Water Quality in the 

Acadian-Pontchartrain Drainages

Louisiana and Mississippi, 1999–2001

U.S. Department of the Interior

U.S. Geological Survey

Circular 1232
Points of Contact and Additional Information

The companion web site for NAWQA summary reports:

http://water.usgs.gov/nawqa/nawqa_sumr.html

Other NAWQA summary reports

River Basin Assessments

Albemarle-Pamlico Drainage Basin (Circular 1157)

Allegheny and Monongahela River Basins (Circular 1202)

Apalachicola-Chattahoochee-Flint River Basin (Circular 1164)

Central Arizona Basins (Circular 1213)

Central Columbia Plateau (Circular 1144)

Central Nebraska Basins (Circular 1163)

Connecticut, Housatonic and Thames River Basins (Circular 1155)

Cook Inlet Basin (Circular 1240)

Delaware River Basin (Circular 1227)

Delmarva Peninsula (Circular 1228)

Eastern Iowa Basins (Circular 1210)

Georgia-Florida Coastal Plain (Circular 1151)

Great and Little Miami River Basins (Circular 1229) 

Great Salt Lake Basins (Circular 1236)

Hudson River Basin (Circular 1165)

Island of Oahu (Circular 1239)

Kanawha - New River Basins (Circular 1204)

Lake Erie - Lake Saint Clair Drainages (Circular 1203)

Long Island - New Jersey Coastal Drainages (Circular 1201)

Lower Illinois River Basin (Circular 1209)

Lower Susquehanna River Basin (Circular 1168)

Lower Tennessee River Basin (Circular 1233)

Las Vegas Valley Area and the Carson and Truckee River Basins (Circular 1170)

Mississippi Embayment (Circular 1208)

Mobile River Basin (Circular 1231)

New England Coastal Basins (Circular 1226)

Northern Rockies Intermontane Basins (Circular 1235)

Ozark Plateaus (Circular 1158)

Potomac River Basin (Circular 1166)

Puget Sound Basin (Circular 1216)

Red River of the North Basin (Circular 1169)

Rio Grande Valley (Circular 1162)

Sacramento River Basin (Circular 1215)

San Joaquin-Tulare Basins (Circular 1159)

Santa Ana Basin (Circular 1238)

Santee River Basin and Coastal Drainages (Circular 1206)

South-Central Texas (Circular 1212)

South Platte River Basin (Circular 1167)

Southern Florida (Circular 1207)

Trinity River Basin (Circular 1171)

Upper Colorado River Basin (Circular 1214)

Upper Illinois River Basin (Circular 1230)

Upper Mississippi River Basin (Circular 1211)

Upper Snake River Basin (Circular 1160)

Upper Tennessee River Basin (Circular 1205)

Western Lake Michigan Drainages (Circular 1156)

White River Basin (Circular 1150)

Willamette Basin (Circular 1161)

Yakima River Basin (Circular 1237)

Yellowstone River Basin (Circular 1234)

National Assessments

The Quality of Our Nation‘s Waters—Nutrients and Pesticides (Circular 1225)

Acadian-Pontchartrain Drainages contact and 

web site:

USGS State Representative

U.S. Geological Survey

Water Resources Discipline

3535 South Sherwood Forest Blvd., Suite 120

Baton Rouge, Louisiana 70816

e-mail: dc_la@usgs.gov

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

National NAWQA Program:

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192

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

Front Cover: Bayou Lacassine near Lake Arthur, Louisiana (photograph by Dennis Demcheck)

Back Cover: Left: Lake Fausse Pointe at Bird Island Chute, Louisiana; middle, Whiskey Chitto near Oberlin, 

Louisiana; right, mature rice near Fordoche, Louisiana (photographs by Dennis Demcheck) 
Water Quality in the Acadian-Pontchartrain

Drainages, Louisiana and Mississippi, 

1999–2001

By Dennis K. Demcheck, Roland W. Tollett, Scott V. Mize, 

Stanley C. Skrobialowski, Robert B. Fendick, Jr., Christopher M. Swarzenski, 

and Stephen Porter

Circular 1232

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

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

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

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

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

endorsement by the U.S. Government.

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

reproduce any copyrighted materials contained within this report.

Suggested citation:

Demcheck, Dennis K., Tollett, Roland, Mize, Scott V., Skrobialowski, Stanley C., Fendick Jr., Robert B., Swarzenski, 

Christoper M., and Porter, Stephen D., 2004, Water quality in the Acadian-Pontchartrain Drainages, Louisiana and 

Mississippi, 1999–2001: Reston, Va., U.S. Geological Survey Circular 1232, 47 p.

Library of Congress Cataloging-in-Publication Data

Water quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001 / 

 by Dennis K. Demcheck ... [et. al.].

 p. cm. -- (Circular ; 1232)

 Includes bibliographical references.

 ISBN 0-607-96400-6 (alk. paper)

 1. Water quality -- Louisiana -- Pontchartrain, Lake, Watershed. 2. Water quality -- 

 Mississippi. I. Demcheck, Dennis K. II. Geological Survey (U.S.) 

 III. U.S. Geological Survey circular ; 1232.

 TD224.L8W37 2004

 363.739’42’0976334--dc22 2004041397
Contents

National Water-Quality Assessment Program ......................................................... iv

What kind of water-quality information does the NAWQA Program provide? ............... v

Introduction to this Report .............................................................................. vi

Summary of Major Findings .............................................................................. 1

Stream and River Highlights ..................................................................... 1

Ground-Water Highlights ........................................................................... 1

Introduction to the Acadian-Pontchartrain Drainages ............................................. 3

Land use affects water quality .................................................................. 4

Water Use in Louisiana ........................................................................... 5

Hydrologic Conditions and Their Effects on Water Quality .................................... 5

Ground Water ....................................................................................... 6

Major Findings ............................................................................................. 8

Surface Water ....................................................................................... 8

Pesticides .......................................................................................... 8

Pesticide compounds vary with land use ................................................ 8

Pesticides occur in mixtures and as degradation products ........................... 9

Pesticides vary seasonally in streams ...................................................... 9

Mississippi River hydrology affects occurrence of atrazine in streams and rivers ... 10

Nutrients ............................................................................................. 15

Nutrient concentrations differ with land use ............................................. 15

Forms of nitrogen vary among streams in the Acadian-Pontchartrain Drainages 

and in the Mississippi River at St. Francisville .................................... 15

Nutrient concentrations vary seasonally in streams .................................... 16

Organochlorine compounds persist in sediment and fish tissue .............................. 18

Elevated levels of mercury are present in fish north of Lake Pontchartrain ............... 19

Aquatic communities are affected by land use and habitat ................................. 20

Ground Water ....................................................................................... 23

Nitrate, Pesticides, and Volatile Organic Compounds .................................... 24

Naturally Occurring Trace Elements and Water Chemistry .............................. 24

Radon .......................................................................................... 25

Study Unit Design ....................................................................................... 27

Stream-Chemistry and Ecology .................................................................. 27

Ground Water ....................................................................................... 28

References Cited .......................................................................................... 31

Glossary ................................................................................................... 33

Appendix—Water Quality Data from the Acadian-Pontchartrain Drainages in a 

National Context ................................................................................. 36
iv

National Water-Quality Assessment Program

The quality of the Nation’s water resources is integrally linked to the long-term availability of 

water that is clean and safe for drinking and recreation and also suitable for industry, irrigation, 

and habitat for fish and wildlife. Recognizing the need for long-term, nationwide assessments 

of water resources, the U.S. Congress has appropriated funds since 1991 for the USGS to conduct the National Water-Quality Assessment (NAWQA) Program. Scientists in the NAWQA 

Program work with partners in government, research, and public interest groups to assess the 

spatial extent of water-quality conditions, how water quality changes with time, and how human 

activities and natural factors affect water quality. This information is useful for guiding watermanagement and protection strategies, research, and monitoring in different hydrologic and 

land-use settings across the Nation.

The Acadian-Pontchartrain Drainages is one of 51 water-quality assessments initiated since 

1991. Together, the 51 major river basins and aquifer systems, referred to as “Study Units,” 

include water resources used by more than 60 percent of the population in watersheds that 

cover about half of the land areas of the conterminous United States. Timing of the assessments 

varies because of the program’s rotational design in which one-third of all Study Units are 

intensively investigated for 3 to 4 years, with trends assessed every 10 years. As indicated on 

the map, the Acadian-Pontchartrain Drainages is part of the third set of intensive investigations 

that began in 1997.

1991–95

1994–98

1997–2001

Not yet scheduled

HighPlains Regional

GroundWaterStudy,

1999–2004

NAWQA Study Units—

Assessment schedule

Acadian-Pontchartrain

Drainages
What kind of water-quality information does the NAWQA 

Program provide?

Water-quality assessments by a single program cannot possibly address all of the Nation’s 

water-resources needs and issues. Therefore, it is necessary to define the context within which 

NAWQA information is most useful. 

• Total resource assessment—NAWQA assessments are long-term and interdisciplinary, 

and include information on water chemistry, hydrology, land use, stream habitat, and 

aquatic life. Assessments are not limited to a specific geographic area or water-resource 

problem at a specific time. Therefore, the findings describe the general health of the total 

water resource, as well as emerging water issues, thereby helping managers and decision 

makers to set priorities.

• Source-water characterization—Assessments focus on the quality of the available, 

untreated resource and thereby complement (rather than duplicate) Federal, State, and 

local programs that monitor drinking water. Findings are compared to drinking-water 

standards and health advisories as a way to characterize the resource.

• Compounds studied—Assessments focus on chemical compounds that have well-established methods of investigation. It is not financially or technically feasible to assess all 

the contaminants in our Nation’s waters. In general, the NAWQA Program investigates 

those pesticides, nutrients, volatile organic compounds, and metals that have been 

or are currently used commonly in agricultural and urban areas across the Nation. A 

complete list of compounds studied is on the NAWQA Web site at http://water.usgs.gov/

nawqa.

• Detection relative to risk—Compounds are measured at very low concentrations, often 

10 to 100 times lower than Federal or State standards and health advisories. Detection of 

compounds, therefore, does not necessarily translate to risks to human health or aquatic 

life. However, these analyses are useful for identifying and evaluating emerging issues, 

as well as for tracking contaminant levels over time.

• Multiple scales—Assessments are guided by a nationally consistent study design and 

uniform methods of sampling and analysis. Findings thereby pertain not only to water 

quality of a particular stream or aquifer, but also contribute to the larger picture of how 

and why water quality varies regionally and nationally. This consistent, multiscale 

approach helps to determine if a water-quality issue is isolated or pervasive. It also 

allows direct comparisons of how human activities and natural processes affect water 

quality in the Nation’s diverse environmental settings. 

v
vi

Introduction to this Report

This report contains the major findings of a 1999–2001 assessment of water quality in the 

Acadian-Pontchartrain Drainages Study Unit. It is one of a series of reports by the National 

Water-Quality Assessment (NAWQA) Program that present major findings in 51 major river 

basins and aquifer systems across the Nation. 

In these reports, water quality is discussed in terms of local, State, and regional issues. Conditions in a particular basin or aquifer system are compared to conditions found elsewhere and 

to selected national benchmarks, such as those for drinking-water quality and the protection of 

aquatic organisms. 

This report is intended for individuals working with water-resource issues in Federal, State, or 

local agencies, universities, public interest groups, or in the private sector. The information will 

be useful in addressing a number of current issues, such as the effects of agricultural and urban 

land use on water quality, human health, drinking water, source-water protection, hypoxia and 

excessive growth of algae and plants, pesticide registration, and monitoring and sampling strategies. This report also is for individuals who wish to know more about the quality of streams 

and ground water in areas near where they live, and how that water quality compares to other 

areas across the Nation.

The water-quality conditions in the Acadian-Pontchartrain Drainages Study Unit summarized in 

this report are discussed in detail in other reports that can be accessed from

(http://la.water.usgs.gov/nawqa/default.htm). Detailed technical information, data and analyses, 

collection and analytical methodology, models, graphs, and maps that support the findings presented in this report in addition to other reports in this series from other basins can be accessed 

from the national NAWQA Web site (http://water.usgs.gov/nawqa).

“The Acadian-Pontchartrain 

Drainages NAWQA program 

has contributed valuable 

information to the U.S. EPA 

Office of Pesticide Program 

(OPP) understanding of the 

occurrence of pesticides in 

ground and surface water in 

one of the nation’s major rice 

and sugarcane production 

areas. As a reliable source of 

comprehensive information, 

results from the USGS’ study 

unit have been used in pesticide exposure and risk assessments. The OPP has found the 

data useful in understanding 

the relationship between land 

use (e.g., agriculture) and the 

frequency and levels of pesticide detections in water.”

Sid Abel,

Environmental Fate and Effects Division, Office of Pesticide Programs, 

U.S. Environmental Protection 

Agency
Summary of Major Findings

1

Stream and River Highlights

Surface water sampled in the Acadian-Pontchartrain 

Drainages of southern Louisiana and southwestern Mississippi 

generally meets State and Federal guidelines for drinkingwater quality and the protection of aquatic life. Agriculture, 

urbanization, and oil and gas production, however, have 

degraded water quality and aquatic communities in rivers, 

streams, and bayous by increasing concentrations of pesticides, nutrients, and suspended sediment and disturbing the 

stream habitat. The combination of low-lying topography, 

slow and sluggish streams, and organic-rich bed sediments 

has resulted in some undesirable chemicals and contaminants, 

particularly pesticides, remaining in the surface-water system 

for prolonged periods.

• Pesticides are widespread in streams. At least one pesticide parent compound or degradation product was 

detected in 272 of 299 water samples (about 91 percent) collected from 8 sites. Concentrations were low, 

however, only rarely exceeding standards and guidelines established to protect human health and aquatic 

life (p. 8).

• Herbicides most heavily used for weed control on rice, 

soybeans, or sugarcane—including atrazine, molinate, 

and tebuthiuron—were the most frequently detected 

compounds in agricultural streams. The insecticide

most heavily used on rice—fipronil—was detected in 

72 percent of all samples from agricultural streams. 

Other insecticides—carbaryl, chlorpyrifos, diazinon, 

and malathion—were detected more frequently and 

usually at higher concentrations in urban Dawson 

Creek within the City of Baton Rouge than in the 

agricultural or mixed land-use streams. Diazinon was 

detected in 47 of 50 samples (about 94 percent) in 

Dawson Creek, and concentrations exceeded guidelines 

for the protection of aquatic life in 21 of 50 samples 

(about 42 percent) (p. 8).

• Concentrations of nitrogen generally were low in 

streams. For example, the median concentration of 

total nitrogen in agricultural streams in the AcadianPontchartrain Drainages (1.2 mg/L) was less than 

one-half the median value for 137 agricultural streams 

sampled across the Nation by the NAWQA Program 

(median of 3.5 mg/L) (p. 15).

• Median concentration of total phosphorus was

0.2 mg/L, and concentrations exceeded the U.S. Environmental Protection Agency (USEPA) desired goal to 

prevent nuisance plant growth (0.1 mg/L) in 90 percent 

of samples collected from streams draining agricultural 

or urban land (p. 15).

• Organochlorine pesticides and PCBs persist in streambed sediment and fish in the Acadian-Pontchartrain 

Drainages, although few concentrations exceeded 

State alert levels or consumption guidelines. The most 

frequently detected organochlorine compounds were 

PCBs, mirex, dieldrin, and degradation products of 

DDT and chlordane (p. 18).

