoms 0.53% Achnanthes exigua var. heterovalva Krasske Diatoms 0.62% Scenedesmus quadricauda (Turp.) Bréb. Green algae 0.42% Achnanthes lanceolata var. apiculata Patr. Diatoms 0.09% Anabaena oscillarioides Bory Blue-green algae 1.58% Cosmarium granatum Bréb. ex Ralfs Green algae 0.32% Diadesmis confervacea Kütz. Diatoms 0.09% Gomphosphaeria lacustris Chod. Blue-green algae 4.32% Amphora montana Krass. Diatoms 0.09% Navicula minima Grun. Diatoms 0.36% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.09% Navicula caterva Hohn & Hellerm. Diatoms 0.45% Nitzschia archibaldii Lange-Bertalot Diatoms 1.25% Totals (cell density and biovolume) 3,820,411 

TM-3 9/13/2000 Subsample Identifier A

Spirogyra sp. Green algae 0.14% Gomphoneis eriense (Grun.) Skv. & Meyer Diatoms 0.10% Placoneis gastrum (Ehr.) Meresch. Diatoms 0.09% Chlamydomonas sp. Green algae 1.16% Anabaena oscillarioides Bory Blue-green algae 6.41% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 64.67% Unknown alga flagellate (<10 μm) Unknown Phyla 2.52% Craticula halophila (Grunow in Van Heurck) Mann Diatoms 0.03% Achnanthes lanceolata var. rostrata Hust. Diatoms 3.33% Cymbella cymbiformis Ag. Diatoms 0.25% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.65% Achnanthes exigua var. heterovalva Krasske Diatoms 1.93% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Hydrocoleum brebissonii Kütz. Blue-green algae 5.32% Calothrix parientina (Näg.) Thuret Blue-green algae 3.21% Sellaphora rectangularis (Greg.) Lange-Bertalot & Metzeltin Diatoms 0.01% Merismopedia convoluta Bréb. Blue-green algae 2.66% Cryptomonas sp. Cryptophytes 1.57% Scenedesmus acutus Meyen Green algae 2.18% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.04% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.23% Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.36% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.16% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.69% Navicula submuralis Hust. Diatoms 0.78% Navicula rhynchocephala Kütz. Diatoms 0.03% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.03% Cosmarium margaritatum (Lund) Roy & Biss. Green algae 0.14% Planothidium lanceolatum Diatoms 0.06% Achnanthes oblongella Østrup Diatoms 0.09% Placoneis elginensis (Greg.) Cox Diatoms 0.01% Navicula arvensis Hust. Diatoms 0.09% Nitzschia amphibia Grun. Diatoms 0.03% Nitzschia fonticola Grun. Diatoms 0.03% Navicula bryophila Peters. & Østr. Diatoms 0.01% Totals (cell density and biovolume) 1,359,844 

TM-3 9/13/2000 Subsample Identifier B Hydrocoleum brebissonii Kütz. Blue-green algae 29.85% 

Craticula halophila (Grunow in Van Heurck) Mann Diatoms 0.10% Cymbella cymbiformis Ag. Diatoms 0.41% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 49.06% Nitzschia commuta Grun. Diatoms 0.02% Sellaphora rectangularis (Greg.) Lange-Bertalot & Metzeltin Diatoms 0.03% Anabaena oscillarioides Bory Blue-green algae 3.13% Chlamydomonas sp. Green algae 0.51% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Placoneis clementis (Grun) Cox Diatoms 0.02% Achnanthes lanceolata var. rostrata Hust. Diatoms 2.42% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.08% Merismopedia convoluta Bréb. Blue-green algae 3.64% Achnanthes exigua var. heterovalva Krasske Diatoms 1.13% Unknown alga flagellate (<10 μ) Unknown Phyla 0.88% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.28% Microcystis sp. Blue-green algae 2.86% Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.93% Placoneis elginensis (Greg.) Cox Diatoms 0.10% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.17% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.75% Scenedesmus acutus Meyen Green algae 0.92% Nitzschia amphibia Grun. Diatoms 0.19% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.10% Cryptomonas sp. Cryptophytes 0.41% Calothrix parientina (Näg.) Thuret Blue-green algae 0.41% Surirella minuta Bréb. Diatoms 0.02% Navicula submuralis Hust. Diatoms 0.37% Nitzschia gracilis Hantz. ex Rabh. Diatoms 0.02% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.01% Gomphonema brasiliense Grun. Diatoms 0.02% Navicula arvensis Hust. Diatoms 0.05% Diadesmis confervacea Kütz. Diatoms 0.01% Synedra rumpens Kütz. Diatoms 0.02% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.01% Karayevia clevei Grun. in Cl. et Grun. Diatoms 0.01% Cymbella hustedtii Krass. Diatoms 0.01% Nitzschia fonticola Grun. Diatoms 0.01% Navicula subminuscula Mang. Diatoms 0.01% Nitzschia siliqua Arch. Diatoms 0.01% Totals (cell density and biovolume) 2,835,731 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
TM-3 9/13/2000 Subsample Identifier C Oscillatoria limosa (Dillw.) Ag. Blue-green algae 2.13% 

