U.S. Department of the Interior

U.S. Geological Survey

Assessment of Stream Conditions and Trends

in Biological and Water-Chemistry Data From Selected Streams

in Chester County, Pennsylvania, 1981-97

by Andrew G. Reif

Water-Resources Investigations Report 02-4242

In cooperation with

CHESTER COUNTY WATER RESOURCES AUTHORITY

New Cumberland, Pennsylvania

2002
ii

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information Copies of this report may be Copies of this report also

write to: purchased from: are available from:

District Chief U.S. Geological Survey Chester County Water Resources Authority

U.S. Geological Survey Branch of Information Services Government Services Center, Suite 270

215 Limekiln Road Box 25286 601 Westtown Road

New Cumberland, Pennsylvania 17070-2424 Denver, Colorado 80225-0286 West Chester, Pennsylvania 19382-4537

Internet: http://pa.water.usgs.gov Telephone: 1-888-ASK-USGS Internet: http://www.chesco.org/water/

index.html
iii

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

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of network and previous investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Hydrologic conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Sampling and analytical methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Field measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Chemical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Biological analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Stream-quality assessment and trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Biological metrics evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Stream-quality assessment criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Reference reaches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Assessment of stream quality using benthic-macroinvertebrate data . . . . . . . . . . . . . . . . . . . . . . . 9

Schuylkill River Basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Pigeon Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Stony Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

French Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Pickering Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Valley Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Delaware River Basin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Darby Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Crum Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Ridley Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

East Branch Chester Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Brandywine Creek Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

West Branch Brandywine Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

East Branch Brandywine Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Main Stem Brandywine Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Red Clay and White Clay Creek Basins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Red Clay Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

White Clay Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

CONTENTS

Page
iv

Stream-quality assessment and trends—Continued

Big Elk and Octoraro Creek Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Big Elk Creek. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

East Branch Octoraro Creek . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Summary of stream-quality conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Trend analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Mann-Kendall test for trend in biological metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Mann-Kendall test for trend in chemical constituents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Specific conductance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Ammonia and phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Stream-bottom sediment samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Selected metals and trace elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Arsenic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Cadmium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Chromium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Copper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Lead. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Zinc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Organochlorine insecticides and polychlorinated biphenyls . . . . . . . . . . . . . . . . . . . . . . . . 41

Chlordane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

DDT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

DDD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

DDE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Dieldrin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

PCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

References cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Appendix 1. Systematic checklist of taxa reported from the Stream Conditions of Chester County

Biological Monitoring Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

CONTENTS—Continued

Page
v

Figure 1. Map showing biological sampling sites and major drainage basin divides in

Chester County, Pennsylvania, and surrounding area . . . . . . . . . . . . . . . . . . . . . . . 2

2-3. Boxplots showing:

2. Range of Hilsenhoff’s biotic index (HBI) values from reference site (site 15),

Pigeon Creek (site 10), and Stony Run (site 6), 1981-97 . . . . . . . . . . . . 10

3. Taxa richness and Ephemeroptera, Plecoptera, and Trichoptera (EPT)

taxa richness from French Creek near Phoenixville

(site 15) and French Creek at Phoenixville (site 16), 1981-97 . . . . . . . . 12

4-6. Graphs showing:

4. Concentrations of zinc and lead and number of Ephemeroptera, Plecoptera,

and Trichoptera (EPT) taxa from French Creek at Phoenixville (site 16),

1981-87. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. Taxa richness and ammonia concentration at Pickering Creek at

Charlestown (site 4), 1981-89. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6. Median values of taxa richness and Ephemeroptera, Plecoptera, and

Trichoptera (EPT) taxa richness from sites in Pickering Creek Basin

and the reference site, 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

7-8. Pie diagrams showing:

7. Community composition of benthic-macroinvertebrate communities

in Valley Creek (site 50) and Little Valley Creek (site 49), 1994 . . . . . . . 14

8. Community composition of benthic-macroinvertebrate communities at

sites 20 and 21 on Ridley Creek, 1996 . . . . . . . . . . . . . . . . . . . . . . . . . . 16

9. Graph showing Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa and

manganese concentrations from East Branch Chester Creek at Greenhill (site 22),

1981-92 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

10. Pie diagrams showing community composition of benthic-macroinvertebrate

communities from the reference site (site 15), East Branch Chester Creek

at Westtown (site 24), and Goose Creek (site 25), 1995 . . . . . . . . . . . . . . . . . . . . 18

11. Boxplots showing concentrations of nitrate, ammonia, and phosphorus from

the reference site (site 15), East Branch Chester Creek at Westtown (site 24),

Goose Creek (site 25), and East Branch Chester Creek below Goose Creek

(site 51), 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

12-13. Graphs showing:

12. Taxa richness and phosphorus concentrations from West Branch

Brandywine Creek at Wawaset (site 38), 1981-97 . . . . . . . . . . . . . . . . . 20

13. Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness from

Buck Run (site 46) and West Branch Brandywine Creek at Wawaset

(site 38), 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

14. Boxplots showing taxa richness, Ephemeroptera, Plecoptera, and Trichoptera (EPT)

taxa richness, and Hilsenhoff’s biotic index (HBI) values from reference site

(site 15), East Branch Brandywine Creek near Downingtown (site 36), West Valley

Creek (site 44), and East Branch Brandywine Creek at Wawaset (site 39),

1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

ILLUSTRATIONS

Page
vi

Figure 15. Graph showing Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness

from site 42 and site 36 on the East Branch Brandywine Creek, 1981-95 . . . . . . . 23

16. Boxplots showing Hilsenhoff’s biotic index (HBI) values from reference site (site 45),

East Branch Red Clay Creek (site 26), and West Branch Red Clay Creek

(site 27), 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

17. Pie diagrams showing community composition of benthic-macroinvertebrate

communities from the reference site (site 45), East Branch Red Clay Creek

(site 26), and West Branch Red Clay Creek (site 27), 1994 . . . . . . . . . . . . . . . . . . 25

18-19. Graphs showing:

18. Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness from

reference site (site 45), East Branch Red Clay Creek (site 26),

and West Branch Red Clay Creek (site 27), 1981-97 . . . . . . . . . . . . . . . 26

19. Numbers of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa from

East Branch White Clay Creek (site 28), Middle Branch White Clay

Creek (site 29), and West Branch White Clay Creek (site 30),

1981-97. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

20. Boxplots showing Hilsenhoff’s biotic index (HBI) values for the reference site

(site 45), East Branch White Clay Creek (site 28), Middle Branch White Clay

Creek (site 29), and West Branch White Clay Creek (site 30), 1981-97 . . . . . . . . . 27

21. Graph showing median values of taxa richness and Ephemeroptera, Plecoptera,

and Trichoptera (EPT) taxa richness from sampling sites in the Red Clay and

White Clay Creek Basins, 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

22. Pie diagrams showing community composition of reference site (site 45),

East Branch Big Elk Creek (site 31), and West Branch Big Elk Creek (site 32),

1993 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

23-27. Graphs showing:

23. Number of Ephemeroptera, Plecoptera, and Trichoptera

(EPT) taxa from the reference site (site 45), East Branch Big Elk

Creek (site 31), and West Branch Big Elk Creek (site 32), 1981-96 . . . . 30

24. Hilsenhoff’s biotic index (HBI) values from East Branch Octoraro Creek

(site 33) and Valley Creek (site 34), 1981-96 . . . . . . . . . . . . . . . . . . . . . 31

25. Nitrate concentrations from the reference site (site 45), East Branch

Octoraro Creek (site 33), and Valley Creek (site 34), 1981-96 . . . . . . . . 31

26. Specific conductance from selected sites, 1981-97. . . . . . . . . . . . . . . . . . . . 34

27. Results of Mann-Kendall test for trend in nitrate from selected sites in

various basins, 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

28. Boxplots showing nitrate concentrations from selected sites, 1981-97 . . . . . . . . . . . . . 35

29. Map showing sampling sites with metal or trace-element concentration above

the threshold effect concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

30. Graph showing percentage of stream-bottom sediment samples with detectable

concentrations of selected pesticides and PCB from selected streams, 1983-97. . 43

31. Boxplots showing concentrations of pesticides and PCBs in stream-bottom sediment

samples from selected streams, 1983-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

ILLUSTRATIONS—Continued

Page
vii

Table 1. U.S. Geological Survey station identification numbers, site numbers, names,

drainage areas, and period of record of sites in the Stream Conditions of

Chester County Biological Monitoring Network, Pennsylvania, 1981-97 . . . . . . . . . 4

2. List of taxonomic references used to identify benthic-macroinvertebrate samples . . . . . 7

3. Stream-quality assessment criteria for Chester County streams. . . . . . . . . . . . . . . . . . . 8

4. Assessment of stream conditions on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Schuylkill River Basin, 1981-97 . . . . . . 9

5. Assessment of stream quality on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Delaware River Basin,

1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6. Assessment of stream quality on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Brandywine Creek Basin,

1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

7. Assessment of stream quality on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Red Clay and White Clay Creek

Basins, 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8. Assessment of stream quality on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Big Elk and Octoraro Creek Basins,

1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

9. Mann-Kendall test of taxa richness, EPT taxa richness, and HBI from selected

streams in Chester County, Pennsylvania, 1981-97 . . . . . . . . . . . . . . . . . . . . . . . . 32

10. Mann-Kendall test of specific conductance and concentrations of nitrate, ammonia,

and phosphorus from selected streams in Chester County, Pennsylvania,

1981-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

11. Occurrence of selected trace elements in samples of stream-bottom sediment

collected in Chester County, Pennsylvania, 1984-97 . . . . . . . . . . . . . . . . . . . . . . . 37

12. Occurrence of selected organochlorine insecticides and polychlorinated biphenyls

in samples of stream-bottom sediment collected at 43 sites in Chester County,

Pennsylvania, 1984-97 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

13. Concentrations of organochlorine insecticides and gross polychlorinated

biphenyls greater than the threshold effect concentration from stream-bottom

sediment samples collected in Chester County, Pennsylvania, 1983-97 . . . . . . . . 42

14-27. Values of total individuals, taxa richness, EPT taxa richness, percentage of EPT

individuals, and Hilsenhoff’s biotic index from the Schuylkill River Basin, 1981-97:

14. Pigeon Creek near Parker Ford (site 10). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

15. Stony Run near Spring City (site 6). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

16. French Creek near Coventryville (site 13). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

17. South Branch French Creek at Coventryville (site 12) . . . . . . . . . . . . . . . . . . . 52

18. French Creek near Pughtown (site 14) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

19. French Creek near Phoenixville (site 15) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

20. French Creek at Railroad Bridge at Phoenixville (site 16). . . . . . . . . . . . . . . . . 54

TABLES

Page
viii

Tables 14-27. Values of total individuals, taxa richness, EPT taxa richness, percentage of EPT

individuals, and Hilsenhoff’s biotic index from the Schuylkill River Basin,

1981-97—Continued:

21. Pickering Creek near Eagle (site 1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

22. Pickering Creek near Chester Springs (site 2) . . . . . . . . . . . . . . . . . . . . . . . . . 55

23. Pickering Creek at Merlin (site 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

24. Pickering Creek at Charlestown Road at Charlestown (site 4) . . . . . . . . . . . . . 56

25. Pickering Creek near Phoenixville (site 5). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

26. Little Valley Creek at Howellville (site 49) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

27. Valley Creek near Valley Forge (site 50) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

28-36. Values of total individuals, taxa richness, EPT taxa richness, percentage of EPT taxa,

and Hilsenhoff’s biotic index from the Delaware River Basin, 1981-97:

28. Darby Creek at Waterloo Mills near Devon (site 17) . . . . . . . . . . . . . . . . . . . . . 58

29. Crum Creek at Whitehorse (site 19) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

30. Ridley Creek at Goshenville (site 20) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

31. Ridley Creek at Dutton Mill near West Chester (site 21). . . . . . . . . . . . . . . . . . 59

32. East Branch Chester Creek at Green Hill (site 22) . . . . . . . . . . . . . . . . . . . . . . 60

33. East Branch Chester Creek at Milltown (site 23). . . . . . . . . . . . . . . . . . . . . . . . 60

34. East Branch Chester Creek at Westtown (site 24) . . . . . . . . . . . . . . . . . . . . . . 61

35. Goose Creek Tributary to East Branch Chester Creek near West

Chester (site 25) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

36. East Branch Chester Creek below Goose Creek near West Chester

(site 51) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

37-47. Values of total individuals, taxa richness, EPT taxa richness, percentage of

EPT taxa, and Hilsenhoff’s biotic index from the Brandywine Creek Basin,

1981-97:

37. West Branch Brandywine Creek at Rock Run (site 37). . . . . . . . . . . . . . . . . . . 62

38. Buck Run at Doe Run (site 46) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

39. Doe Run at Springdell (site 45). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

40. West Branch Brandywine Creek at Wawaset (site 38) . . . . . . . . . . . . . . . . . . . 64

41. East Branch Brandywine Creek near Cupola (site 48) . . . . . . . . . . . . . . . . . . . 64

42. East Branch Brandywine Creek at Glenmoore (site 42) . . . . . . . . . . . . . . . . . . 65

43. Indian Run near Springton (site 47) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

44. East Branch Brandywine Creek near Downingtown (site 36) . . . . . . . . . . . . . . 66

45. Valley Creek at Mullsteins Meadow near Downingtown (site 44) . . . . . . . . . . . 66

46. East Branch Brandywine Creek at Wawaset (site 39). . . . . . . . . . . . . . . . . . . . 67

47. Brandywine Creek near Chadds Ford (site 40) . . . . . . . . . . . . . . . . . . . . . . . . . 67

TABLES—Continued

Page
ix

Tables 48-52. Values of total individuals, taxa richness, EPT taxa richness, percentage of EPT

taxa, and Hilsenhoff’s biotic index from the Red Clay and White Clay Creek

Basins, 1981-97:

48. West Branch Red Clay Creek at Kennett Square (site 27) . . . . . . . . . . . . . . . . 68

49. East Branch Red Clay Creek near Five Point (site 26) . . . . . . . . . . . . . . . . . . . 68

50. East Branch White Clay Creek at Avondale (site 28) . . . . . . . . . . . . . . . . . . . . 69

51. Middle Branch White Clay Creek at Wickerton (site 29) . . . . . . . . . . . . . . . . . . 69

52. West Branch White Clay Creek near Chesterville (site 30). . . . . . . . . . . . . . . . 70

53-56. Values of total individuals, taxa richness, EPT taxa richness, percentage of EPT taxa,

and Hilsenhoff’s biotic index from the Big Elk and Octoraro Creek Basins, 1981-97:

53. East Branch Big Elk Creek at Elkview (site 31). . . . . . . . . . . . . . . . . . . . . . . . . 70

54. West Branch Big Elk Creek near Oxford (site 32) . . . . . . . . . . . . . . . . . . . . . . . 71

55. East Branch Octoraro Creek at Christiana (site 33) . . . . . . . . . . . . . . . . . . . . . 71

56. Valley Creek near Atglen (site 34). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

TABLES—Continued

Page
x

Abbreviated water-quality units used in this report

micrograms per gram (μg/g)

micrograms per kilogram (μg/kg)

milligram per liter (mg/L)

millimeter (mm)

micron (μm)

inch (in.) 2.54 centimeter

foot (ft) 0.3048 meter

square mile (mi2) 2.590 square kilometer

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

degree Fahrenheit (°F) °C = 5/9 (°F-32) degree Celsius

CONVERSION FACTORS AND ABBREVIATIONS

Multiply By To obtain
1

Assessment of Stream Conditions and Trends

in Biological and Water-Chemistry Data

from Selected Streams in Chester County, Pennsylvania, 1981-97

by Andrew G. Reif

ABSTRACT

Biological, chemical, and physical data were collected from a network of 43 sites in Chester County,

Pa., from 1981 to 1997. The goal of the network is to assess stream conditions and determine trends in

benthic-macroinvertebrate and water-chemistry data. Most sites in the network were assessed as

nonimpacted or slightly impacted on the basis of biological metric analysis of benthic-macroinvertebrate

data. Sites assessed as impacted were affected by habitat degradation, organic pollution, or toxins.

Analysis of calculated biological metrics indicates that most sites were assessed as nonimpacted or slightly

impacted between 1981 and 1997. Sites in the Pigeon, French, Pickering, and upper East Branch

Brandywine Creek Basins generally were assessed as nonimpacted with stable physical and chemical data

through the 17-year period. Sites in the Darby, Crum, Ridley, Valley, and lower East Branch Brandywine

Creek Basins are being degraded from the reference conditions, primarily because of habitat alteration.

The areas with the poorest stream quality were sites with greater than 50 percent agricultural land use,

sites with greater than 10 percent impervious surface, and sites affected by wastewater-treatment plant

discharges. These sites are being degraded by erosion, sedimentation, and nutrient enrichment. Trend

analysis indicates that calculated biological metrics at most sites improved or remained unchanged

between 1981 and 1997. Trend analysis on chemical constituents indicated that concentrations of nitrate

and chloride were increasing, and concentrations of phosphorus and ammonia were unchanged or

declining across Chester County from 1981 to 1997. The highest concentrations of ammonia and chloride

were at locations affected by wastewater-treatment plant discharges. Concentrations of pesticides and

other organic compounds in stream-bottom sediments decreased between 1983 and 1997 but these

compounds still are present at low concentrations throughout Chester County.

INTRODUCTION

The Chester County Water Resources Authority (CCWRA) and the U.S. Geological Survey (USGS)

established a long-term stream-quality monitoring network in 1970. The goal of the network is to assess

the quality of streams in Chester County, Pa., and to further the understanding of stream changes in

response to urbanization using benthic-macroinvertebrate data (Lium, 1977). Benthic macroinvertebrates

are aquatic insects and other invertebrates that live on the stream bottom. They are useful in evaluating

stream quality because their habitat preference and low mobility cause them to be affected directly by

water quality, physical conditions, and riparian habitat. By evaluating the diversity and community

structure of benthic-macroinvertebrate populations, a determination of stream quality can be made.

Samples of benthic macroinvertebrates and stream water for the Stream Conditions of Chester

County Biological Monitoring Network have been collected annually from up to 51 sites since 1970.

Samples of stream-bottom sediment have been collected twice at most sampling sites and have been

analyzed for metals and pesticides. This database represents one of the longest nearly continuous waterquality data sets in the country. Data from 1970 to 1980 were analyzed for trends in benthic-macroinvertebrate diversity by Moore (1987).

The streams included in the network drain nearly 95 percent of the county (fig. 1). Valley Creek,

Pickering Creek, Stony Run, Pigeon Creek, and French Creek are tributaries to the Schuylkill River. Darby,

Crum, Ridley, and Chester Creeks are tributaries to the Delaware River. Buck Run, Doe Run, Indian Run,

and Valley Creek (also called West Valley Creek) are tributaries to the Brandywine Creek. Red Clay, White

Clay, and Brandywine Creeks are tributaries to the Christina River, itself a tributary to the Delaware River.
2

Big Elk Creek flows into the Chesapeake Bay. Octoraro Creek is a tributary to the Susquehanna River. All

streams sampled originate within the boundaries of Chester County, except for the headwaters of the West

Branch Brandywine, French, and Octoraro Creeks. The Octoraro Creek forms part of the western border of

the county, and its headwaters lie in both Chester and Lancaster Counties (fig. 1).

Figure 1. Biological sampling sites and major drainage basin divides in Chester County, Pennsylvania, and

surrounding area.

02 68 4 MILES

KILOMETERS

COUNTY BOUNDARY

EXPLANATION

02 68 4 STATE BOUNDARY

76°

75°45′

75°30′

40°

39°45′

40

CHESTER

PENNSYLVANIA

Schuylkill River Watershed

Brandywine Creek Watershed

Big Elk Creek

Watershed

Pequea Creek

DELAWARE

Marsh Creek

Reservoir

Rock Run

Reservoir

36

14

6

1

5

50

49

17

21

20

51

24

23

25

Delaware

River Watershed

44

48

37

22

33

32

30

29

28 26

27

2

13 10

15

16

47

42

12

3

19

34 38 39

4

46

45

31

Watershed

Octoraro Creek

Watershed

Northeast Creek

COUNTY

LANCASTER

COUNTY

PHILADELPHIA

Watershed

Christina River Watershed

PENNSYLVANIA

MARYLAND

10 BIOLOGICAL SAMPLING STATION

AND IDENTIFICATION NUMBER

WATERSHED BOUNDARY
3

Purpose and Scope

This report evaluates chemical, biological, and field data collected from 1981 to 1997 as part of the

Stream Conditions of Chester County Biological Monitoring Network. Stream-quality conditions were

assessed by analyzing benthic-macroinvertebrate communities. Trends in benthic-macroinvertebrate

diversity were analyzed to evaluate changes in stream quality over time. Chemical data were evaluated for

trends and relations between chemical and benthic-macroinvertebrate data. The results of this report will

allow Chester County government agencies to identify streams or reaches of streams that are biologically

stressed and will allow them to assess the effects of past environmental and land-use practices. This

information also will assist Chester County and its municipalities in future land-use and resourcemanagement decisions in support of Chester County’s Landscapes Program (Chester County, 1996) and

other related programs.

Description of Network and Previous Investigations

This investigation began in the fall of 1969 with a reconnaissance of Chester County to determine the

general conditions of streams and land-use patterns. In 1970, the reconnaissance served as a guide to

establishing a chemical and biological stream-quality network of 50 sites in 13 stream basins. The sites

were established on the basis of equal cumulative square miles of drainage area within each basin (Lium,

1977). The sites also were established away from any known point source of pollution so that the water

quality of the overall stream could be assessed. Twelve sites were added and 9 sites were discontinued

between 1972 and 1982. Forty-three sites were sampled between 1981 and 1997. The locations of the

43 sampling sites are shown in figure 1, and drainage areas and periods of record are listed in table 1. This

network of sampling sites and the biological, physical, and chemical data collected at these sites between

1981 and 1997 are the basis for this investigation.

The physical, chemical, and biological data, which this investigation is based on, are contained in

three USGS data reports. Complete analytical and biological results are given by Moore (1989) for 1969-80,

by Reif (1999) for 1981-94, and by Reif (2000) for 1995-97. The physical and chemical data for the 1974-97

water years1 also have been published in the USGS annual water-resources data reports for Pennsylvania

(U.S. Geological Survey, 1975-98).

Lium (1977) developed a biotic index that used a 10-point rating scale to assess the environmental

conditions at the 50 sites on the basis of data published in his 1976 report (Lium, 1976). The ratings

developed by Lium indicated most streams studied were experiencing nutrient enrichment and (or)

sediment deposition. In 1967-68, a study was conducted by Miller and others (1971) in the Pickering and

East Branch Brandywine Creek Basins to document the present hydrologic conditions of these two small

basins prior to urbanization.

Moore (1987) evaluated the physical, chemical, and biological data collected as part of the Stream

Conditions of Chester County program from 1969 to 1980. This study showed statistically valid upward

trends in Brillouin’s diversity index during 1970-80 at 27 sites, which indicate improved environmental

quality. Both Lium (1977) and Moore (1987) observed that total dissolved solids correlated significantly

with the biotic index and the diversity index.

A report by Sloto (1987) evaluated the effects of urbanization on the water resources of four basins in

eastern Chester County. This study showed those basins with the largest increase in urbanization also had

the greatest upward change in benthic-macroinvertebrate diversity. Sloto attributed this to decreased

pesticide use in urbanizing basins and to the burial and (or) flushing of older pesticides.