• Mercury is widespread in sediment and fish, detected 

in all 21 bed-sediment samples and in all 19 fish-tissue samples. Concentrations of mercury in fish tissue 

exceeded one component used in the Louisiana State 

alert level assessment process in 8 of 19 streams. The 

highest concentrations were measured in tissue of fish 

collected (largemouth bass and selected species of 

sunfish) in sandy streams north of Lake Pontchartrain 

and in streams in the western part of the Study Unit 

(p. 19).

• Aquatic invertebrate and fish communities in southern 

Louisiana streams, rivers, and bayous differ among 

ecoregions and land uses. Diverse, abundant, and 

pollution-intolerant communities are associated with 

undeveloped and forest basins in the northern part 

of the Acadian-Pontchartrain Drainages study unit. 

More tolerant species, such as midges, worms, snails, 

catfish, gar, and certain sunfish are in the southern part 

(p. 20, 22).

Major Influences on Water Quality in Streams and 

Rivers

• Runoff from agriculture, aquaculture, and urban 

areas.

• Contamination of fish tissue and sediment by persistent organic chemicals and trace elements, such 

as mercury.

Ground-Water Highlights

The Chicot aquifer system, located west of the Mississippi River, and the Chicot equivalent aquifer system, located 

east of the river, are primary sources for domestic and publicwater supplies within the Acadian-Pontchartrain Drainages 

Study Unit and are designated as sole-source aquifers by the 

USEPA. The quality of water throughout these aquifer systems 

generally is of high quality and acceptable for drinking and 

other purposes. The water generally meets Federal guidelines 

established by the USEPA to protect drinking water.

• Nitrate, pesticide parent compounds and degradation 

products, and volatile organic compounds (VOCs) were 
Shallow Ground Water Supply Wells

Selected Indicators of Ground-Water Quality

Insecticides

Herbicides

Nitrate

Nutrients

Proportion of samples with detected concentrations

greater than or equal to health-related national

guidelines for drinking water

Proportion of samples with detected concentrations

less than health-related national guidelines for

drinking water

Proportion of samples with no detections

— Not assessed

Radon

Arsenic

Trace elements in water

Small Streams Major Rivers

Undeveloped

Selected Indicators of Streamwater Quality

Mixed

Land Uses

—

Insecticides

Proportion of samples with detected concentrations greater than or

equal to health-related national guidelines for drinking water, protection

of aquatic life, or the desired goal for preventing nuisance plant growth

Proportion of samples with detected concentrations less than healthrelated national guidelines for drinking water, protection of aquatic life, or

below the desired goal for preventing nuisance plant growth

Proportion of samples with no detections

Not assessed

Urban Agricultural

Nutrients

Organochlorines

in sediment

Pesticides

Total

phosphorus

Herbicides

Trace

elements

in sediment

Trace elements in tissue

Volatile organics

—

Organo- chlorines in tissue

Semivolatile

organics

—

—

2 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

• Concentrations of radon in samples collected from 

94 wells were elevated, and values exceeded the 

USEPA proposed drinking-water standard of 300 picocuries per liter (pCi/L) in 53 wells (about 55 percent). 

The source of uranium (from which radon is derived) in 

rocks underlying the Acadian-Pontchartrain Drainages 

is uncertain (p. 25).

detected at low concentrations in the Chicot and Chicot 

equivalent aquifer systems, in large part because 

downward movement of waters is impeded by a thick, 

relatively impermeable layer of clay below the soil 

(p. 24).

• Concentrations of trace elements in ground-water 

samples generally were low, rarely exceeding any 

USEPA drinking-water standards, although such 

standards have been established for only 12 of 24 trace 

elements included in this study. Arsenic exceeded the 

USEPA drinking-water standard of 10 μg/L in one well, 

which is not used for drinking supplies (p. 24).

• Natural chemistry of ground water in the Chicot and 

Chicot equivalent aquifer systems is similar. Concentrations of dissolved solids, calcium, sodium, bicarbonate, chloride, and iron, and values of pH typically were 

lowest in wells in the outcrop areas of the two systems 

(p. 25). 

Major Influences on Ground-Water Quality

• Geologic features, including a thick, relatively 

impermeable layer of clay below the soil that protects ground water from agricultural chemicals and 

other surface contaminants.

• Hydrologic features, including depth to water, 

recharge areas, and depth of flowpath.

• Agricultural and urban activities, including pumping for irrigation and domestic supply.
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Figure 1. The Acadian-Pontchartrain Drainages support a variety of water needs for humans, aquatic life, and wildlife, including substantial rice, sugarcane, and crawfish industries; wintering and feeding grounds for geese and shorebirds; and oil and gas production.

About 3 million people live in the Acadian-Pontchartrain Drainages. More than two-thirds live in 

the three largest urban areas, which include New 

Orleans, Baton Rouge, and Lafayette.

Crawfish farming is an important industry in the Mermentau River Basin in the 

central and western parts 

of the Study Unit where rice 

also is grown.

Rice is the most important 

crop produced in the Study 

Unit. Total rice acreage in the 

seven Parishes (Counties) of 

the Mermentau River Basin 

(Acadia, Allen, Evangeline, 

Jefferson Davis, Lafayette, 

St. Landry, and Vermilion) 

exceeds 300,000 acres.

Rice fields in southwestern Louisiana 

are primary wintering grounds for 

tens of thousands of geese and are 

important stopover feeding areas for 

migratory shorebirds.

Oil and gas production, distribution, and 

processing are common in the southern 

part of the Study Unit.

Crawfish harvesting boat.

Introduction 3

Introduction to the Acadian-Pontchartrain Drainages

The Acadian-Pontchartrain Drainages Study Unit 

(fig. 1) encompasses 26,000 square miles (mi2) of rolling 

hills, deltaic plains, and hardwood-dominated bottomland in southern Louisiana and southwestern Mississippi. 

Elevations range from 

sea level in the southern 

coastal marshes to more 

than 600 feet in the rolling hills of southwestern 

Mississippi. The area is 

classified as subtropical, with average annual 

precipitation ranging from 

55 to 62 inches.
Figure 2. The Acadian-Pontchartrain Drainages lie within parts of six ecoregions. The red 

line is the approximate northern boundary of the flat Louisiana coastal plains.

Mississippi Valley

Loess Plains Southeastern

Plains

Southern

Coastal Plains

South

Central

Plains

Western Gulf

Coastal Plains Mississippi

Alluvial

Plain

100 MILES

0 20 40 60 80 100 KILOMETERS

0 20 40 60 80

4 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Land use affects water 

quality

Approximately 50 percent of 

the Acadian-Ponchartrain Drainages 

is covered by agricultural cropland 

interspersed with pasture, woodlands, 

or forests (fig. 1). The remaining land 

is marshes (about 25 percent), swamp 

land (about 20 percent), and open 

water (about 5 percent). Agricultural 

land is most common in the Western 

Gulf Coastal Plains, where thick loess

and a loamy and clayey alluvium are 

ideally suited for rice cultivation. Rice 

is the most important agricultural crop 

produced in the basin. Total rice acreage in the seven Parishes (Counties) of 

the Mermentau River Basin (Acadia, 

Allen, Evangeline, Jefferson Davis, 

Lafayette, St. Landry, and Vermilion) 

was nearly 400,000 acres in 1998 and 

about 340,000 acres in 2000 (Louisiana 

Cooperative Extension Service, 1998, 

2000). Rice is routinely treated with the 

insecticide fipronil, which can be toxic 

to aquatic life. Releases of water from 

the rice fields during March through 

May result in elevated concentrations of 

insecticides and suspended sediment in 

receiving streams and bayous.

Sugarcane is the predominant crop 

in the southern and southeastern parts of 

the Study Unit and is grown in scattered 

areas in the southwestern part. More 

than 460,000 acres of sugarcane were 

planted in 1999. This crop routinely 

is treated with the herbicide atrazine 

for broadleaf weed control. Atrazine is 

applied several times each year at both 

pre-emergent and post-emergent stages 

of the plants.

Aquaculture, primarily crawfish 

farming, is important in the central and 

western parts of the Study Unit in the 

Mermentau River Basin, where rice also 

is grown. There were about 80,000 acres 

of crawfish ponds in the AcadianPontchartrain Drainages in 1999. 

Two species are grown commercially, 

including the red swamp crawfish (Procambarus clarkii) and the white river 

crawfish (Procambarus zonangulus). 

Crawfish ponds may be managed solely 

for the purpose of cultivating crawfish, 

or rice and crawfish may be doublecropped annually. In double-cropping, 

rice is planted in flooded fields during 

March and April, drained, re-flooded in 

June, and stocked with crawfish. The 

fields are drained again in August for 

harvesting, re-flooded in October, and 

crawfish are harvested from November 

through the next April (Avery and Lorio, 

1999).

Nearly 3 million people live in the 

Acadian-Pontchartrain Drainages. More 

than two-thirds live in the large population centers (greater than 250,000), 

including New Orleans, Baton Rouge, 

and Lafayette (2000 Census). Although 

urban areas account for only 1 percent 

of the land in the Study Unit, their effect 

on water quality and aquatic life can be 

substantial. Contaminant sources associated with urban areas include septic systems and wastewater effluent; fertilizers

and pesticides used on lawns, gardens, 

parks, rights-of-way, and golf courses; 

and runoff containing oil, solvents, metals, and other contaminants from streets 

and parking lots.

Oil and gas production, distribution, and processing are major and 

conspicuous features of the landscape in 

the southeastern parts of the Study Unit. 

Thousands of miles of pipeline canals 

The Acadian-Pontchartrain Drainages lie within parts of six U.S. Environmental Protection Agency ecoregions 

(fig. 2), including the South Central 

Plains, Western Gulf Coastal Plains, 

Southeastern Plains, Southern Coastal 

Plains, Mississippi Valley Loess Plains, 

and the Mississippi Alluvial Plain 

(Omernik, 1985). The South Central 

Plains in the northwestern part of the 

Study Unit is characterized by low hills 

and forests with longleaf and shortleaf 

pine. The Western Gulf Coastal Plains in 

the southwest comprise five major bayous that divide the basin into a series of 

broad, flat-lying areas separated by bottomland hardwood riparian corridors, 

which vary in width from only a few 

hundred feet to several miles. The upper 

part of this ecoregion is characterized 

by rolling, pine-covered hills with sandy 

streams. The Southeastern Plains and 

Southern Coastal Plains in the eastern 

part of the Study Unit consists of small 

streams and mixed longleaf pine forest. 

The Mississippi Valley Loess Plains, 

east of the Mississippi River, consist of 

rolling hills, loessial (windblown) soils, 

small branching streams, and mixed 

hardwoods. The Mississippi Alluvial 

Plain is characterized by low relief and 

slope, cypress swamps, and fresh-tosaline marshes.
Figure 3. Rice irrigation is a major use of water in southwestern Louisiana.

0

100

200

300

400

500

600

Public supply Livestock Rice irrigation General irrigation Aquaculture

WATER USE CATEGORY

WIT

H

D

R

AWALS, IN

MILLIO

N

G

ALLO

N

S

P

E

R

D

AY

Ground water

Surface water

Introduction 5

and oilfield-support canals have facilitated saltwater intrusion from coastal 

areas into historically fresh marshes and 

allowed interbasin flow of water from 

the Atchafalaya and Mississippi-Atchafalaya River system. The production 

of oil and gas also is common, though 

declining, in the southwestern part of the 

Study Unit, where individual oil wells 

often are drilled in rice fields and separated from the fields by a low earthen 

berm. Rice fields in southwestern 

Louisiana are wintering grounds for tens 

of thousands of geese and are important 

stopover feeding areas for migratory 

shorebirds. Southwestern Louisiana 

fulfills a variety of important functions 

for both humans and wildlife.

Water Use in Louisiana

Extensive surface-water and 

ground-water resources within the 

Acadian-Pontchartrain Drainages are 

used for rice agriculture, crawfish 

aquaculture, and drinking-water supplies. Ground water used for domestic 

and public-water supply accounted for 

about 300 million gallons per day in 

2000 (Sargent, 2002, fig. 3). Surfacewater sources (also about 300 million 

gallons per day in 2000) supply drinking 

water to residents. Some surface water 

is transported from outside the Study 

Unit to supplement water needs within 

the drainages. Specifically, water from 

the Mississippi River is used to supply 

drinking water to residents in the City 

of New Orleans and water for industries 

and power-generation facilities along the 

Mississippi River from Baton Rouge to 

New Orleans (not included in numbers 

in fig. 3).

Large amounts of water are used 

to support rice agriculture, primarily in the Mermentau River Basin. In 

2000, 563 million gallons of ground 

water per day was withdrawn from the 

Chicot aquifer system for rice irrigation (fig. 3). Surface-water sources also 

are used for rice agriculture, contributing about 150 million gallons per day. 

Both surface water and ground water 

also are used for crawfish farming in 

the Mermentau River Basin. Because 

of the double-cropping practice involving rice production and crawfish, water 

is recycled between the ground-water 

and surface-water systems. Specifically, 

ground water is pumped onto rice fields, 

released to drainage ditches and streams 

after a brief period, and later possibly 

reused for other surface-water purposes 

farther downstream.

The types of water used within the 

Mermentau River Basin vary geographically. Ground water supplies most 

needs, including those for drinking and 

irrigation, in the northeastern part of the 

basin. The southern part of the basin 

relies heavily on surface water for irrigation.

A drought in southern Louisiana, 

which began in the spring of 1999 and 

lasted into the summer of 2001, caused a 

decrease in the availability of fresh surface water, particularly in the southwestern part of the Study Unit. As a result, 

rice farmers had to depend more heavily 

on ground-water supplies, and in many 

cases planted fewer acres of rice.

Hydrologic Conditions 

and Their Effects on 

Water Quality

Hydrologic conditions are complex 

in the Acadian-Pontchartrain Drainages 

Study Unit because of its location at 

the terminus of the Mississippi River, 

low-lying topography, and an extensive levee network. Specifically, water 

resources in the central part of the Study 

Unit are affected by inputs from the 

Mississippi River, which drains more 

than 40 percent of the continental United 

States. Studies conducted in the last 

decade show that considerable amounts 

of compounds from both natural and 

human sources, such as total nitrogen, 

originate from upstream watersheds in 

the Mississippi River Basin quite distant 

from Louisiana and the river’s receiving 

water, the Gulf of Mexico (Alexander 

and others, 2000). 

The generally low-lying topography of southern Louisiana results in low 

stream gradients and flow velocities, 

the latter typically less than 1 foot per 
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Figure 4. Streamflow at Whiskey Chitto Creek, 1999–2001, was lower than the 62-year 

historical average because of a drought (classified as “Extreme”) from the fall of 1999 to 

the fall of 2000 (John M. Grymes, Louisiana State Climatologist, written commun., 2002).

6 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

second. The low gradients can result in 

reverse, upstream flow in some streams. 

For example, upstream flows typically 

occur in the summer and fall in the Mermentau River, which is tidally affected. 

Upstream flow can be enhanced by natural events, such as storms and sustained 

winds from the south in conjunction 

with unusually high tides. These reverse 

flows can increase in magnitude and 

duration during periods of low stream 

discharge, such as those during the 

drought of 1999–2001.

Natural hydrology of the AcadianPontchartrain Drainages has been modified by an extensive levee network built 

for flood control that began in the early 

1800’s. The scale and magnitude of the 

modifications were accelerated after the 

great Mississippi River flood in 1927, 

with the unintended consequence that 

coastal wetlands were isolated from the 

Mississippi River. River sediment and 

nutrients needed to maintain freshwater 

and saltwater wetlands no longer nourish 

and sustain the valuable wetlands but 

rather are deposited in the Gulf of Mexico. Such modifications also have facilitated unnatural basin interflow, such as 

in the Gulf Intracoastal Waterway, which 

allows water from the Atchafalaya River 

to flow east and west to points 30 to 50 

miles away (Swarzenski, 2003).