Cymbella cymbiformis Ag. Diatoms 0.53% Hydrocoleum brebissonii Kütz. Blue-green algae 15.43% Microcystis sp. Blue-green algae 16.37% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 51.03% Nitzschia commuta Grun. Diatoms 0.03% Anabaena oscillarioides Bory Blue-green algae 2.86% Achnanthes lanceolata var. rostrata Hust. Diatoms 2.70% Merismopedia convoluta Bréb. Blue-green algae 4.33% Craticula halophila (Grunow in Van Heurck) Mann Diatoms 0.02% Synedra ulna (Nitz.) Ehr. Diatoms 0.02% Placoneis elginensis (Greg.) Cox Diatoms 0.16% Navicula pupula var. rostrata Hust. Diatoms 0.01% Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.68% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.17% Unknown alga flagellate (<10 μ) Unknown Phyla 0.49% Achnanthes exigua var. heterovalva Krasske Diatoms 0.50% Chlamydomonas sp. Green algae 0.10% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.46% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.09% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.03% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.06% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.01% Navicula heufleri var. leptocephala (Brèb ex Grun.) Perag. Diatoms 0.03% Encyonema silesiacum (Bleisch) Mann Diatoms 0.02% Scenedesmus acutus Meyen Green algae 0.28% Eunotia implicata Nörpel, Lange-Bert. & Alles Diatoms 0.01% Nitzschia amphibia Grun. Diatoms 0.04% Navicula minima Grun. Diatoms 0.18% Cryptomonas sp. Cryptophytes 0.10% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.03% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Navicula capitata var. hungarica (Grun.) Ross Diatoms 0.01% Encyonema minutum (Hilse) Mann Diatoms 0.02% Gomphonema brasiliense Grun. Diatoms 0.01% Navicula submuralis Hust. Diatoms 0.03% Sellaphora seminulum (Grun.) Mann Diatoms 0.02% Navicula arvensis Hust. Diatoms 0.01% Navicula cincta var. rostrata Reim. Diatoms 0.01% Navicula bryophila Peters. & Østr. Diatoms 0.01% Nitzschia siliqua Arch. Diatoms 0.01% Totals (cell density and biovolume) 2,778,226 

TM-3 8/7/2001 Subsample Identifier A

Oedogonium sp. Green algae 1.19% Mougeotia sp. Green algae 2.14% Cosmarium botrytes Meneghini Green algae 0.36% Staurastrum punctulatum Brébisson Green algae 0.12% Cymbella affinis Kütz. Diatoms 1.46% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 10.24% Fragilaria crotonensis Kitton Diatoms 1.61% Nitzschia palea (Kütz.) W. Sm. Diatoms 1.43% Gomphonema rhombicum Fricke Diatoms 0.94% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 51.01% Navicula molestiformis Hust. Diatoms 0.03% Navicula radiosa Kützing Diatoms 0.15% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.43% Oscillatoria sp. 1 ANS FWA Blue-green algae 19.14% Nitzschia amphibia Grun. Diatoms 0.52% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.40% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.30% Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.90% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.06% Anabaena oscillarioides Bory Blue-green algae 2.62% Cyclotella meneghiniana Kütz. Diatoms 0.06% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Placoneis elginensis (Greg.) Cox Diatoms 0.09% Scenedesmus perforatus Lemmermann Green algae 0.48% Encyonema minutum (Hilse) Mann Diatoms 0.12% Cosmarium granatum Bréb. ex Ralfs Green algae 0.24% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.03% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.06% Cosmarium quadrum Lundell Green algae 0.12% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.09% Cymbella hustedtii Krass. Diatoms 0.06% Brachysira neoexilis Lange-Bertalot Diatoms 0.03% Achnanthes exigua var. heterovalva Krasske Diatoms 0.06% Fragilaria nanana Lange-Bertalot Diatoms 0.03% Nitzschia nana Grun. in V. H. Diatoms 0.03% Nitzschia perminuta (Grun.) Peragallo Diatoms 0.03% Navicula gysingensis Foged Diatoms 0.03% Merismopedia tenuissima Lemmermann Blue-green algae 2.38% Totals (cell density and biovolume) 2,213,197 