Hardy and others (1995) examined land-use changes and concentrations of organochlorine

compounds in stream-bottom sediment in relation to the trends in diversity indices of benthicmacroinvertebrate communities. This report showed upward trends in benthic-macroinvertebrate

community diversities were associated with increases in residential land use and decreases in agricultural

1 The 12-month period October 1 through September 30. The water year is designated by the calendar year in which it

ends.
4

Table 1. U.S. Geological Survey station identification numbers, site numbers, names, drainage areas, and period of

record of sites in the Stream Conditions of Chester County Biological Monitoring Network, Pennsylvania, 1981-97

[—, no data]

U.S. Geological

Survey station

identification

number

Site

number

(fig. 1)

Name

Drainage

area

(square

miles)

Period of record

Biological Chemical Bottom

sediment

Schuylkill River Basin

01472080 10 Pigeon Creek near Parker Ford 12.00 1970-97 1969-97 1985,1996

01472109 6 Stony Run near Spring City 2.00 1970-96 1969-96 1985,1996

01472138 13 French Creek near Coventryville 19.90 1970-97 1969-97 1986,1997

01472140 12 South Branch French Creek at Coventryville 12.40 1970-97 1969-97 1985,1997

01472154 14 French Creek near Pughtown 46.10 1970-97 1969-97 1985,1997

01472157 1 15 French Creek near Phoenixville 59.10 1970-97 1969-97 1994

014721612 16 French Creek at Railroad Bridge at Phoenixville 70.70 1980-97 1970-97 1985,1994

01472170 1 Pickering Creek near Eagle 3.09 1970-96 1969-96 1987,1996

01472174 2 Pickering Creek near Chester Springs 5.98 1970-95 1969-95 1986

014721854 3 Pickering Creek at Merlin 21.20 1970-97 1969-97 1986,1997

014721884 4 Pickering Creek at Charlestown Road at

Charlestown

 27.50 1972-96 1969-96 1985

01472190 5 Pickering Creek near Phoenixville 31.40 1970-97 1969-97 1986,1994

01473167 49 Little Valley Creek at Howellville 6.45 1973-96 1970-96 1986,87,93

01473168 50 Valley Creek near Valley Forge 12.70 1973-96 1970-96 1985,1993

Delaware River Basin

01475300 17 Darby Creek at Waterloo Mills near Devon 5.15 1970-96 1969-96 1996

01475840 19 Crum Creek at Whitehorse 10.10 1970-96 1969-96 1986,1996

01476430 20 Ridley Creek at Goshenville 4.22 1970-96 1969-96 1985

01476435 21 Ridley Creek at Dutton Mill near West Chester 9.71 1970-96 1969-96 1986

01476790 22 East Branch Chester Creek at Green Hill .63 1970-97 1969-97 1986,1997

01476830 23 East Branch Chester Creek at Milltown 5.77 1970-96 1969-96 1986,1996

01476835 24 East Branch Chester Creek at Westtown 10.40 1970-97 1969-97 1985,1994

01476840 25 Goose Creek Tributary to East Branch Chester

Creek near West Chester

 4.28 1975-82

1988-97

1970-82

1988-97

1988,1993

01476848 51 East Branch Chester Creek below Goose Creek near

West Chester

 19.20 1983-97 1970-97 1986,1994

Brandywine Creek Basin

01480434 37 West Branch Brandywine Creek at Rock Run 37.30 1970-96 1970-96 —

01480629 46 Buck Run at Doe Run 22.60 1973-97 1971-97 1985,1995

01480632 1 45 Doe Run at Springdell 11.80 1973-97 1971-97 1986

01480640 38 West Branch Brandywine Creek at Wawaset 134.00 1970-97 1970-97 1985,1993

01480648 48 East Branch Brandywine Creek near Cupola 5.98 1973-95 1971-95 1986

01480653 42 East Branch Brandywine Creek at Glenmoore 16.50 1973-95 1971-95 1985

01480656 47 Indian Run near Springton 4.26 1974-95 1971-95 1986,1995

01480700 36 East Branch Brandywine Creek near Downingtown 60.60 1970-96 1970-96 1985

01480903 44 Valley Creek2

 at Mullsteins Meadows near

Downingtown

 16.10 1973-97 1971-97 1985,1995

01480950 39 East Branch Brandywine Creek at Wawaset 123.00 1979-97 1970-97 1986,1993

01481030 40 Brandywine Creek near Chadds Ford 291.00 1972-97 1970-97 1985,1997

Red Clay and White Clay Creek Basins

01479680 27 West Branch Red Clay Creek at Kennett Square 9.79 1970-97 1970-97 1983,86,93

01479800 26 East Branch Red Clay Creek near Five Point 10.20 1970-97 1970-97 1985,1993

01478120 28 East Branch White Clay Creek at Avondale 11.30 1970-97 1970-97 1985,1993

01478190 29 Middle Branch White Clay Creek at Wickerton 9.94 1970-97 1970-97 1986,1993

01478220 30 West Branch White Clay Creek near Chesterville 9.92 1970-97 1970-97 1985,1993
5

land use. It also described an association between low community diversity values and concentrations of

organochlorine compounds above 45 μg/kg in stream-bottom material. Data collected as part of the

Stream Conditions of Chester County program were used in this report.

Description of Study Area

Chester County is a 760-mi2 area in southeastern Pennsylvania near Philadelphia (fig. 1). It lies in

the Piedmont Physiographic Province of the Appalachian Highlands. The topography of the area is

characterized by gently rolling hills underlain by deeply weathered crystalline rock. The streams included

in this study drain nearly 95 percent of Chester County. The largest basin is the Brandywine Creek Basin,

which drains 38 percent (290 mi2) of the county. The eastern part of the county is more developed; the

southern and western parts of the county contain more farm and pasture land. Major crops are hay, corn,

vegetables, and mushrooms. Dairy farms and nurseries also are prevalent in the area.

Chester County has undergone and continues to experience rapid population growth. The county’s

population nearly doubled between 1960 and 1995, increasing from 210,600 to 412,000. Population

projections indicate the county will have 489,000 residents by 2020 (Chester County, 1996). In response to

this rapid urbanization, open space and farmland have been converted to residential and commercial land.

Farmland in the county decreased from 47 percent in 1974 to 37 percent in 1992. The percentage of

developed land is projected to increase from 23 percent in 1990 to 38 percent in 2020 (Chester County,

1996).

Climate

The study area has a humid, modified continental climate characterized by warm summers and

moderately cold winters. The normal (1961-90) mean annual temperature at Phoenixville is 51.7°F. The

normal (1961-90) mean temperature for January, the coldest month, is 28°F, and the normal mean

temperature for July, the warmest month, is 73.8°F. The normal (1961-90) annual precipitation at Phoenixville is 42.56 in. (Owenby and Ezell, 1992). Precipitation is distributed about evenly throughout the year;

slightly more occurs during the warmer months because of localized thunderstorms.

Hydrologic Conditions

The water-chemistry and biological conditions that exist during a particular year are conditional on

the hydrological conditions that were present. Extremely low or high flow conditions can be a major factor

controlling the benthic-macroinvertebrate community at a site.

Between 1981 and 1997, there were several years when hydrologic conditions may have had a large

effect on the benthic-macroinvertebrate communities sampled. Annual mean discharges were 25 percent

below average during the years 1981, 1985, 1986, 1992, and 1995. During these years, adverse conditions

Big Elk and Octoraro Creek Basins

01494900 31 East Branch Big Elk Creek at Elkview 11.10 1970-97 1970-97 1986,1994

01494950 32 West Branch Big Elk Creek near Oxford 10.00 1970-96 1970-96 1985,1994

01578340 33 East Branch Octoraro Creek at Christiana 11.80 1970-97 1970-97 1994

01578343 34 Valley Creek near Atglen 10.50 1970-96 1970-96 1985

1 Reference reach.

2 Also called West Valley Creek.

Table 1. U.S. Geological Survey station identification numbers, site numbers, names, drainage areas, and period of

record of sites in the Stream Conditions of Chester County Biological Monitoring Network, Pennsylvania, 1981-97

—Continued

[—, no data]

U.S. Geological

Survey station

identification

number

Site

number

(fig. 1)

Name

Drainage

area

(square

miles)

Period of record

Biological Chemical Bottom

sediment
6

may have been present because of low-flow conditions. Under low-flow conditions, water temperatures

are higher, chemical constituents can be concentrated, and algal growth can increase; these changes can

cause wide fluctuations in dissolved oxygen concentrations. Flows greater than 25 percent of the mean

were recorded in 1984, 1994, 1996, and 1997. High flows can cause a disruption of the bottom habitat that

can adversely affect benthic-macroinvertebrate communities.

Acknowledgments

The cooperation of the Chester County Board of Commissioners, the Chester County Water

Resources Authority, Chester County Planning Commission, and the Chester County Health Department

is gratefully acknowledged. Special thanks are extended to David C. Yaeck, Irene B. Brooks, and Janet L.

Bowers, Executive Directors of the Chester County Water Resources Authority, for their interest

throughout the program’s history. Many colleagues, all USGS personnel except Dr. Richard McLean, have

provided valuable information and comments for this report. These include Dr. J. Kent Crawford and Dr.

Richard McLean for their guidance; Michael D. Bilger, Dr. Martin Gurtz, and Ronald A. Sloto for the

review of the manuscript; and Kim L. Otto, Joanne Koch, and Terriann Preston for their technical and

editorial input.

SAMPLING AND ANALYTICAL METHODS

Field Measurements

Dissolved oxygen, pH, water temperature, specific conductance, alkalinity, and streamflow were

measured at each site once a year in the fall. Field meters were calibrated prior to each use, and records of

each meter’s performance are kept with the meter and recorded on each field data sheet. Calibration

standards for pH and specific conductance were obtained from the USGS laboratory in Ocala, Fla.

Chemical Analysis

Samples for chemical analysis were collected at the same time as the biological samples by use of

techniques described by Brown and others (1970, p. 5). Chemical samples collected from 1981 to 1984 were

analyzed at the USGS National Water-Quality Laboratory in Atlanta, Ga. Chemical samples collected from

1985 to 1997 were analyzed at the USGS National Water-Quality Laboratory in Arvada, Colo. Water

samples were analyzed for nutrients, major ions, and selected metals. Quality-control samples consisting

of replicates and field blanks were collected to provide quantitative information on the precision and bias

of the overall field and laboratory process. Constituent concentrations in field blanks almost always were

less than the minimum reporting levels and replicate samples generally were within 10 percent. These

results indicate no systematic bias and good precision in the reported water-quality data.

Stream-bottom sediment samples were collected from 1985 through 1987 and from 1993 through

1994. Most sites were sampled once during each period. Samples of stream-bottom sediment were

collected from depositional areas where water depth was less than 2 ft. Samples were collected by hand

from the top 6 to 12 in. of stream-bottom sediment with a polyethylene scoop and washed through a 2-mm

polyethylene sieve with native water. The sample was homogenized in a polyethylene basin and

transferred to clean glass or polyethylene containers and placed on ice for shipment to the USGS

laboratory.

Samples of stream-bottom sediment were analyzed for selected metals, pesticides, gross

polychlorinated biphenyls (PCB), and gross polychlorinated naphthalenes (PCN). Analyses for selected

metals included arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, and zinc. Metal

concentrations were determined by atomic absorption spectrometry (Fishman and Friedman, 1989).

Analyses for organochlorine insecticides included aldrin, chlordane, DDD, DDE, DDT, dieldrin,

endosulfan, endrin, heptachlor, heptachlor epoxide, lindane, methoxychlor, mirex, perthane, and

toxaphene. Concentrations of organochlorine pesticides, PCB, and PCN were determined by gas

chromatography using a flame photometric detector (Wershaw and others, 1987). Concentrations of total

carbon were determined by the induction furnace method (Wershaw and others, 1987). All results are

reported as dry weights.
7

Biological Analysis

Biological samples consisted of benthic macroinvertebrates collected annually from October through

November. During each visit, benthic macroinvertebrates were sampled by collecting 10 rocks (45-90 mm

in diameter) at random from a riffle area (Lium, 1974). All organisms that were dislodged or washed off

the rocks were collected in the sampler or with a sieve with a 210-μm mesh. All invertebrates from the

rocks were composited in a container and stored in 70 percent ethanol for later identification. A complete

description of the sampling technique is described by Moore (1987, p. 7). Benthic-macroinvertebrate

samples collected from 1980 to 1997 were identified at the USGS office in Malvern, Pa. Benthic

macroinvertebrates were identified to the lowest taxonomic level possible. A systematic checklist of taxa

reported is presented in appendix 1. A reference collection of identified organisms is maintained at the

USGS, Water Resources Division, Malvern, Pa. Unusual taxa were confirmed by expert taxonomists. A list

of taxonomic references on which the identifications were based is given in table 2. Taxa richness, modified

Hilsenhoff’s Biotic Index (HBI), Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa richness, and

percentage EPT were calculated for each benthic-macroinvertebrate sample (tables 14-56, pages 51-72).

STREAM-QUALITY ASSESSMENT AND TRENDS

Biological Metrics Evaluation

The analysis of overall stream quality on the basis of benthic-macroinvertebrate sampling uses

various biological metrics. Numerous biological metrics commonly are used to describe benthicmacroinvertebrate communities including taxa richness, EPT taxa richness, percent EPT taxa, and the HBI.

Each biological metric evaluates a different aspect of the invertebrate community and how it relates to

overall stream quality. By examining all these biological metrics together, an evaluation of the overall

stream quality can be made. A complete listing of the biological metrics calculated for each site is

presented in tables 14-56 (pages 51-72). Benthic-macroinvertebrate data from 1981 to 1997 were used in the

assessments. Data prior to 1981 were used only as a historical reference. The biological metrics used are

described below.

Taxa richness is a measure of the number of distinct taxonomic groups (taxa) in a collection.

Richness measures the overall diversity of the biological community sampled. Taxa richness tends to

decrease with decreasing stream quality (Weber, 1973; Resh and Grodhaus, 1983). The availability of

adequate food, habitat, and niche space to support a variety of taxa is an indication of a healthy biological

community and typically is reflected in increasing taxa richness (Plafkin and others, 1989).

EPT taxa richness is the total number of taxa within the orders Ephemeroptera (mayflies),

Plecoptera (stoneflies), and Trichoptera (caddisflies). Percentage EPT individuals is the total number of

EPT individuals divided by the total number of individuals in the sample. These three orders of insects

generally are considered “pollution sensitive” and their presence is associated with good stream quality

(Lenat, 1988). EPT taxa richness and (or) the percentage EPT individuals increase with improving stream

quality.

Hilsenhoff’s biotic index (HBI) is based on the sensitivity of organisms to stream-quality

conditions. The HBI uses assigned tolerance values that range from 0 to 10. A zero value is assigned to

organisms least tolerant of organic pollution, and a 10 is assigned to organisms most tolerant of organic

pollution. Species intermediate in their tolerance of organic pollution were assigned intermediate values

Table 2. List of taxonomic references used to identify benthic-macroinvertebrate samples

Taxonomic group Reference

Turbellaria, Nemertea, Nematoda, Gastropoda, Bivalvia,

Annelida, Crustacea, Arachnida Pennak, 1989, Peckarsky and others, 1990

Ephemeroptera, Plecoptera, Megaloptera, Neuroptera,

Lepidoptera, Coleoptera, Diptera

Brigham and others, 1982, Peckarsky and others, 1990;

Merritt and Cummins, 1996

Trichoptera Wiggins, 1996
8

(Hilsenhoff, 1982). The HBI is calculated by multiplying the number of individuals of each taxon by its

assigned tolerance value, summing these products, and dividing by the total number of individuals.

Tolerance values are from the genus- and species-level biotic index developed by the State of New York

(Bode, 1991). HBI values from 0 to 4.5 have been associated with nonimpacted sites, 4.51 to 6.50 have been

associated with slightly impacted sites, 6.51 to 8.50 have been associated with moderately impacted sites,

and 8.51 to 10.00 are associated with severely impacted sites (Bode, 1993).

Stream-Quality Assessment Criteria

Streams in the network were assessed as nonimpacted, slightly impacted, moderately impacted, or

severely impacted on the basis of calculated biological metric values (table 3). Each biological metric

assesses a different part of the benthic-macroinvertebrate community structure to produce an overall

assessment of stream-quality conditions.

Nonimpacted: Biological metrics indicate excellent stream conditions. The benthicmacroinvertebrate community is balanced and diverse. The community is dominated by “pollution

sensitive” and facultative groups including mayflies, stoneflies, and caddisflies. “Pollution tolerant”

groups may be present but are not dominant. Water-quality and habitat conditions are not limiting the

benthic-macroinvertebrate community. Nonimpacted sites include pristine habitats and those receiving

inputs that minimally affect the benthic-macroinvertebrate community.

Slightly Impacted: Biological metrics indicate good stream conditions. The benthicmacroinvertebrate community is less diverse than at nonimpacted sites but still contains mayflies,

caddisflies, and possibly some stoneflies. The community structure typically is dominated by a few taxa

including caddisflies, Elmidae (riffle beetles), and chironomids. Water-quality and physical conditions are

affecting the benthic-macroinvertebrate community. Slightly impacted sites commonly receive some

wastewater inputs and (or) agricultural/urban runoff.

Moderately Impacted: Biological metrics indicate fair stream conditions. The benthicmacroinvertebrate community is disturbed and noticeably altered from a nonimpacted site. Mayflies and

stoneflies are rare, and caddisfly taxa may be limited. The benthic-macroinvertebrate community is

dominated by “pollution tolerant” and facultative organisms including chironomids and oligochaetes

(aquatic earthworms). One or a few groups usually dominate the community. Stream-quality conditions

are major factors affecting the benthic-macroinvertebrate community. Moderately impacted sites

commonly receive heavy wastewater inputs and (or) agricultural/urban runoff.

Severely Impacted: Biological metrics indicate poor stream quality. The benthic-macroinvertebrate

community is limited with poor diversity. Mayflies, stoneflies, and caddisflies are rare, and the community

usually is dominated by chironomids and aquatic earthworms. The community may have low numbers of

individuals or very high numbers of a few taxa. Severely impacted sites commonly receive inputs of a

toxin or have extremely low concentrations of dissolved oxygen. Stream-quality conditions are severely

affecting the benthic-macroinvertebrate community. Severely impacted sites commonly receive heavy

wastewater inputs, agricultural/urban runoff, and possibly toxic substances.

Table 3. Stream-quality assessment criteria for Chester County,

Pennsylvania, streams (adapted from Bode, 1993)

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s

biotic index; >, greater than]

Stream-quality

assessment Taxa richness EPT taxarichness HBI

Nonimpacted >30 >10 0 - 4.50

Slightly impacted 21 - 30 6 -10 4.51 - 6.50

Moderately impacted 11 - 20 2 -5 6.51 - 8.50

Severely impacted 0 - 10 0 - 1 8.51 - 10
9

Reference Reaches

Reference reaches are sites that represent good stream conditions in a particular area. Reference sites

are considered those minimally affected by anthropogenic impacts. These sites have stable habitat, nontoxic water chemistry, and healthy biological conditions. Other sites with similar stream characteristics can

be compared to the reference reach to determine impacts. The sites were selected on the basis of historical

data that indicated good stream quality. Two sites were selected to represent reference conditions in areas

of agricultural and nonagricultural land use.

French Creek near Phoenixville (site 15) was chosen as the reference site for the Schuylkill River

Basin, Delaware River Basin, and East Branch Brandywine Creek Basin. This site has a diverse and stable

benthic-macroinvertebrate community, stable habitat, and consistent chemical data. It receives no direct

discharges and has a stable land use that is low in impervious surface and low in intense agricultural

lands. Doe Run at Springdell (site 45) was chosen as the reference site for the West Branch Brandywine,

Red Clay, White Clay, Big Elk, and Octoraro Creek Basins. Areas minimally affected by human activities

are difficult to find in these basins. Although this site is affected by anthropogenic impacts, including

agricultural activities, it represents stable stream conditions in the area.

Assessment of Stream Quality Using Benthic-Macroinvertebrate Data

Schuylkill River Basin

Streams sampled in the Schuylkill River Basin include Pigeon Creek, Stony Run, French Creek,

Pickering Creek, Little Valley Creek, and Valley Creek. The Schuylkill River Basin drains the northern part

of the county, including the Boroughs of Phoenixville and Spring City. Land use in the basin is dominated

by a mix of agriculture, forested, and residential areas. Assessments of stream conditions, on the basis of

macroinvertebrate criteria, are presented in table 4.

Table 4. Assessment of stream conditions on the basis of median values of taxa

richness, EPT taxa richness, and HBI for sites in the Schuylkill River Basin,

Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s biotic index;

Assessment based on values presented in tables 14-27]

U.S. Geological

Survey station

identification

number

Site

number

Taxa

richness

EPT taxa

richness HBI

Pigeon Creek

01472080 10 Nonimpacted Nonimpacted Nonimpacted

Stony Run

01472109 6 Nonimpacted Nonimpacted Slightly impacted

French Creek

01472138 13 Nonimpacted Nonimpacted Slightly impacted

01472140 12 Nonimpacted Nonimpacted Nonimpacted

01472154 14 Nonimpacted Nonimpacted Nonimpacted

01472157 15 Nonimpacted Nonimpacted Nonimpacted

014721612 16 Slightly impacted Slightly impacted Slightly impacted

Pickering Creek

01472170 1 Slightly impacted Nonimpacted Slightly impacted

01472174 2 Slightly impacted Nonimpacted Nonimpacted

014721854 3 Nonimpacted Nonimpacted Slightly impacted

014721884 4 Nonimpacted Nonimpacted Slightly impacted

01472190 5 Nonimpacted Nonimpacted Slightly impacted

Valley Creek Basin

01473167 49 Moderately impacted Slightly impacted Nonimpacted

01473168 50 Slightly impacted Slightly impacted Slightly impacted
10

Pigeon Creek

Pigeon Creek near Parker Ford (site 10) was sampled annually from 1981 through 1997. Pigeon

Creek has a drainage area of 12.0 mi2 and is approximately 24 ft wide at site 10. The predominant land-use

categories at site 10 are agriculture (36 percent), forested (36 percent), and residential (25 percent)

(Delaware Valley Regional Planning Commission, 1997).

Pigeon Creek was assessed as nonimpacted on the basis of calculated biological metrics (table 4).

The benthic-macroinvertebrate data collected at this site indicate a diverse and stable benthicmacroinvertebrate community with numerous “pollution sensitive” organisms. The physical and chemical

data collected in conjunction with the benthic-macroinvertebrate samples indicate stable physical,

chemical, and biological conditions with no adverse effects of habitat alteration, siltation, or nutrient

enrichment. Samples of stream-bottom sediment collected in 1985 contained no detectable concentrations

of pesticides or PCBs. Taxa richness and the number of EPT taxa increased in 1987 and remained higher

through 1997 (table 14, page 51), but there were no changes in measured habitat or chemical data to

explain the increase in taxa. This site had similar numbers of taxa and EPT taxa but slightly larger HBI

values (median = 4.28, indicating a less healthy benthic-macroinvertebrate community) when compared to

the reference site. The increased HBI values were the result of occasionally high numbers of chironomids,

which can be an indication of degraded stream conditions (Plafkin and others, 1989) (fig. 2).

Stony Run

Stony Run near Spring City (site 6) was sampled annually from 1981 through 1996. Stony Run is a

small headwater stream with a drainage area of 2.0 mi2 at site 6. The stream is approximately 6 ft wide.

The predominant land-use categories at site 6 are agriculture (63 percent), residential (22 percent), and

forested (11 percent) (Delaware Valley Regional Planning Commission, 1997).

Stony Run was assessed as nonimpacted on the basis of median values of taxa richness and EPT taxa

richness and as slightly impacted on the basis of the HBI index (table 4). The benthic macroinvertebrates

collected at this site had consistent numbers of taxa but increasing numbers of EPT taxa and slightly

decreasing HBI values after 1988 (table 15, page 51). The benthic-macroinver-tebrate community after 1988

also contained lower numbers of gastropods (snails) and aquatic earthworms than prior to 1988, which

generally decreased the HBI values. The decreasing HBI values and increasing numbers of EPT taxa—both

indications of improved stream quality—occurred in conjunction with decreasing concentrations of

REFERENCE SITE SITE

1

6

2

3

4

5

HBI

EXPLANATION

25th percentile

Median

75th percentile

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

interquartile range outside the quartile

and more than 1.5 times the

Outlier data value less than or equal to 3

SITE 10 6

INCREASING PERCENTAGE AGRICULTURE IN BASIN

DECREASING STREAM SIZE

Figure 2. Range of Hilsenhoff’s biotic index (HBI) values from reference site (site 15), Pigeon Creek

(site 10), and Stony Run (site 6), Chester County, Pennsylvania, 1981-97.
11

ammonia, phosphorus, sodium, potassium, and chloride and a reduction in siltation. The improved

chemical conditions and increased diversity in benthic-macroinvertebrate communities occurred after

1988.

The benthic-macroinvertebrate community was diverse with large numbers of mayflies, caddisflies,

and riffle beetles and a small but consistent population of stoneflies, which are indications of good stream

quality. The invertebrate community also contained occasionally large numbers of “pollution tolerant”

organisms, which can be an indication of degraded stream quality. This large number of “pollution

tolerant” organisms caused the HBI values to indicate slightly impacted conditions (table 4). The benthicmacroinvertebrate community contained similar taxa richness numbers but reduced EPT taxa richness

and increased HBI values when compared to the reference site. The difference in biological metrics

between site 6 and the reference site corresponds to the large percentage of agriculture in the basin and the

small stream size at site 6 (fig. 2). Agriculture in a basin can cause increased sediment and pesticide loads

that can negatively affect benthic macroinvertebrates. Minshall and others (1985) and Grubaugh and

others (1996) have shown that small streams (first and second order) have reduced taxa richness when

compared to larger streams (fourth and fifth order streams).