Extreme events can substantially 

affect stream hydrology in the AcadianPonchartrain Drainages. For example, 

streamflow during the extreme drought 

over the 2-year period 1999–2000 was 

below historical average conditions 

(fig. 4). Streamflow increased to more 

normal levels in 2001, when precipitation was greater.

Water quality in streams, rivers, and 

shallow aquifers (ground water) varies in 

response to changing hydrologic conditions. Thus, information on streamflow 

is critical for assessing water-quality 

conditions and ecosystem health. When 

precipitation and runoff are below 

average, streamflow is lower than normal, and concentrations of suspended 

sediment and constituents that attach to 

sediment particles, such as phosphorus 

and some trace elements, often are lower 

than average. In contrast, concentrations 

of dissolved constituents, particularly 

those contributed by ground water and 

sewage treatment effluent, often are 

higher than average during low precipitation and streamflow conditions.

Ground Water

Southern Louisiana and southwestern Mississippi are underlain by a thick 

sequence of southerly and southeasterly 

dipping interbedded clays, silts, and 

gravels. To the west of the Mississippi River, the Chicot aquifer system 

includes two major units—an upper and 

a lower sand (Nyman, 1984) (fig. 5). 

These sands are several hundred feet 

thick and are separated in places by 

thick, discontinuous clays. At the top 

of the Chicot aquifer system is a layer 

of clay that acts as a surficial confining 

unit. The thickness of this clay layer 

averages about 100 feet in the AcadianPontchartrain Drainages Study Unit. 

The clay layer once was thought to be 

impermeable, but results of simulations 

made with ground-water models indicate 

that as much as 6 inches of water per 

year, primarily from the land surface, 

recharge the Chicot aquifer system near 

major pumping centers (Nyman and 

others, 1990, p. 33). Ground water in the 

outcrop area in the northern part of the 

Study Unit is considered unconfined or 

semiconfined. This water flows generally south from the outcrop areas to 

deeper parts of the system, where it is 

confined. Ground water in the outcrop 

areas is more vulnerable to contamination from overlying land-use activities 

than deeper ground water that travels 

along regional flow paths in the southern 

part of the Study Unit. This description 

of the Chicot aquifer system also applies 

to the Chicot equivalent aquifer system 

(which is the upper part of the Southern 

Hills regional aquifer system) to the east 

of the Mississippi River.
Figure 5. The Chicot and Chicot equivalent aquifer systems are both characterized by water-rich sands interlayered in places 

by discontinuous clay layers.�����

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Introduction 7
8 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Major Findings

Surface Water

Water quality of streams and rivers 

in the Acadian-Pontchartrain Drainages 

of southern Louisiana is generally good. 

Land-use activities related to agriculture, 

urbanization, and oil and gas production, 

however, have increased the frequency 

of occurrence and concentrations of 

pesticides and other organic compounds, 

nutrients, and suspended sediment 

in surface waters and have disturbed 

aquatic habitats. 

Pesticides

Pesticides, which are used to 

control weeds, insects, and fungi, can 

have unintended effects on the health 

of humans and aquatic communities. Although the concentrations of 

pesticides in streams and rivers in the 

Acadian-Pontchartrain Drainages infrequently exceeded standards and guidelines to protect human health and aquatic 

life, the occurrence of these compounds 

was widespread. Specifically, at least 

one pesticide parent compound or 

degradation product was detected in 272 

of 299 water samples (about 91 percent) 

collected at eight stream sites. In all, 

58 different pesticides or their degradation products, including 38 herbicides 

and 20 insecticides, were detected. 

In addition, these compounds seldom 

occurred alone. Mixtures of pesticides 

were frequently detected, and the effects 

of long-term exposure to mixtures of 

pesticides, even at low concentrations, 

are poorly understood.

Pesticide compounds vary with 

land use

The types of pesticide compounds 

and the degree of contamination in 

streams are closely linked to land use 

and to the chemicals used in each setting. For example, in the Mermentau 

River Basin, a total of 47 different pesticides and degradation products were 

detected in streams draining agricultural 

areas. Herbicides most heavily used for 

weed control on major agricultural crops 

or highway margins—including atrazine, 

molinate, and tebuthiuron—were the 

most frequently detected in the agricultural streams. The most heavily used 

and most frequently detected insecticide in the agricultural streams of the 

Mermentau Basin was fipronil. Atrazine 

was detected in nearly 100 percent of 

the samples; tebuthiuron was detected in 

more than 95 percent, molinate in about 

75 percent, and fipronil in about 72 

percent of samples (Skrobialowski and 

others, 2003).

Although pesticides commonly 

were detected, concentrations were low 

(generally below 0.1 μg/L), and only a 

few exceeded guidelines established for 

the protection of aquatic life. Specifically, concentrations of atrazine in the 

Mermentau River Basin exceeded the 

guideline for the protection of aquatic 

life (1.8 μg/L) in 27 samples from 14 

sites in the Mermentau Basin. The 

largest concentration of tebuthiuron 

(6.33 μg/L) was detected at one site on 

Bayou des Cannes and was the only 

detection exceeding the Canadian Council of the Ministers of the Environment 

guideline for the protection of aquatic 

life (1.6 μg/L). No standards or guidelines have been established for molinate 

and fipronil.

Pesticides are not just an agricultural problem. In fact, pesticides also 

are prevalent in urban streams because 

of chemicals used on lawns, parks, 

golf courses, and rights-of-way, and 

commonly were detected at greater 

frequencies and concentrations in these 

areas than in other land-use settings. 

Specifically, the insecticides carbaryl, 

chlorpyrifos, diazinon, and malathion 

were detected more frequently and 

usually at higher concentrations in the 

urban Dawson Creek within the city 

of Baton Rouge, than in the agricultural or mixed land-use sites. Diazinon 

was detected in 47 of 50 samples (94 

percent) in Dawson Creek, but in only 

95 of 242 samples (39 percent) collected 

from agricultural streams. Concentrations of diazinon in Dawson Creek 

exceeded guidelines for the protection of 

aquatic life (0.08 μg/L established by the 

International Joint Commission) in 21 of 

50 samples (42 percent). Samples from 

Dawson Creek also contained 10 herbicides (such as atrazine, simazine, 

and prometon used in lawn care and 

in maintenance of rights-of-way) and 

four atrazine degradation products.

Major rivers and streams draining areas of mixed land use commonly 

contain pesticides from both agricultural 

and urban sources, resulting in a wider 

mix of compounds, including pesticides 

commonly associated with agriculture 

(atrazine, tebuthiuron, molinate, and 

fipronil) and those associated with 

urban areas (prometon, diazinon, and 

carbaryl). The broader suite is illustrated 

by samples collected from Bayou Grosse 

Tete at Rosedale, where 20 pesticides 

were detected. The 7 pesticides detected 

in the highest concentrations are shown 

in figure 6. 

NAWQA findings show that the 

occurrence of pesticides in streams is 

strongly related to land use, chemical application, and nonpoint source

runoff. Understanding the relations 

among pesticide occurrence, land use, 

and nonpoint source runoff is a major 

step toward reducing contaminant 

levels in urban and agricultural settings. 

While commercial, urban, and agricultural chemical application activities fall within the scope of State and 

Federal regulation, it is the applicator’s 

responsibility to use pesticides properly. 

Information about current chemical use 

by landowners is generally insufficient, 

however, and in urban areas is virtually 

These findings are supported by the 

NAWQA study design described on 

pages 27–30.
What concentrations of pesticides are considered safe for 

aquatic life?

Several agencies, including U.S. Environmental Protection Agency (USEPA), 

Environment Canada, and the IJC (International Joint Commission), have 

established guidelines to protect aquatic life. These guidelines are designed to 

prevent adverse short-term (acute) and long-term (chronic) effects on aquatic 

life. The aquatic-life guidelines or benchmarks developed by USEPA are based 

on 4-day average concentrations, are intended to protect 95 percent of the 

aquatic species, and should not be exceeded more than once in 3 years. The 

Canadian and IJC aquatic-life guidelines, which are more stringent than those 

of the USEPA, indicate a single maximum concentration that should never 

be exceeded. Aquatic-life guidelines have been developed for 14 pesticides 

analyzed for this study.

Figure 6. Pesticides in Bayou Grosse Tete showed a broad mix of herbicides and insecticides, which reflects the urban and agricultural nature of the area.

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Major Findings 9

unavailable for local and regional waterresource management and decisionmaking. Improved tracking of chemical use 

and continued monitoring for pesticides 

in streams would help identify suspected 

sources (for example nonpoint runoff) 

of specific contaminants and support 

appropriate management actions.

Pesticides occur in mixtures 

and as degradation products

Pesticides seldom occurred alone 

in streams. More than 75 percent of 

the samples collected from agricultural 

streams draining the Mermentau River 

Basin contained at least three compounds. The Mermentau River Basin is 

primarily a rice and soybean agricultural 

area, and these uses are reflected in the 

detection of the herbicides atrazine, 

molinate, tebuthiuron, and the insecticide fipronil. The urban site Dawson 

Creek at Baton Rouge also was characterized by mixtures of insecticides 

such as diazinon and malathion with the 

herbicide 2,4-D.

Chemical degradation products are 

often as common in streams as parent 

compounds (U.S. Geological Survey, 

1999). For example, two atrazine degradation products, 2-hydroxyatrazine and 

deethylatrazine, were detected in 84 and 

90 percent, respectively, of the samples 

collected from the agricultural Mermentau River Basin (where atrazine was 

detected in 100 percent of the samples). 

The highest concentrations of desulfinylfipronil, a rapidly formed, light-induced 

degradation product of fipronil, were 

typically found with the highest concentrations of the parent compound at 14 of 

17 sites. Degradation products can have 

similar, lesser, or even greater toxicities 

than parent compounds. Possible risks 

to human health and aquatic life from 

degradation products are not well understood, and drinking-water standards or 

aquatic-life guidelines have not been 

established for many of these products 

(see inset, p. 14).

Pesticides vary seasonally in 

streams

Concentrations of pesticides varied 

seasonally in streams in response to 

seasonal patterns of chemical use and 

the frequency and magnitude of runoff 

from precipitation and irrigation. For 

example, elevated concentrations of 

atrazine, molinate, tebuthiuron, and 

fipronil generally were elevated in the 

Mermentau River in April and May 

(fig. 7). The seasonal peaks are coincident with applications of pesticides 

on corn, sugarcane, and rice, as well as 

the draining of ricefields (particularly 

associated with elevated concentrations 

of molinate and fipronil). Concentrations 

of molinate were the highest among all 

agricultural pesticides, reaching a maximum of more than 150 μg/L in a small 

tributary of the Mermentau River in 

2000. Tebuthiuron, which is used more 

broadly and throughout the year for general weed control on crops (except for 

rice) as well as for nonagricultural uses 

such as along roads and other rightsof-way, does not demonstrate seasonal 

peaks as pronounced as those for other 

pesticides in agricultural streams.

Seasonal patterns in concentrations of herbicides and insecticides were 

highly variable and less predictable in 

the urban Dawson Creek than in the 

agricultural streams (fig. 8). For example, concentrations of the broad-spectrum herbicide 2,4-D peaked in April, 
Figure 8. Relatively low concentrations of pesticides were punctuated with highly variable 

and unpredictable peaks in the urban Dawson Creek.

Figure 7. Pesticides in the Mermentau River at Mermentau, Louisiana varied seasonally 

in response to seasonal use of the chemicals and the frequency and magnitude of runoff 

from precipitation and irrigation.

Atrazine

Molinate

Tebuthiuron

Fipronil

DATE

1999 2000 2001

Jan. 21

Mar. 21

May 12May 12May 12

July 12July 12July 12

Sep. 12Sep. 12

Nov. 12Nov. 12

Jan. 12Jan. 12

Mar. 12Mar. 12

0

1

2

3

4

5

6

1998

Nov. 12

PESTICIDE CONCENTRATION,

IN MICRO

GRA

MS PER LITER

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10 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

June, and September 1999, and in April, 

June, and July of 2000 (reaching a maximum of 4.1 μg/L); but otherwise concentrations were low, generally below 

0.5 μg/L. Prometon was detected at 24.8 

μg/L in April 2000 but never above 0.25 

μg/L throughout the remaining 2-year 

sampling period. Temporal patterns in 

the concentrations of pesticides in the 

urban creek most likely reflect targeted 

and sporadic applications as needed, as 

opposed to patterns in streams drainNAWQA findings clearly show 

seasonal variations. Improved information and monitoring of temporal 

patterns will aid in water management 

and watershed protection because 

seasonal peaks significantly affect the 

timing of the highest concentrations 

in drinking-water supplies and aquatic 

habitats (possibly affecting, for 

example, critical life stages of aquatic 

organisms).

Mississippi River hydrology 

affects occurrence of atrazine in streams and rivers

Concentrations of atrazine can 

vary seasonally, in large part because 

of the fluctuating regional inputs from 

the Mississippi River, which drains 

more than 40 percent of the continental United States, and local inputs 

from streams draining agricultural 

and urban areas within the AcadianPontchartrain Drainages (Demcheck 

and Swarzenski, 2003). For example, 

water samples collected from the 

Mississippi River at Baton Rouge 

showed peak concentrations during 

May and June over a 2-year period, 

1999–2000. This period of increased 

chemical concentrations in the water 

is commonly referred to as the “spring 

flush” and is the result of chemical 

applications and subsequent runoff 

in the upstream agricultural areas of 

the Midwest (Goolsby and Battaglin, 

2000) (fig. 9).

In contrast, water samples collected from Bayou Grosse Tete at 

Rosedale, which is hydrologically 

isolated from the Mississippi River 

and is affected mostly by local urban 

and agricultural land use in the

Terrebonne basin, showed pronounced 

atrazine peaks in April, well before 

atrazine is transported to southern 

Louisiana from upstream sources 

by the Mississippi River (fig. 10). 

Concentrations reflect applications 

of atrazine on corn and sugarcane, 

as well as applications in residential 

areas and light commercial businesses 

on both sides of the bayou. Seasonal 

peak concentrations in Bayou Grosse 

ing agricultural areas, where pesticides 

are applied at specific times during the 

growing season. For example, 2,4-D 

is used in Baton Rouge for control of 

exotic and invasive plant species, such as 

water hyacinth, that interfere with urban 

stormwater drainage and navigation. It is 

likely that the mild winters of 1999 and 

2000, combined with drought conditions, necessitated several applications 

of 2,4-D during those years.
DATE

1998 1999 2000

0

5

10

15

20

25

30

35

40

45

O N D J F M A M J J A S O N D J F M A M J J A S

CONCENTRATION, IN MICRO

GRA

MS PER LITER

April 9, 1999

April 10, 2000 Atrazine

Figure 11. Atrazine in Bayou Boeuf at Amelia was detected at low-level concentrations 

throughout the year.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

DATE

1999 2000

Sept. 1

Nov. 13

Jan. 13Jan. 13

Mar. 13Mar. 13

May 13May 13

Jul. 13Jul. 13

Sept. 13Sept. 13

Nov. 13

ATRAZINE, IN MICRO

GRA

MS

PER LITER

Figure 9. Atrazine in the Mississippi River at Baton Rouge generally 

peaks in the months of May and June.

Figure 10. Atrazine in Bayou Grosse Tete at Rosedale comes from local 

urban and agricultural sources in the Terrebonne basin and generally 

peaks in April.