TM-3 8/7/2001 Subsample Identifier B Oedogonium sp. Green algae 1.52% 

Mougeotia sp. Green algae 0.23% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 72.74% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 8.21% Cymbella affinis Kütz. Diatoms 0.73% Nitzschia palea (Kütz.) W. Sm. Diatoms 1.40% Navicula molestiformis Hust. Diatoms 0.04% Synedra ulna (Nitz.) Ehr. Diatoms 0.04% Nitzschia modesta Hustedt Diatoms 0.02% Fragilaria crotonensis Kitton Diatoms 0.40% Gomphonema rhombicum Fricke Diatoms 0.25% Nitzschia amphibia Grun. Diatoms 0.42% Oscillatoria sp. 1 ANS FWA Blue-green algae 9.46% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.04% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Scenedesmus quadricauda (Turp.) Bréb. Green algae 1.17% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.17% Encyonema minutum (Hilse) Mann Diatoms 0.15% Navicula gregaria Donk. Diatoms 0.04% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.10% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.04% Navicula radiosa Kützing Diatoms 0.02% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 0.08% Cyclotella meneghiniana Kütz. Diatoms 0.02% Navicula capitatoradiata Germain Diatoms 0.02% Placoneis elginensis (Greg.) Cox Diatoms 0.02% Cymbella naviculiformis Auerswald ex Héribaud Diatoms 0.04% Diadesmis confervacea Kütz. Diatoms 0.02% Cymbella hustedtii Krass. Diatoms 0.04% Achnanthes exigua var. heterovalva Krasske Diatoms 0.06% Cosmarium granatum Bréb. ex Ralfs Green algae 0.06% Gomphonema kobayasii Kociolek & Kingston Diatoms 0.02% Scenedesmus ecornis (Ralfs) Chod. Green algae 0.35% Nitzschia perminuta (Grun.) Peragallo Diatoms 0.04% Nitzschia fonticola Grun. Diatoms 0.04% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.06% Brachysira neoexilis Lange-Bertalot Diatoms 0.02% Merismopedia tenuissima Lemmermann Blue-green algae 1.87% Navicula atomus (Kütz.) Grun. Diatoms 0.02% Totals (cell density and biovolume) 3,503,954 

TM-3 8/7/2001 Subsample Identifier C

Oedogonium sp. Green algae 0.89% Closterium moniliferum Ehrenberg Green algae 0.09% Cosmarium botrytes Meneghini Green algae 0.09% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 14.59% Navicula molestiformis Hust. Diatoms 0.10% Cymbella affinis Kütz. Diatoms 1.04% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Nitzschia palea (Kütz.) W. Sm. Diatoms 1.46% Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 40.92% Fragilaria crotonensis Kitton Diatoms 0.90% Gomphonema rhombicum Fricke Diatoms 0.38% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.59% Oscillatoria sp. 1 ANS FWA Blue-green algae 24.27% Nitzschia amphibia Grun. Diatoms 0.59% Eunotia bilunaris (Ehrenberg) Mills Diatoms 0.10% Scenedesmus quadricauda (Turp.) Bréb. Green algae 2.48% Euglena sp. Euglenoids 0.09% Navicula viridula var. rostellata (Kütz.) Cl. Diatoms 0.07% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.03% Navicula cryptotenella L.B. in Kramm. & L.-B. Diatoms 0.17% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.07% Placoneis elginensis (Greg.) Cox Diatoms 0.07% Encyonema minutum (Hilse) Mann Diatoms 0.17% Scenedesmus spinosus Chodat Green algae 1.77% Navicula schroeteri var. escambia Patr. Diatoms 0.03% Navicula gregaria Donk. Diatoms 0.03% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.07% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.21% Ankistrodesmus falcatus (Corda) Ralfs Green algae 0.09% Nitzschia fonticola Grun. Diatoms 0.10% Merismopedia tenuissima Lemmermann Blue-green algae 8.15% Navicula decussis Østr. Diatoms 0.03% Achnanthes exigua var. heterovalva Krasske Diatoms 0.10% Nitzschia debilis Arnott Diatoms 0.03% Brachysira neoexilis Lange-Bertalot Diatoms 0.03% Nitzschia cf. lacuum Lange-Bert. Diatoms 0.07% Navicula reichardtiana Lange-Bert. Diatoms 0.03% Cymbella hustedtii Krass. Diatoms 0.03% Navicula subminuscula Mang. Diatoms 0.03% Totals (cell density and biovolume) 2,983,663 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
TM-3 9/19/2002 Subsample Identifier A