French Creek

Five sampling sites were on French Creek (sites 12-16) between Coventryville in the headwaters and

Phoenixville near the confluence with the Schuylkill River. The drainage area of French Creek at the most

downstream location (site 16) is 70.7 mi2. The stream is approximately 15 ft wide at site 12 and is 50 ft wide

at site 16. The predominant land-use categories at site 16 are forested (47 percent), agriculture (35 percent),

and residential (13 percent) (Delaware Valley Regional Planning Commission, 1997). The sites were

sampled annually from 1981 through 1997.

French Creek from Coventryville to above Phoenixville (sites 12-15) was assessed as nonimpacted

on the basis of calculated biological metrics, except site 13, which was assessed as slightly impacted on the

basis of HBI values (table 4). The benthic-macroinvertebrate data collected from these sites indicate a

diverse and stable benthic-macroinvertebrate community with numerous “pollution sensitive” organisms

including a large and diverse stonefly population. The physical and chemical data collected in conjunction

with the benthic-macroinvertebrate samples indicate no adverse effects of habitat alteration, siltation, or

nutrient enrichment and stable water-chemistry conditions. These sites had similar biological metric

values when compared to the reference site, which is in the basin (site 15).

The benthic-macroinvertebrate community at site 16 was degraded compared with those at

upstream sites. Site 16 is near the confluence with the Schuylkill River and is downstream of the Borough

of Phoenixville. The area immediately upstream of the site is an old heavy industrial area that is being

converted to a light industrial/business area. The benthic-macroinvertebrate data collected from this site

had lower taxa richness, fewer EPT taxa (fig. 3), and higher HBI values than the other sites on French

Creek. Site 16 was assessed as slightly impacted on the basis of all three biological metrics (table 4).

Although this site was assessed as slightly impacted, it has improved since 1982. Taxa richness and EPT

taxa richness have increased and HBI values have decreased from 1981 to 1997, although they were

variable (table 20, page 54). Decreases in concentrations of ions and metals at the site after 1982 correspond

to the increased diversity in the benthic-macroinvertebrate community (fig. 4).

Pickering Creek

Five sampling sites were on Pickering Creek (sites 1-5). Predominant land use at site 5 is agriculture

(42 percent), forested (36 percent), and residential (17 percent) (Delaware Valley Regional Planning

Commission, 1997). The drainage area of Pickering Creek at site 5 is 31.4 mi2. The stream is approximately

15 ft wide at site 1 and is 50 ft wide at site 5. The sites were sampled annually from 1981 through 1997.

The Pickering Creek sites were all assessed as nonimpacted or slightly impacted on the basis of

calculated biological metrics (table 4). The benthic-macroinvertebrate data collected from these sites

indicate a diverse but variable benthic-macroinvertebrate community with numerous “pollution

sensitive” organisms including large and diverse stonefly and mayfly populations. Large populations of
12

“pollution tolerant” organisms occasionally were present in the downstream sites. Biological metrics

indicated steady or slightly improving stream conditions in Pickering Creek from 1986 to 1997 (tables 21-

25, pages 54-56). Physical and chemical data collected in conjunction with the benthic-macroinvertebrate

samples also indicate stable habitat and consistent water chemistry that support the stable benthicmacroinvertebrate community.

All sites in the basin had concentrations of ammonia that were elevated over the reference site from

1983 to 1984. The ammonia concentrations declined in 1985 and remained lower throughout the study

period. Sites 1-4 had increased numbers of taxa after 1985 when the lower ammonia concentrations were

measured (fig. 5).

The most upstream sites (sites 1 and 2) had reduced numbers of taxa and EPT taxa when compared

to the other sites in the basin and the reference site but still contained numerous “pollution sensitive”

organisms. The reduced numbers of taxa at sites 1 and 2 may be because of limited habitat, food, and flow

in headwater streams and not related directly to degraded stream conditions. Minshall and others (1985)

and Grubaugh and others (1996) have shown that taxa richness decreases as stream size decreases. Taxa

richness and EPT taxa richness increased with increasing stream size; sites 4 and 5 have numbers of taxa

similar to the reference site (fig. 6). Both sites had low summer flow and variable stream bottoms.

SITE 15 SITE 15 SITE 16 SITE 16

0

50

10

20

30

40

NUMBER OF TAXA

EXPLANATION

25th percentile

Median

75th percentile

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

interquartile range outside the quartile

and more than 1.5 times the

Outlier data value less than or equal to 3

TAXA

EPT

INCREASING

Figure 3. Taxa richness and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness from

French Creek near Phoenixville (site 15) and French Creek at Phoenixville (site 16), Chester County,

Pennsylvania, 1981-97.

RICHNESS

TAXA

RICHNESS

TAXA

RICHNESS

EPT

TAXA

RICHNESS

STREAM QUALITY

1981 1987 1983 1985

0

400

100

200

300

CONCENTRATION,

0

12

2

4

6

8

10 EXPLANATION

ZINC

LEAD

EPT TAXA

Figure 4. Concentrations of zinc and lead and number of Ephemeroptera, Plecoptera,

and Trichoptera (EPT) taxa from French Creek at Phoenixville (site 16), Chester

County, Pennsylvania, 1981-87. IN MICROGRAMS PER LITER

NUMBER OF TAXA
13

Valley Creek

Two sampling sites were in the Valley Creek Basin. Site 49 is on Little Valley Creek near its

confluence with Valley Creek, and site 50 is on Valley Creek upstream of Little Valley Creek. Little Valley

Creek is 11 ft wide at site 49 and has a drainage area of 6.45 mi2. Valley Creek is 32 ft wide at site 50 and has

a drainage area of 12.7 mi2. The predominant land-use categories at site 50 are forested (33 percent),

residential (28 percent), commercial (10 percent), parking/transportation (6 percent), and agriculture

(10 percent) (Delaware Valley Regional Planning Commission, 1997). The basin contains major highways

and business areas with 9 percent impervious surface at site 50. The sites were sampled annually from

1981 through 1996.

The benthic-macroinvertebrate communities collected from these sites have relatively low but

consistent numbers of total taxa and EPT taxa. Site 49 was assessed as moderately impacted on the basis of

taxa richness, slightly impacted on the basis of EPT taxa richness, and nonimpacted on the basis of HBI

(table 4). Although the number of taxa was low at site 49, the percent of EPT taxa was above 50 percent,

which indicates good stream conditions (table 26, page 57). Physical and chemical data from this site

indicate low nutrient enrichment and stable water chemistry that correspond to the stable benthicmacroinvertebrate community found there.

1981 1989 1983 1985 1987

40

25

30

35

0

0.20

0.05

0.10

0.15

AMMONIA CONCENTRATION

TAXA RICHNESS

AMMONIA CONCENTRATION,

Figure 5. Taxa richness and ammonia concentration at Pickering

Creek at Charlestown (site 4), Chester County, Pennsylvania, 1981-89.

20

IN MILLIGRAM PER LITER

NUMBER OF TAXA

REFERENCE SITE 1 SITE 2 SITE 3 SITE 4 SITE 5

10

40

15

20

25

30

35

EXPLANATION

TAXA RICHNESS

EPT TAXA RICHNESS

SITE

 (SITE 15)

Figure 6. Median values of taxa richness and Ephemeroptera, Plecoptera, and

Trichoptera (EPT) taxa richness from sites in Pickering Creek Basin and the reference

site, Chester County, Pennsylvania, 1981-97. NUMBER OF TAXA
14

Site 50 was assessed as slightly impacted on the basis of calculated biological metrics (table 4). Site

50 had values of taxa richness and EPT taxa richness similar to those at site 49, but the community at site

50 contains higher numbers of “pollution tolerant” organisms including chironomids, tipulids (crane

flies), and Turbellaria (flatworms) (fig. 7). The physical and chemical data collected in conjunction with the

benthic-macroinvertebrate samples indicate low nitrate concentrations (less than 3.0 mg/L) at both sites

but occasional ammonia concentrations above 0.10 mg/L at site 50. Site 50 also had degraded habitat

caused by siltation. The benthic-macroinvertebrate community was consistent and did not respond to

small changes in the water chemistry at this site.

Valley and Little Valley Creeks are limestone streams with naturally high conductance and

alkalinity. The low numbers of taxa and EPT taxa that indicate the streams are slightly to moderately

impacted may be because the basins have greater than 10 percent impervious surfaces and (or) because of

naturally high conductance and alkalinity found in limestone streams. A limestone reference stream was

not available in the area for comparison. Site 49 was affected by PCB contamination from the Paoli Rail

Yard Superfund Site in the 1970s and 1980s, although recently collected samples of stream-bottom

sediment contained low concentrations of PCBs.

Sites in the Schuylkill River Basin are varied in land use from agricultural in Pigeon Creek and Stony

Run to forested/residential in French and Pickering Creeks to urban/residential in Valley and Little Valley

Creeks. In general, these streams were nonimpacted or slightly impacted and had stable benthicmacroinvertebrate communities and water chemistry; nitrate concentrations generally were less than

4.0 mg/L and phosphorus concentrations were less than the U.S. Environmental Protection Agency

(USEPA) desired goal of 0.1 mg/L (U.S. Environmental Protection Agency, 1994b). Samples of streambottom sediment contained concentrations of chlordane and dieldrin above the threshold effect

concentration in the 1980s but decreased to below the threshold effect concentration in the 1990s.

Concentrations below the threshold effect concentration have little or no biological effect on the majority

of benthic organisms (MacDonald and others, 2000).

Delaware River Basin

Streams sampled in the Delaware River Basin include Darby, Crum, Ridley, East Branch Chester, and

Goose Creeks. The Delaware River Basin drains a small part of eastern Chester County including the

Boroughs of Malvern and West Chester. The streams are small headwater streams in a suburban setting.

Land use in the basin is dominated by a mix of residential, urban, and forested areas. Assessments of

stream quality, on the basis of benthic-macroinvertebrate data, are presented in table 5.

Chironomidae

Coleoptera

Oligochaeta

Ephemeroptera,

Simuliidae

Other

Chironomidae

Oligochaeta

Simuliidae

Other

Coleoptera

Site 50 Site 49

Figure 7. Community composition of benthic-macroinvertebrate communities in Valley Creek (site 50)

and Little Valley Creek (site 49), Chester County, Pennsylvania, 1994.

Plecoptera, and

Trichoptera

Ephemeroptera,

Plecoptera, and

Trichoptera
15

Darby Creek

Site 17, Darby Creek at Waterloo Mills near Devon, was sampled annually from 1981 to 1996. Darby

Creek is a small headwater stream at site 17 with a drainage area of 5.15 mi2. The stream is approximately

20 ft wide, and the predominant land-use categories at site 17 are residential (71 percent), forested

(12 percent), and agriculture (6 percent) (Delaware Valley Regional Planning Commission, 1997).

Site 17 was assessed as nonimpacted or slightly impacted on the basis of calculated biological

metrics (table 5). The benthic macroinvertebrates collected from this site were highly variable in total

number of individuals and taxa richness (table 28, page 58) but consistently contained “pollution

sensitive” organisms including mayflies and caddisflies but few stoneflies. The number of “pollution

sensitive” organisms generally were declining and highly variable since 1989. Physical and chemical data

from this site indicate low nutrient concentrations and stable water chemistry but unstable substrate and

flow fluctuations. The lack of stable substrate and susceptibility to flow fluctuation, potentially from

increased peak streamflows caused by urbanization, is the most likely cause of the variable communities.

Darby Creek is one of two basins sampled that has over 10-percent impervious surface and over 30-

percent urbanized areas. This level of impervious surface can cause the degraded conditions present at

this site (Schueler, 1995).

Crum Creek

Crum Creek at Whitehorse (site 19) was sampled annually from 1981 through 1996. Crum Creek is a

small headwater stream in Chester County with a drainage area of 10.1 mi2 at site 19. The stream is

approximately 20 ft wide at this site. The predominant land-use categories at site 19 are residential

(41 percent), forested (27 percent), and agriculture (17 percent) (Delaware Valley Regional Planning

Commission, 1997).

Crum Creek was assessed as nonimpacted or slightly impacted on the basis of the calculated

biological metrics (table 5). The benthic macroinvertebrates collected from this site had a mix of “pollution

sensitive” organisms and occasionally large populations of “pollution tolerant” organisms. Waterchemistry data from this site do not suggest a direct cause for the increased numbers of “pollution

tolerant” taxa. Chloride concentrations were increasing but nutrient concentrations were low and the

Table 5. Assessment of stream quality on the basis of median values of taxa richness, EPT taxa

richness and HBI for sites in the Delaware River Basin, Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s biotic index; Assessment based on

values presented in tables 28-36]

U.S. Geological

Survey station

identification

number

Site

number Taxa richness EPT taxarichness HBI

Darby Creek

01475300 17 Slightly impacted Nonimpacted Slightly impacted

Crum Creek

01475840 19 Nonimpacted Nonimpacted Slightly impacted

Ridley Creek

01476430 20 Slightly impacted Nonimpacted Slightly impacted

01476435 21 Slightly impacted Nonimpacted Slightly impacted

Chester Creek Basin

01476790 22 Slightly impacted Slightly impacted Nonimpacted

01476830 23 Slightly impacted Nonimpacted Slightly impacted

01476835 24 Slightly impacted Nonimpacted Slightly impacted

01476840 25 Moderately impacted Moderately impacted Slightly impacted

01476848 51 Slightly impacted Slightly impacted Slightly impacted
16

other water-chemistry constituents measured were consistent. Habitat information indicates heavy

sediment on the stream bottom is degrading the habitat and may be causing the slightly impacted benthicmacroinvertebrate communities.

Ridley Creek

Two sampling sites in the Ridley Creek Basin (sites 20 and 21) were sampled annually from 1981

through 1996. Ridley Creek is a small headwater stream in Chester County with a drainage area of 9.71 mi2

at site 21. The stream is approximately 10 ft wide at site 20 and is 22 ft wide at site 21. The predominant

land-use categories at site 21 are residential (46 percent), forested (22 percent), and agriculture (21 percent)

(Delaware Valley Regional Planning Commission, 1997).

Both sites on Ridley Creek were assessed as nonimpacted or slightly impacted on the basis of

calculated biological metrics (table 5). The benthic-macroinvertebrate community at site 20 contained

highly variable values for total individuals and relatively low taxa richness (table 30, page 59). Between

1988 and 1994, EPT taxa richness decreased and HBI values increased indicating degraded stream quality.

Water chemistry did not change between 1988 and 1994, but this site is a small headwater stream and is

subject to unstable physical conditions and heavy siltation. The variable macroinvertebrate communities

at site 20 may be because of these variable habitat conditions.

Site 21 had a more consistent community of “pollution sensitive” organisms and taxa richness

comparable to site 20, but it also had larger populations of “pollution tolerant” organisms (fig. 8). There

were no trends in taxa richness or HBI values at site 21 since 1981. Site 21 had stable habitat conditions that

allowed it to support a more consistent macroinvertebrate community than site 20.

East Branch Chester Creek

Five sites in the East Branch Chester Creek Basin were sampled annually between 1981 and 1997.

Sites 22, 23, 24, and 51 are on the East Branch Chester Creek, and site 25 is on Goose Creek, which is a

tributary to the East Branch Chester Creek. Drainage areas range in size from 0.63 mi2 at site 22 to 19.2 mi2

at site 51. The stream is approximately 7 ft wide at site 22 and is 25 ft wide at site 51. The predominant

land-use categories at site 51 are residential (50 percent), forested (18 percent), and agriculture (12 percent)

(Delaware Valley Regional Planning Commission, 1997).

Chironomidae

Oligochaeta

Simuliidae Simuliidae

Other

Oligochaeta

Site 20 Site 21

Figure 8. Community composition of benthic-macroinvertebrate communities at

sites 20 and 21 on Ridley Creek, Chester County, Pennsylvania, 1996.

Coleoptera Coleoptera

Ephemeroptera,

Plecoptera, and

Trichoptera Ephemeroptera,

Plecoptera, and

Trichoptera

Chironomidae

Other
17

Sites 22 and 23 were assessed as slightly impacted on the basis of two of the three biological metrics

(table 5). Benthic-macroinvertebrate data from site 22 indicate low taxa richness, but approximately

50 percent of the taxa are EPT taxa, which is an indication of good stream quality (table 32, page 60).

Benthic-macroinvertebrate data from site 23 have variable taxa numbers but increasing HBI values after

1987 (table 33, page 60). Both sites had reduced taxa richness and EPT taxa richness and higher HBI values

than the reference site. The reduced taxa numbers are typical of a small headwater stream and not

necessarily degraded stream conditions. The elevated HBI values were caused by higher numbers of

“pollution tolerant” organisms including flatworms, aquatic worms, chironomids, and crane flies. These

organisms along with heavy algal growth on the stream bottom are an indication of organic enrichment.

Physical and chemical data indicate increasing concentrations of sodium, chloride, and calcium after 1987

when the HBI values at site 23 were increasing.

A major event in 1989-91 at site 22 caused a sharp reduction in EPT taxa and a sharp increase in HBI

values (table 32, page 60). The benthic-macroinvertebrate community was affected negatively by an

increase in dissolved manganese concentrations and manganese precipitate on the stream bottom. The

manganese was from a ground-water airstripper that was discharging into the stream above site 22. When

the airstripper was shut off, the benthic macroinvertebrates recovered (fig. 9). Site 23 was not affected by

the manganese because it is downstream of a small reservoir that may have acted as a buffer.

Site 24 was assessed as slightly impacted on the basis of two of the three biological metrics (table 5).

Benthic-macroinvertebrate data from site 24 indicate a variable benthic-macroinvertebrate community

along with variable water chemistry. This site was distinctly different from the reference site in benthicmacroinvertebrate community structure and nutrient water chemistry (figs. 10 and 11). The numbers of

“pollution tolerant” organisms, including aquatic worms, chironomids, and black flies, and the

concentrations of ammonia and phosphorus occasionally were high, indicating an unstable chemical and

biological environment. Phosphorus concentrations were above the USEPA recommended limit of

0.10 mg/L. A small wastewater-treatment plant upstream of this site is degrading the stream quality at

this site.

Site 25 is on Goose Creek, a tributary to the East Branch Chester Creek, and site 51 is on East Branch

Chester Creek below Goose Creek. Both sites were moderately or slightly impacted on the basis of all three

calculated biological metrics (table 5). These sites are downstream of a discharge from a wastewatertreatment plant, and the benthic-macroinvertebrate community is affected by organic pollution. The

benthic-macroinvertebrate community and water chemistry were improved greatly between 1982 and

1988 after an upgrade in the wastewater-treatment plant. Taxa richness and EPT taxa richness increased

and HBI values decreased (table 35, page 61); concentrations of nutrients and ions all decreased in 1988.

The benthic-macroinvertebrate community, however, was different substantially from the reference site. It

was dominated by “pollution tolerant” organisms including flatworms, aquatic worms, chironomids, and

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992

YEAR

2

16

4

6

8

10

12

14

NUMBER OF TAXA

0

200

50

100

150

MANGANESE CONCENTRATION,

EPT TAXA

MANGANESE CONCENTRATION

Figure 9. Ephemeroptera, Plecoptera, and Trichoptera (EPT)

taxa and manganese concentrations from East Branch Chester

Creek at Greenhill (site 22), Chester County, Pennsylvania, 1981-92. IN MILLIGRAMS PER LITER
18

Chironomidae

Coleoptera

Simuliidae

Other

Chironomidae

Coleoptera

Oligochaeta

Simuliidae

Other

Chironomidae

Coleoptera

Simuliidae

Other

Site 15 Site 24 Site 25

Figure 10. Community composition of benthic-macroinvertebrate communities from the reference site

(site 15), East Branch Chester Creek at Westtown (site 24), and Goose Creek (site 25), Chester County,

Pennsylvania, 1995.

(Reference Site)

Ephemeroptera,

Plecoptera, and

Trichoptera

Ephemeroptera,

Plecoptera, and

Trichoptera Ephemeroptera,

Plecoptera, and

Trichoptera

Oligochaeta

REFERENCE SITE SITE SITE

0

30

10

20

NITRATE CONCENTRATION AS N,

REFERENCE SITE SITE SITE

0

5

1

2

3

4

REFERENCE SITE SITE SITE

0

4

1

2

3

EXPLANATION

25th percentile

Median

75th percentile

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

interquartile range outside the quartile

and more than 1.5 times the

Outlier data value less than or equal to 3

interquartile range outside the quartile

Outlier data value more than 3 times the

SITE 24 25 51

SITE 24 25 51 SITE 24 25 51

Figure 11. Concentrations of nitrate, ammonia, and phosphorus from the reference

site (site 15), East Branch Chester Creek at Westtown (site 24), Goose Creek

(site 25), and East Branch Chester Creek below Goose Creek (site 51), Chester

County, Pennsylvania, 1981-97. IN MILLIGRAMS PER LITER IN MILLIGRAMS PER LITER AMMONIA CONCENTRATION,

IN MILLIGRAMS PER LITER

PHOSPHORUS CONCENTRATION,
19

crane flies (fig. 10). Nitrate concentrations at sites 25 and 51 consistently were above the USEPA drinking

water standard of 10 mg/L, and phosphorus concentrations were 10 times the recommended limit of

0.10 mg/L. Concentrations of ammonia and major ions were elevated over other sites in the basin (fig. 11).

The degraded stream quality created by the discharges from the wastewater-treatment plant is limiting the

benthic macroinvertebrates in Goose Creek and East Branch Chester Creek below Goose Creek.

Sites in the Delaware River Basin are mostly suburban streams; residential land use is dominant in

the basin. Most streams were degraded in taxa richness and HBI values when compared to the reference

site. Sites have specific problems that cause them to be degraded, ranging from altered habitat to the

effects of discharges from wastewater-treatment plants. Discharges from a wastewater-treatment plant

have a negative effect on Goose Creek and the East Branch Chester Creek below Westtown. The percent

impervious surface is above 10 percent in Darby Creek and is above 5 percent in Crum, Ridley, and

Chester Creeks. Stream degradation is likely to occur when percent impervious reaches 10 to 20 percent in

the basin (Schueler, 1995). Samples of stream-bottom sediment contained concentrations of chlordane,

DDT, and PCBs above the threshold effect concentration in the 1980s, but concentrations of these

compounds decreased to below the threshold effect concentration in the 1990s. Concentrations below the

threshold effect concentration have little or no biological effect on the majority of benthic organisms

(MacDonald and others, 2000). The concentrations were highest in samples from Goose Creek and East

Branch Chester Creek below Goose Creek.

Brandywine Creek Basin

Streams sampled in the Brandywine Creek Basin were the West Branch Brandywine Creek, Buck

Run, Doe Run, East Branch Brandywine Creek, Indian Run, West Valley Creek, and the main stem

Brandywine Creek. The Brandywine Creek Basin drains the center of the county and includes the

Boroughs of Coatesville, Downingtown, and West Chester. Land use in the basin is dominated by a mix of

agriculture, forested, and residential areas. Assessments of stream quality, on the basis of benthicmacroinvertebrate criteria, are presented in table 6.

Table 6. Assessment of stream quality on the basis of median values of

taxa richness, EPT taxa richness, and HBI for sites in the Brandywine

Creek Basin, Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s biotic index;

Assessment based on values presented in tables 37-47]

U.S. Geological

Survey station

identification

number

Site

number Taxa richness EPT taxarichness HBI

West Branch Brandywine Creek

01480434 37 Nonimpacted Nonimpacted Slightly impacted

01480640 38 Slightly impacted Nonimpacted Slightly impacted

Buck Run

01480629 46 Slightly impacted Nonimpacted Slightly impacted

Doe Run

01480632 45 Slightly impacted Nonimpacted Slightly impacted

East Branch Brandywine Creek

01480648 48 Nonimpacted Nonimpacted Slightly impacted

01480653 42 Nonimpacted Nonimpacted Nonimpacted

01480700 36 Nonimpacted Nonimpacted Slightly impacted

01480950 39 Nonimpacted Nonimpacted Nonimpacted

Indian Run

01480656 47 Nonimpacted Nonimpacted Nonimpacted

West Valley Creek

01480903 44 Slightly impacted Nonimpacted Nonimpacted

Main Stem Brandywine Creek

01481030 40 Nonimpacted Nonimpacted Slightly impacted
20

West Branch Brandywine Creek

Four sampling sites were in the West Branch Brandywine Creek Basin—two on the West Branch

Brandywine Creek (sites 37 and 38), one on Buck Run (site 46), and one on Doe Run (site 45). Drainage

areas range from 11.8 mi2 at site 45 to 134 mi2 at site 38. The stream is approximately 40 ft wide at site 37

and is 55 ft wide at site 38. The predominant land-use categories at site 38 are agriculture (50 percent),

forested (29 percent), and residential (14 percent) (Delaware Valley Regional Planning Commission, 1997).