May 25, 1999

June 30, 2000

DATE

1999 2000 2001

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Jan. Mar. May July Sept. Nov. Jan. Mar. May July Sept. Nov. Jan.

CONCENTRATION, IN MICRO

GRA

MS PER LITER

Atrazine at:

Baton Rouge

St. Francisville

Major Findings 11

Tete greatly exceeded those in the Mississippi River at Baton Rouge, reaching 

a maximum of 42 μg/L

(fig. 6). Water in the bayou is not used as 

a major drinking water source, but some 

downstream communitities mix water 

from this bayou with water from other 

sources for drinking-water supply. 

Control measures are being implemented by local and State water managers 

to reduce applications of atrazine and 

to promote the use of activated carbon 

filters at downstream public-watersupply intakes.

Samples collected from Bayou 

Boeuf at Amelia demonstrate dual 

effects of local and regional inputs 

of atrazine (fig. 11). Specifically, this 

bayou receives water directly from the 

Atchafalaya River, which carries atrazine transported from agricultural land 

throughout the Midwest and runoff from 

nearby sugarcane fields where atrazine is 

applied. The overall temporal pattern in 

concentrations of atrazine from Bayou 

Boeuf shows broader and smaller peaks 

of longer duration than those demonstrated by the Mississippi River at Baton 

Rouge and Bayou Grosse Tete at Rosedale. Water from these diverse sources 

combined with tidally caused backwater 

effects that often impede efficient drainage in this low-relief area interact to 

produce this pattern. The water does not 

move quickly or efficiently enough to 

produce a sharp peak in atrazine concentration. The basin also drains so slowly 

that any atrazine in the water takes a 

prolonged amount of time to be removed 

from the basin.

For additional information on pesticides in surface-water resources 

of the Acadian-Pontchartrain 

Drainages, refer to Skrobialowski 

and others (2003), Demcheck and 

Swarzenski (2003), and Demcheck and Skrobialowski (2003). 

These reports also are available at http://la.water.usgs.gov/

publications.html
Fipronil—A relatively new insecticide applied in southern Louisiana

Fipronil, a relatively new insecticide licensed for use in 1996, came into widespread use in Louisiana in 1999, replacing 

carbofuran. Fipronil is licensed for use on a large and growing list of targeted organisms, including fleas, termites, water 

weevils, and fire ants. In the summer of 1999, public concerns arose in Louisiana over the use of fipronil-coated rice seed 

and its possible negative effects on crawfish populations.

In response to these concerns, the NAWQA Program initiated a study of fipronil and three degradation products in water 

and sediment. Fipronil was detected in about 72 percent of water samples from 19 sites on agricultural streams in the 

Mermentau River Basin. Concentrations of fipronil ranged from less than 0.004 μg/L to 6.41 μg/L in a small headwater tributary surrounded by ricefields. Concentrations exceeded the freshwater acute numeric target for Total Maximum 

Daily Loads (TMDL) (4.6 μg/L) at 3 sites and the chronic numeric target for TMDL (2.3 μg/L) at 14 additional sites 

(U.S. Environmental Protection Agency, 2002b). For additional information concerning the TMDL program in Louisiana, 

see http://www.deq.state.la.us/technology/tmdl/.

Concentrations of fipronil vary 

seasonally in water, mostly in 

response to agricultural practices. 

Specifically, the maximum concentrations occurred in the headwaters 

of small bayous surrounded by rice 

agriculture during March and April 

(fig. 12), which coincided with the 

release of ricefield tailwaters. The 

maximum concentration detected 

in the main stem of the Mermentau 

River was 3 μg/L. The peak concentration of fipronil occurred concurrently with or slightly before the 

peak concentrations of other ricefield pesticides, including molinate 

(Goree and others, 2000, 2001).

Typical of many recently introduced 

pesticides, fipronil degrades quickly into other forms or “degradation products.” In fact, the highest concentrations of 

the photodegradate desulfinylfipronil were found with the highest fipronil concentrations at 14 out of 17 sampling sites, 

indicating that aerobic, light-induced degradation occurs rapidly while relatively large amounts of the parent compound 

are still present in water (fig. 12). Other degradation products, fipronil sulfide and fipronil sulfone, generally were initially 

detected in lower concentrations, most likely because they are produced in soils, either aerobically or anaerobically, rather 

than by light (Connelly, 2001). As degradation processes proceed, however, the degradation products begin to be detected 

in higher concentrations than the parent compound. This is shown in figure 12, but the logarithmic scale used tends to deemphasize the differences in concentrations between the parent compound and the various degradation products.

Bed-sediment samples contained no detectable levels of the fipronil parent compound (fig. 13). Fipronil degradation products, however, were detected in sediment at all 17 sites. Fipronil sulfide, produced by sulfide-reduction processes occurring in anaerobic sediment, was detected at all 17 sites at the highest concentrations, ranging from 0.6 μg/kg to as much 

as nearly 25 μg/kg. Desulfinylfipronil also was detected at all sites, ranging from 0.55 μg/kg up to about 7 μg/kg. Fipronil 

sulfone, a soil-oxidation product, was detected at 16 of 17 sites, with a maximum concentration of 10.5 μg/kg. Concentrations of the three degradation products in bed sediments increased downstream, with maximum concentrations at the most 

downstream sites on the main stem of the Mermentau River (fig. 13).

Figure 12. Concentrations of fipronil and its degradation products in the Mermentau 

River at Mermentau typically peak in late March through mid April after applications.

0.001

3/23 4/22 5/22 6/21

2000 2001

7/21 8/20 9/19 10/19 11/18 12/18 1/17 2/16 3/18 4/17

0.01

0.1

1

10

Fipronil

Desulfinylfipronil

Fipronil sulfide

Fipronil sulfone

C

ONCENT

R

ATION, IN MIC

R

O

G

A

M

S

PER LITER

DATE

12 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001
The presence of fipronil and, particularly, its degradation products in 

the Mermentau River Basin are of 

concern to water-resource managers because of their possible effects 

on aquatic life. Fipronil degradation 

products are more persistent and can 

be more toxic to aquatic life than the 

parent compound (Connelly, 2001). 

Specifically, the USEPA reports that 

fipronil sulfone is about 6.5 times 

more toxic, and fipronil sulfide is 

nearly 2 times more toxic to freshwater invertebrates than the parent 

compound (U.S. Environmental 

Protection Agency, 1996).

Changes in invertebrate communities 

in the Mermentau River Basin are 

associated with elevated concentrations of fipronil. For example, abundances of tolerant mayflies in the genus Caenis and 

midges in the genus Rheotanytarsus decreased with increasing fipronil concentrations (fig. 14). Concentrations of fipronil 

in selected stream samples in the Mermentau River Basin were more than 10 times the known acute lethal concentration 

to selected midge larvae of 0.5 μg/L. Similar patterns occur in other midges as well. The overall abundance of aquatic 

invertebrates also was lower in streams with elevated concentrations of the degradation products fipronil sulfone, fipronil 

sulfide, and desulfinylfipronil.

Figure 14. Decreases in mayfly and midge abundance correspond to increases in fipronil concentrations in the Mermentau River basin.

4 5 6 7

FIPRONIL CONCENTRATION,

IN MICROGRAMS PER LITER

MID

GE ABUND

ANCE

M

AYFLY

ABUND

ANCE

0 1 2 3

0 0

10

10

20

20

30

30 40

Caenis species

Mayfly

Rheotanytarsus species

Midge

FIPRONIL CONCENTRATION,

IN MICROGRAMS PER LITER

0 1 2 3 4 5 6 7

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Figure 13. Fipronil degradation products were detected in bed sediments of the Mermentau River Basin, generally increasing in a 

downstream direction. 

Major Findings 13
0

0

0

20

20

20

40

40

40

60

60

60

80

80

80

100

100

100

FREQUENCY

OF DETECTION, IN PERCENT, ABO

VE 0.01 MICRO

GRA

M PER LITER

INSECTICIDES

SURFACE WATER–

Acadian-Pontchartrain Drainages

EXPLANATION

SURFACE WATER–National

HERBICIDES

Malathion

Chlorpyrifos

Fipronil

Fipronil sulfone

Fipronil sulfide

Atrazine

Metolachlor

Deethylatrazine

(atrazine degradation product)

Prometon

Cyanazine

Simazine

Diazinon

Molinate

Metribuzin

Thiobencarb

Tebuthiuron

Agricultural land

Urban land

Mixed land use

no data

no datano data

no data

no datano data

no data

no datano data

in the urban Dawson Creek than others 

nationally. Higher frequencies of these 

compounds in the Study Unit most 

likely reflect a longer growing season 

and increased survival of insect pests 

in the subtropical climate of the Acadian-Pontchartrain Drainages (which, 

in other parts of the Nation, are naturally controlled by winters), requiring 

applications of pesticides throughout 

much of the year.

Major rivers and streams in the 

Acadian-Pontchartrain Drainages 

Study Unit draining areas of mixed 

land use commonly contain pesticides 

from both agricultural and urban 

sources, resulting in a wide mix of 

compounds, including pesticides 

commonly associated with agriculture (atrazine, tebuthiuron, molinate, 

and fipronil) and those associated 

with urban areas such as diazinon. 

Frequency of detections, particularly 

for herbicides, was greater in streams 

in the Acadian-Pontchartrain Drainages than nationally.

The types of pesticides detected 

in the Acadian-Pontchartrain 

Drainages generally are among the 

top pesticides most often detected 

nationally, in addition to others—

including molinate and fipronil—

used heavily in the Study Unit for 

weed control or pest control on rice. 

For example, the herbicide molinate 

was detected in 59 percent of the 

agricultural samples, compared 

to 8 percent nationally. Because 

minimum detection levels change as 

analytical methods are refined, for 

the purposes of this comparison only 

pesticide detection greater than 0.01 

μg/L were used. Using a consistent 

minimum detection level facilitates 

comparisons between different 

studies. Fipronil and its degradation products were detected in about 

60 percent of water samples in the 

Acadian-Pontchartrain Drainages. 

No data for fipronil are available 

for samples collected in other river 

basins nationwide. The compound 

is now included in analyses by the 

NAWQA Program as this insecticide is licensed for use on a growing number of insect pests such as 

ants, fleas, and termites, and the use 

of fipronil is expected to increase 

substantially throughout the Nation 

in the coming years. Atrazine, the 

most heavily applied and commonly 

detected herbicide in the Nation’s 

waters also is the most commonly 

detected herbicide in southern 

Louisiana.

Diazinon, a commonly used 

insecticide in urban areas across 

the Nation, was detected more 

frequently in the urban Dawson 

Creek within Baton Rouge (about 

90 percent of samples) than in 

33 urban streams sampled across 

the Nation (about 54 percent). 

Similarly, atrazine and simazine, 

herbicides commonly used in lawn 

care, were detected more frequently 

Occurrence of Pesticides in the Acadian-Pontchartrain Drainages

14 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001
Pesticide risks to humans and aquatic life remain unclear

Although pesticides and their degradation products were detected frequently, 

concentrations generally were lower than current standards and guidelines for 

drinking water and human health. The risks to humans and aquatic life from 

present-day levels of pesticide exposure, however, remain unclear. Pesticide 

information gathered in the Acadian-Pontchartrain Drainages indicated that 

pesticide exposure is complicated by lengthy periods of low concentrations 

that are punctuated by seasonal spikes of much higher concentrations, in addition to complex mixtures of compounds and degradation products. Possible 

risks implied by these patterns of exposure have not been fully evaluated for 

several reasons. First, drinking-water standards or guidelines have not been 

established for many pesticides and their degradation products. Specifically, 

only 27 of the pesticides for which samples were analyzed in this study have 

current U.S. Environmental Protection Agency (USEPA) human health standards. Additionally, current standards do not yet address exposure to pesticide 

mixtures and the possibility that the presence of multiple compounds, even 

at low concentrations, may have adverse cumulative health effects. Further, 

standards and guidelines usually are based on expected long-term exposure 

to constant concentrations rather than lengthy periods of low concentrations 

punctuated by brief pulses of high concentrations. Finally, various potential 

effects, such as endocrine disruption and unique responses of sensitive individuals, have not yet been completely assessed.

Major Findings 15

For example, the median value for nitrogen in 137 agricultural streams sampled 

across the Nation was about 3.5 mg/L, 

more than twice the value measured 

in agricultural streams in the AcadianPontchartrain Drainages. The median 

concentration of phosphorus in the eight 

streams sampled in the Acadian-Pontchartrain Drainages was 0.2 mg/L, a 

value similar to that in streams sampled 

across the Nation.

Transport of nutrients in the 

environment depends on chemical mobility. Some compounds, 

such as nitrate, readily dissolve 

and move with water in streams 

and ground water. Many forms of 

phosphorus, however, attach to 

soil particles rather than dissolve; 

a large proportion of phosphorus is 

transported to streams with eroded 

soil, particularly during times of 

high runoff from precipitation or 

irrigation.

Nutrients

Nitrogen and phosphorus occur 

naturally in streams, but human activities—including the use of fertilizers 

in agricultural and urban areas and 

the discharge of municipal wastewater—can contribute to increases in the 

natural concentrations of these nutrients. 

Nitrogen and phosphorus are essential 

to the growth and health of plants and 

animals, but elevated concentrations of 

these nutrients are a potential concern 

for human health and aquatic life.

Excessive concentrations can contribute 

to the overgrowth of algae and other 

nuisance plants, whose death and subsequent decay can cause oxygen levels 

in streams to decrease substantially during warm weather and at night (see inset 

on Hypoxia, p. 17).

Concentrations of nitrogen generally were low in the Acadian-Pontchartrain Drainages. Specifically, median 

concentration of nitrogen was 1.2 mg/L 

for the eight streams sampled. The nitrogen levels generally were less than those 

found in other streams sampled across 

the Nation by the NAWQA Program. 

Nutrient concentrations differ 

with land use

Concentrations of nutrients differed 

with land use, with the largest concentrations detected in streams draining 

basins with large areas of agricultural 

or urban land. Specifically, the median 

concentration of nitrogen was slightly 

greater than 1 mg/L—a concentration 

considered to represent naturally occurring or “background” conditions for the 

Nation as a whole—in agricultural and 

urban basins, but only about 0.4 mg/L in 

the undeveloped basins (fig. 15A). The 

maximum concentration for total nitrogen (5.8 mg/L) was measured in Bayou 

Grosse Tete, which drains a mix of agricultural and urban land. Concentrations 

of total phosphorus were greatest in the 

urban stream, Dawson Creek, with a 

median concentration of 0.46 mg/L and 

maximum concentration of 1.1 mg/L 

(fig. 15B). Elevated phosphorus concentrations, however, also were detected in 

streams draining agricultural land. In 

fact, concentrations of total phosphorus 

exceeded the USEPA desired goal to 

prevent nuisance plant growth

(0.1 mg/L) in 90 percent of samples collected from streams draining agricultural 

or urban land, but in only 17 percent of 

samples from streams draining undeveloped land.

Forms of nitrogen vary among 

streams in the AcadianPontchartrain Drainages and in 

the Mississippi River at

St. Francisville

Overall, organic nitrogen was 

the most frequently detected form of 

nitrogen in the 368 samples collected 

from the eight streams in the AcadianPontchartrain Drainages, accounting for 

about two-thirds of the total nitrogen 

(fig. 16). Large percentages of organic 

nitrogen generally indicate suspended 

algae (phytoplankton) or other organic 

matter in the water. Ammonia generally 

was minimal except in the urban Dawson Creek, where it accounted for about 

25 percent of the total nitrogen con-
Figure 15. Concentrations of total nitrogen 

(A) and phosphorus (B) differ with land use, 

with the largest concentrations in streams 

draining agricultural or urban land.

