National Water-Quality Assessment Program

Water-Resources Investigations Report 03-4185

ENVIRONMENTAL SETTING, WATER QUALITY,

AND ECOLOGICAL INDICATORS OF SURFACEWATER QUALITY IN THE MERMENTAU RIVER

BASIN, SOUTHWESTERN LOUISIANA, 1998-2001

U.S. Geological Survey

U.S. Department of the Interior
Front cover:

Background: Mature rice plants (Oryza sativa) in the Mermentau River Basin, southwestern 

Louisiana

(Photograph by Dennis K. Demcheck, U.S. Geological Survey)

Top left: Rice water weevil, adult (Lissorhoptrus oryzophilus) on rice stalk

(Photograph provided by Kelly V. Tindall, Department of Entomology, Louisiana State University, 

Baton Rouge, Louisiana)

Top right: Ground water for rice field irrigation in the Mermentau River Basin, southwestern 

Louisiana

(Photograph by Dennis K. Demcheck, U.S. Geological Survey)

Lower left: Rice water weevil, larva (Lissorhoptrus oryzophilus) on rice roots

(Photograph provided by Kelly V. Tindall, Department of Entomology, Louisiana State University, 

Baton Rouge, Louisiana)

Lower right: Hydropsychidae, larva, net-spinning caddisfly

(Photograph provided by Elaine Esteban, Department of Biology, California State University, 

Chico, California)
Environmental Setting, Water Quality, and 

Ecological Indicators of Surface-Water 

Quality in the Mermentau River Basin, 

Southwestern Louisiana, 1998-2001

By Stanley C. Skrobialowski, Scott V. Mize, and Dennis K. Demcheck

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 03-4185

National Water-Quality Assessment Program

Baton Rouge, Louisiana

2004
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of trade, product, industry, or firm names in this report is for descriptive or location purposes only and does not constitute 

endorsement of products by the U.S. Government nor impute responsibility for any present or potential effects on the natural 

resources.

For additional information contact: Copies of this report can be purchased

from:

District Chief

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Information regarding the National Water-Quality Assessment (NAWQA) Program is available on 

the Internet via the World Wide Web. You may connect to the NAWQA Home Page using the 

Universal Resource Locator (URL) at:

http://water.usgs.gov/nawqa
FOREWORD

The U.S. Geological Survey (USGS) is committed 

to serve the Nation with accurate and timely scientific information that helps enhance and protect the 

overall quality of life, and facilitates effective management of water, biological, energy, and mineral 

resources. Information on the quality of the Nation’s 

water resources is of critical interest to the USGS 

because it is so integrally linked to the long-term 

availability of water that is clean and safe for drinking and recreation and that is suitable for industry, 

irrigation, and habitat for fish and wildlife. Escalating population growth and increasing demands for 

the multiple water uses make water availability, now 

measured in terms of quantity and quality, even 

more critical to the long-term sustainability of our 

communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program to support

national, regional, and local information needs and

decisions related to water-quality management and

policy. Shaped by and coordinated with ongoing

efforts of other Federal, State, and local agencies,

the NAWQA Program is designed to answer: What

is the condition of our Nation’s streams and ground

water? How are the conditions changing over time?

How do natural features and human activities affect

the quality of streams and ground water, and where

are those effects most pronounced? By combining

information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA

Program aims to provide science-based insights for

current and emerging water issues. NAWQA

results can contribute to informed decisions that

result in practical and effective water-resource management and strategies that protect and restore water

quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than

50 of the Nation’s most important river basins and

aquifers, referred to as Study Units. Collectively,

these Study Units account for more than 60 percent

of the overall water use and population served by

public water supply, and are representative of the

Nation’s major hydrologic landscapes, priority ecological resources, and agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling and analysis. The assessments thereby build local 

knowledge about water-quality issues and trends in 

a particular stream or aquifer while providing an 

understanding of how and why water quality varies 

regionally and nationally. The consistent, multiscale approach helps to determine if certain types of 

water-quality issues are isolated or pervasive, and 

allows direct comparisons of how human activities 

and natural processes affect water quality and ecological health in the Nation’s diverse geographic and 

environmental settings. Comprehensive assessments on pesticides, nutrients, volatile organic compounds, trace metals, and aquatic ecology are 

developed at the national scale through comparative 

analysis of the Study-Unit findings. 

The USGS places high value on the communication 

and dissemination of credible, timely, and relevant 

science so that the most recent and available knowledge about water resources can be applied in management and policy decisions. We hope this 

NAWQA publication will provide you the needed 

insights and information to meet your needs, and 

thereby foster increased awareness and involvement in the protection and restoration of our 

Nation’s waters. 

The NAWQA Program recognizes that a national 

assessment by a single program cannot address all 

water-resource issues of interest. External coordination at all levels is critical for a fully integrated 

understanding of watersheds and for cost-effective 

management, regulation, and conservation of our 

Nation’s water resources. The Program, therefore, 

depends extensively on the advice, cooperation, and 

information from other Federal, State, interstate, 

Tribal, and local agencies, non-government organizations, industry, academia, and other stakeholder 

groups. The assistance and suggestions of all are 

greatly appreciated.

Robert M. Hirsch

Associate Director for Water

v

CONTENTS

Foreword ................................................................................................................................................................ iii

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

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

Purpose and Scope .......................................................................................................................................... 2

Acknowledgments .......................................................................................................................................... 3

Environmental Setting............................................................................................................................................ 3

Land Use ......................................................................................................................................................... 3

Water Availability and Use ............................................................................................................................. 9

Hydrology ....................................................................................................................................................... 9

Aquatic Invertebrate Communities................................................................................................................. 12

Data Collection and Methods of Study .................................................................................................................. 12

Site Selection .................................................................................................................................................. 13

Data Analysis.................................................................................................................................................. 14

Water-Quality Characteristics ................................................................................................................................ 17

Nutrients.......................................................................................................................................................... 18

Major Inorganic Ions and Trace Elements...................................................................................................... 24

Pesticides ........................................................................................................................................................ 25

Ecological Indicators of Surface-Water Quality .................................................................................................... 29

Comparison of Site Groups............................................................................................................................. 30

Study-Design Site Groups ....................................................................................................................... 30

Stream Habitat Characteristics ......................................................................................................... 30

Aquatic Invertebrate Communities................................................................................................... 31

Canonical Correspondence Analysis Site Groups ................................................................................... 34

Water-Quality Characteristics........................................................................................................... 37

Stream Habitat Characteristics ......................................................................................................... 38

Aquatic Invertebrate Communities................................................................................................... 38

Relations Between Species and Environmental Variables....................................................................... 41

Summary and Conclusions..................................................................................................................................... 41

References Cited .................................................................................................................................................... 44

Appendixes............................................................................................................................................................. 49

1. Complete names for surface-water and ecological data-collection sites in the Mermentau River 

Basin and adjacent Calcasieu River Basin in southwestern Louisiana, 1998-2001 ........................... 50

2. Pesticides and degradation products analyzed, use, and occurrence in ground- and surface-water 

samples from the Mermentau River Basin, southwestern Louisiana, 1998-2001.............................. 51

3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001................................................................................................... 54

4. Selected physiochemical properties and fipronil concentrations for ecological data-collection 

sites in southwestern Louisiana, 2001................................................................................................ 60

5. Mean quantitative habitat variables from ecological data-collection sites in southwestern 

Louisiana, 2001 .................................................................................................................................. 61

6. Classification ranking of U.S. Environmental Protection Agency's Rapid Bioassessment 

Protocols habitat variables for ecological data-collection sites in southwestern Louisiana, 2001..... 63

7. Habitat assessment results using U.S. Environmental Protection Agency's Rapid Bioassessment 

Protocols for ecological data-collection sites in southwestern Louisiana, 2001................................ 64

8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection 

sites in southwestern Louisiana, March-April 2001........................................................................... 65

9. Loadings of environmental variables on the first two principal components (PC) derived from 

principal components analysis (PCA) of ecological data-collection sites in southwestern 

Louisiana, 2001 .................................................................................................................................. 73
vi

FIGURES

1-4. Maps showing:

1. Location of continuous-discharge surface-water sites and ground-water wells sampled in the 

Mermentau River Basin, southwestern Louisiana, 1998-2001.......................................................... 4

2. Land use and location of surface-water data-collection sites in the Mermentau River Basin, 

southwestern Louisiana, 1998-2001 .................................................................................................. 5

3. Land use and long-term water-quality data-collection sites in southwestern Louisiana, 

1998-2001 .......................................................................................................................................... 7

4. Soils and location of surface-water data-collection sites in the Mermentau River Basin, 

southwestern Louisiana, 1998-2001 .................................................................................................. 8

5. Bar chart showing sources and quantities of water used in the Mermentau River Basin, southwestern

Louisiana, 2000......................................................................................................................................... 10

6. Graph showing discharge for selected sites in the Mermentau River Basin, southwestern Louisiana, 

1998-2001 ................................................................................................................................................. 11

7. Flowchart of statistical analysis of ecological data used in the study....................................................... 15

8. Boxplots showing concentrations of selected nutrients and major inorganic ions in ground water and

surface water from the Mermentau River Basin, southwestern Louisiana, 1998-2001 ............................ 21

9. Photograph showing grazing livestock near a surface-water data-collection site in the Mermentau 

River Basin, southwestern Louisiana ........................................................................................................ 22

10-15. Graphs showing:

10. Concentrations of nitrite plus nitrate, potassium, and suspended sediment at the Mermentau datacollection site in the Mermentau River Basin, southwestern Louisiana, 1998-2001......................... 23

11. Drinking-water and aquatic-life criteria, and maximum detected concentrations of selected 

pesticides in ground water in the Mermentau River Basin, southwestern Louisiana, 2000-2001..... 25

12. Drinking-water and aquatic-life criteria, and maximum detected concentrations of selected 

pesticides in surface water in the Mermentau River Basin, southwestern Louisiana, 1998-2001..... 27

13. Concentrations of selected pesticides at the Mermentau data-collection site in the Mermentau 

River Basin, southwestern Louisiana, 1998-2001 ............................................................................. 28

14. Composition of predominant groups of aquatic invertebrates at basin and intensity site groups 

in southwestern Louisiana, 2001........................................................................................................ 33

15. Median abundances of aquatic invertebrates, Chironomidae (midges), and Tanytarsini midges 

at basin and intensity site groups in southwestern Louisiana, 2001 .................................................. 33

16. Canonical correspondence analysis (CCA) ordination biplot showing site (A) and species (B) 

locations in relation to environmental variables of ecological data-collection sites in southwestern 

Louisiana, 2001......................................................................................................................................... 35

17. Map showing land use and location of ecological data-collection sites and canonical 

correspondence analysis (CCA) site groups in southwestern Louisiana, 2001 ........................................ 36

18. Graph showing composition of predominant groups of aquatic invertebrates at canonical

correspondence analysis (CCA) site groups in southwestern Louisiana, 2001 ........................................ 40

19. Graph showing median abundances of aquatic invertebrates, Chironomidae (midges), and Tanytarsini 

midges at canonical correspondence analysis (CCA) site groups in southwestern Louisiana, 2001........ 40

20. Scatter plots showing relative abundances of Caenis sp. (mayfly) and Rheotanytarsus sp. (midge),

and significant habitat and water-quality variables identified by canonical correspondence

analysis (CCA) for ecological data-collection sites in southwestern Louisiana, 2001............................. 42

TABLES

1. Surface-water and ecological data-collection sites in the Mermentau River Basin and adjacent Calcasieu 

River Basin, southwestern Louisiana, 1998-2001 .......................................................................................... 6

2. Annual mean flow for selected sites in the Mermentau River Basin, 1999-2001, and period of record........ 11

3. Drinking-water regulations, health advisory levels, and aquatic-life criteria for selected pesticides............. 16

4. Minimum, median, and maximum concentrations of selected nitrogen species for ground- and surfacewater samples from the Mermentau River Basin, southwestern Louisiana, 1998-2001 ................................ 19
vii

5. Maximum concentrations and occurrence of selected nutrients in ground water and surface water in the 

Mermentau River Basin, southwestern Louisiana, 1998-2001....................................................................... 20

6. Minimum, median, and maximum concentrations of selected phosphorus species for ground- and 

surface-water samples from the Mermentau River Basin, southwestern Louisiana, 1998-2001.................... 20

7. Maximum concentrations and occurrence of selected major inorganic ions in ground water and surface 

water in the Mermentau River Basin, southwestern Louisiana, 1998-2001................................................... 24

8. Median stream habitat variables for study-design site groups in southwestern Louisiana, 2001................... 31

9. Median aquatic invertebrate metrics for basin and intensity site groups in southwestern Louisiana, 2001... 32

10. Canonical correlation coefficients of environmental variables with the first four canonical 

correspondence analysis axes for aquatic invertebrates at ecological data-collection sites in

southwestern Louisiana, 2001......................................................................................................................... 34

11. Median water-quality variables for canonical correpondence analysis (CCA) site groups in southwestern 

Louisiana, 2001............................................................................................................................................... 37

12. Median stream habitat variables for canonical correpondence analysis (CCA) site groups in southwestern 

Louisiana, 2001............................................................................................................................................... 38

13. Median aquatic invertebrate metrics for canonical correpondence analysis (CCA) site groups in 

southwestern Louisiana, 2001......................................................................................................................... 39

CONVERSION FACTORS, DATUMS, AND ABBREVIATED WATER-QUALITY UNITS

Multiply By To obtain

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

foot per second (ft/s) 0.3048 meter per second (m/s)

yard (yd) 0.9144 meter (m)

mile (mi) 1.609 kilometer (km)

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

million gallons per day (Mgal/d) 3, 785 cubic meters per day (m3/d)

Temperature in degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 x °C) + 32.

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29)—a geodetic datum 

derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level

Datum of 1929.

Horizontal coordinate information is referenced to the North American Datum of 1983.

Abbreviated water-quality units:

micrograms per liter (μg/L)

micrograms per kilogram (μg/kg)

microsiemens per centimeter at 25 degrees Celsius (μS/cm)

milligrams per liter (mg/L)

organisms per square meter (organisms/m2)
viii
1

Environmental Setting, Water Quality, and 

Ecological Indicators of Surface-Water 

Quality in the Mermentau River Basin, 

Southwestern Louisiana, 1998-2001

By Stanley C. Skrobialowski, Scott V. Mize, and Dennis K. Demcheck

ABSTRACT

The U.S. Geological Survey collected data from 29 

wells and 24 surface-water sites in the Mermentau River 

Basin, 1998-2001, to better understand ground-water and 

surface-water quality; aquatic invertebrate communities; 

and habitat conditions, in relation to land use. This study 

was a part of the National Water-Quality Assessment 

Program, which was designed to assess water quality as 

it relates to various land uses. Water-quality data were 

evaluated with criteria established for the protection of 

drinking water and aquatic life, and bed-sediment data 

were compared to aquatic-life criteria. Water-quality and 

ecological data were analyzed statistically in relation to 

drainage area and agricultural land-use intensity.

Concentrations of nutrients and major inorganic 

ions in ground water and surface water generally were 

highest in the southeastern part of the study area where 

soils contain thick loess deposits. Peak concentrations of 

nutrients in surface water occurred March-May at two 

sites with high agricultural intensity; the lowest concentrations occurred August-January. The greatest potential 

for eutrophic conditions in surface water, based on nutrient concentrations, existed March-May, at about the 

same time or shortly after ricefields were drained. Secondary Maximum Contaminant Levels established by 

the U.S. Environmental Protection Agency (USEPA) 

were exceeded for sulfate, chloride, iron, or manganese 

in samples from 20 wells, and for iron or manganese in 

samples from all surface-water sites.

Fewer pesticides were detected in ground water 

than in surface water. In 11 of the 29 wells sampled, at 

least one pesticide or pesticide degradation product was 

detected. The most frequently detected pesticides or pesticide degradation products in ground water were the herbicides bentazon and atrazine. Concentrations of 47 

pesticides and degradation products were detected in surface water. At least 3 pesticides were detected in all surface-water samples. In 72 percent of the samples at least 

5 hydrophylic pesticides were detected, and in more than 

70 percent of the samples at least 3 hydrophobic pesticides were detected. Although atrazine concentrations in 

three samples collected in the spring exceeded 3 μg/L 

(micrograms per liter), the USEPA Maximum Contaminant Level of 3 μg/L was not exceeded because it is 

based on an annual average of quarterly samples. Concentrations larger than 3.0 μg/L were not detected in 

samples collected during other times of the year. Tebuthiuron was detected at all surface-water sites; the largest 

concentration (6.33 μg/L) was detected at a site on 

Bayou des Cannes, and was the only detection that 

exceeded the criterion (1.6 μg/L) for the protection of 

aquatic life. Malathion was detected at 16 surface-water 

sites; the largest concentration (0.113 μg/L) was detected 

at a site on Bayou Lacassine, and was the only detection 

that exceeded the criterion (0.1 μg/L) for the protection 

of aquatic life. Concentrations of fipronil exceeded 

numeric targets for acute total maximum daily loads 

(2.3 μg/L) at 3 sites and chronic total maximum daily 

loads (4.6 μg/L) at 14 sites. Maximum pesticide concentrations in surface water usually occurred in the 

spring at about the same time or shortly after ricefields 

were drained.

Concentrations of DDE in bed sediment at two sites 

exceeded interim freshwater sediment quality guidelines 

for the protection of aquatic life. Fipronil sulfide and 

desulfinylfipronil were detected at all 17 sites from 

which bed-sediment samples were collected, but there 

are no current (2002) guidelines with which to evaluate 

the environmental effects of fipronil and degradation 

products.

Two methods were used to group the ecological 

data-collection sites: (1) Sites were grouped before data 

collection (according to the study design) using drainage 
2

area and agricultural land-use intensity, and (2) sites 

were grouped statistically after data collection using 

canonical correspondence analysis (CCA) and classification (cluster analysis) techniques on surface-water 

quality, habitat, and aquatic invertebrate data. Aquatic 

invertebrate communities were used as ecological indicators of surface-water quality and habitat conditions at 

these sites. The CCA identified four significant environmental variables (instream cover score, percentage of 

open canopy, concentrations of dissolved oxygen, and 

maximum concentrations of dissolved fipronil) that 

described the distribution of aquatic invertebrate communities among ecological data-collection sites. Results 

from the CCA were used in a cluster analysis to identify 

four site groups that had similar water quality, habitat, 

and aquatic invertebrate characteristics. Environmental 

variables and biological metrics within the study-design 

(a priori, before sampling) and CCA-assigned (posteriori, after sampling) site groups were compared.

Median values of 17 water-quality variables were 

lowest at sites in the northern part of the study area, 

where less than 45 percent of a drainage area is used for 

rice cultivation. Median values of 11 water-quality variables were highest at sites in the southeastern part of the 

study area, where the percentage of a drainage area used 

for rice cultivation varies. Median values of turbidity, 

and concentrations of total ammonia plus organic nitrogen, nitrate, total phosphorus, and dissolved fipronil, 

were highest at sites in the north-central part of the study 

area. Possible explanations for the differences in water 

quality among ecological data-collection sites may be 

the differences in (1) general soil composition and drainage characteristics, and (2) percentage of land used for 

agriculture in these basins.

Habitat characteristics including channel size and 

morphology, water clarity, open canopy, and substrate 

differed between streams in the northern and southern 

parts of the study area. Stream habitat ratings were based 

on the total of 10 habitat parameter scores, using the 

Rapid Bioassessment Protocols habitat characterization. 

Scores increase as habitat quality increases. Ratings 

were suboptimal (102-154) to optimal (155-200) for 16 

of the 19 ecological data-collection sites. Three sites 

were rated marginal (49-101). Differences in channel 

size, bank stability, and pool substrate may account for 

some differences in aquatic invertebrate communities 

between site groups distinguished by agricultural intensity.

Organisms tolerant of turbidity, organic enrichment, 

and low dissolved-oxygen concentrations were common 

in the study area and dominated the aquatic invertebrate 

community. Metrics for aquatic invertebrate communities were significantly different (p ≤ 0.05) among agricultural land-use intensity site groups and CCA site 

groups in (1) percentage of noninsects, (2) abundance of 

midge taxa, (3) abundance of feeding groups, and (4) 

number of tolerant organisms. Dominance and diversity 

metrics were significantly different (p ≤ 0.05) among 

CCA site groups. In this report, the maximum concentration of dissolved fipronil was the only significant environmental variable related to consistent decreases in 

relative abundance of many species, notably midges. 

Low species abundance in this report was associated with 

lower concentrations of fipronil degradation products 

than of the parent compound fipronil.

INTRODUCTION

The National Water-Quality Assessment 

(NAWQA) Program is a long-term program of the U.S. 

Geological Survey (USGS) designed to describe the status and trends in the quality of the Nation’s surface- and 

ground-water resources and to provide an understanding 

of the natural and human factors that can affect the quality of these resources (Gilliom and others, 1995). The 

program is interdisciplinary and integrates biological, 

chemical, and physical data to assess the Nation’s water 

quality at local, regional, and national scales. Assessing 

the quality of water in every part of the Nation would not 

be practical; therefore, NAWQA Program studies are 

conducted in a set of areas called study units. The Acadian-Pontchartrain (ACAD) is one such Study Unit, and 

consists of all or parts of 39 parishes in southern Louisiana and 5 counties in southwestern Mississippi (Demas 

and others, 1999). The 26,000-mi2 ACAD Study Unit 

includes the Mermentau River Basin, a distinctive agricultural area in southwestern Louisiana. Water-quality 

and ecological data are needed to describe interactions 

between ground- and surface-water components of the 

hydrologic cycle and to determine the effects of agricultural land use on water quality in the Mermentau River 

Basin.

Purpose and Scope

This report characterizes ground-water and surfacewater quality and ecological indicators (aquatic invertebrate communities and habitat conditions) for selected 

sites in the Mermentau River Basin. Bed-sediment quality also is characterized at selected sites. The environmental setting, including agricultural, industrial, wateravailability and use, and hydrologic characteristics of the 

Mermentau River Basin are described. This report (1) 

describes the occurrence and distribution of selected 

nutrients, major inorganic ions, trace elements, and pesticides in ground water and surface water, suspended sed-
3

iment in surface water, and selected pesticides in bed 

sediment; (2) characterizes stream habitat conditions at 

selected sites; and (3) assesses responses of aquatic 

invertebrate communities to surface-water quality and 

habitat conditions among selected sites. This report 

relates agricultural intensity (the percentage of land used 

for rice cultivation) to pesticide concentrations in water, 

aquatic community composition, and stream habitat 

characteristics.

The study area encompasses the Mermentau River 

Basin. Ground-water samples were collected once from 

29 wells (19-230 ft deep) in the study area during January 2000-January 2001 (fig. 1). Surface-water samples 

were collected from 3 sites during November 1998-September 1999; 17 sites during October 1999-September 

2000; and 18 sites during October 2000-September 2001 

(fig. 2, table 1). Ecological (habitat and aquatic invertebrate) data were collected in 2001 for 18 surface-water 

sites in the Mermentau River Basin and an additional site 

in the adjacent Calcasieu River Basin (fig. 3, table 1). 

Data from the additional site were used for comparison 

only, and the site was not intended to represent water 

quality in the Calcasieu River Basin. The additional site 

was used to compare conditions at a relatively undisturbed site with those at the agricultural sites in the Mermentau River Basin. The Calcasieu River Basin site was 

the best approximation to a large-basin, low agriculturalintensity site that was available. There were few suitable 

sites in the Mermentau River Basin with large basins and 

low agricultural intensity for comparison. Bed-sediment 

samples were collected under low-flow conditions from 

17 surface-water sites August-September 2000. Streamhabitat characteristics were documented and aquatic 

invertebrate samples were collected March-April 2001 

for all 19 surface-water sites sampled in 2001.

Acknowledgments

The authors thank Keith Fontenot, Ronnie Levy, 

and Eddie Eskew of the Louisiana Cooperative Extension Service, Louisiana State University Agricultural 

Center for their cooperation in evaluating the extent of 

rice cultivation in the Mermentau River Basin. The 

authors also thank the many owners of domestic wells for 

allowing access to their property and wells. Appreciation is extended to the following USGS employees: 

Stephen D. Porter and Lawrence R. Deweese for project 

development and support and critical study design 

review; Thomas F. Cuffney for reviewing the design of 

the study; Patricia J. D’Arconte for assistance with GIS 

support; Stephen D. Porter, Lawrence R. Deweese, Jeffrey A. Brantly, Van G. Bergeron, C. Paul Frederick, 

Kevin J. Grimsley, Cindy G. Sibley, Lane B. Simmons, 

and William B. Snee for assistance in data collection; and 

Stephen D. Porter, Lawrence R. DeWeese, Douglas A. 

Harned, and Thomas F. Cuffney for providing critical 

reviews that improved the quality of the report.

ENVIRONMENTAL SETTING

The Mermentau River Basin is located in the Western Gulf Coastal Plains ecoregion of southwestern Louisiana (Omernik, 1987). The area also is called coastal 

prairie or wet prairie (Brown, 1972). Historically, the 

area was a tallgrass prairie similar in many ways to the 

tallgrass prairie in the midwestern United States (Allain 

and others, 2000).

Soils in the Mermentau River Basin (fig. 4) consist 

of a thick loess in the eastern part of the study area 

(fig. 4), the area most used for soybean production 

(fig. 2). Most of the central and southern parts of the 

basin, however, consist of clayey and loamy alluvial 

deposits which are ideally suited for rice cultivation. 

Rice cultivation within the last 100 years has caused 

leaching of salts and fine clays to form a hardpan underlying ricefields (Lovelace, 1999). Alluvial soils in the 

northwestern part of the basin contain more silt and sand 

and consist of loamy and silty deposits and loamy fluvial 

deposits than other parts of the basin. The streambed 

substrate in the tributaries and main channel of the Mermentau River is silt or clay. The substrate in the mainstem and smaller tributaries also can be a soft flocculent 

muck rich in organic matter.

The area drained by the upper Calcasieu River 

Basin (fig. 3) is located in the Western Gulf Coastal 

Plains ecoregion, is primarily forested, and has geomorphic features and hydrology typical of an upland basin. 

The streams drain an area of rolling pine hills with sandy 

soils. Ground-water contributions to the stream during 

the late summer result in orange-red iron oxide coatings 

on the sandy substrate.

Land Use

Most land in the Mermentau River Basin has been 

altered for agricultural crops such as rice, soybeans, and 

sugarcane, and for pasture (fig. 3). Other land uses 

include crawfish farming and oil and gas exploration and 

production. The northwestern part of the basin is mostly 

forested and land in the remainder of the basin is used 

predominantly for rice agriculture.

Forest consisting of mixed pine-hardwoods in the 

upper basin changes to water tupelo and cypress riparian 

zones as the land flattens toward the lower basin. The 

mid-to-lower reaches of the Mermentau River are bordered by a water tupelo and cypress riparian zone that 
Index Map

Arkansas

Louisiana

iss s ippi

M

i s

Texas

Mermentau River

 Basin

Mermentau River Basin boundary

EXPLANATION

Continuous-discharge site and site 

 name (see table 1, appendix 1)

Well and well number

30 MILES

0 30 KILOMETERS

0

Figure 1. Continuous-discharge surface-water sites and ground-water wells sampled in the Mermentau

River Basin, southwestern Louisiana, 1998-2001.

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12

M e t: o fi d f ff i ap o o tm n f s tat o lo e , ap cr di M di e rom O ic al M f L uisiana, Depar e t o Tran por i n and Deve pm nt 1986

BAYOU NEZPIQUE

NEAR BASILE

DES CANNES

MERMENTAU

LACASSINE

DES CANNES

17

55

VERNON

VANE

LINE

E

G

ALLEN

T

L

S

A

DRY

N

JEFFERSON

DAVIS

ACADIA

CAMERON VERMILION

LAFAYETTE

RAPIDES AVOYELLES

4
Index Map

Arkansas

Louisiana

iss s ipp

M

i s i

Texas

Mermentau River

 sin Ba

Mermentau River Basin boundary

EXPLANATION

Forest

Rice

Urban

Water

Soybean

Data-collection site and site name 

(see table 1, appendix 1)

Figure 2. Land use and location of surface-water data-collection sites in the Mermentau River Basin, southwestern Louisiana,

1998-2001.

93° 00 ́ 92° 30 ́ 92° 00 ́

3 0 0° 0 ́

3 3  ́ 0° 0 Map : o i f f o m n f s at l credit M dif ed rom Of icial Map f Louisiana, Depart e t o Tran port ion and Deve opment, 1986

BOGGY

CANEY

NEZPIQUE

CASTOR

GUIDRY

BLUE

DES CANNES

UPPER

DES CANNES

MALLET

CHURCH POINT

WIKOFF

IOTA

ROANOKE PLAQUEMINE THERIOT

PANCHOVILLE

EAST 

LACASSINE

CHENE MERMENTAU

LACASSINE

LAKE ARTHUR

RICEVILLE

TORTUE

GRAND

 MARAIS

WIKOFF

e in me uqal P

30 MILES

0 30 KILOMETERS

0

VERNON

VANE

LINE

E

G

ALLEN

T

L

S

A

DRY

N

JEFFERSON

DAVIS

ACADIA

CAMERON VERMILION

LAFAYETTE

RAPIDES AVOYELLES

Cal

asi

c

eu

s e d

n

Ca

es

n

i R er v

ue

Que

de

T

u

ort e

a B y uo

Nezpiq

e u

iv R er

erm

l

n

V

i io

er

Riv

y u

Ba o

a B y uo

B

y u a o a

Lac ssine

Mer

n

u

m

ta

e

Bayou

u

e

Br l

5

Land-use data

(source: Joseph Holmes, Louisiana

 Department of Environmental Quality,

 written commun., 2001)
6

1 Complete site name is listed in appendix 1. 2 Water-quality samples only.

3 Water-quality and bed-sediment samples, except as noted. 4 Water-quality and ecological samples and data. 5 Estimated value.

6 Shown in figure 3.

Table 1. Surface-water and ecological data-collection sites in the Mermentau River Basin and adjacent Calcasieu 

River Basin, southwestern Louisiana, 1998-2001

[Basin size: A drainage area greater than or equal to 70 square miles represents a large basin, and a drainage area smaller than 70 square miles 

represents a small basin. Agricultural land-use intensity: A basin in which the land used for rice cultivation is at least 45 percent of the drainage 

area is considered high agricultural intensity, and less than 45 percent is considered low agricultural intensity. All sites are short-term except sites 

1, 7, 11, and 25, which are long-term. X, sampled]

Site

number

(fig. 2)

Abbreviated site 

name1

U.S. Geological 

Survey station 

number 

Drainage 

area 

(square 

miles)

Basin

size

Drainage 

area used 

for rice 

(percent)

Agricultural

land-use

intensity

Sampling period

2Nov. 