Cymbella turgidula Grunow Diatoms 19.31% Synedra ulna (Nitz.) Ehr. Diatoms 0.65% Encyonopsis microcephala (Grun.) Kram. Diatoms 1.64% Cymbella hustedtii Krass. Diatoms 10.47% Cymbella mesiana Cholnoky Diatoms 0.98% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 50.24% Hippodonta capitata (Ehrenberg) Lange-Bertalot, Metzeltin et Witkowski Diatoms 0.33% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.49% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 1.64% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 4.58% Gomphonema patrickii Kociolek & Stoermer Diatoms 1.23% Gomphonema turris Ehrenberg Diatoms 0.25% Navicula notha Wallace Diatoms 1.80% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.98% Cyclotella meneghiniana Kütz. Diatoms 0.33% Navicula cryptocephala Kütz. Diatoms 0.82% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.33% Encyonema minutum (Hilse) Mann Diatoms 0.49% Nitzschia amphibia Grun. Diatoms 0.49% Cosmarium granatum Bréb. ex Ralfs Green algae 0.99% Planothidium rostratum (Østrup) Lange-Bertalot Diatoms 0.49% Geissleria decussis (Hustedt) Lange-Bertalot et Metzeltin Diatoms 0.16% Euastrum ciastonii Raciborski Green algae 0.33% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.65% Nitzschia fonticola Grun. Diatoms 0.16% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 0.16% Totals (cell density and biovolume) 1,767,127 

TM-3 9/19/2002 Subsample Identifier B

Closterium moniliferum Ehrenberg Green algae 0.33% Cymbella turgidula Grunow Diatoms 15.12% Synedra ulna (Nitz.) Ehr. Diatoms 0.65% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 55.76% Cymbella hustedtii Krass. Diatoms 5.04% Rhopalodia gibba (Ehr.) O. Müll. Diatoms 0.16% Encyonema silesiacum (Bleisch) Mann Diatoms 0.65% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 6.83% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 1.14% Navicula cryptocephala Kütz. Diatoms 1.30% Navicula notha Wallace Diatoms 1.95% Gomphonema gracile Ehr. emend. V. H. Diatoms 0.27% Synedra acus Kützing Diatoms 0.16% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.81% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.81% Fragilaria vaucheriae (Kützing) Petersen Diatoms 0.81% Gomphonema patrickii Kociolek & Stoermer Diatoms 0.54% Encyonopsis microcephala (Grun.) Kram. Diatoms 2.11% Nitzschia amphibia Grun. Diatoms 0.49% Cosmarium margaritatum (Lund) Roy & Biss. Green algae 0.99% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.65% Achnanthidium pyrenaicum (Hustedt) Kobayasi Diatoms 0.81% Psammothidium subatomoides (Hustedt) Bukhtiyarova et Round Diatoms 0.65% Planothidium rostratum (Østrup) Lange-Bertalot Diatoms 0.49% Geissleria decussis (Hustedt) Lange-Bertalot et Metzeltin Diatoms 0.16% Micrasterias radiosa Ralfs Green algae 0.33% Scenedesmus quadricauda (Turp.) Bréb. Green algae 0.66% Nitzschia fonticola Grun. Diatoms 0.16% Nitzschia perminuta (Grun.) Peragallo Diatoms 0.16% Totals (cell density and biovolume) 2,320,269 