Figure 16. Organic nitrogen is the most 

common form of nitrogen in streams in 

the Acadian-Pontchartrain Drainages, 

whereas nitrate is the most common form 

in the main stem of the Mississippi River 

near St. Francisville.

LAND USE COMPARISON

WITH MISSISSIPPI RIVER

MEDIAN C

ONCENT

R

ATION OF NIT

R

O

GEN FO

R

M

S,

IN MILLIG

R

A

M

S PER LITER

0

1

2

3

A

GRICULTURAL

URBAN

MISSISSIPPI RIVER

UNDEVELOPED

A

GRICULTURAL/

URBAN

ORGANIC NITROGEN

NITRATE

AMMONIA

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16 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

June and July (representing the “spring 

flush” from agricultural applications 

and subsequent runoff in the upstream 

agricultural areas of the Midwest). Peaks 

in concentrations of total phosphorus 

in the Bayou Lacassine, which reflects 

releases of highly turbid water from the 

ricefields, were more pronounced than 

those in the Mississippi River (fig. 17).

centration. Nitrate generally was not a 

dominant form of nitrogen in any of the 

streams draining the Acadian-Pontchartrain Drainages (fig. 16). This is due, in 

large part, to nitrate being readily taken 

up by plants in the subtropical environmental setting, or being converted to 

other forms through denitrification or 

mineralization.

The low occurrence of nitrate 

relative to other forms of nitrogen in 

the Acadian-Pontchartrain streams is 

in contrast to the presence of nitrate 

in the Mississippi River, which 

integrates upstream regional conditions. Nitrate is the dominant form of 

nitrogen in the Mississippi River near 

St. Francisville, Louisiana, where it 

accounts for nearly 70 percent of the 

total nitrogen (fig. 16). The relatively 

large proportion of nitrate in the 

Mississippi River is attributable to 

large amounts of fertilizers used on 

farmland in the Midwest, high water 

turbidity that limits plant growth and 

nitrogen uptake in the river, and its 

relatively large channel size. Apparently, nitrate is not as readily assimilated or removed by natural processes 

in the larger Mississippi River as in 

the smaller streams and tributaries 

of the Acadian-Pontchartrain Drainages. The controlling effects of stream 

channel size and other hydrologic 

and basin characteristics are documented throughout the Mississippi 

River Basin, clearly showing that the 

proximity of nitrogen sources to large 

streams and rivers increases transport 

of the nitrate and nutrients down the 

Mississippi River (Alexander and 

others, 2000) and ultimately to its 

receiving water, the Gulf of Mexico 

(see inset on p. 17 for nutrient effects 

on the Gulf of Mexico).

Nutrient concentrations vary 

seasonally in streams

Concentrations of total nitrogen 

and phosphorus varied seasonally in 

all streams, with maximum concentrations occurring during April through 

June (fig. 17), reflecting agricultural 

applications of fertilizers in the 

region. Minimum concentrations 

generally occurred during the fall and 

winter months. Similar to seasonality 

patterns with atrazine, peaks in concentrations in total nitrogen in streams 

in the Acadian-Pontchartrain Drainages occurred earlier than in the Mississippi River near St. Francisville, 

where peaks generally occurred in 

For additional information on 

nutrients in surface-water resources 

of the Acadian-Pontchartrain 

Drainages, refer to Skrobialowski 

and others (2003). This report also 

is available at http://la.water.usgs.

gov/publications.html
Nutrients in the Mississippi River Basin contribute to hypoxia in the Gulf of Mexico

Nutrients from the Mississippi River Basin may pose an environmental threat to the Gulf of Mexico, which is experiencing 

hypoxic areas and degradation of aquatic resources (Rabalais and others, 1996). The hypoxic zone (an area with concentrations of dissolved oxygen less than 2 mg/L) develops each spring and summer on the Louisiana-Texas shelf of the Gulf 

of Mexico. Hypoxia can cause stress or death in bottom-dwelling organisms that cannot leave the zone. The midsummer 

extent of the hypoxic zone varies greatly from year to year but in general has more than doubled in size since it was first 

systematically mapped in 1985. One of the principal causes for the increasing size of the hypoxic zone is believed to 

be the increasing supply of phosphorus and nitrogen, particularly nitrate from agricultural sources (Burkart and James, 

1999) delivered to the gulf each year from the Mississippi River Basin. Concentrations of nitrate have increased severalfold during the past 100 years in streams draining parts of the Mississippi Basin, and the annual delivery of nitrate from 

the Mississippi River to the gulf has nearly tripled since the late 1950s. The amount of nitrate delivered peaked in the late 

1970’s and has remained constant or decreased slightly since then. (For more detailed information, refer to Goolsby and 

Battaglin, 2000, and website http://webserver.cr.usgs.gov/midconherb/index.html).

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0

0

J J J J J J J J

1999 2000 2001

DATE

Mississippi River

Mississippi River

Bayou Lacassine

Bayou Lacassine

1998

TOTAL NITRO

GEN, IN MILLIGRA

MS PER LITER TOTAL PHOSPHORUS, IN MILLIGRA

MS PER LITER

N D F M A M A S O N D F M A M A S O N D F M A M J A S O

0.5

1

1.5

2

2.5

3

3.5

4

TOTAL NITROGEN

TOTAL PHOSPHORUS

Figure 17. Concentrations of total nitrogen and phosphorus varied seasonally in all 

streams in the Acadian-Pontchartrain Drainages, with maximum concentrations occurring during April through June. Peaks generally are earlier than peaks in the Mississippi 

River near St. Francisville, which occurred in June and July.

Major Findings 17
Elevated nutrients threaten floating freshwater marshes 

in Jean Lafitte National Historical Park

The Barataria Preserve of Jean Lafitte National Historical Park and Preserve 

is a 20,000-acre wetland complex comprising swamp forests and marshes 

located about 15 miles southwest of New Orleans. The park contains a 

flourishing example of floating marshes, a globally rare type that dominates 

freshwater reaches of coastal Louisiana. Floating marshes move vertically to 

some degree in response to changes in water levels because of their buoyant, 

organic-rich peat substrate.

Beginning in the 1930s, with the construction of flood control levees and 

canals along the Mississippi River, water has been less available to the wetlands. In fact, loss of wetlands has amounted to about 25 to 35 square miles 

per year, which can have significant economic and ecological implications. 

Strategies are in place for diverting water from the Mississippi River and 

restoring the natural wetland hydrology that was typical before the building of 

the levees.

Water introduced from the Mississippi River for wetland restoration purposes, 

however, may have negative consequences for the health of floating marshes. 

Floating marshes are widespread in areas where nutrient concentrations are 

naturally low (about 0.04 mg/L) and the inflow of river water, mineral sediments, and contaminants such as herbicides are scarce. Nutrient concentrations such as nitrate in the Mississippi River have increased (to about a median 

of 1.3 mg/L) and herbicides are newly present in the Mississippi River since 

the last time many freshwater marshes were regularly inundated by overbank 

flooding in coastal Louisiana, prior to the 1930s. The long-term effects of the 

elevated concentrations of nutrients and low-level concentrations of herbicides

(0.2–2.0 μg/L of atrazine, for example) on the floating marshes are not known.

18 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Organochlorine compounds persist in sediment and fish tissue

Most organochlorine pesticides 

and PCBs have not been manufactured 

or used in the United States for 25 to 30 

years; but because of their widespread 

use and chemical stability (persistence), 

they were detected commonly in streambed sediment and in whole-fish tissue 

samples from 21 streams in the AcadianPontchartrain Drainages in 1999–2001 

(fig. 18). Many of these compounds are 

classified as endocrine disruptors and 

are known to cause liver and kidney 

lesions in fish. The compounds also pose 

a threat to fish-eating wildlife, and some 

are a concern for human consumption 

because of possible carcinogenic toxicity.

Organochlorine compounds are not 

readily soluble in water but instead bind 

strongly to soil particles and are carried 

with eroded soils to streams by runoff.

The most frequently detected 

organochlorine compounds were PCBs, 

mirex, dieldrin, and degradation products of DDT (such as p,p ́-DDE and

p,p ́-DDD) and chlordane (such as transNonachlor, cis-Chlordane, cis-Nonachlor, trans-Chlordane, and oxychlordane) 

(fig.18). p,p ́-DDE accounted for the 

most detections, with detections in 

sediment samples from 8 of 21 streams 

(Skrobialowski, 2002) and in fish-tissue 

samples from 11 of 19 streams. Organochlorine compounds generally were 

detected more frequently in fish tissue 

than in sediment. For example, PCBs 

were detected in fish-tissue samples 

from 8 of 19 streams but in bed-sediment samples from only one stream.

Organochlorine compounds were 

detected more frequently in streambed 

sediment and fish tissue at sites draining agricultural and urban land than 

at sites draining undeveloped areas. 

Occurrences of chlordane and dieldrin 

reflect their past use for termite control 

in urban areas, whereas mirex was used 

extensively for control of fire ants. The 

occurrence of DDT reflects its principal 

use as an insecticide and the occurrence 

of PCBs reflect their uses as industrial 

chemicals in hydraulic lubricants and 

heat-resistent oils in electrical transformers.

When compared to the national 

range of detected concentrations, total 

concentrations of DDT and its degradation compounds, chlordane, and PCBs in 

bed sediment and fish tissue in southern 

Louisiana were generally in the medium 

range (middle 50 percent, nationally) 

to high range (highest 25 percent, 

nationally) for sites draining urban and 

agricultural lands and in the low range 

(lowest 25 percent, nationally) for sites 

draining mixed land uses (see Appendix). Concentrations of total chlordane in bed sediment samples at 2 of 

21 streams (Dawson Creek and Bayou 

Lafourche) exceeded the Canadian 

Council of Ministers of the Environment’s Probable Effects Level (PEL) of 

8.87 μg/kg (micrograms per kilogram) 

(Skrobialowski, 2002) and were among 

the highest in the national range of 

detected concentrations. Concentrations 

of p,p ́-DDE in bed-sediment samples at 

2 streams (Bayou Teche, and Vermilion 

River at Perry) exceeded the PEL of 

6.75 μg/kg for total degradates. Compounds exceeding the PEL are likely 

to result in adverse effects on aquatic 

organisms. At some sites, concentrations 

of total PCBs and DDT compounds 

exceeded the New York State Department of Environmental Conservation 

(NYSDEC) criteria for the protection 

of fish-eating wildlife (Nowell and 

others, 1987). Concentrations above the 

criteria may have a detrimental effect on 
Guidelines for Protection of Aquatic Life and Wildlife

Contaminant concentrations in streambed sediment are compared with the 

guidelines for the protection of aquatic life established by the Canadian 

Council of Ministers of the Environment (1999). The Probable Effect Level 

(PEL) defines the level above which adverse effects to biota are expected to 

occur frequently. These guidelines are based on chronic (long-term) effects 

of individual contaminants on aquatic invertebrates. Contaminants in fish are 

compared with the New York State Department of Environmental Conservation (NYSDEC) guidelines for the protection of birds and other wildlife that 

consume fish (Nowell and others, 1987).

Figure 18. Organochlorine compounds persist 

in both bed sediment and whole-fish tissue in 

southern Louisiana streams, particularly those 

draining agricultural and urban areas.

0

2

4

6

8

10

12

ORGANOCHLORINE COMPOUNDS

Fish tissue

Bed sediment

p,p'-DDE

trans-Nonachlor

Total PCBs

Dieldrin

trans-Chlordane

Oxychlordane

cis-Chlordane

Mirex

cis-Nonachlor

p,p'-DDD

p,p'-DDT

NUMBER OF DETECTIONS

FRO

M 21 STREA

MS

Major Findings 19

streams in the Acadian-Pontchartrain 

Drainages. The highest concentrations 

of total mercury in bed sediment were 

detected in samples from Tchefuncte 

River near Covington (0.27 μg/g), Bayou 

Lafourche at Thibodaux (0.15 μg/g), and 

Dawson Creek at Baton Rouge (0.10 μg/

g). These concentrations were relatively 

low, however, and none exceeded the 

PEL for mercury in sediment 

(0.486 μg/g). NAWQA findings showed 

that concentrations of mercury in sediment were not geographically clustered 

but rather were distributed throughout 

the Study Unit, which may reflect an 

atmospheric nonpoint source of mercury.

In contrast to the finding for 

mercury in sediments, concentrations of 

total mercury in game fish (largemouth 

bass and selected species of sunfish) 

exhibited a distinct geographic distribution pattern (fig. 19). Specifically, the 

highest concentrations (greater than 500 

nanograms per gram) were found in 

tissue of fish collected in sand-bottom 

streams north of Lake Pontchartrain 

and in streams in the western part of the 

Study Unit; the lowest concentrations 

generally were found in tissue of fish 

collected in the silt- and clay-bottom 

streams in the flat southern Louisiana 

coastal marshes (fig. 19). This geographic distribution appears to be controlled by regional differences in environmental conditions, which correspond 

with chemical and physical properties 

of the landscape and the efficiency with 

which inorganic mercury is converted to 

methylmercury, the form most readily 

bioaccumulated in fish (see inset, p. 21). 

For example, streams north of Lake Pontchartrain are relatively acidic (low pH), 

which could potentially increase the 

solubility of mercury and enhance the 

conversion of mercury to the methylated 

form. In 8 of 19 streams sampled, concentrations of mercury in edible portions 

of fish tissue exceeded one component 

(500 nanograms per gram mercury in 

fish edible portions) considered by the 

Louisiana State Departments of Health 

and Hospitals and Environmental 

Quality in their alert-level assessment 

process. These findings confirm previous data for mercury in edible fish fillets 

collected by the Louisiana Department 

fish-eating organisms. Concentrations of 

total PCBs exceeded the NYSDEC criteria of 110 μg/kg for fish in five of the 

8 streams. Concentrations of total DDT

exceeded the NYSDEC criteria of

200 μg/kg at Bayou Teche, reaching a 

maximum of about 350 μg/kg.

Semivolatile organic contaminants (SVOCs), such as the combustion 

byproducts polyaromatic hydrocarbons 

(PAHs), were detected frequently in 

sediment (SVOCs were not measured in 

fish because they do not bioaccumulate 

in fish). Specifically, sediment samples 

from 10 of 21 streams contained detectable concentrations of one or more 

SVOC compounds. Concentrations 

generally were low, except for those of 

pyrene, phenanthrene, acenaphthene, 

and anthracene, which exceeded PELs 

at five sites across the Acadian-Pontchartrain Drainages. Some PAHs are 

potentially toxic and carcinogenic.

For additional information on 

organochlorine compounds in 

bed sediment in streams of the 

Acadian-Pontchartrain Drainages, 

refer to Skrobialowski (2002). 

This report also is available at 

http://la.water.usgs.gov/pdfs/

BedSediment.pdf

Elevated levels of

mercury are present in 

fish north of Lake

Pontchartrain

Mercury has more than 2,000 

uses in industry, medicine, agriculture, and commerce. Mercury also 

is released to the atmosphere as a 

by-product of coal combustion and 

waste incineration (David Krabbenhoft, U.S Geological Survey, written 

commun., 2003). For most ecosystems, atmospheric deposition is the 

primary source of mercury. Over the 

last 50 years, atmospheric emissions 

have increased mercury levels about 

three to five-fold, and have caused 

corresponding increases in mercury 

levels in terrestrial and aquatic ecosystems.

Mercury was detected in all 

21 bed-sediment samples and in all 

19 fish-tissue samples collected from 
Figure 19. Concentrations of total mercury in fish-tissue samples were highest in sandbottom streams north of Lake Pontchartrain and lowest in the flat southern Louisiana 

coastal marshes.