1998-

Sept. 

1999

3Oct. 

1999-

Sept. 

2000

4Oct. 

2000-

Sept. 

2001

Mermentau River Basin

1 Des Cannes 08010000 142 Large 95 High X X X

2 Wikoff 08010500 63 Small 54 High X X

3 Plaquemine 08011020 320 Large 64.7 High X X

4 Boggy 08011500 65 Small 0 Low X

5 Castor 08011800 33 Small 42.4 Low X

6 Nezpique 08011860 166 Large 21.7 Low X X

7 Mermentau 08012150 1,381 Large 66.5 High X X X

8 Riceville 08012300 236 Large 76.3 High X

9 Lake Arthur 08012400 1,702 Large 69 High X

10 Chene 08012447 100 Large 97 High X

11 Lacassine 08012470 296 Large 89.5 High X X X

12 Tortue 300446092214200 97 Large 74.2 High X X

13 Grand Marais 300514092173500 26 Small 38.5 Low X

14 Theriot 301154092145900 37 Small 62.2 High X

15 East Lacassine 301520092491800 15 Small 100 High X X

16 Roanoke 301538092421900 56 Small 100 High X

17 Iota 301959092323400 333 Large 50 High X

18 Panchoville 302128092373800 550 Large 45 High X

19 Church Point 302403092152300 74 Large 25.7 Low X X

20 Mallet 302749092203500 91 Large 86.8 High X X

21 Guidry 303206092360000 381 Large 36.6 Low X X

22 Blue 303209092401800 80 Large 53.8 High X

23 Upper Des Cannes 303755092190400 46 Small 91.3 High X

24 Caney 304130092344100 18 Small 0 Low X

Calcasieu River Basin (additional site)

6

25 Whisky 08014500 504 Large 58 Low X 2X X
25

1

7

11

11

Calcasieu River

Basin

Index Map

ACAD Study 

Unit boundary

Arkansas

Louisiana

s Missi sippi

Texas

Mermentau River

Basin

Map credit: Modified f om Off cial Map of Louisi a, epartment of T ans ortatio an evelopme t, 1986 r i an D r p n d D n

S BIN A E

AKE L

I U CALCA E S

K LA E

WHITE

LAKE

GRAND

LAKE

Ca si lca eu

ver Ri

s de

s anne C

nt Merm au e

Ri r ve

Ba ou y

ATC

F L YA

HA

A

A

IVER R

Q e e u u de

e Tortu

ay u B o

N zp e e iqu

iver R

H uso n o t

River

VERMILION

BAY WEST COTE

BLANCHE BAY

rm l o Ve i i n

River

e h T c e

Bayou

GULF O ME ICO F X

92° 00 ́

92° 03  ́

93° 00 ́

93° 30 ́

3  ́ 0° 00

0° 3 3 0 ́

0 ́ 31° 0

B y a ou

Calcasieu

B y u a o

a in L cass e

30 MILES

0 30 KILOMETERS

0

B you a

r e B ul Plaquem ne i

Lower Mud

Lake

Whisky Chitto Cr ek e

Figure 3. Land use and long-term water-quality data-collection sites in southwestern Louisiana, 1998-2001.

Study area boundary

Basin boundary

Long-term data-collection site

and un mber (see table 1)

EXPLANATION

Rice

Soybean

Sugarcane

Cotton

Urban

Pasture

Forest

Wildlife preserve

Marsh

Water

Aquaculture

Catfish 

Point

Gulf Intracoastal Waterway

Jennings

BEAUREGARD

VERNON

EVANGELINE

ALLEN

ST LANDRY

JEFFERSON

DAVIS

CALCASIEU

ACADIA

VERMILION IBERIA

ST. MARTIN

CAMERON

LAFAYETTE

RAPIDES

AVOYELLES

7

Land-use ad ta

 (source: Joseph Holmes, Louisiana

Department of Environmental Quality,

written commun., 02 01)
Index Map

Arkansas

Louisiana

s s ipp

Mi si s i

Texas

Mermentau River

 Basin

Mermentau River Basin boundary

EXPLANATION

Figure 4. Soils and location of surface-water data-collection sites in the Mermentau River Basin, southwestern Louisiana 1998-2001.

Clayey and loamy alluvial deposits

Loamy and clayey alluvial and outwash 

 deposits

Loamy fluvial deposits

Fresh organic and mineral deposits

Water

Thick loess deposits

Loamy and silty deposits

Data-collection site and site name 

(see table 1, appendix 1)

93° 00 ́ 92° 30 ́ 92° 00 ́

30° 00 ́ 30 30 °  ́

e in me uqal P

Bayou

u

e

Br l

M re t: o fi d f ff i ap o o i tm n of s tat o n v lo e , ap c di M di e rom O ic al M f L u siana, Depar e t Tran por i n a d De e pm nt 1986

BOGGY

CANEY

NEZPIQUE

CASTOR

GUIDRY

BLUE

DES CANNES

UPPER

DES CANNES

MALLET

CHURCH POINT

WIKOFF

IOTA

ROANOKE PLAQUEMINE THERIOT

PANCHOVILLE

EAST 

LACASSINE

CHENE MERMENTAU

LACASSINE

LAKE ARTHUR

RICEVILLE

TORTUE

GRAND

 MARAIS

WIKOFF

30 MILES

0 30 KILOMETERS

0

VERNON

VANE

LINE

E

G

ALLEN

T

L

S

A

DRY

N

JEFFERSON

DAVIS

ACADIA

CAMERON VERMILION

LAFAYETTE

RAPIDES AVOYELLES

Cal

asi

c

eu

s e d

n

Ca

es

n

i R er v

Queue

e d

To

ue

rt

a B y uo

Nezpiq

e u

iv R er

erm

l

n

V

i io

er

Riv

y u

Ba o

a B y uo

B

y u a o a

Lac ssine

Mer

n

u

m

ta

e

8

Soils ata d

 (source: Touchet and others, 1974)
9

typically is flooded more than half of the year. Banks 

along the tributaries generally are low with water tupelo 

and cypress extending into the streams. Along parts of 

the lower reaches, banks are not discernible as the water 

extends into a bottomland hardwood flood plain. In 

places, the flood plain abruptly ends at ricefield levees or 

roadways.

Rice is the most important agricultural crop produced in the basin. Total rice acreage in the seven parishes (Acadia, Allen, Evangeline, Jefferson Davis, 

Lafayette, St. Landry, and Vermilion) of the Mermentau 

River Basin was almost 400,000 acres in 1998 and about 

340,000 acres in 2000 (Louisiana Cooperative Extension 

Service, 1998, 2000). Soybeans are rotated periodically 

with rice in the basin, but areas where this occurs are 

shown only as rice acreage in figure 3 because rice is the 

most frequently cultivated crop. Although sugarcane is 

grown in the southwestern part of the basin, the acreage 

is too small and scattered to be delineated in figure 3.

Rice cultivation practices in the Mermentau River 

Basin use substantial amounts of ground water and surface water. Aerial application of seed on flooded fields 

is the predominant method of planting rice in the basin. 

The flooding of ricefields also suppresses red rice, a wild 

variety with no commercial value, and allows crawfish 

farming in the ricefields (Linscombe and others, 1999). 

After the aerial seeding of rice, the water is retained on 

the field for about 1 to 2 days and released. The field is 

allowed to drain only long enough for the young seedlings to become anchored, about 3 to 5 days. Releases of 

ricefield water (called tailwater) into the streams result in 

very high turbidities during March through May. The 

field is then reflooded until the rice nears maturity. Rice 

typically is harvested in July and August. A second rice 

crop may be harvested in September and October from 

volunteers of the first harvest, depending on prices and 

the climate for the particular year.

About 30,000-40,000 acres in the Mermentau River 

Basin were used for crawfish farming in 2000. Two species are grown commercially, the red swamp crawfish 

and the white river crawfish. There are two basic methods for growing crawfish: permanent ponds and rotational ponds. Permanent ponds are dedicated solely for 

the production of crawfish and generally are located east 

of the Mermentau River Basin. Rotational ponds are the 

most common method of crawfish production in the 

basin. In this aquacultural practice rice and crawfish are 

double-cropped annually. Typically, rice is planted in 

March and April. Land is reflooded and, by June, the 

flooded fields are stocked with crawfish. Rice is harvested by August, land is reflooded in October, and crawfish are harvested in November through April (Avery and 

Lorio, 1999).

The primary industry affecting water quality in the 

Mermentau River Basin is oil and gas exploration and 

production (Demas and others, 1999). The first oil well 

in Louisiana was drilled near Jennings, Louisiana, in 

September 1901, soon after the first great gusher in 

America, at Spindletop, Texas, in January 1901 (Spearing, 1995). Since then, oil and gas production facilities 

and their associated pipelines have become major and 

conspicuous features of the landscape of the area. Most 

facilities are quite small, occupying only a few acres or 

less. Although oil and gas production from the fields in 

the basin is declining, wells, pipelines, and oil and gas 

production and distribution facilities are located throughout the area. Individual oil wells among rice fields are 

separated from the fields by low earthen berms.

Water Availability and Use

Ground water and surface water are used for rice 

cultivation and crawfish farming in the Mermentau River 

Basin (fig. 5). Rice farmers in the southern part of the 

basin rely on surface water for irrigation, whereas farmers in the northern part of the basin rely on ground water. 

The 540 Mgal/d combined ground- and surface-water 

withdrawals for rice irrigation in 2000 was 87 percent of 

the total water used in the basin (B.P. Sargent, U.S. Geological Survey, written commun., 2002). More than 80 

percent of the water used for rice irrigation was from 

ground-water sources in the Chicot aquifer system.

A drought occurred throughout southwestern Louisiana in 1998-2000. May 1998 was one of the driest 

Mays in more than 100 years. The drought was classified 

as mild in 1998 and intensified to severe conditions during the latter half of 1999. Conditions further intensified 

to extreme through October 2000, then subsided in 

November 2000, one of the wettest Novembers on record 

(John M. Grymes, III, Louisiana State Climatologist, 

written commun., 2002). The drought caused rice farmers to use more ground water or forego planting.

Hydrology

The Mermentau River Basin has a drainage area of 

about 3,800 mi2

 (Sloss, 1971), and includes most of a 

seven-parish area (fig. 3). The Mermentau River begins 

at the confluence of three major tributaries: Bayou Nezpique, Bayou des Cannes, and Bayou Plaquemine Brule 

(fig. 1). Downstream from the confluence, Bayou 

Lacassine enters the Mermentau River from the west, 
10

Figure 5. Sources and quantities of water used in the Mermentau River Basin, southwestern Louisiana, 2000.

500

450

400

350

300

250

200

150

100

50

0

Aquaculture

Ground Water

Aquaculture

Surface Water

Rice Irrigation

Ground Water

Rice Irrigation

Surface Water

Public Supply

Ground Water

WATER-USE CATEGORY AND SOURCE OF WATER

QUANTITY, IN MILLION GALLONS PER DAY

and Bayou Queue de Tortue enters the river from the east. 

The five bayous divide the Mermentau River Basin into 

a series of broad, flat areas ideal for agriculture. These 

areas are separated by bottomland hardwood riparian 

corridors that vary in width from only a hundred feet to 

several miles. Land-surface elevations are less than 

100 ft above NGVD 29 in most of the basin and less than 

25 ft above NGVD 29 along the Mermentau River mainstem. Thus, the Mermentau River Basin is characterized 

by a low gradient and dendritic river system that drains 

to the Gulf of Mexico.

Hydrology in the Mermentau River Basin is complicated by the extensive use of ground water for irrigation and by modifications for agriculture and navigation. 

Water used to flood ricefields may enter the Chicot aquifer system, be reused downstream for agriculture, or 

drain to the Gulf of Mexico. During the study described 

in this report, a dam was constructed upstream from one 

of the long-term surface-water sites, Des Cannes, 

because a train derailed and spilled chemicals (National 

Transportation Safety Board, 2002). Modifications of 

streams for navigation and water-control structures are 

common in the basin.

The Mermentau River Basin is characterized by 

free-flowing streams in the north. The low gradient and 

low topographic relief in the southern part of the basin 

create both bidirectional (downstream and upstream) and 

interbasin flow, with water velocities typically less than 

1 ft/s. The river is tidally affected, and most upstream 

(negative) flow occurs in the summer and fall. Negative 

flow can be caused by natural events such as storms and 

sustained winds from the south in conjunction with 

unusually high tides. These negative flows can be 

increased in magnitude and duration during low-discharge periods, such as occurred during the drought of 

1999-2000 (fig. 6). Pumping of surface water for irrigation may cause bidirectional flow, but typically only in 

the smaller tributaries.

The naturally low gradient and human-made canals 

and waterways allow interbasin flows. The primary flow 

route is the Gulf Intracoastal Waterway (GIWW), constructed in 1940 (fig. 3). The GIWW crosses the Mermentau River north of Grand Lake and is a major route 

for east-west barge traffic along the Gulf Coast. A complex series of gates and locks is operated by the U.S. 

Army Corps of Engineers (USACE) to manage the 

waterway. The GIWW hydraulically connects the Mermentau River Basin with the Calcasieu River Basin to the 

west and the Teche-Vermilion Basin to the east.

In the 1970’s, the natural mouth of the Mermentau 

River was bypassed with the construction of a separate 

4.6-mi navigation channel from Lower Mud Lake to the 

Gulf of Mexico. This navigation channel, the GIWW, 

and other hydrologic modifications throughout southwestern Louisiana are managed by numerous water-control structures. One such structure on the Mermentau
11

River south of Grand Lake at Catfish Point. The purposes of the gated control structure are to reduce northward movement of saltwater and to maintain a sufficient 

freshwater stage for farmers, especially rice farmers, in 

the Mermentau River Basin. The USACE maintains the 

stage on the mainstem of the Mermentau River at about 

2 ft above NGVD 1929 (Steven Schinetsky, U.S. Army 

Corps of Engineers, oral commun., 2002), sometimes by 

closing the control structure at Catfish Point. The river 

upstream from Catfish Point appears to cease flowing 

during periods of closure.

On May 27, 2000, a train with 17 cars of hazardous 

materials and residues derailed about 0.5 mi upstream 

from Des Cannes and 2 mi west of Eunice, Louisiana 

(National Transportation Safety Board, 2002). The 

derailment resulted in the release of hazardous materials 

to a ditch and pond draining to Bayou des Cannes. No 

chemicals spilled directly into the bayou. Because an 

earthen dam was constructed about 100 yd upstream 

from the Des Cannes site, streamflow data from nearby 

Bayou Nezpique near Basile (a continuous-discharge site 

only) were used to augment streamflow data from the 

Des Cannes site (fig. 1). Continuous streamflow data are 

available from four sites in the Mermentau River 

Basin—Bayou Nezpique near Basile, Des Cannes, 

Lacassine, and Mermentau (fig. 1). Annual streamflow 

data are available only for Bayou Nezpique near Basile, 

and Des Cannes (table 2). Streamflow is bidirectional at 

Lacassine and Mermentau and these sites lack sufficient 

data to determine annual streamflow statistics.

A combination of ground water and surface water is 

used for agriculture and aquaculture. Because of the 

hardpan clay layer underlying the ricefields, a substantial 

amount of tailwater enters surface water as runoff. It 

then may be pumped from a waterway to irrigate another 

field or used for aquaculture farther downstream. Thus, 

-5000

0

5000

10000

15000

20000

10/1/1998

12/12/1998

2/22/1999

5/5/1999

7/16/1999

9/26/1999

12/7/1999

2/17/2000

4/29/2000

7/10/2000

9/20/2000

12/1/2000

2/11/2001

4/24/2001

7/5/2001

9/15/2001

Mermentau River at Mermentau

Bayou Lacassine nr Lake Arthur

Bayou des Cannes near Eunice

DROUGHT

DATE

DISCHARGE, IN CUBIC FEET PER SECOND

20,000

15,000

10,000

5,000

0

-5,000

Oct. 1

Nov. 2

Dec. 4

Jan. 5

Feb. 6

Mar. 10

Apr. 11

May 13

June 14

July 16

Aug. 17

Sept. 18

Oct. 20

Nov. 21

Dec. 23

Jan. 24

Feb. 25

Mar. 28

Apr. 29

May

31

June

July 2

Aug. 3

Sept. 4

Oct. 6

Nov. 7

Dec. 9

Jan. 10

Feb. 11

Mar. 15

Apr. 16

May 18

June 19

July

21

Aug. 22

Sept. 23

1998 1999 2000 2001

[Negative discharge indicates reverse flow.]

Mermentau

Lacassine

Des Cannes

DROUGHT PERIOD

Figure 6. Discharge for selected sites in the Mermentau River Basin, southwestern Louisiana, 1998-2001.

Table 2. Annual mean flow for selected sites in the 

Mermentau River Basin, 1999-2001, and period of 

record

Site name

Annual mean flow

(cubic feet per second)

1999 2000 2001

Period of 

record,

1939-

2001

Des Cannes 201 79.4 322 275

Bayou Nezpique 

near Basile

651 169 801 833
12

aquatic life is exposed to both ground water and surface 

water. Also, tidal effects and bidirectional flows preclude the use of stage-discharge relations to calculate 

streamflow at all but the most upstream sites. The 

bidirectional-discharge hydrographs from the Mermentau and Lacassine sites define specific hydrologic conditions only at those two locations. They are useful in 

describing the overall hydrologic conditions in the basin, 

but cannot provide information such as loads that can be 

used for management decisions. For these reasons the 

integrated assessment for this study of surface-water 

quality, ground-water quality, bed-sediment quality, and 

ecological indicators is restricted to approximately 

2,000 mi2 of the Mermentau River Basin north of the 

Lake Arthur and Lacassine sites.

Aquatic Invertebrate Communities

The most important factors influencing the occurrence and distribution of aquatic invertebrates are stream 

velocity, water temperature, dissolved substances, and 

substrate (Hynes, 2001). Because of low water velocities, elevated water temperatures, and soil types of the 

Mermentau River Basin, an aquatic environment that is 

not conducive to a diverse aquatic invertebrate community is expected. Snags provide a firm substrate and 

opportunities for colonization often lacking in the clays 

and mucks of the streambed and banks. Snags also allow 

aquatic invertebrates to move closer to the water surface 

during periods of low dissolved-oxygen concentrations 

and high turbidities. These populations typically include 

the larvae of chironomid midges, snails, amphipod crustaceans, and worms. DeWalt (1997), in a study designed 

to locate and characterize wadeable reference streams in 

this basin, noted that low dissolved-oxygen concentrations significantly distinguish this area from other Louisiana lowlands.

 The Mermentau River Basin, especially in the midto-lower reaches, typically supports dense growth of 

exotic macrophyte (aquatic plant) species. Among these 

are water hyacinth (Eichhornia crassipes), alligator 

weed (Alternanthera philoxeroides), and water spangle 

(Salvinia minima). During mild winters these macrophytes may not experience a complete dieback and may 

cover the water surface, reducing light penetration and 

lowering dissolved-oxygen concentrations. These 

plants, however, provide extensive habitat for aquatic 

invertebrates. Amphipod crustaceans in particular can be 

found in abundance among the root systems of water 

hyacinth.

Naturally occurring habitat conditions in the basin 

favor an aquatic invertebrate community tolerant of turbidity, organic enrichment, and low dissolved-oxygen 

conditions. The net effect of these natural environmental 

stressors is to produce a biological community that is, at 

first examination, indicative of streams that have been 

adversely affected by human activities. However, what 

may appear to be a degraded or depauperate biological 

assemblage may in fact be a healthy community where 

multiple environmental stressors limit diversity and sensitive taxa.

DATA COLLECTION AND METHODS OF 

STUDY

Ground-water sample collection was consistent 

with national goals for the ground-water component of 

the NAWQA program (Leahy and others, 1990). Samples were collected from wells drilled specifically for the 

NAWQA program and from existing domestic wells that 

met specific criteria. Surface-water samples were collected from 24 long- and short-term sites with varied 

agricultural intensity in the Mermentau River Basin. 

These sites are referred to in this report by the site names 

listed in table 1. Long-term sites were sampled to characterize temporal and spatial water-quality conditions, 

and short-term sites were sampled to characterize water 

quality during the spring months.

Water samples from wells and surface-water sites 

were collected for the analysis of nutrients, major inorganic ions, trace elements, and pesticides; samples from 

surface-water sites also were analyzed for suspended 

sediment. Water samples were collected from 29 wells 

(fig. 1). The wells were sampled once during the period 

January 2000-January 2001, and the well depths ranged 

from 19 to 230 ft. Surface-water samples were collected 

at 25 sites (24 sites in the Mermentau River Basin and 

one additional site in the Calcasieu River Basin) during 

the period of sample collection for the study described in 

this report. Bed-sediment samples were collected at 17 

sites (table 1) during low-flow conditions August-September 2000. Aquatic invertebrate samples and stream 

habitat data were collected at 18 sites in the Mermentau 

River Basin and at one additional site in the Calcasieu 

River Basin during March-April 2001.

Procedures used to collect and process water samples followed standard USGS guidelines and are 

described by U.S. Geological Survey (1997 to present), 

Shelton (1994), Gilliom and others (1995), Mueller and 

others (1997), and Koterba and others (1995). Water 

samples were analyzed at the USGS National Water 

Quality Laboratory (NWQL) in Denver, Colo., using 

methods described by Fishman and Friedman (1989), 

Sandstrom and others (1992), Sandstrom (1995), Zaugg 
13

and others (1995), and Madsen and others (2003). 

Water-quality samples were analyzed for a special group 

of pesticides using a new method that was approved by 

the USGS Office of Water Quality in April 2001 (app. 2 

and 3) (Furlong and others, 2001). Although this analytical method did not change following approval, data 

analyzed before method approval are considered provisional. Samples analyzed with this method and data used 

for analysis in this report were collected after January 

2000 but before April 2001; therefore, the data are provisional. Ground-water quality data are available in 

reports by Tollett and Fendick (2004) and Tollett and others (2003). Surface-water quality data are available in 

Goree and others (2000, 2001, and 2002) and in appendixes 2 and 3.

Turbidity was measured at the USGS Laboratory in 

Baton Rouge, La., using a turbidimeter according to 

methods described by the manufacturer (Hach Company, 

1999). Water clarity was estimated as a function of light 

extinction with depth in the water column. The euphotic 

zone depth (Moulton and others, 2002) and Secchi depth 

(Wetzel and Likens, 1991) measurements were used to 

estimate water clarity at ecological data-collection sites.

Subsamples of bed sediment (table 1) were collected with fluoropolymer tubes and spatulas at wadeable sites and with a fluoropolymer-coated Petite-Ponar 

dredge suspended from a bridge or boat at non-wadeable 

sites. At each site, the top layer (0.5 to 0.75 in. deep) of 

each subsample was retained and composited in a container with other subsamples. Methods used to process 

bed-sediment samples are described by Shelton and 

Capel (1994). Analytical methods used by the NWQL 

for the determination of pesticides in bed sediment are 

described by Foreman and others (1995). Bed-sediment 

data are available in Goree and others (2001).

Stream habitat characteristics were documented at 

the time of aquatic invertebrate sampling. Habitat 

assessment included a combination of qualitative rankings and quantitative measurements. The qualitative 

rankings were determined by characterizing instream 

habitat measures such as substrate, sediment deposition, 

channel flow, and channel alterations, and riparian-zone 

features at the site, consistent with U.S. Environmental 

Protection Agency (USEPA) Rapid Bioassessment Protocols (RBP) for low-gradient streams (Barbour and 

others, 1999). Ten stream habitat parameters were 

scored on a scale of 0 to 20 (highest) for each sampling 

reach. Scores increase as habitat quality increases. A 

total score for each site was used to obtain a final stream 

habitat rating. Quantitative assessment of physical habitat conditions at the site included measurements of 

instream characteristics (such as stream width, depth, 

flow, turbidity, and bed-sediment particle-size distributions) and riparian characteristics (such as bank structure, riparian vegetation, and canopy cover) at three 

equally spaced transects in the sampling reach. The 

quantitative measurements of habitat conditions are 

described by Fitzpatrick and others (1998).

Aquatic invertebrate community surveys are one of 

the few means of directly assessing the biological integrity of a site and defining a group of aquatic organisms 

sensitive to changes in water chemistry and physical habitat (Meador and Gurtz, 1994). The aquatic health of 

stream reaches can be characterized by evaluating the 

results of qualitative and quantitative measurements of 

the aquatic invertebrate community. Results of aquatic 

invertebrate surveys were used to characterize the distribution and community structure of aquatic invertebrate 

species and their relation to the quality of both water and 

bed sediment. The species composition and community 

structure of aquatic invertebrates respond to and indicate 

physical and chemical conditions present in a stream for 

time scales ranging from months to years (Cuffney and 

others, 1993).

Aquatic invertebrate samples were collected at 

19 sites (March-April 2001) and analyzed as indicators 

of water quality to assess the influence of drainage area 

and agricultural land-use intensity on aquatic health. 

Samples from instream submerged woody debris (snags) 

in the stream reach were collected to represent the taxonomically richest-targeted habitat areas in accordance 

with USGS NAWQA Protocols (Cuffney and others, 

1993). The Biology Unit of the USGS NWQL used 

methods described by Moulton and others (2000) for the 

identification and enumeration of invertebrate samples.

Site Selection

Water-quality data were collected from 29 wells 

(fig. 1) and 25 surface-water sites; aquatic invertebrate 

samples were collected and habitat characteristics were 

documented for 19 surface-water sites. Tollett and Fendick (2004) and Tollett and others (2003) described well 

site selection and installation.

The study included 24 surface-water sites in the 

Mermentau River Basin (fig. 2, table 1) and, because no 

suitable reference site was available in the Mermentau 

River Basin, an additional site in the adjacent Calcasieu 

River Basin (fig. 3, table 1). The additional site is considered to be influenced minimally by agricultural practices, and to represent natural physical, chemical, and 

ecological characteristics for areas evaluated in this 

report. Surface-water data collection occurred in three 

overlapping phases during the study (table 1). Three 

sites were selected to characterize the effects of land use 

on water quality over time (long-term sites). These sites 
14

were sampled monthly November 1998-September 2001 

and semimonthly February-June 1999 and 2000. Fourteen short-term sites were selected to characterize the 

occurrence and distribution of land-use effects on water 

quality in the basin. These sites were sampled monthly 

February-June 2000. Nineteen sites were selected to 

compare water-quality characteristics with drainage area 

and agricultural land-use intensity March-May 2001. 

These included the 3 long-term sites in the Mermentau 

River Basin, 1 long-term reference site in the Calcasieu 

River Basin, 8 of the short-term sites sampled in 2000, 

and 7 additional short-term sites. Bed-sediment samples 

were collected once at 17 surface-water sites during lowflow conditions August-September 2000.

Two methods were used to group sites. Nineteen 

ecological data-collection sites were grouped before data 

collection according to the study design based on drainage area and agricultural intensity and grouped statistically after data collection using ordination (CCA) and 

classification (cluster analysis) techniques on surfacewater quality, habitat, and aquatic invertebrate data 

(table 1, fig. 7). Drainage areas greater than or equal to 

70 mi2 were considered large basins and those smaller 

than 70 mi2

 were considered small basins. Sites were 

selected to represent water-quality conditions influenced 

by differences in agricultural intensity as indicated by the 

percentage of the basin used for rice cultivation. In this 

report, the term “high-intensity” describes an area where 

at least 45 percent of the drainage area is used for rice 

cultivation; “low-intensity” is used to describe an area 

where less than 45 percent of the drainage area is used 

for rice cultivation. A Geographic Information Systems 

(GIS) coverage was used to determine basin areas 

(Joseph Holmes, Louisiana Department of Environmental Quality, written commun., 2001). Rice areas also 

were determined from this GIS coverage and verified by 

county agricultural agents within parishes in the basin.

Data Analysis

Concentrations of nutrients, major inorganic ions, 

trace elements, and pesticides were evaluated in relation 

to land use and to national drinking-water regulations or 

criteria. Concentrations in ground water were compared 

with those in surface water. Nutrients, major inorganic 

ions, and trace elements were detected frequently in both 

ground water and surface water and are discussed 

concurrently. Maximum pesticide concentrations are 

compared to available aquatic-life criteria, and concentrations for one insecticide, fipronil, are compared to 

numeric targets for total maximum daily loads (TMDL’s) 

established by USEPA (2002b). Pesticides were detected 

infrequently in ground water and, other than in general 

terms, are discussed separately from those in surface 

water.

Primary and Secondary Drinking Water Regulations (U.S. Environmental Protection Agency, 2000a) 

were used to evaluate concentrations of nitrate and 

selected major inorganic ions, as shown below.

1Maximum Contaminant Level.

2Secondary Maximum Contaminant Level.

Primary Drinking Water Regulations and health 

advisories were used to evaluate concentrations of pesticides (table 3). Primary and Secondary Drinking Water 

Regulations and health advisory levels were established 

by USEPA (2000a) and include the following:

1. Enforceable Maximum Contaminant Levels 

(MCL’s), established to protect public health 

by limiting the levels of contaminants in 

drinking water;

2. Nonenforceable Secondary Maximum 

Contaminant Levels (SMCL’s), available for 

some nutrients and major inorganic ions, 

established to limit cosmetic (such as skin or 

tooth discoloration) or aesthetic (such as 

taste, odor, or color) effects in drinking water; 

and

3. Nonenforceable health advisory (HA) levels, 

established to avoid adverse noncarcinogenic 

effects for a lifetime of exposure.