TM-3 9/19/2002 Subsample Identifier C Spirogyra sp. Green algae 0.61% 

Cymbella turgidula Grunow Diatoms 12.86% Synedra ulna (Nitz.) Ehr. Diatoms 0.49% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 56.70% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Cymbella hustedtii Krass. Diatoms 9.72% Cymbella mesiana Cholnoky Diatoms 0.33% Fragilaria capucina var. rumpens (Kützing) Lange-Bertalot Diatoms 6.43% Gomphonema patrickii Kociolek & Stoermer Diatoms 1.83% Gomphonema parvulum (Kütz.) Kütz. Diatoms 1.83% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 1.65% Encyonema silesiacum (Bleisch) Mann Diatoms 0.33% Navicula cryptocephala Kütz. Diatoms 1.15% Cocconeis placentula var. lineata (Ehr.) V. H. Diatoms 0.33% Gomphonema gracile Ehr. emend. V. H. Diatoms 0.30% Nitzschia amphibia Grun. Diatoms 0.99% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.33% Navicula notha Wallace Diatoms 0.99% Cymbella affinis Kütz. Diatoms 0.16% Encyonema minutum (Hilse) Mann Diatoms 0.66% Gomphonema subclavatum var. mexicanum (Grun. in V. H.) Patr. Diatoms 0.16% Planothidium rostratum (Østrup) Lange-Bertalot Diatoms 0.49% Achnanthidium exiguum var. heterovalvum (Krasske) Czarnecki Diatoms 0.33% Psammothidium subatomoides (Hustedt) Bukhtiyarova et Round Diatoms 0.49% Encyonopsis microcephala (Grun.) Kram. Diatoms 0.49% Nitzschia fonticola Grun. Diatoms 0.33% Totals (cell density and biovolume) 1,948,694 

TM-4 9/13/2000 Subsample Identifier A

Scenedesmus acutus Meyen Green algae 58.62% Scenedesmus quadricauda (Turp.) Bréb. Green algae 20.74% Unknown alga flagellate (<10 μ) Unknown Phyla 4.29% Achnanthes exigua var. heterovalva Krasske Diatoms 5.04% Anabaena oscillarioides Bory Blue-green algae 2.49% Placoneis elginensis (Greg.) Cox Diatoms 0.11% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.03% Planothidium lanceolatum Diatoms 0.25% Glenodinium sp. Dinoflagellates 0.20% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Psammothidium bioretii (Germ.) Bukht. et Round Diatoms 0.03% Oscillatoria sp. 1 ANS FWA Blue-green algae 6.78% Navicula submuralis Hust. Diatoms 0.66% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.17% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.39% Achnanthes oblongella Østrup Diatoms 0.13% Cymbella affinis Kütz. Diatoms 0.02% Nitzschia sinuata var. tabellaria (Grun.) Grun. in V.H. Diatoms 0.02% Synedra rumpens Kütz. Diatoms 0.01% Totals (cell density and biovolume) 1,175,777 

TM-4 9/13/2000 Subsample Identifier B Scenedesmus acutus Meyen Green algae 70.45% 

Anabaena oscillarioides Bory Blue-green algae 13.31% Chlamydomonas sp. Green algae 1.46% Scenedesmus quadricauda (Turp.) Bréb. Green algae 7.47% Unknown alga flagellate (<10 μ) Unknown Phyla 2.19% Achnanthes exigua var. heterovalva Krasske Diatoms 1.60% Caloneis amphisbaena (Bory) Cleve Diatoms 0.01% Euglena sp. Euglenoids 0.08% Navicula submuralis Hust. Diatoms 0.49% Oscillatoria sp. 1 ANS FWA Blue-green algae 2.60% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.05% Planothidium lanceolatum Diatoms 0.04% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.00% Navicula arvensis Hust. Diatoms 0.07% Cryptomonas sp. Cryptophytes 0.08% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.07% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.00% Neidium alpinum Hust. Diatoms 0.01% Achnanthes oblongella Østrup Diatoms 0.01% Totals (cell density and biovolume) 1,356,704 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
TM-4 9/13/2000 Subsample Identifier C

