Prepared in cooperation with the

Arkansas Soil and Water Conservation Commission

WATER-QUALITY, BIOLOGICAL, AND HABITAT ASSESSMENT OF THE BOEUF RIVER BASIN, SOUTHEASTERN ARKANSAS, 1994-96
Water-Resources Investigations Report 02-4187

 
WATER-QUALITY, BIOLOGICAL, AND HABITAT ASSESSMENT OF THE BOEUF RIVER BASIN, SOUTHEASTERN ARKANSAS, 1994-96By C. Shane Barks, James C. Petersen, and Faron D. Usrey
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 02-4187

Prepared in cooperation with the

Arkansas Soil and Water Conservation Commission

Little Rock, Arkansas 2002

U.S. DEPARTMENT OF THE INTERIOR
GALE A. NORTON, Secretary
U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

For additional information 	Copies of this report can bewrite to: 	purchased from:District Chief	U.S. Geological SurveyU.S. Geological Survey, WRD	Branch of Information Services401 Hardin Road	Box 25286Little Rock, Arkansas 72211	Denver Federal Center	Denver, Colorado 80225
 
Abstract	1

Introduction	2

Purpose and Scope	2

Description of Study Area	2

Acknowledgments	2

Data Collection Methods	4

Water-Quality and Discharge Data	4

Biological and Habitat Data	7

Data Analysis Methods	8

Water Quality	8

Bioassessment	8

Water-Quality, Biological, and Habitat Assessment	10

Water Quality	10

Benthic Macroinvertebrate Communities and Physical Habitat	23

Summary	34

References	35

ILLUSTRATIONS

Figure 		1. Map showing location of study area	3

		2. Photograph showing cotton field storm monitoring station at Coon Bayou Tributary near Tillar, Arkansas			5

		3. Photograph showing forested storm monitoring station at Boeuf River Diversion Canal nearHudspeth, Arkansas			6

		4. Hydrograph and hyetograph showing discharge and rainfall record of storm at the cotton field site 07369654 Coon Bayou Tributary near Tillar, Arkansas, November 1-2, 1996			6

		5. Boxplot showing ranges and distributions of suspended solids and nutrient concentrations at25 ambient sites sampled during a period of relatively low streamflow in November andDecember 1994			11

		6. Boxplots showing ranges and distributions of dissolved chloride, suspended solids, and nutrientevent-mean concentrations at cotton field and forested sites			17

		7. Graph showing measured and estimated total nitrogen storm loads	18

		8. Graph showing sampled concentrations with percent volume of catfish pond drained	20

		9. Graph showing relation of biological condition score to habitat score	30

		10. Graph showing relation of biological condition score to dissolved oxygen concentration	33

		11. Graph showing relation of biological condition score to suspended solids concentration	33

 

TABLES

Table 1. Water-quality and rapid bioassessment sampling sites				4

	2. Water quality of samples from the 25 ambient sites		12

	3. Storm events sampled			14

	4. Water quality of composited storm runoff samples from the cotton field site			15

	5. Water quality of composited storm runoff samples from the forest site			16

	6. Mean and median event-mean concentrations by sites			18

	7. Regression coefficients and error statistics for percent load regression equations at the				forested site	19

	8. Regression coefficients and error statistics for load regression equations at the cotton

				field site	19

	9. Regression coefficients and error statistics for load regression equations at the forested

				site	19

	10. Estimated annual yields for 1996 calendar year				20

	11. Water quality of grab samples collected during draining of the catfish pond				21

	12. Selected constituent loads from catfish pond drainage, April-May 1995				22

	13. Abundances, tolerance values, and feeding groups of macroinvertebrate taxa collected from 25				sites in the Boeuf River Basin and a reference site	24

	14. Bioassessment metrics for samples collected from sites in the Boeuf River Basin and a				reference site	28

	15. Comparison of bioassessment metrics for samples collected from sites in the Boeuf River				Basin to a reference site	29

	16. Comparison of biological condition scores for samples collected from sites in the Boeuf River				Basin to a reference site	31

	17. Relative percent difference values for metrics and scores associated with duplicate samples				32

	18. Physical habitat score assessment of the Boeuf River and its tributaries				32

	19. Correlations between water quality and biological condition scores				33

 
WATER-QUALITY, BIOLOGICAL, AND HABITAT ASSESSMENT OF THE BOEUF RIVER BASIN, SOUTHEASTERN ARKANSAS, 1994-96By C. Shane Barks, James C. Petersen, and Faron D. Usrey
ABSTRACT

Water-quality and biological samples were collected at several sites in the Boeuf River Basin between November 1994 and December 1996. Water-quality and benthic macroinvertebrate community samples were collected and habitat was measured once at 25 ambient monitoring sites during periods of seasonal low flow. Water-quality storm-runoff samples were collected during 11 storm events at two sites (one draining a cotton field and one draining a forested area). Water-quality samples were collected at one site during the draining of a catfish pond.

Water-quality samples from the 25 ambient sites indicate that streams in the Boeuf River Basin typically are turbid and nutrient enriched in late fall during periods of relatively low flow. Most suspended solids concentrations ranged from about 50 to 200 milligrams per liter (mg/L), most total nitrogen concentrations ranged from about 1.1 to 1.8 mg/L, and most total phosphorus concentrations ranged from about 0.25 to 0.40mg/L.

Suspended solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, and dissolved orthophosphorus concentrations from samples collected during storm events were typically higher at the cotton field site than at the forested site. Estimated annual yields of suspended solids, nitrogen, and phosphorus were substantially higher from the cotton field than from the forested area. Dissolved chloride concentrations typically were higher at the forested site than from the cotton field site. Typically, the suspended solids and nutrient concentrations from the 25 ambient sites were lower than concentrations in runoff from the cotton field but higher than concentrations in runoff from the forest area. Concentrations of sulfate, chloride, suspended solids, and some nutrients in samples from the catfish pond generally were greater than concentrations in samples from other sites. Total phosphorus, orthophosphorus, and fecal coliform bacteria concentrations from the catfish pond generally were lower than concentrations in samples from other sites.

Biological condition scores calculated using macroinvertebrate samples and U.S. Environmental Protection Agency Rapid Bioassessment Protocol II indicated that most of the 25 ambient sites would be in the "moderately impaired" category. However, substantial uncertainty exists in this rating because bioassessment data were compared with data from a reference site outside of the Boeuf River Basin sampled using different methods. Several metrics indicated that communities at most of the ambient sites are composed of more tolerant macroinvertebrates than the community at the reference site.

Habitat assessments (using Rapid Bioassessment Protocol II) indicated the reference site outside the Boeuf River Basin had better habitat than the ambient sites. Physical habitat scores for the 25 ambient sites indicated that most ambient sites had poor bottom substrate cover, embeddedness values, and flow and had poor to fair habitat related to most other factors. Most habitat factors at the reference site were considered good to excellent.

Part of the variation in biological condition scores was explained by physical habitat scores and concentrations of suspended solids and dissolved oxygen. However, a considerable amount of variability in biological condition scores is not explained by these factors.

INTRODUCTION

The Boeuf River Basin has undergone major land changes during the last century. Deforestation of bottomland hardwoods, increased agricultural land-use, and channelization of natural stream geomorphology for flood control and irrigation are the main changes that have occurred within the basin. Data collected by the Arkansas Department of Environmental Quality (formerly Arkansas Department of Pollution Control and Ecology) in the Boeuf River Basin indicate that aquatic life is impacted by runoff of silt and nutrients from agricultural activities (Arkansas Department of Pollution Control and Ecology, 1996; 1998). Discharge from aquaculture reservoirs within the Boeuf River Basin also may impact the water quality of the receiving streams. 

In 1994, the U.S. Geological Survey (USGS), in cooperation with the Arkansas Soil and Water Conservation Commission, began a study to assess the water quality in selected drainages within the Boeuf River Basin. The objectives of this study were to sample concentrations of dissolved chloride, suspended solids and nutrients from three different land-use drainages (cotton field, catfish pond, and forested); estimate individual storm loads, annual loads, and yields with each of the three drainages; and collect and compile baseline data on benthic macroinvertebrate communities and water quality for 25 sites in the basin.

Purpose and Scope

The purpose of this report is to describe the results of a water-quality and biological investigation of selected drainages in the Boeuf River Basin of southeastern Arkansas. Water quality is assessed using water-quality data collected during three types of sampling efforts--a synoptic sampling of 25 sites during relatively low flow conditions during November through December 1994, stormwater runoff sampling of a forested area and a cotton field during January 1995 through December 1996, and sampling of a catfish pond discharge in April and May of 1995. Biological benthic macroinvertebrate and habitat information for the 25 synoptic sites also was used in the assessment. Thus, four aspects of water quality in the Boeuf River Basin were sampled--late-fall to winter low flow, stormwater runoff from areas of negligible and more intensive agricultural land practices, periodic discharges from catfish ponds, and biological communities integrating the effects of water quality and habitat conditions.

Samples were collected between November 1994 and December 1996. Water-quality data were collected one time per site during November and December 1994 at 25 sites distributed throughout much of the basin. Discharge and water-quality data were collected downstream from a cotton field and downstream from a forested area during 11 storms during January 1995 through December 1996. Data also were collected during the draining of a catfish pond in April and May 1995. Benthic macroinvertebrate and physical habitat data were collected at the 25 sites sampled in November and December 1994 as part of a bioassessment (Plafkin and others, 1989).

Description of Study Area

The Boeuf River Basin (fig. 1) is located in the Mississippi Alluvial Plain physiographic province in southeastern Arkansas. The drainage area of the Boeuf River at the Arkansas-Louisiana State line is 755 square miles (Yanchosek and Hines, 1979). The basin drains from north to south through a network of channels, canals and ditches. 

The land use in this area is predominately agriculture and aquaculture. In Desha and Chicot Counties (which include most of the basin), the primary crops grown in 1995 were soybeans (26 percent of the land in the two counties), cotton (16 percent), and rice (10 percent) (Arkansas Agricultural Statistics Service, 2001a). Catfish and minnows are produced by commercial aquaculture operations in the area. Area of catfish ponds in Desha and Chicot Counties in 1999 was 11,600 acres; this is about 35 percent of the total catfish pond acreage in Arkansas (Arkansas Agricultural Statistics Service, 2001b).

Acknowledgments

The authors express appreciation to Mr. Jimmy Appleberry and the Dermott Hunting Club for allowing the installation and operation of water data collection equipment on their properties, and to Mr. David Yocum for allowing access to his property to perform data collection.