These sites were sampled annually from 1981 through 1997.

Sites 37 and 38 were assessed as nonimpacted or slightly impacted on the basis of calculated

biological metrics (table 6). The benthic-macroinvertebrate community at these sites was diverse with a

large number of “pollution sensitive” organisms, which are indications of good stream conditions.

“Pollution tolerant” organisms were present in occasionally high numbers (where 57 percent of

individuals were midges in 1991) , particularly at site 37, indicating some disturbance. Site 37 had

consistent taxa richness and EPT taxa richness (table 37, page 62) along with consistent water chemistry

since 1981. Site 38 had an increase in taxa richness in 1989 (table 40, page 64) that corresponds to a decrease

in phosphorus concentrations at the same time. Concentrations of phosphorus decreased from above the

USEPA recommended level of 0.1 mg/L in 1990 to 0.04 mg/L in 1994; taxa richness rose from 23 to 37

(fig. 12). Other chemical constituents were stable over the period of record. Sites 37 and 38 had increased

taxa richness and EPT taxa richness when compared to the reference site but also have slightly higher HBI

values.

Buck Run (site 46) and Doe Run (site 45) were assessed as slightly impacted on the basis of median

values of taxa richness and HBI and were assessed as nonimpacted on the basis of EPT taxa richness

(table 6). The benthic-macroinvertebrate community at both sites was diverse with large numbers of

mayflies, caddisflies, and riffle beetles, which are indications of good stream quality. “Pollution tolerant”

organisms occasionally were present in high numbers, indicating some disturbance. Both sites had an

increase in EPT taxa richness and a decrease in HBI values around 1986 (tables 38 and 39, page 63) that

correspond to a decrease in concentrations of phosphorus similar to that noted at site 38. Since 1986, the

benthic-macroinvertebrate, habitat, and chemical data indicate stable conditions at both sites. Site 45 is the

reference site for the western and southern part of the county.

The sites in the West Branch Brandywine Creek had diverse benthic-macroinvertebrate communities

that increased in taxa richness and EPT taxa richness (fig. 13) and decreased in HBI values over time.

Water chemistry generally was stable with slightly increasing concentrations of nitrate and major ions and

decreasing concentrations of ammonia and phosphorus. Samples of stream-bottom sediment generally

contained pesticide concentrations that were below the threshold effect concentration and were decreasing

over time. Habitat was fairly stable, although siltation was a problem at most sites. The West Branch

1983 1985 1987 1989 1991 1993 1995 1997

20

45

25

30

35

40

0

0.20

0.05

0.10

0.15

TAXA RICHNESS

PHOSPHORUS CONCENTRATION

PHOSPHORUS CONCENTRATION,

Figure 12. Taxa richness and phosphorus concentrations from West

Branch Brandywine Creek at Wawaset (site 38), Chester County,

Pennsylvania, 1981-97.

IN MILLIGRAM PER LITER

1981

NUMBER OF TAXA
21

Brandywine Creek is affected by agricultural and urban runoff and discharges from wastewater-treatment

plants but benthic-macroinvertebrate communities and water chemistry were stable, indicating good

overall stream conditions.

East Branch Brandywine Creek

Six sampling sites were in the East Branch Brandywine Creek Basin—four sites on the East Branch

Brandywine Creek (sites 48, 42, 36, and 39), one site on Indian Run (site 47), and one site on West Valley

Creek (site 44). Drainage areas range in size from 4.26 mi2 at site 47 to 123 mi2 at site 39. The stream ranges

in size from approximately 15 ft wide at site 48 to 52 ft wide at site 39. The predominant land-use

categories at site 39 are forested (34 percent), agriculture (30 percent), and residential (26 percent)

(Delaware Valley Regional Planning Commission, 1997). These sites were sampled annually from 1981

through 1997.

Sites 42 and 48 are on the upper East Branch Brandywine Creek. Site 47 is on Indian Run, a tributary

to the upper East Branch Brandywine Creek. These sites were assessed as nonimpacted on the basis of

calculated biological metrics except for site 48, which was assessed as slightly impacted on the basis of

median values of HBI (table 6). The benthic-macroinvertebrate community at all of these sites was diverse

with large numbers of “pollution sensitive” organisms and low populations of “pollution tolerant”

organisms. Sites 42 and 47 have had consistent benthic-macroinvertebrate communities and stable habitat.

Water-chemistry data indicate low but increasing concentrations of nitrate and major ions and decreasing

concentrations of phosphorus and ammonia. These sites had biological metric values and chemical

concentrations similar to the reference site.

Site 48 is in the headwaters and had varied benthic-macroinvertebrate, physical, and chemical data.

The benthic-macroinvertebrate community at site 48 was variable with occasionally large numbers of

individuals (table 41, page 64). Chemical data indicate occasionally increased ammonia concentration and

increasing concentrations of nitrate and major ions. East Branch Brandywine Creek at site 48 is a small

headwater stream (5.98-mi2 drainage area), and the variable benthic-macroinvertebrate communities may

be because of the inconsistent water chemistry and shifting stream bottom noted at this site.

Sites 36, 39, and 44 are on the lower East Branch Brandywine Creek. These sites were assessed as

nonimpacted or slightly impacted on the basis of median values of the biological metrics measured

(table 6). The invertebrate communities at all of these sites were diverse with large numbers of mayflies,

caddisflies, and riffle beetles, which indicate good stream quality. Although sites 39 and 44 were assessed

as nonimpacted or slightly impacted, their water chemistry and benthic-macroinvertebrates communities

have been inconsistent.

1983 1985 1987 1989 1991 1993 1995 1997

5

20

10

15

NUMBER OF EPT TAXA

BUCK RUN

(SITE 46)

WEST BR. BRANDYWINE

AT WAWASET (SITE 38)

Figure 13. Ephemeroptera, Plecoptera, and Trichoptera

(EPT) taxa richness from Buck Run (site 46) and West

Branch Brandywine Creek at Wawaset (site 38), Chester

County, Pennsylvania, 1981-97.

1981
22

Concentrations of ammonia and phosphorus at site 39 were elevated over the reference site and sites

upstream on the East Branch Brandywine Creek from 1981 to 1985. Concentrations decreased after 1986

and EPT taxa richness increased from 1986 to 1991 (table 46, page 67). EPT taxa richness declined after

1991 without any associated change in measured water chemistry.

Site 44 had very variable metric numbers with large changes year to year (table 45, page 66).

“Pollution tolerant” organisms occasionally are present in relatively high numbers and dense growths of

algae were always present. These indicate possible organic enrichment. Chemical data indicate consistent

water chemistry. Biological metric values at site 44 indicate degraded stream quality when compared to

the reference site (fig. 14). Ground-water discharge from limestone formations along with nutrient

enrichment may be factors in the reduced taxa at site 44. Site 44 is immediately downstream from Broad

Run, which has an increased nutrient load because of a small wastewater-treatment discharge and groundwater discharge from unsewered parts of the West Valley Creek Basin (Senior and others, 1997).

Sites in the upper part of the East Branch Brandywine Creek (sites 42 and 47) had consistent

macroinvertebrate communities that were assessed as nonimpacted (table 6). Sites in the lower part of the

East Branch Brandywine Creek (sites 36, 44, and 39) had lower taxa richness and EPT taxa richness and

REFERENCE SITE 36 SITE 44 SITE 39

10

60

20

30

40

50

25th percentile

Median

75th percentile

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

REFERENCE SITE 36 SITE 44 SITE 39

0

40

10

20

30

REFERENCE SITE 36 SITE 44 SITE 39

6

2

3

4

5

HBI

SITE

SITE

SITE

EXPLANATION

Figure 14. Taxa richness, Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness, and

Hilsenhoff’s biotic index (HBI) values from reference site (site 15), East Branch Brandywine Creek near

Downingtown (site 36), West Valley Creek (site 44), and East Branch Brandywine Creek at Wawaset

(site 39), Chester County, Pennsylvania, 1981-97.

(SITE 15)

(SITE 15) (SITE 15)

NUMBER OF TAXA NUMBER OF TAXA

TAXA RICHNESS

EPT TAXA RICHNESS HBI
23

higher HBI values from 1981 to 1987. After 1987, sites in the lower East Branch Brandywine Creek had

increasing taxa richness and EPT taxa richness and decreasing HBI values; sites in the upper East Branch

Brandywine Creek remained unchanged. By the mid 1990s, the sites on the upper and lower parts of the

East Branch Brandywine Creek had similar biological metrics (fig. 15). Samples of stream-bottom sediment

generally contained pesticide concentrations that were below the threshold effect concentration and were

decreasing over time.

Main Stem Brandywine Creek

The site on the main stem Brandywine Creek is near Chadds Ford (site 40). The drainage area at

site 40 is 291 mi2. This site is the largest in the Stream Conditions of Chester County Biological Monitoring

Network. The stream is 100 ft wide and less than 2 ft deep at the sampling site. The predominant land-use

categories at site 40 are agriculture (39 percent), forested (31 percent), and residential (21 percent)

(Delaware Valley Regional Planning Commission, 1997). This site was sampled annually from 1981

through 1995 and in 1997.

The main stem Brandywine Creek was assessed as nonimpacted on the basis of median values of

taxa richness and EPT taxa richness and as slightly impacted on the basis of HBI values (table 6). Taxa

richness and EPT taxa richness increased and HBI values decreased starting around 1987 (table 47). Site 40

had a decrease in concentrations of ammonia and phosphorus associated with improved stream

conditions similar to that measured in the East and West Branch Brandywine Creeks. The benthicmacroinvertebrate community at this site was diverse with large numbers of “pollution sensitive”

organisms including mayflies, caddisflies, and riffle beetles, which are indications of good stream quality.

“Pollution tolerant” organisms are present but in relatively low numbers. This site had similar taxa

richness and EPT taxa richness but slightly increased HBI values when compared to the reference site. This

site receives a mix of agricultural, urban, and wastewater-treatment plant discharges but contains a

benthic-macroinvertebrate community that indicates good stream conditions. Most inputs that could

impair water quality are far enough upstream to be attenuated at the main stem Brandywine Creek site.

Water-quality conditions at this site also may be buffered by large acreages of wetland immediately

upstream from the sampling location.

1983 1985 1987 1989 1991 1993 1995

10

30

15

20

25

NUMBER OF EPT TAXA

SITE 36

SITE 42

Figure 15. Ephemeroptera, Plecoptera, and Trichoptera (EPT)

taxa richness from site 42 and site 36 on the East Branch

Brandywine Creek, Chester County, Pennsylvania, 1981-95.

1981
24

Red Clay and White Clay Creek Basins

Streams sampled in the Red Clay and White Clay Creek Basins were the East Branch Red Clay

Creek, West Branch Red Clay Creek, East Branch White Clay Creek, Middle Branch White Clay Creek, and

the West Branch White Clay Creek. The Red Clay and White Clay Creek Basins drain the south-central

part of the county, including the boroughs of Kennett Square, Avondale, and West Grove. Land use in both

basins is dominated by a mix of agriculture (including mushroom farming), residential, and forested areas.

Assessments of stream quality, on the basis of benthic-macroinvertebrate criteria, are presented in table 7.

Red Clay Creek

Two sampling sites were in the Red Clay Creek Basin—one on the West Branch (site 27) and one on

the East Branch (site 26). The drainage areas are approximately 10 mi2, and the stream is approximately

17 ft wide at both sites. The predominant land-use categories in the entire basin are agriculture

(50 percent), residential (21 percent), and forested (20 percent) (Delaware Valley Regional Planning

Commission, 1997). The agricultural land use in the basin includes a large mushroom-producing area in

the central and western parts of the basin and surrounding the Borough of Kennett Square. Water quality

in the Red Clay Creek Basin has been affected by the use of fertilizers and pesticides related to general

agriculture and the mushroom industry. Spent compost may contain potential contaminants including

organochlorine and organophosphorus insecticides and heavy metals. The basin also has potential

contaminants, including PCBs, associated with industrial and commercial land use (Sloto, 1987). The sites

were sampled annually from 1981 through 1997.

Sites in the Red Clay Creek Basin had benthic-macroinvertebrate communities with few EPT taxa

and HBI values elevated over reference sites and sites in surrounding basins (fig. 16). Both sites were

assessed as slightly or moderately impacted on the basis of calculated biological metrics (table 7).

Dominant taxa were “pollution tolerant” organisms including chironomids, aquatic worms, and crane

flies (fig. 17). Field observations have noted that heavy siltation and algal growth are degrading the

physical habitat at both sites. Chemical data indicate steady concentrations of nutrients and major ions but

at levels elevated over the reference site. Samples of stream-bottom sediment collected in the mid-1980s at

both sites contained concentrations of DDT and PCBs above the threshold effect concentration (table 13).

Concentrations above the threshold effect concentration are likely to cause changes in the composition of

benthic-macroinvertebrate communities (MacDonald and others, 2000).

Table 7. Assessment of stream quality on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Red Clay and White Clay Creek Basins, Chester County,

Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s biotic index;

Assessment based on values presented in tables 48-52]

U.S. Geological

Survey station

identification

number

Site

number Taxa richness EPT taxarichness HBI

Red Clay Creek

01479680 27 Moderately impacted Moderately impacted Slightly impacted

01479800 26 Moderately impacted Moderately impacted Slightly impacted

White Clay Creek

01478120 28 Slightly impacted Slightly impacted Slightly impacted

01478190 29 Slightly impacted Nonimpacted Slightly impacted

01478220 30 Slightly impacted Nonimpacted Slightly impacted
25

REFERENCE SITE 26 SITE 27

4

8

5

6

7

HBI

EXPLANATION

25th percentile

Median

75th percentile

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

interquartile range outside the quartile

and more than 1.5 times the

Outlier data value less than or equal to 3

SITE

(SITE 45)

Figure 16. Hilsenhoff’s biotic index (HBI) values from reference site (site 45), East Branch Red Clay

Creek (site 26), and West Branch Red Clay Creek (site 27), Chester County, Pennsylvania, 1981-97.

Chironomidae

Coleoptera

Simuliidae

Other

Chironomidae

Coleoptera

Oligochaeta

Simuliidae

Other

Chironomidae

Coleoptera Oligochaeta

Other

Simuliidae

Reference Site

(Site 45)

Site 26 Site 27

Figure 17. Community composition of benthic-macroinvertebrate communities from the reference site

(site 45), East Branch Red Clay Creek (site 26), and West Branch Red Clay Creek (site 27), Chester County,

Pennsylvania, 1994.

Ephemeroptera,

Plecoptera, and

Trichoptera

Ephemeroptera,

Plecoptera, and

Trichoptera

Ephemeroptera,

Plecoptera, and

Trichoptera
26

Although biological metrics indicated slightly or moderately impacted conditions at both sites,

stream conditions have been improving over time. Taxa richness and EPT taxa richness have increased and

HBI values at site 26 decreased after 1993 (tables 48 and 49, page 68). Stream-bottom sediment data

indicate pesticide and PCB contamination was reduced between 1983 and 1993 (table 13). The

improvement in benthic-macroinvertebrate communities is most likely because of the decrease in the

toxicity of stream sediments. Despite the improvement, both sites have benthic-macroinvertebrate

communities that differ greatly from the reference conditions (figs. 16 and 18). These sites are subject to

urban and agricultural runoff and habitat degradation because of siltation.

White Clay Creek

Three sampling sites were in the White Clay Creek Basin—one on the East Branch (site 28), one on

the Middle Branch (site 29), and one on the West Branch (site 30). The drainage area at each site is

approximately 10 mi2. The stream sites are approximately 20 to 35 ft wide. The predominant land-use

categories at the three sites sampled are agriculture (61 percent), forested (22 percent), and residential

(13 percent) (Delaware Valley Regional Planning Commission, 1997). The sites were sampled annually

from 1981 through 1995 and 1997.

The three sites in the White Clay Creek Basin were assessed as nonimpacted or slightly impacted on

the basis of calculated biological metrics (table 7). All sites had benthic-macroinvertebrate communities

that had relatively high numbers of “pollution tolerant” organisms compared to the reference site,

including chironomids, flatworms, and crane flies. Between 1981 and 1997, these sites had an increase in

taxa richness and EPT taxa richness (tables 50-52, page 69-70), which is an indication of improved stream

conditions (fig. 19). Biological metrics indicated that stream conditions improved in an east to west

direction within the basin (fig. 20). The biological metrics at site 30 on the West Branch White Clay Creek

consistently indicated better stream conditions when compared to site 28 on the East Branch. Waterchemistry data have a pattern similar to the benthic-macroinvertebrate data. Concentrations of nutrients

and major ions decreased in an east to west direction in the basin; the East Branch is elevated over the

reference site and the West and Middle Branches. Site 28 is in the Borough of Avondale and receives

localized urban runoff and agricultural runoff. Sites 29 and 30 are away from any direct urban influences.

The sites in the Red and White Clay Creek Basins had benthic-macroinvertebrate communities that

indicate improved stream conditions from 1981 to 1997. These sites, however, were degraded from the

reference conditions. Biological metrics indicate improved stream conditions in an east to west direction in

the White Clay Creek Basin (fig. 21). Water chemistry generally was stable with slightly increasing

concentrations of nitrates and major ions along with decreasing concentrations of ammonia and

1983 1985 1987 1991 1993 1995 1997

0

25

5

10

15

20

NUMBER OF EPT TAXA

EXPLANATION

REFERENCE SITE

(SITE 45)

SITE 26

SITE 27

Figure 18. Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa richness from

reference site (site 45), East Branch Red Clay Creek (site 26), and West Branch Red

Clay Creek (site 27), Chester County, Pennsylvania, 1981-97.

1981 1989
27

1983 1985 1987 1989 1991 1993 1995 1997

5

20

10

15

EXPLANATION

SITE 28

SITE 29

SITE 30

1981

Figure 19. Numbers of Ephemeroptera, Plecoptera, and Trichoptera

(EPT) taxa from East Branch White Clay Creek (site 28), Middle Branch

White Clay Creek (site 29), and West Branch White Clay Creek (site 30),

Chester County, Pennsylvania, 1981-97. NUMBER OF EPT TAXA

REFERENCE SITE 28 SITE 29 SITE 30

4.0

6.5

4.5

5.0

5.5

6.0

HBI

EXPLANATION

25th percentile

Median

75th percentile

interquartile range outside the quartile

Data value less than or equal to 1.5 times the

interquartile range outside the quartile

and more than 1.5 times the

Outlier data value less than or equal to 3

interquartile range outside the quartile

Outlier data value more than 3 times the

SITE

Figure 20. Hilsenhoff’s biotic index (HBI) values for the reference site (site 45), East Branch White Clay

Creek (site 28), Middle Branch White Clay Creek (site 29), and West Branch White Clay Creek (site 30),

Chester County, Pennsylvania, 1981-97.

 (SITE 45)
28

phosphorus. Although water chemistry was stable and similar to the reference conditions, the stream

bottom was subjected to heavy siltation at sites 26, 27, and 28. These sites receive runoff from urban and

agricultural areas including heavy mushroom farming.

Big Elk and Octoraro Creek Basins

Streams sampled in the Big Elk Creek Basin were the East Branch and West Branch Big Elk Creek.

The Big Elk Creek Basin drains the southwest part of Chester County including the borough of Oxford.

Streams sampled in the Octoraro Creek Basin were East Branch Octoraro Creek and Valley Creek. The

Octoraro Creek Basin drains the southwestern part of the county and includes the boroughs of Parkesburg

and Atglen. Land use in the basin is dominated by a mix of agriculture and forested areas. Assessments of

stream quality, on the basis of benthic-macroinvertebrate criteria, are presented in table 8.

Table 8. Assessment of stream quality on the basis of median values of taxa richness,

EPT taxa richness, and HBI for sites in the Big Elk and Octoraro Creek Basins,

Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s biotic index; Assessment

based on values presented in tables 53-56]

U.S. Geological

Survey station

identification

number

Site number Taxa richness EPT taxa richness HBI

Big Elk Creek

01494900 31 Slightly impacted Nonimpacted Slightly impacted

01494950 32 Slightly impacted Nonimpacted Slightly impacted

Octoraro Creek

01578340 33 Slightly impacted Nonimpacted Slightly impacted

01578343 34 Slightly impacted Nonimpacted Slightly impacted

27 26 28 29 30

SITE NUMBER

30

0

5

10

15

20

25

EXPLANATION

TAXA RICHNESS

EPT TAXA RICHNESS

Figure 21. Median values of taxa richness and Ephemeroptera, Plecoptera, and Trichoptera (EPT)

taxa richness from sampling sites in the Red Clay and White Clay Creek Basins, Chester County,

Pennsylvania, 1981-97. NUMBER OF TAXA
29

Big Elk Creek

Two sampling sites were in the Big Elk Creek Basin—one on the East Branch (site 31) and one on the

West Branch (site 32). The drainage area of each site is approximately 10 mi2. The stream is approximately

18 ft wide at site 31 and is 30 ft wide at site 32. The predominant land-use categories in the basin are

agriculture (68 percent), forested (15 percent), and residential (12 percent) (Delaware Valley Regional

Planning Commission, 1997). These sites were sampled annually from 1981 through 1997.

Both sites in the Big Elk Creek Basin were assessed as slightly impacted on the basis of median

values of taxa richness and HBI and as nonimpacted on the basis of EPT taxa richness (table 8). Through

1993, both sites had taxa richness and EPT taxa richness values similar to the reference site but higher HBI

values because of a relatively high number of “pollution tolerant” organisms (compared to the reference

site) including chironomids and crane flies (fig. 22). These sites had increased concentrations of nutrients

and major ions and heavier sedimentation when compared to the reference site. The degraded chemical

and physical conditions are affecting the benthic-macroinvertebrate communities negatively in the Big Elk

Creek Basin.

Chironomidae

Coleoptera

Simuliidae

Other

Coleoptera

Oligochaeta

Tipulidae

Other

Coleoptera

Other

Reference Site

(Site 45)

Site 31 Site 32

Figure 22. Community composition of reference site (site 45), East Branch Big Elk Creek (site 31),

and West Branch Big Elk Creek (site 32), Chester County, Pennsylvania, 1993.

Chironomidae

Chironomidae

Ephemeroptera,

Plecoptera, and

Trichoptera

Ephemeroptera,

Plecoptera, and

Trichoptera

Ephemeroptera,

Plecoptera, and

Trichoptera

Tipulidae
30

Both sites had a decrease in taxa richness and EPT taxa richness starting in 1994. The decrease in

organisms was most noticeable at site 31 where EPT taxa richness declined from 13 in 1992 to 3 in 1996

(fig. 23). Analysis of physical and chemical data did not reveal any change in the habitat or water

chemistry at these sites to explain the decrease in taxa. The sudden drop in taxa from all groups of benthic

macroinvertebrates may be caused by some factor not measured in the physical or chemical sampling,

such as pesticide contamination.

East Branch Octoraro Creek

Two sampling sites were in the East Branch Octoraro Creek Basin—one on the East Branch Octoraro

Creek (site 33) and one on Valley Creek (site 34). The drainage area of both sites is approximately 10 mi2.

The stream is approximately 21 ft wide at site 34 and is 55 ft wide at site 33. The predominant land-use

categories at site 33 are agriculture (69 percent), forested (15 percent), and residential (11 percent)

(Delaware Valley Regional Planning Commission, 1997; Lancaster County, 2002). These sites were sampled

annually from 1981 through 1997.

Both sampling sites were assessed as nonimpacted or slightly impacted on the basis of calculated

biological metrics (table 8). The benthic-macroinvertebrate community at site 33 occasionally had high

numbers of “pollution tolerant” organisms including chironomids, black flies, aquatic worms, and crane

flies, but this number was offset by a large population of “pollution sensitive” organisms. These year-toyear differences in community composition are reflected in widely fluctuating values of the HBI (fig. 24).