Scenedesmus acutus Meyen Green algae 51.93% Achnanthes exigua var. heterovalva Krasske Diatoms 13.06% Anabaena oscillarioides Bory Blue-green algae 6.13% Planothidium lanceolatum Diatoms 1.81% Unknown alga flagellate (<10 μ) Unknown Phyla 3.14% Neidium ampliatum (Ehr.) Kramm. Diatoms 0.04% Scenedesmus quadricauda (Turp.) Bréb. Green algae 5.71% Capartogramma crucicula (Grun. ex Cl.) Ross Diatoms 0.11% Chlamydomonas sp. Green algae 0.43% Navicula submuralis Hust. Diatoms 3.23% Navicula arvensis Hust. Diatoms 1.88% Eunotia exigua (Bréb. ex Kütz.) Rabh. Diatoms 0.57% Placoneis elginensis (Greg.) Cox Diatoms 0.14% Oscillatoria sp. 1 ANS FWA Blue-green algae 10.27% Cryptomonas sp. Cryptophytes 0.86% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.46% Neidium alpinum Hust. Diatoms 0.14% Achnanthes oblongella Østrup Diatoms 0.11% Totals (cell density and biovolume) 896,326 

CEN 9/14/2000 Subsample Identifier A

Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 59.48% Achnanthes exigua var. heterovalva Krasske Diatoms 9.11% Nitzschia amphibia Grun. Diatoms 1.56% Oscillatoria sp. 1 ANS FWA Blue-green algae 17.04% Lyngbya sp. 1 ANS FWA Blue-green algae 9.88% Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.07% Scenedesmus acutus Meyen Green algae 0.94% Scenedesmus acuminatus (Lagerh.) Chod. Green algae 0.75% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.15% Diadesmis confervacea Kütz. Diatoms 0.11% Scenedesmus quadricauda (Turp.) Bréb. Green algae 0.19% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Scenedesmus ecornis (Ralfs) Chod. Green algae 0.56% Gomphonema minutum (Ag.) Ag. Diatoms 0.04% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.04% Navicula seminulum Grun. Diatoms 0.07% Totals (cell density and biovolume) 4203371 

CEN 9/14/2000 Subsample Identifier B Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 63.59% 

Achnanthes exigua var. heterovalva Krasske Diatoms 14.03% Nitzschia amphibia Grun. Diatoms 1.04% Lyngbya sp. 1 ANS FWA Blue-green algae 9.83% Hydrocoleum brebissonii Kütz. Blue-green algae 1.70% Scenedesmus acutus Meyen Green algae 1.70% Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.10% Oscillatoria sp. 1 ANS FWA Blue-green algae 6.67% Scenedesmus acuminatus (Lagerh.) Chod. Green algae 0.73% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.16% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.05% Scenedesmus quadricauda (Turp.) Bréb. Green algae 0.24% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.05% Diadesmis confervacea Kütz. Diatoms 0.05% Navicula seminulum Grun. Diatoms 0.05% Totals (cell density and biovolume) 2,561,002 

CEN 9/14/2000 Subsample Identifier C Amphithrix janthina (Mont.) Born. and Flah. Blue-green algae 66.92% 

Hydrocoleum brebissonii Kütz. Blue-green algae 9.68% Achnanthes exigua var. heterovalva Krasske Diatoms 6.73% Mougeotia sp. Green algae 0.10% Scenedesmus acutus Meyen Green algae 3.24% Oscillatoria sp. 1 ANS FWA Blue-green algae 9.73% Nitzschia amphibia Grun. Diatoms 0.49% Scenedesmus acuminatus (Lagerh.) Chod. Green algae 0.61% Lyngbya sp. 1 ANS FWA Blue-green algae 2.13% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.02% Nitzschia palea (Kütz.) W. Sm. Diatoms 0.07% Sellaphora pupula (Kütz.) Meresckowsky Diatoms 0.02% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.02% Scenedesmus ecornis (Ralfs) Chod. Green algae 0.20% Navicula seminulum Grun. Diatoms 0.02% Totals (cell density and biovolume) 5,360,029 