 

1. Location of study area.

DATA COLLECTION METHODS

Water-quality and streamflow data were collected at 25 synoptic sites, 2 stormwater runoff sites, and 1 catfish pond drainage site (fig. 1, table 1). Biological (macroinvertebrate) and physical habitat data also were collected at the 25 ambient sites. The 25 ambient sites were selected primarily based on biological sampling criteria to be described later.

Water-Quality and Discharge Data

Water-quality samples at the 25 ambient sites were collected in conjunction with the macroinvertebrate bioassessment. Sample collection, processing, and preservation methods followed guidelines outlined by Shelton (1994). Prior to water sampling, the stream was divided into equal-width-increments (EWI). This EWI procedure resulted in 10 sampling points across the cross section. Water was collected at each sampling point with a Teflon/polypropylene depth integrating sampler. Samples were collected in November and December 1994 during a period of relatively low flow.

Water-quality analyses included specific conductance, pH, temperature, dissolved oxygen, turbidity, suspended solids, sulfate, chloride, fluoride, and nutrients. Specific conductance, pH, temperature, and dissolved oxygen were determined on-site using field meters. Analyses of the remaining constituents were conducted at the USGS Water Quality Laboratory in Ocala, Florida. 

 

Water-quality and rapid bioassessment sampling sites 

[RBA, rapid bioassessment]

USGS station

identification

number

Site number

Station name

Site type

073676583
1
Canal 19 (Bayou Macon) near Winchester, Ark.

Ambient-RBA

073676585
2
Canal 19 (Bayou Macon) near Tillar, Ark.

Ambient-RBA

073676587
3
Canal 19 (Bayou Macon) near McArthur, Ark.

Ambient-RBA

073676593
4
Canal 18 (Bayou Macon Diversion) near McGehee, Ark.

Ambient-RBA

073676595
5
Canal 19 (Bayou Macon) near Halley, Ark.

Ambient-RBA

073676597
6
Canal 19 (Bayou Macon) near Bellaire, Ark.

Ambient-RBA

073676604
7
Diversion Canal Boeuf River beside Highway 293 near Hudspeth, Ark.

Ambient-RBA

073676607
8
Diversion Canal Boeuf River near Hudspeth, Ark.

Forest storm runoff-

ambient-RBA

0736766077
9
Fish Pond Drainage near Jerome, Ark.

Catfish pond drainage

073676612
10
Boeuf River northwest of Chicot, Ark.

Ambient-RBA

073676614
11
Boeuf River near Chicot, Ark.

Ambient-RBA

073676616
12
Bill Young Bayou near Chicot, Ark.

Ambient-RBA

073676618
13
Boeuf River northwest of Eudora, Ark.

Ambient-RBA

073676625
14
Big Bayou Slough near Dermott, Ark.

Ambient-RBA

07367663
15
Big Bayou near Dermott, Ark.

Ambient-RBA

07367665
16
Drainage Ditch to Big Bayou near Jerome, Ark.

Ambient-RBA

07367666
17
Big Bayou near Jerome, Ark.

Ambient-RBA

07367669
18
Big Bayou near Portland, Ark.

Ambient-RBA

07367681
19
Boeuf River Tributary near Eudora, Ark.

Ambient-RBA

07367692
20
Fleschmans Bayou near Empire, Ark.

Ambient-RBA

07369630
21
Canal 81 near Watson, Ark.

Ambient-RBA

07369635
22
Cypress Creek near Kelso, Ark.

Ambient-RBA

07369640
23
Canal 66 near Kelso, Ark.

Ambient-RBA

07369645
24
Coon Bayou near McArthur, Ark.

Ambient-RBA

07369653
25
Canal 43 near Watson, Ark.

Ambient-RBA

07369654
26
Coon Bayou Tributary near Tillar, Ark.

Cotton field storm runoff

07369657
27
Canal 43 near Halley, Ark.

Ambient-RBA

Two sites were selected to monitor storm runoff water quality. One site (site 26) was downstream from a homogenous agricultural land use (cotton) and the other site (site 8) was downstream from a forested area. The agricultural site selected was located in west-central Desha County. The monitoring station for the agricultural site was established on a ditch that drains approximately 76 acres of a cotton field and is a tributary to Coon Bayou. The forested site was located in north-central Chicot County. The monitoring station for the forested site was established on a ditch that drains approximately 1,230 acres and drains into the Boeuf River Diversion Canal. It is possible that the size of the basin that drains to the location of the monitoring station could change with extreme magnitudes of storm runoff events. The ditch intersects other ditches at three places within the basin and during events with extreme runoff water may be diverted into or out of the ditch.

Streamflow-gaging stations (Buchanan and Somers, 1974) were installed at both storm runoff sites (figs. 2 and 3). A sharp-crested rectangular weir was installed at the cotton-field site and a 24-in. diameter culvert was installed at a dirt road crossing downstream of the forested site. Stage-discharge ratings (Kennedy, 1984) were developed using indirect measurement computations for weirs (Hulsing, 1984) and indirect measurement computations for culverts (Bodhaine, 1982). The ratings were verified using current-meter streamflow measurements (Buchanan and Somers, 1984). Stage data were collected at 0.01-foot increments at both sites using float and stilling-well combinations (Buchanan and Somers, 1974). Staff gages were installed and read during storm events to verify stage data. Continuous stream-stage data were measured and recorded on an electronic data logger in 15-minute increments. Using the stage data and the stage-discharge ratings, continuous discharge values were computed (Kennedy, 1989) and recorded in 15-minute increments. Continuous rainfall data were collected at both sites using tipping-bucket rain gages. Rainfall data were collected at 0.01-inch increments and recorded at 15-minute increments.

 

 

2. Cotton field storm monitoring station at Coon Bayou Tributary near Tillar, Arkansas.

 

3. Forested storm monitoring station at Boeuf River Diversion Canal near Hudspeth, Arkansas.

Automatic samplers using peristaltic pumps powered by 12-volt batteries were installed at each site and used to collect storm-water samples. The sample water was pumped into four 1-gallon glass bottles contained within the automatic sampler. A data logger was used to control the automatic sampler. The data logger was programmed to read the stage, compute a discharge, and compute the volume of water that passed the monitoring station during 15-minute increments. Each time a designated volume of water passed the monitoring station the data logger would send a voltage pulse to the sampler causing it to activate and take a sample. With this setup, the sampler would take a flow-weighted composite sample throughout the storm hydrograph. The hydrograph and hyetograph in figure 4 show a typical sampled storm with rainfall intensity, instantaneous discharge, and sample activations plotted against time.

 

At the cotton field site, the entire storm-runoff hydrographs were sampled with the automatic sampler for every storm event. Because of the length of the storm runoff events at the forested site, the entire hydrograph was sampled only once. During the other sampled events, samples were taken at least until the peak of the hydrograph had passed.

Water-quality analyses were performed on the flow-weighted composite samples from both storm runoff sites between January 1995 and December 1996 for specific conductance, pH, turbidity, suspended solids, sulfate, chloride, fluoride, nutrients, and fecal coliform and fecal streptococcus bacteria. Bacteria concentrations were determined at the USGS laboratory in Little Rock, Arkansas. Specific conductance and pH were determined on-site for the composite sample. Other constituents were analyzed at the USGS Water Quality Laboratory in Ocala, Florida. 

The catfish pond site was in central Chicot County. The pond is used to raise fingerling catfish. It is a levee type pond that drains into the Main Ditch Canal of the Boeuf River when the drainpipe valve is open. Samples were collected from the pond effluent as the pond was being drained between April 17 and May 7, 1995. The volume of water in the pond before draining was approximately 10.8 acre-feet. Effluent samples were collected using a polyethylene churn splitter at the drainpipe. Two samples were collected on April 17 after the drainpipe valve was opened and one sample was collected on April 18. The catfish-pond manager closed the valve on April 19 through April 25 to allow for time to seine the fish out of the pond. After the valve was reopened, samples were collected daily from April 26 through April 28. The valve was closed again from April 29 through May 3. After the valve was reopened, daily samples were collected from May 4 through May 7 when the pond completed draining. Ten samples were collected as the pond drained.

The pond water-surface level was flagged on the side of the levee before the drain valve was initially opened and each time a sample was collected. A total station surveying instrument was used to collect data to calculate the pond areas and volumes that corresponded with the water-surface level initially and at the time each sample was collected.

Biological and Habitat Data

During an initial reconnaissance conducted in early November 1994, 40 sites within the study area were evaluated based on absence or presence of stream discharge and recent anthropogenic disturbances. Twenty-five sites were selected for bioassessment using the U.S. Environmental Protection Agency (USEPA) Rapid Bioassessment Protocol II (Plafkin and others, 1989). The selected sites had discharges of at least 0.5 cubic feet per second (ft*3*/s) and no evidence of recent bank, substrate, or channelization disturbances. Homogeneous dispersal of sites throughout the study area was limited by a lack of sites meeting these criteria in some areas.

During November and December 1994, macroinvertebrate communities were qualitatively sampled using a D-frame kick net with a mesh size of 425 microns. A reach length of 25 to 50 meters (82 to 164 feet) typically was sampled for 60 minutes. Reaches were sampled for less than 60 minutes (sample collection time) when the stream reach had a very homogeneous habitat and all available habitat within the reach could be adequately sampled in less than 60 minutes. In these situations, sample collection time was reduced to a minimum of 30 minutes. Samples were collected by kick netting, dipping, and hand picking from bottom substrates, vegetation, and rip rap. 

Samples were sorted and organisms were enumerated at the site. The original sample was dispensed into a 5-gallon container and mixed until contents were judged homogeneous. Then a small aliquot was transferred into a white picking pan measuring approximately 15 *×* 20 inches. Organisms in the subsample pan were removed, labeled, and preserved in a container of 10 percent formalin. If the first aliquot contained at least 100 invertebrates the subsample was complete. However, if a minimum of 100 invertebrates was not found in the first aliquot, the sample again was mixed and a second aliquot was processed. Subsample aliquots were processed until at least 100 organisms were removed or the sample was completely processed. At two sites (sites 12 and 16), the sample in the 5-gallon container was thoroughly mixed and then split into two subsamples. Comparison of the results of these duplicate samples provided some measure of the variability of the processing steps following sample collection.

Stream habitat was assessed using methods described in Plafkin and others (1989). Habitat parameters (bottom substrate or available cover, substrate embeddedness, flow, channel alteration, bottom scouring and deposition, run-to-bend ratio, bank stability, bank vegetative stability, and streamside cover) were given a rating score according to qualitative parameter descriptions. All parameter scores were then summed to calculate a total score.

