National Water-Quality Assessment Program U.S. Department of the Interior - U.S. Geological Survey

Number and Size of Black Bass Reflect Water Quality in the Lower 

Mississippi River Delta

Significant Findings:

Black bass were absent in samples collected at 

some sites, but were abundant in samples collected 

at other sites.

Black bass populations were either more plentiful 

or the individual fish were larger at sites where the 

water quality was favorable.

Black bass populations are considered to be useful 

indicators of water-quality conditions in the Delta.

Introduction

Black bass are the most popular and most economically important 

freshwater game fish in the United States, especially in the 

southeastern part of the country. In a 1996 national recreational 

survey, 52 percent of anglers in the southeastern United States 

fished for black bass. Each year, anglers spend billions of dollars 

in pursuit of black bass. As a result of the popularity and 

economic importance of black bass, there is widespread interest in 

maintaining healthy populations.

This particular study shows that black bass populations in streams 

in the Lower Mississippi River floodplain (locally known as the

Delta) reflect differences in stream 

water quality. This suggests that black 

bass populations could be expected to 

improve in some streams if waterquality conditions were to improve.

In the Delta, physical characteristics 

of the natural streams, combined with 

human activities and practices, have 

resulted in a unique set of ecological 

conditions. For example, compared to 

upland streams, Delta streams 

naturally have lower velocities, higher 

turbidity, and less stable concentrations of dissolved oxygen. 

Furthermore, clearing of bottomland 

hardwoods from much of the land in 

the Delta, including the stream banks, 

has resulted in a loss of tree canopy, 

which has affected Delta streams in at 

least three important ways. There has

| | Lower Mississippi River 

Delta Study Area

 State Boundary Lines 

Streams and Rivers

Figure 1. Lower Mississippi River Delta and sampling sites located within 

the Mississippi Embayment Study Unit boundary.

Successful fisherman on a 

Delta stream. (Photograph 

by Keith Sutton, Arkansas 

Game and Fish Commission)

National Water-Quality Assessment Program

The National Water-Quality Assessment (NAWQA) Program of 

the U.S. Geological Survey is designed to describe current 

water-quality conditions for a large part of the Nation's groundand surface-water resources, to describe how water quality is 

changing over time, and to improve our understanding of the 

natural and human factors that affect water quality. These goals 

are being achieved through investigations of more than 50 study 

units that include some of the Nation's most important river 

basins and aquifer systems. The Mississippi Embayment Study 

Unit is one area being investigated as part of the NAWQA 

Program (fig. 1).
been 1) a reduction of 

fallen limbs and trees in the 

streams, which is a 

preferred habitat of many 

fish species; 2) an increase 

in water temperatures 

because there is less shade; 

and 3) a reduction in the 

amount of organic matter 

(for example, leaves), 

which is an important food 

source for organisms at the 

bottom of the food chain in 

the aquatic environment.

Bass fishing is a sport that appeals to 

all ages. Lastly, most streams in the

Delta have been

channelized to facilitate drainage and to control flooding. As a

result of human activities such as stream-channel dredging, the

natural in-stream habitats of most Delta streams have been altered.

Data Collection

From 1994 to 1998, the U.S. Geological Survey, through the 

National Water-Quality Assessment Program (NAWQA), studied 

water-quality conditions at 36 sites in Delta streams in parts of the 

States of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, 

and Tennessee (fig. 1).

Chemical Sampling

Many chemical measures of the water, sediments, and fish were 

made at the 36 stream sampling sites. Four of those chemical 

measures were evaluated relative to black bass populations: 

turbidity, total ammonia plus organic nitrogen, the total number of 

herbicides found in the water, and concentrations of residual total 

DDT found in fish-tissue (carp) samples. These four chemical 

measures are considered representative of water-quality 

conditions of streams in the study area.

Turbidity (a measure of water clarity) is used to indicate the 

amount of material suspended in the stream water. High turbidity 

levels are common in watersheds where the combination of land 

use and natural soil properties results in a significant amount of 

erosion into streams and other water bodies.