Taxa richness and EPT taxa richness were stable since 1982 (tables 55 and 56, pages 71-72). Physical and

chemical data indicate increasing concentrations of nitrate and major ions and decreasing concentrations

of ammonia and phosphorus at these sites. The nitrate concentrations increased from 5.10 mg/L in 1981 to

9.0 mg/L in 1997 (fig. 25). Heavy agriculture in the basin is the most likely source of the nutrient

enrichment. Despite the increased concentrations of nitrate, the benthic-macroinvertebrate data indicate

improved stream quality. The improved stream quality most likely is related to the decreased ammonia

concentrations, which can lead to increased concentrations of dissolved oxygen.

Site 34 had very inconsistent benthic-macroinvertebrate and water-chemistry data from 1981 to

1997. Site 34 had a benthic-macroinvertebrate community with occasionally high numbers of “pollution

tolerant” organisms including chironomids, black flies, worms, and crane flies. Biological metrics were

variable, indicating inconsistent stream conditions (table 56, page 72). Water chemistry at site 34 also was

highly variable; concentrations of nutrients and major ions were elevated over reference conditions.

Nitrate concentrations increased and phosphorus concentrations decreased since 1981 in a pattern similar

to the East Branch Octoraro Creek (fig. 25). However, ammonia concentrations increased at site 34 from

0.050 mg/L in 1981 to a maximum of 0.34 mg/L in 1994. An increase in ammonia can lead to a decrease in

1981 1983 1985 1987 1989 1991 1993 1995

YEAR

20

5

10

15

NUMBER OF EPT TAXA

Figure 23. Number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa from the

reference site (site 45), East Branch Big Elk Creek (site 31), and West Branch Big Elk Creek

(site 32), Chester County, Pennsylvania, 1981-96.

0

EXPLANATION

REFERENCE SITE

(SITE 45)

SITE 31

SITE 32
31

dissolved oxygen, which can affect the benthic-macroinvertebrate communities negatively. The physical

habitat at the site was stable, but the stream bottom was subjected to heavy sedimentation. Nutrient

enrichment, including elevated concentrations of ammonia, are most likely from heavy agriculture and a

small wastewater-treatment plant that discharges into the stream upstream of the site.

The sites in the East Branch Octoraro Creek Basin had water chemistry and benthic-macroinvertebrate community structure that was different from reference conditions. Both streams had higher

concentrations of nutrients and major ions, and the concentration of nitrate has been increasing since 1981.

The benthic-macroinvertebrate community contained increased numbers of “pollution tolerant”

organisms compared to the reference site, indicating degraded stream conditions. Although both sites

differ from the reference conditions, the calculated biological metrics indicate improving stream quality at

site 33 on the East Branch Octoraro Creek and declining stream quality at site 34 on Valley Creek. Nitrate

concentrations at site 33 were higher than site 34, but concentrations of ammonia and phosphorus were

lower. The difference in nutrient concentrations may be because of discharge from a wastewater-treatment

plant that affects site 34.

1981 1983 1985 1987 1989 1991 1993 1995

3.5

6.0

4.0

4.5

5.0

5.5

HBI

EXPLANATION

SITE 33

SITE 34

Figure 24. Hilsenhoff’s biotic index (HBI) values from East Branch Octoraro

Creek (site 33) and Valley Creek (site 34), Chester County, Pennsylvania,

1981-96.

1981 1983 1985 1987 1989 1991 1993 1995

2

12

4

6

8

10

NITRATE AS N,

EXPLANATION

REFERENCE

SITE (SITE 45)

SITE 33

SITE 34

Figure 25. Nitrate concentrations from the reference site (site 45), East Branch Octoraro

Creek (site 33), and Valley Creek (site 34), Chester County, Pennsylvania, 1981-96. IN MILLIGRAMS PER LITER
32

Summary of Stream-Quality Conditions

Benthic-macroinvertebrate samples collected in Chester County from 1981 to 1997 indicate

nonimpacted or slightly impacted conditions at most of the 43 sites sampled. Sites in the Pigeon, French,

Pickering, and upper East Branch Brandywine Creek Basins generally were assessed as nonimpacted with

stable physical and chemical data. These sites receive minimal disturbance. Sites in the Darby, Crum,

Ridley, Valley, and lower East Branch Brandywine Creek Basins are being degraded compared with

reference conditions, possibly resulting from habitat alteration.

Sites in the West Branch Brandywine, Red Clay, White Clay, Big Elk, and Octoraro Creek Basins had

benthic-macroinvertebrate communities that indicated a degradation in stream conditions from reference

conditions. These basins have more agricultural land, which can cause increased concentrations of

nutrients and major ions and increased sedimentation. Sites near discharges from wastewater-treatment

plants have benthic-macroinvertebrate communities that indicate the poorest stream conditions.

Along with general patterns in benthic-macroinvertebrate communities, the community structure

shows incidents of dramatic changes. Examples of these include a significant change in taxa richness, EPT

taxa richness, and HBI values between 1989 and 1991 at site 22 and between 1993 and 1996 at site 31. The

degraded stream quality at site 22 was caused by an increase in manganese concentrations from a

malfunctioning ground-water air stripper discharging into the stream. The benthic macroinvertebrates at

site 22 recovered when the air stripper was shut off. The degraded stream quality at site 31 could not be

attributed to any measured change in physical or chemical conditions.

Trend Analysis

Biological organisms usually are found in nature in a nonrandom distribution. This nonrandom

distribution is a result of habitat and behavior requirements of the individual organisms (Greeson and

others, 1977). Nonparametric statistical methods are suggested for the detection of trends in streamquality data because of the problems of skewness and serial correlation (Hirsch and others, 1982). The

Mann-Kendall test for trend, a nonparametric, distribution-free statistical test for monotonic trend with

time, was used to detect trends in taxa richness, EPT taxa richness, and HBI at each site. The Mann-Kendall

test for trend also was used to detect trends in specific conductance and concentrations of nitrate,

ammonia, and phosphorus at each site.

Mann-Kendall Test for Trend in Biological Metrics

The Mann-Kendall test for trend was used to detect trends in taxa richness, EPT taxa richness, and

HBI from 1981 through 1997 at each of the 43 sampling sites. This statistical technique was used by Moore

(1987) and Hardy and others (1995) to evaluate trends in values of Brillouin’s diversity index from sites in

the Stream Conditions of Chester County Biological Monitoring Network. The results of the trend test are

presented in table 9. Trends were considered significant if the p value was greater than 90 percent.

Table 9. Mann-Kendall test of taxa richness, EPT taxa richness, and HBI from selected streams in Chester

County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; HBI, Hilsenhoff’s biotic index; p>90, trends were considered

significant if the p value was greater than 90 percent]

 Basin

Number

of

sites

Taxa richness1

1 Positive trend for taxa richness indicates improving biological community.

EPT taxa richness2

2 Positive trend for EPT taxa richness indicates improving biological community.

HBI3

3 Negative trend for HBI indicates improving biological community.

Positive

trends

(p>90)

Negative

trends

(p>90)

Positive

trends

(p>90)

Negative

trends

(p>90)

Positive

trends

(p>90)

Negative

trends

(p>90)

Schuylkill River Basin 14 5 0 6 0 1 3

Delaware River Basin 9 1 0 1 1 3 2

Brandywine Creek Basin 11 4 0 5 1 0 3

Red/White Clay Creek Basins 5 5 0 5 0 0 0

Big Elk/Octoraro Creek Basins 4 1 1 1 1 0 2
33

Trends in biological metrics from the 43 sites in Chester County indicate unchanged or improving

stream conditions at most sites between 1981 and 1997. Positive trends were measured at 37 percent of the

sites for taxa richness and at 42 percent of the sites for EPT taxa richness. One site had a decreasing trend

in taxa richness and three sites had decreasing trends in EPT taxa richness. Decreasing trends in HBI were

measured at 27 percent of the sites and positive trends at 9 percent of the sites. Increasing taxa richness

and decreasing HBI are indications of improved stream quality. Significant trends in these biological

metrics indicate values that are changing in one direction over time. Temporary changes in stream quality

may occur within the time period and not be reflected in a significant trend.

The improvement in stream conditions may be the result of various factors, including upgrading

and eliminating wastewater-treatment plants, reducing organochlorine pesticide use, changing land use

from agriculture to suburban, and improving farm-management procedures. These factors have improved

the water chemistry and reduced the toxicity and amount of sediment reaching the stream bottom.

The basins that showed the most consistent improvement in biological metric values were Red Clay

and White Clay Creeks. All five sites in the basins had significant increases in taxa richness and EPT taxa

richness from 1981 to 1997. Although the trends in taxa richness and EPT taxa richness are indicating

better stream conditions in these basins, the samples from the Red Clay Creek Basin have low taxa richness

and EPT taxa richness and high HBI values compared to other sites in Chester County. The HBI at the Red

Clay Creek sites had no significant trend from 1981 to 1997, despite the increase in total taxa and EPT taxa;

these patterns suggest that the communities are still dominated by “pollution tolerant” organisms. These

streams are in an area where mushroom farming is common and, therefore, have high concentrations of

nutrients and heavy sedimentation. Decreasing toxicity of bottom sediments may be one factor for the

observed changes in biological communities.

Mann-Kendall Test For Trend in Chemical Constituents

Samples of stream water were collected in conjunction with each benthic-macroinvertebrate sample.

Concentrations of nutrients, major ions, and dissolved metals were determined. Changing concentrations

of these constituents over time is a factor affecting the benthic-macroinvertebrate communities. The MannKendall test for trend was calculated to evaluate trends in specific conductance and concentrations of

nitrate, ammonia, and phosphorus (table 10). The constituents were chosen because they were analyzed

over the complete period of record, they are found in concentrations that could affect the benthicmacroinvertebrate community, and they are associated with common water-quality problems in Chester

County.

Table 10. Mann-Kendall test of specific conductance and concentrations of nitrate, ammonia, and phosphorus from

selected streams in Chester County, Pennsylvania, 1981-97

[Positive trends indicate deteriorating water-quality conditions; p>90, trends were considered significant if the p value

was greater than 90 percent]

 Basin

Number

of

sites

Specific

conductance Nitrate Ammonia Phosphorus

Sites

with

positive

trends

(p>90)

Sites

with

negative

trends

(p>90)

Sites

with

positive

trends

(p>90)

Sites

with

negative

trends

(p>90)

Sites

with

positive

trends

(p>90)

Sites

with

negative

trends

(p>90)

Sites

with

positive

trends

(p>90)

Sites

with

negative

trends

(p>90)

Schuylkill River Basin 14 10 0 1 1 0 4 0 2

Delaware River Basin 9 7 1 1 1 0 2 1 3

Brandywine Creek Basin 11 10 0 8 1 0 3 0 4

Red/White Clay Creek Basins 5 5 0 2 0 0 1 0 3

Big Elk/ Octoraro Creek

Basins

4 4 0 4 0 13 01
34

Specific conductance

Specific conductance is the capacity of water to conduct an electrical current at 25°C. Specific

conductance is a measure of the total inorganic dissolved solids in the water. Charged ions such as

chloride, potassium, and sodium dissolved in the water will increase the conductance. These ions are nontoxic to aquatic life at concentrations found in Chester County streams. Sources of ions in surface water

include ground-water discharges, wastewater-treatment and septic discharges, and overland runoff.

Specific conductance values increased at 36 of the 43 sites sampled from 1981 to 1997 (table 10). The

increasing values were measured throughout Chester County in areas of different land use and in various

size basins (fig. 26). Specific conductance is an indirect measurement of dissolved ions. Increasing specific

conductance may be related to increased runoff from impervious surfaces and wastewater-treatment and

septic discharges. The only site with a decreasing trend in specific conductance was Goose Creek in the

East Branch Chester Creek Basin. This site is below the discharge of a wastewater-treatment plant

upgraded in the mid 1980s. Although the conductance was declining at this site, it was two to four times

higher than at other sites in the Delaware River Basin and had the highest median conductance of all sites

sampled from 1981 to 1997. There is little relation between specific conductance trends and trends in the

biological metrics calculated for this study. Although specific conductance is a good measure of general

water-quality contamination, it has limited value for isolating causes for trends of biological communities.

Nutrients

Nutrients (nitrogen and phosphorus compounds) are naturally occurring compounds needed for

plant growth and commonly are found in elevated concentrations above background levels because of

human activities. Nutrient sources include commercial fertilizers and manure, wastewater-treatment

discharges, septic systems, and atmospheric deposition. Elevated nutrient concentrations can cause

increased plant growth in the stream that can alter benthic-macroinvertebrate communities and cause low

concentrations of dissolved oxygen (hypoxia) that can be fatal to aquatic organisms.

Nitrate.—Nitrate is the primary form of nitrogen dissolved in stream water. Nitrate is non-toxic to

aquatic life at concentrations found in Chester County streams, but high concentrations can cause

increased algal growth, which decays and results in low concentrations of dissolved oxygen. Degraded

benthic-macroinvertebrate communities in high nitrate conditions are caused by the low concentrations of

1981 1997 1985 1990 1995

YEAR

100

400

150

200

250

300

350

SPECIFIC CONDUCTANCE,

EXPLANATION

PICKERING CREEK

CHESTER CREEK

BRANDYWINE CREEK

WEST BRANCH BIG ELK CREEK

(SITE 5)

(SITE 24)

(SITE 32)

(SITE 40)

Figure 26. Specific conductance from selected sites in Chester County, Pennsylvania, 1981-97. IN MICROSIEMENS PER CENTIMETER AT 25°C
35

dissolved oxygen and not the high nitrate concentrations. Areas with increasing trends in nitrate

concentrations are likely to have decreasing concentrations of dissolved oxygen that may result in

degraded benthic-macroinvertebrate communities. A drinking-water standard of 10 mg/L has been

established for nitrate, although concentrations above 0.3 mg/L can cause increased plant productivity,

which can lead to low concentrations of dissolved oxygen and decreased benthic-macroinvertebrate

diversity (U.S. Environmental Protection Agency, 1994a).

Increasing trends in nitrate concentrations were measured at 16 of 43 sites between 1981 and 1997.

Three sites had decreasing trends in nitrate and 24 sites had no significant trends (table 10). The sites with

increasing trends in nitrate concentrations are concentrated in the central and western parts of Chester

County where agricultural land use is higher than in the Schuylkill and Delaware River Basins (fig. 27).

Nitrate concentrations also follow an east to west pattern; the highest concentrations are in the Octoraro

Creek Basin (fig. 28). Elevated nitrate concentrations (above 10 mg/L) also are common at sites

SCHUYLKILL DELAWARE EAST BR. WEST BR. RED/WHITE BIG ELK/

14

0

2

4

6

8

10

12

NUMBER OF SITES

EXPLANATION

NO TREND

INCREASING TREND

DECREASING TREND

RIVER

BASIN

RIVER

BASIN

BRANDYWINE

CREEK

BRANDYWINE

CREEK

CLAY

BASINS

OCTORARO

CREEK

BASINS

CREEK

 BASIN BASIN

Figure 27. Results of Mann-Kendall test for trend in nitrate from selected sites in various basins, Chester

County, Pennsylvania, 1981-97.

FRENCH EAST BR. EAST BR. WEST BR. EAST BR. WEST BR. EAST BR. 0

12

2

4

6

8

10

NITRATE CONCENTRATION,

25th percentile

Median

75th percentile

1.5 times the interquartile range

Data value less than or equal to

1.5 times the interquartile range

equal to 3 and more than

Outlier data value less than or

(SITE15)

BRANDY-

(SITE 39)

BRANDY-

(SITE 38)

RED CLAY

(SITE 26)

BIG ELK

(SITE 32) (SITE 33)

OCTORARO

(SITE 24)

CHESTER

EXPLANATION

Figure 28. Nitrate concentrations from selected sites in Chester County, Pennsylvania, 1981-97.

 CREEK WINE WINE CREEK CREEK CREEK

CREEK

IN MILLIGRAMS PER LITER

outside the quartile

outside the quartile
36

downstream of wastewater-treatment plant discharges in all basins. Nitrate concentrations downstream of

wastewater-treatment plants also are related to the conversion of ammonia to nitrate. The conversion of

ammonia to nitrate decreases the toxicity to the benthic macroinvertebrates but does not decrease the

potential for eutrophication.

Ammonia and phosphorus.—Ammonia is a dissolved form of nitrogen that, at high

concentrations, is toxic to aquatic organisms. The USEPA has set an aquatic-life criteria in surface waters of

0.07 to 2.1 mg/L ammonia-nitrogen depending on water temperature and pH (U.S. Environmental

Protection Agency, 1986). Although no national criterion has been established, the USEPA recommends

that concentrations of total phosphorus not exceed 0.1 mg/L in flowing waters for the prevention of

nuisance plant growth (U.S. Environmental Protection Agency, 1994b). Excess phosphorus can cause

increased plant production that can lead to low concentrations of dissolved oxygen and degraded habitat

that can cause decreased benthic-macroinvertebrate diversity.

A decreasing trend in the concentration of ammonia was measured at 13 of 43 sites (table 10)

between 1981 and 1997. Phosphorus concentrations also had a decreasing trend at 13 of 43 sites during the

same time period (table 10). The decreasing trends were found in all basins in areas of various land use.

Concentrations of ammonia and phosphorus are elevated above reference conditions in heavy agricultural

areas and near wastewater-treatment discharges. Improvements in wastewater-treatment, restrictions on

phosphate detergents, and reduced agricultural runoff have decreased the phosphorus concentrations

throughout Chester County. Ammonia concentrations also have decreased as a result of upgrades to

wastewater-treatment plants. Upon oxidation, ammonia is converted to nitrate, which is less toxic to

benthic macroinvertebrates. Sampling sites that were not in agricultural areas or near wastewatertreatment discharges had low concentrations of ammonia and phosphorus in 1981 that remained low

through 1997.

Increasing trends in specific conductance were measured from all basins in the county across

various land uses. Trends in nutrient concentrations follow more of a spatial pattern related to land use.

Nutrient concentrations in the Schuylkill and Delaware River Basins generally are unchanged except in

areas affected by discharges from wastewater-treatment plants. Most sites in these basins had relatively

low concentrations of nitrate, ammonia, and phosphorus in the early 1980s, and the concentrations of

these constituents have remained consistent over time. The sites near discharges from wastewatertreatment plants have decreasing concentrations of nutrients, but the concentrations are still elevated over

reference conditions. Nutrient concentrations in the Brandywine, Red Clay, White Clay, Big Elk, and

Octoraro Creek Basins generally are higher and more variable than in the eastern part of the county.

Nitrate concentrations generally are increasing, but concentrations of ammonia and phosphorus are

decreasing. Decreasing phosphorus concentrations are likely the result of upgrades in wastewatertreatment plants, restrictions on phosphate detergents, and reduced fertilizer runoff. Increasing nitrate and

decreasing ammonia concentrations are likely the result of improved wastewater-treatment processes that

convert ammonia to nitrate. As a result, the toxicity to aquatic life has decreased, but the concentrations of

total nitrogen have remained the same. Elevated concentrations of nutrients can cause algal blooms that

can result in low concentrations of dissolved oxygen and poor habitat conditions that can cause decreased

benthic-macroinvertebrate communities.

Dissolved-oxygen concentrations have been measured at three continuous monitoring stations in

the Brandywine Creek Basin since 1972. Data from these monitoring stations indicate the concentrations of

minimum dissolved oxygen have increased over time. In 1997, there only were 3 days when the minimum

concentration of dissolved oxygen was below 5.0 mg/L on the East Branch Brandywine Creek below

Downingtown compared to 103 days in 1981. This increase in minimum dissolved-oxygen concentrations

is a major factor for the improvement in benthic-macroinvertebrate communities throughout Chester

County between 1981 and 1997.
37

Stream-Bottom Sediment Samples

Metals, trace elements, and organic contaminants may accumulate and become concentrated in

stream-bottom sediments. The concentration of these substances in the stream-bottom sediments can

exceed those of the overlying water by an order of magnitude (Horowitz, 1991). Concentrations of organic

contaminants, trace elements, and metals in stream-bottom sediments may occur naturally from the local

geology or be related to human influences. Bottom-dwelling and bottom-feeding organisms provide a

pathway for contaminants to enter the food web (Hem, 1985; Horowitz, 1991).

Sampling for selected metals and trace elements was conducted during the period 1993 to 1997 at 36

of the 43 sites, and for organic contaminants during 1983 to 1997 at all 43 sites. Information gathered from

stream-bottom sediment sampling was used to help assess the benthic-macroinvertebrate samples and

provide data that can be used to examine trends in sediment quality. Sampling locations at each site were

selected in depositional areas. Depositional areas contain fine-grained particles that usually are associated

with high concentrations of organic compounds, metals, and trace elements (Horowitz, 1991). Samples

were collected by hand from the top 6 to 12 in. of sediment according to the methods of Wershaw and

others (1987, p. 7-8). The sample was homogenized by mixing and transferred to clean glass or

polyethylene containers and placed on ice for shipment to the USGS National Water-Quality Laboratory in

Arvada, Colo. Metal concentrations were determined by atomic absorption spectrometry (Fishman and

Friedman, 1989). Concentrations of organochlorine and organophosphorus pesticides and PCB were

determined by gas chromatography using a flame photometric detector (Wershaw and others, 1987). All

results are reported as dry weights.

Selected Metals and Trace Elements

Metals and trace elements in small quantities are needed for normal plant and animal development.

However, some metals and trace elements, such as mercury and arsenic, can be toxic at low concentrations

(Meade, 1995). Metals and trace elements in stream-bottom sediments come from natural as well as

artificial sources. Natural sources are from rock weathering, soil erosion, and the dissolution of salts.

Artificial sources include wastewater discharges, industrial activities, mining, and agriculture.

Samples for analysis of metals and trace elements were collected once from stream-bottom sediment

at 36 of the 43 sites between 1993 and 1997. Sites 2, 16, 20, 21, 34, 36, and 37 were not sampled. Statistics for

arsenic, cadmium, chromium, copper, iron, lead, manganese, mercury, and zinc are presented in table 11.

Metals and trace elements were evaluated by use of guidelines developed by MacDonald and others

(2000). These sediment-quality guidelines include the threshold effect concentration. Concentrations

below the threshold effect concentration are unlikely to cause harmful effects (MacDonald and others,

2000).

Table 11. Occurrence of selected trace elements in samples of stream-bottom

sediment collected in Chester County, Pennsylvania, 1984-97

[μg/g, microgram per gram]

Constituent

Number

of

samples

Percentage of

samples with

detectable

concentrations

Range of detected

concentrations

(μg/g)

Threshold

effect

concentration1

1 A level of sediment contamination below which harmful effects are unlikely to be observed

(MacDonald and others, 2000).

Percentage of

samples with

concentration

greater than

threshold

effect

concentration

Arsenic 35 86 1.0 - 6.0 9.79 0

Cadmium 36 5.6 1.0 .99 8.3

Chromium 36 100 1.0 - 50 43.4 8.3

Copper 36 86 10. - 42 31.6 2.8

Lead 36 83 10. - 80 35.8 17

Mercury 36 86 .01 - .76 .18 11

Zinc 36 100 7.0 - 170 121 5.6
38

Arsenic, chromium, copper, lead, mercury, and zinc were detected in more than 83 percent of the

samples. Cadmium was detected in less than 6 percent of the samples. The percentage of samples

exceeding the threshold effect concentration was below 10 percent for arsenic, cadmium, chromium,

copper, and zinc and between 10 and 17 percent for lead and mercury (table 11).

Arsenic

Arsenic is a trace element on the USEPA Priority Pollutants list (U.S. Environmental Protection

Agency, 1994b). Arsenic occurs naturally and is used in industrial processes including bronze production,

pesticides, transistors, and treated lumber (Weast, 1983). Arsenic was detected in 86 percent of 35 samples

(table 11); concentrations ranged from 1.0 to 6.0 μg/g, which are below the threshold effect concentration

(9.79 μg/g). The highest detected arsenic concentration (6.0 μg/g) was at site 49 on Little Valley Creek.

These data suggest arsenic is not affecting benthic-macroinvertebrate communities adversely in Chester

County.

Cadmium

Cadmium is a toxic trace element on the USEPA Priority Pollutants list (U.S. Environmental

Protection Agency, 1994b). Cadmium is used for electroplating, solder, batteries, and pigments (Weast,

1983). Cadmium was detected in 3 of the 36 (8 percent) samples collected (table 11). The concentration of

cadmium detected in the samples was 1 μg/g, which is slightly above the threshold effect concentration.