Data Analysis Methods

At the cotton field site, forest site, and catfish pond, water-quality and discharge data were used to compute constituent loads associated with storms (cotton field and forest sites) or the draining of the pond. Boxplots and the Wilcoxon rank sum test (Helsel and Hirsch, 1992) were used to summarize and compare the water-quality data. USEPA Rapid Bioassessment Protocol II data-analysis methods (Plafkin and others, 1989) were used for an assessment of biological conditions at the 25 ambient sites.

Water Quality

Data from the flow-weighted composite water-quality samples provided the mean concentrations of constituents for the sampled event. At the cotton field site, the entire storms were sampled; therefore, the sample event-mean concentrations were the same as the storm event-mean concentrations. 

Loads for the cotton field site were computed using the flow-weighted composite samples for dissolved chloride, suspended solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, and dissolved orthophosphorus. The loads were computed using the sampled event-mean concentrations (EMCs) and the runoff volumes (RVs). The RVs were computed for each event by multiplying the event-mean discharges by the length of time each event occurred. A load for a given sampling event (i) is computed by the equation
 
where

LOAD*i*is constituent load (in pounds) for event i;

EMC*i* 		is event-mean concentration of constituent (in milligrams per liter) for event i; 

RV*i*			is runoff volume (in cubic feet) for event i, and;

6.245 x 10*-5* is the conversion from milligrams per liter to pounds per cubic foot.

Because the EMCs sampled at the cotton field site represent the entire storms sampled, the computed loads at this site are considered storm loads. 

Constituent loads computed for the forested site are for the sampled event and not the complete storm event except for the one complete storm event that was sampled at the forested site. The sampled event was subdivided and used to develop relations between percent storm load for a constituent and percent runoff volume, which then were used for estimating storm loads. The relations developed were second-order polynomial regression equations in the form of:
 
 

where

PERCLOAD*i* is percent of storm load computed for storm i;

b*0*,b*1*,b*2* 	      are regression coefficients; and

PERCRV*i* 		    is percent of storm runoff-volume sampled for storm i. 

Storm loads for the forested site for each constituent were computed by dividing the sampled event loads by the estimated PERCLOAD for each storm.

The standard error of estimates (SE) and the coefficient of determination (R*2*) were computed for each equation. The SE is a measure of the error about the regression. A smaller SE indicates a more precise prediction. The R*2* is the proportion of the variation in the response variable explained by the explanatory variables. A greater R*2* indicates a better fit.

The EMCs for the forested site were computed using the estimated storm-load and the storm-runoff volumes. A storm EMC for a given storm (i) is computed by the equation
 
where

EMC*i*   is event-mean concentration of constituent (in milligrams per liter) for storm i;

LOAD*i* is pollutant load (in pounds) for storm i; 

RV*i*      is runoff volume (in cubic feet) for storm i, and;

1.601 x 10*4* is the conversion from pounds per cubic foot to milligrams per liter.

Mean EMCs of all the storm samples combined, were computed for dissolved chloride, suspended solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, and dissolved orthophosphorus at both sites. Three methods were used to compute the mean EMCs: volume-weighted, logarithmic-transformed, and arithmetic. The volume-weighted mean EMC was computed using the equation
 
where

VWMEMC is volume-weighted mean EMC of aconstituent (in milligrams per liter) fora site.

The logarithmic-transformed mean EMCs were computed by transforming the EMCs to base-10 logarithms, summing the values, dividing by the number of storms, and retransforming the value. The arithmetic mean was computed by summing EMCs and dividing by the number of storms. 

Regression equations were developed to estimate storm loads for unsampled storms for suspended solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, and dissolved orthophosphorus at both sites. Size of the data set limited the number of explanatory variables that could be used in the regression analysis. Explanatory variables used were RV and a seasonal factor for the cotton field site, and RV for the forested site. The seasonal factor was used to explain the agricultural condition of the cotton field. Regression equations were not developed for estimating storm loads for dissolved chloride because there is not a good correlation between the dissolved chloride storm loads and the RVs.

For the cotton field and forested sites the regression equations, using a logarithmic transformation (log base-10) of the response and explanatory variables are in the following form:
 
 

where

SEASON is 0 for storms occurring March 1 through July 15, and 1 for storms occurring July 16 through February 28.

When equation 5 is retransformed it becomes
 
where

 is .

The retransformation of a log-transformed regression model provides a consistent estimator of median response but systematically underestimates the mean response (Miller, 1984). Therefore, a bias-correction factor (BCF) needs to be included in the retransformed regression equation if an unbiased estimate of the mean is to be obtained. A BCF was computed for each equation by using a smearing estimate that is a nonparametric method based on the average residuals in original units (Duan, 1983). After applying the BCF to equation 6, the form of the equation becomes
 
To estimate annual loads at both sites for the 1996 calendar year, the appropriate storm load equations were applied to all of the unsampled runoff-producing storms during the year. Base-flow samples collected at the forested site were used to estimate the base-flow loads that occurred during the year at that site. Annual loads were estimated by summing the sampled loads, the estimated unsampled loads, and at the forested site the base flow loads that occurred during the year. 

The constituent loads released during the draining of the catfish pond were determined by multiplying the concentrations by the change in volume of water that occurred between samples. The total loads from the drainage were determined by summing the individual sampled loads.

Selected water-quality data were graphically summarized and compared using boxplots.   The Wilcoxon rank sum test (a non-parametric test comparing ranked data) was used to compare selected water-quality data from storms at the cotton field and forest sites. 

Bioassessment

The USEPA Rapid Bioassessment Protocol II data-analysis methods (Plafkin and others, 1989) require comparisons to a reference site. No suitable bioassessment reference sites representative of relatively undisturbed conditions were found in the Boeuf River Basin. All sites evaluated were affected by land clearing, channelization, and bank disturbances. Boat Gunwale Slash, a least-disturbed reference stream for the Mississippi Alluvial Plain (Delta) ecoregion (Bennett and others, 1987), was used in this assessment as the reference stream for rapid bioassessment comparisons. 

Benthic macroinvertebrate data for Boat Gunwale Slash were obtained directly from Bennett and others (1987). The habitat parameter and total scores for the reference site were calculated based upon interpretation of the physical description presented in Bennett and others (1987).

Organisms from the Boeuf River Basin samples were identified to the family level using dichotomous keys (Merritt and Cummins, 1984; Pennak, 1989), enumerated, categorized by tolerance value and functional feeding group (Plafkin and others, 1989; Merritt and Cummins, 1984; and Lenat, 1993), and entered (along with data from the reference site) into a rapid bioassessment protocol metric calculation spreadsheet template provided by the USEPA (Howell, 1989). The spreadsheet subsequently was modified by the USGS to add some families that were present in the study area samples but not included in the provided spreadsheet. Taxa richness, family biotic index, ratio of scraper to filtering collector abundance, ratio of EPT (Ephemeroptera, Plecoptera, and Trichoptera) to Chironomidae abundances, percent contribution of dominant family, EPT index, ratio of shredder to total abundance, and the community loss index are the seven metrics used in the benthic invertebrate Rapid Bioassessment Protocol II (Plafkin and others, 1989). The spreadsheet provided by the USEPA calculated these seven metrics except that, for this study:

(1) ratio of scraper to filterer plus scraper abundance replaced scraper to filtering collector abundance, and

(2) ratio of EPT (Ephemeroptera, Plecoptera, and Trichoptera) to Chironomidae plus EPT abundance replaced ratio of EPT (Ephemeroptera, Plecoptera, and Trichoptera) to Chironomidae abundance.

A metric value "normalized" to the reference site metric value then was calculated for most metrics at each of the Boeuf River Basin sites. The normalized metrics were calculated as a ratio of the metric value at the reference site and the metric value at the Boeuf River Basin site; except the biological condition score for the percent contribution of dominant family was expressed as the actual percent contribution and the community loss index was not compared to the reference station, because a comparison to the reference station is incorporated into the index. Each metric value obtained was given a metric score of 0, 3, or 6, based on criteria given in Plafkin and others (1989). For each site, a biological condition score was calculated by summing the metric scores.   Biological condition scores were compared to the biological condition score for the reference site. A biological condition category then was assigned to each bioassessment site based on the comparison of biological condition scores at the bioassessment site to the reference site score and criteria in Plafkin and others (1989).

Relations between benthic macroinvertebrate communities, physical habitat, and water quality were examined using the Spearman's correlation test (Helsel and Hirsch, 1992). Biological community scores were tested for correlation with physical habitat scores and with water-quality values. The strongest correlations also were examined using x-y plots.

Metrics and scores for duplicate samples from sites 12 and 16 were compared using relative percent difference. Relative percent difference was calculated using the formula 
 
where RPD is relative percent difference (percent), and a and b are the valuesassociated with the duplicate samples from a site.

WATER-QUALITY, BIOLOGICAL, AND HABITAT ASSESSMENT

Concentrations, loads, and other water-quality associated results for the ambient, cotton field, forest, and catfish pond sites are described in this section. Benthic macroinvertebrate and habitat results also are discussed.

Water Quality

Water-quality samples from the 25 ambient sites (which were at locations where recent bank, substrate, or channelization disturbances were not evident) indicate that streams in the Boeuf River Basin typically are turbid and nutrient enriched during the late fall during periods of relatively low flow (fig. 5, table 2). Most suspended solids concentrations (residue at 105 degrees Celsius) ranged from about 50 to 200 mg/L. Most total nitrogen concentrations ranged from about 1.1 to 1.8 mg/L. Much of the nitrogen was ammonia plus organic nitrogen, which typically ranged from about 0.8 to 1.5 mg/L. Total phosphorus and dissolved orthophosphorus typically ranged from about 0.25 to 0.40 mg/L and 0.10 to 0.25 mg/L, respectively. 