Total ammonia plus organic nitrogen (a measure of nutrients) 

indicates the amount of nitrogen present in the water; nutrients 

commonly are introduced to streams through runoff of agricultural 

fertilizers and/or wastewater discharge. Excess nutrients in 

streams can result in the overgrowth of nuisance algae and aquatic 

plants. When extensive plant growth dies and decays, oxygen in 

the stream is depleted, which can stress the aquatic organisms.

The total number of herbicides in water is the sum of the 

number of herbicides detected in all water samples collected at a 

site. Although herbicides themselves probably have a limited 

direct influence on fish, the number of herbicides detected likely 

is representative of the amount of agricultural land use in a 

watershed upstream from a sampling site.

Finally, concentrations of total DDT in fish tissue provide an 

indication of long-term agricultural land use and insecticide 

applications in a watershed. DDT has not been actively used as 

an insecticide in the United States for nearly 30 years, and 

therefore its presence indicates historical land-use patterns.

Fish Sampling

Like many other fish, black bass are long-lived. For that reason, 

black bass populations reflect cumulative changes in their 

environment over time. Consequently, the number and size of 

black bass could directly reflect long-term water-quality 

conditions in Delta streams. Various characteristics of a fish 

population can be assessed and compared to chemical measures in 

order to evaluate water-quality conditions of a stream. These 

characteristics simply represent specific aspects of a fish 

population that are easily measured.

Biologists commonly use measures (or metrics) of a fish 

population to monitor disturbances in aquatic environments 

(streams, rivers, and lakes), and to study the effects of land use on 

those environments.

Electrofishing is a sampling method used to collect fish for water-quality 

assessments.

Fish were collected for this study with a small electrofishing boat 

and a fish seine. At 34 of the 36 sampling sites, fish were 

collected from a stretch of stream that was about 500 yards long. 

At the two remaining sites, beaver dams and logs limited 

sampling to a stretch of stream that was about 250 yards long. A 

total of 94 fish species were collected, identified, weighed, 

measured, and examined for signs of disease.

Two of the fish species collected were the largemouth bass 

(Microptems salmoides) and the spotted bass (Micropterus 

punctulatus), both of which are black bass species. In this report, 

the term "black bass" is used to refer to these two species.

In this study, the sum of the lengths for all black bass collected at 

a particular site was the measure or "black bass metric" used to 

compare black bass populations to stream water-quality 

conditions. This fish metric represents both the number and the 

size of black bass found at a site.

The largemouth bass is probably the most important freshwater 

gamefish in the United States. (Photograph by Eugene Hester)
Understanding the Data

Two different methods of analysis were used to evaluate the 

relation between the black bass metric and the four chemical 

measures. Initially, data for all of the chemical measures were 

grouped into low, medium, and high values; each site was then 

color-coded and plotted on maps of the Delta. Trends observed 

from a visual comparison of the data were then tested by using 

statistical techniques.

Visual Comparison

In the maps shown in figures 2 through 5, sites having the lowest 

values for turbidity, total ammonia plus organic nitrogen, the total 

number of herbicides in the water, and the concentrations of 

residual total DDT measured in fish tissue are depicted as small 

blue triangles. Sites having medium values are shown as green 

squares on the maps, and sites having the highest values are 

depicted as yellow circles.

EXPLANATION

Number of herbicide detections

A <5

 5-9

O >9

EXPLANATION

Average turbidity, 

in nephelometric units

A <24

 24-53

O >53

Figure 4. Number of herbicide detections in samples collected 

at 36 sites in the Lower Mississippi River Delta, 1998.

Figure 2. Average turbidity measured in samples collected at 36 sites 

in the Lower Mississippi River Delta, 1997-98.

EXPLANATION

DDT in fish tissue, in parts per billion

A <300

 300-1,800

O >1,800

EXPLANATION

Mean total ammonia plus organic nitrogen, 

in milligrams per liter

A <0.75

 0.75-1.00

O >1.00

Figure 3. Mean total ammonia plus organic nitrogen measured in samples 

collected at 36 sites in the Lower Mississippi River Delta, 1998.