These samples were collected from Little Valley Creek (site 49), Valley Creek (site 50), and East Branch

Chester Creek (site 25). Cadmium concentrations measured in the stream-bottom sediments do not appear

to be affecting the benthic-macroinvertebrate communities in Chester County.

Chromium

Chromium is a toxic trace element on the USEPA Priority Pollutants list (U.S. Environmental

Protection Agency, 1994b). Chromium is used in steel production and fabrication, leather tanning, and in

glass and textiles (Weast, 1983). Chromium was detected in all 36 samples collected. Detected

concentrations ranged from 1.0 to 50 μg/g. Chromium concentrations exceeded the threshold effect

concentration of 43.4 μg/g in 8 percent of the 36 samples (table 11). The highest concentrations (50 μg/g)

were at site 1 on Pickering Creek, site 38 on West Branch Brandywine Creek, and site 33 on East Branch

Octoraro Creek. Benthic-macroinvertebrate communities at these sites were either nonimpacted or slightly

impacted. So, although chromium is ubiquitous in Chester County streams, it does not appear to be a

factor in the impairment of benthic-macroinvertebrate communities.

Copper

Copper is a toxic trace element on the USEPA Priority Pollutants list (U.S. Environmental Protection

Agency, 1994b). Copper is used by the electrical industry and in algicides and insecticides (Weast, 1983).

Copper was detected in 31 of the 36 (86 percent) samples collected. Detected concentrations ranged from

10 to 42 μg/g. Copper concentrations exceeded the threshold effect concentration of 31.6 μg/g in

2.8 percent of the 36 samples (table 11). The highest concentration (42 μg/g) was at site 25 on East Branch

Chester Creek.

Lead

Lead is a widely dispersed naturally occurring metal on the USEPA Priority Pollutants list (U.S.

Environmental Protection Agency, 1994b). Lead is used for batteries, plumbing, and insecticides (Weast,

1983). Lead was detected in 30 of the 36 (83 percent) samples collected. Detected concentrations ranged

from 10 to 80 μg/g. Lead concentrations exceeded the threshold effect concentration of 35.8 μg/g in

17 percent of the 36 samples (table 11). Sites that exceeded the threshold effect concentration were

primarily in the Schuylkill River Basin (sites 14, 16, and 50). The highest concentration (80 μg/g) was at

site 16 on French Creek. This site was judged to be slightly impacted. Lead may be a contributing factor to

these impacts.
39

Mercury

Mercury is a toxic trace element on the USEPA Priority Pollutants list (U.S. Environmental

Protection Agency, 1994b). Mercury has been used widely in industrial products and processes and

pesticides and will bioaccumulate in stream organisms (Hem, 1985). Mercury was detected in 31 of 36

(86 percent) samples collected and concentrations ranged from 0.01 to 0.76 μg/g. Mercury concentrations

exceeded the threshold effect concentration of 0.18 μg/g in 11 percent of 36 samples (table 11). Sites that

exceeded the threshold effect concentration were in the East Branch Chester Creek (site 24, 25, and 51) and

West Branch Brandywine Creek Basins (site 46). The highest concentration (0.76 μg/g) was at site 25 on

Goose Creek. The biological community in Goose Creek was judged to be moderately impacted. Mercury

may be a causative factor to this impairment.

Zinc

Zinc is a trace element that occurs naturally in the Earth’s crust and is on the USEPA Priority

Pollutants list (U.S. Environmental Protection Agency, 1994b). Zinc is important to the normal

development of animals but is toxic in higher concentrations (Weast, 1983). Zinc was detected in all

36 samples collected. Concentrations ranged from 7 to 170 μg/g and exceeded the threshold effect

concentration of 120 μg/g in only two samples, Goose Creek (site 25) and East Branch Chester Creek

(site 27) (table 11). Zinc concentrations most likely are not causing biological impairments in Chester

County streams.

In general, background metal and trace-element concentrations in samples of stream-bottom

sediment collected throughout Chester County were not a water-quality problem. Sites with

concentrations of metals or trace elements above the threshold effect concentration were in the French

Creek Basin (sites 14 and 16), Pickering Creek (site 1), Valley Creek (site 50), East Branch Chester Creek

(sites 22, 25, and 51), Brandywine Creek (sites 38, 40, and 46), and the Octoraro Creek (site 33) (fig. 29).

Background concentrations of ground water in the northeastern part of the county indicate the elevated

concentrations, above background levels, of metals and trace elements at sites in the French, Pickering,

and Valley Creeks may be from natural sources (Sloto, 1987). The elevated concentrations at sites 22, 25,

and 40 may be affected by natural sources and past and present industrial activities or wastewater

discharges near those sites.
40

Figure 29. Sampling sites with metal or trace-element concentration above the threshold effect concentration, Chester

County, Pennsylvania.

02 68 4 MILES

KILOMETERS

COUNTY BOUNDARY

EXPLANATION

02 68 4

STATE BOUNDARY

76°

75°45′

75°30′

40°

39°45′

40

Schuylkill River Watershed

Brandywine Creek Watershed

Big Elk Creek

Watershed

Pequea Creek

DELAWARE

Marsh Creek

Reservoir

Rock Run

Reservoir

14

6

1

5

50

49

17

51

24

25

Delaware

River Watershed

44

48

37

22

33

32

30

29

28 26

27

13 10

15

16

47

42

12

3

19

38 39

4

46

45

31

Watershed

Octoraro Creek

Watershed

Northeast Creek

Watershed

Christina River Watershed

PENNSYLVANIA

MARYLAND

METAL OR TRACE-ELEMENT CONCENTRATION

ABOVE THRESHOLD EFFECT CONCENTRATION

WATERSHED BOUNDARY

METAL OR TRACE-ELEMENT CONCENTRATION

BELOW THRESHOLD EFFECT CONCENTRATION
41

Organochlorine Insecticides and Polychlorinated Biphenyls

Organochlorine insecticides are used in agriculture and urban areas to control insects. PCBs have

been used in electrical transformers, plasticizers, and flame retardants. These compounds have low

solubility in water, are persistent in the environment, and are bioaccumulated by many organisms. Each of

these compounds can impair aquatic organisms living in or on the stream bottom.

Samples of stream-bottom sediment were collected from the 43 sites in the study area from 1983

through 1997 and analyzed for organochlorine insecticides and gross PCBs. Most sites were sampled

twice, once between 1983 and 1989 and once between 1993 and 1997. Of the 15 organochlorine insecticides

analyzed, 14 were detected. PCBs were detected in 55 of 82 samples collected. The most frequently

detected compounds were chlordane, dieldrin, DDD, DDE, DDT, and PCBs (table 12).

Chlordane

Chlordane is a synthetic organic compound used as an insecticide around the foundations of

buildings for termite and ant control until the mid-1980s (U.S. Environmental Protection Agency, 1990).

Chlordane is on the USEPA Priority Pollutants list (U.S. Environmental Protection Agency, 1994b).

Chlordane was detected in 61 percent of the 80 samples collected. Concentrations of chlordane

ranged from 1.0 to 110 μg/kg and exceeded the threshold effect concentration of 3.24 μg/kg in 42 percent

of the samples from 56 percent of the sites (table 12). Sites that exceeded the threshold effect concentration

were on Stony Run (site 6), French Creek (sites 13 and 16), Little Valley Creek (site 49), Darby Creek

(site 17), East Branch Chester Creek (sites 22, 25, and 51), Brandywine Creek (sites 39 and 46), and East

Branch Big Elk Creek (site 31). The highest concentration (110 μg/kg) was at site 51 on East Branch Chester

Creek in 1986 (table 13). Thirty-six sites were sampled once between 1983 and 1987 and once between 1993

and 1997. Of these 36 paired sites, chlordane was detected in 61 percent of samples collected between 1983

and 1987 and in 69 percent of samples collected between 1993 and 1997 (fig. 30). The 36 sites had a median

concentration of 5 mg/kg with a maximum concentration of 110 mg/kg in 1983-87 and a median

concentration of 5 mg/kg with a maximum concentration of 32 mg/kg in 1993-97 (fig. 31). This result

indicates elevated chlordane concentrations are less common, but low level chlordane concentrations are

persistent throughout Chester County.

Table 12. Occurrence of selected organochlorine insecticides and polychlorinated biphenyls in samples of streambottom sediment collected at 43 sites in Chester County, Pennsylvania, 1984-97

[μg/kg, micrograms per kilogram]

Constituent

Number

of

samples

Percentage

of samples

with detectable

concentrations

Percentage

of sites with

detectable

concentrations

Range of detected

concentrations

(μg/kg)

Threshold

effect

concentration1

(μg/kg)

1 A level of sediment contamination below which harmful effects are unlikely to be observed (MacDonald and others, 2000).

Percentage of

samples with

concentration

greater than

threshold effect

concentration

Percentage of

sites with

concentration

greater than

threshold

effect

concentration

Chlordane 80 61 70 1.0 - 110 3.24 42 56

DDT 79 53 70 .10 - 61 4.16 6 7

DDD 79 75 93 .10 - 260 4.88 4 5

DDE 77 88 95 .10 - 22 3.16 5 9

Dieldrin 80 64 77 .10 - 5.4 1.90 8 14

PCB 82 67 74 1.0 - 15,000 59.8 10 12
42

Table 13. Concentrations of organochlorine insecticides and gross polychlorinated

biphenyls greater than the threshold effect concentration1 from stream-bottom

sediment samples collected in Chester County, Pennsylvania, 1983-97

[All concentrations are in micrograms per kilogram; —, concentration did not exceed or equal

threshold effect concentration1; PCB, gross polychlorinated biphenyls]

U.S.

Geological

Survey

station

identification

number

Site

number Year Chlordane DDT DDD DDE Dieldrin PCB

Schuylkill River Basin

01472109 6 1985 6.0 — — — — —

1996 10 — — — —

01472138 13 1997 12 — — — — —

01472140 12 1985 — — — — 4.8 —

01472154 14 1985 6.0 — — — — —

014721612 16 1985 5.0 — — — 5.4 —

1994 24 — — — — —

01473167 49 1986 — — — — — 15,000

1987 13 — — — — 540

1993 5.0 — — — — —

01473168 50 1985 5.0 — — — — —

1993 5.0 — 10 — —

Delaware River Basin

01475300 17 1986 — — — — 2.7 95

1996 14 — — — 2.0 —

01475840 19 1986 7.0 — — — — —

6.0 — — — — —

01476430 20 1985 7.0 — — — — —

01476790 22 1986 30 — — — — —

1997 32 — — — 3.9 —

01476830 23 1996 7.0 — — — — —

01476835 24 1985 7.0 — — — — —

1994 6.0 — — — — —

01476840 25 1988 51 13 7.5 — — 120

1993 10 12 — — — —

01476848 51 1986 110 — 5.0 — — 73

Brandywine Creek Basin

01480629 46 1995 9.0 — — — — —

01480632 45 1986 4.0 — — — — —

01480640 38 1993 4.0 — — — — —

01480903 44 1985 4.0 — — — — —

1995 5.0 — — — — —

01480950 39 1986 32 — — 4.1 3.2 —

01481030 40 1997 5.4 — — — — —

Red Clay/White Cay Creek Basins

01478120 28 1985 — — 6.3 — — —

01479680 27 1983 — 15 260 — 2.5 5,600

1986 — — — — — 1,400

1993 7.0 27 23 20 — 550

01479800 26 1985 5.0 61 36 22 — —

Big Elk/Octoraro Creek Basins

01494900 31 1986 29 — — 7.4 — —

01578343 33 1986 4.0 — 4.8 — —

1994 5.0 — — — — —

1 A level of sediment contamination below which harmful effects are unlikely to be observed

(MacDonald and others, 2000).
43

DDT

DDT is the common name for a mixture of compounds in which the main component is

1,1,1,-trichloro-2,2-bis (p-chlorophenyl) ethane. DDT was banned in 1973 but because of its widespread

use and chemical stability it still is detectable (Ware, 1989). DDT was detected in 53 percent of the

79 samples collected (table 12). The concentrations of DDT ranged from 0.1 to 61 μg/kg and exceeded the

threshold effect concentration of 4.16 μg/kg in 6 percent of the samples and from 7 percent of the sites

(table 12). Sites that exceeded the threshold effect concentration were on East Branch Chester Creek

(site 25) and Red Clay Creek (sites 26 and 27). The highest concentration (61 μg/kg) was at site 26 on East

Branch Red Clay Creek in 1985 (table 13). Thirty-three sites were sampled once between 1983 and 1987 and

once between 1993 and 1997. Of these 33 paired sites, DDT was detected in 45 percent of samples collected

between 1983 and 1987 and in 73 percent of samples collected between 1993 and 1997 (fig. 30). The 33 sites

had a median concentration of 1.30 μg/kg with a maximum concentration of 61 μg/kg in 1983-87 and a

median concentration of 0.6 μg/kg with a maximum concentration of 27 μg/kg in 1993-97 (fig. 31). High

concentrations of DDT were less common in the samples collected during the 1990s, but low

concentrations are persistent throughout Chester County.

At sites where DDT was detected, the DDE/DDT ratio was greater than 1 at 57 percent of sites

sampled between 1983 and 1987 and at 71 percent of sites sampled between 1993 and 1997, indicating

long-term degradation of the DDT to DDE. The reduction in DDT concentrations may be from

degradation, downstream movement of contaminated sediments, and influx of less contaminated

sediments.

DDD

DDD is an insecticide and is also a breakdown product of DDT. DDD was banned in 1973 but

because of its widespread use and chemical stability still is detectable (Ware, 1989). DDD was detected in

75 percent of the 79 samples collected (table 12). The concentration of DDD ranged from 0.1 to 260 μg/kg

and exceeded the threshold effect concentration of 4.88 μg/kg in 4 percent of the samples and from

5 percent of the sites (table 12). Sites that exceeded the lowest effects concentration were on East Branch

Chester Creek (sites 25 and 51), East Branch White Clay Creek (site 28), and Red Clay Creek (sites 26 and

CHLORDANE DDD DDE DDT DIELDRIN PCB

CONSTITUENT

40

100

50

60

70

80

90

PERCENTAGE OF PAIRED SAMPLES

EXPLANATION

1983-87

1993-97

Figure 30. Percentage of stream-bottom sediment samples with detectable

concentrations of selected pesticides and PCB from selected streams in Chester

County, Pennsylvania, 1983-97. WITH DETECTABLE CONCENTRATIONS
44

83-87 93-97 1

1,000

2

3

4

5

7

10

20

30

4050

70

100

200

300

400 500

700

CHLORDANE CONCENTRATION,

83-87 93-97

0.01

10

0.02

0.03

0.04 0.05

0.07

0.1

0.2

0.3

0.4 0.5

0.7

1

2

3

4

5

7

DIELDREN CONCENTRATION,

83-87 93-97 1

100,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

10,000

20,000

50,000

PCB CONCENTRATION,

83-87 93-97 0.01

100

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

DDE CONCENTRATION,

83-87 93-97 0.01

100

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

DDT CONCENTRATION,

83-87 93-97 0.01

1,000

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

DDD CONCENTRATION

EXPLANATION

25th percentile

Median

75th percentile

1.5 times the interquartile range

Data value less than or equal to

interquartile range outside the quartile

to 3 and more than 1.5 times the

Outlier data value less than or equal

Figure 31. Concentrations of pesticides and PCBs in stream-bottom sediment samples from selected streams in

Chester County, Pennsylvania, 1983-97. IN MICROGRAMS PER KILOGRAM

IN MICROGRAMS PER KILOGRAM

IN MICROGRAMS PER KILOGRAMIN MICROGRAMS PER KILOGRAM

IN MICROGRAMS PER KILOGRAM

IN MICROGRAMS PER KILOGRAM

YEARS YEARS

outside the quartile
45

27). The highest concentration (260 μg/kg) was at site 27 on West Branch Red Clay Creek in 1983 (table 13).

Thirty-four sites were sampled once between 1983 and 1987 and once between 1993 and 1997. Of these

34 paired sites, DDD was detected in 74 percent of samples collected between 1983 and 1987 and in

79 percent of samples collected between 1993 and 1997 (fig. 30). The 34 sites had a median concentration of

0.8 μg/kg with a maximum concentration of 260 μg/kg in 1983-87 and a median concentration of

0.6 μg/kg with a maximum concentration of 23 μg/kg in 1993-97 (fig. 31). These concentrations are an

indication that although DDD is persistent in stream-bottom sediments throughout Chester County, the

concentrations are decreasing over time.

DDE

DDE is not produced as a pesticide but is a breakdown product of DDT. DDE was detected in

88 percent of the 77 samples collected (table 12). The detectable concentration of DDE ranged from 0.1 to

22 μg/kg and exceeded the threshold effect concentration of 3.16 μg/kg in 5 percent of the samples and

from 9 percent of the sites (table 12). Sites that exceeded the threshold effect concentration were on Valley

Creek (site 50), East Branch Brandywine Creek (site 39), Red Clay Creek (sites 26 and 27), East Branch Big

Elk Creek (site 31), and East Branch Octoraro Creek (site 33). The highest concentration (22 μg/kg) was at

site 26 on East Branch Red Clay Creek in 1985 (table 13). Thirty-three sites were sampled once between

1983 and 1987 and once between 1993 and 1997. Of these 33 paired sites, DDE was detected in 91 percent

of samples collected between 1983 and 1987 and in 88 percent of samples collected between 1993 and 1997

(fig. 30). The 33 sites had a median concentration of 0.6 μg/kg with a maximum concentration of 22 μg/kg

in 1983-87 and a median concentration of 0.7 μg/kg with a maximum concentration of 20 μg/kg in 1993-97

(fig. 31). High concentrations of DDE were less common in the samples collected during the 1990s, but low

concentrations are persistent throughout Chester County.

Dieldrin

Dieldrin is an isomer of endrin and has been used as a contact insecticide. All uses of dieldrin were

prohibited by the USEPA in 1986 (Ware, 1989). Dieldrin was detected in 64 percent of the 80 samples

collected (table 12). The concentrations of dieldrin ranged from 0.1 to 5.4 μg/kg (table 12) and exceeded

the threshold effect concentration of 1.90 μg/kg in 8 percent of the samples from 14 percent of the sites

(table 13). Sites that exceeded the threshold effect concentration were on French Creek (sites 12 and 16),

Darby Creek (site 17), East Branch Chester Creek (site 22), East Branch Brandywine Creek (site 39), and

West Branch Red Clay Creek (site 27). The highest concentration (5.4 μg/kg) was at site 16 on French Creek

in 1985 (table 13). Thirty-three sites were sampled once between 1983 and 1987 and once between 1993 and

1997. Of these 33 paired sites, dieldrin was detected in 70 percent of samples collected between 1983 and

1987 and in 67 percent of samples collected between 1993 and 1997 (fig. 30). The 33 sites had a median

detectable concentration of 0.35 μg/kg with a maximum concentration of 4.8 μg/kg in 1983-87 and a

median detectable concentration of 0.35 μg/kg with a maximum concentration of 5.4 μg/kg in 1993-97

(fig. 31). This result indicates concentrations of chlordane in stream-bottom sediments did not change

between the 1980s and the 1990s. It still is widespread throughout Chester County in low concentrations in

drainage basins of various sizes and among various land uses.

PCBs

PCBs are a group of compounds commonly used in electrical transformers and lubricants. PCBs

have been banned in the United States since 1977, but because of their high stability, they still persist in the

environment (Tigler and others, 1990). PCBs were detected in 67 percent of 82 samples of stream-bottom

sediment collected between 1983 and 1997 (table 12). The concentrations of PCBs ranged from 1.0 to

15,000 μg/kg and exceeded the threshold effect concentration of 59.8 μg/kg in 10 percent of the samples

and from 12 percent of the sites (table 12). The highest concentrations of PCBs were at sites 27 and 49

where the concentration of PCBs was 5,600 μg/kg and 15,000 μg/kg, respectively (table 13). Thirty-seven

sites were sampled once between 1983-87 and once between 1993-97. Of these 37 paired sites, PCB was

detected in 65 percent of samples collected between 1983 and 1987 and in 73 percent of samples collected

between 1993 and 1997 (fig. 30). The 37 sites had a median detectable concentration of 8.00 μg/kg with a
46

maximum concentration of 15,000 μg/kg in 1983-87 and a median detectable concentration of 9.40 μg/kg

with a maximum concentration of 550 μg/kg in 1993-97 (fig. 31). Although maximum concentrations are

declining over time, low concentrations did not change between the 1980s and the 1990s. It still is

widespread throughout Chester County in low concentrations in drainage basins of various sizes and

among various land uses.

The high concentration at site 27, West Branch Red Clay Creek at Kennett Square, was because of

contamination from a landfill fire, and at site 49, Little Valley Creek at Howellville, the high concentration

was caused by runoff from the Paoli Train Yard Superfund Site. The concentration of PCBs has dropped

dramatically at both sites after the source of the PCBs was contained. The contaminated sediment has

washed downstream or been buried by less contaminated sediments.

Overall, the concentrations of organochlorine insecticides and PCBs in stream-bottom sediments has

decreased across Chester County between 1983 and 1997. This reduction is because of the limitations and

restriction on the uses of these substances and decreased agricultural land use in the county. The

compounds in the sediments are degrading, being washed downstream, and mixing and being buried

with sediment containing lower concentrations of these substances. Many of these compounds, however,

are stable and will remain in the stream system for many years. The concentrations of most compounds

detected do not pose a serious threat to the aquatic life on the stream bottom.
47

SUMMARY

Water-chemistry, bottom-sediment chemistry, and benthic-macroinvertebrate data were collected by

the U.S. Geological Survey, in cooperation with the Chester County Water Resources Authority at 43 sites

from 1981 to 1997 as part of the Stream Conditions of Chester County Biological Monitoring Network.

Stream-quality conditions were assessed using biological metrics to evaluate benthic-macroinvertebrate

communities. Trends in benthic-macroinvertebrate diversity and water chemistry were analyzed to

evaluate changes in stream conditions over time. Chemical and benthic-macroinvertebrate data were

compared to find relations between water chemistry and benthic-macroinvertebrate communities.

The 43 sites sampled in Chester County from 1981 to 1997 have varied benthic-macroinvertebrate

communities that are related to many factors including land use, point discharges, and natural stream

conditions. Although the streams each have unique combinations of these factors, some general patterns

in the data are present. Sites in the Pigeon, French, Pickering, and East Branch Brandywine Creeks

generally have consistent benthic-macroinvertebrate communities that indicate good stream conditions.

Benthic-macroinvertebrate communities in the Darby, Crum, Ridley, and Valley Creek Basins are being

degraded from the reference conditions. The degraded benthic-macroinvertebrate communities are

associated with habitat alteration probably caused by increased urban areas and impervious surfaces in

these basins. Sites in the West Branch Brandywine and White Clay Creek Basins have benthic-macroinvertebrate communities that indicate some degradation in stream conditions because of sedimentation but

good overall stream conditions. Benthic-macroinvertebrate communities in the Red Clay, Big Elk, and

Octoraro Creek Basins are being degraded from the reference conditions by increased nutrient concentrations (which may result in low dissolved-oxygen concentrations) and by heavy sedimentation caused by

agricultural land use and construction activities. Sites in the Red Clay Creek have benthic-macroinvertebrate communities that indicate improving but still highly degraded stream conditions when compared to

reference conditions.

Trend analysis of biological-metric values indicates most sites in the Stream Conditions of Chester

County Biological Monitoring program have increased in diversity or have remained unchanged between

1981 and 1997. This improvement was likely because of various factors including upgrading and

eliminating wastewater-treatment plants, decreasing agricultural land use, and improving farm management procedures. Upgrades in sewage-treatment plants have resulted in improved water quality by

decreasing concentrations of ammonia and phosphorus. This improvement has lead to less toxic and

better oxygenated waters. The decrease in agricultural lands and improved farm-management procedures

have reduced sediment loads and organochlorine pesticide concentrations. The basins that showed the

greatest improvement in diversity were basins that had very low diversities in the past. These areas,

however, are affected by wastewater discharges, pesticides, and nutrient enrichment and still have the

poorest stream condition in the network.