Aquatic-life criteria for pesticides in freshwater 

include USEPA water-quality criteria (2002a), USEPA 

TMDL’s (2002b), and Canadian water-quality guidelines 

for the protection of aquatic life (Canadian Council of 

Ministers of the Environment, 2001) (table 3). These 

criteria are based on single-chemical toxicity tests and do 

not consider synergistic or antagonistic effects of pesticide mixtures. Criteria from USEPA (2002a) are 

estimates of the highest concentration to which an 

aquatic community can be exposed indefinitely without

Constituent Concentration Drinking Water 

Regulation

Nitrate 10 mg/L MCL1

Chloride 250 mg/L SMCL2

Sulfate 250 mg/L SMCL2

Iron 300 μg/L SMCL2

Manganese 50 μg/L SMCL2
15

GROUPING OF ECOLOGICAL DATA-COLLECTION SITES FOR STATISTICAL ANAL

(n is number of samples)

a priori groups

(grouping before sampling and analysis)

posteriori groups

(grouping after sampling and a

Study-design site groups

(n = 19)

Principal

components

analysis (PCA)

(Environmental variables)

(n = 19)

Water-quality 

and habitat

data

Aquatic

invertebra

data

Basin site groups

(based on drainage area)

(n = 19)

Intensity site groups

(based on agricultural land use)

(n = 19)

Canonical correspondence analysis (

(based on environmental and specie

(n = 19)

Drainage

area ≥ 70

square miles

Drainage

area < 70

square miles

≥ 45 percent

rice cultivation

< 45 percent

rice cultivation Group assignments based on cluster a

Large

(n = 11)

Small

(n = 8)

High

(n = 11)

Low

(n = 8)

Group A

(n = 3)

Group B

(n = 4)

Group 

(n = 

Figure 7. Flowchart of statistical analysis of ecological data used in the study. Median values of the basin and intensity site groups (b

significant differences (p ≤ 0.05) using a two-factor analysis of variance (Wilkinson and Coward, 1998) on ranked data (Helsel and Hir

correspondence analysis site groups (green text) were tested for significant differences (p ≤ 0.05) using a one-factor analysis of varianc

ranked data (Wilkinson, 1998).
16

1 U.S. Environmental Protection Agency (2000a).

2 Canadian Council of Ministers of the Environment (2001).

3 U.S. Environmental Protection Agency (2002a).

4 The USEPA aquatic-life criteria for malathion and chlorpyrifos are maximum concentrations to which an aquatic organism can be exposed 

without harmful effects, and should not be exceeded more than once every 3 years.

5

 U.S. Environmental Protection Agency (2002b).

Table 3. Drinking-water regulations, health advisory levels, and aquatic-life criteria for selected pesticides

[Concentrations are in micrograms per liter. USEPA, U.S. Environmental Protection Agency; MCL, Maximum Contaminant Level; HA, health 

advisory; *, based on an annual mean of quarterly samples; --, none; CCME, Canadian Council of Ministers of the Environment]

Compound

USEPA drinking-water MCL or HA 1 Aquatic-life criteria

Criterion Type of standard Criterion Source

Alachlor 2 MCL -- --

Atrazine *3 MCL 1.8 CCME2

Bentazon 200 HA -- --

Bromacil 90 HA 5 CCME2

Carbaryl 700 HA .2 CCME2

Carbofuran 40 MCL 1.8 CCME2

Chlorpyrifos 20 HA .041 USEPA3, 4

Cyanazine 1 HA 2 CCME2

2,4-D 70 MCL -- --

Dacthal (DCPA) 70 HA -- --

Diazinon 0.6 HA -- --

Dinoseb 7 MCL .05 CCME2

Diphenamid 200 HA -- --

Diuron 10 HA -- --

Fipronil (chronic) -- -- 2.3 USEPA5

Fipronil (acute) -- -- 4.6 USEPA5

Fluometuron 90 HA -- --

Malathion 100 HA .1 USEPA3, 4

MCPA 4 HA -- --

Methomyl 200 HA -- --

Methyl Parathion 2 HA -- --

Metolachlor 100 HA 7.8 CCME2

Metribuzin 200 HA 1 CCME2

Picloram 500 MCL 29 CCME2

Prometon 100 HA -- --

Propachlor 90 HA -- --

Simazine 4 MCL 10 CCME2

Tebuthiuron 500 HA 1.6 CCME2

Trifluralin 5 HA .2 CCME2

resulting in an unacceptable effect. Numeric targets for 

chronic and acute TMDL’s for fipronil were established 

primarily for fish and wildlife propagation (U.S. Environmental Protection Agency, 2002b). Acute numeric 

targets apply to stream mixing zones, areas defined by 

the Louisiana Department of Environmental Quality 

(2003) as “portions of water bodies where effluent waters 

are dispersed into receiving waters.” Chronic numeric 

targets apply to portions of the water body outside mixing zones. Canadian water-quality guidelines for 12 pesticides were established to protect species of aquatic life.

Ecological data were summarized and compared 

with surface-water quality data. Water quality (app. 4), 

quantitative habitat (app. 5) and qualitative habitat data 

(app. 6 and 7) used for the statistical analyses are 

included in this report. When appropriate, log and 

square-root transformations of water-quality and habitat 

data and natural log transformations of aquatic inverte-
17

brate data (app. 8) were performed to approximate normal distributions.

The mean values of quantitative habitat variables 

for the site (reach) were used for analysis of habitat data, 

except euphotic and Secchi-disk depths, which were 

measured once for the reach. Ranked and scored values 

were used for bank-erosion score and bank-stability 

index variables so these variables could be statistically 

analyzed. Each reach was ranked in the same way with 

a score from 1 to 6 that represented the number of 

observed stream banks with erosion at six transect points 

within the reach. The bank-stability index was determined as described in Fitzpatrick and others (1998).

Aquatic invertebrate community data were processed using the Invertebrate Data Analysis System 

(IDAS, version 2.0.6) a program developed by Thomas 

Cuffney (USGS, written commun., 2001) for the compilation and analysis of NAWQA invertebrate samples. 

Ambiguous taxa were resolved using IDAS by combining the abundance of children (species or genus) of 

ambiguous parents and adding abundance to the parent 

(genus or family). Invertebrate taxa in the dataset that 

were difficult or impossible to identify, terrestrial adults, 

and rare taxa (occurring at only one site) were eliminated 

from the final analysis. Aquatic invertebrate community 

metrics were calculated in IDAS and statistically analyzed based on this processed dataset.

Exploratory analysis of environmental variables—

water-quality and habitat data—(fig. 7) was performed 

using principal component analysis (PCA) to reduce the 

number of environmental variables (ter Braak and Smilauer, 1998). Redundant variables were removed from 

subsequent analyses and surrogate variables were identified to represent a group of correlated variables. 

Results of a correspondence analysis (CA) of the aquatic 

invertebrate data (ter Braak and Smilauer, 1998) showed 

an arch effect with sites and species grouped along the 

x- and y-axes, which warranted use of detrended correspondence analysis (DCA) to examine distributions of 

aquatic invertebrate communities (Jongman and others, 

1995). Distributions of aquatic invertebrate communities at five or more sites (38 species) were investigated by 

DCA.

Direct gradient analysis was performed using 

canonical correspondence analysis (CCA) (fig. 7) to 

evaluate patterns among sites based on the relative abundance of aquatic invertebrates and on environmental 

variables (ter Braak and Smilauer, 1998). The CCA was 

used to establish similarity between sites based on study 

results and to identify important environmental variables 

that influenced aquatic invertebrate communities. The 

CCA included 36 environmental variables determined by 

PCA to be important from 19 sites. This determination 

was based on (1) results of final PCA analyses of waterquality and habitat variables (app. 9); (2) correlations 

between environmental variables, based on a Spearman 

rank correlation test with an alpha value of 0.05 

(Wilkinson, Engelman, and Marcantonio, 1998); and 

(3) variables considered important for describing water 

quality and aquatic invertebrate communities in an agricultural land-use setting in southwestern Louisiana. The 

forward selection process of the CCA was used to test 

environmental variables for statistical significance 

(p ≤ 0.05) using a Monte Carlo simulation before adding 

it to the final model (ter Braak and Smilauer, 1998).

Cluster analysis (fig. 7) was used to determine 

which sites had similar water quality, habitat, and aquatic 

invertebrate characteristics. Ward's method of hierarchical cluster analysis (Wilkinson and others, 1998) was 

used with a correlation matrix derived from site scores of 

the first two axes of the CCA. A correlation distance of 

2 (cut-level) was used to determine the number of clusters, and discriminate analysis (Engelman, 1998) of cluster analysis groups was used to verify group assignment.

Environmental variables and aquatic invertebrate 

metrics within the study-design (a priori, before sampling) and CCA (posteriori, after sampling) site groups 

were compared (fig. 7). Differences in median values 

among site groups were determined using nonparametric 

statistical methods with an alpha level of 0.05. Differences were determined for large-basin (n = 11 sites) and 

small-basin (n = 8 sites) site groups, and for high-intensity (n = 11 sites) and low-intensity (n = 8 sites) site 

groups, using a two-factor analysis of variance 

(ANOVA) (Wilkinson and Coward, 1998) on ranked data 

(Helsel and Hirsch, 1992). CCA site groups (A, n = 3 

sites; B, n = 4 sites; C, n = 6 sites; and D, n = 6 sites) were 

tested using a one-factor ANOVA on ranked data 

(Kruskal-Wallis test). When results from the KruskalWallis test indicated significant differences, the Tukeys 

(Wilkinson, 1998) multiple comparison test was used on 

ranked data (Helsel and Hirsch, 1992) to determine 

which site groups were significantly different (fig. 7). 

Relations between significant variables and relative 

abundances of aquatic invertebrates at sites were examined to evaluate invertebrate relations to these variables.

WATER-QUALITY CHARACTERISTICS

Median concentrations of nutrients and concentrations of pesticides generally were lower in ground water 

than in surface water, but median concentrations of major 

inorganic ions and trace elements often were higher in 

ground water than in surface water. The MCL for nitrate 

and the SMCL’s for sulfate, iron, and manganese were 

exceeded in ground water; the SMCL’s for sodium, iron, 
18

and manganese were exceeded in surface water. Concentrations of nutrients and major inorganic ions in 

ground water and surface water generally were largest in 

the southeastern part of the study area. In ground water, 

concentrations of 16 pesticides and degradation products 

were detected but did not exceed MCL’s, HA’s, or 

aquatic-life criteria. In surface water, 59 pesticides and 

degradation products were detected. Concentrations of 

three pesticides exceeded criteria for the protection of 

drinking water or aquatic life, and peak concentrations of 

one pesticide exceeded numeric targets for TMDL’s.

Nutrients

Nitrogen and phosphorus are nutrients of particular 

importance because they are necessary for the proper 

growth and development of plants, but can cause the 

eutrophication of lakes, streams, and rivers, and at high 

levels may adversely affect human health. Eutrophication is the enrichment of a water body with nutrients that 

can occur naturally, but most often results from discharge 

of wastewater effluent, or runoff from agricultural areas. 

Streams enriched with nutrients might be subject to 

excessive plant growth resulting in algal blooms and 

propagation of invasive aquatic plants, such as waterhyacinth and hydrilla, that contribute to recreational 

impairment and adverse effects on aquatic life. The 

USEPA (2002b) has identified Bayou Nezpique, Bayou 

Mallet, and Bayou des Cannes as impaired by nutrients, 

and Bayou Plaquemine Brule, Bayou Queue de Tortue, 

Bayou Lacassine, and the Mermentau River as impaired 

specifically by nitrogen. The USEPA (2002b) established an MCL of 10 mg/L for nitrate as nitrogen in 

drinking water because concentrations greater than this 

increase the risks of methemoglobinemia (blue-baby 

syndrome) (Hem, 1992). Nitrogen concentrations determined for this study include ammonia; dissolved and 

total ammonia plus organic nitrogen; nitrite; and nitrite 

plus nitrate as nitrogen. Minimum, median, and maximum concentrations of nitrogen are shown in table 4. 

Maximum concentrations of nutrients in surface water 

occurred at sites with high agricultural intensity between 

February and July.

Ammonium is the recommended form of nitrogen 

used to fertilize rice because nitrate is reduced to nitrous 

oxide and nitrogen gas in flooded rice fields. The highest 

concentrations of dissolved ammonia and dissolved 

ammonia plus organic nitrogen in ground and surface 

water occurred in the southeastern part of the study area. 

Although the median concentration of dissolved ammonia in surface water (0.11 mg/L) was more than three 

times the median concentration in ground water 

(0.032 mg/L) (table 4), the maximum concentration 

occurred in ground water (2.56 mg/L at well 41) 

(table 5). The maximum concentration in surface water 

(1.65 mg/L) occurred at Theriot (table 5), a site with high 

agricultural intensity. The median concentration of dissolved ammonia plus organic nitrogen in surface water 

(0.86 mg/L) was more than eight times the median concentration in ground water (less than 0.10 mg/L). Concentrations of dissolved ammonia greater than 0.50 mg/L 

and concentrations of ammonia plus organic nitrogen 

greater than 2.0 mg/L occurred at surface-water sites that 

drained areas with high agricultural intensity. The maximum concentration of dissolved ammonia plus organic 

nitrogen occurred in surface water (4.0 mg/L at Theriot); 

the maximum concentration in ground water (2.7 mg/L) 

occurred at well 41. Concentrations of total ammonia 

plus organic nitrogen were determined for surface-water 

samples only (table 4); the median concentration was 

1.3 mg/L and the highest concentration (5.1 mg/L) 

occurred at Mermentau, a site with high agricultural 

intensity.

The median concentration of nitrite plus nitrate 

(nitrate) was higher in surface water (0.230 mg/L) than 

in ground water (less than 0.050 mg/L), but the highest 

concentration (12.6 mg/L) occurred in ground water 

(fig. 8) at well 22. Concentrations greater than 

1.00 mg/L occurred at three sites (Des Cannes, Iota, and 

Plaquemine) with high agricultural intensity; however, 

the maximum concentration in surface water 

(3.03 mg/L) occurred at the Church Point site, a site with 

low agricultural intensity. The peak nitrate concentrations at Church Point may have been caused by livestock 

(fig. 9) and at the other three sites by fertilizer applications in fall and spring (fig. 10). The nitrate concentration at well 22 (12.6 mg/L) was the only exceedance of 

the USEPA (2000a) MCL for nitrate (10 mg/L) in 

ground- or surface-water samples. This well is shallow 

(30 ft), and land around the well was used previously for 

poultry and swine production. Leaching of animal waste 

may account for the nitrate concentration in the well.

Nutrients from ground water used for agricultural 

irrigation do not contribute significantly to eutrophication in surface water. Concentrations of nitrogen and 

phosphorus in samples from ground water generally 

were below the thresholds for total nitrogen (1.50 mg/L) 

and total phosphorus (0.075 mg/L) indicating eutrophic 

potential (Dodds and others, 1998), whereas concentrations in samples from surface water generally exceeded 

the thresholds. In ground water, the median concentration of total dissolved nitrogen (the sum of dissolved 

ammonia plus organic nitrogen and nitrite plus nitrate) 

was less than the sum of detection limits (0.15 mg/L) 

(table 4), and the median concentration of dissolved 

phosphorus was 0.07 mg/L (table 6). In surface water, 
19

1 Samples were collected more than once November 1998-September 2001.2 Minimum detected concentration.3 Samples were collected once between January 2000 and January 2001.

Table 4. Minimum, median, and maximum concentrations of selected nitrogen species for ground- and surface-water samples from the 

southwestern Louisiana, 1998-2001

[Total nitrogen includes the sum of total ammonia plus organic nitrogen and dissolved nitrite plus nitrate. Concentrations are in milligrams per liter. <, less than indicated 

Month

Number

of

samples

Ammonia, dissolved

Ammonia plus organic nitrogen

Nitrite plus nitrate, 

Dissolved Total dissolved 

Minimum Median Maximum Minimum Median Maximum Minimum Median Maximum Minimum Median Maximum 

Surface water1

January 9 <0.02 0.052 0.129 <0.10 0.62 0.85 0.74 1.1 1.5 0.050 0.240 0.463 February 26 <.02 .026 .257 .21 .62 1.3 .60 .98 1.7 .050 .076 3.03 March 43 <.02 .126 .976 .39 .86 3.3 .66 2.0 4.8 .050 .272 .724 April 44 .02 .166 .812 .11 1.2 2.7 .57 2.2 5.1 <.047 .448 .993 May 37 .02 .198 1.65 .68 1.2 4.0 1.0 1.7 4.8 .042 .371 1.47 June 35 <.02 .113 .873 .58 .91 2.1 .88 1.3 2.4 .050 .199 .767 July 12 .03 .093 .154 .17 .65 1.6 .79 .98 1.6 .050 .179 .557 August 8 <.02 .090 .161 .43 .62 .79 .72 .87 1.0 .027 .050 .410 September 8 <.02 .059 .223 .50 .59 .98 .69 .82 1.3 .050 .050 .379 October 6 <.02 .039 .065 .46 .62 .65 .69 .84 1.1 <.047 .066 .221 November 9 <.02 .101 .262 .41 .70 .96 .43 .92 1.3 .050 .210 .667 December 9 <.02 .041 .231 .44 .67 .91 .65 .90 1.5 .026 .124 .423 All samples 246 <.02 .110 1.65 <.10 .86 4.0 .43 1.3 5.1 2.026 .230 3.03 

Ground water3

All samples 29 <.02 .032 2.56 <.10 <.10 2.7 NA NA NA <.047 <.050 12.6 
20

the median concentration of total nitrogen (the sum of 

total ammonia plus organic nitrogen and dissolved nitrite 

plus nitrate) was greater than the eutrophic threshold 

March-June and December, and the median concentration of total phosphorus was greater than the eutrophic 

threshold throughout the year. Thus, the greatest potential for eutrophic conditions in surface water, based on 

nutrient concentrations, existed March-June, about the 

same time ricefields were drained, and December, 

shortly after fertilizers were applied.

Table 5. Maximum concentrations and occurrence of selected nutrients in ground water and surface water in the 

Mermentau River Basin, southwestern Louisiana, 1998-2001

[Concentrations are in milligrams per liter. NA, not applicable]

Nutrient

Ground water Surface water

Concentration Well number Concentration Site name

Dissolved ammonia 2.56 41 1.65 Theriot

Dissolved ammonia plus organic nitrogen 2.7 41 4.0 Theriot

Nitrite plus nitrate, dissolved 12.6 22 3.03 Church Point

Dissolved phosphorus .445 41 1.33 Church Point

Orthophosphorus, dissolved .249 24 1.20 Church Point

Total phosphorus NA NA 1.83 Church Point

1

 Samples were collected more than once November 1998-September 2001.

2

 Samples were collected once between January 2000 and January 2001.

Table 6. Minimum, median, and maximum concentrations of selected phosphorus species for ground- and surfacewater samples from the Mermentau River Basin, southwestern Louisiana, 1998-2001

[Concentrations are in milligrams per liter. <, less than indicated value; E, estimated; NA, not analyzed]

Month

Dissolved phosphorus Orthophosphorus Total phosphorus

Minimum Median Maximum Minimum Median Maximum Minimum Median Maximum

Surface water1

January 0.020 0.095 0.155 0.010 0.072 0.116 0.078 0.198 0.344

February .018 .062 .715 .010 .042 .642 .057 .204 .697

March .012 .066 1.33 <.010 .055 1.20 .034 .469 1.83

April .014 .091 .650 E.016 .055 .550 .004 .419 1.18

May .015 .114 .631 .013 .077 .623 .057 .286 .745

June .055 .130 .477 .016 .099 .416 .164 .288 .795

July .055 .108 .143 .035 .088 .122 .179 .236 .329

August .079 .091 .147 .061 .072 .121 .189 .210 .238

September .023 .117 .183 .010 .090 .161 .096 .222 .332

October .032 .082 .098 .020 .064 .078 .110 .175 .223

November .030 .077 .188 .016 .057 .170 .081 .173 .381

December .019 .081 .120 .014 .051 .108 .068 .191 .382

All samples .012 .094 1.33 <.010 .066 1.20 .004 .266 1.83

Ground water2

All samples E.003 .070 .445 <.010 .056 .249 NA NA NA
4

3

2

1

12

10

8

6

4

2

2.5

2.0

1.5

1.0

0.5

DISSOLVED 

AMMONIA

TOTAL AMMONIA PLUS 

ORGANIC NITROGEN

DISSOLVED NITRITE 

PLUS NITRATE

DISSOLVED AMMONIA 

PLUS ORGANIC NITROGEN

C

O

N

C

E

N

T

R

ATIO

N

S, IN

MIL

LIG

R

A

M

S

P

E

R

LIT

E

R

50

Ground

Water

100

4,000

3,000

1,500

200

400

5,000 2,000

250

500

2,000

1,000

1,000

500

150

200

100

300

Surface

Water

MANGANESE

SULFATE

40

60

20

100

120

40

20

60

80

CALCIUM

250

300

100

SODIUM

MAGNESIUM

Median

25th percentile

75th percentile

Observation equal to or less than

1.5 times the interquartile range

Observation less than or equal to

1.5 times the interquartile range

Low outlier

High outlier

EXPLANATION

Maximum Contaminant Level 

Figure 8. Concentrations of selected nutrients and major inorganic ions in ground water and surface water from the 

Mermentau River Basin, southwestern Louisiana 1998-2001. Maximum Contaminant Levels and Secondary 

Maximum Contaminant Levels established by the U.S. Environmental Protection Agency (2000a).

IRON

CHLORIDE

C

O

N

C

E

N

T

R

ATIO

N

S, IN

MIC

R

O

G

R

A

M

S

P

E

R

LIT

E

R

Ground

Water

Surface

Water

0 0

0

Ground

Water

Surface

Water

Ground

Water

Surface

Water

Ground

Water

Surface

Water

15

20

10

5

POTASSIUM

Ground

Water

Surface

Water

Ground

Water

Surface

Water

Ground

Water

Surface

Water

600

0

24

0 0 0

0

Ground

Water

Surface

Water

Ground

Water

Surface

Water

Ground

Water

Surface

Water

Ground

Water

Surface

Water

0

5

4

3

2

1

0 0

Secondary Maximum 

Contaminant Level 

21
22

Figure 9. Grazing livestock near a surface-water data-collection site in the Mermentau River Basin, southwestern 

Louisiana.

Photograph by Dennis K. Demcheck, U.S. Geological Survey, 2001

Comparisons between thresholds and the concentrations determined during the sampling period should be 

made carefully for the following reasons:

1. Nutrient concentrations greater than the 

thresholds might not cause excessive or 

nuisance plant growth immediately, because 

other factors such as turbidity and stream 

shading affect light penetration, and 

influence photosynthesis and aquatic-plant 

productivity. Downstream, these factors 

might become more favorable for eutrophic 

conditions to occur.

2. Drought and streamflow conditions that 

occurred during the sampling period may not 

represent long-term conditions (fig. 6).

3. Nutrient thresholds are probably lower for 

subtropical streams, including those found in 

the study area, than for the more northern 

temperate streams for which they were 

developed (Walter Dodds, Kansas State 

University, written commun., June 6, 2002).

Phosphorus exists in natural water in several forms 

but transformation pathways for phosphorus are not as 

numerous as those for nitrogen. Most phosphorus in 

aquatic systems is not available for biological uptake 

because the solubility of phosphorus is relatively low and 

phosphorus adsorbs strongly to particles. Concentrations of dissolved phosphorus and orthophosphorus in 

ground water and surface water, and total phosphorus in 

surface water were determined for this study and are 

listed in table 6.

The median concentration of dissolved phosphorus 

was 0.070 mg/L in ground water and 0.094 mg/L in surface water (table 6). The highest concentrations of phosphorus in surface water occurred February-June. 

Concentrations greater than 0.25 mg/L were detected at 
23

Figure 10. Concentrations of nitrite plus nitrate, potassium, and suspended sediment at the Mermentau data-collection

site in the Mermentau River Basin, southwestern Louisiana, 1998-2001.

600

500

400

300

200

100

0

10.00

1.00

0.10

0.01

Nov.

Jan.

Mar.

May

July

Sept.

Nov.

Jan.

Mar.

May

July

Sept.

Nov.

Jan.

Mar.

May

July

Sept.

1998 1999 2000 2001

DATE

NITRITE PLUS NITRATE AND P

OTASSIUM 

CONCENTRATIONS, IN MILLIGRAMS PER LITER

SUSPENDED-SEDIMENT CONCENTRATIONS, 

IN MILLIGRAMS PER LITER

Potassium

Nitrite plus nitrate

Suspended sediment

Period of rice seeding

Period of fertilizer application

EXPLANATION

six sites in the eastern half of the study area: Plaquemine, 

Wikoff, Grand Marais, Mallet, Church Point, and Theriot. The highest concentration of dissolved phosphorus 

(1.33 mg/L) was detected in surface water at the Church 

Point site and was more than four times the maximum 

concentration in ground water (0.445 mg/L at well 41). 

The median concentration of orthophosphorus was 

0.056 mg/L in ground water and 0.066 mg/L in surface 

water. Concentrations greater than 0.25 mg/L were 

detected at six sites: Chene, Plaquemine, Wikoff, Grand 

Marais, Church Point, and Theriot. The highest concentration of orthophosphorus (1.20 mg/L) was detected in 

surface water at the Church Point site (table 5), and was 

more than four times the maximum concentration in 

ground water (0.249 mg/L at well 24). Orthophosphorus 

was not detected at three of the northernmost sites with 

low agricultural intensity, Boggy, Caney, and Castor. 

Total phosphorus concentrations were determined for 

surface-water samples only and correlate positively with 

suspended-sediment concentrations (Pearson r = 0.72). 

The maximum concentration (1.83 mg/L) occurred at the 

Church Point site. The median concentration of total 

phosphorus was 0.266 mg/L. Concentrations greater 

than 1.00 mg/L were detected at three sites: East Lacassine, Blue, and Church Point. Elevated concentrations of 

phosphorus in ground water may result from marine 

deposits (Hem, 1992) or agriculture, and in surface water 

may result from agriculture. The Church Point site 

drains a large area with low agricultural intensity, and 

grazing livestock may have caused the relatively high 

phosphorus concentration. In a previous study, Demcheck (1994) found similar results for Church Point and 

suggested the elevated phosphorus concentrations might 

result from runoff of agricultural fertilizer. The highest 

phosphorus concentrations coincide with fertilizer applications in mid-spring and late fall.
24

Major Inorganic Ions and Trace Elements

Dissolved concentrations of 7 major inorganic ions 

were determined for ground- and surface-water samples, 

and dissolved concentrations of 16 trace elements were 

determined for samples from all wells and one surfacewater site, Mermentau. Concentrations of major inorganic ions and trace elements were compared with 

MCL’s and SMCL’s (U.S. Environmental Protection 

Agency, 2000a). MCL’s were established to protect public health by limiting the levels of contaminants in drinking water; SMCL’s were established to limit cosmetic 

(for example, skin or tooth discoloration) or aesthetic 

affects (for example, taste, odor, or color) in drinking 

water. No MCL’s were exceeded in either ground- or surface-water samples; however, one or more SMCL’s were 

exceeded in samples from 20 wells and all the surfacewater sites (fig. 8). Concentrations of antimony, arsenic, 

barium, beryllium, cadmium, chromium, copper, lead, 

selenium, and thallium generally were below detection 

limits, but when detected did not exceed MCL’s.

Median concentrations of calcium and magnesium 

in ground water were more than three times the median 

concentrations in surface water (fig. 8). The median concentrations for calcium and magnesium in ground water 

were 66.0 mg/L and 25.2 mg/L; maximum concentrations occurred at well 35 (129 mg/L) and well 8 

(61.1 mg/L). The median concentrations for calcium and 

magnesium in surface water were 15.9 mg/L and 

7.02 mg/L; maximum concentrations occurred at Theriot 

(69.3 mg/L) and Lacassine (38.5 mg/L), sites with high 

agricultural intensity (table 7).

Median potassium concentrations were about three 

times higher in surface water than in ground water 

(fig. 8). The maximum and median potassium concentrations in ground water were 3.61 mg/L and 1.52 mg/L 

and in surface water were 22.8 mg/L and 4.31 mg/L. The 

maximum concentration detected in ground water was at 

well 10 and in surface water was at Theriot (table 7). 

Potassium concentrations in surface water peaked twice 

annually (fig. 10), in mid-spring and late fall; peaks 

probably were caused by runoff from fertilizer applications and by re-solution of detrital plant material (Hem, 

1992).

Median concentrations of sodium and chloride 

(fig. 8) were higher in ground water than in surface 

water, but the highest concentrations of both constituents 

occurred in surface water (fig. 8). The median sodium 

concentration in ground water was 64.3 mg/L and the 

median chloride concentration was 101 mg/L; the highest concentrations were 275 mg/L at well 7, and 

328 mg/L at well 22 (table 7). Chloride concentrations 

in ground water exceeded the SMCL (250 mg/L) (U.S. 

Environmental Protection Agency, 2000a) in four wells: 

well 35 (264 mg/L), well 25 (281 mg/L), well 7 

(293 mg/L), and well 22 (328 mg/L). The median chloride and sodium concentrations in surface water were 

33.4 mg/L and 33.0 mg/L. The maximum concentrations of sodium (327 mg/L) and chloride (586 mg/L) in 

surface water occurred at Lacassine (table 7) in March 

2000 and probably resulted from saltwater intrusion 

induced by flow reversal (bidirectional) during the 

drought. The chloride concentration exceeded the 

SMCL (U.S. Environmental Protection Agency, 2000a).

Table 7. Maximum concentrations and occurrence of selected major inorganic ions in ground water and surface water 

in the Mermentau River Basin, southwestern Louisiana, 1998-2001

[mg/L, milligrams per liter; μg/L, micrograms per liter]

Major inorganic ion

Ground water Surface water

Concentration Well number Concentration Site name

Calcium, in mg/L 129 35 69.3 Theriot

Magnesium, in mg/L 61.1 8 38.5 Lacassine

Potassium, in mg/L 3.61 10 22.8 Theriot

Sodium, in mg/L 275 7 327 Lacassine

Chloride, in mg/L 328 22 586 Lacassine

Alkalinity as calcium 

carbonate, in mg/L

546 10 380 Theriot

Sulfate, in mg/L 272 10 79.2 Lacassine

Iron, in μg/L 2,190 49 1,430 Chene

Manganese, in μg/L 739 9 5,270 Boggy
25

The median value for alkalinity in ground water was 

more than three times that in surface water. The maximum and median values were 546 mg/L and 302 mg/L in 

ground water, and 380 mg/L and 82 mg/L in surface 

water. The highest value in ground water was at well 10 

and in surface water at Theriot (table 7).

Median and maximum sulfate concentrations were 

higher in ground water than in surface water (fig. 8). In 

ground water, the median concentration was 6.1 mg/L; 

the maximum concentration (272 mg/L) occurred at 

well 10 and was the only concentration to exceed the 

SMCL (250 mg/L) (U.S. Environmental Protection 

Agency, 2000a). In surface water, the median concentration was 4.55 mg/L, and the maximum concentration 

occurred at Lacassine (79.2 mg/L) during March 2000.

Iron concentrations exceeded the SMCL (300 μg/L) 

(U.S. Environmental Protection Agency, 2000a) in 

ground water and surface water (fig. 8). Although the 

median iron concentration in ground water (20 μg/L) 

was one-third the median in surface water (60 μg/L), the 

highest concentration occurred in ground water. In seven 

wells, iron concentrations exceeded the SMCL; the maximum (2,190 μg/L) occurred at well 49. Iron concentrations in surface water exceeded the SMCL at eight sites: 

Blue, Lacassine, Mermentau, Boggy, East Lacassine, 

Caney, Castor, and Chene; the maximum, 1,430 μg/L, 

occurred at Chene in May 2000 (table 7).