Figure 20. As concentrations of methylmercury increase in water, concentrations also 

increase in fish.

Bayou

Des Cannes

Bayou

Lake Pontchartrain Lake Maurepas

Grand

Lake

Calcasieu

White Lake Lake Salvador

Lac Des Allemandes

Tickfaw

Tchefuncte

Tangipahoa River

River

R

River

River

River R

Vermilion

Whiskey Chitto

Cr

River

Mississippi

Amite

Atchafalaya

Bayou

Grosse Tete

Nezpique

River

Mermenta

Calcasieu u

Lake

Cocodrie Lake

0 20 40 60 80 100 MILES

Covington

Houma

Baton

Rouge

Lafayette

St. Martinville

Lake

Charles Eunice

Alexandria

New

Orleans

Total mercury in

fish-tissue samples,

in nanograms per

gram

EXPLANATION

Greater than 500

300–500

0–300

0 20 40 60 80 100 KILOMETERS

TOTAL MERCURY IN FISH TISSUE,

IN NANO

GRA

MS PER GRA

M, DRY

WEIGHT

0

100

200

300

400

500

600

700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

METHYLMERCURY IN WATER,

IN NANO

GRA

MS PER LITER

Calcasieu River

near Kinder, LA

Turtle Bayou near

Bayou Penchant

Mermentau River

at Mermentau, LA

Bayou Lacassine

near Lake Arthur, LA

Water

Fish tissue

20 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

of Environmental Quality in this area, 

which led to fish-consumption advisories for humans. Concentrations of 

mercury in fish, however, are not used 

alone to determine risk assessment and 

do not absolutely determine whether an 

advisory will be issued for fish taken 

from the water body. For additional 

information, see http://www.deq.state.

la.us/surveillance/mercury/index.htm.

NAWQA findings at four streams 

in the Acadian-Pontchartrain Drainages 

For additional information on 

mercury in bed sediment in streams 

of the Acadian-Pontchartrain 

Drainages, refer to Skrobialowski 

(2002). This report also is available 

at http://la.water.usgs.gov/pdfs/

BedSediment.pdf. Additional information on mercury can be found at 

http://infotrek.er.usgs.gov/mercury.

Aquatic communities are 

affected by land use and 

habitat

Aquatic communities in southern 

Louisiana streams, rivers, and bayous 

differ among land uses. Specifically, 

the percentages of pollution-intolerant 

invertebrate and fish taxa were greatest for two undeveloped streams and 

lowest at an urban stream. The undeveloped streams were dominated by 

invertebrate species that are intolerant 

to pollution or degraded water quality, 

including selected mayfly, caddisfly, and 

stonefly species (referred to as “EPT 

taxa”) (fig. 21), as well as intolerant fish 

species (fig. 22), such as darters and 

selected minnows. Streams in the relatively undeveloped basins in the northern, forested, sandy areas of the Western 

Gulf Coastal Plains and Southeastern 

Plains ecoregions (Tchefuncte River and 

Whiskey Chitto Creek) are characterized 

by cooler water temperatures, low concentrations of suspended sediment and 

clear water, substantial ground-water 

inputs, and moderate flow velocities—

all of which are related to greater landsurface relief and stream-channel slope 

than in the more southern areas of these 

ecoregions. In addition, stream habitat 

generally is undisturbed in the undeveloped basins, with relatively coarse and 

stable stream-bottom substrates (such 

as sand), riparian tree shading, and 

submerged woody debris, which provide 

habitat and food resources for aquatic 

communities to thrive.

In contrast, the aquatic communities in the southern part of the Western 

Gulf Coastal Plain ecoregion (Bayou 

that had data for methylmercury in water 

and total mercury in fish showed that 

as the concentrations of methylmercury 

increase in water, the total mercury 

concentrations also increase in fish (fig. 

20). Data on methylmercury in water are 

not commonly collected and available in 

most monitoring programs, however, as 

compared to data on total mercury. 
Greaterthan 8 percent

Less than 8 but greaterthan 4 percent

Less than 4 but greaterthan 2 percent

Less than 2 percent

Percentage of methylmercury

to total mercury

Acadian-Pontchartrain

Drainages

EXPLANATION

Major Findings 21

Mercury in the Acadian-Pontchartrain Drainages is evaluated as 

part of a national study

In 1998, USGS examined 

mercury contamination in streams—

including that in water, sediment, and 

fish—at a national scale (Krabbenhoft and others, 1999). Samples for 

analysis of mercury were collected at 

106 stream sites within 21 major river 

basins across the Nation, including 

the Acadian-Pontchartrain Drainages. 

Findings showed that the occurrence 

of mercury is not limited to local 

sites, such as those associated with 

the discharge of mining and industrial wastes, but rather is a National 

contamination issue. The findings also 

begin to explain mercury distribution 

patterns at many geographic scales 

across the Nation. Specifically, the 

findings showed that the occurrence 

and concentration of methylmercury 

(the most toxic and bioaccumulated 

form of mercury) generally corresponds with the amount of wetlands 

in the watershed, and that concentrations are affected by chemical and 

environmental conditions, such as the 

presence of sulfur, carbon, organic 

matter, and dissolved oxygen. These 

variables are conducive to methylation and an increase in the relative 

amounts (or ratio) of methylmercury 

to total mercury. From a national 

perspective, basins with the greatest 

percentage of methylmercury to total 

mercury (greater than 8 percent) in 

sediment and water were along the 

East Coast (see map). The ratio of 

methylmercury to total mercury in 

the Acadian-Pontchartrain Drainages 

was in the middle range of the 21 

basins—a ratio of less than 8 percent 

but greater than 4 percent. Explanations for the relatively high methylation efficiency in the Acadian-Pontchartrain Drainages are not consistent 

with those for other basins across the 

Nation, particularly the strong relation 

between methylation and wetlands. 

Specifically, some of the highest concentrations of mercury were detected 

in sand-bottom streams north of Lake 

Pontchartrain, as opposed to silt- and 

clay-bottom streams in the southern Louisiana wetlands. As a result, 

further USGS studies are ongoing to 

improve understanding of processes 

controlling mercury in water, sediment, and fish in the Lake Pontchartrain Basin.
Figure 22. The richness (reflecting total number of fish species) and the percentage of 

pollution-intolerant species were lowest for Dawson Creek, an urban stream. (n, number 

of sites)

Figure 21. The richness (reflecting total number of taxa) and percentage of pollutionintolerant aquatic invertebrate communities (represented by EPT taxa) decrease in 

streams draining agriculture and urban areas. (n, number of sites)

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(n=3)

Urban

(n=1)

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(n=2)

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Figure 23. Algal biovolume was lowest in agricultural streams, which are associated with 

relatively high suspended sediment. Despite elevated suspended sediment in large rivers, 

algal biovolume is large, mostly composed of green algae that attach to submerged 

vegetation and wood. (n, number of sites)

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22 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Des Cannes, Bayou Lacassine, and 

the Mermenteau River) generally are 

dominated by species considered to be 

pollution-tolerant invertebrates (such 

as midges, worms, and snails) and fish 

(such as gar, catfish, and certain sunfish). Natural habitat conditions in these 

basins favor an aquatic community that 

is tolerant of turbidity, organic enrichment, and low levels of dissolved oxygen. The net effect is a biological community in these southern areas that is, at 

first examination, indicative of streams 

that have been adversely affected by 

human activity, when, in fact, it may be 

a naturally occurring “healthy” community in which natural environmental 

stressors exclude sensitive species and 

limit species richness and diversity. Consequently, southern Louisiana streams 

support aquatic communities that are 

uniquely adapted to these habitat conditions. Agricultural activity that results in 

warmer stream temperatures, straighter 

channels, and increased turbidity, 

however, can alter these unique natural 

environments and place additional stress 

on the aquatic communities.

NAWQA findings show that chemical and physical characteristics play 

a role in the distribution of biological 

communities. Specifically, disturbance 

to the physical habitat of streams and 

changes in stream temperature and 

hydrology that are associated with 

watershed development (including for 

agricultural and urban uses) can affect 

aquatic health of streams as much as, or 

even more than, chemical water-quality 

degradation. Improvements to stream 

quality will, therefore, require consideration and management of physical alterations to landscapes and stream habitats 

in addition to management of chemical 

use and nonpoint source runoff.

Attached algal communities also 

differ among land uses, and are controlled primarily by availability of light 

and turbidity of water, rather than by 

elevated concentrations of nutrients. 

Specifically, total algal biovolume (proportional to algal biomass) was larger 

in the undeveloped streams than in the 

agricultural and urban streams (fig. 23). 

The larger algal biovolume in the undeveloped streams was associated with rel-
Habitat conditions and aquatic invertebrate communities are most degraded in the downstream parts of the Mermentau River Basin

Invertebrate communities change in a downstream direction in the Mermentau River Basin (fig. 24). Specifically, invertebrates tolerant to pollution are dominant at the large, downstream sites (those draining areas larger than 70 square 

miles), which are associated with organic enrichment (elevated dissolved organic carbon), low concentrations of dissolved 

oxygen, low or stagnant water velocity, elevated water temperatures, high water turbidity, and silt-clay-dominated streambottoms. In addition, these 

sites are associated with 

elevated concentrations of 

insecticides and degradation compounds in water 

and sediment (such as 

fipronil and its degradation 

products) associated with 

rice agriculture. Aquatic 

invertebrate communities 

are dominated by more 

pollution-intolerant species 

at the smaller upstream sites 

in the Mermentau River 

Basin, where streams feature coarse and stable substrates, undisturbed stream 

habitat, woody debris, 

cooler water temperatures, 

relatively quick velocities, 

and relatively good water 

quality, all of which provide 

conditions more favorable 

for sustaining productive 

and diverse invertebrate 

communities.

Figure 24. Aquatic invertebrates with low tolerance to pollution are more common in

streams with less area used for rice cultivation. Lower tolerance values correspond to

better water-quality and habitat conditions.

8.5

8.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

0 45 100

Caney Creek near Oakdale

HIGH

RANGES OF DRAINAGE AREA USED FOR RICE (PERCENT)

T

OLER

ANCE VALUES

OF

A

QUATIC INVER

TEBR

ATES

Boggy Bayou near Pine Prairie

Bayou Nezpique near Basile

Bayou Plaquemine Brule near Church Point

Bayou Nezpique at Guidry Road

Bayou Grand Marais near Kaplan

Castor Creek near Oberlin

Bayou Blue near Elton

Bayou Wikoff near Rayne

Bayou Queue de Tortue at Theroit Road

Bayou Plaquemine Brule at Estherwood

Mermentau River at Mermentau

Bayou Queue de Tortue near Lelieux

Bayou Mallet near Eunice

Bayou Lacassine near Lake Arthur

Bayou des Cannes near Ville Platte

Bayou des Cannes near Eunice

East Bayou Lacassine at Welsh

LOW

UPSTREAM

SITES

DOWNSTREAM

SITES

SITES

TOLERANT

ORGANISMS

SENSITIVE

ORGANISMS

Major Findings 23

atively low concentrations of suspended 

sediment and low turbidity, which 

allows increased light for algal growth. 

Agricultural and urban streams are more 

turbid, with elevated concentrations of 

suspended sediment, which reduces the 

light available for algal growth. Despite 

elevated concentrations of suspended 

sediment in large rivers (Mermentau 

River and Bayou Boeuf), total algal biovolume is large. This is caused, in part, 

by large quantities of the common green 

algae Oedogonium. Oedogonium grows 

on emergent aquatic vegetation and submerged wood (Prescott, 1968) in marshy 

areas connected to main river channels 

with low stream velocities, where suspended sediment particles settle.

Ground Water

The Chicot aquifer system, located 

west of the Mississippi River, and the 

Chicot equivalent aquifer system (which 

is the upper part of the Southern Hills 

regional aquifer system), to the east of 

the river, are designated as sole-source 

aquifers by the U.S. Environmental 

Protection Agency (2002d). These 

aquifer systems are primary drinkingwater sources for domestic and public 

supply and, therefore, require protection because they are susceptible to 

contamination from overlying land-use 

activities. Ground water sampled by the 

NAWQA Program in the Acadian-Pontchartrain Drainages during 1999–2000 

included 115 wells, 60 of which are used 

for domestic supply (median depth of 

120 feet). The remaining wells (median 

depth 26 feet) are monitoring wells

installed for this study (see Study Unit 

Design). Water throughout these aquifer 

systems generally is of high quality. The 

water generally meets Federal guidelines 

established to protect drinking water 

by the USEPA, but guidelines have not 

been established for many of the compounds measured.
Figure 25. Pesticides were commonly detected in shallow ground 

water underlying agricultural and urban areas. VOCs were detected 

in very low concentrations most frequently in shallow outcrop 

areas.

DOMESTIC

WELLS

AGRICULTURAL

WELLS

URBAN

WELLS

PER

CENTA

GE OF WELLS

WITH ONE O

R

M

O

RE DETEC

TIONS

Pesticides

Volatile organic compounds (VOCs)

80

70

60

50

40

30

20

10

0

24 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Nitrate, Pesticides, and 

Volatile Organic Compounds

Agricultural and urban activities 

have had minimal effects on groundwater quality in the Chicot and the 

Chicot equivalent aquifer systems. This 

is, in large part, because the downward 

movement of water is impeded by a relatively impermeable layer of clay below 

the soils. This clay layer, however, is 

not continuous or completely impermeable throughout the entire area overlying 

the Chicot aquifer. Isolated areas exist 

where downward flow from the surface 

or lateral flow to adjacent streams is 

possible.

Concentrations of nitrate were 

low, with samples from only eight wells 

exceeding 2 mg/L, which is considered 

to be the naturally occurring (or “background”) level above which the effects 

of human activities are indicated (Mueller and Helsel, 1996; Nolan and Hitt, 

2003). Samples from two of the eight 

wells exceeded the USEPA drinkingwater standard of 10 mg/L for nitrate. 

These two wells are not used for drinking-water supply but rather are used 

for monitoring the quality of shallow 

ground water underlying agricultural 

land in the Mermentau River Basin. 

These two wells were completed below 

the clay layer, supporting the concept 

that the clay layer is semipermeable.

Pesticides and degradation products were detected in water from 26 

of 115 wells (about 23 percent). Pesticide compounds were most commonly 

detected in shallow monitoring wells 

(median depth of 26 feet) in the ricegrowing areas in the Mermentau River 

Basin (fig. 25). The most commonly 

detected compounds were atrazine and 

its degradation product, deethylatrazine. 

Concentrations were low and always 

below USEPA drinking-water standards. 

Two degradation products of fipronil, 

fipronil RPA and fipronil sulfone, were 

detected in one well. The degradation 

products were not detected upon resampling. The absence of fipronil in ground 

water most likely reflects its chemical 

tendency to readily break down in the 

environment as well as its relatively 

recent introduction to the environment, 

which may not have allowed enough 

time for this compound to move vertically through the clay layer and reach 

the ground-water system.

Volatile organic compounds 

(VOCs) were detected in 18 of 28 shallow monitoring wells (median depth of 

58 feet) in an urban area near Lafayette 

(fig. 25). VOCs also were detected in 44 

of 60 domestic wells (about 73 percent) 

sampled throughout the Chicot and 

Chicot equivalent aquifer systems. The 

concentrations, however, were very low. 