Trend analysis on chemical constituents indicates concentrations of nitrate and chloride are

increasing and concentrations of phosphorus and ammonia are unchanged or declining across Chester

County. Elevated concentrations of nitrate and phosphorus generally were in basins that were above

50 percent agricultural land use or were affected by wastewater discharges. The highest concentrations of

ammonia and chloride were associated with wastewater-treatment plant discharges. The median

concentration of nutrients in the county generally was low in areas with agricultural land use below

35 percent and high in areas of wastewater-treatment plant discharge and where agricultural land use is

above 50 percent. Although the nutrient concentrations are low (below 2 mg/L) or moderate (below

5.0 mg/L) in most of Chester County, the upward trends in nitrate concentrations could lead to degraded

stream-quality conditions associated with nutrient enrichment in the future.

Background metal and trace-element concentrations in samples of stream-bottom sediment

collected throughout Chester County were not a stream-quality problem. The concentrations of pesticides

and other organic compounds in stream-bottom sediments have decreased across Chester County

between 1983 and 1997. This reduction is because of limitations and restriction on the uses of these substances. The compounds in the sediments are degrading, being washed downstream, and mixing and

being buried with sediment containing lower concentrations of these substances. Many of these compounds, however, are very stable and will remain in the stream system for many years. The concentrations

of most compounds detected do not pose a serious threat to the aquatic life on the stream bottom.
48

REFERENCES CITED

Bode, R.W., 1991, Quality assurance work plan for biological stream monitoring in New York State: New

York Department of Environmental Conservation Technical Report, 79 p.

_____1993, 20 year trends in water quality of rivers and streams in New York State on the basis of

macroinvertebrate data 1972-1992: New York Department of Environmental Conservation

Technical Report, 196 p.

Brigham, A.R., Brigham, W.U., and Gnilka, A., eds., 1982, Aquatic insects and oligochaetes of North and

South Carolina: Mahomet, Ill., Midwest Aquatic Enterprises, 837 p.

Brown, E., Skougstad, M.W., and Fishman, M.J., 1970, Methods for collection and analysis of water

samples for dissolved minerals and gases: U.S. Geological Survey Techniques of Water-Resources

Investigations, book 5, chap. A1, 160 p.

Chester County, 1996, Landscapes—Managing change in Chester County 1996-2020—Comprehensive

plan policy element: West Chester, Chester County, Pa., 128 p.

Delaware Valley Regional Planning Commission, 1997, Land-use data (digital database).

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for determination of inorganic substances in water

and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations,

book 5, chap. A1, 545 p.

Greeson, P.E., Ehlke, T.A., Irwin, G.A., Lium, B.W., and Slack, K.V., 1977, Methods for the collection and

analysis of aquatic biological and microbiological samples: U.S. Geological Survey Techniques of

Water-Resources Investigations, book 5, chap. A4, 332 p.

Grubaugh, J.W., Wallace, J.B., and Houston, E.S., 1996, Longitudinal changes of macroinvertebrate

communities along an Appalachian stream continuum: Canadian Journal of Fisheries and Aquatic

Sciences, v. 53, p. 896-909.

Hardy, M.A., Wetzel, K.L., and Moore, C.R., 1995, Land use, organochlorine compound concentrations,

and trends in benthic-invertebrate communities in selected stream basins in Chester County,

Pennsylvania: U.S. Geological Survey Water-Resources Investigations Report 94-4064, 78 p.

Hem, J.D., 1985, Study and interpretation of the chemical characteristics of natural water (3d ed.):

U.S. Geological Survey Water-Supply Paper 2254, 263 p.

Hilsenhoff, W.L., 1982, Using a biotic index to evaluate water quality in streams: Wisconsin Department

of Natural Resources Technical Bulletin, no. 132, 22 p.

Hirsch, R.M., Slack, J.R., and Smith, R.A., 1982, Techniques of trend analysis for monthly water-quality

data: Water Resources Research, v. 18, no. 1, p. 107-121.

Horowitz, A.J., 1991, A primer on sediment-trace element chemistry (2d rev. ed.): Boca Raton, Fla., Lewis

Publishers, 136 p.

Lancaster County, 2002, GIS Department land-use data (digital database).

Lenat, D.R., 1988, Water quality assessment of streams using a qualitative collection method for benthicmacroinvertebrates: Journal of the North American Benthological Society, v. 7, p. 222-233.

Lium, B.W., 1974, Some biological aspects of pools and riffles in gravel bed streams in Western United

States: U.S. Geological Survey Journal of Research, v. 2, no. 3, p. 379-384.

_____1976, Limnological data for the major streams in Chester County, Pennsylvania: U.S. Geological

Survey Open-File Report (unnumbered), 219 p.

_____1977, Limnological studies of the major streams in Chester County, Pennsylvania: U.S. Geological

Survey Open-File Report 77-462, 37 p.
49

REFERENCES CITED—CONTINUED

MacDonald, D.D., Ingersoll, C.G., and Berger, T.A., 2000, Development and evaluation of consensus-based

sediment quality guidelines for freshwater ecosystems: Archives of Environmental Contamination

and Toxicology, v. 39, p. 20-31.

Meade, R.H., ed., 1995, Contaminants in the Mississippi River, 1987-92: U.S. Geological Survey Circular

1133, 140 p.

Merritt, R.W., and Cummins, K.W., eds., 1996, An introduction to the aquatic insects of North America

(3d ed.): Dubuque, Iowa, Kendall Hunt Publishing Company, 862 p.

Miller, R.A., Troxell, J., and Leopold, L.B., 1971, Hydrology of two small river basins in Pennsylvania

before urbanization: U.S. Geological Survey Professional Paper 701-A, 57 p.

Minshall, G.W., Petersen, R.C., Jr., and Nimz, C.F., 1985, Species richness in streams of different size from

the same drainage basin: American Naturalist, v. 125, p. 16-38.

Moore, C.R., 1987, Determination of benthic-invertebrate indices and water-quality trends of selected

streams in Chester County, Pennsylvania, 1969-80: U.S. Geological Survey Water-Resources

Investigations Report 85-4177, 62 p.

_____1989, Physical, chemical, and biological data for selected streams in Chester County, Pennsylvania,

1969-80: U.S. Geological Survey Open-File Report 85-686, 289 p.

Owenby, J.R., and Ezell, D.S., 1992, Monthly station normals of temperature, precipitation, and heating

and cooling degree days, 1961-1990, Pennsylvania: National Oceanic and Atmospheric

Administration Climatography of the United States No. 81, 25 p.

Peckarsky, B.L., Fraissinet, P.R., Penton, M.A., and Conklin, D.J., Jr., 1990, Freshwater macroinvertebrates

of Northeastern North America: Ithaca, N.Y., Cornell University Press, 442 p.

Pennak, R.W., 1989, Fresh-water invertebrates of the United States (3d ed.): New York, John Wiley and

Sons, 803 p.

Plafkin, J.L., Barbour, M.T., Porter, K.D., Gross, S.K., and Hughes, R.M., 1989, Rapid bioassessment

protocols for use in streams and rivers—Benthic macroinvertebrates and fish: Washington D.C.,

Office of Water Regulations and Standards, U.S. Environmental Protection Agency,

EPA/444/4-89/001.

Reif, A.G., 1999, Physical, chemical, and biological data for selected streams in Chester County,

Pennsylvania, 1981-94: U.S. Geological Survey Open-File Report 99-216, 607 p.

_____2000, Physical, chemical, and biological data for selected streams in Chester County, Pennsylvania,

1995-97: U.S. Geological Survey Open-File Report 00-238, 146 p.

Resh, V.H., and Grodhaus, G., 1983, Aquatic insects in urban environments, in Frankie, G.W., and Koehler,

C.S., eds., Urban Entomology: New York, Interdisciplinary Perspectives, Praeger Publishers, p. 247-

76.

Schueler, T., 1995, The importance of imperviousness: Watershed Protection Techniques, v. 1, no. 3, p. 100-

111.

Senior, L.A., Sloto, R.A., and Reif, A.G., 1997, Hydrology and water quality of the West Valley Creek Basin,

Chester County, Pennsylvania: U.S. Geological Survey Water-Resources Investigations Report 94-

4137, 131 p.

Sloto, R.A., 1987, Effect of urbanization on the water resources of eastern Chester County,

Pennsylvania: U.S. Geological Survey Water-Resources Investigations Report 87-4098, 131 p.

Tigler, J.N., Galloway, R.E., Jr., Hegstrom, L.J., Seivard, L.D., and Gregory, R.A., 1990, Comprehensive

review of selected toxic substances-Environmental samples in Virginia: Virginia State Water

Control Board Information Bulletin Number 583, 232 p.
50

REFERENCES CITED—CONTINUED

U.S. Environmental Protection Agency, 1986, Quality criteria for water, 1986: EPA 440/5-86-001, 256 p.

_____1990, Suspended, cancelled, and restricted pesticides: U.S. Environmental Protection Agency, Office

of Pesticides and Toxic Substances 20T-4002.

_____1994a, National primary drinking water standards: EPA 810-F-94-001A, 8 p.

_____1994b, Water quality standards handbook (2nd ed.): EPA-823-B-94-005b, Appendix P, 3 p.

U.S. Geological Survey, 1975-98, Water resources data for Pennsylvania, 1974-98—vol. 1: U.S. Geological

Survey Water Data Reports PA-74-1 to PA-98-1 (published annually).

Ware, G.W., 1989, The pesticide book (3d ed): Fresno, Calif., Thomas Publications, 340 p.

Weast, R.C., ed., 1983, CRC handbook of chemistry and physics (63rd ed.): Boca Raton, Fla., CRC Press,

Inc., 2,381 p.

Weber, C.I., ed., 1973, Biological field and laboratory methods for measuring the quality of surface waters

and effluents: Cincinnati, Ohio, U.S. Environmental Protection Agency, EPA-670/4-73-001.

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe, L.E., eds., 1987, Methods for determination of

organic substances in water and fluvial sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A3, 80 p.

Wiggins, G.B., 1996, Larvae of the North American caddisfly genera (Trichoptera) (2d ed.): Toronto,

University of Toronto Press, 457 p.
51

Table 14. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Pigeon Creek near Parker Ford

(site 10), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,785 33 18 69 4.46

1982 1,691 30 18 63 4.32

1983 969 24 18 83 4.24

1984 1,492 29 18 74 4.28

1985 1,032 21 13 69 4.99

1986 1,133 24 16 84 4.28

1987 2,098 39 20 56 4.14

1988 2,397 31 22 70 4.22

1989 2,270 40 23 67 3.82

1990 1,947 32 20 77 3.50

1991 1,705 34 21 75 4.29

1992 440 30 16 72 4.69

1993 1,161 35 22 51 4.30

1994 1,599 41 26 58 4.16

1995 930 39 23 58 3.99

1996 1,685 40 22 22 5.25

1997 1,918 36 25 58 5.23

Median 1,685 33 20 69 4.28

Table 15. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Stony Run near Spring City

(site 6), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,760 32 14 40 5.14

1982 1,265 27 15 67 4.39

1983 2,082 37 16 42 5.21

1984 998 26 12 60 4.56

1985 550 26 12 32 5.47

1986 651 38 16 67 4.71

1987 1,467 34 15 42 5.25

1988 816 24 15 65 4.72

1989 2,122 35 16 55 4.60

1990 2,129 37 16 66 4.53

1991 1,489 35 18 61 4.47

1992 671 29 14 70 4.17

1993 993 24 13 77 4.39

1994 1,010 36 18 60 4.72

1995 744 39 19 68 4.25

1996 1,860 34 18 39 4.91

1997 — — — — —

Median 1,138 34 16 60 4.66
52

Table 16. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from French Creek near

Coventryville (site 13), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,542 42 28 72 3.88

1982 2,380 34 22 44 4.47

1983 1,615 37 26 79 4.25

1984 1,295 27 20 76 4.51

1985 535 36 19 39 4.83

1986 1,395 31 20 48 4.89

1987 1,338 31 21 30 5.10

1988 1,846 31 21 55 4.71

1989 1,643 51 24 38 4.56

1990 1,507 46 25 47 4.56

1991 597 35 19 41 4.69

1992 573 29 16 59 4.30

1993 732 38 20 58 4.52

1994 1,029 32 17 49 4.83

1995 414 34 18 44 4.60

1996 — — — — —

1997 1,080 32 19 53 4.60

Median 1,317 34 20 49 4.58

Table 17. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from South Branch French Creek

at Coventryville (site 12), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,197 32 13 75 4.13

1982 2,649 33 12 54 4.50

1983 1,697 31 12 89 3.88

1984 1,563 26 12 74 4.44

1985 785 32 24 71 4.17

1986 1,312 39 26 82 3.66

1987 2,014 40 26 59 4.50

1988 3,070 40 27 75 4.11

1989 2,447 41 24 79 3.70

1990 643 36 26 66 3.40

1991 1,737 43 27 83 3.94

1992 1,336 48 31 69 3.78

1993 1,432 42 24 63 4.30

1994 565 29 20 65 4.34

1995 585 32 16 51 4.32

1996 — — — — —

1997 1,527 32 18 75 4.66

Median 1,480 35 24 73 4.15
53

Table 18. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from French Creek near Pughtown

(site 14), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,760 35 20 76 4.18

1982 1,543 29 20 68 5.05

1983 1,432 40 20 84 4.29

1984 1,716 31 20 78 4.64

1985 421 24 18 81 4.27

1986 1,416 32 21 63 4.58

1987 1,331 31 17 23 5.44

1988 2,589 33 25 65 4.20

1989 1,489 38 23 78 3.86

1990 747 35 22 73 3.95

1991 1,545 36 23 61 4.54

1992 1,025 40 27 66 4.43

1993 765 34 21 77 3.99

1994 1,212 40 24 84 4.15

1995 388 34 23 68 4.33

1996 — — — — —

1997 800 33 20 79 3.86

Median 1,374 34 21 74 4.28

Table 19. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from French Creek near

Phoenixville (site 15), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 3,427 32 20 91 1.96

1982 548 22 16 66 4.61

1983 1,141 28 17 87 2.31

1984 821 29 21 58 4.20

1985 226 30 16 73 3.81

1986 712 36 18 66 3.39

1987 600 35 20 29 5.05

1988 2,496 41 22 85 3.53

1989 203 35 18 39 4.91

1990 271 38 12 27 4.55

1991 1,254 38 24 85 4.80

1992 825 45 24 53 4.30

1993 587 34 23 80 3.12

1994 1,045 47 30 73 3.86

1995 281 35 23 74 3.24

1996 198 21 14 40 4.62

1997 1,677 37 23 87 3.26

Median 712 35 20 76 3.86
54

Table 20. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT taxa richness, and Hilsenhoff’s biotic index from French Creek at Railroad

Bridge at Phoenixville (site 16), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; <, less than; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 240 8 1 <1 6.13

1982 619 20 6 8 8.24

1983 343 24 7 4 7.52

1984 2,247 18 3 <1 6.48

1985 72 21 11 50 5.08

1986 605 21 8 44 4.98

1987 489 25 10 23 5.35

1988 1,340 20 8 70 4.75

1989 270 36 12 13 6.39

1990 113 22 5 5 7.09

1991 727 24 8 19 5.52

1992 115 13 1 2 6.30

1993 985 33 14 42 5.00

1994 656 22 9 28 5.36

1995 90 19 9 51 4.94

1996 — — — — —

1997 1,234 26 13 47 5.08

Median 547 22 7 19 5.44

Table 21. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Pickering Creek near Eagle

(site 1), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,301 23 13 40 5.12

1982 2,643 22 13 24 5.36

1983 2,715 31 16 63 5.01

1984 1,537 23 13 77 5.13

1985 765 31 12 59 5.09

1986 1,102 32 17 69 4.81

1987 1,431 25 14 72 5.18

1988 2,728 29 16 60 4.60

1989 1,088 32 17 53 4.71

1990 1,000 23 16 60 4.91

1991 725 29 16 72 4.78

1992 328 21 13 77 4.14

1993 872 26 12 53 5.29

1994 560 27 15 31 5.23

1995 533 23 12 40 5.28

1996 757 28 16 50 4.31

1997 — — — — —

Median 1,044 27 15 59 5.05
55

Table 22. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Pickering Creek near

Chester Springs (site 2), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 747 20 12 33 4.70

1982 1,084 26 14 59 3.69

1983 526 24 16 77 3.78

1984 1,350 21 16 85 3.73

1985 595 28 11 82 4.24

1986 488 30 19 58 3.99

1987 170 18 13 91 3.08

1988 1,340 24 15 86 3.62

1989 1,076 35 18 70 4.19

1990 502 32 18 68 3.97

1991 766 39 23 77 3.97

1992 295 35 16 65 4.25

1993 219 21 12 72 4.37

1994 871 39 23 49 4.40

1995 223 26 14 41 4.51

1996 — — — — —

1997 — — — — —

Median 595 26 16 70 3.99

Table 23. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Pickering Creek at Merlin

(site 3), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,757 27 17 48 4.83

1982 2,123 30 19 65 4.81

1983 935 25 17 77 4.47

1984 2,005 24 18 62 5.08

1985 912 39 22 79 4.31

1986 1,049 36 19 32 5.02

1987 1,396 38 23 37 5.51

1988 1,047 24 15 50 4.42

1989 1,015 45 24 44 4.64

1990 430 29 17 45 4.13

1991 956 33 20 28 5.29

1992 1,522 44 22 47 3.58

1993 939 30 15 51 4.75

1994 780 31 17 37 4.93

1995 457 31 15 55 4.15

1996 — — — — —

1997 1,463 41 22 33 4.72

Median 1,031 31 19 48 4.73
56

Table 24. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Pickering Creek at

Charlestown Road at Charlestown (site 4), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 3,611 32 21 54 4.92

1982 1,887 31 23 78 4.65

1983 1,316 27 19 69 4.77

1984 1,943 26 16 81 4.49

1985 557 27 18 84 4.28

1986 2,593 38 22 56 4.89

1987 2,312 36 24 91 3.95

1988 4,090 36 21 62 4.65

1989 1,147 39 22 56 4.65

1990 1,684 37 20 67 5.01

1991 1,514 34 19 72 4.70

1992 2,247 46 23 59 4.89

1993 2,535 48 28 66 4.53

1994 1,310 40 23 78 4.40

1995 811 42 21 53 4.48

1996 1,325 37 21 74 4.56

1997 — — — — —

Median 1,786 37 22 68 4.65

Table 25. Values of total individuals, taxa richness, EPT individuals, percentage

of EPT taxa richness, and Hilsenhoff’s biotic index from Pickering Creek near

Phoenixville (site 5), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,081 32 22 48 5.02

1982 3,232 39 24 65 4.85

1983 2,183 38 22 79 4.31

1984 1,513 32 23 80 3.98

1985 438 30 18 83 4.03

1986 1,150 40 21 46 4.43

1987 2,029 39 24 65 4.59

1988 2,651 28 17 71 5.09

1989 373 34 19 67 4.58

1990 948 30 19 83 4.99

1991 3,066 42 24 49 4.66

1992 1,775 47 27 55 4.80

1993 1,259 36 20 80 5.04

1994 1,177 29 17 75 5.01

1995 872 35 24 63 4.74

1996 418 26 17 42 4.77

1997 1,530 36 23 78 4.18

Median 1,513 35 22 67 4.74
57

Table 26. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Little Valley Creek at

Howellville (site 49), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,871 20 8 56 4.75

1982 2,454 21 9 61 4.59

1983 1,231 18 7 80 3.67

1984 1,218 17 6 75 3.45

1985 551 20 7 80 3.91

1986 1,102 17 7 66 4.46

1987 1,357 15 7 70 3.46

1988 1,375 20 10 71 3.68

1989 346 17 7 68 3.66

1990 518 15 10 52 3.44

1991 481 14 8 39 4.63

1992 913 19 7 63 4.07

1993 804 16 7 41 4.56

1994 1,068 15 7 64 3.98

1995 395 22 10 39 4.24

1996 113 16 8 38 4.50

1997 — — — — —

Median 991 17 7 64 4.03

Table 27. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Valley Creek near Valley

Forge (site 50), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,183 20 6 32 5.47

1982 3,144 20 7 44 5.43

1983 1,745 16 6 55 5.08

1984 2,073 21 8 28 5.51

1985 1,354 19 6 23 5.69

1986 1,820 19 8 44 5.00

1987 1,625 22 8 34 5.10

1988 2,278 15 6 37 5.57

1989 1,046 22 7 26 5.25

1990 1,557 19 7 39 5.07

1991 1,020 21 8 25 4.99

1992 1,848 23 9 27 5.07

1993 1,307 22 8 25 5.10

1994 1,561 23 9 25 5.05

1995 1,032 18 5 46 4.59

1996 870 23 8 15 4.70

1997 — — — — —

Median 1,593 21 8 30 5.08
58

Table 28. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Darby Creek at Waterloo Mills

near Devon (site 17), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 524 23 10 45 4.88

1982 215 20 9 44 4.60

1983 403 28 11 76 4.35

1984 1,208 28 13 66 4.68

1985 968 26 13 61 4.87

1986 706 26 12 71 4.16

1987 1,115 27 11 57 4.27

1988 2,008 24 13 42 5.06

1989 1,165 39 18 56 4.24

1990 450 19 12 55 4.38

1991 1,352 24 10 36 5.06

1992 918 35 12 40 4.77

1993 369 19 8 82 4.29

1994 883 29 14 55 5.28

1995 463 25 9 6 7.12

1996 256 20 10 21 4.62

1997 — — — — —

Median 795 28 13 56 4.60

Table 29. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Crum Creek at Whitehorse

(site 19), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 992 38 16 56 4.89

1982 1,636 35 16 53 5.27

1983 525 30 16 34 4.88

1984 1,222 26 12 74 4.98

1985 568 28 14 43 5.20

1986 907 28 16 67 5.27

1987 1,285 33 18 53 4.92

1988 2,028 24 14 29 5.56

1989 1,644 38 20 48 5.53

1990 1,117 37 18 50 5.04

1991 1,789 36 18 30 5.29

1992 1,881 32 19 36 5.74

1993 538 25 13 42 5.12

1994 1,240 32 16 46 5.22

1995 603 33 15 20 5.69

1996 886 29 14 21 5.17

1997 — — — — —

Median 1,170 32 16 44 5.21
59

Table 30. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Ridley Creek at Goshenville

(site 20), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 241 27 10 37 4.78

1982 1,345 29 15 75 4.46

1983 855 22 9 53 4.35

1984 1,688 21 13 60 4.48

1985 722 19 11 37 4.97

1986 980 26 12 67 4.40

1987 1,881 30 12 51 4.79

1988 1,660 26 13 51 4.94

1989 767 26 9 31 5.29

1990 757 30 11 17 5.28

1991 547 20 5 41 5.16

1992 1,297 31 9 18 5.35

1993 511 24 7 18 4.97

1994 572 26 9 35 4.96

1995 412 25 12 32 4.27

1996 201 19 7 30 4.64

1997 — — — — —

Median 762 26 11 37 4.87

Table 31. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Ridley Creek at Dutton Mill

near West Chester (site 21), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,407 33 20 67 4.64

1982 1,578 27 16 59 4.77

1983 1,697 32 16 70 4.21

1984 3,842 26 16 66 4.61

1985 1,617 27 14 60 4.59

1986 1,629 30 13 49 4.68

1987 1,198 27 14 51 4.43

1988 2,446 25 16 72 4.18

1989 1,347 29 12 37 4.86

1990 2,813 39 17 59 4.48

1991 1,509 21 10 41 5.03

1992 1,391 32 16 54 4.62

1993 1,467 36 17 56 4.62

1994 1,322 28 14 60 4.67

1995 915 36 16 58 4.65

1996 633 34 16 51 4.69

1997 — — — — —

Median 1,488 30 16 58 4.63
60

Table 32. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Chester

Creek at Green Hill (site 22), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; <, less than; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 323 25 11 74 3.37

1982 464 20 10 79 3.66

1983 319 22 11 81 3.15

1984 519 21 10 83 2.94

1985 247 13 9 76 3.20

1986 338 21 10 75 3.54

1987 1,304 32 15 52 5.31

1988 1,014 19 12 62 3.72

1989 231 22 4 5 8.05

1990 425 16 3 <1 6.14

1991 505 23 8 10 6.48

1992 451 19 11 65 4.82

1993 106 15 10 54 4.66

1994 294 23 10 39 4.57

1995 331 22 11 77 3.97

1996 — — — — —

1997 250 17 9 72 4.16

Median 335 21 10 64 4.06

Table 33. Values of total individuals, taxa richness, EPT taxa richness, percentage of

EPT individuals, and Hilsenhoff’s biotic index from East Branch Chester Creek

at Milltown (site 23), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,371 28 11 56 5.09