Manganese concentrations exceeded the SMCL 

(50 μg/L) (U.S. Environmental Protection Agency, 

2000a) in ground water and surface water. The median 

manganese concentration in ground water (121 μg/L) 

was less than the median in surface water (150 μg/L). 

The maximum concentration in surface water was more 

than seven times the maximum in ground water (table 7). 

Manganese concentrations exceeded the SMCL in 17 

wells. Manganese concentrations in ground water 

exceeding the SMCL ranged between 52.8 μg/L and 

739 μg/L; the maximum occurred at well 9. Manganese 

concentrations exceeded the SMCL at all surface-water 

sites and were highest at Blue, Caney, Boggy, and Castor, 

in the northwestern part of the study area; the maximum 

(5,270 μg/L) occurred at Boggy. Manganese leached 

from geologic deposits may cause the higher concentrations.

Pesticides

Fewer pesticides were detected in ground water 

than in surface water. Thirty-eight percent of the samples collected from wells contained at least one pesticide, 

and all surface-water samples contained at least three 

pesticides. Pesticide concentrations in ground water did 

not exceed criteria for drinking water or the protection of 

aquatic life (fig. 11). In surface water, however, concentrations of atrazine, malathion, and tebuthiuron exceeded 

Figure 11. Drinking-water and aquatic-life criteria, and maximum detected concentrations of selected pesticides in 

ground water in the Mermentau River Basin, southwestern Louisiana, 2000-2001 (Diuron was detected, but concentration was not quantified).

1,000.00

100.00

10.00

1.00

0.10

0.01

C

0.00

ONC

ENTRATI

ON, IN 

MICR

OGRA

M

S

PER LITER

2,4-D

Malathion

Bentazon

Chlorimuron-Ethyl

Metribuzin

Metolachlor

Picloram

Imazaquin

Alachlor

Metalaxyl

Deethylatrazine

Atrazine

Diethyldeisopropylatrazine

2-Hydroxyatrazine

Flumetsulam

Tebuthiuron

Chlorpyrifos

3 (4-Chlorophenyl)-1-

Methyl Urea

Diuron

PESTICIDE

Maximum concentration

Drinking-water criterion

Aquatic-life criterion
26

criteria for the protection of drinking water or aquatic life 

(fig. 12). Concentrations of fipronil exceeded USEPA 

(2002b) numeric targets for TMDL’s (table 3). Although 

atrazine concentrations in three samples collected in the 

spring exceeded 3 μg/L, the MCL (U.S. Environmental 

Protection Agency, 2000a) was not exceeded because it 

is based on an annual average of quarterly samples. Concentrations larger than 3 μg/L were not detected in samples collected during other times of the year, and the 

average annual concentrations did not exceed 3 μg/L for 

sites sampled throughout the year.

Concentrations were determined for 109 pesticides 

and degradation products in samples from 29 wells. 

Concentrations were detected in less than 1 percent (25) 

of the analyses for ground-water samples; 19 pesticides 

and degradations products were detected (fig. 11). Pesticides and degradation products were detected in samples from 11 wells; samples from wells 6 and 35 each 

accounted for 24 percent of the detections. Pesticides 

and degradation products detected most frequently were 

the herbicides bentazon (3 detections) and atrazine 

(5 detections).

Concentrations were determined for 109 pesticides 

and degradation products in surface-water samples; concentrations were detected in 20 percent of these analyses. 

Concentrations of 47 pesticides and degradation products were detected in surface water; at least 3 pesticides 

were detected in all samples. Annual maximum concentrations of different pesticides and pesticide degradation 

products usually occurred during the spring, about the 

time ricefields were drained, as shown in figure 13 for 

the Mermentau site. More than 190 samples collected 

from 24 surface-water sites were analyzed for 

51 hydrophilic pesticides and degradation products 

(app. 2); 28 pesticides were detected. A total of 36 samples collected from Des Cannes, Lacassine, and Mermentau sites were analyzed for 58 hydrophobic 

pesticides and degradation products. Nineteen pesticides 

were detected, and at least 3 were detected in more than 

70 percent of the samples.

The herbicides atrazine, molinate, and tebuthiuron, 

and the insecticide fipronil were detected in samples collected from all surface-water sites. Herbicides were 

detected more frequently and in larger concentrations 

than insecticides. Atrazine occurred in over 92 percent 

of the samples; concentrations in 3 samples exceeded the 

criterion (3 μg/L) for drinking water, and concentrations 

in 10 samples exceeded the criterion for the protection of 

aquatic life (1.8 μg/L). Molinate occurred in more than 

86 percent of the samples and at the largest concentration 

(154 μg/L) for any of the pesticides detected in the study 

area. Tebuthiuron and malathion each were detected 

once in concentrations exceeding criteria for the protection of aquatic life. Fipronil concentrations at 17 sites 

exceeded the freshwater chronic numeric target concentration for TMDL of 2.3 μg/L (table 3), and at 3 sites 

exceeded the acute numeric target concentration for 

TMDL of 4.6 μg/L (U.S. Environmental Protection 

Agency, 2002b).

Atrazine is the most commonly used herbicide in 

the United States (Hayes and others, 2002). Two atrazine 

degradation products, 2-hydroxyatrazine and deethylatrazine, were detected in 83 and 90 percent of the samples. Although concentrations at Riceville (5.23 μg/L) 

and Lacassine (5.83 and 8.91 μg/L) exceeded 3 μg/L, the 

USEPA (2000a) MCL (3 μg/L) was not exceeded 

because it is based on an annual average of quarterly 

samples. Concentrations at Riceville, Mermentau, and 

Lacassine exceeded the criterion for the protection of 

aquatic life (1.8 μg/L). There is some evidence that atrazine disrupts the endocrine system in some amphibians at 

concentrations less than 1 μg/L (Hayes and others, 

2002). Concentrations greater than 1 μg/L were detected 

at Des Cannes, Mermentau, Riceville, Lake Arthur, 

Lacassine, Tortue, Church Point, and Mallet sites. Concentrations greater than 0.1 μg/L were detected at all 

sites except Boggy, Castor, Blue, Upper Des Cannes, and 

Caney.

Tebuthiuron, a urea-based broad-spectrum herbicide, is used to control weeds in rights-of-way, industrial 

sites, and rangeland (Oregon State University, 1996). 

Tebuthiuron was detected at all the surface-water sites 

and in 95 percent of all surface-water samples. The largest concentration (6.33 μg/L) was detected at the Des 

Cannes site and was the only detection exceeding the criterion (1.6 μg/L) for the protection of aquatic life 

(table 3).

Malathion, an organophosphate insecticide, is used 

for public health mosquito control (U.S. Environmental 

Protection Agency, 2000b), recommended for control of 

household insects by homeowners (Louisiana State University Agricultural Center, 2002), and recommended for 

control of stinkbugs associated with rice agriculture 

(Louisiana State University Agricultural Center, 2001). 

Malathion was detected at 16 surface-water sites; the 

largest concentration (0.113 μg/L) occurred at the 

Lacassine site and was the only detection that exceeded 

the criterion (0.1 μg/L) for the protection of aquatic life 

(table 3).

In 1999, carbofuran was replaced with fipronil, a 

relatively new phenypyrazole insecticide, to control the 

rice water weevil. Carbofuran was sprayed in areas 

where the rice water weevil was observed, whereas 

fipronil is used prophylactically as a seed coating prior to 

planting (fig. 13). Fipronil was detected in more than
1,000.00

100.00

10.00

1.00

0.10

0.01

0.001

C

O

N

C

E

N

T

R

ATIO

N, IN

MIC

R

O

G

R

A

M

S

P

E

R

LIT

E

R

PESTICIDE

Figure 12. Drinking-water and aquatic-life criteria, and maximum pesticides 

in surface water in the Mermentau River Basin, southwestern Louisiana, 1998-2001.

detected concentrations of selected 

n

Triflurali

P

z

l

ropicona oe

i

Simaz ne

b

i

Te

uthu ron

Sulfometuron-methyl

Thiobencarb

riclopyr

T

E ho

ropho

t

p

s

za

in

Ima

qu

Fluometur

no

MCPA

ala h

n

M

t io

r

Metolachlo

Me alaxyl

t

Methomyl

Methyl-Parathi no

Prom

t n

e o

Metri uzin

b

M li

t

o na e

p, ’ E

p -DD

P n

methal n

e

di

i

Propachlor

Propanil

idur

n

S

o

Maximum concentration

Drinking-water criterion

Aquatic-life criterion

1,000.00

100.00

10.00

1.00

0.10

0.01

0.001

C

O

N

C

E

N

T

R

ATIO

N, IN

MIC

R

O

G

R

A

M

S

P

E

R

LIT

E

R

Diur

n

i

o

Deethylatraz ne

ei opro yla

zin

D

s

p

tra

e

i

n

D eldri

Diazin

no

Dinoseb

D

na

iphe

mid

Fip onil (acut )

r

e

Fp ronil (chr

nic)

i

o

EPTC

2, - 4 D

2

i -H dro yatraz ne

y

x

, -Dm eth l ster

2 4

y e

A

l

n

cif uorfe

Acetochlor

Bensul uron-methyl

f

Ala

hlor

c

i

Atraz ne

Benomyl

Chlorimuron-ethyl

Bentazon

Brom

cil

a

C rbary

a

l

arbofu

n

C

ra

o

rifo

Chl rpy

s

ya

zin

C

na

e

o

i

Deethyldeis propylatraz ne

Maximum concentration

Drinking-water criterion

Aquatic-life criterion

27
6

5

4

3

2

1

0

Nov.

a . J

n

Mar.

May

J

y ul

S . ept

Nov.

Jan.

a . M r

y

Ma

J

y ul

S

t. ep

N

v. o

. Jan

Mar.

M

ya

July

Sept.

1998 1999 2000 2001

DATE

C

O

N

C

E

N

T

R

ATIO

N, IN

MIC

R

O

G

R

A

M

S

P

E

R

LIT

E

R

Atrazine

Molinate

Metolachlor

Tebuthiuron

Carbofuran

Fipronil

EXPLANATION

Figure 13. Concentrations of selected pesticides at the Mermentau data-collection site in the Mermentau River Basin, southwestern 

Louisiana, 1998-2001.

28
29

72 percent of the surface-water samples. Maximum concentrations of fipronil and degradation products occurred 

in the headwaters of small bayous surrounded by rice 

agriculture during March and April, which coincided 

with the release of ricefield tailwaters (Demcheck and 

Skrobialowski, 2003). Concentrations of fipronil at surface-water sites (app. 3) ranged from less than 

0.004 μg/L to 6.41 μg/L and exceeded the freshwater 

acute numeric target for TMDL (4.6 μg/L) at Grand 

Marais (5.19 μg/L), East Lacassine (5.29 μg/L), and 

Blue (6.41 μg/L), and the chronic numeric target for 

TMDL (2.3 μg/l) (U.S. Environmental Protection 

Agency, 2002b) at 14 other surface-water sites. Fipronil 

can be degraded by several pathways into at least six degradation products, four of which were analyzed for and 

detected in this study: RPA 105048, fipronil sulfone, 

fipronil sulfide, and desulfinylfipronil. Each of the 

reported degradation products occurred in more samples 

than the parent compound. Fipronil sulfone, fipronil sulfide, and desulfinylfipronil are more persistent and toxic 

to some aquatic life than the parent compound (Connelly, 

2001). Fipronil is toxic to hatchling crawfish at concentrations as low as 4.95 μg/L and toxic to large crawfish 

at 43.5 μg/L (Ottea and Romaire, 2001). Fipronil concentrations as low as 0.005 μg/L can affect survival, 

reproduction and growth of estuarine shrimp (U.S. Environ-mental Protection Agency, 1996). The USEPA 

(1996) also states

1. Fipronil sulfone is 3.3 times more toxic to 

native bluegill sunfish than the parent 

compound;

2. Fipronil sulfone is 6.6 times more toxic and 

fipronil sulfide is 1.9 times more toxic to 

freshwater invertebrates than the parent 

compound; and 

3. Desulfinylfipronil is extremely stable and is 

more toxic than the parent compound.

Demcheck and Skrobialowski (2003) also found 

that fipronil rapidly degrades within the water column, 

usually within 3 months. Desulfinylfipronil is the primary degradation product in the water column, whereas 

fipronil sulfone and fipronil sulfide are predominant in 

bed sediment.

Bed-sediment samples collected at 17 surface-water 

sites in 2000 were analyzed for hydrophobic pesticides. 

Of the 39 pesticides analyzed, only degradation products 

from DDT and fipronil were detected. Degradation 

products from DDT, mostly DDE, were detected in bottom material from 10 sites (Goree and others, 2002). 

Concentrations of DDE at Des Cannes and the Church 

Point site exceeded interim freshwater sediment quality 

guidelines (1.42 μg/kg) for the protection of aquatic life 

(Canadian Council of Ministers of the Environment, 

1999). Of the fipronil degradation products, concentrations of fipronil sulfide were highest and were detected at 

all 17 sites, fipronil sulfone was detected at 16 sites, and 

desulfinylfipronil was detected at 17 sites. Demcheck 

and Skrobialowski (2003) concluded fipronil degradation products in bed sediment accumulate and concentrations generally increase from headwater streams to the 

mainstem of the Mermentau River. Guidelines are not 

available (2002) to evaluate the environmental effects of 

fipronil and fipronil degradation products in bed sediment.

ECOLOGICAL INDICATORS OF 

SURFACE-WATER QUALITY

Results of ANOVA testing of study-design and 

CCA site groups indicated that habitat characteristics 

including channel size and morphology, water clarity, 

open canopy, and substrate differed between streams in 

the northern and southern parts of the study area. In the 

northern part of the study area, characterized by low agricultural intensity, streams drain a transitional zone where 

mixed pine hardwood forests change to wet prairie. 

These small streams with incised channels were typically 

clear, with little open canopy, and contained fine sand to 

clay substrates with abundant woody debris. In the 

southern part of the study area, characterized by high 

agricultural intensity, streams drain treeless wet prairie 

where an impermeable clay layer (hardpan) prevents vertical drainage of surface water and growth of tree roots. 

Where the hardpan is discontinuous, water cypresstupelo hardwoods grow along flood plains and wetlands, 

which may contain submerged and emergent macrophytes (aquatic plants). These large, wide streams typically were turbid, had open canopy, and contained 

organic-rich silt and clay substrates with some woody 

debris.

Stream habitat ratings were based on the total of 10 

habitat parameter scores using the RBP habitat characterization (Barbour and others, 1999). Scores increase as 

habitat quality increases. Ratings at 16 of 19 sites ranged 

from suboptimal (102-154) to optimal (155-200) for biological communities (app. 6 and 7). Theriot, Tortue, and 

Grand Marais sites were rated as marginal (49-101) for 

biological communities because of disturbances in the 

habitat. Heavy deposits of sediment in the stream at 

these sites may affect availability of aquatic invertebrate 

habitat by decreasing potential colonization locations 

because of silt- and clay-coated woody debris. At Tortue 

and Grand Marais, the streams have been channelized 

and lack the microhabitat diversity normally present at 

other similar-size stream reaches studied. Decreased 
30

bank stability at Tortue and the reduced riparian vegetative zone at Grand Marais also contributed to lower RBP 

habitat scores for these sites.

Typically, organisms considered tolerant of turbidity, organic enrichment, and low dissolved-oxygen concentrations were common in the entire study area and 

dominated the overall aquatic invertebrate community. 

Sensitive taxa such as Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT) 

were rare at all sites in the Mermentau River Basin and 

were only abundant at the Whisky site in the Calcasieu 

River Basin. Tolerant taxa abundant throughout the Mermentau River Basin included Diptera (true flies), especially the family Chironomidae (midges); Tubificida 

(aquatic worms); the tolerant Ephemeroptera family 

Caenidae (caenids); and the Gastropoda (snails, limpets) 

family Physidae (pouch snails).

A total of 22,678 aquatic invertebrates were collected at ecological data-collection sites, including 

95 species, 80 genera, and 43 families. Taxon groups of 

Diptera were the most common (40 species), followed by 

Coleoptera (beetles; 14 species), Trichoptera (7 species), 

Ephemeroptera (6 species), and Gastropoda (5 species). 

Greater than 80 percent of all sampled aquatic invertebrates were accounted for by the orders Diptera (46 percent), Amphipoda (scuds, sideswimmers; 18 percent), 

Tubificida (7 percent), Ephemeroptera (6 percent), and 

Gastropoda (5 percent) (app. 8).

Comparison of Site Groups

The study design, based on drainage area and agricultural land-use intensity, was used to determine natural 

and human-related influences on surface-water quality at 

19 ecological data-collection sites. Aquatic invertebrate 

communities were used as ecological indicators of water 

quality and habitat conditions at these sites. Through 

CCA, four significant (p ≤ 0.05) environmental variables 

(instream cover score, percentage of open canopy, and 

concentrations of dissolved oxygen and maximum dissolved fipronil) were identified that described the distribution of aquatic invertebrate communities among 

ecological data-collection sites. Cluster analysis of CCA 

site scores from the first two axes identified four site 

groups which separated ecological data-collection sites 

geographically within the study. Environmental variables and aquatic invertebrate metrics within the studydesign (a priori, before sampling) and CCA (posteriori, 

after sampling) site groups were compared (fig. 7).

Study-Design Site Groups

The study was designed to determine significant 

differences in chemical, biological, and physical habitat 

indicators of surface-water quality among (1) basin site 

groups (large and small), and (2) intensity site groups 

(high and low agricultural intensity). Low-intensity sites 

were used to characterize natural chemical, biological, 

and physical habitat conditions. Site groups were compared to evaluate aquatic invertebrate relations to environmental variables.

Stream Habitat Characteristics

Significant statistical differences (p ≤ 0.05) in 

stream habitat characteristics occurred between basin 

and intensity site groups (table 8). Bank erosion scores 

and bankfull and wetted channel widths differed between 

basin site groups, whereas the bank stability index and 

pool substrate differed between intensity site groups. 

Differences in bank characteristics, channel width, and 

pool substrate may account for some differences in 

aquatic invertebrate communities among site groups.

Generally, median bank erosion scores and median 

measurements of bankfull and wetted channel widths 

were greatest at sites with large drainage areas. Median 

bank erosion scores at large-basin sites were 2.5 times 

the scores at small-basin sites. Median bankfull and wetted channel widths at large-basin sites were at least two 

times the median at small-basin sites.

Generally, the median bank stability index and pool 

substrate characterization score were lowest at all site 

groups with high agricultural intensity. The bank stability index (Fitzpatrick and others, 1998) was used to 

assess stream bank structure among site groups and 

included bank measurements of angle, vegetative cover, 

height, and substrate. A higher bank stability index indicated a less stable bank. Eighty percent of the sites were 

classified as having unstable banks. High-intensity sites 

had greater bank stability (smaller median bank stability 

index) than low-intensity sites. Differences in the bank 

stability index between intensity site groups were attributed to differences in bank height. As bank height 

increased the bank stability index increased. The median 

pool substrate characterization score at low-intensity 

sites was more than 1.5 times the score at high-intensity 

sites. The high-intensity sites had mud- or clay-dominated pool substrate containing few or no root mats and 

little or no submerged vegetation. Pool substrate at lowintensity sites was fine sand mixed with mud or clay with 

some root mats and submerged vegetation.
31

Table 8. Median stream habitat variables for study-design site groups in southwestern Louisiana, 2001

[Boldface values indicate significant differences (p ≤ 0.05) among site groups. Pool substrate characterization protocols from Barbour and 

others (1999). n, number of sites; RBP, Rapid Bioassessment Protocols (Barbour and others, 1999)]

Stream habitat variables

Basin

site groups

Intensity

site groups

Large

(n=11)

Small

(n=8)

High

(n=11)

Low

(n=8)

Quantitative measurements

Bank angle (degrees) 49 48 53 43

Bank erosion score 5 2 4 3

Bank height (meter) 3.1 2.0 1.3 3.2

Bank stability index 13 12 11 13

Bankfull channel width (meter) 28.6 14.3 21.6 20.3

Wetted channel width (meter) 20.4 6.8 16.2 9.2

Qualitative measurements (score)

Pool substrate characterization (0-20) 13 9 9 15

RBP total site score (0-200) 142 149 142 163

Aquatic Invertebrate Communities

Significant statistical differences (p ≤ 0.05) in 

aquatic invertebrate community metrics occurred 

between basin and intensity site groups (table 9). Generally, aquatic invertebrate community structures were 

significantly different based on the percentage of noninsects, abundance of midge taxa, abundance and percentage of feeding groups, and number of tolerant organisms 

between intensity site groups. A significant interaction 

between drainage area and agricultural intensity is evident in the percentage of noninsects and the percentage 

of collector-gatherer taxa. The percentage of noninsects, 

notably Amphipods and Gastropods, was largest in largebasin sites with high intensity. Highest abundances of 

total aquatic invertebrates occurred at low-intensity sites 

regardless of drainage area. The abundance of midges, 

particularly the percentage of Tanytarsini midges, largely 

accounts for the differences in abundance of total aquatic 

invertebrates (total abundance) between intensity site 

groups. Diversity metrics were similar within basin and 

intensity site groups. Percentages of collector-gatherers, 

notably Orthocladiinae midges, generally were higher at 

small-basin sites, particularly those with high agricultural intensity. The abundance of omnivores was higher 

and percentage of shredder taxa was lower at low-intensity sites. The abundance-weighted tolerance (biotic 

index) was consistent with composition metrics and indicated the most tolerant organisms typically were present 

at high-intensity sites. 

The largest differences in percentages of predominant groups occurred between intensity site groups 

(fig. 14). All predominant groups except Diptera, Malacostraca, and Oligochaeta varied by less than 7 percent 

between large- and small-basin and between high- and 

low-intensity site groups. Diptera dominated low-intensity sites regardless of drainage area. Low-intensity sites 

had 22 percent more Diptera and 18 percent fewer Malacostraca than high-intensity sites. Malacostraca, particularly more tolerant Amphipods such as Hyalella azteca

and the Gastropoda families Physidae and Planorbidae 

(orb snails), dominated large-basin sites with high intensity. Oligochaeta, especially tubificids, were more abundant at small-basin sites than at large-basin sites.

Median abundance of aquatic invertebrates, midges, 

and Tanytarsini midges varied between intensity site 

groups (fig. 15, table 9). Generally, abundances doubled 

from high- to low-intensity sites regardless of drainage 

area. The abundance of Tanytarsini midges was expected 

to decrease with increased perturbation at a site (Barbour 

and others, 1999). The percentage of Tanytarsini midges 

remained the same between large- and small-basin sites 

but increased from 4 percent at the high-intensity sites to 

16 percent at the low-intensity sites (table 9). The 

smaller abundance of total aquatic invertebrates, midges, 

and Tanytarsini midges at high-intensity sites indicated 

that these organisms may be sensitive to water-quality 

and habitat conditions associated with agricultural intensity.
32

1 Brower, J.E., and Zar, J.H., 1984, Field and laboratory methods for general ecology (2d ed.): Dubuque, Iowa, Wm. C. Brown Publishers, 

p. 226.

2 Feeding and tolerance metrics based on Barbour and others (1999, app. B).

Table 9. Median aquatic invertebrate metrics for basin and intensity site groups in southwestern Louisiana, 2001

[Median densities and taxa of aquatic invertebrates are rounded to the nearest whole number. Densities are reported as organisms per square meter. 

Boldface values indicate significant differences (p ≤ 0.05) among site groups, based on results of two-factor analysis of variance (ANOVA). 

n, number of sites; <, less than value indicated]

Aquatic invertebrate metrics

Basin site groups Intensity site groups

Large

(n=11)

Small

(n=8)

High

(n=11)

Low

(n=8)

Composition metrics

Abundance (number of organisms)

Abundance (total) 707 991 707 1,602

Amphipoda (percent) 2 1 8 <1.0

Chironomidae (total) 228 359 202 929

Mollusca and Crustacea (percent) 20 5 35 5

Noninsects (percent) 36 25 42 14

Orthocladiinae midges (percent) 2 12 3 12

Tanytarsini midges (percent) 9 9 4 16

Richness (number of non-ambiguous taxa)

Gastropoda taxa 1 1 2 1

Orthocladiinae midge taxa 2 4 2 4

Diversity metrics

Five most abundant taxon (percent) 72 74 75 71

Shannon’s diversity1 .95 .93 .92 .97

Feeding metrics2

Abundance (number of organisms)

Collector-gatherers (percent) 57 74 62 61

Omnivores (total) 0 3 0 7

Richness (number of non-ambiguous taxa)

Collector-gatherer taxa (percent) 44 48 44 46

Shredder taxa (percent) 5 4 5 4

Tolerance metrics2

Abundance-weighted tolerances (biotic index) 7.04 6.31 7.11 6.18

Median abundance and richness as measures of 

feeding differed between basin and intensity site groups

(table 9). Median percentage of collector-gatherers for 

small-basin site group (74 percent) was greater than for 

the large-basin site group (57 percent). Unlike the percentages of collector-gatherers, which were similar 

among intensity sites, the median percentages of Orthocladiinae midges were four times higher at the low-intensity site group (12 percent) than at the high-intensity site 

group (3 percent). The presence of omnivores was 

restricted to low-intensity sites. The percentage of shredders was expected to decrease with increased perturbation at a site (Barbour and others, 1999); however, the 

median percentage of shredder taxa for the high-intensity 

site group (5 percent) was greater than the median for 

the low-intensity site group (4 percent). The variable 

patterns in feeding metrics among site groups may be 

complicated by the presence of aquatic macrophytes 

(plants) at the large-basin sites. Collector-gatherer feeding groups are influenced more by water-quality and
0

10

20

30

40

50

60

70

80

90

100

STUDY-DESIGN SITE GROUPS

M

E

DIA

N

P

R

E

D

O

MIN

A

N

T IN

V

E

R

T

E

B

R

AT

E

G

R

O

U

P

S, IN

P

E

R

C

E

N

T

 LARGE 

 BASIN

 SMALL

 BASIN

 HIGH 

 INTENSITY

 LOW

 INTENSITY

Other Insects

 (springtails, hellgrammites, dobson, 

 damsel and dragonflies)

Malacostraca

 (amphipods, decapods, and 

 isopods)

Mollusca 

(gastropods and bivalves)

Oligochaeta

(aquatic worms)

Other Noninsects (hydras, 

 flatworms, roundworms, 

 leeches, and arthropods)

EXPLANATION

HIGH INTENSITY- Percentage of 

 drainage area used for rice 

 cultivation > 45 percent

LOW INTENSITY- Percentage of 

 drainage area used for rice 

 cultivation < 45 percent 

PREDOMINANT INVERTEBRATE 

GROUPS

Ephemeroptera, Plecoptera, 

 Trichoptera (mayflies, stoneflies, 

 and caddisflies)

Coleoptera

(beetles)

Diptera

(true flies and midges)

LARGE BASIN- Drainage area > 

70 square miles

SMALL BASIN- Drainage area < 

70 square miles

Figure 14. Composition of predominant groups of aquatic invertebrates at basin and intensity site groups in 

southwestern Louisiana, 2001 (data listed in appendix 8).

 STUDY-DESIGN SITE GROUPS

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

Aquatic invertebrates

Chironomidae (midges)

Tanytarsini midges

EXPLANATION

M

E

DIA

N

A

B

U

N

D

A

N

C

E

O

F

O

R

G

A

NIS

M

S

P

E

R

S

Q

U

A

R

E

M

E

T

E

R

STUDY-DESIGN SITE GROUPS

 LARGE 

 BASIN

 SMALL

 BASIN

 HIGH 

 INTENSITY

 LOW

 INTENSITY

 ABUNDANCE OF ORGANISMS 

 STUDY-DESIGN SITE GROUPS 

Figure 15. Median abundances of aquatic invertebrates, Chironomidae (midges), and Tanytarsini midges 

at basin and intensity site groups in southwestern Louisiana, 2001 (data listed in appendix 8).

LARGE BASIN- Drainage area > 

 70 square miles

SMALL BASIN- Drainage area < 

 70 square miles

HIGH INTENSITY- Percentage of 

 drainage area used for rice 

 cultivation > 45 percent

LOW INTENSITY- Percentage of 

 drainage area used for rice 

 cultivation < 45 percent 

33
34

habitat conditions associated with drainage area than by 

conditions associated with agricultural intensity.

The abundance-weighted tolerance (biotic index) 

results were consistent with composition metrics results 

and indicated most tolerant organisms occurred at highintensity sites, mainly the large high-intensity sites 

(table 9). The abundance-weighted values were calculated by weighting the tolerance value by the abundance 

of the organism in the sample. Tolerance values were 

based on a scale from 0 to 10, where 0 represented the 

tolerance value of an extremely sensitive organism and 

10 represented the value for a tolerant organism. Thus, 

a higher abundance-weighted tolerance value indicated 

that the communities at these sites were composed of 

more organisms considered tolerant to many types of 

stress associated with stream disturbance. Median abundance-weighted tolerance was greater at the high-intensity sites (7.11) than at the low-intensity sites (6.18).

Canonical Correspondence Analysis Site 

Groups

For this report, CCA (ter Braak and Smilauer, 1998) 

was used to evaluate patterns among sites based on the 

relative abundance of aquatic invertebrates and environmental variables. The CCA and the forward selection 

process reduced 36 environmental variables to 4 that best 

described the relations among water quality, habitat, and 

invertebrate communities among sites. The CCA identified four significant (p ≤ 0.05) environmental variables 

(instream cover score, percentage of open canopy, concentrations of dissolved oxygen, and maximum concentration of dissolved fipronil) that described the distribution of aquatic invertebrate communities among ecological data-collection sites (fig. 16). The first CCA axis 

represents the dissolved oxygen and open canopy gradient, and the second CCA axis represents the instream 

cover and fipronil concentration gradient. The labeled 

arrows (vectors) in the CCA biplot indicate spatial associations of site and species scores with environmental 

variables. The value of the environmental variable 

increases in the direction the vector points. The length of 

the vector reflects the importance of the environmental 

variable in the CCA model. Vectors parallel to an axis 

are highly correlated with that axis and vectors perpendicular to an axis are poorly correlated with that axis 

(table 10).

Cluster analysis using site scores from the first two 

CCA axes (Wilkinson and others, 1998) identified four 

site groups (A, B, C, and D) that had similar water quality, habitat, and aquatic invertebrate characteristics. 

These site groups were geographically separated within 

the study (fig. 17). Group A included 2 sites in the northern part of the Mermentau River Basin and 1 site in the 

adjacent Calcasieu River Basin. Other sites, all in the 

Mermentau River Basin, were grouped as follows: 4 sites 

in the southeastern part of the basin (group B), 6 sites in 

the north-central and southeastern parts (group C), and 6 

in the south-central and southwestern parts (group D). 