Data from previous investigations suggest that concentrations of suspended solids and some nutrients in the Boeuf River Basin are higher than in much of the Mississippi Alluvial Plain in Arkansas. Median concentrations of total suspended solids, total phosphorus, and dissolved phosphorus from samples collected during all seasons at several sites in the Mississippi Alluvial Plain (Petersen, 1988; Petersen, 1992) usually were lower than 50 mg/L, 0.25 mg/L, and 0.10 mg/L, respectively. Median concentrations of total ammonia plus organic nitrogen and total nitrogen for the sites in the Boeuf River Basin were similar to medians reported by Petersen (1988, 1992). Total suspended solids and nutrient concentrations for the sites in the Boeuf River Basin generally were similar to concentrations for sites sampled in previous USGS investigations (Bryant and others, 1978; Lamb, 1979; Petersen, 1981). However, in two basins, suspended solids (Flat Bayou) or total phosphorus (L'Anguille) concentrations were substantially lower than concentrations from the Boeuf River Basin. Data collected as part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program (Coupe, 2002) in the Mississippi Embayment study unit (an area primarily containing the Mississippi Alluvial Plain of Arkansas, Louisiana, Mississippi, and nearby states) indicate that the November-December sample concentrations of total nitrogen, total phosphorus, and dissolved orthophosphorus from the Boeuf River Basin are slightly higher than November-December sample concentrations from several other streams in the Mississippi Alluvial Plain. 

Values listed as water-quality standards or guidelines by the Arkansas Pollution Control and Ecology Commission (1998) occasionally were exceeded (or, in the case of dissolved oxygen were less than the standard) in samples from the ambient sites (table 2). However, conditions listed in the standards sometimes provided exceptions or specific sampling criteria that must be met to legally apply the standard. For example, the numeric turbidity standard only applies to turbidities resulting from "waste discharges or instream activity", the total phosphorus guideline does not apply in waters "highly laden with natural silts...which reduce the penetration of sunlight needed for plant photosynthesis...", and the chloride and sulfate standards are based on multiple samples collected over 30 to 360 days. Therefore, the following comparisons to the standards and guidelines are for general comparison and do not necessarily imply violation. The standard for turbidity in channel-altered Delta (Mississippi Alluvial Plain) streams (75 nephelometric turbidity units) was exceeded at about half of the sites. The total phosphorus guideline (0.1 mg/L) was exceeded at all but one site. Chloride (160 mg/L) and sulfate (30 mg/L) standards for the Boeuf River Basin were exceeded at one and two sites, respectively. The primary season dissolved oxygen standard (5 mg/L) was not met at two sites.

Typically the suspended solids and nutrient concentrations from the ambient sites (sampled during a period of relatively low streamflow) were lower than concentrations in runoff from the cotton field but higher than concentrations in runoff from the forest area. These differences indicate that suspended solids and nutrient concentrations in the Boeuf River Basin are affected by streamflow and land use.

 

5. Ranges and distributions of suspended solids and nutrient concentrations at 25 ambient sites sampled during a period of relatively low streamflow in November and December 1994.

 

Water quality of samples from the 25 ambient sites

[*μ*S/cm, microsiemens per centimeter at 25 degrees Celsius; deg C, degrees Celsius; mg/L, milligrams per liter; NTU, nephelometric turbidity units;five-digit numbers in parentheses are water-quality parameter codes; --, no data; <, less than]

Site

number

Date

Spe-

cific

con-

duct-

ance

(*μ*S/cm)

(00095)

pH

water

whole

field

(stand-

ard

units)

(00400)

Temper-

ature

water

(deg C)

(00010)

Oxygen,

dis-

solved

(mg/L)

(00300)

Oxygen,

dis-

solved

(percent

satur-

ation)

(00301)

Tur-

bid-

ity

(NTU)

(00076)

Resi-

due

total

at 105

deg.C,

 sus-

pended

(mg/L)

(00530)

Sul-

fate

dis-

solved

(mg/L

as

SO*4*)

(00945)

Chlo-

ride,

dis-

solved

(mg/L

as Cl)

(00940)

Fluo-

ride,

dis-

solved

(mg/L

as F)

(00950)

1

11/29/1994
201
7.4

10.8

9.6

86

150

90

8.3

17

0.3

2

11/23/1994
340
8.1

11.3

10.9

98

35

36

15

43

0.5

3

11/07/1994
345
8.2

18.6

10.5

111

140

150

10

26

0.2

4

11/21/1994
269
7.5

16.6

7.4

76

73

88

10

23

0.2

5

11/21/1994
303
8.1

16.1

9.3

94

82

120

12

32

0.4

6

11/22/1994
340
7.0

17.5

10.7

111

78

120

15

32

0.4

7

11/09/1994
150
6.6

20.3

5.3

59

96

100

7.4

19

0.1

8

11/08/1994
161
6.5

18.3

3.9

42

7.7

20

3.6

16

<.1

10

11/30/1994
153
7.1

13.1

10.1

95

--

240

8.5

13

0.1

11

11/30/1994
156
7.1

13.4

10.3

97

--

210

8.6

14

0.2

12

12/07/1994
717
7.4

14.6

9.2

90

110

120

24

160

0.2

13

12/02/1994
182
7.1

11.8

10.1

93

--

190

9.8

19

0.1

14

11/22/1994
270
6.9

12.2

8.8

81

41

52

5.9

36

0.1

15

11/22/1994
320
6.9

12.7

7.9

74

42

84

7.7

38

0.3

16

11/09/1994
312
6.9

17.5

2.9

31

100

120

7.0

43

0.2

17

11/09/1994
224
6.9

17.7

6.7

70

--

32

--

--

--

18

12/07/1994
281
7.1

13.6

8.8

85

140

140

11

44

0.2

19

12/06/1994
125
6.5

12.5

4.5

42

87

52

6.2

12

<.1

20

12/06/1994
221
7.3

13.6

10.0

96

54

36

3.9

19

0.2

21

11/29/1994
497
7.6

11.8

8.6

79

140

100

24

51

0.2

22

12/01/1994
366
7.5

8.3

8.4

71

190

90

27

39

0.2

23

12/01/1994
389
7.4

8.7

7.6

65

160

270

47

37

0.1

24

11/07/1994
640
7.8

19.3

8.9

96

42

58

31

100

0.2

25

11/29/1994
514
7.6

11.2

9.2

83

120

100

24

66

0.2

27

12/01/1994
225
7.0

12.4

8.8

82

--

410

17

27

0.1

 

2. Water quality of samples from the 25 ambient sites--Continued

[*μ*S/cm, microsiemens per centimeter at 25 degrees Celsius; deg C, degrees Celsius; mg/L, milligrams per liter; NTU, nephelometric turbidity units;five-digit numbers in parentheses are water-quality parameter codes; --, no data; <, less than]

Site

number

Date

Nitro-

gen

nitrate

dis-

solved

(mg/L

as N)

(00618)

Nitro-

gen

nitrite

dis-

solved

(mg/L

as N)

(00613)

Nitro-

gen

NO*2*+

NO*3*

dis-

solved

(mg/L

as N)

(00631)

Nitro-

gen

ammo-

nia

dis-

solved

(mg/L

as N)

(00608)

Nitro-

gen

organic

total

(mg/L

as N)

(00605)

Nitro-

gen

ammo-

nia+

organic

total

(mg/L

as N)

(00625)

Nitro-

gen,

total

(mg/L

as N)

(00600)

Phos-

phorus

total

(mg/L

as P)

(00665)

Phos-

phorus

dis-

solved

(mg/L

as P)

(00666)

Phos-

phorus

ortho,

dis-

solved

(mg/L

as P)

(00671)

1

11/29/1994

0.37

0.01

0.38

0.08

1.2

1.3

1.7

0.60

0.43

0.41

2

11/23/1994

0.22

0.01

0.23

0.04

0.89

0.93

1.2

0.34

0.28

0.24

3

11/07/1994

0.38

0.03

0.41

0.16

1.2

1.4

1.8

0.38

0.19

0.19

4

11/21/1994

0.14

0.01

0.15

0.07

0.90

0.97

1.1

0.30

0.19

0.18

5

11/21/1994

0.19

0.02

0.21

0.02

0.62

0.64

0.85

0.26

0.13

0.11

6

11/22/1994

0.27

0.02

0.29

0.04

1.1

1.1

1.4

0.28

0.07

0.06

7

11/09/1994

0.04

0.01

0.05

0.04

0.76

0.80

0.85

0.32

0.17

0.16

8

11/08/1994

--

0.01

<.02

0.01

1.3

1.3

--

0.17

0.14

0.12

10

11/30/1994

0.27

0.01

0.28

0.09

1.3

1.4

1.7

0.40

0.19

0.17

11

11/30/1994

0.27

0.01

0.28

0.08

1.4

1.5

1.8

0.40

0.22

0.20

12

12/07/1994

0.07

0.01

0.08

0.02

1.6

1.6

1.7

0.24

0.04

0.02

13

12/02/1994

0.23

0.06

0.29

0.15

1.2

1.4

1.7

0.33

0.15

0.16

14

11/22/1994

0.09

0.01

0.10

0.07

0.92

0.99

1.1

0.23

0.14

0.13

15

11/22/1994

0.25

0.04

0.29

0.19

1.5

1.7

2.0

0.39

0.25

0.24

16

11/09/1994

0.24

0.04

0.28

0.17

1.5

1.7

2.0

0.30

0.10

0.08

17

11/09/1994

0.37

0.04

0.41

0.16

1.3

1.5

1.9

0.43

0.20

0.20

18

12/07/1994

0.26

0.01

0.27

0.06

1.1

1.2

1.5

0.32

0.13

0.09

19

12/06/1994

0.11

0.01

0.12

0.08

1.2

1.3

1.4

0.40

0.26

0.15

20

12/06/1994

0.11

0.01

0.12

0.02

0.80

0.82

0.94

0.25

0.18

0.14

21

11/29/1994

0.46

0.02

0.48

0.03

1.1

1.1

1.6

0.26

0.16

0.17

22

12/01/1994

0.41

0.01

0.42

0.07

1.1

1.2

1.6

0.46

0.24

0.23

23

12/01/1994

0.20

0.01

0.21

0.10

1.2

1.3

1.5

0.49

0.38

0.38

24

11/07/1994

--

<.01

<.02

0.01

0.71

0.72

--

0.08

0.02

0.02

25

11/29/1994

--

<.01

0.16

0.03

0.93

0.96

1.1

0.23

0.12

0.13

27

12/01/1994

0.36

0.01

0.37

0.10

1.5

1.6

2.0

0.37

0.14

0.14

Eleven storm events were sampled at the cotton field and forested sites. The rainfall amounts for the storms sampled ranged from 0.54 to 1.74 inches. at the cotton field site and from 1.14 to 4.31 inches at the forested site (table 3). The runoff volumes varied with each event depending upon the rainfall amount, intensity and antecedent conditions, time of the year, and agricultural condition of the field. Water-quality data associated with these storm events are listed in tables 4 and 5.