TSB 9/13/2000 Subsample Identifier A

Diadesmis confervacea Kütz. Diatoms 13.09% Hydrocoleum brebissonii Kütz. Blue-green algae 28.15% Nitzschia amphibia Grun. Diatoms 6.55% Nitzschia palea (Kütz.) W. Sm. Diatoms 2.22% Oscillatoria sp. 1 ANS FWA Blue-green algae 31.74% Achnanthes exigua var. heterovalva Krasske Diatoms 3.46% Gomphonema patrickii Kociolek & Stoermer Diatoms 0.25% Navicula minima Grun. Diatoms 4.94% Euglena sp. Euglenoids 0.13% Gomphonema parvulum (Kütz.) Kütz. Diatoms 0.86% Gomphonema augur var. turris (Ehr.) Lange-Bert. Diatoms 0.12% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 2.10% Scenedesmus acuminatus (Lagerh.) Chod. Green algae 1.06% Navicula laevissima Kütz. Diatoms 0.12% Navicula seminulum Grun. Diatoms 0.49% Caloneis bacillum (Grun.) Cl. Diatoms 0.12% Scenedesmus ecornis (Ralfs) Chod. Green algae 1.86% Navicula cryptocephala Kütz. Diatoms 0.12% Nitzschia fonticola Grun. Diatoms 0.37% Cyclotella atomus Hust. Diatoms 0.12% Nitzschia archibaldii Lange-Bertalot Diatoms 2.10% Totals (cell density and biovolume) 4,586,021 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
TSB 9/13/2000 Subsample Identifier B Diadesmis confervacea Kütz. Diatoms 23.46% 

Nitzschia amphibia Grun. Diatoms 8.60% Pinnularia brebissonii (Kütz.) Rabh. Diatoms 0.18% Hydrocoleum brebissonii Kütz. Blue-green algae 9.37% Scenedesmus acuminatus (Lagerh.) Chod. Green algae 6.88% Gomphonema parvulum (Kütz.) Kütz. Diatoms 3.22% Nitzschia palea (Kütz.) W. Sm. Diatoms 1.97% Achnanthes exigua var. heterovalva Krasske Diatoms 4.84% Navicula minima Grun. Diatoms 7.52% Oscillatoria sp. 1 ANS FWA Blue-green algae 21.41% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.18% Navicula seminulum Grun. Diatoms 1.07% Cyclotella meneghiniana Kütz. Diatoms 0.18% Lyngbya sp. 1 ANS FWA Blue-green algae 5.54% Scenedesmus ecornis (Ralfs) Chod. Green algae 3.06% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.90% Navicula subminuscula Mang. Diatoms 0.72% Encyonema minutum (Hilse) Mann Diatoms 0.18% Gomphonema kobayasii Kociolek & Kingston Diatoms 0.18% Nitzschia fonticola Grun. Diatoms 0.18% Nitzschia archibaldii Lange-Bertalot Diatoms 0.36% Totals (cell density and biovolume) 2069048 

TSB 9/13/2000 Subsample Identifier C Oedogonium sp. Green algae 2.41% 

Diadesmis confervacea Kütz. Diatoms 28.40% Hydrocoleum brebissonii Kütz. Blue-green algae 19.66% Nitzschia amphibia Grun. Diatoms 8.65% Euglena sp. Euglenoids 0.34% Navicula clementis Grun. Diatoms 0.16% Oscillatoria sp. 1 ANS FWA Blue-green algae 24.48% Scenedesmus acuminatus (Lagerh.) Chod. Green algae 3.45% 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)
Nitzschia palea (Kütz.) W. Sm. Diatoms 1.14% Achnanthes exigua var. heterovalva Krasske Diatoms 3.26% Nitzschia intermedia Hantz. ex Cl. et Grun. Diatoms 0.33% Gomphonema parvulum (Kütz.) Kütz. Diatoms 1.14% Achnanthes lanceolata var. rostrata Hust. Diatoms 0.16% Navicula minima Grun. Diatoms 2.94% Navicula seminulum Grun. Diatoms 0.98% Achnanthidium minutissimum (Kütz.) Czarnecki Diatoms 0.82% Nitzschia fonticola Grun. Diatoms 0.49% Navicula subminuscula Mang. Diatoms 0.49% Scenedesmus ecornis (Ralfs) Chod. Green algae 0.69% Totals (cell density and biovolume) 2,929,878 

Appendix table 3-2. Periphyton taxa and cell density and biovolume by taxon for samples from selected sites in the Threemile Creek bas

2000–2002.—Continued

[cells/cm2, cells per square centimeter; μm3/cm2, cubic micrometers per square centimeter; μm,micrometer]

Scientific name Algae group

Percentage o

Cell density

(cells/cm2)