Discriminate analysis (Engelman, 1998) showed statistical significance (Wilk’s lambda = 0.014, p ≤ 0.001) of 

cluster analysis site group assignments with 89 percent 

of sites correctly classified to CCA site groups.

Figure 16 shows the distribution of ecological datacollection sites and site groups in relation to CCA environmental variables. The highest instream cover and 

smallest fipronil concentrations were present at sites in 

group A. Sites in group B were characterized by moderate instream cover, open canopy, and dissolved oxygen 

concentrations, and small fipronil concentrations. Group 

C sites were characterized by large dissolved-oxygen and 

fipronil concentrations. The largest amount of open canopy and the smallest dissolved-oxygen concentrations 

were present at sites in group D. Figure 16 also shows 

the CCA distribution of relative abundances of aquatic 

Table 10. Canonical correlation coefficients of environmental variables with the first four canonical correspondence 

analysis axes for aquatic invertebrates at ecological data-collection sites in southwestern Louisiana, 2001

[Numbers in parentheses are eigenvalues]

Canonical correspondence analysis model

environmental variables

Axis 1

(0.31)

Axis 2

(0.18)

Axis 3

(0.16)

Axis 4

(0.09)

Open canopy 0.67 0.16 0.14 0.80

Instream cover - .21 .32 - .80 .56

Dissolved oxygen - .64 - .51 .14 .69

Dissolved fipronil (maximum) < .01 - .96 - .53 - .07

Cumulative percent of species variance explained 16.0 25.4 33.6 38.4

Cumulative percent of species-environment variance explained 41.8 66.2 87.4 100
Environmental variable and 

variable name

Species and species 

abbreviation (See appendix 8 

for scientific names)

EXPLANATION

SPECIES GROUPS

Chironomidae (midges)

Othrocladiinae midges

Tanytarsini midges

Ephemeroptera, Plechoptera, Trichoptera

Noninsects

Other insects

Glydipes

GROUP A CCA site group

C

C

A

AXIS 1

Percentage

open

canopy

Maximum dissolved

fipronil concentration

Whisky

Tortue

Blue

Boggy

Des Cannes

East Lacassine

Plaquemine

Mermentau

Nezpique

Caney

Guidry

Wikoff

Grand

Marais

Castor

Upper

Des Cannes

Theriot

Mallet

Church

Point

Lacassine

Instream

cover score

Dissolved

oxygen

concentration

-1.0

-1.0

0

0 1.0

GROUP A

GROUP B

GROUP D

GROUP C

1.0

CCA AXIS 2

C

C

A

AXIS 1

Rheocric

Hyazteca

Glydipes

Ablabesm

Hedrodon

Acari

Bezzpalp

Mictanyt

Chpsyche

Rheotany

Tanytars

Hydrinae

Enchidae

Atrichop

Corynon

Caenis

Tropist

Hydra

Criortho

Megadril

Enochrus

Lirceus

Dicdipes

Tribelos

Physella

Nematoda

Thienema

Naididae

Turbell

icr m n M o e

Nanoclad

r pid Eo ae

Cricotop

Tubfidae

Chironom

Collemb

Crangony

Scirtdae

-1.0

0

1.0

-0.5

0.5

0.5

-0.5

-0.5 -0.5

Maximum dissolved

fipronil concentration

Percentage

open

Dissolved canopy

oxygen

concentration

Instream

cover score

Ecological sampling site and 

abbreviation (See table 1 and 

appendix 1 for site names)

Church

 Point

Small basin site with low intensity

Large basin site with low intensity

Small basin site with high intensity

Large basin site with high intensity

BASIN AND INTENSITY SITE GROUPS

Instream 

cover 

score

Figure 16. Canonical correspondence analysis (CCA) ordination biplot showing site (A) and species (B) locations 

in relation to environmental variables of ecological data-collection sites in southwestern Louisiana, 2001. The 

environmental variables shown are related significantly (p≤0.05) to one or more of the CCA axes. The value of the 

environmental variable increases in the direction the arrow (vector) points. The length of the vector reflects the 

importance of an environmental variable and direction of influence in the CCA model.

B

A

35

37

invertebrate species in relation to environmental variables. Communities at large-basin sites tended to vary 

along the dissolved-oxygen and open-canopy gradient, 

whereas communities at small-basin sites tended to vary 

along the instream-cover and fipronil-concentration gradient.

Water-Quality Characteristics

Significant statistical differences (p ≤ 0.05) in 

water-quality characteristics occurred among CCA site 

groups (table 11). Median values were smallest for 17 

water-quality variables at group A sites and largest for 

11 water-quality variables at group B sites. Median values of turbidity, and concentrations of total ammonia 

plus organic nitrogen, nitrate, total phosphorus, and dissolved fipronil, were largest at group C sites. Group D 

sites were characterized by midrange concentrations for 

all water-quality variables except concentrations of dissolved oxygen, which were lowest.

Possible explanations for the differences in water 

quality among site groups include the differences in (1) 

general soil composition and drainage characteristics 

(Touchet and others, 1974), and (2) the percentage of 

land used for agriculture in these basins. Drainage areas 

for sites in group A are low in agricultural intensity and 

contain pine uplands and alluvial terraces. Soils are 

acidic and loamy with moderate sand content and are 

moderately well-drained. Drainage areas for group B 

Table 11. Median water-quality variables for canonical correspondence analysis (CCA) site groups in

southwestern Louisiana, 2001

[Boldface values indicate significant differences (p ≤ 0.05) among site groups, based on Kruskal-Wallis test; for each variable, values preceded by 

the same superscript letter are not significantly different from each other. n, number of sites; mg/L, milligrams per liter; μS/cm, microsiemens per 

centimeter at 25 degrees Celsius; NTU, nephelometric turbidity units; <, less than indicated value; μg/L, micrograms per liter]

Water-quality variable

CCA site groups

A

(n=3)

B

(n=4)

C

(n=6)

D

(n=6)

Physiochemical properties

Specific conductance (μS/cm) a 44 b 360 140 b 162

Dissolved oxygen (mg/L) 7.3 6.3 7.4 5.5

Turbidity (NTU’s) 15 201 455 240

Major inorganic ions (mg/L)

Calcium, dissolved a 3.0 b 28 a, c 7.9 b, c 11

Magnesium, dissolved a 1.0 b 9.9 a, c 3.0 b, c 4.1

Potassium, dissolved a 1.3 b 4.5 b 4.1 3.5

Sodium, dissolved 3.4 28 11 13

Alkalinity, as CaCO3 a 8 b 141 30 b 51

Chloride, dissolved 3.3 22 13 13

Nutrients (mg/L)

Nitrogen (as N):

Ammonia + organic, total .7 1.8 3.1 2.1

Ammonia + organic, dissolved .5 1.0 .8 .9

Nitrate, dissolved .10 .27 .33 .21

Nitrite, dissolved a <.01 b .04 b .03 .02

Phosphorus (as P):

Total .05 .68 .82 .49

Dissolved a .02 b .23 .04 b .12

Ortho, dissolved a .01 b .18 .03 b .09

Organic carbon (mg/L)

Carbon, organic (suspended) a 1.4 b 4.0 b 4.0 b 4.0

Insecticide (μg/L)

Fipronil, dissolved (maximum) a .0044 a, c.184 b 2.4556 b, c 1.615
38

sites are mixed in agricultural intensity and contain loess 

uplands and low terrace areas that are influenced by post 

prairie-age loess. Soils are loamy with clayey subsoil, 

and are poorly drained. Drainage areas for group C sites 

are mixed in agricultural intensity. Soils contain alluvial 

and outwash deposits, are loamy with clayey subsoils, 

and are poorly drained. Increased turbidity and 

increased concentrations of nutrients and insecticides, 

which are normally associated with agricultural activities, occurred at group C sites. Drainage areas for sites 

in group D are high in agricultural activities. Group D 

sites contain mixtures of upstream water, which may 

explain the midrange concentrations of water-quality 

constituents at these sites.

Stream Habitat Characteristics

Water clarity and the amount of open canopy among 

CCA site groups were significantly different (p ≤ 0.05) 

(table 12). Streams in group A were clear with little open 

canopy. Streams in group B were slightly turbid with 

some open canopy. In group C, streams were turbid with 

some open canopy; water clarity was lowest and turbidity 

highest in these streams. Streams in group D were 

slightly turbid, with open canopy. Median euphotic and 

Secchi disk depths were greater for group A (1.35 m and 

0.66 m) than for group C (0.13 m and 0.03 m). Median 

values for open canopy differed between group A 

(8 percent) and group D (65 percent), and between 

group C (26 percent) and group D. Differences in water 

clarity probably were related to agricultural intensity, 

whereas differences in the canopy were probably related 

to drainage-area characteristics. Differences in water 

clarity and open canopy may account for some differences in aquatic invertebrate communities.

Aquatic Invertebrate Communities

Aquatic invertebrate community metrics were significantly different (p ≤ 0.05) in the percentage of noninsects, abundance of midge taxa, abundance of feeding 

groups, and number of tolerant organisms among intensity (table 9) and CCA (table 13) site groups. Comparable to the large basin sites with high intensity, 

noninsects, notably Amphipods, dominated sites in 

group D. Similar to intensity site groups, CCA site 

groups differed in abundance of total aquatic invertebrates, midges, and Tanytarsini midges. The relative 

highest total abundances were at groups A and D. The 

relative abundance of midges, particularly the percentage 

of Tanytarsini midges, largely accounts for the differences in total abundance between groups A and D. 

Diversity metrics were similar between basin and intensity site groups but dominance and diversity differed significantly among CCA site groups. Diversity metrics 

differed between groups B and C and between groups B 

and D. Although the abundance and richness of collector-gatherers were similar among CCA site groups, the 

percentage of collector-gatherer Orthocladiinae midges 

generally was larger in small headwater streams, particularly in groups A and B. The abundance-weighted tolerance (biotic index) indicated the most tolerant 

organisms typically were present at sites in group D, similar to large basin sites with high intensity.

Figure 18 shows the composition of predominant 

invertebrate groups for the CCA site groups. Among all 

CCA site groups, the composition of predominant invertebrate groups was most balanced in group B. The greatest shifts in predominant invertebrate groups was 

between groups A and D. Diptera dominated group A 

(similar to small basins with low intensity) and Malacostraca, especially Amphipoda, dominated site group D 

(similar to large basins with high intensity). The median 

percentage of Amphipoda (table 13) for group D 

(38 percent) differed from all other CCA site groups (all 

less than 1 percent). The median percentages of Mollusca plus Crustacea (table 13), as well as noninsects 

(table 13), differed between group D (45, 58 percent) and 

group A (4, 6 percent) and between group C (5, 15 percent) and group D. Although not sampled for aquatic 

invertebrates, macrophytes such as water hyacinth and 

alligator weed provide good habitat for Molluscs and 

Crustaceans, especially Amphipods, at group D sites.

Table 12. Median stream habitat variables for canonical correspondence analysis (CCA) site groups in southwestern 

Louisiana, 2001

[Boldface values indicate significant differences (p ≤ 0.05) among site groups, based on Kruskal-Wallis test; for each variable, values preceded by 

the same superscript letter are not significantly different from each other. n, number of sites]

Stream-habitat variable

CCA site groups

A

(n=3)

B

(n=4)

C

(n=6)

D

(n=6)

Quantitative measurements

Euphotic depth (meter) 1.35 0.31 0.13 0.21

Open canopy (percent) a 8 25 a 26 b 65

Secchi disk depth (meter) .66 .09 .03 .08
39

1 Brower, J.E., and Zar, J.H., 1984, Field and laboratory methods for general ecology (2d ed.): Dubuque, Iowa, Wm. C. Brown Publishers, 

p. 226.

2 Feeding and tolerance metrics based on Barbour and others (1999).

Table 13. Median aquatic invertebrate metrics for canonical correspondence analysis (CCA) site groups in 

southwestern Louisiana, 2001

[Median densities of aquatic invertebrates are rounded to the nearest whole number and reported as organisms per square meter. Boldface values 

indicate significant differences (p ≤ 0.05) among site groups, based on results of Kruskal-Wallis test; for each variable, values preceded by the same 

superscript letter are not significantly different from each other. n, number of sites; <, less than indicated value.]

Aquatic invertebrate metrics

CCA site groups

A

(n=3)

B

(n=4)

C

(n=6)

D

(n=6)

Composition metrics

Abundance (number of organisms)

Abundance (total) 2,323 872 448 1,260

Amphipoda (percent) a <1.0 a

 <1.0 a <1.0 b 38

Chironomidae (total) 1,235 367 151 171

Mollusca and Crustacea (percent) a 4 19 a 5 b 45

Noninsects (percent) a 6 35 a 15 b 58

Orthocladiinae midges (percent) a 13 a 15 b 2 b 2

Tanytarsini midges (percent) 33 11 11 <1.0

Richness (number of non-ambiguous taxa)

Gastropoda taxa a 1 2 a 1 b 3

Orthocladiinae midge taxa a 5 a 4 b 2 b 2

Diversity metrics

Five most abundant taxon (percent) 71 a 67 b 75 b 79

Shannon’s diversity1 .98 a 1.1 b .92 b .89

Feeding metrics2

Abundance (number of organisms)

Collector-gatherer (percent) 62 62 55 64

Omnivores (total) a 17 6 b 0 b 0

Richness (number of non-ambiguous taxa)

Collector-gatherer taxa (percent) 47 46 38 49

Shredder taxa (percent) <1.0 4 7 5

Tolerance metrics2

Abundance-weighted tolerances (biotic index) 5.92 6.67 6.83 7.51

Similar to intensity site groups, median abundance 

of total aquatic invertebrates, midges, and Tanytarsini 

midges varied among CCA site groups (fig 19, table 13). 

Except for the total abundance in group D (which was 

composed of over 50 percent noninsects), abundances 

generally decreased gradually in order of group A > 

group B > groups C and D. Relative total abundance was 

more than five times higher in group A (2,323 organisms/m2

) than in group C (448 organisms/m2). The 

abundance of midges, particularly the percentage of 

Tanytarsini, largely accounts for the differences in total 

abundance between groups A and D. Tanytarsini midge 

abundances were the highest in group A (33 percent), 

composing one-third of the midge population, and lowest 

at group D (<1.0 percent). A gradual decrease in the 

abundances of midges and Tanytarsini midges indicated 

that these organisms may be sensitive to a gradient of 

water-quality and habitat conditions associated with 

CCA site groups.

Significant differences in median diversity metrics 

at CCA site groups included the percentage of the five 

most abundant taxon and the Shannon’s diversity (Thomas Cuffney, U.S. Geological Survey, written commun., 

2002) (table 13). In group B, the percentage of dominant taxon was smaller (67 percent) and the Shannon’s 

diversity was higher (1.1) than in group C (75 percent, 

0.92) and group D (79 percent, 0.89). Lower dominance 

and higher Shannon’s diversity values indicated aquatic 

invertebrate communities in group B were more diverse 

with respect to predominant invertebrate groups

(fig. 18).
0

500

1,000

1,500

2,000

2,500

GROUP A GROUP B

CCA SITE GROUPS

GROUP C GROUP D

M

E

DIA

N

A

B

U

N

D

A

N

C

E

O

F

O

R

G

A

NIS

M

S

P

E

R

S

Q

U

A

R

E

M

E

T

E

R

Figure 19. Median abundances of aquatic invertebrates, Chironomidae (midges), and Tanytarsini midges 

at canonical correspondence analysis (CCA) site groups in southwestern Louisiana, 2001 (data listed in 

appendix 8).

Aquatic invertebrates

Chironomidae (midges)

Tanytarsini midges

EXPLANATION

Figure 18. Composition of predominant groups of aquatic invertebrates at canonical correspondence 

analysis (CCA) site groups in southwestern Louisiana, 2001 (data listed in appendix 8).

0

10

20

30

40

50

60

70

80

90

100

 GROUP A GROUP B GROUP C GROUP D

CCA SITE GROUPS

M

E

DIA

N

P

R

E

D

O

MIN

A

N

T IN

V

E

R

T

E

B

R

AT

E

G

R

O

U

P

S, IN

P

E

R

C

E

N

T

Malacostraca

(amphipods, decapods, and isopods)

Mollusca 

(gastropods and bivalves)

Oligochaeta

(aquatic worms)

Other Noninsects

(hydras, flatworms, roundworms, 

 leeches, and arthropods)

EXPLANATION

Other Insects

 (springtails, hellgrammites, dobson, 

 damsel and dragonflies)

Ephemeroptera, Plecoptera, Trichoptera

(mayflies, stoneflies, and caddisflies)

Coleoptera

(beetles)

Diptera

(true flies and midges)

40
41

Median abundance and richness as measures of 

feeding differed among CCA groups (table 13). Unlike 

results for basin and intensity site groups, abundance and 

richness of collector-gatherers except Orthocladiinae 

midges were similar among CCA groups. Orthocladiinae midge abundances were more than five times higher 

in groups A (13 percent) and B (15 percent) than in 

groups C (2 percent) and D (2 percent). Orthocladiinae 

midge richness was higher in groups A (5) and B (4) than 

in groups C (2) and D (2). Omnivores were present only 

at low-intensity sites and in groups A and B. Median 

abundance of omnivores was highest in group A (17).

The abundance-weighted tolerance values (biotic 

index) were highest for group D sites (table 13) and large 

basin sites with high intensity (table 9). The median 

abundance-weighted tolerance values differed between 

groups A (5.92) and D (7.51). Patterns in abundanceweighted tolerance were similar for basin and intensity 

site groups and CCA site groups, and indicated greater 

abundance of sensitive organisms at low-intensity sites.

Relations Between Species and 

Environmental Variables

Scatter plots were used to evaluate relations 

between aquatic invertebrates and significant environmental variables from the CCA model. One genus of tolerant mayfly, Caenis, and one genus of midge, 

Rheotanytarsus, were selected to illustrate these relations. These species were selected because of their wide 

distribution among ecological data-collection sites and 

because the observed patterns were common for many 

other species. The environmental variables used for the 

evaluation were instream cover score, percentage of open 

canopy, concentrations of dissolved oxygen, and maximum concentrations of dissolved fipronil.

The relative abundance of Caenis sp. (fig. 20) 

decreased with increasing instream cover and fipronil 

concentrations but showed little to no relation to 

dissolved-oxygen concentrations or open canopy. 

Caenis sp. abundance may be an indicator of water quality in streams influenced by fipronil because this species 

exhibits little sensitivity to most environmental variables 

except increasing instream cover and concentrations of 

fipronil. Tanytarsini midges, particularly Rheotanytarsus sp. (fig. 20), were similarly sensitive to fipronil as 

Caenis sp., but also to other environmental variables. 

Relative abundance of Rheotanytarsus sp. increased as 

dissolved oxygen and instream cover increased, and 

decreased as open canopy increased. Relative abundance 

of Orthocladiinae midges and the amphipod, Hyalella 

azteca, were similar to that of Rheotanytarsus sp. in similar habitats. Orthocladiinae midges may be an indicator 

of water quality for small-basin sites. Hyalella azteca

favored large-basin sites, notably those with high agricultural intensity. The Hyalella azteca amphipod 

decreased in relative abundance as dissolved oxygen 

increased, and increased as open canopy increased.

Ali and others (1998) showed two species of chironomid (midge) larvae were highly susceptible to 

fipronil. In the study described in this report, scatter 

plots (fig. 20) indicate that an increase in the maximum 

concentration of dissolved fipronil was the only significant environmental variable in the CCA model that was 

related to consistent decreases in relative abundance for 

many species, notably midges. The degradation products 

of fipronil also are toxic. The USEPA (1996) states that 

fipronil sulfone is 6.6 times more toxic, and fipronil sulfide is 1.9 times more toxic to freshwater invertebrates 

than the parent compound. Findings in this study were 

similar to those of the USEPA: Relative abundances for 

many species decreased at lower concentrations of 

fipronil degradation products (fipronil sulfone, fipronil 

sulfide, and desulfinylfipronil) than of the fipronil parent 

compound. Demcheck and Skrobialowski (2003) concluded these fipronil degradation products accumulate in 

bed sediment, and concentrations generally increase 

from headwater streams to the mainstem of the Mermentau River. This possibly would explain the negative 

response between aquatic invertebrate abundance and 

fipronil.

SUMMARY AND CONCLUSIONS

A study was completed in the Mermentau River 

Basin in 2001 to better understand the relations among 

ground-water and surface-water and bed-sediment quality; aquatic invertebrate communities; and habitat conditions with respect to land use and agricultural intensity. 

The study area is located entirely within the Acadian 

Pontchartrain Study Unit, a part of the National WaterQuality Assessment Program. Water from wells and 

streams used to irrigate ricefields is returned to streams 

and bayous and may return to the ground through infiltration, be used downstream for agriculture, or drain to 

the Gulf of Mexico. Low-gradient streams with bidirectional flow, modifications for navigation, and water control structures are characteristic of the hydrology in the 

study area. The northwestern part of the study area is 

mostly forested and land in the remainder of the study 

area is used for rice agriculture. Throughout the study 

area, a drought occurred in 1999 and intensified to 

extreme conditions in 2000. Soils contain more sand and 

are moderately well drained in the northwestern part of 

the study area, are loamy and clayey in the center and 

south, and contain thick loess deposits in the southeastern part.
R

E

L

ATIV

E

A

B

U

N

D

A

N

C

E

O

F

CA

E

NIS

S

P. (M

AY

F

LY)

R

E

L

ATIV

E

A

B

U

N

D

A

N

C

E

O

F

R

H

E

O

TA

N

YTA

R

S

U

S

S

P. (MID

G

E)

INSTREAM COVER SCORE 

0 5 10 15 20 25

0

10

20

30

0 5 10 15 20 25

0

10

20

30

40

PERCENTAGE OPEN CANOPY 

0 10 20 30 40 50 60 70 80

0

10

20

30

0 10 20 30 40 50 60 70 80

0

10

20

30

40

MAXIMUM DISSOLVED FIPRONIL, IN MICROGRAMS PER LITER 

0 1 2 3 4 5 6 7

0

10

20

30

0 1 2 3 4 5 6 7

0

10

20

30

40

Figure 20. Relative abundances of Caenis sp. (mayfly) and Rheotanytarsus sp. (midge), and significant habitat and 

water-quality variables identified by canonical correspondence analysis (CCA) for ecological data-collection sites in 

southwestern Louisiana, 2001. Increases in concentration of maximum dissolved fipronil was the only significant 

variable in the CCA model that was related to consistent decreases in relative abundance for many species.

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER 

3 4 5 6 7 8 9 10

0

10

20

30

40

3 4 5 6 7 8 9 10

0

10

20

30

42
43

Water-quality data were compared to drinkingwater and aquatic-life criteria and bed-sediment data 

were compared to aquatic-life criteria. Water-quality 

data were analyzed statistically and related to agricultural land-use intensity. Samples from 29 wells and 24 

stream sites analyzed for selected nutrients, major inorganic ions, and pesticides indicate the following:

Nutrients

• Concentrations of nutrients and major inorganic 

ions in ground and surface water generally were 

largest in the southeastern part of the study area, an 

area of intense agriculture.

• The only drinking water regulation exceeded in a 

ground-water sample was that for nitrate in a well 

located in an area previously used for raising poultry and swine.

• Concentrations of nutrients from ground water used 

for agricultural irrigation were not high enough to 

contribute to eutrophication in surface water.

• The greatest potential for eutrophic conditions in 

surface water, based on nutrient thresholds, 

occurred March-May, at about the same time or 

shortly after ricefields were drained.

Major Inorganic Ions and Trace Elements

• Secondary Maximum Contaminant Levels established by the U.S. Environmental Protection 

Agency were exceeded in samples from 20 wells—

sulfate in 1 well, chloride in 4 wells, iron in 7 wells, 

and manganese in 17 wells.

• Secondary Maximum Contaminant Levels were 

exceeded in samples from all surface-water sites—

iron at 8 sites, and manganese at all sites.

• The maximum concentrations of sodium and chloride in surface water occurred at Bayou Lacassine 

near Lake Arthur and probably resulted from saltwater intrusion induced by reverse flow during the 

drought.

Pesticides

• Fewer pesticides and degradation products were 

detected in ground water than in surface water. 

Concentrations were lower in ground water than in 

surface water, and did not exceed drinking water or 

aquatic life criteria. Concentrations were detected 

in less than 1 percent of all analyses; 19 pesticides 

and degradation products were detected in samples 

from 11 wells.

• Pesticides and degradation products most frequently detected in ground water were the herbicides bentazon and atrazine.

• Concentrations of 47 pesticides and degradation 

products were detected in surface water. At least 3 

pesticides were detected in all surface-water samples. In 72 percent of the samples at least 

5 hydrophylic pesticides were detected, and in more 

than 70 percent of the samples at least 3 hydrophobic pesticides were detected.

• Although atrazine concentrations in three surfacewater samples exceeded 3 μg/L (micrograms per 

liter), the Maximum Contaminant Level established 

by the U.S. Environmental Protection Agency was 

not exceeded because it is based on an annual average of quarterly samples. Concentrations larger 

than 3.0 μg/L were not detected in samples collected during other times of the year, and the average annual concentrations did not exceed 3 μg/L for 

sites sampled throughout the year.

• Pesticides concentrations in surface water exceeded 

aquatic-life criteria for atrazine (1.8 μg/L), tebuthiuron (1.6 μg/L), and malathion (0.1 μg/L).

• Fipronil was detected in concentrations exceeding 

the numeric targets for acute total maximum daily 

loads (2.30 μg/L) at 3 surface-water sites and the 

numeric targets for chronic total maximum daily 

loads (4.6 μg/L) at 14 sites.

• Maximum pesticide concentrations in surface water 

usually occurred in the spring at about the same 

time or shortly after ricefields were drained.

• Concentrations of DDE in bed sediment at Des 

Cannes and Church Point sites exceeded interim 

freshwater sediment-quality guidelines for the protection of aquatic life.

• Fipronil sulfide was detected at all bed-sediment 

sites, but there are no current (2002) guidelines with 

which to evaluate the environmental effects of 

fipronil and degradation products.

The study design, based on drainage basin area and 

agricultural land-use intensity, was used to determine 

differences in natural and human-related influences on 

surface-water quality at 19 ecological data-collection 

sites. Aquatic invertebrate communities were used as 

indicators of surface-water quality and habitat conditions 

at these sites. Canonical correspondence analysis (CCA) 

identified four significant environmental variables 

(instream cover score, percentage of open canopy, and 

concentrations of dissolved oxygen and maximum dissolved fipronil) that described the distribution of aquatic 

invertebrate communities among ecological data-collection sites. Cluster analysis revealed four site groups 

which separated ecological data-collection sites geographically within the study. Environmental data and 

aquatic invertebrate metrics within the study design and 

CCA-assigned site groups were compared and indicate 

the following: 
44

• Stream habitat ratings using RBP habitat characterizations were rated optimal to marginal for all ecological data-collection sites; ratings for 16 sites 

were rated optimal to suboptimal.

• Generally, median bank erosion scores and median 

measurements of bankfull and wetted channel 

widths were greatest at all site groups with large 

drainage areas.

• Generally, the median bank stability index and pool 

substrate characterization score were lowest at all 

site groups with high agricultural intensity.

• Median values were lowest for 17 water-quality 

variables at group A sites and highest for 11 waterquality variables at group B sites.

• Possible explanations for the differences in water 

quality among site groups include the differences in 

general soil types and agricultural land use in these 

basins.

• Increased turbidity and concentrations of nutrients 

and insecticides, which normally are associated 

with agricultural activities, occurred at group C 

sites.

• Water clarity and the amount of open canopy differed among CCA site groups.

• Organisms tolerant of turbidity, organic enrichment, 

and low dissolved-oxygen concentrations are common in the study and dominated the aquatic invertebrate community.

• Aquatic invertebrate communities at large-basin 

sites tended to vary along the dissolved-oxygen and 

open-canopy gradient, whereas communities at 

small-basin sites tended to vary along the instreamcover and fipronil-concentration gradient.

• Aquatic invertebrate communities were significantly different in percentage of noninsects, abundance aof midge taxa, abundance of feeding groups, 

and number of tolerant organisms among intensity 

and CCA site groups.

• Diversity metrics were similar among study-design 

site groups but significant differences in dominance 

and diversity occurred among CCA site groups.

• In this study, the maximum concentration of dissolved fipronil was the only significant environmental variable related to consistent decreases in 

relative abundance for many species, notably 

midges.

• Relative abundances for many species decreased at 

lower concentrations of the fipronil degradation 

products (fipronil sulfone, fipronil sulfide, and desulfinylfipronil) than of the fipronil parent compound.

REFERENCES CITED

Ali, Arshad, Nayar, J.K., and Gu, W.D., 1998, Toxicity 

of a phenyl pyrazole insecticide, fipronil, to mosquito 

and chironomid midge larvae in the laboratory: 

Journal of the American Mosquito Control Assoc., 

v. 14, no. 2, p. 216-218.

Allain, Larry, Vidrine, Malcolm, Grafe, Vicki, Allen, 

Charles, and Johnson, Steve, 2000, Paradise lost? The 

Coastal Prairie of Louisiana and Texas: U.S. Fish and 

Wildlife Service, 39 p.

Avery, Jimmy, and Lorio, Wendell, 1999, Louisiana 

Cooperative Extension Service, Crawfish production 

manual: Baton Rouge, La., Louisiana State University 

Agricultural Center, Pub. 2637, 38 p.

Barbour, M.T., Gerritsen, Jeroen, Snyder, B.D., and 

Stribling, J.B., 1999, Rapid Bioassessment Protocols 

for use in streams and wadeable rivers—Periphyton, 

benthic macroinvertebrates and fish (2d ed.): 

Washington, D.C., U.S. Environmental Protection 

Agency, Office of Water, EPA-841-B-99-002, 339 p.

Brower, J.E., and Zar, J.H., 1984, Field and laboratory 

methods for general ecology (2d ed.): Dubuque, Iowa, 

Wm. C. Brown Publishers, p. 226.

Brown, C.A., 1972, Wildflowers of Louisiana and 

adjoining states: Baton Rouge, La., Louisiana State 

University Press, 247 p.

Canadian Council of Ministers of the Environment, 

1999, Canadian environmental quality guidelines, 

Canadian sediment quality guidelines for the 

protection of aquatic life—Summary tables, exerpt 

from Publication no. 1299, ISBN 1-896997-34-1: 

accessed March 1, 2001, at URL 

http://www.ec.gc.ca/ceqg-rcqe/sedtbl_e.PDF

Canadian Council of Ministers of the Environment, 

2001, Canadian water quality guidelines for the 

protection of aquatic life—Summary table, Canadian 

environmental quality guidelines, 1999: Winnipeg, 

Canadian Council of Ministers of the Environment, 

7 p.