3. Storm events sampled

Site

Storm number

Date

Rainfall

(inches)

Runoff volume

(thousand cubic feet)

Cotton field

1

March 4-5, 1995

0.54
100
2

March 14-15, 1995

1.74
172
3

July 5, 1995

1.53
72.2
4

April 21, 1996

1.22
7.58
5

April 22-23, 1996

1.30
88.9
6

April 29, 1996

1.07
12.3
7

July 20-21, 1996

0.57
22.2
8

July 24-25, 1996

1.40
57.2
9

November 1-2, 1996

1.26
62.6
10

November 7-8, 1996

1.10
89.7
11

December 16-18, 1996

1.41
100
Forested

1

January 5-11, 1995

1.19
1,678
2

March 3-6, 1995

1.16
1,421
3

March 7-11, 1995

2.10
4,071
4

July 5-8, 1995

4.31
571
5

March 24-29, 1996

1.14
853
6

April 22-24, 1996

0.76
305
7

July 28-30, 1996

1.79
237
8

October 25-28, 1996

2.77
447
9

November 1-5, 1996

2.36
856
10

November 7-12, 1996

1.45
846
11

December 16-20, 1996

3.10
1,982
 

4.  Water quality of composited storm runoff samples from the cotton field site

[*μ*S/cm, microsiemens per centimeter at 25 degrees Celsius; NTU, nephelometric turbidity units; mg/L, milligrams per liter; cols./100 mL, colonies per 100 milliliters; --, no data; Five digit numbers in parentheses are water-quality parameter codes; K, results based on colony count outside the acceptance range (non-ideal colony count)]

Date

Spe-

cific

con-

duct-

ance

(*μ*S/cm)

(00095)

pH

water

whole

field

(stand-

ard

units)

(00400)

Tur-

bid-

ity

(NTU)

(00076)

Residue

total at

105 deg.C,

 sus-

pended

(mg/L)

(00530)

Sulfate

dis-

solved

(mg/L

as

SO*4*)

(00945)

Chlo-

ride,

dis-

solved

(mg/L

as Cl)

(00940)

Fluo-

ride,

dis-

solved

(mg/L

as F)

(00950)

Nitro-

gen

nitrate

dis-

solved

(mg/L

as N)

(00618)

Nitro-

gen

nitrite

dis-

solved

(mg/L

as N)

(00613)

March 4-5, 1995

69

7.0

2,300

1,700

3.9

10

0.1

0.41

0.01

March 14-15, 1995

36

6.9

4,300

90

1.6

3.6

0.1

0.12

0.01

July 5, 1995

16

7.1

960

1,300

0.3

0.3

0.1

0.24

0.02

April 21, 1996

94

6.5

1,600

1,500

4.5

8.0

0.3

1.36

0.04

April 22-23, 1996

61

6.9

1,500

1,800

2.5

6.1

0.2

0.55

0.01

April 29, 1996

60

6.2

1,200

1,300

4.2

4.2

0.2

0.46

0.01

July 20-21, 1996

212

7.9

31

130

8.0

9.4

0.2

0.11

0.04

July 24-25, 1996

52

6.5

77

120

2.0

2.0

0.1

--

<0.01

November 1-2, 1996

62

6.4

19

27

1.7

0.8

<0.1

0.15

0.01

November 7-8, 1996

54

6.6

75

65

1.1

0.8

<0.1

--

<0.01

December 16-18, 1996

39

8.0

18

18

1.2

0.6

<0.1

--

<0.01

 

Date

Nitrogen

NO*2*+

NO*3*

dis-

solved

(mg/L

as N)

(00631)

Nitro-

gen

ammo-

nia

dis-

solved

(mg/L

as N)

(00608)

Nitro-

gen

organic

total

(mg/L

as N)

(00605)

Nitro-

gen

ammo-

nia+

organic

total

(mg/L

as N)

(00625)

Nitro-

gen,

total

(mg/L

as N)

(00600)

Phos-

phorus

total

(mg/L

as P)

(00665)

Phos-

phorus

dis-

solved

(mg/L

as P)

(00666)

Phos-

phorus

ortho,

dis-

solved

(mg/L

as P)

(00671)

Coli-

form,

fecal,

0.7

um-mf

(cols./

100 mL)

(31625)

Strep-

tococci

fecal,

kf agar

(cols./

100 mL)

(31673)

March 4-5, 1995

0.42

0.15

6.6

6.7

7.1

3.5

0.81

0.80

520

10,000

March 14-15, 1995

0.13

0.05

3.5

3.6

3.7

1.9

0.45

0.47

K1,600

11,000

July 5, 1995

0.26

0.46

2.4

2.9

3.2

1.0

0.28

0.24

>6,000

20,000

April 21, 1996

1.4

0.65

6.7

7.3

8.7

3.8

0.65

0.69

K18,000

K16,000

April 22-23, 1996

0.56

0.10

7.9

8.0

8.6

3.9

0.61

0.61

K1,300

K2,000

April 29, 1996

0.47

0.05

5.2

5.2

5.7

2.3

0.29

0.30

41,000

>100,000

July 20-21, 1996

0.15

0.54

1.6

2.1

2.2

0.87

0.06

0.06

2,000

K270

July 24-25, 1996

0.36

0.01

1.3

1.3

1.7

0.40

0.15

0.14

32,000

57,000

November 1-2, 1996

0.16

0.09

1.2

1.3

1.5

1.2

1.0

0.98

31,000

>100,000

November 7-8, 1996

0.08

0.05

0.36

0.41

0.49

0.98

0.59

0.58

K7,000

86,000

December 16-18, 1996

0.07

0.05

0.59

0.64

0.71

0.48

0.35

0.38

K64,000

67,000

 

5. Water quality of composited storm runoff samples from the forest site

[*μ*S/cm, microsiemens per centimeter at 25 degrees Celsius; NTU, nephelometric turbidity units; mg/L, milligrams per liter; cols./100 mL, colonies per 100 milliliters; --, no data; Five digit numbers in parentheses are water-quality  parameter codes; K, results based on colony count outside the acceptance range (non-ideal colony count)]

Date

Spe-

cific

con-

duct-

ance

(*μ*S/cm)

(00095)

pH

water

whole

field

(stand-

ard

units)

(00400)

Tur-

bid-

ity

(NTU)

(00076)

Residue

total at

105 deg.C,

 sus-

pended

(mg/L)

(00530)

Sulfate

dis-

solved

(mg/L

as

SO*4*)

(00945)

Chlo-

ride,

dis-

solved

(mg/L

as Cl)

(00940)

Fluo-

ride,

dis-

solved

(mg/L

as F)

(00950)

Nitro-

gen

nitrate

dis-

solved

(mg/L

as N)

(00618)

Nitro-

gen

nitrite

dis-

solved

(mg/L

as N)

(00613)

January 5-11, 1995

60

6.7

40

32

1.8

5.1

<.1

0.06

0.01

March 3-6, 1995

56

6.9

22

18

1.2

2.5

<.1

--

0.01

March 7-11, 1995

47

6.6

22

18

0.7

1.7

<.1

--

0.01

July 5-8, 1995

80

6.9

290

350

9.0

4.3

<.1

0.05

0.03

March 24-29, 1996

70

7.0

28

21

5.1

2.9

<.1

0.05

0.02

April 22-24, 1996

113

7.1

22

14

1.5

2.1

<.1

--

0.01

July 28-30, 1996

815

7.3

5.3

11

35

120

0.2

0.06

0.02

October 25-28, 1996

161

6.4

71

43

11

17

<.1

--

<.01

November 1-5, 1996

165

6.1

30

28

8.3

20

<.1

--

<.01

November 7-12, 1996

160

6.8

41

37

6.5

17

<.1

--

<.01

*1*December 16, 1996

79

7.4

34

30

2.2

6.2

<.1

--

<.01

*1*December 17, 1996

76

7.3

22

20

1.9

5.3

<.1

--

<.01

*1*December 18, 1996

76

--

17

11

2.2

6.2

<.1

--

<.01

*1*December 19, 1996

75

8.0

15

8

2.3

6.7

<.1

--

<.01

*1*December 20, 1996

82

7.5

12

8

2.2

6.3

<.1

--

<.01

 

Date

Nitrogen

NO*2*+

NO*3*

dis-

solved

(mg/L

as N)

(00631)

Nitro-

gen

ammo-

nia

dis-

solved

(mg/L

as N)

(00608)

Nitro-

gen

organic

total

(mg/L

as N)

(00605)

Nitro-

gen

ammo-

nia+

organic

total

(mg/L

as N)

(00625)

Nitro-

gen,

total

(mg/L

as N)

(00600)

Phos-

phorus

total

(mg/L

as P)

(00665)

Phos-

phorus

dis-

solved

(mg/L

as P)

(00666)

Phos-

phorus

ortho,

dis-

solved

(mg/L

as P)

(00671)

Coli-

form,

fecal,

0.7

um-mf

(cols./

100 mL)

(31625)

Strep-

tococci

fecal,

kf agar

(cols./

100 mL)

(31673)

January 5-11, 1995

0.07

0.02

1.1

1.1

1.2

0.15

0.10

0.10

--

--

March 3-6, 1995

<.02

0.02

1.1

1.1

--

0.12

0.11

0.06

K190

480

March 7-11, 1995

<.02

0.02

0.84

0.86

--

0.14

0.12

0.09

460

K1,300

July 5-8, 1995

0.08

0.03

3.3

3.3

3.4

0.51

0.08

0.07

>1,200

>10,000

March 24-29, 1996

0.07

0.04

1.5

1.5

1.6

0.17

0.12

0.09

720

K470

April 22-24, 1996

<.02

0.06

1.5

1.6

--

0.32

0.18

0.18

380

2,700

July 28-30, 1996

0.08

0.06

0.73

0.79

0.87

0.07

0.03

0.05

K450

K990

October 25-28, 1996

<.02

0.03

1.1

1.1

--

0.23

0.14

0.16

K730

K610

November 1-5, 1996

0.02

<.01

--

1.0

1.0

0.24

0.14

0.08

5,400

7,800

November 7-12, 1996

<.02

<.01

--

1.4

--

0.22

0.16

0.10

K1,900

K2,900

1December 16, 1996

0.03

0.02

1.1

1.1

1.1

0.23

0.14

0.13

K7,100

K15,000

*1*December 17, 1996

<.02

<.01

--

0.88

--

0.18

0.13

0.12

K6,200

K12,000

*1*December 18, 1996

<.02

<.01

--

0.99

--

0.16

0.12

0.11

2,500

5,700

*1*December 19, 1996

<.02

<.01

--

1.0

--

0.14

0.10

0.10

600

1,900

*1*December 20, 1996

<.02

0.02

1.2

1.2

--

0.29

0.11

0.10

120

250

The median of the event-mean concentrations of dissolved chloride in samples from the cotton field site was significantly (p<0.05) less than the median of the event-mean concentrations in samples from the forested site (fig. 6). The median of the event-mean concentrations of suspended solids in samples from the cotton field site (130 mg/L) was significantly (p<0.05) greater than the median of the event-mean concentrations in samples from the forested site (fig. 6). The

higher suspended solids concentrations in the cotton

 

 

 

field site are expected because of the tilled soil of the cotton field compared to the soil of the forested site that was densely vegetated. 