1982 1,700 27 11 58 5.16

1983 1,247 31 11 53 5.01

1984 1,085 29 14 71 5.09

1985 991 25 12 53 4.36

1986 518 19 10 53 4.02

1987 2,252 31 14 68 4.46

1988 2,477 24 14 44 5.03

1989 4,174 33 14 25 5.89

1990 2,625 33 16 36 5.45

1991 1,731 26 14 37 5.34

1992 2,926 38 14 29 5.43

1993 693 20 11 17 5.47

1994 2,643 30 13 25 5.70

1995 281 25 10 31 5.71

1996 1,594 29 10 30 5.64

1997 — — — — —

Median 1,647 29 13 41 5.25
61

Table 34. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Chester Creek

at Westtown (site 24), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,783 28 13 41 5.23

1982 3,535 22 10 32 4.63

1983 2,250 30 15 64 4.77

1984 2,424 30 15 65 4.99

1985 1,365 25 12 14 5.05

1986 1,026 19 10 71 4.41

1987 2,592 29 12 35 4.91

1988 1,677 22 11 41 4.80

1989 1,518 27 8 16 6.26

1990 3,187 33 11 37 5.64

1991 1,808 27 13 44 4.86

1992 2,471 24 11 24 5.17

1993 643 24 9 41 4.65

1994 767 24 13 34 4.94

1995 464 26 10 24 5.34

1996 1,386 30 13 54 4.74

1997 1,291 26 12 55 4.65

Median 1,677 26 12 41 4.91

Table 35. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Goose Creek Tributary to

East Branch Chester Creek near West Chester (site 25), Chester County,

Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; <, less than; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 356 9 3 2 6.00

1982 9,644 8 3 <1 5.29

1983 — — — — —

1984 — — — — —

1985 — — — — —

1986 — — — — —

1987 — — — — —

1988 587 12 5 29 5.08

1989 3,091 17 4 <1 5.95

1990 1,111 20 6 3 5.67

1991 2,108 17 6 2 5.60

1992 1,095 20 6 23 5.45

1993 765 16 3 32 5.67

1994 671 11 4 27 5.05

1995 1,868 18 5 21 5.59

1996 1,298 19 5 58 4.99

1997 1,320 12 5 69 4.82

Median 1,205 17 5 12 5.52
62

Table 36. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Chester Creek

below Goose Creek near West Chester (site 51), Chester County, Pennsylvania,

1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; <, less than; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 — — — — —

1982 — — — — —

1983 2,869 22 5 3 7.33

1984 2,874 22 6 22 5.87

1985 4,236 19 2 <1 7.05

1986 1,514 23 6 42 5.25

1987 12,174 20 4 7 7.63

1988 3,963 17 6 49 5.65

1989 926 28 7 40 6.20

1990 3,033 31 10 52 4.95

1991 3,951 27 11 52 5.18

1992 3,046 26 12 33 4.99

1993 1,169 28 11 20 5.83

1994 2,093 32 11 42 4.85

1995 589 22 8 34 4.61

1996 — — — — —

1997 2,219 18 7 68 4.59

Median 2,872 23 7 37 5.45

Table 37. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from West Branch Brandywine Creek

at Rock Run (site 37), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 551 29 19 67 3.98

1982 1,086 31 21 63 4.58

1983 1,241 31 19 87 5.22

1984 1,052 30 20 78 4.93

1985 1,711 32 19 63 4.88

1986 646 34 19 73 4.21

1987 1,278 36 21 53 4.86

1988 1,182 28 16 85 5.26

1989 1,399 37 19 58 4.85

1990 1,020 29 21 73 4.88

1991 1,793 38 23 33 5.10

1992 1,376 38 22 58 4.60

1993 665 31 18 53 4.74

1994 1,471 32 18 53 5.16

1995 440 36 18 46 4.67

1996 511 27 17 74 4.03

1997 — — — — —

Median 1,134 32 19 63 4.85
63

Table 38. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Buck Run at Doe Run (site 46),

Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,026 19 8 72 5.03

1982 1,647 16 6 74 5.20

1983 1,846 17 9 88 5.43

1984 2,272 21 10 68 5.07

1985 1,091 21 10 47 4.55

1986 1,769 23 14 80 4.96

1987 1,644 25 11 61 5.33

1988 2,070 24 15 68 4.90

1989 1,353 32 13 83 5.08

1990 1,804 39 19 58 5.12

1991 1,756 26 13 83 5.15

1992 1,432 34 16 77 4.50

1993 1,403 31 16 69 4.90

1994 2,602 24 13 73 4.71

1995 674 27 10 45 4.43

1996 — — — — —

1997 1,405 31 15 52 4.83

Median 1,646 25 13 71 4.99

Table 39. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Doe Run at Springdell

(site 45), Chester County, Pennsylvania, 1981-97

{EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,133 24 13 58 4.37

1982 1,620 25 14 37 4.84

1983 1,405 23 11 69 4.82

1984 1,608 22 13 62 4.55

1985 974 20 9 71 4.42

1986 774 19 12 66 4.96

1987 1,617 26 13 62 5.06

1988 1,818 22 15 72 4.62

1989 1,430 34 18 79 4.21

1990 1,752 25 15 62 4.91

1991 1,392 29 15 49 4.51

1992 1,195 23 14 54 4.68

1993 1,229 32 16 76 4.53

1994 1,300 23 11 67 4.51

1995 820 32 20 49 4.22

1996 — — — — —

1997 1,078 26 16 52 4.19

Median 1,346 25 14 62 4.54
64

Table 40. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from West Branch Brandywine Creek

at Wawaset (site 38), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 598 31 15 82 4.48

1982 1,655 21 13 75 4.79

1983 1,110 27 14 78 4.74

1984 1,402 22 9 37 4.90

1985 1,085 24 11 27 5.27

1986 769 24 12 66 4.38

1987 402 23 13 55 4.61

1988 1,939 22 13 84 4.40

1989 1,631 31 15 46 4.75

1990 1,532 39 22 69 4.16

1991 1,418 31 17 70 3.88

1992 1,041 34 18 41 4.70

1993 764 39 20 52 4.37

1994 1,005 37 23 82 4.23

1995 547 43 22 63 4.03

1996 861 30 14 54 4.81

1997 1,476 38 21 56 4.62

Median 1,085 30 13 61 4.61

Table 41. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Brandywine

Creek near Cupola (site 48), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,310 43 24 59 4.83

1982 2,529 35 20 61 4.99

1983 733 32 16 65 4.39

1984 1,652 24 14 71 4.29

1985 689 28 13 48 4.65

1986 895 33 18 48 4.20

1987 1,139 31 14 31 5.06

1988 1,984 32 15 33 4.78

1989 3,846 46 24 42 4.73

1990 538 25 14 26 4.86

1991 926 37 21 30 4.94

1992 610 25 11 51 4.34

1993 2,016 49 24 13 5.83

1994 973 31 14 33 4.90

1995 648 35 20 29 4.35

1996 — — — — —

1997 — — — — —

Median 973 32 16 42 4.78
65

Table 42. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Brandywine

Creek at Glenmoore (site 42), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 752 36 19 83 3.84

1982 1,708 47 23 60 4.43

1983 1,338 45 25 70 4.33

1984 1,008 36 23 73 4.45

1985 1,361 43 22 63 4.43

1986 723 48 25 77 4.09

1987 1,435 36 22 67 4.25

1988 1,671 33 19 60 4.58

1989 2,617 46 22 45 4.50

1990 973 41 22 46 4.78

1991 1,825 42 20 49 4.48

1992 1,330 50 29 39 4.08

1993 1,554 48 25 53 3.81

1994 1,378 47 27 58 4.70

1995 625 34 18 30 4.78

1996 — — — — —

1997 — — — — —

Median 1,361 43 22 58 4.43

Table 43. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Indian Run near Springton

(site 47), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,050 37 23 60 3.70

1982 1,883 40 24 51 4.06

1983 1,165 38 22 79 2.97

1984 1,027 33 21 74 3.54

1985 729 29 20 68 3.79

1986 688 34 25 82 2.94

1987 640 35 19 46 4.32

1988 787 29 21 75 3.28

1989 1,288 32 18 54 4.06

1990 840 32 20 42 4.16

1991 589 31 21 55 3.97

1992 440 25 17 63 3.66

1993 770 34 22 53 3.80

1994 1,232 34 20 53 4.20

1995 647 33 19 45 4.11

1996 — — — — —

1997 — — — — —

Median 787 33 21 55 3.80
66

Table 44. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Brandywine

Creek near Downingtown (site 36), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,450 28 15 68 4.50

1982 11,821 23 14 12 5.71

1983 2,848 31 15 56 4.68

1984 5,962 33 21 20 5.39

1985 1,866 30 18 58 4.92

1986 2,232 31 20 41 4.69

1987 2,179 31 18 50 4.80

1988 1,499 24 16 65 4.69

1989 2,207 41 23 37 4.96

1990 2,488 46 26 66 4.40

1991 1,398 41 26 60 4.44

1992 2,426 46 28 46 4.50

1993 1,896 49 29 77 3.75

1994 1,022 38 23 80 4.19

1995 1,508 41 26 66 4.31

1996 1,347 49 27 49 3.73

1997 — — — — —

Median 2,193 36 22 57 4.59

Table 45. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from West Valley Creek at Mullsteins

Meadow near Downingtown (site 44), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,812 33 19 58 4.50

1982 1,556 33 17 71 4.68

1983 1,918 26 16 76 4.22

1984 1,475 25 15 70 4.41

1985 2,091 33 18 52 4.41

1986 1,079 24 12 70 4.83

1987 2,352 33 19 64 4.55

1988 2,626 22 15 75 4.61

1989 1,105 30 16 76 3.79

1990 1,100 28 14 81 4.04

1991 1,499 21 13 51 4.58

1992 1,380 28 18 52 4.08

1993 1,179 36 20 60 4.12

1994 1,163 27 14 55 4.50

1995 1,327 34 19 47 4.17

1996 — — — —

1997 3,137 36 20 49 4.72

Median 1,487 29 17 62 4.45
67

Table 46. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Brandywine Creek

at Wawaset (site 39), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 641 31 13 44 5.21

1982 2,825 36 11 32 5.07

1983 771 36 13 45 5.06

1984 2,999 42 17 40 5.11

1985 699 27 13 44 4.82

1986 2,583 44 20 56 4.34

1987 1,115 40 17 60 4.50

1988 1,357 28 16 76 4.41

1989 2,698 40 19 57 4.33

1990 3,793 44 21 63 3.98

1991 11,771 50 21 89 3.30

1992 1,354 19 10 49 4.46

1993 1,701 33 13 61 3.91

1994 792 41 18 36 5.30

1995 307 33 14 59 4.60

1996 880 32 15 33 5.06

1997 2,123 30 16 69 4.15

Median 1,354 36 16 56 4.50

Table 47. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Brandywine Creek near

Chadds Ford (site 40), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 651 23 11 53 4.67

1982 1,673 30 15 52 4.83

1983 1,009 32 17 52 4.76

1984 1,446 24 12 37 5.03

1985 993 25 14 52 4.78

1986 428 36 15 48 4.76

1987 1,046 37 21 36 5.11

1988 1,824 25 16 66 4.63

1989 2,155 37 19 56 3.95

1990 1,702 31 19 46 4.26

1991 2,380 31 18 39 4.72

1992 1,835 29 17 63 3.96

1993 1,142 36 21 58 4.31

1994 1,424 32 21 79 4.42

1995 1,208 33 16 67 4.11

1996 — — — — —

1997 3,000 41 22 58 4.13

Median 1,435 32 17 52 4.65
68

Table 48. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from West Branch Red Clay

Creek at Kennett Square (site 27), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; <, less than]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 211 11 1 <1 5.70

1982 777 13 1 <1 6.16

1983 84 11 1 5 5.93

1984 468 10 0 0 5.75

1985 326 18 2 2 5.88

1986 107 10 1 <1 5.68

1987 267 15 1 <1 6.68

1988 546 17 3 1 5.71

1989 758 33 15 40 4.90

1990 1,843 26 6 4 5.75

1991 424 14 3 6 7.45

1992 410 14 3 43 4.55

1993 834 28 7 9 6.37

1994 922 24 7 3 6.21

1995 323 22 6 14 5.41

1996 178 15 6 15 5.75

1997 790 26 9 15 5.94

Median 424 15 3 4 5.75

Table 49. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Red Clay Creek

near Five Point (site 26), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; <, less than]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,055 14 0 0 5.64

1982 285 16 4 15 5.70

1983 577 17 2 74 4.48

1984 2,375 12 1 <1 5.88

1985 627 16 2 <1 5.70

1986 34 10 1 2 4.91

1987 577 17 3 3 5.37

1988 920 11 0 0 5.36

1989 545 17 3 <1 5.38

1990 2,652 19 4 <1 5.78

1991 700 15 2 <1 5.40

1992 1,0534 26 7 1 5.67

1993 761 23 5 10 5.93

1994 998 21 6 5 5.22

1995 514 22 8 49 4.58

1996 1,240 22 7 29 4.98

1997 1,213 17 7 40 4.59

Median 761 17 3 2 5.38
69

Table 50. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch White Clay

Creek at Avondale (site 28), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 836 18 5 28 5.50

1982 1,295 23 8 34 5.79

1983 1,368 18 8 72 4.64

1984 932 16 9 24 5.03

1985 1,007 22 10 35 4.94

1986 1,026 19 10 28 4.64

1987 4,223 19 7 8 6.32

1988 2,624 19 9 28 4.92

1989 1,797 29 14 48 4.57

1990 1,492 20 8 30 4.93

1991 2,007 19 11 29 4.92

1992 2,514 29 13 33 5.07

1993 2,090 27 14 23 5.03

1994 1,779 28 14 24 5.08

1995 1,543 28 11 21 5.10

1996 — — — — —

1997 1,717 24 10 36 4.48

Median 1,630 21 10 29 4.98

Table 51. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Middle Branch White Clay

Creek at Wickerton (site 29), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 780 16 5 21 5.67

1982 1,697 19 8 70 4.63

1983 833 17 8 69 4.42

1984 1,742 19 12 52 4.75

1985 1,265 25 12 33 4.85

1986 898 24 10 53 4.54

1987 1,314 23 9 32 4.79

1988 3,440 21 9 59 4.85

1989 1,438 26 12 42 5.27

1990 2,008 29 13 44 4.96

1991 2,464 24 12 52 4.79

1992 1,458 32 13 56 4.83

1993 829 19 10 73 4.65

1994 1,912 24 12 52 4.72

1995 1,841 28 14 38 5.03

1996 — — — — —

1997 1,371 29 17 54 4.83

Median 1,448 24 12 52 4.81
70

Table 52. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from West Branch White Clay Creek

near Chesterville (site 30), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,216 22 10 53 4.89

1982 2,270 23 13 80 5.47

1983 794 23 10 31 4.77

1984 1,232 23 11 74 4.96

1985 836 29 15 40 4.94

1986 1,079 24 13 71 4.34

1987 1,665 24 14 65 4.40

1988 2,065 23 14 81 4.58

1989 1,114 34 17 57 4.63

1990 1,794 29 16 64 4.85

1991 1,438 27 17 59 4.92

1992 1,472 34 17 59 4.36

1993 1,270 33 18 38 4.83

1994 1,027 25 16 50 4.15

1995 637 30 17 39 4.79

1996 — ————

1997 1,470 27 15 53 4.42

Median 1,251 26 15 58 4.78

Table 53. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Big Elk Creek

at Elkview (site 31), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 846 25 12 29 5.52

1982 1,416 26 12 29 5.26

1983 1,171 23 13 60 5.14

1984 1,216 25 13 59 5.42

1985 546 22 7 29 5.36

1986 851 20 8 41 5.33

1987 1,638 21 7 4 6.42

1988 1,357 26 13 39 4.97

1989 1,722 26 12 33 5.37

1990 1,387 23 11 16 5.32

1991 810 15 7 16 5.50

1992 755 26 13 28 5.02

1993 948 26 11 23 4.83

1994 553 17 7 27 5.30

1995 124 14 4 13 6.23

1996 71 11 3 20 4.96

1997 529 13 4 2 4.76

Median 851 23 11 28 5.32
71

Table 54. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from West Branch Big Elk Creek

near Oxford (site 32), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 1,517 30 14 75 4.83

1982 2,458 26 10 73 5.13

1983 1,203 28 14 51 5.16

1984 1,875 23 10 81 4.97

1985 1,124 21 12 53 4.98

1986 1,402 24 13 69 4.51

1987 1,309 22 13 38 5.30

1988 2,245 20 11 55 4.85

1989 1,533 25 12 68 4.77

1990 1,536 27 14 51 4.94

1991 2,733 32 17 52 4.87

1992 752 27 16 45 4.93

1993 424 18 9 45 4.40

1994 1,587 29 13 58 4.84

1995 85 15 7 19 3.84

1996 290 20 11 36 4.63

1997 — — — — —

Median 1,460 25 13 52 4.86

Table 55. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from East Branch Octoraro Creek

at Christiana (site 33), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 978 18 7 45 5.82

1982 1,670 24 11 56 5.60

1983 856 25 9 75 5.25

1984 1,518 21 12 45 5.07

1985 593 25 11 67 5.05

1986 1,110 27 11 52 4.66

1987 1,421 27 11 40 5.80

1988 1,953 20 9 76 4.19

1989 2,083 30 12 73 4.05

1990 1,419 33 15 58 4.62

1991 1,476 28 14 47 5.01

1992 1,268 23 10 42 4.66

1993 558 22 11 56 3.59

1994 2,194 31 15 27 5.31

1995 719 26 13 64 3.96

1996 847 25 8 57 4.54

1997 1,478 29 14 64 4.42

Median 1,419 25 11 56 4.66
72

Table 56. Values of total individuals, taxa richness, EPT taxa richness, percentage

of EPT individuals, and Hilsenhoff’s biotic index from Valley Creek near Atglen

(site 34), Chester County, Pennsylvania, 1981-97

[EPT, Ephemeroptera, Plecoptera, Trichoptera; —, no data]

Year Total

individuals

Taxa

richness

EPT

taxa

richness

Percentage

of EPT

individuals

Hilsenhoff’s

biotic

index

1981 2,173 21 11 62 4.29

1982 2,478 32 14 61 4.66

1983 930 23 13 72 5.02

1984 2,239 30 15 40 5.11

1985 962 28 15 72 4.86

1986 783 23 13 47 4.70

1987 2,316 31 15 46 5.54

1988 2,916 24 13 62 4.88

1989 3,051 39 19 68 4.54

1990 1,262 28 14 55 4.62

1991 3,201 32 14 43 4.96

1992 1,788 27 12 34 4.68

1993 825 18 6 50 4.39

1994 2,936 23 8 17 5.26

1995 460 21 10 45 5.05

1996 1,855 31 13 31 5.32

1997 — ——— —

Median 2,014 28 13 49 4.87
73

APPENDIX 1. SYSTEMATIC CHECKLIST OF TAXA REPORTED

FROM THE STREAM CONDITIONS OF CHESTER COUNTY

BIOLOGICAL MONITORING NETWORK, CHESTER COUNTY, PENNSYLVANIA

Hydrozoa (Hydroids)

Hydra sp.

Platyhelminthes (Flatworms)

Planariidae

Nematoda (Round Worms)

Nemertea (Proboscis worms)

Prostoma sp.

Gastropoda (Snails)

Amnicola sp.

Campeloma sp.

Ferrissia sp.

Goniobasis sp.

Gyraulus sp.

Helisoma sp.

Lymnaea sp.

Menetus sp.

Physa sp.

Planorbula sp.

Bivalvia (Clams)

Musculium sp.

Pisidium sp.

Sphaerium sp.

Annelida (Segmented worms)

Erpobdella sp.

Helobdella sp.

Hirudinea

Lumbriculidae

Naididae

Oligochaeta

Polychaeta

Sabellidae

Tubificidae

Cladocera (Water fleas)

Cyclopoida (Copepods)

Cyclopidae

Podacopa (Seed shrimps)

Isopoda (Sow bugs)

Caecidotea sp.

Lirceus sp.

Amphipoda (Scuds)

Crangonyx sp.

Gammarus sp.

Hyallela azteca
74

Decapoda (Crayfish)

Cambarus sp.

Orconectes sp.

Procambarus sp.

Arachnida (Water mites)

Acarina

Ephemeroptera (Mayflies)

Ameletus sp.

Anthopotamus sp.

Baetis sp.

Caenis sp.

Centroptilum sp.

Epeorus sp.

Ephemera sp.

Ephemerella sp.

Eurylophlebia sp.

Habrophlebia sp.

Heptagenia sp.

Isonychia sp.

Paraleptophlebia sp.

Potamanthus sp.

Serratella sp.

Siphlonurus sp.

Stenacron sp.

Stenonema sp.

Tricorythodes sp.

Odonata (Dragonflies and Damselflies)

Aeshna sp.

Amphiagrion sp.

Argia sp.

Boyeria sp.

Calopteryx sp.

Enallagma sp.

Gomphus sp.

Hetaerina sp.

Ischnura sp.

Lanthus sp.

Macromia sp.

Nehalennia sp.

Ophiogomphus sp.

Stylogomphus sp.
75

Plecoptera (Stoneflies)

Acroneuria sp.

Agnetina sp.

Allocapnia sp.

Belonuria sp.

Hastaperla sp.

Isoperla sp.

Leuctra sp.

Neoperla sp.

(Neo)phasganophora sp.

Paracapnia sp.

Paragnetina sp.

Paraleuctra sp.

Paranemoura sp.

Peltoperla sp.

Strophopteryx sp.

Taeniopteryx sp.

Hemiptera (Bugs)

Gerris sp.

Mesovelia sp.

Metrobates sp.

Microvelia sp.

Rhagovelia sp.

Rheumatobates sp.

Sigara sp.

Trepobates sp.

Trichocorixa sp.

Megaloptera (Alderflies and Dobsonflies)

Chauliodes sp.

Corydalus sp.

Nigronia sp.

Sialis sp.

Neuroptera (Spongillaflies)

Climacia sp.

Climacia areolaris

Sisyridae

Lepidoptera (Butterflies and Moths)

Archanara sp.

Nymphula sp.

Petrophila sp.

Synclita sp.
76

Trichoptera (Caddisflies)

Agraylea sp.

Anisocentropus pyraloides

Apatania sp.

Brachycentrus sp.

Ceraclea sp.

Cheumatopsyche sp.

Chimarra sp.

Culoptila sp.

Cyrnellus sp.

Diplectrona sp.

Dolophilodes sp.

Glossosoma sp.

Goera sp.

Helicopsyche sp.

Hydatophylax sp.

Hydropsyche sp.

Hydroptila sp.

Lepidostoma sp.

Leucotrichia sp.

Lype sp.

Macronema sp.

Micrasema sp.

Molanna sp.

Mystacides sp.

Nectopsyche sp.

Neophylax sp.

Neureclipsis sp.

Nyctiophylax sp.

Ochrotrichia sp.

Oecetis sp.

Parapsyche sp.

Phylocentropus sp.

Polycentropus sp.

Potamyia sp.

Protoptila sp.

Psilotreta sp.

Psychomyia sp.

Rhyacophila sp.

Rhyacophila fuscula

Stactobiella sp.

Symphitopsyche sp.

Triaenodes sp.

Wormaldia sp.
77

Coleoptera (Beetles)

Agabus sp.

Anchytarsus bicolor

Ancyronyx sp.

Ancyronyx variegata

Berosus sp.

Chrysomelidae

Curculionidae

Dineutus sp.

Dubiraphia sp.

Ectopria sp.

Ectopria nervosa

Helichus sp.

Helophorus sp.

Hydrobius sp.

Hydrochara sp.

Hygrotus sp.

Laccophilus sp.

Limnebius sp.

Macronychus sp.

Macronychus glabratus

Microcylloepus sp.

Optioservus sp.

Oulimnius sp.

Promoresia sp.

Psephenus sp.

Stenelmis sp.

Diptera (Flies)

Antocha sp.

Atherix sp.

Blepharoceridae

Ceratopogonidae (Heleidae)

Chaoborus sp.

Chelifera sp.

Chironomidae

Clinocera sp.

Dicranota sp.

Dixa sp.

Ephydridae

Helius sp.

Hemerodromia sp.

Hexatoma sp.

Limnophora sp.

Muscidae

Prosimulium sp.

Simulium sp.

Stratiomys sp.

Syrphidae Tabanus sp. Telmatoscopus sp. Tipula sp.