Connelly, Pete, 2001, Environmental fate of fipronil: 

California Environmental Protection Agency, Department of Pesticide Regulation: accessed on October 16, 

2002, at URL

http://www.pw.ucr.edu/textfiles/fipronil.pdf

Cuffney, T.F., Gurtz, M.E., and Meador, M.R., 1993, 

Methods for collecting benthic invertebrate samples as 

part of the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 93-

406, 66 p.
45

Demas, C.R., Demcheck, D.K., Anderson, M.L., and 

Garon, J.D., 1999, National Water-Quality Assessment Program—Acadian-Pontchartrain Study Unit: 

U.S. Geological Survey Fact Sheet FS-185-99, 4 p.

Demcheck, D.K., 1994, Louisiana hydrologic atlas map 

no. 7: Water-quality survey of the Mermentau River 

Basin, 1989-90: U.S. Geological Survey WaterResources Investigations Report 92-4181, 3 sheets.

Demcheck, D.K., and Skrobialowski, S.C., 2003, 

Fipronil and degradation products in the rice-producing areas of the Mermentau River Basin, Louisiana, 

February-September 2000: U.S. Geological Survey 

Fact Sheet FS-010-03, 6 p.

DeWalt, R.E., 1997, Fish and macroinvertebrate taxonomic richness, habitat quality, and in-situ water 

chemistry of ecoregion reference streams in the Western Gulf Coastal Plains and Terrace Uplands Ecoregions of southern Louisiana: Prepared for Louisiana 

Department of Environmental Quality, 72 p.

Dodds, W.K., Jones, J.R., and Welch, E.B., 1998, Suggested classification of stream trophic state—distributions of temperate stream types by chlorophyll, total 

nitrogen, and phosphorus: Water Research, v. 32, no. 

5, p. 1455-1462.

Engelman, Laszlo, 1998, Discriminant analysis, in

SYSTAT 8.0 Statistics, Wilkinson, Leland (ed.): 

Chicago, SPSS Inc., p. 245-296.

Fishman, M.J., and Friedman, L.C., 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.

Fitzpatrick, F.A., Waite, I.R., D’Arconte, P.J., Meador, 

M.R., Maupin, M.A., and Gurtz, M.E., 1998, Revised 

methods for characterizing stream habitat in the 

National Water-Quality Assessment Program: U.S. 

Geological Survey Water-Resources Investigations 

Report 98-4052, 67 p.

Foreman, W.T., Connor, B.F., Furlong, E.T., Vaught, 

D.G., and Merten, L.M., 1995, Methods of analysis by 

the U.S. Geological Survey National Water Quality 

Laboratory—Determination of organochlorine pesticides and polychlorinated biphenyls in bottom sediment by dual capillary-column gas chromatography 

with electron-capture detection: U.S. Geological Survey Open-File Report 95-140, 78 p.

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, 

P.P., Coffey, L.J., and Burkhardt, M.R., 2001, Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory–Determination of 

pesticides in water by graphitized carbon-based solidphase extraction and high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey 

Water-Resources Investigations Report 01-4134, 73 p.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, 

Design of the National Water-Quality Assessment 

Program—occurrence and distribution of waterquality conditions: U.S. Geological Survey Circular 

1112, 33 p.

Goree, B.B., Lovelace, W.M., Montgomery, P.A., 

Resweber, J.C., Sasser, D.C., Jr., and Walters, D.J., 

2001, Water resources data—Louisiana, water year 

2000: U.S. Geological Survey Water-Data Report 

LA-00-1, 563 p.

Goree, B.B., Lovelace, W.M., Montgomery, P.A., 

Resweber, J.C., Sasser, D.C., Jr., and Walters, D.J., 

2002, Water resources data—Louisiana, water year 

2001: U.S. Geological Survey Water-Data Report 

LA-01-1, 638 p.

Goree, B.B., Lovelace, W.M., Montgomery, P.A., 

Resweber, J.C., and Walters, D.J., 2000, Water 

resources data—Louisiana, water year 1999: U.S. 

Geological Survey Water-Data Report LA-99-1, 

635 p.

Hach Company, 1999, Model 2100N laboratory turbidimeter instruction manual: Loveland, Colo., Hach 

Company, 79 p.

Hayes, T.B., Collins Atif, Lee, Melissa, Mendoza, 

Magdelena, Noriega, Nigel, Stuart, A.A., and Vonk, 

Aaron, 2002, Hermaphroditic, demasculinized frogs 

after exposure to the herbicide atrazine at low ecologically relevant doses: Proceedings of the National 

Academy of Sciences, v. 99, no. 8, p. 5476-5480.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods 

in water resources: New York, Elsevier Science 

Publishers, 522 p.

Hem, J.D., 1992, Study and interpretation of chemical 

characteristics of natural water (3d ed.): U.S. Geological Survey Water-Supply Paper 2254, p. 263.

Hynes, H.B.N., 2001, The ecology of running waters: 

Caldwell, N.J., The Blackburn Press, 555 p.
46

Jongman, R.H.G., ter Braak, C.J.F., and van Tongeren, 

O.F.R., 1995, Data analysis in community and landscape ecology: Cambridge, U.K., Cambridge University Press, 299 p.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, 

Ground-water data-collection protocols and procedures for the National Water-Quality Assessment Program—Collection and documentation of waterquality samples and related data: U.S. Geological Survey Open-File Report 95-399, accessed September 13, 

2002, at URL http://water.usgs.gov/nawqa/OFR95-

399.html

Leahy, P.P., Rosenshein, J.S., and Knopman, D.S., 1990, 

Implementation plan for the National Water-Quality 

Assessment Program: U.S. Geological Survey OpenFile Report 90-174, 10 p.

Linscombe, S.D., Saichuk, J.K., Seiban, K.P., Bollich, 

P.K., and Funderburg, E.R., 1999, General agronomic 

guidelines, in Louisiana Cooperative Extension Service, Louisiana rice production handbook: Baton 

Rouge, La., Louisiana State University Agricultural 

Center, Pub. 2321, p. 5-12.

Louisiana Cooperative Extension Service, 1998, Louisiana summary—Agriculture and natural resources: 

Baton Rouge, La., Louisiana State University Agricultural Center, Pub. 2382, 318 p.

Louisiana Cooperative Extension Service, 2000, Louisiana summary—Agriculture and natural resources: 

Baton Rouge, La., Louisiana State University Agricultural Center, Pub. 2382, 322 p.

Louisiana Department of Environmental Quality, 2003, 

Title 33 Environmental Regulatory Code, Part IX: 

accessed April 14, 2003, at URL 

http://www.deq.state.la.us/planning/regs/title33/

33v09.pdf

Louisiana State University Agricultural Center, 2001, 

Louisiana recommendations for control of insects on 

rice: accessed August 14, 2002, at URL 

http://www.agctr.lsu.edu/Subjects/guides/pests/pdfs/

RICE-2001.pdf

Louisiana State University Agricultural Center, 2002, 

Louisiana recommendations for control of household 

insects by homeowners: accessed August 14, 2002, at 

URL http://www.agctr.lsu.edu/Subjects/guides/pests/

pdfs/RICE-2001.pdf

Lovelace, J.K., 1999, Distribution of saltwater in the 

Chicot aquifer system of southwestern Louisiana, 

1995-96: Louisiana Department of Transportation 

and Development Water Resources Technical Report 

no. 66, 61 p.

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, 

Methods of analysis by the U.S. Geological Survey 

National Water Quality Laboratory—A method 

supplement for the determination of fipronil and 

degradates in water by gas chromatography/mass 

spectrometry: U.S. Geological Survey Open-File 

Report 02-462, 11 p.

Meador, M.R., and Gurtz, M.E., 1994, Biology as an 

integrated component of the U.S. Geological Survey’s 

National Water-Quality Assessment Program: U.S. 

Geological Survey Open-File Report 94-83, 4 p.

Moulton, S.R., II, Carter, J.L., Grotheer, S.A., Cuffney, 

T.F., and Short, T.M., 2000, Methods of analysis by 

the U.S. Geological Survey National Water Quality 

Laboratory—Processing, taxonomy, and quality 

control of benthic macroinvertebrate samples: U.S. 

Geological Survey Open-File Report 00-212, 49 p.

Moulton, S.R., II, Kennen, J.G., Goldstein, R.M., and 

Hambrook, J.A., 2002, Revised protocols for 

sampling algal, invertebrate, and fish communities in 

the National Water-Quality Assessment Program: 

U.S. Geological Survey Open-File Report 02-150, 

75 p.

Mueller, D.K., Martin J.D., and Lopes, T.J., 1997, 

Quality-control design for surface-water sampling in 

the National Water-Quality Assessment Program: 

U.S. Geological Survey Open-File Report 97-223, 

17 p.

National Transportation Safety Board, 2002, Railroad 

Accident Report—Derailment of Union Pacific 

Railroad train QFPLI-26 at Eunice, Louisiana, May 

27, 2000: Washington, D.C., National Transportation 

Safety Board, PB2002-916303, 39 p.

Omernik, J.M., 1987, Ecoregions of the conterminous 

United States on a scale of 1:7,500,000: Annuals of 

the Association of American Geographers, v. 77, 

p. 118-125.

Oregon State University, 1996, Tebuthiuron: Extension 

Toxicology Network, Pesticide information profiles: 

accessed on August 16, 2002, at URL 

http://ace.ace.orst.edu/info/extoxnet/pips/

tebuthiu.htm

Ottea, Jim, and Romaire, Robert, 2001, Effects of size 

and temperature on the acute toxicity of fipronil 

(Icon) to red swamp crawfish, Procambarus clarkii: 

accessed on April 15, 2003, at URL 

http://www.lsuagcenter.com/Subjects/icon/pdfs/

IconToxicityTestforWeb_final_1.pdf
47

Sandstrom, M.W., 1995, Filtration of water-sediment 

samples for the determination of organic compounds: 

U.S. Geological Survey Water-Resources Investigations Report 95-4105, 13 p.

Sandstrom, M.W., Wydoski, D.S., Schroeder, M.P., 

Zamboni, J.L., and Foreman, W.T., 1992, Methods of 

analysis by the U.S. Geological Survey National 

Water Quality Laboratory—Determination of 

organonitrogen herbicides in water by solid-phase 

extraction and capillary-column gas 

chromatography/mass spectrometry with selected-ion 

monitoring: U.S. Geological Survey Open-File 

Report 91-519, 26 p.

Shelton, L.R., 1994, Field guide for collecting and 

processing stream-water samples for the National 

Water-Quality Assessment Program: U.S. Geological 

Survey Open-File Report 94-0455, 42 p.

Shelton, L.R., and Capel, P.D., 1994, Guidelines for 

collecting and processing samples of streambed 

sediment for the analysis of trace elements and organic 

contaminants for the National Water-Quality 

Assessment Program: U.S. Geological Survey OpenFile Report 94-458, 20 p.

Sloss, Raymond, 1971, Drainage area of Louisiana 

streams: Louisiana Department of Public Works 

Basic Records Report no. 6, 117 p.

Spearing, Darwin, 1995, Roadside geology of Louisiana: 

Missoula, Mont., Mountain Press, 225 p.

ter Braak, C.J.F., and Smilauer, Petr, 1998, CANOCO 

reference manual and user’s guide to Canoco for Windows—Software for canonical community ordination 

(version 4.0): New York, Microcomputer Power, 

352 p.

Tollett, R.W., and Fendick, R.B., Jr, 2004, Quality of 

water from shallow wells in the rice-growing area in 

southwestern Louisiana, 1999 through 2001: U.S. 

Geological Survey Water-Resources Investigations 

Report 03-4050, 44 p.

Tollett, R.W., Fendick, R.B., Jr., and Simmons, L.B., 

2003, Quality of water in domestic wells in the Chicot 

and Chicot equivalent aquifer systems, southern Louisiana and southwestern Mississippi, 2000-2001: U.S. 

Geological Survey Water-Resources Investigations 

Report 03-4122, 85 p.

Touchet, A.B., Clark, H.L., Redlich, C.M., Roy, A.J., 

Griffis, B.J., Zaunbrecher, S.J., and Hollier, R.M., 

1974, Soil survey of Evangeline Parish, Louisiana: 

U.S. Department of Agriculture, Soil Conservation 

Service in cooperation with the Louisiana Agricultural 

Experiment Station, 68 p. (also includes 56 map sheets 

and 2 index maps, various scales)

U.S. Environmental Protection Agency, 1996, New pesticide Fact Sheet: Washington, D.C., U.S. Environmental Protection Agency, Office of Prevention, 

Pesticides and Toxic Substances, EPA 737-F-96-005, 

10 p.

U.S. Environmental Protection Agency, 2000a, Drinking 

water standards and health advisories: Washington, 

D.C., U.S. Environmental Protection Agency, Office 

of Water, EPA 822-B-00-001, variously paginated.

U.S. Environmental Protection Agency, 2000b, 

Malathion summary, Office of Pesticide Programs: 

accessed August 14, 2002, at URL 

http://www.epa.gov/pesticides/op/malathion/

summary.htm

U.S. Environmental Protection Agency, 2002a, National 

recommended water quality criteria—2002: 

Washington, D.C., U.S. Environmental Protection 

Agency, Office of Science and Technology, Office of 

Water (4304T) EPA 822-R-02-047, 33 p.

U.S. Environmental Protection Agency, 2002b, Total 

maximum daily load for the pesticide fipronil in the 

Mermentau River Basin: accessed October 16, 2002, 

at URL http://www.epa.gov/region6/water/ecopro/

latmdl/fipronil_merm(f).pdf

U.S. Environmental Protection Agency, 2002c, Total 

maximum daily loads: accessed December 13, 2002, 

at URL 

http://oaspub.epa.gov/waters/waters_list.tmdls?state=

LA

U.S. Geological Survey, 1997 to present, National field 

manual for the collection of water-quality data: U.S. 

Geological Survey Techniques of Water-Resources 

Investigations, book 9, chaps. A1-A9, 2 v., variously 

paged. [Also available online at 

http://pubs.water.usgs.gov/twri9A . Chapters 

originally were published from 1997-1999; updates 

and revisions are ongoing and are summarized at: 

http://water.usgs.gov/owq/FieldManual/mastererrata.

html ]

Wetzel, R.G., and Likens, G.E., 1991, Limnological 

analyses (2d ed.): New York, Springer-Verlag 

Publishing, p. 21.

Wilkinson, Leland, 1998, Nonparametric statistics, in

SYSTAT 8.0 Statistics, Wilkinson, Leland (ed.): Chicago, SPSS Inc., p. 693-714.

Wilkinson, Leland, and Coward, Mark, 1998, Linear 

models II—Analysis of variance, in SYSTAT 8.0 

Statistics, Wilkinson, Leland (ed.): Chicago, SPSS 

Inc., p. 401-456.
48

Wilkinson, Leland, Engelman, Laszlo, Corter, James, 

and Coward, Mark, 1998, Cluster analysis, in

SYSTAT 8.0 Statistics, Wilkinson, Leland (ed.): 

Chicago, SPSS Inc., p. 53-86.

Wilkinson, Leland, Engelman, Laszlo, and Marcantonio, 

Rick, 1998, Correlations, similarities, and distance 

measures, in SYSTAT 8.0 Statistics, Wilkinson, 

Leland (ed.): Chicago, SPSS Inc., p. 115-148.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, K.M., 1995, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory--Determination of pesticides in water by C-18 

solid-phase extraction and capillary-column gas chromatography/mass spectrometry with selected-ion 

monitoring: U.S. Geological Survey Open-File Report 

95-181, 60 p.
49

APPENDIXES

1. Complete names for surface-water and ecological data-collection sites in the Mermentau River Basin and 

adjacent Calcasieu River Basin in southwestern Louisiana, 1998-2001

2. Pesticides and degradation products analyzed, use, and occurrence in ground- and surface-water samples 

from the Mermentau River Basin, southwestern Louisiana, 1998-2001

3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, southwestern Louisiana, 1999-2001

4. Selected physiochemical properties and fipronil concentrations for ecological data-collection sites in 

southwestern Louisiana, 2001 

5. Mean quantitative habitat variables from ecological data-collection sites in southwestern Louisiana, 2001 

6. Classification ranking of U.S. Environmental Protection Agency's Rapid Bioassessment Protocols habitat variables for ecological data-collection sites in southwestern Louisiana, 2001

7. Habitat assessment results using U.S. Environmental Protection Agency's Rapid Bioassessment Protocols for ecological data-collection sites in southwestern Louisiana, 2001

8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001

9. Loadings of environmental variables on the first two principal components (PC) derived from principal 

components analysis (PCA) of ecological data-collection sites in southwestern Louisiana, 2001
50

1

 Shown in figure 3.

Appendix 1. Complete names for surface-water and ecological data-collection sites in the Mermentau River Basin 

and adjacent Calcasieu River Basin in southwestern Louisiana, 1998-2001

Site

number

(fig. 2)

Abbreviated site 

name Complete site name

U.S. Geological 

Survey station 

number 

Mermentau River Basin 

1 Des Cannes Bayou des Cannes near Eunice 08010000

2 Wikoff Bayou Wikoff near Rayne 08010500

3 Plaquemine Bayou Plaquemine Brule at Estherwood 08011020

4 Boggy Boggy Bayou at State Hwy. 106 near Pine Prairie 08011500

5 Castor Castor Creek at Cottongin Castor Road near Oberlin 08011800

6 Nezpique Bayou Nezpique at State Hwy. 376 north of Basile 08011860

7 Mermentau Mermentau River at Mermentau 08012150

8 Riceville Bayou Queue de Tortue at Riceville 08012300

9 Lake Arthur Mermentau River at Lake Arthur 08012400

10 Chene Bayou Chene at State Hwy. 382 near Welsh 08012447

11 Lacassine Bayou Lacassine near Lake Arthur 08012470

12 Tortue Bayou Queue de Tortue at State Hwy. 13 near Lelieux 300446092214200

13 Grand Marais Bayou Grand Marais at State Hwy. 699 near Kaplan 300514092173500

14 Theriot Bayou Queue de Tortue at Theriot Road near Rayne 301154092145900

15 East Lacassine East Bayou Lacassine at State Hwy. 99 north of Welsh 301520092491800

16 Roanoke West Bayou Grand Marais at Aaron Road near Roanoke 301538092421900

17 Iota Bayou des Cannes at State Hwy. 98 west of Iota 301959092323400

18 Panchoville Bayou Nezpique near Panchoville 302128092373800

19 Church Point Bayou Plaquemine Brule at State Hwy. 370 near Church Point 302403092152300

20 Mallet Bayou Mallet at State Hwy. 367 near Eunice 302749092203500

21 Guidry Bayou Nezpique at Guidry Road north of Basile 303206092360000

22 Blue Bayou Blue at State Hwy. 26 near Elton 303209092401800

23 Upper Des Cannes Bayou des Cannes at State Hwy. 104 near Ville Platte 303755092190400

24 Caney Caney Creek at Bond Road near Oakdale 304130092344100

Calcasieu River Basin (additional site)

125 Whisky Whisky Chitto Creek near Oberlin 08014500
51

Appendix 2. Pesticides and degradation products analyzed, use, and occurrence in ground- and surface-water samples 

from the Mermentau River Basin, southwestern Louisiana, 1998-2001—Continued

Pesticide or degradation product Use

Ground water Surface water

Number of 

samples 

collected

Samples with 

detected 

concentrations

(percent)

Number of 

samples 

collected

Samples with 

detected 

concentrations

(percent)

2,4-D H 29 3 36 77.8

2,4-D methyl ester H 29 0 36 27.8

2,4-DB H 29 0 36 .0

2,6-Diethylaniline H, DP 29 0 242 .0

2-Hydroxyatrazine H, DP 29 3 36 83.3

3(4-Chlorophenyl)-1-methyl urea H, DP 29 3 36 .0

3-Hydroxycarbofuran I, DP 29 0 36 .0

3-Ketocarbofuran I, DP 29 0 36 .0

Acetochlor H 29 0 242 .4

Acifluorfen H 29 0 36 .0

Alachlor H 29 3 242 10.7

Aldicarb I 29 0 36 .0

Aldicarb sulfone I, DP 29 0 36 .0

Aldicarb sulfoxide I, DP 29 0 36 .0

alpha-HCH I 29 0 242 .0

Atrazine H 29 3 242 99.6

Bendiocarb I 29 0 36 .0

Benfluralin H 29 0 242 .0

Benomyl F 29 0 36 36.1

Bensulfuron-methyl H 29 0 36 47.2

Bentazon H 29 10 36 75.0

Bromacil H 29 0 36 22.2

Bromoxynil H 29 0 36 .0

Butylate H 29 0 242 .0

Carbaryl I 29 0 241 26.1

Carbofuran I 29 0 242 25.2

Chloramben, methyl ester H 29 0 36 .0

Chlorimuron-ethyl H 29 3 36 2.8

Chlorothalonil H 29 0 36 .0

Chlorpyrifos I 29 3 242 5.8

Clopyralid H 29 0 36 .0

Cyanazine H 29 0 242 .8

Cycloate H 29 0 36 .0

Dacthal (DCPA) H 29 0 242 .4

Dacthal monoacid H, DP 29 0 36 .0

Deethylatrazine H, DP 29 3 242 90.1

Deethyldeisopropylatrazine H, DP 29 7 36 13.9

Deisopropylatrazine H, DP 29 0 36 22.2

Desulfinylfipronil I, DP 29 0 186 89.2

Diazinon I 29 0 242 39.3

Dicamba H 29 0 36 .0

Appendix 2. Pesticides and degradation products analyzed, use, and occurrence in ground- and surface-water samples 

from the Mermentau River Basin, southwestern Louisiana, 1998-2001

[H, herbicide; DP, degredation product; I, insecticide; F, fungicide; Pesticides in bold italics were analyzed before analytical method approval, and 

data in this report are provisional.]
52

Dichlorprop H 29 0 36 0.0

Dieldrin I 29 0 242 .8

Dinoseb H 29 0 36 2.8

Diphenamid H 29 0 36 33.3

Disulfoton I 29 0 242 .0

Diuron H 29 3 36 91.7

EPTC H 29 0 242 11.6

Ethalfluralin H 29 0 242 .0

Ethoprophos I 29 0 242 5.4

Fenuron H 29 0 36 .0

Fipronil I 29 0 192 72.4

Fipronil degradate RPA105048 I, DP 29 0 207 84.1

Fipronil Sulfone I, DP 29 0 207 87.4

Fipronil Sulfide I, DP 29 0 207 88.8

Flumetsulam H 29 3 36 .0

Fluometuron H 29 0 36 5.6

Fonofos I 29 0 242 .0

Imazaquin H 29 7 36 8.3

Imazethapyr H 29 0 36 .0

Imidacloprid I 29 0 36 .0

Lindane I 29 0 242 .0

Linuron H 29 0 242 .0

Malathion I 29 3 242 19.4

MCPA H 29 0 36 2.8

MCPB H 29 0 36 .0

Metalaxyl F 29 3 36 38.9

Methiocarb I 29 0 36 .0

Methomyl I 29 0 36 .0

Methomyl oxime I, DP 29 0 36 .0

Methyl-Azinphos I 29 0 242 .0

Methyl-Parathion I 29 0 242 1.2

Metolachlor H 29 7 242 92.6

Metribuzin H 29 3 242 33.1

Metsulfuron methyl H 29 0 36 .0

Molinate H 29 0 242 86.4

Napropamide H 29 0 242 2.1

Neburon H 29 0 36 .0

Nicosulfuron H 29 0 36 .0

Norflurazon H 29 0 36 .0

Oryzalin H 29 0 36 .0

Oxamyl I, DP 29 0 36 .0

Appendix 2. Pesticides and degradation products analyzed, use, and occurrence in ground- and surface-water samples 

from the Mermentau River Basin, southwestern Louisiana, 1998-2001—Continued

Pesticide or degradation product Use

Ground water Surface water

Number of 

samples 

collected

Samples with 

detected 

concentrations

(percent)

Number of 

samples 

collected

Samples with 

detected 

concentrations

(percent)
53

Oxamyl oxime I, DP 29 0 36 0.0

p,p'-DDE I, DP 29 0 242 .4

Parathion I 29 0 242 .0

Pebulate H 29 0 242 .0

Pendimethalin H 29 0 242 4.1

Permethrin-cis I 29 0 242 .0

Phorate I 29 0 242 .0

Picloram H 29 3 36 .0

Prometon H 29 0 242 44.2

Propachlor H 29 0 242 1.2

Propanil H 29 0 242 10.3

Propargite I 29 0 241 .0

Propham H 29 0 36 .0

Propiconazole F 29 0 36 25.0

Propoxur I 29 0 36 2.8

Propyzamide H 29 0 242 .0

Siduron H 29 0 36 2.8

Simazine H 29 0 239 32.6

Sulfometuron-methyl H 29 0 36 30.6

Tebuthiuron H 29 7 242 95.0

Terbacil H 29 0 36 .0

Terbufos I 29 0 242 .0

Thiobencarb H 29 0 242 18.2

Tri-allate H 29 0 242 .0

Tribenuron-methyl H 29 0 36 .0

Triclopyr H 29 0 36 52.8

Trifluralin H 29 0 242 4.1

Appendix 2. Pesticides and degradation products analyzed, use, and occurrence in ground- and surface-water samples 

from the Mermentau River Basin, southwestern Louisiana, 1998-2001—Continued

Pesticide or degradation product Use

Ground water Surface water

Number of 

samples 

collected

Samples with 

detected 

concentrations

(percent)

Number of 

samples 

collected

Samples with 

detected 

concentrations

(percent)
54

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001

USGS station 

number

Abbreviated site 

name1 Date

Degradation product

Fipronil

Desulfinylfipronil

Fipronil 

degradate RPA 

105048

Fipronil 

sulfide

Fipronil 

sulfone

08010000 Des Cannes 03/10/1999 <0.010 <0.005 <0.010 <0.001 <0.004

08010000 Des Cannes 03/24/1999 .519 E.005 .043 .11 3.01

08010000 Des Cannes 04/07/1999 .889 .017 .124 .203 2.81

08010000 Des Cannes 04/20/1999 1.26 .046 .278 .302 3.22

08010000 Des Cannes 05/13/1999 .331 .039 .14 .087 .37

08010000 Des Cannes 05/26/1999 .341 .033 .226 .101 .198

08010000 Des Cannes 06/09/1999 .189 .025 .152 .067 .11

08010000 Des Cannes 06/24/1999 .186 .022 .119 .058 .233

08010000 Des Cannes 02/22/2000 NA .013 NA .014 <.005

08010000 Des Cannes 03/09/2000 NA .014 NA .012 <.044

08010000 Des Cannes 04/05/2000 .166 .015 .045 .05 .799

08010000 Des Cannes 04/18/2000 .593 .031 .124 .163 2.69

08010000 Des Cannes 05/10/2000 .102 .015 .076 .039 .088

08010000 Des Cannes 06/21/2000 .046 .015 .058 .03 .014

08010000 Des Cannes 06/27/2000 .061 .016 .081 .04 .016

08010000 Des Cannes 07/19/2000 <.010 <.005 <.010 <.001 <.004

08010000 Des Cannes 08/23/2000 .054 .013 .064 .037 .013

08010000 Des Cannes 11/14/2000 .011 .011 .012 .007 E.004

08010000 Des Cannes 12/14/2000 E.008 .009 .011 .007 <.004

08010000 Des Cannes 01/18/2001 E.005 .008 E.008 .006 <.004

08010000 Des Cannes 02/15/2001 E.009 .008 .013 .007 <.004

08010000 Des Cannes 03/28/2001 .336 .007 .029 .067 1.46

08010000 Des Cannes 04/16/2001 .607 .024 .163 .223 3.96

08010000 Des Cannes 05/16/2001 0.419 0.062 0.169 0.103 0.455

08010000 Des Cannes 06/11/2001 .027 .009 .024 .013 .031

08010500 Wikoff 02/23/2000 NA E.024 NA .004 <.004

08010500 Wikoff 03/21/2000 .091 E.004 .026 .018 .106

08010500 Wikoff 04/19/2000 .482 .017 .044 .09 1.07

08010500 Wikoff 06/01/2000 .038 .011 .027 .015 .008

08010500 Wikoff 06/27/2000 E.009 <.005 .012 .006 <.004

08010500 Wikoff 03/14/2001 <.010 <.005 <.010 <.001 <.004

08010500 Wikoff 04/24/2001 .041 .011 .02 .017 .03

08010500 Wikoff 05/24/2001 E.006 <.005 E.006 0.003 E.003

08011020 Plaquemine 02/23/2000 NA .013 NA .013 <.004

08011020 Plaquemine 04/20/2000 .541 .028 .105 .144 2.47

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001

[Concentrations in micrograms per liter; <, less than; NA, not analyzed; E, estimated]
55