The minimum concentration detected in 

the domestic wells was 0.03 μg/L, the 

maximum was 70 μg/L (methyl ethyl 

ketone), and the median concentration of 

VOCs was 0.27 μg/L. All detected concentrations were below USEPA drinking 

water standards. Detections were most 

frequent in wells in the outcrop areas of 

these aquifer systems, which are in the 

northern part of the Study Unit. Greater 

detection of VOCs in the outcrop areas 

most likely represents recently recharged 

and shallow ground water that is more 

vulnerable to contamination from 

overlying land-use activities than deeper 

ground water that travels along regional 

flow paths in the southern part of the 

Study Unit.

The most frequently detected 

VOCs in the shallow monitoring and 

domestic wells were chloroform (35 

wells) and carbon disulfide (19 wells). 

Individual VOCs seldom occurred alone; 

mixtures of two or more compounds 

were detected in samples from 18 of the 

wells. The most common mixture was 

toluene and carbon disulfide, detected in 

samples from 14 wells.

Naturally Occurring Trace 

Elements and Water Chemistry

Most trace elements detected in 

ground water in the Acadian-Pontchartrain drainages occur naturally, reflecting 

the chemistry of the geologic material 

underlying the Study Unit. Concentrations of trace elements in ground water 

underlying the Acadian-Pontchartrain 

Drainages generally are low, rarely 

exceeding any USEPA drinking-water 

standards, although such standards have 

been established for only 12 of 24 trace 

elements included in this study. Arsenic 

exceeded the USEPA drinking-water 

standard of 10 μg/L in one well sampled 

in the Chicot aquifer system near the 

Vermilion River, with a maximum 

concentration of 55.3 μg/L. This well 

is not used for drinking-water supply. 

The source of the arsenic in this 90-foot 

well is not known. Concentrations of 

iron in samples collected from 16 wells 
Figure 26. Values for dissolved solids were lowest in wells in the outcrop areas of the Chicot and Chicot 

equivalent aquifer systems.

DIS

S

OLVED

S

OLID

S, IN MILLIG

R

A

M

S PER LITER

0

100

200

300

400

500

600

700

800

900

CHO CHS CEO CES

EXPLANATION

Wells in the outcrop area of the Chicot aquifer system

in southwestern Louisiana

Wells south of the outcrop area of the Chicot aquifer system

in southwestern Louisiana

Wells in the outcrop area of the Chicot equivalent aquifer

system in southeastern Louisiana and southwestern

Mississippi

Wells south of the outcrop area of the Chicot equivalent

aquifer system in southeastern Louisiana and southwestern

Mississippi

Maximum concentration

75th percentile

90th percentile

Median (50th percentile)

25th percentile

10th percentile

CHO

CHO

CHS

CHS

CEO

CEO

CES

CES

Major Findings 25

in the Chicot aquifer system and 6 wells 

in the Chicot equivalent aquifer system 

exceeded the USEPA Secondary Maximum Contaminant Level (SMCL) of 

300 μg/L, with a maximum concentration of 8,670 μg/L. Similarly, concentrations of manganese in samples collected 

from 19 wells in the Chicot aquifer 

system and 7 wells in the Chicot equivalent aquifer system exceeded the USEPA 

SMCL of 50 μg/L, with a maximum 

concentration of 481 μg/L. Elevated 

concentrations of iron and manganese 

reported in the NAWQA study are consistent with those previously reported 

by Fendick and Tollett (2003). SMCLs 

are nonenforceable guidelines intended 

to prevent undesirable cosmetic and 

esthetic effects (such as taste and odor) 

of drinking water.

NAWQA findings clearly demonstrate similarities in the natural chemistry of ground water between the Chicot 

aquifer system west of the Mississippi 

River and the Chicot equivalent aquifer system east of the river. Values for 

dissolved solids (fig. 26), pH, calcium, 

sodium, bicarbonate, chloride, and iron 

typically were lowest in wells in the 

outcrop areas of the two systems. As 

water moves from the outcrop areas of 

the two aquifer systems along regional 

flow paths to the southern part of the 

Study Unit, it dissolves various minerals 

and its chemistry changes. The water is 

then less acidic and has a greater amount 

of dissolved constituents than water in 

the outcrop areas.

Radon

Radon is a colorless, odorless, gas 

that forms naturally in rocks and soils 

through the radioactive decay of radium, 

a product of uranium decay. Radon from 

ground water is released into household 

air when water is used for showering, 

washing, and other everyday purposes. 

According to the U.S. Surgeon General, 

exposure to airborne radon is second 

only to cigarette smoking as a cause of 

lung cancer. The risk of cancer increases 

with exposure to increasing levels of 

radon (U.S. Environmental Protection 

Agency, 1994).

Concentrations of radon are 

elevated in the Chicot and Chicot 

equivalent aquifer systems. Concentrations in samples collected from 

53 of 94 wells (about 55 percent) 

exceeded the proposed drinking-water 

standard of 300 pCi/L (fig. 27). The 

maximum concentration recorded was 

2,220 pCi/L. Although elevated concentrations occurred in both the Chicot 

and Chicot equivalent aquifer systems, 

there appear to be two distinct groups 

of concentrations (fig. 27). The majority of the elevated concentrations were 

detected in southwestern Louisiana. The 

median concentration of radon for 60 

domestic wells was 225 pCi/L, which is 

well within the drinking-water standard. 

Samples collected from four domestic 

wells in the Chicot aquifer system 

and five domestic wells in the Chicot 

equivalent aquifer system had radon 

concentrations exceeding the 300 pCi/L 

standard. No sample had concentrations 

that exceeded the USEPA proposed 

alternative maximum contaminant level 

for radon of 4,000 pCi/L. The source of 

uranium in rocks underlying the Acadian-Pontchartrain Drainages is unclear.
0

500

1,000

1,500

2,000

2,500

(4,191) Sample size

R

A

D

ON C

ONCENT

R

ATIONS, IN PIC

O

CURIES PER LITER

90th percentile

75th percentile

25th percentile

10th percentile

Median (50th per- M centile) CL

AcadianPontchartrain

Drainages

samples

(94) Sample size

All NAWQA

Samples

(1991–2001)

ACAD

MEDIAN

(316)

Figure 27. Concentrations of radon in ground water underlying the Acadian-Pontchartrain 

Drainages exceeded the USEPA drinking-water standard in about 55 percent of 94 wells.

Figure 28. General patterns of radon occurrence in ground water in the United States 

indicate that concentrations of radon in southern Louisiana should be relatively low (U.S. 

Environmental Protection Agency, 2002e).

450 to 2,000

Mean radon in ground water, in

picocuries per liter NOTE: State averaging of

data may obscure local

variations in radon levels.

EXPLANATION

300 to 450

150 to 300

Less than 150

26 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Concentrations of radon in ground 

water underlying the Acadian-Pontchartrain Drainages are generally below 

concentrations in ground water collected across the Nation by the NAWQA 

Program (median of about 400 pCi/L 

for 4,191 samples) (fig. 27). Elevated 

concentrations in the Study Unit are still 

somewhat surprising, however, because 

previous studies by the USEPA indicate 

that concentrations of radon generally 

are less than 150 pCi/L in southern 

Louisiana (U.S.Environmental Protection Agency, 2002e) (fig. 28).

For additional information on 

nitrate, pesticides, VOCs in 

ground water, naturally occurring 

trace elements and chemistry in 

ground water, and radon in ground 

water, refer to Tollett and others (2003) (in press), Tollett and 

Fendick (2003) (in press), and 

Fendick and Tollett (2003) (in 

press).
Stream sampling sites, Acadian-Pontchartrain Drainages, 1998-2001

Site number Site name Site type

Basin area

(square miles)

1 Bayou Boeuf at Amelia Agricultural 141.0

2 Tchefuncte River near Covington Agricultural/undeveloped 145.0

3 Dawson Creek at Baton Rouge Urban 15.1

4 Bayou Grosse Tete at Rosedale Agricultural/urban 176.0

5 Bayou des Cannes near Eunice Agricutural/urban 142.0

6 Mermentau River at Mermentau Mixed land use 1,381.0

7 Bayou Lacassine near Lake Arthur Agricultural 296.0

8 Whiskey Chitto Creek near Oberlin Undeveloped, forested 504.0

92°

91°

90°

89°

29°

30°

31°

93°

Intracoa l sta Waterway

Gulf

Sabine River

Red

River

Bayou Teche

Des Cannes

Bayou

Lake Pontchartrain

Lake Maurepas

Grand

Lake

Calcasieu

White Lake

Lake Salvador

Lac Des Allemandes

Tickfaw

Tchefuncte

Tangipahoa

Rive

A

r

mite Ri r ve

River

River

River

River

R

Whiskey

Chitto

Cr

River

Mississippi

Atchafalaya

Bayou

Bayou Lafourche

Grosse Tete

Ve mr ilion River

Calcasieu

Lake Jean Lafitte

National Park

Davis Pond

Diversion

EXPLANATION

Agricultural herbicide study

Agricultural insecticide studies

Intensive site and site number

Ecological study

Bed sediment and tissue study

G u l f

o f M e x i c o

Baton

Rouge

Lafayette

Lake

Charles

LaPlace

Rosedale

Tunica

Amelia

New Orleans

M I S S I S S I P P I

0

0

15

15

30

30

45

45

60 MILES

60 KILOMETERS

L O U I S I A N A

8

7

6

5

1

3 4

2

2

Study Unit Design 27

Study Unit Design

The Acadian-Pontchartrain Drainages study design 

includes assessments of physical, chemical, and biological characteristics of surface and ground water. This design 

includes national components and work elements specific to 

these southern Louisiana drainages. Information was collected 

on stream chemistry and ecology and ground-water chemistry 

using nationally consistent protocols and methods (Gilliom 

and others, 1995). Thus, water-quality findings in the basin 

can be compared to findings in other basins and be placed in a 

regional and national context.

Stream-Chemistry and Ecology

The sampling network was designed to measure how 

natural factors and human activities such as different land uses 

affect water quality in eight representative drainages. Surfacewater chemistry, aquatic ecology, bed sediment, and fish-tissue monitoring was conducted at intensive sampling sites. 

Additional bed sediment and tissue samples were collected 

throughout the drainages at sites representing a variety of land 

uses, including undeveloped reference areas. In southeastern 

Louisiana a synoptic study was conducted to evaluate 

concentrations and sources of agricultural chemicals, particularly herbicides. These basins receive 

water both from local drainages and the Mississippi River system. Two special synoptic 

studies were conducted in southwestern 

Louisiana to determine the occurrence, distribution, and effects of 

fipronil, a new insecticide introduced into the rice-growing 

areas in 1999. The first study 

(2000) documented the 

occurrence and distribution of the insecticide, 
EXPLANATION

EXPLANATION

Urban

Rice

Soybean

Sugarcane

Pasture

Forest

Chicot sole-source aquifer

Chicot Equivalent aquifer system

Rice-growing area

Outcrop area

Urban land-use study

Rice land-use study

Major aquifer study,Chicot aquifer system

Major aquifer study,Chicot Equivalent aquifer system

28 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

and the second study (2001) assessed possible effects of this 

pesticide and its degradation products on aquatic invertebrate 

communities.

Ground Water

Ground-water studies focused on the Chicot aquifer, 

designated as a sole-source aquifer by the U.S. Environmental 

Protection Agency. This aquifer system, divided by the Mississippi River into the Chicot and Chicot Equivalent aquifer 

systems, is heavily utilized for agricultural, aquacultural, and 

domestic water-supply purposes. Ground-water studies were 

designed to measure water quality in:

• Domestic wells screened at various depths in the Chicot and Chicot Equivalent aquifer systems

• Shallow ground water in a rice-agriculture and crawfish 

aquaculture area in southwestern Louisiana

• Shallow ground water in an area overlain by urban land 

use (City of Lafayette, Louisiana)

Additional Information

For detailed information regarding sites where waterquality and ecological data were collected in the Acadian-Pontchartrain Drainages, please access

http://la.water.usgs.gov/nawqa/.
Study Unit Design 29

Study

component What data are collected and why Types of sites sampled

Number 

of sites 

sampled

Sampling frequency and period

Stream Chemistry

Intensive 

sites—

General 

water quality

Streamflow, nutrients, major ions, bacteria, organic carbon, pesticides, pesticide 

degradation products, chlorophyll, 

suspended sediment, and physical parameters. To determine how often and how 

much of a constituent is found, over 

time, in response to different seasonal 

or land-use patterns.

Includes one small urban basin 

(Dawson Creek), one large 

agricultural basin (3 sites in the 

Mermentau River Basin), 

4 mixed agricultural/urban sites, 

and one reference site (Whiskey 

Chitto).

8 Biweekly during February–June, 

monthly rest of year 1999–2000, 

monthly in 2001.

Synoptic 

study—

Agricultural 

herbicides

Nutrients, major ions, organic carbon, 

pesticides, pesticide metabolites, chlorophyll, suspended sediment, and physical 

parameters. To evaluate concentrations 

and sources of agrichemicals, especially atrazine.

Includes sites on the Mississippi 

and Atchafalaya Rivers, as well 

as smaller streams and bayous 

in southeastern Louisiana.

17 Every 6 weeks from March to 

August 1999.

Synoptic 

study—

Agricultural 

insecticides

Nutrients, major ions, organic carbon, 

pesticides, pesticide metabolites, chlorophyll, suspended sediment, and physical 

parameters. To evaluate concentrations 

and sources of agrichemicals, especially fipronil.

Streams draining basins from 

15 to 1,702 square miles along a 

gradient of agricultural land-use 

intensity.

17 Water, monthly February–June 

2000.

Bed sediment once in August–

September 2000.

Stream Ecology

Aquatic 

biota—

Fixed sites

Algal, benthic invertebrate, and fish communities. Stream habitat conditions. To 

characterize aquatic biota in relation 

to habitat and water quality.

Sites located at intensive waterquality sites.8 Once in 1999 and once in 2001.

Streambed 

sediments

and fish 

tissue—

Fixed sites

Organochlorine pesticides and semivolatile organic compounds in sieved 

sediment and whole fish. Trace elements in sieved sediment and fish livers. 

Mercury in muscle tissue. To measure 

concentrations of contaminants in relation to different land uses.

Eight at intensive fixed sites.

13 additional sites representing 

agricultural, urban, mixed, and 

unimpacted land uses.

21 Once in June–September 1998.

Aquatic 

biota—

Agricultural 

insecticide 

study

Nutrients, major ions, organic carbon, 

pesticides, pesticide metabolites, chlorophyll, streamflow, suspended sediment, 

and physical parameters. To evaluate 

effects of agrichemicals, especially 

fipronil, on aquatic invertebrate communities.

Sites located in areas of high 

and low agricultural intensity, 

and small and large basin size 

in the Mermentau River Basin, 

and one reference site (Whiskey 

Chitto) in the Calcasieu River 

Basin.

19 Once in March 2001.

Ground-Water Chemistry

Agricultural land-use 

study, Chicot 

aquifer 

system

Water-level, physical parameters, nutrients, major ions, organic carbon, trace 

elements, pesticides, pesticide metabolites, CFCs (for age-dating), radon. To 

determine the effects of land use on 

shallow ground-water quality in this 

sole-source aquifer system.

27 shallow monitor wells in 

areas where shallow sands of 

the Chicot aquifer system are 

overlain by rice and rowcrop 

agriculture.

27 Once in January–September 2000.
30 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Study

component What data are collected and why Types of sites sampled

Number 

of sites 

sampled

Sampling frequency and period

Ground-Water Chemistry—Continued

Major Aquifer Survey—

Chicot aquifer system

Water-level, physical parameters, nutrients, major ions, organic carbon, trace elements, pesticides, pesticide metabolites, 

VOCs, tritium, radon. To broadly assess 

the quality of ground water withdrawn 

for domestic use from this sole-source 

aquifer system.