Median nutrient event-mean concentrations of total nitrogen, total ammonia plus organic nitrogen, total phosphorus, and dissolved orthophosphorus were all significantly (p<0.05) higher in samples from the cotton field than in the forested site (fig. 6). The higher nutrient concentrations may result from fertilizer applications to the cotton field.

 

 

 

The computed mean EMCs using the volume-weighted, logarithmic-transformed, and arithmetic methods are shown in table 6. The median also is shown for the constituents by site in table 6.

Event-mean concentrations for all but two of the constituents were normally distributed. The EMCs for dissolved chloride at the forested site and suspended solids at the cotton field site are not normally distributed. Because the EMCs for these sites are not normally distributed, the median and the log-transformed mean were better estimators of the central tendency of the data than the arithmetic mean and the volume-weighted mean.

Regression coefficients and error statistics for regression equations used to calculate loads are listed in tables 7-9. Standard errors for the load regression equations ranged from 54 to 135 percent for the cotton field site (table 8) and 21 to 48 percent for the forested site (table 9). The coefficients of determination ranged from 0.75 to 0.86 for the cotton field site and 0.80 to 0.94 for the forested site. No coefficient for the seasonal explanatory variable was included in the load regression equation for the forested site (table 9) because the seasonal variable was not significantly correlated to loads at this site. An example of the estimated loads plotted against the measured loads for total nitrogen is shown in figure 7 for all sampled storms at both sites.

 

7. Measured and estimated total nitrogen storm loads.
 
6. Mean and median event-mean concentrations by sites

Constituent,

in mg/L

Site

Event-mean concentrations

(milligrams per liter)

Volume-

weighted

mean

Log-

transformed

mean

Arithmetic

mean

Median

Dissolved chloride

Cotton field

3.6

2.4

4.2

3.6

 

Forested

7.8

7.1

18

4.6

Suspended solids

Cotton field

619

258

732

130

 

Forested

15.2

15.2

16.3

16.4

Total nitrogen

Cotton field

3.6

2.8

4.0

3.2

 

Forested

1.0

1.1

1.1

1.0

Total ammonia plus organic

nitrogen as nitrogen

Cotton field

3.4

2.5

3.6

2.9

 

Forested

1.0

1.1

1.1

1.0

Total phosphorus

Cotton field

1.8

1.4

1.8

1.2

 

Forested

.14

.14

.15

.13

Dissolved orthophosphorus

Cotton field

.51

.38

.48

.47

 

Forested

.09

.08

.09

.09

7. Regression coefficients and error statistics for percent load regression equations at the forested site

[b, regression coefficient; R*2*, coefficient of determination; SE, standard error of estimate in percent; equation form is

]

 

Constituent

Regression coefficients

 

Error statistics

b*0*

b*1*

b*2*

 

R*2*

SE

Dissolved chloride

0.073

0.714

0.214

 

1.00

0.2

Suspended solids

.071

1.645

-.727

 

1.00

3.7

Total nitrogen

.078

.746

.172

 

1.00

1.8

Total ammonia plus organicnitrogen

.078

.746

.172

 

1.00

1.8

Total phosphorus

.049

1.179

-.230

 

1.00

.7

Dissolved orthophosphorus

-.017

1.235

-.222

 

1.00

1.4

 

8. Regression coefficients and error statistics for load regression equations at the cotton field site

[b, regression coefficient; R*2*, coefficient of determination; SE, standard error of estimate in percent; equation form is

, ]

Constituent

Regression coefficients

 

Error statistics

b*0*

b*1*

b*2*

BCF

 

R*2*

SE

Suspended solids

1.137

0.493

-1.184

1.321

 

0.77

135

Total nitrogen

-2.230

.740

-.671

1.081

 

.85

54

Total ammonia plus organic

nitrogen 

-2.386

.765

-.704

1.087

 

.86

54

Total phosphorus

-3.268

.884

-.522

1.087

 

.83

57

Dissolved orthophosphorus

-5.658

1.242

-.253

1.278

 

.75

111

 

9. Regression coefficients and error statistics for load regression equations at the forested site

[b, regression coefficient; R*2*, coefficient of determination; SE, standard error of estimate in percent; equation form is

, ]

Constituent

Regression coefficients

 

Error statistics

b*0*

b*1*

BCF

 

R*2*

SE

Suspended solids

-3.276

1.043

1.073

 

0.84

44

Total nitrogen

-3.570

.900

1.019

 

.94

21

Total ammonia plus organic

nitrogen 

-3.655

.912

1.021

 

.93

23

Total phosphorus

-4.880

.969

1.079

 

.80

48

Dissolved orthophosphorus

-5.219

.992

1.068

 

.85

42

 

The 1996 annual flow volumes and loads were divided by the drainage areas to calculate annual yields for the sites (table 10). The basin yields for the five constituents ranged from about 2 to 27 times greater at the cotton field site, although the flow volume per acre and rainfall were greater at the forested site. Fifty-three percent of the flow was sampled at the cotton field site and 23 percent of the flow was sampled at the forested site. 

Water released from the catfish pond (fig. 8, table 11) generally had high (relative to concentrations in forest and cotton field runoff and in low flow samples from ambient sites) concentrations of sulfate, chloride, suspended solids, and some nutrients. Sulfate and chloride concentrations from the catfish pond were typically substantially higher than concentrations in cotton field or forested runoff samples (fig. 6, tables 2 and 3) and somewhat higher than concentrations from the low flow samples from ambient sites (table 2). Suspended solids concentrations from the catfish pond samples typically were higher than concentrations in samples from the ambient sites (table 2) and in runoff samples from the forested site (fig. 6, table 5), but often were lower than concentrations in samples from the cotton field runoff (fig. 6, table 4). Concentrations of nitrogen species (total ammonia plus organic nitrogen, nitrite plus nitrate, and total nitrogen) typically were higher in samples from the catfish pond than in samples from any of the other types of sites (fig. 6, tables 2, 4, and 5).
 
10. Estimated annual yields for 1996 calendar year

[RV, runoff volume per acre; ft*3*/acre, cubic feet per acre; SS, suspended solids; TN, total nitrogen; TKN, totalammonia plus organic nitrogen; TP, total phosphorus; DOP, dissolved orthophosphorus; ( ), percent of volumeof yield sampled]

Site

Rain

(inches)

RV

(ft*3*/acre)

Yield, in pounds per acre

SS

TN

TKN

TP

DOP

Cotton field

41.14

16,750

496

2.97

2.67

1.49

0.51

 

 

(53)

(52)

(53)

(54)

(57)

(57)

 

 

 

 

 

 

 

 

Forested

52.56

19,190

18.1

1.31

1.29

.18

.11

 

 

(23)

(29)

(25)

(25)

(28)

(27)
 
8. Sampled concentrations with percent volume of catfish pond drained.
 
11. Water quality of grab samples collected during draining of the catfish pond

[*μ*S/cm, microsiemens per centimeter at 25 degrees Celsius; deg C, degrees Celsius; mg/L, milligrams per liter; cols./100 mL, colonies per 100 milliliters; five-digit numbers in parentheses are water-quality parameter codes; --, no data]

Date

Time

Spe-

cific

con-

duct-

ance

(*μ*S/cm)

(00095)

pH

water

whole

field

(stand-

ard

units)

(00400)

Temper-

ature

water

(deg C)

(00010)

Tur-

bid-

ity

(NTU)

(00076)

Residue

total at

105 deg.C,

 sus-

pended

(mg/L)

(00530)

Sulfate

dis-

solved

(mg/L

as

SO*4*)

(00945)

Chlo-

ride,

dis-

solved

(mg/L

as Cl)

(00940)

Fluo-

ride,

dis-

solved

(mg/L

as F)

(00950)

Nitro-

gen

nitrate

dis-

solved

(mg/L

as N)

(00618)

Nitro-

gen

nitrite

dis-

solved

(mg/L

as N)

(00613)

4/17/1995

1115

685

7.8

24

180

230

26

96

0.5

0.48

0.17

4/17/1995

1500

710

7.7

--

120

120

26

96

0.5

0.50

0.17

4/18/1995

1045

690

7.9

22

180

80

27

96

0.5

0.48

0.17

4/26/1995

1115

610

8.1

20

130

180

28

87

0.4

0.70

0.15

4/27/1995

945

600

8.0

18

120

150

28

86

0.4

0.70

0.14

4/28/1995

915

630

7.6

18

450

390

29

85

0.4

0.67

0.12

5/04/1995

1100

660

7.9

19

140

230

31

87

0.4

0.42

0.07

5/05/1995

1015

650

7.9

21

180

280

31

88

0.4

0.52

0.10

5/06/1995

1020

647

7.9

21

170

290

31

88

0.4

0.42

0.09

5/07/1995

1015

690

8.0

21

400

350

31

87

0.4

0.37

0.05
 
Date

Time

Nitrogen

NO*2*+

NO*3*

dis-

solved

(mg/L

as N)

(00631)

Nitro-

gen

ammo-

nia

dis-

solved

(mg/L

as N)

(00608)

Nitro-

gen

organic

total

(mg/L

as N)

(00605)

Nitro-

gen

ammo-

nia+

organic

total

(mg/L

as N)

(00625)

Nitro-

gen,

total

(mg/L

as N)

(00600)

Phos-

phorus

total

(mg/L

as P)

(00665)

Phos-

phorus

dis-

solved

(mg/L

as P)

(00666)

Phos-

phorus

ortho,

dis-

solved

(mg/L

as P)

(00671)

Coli-

form,

fecal,

0.7

um-mf

(cols./

100 mL)

(31625)

Strep-

tococci

fecal,

kf agar

(cols./

100 mL)

(31673)

4/17/1995

1115

0.65

1.6

3.3

4.9

5.6

0.39

0.08

0.03

K27

980

4/17/1995

1500

0.67

1.6

3.3

4.9

5.6

0.41

0.09

0.03

K27

K960

4/18/1995

1045

0.65

1.6

3.2

4.8

5.4

0.35

0.06

0.03

K17

>500

4/26/1995

1115

0.85

1.5

2.3

3.8

4.7

0.23

0.07

0.08

100

K7,600

4/27/1995

945

0.84

1.5

2.2

3.7

4.5

0.27

0.05

0.03

92

4600

4/28/1995

915

0.79

1.6

2.8

4.4

5.2

0.33

0.03

0.03

89

K6,500

5/04/1995

1100

0.49

0.81

2.2

3.0

3.5

0.24

0.04

0.02

K350

3,500

5/05/1995

1015

0.62

1.1

2.7

3.8

4.4

0.35

0.04

0.03

150

2,100

5/06/1995

1020

0.51

0.92

3.1

4.0

4.5

0.34

0.05

0.03

K68

930

5/07/1995

1015

0.42

0.08

5.5

5.6

6.0

0.58

0.04

0.03

67

K1,500

Concentrations of total phosphorus and orthophosphorus generally were lower in samples from the catfish pond (table 11) than in samples from the cotton field runoff, forest runoff, or ambient site low flow (fig. 6, tables 2, 4, and 5). Fecal coliform bacteria concentrations from the catfish pond samples (table 11) almost always were lower than concentrations in the forest or cotton field runoff samples (tables 4 and 5).