08011020 Plaquemine 06/01/2000 0.157 0.017 0.129 0.062 0.243

08011020 Plaquemine 06/28/2000 .049 .013 .066 .034 .019

08011020 Plaquemine 03/13/2001 E.003 E.002 E.005 .003 <.004

08011020 Plaquemine 04/24/2001 .382 .013 .081 .11 1.89

08011020 Plaquemine 05/21/2001 .131 .014 .077 .042 .293

08011500 Boggy 03/20/2001 <.010 <.005 E.001 <.001 <.004

08011500 Boggy 04/26/2001 E.002 <.005 E.002 <.001 E.004

08011500 Boggy 05/23/2001 E.002 <.005 E.002 <.001 <.004

08011800 Castor 03/20/2001 E.002 E.002 E.006 .002 <.004

08011800 Castor 04/26/2001 .297 .011 .364 .151 2.76

08011800 Castor 05/22/2001 .175 .024 .433 .101 .704

08011860 Nezpique 02/22/2000 NA .01 NA .006 <.004

08011860 Nezpique 03/21/2000 .151 .011 .053 .065 1.29

08011860 Nezpique 04/18/2000 .158 .017 .109 .052 .593

08011860 Nezpique 05/30/2000 .063 <.005 .148 .03 .028

08011860 Nezpique 06/2//2000 .036 .011 .087 .022 .009

08011860 Nezpique 03/27/2001 0.146 E0.004 0.021 0.034 1.48

08011860 Nezpique 04/25/2001 .109 .006 .086 .047 .351

08011860 Nezpique 05/23/2001 .085 .014 .13 .034 .203

08012150 Mermentau 03/09/1999 <.010 <.005 <.010 <.001 <.004

08012150 Mermentau 03/23/1999 E.004 <.005 <.010 <.001 .059

08012150 Mermentau 04/08/1999 .285 E.005 .046 .104 2.22

08012150 Mermentau 04/21/1999 .504 .013 .14 .189 2.7

08012150 Mermentau 05/14/1999 .968 .036 .308 .267 2.36

08012150 Mermentau 05/26/1999 .522 .027 .226 .196 1.66

08012150 Mermentau 06/08/1999 .228 .03 .226 .117 .51

08012150 Mermentau 06/23/1999 .096 .019 .143 .048 .085

08012150 Mermentau 01/11/2000 NA .017 NA .012 .006

08012150 Mermentau 02/23/2000 NA .011 NA .015 .006

08012150 Mermentau 03/08/2000 NA .013 NA .013 <.004

08012150 Mermentau 03/23/2000 .037 .011 .03 .018 .193

08012150 Mermentau 04/04/2000 .51 .018 .103 .163 3

08012150 Mermentau 04/19/2000 .207 .017 .071 .064 1.02

08012150 Mermentau 05/09/2000 .068 .014 .059 .038 .188

08012150 Mermentau 05/31/2000 .101 .017 .083 .044 .188

08012150 Mermentau 06/20/2000 .109 .017 .122 .052 .109

08012150 Mermentau 06/28/2000 .086 .022 .115 .052 .059

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001—Continued

USGS station 

number

Abbreviated site 

name1 Date

Degradation product

Fipronil

Desulfinylfipronil

Fipronil 

degradate RPA 

105048

Fipronil 

sulfide

Fipronil 

sulfone
56

08012150 Mermentau 07/18/2000 0.04 0.015 0.074 0.035 0.016

08012150 Mermentau 08/22/2000 .039 .009 .062 .031 .017

08012150 Mermentau 09/28/2000 .036 .007 .055 .03 .014

08012150 Mermentau 11/14/2000 E.009 .011 .013 .01 .004

08012150 Mermentau 12/13/2000 E.008 .011 .015 .009 <.004

08012150 Mermentau 01/17/2001 E.006 .01 .011 .009 .006

08012150 Mermentau 02/13/2001 E.005 .007 .011 .006 <.004

08012150 Mermentau 03/29/2001 0.092 E0.004 0.016 0.03 0.82

08012150 Mermentau 04/17/2001 .119 .006 .041 .054 1.08

08012150 Mermentau 05/17/2001 .32 .029 .165 .127 1.37

08012150 Mermentau 06/12/2001 .018 .007 .027 .014 .044

08012300 Riceville 02/24/2000 NA .018 NA .01 <.004

08012300 Riceville 03/23/2000 .305 .016 .037 .064 1.64

08012300 Riceville 04/20/2000 .534 .031 .167 .194 3.23

08012300 Riceville 06/01/2000 .158 .027 .14 .063 .282

08012300 Riceville 06/29/2000 .052 .017 .084 .039 .016

08012400 Lake Arthur 02/24/2000 NA .009 NA .015 <.004

08012400 Lake Arthur 03/23/2000 .034 .01 .028 .016 .09

08012400 Lake Arthur 04/20/2000 .195 .016 .064 .06 .915

08012400 Lake Arthur 06/01/2000 .112 .018 .08 .046 .161

08012400 Lake Arthur 06/29/2000 .1 .018 .113 .053 .077

08012447 Chene 02/24/2000 NA .02 NA .012 <.004

08012447 Chene 03/23/2000 .09 .013 .045 .067 1.44

08012447 Chene 04/20/2000 .284 .022 .122 .012 2.6

08012447 Chene 05/31/2000 .092 .027 .107 .043 .086

08012447 Chene 06/28/2000 .115 .032 .169 .058 .047

08012470 Lacassine 03/09/1999 <.010 <.005 <.010 <.001 <.004

08012470 Lacassine 03/24/1999 E.008 <.005 <.010 .003 .149

08012470 Lacassine 04/08/1999 .229 E.004 .038 .076 2.35

08012470 Lacassine 04/21/1999 .206 E.003 .054 .07 1.66

08012470 Lacassine 05/13/1999 .138 .007 .063 .043 .465

08012470 Lacassine 05/26/1999 .141 .006 .056 .047 .457

08012470 Lacassine 06/08/1999 .12 .005 .047 .036 .253

08012470 Lacassine 06/24/1999 .139 .012 .108 .051 .256

08012470 Lacassine 02/24/2000 NA .01 NA .01 <.004

08012470 Lacassine 03/08/2000 NA 0.006 NA 0.009 <0.004

08012470 Lacassine 03/23/2000 0.025 E.005 0.011 .008 <.004

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001—Continued

USGS station 

number

Abbreviated site 

name1 Date

Degradation product

Fipronil

Desulfinylfipronil

Fipronil 

degradate RPA 

105048

Fipronil 

sulfide

Fipronil 

sulfone
57

08012470 Lacassine 04/04/2000 0.226 0.01 0.077 0.081 1.94

08012470 Lacassine 04/20/2000 .219 .022 .08 .068 1.04

08012470 Lacassine 05/09/2000 .059 .015 .048 .029 .176

08012470 Lacassine 06/01/2000 .08 .019 .072 .033 .097

08012470 Lacassine 06/20/2000 .094 .014 .075 .033 .056

08012470 Lacassine 06/28/2000 .121 .015 .085 .042 .052

08012470 Lacassine 07/18/2000 .057 .022 .09 .039 .02

08012470 Lacassine 08/23/2000 .051 .012 .054 .03 .013

08012470 Lacassine 11/14/2000 .015 .012 .021 .012 .007

08012470 Lacassine 12/13/2000 E.009 .021 .013 .008 <.004

08012470 Lacassine 01/17/2001 E.006 .014 .01 .006 <.004

08012470 Lacassine 02/13/2001 E.006 .012 .011 .006 <.004

08012470 Lacassine 03/15/2001 E.008 .006 E.008 .005 .05

08012470 Lacassine 03/22/2001 .013 .007 E.007 .004 .048

08012470 Lacassine 03/29/2001 <.010 <.005 <.010 <.001 <.004

08012470 Lacassine 04/05/2001 .028 .006 .016 .013 .35

08012470 Lacassine 04/13/2001 .044 .007 .024 .018 .464

08012470 Lacassine 04/17/2001 .074 .008 .041 .034 .897

08012470 Lacassine 042/7/2001 .068 .009 .06 .029 .545

08012470 Lacassine 05/17/2001 .085 .017 .078 .037 .46

08012470 Lacassine 06/12/2001 .018 .009 .03 .013 .04

08014500 Whisky 04/05/2000 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 06/21/2000 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 08/23/2000 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 09/29/2000 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 11/14/2000 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 12/14/2000 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 01/17/2001 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 02/13/2001 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 03/28/2001 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 04/17/2001 <.010 <.005 <.010 <.001 <.004

08014500 Whisky 06/12/2001 <.010 <.005 <.010 <.001 <.004

300446092214200 Tortue 02/25/2000 NA .019 NA .009 <.004

300446092214200 Tortue 03/24/2000 .47 .007 .069 .16 4.07

300446092214200 Tortue 06/01/2000 .236 .026 .184 .11 .807

300446092214200 Tortue 06/28/2000 .03 .007 .062 .024 .007

300446092214200 Tortue 03/13/2001 E.003 E.002 E.005 .003 <.004

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001—Continued

USGS station 

number

Abbreviated site 

name1 Date

Degradation product

Fipronil

Desulfinylfipronil

Fipronil 

degradate RPA 

105048

Fipronil 

sulfide

Fipronil 

sulfone
58

300446092214200 Tortue 04/23/2001 0.32 0.013 0.123 0.119 1.86

300446092214200 Tortue 05/21/2001 .122 .007 .07 .039 .432

300514092173500 Grand Marais 03/23/2001 .059 E.003 E.006 .011 .324

300514092173500 Grand Marais 04/23/2001 .085 .014 .017 .018 .156

300514092173500 Grand Marais 05/21/2001 .037 .006 .016 .006 .006

301154092145900 Theriot 03/16/2001 E.002 <.005 E.003 <.001 <.004

301154092145900 Theriot 04/23/2001 .145 .014 .087 .052 .287

301154092145900 Theriot 05/21/2001 .048 .007 .044 .018 .035

301520092491800 East Lacassine 02/24/2000 NA .048 NA .019 <.004

301520092491800 East Lacassine 03/23/2000 .2 E.003 .046 .132 E5.29

301520092491800 East Lacassine 04/19/2000 .4 .014 .171 .205 4.54

301520092491800 East Lacassine 05/31/2000 .082 .019 .163 .079 .09

301520092491800 East Lacassine 06/28/2000 .041 .012 .1 .046 .024

301520092491800 East Lacassine 03/14/2001 E.004 .006 E.008 .005 <.004

301520092491800 East Lacassine 04/24/2001 E.009 .01 .012 .01 .027

301520092491800 East Lacassine 05/22/2001 .139 .024 .131 .115 .176

301538092421900 Roanoke 02/23/2000 NA .021 NA .017 .007

301538092421900 Roanoke 03/22/2000 .12 .007 .043 .066 1.28

301538092421900 Roanoke 04/19/2000 .425 .021 .128 .202 E5.19

301538092421900 Roanoke 05/31/2000 .066 .016 .145 .057 .047

301538092421900 Roanoke 06/28/2000 .033 .01 .097 .037 .017

301959092323400 Iota 02/23/2000 NA .008 NA .013 .005

301959092323400 Iota 03/22/2000 .416 .017 .071 .116 2.69

301959092323400 Iota 04/19/2000 .413 .02 .137 .126 2.26

301959092323400 Iota 05/31/2000 .171 .026 .214 .07 .104

302128092373800 Panchoville 02/23/2000 .052 .012 .042 .012 <.004

302128092373800 Panchoville 04/19/2000 .36 .021 .149 .143 3.24

302128092373800 Panchoville 05/31/2000 .079 .017 .172 .051 .083

302128092373800 Panchoville 06/28/2000 .071 .017 .186 .05 .03

302403092152300 ChurchPoint 02/22/2000 NA <.005 NA <.005 <.004

302403092152300 ChurchPoint 03/21/2000 1.13 .015 .034 .126 1.59

302403092152300 ChurchPoint 04/18/2000 .036 E.002 .018 .011 .128

302403092152300 ChurchPoint 05/30/2000 E.005 <.005 E.008 .004 <.004

302403092152300 ChurchPoint 06/27/2000 E.004 <.005 E.007 .004 <.004

302403092152300 ChurchPoint 03/22/2001 E.004 E.003 E.003 .003 .043

302403092152300 ChurchPoint 04/24/2001 E.004 E.009 E.006 .004 .005

302403092152300 ChurchPoint 05/24/2001 E.002 <.005 E.002 E.002 E.004

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001—Continued

USGS station 

number

Abbreviated site 

name1 Date

Degradation product

Fipronil

Desulfinylfipronil

Fipronil 

degradate RPA 

105048

Fipronil 

sulfide

Fipronil 

sulfone
59

1 Complete site name is listed in appendix 1.

302749092203500 Mallet 02/22/2000 NA E0.005 NA 0.005 <0.004

302749092203500 Mallet 04/18/2000 0.13 .014 0.043 .044 .829

302749092203500 Mallet 05/30/2000 .282 .022 .043 .027 .298

302749092203500 Mallet 06/27/2000 .018 E.003 .022 .008 <.004

302749092203500 Mallet 04/18/2001 .143 .005 .064 .044 .442

302749092203500 Mallet 05/23/2001 .018 .005 .026 .007 .015

303206092360000 Guidry 02/22/2000 NA .008 NA .012 <.004

303206092360000 Guidry 03/21/2000 .651 .017 .067 .146 3.94

303206092360000 Guidry 04/18/2000 .242 .016 .109 .089 1.7

303206092360000 Guidry 05/30/2000 .082 .014 .127 .049 .297

303206092360000 Guidry 06/27/2000 .059 .016 .12 .037 .019

303206092360000 Guidry 03/27/2001 .106 .006 .021 .041 1.33

303206092360000 Guidry 04/25/2001 .225 .012 .129 .125 2.15

303206092360000 Guidry 05/22/2001 .132 .021 .153 .066 .258

303209092401800 Blue 03/21/2001 .141 .009 .024 .034 1.34

303209092401800 Blue 04/25/2001 .475 .025 .372 .282 E6.41

303209092401800 Blue 05/22/2001 .205 .026 .507 .123 1.09

303755092190400 Upper Des Cannes 03/21/2001 1.54 .021 .078 .196 3.85

303755092190400 Upper Des Cannes 04/26/2001 .536 .022 .133 .132 .879

303755092190400 Upper Des Cannes 05/23/2001 .243 .029 .188 .079 .185

304130092344100 Caney 03/19/2001 <.010 <.005 <.010 <.001 <.004

304130092344100 Caney 04/25/2001 E.001 <.005 E.001 <.001 .005

304130092344100 Caney 05/23/2001 <.010 <.005 <.010 <.001 <.004

Appendix 3. Concentrations of fipronil and degradation products in surface water, Mermentau River Basin, 

southwestern Louisiana, 1999-2001—Continued

USGS station 

number

Abbreviated site 

name1 Date

Degradation product

Fipronil

Desulfinylfipronil

Fipronil 

degradate RPA 

105048

Fipronil 

sulfide

Fipronil 

sulfone
60

1

 Complete site name is listed in appendix 1.

2 Maximum dissolved fipronil concentration of three water-quality samples collected between March and May 2001.

* Estimated value.

Appendix 4. Selected physiochemical properties and fipronil concentrations for ecological data-collection sites in southwestern Louisiana, 2001

[mg/L, milligram per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees Celsius, NTU, nephelometric turbidity units; μg/L, micrograms per liter]

Site 

number

(fig. 17)

Abbreviated site 

name1 USGS station number Date Time

Dissolved 

oxygen, field

(mg/L)

pH, field

(standard 

units)

Specific

conductance,

field

(μS/cm)

Temperature, 

field

(oC)

Turbidity,

laboratory

(NTU)

Maximum 

dissolved 

fipronil2

(μg/L)

1 Des Cannes 08010000 4/16/2001 1300 3.7 7.8 424 27.7 49 3.960

2 Wikoff 08010500 3/14/2001 1515 6.0 7.6 155 18.9 64 .030

3 Plaquemine 08011020 3/13/2001 1030 6.0 7.5 161 19.1 254 1.890

4 Boggy 08011500 3/20/2001 1000 7.3 6.4 36 13.1 8 <.004

5 Castor 08011800 3/20/2001 1530 7.0 6.4 49 13.6 26 2.760

6 Nezpique 08011860 3/27/2001 0930 7.6 7.3 117 13.2 434 1.480

7 Mermentau 08012150 3/29/2001 0700 6.2 7.3 162 12.8 514 1.370

11 Lacassine 08012470 3/15/2001 1045 3.6 6.8 126 17.3 198 .897

12 Tortue 300446092214200 3/13/2001 1730 5.0 7.5 175 19.9 349 1.860

13 Grand Marais 300514092173500 3/23/2001 0830 6.5 8.1 367 18.9 1,043 .324

14 Theriot 301154092145900 3/16/2001 1200 7.5 7.9 168 16.4 345 .287

15 East Lacassine 301520092491800 3/14/2001 1000 7.1 7.4 107 19.0 226 .176

19 Church Point 302403092152300 3/22/2001 1115 8.1 8.1 352 14.5 276 .043

20 Mallet 302749092203500 4/18/2001 0700 4.7 7.9 434 18.0 125 .442

21 Guidry 303206092360000 3/27/2001 1515 7.9 7.7 162 13.9 758 2.150

22 Blue 303209092401800 3/21/2001 1500 7.3 6.7 95 14.0 476 6.410*

23 Upper Des Cannes 303755092190400 3/21/2001 0930 7.0 7.5 250 13.5 650 3.850

24 Caney 304130092344100 3/19/2001 1230 5.9 6.5 44 12.8 16 .005

25 Whisky 08014500 4/17/2001 1530 9.6 7.2 55 21.4 15 <.004
61

Appendix 5. Mean quantitative habitat variables from ecological data-collection sites in southwestern Louisiana, 2001

[--, not available]

Site 

number 

(fig. 17)

Abbreviated

site name1 USGS station number Date Time

Drainage 

area,

square 

miles

Bank angle,2

degrees

Bank 

erosion 

score3

Bank 

height,2 

meter

Bank 

stability 

index2

Bank 

vegetative 

cover,2 

percent

Euphotic 

zone depth,4 

meter

1 Des Cannes 08010000 4/16/2001 1300 142 49.2 5 3.3 13 73.3 0.22

2 Wikoff 08010500 3/14/2001 1515 63 47 2 1.3 11.35 45 .47

3 Plaquemine 08011020 3/13/2001 1030 320 60 6 0.8 9.7 86.7 .20

4 Boggy 08011500 3/20/2001 1000 65 65.2 2 2.3 13 35 1.35

5 Castor 08011800 3/20/2001 1530 33 31.8 1 3.2 12.35 41.7 .61

6 Nezpique 08011860 3/27/2001 0930 166 42.2 3 3.1 12.65 55 .14

7 Mermentau 08012150 3/29/2001 0700 1,381 -- -- -- -- -- .13

11 Lacassine 08012470 3/15/2001 1045 296 -- -- -- -- -- .26

12 Tortue 300446092214200 3/13/2001 1730 97 73.3 6 1.2 10.7 66.7 .15

13 Grand Marais 300514092173500 3/23/2001 0830 26 38.2 2 2.3 11.35 66.7 .06

14 Theriot 301154092145900 3/16/2001 1200 37 49 5 1.3 12.2 25 .14

15 East Lacassine 301520092491800 3/14/2001 1000 15 52.7 2 0.6 9.7 85 .24

19 Church Point 302403092152300 3/22/2001 1115 74 48.8 5 4.4 14.15 75 .14

20 Mallet 302749092203500 4/18/2001 0700 91 54.5 4 1.6 12.15 35 .49

21 Guidry 303206092360000 3/27/2001 1515 381 41.8 6 3.9 14 38.3 .09

22 Blue 303209092401800 3/21/2001 1500 80 47.3 3 1.2 11.7 31.7 .13

23 Upper Des Cannes 303755092190400 3/21/2001 0930 46 60.3 2 1.7 11.35 76.7 .11

24 Caney 304130092344100 3/19/2001 1230 18 44.7 1 2.7 13.85 23.3 1.30

25 Whisky 08014500 4/17/2001 1530 504 51.8 5 3.7 16.85 41.7 2.28
62

1 Complete site name is listed in appendix 1. 2

 Habitat variables measured according to Fitzpatrick and others (1998). 3 Percent availability was ranked and scored for habitat variables measured according to Fitzpatrick and others (1998). 4

 Euphotic zone depth measured according to Moulton and others (2002). 5

 Secchi disk depth measured according to Wetzel and Likens (1991). 6 Width-to-depth ratio determined by dividing stream wetted width by the stream depth.

Appendix 5. Mean quantitative habitat variables from ecological data-collection sites in southwestern Louisiana, 2001—Continued

Site 

number 

(fig. 17)

Abbreviated site 

name1

Habitat 

cover,3 

percent

Open 

canopy,2 

percent

Riparian 

canopy 

closure,2 

percent

Secchi disk 

depth,5

meter

Stream 

bankfull 

channel 

width,2

meter

Stream 

depth,2

meter

Stream open 

angle,2

degrees

Stream 

velocity,2

square foot 

per second

Stream 

wetted 

channel 

width,2

meter

Width-to-depth 

ratio6

1 Des Cannes 27.8 25 69.6 0.03 22.6 0.95 45 0 16.2 17.1

2 Wikoff 33.3 8.7 90.2 .18 11.4 .75 15.7 .94 8.53 11.4

3 Plaquemine 44.4 68.3 74.5 .1 58.8 -- 123 -- 57 --

4 Boggy 38.9 7.6 84.3 .655 17.5 .88 13.7 .03 11.1 12.6

5 Castor 30.6 27.6 57.8 .325 21.6 .54 49.7 .29 7 13

6 Nezpique 30.6 19.4 85.3 .06 26.5 .97 35 .81 15.8 16.3

7 Mermentau 47.2 78.9 89.2 .04 113 9.72 142 -- 113 11.6

11 Lacassine 47.2 75.4 82.4 .09 112 4.74 136 -- 112 23.6

12 Tortue 38.9 56.1 81.4 .07 28.6 -- 101 -- 26.5 --

13 Grand Marais 38.9 41.5 33.3 .025 14.3 .54 74.7 .16 6.6 12.2

14 Theriot 30.6 25.2 58.8 .025 14.1 .8 45.3 1.17 5.59 6.99

15 East Lacassine 22.2 61.7 5.9 .1 6.9 .63 111 1.19 5.88 9.3

19 Church Point 30.6 50 5.9 .04 18.9 .45 90 .51 7.23 16.1

20 Mallet 33.3 6.9 92.2 .14 15.8 .52 12.3 .1 10.8 20.8

21 Guidry 30.6 27 81.4 .025 31.1 1.86 48.7 .21 20.4 11

22 Blue 41.7 3 84.3 .03 17.1 1.16 5.3 .63 12 10.3

23 Upper Des Cannes 41.7 27.6 79.4 .025 21.6 1.36 49.7 17.1 12.6

24 Caney 36.1 5.6 88.2 .575 14.3 .46 10 .18 5.47 11.9

25 Whisky 36.1 31.1 90.2 1.23 39.3 .88 56 .94 28.6 32.5
63

Appendix 6. Classification ranking of U.S. Environmental Protection Agency’s Rapid Bioassessment Protocols habitat variables for ecological data-collection sites 

in southwestern Louisiana, 2001

[>, greater than; <, less than; SAV, submerged aquatic vegetation]

* RBP = Rapid Bioassessment Protocols include a visual-based habitat assessment for low gradient streams, modified for use in this study (Barbour and others, 1999).

1

 RBP habitat rank was based on a score ranging from 0-20 for each habitat parameter with the exception of bank vegetation protection, bank stability, and riparian vegetative zone width, which were 

based on scores from 0-10 for the right streambank and scores from 0-10 for the left streambank. Numbers in parenthesis represent the range of scores within each category.

2 Instream cover was based on the percentage of mix of submerged logs, undercut banks, or other stable habitat at the site.

3

 Pool substrate characterization was based on the mixture of substrate materials, availability of root mats and submerged aquatic vegetation (SAV’s) at the site.

4

 Pool variability was based on the quality of pools (pool width compared to stream width and pool depth compared to stream depth) at the site.

5

 Sediment deposition was based on the percentage of stream bottom affected by recent sediment deposition (enlargement of islands or point bars) at the site.

6 Channel flow status was based on the percentage of available channel exposed at the site.

7

 Channel alteration was based on the percentage of disrupted stream bottom and streambanks due to dredging, channelization, or other disruptive stream activities at the site.

8

 Channel sinuosity was based on the amount of stream length increase due to bends in the stream compared to a straight line at the site.

9

 Bank stability was based on the evidence of streambank erosion or bank failure and potential for future problems at the site.

10 Bank vegetation protection was based on the percentage of vegetative cover on the streambank at the site.

11 Riparian vegetative zone width was the width of the riparian zone not affected by human activities at the site.

12 RBP site score range represents the sum of each habitat parameter score for a site; these ranges correspond to the RBP site habitat rating for the site.

13 RBP site habitat rating is the overall stream habitat rating for the site, based on the total score for the site; the score is based on the RBP site score range.

RBP*

Habitat

Category1

Habitat variables

Instream

cover2

(percent submerged 

habitat)

Pool substrate

characterization3

(substrate quality) 

Pool variability4

(pool quality)

Sediment

deposition5

(percent recent 

deposition)

Channel flow

status6

(percent available 

channel exposed)

Channel

alteration7

(percent 

channelized 

stream reach)

Optimal (16-20) >50 Mixed bottom, roots, SAV Mixed shallow and deep <5 Minimal Minimal

Suboptimal (11-15) 30-50 Mixed bottom, roots Large and deep 20-50 <25 <40

Marginal (6-10) 10-30 Mud bottom, little roots Small and deep 50-80 25-75 40-80

Poor (0-5) <10 Clay bottom, no roots Small and shallow >80 >75 >80

RBP*

Habitat

Category1

Habitat variables

Channel

sinuosity8

(stream bends 

increase length)

Bank

stability9

(erosion of 

streambanks)

Bank vegetation 

protection10

(percent vegetative 

cover)

Riparian

vegetative zone

width11

(meter) 

RBP*

site 

score range12

RBP*

site habitat

rating13

Optimal (16-20) 3-4 times Stable >90 >18 200-155 Optimal

Suboptimal (11-15) 2-3 times Moderately stable 70-90 12-18 154-102 Suboptimal

Marginal (6-10) 1-2 times Moderately unstable 50-70 6-12 101-49 Marginal

Poor (0-5) Straight Unstable <50 <6 48-0 Poor
64

Appendix 7. Habitat assessment results using U.S. Environmental Protection Agency’s Rapid Bioassessment Protocols for ecological data-collection sites in 

southwestern Louisiana, 2001

1

 Habitat variables descriptions are included in appendix 6.

2

 Complete site name is listed in appendix 1.

* RBP = Rapid Bioassessment Protocols include a visual-based habitat assessment for low gradient streams, modified for use in this study (Barbour and others, 1999).

Habitat variables 1

Site 

number 

(fig. 17)

Abbreviated

site name2

Instream

cover

(percent 

submerge

d habitat)

Pool 

substrate

characterization

(substrate 

quality)

Pool

variability

(pool

quality)

Sediment

deposition

(percent 

recent 

deposition)

Channel

flow

status

(percent 

available 

channel 

exposed)

Channel

alteration

(percent 

channelized 

stream 

reach)

Channel

sinuosity

(stream 

bends 

increase 

length)

Bank

stability

(erosion of 

streambank)

Bank 

vegetation 

protection

(percent 

vegetative 

cover)

Riparian

vegetative zone

width

(meter)

RBP*

site

score 

range

RBP*

site habitat

rating

1 Des Cannes 15 14 18 3 18 8 6 10 20 20 132 Suboptimal

2 Wikoff 14 9 16 12 18 17 8 14 16 20 144 Suboptimal

3 Plaquemine 16 9 13 7 15 15 9 6 18 20 128 Suboptimal

4 Boggy 18 15 17 20 18 20 18 12 20 20 178 Optimal

5 Castor 14 18 19 18 16 15 14 14 16 18 162 Optimal

6 Nezpique 16 15 18 11 17 20 18 14 14 20 163 Optimal

7 Mermentau 20 15 18 13 20 8 15 20 20 20 169 Optimal

11 Lacassine 18 15 15 8 18 20 20 20 20 20 174 Optimal

12 Tortue 9 8 12 3 14 6 3 2 14 18 89 Marginal

13 Grand Marais 13 8 8 3 18 10 3 6 16 4 89 Marginal

14 Theriot 7 78 1 14 10 6 10 10 15 88 Marginal

15 East Lacassine 2 3 15 17 18 13 8 14 9 8 107 Suboptimal

19 Church Point 11 13 8 14 14 18 13 16 12 8 127 Suboptimal

20 Mallet 17 13 8 4 17 19 18 16 10 20 142 Suboptimal

21 Guidry 16 10 13 8 17 15 19 8 10 20 136 Suboptimal

22 Blue 16 10 18 15 20 20 20 18 18 20 175 Optimal

23 Upper Des Cannes 14 8 13 6 18 18 17 20 20 20 154 Suboptimal

24 Caney 18 15 16 15 18 20 10 18 20 20 170 Optimal

25 Whisky 20 20 20 15 20 20 18 18 20 20 191 Optimal
65

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Des

Cannes Wikoff

Plaquemine Boggy CastorNezpique

Mermentau

Lacassine Tortue 

CNIDARIA (coelenterates) – -- -- -- -- -- -- -- -- --

HYDROZOA (hydras) – -- -- -- -- -- -- -- -- --

HYDROIDA – -- -- -- -- -- -- -- -- --

Hydridae – -- -- -- -- -- -- -- -- --

Hydra sp. Hydra -- -- 10 41 10 -- -- 140 --

PLATYHELMINTHES (flatworms) – -- -- -- -- -- -- -- -- --

TURBELLARIA (free-living flatworms) Turbell 18 -- 5 8 35 12 40 107 5

NEMATODA (roundworms) Nematoda -- -- 5 25 10 33 10 -- --

MOLLUSCA (clams, snails, and limpets) – -- -- -- -- -- -- -- -- --

BIVALVIA (bivalue molluscs) – -- -- -- -- -- -- -- -- --

VENEROIDA – -- -- -- -- -- -- -- -- --

Sphaeriidae (fingernail clams) – -- -- -- -- -- -- -- -- --

Eupera cubensis sp. – 25 -- -- -- -- 5 6 -- --

Musculium sp. – -- -- -- -- -- -- 10 2 --

GASTROPODA (snails, limpets) – -- -- -- -- -- -- -- -- --

BASOMMATOPHORA – -- -- -- -- -- -- -- -- --

Ancylidae (limpets) – -- -- -- -- -- -- -- -- --

Laevapex sp. – -- -- -- -- -- -- -- -- --

Lymnaeidae (pond snails) – -- -- -- -- -- -- -- -- --

Pseudosuccinea columella – -- -- -- -- -- -- 40 54 5

Physidae (pouch snails) – -- -- -- -- -- -- -- -- --

Physella sp. Physella 4 9 25 8 37 61 110 177 22

Planorbidae (orb snails) – -- -- -- -- -- -- -- -- --

Micromenetus sp. Micromen -- 22 -- -- -- -- 60 32 17

Planorbella sp. – -- -- -- -- -- -- -- -- --

ANNELIDA (segmented worms) – -- -- -- -- -- -- -- -- --

HIRUDINEA (leeches) – -- -- -- -- -- -- -- -- --

ARHYNCHOBDELLAE – -- -- -- -- -- -- -- -- --

Erpobdellidae Erpobidae -- 4 5 -- -- 23 10 -- --

RHYNCHOBDELLAE – -- -- -- -- -- -- -- -- --

Glossiphoniidae – 2 -- -- -- -- -- -- -- --

OLIGOCHAETA (aquatic worms) – -- -- -- -- -- -- -- -- --

ENCHYTRAEIDA – -- -- -- -- -- -- -- -- --

Enchytraeidae Enchidae -- -- -- -- 40 5 -- --

LUMBRICULIDA – -- -- -- -- -- -- -- -- --

Lumbriculidae – -- -- -- 8 -- -- 17 -- --

Megadrile sp. Megadrill -- -- 2 -- -- -- 6 -- --

TUBIFICIDA – -- -- -- -- -- -- -- -- --

Naididae Naididae -- -- -- -- -- -- -- 32 71

Tubificidae Tubfidae 18 99 -- -- 10 5 23 -- --

ARTHROPODA (arthropods) – -- -- -- -- -- -- -- -- --

ARACHNIDA (eight-legged arthropods) – -- -- -- -- -- -- -- -- --

ACARI (water mites) Acari -- 13 -- -- -- 5 -- -- --

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001

[Densities and total number of aquatic invertebrates are rounded to the nearest whole number and reported as organisms per square meter; –, species 

not used as part of canonical correspondence analysis; --, species not collected; *, Subfamily; **, Tribe]
66