30 domestic wells screened at 

various depths in the Chicot 

aquifer system.

30 Once in June 2000–February 

2001.

Major Aquifer Survey—

Chicot equivalent aquifer 

system

Water-level, physical parameters, nutrients, major ions, organic carbon, trace elements, pesticides, pesticide metabolites, 

VOCs, tritium, radon. To broadly assess 

the quality of ground water withdrawn 

for domestic use from this sole-source 

aquifer system.

30 domestic wells screened at 

various depths in the Chicot 

equivalent aquifer system.

30 Once in February–September 

2001.

Urban landuse study—

Lafayette, La.

Water-level, physical parameters, nutrients, major ions, organic carbon, trace elements, pesticides, pesticide metabolites, 

VOCs, CFCs (for age-dating), radon. 

To evaluate the effects of residentialcommercial development on shallow 

ground-water quality.

28 shallow monitor wells in 

areas where the Chicot aquifer 

system is overlain by residential-commercial areas developed 

in the last 30 years. Two wells 

were installed in undeveloped 

areas to serve as reference wells 

for the two land-use studies.

28 Once in December 2001–

February 2002.
References Cited 31

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Glossary 33

Glossary

Algae Chlorophyll-bearing nonvascular, primarily aquatic 

species that have no true roots, stems, or leaves; most algae 

are microscopic, but some species can be as large as vascular 

plants. 

Alluvium Deposits of clay, silt, sand, gravel or other particulate rock material left by a river in a streambed, on a flood 

plain, delta, or at the base of a mountain. 

Ammonia A compound of nitrogen and hydrogen (NH3) that 

is a common byproduct of animal waste. Ammonia readily 

converts to nitrate in soils and streams. 

Aquatic-life guidelines Specific levels of water quality 

which, if reached, may adversely affect aquatic life. These are 

nonenforceable guidelines issued by a governmental agency or 

other institution. 

Aquifer A water-bearing layer of soil, sand, gravel, or rock 

that will yield usable quantities of water to a well. 

Background concentration A concentration of a substance in 

a particular environment that is indicative of minimal influence 

by human (anthropogenic) sources. 

Bed sediment The material that temporarily is stationary in 

the bottom of a stream or other watercourse. 

Benthic invertebrates Insects, mollusks, crustaceans, 

worms, and other organisms without a backbone that live in, 

on, or near the bottom of lakes, streams, or oceans. 

Bioaccumulation The net accumulation of a substance by an 

organism as a result of uptake from all environmental sources, 

including gills, epithelial tissues, and dietary sources. 

Biomass The amount of living matter, in the form of organisms, present in a particular habitat, usually expressed as 

weight per unit area. 

Chlordane-Octachloro-4,7-methanotetrahydroindane An 

organochlorine insecticide no longer registered for use in the 

United States Technical chlordane is a mixture in which the 

primary components are cis- and trans-chlordane, cis- and 

trans-nonachlor, and heptachlor. 

Community In ecology, the species that interact in a common 

area. 

Concentration The amount or mass of a substance present 

in a given volume or mass of sample. Usually expressed as 

microgram per liter (water sample) or micrograms per kilogram (sediment or tissue sample). 

Confining layer A layer of sediment or lithologic unit of low 

permeability that bounds an aquifer. 

Contamination Degradation of water quality compared to 

original or natural conditions due to human activity. 

Cubic foot per second (ft3/s, or cfs) Rate of water discharge 

representing a volume of 1 cubic foot passing a given point 

during 1 second, equivalent to approximately 7.48 gallons per 

second or 448.8 gallons per minute or 0.02832 cubic meter per 

second. 

Degradation products Compounds resulting from transformation of an organic substance through chemical, photochemical, and/or biochemical reactions. 

Denitrification A process by which oxidized forms of nitrogen such as nitrate (NO3

-

) are reduced to form nitrites, nitrogen 

oxides, ammonia, or free nitrogen: commonly brought about 

by the action of denitrifying bacteria and usually resulting in 

the escape of nitrogen to the air. 

DDT Dichloro-diphenyl-trichloroethane. An organochlorine 

insecticide no longer registered for use in the United States. 

Discharge Rate of fluid flow passing a given point at a given 

moment in time, expressed as volume per unit of time. 

Dissolved constituent Operationally defined as a constituent 

that passes through a 0.45-micrometer filter. 

Dissolved solids Amount of minerals, such as salt, that are 

dissolved in water; amount of dissolved solids is an indicator 

of salinity or hardness. 

Drainage basin The portion of the surface of the Earth that 

contributes water to a stream through overland runoff, including tributaries and impoundments. 

Drinking-water standard or guideline A threshold concentration in a public drinking-water supply, designed to protect 

human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum contamination levels for public water systems required 

to protect the public welfare; guidelines have no regulatory 

status and are issued in an advisory capacity. 

Ecoregion An area of similar climate, landform, soil, 

potential natural vegetation, hydrology, or other ecologically 

relevant variables. 

Endocrine system The collection of ductless glands in animals that secrete hormones, which influence growth, gender 

and sexual maturity. 

EPT richness index An index based on the sum of the number of taxa in three insect orders, Ephemeroptera (mayflies), 

Plecoptera (stoneflies), and Trichoptera (caddisflies), that are 

composed primarily of species considered to be relatively 

intolerant to environmental alterations. 

Eutrophication The process by which water becomes 

enriched with plant nutrients, most commonly phosphorus and 

nitrogen. 

Fertilizer Any of a large number of natural or synthetic materials, including manure and nitrogen, phosphorus, and potassium compounds, spread on or worked into soil to increase its 

fertility.
34 Water Quality in the Acadian-Pontchartrain Drainages, Louisiana and Mississippi, 1999–2001

Ground water In general, any water that exists beneath the 

land surface, but more commonly applied to water in fully 

saturated soils and geologic formations. 

Habitat The part of the physical environment where plants 

and animals live. 

Herbicide A chemical or other agent applied for the purpose 

of killing undesirable plants. See also Pesticide. 

Insecticide A substance or mixture of substances intended to 

destroy or repel insects.

Intensive site Basic fixed sites with increased sampling 

frequency during selected seasonal periods and analysis of dissolved pesticides for 1 year.

Intolerant organisms Organisms that are not adaptable to 

human alterations to the environment and thus decline in numbers where human alterations occur. See also Tolerant species. 

Invertebrate An animal having no backbone or spinal column. See also Benthic invertebrate. 

Loess Homogeneous, fine-grained sediment made up primarily of silt and clay, and deposited over a wide area (probably 

by wind). 

Median The middle or central value in a distribution of data 

ranked in order of magnitude. The median is also known as the 

50th percentile. 

Micrograms per liter (μg/L) A unit expressing the concentration of constituents in solution as weight (micrograms) of solute per unit volume (liter) of water; equivalent to one part per 

billion in most streamwater and ground water. One thousand 

micrograms per liter equals 1 mg/L. 

Midge A small fly in the family Chironomidae. The larval 

(juvenile) life stages are aquatic. 

Milligrams per liter (mg/L) A unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water; equivalent 

to one part per million in most streamwater and ground water. 

One thousand micrograms per liter equals 1 mg/L. 

Monitoring well A well designed for measuring water levels 

and testing ground-water quality. 

Nitrate An ion consisting of nitrogen and oxygen (NO3

-

). 

Nitrate is a plant nutrient and is very mobile in soils. 

Nonpoint source A pollution source that cannot be defined 

as originating from discrete points such as pipe discharge. 

Areas of fertilizer and pesticide applications, atmospheric 

deposition, manure, and natural inputs from plants and trees 

are types of nonpoint source pollution. 

Nutrient Element or compound essential for animal and 

plant growth. Common nutrients in fertilizer include nitrogen, 

phosphorus, and potassium. 

Organochlorine compound Synthetic organic compounds 

containing chlorine. As generally used, term refers to compounds containing mostly or exclusively carbon, hydrogen, 

and chlorine. Examples include organochlorine insecticides, 

polychlorinated biphenyls, and some solvents containing 

chlorine. 

Pesticide A chemical applied to crops, rights of way, lawns, 

or residences to control weeds, insects, fungi, nematodes, 

rodents or other “pests.” 

pH The logarithm of the reciprocal of the hydrogen ion 

concentration (activity) of a solution; a measure of the acidity 

(pH less than 7) or alkalinity (pH greater than 7) of a solution; 

a pH of 7 is neutral. 

Phosphorus A nutrient essential for growth that can play a 

key role in stimulating aquatic growth in lakes and streams. 

Picocurie (pCi) One trillionth (10-12) of the amount of radioactivity represented by a curie (Ci). A curie is the amount of 

radioactivity that yields 3.7 x 1010 radioactive disintegrations 

per second (dps). A picocurie yields 2.22 disintegrations per 

minute (dpm) or 0.037 dps. 

Polychlorinated biphenyls (PCBs) A mixture of chlorinated 

derivatives of biphenyl, marketed under the trade name Aroclor with a number designating the chlorine content (such as 

Aroclor 1260). PCBs were used in transformers and capacitors 

for insulating purposes and in gas pipeline systems as a lubricant. Further sale for new use was banned by law in 1979. 

Polycyclic aromatic hydrocarbon (PAH) A class of organic 

compounds with a fused-ring aromatic structure. PAHs result 

from incomplete combustion of organic carbon (including 

wood), municipal solid waste, and fossil fuels, as well as from 

natural or anthropogenic introduction of uncombusted coal and 

oil. PAHs include benzo(a)pyrene, fluoranthene, and pyrene. 

Radon A naturally occurring, colorless, odorless, radioactive gas formed by the disintegration of the element radium; 

damaging to human lungs when inhaled. 

Riparian Areas adjacent to rivers and streams with a high 

density, diversity, and productivity of plant and animal species 

relative to nearby uplands. 

Runoff Excess rainwater or snowmelt that is transported to 

streams by overland flow, tile drains, or ground water. 

Secondary maximum contaminant level (SMCL) The maximum contamination level in public water systems that, in 

the judgment of the U.S. Environmental Protection Agency 

(USEPA), are required to protect the public welfare. SMCLs 

are secondary (nonenforceable) drinking-water regulations established by the USEPA for contaminants that may 

adversely affect the odor or appearance of such water. 

Semivolatile organic compound (SVOC) Operationally 

defined as a group of synthetic organic compounds that 

are solvent-extractable and can be determined by gas 

chromatography/mass spectrometry. SVOCs include phenols, 

phthalates, and polycyclic aromatic hydrocarbons (PAHs). 

Sole-source aquifer A ground-water system that supplies 

at least 50 percent of the drinking water to a particular human 

population; the term is used to denote special protection 

requirements under the Safe Drinking Water Act and may be 
Glossary 35

used only by approval of the U.S. Environmental Protection 

Agency. 

Species Populations of organisms that may interbreed and 

produce fertile offspring having similar structure, habits, and 

functions. 

Species diversity An ecological concept that incorporates 

both the number of species in a particular sampling area and 

the evenness with which individuals are distributed among the 

various species. 

Species (taxa) richness The number of species (taxa) present in a defined area or sampling unit. 

Streamflow A type of channel flow, applied to that part 

of surface runoff in a stream whether or not it is affected by 

diversion or regulation. 

Suspended sediment Particles of rock, sand, soil, and 

organic detritus carried in suspension in the water column, in 

contrast to sediment that moves on or near the streambed. 

Taxon (plural taxa) Any identifiable group of taxonomically 

related organisms. 

Tolerance value A numerical indication on a 0 to 10 scale of 

the sensitivity of organisms to many types of stress associated 

with stream disturbance.

Tolerant species Those species that are adaptable to 

(tolerant of) human alterations to the environment and often 

increase in number when human alterations occur. 

Total DDT The sum of DDT and its metabolites (breakdown 

products), including DDD and DDE. 

Trace element An element found in only minor amounts 

(concentrations less than 1.0 milligram per liter) in water or 

sediment; includes arsenic, cadmium, chromium, copper, lead, 

mercury, nickel, and zinc. 

Triazine herbicide A class of herbicides containing a symmetrical triazine ring (a nitrogen-heterocyclic ring composed of three nitrogens and three carbons in an alternating 

sequence). Examples include atrazine, propazine, and simazine. 

Turbidity Reduced clarity of surface water because of suspended particles, usually sediment. 

Unconfined aquifer An aquifer whose upper surface is a 

water table; an aquifer containing unconfined ground water. 

Volatile organic compounds (VOCs) Organic chemicals 

that have a high vapor pressure relative to their water solubility. VOCs include components of gasoline, fuel oils, and 

lubricants, as well as organic solvents, fumigants, some inert 

ingredients in pesticides, and some by-products of chlorine 

disinfection. 

Water-quality guidelines Specific levels of water quality which, if reached, may adversely affect human health or 

aquatic life. These are nonenforceable guidelines issued by a 

governmental agency or other institution. 

Wetlands Ecosystems whose soil is saturated for long periods seasonally or continuously, including marshes, swamps, 

and ephemeral ponds. 

Withdrawal The act or process of removing; such as removing water from a stream for irrigation or public water supply.
36 Water Quality in the Acadian-Pontchartrain Drainages

Appendix—Water-Quality Data from the Acadian-Pontchartrain 

Drainages in a National Context

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Coordination with agencies and organizations in the Acadian-Pontchartrain Drainages was integral 

to the success of this water-quality assessment. We thank those who served as members of our 

liaison committee. 

Federal Agencies

U.S. Army Corps of Engineers

U.S. Environmental Protection Agency

National Park Service

Natural Resources Conservation Service

State Agencies

Louisiana Department of Environmental Quality

Louisiana Department of Natural Resources

Louisiana Department of Agriculture and Forestry

Universities

Louisiana State University, Baton Rouge

Other public and private organizations

The Nature Conservancy

Lake Pontchartrain Basin Foundation

Coalition to Restore Coastal Louisiana

Barataria-Terrebonne National Estuary Program

We thank the following individuals for contributing to this effort. 

We thank Mr. Murphy Cormier for continued access to Bayou Lacassine. We also thank the many landowners who allowed the 

USGS to install monitoring wells, sample existing wells on their property, and those that allowed us access to sampling sites.

Billy Justus (USGS) played a major role in the collection and identification of fish community data.

Field work to collect water-quality samples required a sustained commitment from many USGS personnel. The dedication shown 

by Van Bergeron and Lane Simmons to execute demanding sampling schedules is greatly appreciated.

Rod deWeese (USGS, Biological Resources Discipline) aided in the collection of ecology samples and provided helpful technical 

advice, both in the field and during report preparation.

Reviewers of this report made many helpful suggestions. Technical comments from USGS personnel, such as Lisa Nowell, Bob 

Gilliom, Ton Nolan, and Mike Meador improved the accuracy of the report and the precision of the language. Technical reviews by 

Jan Boydstun, Emelise Cormier, Kris Pintado, Dugan Sabins, and Al Hindrichs of the Louisiana Department of Environmental Quality 

improved the report.

Editorial and technical guidance by Pixie Hamilton, Chet Zenone, and Gary Rowe is especially appreciated. Their advice and assistance in the later stages of the report process is a commendable example of personnel from Regional and National centers aiding 

individual study units.

Illustrations, report layout, and editorial changes through numerous revisions were skillfully and artfully rendered by Sue Roberts. 

Editorial reviews by Jim Wilson, Betty Palcsak, and Mary Kidd improved the readability of the manuscript.
Demcheck and others— Water Quality in the Acadian-Pontchartrain Drainages 

U.S. Geological Survey Circular 1232

National Water-Quality Assessment (NAWQA) Program

Acadian-Pontchartrain Drainages

NAWQA

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