Figure 5. Amounts of DDT in fish tissue collected at 36 sites in the 

Lower Mississippi River Delta, 1998.

In general, chemical measures with high values are associated 

with less favorable water-quality conditions, whereas chemical 

measures with low values are associated with more favorable 

water-quality conditions. Sites associated with high chemical 

values were generally in the southern part of the study area in 

northwestern Mississippi and in northeastern Louisiana. Sites 

associated with low chemical values were generally in the 

northernmost parts of the study area, primarily in southeastern 

Missouri and northeastern Arkansas.

The distribution of the black bass metric at the 36 sampling sites 

is shown in figure 6. Blue triangles indicate where metric values 

were the highest, green squares indicate where values were 

medium, and yellow circles depict where metric values were the 

lowest. Unlike chemical measures where low values indicate 

favorable (or good) water quality, low black bass metric values 

indicate black bass populations that are few in number and/or 

small in size. Consequently, low black bass metric values indicate 

unfavorable water-quality conditions.
EXPLANATION

Sum of lengths of bass, 

in millimeters

O <235

 235-1,700

A >1,700

Figure 6. Sum of lengths of all bass collected at 36 sites in the Lower 

Mississippi River Delta, 1998.

In general, the distribution of the black bass metric values was 

similar to that of the chemical measures. High metric values, 

which reflect favorable water-quality conditions, were generally 

associated with sites in the northern part of the study area. Low 

metric values, which reflect unfavorable water-quality conditions, 

were generally associated with sites in the southernmost parts of 

the study area.

Statistical Comparison

Statistical techniques allow data to be compared in a more 

objective manner. A statistical test called a T-test indicated that 

the four chemical measures and the black bass metric at the 18 

northernmost sites of the study area were statistically different 

from those at the 18 southernmost sites (p<0.002).

A second statistical procedure used to compare the bass metric to 

the four chemical measures was the correlation procedure. The 

four chemical measures were all negatively correlated with the 

black bass metric. In other words, as turbidity, nutrients, numbers 

of herbicides, and DOT concentrations increased, the size and 

abundance of the black bass decreased. Correlations between the 

four chemical measures and the black bass metric ranged from 

-0.52 to -0.63 (table 1). Statistically, a value of 0 would mean that 

there was no correlation or relation between the chemical measure 

and the black bass metric, whereas a value of 1.0 or -1.0 would 

indicate a "perfect" correlation.

Table 1. Spearman rho correlations of a black bass metric and four 

chemical measures of water quality at 36 sites in the Lower 

Mississippi River Delta

[All correlations are significant, p<0.005] Number of 

herbicides 

Ammonia1 Turbidity1 DDT2 detected1

-0.55 -0.63 -0.52 -0.62

1 - Values are averages of multiple measurements

2 - Measured in fish tissue (carp)

Conclusion

In general, more black bass and larger black bass were collected at 

sites where the water quality was good or favorable; conversely, 

fewer black bass and smaller black bass were collected at sites 

where the water quality was less favorable. Sites having the most 

and the largest black bass and having the most favorable water 

quality were generally in the northern part of the study area. 

The results of this study suggest that changes in ecological 

conditions could change water-quality conditions and potentially 

affect black bass populations in some Delta streams.

Sources of Additional Information

U.S. Department of the Interior, Fish and Wildlife Service, and 

U.S. Department of Commerce, Bureau of Census, 1997, 

Black bass fishing in the U.S.: Addendum to the 1996 

national survey of fishing, hunting and wildlifeassociated recreation, 16 p.

Copies of this fact sheet and information about the Mississippi 

Embayment NAWQA Program can be obtained from:

NAWQA Project Chief

U.S. Geological Survey

308 S. Airport Road

Pearl, MS 39208

(601) 933-2982

or from our web site at http://ms.water.usgs.gov/misenawqa

By: Billy G. Justus, B.J. Caskey, and Barbara A. Kleiss 

Design and layout by: Michael T. Wade

U.S. Department of the Interior 

U.S. Geological Survey Printed on recycled paper

Fact Sheet FS-080-01 

September 2001