MALACOSTRACA (crustaceans) -- -- -- -- -- -- -- -- -- --

AMPHIPODA (scuds, sideswimmers) – -- -- -- -- -- -- -- -- --

Crangonyctidae – -- -- -- -- -- -- -- -- --

Crangonyx sp. Crangony -- -- -- 58 10 -- 6 11 --

Hyalellidae – -- -- -- -- -- -- -- -- --

Hyalella azteca Hyazteca 20 1 205 -- -- -- 722 1,171 1,363

DECAPODA (crayfishes, shrimps) – -- -- -- -- -- -- -- -- --

Palaemonidae (prawns and river shrimps) – -- -- -- -- -- -- -- -- --

Palaemonetes kadiakensis – -- -- -- -- -- -- -- -- --

ISOPODA (aquatic sow bugs) – -- -- -- -- -- -- -- -- --

Asellidae – -- -- -- -- -- -- -- -- --

Caecidotea sp. – -- -- -- -- 10 -- -- -- --

Lirceus sp. Lirceus -- -- -- 19 -- -- -- 11 --

INSECTA (insects) – -- -- -- -- -- -- -- -- --

COLEOPTERA (beetles) – -- -- -- -- -- -- -- -- --

Carabidae (predaceous ground beetles) – 2 -- -- -- -- -- -- -- --

Curculionidae (weevils) – 4 -- -- -- -- -- -- -- --

Dytiscidae (predaceous diving beetles) – -- -- -- -- -- -- -- -- --

Thermonectus sp. – -- -- -- -- -- -- -- -- --

Hydroporinae* Hydrinae 11 -- -- -- -- -- 6 -- 17

Laccophilinae* – -- -- -- -- -- -- -- -- --

Laccophilus sp. – -- -- -- -- -- -- -- -- --

Elmidae (riffle beetles) – -- -- -- -- -- -- -- -- --

Macronychus glabratus – -- -- -- -- -- -- -- -- --

Stenelmis sp. – -- 4 -- -- -- -- -- -- --

Hydrophilidae (water scavenger beetles) – -- -- -- -- -- -- -- -- --

Berosus sp. – 2 -- 2 -- -- -- -- -- --

Enochrus sp. Enochrus -- -- -- -- -- -- 6 -- --

Helochares sp. – -- -- -- -- -- -- -- -- --

Tropisternus sp. Tropist -- 4 -- -- -- -- -- -- 11

Noteridae (burrowing water beetles) – -- -- -- -- -- -- -- -- --

Hydrocanthus sp. – -- -- -- -- -- -- -- -- --

Suphisellus bicolor – -- -- -- -- -- -- -- -- 5

Scirtidae (marsh beetles) Scirtdae -- -- 43 -- -- 5 -- -- 5

COLLEMBOLA (springtails) Collemb 7 -- 5 -- 30 12 -- 11 5

DIPTERA (true flies) – -- -- -- -- -- -- -- -- --

Ceratopogonidae (biting midges, no-see-ums) – -- -- -- -- -- -- -- -- --

Ceratopogoninae* – -- -- -- -- -- -- -- -- --

Bezzia/Palpomyia sp. Bezzpalp -- -- -- -- 30 -- 6 -- --

Forcipomyiinae* – -- -- -- -- -- -- -- -- --

Atrichopogon sp. Atrichop -- -- -- 8 30 -- -- -- --

Chironomidae (midges) – -- -- -- -- -- -- -- -- --

Chironominae* – -- -- -- -- -- -- -- -- --

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Des

Cannes Wikoff

Plaquemine Boggy CastorNezpique

Mermentau

Lacassine Tortue 
67

Chironomini** – -- -- -- -- -- -- -- -- --

Chironomus sp. Chironom -- 4 10 -- 20 -- -- -- --

Dicrotendipes sp. Dicdipes 63 77 14 803 377 390 23 11 5

Endochironomus sp. – -- -- -- -- -- -- 40 -- --

Glyptotendipes sp. Glydipes -- -- 109 -- -- -- 216 623 11

Goeldichironomus sp. – -- -- -- -- -- -- -- -- --

Kiefferulus sp. – -- -- -- -- -- -- -- -- --

Parachironomus sp. – -- -- -- -- -- -- -- -- --

Phaenopsectra/Tribelos sp. – -- 4 -- -- -- -- -- 43 --

Polypedilum sp. – -- -- -- -- -- -- 6 11 --

Stenochironomus sp. – -- -- -- -- -- 5 -- -- --

Tribelos sp. Tribelos -- 26 -- -- -- 5 6 32 5

Zavreliella marmorata – -- -- -- -- -- -- -- -- --

Pseudochironomini** – -- -- -- -- -- -- -- -- --

Pseudochironomus sp. – 4 -- -- -- -- -- 17 -- --

Tanytarsini** – -- -- -- -- -- -- -- -- --

Cladotanytarsus sp. – -- -- 5 -- -- -- -- -- --

Micropsectra/Tanytarsus sp. Mictanyt -- 4 10 124 50 12 -- -- --

Rheotanytarsus sp. Rheotany 9 30 5 306 79 23 -- -- --

Tanytarsus sp. Tanytars -- 77 33 340 367 80 6 -- --

Diamesinae* – -- -- -- -- -- -- -- -- --

Potthastia sp. – -- -- -- 17 -- -- -- -- --

Orthocladiinae* – -- -- -- -- -- -- -- -- --

Corynoneura sp. Corynon -- 125 10 207 10 -- -- 11 --

Cricotopus sp. Cricotop 2 112 5 -- -- -- -- -- --

Cricotopus/Orthocladius sp. Criortho -- 30 -- -- -- -- -- -- --

Gymnometriocnemus sp. – -- -- -- -- -- -- -- -- --

Nanocladius sp. Nanoclad 2 17 14 108 -- 5 -- 75 5

Parakiefferiella sp. – -- -- -- 157 10 -- -- -- --

Parametriocnemus sp. – -- -- -- -- 10 -- -- -- --

Rheocricotopus sp. Rheocric -- -- -- 17 -- -- -- -- --

Thienemanniella sp. Thienema -- 9 5 58 -- 5 -- -- 5

Tvetenia sp. – -- -- -- -- -- -- -- -- --

Tanypodinae* – -- -- -- -- -- -- -- -- --

Natarsiini** – -- -- -- -- -- -- -- -- --

Natarsia sp. – -- -- -- -- -- -- -- -- --

Pentaneurini** – -- -- -- -- -- -- -- -- --

Ablabesmyia sp. Ablabesm 2 -- 10 30 6 75 11

Larsia sp. – -- -- -- -- -- -- -- -- --

Thienemannimyia group sp. – -- -- -- -- -- -- -- -- --

Procladiini** – -- -- -- -- -- -- -- -- --

Procladius sp. – -- -- -- -- -- -- -- -- --

Ephydridae (shore and brine flies) – -- -- -- -- -- -- -- -- --

Psychodidae (moth flies) – -- -- -- -- -- -- -- -- --

Psychoda sp. – -- -- -- -- 10 -- -- -- --

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Des

Cannes Wikoff

Plaquemine Boggy CastorNezpique

Mermentau

Lacassine Tortue 
68

Simuliidae (black flies) – -- -- -- -- -- -- -- -- --

Simulium sp. – -- -- -- 10 -- -- -- -- --

Stratiomyidae (soldier flies) – -- -- -- -- -- -- -- -- --

Stratiomyinae* – -- -- -- -- -- -- -- -- --

Hedriodiscus/Odontomyia sp. Hedrodon 47 -- 24 -- -- -- 6 -- --

Tabanidae – -- -- -- -- -- -- -- -- --

Tabanus sp. – -- -- -- -- -- -- -- -- --

EPHEMEROPTERA (mayflies) – -- -- -- -- -- -- -- -- --

Baetidae – -- -- -- -- -- -- -- -- --

Baetis intercalaris – -- -- -- -- -- -- -- -- --

Callibaetis sp. – -- -- -- -- -- -- -- -- --

Caenidae – -- -- -- -- -- -- -- -- --

Caenis sp. Caenis -- 116 33 -- -- 14 56 150 49

Heptageniidae – -- -- -- -- -- -- -- -- --

Stenacron sp. – -- -- -- -- -- -- -- -- --

Stenonema sp. – -- -- -- -- -- -- -- -- --

Isonychiidae – -- -- -- -- -- -- -- -- --

Isonychia sp. – -- -- -- -- -- -- -- -- --

MEGALOPTERA (dobsonflies/hellgrammites) – -- -- -- -- -- -- -- -- --

Corydalidae – -- -- -- -- -- -- -- -- --

Corydalus cornutus – -- -- -- -- -- -- -- -- --

ODONATA (damsel/dragonflies) – -- -- -- -- -- -- -- -- --

Coenagrionidae – -- -- -- -- -- -- -- -- --

Argia, sp. – -- 4 -- -- -- -- -- -- --

Corduliidae – -- -- -- -- -- -- -- -- --

Epitheca princeps – -- -- -- -- -- -- -- 30 --

PLECOPTERA (stoneflies) – -- -- -- -- -- -- -- -- --

Perlidae – -- -- -- -- -- -- -- -- --

Perlesta sp. – -- -- -- -- -- -- -- -- --

TRICHOPTERA (caddisflies) – -- -- -- -- -- -- -- -- --

Glossosomatidae – -- -- -- -- -- -- -- -- --

Protoptila sp. – -- -- -- -- -- -- -- -- --

Hydroptilidae (microcaddis) – -- -- -- -- -- -- -- -- --

Hydroptila sp. – -- -- -- -- -- -- -- -- --

Hydropsychidae – -- -- -- -- -- -- -- -- --

Cheumatopsyche sp. Chpsyche -- 22 -- -- -- -- -- -- --

Hydropsyche sp. – -- -- -- -- -- -- -- -- --

Macrostemum carolina – -- -- -- -- -- -- -- -- --

Leptoceridae – -- -- -- -- -- -- -- -- --

Oecetis sp. – -- -- -- -- -- -- 6 32 --

Polycentropodidae – -- -- -- -- -- -- -- -- --

Paranyctiophylax sp. – -- -- -- -- -- -- -- -- --

TOTAL ABUNDANCE 245 814 590 2,323 1,213 702 1,468 2,842 1,619

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Des

Cannes Wikoff

Plaquemine Boggy CastorNezpique

Mermentau

Lacassine Tortue 
69

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Grand 

Marais Theriot

East

Lacassine Church 

Point Mallet Guidry Blue

Upper 

Des 

Cannes Caney Whisky 

CNIDARIA (coelenterates) – -- -- -- -- -- -- -- -- -- --

HYDROZOA (hydras) – -- -- -- -- -- -- -- -- -- --

HYDROIDA – -- -- -- -- -- -- -- -- -- --

Hydridae – -- -- -- -- -- -- -- -- -- --

Hydra sp. Hydra 58 -- -- 11 18 -- -- -- 12 --

PLATYHELMINTHES (flatworms) – -- -- -- -- -- -- -- -- -- --

TURBELLARIA (free-living flatworms) Turbell 20 3 14 26 9 6 3 48 12 --

NEMATODA (roundworms) Nematoda 6 7 6 11 -- -- -- 19 -- 11

MOLLUSCA (clams, snails, and limpets) – -- -- -- -- -- -- -- -- -- --

BIVALVIA (bivalue molluscs) – -- -- -- -- -- -- -- -- -- --

VENEROIDA – -- -- -- -- -- -- -- -- -- --

Sphaeriidae (fingernail clams) – -- -- -- -- -- -- -- -- -- --

Eupera cubensis sp. – 6 -- -- -- -- -- -- -- -- --

Musculium sp. – -- -- -- -- -- -- -- -- -- --

GASTROPODA (snails, limpets) – -- -- -- -- -- -- -- -- -- --

BASOMMATOPHORA – -- -- -- -- -- -- -- -- -- --

Ancylidae (limpets) – -- -- -- -- -- -- -- -- -- --

Laevapex sp. – 12 -- -- -- -- -- -- -- -- --

Lymnaeidae (pond snails) – -- -- -- -- -- -- -- -- -- --

Pseudosuccinea columella – -- -- 8 -- -- -- -- -- -- --

Physidae (pouch snails) – -- -- -- -- -- -- -- -- -- --

Physella sp. Physella 6 19 39 52 9 -- 2 24 36 --

Planorbidae (orb snails) – -- -- -- -- -- -- -- -- -- --

Micromenetus sp. Micromen -- -- -- -- 317 6 -- -- -- --

Planorbella sp. – -- -- 6 -- -- -- -- -- -- --

ANNELIDA (segmented worms) – -- -- -- -- -- -- -- -- -- --

HIRUDINEA (leeches) – -- -- -- -- -- -- -- -- -- --

ARHYNCHOBDELLAE – -- -- -- -- -- -- -- -- -- --

Erpobdellidae Erpobidae 6 -- 39 56 27 -- -- -- -- --

RHYNCHOBDELLAE – -- -- -- -- -- -- -- -- -- --

Glossiphoniidae – -- -- -- -- -- -- -- -- -- --

OLIGOCHAETA (aquatic worms) – -- -- -- -- -- -- -- -- -- --

ENCHYTRAEIDA – -- -- -- -- -- -- -- -- -- --

Enchytraeidae Enchidae 6 9 -- 52 -- -- 11 76 -- --

LUMBRICULIDA – -- -- -- -- -- -- -- -- -- --

Lumbriculidae – -- -- -- -- -- -- -- -- -- --

Megadrile sp. Megadrill -- 6 146 26 9 -- -- -- -- 14

TUBIFICIDA – -- -- -- -- -- -- -- -- -- --

Naididae Naididae 38 -- -- -- 9 -- -- -- 893 --

Tubificidae Tubfidae 12 -- -- 258 9 -- -- 5 -- --

ARTHROPODA (arthropods) – -- -- -- -- -- -- -- -- -- --

ARACHNIDA (eight-legged arthropods) – -- -- -- -- -- -- -- -- -- --

ACARI (water mites) Acari 17 12 -- -- 9 -- 24 19 -- 119
70

MALACOSTRACA (crustaceans) – -- -- -- -- -- -- -- -- -- --

AMPHIPODA (scuds, sideswimmers) – -- -- -- -- -- -- -- -- -- --

Crangonyctidae – -- -- -- -- -- -- -- -- -- --

Crangonyx sp. Crangony 248 3 -- -- -- -- -- -- -- --

Hyalellidae – -- -- -- -- -- -- -- -- -- --

Hyalella azteca Hyazteca 44 -- 279 -- -- 2 -- -- -- --

DECAPODA (crayfishes, shrimps) – -- -- -- -- -- -- -- -- -- --

Palaemonidae (prawns and river 

shrimps) – -- -- -- -- -- -- -- -- -- --

Palaemonetes kadiakensis – -- -- -- -- -- -- -- -- 3 --

ISOPODA (aquatic sow bugs) – -- -- -- -- -- -- -- -- -- --

Asellidae – -- -- -- -- -- -- -- -- -- --

Caecidotea sp. – -- -- 41 -- -- -- -- -- 48 --

Lirceus sp. Lirceus -- -- -- 11 18 -- -- -- 24 --

INSECTA (insects) – -- -- -- -- -- -- -- -- -- --

COLEOPTERA (beetles) – -- -- -- -- -- -- -- -- -- --

Carabidae (predaceous ground beetles) – -- -- -- -- -- -- -- -- -- --

Curculionidae (weevils) – -- 6 -- -- -- 25 3 -- -- --

Dytiscidae (predaceous diving beetles) – -- -- -- -- -- -- -- -- -- --

Thermonectus sp. – -- 1 -- -- -- -- -- -- -- --

Hydroporinae* Hydrinae -- 10 6 -- -- -- -- 10 -- --

Laccophilinae* – -- -- -- -- -- -- -- -- -- --

Laccophilus sp. – -- -- -- -- 27 -- -- 10 -- --

Elmidae (riffle beetles) – -- -- -- -- -- -- -- -- -- --

Macronychus glabratus – -- -- -- -- -- -- -- -- -- 60

Stenelmis sp. – -- 1 -- 191 -- -- -- -- -- 95

Hydrophilidae (water scavenger beetles) – -- -- -- -- -- -- -- -- -- --

Berosus sp. – 6 -- -- -- -- 6 -- -- -- --

Enochrus sp. Enochrus 6 1 -- -- -- -- -- -- -- --

Helochares sp. – -- 1 -- -- -- -- -- -- -- --

Tropisternus sp. Tropist -- 1 -- -- -- -- -- -- -- --

Noteridae (burrowing water beetles) – -- -- -- -- -- -- -- -- -- --

Hydrocanthus sp. – -- 3 -- -- -- -- -- -- -- --

Suphisellus bicolor – 17 9 -- -- -- -- -- -- -- --

Scirtidae (marsh beetles) Scirtdae -- 10 -- -- -- 12 -- -- -- --

COLLEMBOLA (springtails) Collemb 20 24 19 78 9 -- 8 210 -- --

DIPTERA (true flies) – -- -- -- -- -- -- -- -- -- --

Ceratopogonidae (biting midges,

no-see-ums) – -- -- -- -- -- -- -- -- -- --

Ceratopogoninae* – -- -- -- -- -- -- -- -- -- --

Bezzia/Palpomyia sp. Bezzpalp -- -- -- -- -- 31 -- -- 24 60

Forcipomyiinae* – -- -- -- -- -- -- -- -- -- --

Atrichopogon sp. Atrichop -- -- -- -- 9 -- -- -- -- 11

Chironomidae (midges) – -- -- -- -- -- -- -- -- -- --

Chironominae* – -- -- -- -- -- -- -- -- -- --

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Grand 

Marais Theriot

East

Lacassine Church 

Point Mallet Guidry Blue

Upper 

Des 

Cannes Caney Whisky 
71

Chironomini** – -- -- -- -- -- -- -- -- -- --

Chironomus sp. Chironom -- -- -- -- 9 -- -- -- 24 --

Dicrotendipes sp. Dicdipes 12 1 -- 601 82 -- 11 67 119 --

Endochironomus sp. – -- -- -- -- -- -- -- -- -- --

Glyptotendipes sp. Glydipes -- 3 -- 11 -- -- -- -- 12 --

Goeldichironomus sp. – -- 4 -- -- -- -- -- -- -- --

Kiefferulus sp. – -- -- -- -- -- -- -- -- 131 --

Parachironomus sp. – 12 -- -- -- -- -- -- -- -- --

Phaenopsectra/Tribelos sp. – -- -- -- -- -- -- -- -- -- --

Polypedilum sp. – -- -- -- -- -- -- -- -- -- --

Stenochironomus sp. – -- -- -- -- -- -- -- -- -- --

Tribelos sp. Tribelos -- -- -- -- -- -- -- 5 -- --

Zavreliella marmorata – -- -- -- -- -- -- -- -- 12 --

Pseudochironomini** – -- -- -- -- -- -- -- -- -- --

Pseudochironomus sp. – -- -- -- -- -- -- -- -- -- 25

Tanytarsini** – -- -- -- -- -- -- -- -- -- --

Cladotanytarsus sp. – -- -- -- 11 9 -- -- -- -- --

Micropsectra/Tanytarsus sp. Mictanyt -- 1 -- 64 -- -- 19 10 83 --

Rheotanytarsus sp. Rheotany -- 1 -- 205 45 -- 2 -- 71 828

Tanytarsus sp. Tanytars -- -- 6 64 9 6 25 10 143 35

Diamesinae* – -- -- -- -- -- -- -- -- -- --

Potthastia sp. – -- -- -- 11 -- -- -- -- -- 11

Orthocladiinae* – -- -- -- -- -- -- -- -- -- --

Corynoneura sp. Corynon -- -- -- 26 -- -- -- 5 36 11

Cricotopus sp. Cricotop 50 4 66 258 9 -- -- 5 12 --

Cricotopus/Orthocladius sp. Criortho 6 -- 8 64 -- -- -- -- 24 35

Gymnometriocnemus sp. – -- 1 -- -- -- -- -- -- -- --

Nanocladius sp. Nanoclad 38 -- -- -- 18 -- -- -- 24 --

Parakiefferiella sp. – -- -- -- 26 -- -- -- -- 119 --

Parametriocnemus sp. – -- -- -- -- -- -- -- -- --

Rheocricotopus sp. Rheocric -- -- -- 11 -- -- -- -- 12 74

Thienemanniella sp. Thienema 20 184 33 64 -- -- -- -- 12 35

Tvetenia sp. – -- -- -- -- 9 -- -- -- -- 158

Tanypodinae* – -- -- -- -- -- -- -- -- -- --

Natarsiini** – -- -- -- -- -- -- -- -- -- --

Natarsia sp. – -- -- -- 11 27 -- 13 -- -- --

Pentaneurini** – -- -- -- -- -- -- -- -- --

Ablabesmyia sp. Ablabesm -- -- -- -- -- -- -- -- --

Larsia sp. – -- -- -- -- -- -- -- 60 --

Thienemannimyia group sp. – -- -- -- 11 -- 6 -- -- -- 25

Procladiini** – -- -- -- -- -- -- -- -- -- --

Procladius sp. – -- -- -- -- -- -- -- -- 12 --

Ephydridae (shore and brine flies) – -- -- -- -- -- -- -- -- 12 --

Psychodidae (moth flies) – -- -- -- -- -- -- -- -- -- --

Psychoda sp. – -- -- -- -- -- -- -- -- 12 --

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Grand 

Marais Theriot

East

Lacassine Church 

Point Mallet Guidry Blue

Upper 

Des 

Cannes Caney Whisky 
72

Simuliidae (black flies) – -- -- -- -- -- -- -- -- -- --

Simulium sp. – -- -- -- -- -- -- -- -- -- --

Stratiomyidae (soldier flies) – -- -- -- -- -- -- -- -- -- --

Stratiomyinae* – -- -- -- -- -- -- -- -- -- --

Hedriodiscus/Odontomyia sp. Hedrodon 6 6 6 -- -- -- -- -- -- --

Tabanidae – -- -- -- -- -- -- -- -- -- --

Tabanus sp. – -- -- -- -- -- -- -- 5 -- --

EPHEMEROPTERA (mayflies) – -- -- -- -- -- -- -- -- -- --

Baetidae – -- -- -- -- -- -- -- -- -- --

Baetis intercalaris – -- -- -- -- -- -- -- -- -- 25

Callibaetis sp. – -- -- 6 -- -- -- -- -- -- --

Caenidae – -- -- -- -- -- -- -- -- -- --

Caenis sp. Caenis 242 36 298 336 -- 6 -- -- -- --

Heptageniidae – -- -- -- -- -- -- -- -- -- --

Stenacron sp. – -- -- -- -- -- 2 -- -- -- --

Stenonema sp. – -- -- -- -- -- -- -- -- -- 11

Isonychiidae – -- -- -- -- -- -- -- -- -- --

Isonychia sp. – -- -- -- -- -- -- -- -- -- 11

MEGALOPTERA (dobsonflies/hellgrammites) – -- -- -- -- -- -- -- -- -- --

Corydalidae – -- -- -- -- -- -- -- -- -- --

Corydalus cornutus – -- -- -- -- -- -- -- -- -- 4

ODONATA (damsel/dragonflies) – -- -- -- -- -- -- -- -- -- --

Coenagrionidae – -- -- -- -- -- -- -- -- -- --

Argia, sp. – -- -- -- 11 -- -- -- -- -- --

Corduliidae – -- -- -- -- -- -- -- -- -- --

Epitheca princeps – -- -- -- -- -- -- -- -- -- --

PLECOPTERA (stoneflies) – -- -- -- -- -- -- -- -- -- --

Perlidae – -- -- -- -- -- -- -- -- -- --

Perlesta sp. – -- -- -- -- -- -- -- -- -- 144

TRICHOPTERA (caddisflies) – -- -- -- -- -- -- -- -- -- --

Glossosomatidae – -- -- -- -- -- -- -- -- -- --

Protoptila sp. – -- -- -- -- -- -- -- -- 12 --

Hydroptilidae (microcaddis) – -- -- -- -- -- -- -- -- -- --

Hydroptila sp. – -- -- 28 -- -- -- -- -- -- --

Hydropsychidae – -- -- -- -- -- -- -- -- -- --

Cheumatopsyche sp. Chpsyche 17 -- -- 11 9 10 -- -- -- 158

Hydropsyche sp. – -- -- -- -- -- -- -- -- -- 361

Macrostemum carolina – -- -- -- -- -- -- -- -- -- 74

Leptoceridae – -- -- -- -- -- -- -- -- -- --

Oecetis sp. – -- -- -- -- -- -- -- -- -- 25

Polycentropodidae – -- -- -- -- -- -- -- -- -- --

Paranyctiophylax sp. – -- -- -- -- -- -- -- -- -- 60

TOTAL ABUNDANCE 930 372 1,052 2,570 707 119 122 525 1,990 2,473

Appendix 8. Taxa and densities of richest-targeted habitat aquatic invertebrates for ecological data-collection sites in 

southwestern Louisiana, March-April 2001—Continued

Taxonomic heirarchy

PHYLUM

CLASS

ORDER

Family

Genus species

Species 

abbreviation

(see

fig. 16)

Densities

Abbreviated site names (see table 1, appendix 1)

Grand 

Marais Theriot

East

Lacassine Church 

Point Mallet Guidry Blue

Upper 

Des 

Cannes Caney Whisky 
73

* Environmental variables with variable number(s) are correlated with these variables based on a Spearmann-rank correlation test with an alpha value of 0.05.

** Separate principal components analysis was performed on stream habitat measurements.

Appendix 9. Loadings of environmental variables on the first two principal components (PC) derived from principal components analysis (PCA) of ecological 

data-collection sites in southwestern Louisiana, 2001

[Environmental variables with boldface values were selected for use in canonical correspondence analysis based on multiple iterations of PCA and/or considered important for describing water quality 

and aquatic invertebrate communities in an agricultural land-use setting in southwestern Louisiana. mi2

, square mile; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; 

NTU, nephelometric turbidity units; oC, degrees Celsius; μg/L, micrograms per liter; m, meter; ft/s, feet per second; RBP, Rapid Bioassessment Protocols (Barbour and others, 1999)]

Number and description of 

environmental variable PC1 PC2 Correlations* Number and description of 

environmental variable PC1 PC2 Correlations*

SITE CHARACTERISTICS WATER QUALITY (Cont.)

General Herbicides and degradation products (Cont.)

1 Drainage basin area (mi2) 0.55 0.42 49, 53 31 Molinate -0.24 0.70 33

2 Rice agriculture by basin (percent) -0.45 0.81 32 Tebuthiuron -0.36 0.49

33 Herbicides, cumulative -0.63 0.68

WATER QUALITY Insecticides and degradation products

Physiochemical Data 34 Desulfinyl -0.81 -0.47 35

Dissolved oxygen (mg/L) 35 Fipronil -0.90 -0.31 37, 38

3 Time of biological sampling 0.19 0.09 36 Fipronil, maximum -0.76 0.06

4 1-month low -0.32 0.37 37 Sulfide -0.74 -0.43 38

pH 38 Sulfone -0.90 -0.37

5 Time of biological sampling -0.53 0.20 6, 9, 10, 15, 27

Specific conductance (μS/cm) STREAM HABITAT** 

6 Time of biological sampling -0.71 -0.03 9, 10, 13, 15, 27, 66 Quantitative measurements (mean values)

Turbidity (NTU’s) 39 Bank angle (degrees) -0.57 -0.56

7 Time of biological sampling -0.79 0.25 18, 24, 28, 44, 48 40 Bank erosion score -0.55 -0.42

Water temperature (°C): 41 Bank height (m) -0.29 -0.83 42

8 Time of biological sampling 0.03 0.12 42 Bank stability index -0.29 -0.85

Water-Quality Data (mg/L) 43 Bank vegetative cover (percent availability) -0.66 -0.43

9 Alkalinity (as calcium carbonate) -0.62 0.06 10, 15, 27 44 Euphotic zone depth (m) 0.44 -0.41 48

10 Calcium, dissolved -0.60 -0.04 15, 27 45 Habitat cover (percent availability) 0.49 0.35

Carbon, organic: 46 Open canopy (percent) -0.06 0.66

11 Dissolved -0.01 -0.06 47 Riparian canopy closure (percent) 0.46 0.04

12 Suspended -0.69 0.19 48 Secchi disk depth (m) 0.45 -0.44

13 Chloride, dissolved -0.85 -0.17 19, 20, 21, 25, 27, 35, 38 49 Stream bankfull channel width (m) -0.60 0.73 53

14 Chlorophyll-a (μg/L) -0.63 0.39 50 Stream depth (m) 0.16 0.64 53

15 Magnesium, dissolved -0.60 -0.02 27 51 Stream open angle (degrees) -0.06 0.66

Nitrogen (as N) 52 Stream velocity (ft/s) -0.09 -0.63

16 Ammonia, dissolved -0.38 0.18 24 53 Stream wetted channel width (m) 0.51 0.68

17 Ammonia + organic, dissolved -0.55 -0.16 54 Visual algae growth (percent availability) -0.19 0.13

18 Ammonia + organic, total -0.85 0.09 24, 28, 44, 48 55 Width-to-depth ratio 0.53 -0.05

19 Nitrite, dissolved 0.28 -0.40 20, 21, 25 56 Woody debris (snag, percent availability) 0.23 0.12

20 Nitrate, dissolved -0.73 -0.28 21 Qualitative measurements

21 Nitrite + nitrate, dissolved -0.74 -0.26 25 RBP parameters (each score, 0-20 )

Phosphorus (as P) 57 Bank stability 0.63 0.13

22 Dissolved -0.13 0.15 23 58 Bank vegetation protection 0.61 0.08

23 Ortho, dissolved -0.19 0.21 59 Channel alteration 0.53 -0.40

24 Total -0.80 0.27 44, 48 60 Channel flow status 0.55 0.07

25 Potassium, dissolved -0.79 -0.06 61 Channel sinuosity 0.72 -0.02

26 Silicon, dissolved 0.08 -0.05 62 Instream cover 0.83 -0.04

27 Sodium, dissolved -0.74 0.03 63 Pool substrate characterization 0.80 -0.19

28 Suspended sediments, total -0.85 0.13 44, 48 64 Pool variability 0.63 -0.06

Herbicides and degradation products 65 Riparian vegetative zone width 0.52 0.08

29 Atrazine -0.31 0.42 33 66 Sediment deposition 0.55 -0.40

30 Metolachlor -0.30 -0.09 67 RBP total site score (0-200) 0.91 -0.13