Concentrations of suspended solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, and dissolved orthophosphorus were relatively constant throughout the draining of the pond (fig. 8). However, there were rather substantial fluctuations of suspended solids and dissolved orthophosphorus in samples collected on April 26 through April 28 (table 11, fig. 8), which were collected after rains on April 18 and April 26 (table 12). Concentrations of all four constituents increased slightly as the percent volume of the pond drained increased from 70 to 100 percent (fig. 8).

The loads (pounds) of suspended solids, nitrogen, and phosphorus released from the catfish varied substantially (table 12). The suspended solids load was 8,050 pounds, while 166 pounds of total nitrogen and 12.0 pounds of total phosphorus were released.
 
12. Selected constituent loads from catfish pond drainage, April-May 1995

[ft*3*/acre, cubic feet per acre; SS, suspended solids; TN, total nitrogen; TKN, total ammonia plus organic nitrogen; TP, total phosphorus; DOP, dissolved orthophosphorus; lbs, pounds]

Sample

Rainfallvolume

(ft*3*)*2*

Sampledvolume

(ft*3*)

Load

Date

Time

SS

(lbs)

TN

(lbs)

TKN

(lbs)

TP

(lbs)

DOP

(lbs)

4/17/1995

11:15

--

27,700

400

9.5

8.5

0.67

0.052

4/17/1995

15:00

--

27,550

210

9.6

8.4

.71

.052

4/18/1995

10:45

28,200

64,800

320

22

19

1.4

.12

4/26/1995

11:15

34,800

75,000

840

22

18

1.1

.37

4/27/1995

09:45

--

21,500

200

6.0

5.0

.36

.040

4/28/1995

09:15

1,080

23,130

560

7.5

6.4

.48

.043

5/04/1995

11:00

9,700

63,800

920

14

12

.96

.080

5/05/1995

10:15

--

90,440

1,600

25

21

2.0

.17

5/06/1995

10:20

3,080

84,800

1,500

24

21

1.8

.16

5/07/1995

10:15

--

69,950

1,500

26

24

2.5

.13

Totals

 

76,860

548,670

8,050

166

145

12.0

1.22

Benthic Macroinvertebrate Communities and Physical Habitat

Taxa abundances for a reference site (Bennett and others, 1987) and 25 sites in the Boeuf River Basin are listed in table 13. Associated tolerance values and feeding groups also are listed.

Because no reference sites were found in the Boeuf River Basin, a site at Boat Gunwale Slash was used as a reference site for comparison with sites in the Boeuf River Basin. Three major factors that should be considered when comparing the Boeuf River Basin sites and benthic macroinvertebrate communities to the Boat Gunwale Slash site and its community are that (1) Boat Gunwale Slash has a drainage area (23 square miles) that is substantially smaller or larger than many of the Boeuf River Basin sites, (2) the Boat Gunwale Slash macroinvertebrate and habitat information was collected in August 1983 (rather than in November or December), and (3) sampling methods differed (one notable difference is that all organisms were enumerated and identified in the Boat Gunwale Slash sample).

Family richness (number of taxa, table 14) was substantially higher at the reference site (29 families) than at the sites in the Boeuf River Basin (8 to 18 families). Samples from most sites had about 31 to 62 percent the family richness of the reference site (table 15). Some difference in richness may be attributable to the larger number of individuals sampled at the reference site.

The family biotic index (which is a family-abundance weighted measure of tolerance) (table 14) generally was substantially lower at the reference site (6.1) than at the sites in the Boeuf River Basin (5.3 to 8.6), indicating that the community from the reference site was composed of a smaller proportion of tolerant individuals than were the communities from the sites in the Boeuf River Basin. Samples from the Boeuf River Basin sites had family biotic index values that were 71 to 107 percent of the index value for the reference site (table 15).

Samples from the Boeuf River Basin sites generally contained a greater proportion of scrapers (relative to filterers) than did the sample from the reference site (table 14). The scraper to filterer plus scraper ratio was 0.74 at the reference site and ranged from 0.20 to 1.00 at Boeuf River Basin sites (table 14). Samples from the Boeuf River Basin sites had ratios that were 27 to 135 percent of the ratio at the reference site; ratios at most Boeuf River Basin sites were 105 to 135 percent of the ratio at the reference site (table 15). This indicates that at the Boeuf River Basin sites a greater proportion of macroinvertebrates were grazing on periphyton than were filtering fine particulate organic matter (FPOM). 

Two tolerance-related metrics that are based on numbers of individuals and families of the generally intolerant Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT) generally indicated those Boeuf River Basin sites that were organically enriched or otherwise stressed. Ratios of EPT to EPT plus Chironomidae (a generally tolerant family of true flies) abundance at Boeuf River Basin sites varied substantially among sites (ranging from 0.00 to 1.00); the ratio at the reference site was 0.55 (table 14).   The EPT index (richness of EPT families) for the reference site (3 families) was higher than at almost all of the Boeuf River Basin sites (range 0 to 4 families, but exceeding 1 family in only 11 of 27 samples). 

Macroinvertebrate samples from the Boeuf River Basin sites generally were composed of a greater percentage of individuals from a single family (percent contribution of dominant family) than was the sample from the reference site. The largest percentage of individuals from a single family at the reference site was 16 percent (table 14). Largest single-family percentages from the Boeuf River Basin sites ranged from 15 to 87 percent and in most cases were at least twice the percentage from the reference site. Presence of families that are extremely numerically dominant indicate environmental stress (Plafkin and others, 1989).

Community loss index (Courtemanch and Davies, 1987) values, which measure the loss of taxa between a reference site and another site, ranged from 1.0 to 3.3 at Boeuf River Basin sites (table 14). Plafkin and others (1989) place all of these values in the middle category (values from 0.5 to 4.0) of biological condition scoring criteria.

Ratios of shredder to total abundance generally did not exceed 0.06 (table 14), indicating that shredders of coarse particulate organic matter are not an important component of the macroinvertebrate community during the late fall. Shredder abundance has been suggested to be linked to abundance of coarse particulate organic matter (leaf litter for example) (Lamberti and Moore, 1984; Merritt and Cummins, 1996). Low abundance of shredders probably is related to the absence of a well established riparian vegetation zone (see streamside cover score in table 18). The ratio for the reference site was slightly higher than most sites in the Boeuf River Basin, possibly because of the presence of a well established riparian zone.

 

13. Abundance, tolerance values, and feeding groups of macroinvertebrate taxa collected from 25 sites in the Boeuf River Basin and a referencesite 

[Reference site data from Bennett and others, 1987]

 

 

 

 

 

Abundance at site

Order

Tolerance

value

Feeding

group

Family

Reference

1

2

3

4

5

6

7

8

10

11

12

12 (duplicate)

13

Oligochaeta

10

Collectors

Oligochaeta

2

1

2

 

 

 

 

 

 

2

 

 

 

 

Hirudinea

8

Predators

Erpobdellidae

2

 

 

1

1

 

 

 

 

 

 

 

 

 

 

9

Predators

Hirudinidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Predators

Glossiphoniidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Predators

Piscicolidae

 

 

 

1

 

 

 

 

 

 

 

 

 

 

Gastropoda

9

Scrapers

Physidae

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6

Scrapers

Viviparidae

11

15

12

20

2

5

16

1

2

4

1

3

1

1

 

6

Scrapers

Planorbidae

1

 

1

 

3

 

 

1

4

 

 

 

 

 

 

6

Scrapers

Ancylidae

1

 

 

 

 

 

 

 

2

 

 

 

 

 

Pelecypoda

8

Filterer collectors

Sphaeriidae

6

3

6

1

 

 

 

 

 

 

 

 

 

 

Decapoda

8

Collectors

Cambaridae

 

 

1

1

2

 

2

1

 

1

2

 

 

1

 

9

Collectors

Palaemonidae

19

 

 

 

6

7

 

2

 

62

105

22

19

103

Amphipoda

7

Collectors

Talitridae

2

 

 

 

 

 

 

31

2

4

 

61

50

 

Ephemeroptera

4

Collectors

Baetidae

15

 

 

 

 

 

 

4

 

 

 

 

 

 

 

7

Collectors

Caenidae

19

17

9

 

39

6

4

14

 

1

1

20

24

1

 

4

Collectors

Ephemeridae

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Scrapers

Heptageniidae

 

 

1

 

 

 

 

 

 

 

 

 

 

 

 

2

Collectors

Leptophlebiidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Plecoptera

1

Shredders

Leuctridae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trichoptera

4

Filterer collectors

Hydropsychidae

 

1

1

 

 

 

 

 

 

 

1

2

8

 

 

4

Collectors

Hydroptilidae

 

1

3

 

 

 

 

 

 

 

 

 

 

 

Anisoptera

1

Predators

Gomphidae

1

 

 

 

 

1

 

2

2

 

1

 

 

2

 

9

Predators

Libellulidae

1

 

 

 

 

 

 

 

4

 

1

4

1

 

 

5

Predators

Protoneuridae

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

9

Predators

Coenagrionidae

 

27

21

9

43

37

50

9

 

8

2

81

44

5

Hemiptera

9

Piercers

Corixidae

 

28

5

 

2

7

3

 

 

1

11

 

 

 

 

5

Piercers

Veliidae

 

 

 

1

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Pleidae

15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Gelastocoridae

2

 

 

 

 

 

4

 

 

 

 

 

 

 

 

5

Predators

Gerridae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Mesoveliidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Hydrometridae

 

 

 

 

1

 

 

 

 

 

 

 

 

 

 

5

Predators

Belostomatidae

 

 

 

 

 

 

 

2

 

1

 

 

 

 

 

5

Predators

Notonectidae

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

5

Predators

Nepidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

Coleoptera

5

Predators

Dytiscidae

7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Scrapers

Elmidae

 

 

 

 

 

 

 

 

 

 

 

4

1

 

 

5

Shredders

Haliplidae

10

2

 

 

4

1

 

12

 

 

 

 

 

 

 

5

Predators

Hydrophilidae

5

 

 

 

2

 

 

2

1

 

 

 

 

 

 

6

Predators

Gyrinidae

 

1

 

 

 

1

 

 

 

1

 

 

 

 

 

4

Collectors

Scirtidae

 

 

 

 

 

 

 

 

 

1

 

 

 

 

 

4

Scrapers

Hydroscaphidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Predators

Carabidae

 

 

 

1

 

 

1

 

 

 

 

 

 

 

 

4

Predators

Noteridae

 

 

1

 

1

 

 

1

 

 

 

 

 

 

 

4

Shredders

Curculionidae

 

 

 

 

 

 

 

 

1

 

1

 

 

 

Diptera

5

Predators

Ceratopogonidae

1

 

 

3

 

 

 

 

 

 

 

 

 

 

 

3

Shredders

Tipulidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Collectors

Chironomidae

31

18

68

49

5

40

18

23

4

9

5

2

6

4

 

8

Collectors

Stratiomyidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Collectors

Culicidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Collectors

Sarcophagidae

 

 

 

3

 

 

 

 

 

 

 

 

 

 

Nematomorpha

8

Predators

Parachordodidae

 

 

 

1

 

1

 

 

 

 

2

2

 

1

 

8

Predators

Chordodidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Isopoda

7

Collectors

Asellidae

35

 

 

 

 

 

 

 

4

 

 

 

2

 

Megaloptera

8

Predators

Sialidae

8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Total number

of individuals

 

 

 

213

114

131

91

111

106

98

105

26

95

133

201

156

119

 

13. Abundances, tolerance values, and feeding groups of macroinvertebrate taxa collected from 25 sites in the Boeuf River Basin and a referencesite--Continued

[Reference site data from Bennett and others, 1987]

 

 

 

 

 

Site

 

Order

Tolerance

value

Feeding

group

Family

Reference

14

15

16

16 (duplicate)

17

18

19

20

21

22

23

24

25

27

Oligochaeta

10

Collectors

Oligochaeta

2

 

 

 

 

 

2

 

 

 

 

 

 

2

 

Hirudinea

8

Predators

Erpobdellidae

2

 

1

 

 

2

 

 

2

 

 

1

 

 

1

 

9

Predators

Hirudinidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Predators

Glossiphoniidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Predators

Piscicolidae

 

 

 

 

 

 

 

 

2

 

 

 

 

 

 

Gastropoda

9

Scrapers

Physidae

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6

Scrapers

Viviparidae

11

3

1

1

 

3

1

3

5

15

14

4

2

3

10

 

6

Scrapers

Planorbidae

1

1

 

 

 

 

 

 

1

3

6

 

 

1

 

 

6

Scrapers

Ancylidae

1

 

 

 

1

9

 

 

 

 

 

 

 

 

 

Pelecypoda

8

Filterer collectors

Sphaeriidae

6

1

 

 

 

 

 

 

2

 

 

 

 

 

2

Decapoda

8

Collectors

Cambaridae

 

1

2

8

6

13

1

 

 

1

 

1

1

2

 

 

9

Collectors

Palaemonidae

19

1

 

 

2

62

22

 

 

30

 

37

77

20

 

Amphipoda

7

Collectors

Talitridae

2

4

 

41

31

 

12

30

 

 

 

4

 

 

 

Ephemeroptera

4

Collectors

Baetidae

15

1

 

 

 

 

 

 

 

3

 

1

 

 

 

 

7

Collectors

Caenidae

19

35

28

 

2

1

48

18

120

6

37

9

4

9

7

 

4

Collectors

Ephemeridae

4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Scrapers

Heptageniidae

 

 

 

 

 

 

 

 

 

 

 

 

 

1

 

 

2

Collectors

Leptophlebiidae

 

 

 

 

 

 

 

 

 

 

 

 

 

3

 

Plecoptera

1

Shredders

Leuctridae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trichoptera

4

Filterer collectors

Hydropsychidae

 

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Collectors

Hydroptilidae

 

 

 

 

 

 

 

 

 

 

 

 

 

1

3

Anisoptera

1

Predators

Gomphidae

1

 

 

1

1

1

1

 

 

 

 

1

 

 

 

 

9

Predators

Libellulidae

1

1

 

6

6

 

1

 

 

 

 

 

 

 

 

 

5

Predators

Protoneuridae

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

9

Predators

Coenagrionidae

 

16

48

24

21

36

28

41

1

1

75

8

12

13

14

Hemiptera

9

Piercers

Corixidae

 

3

3

 

 

 

4

1

 

15

27

11

 

 

55

 

5

Piercers

Veliidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Pleidae

15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Gelastocoridae

2

 

 

 

 

 

 

 

 

1

 

4

 

 

 

 

5

Predators

Gerridae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Mesoveliidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Hydrometridae

 

2

 

 

 

 

 

1

 

1

 

16

3

3

 

 

5

Predators

Belostomatidae

 

4

 

 

 

2

 

1

 

9

1

 

 

1

 

 

5

Predators

Notonectidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

5

Predators

Nepidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Coleoptera

5

Predators

Dytiscidae

7

 

 

 

 

 

 

 

 

 

 

1

 

 

 

 

5

Scrapers

Elmidae

 

 

 

 

2

 

 

 

 

 

1

 

 

 

1

 

5

Shredders

Haliplidae

10

8

6

 

6

4

 

 

 

59

 

6

1

9

3

 

5

Predators

Hydrophilidae

5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6

Predators

Gyrinidae

 

 

 

 

 

 

6

 

 

2

 

 

 

27

5

 

4

Collectors

Scirtidae

 

 

 

 

2

 

 

 

 

 

 

 

 

 

1

 

4

Scrapers

Hydroscaphidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Predators

Carabidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4

Predators

Noteridae

 

 

 

 

1

1

 

 

 

5

 

8

 

 

1

 

4

Shredders

Curculionidae

 

 

 

1

 

 

 

 

 

 

 

 

 

 

 

Diptera

5

Predators

Ceratopogonidae

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3

Shredders

Tipulidae

 

 

 

 

 

 

 

 

 

 

 

3

 

 

 

 

4

Collectors

Chironomidae

31

11

33

6

1

1

11

6

14

9

 

6

2

8

6

 

8

Collectors

Stratiomyidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8

Collectors

Culicidae

 

 

 

 

 

 

 

 

 

 

 

1

 

 

 

 

8

Collectors

Sarcophagidae

 

 

 

 

1

 

 

 

 

 

 

 

 

 

 

Nematomorpha

8

Predators

Parachordodidae

 

5

1

 

1

 

1

4

1

 

1

 

1

 

1

 

8

Predators

Chordodidae

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Isopoda

7

Collectors

Asellidae

35

 

 

13

24

2

 

1

 

 

 

 

 

 

 

Megaloptera

8

Predators

Sialidae

8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Total number

of individuals

 

 

 

213

98

123

101

108

137

138

106

148

160

162

122

103

103

110

 

14. Bioassessment metrics for samples collected from sites in the Boeuf River Basin and a reference site

[EPT, Ephemeroptera, Plecoptera, and Trichoptera; N/A, not applicable]

 

 

Site

 

Rapid bioassessment metrics

Reference

1

2

3

4

5

6

7

8

10

11

12

12 (duplicate)

13

Number of taxa (family richness)

29

11

13

12

13

10

8

14

10

12

12

10

10

9

Family biotic index

6.1

7.3

5.7

5.3

7.6

6.7

7.3

6.0

5.9

8.2

8.6

8.0

7.5

8.6

Scraper/(filterer + scraper) abundances

0.74

0.79

0.67

0.95

1.00

1.00

1.00

1.00

1.00

1.00

0.50

0.78

0.20

1.00

EPT/(Chironomidae + EPT) abundances

0.55

0.51

0.17

0.00

0.89

0.13

0.18

0.44

0.00

0.10

0.29

0.92

0.84

0.20

Percent contribution of dominant family

16

25

52

54

39

38

51

30

15

65

79

40

32

87

EPT index (family)

3

3

4

0

1

1

1

2

0

1

2

2

2

1

Community loss index

N/A

2.1

1.8

2.0

1.6

2.3

3.1

1.4

2.0

1.9

1.9

2.3

2.2

2.7

Shredder/total abundance

0.05

0.02

0.00

0.00

0.04

0.01

0.00

0.11

0.04

0.00

0.01

0.00

0.00

0.00

 

 

 

Site

Rapid bioassessment metrics

Reference

14

15

16

16 (duplicate)

17

18

19

20

21

22

23

24

25

27

Number of taxa (family richness)

29

17

9

9

16

13

13

10

9

15

8

18

9

15

14

Family biotic index

6.1

6.8

7.0

7.4

7.3

8.3

7.5

7.6

6.7

6.3

8.1

7.0

8.6

6.7

7.8

Scraper/(filterer + scraper) abundances

0.74

0.67

1.00

1.00

1.00

1.00

1.00

1.00

0.75

1.00

1.00

1.00

1.00

1.00

0.85

EPT/(Chironomidae + EPT) abundances

0.55

0.77

0.46

0.00

0.67

0.50

0.81

0.75

0.90

0.50

1.00

0.63

0.67

0.64

0.63

Percent contribution of dominant family

16

36

39

41

29

45

35

39

81

37

46

30

75

26

50

EPT index (family)

3

3

1

0

1

1

1

1

1

2

1

2

1

4

2

Community loss index

N/A

1.1

2.7

2.6

1.3

1.5

1.6

2.4

2.6

1.4

3.3

1.0

2.7

1.5

1.6

Shredder/total abundance

0.05

0.08

0.05

0.01

0.06

0.03

0.00

0.00

0.00

0.37

0.00

0.07

0.01

0.09

0.03

 

15. Comparison of bioassessment metrics for samples collected from sites in the Boeuf River Basin to a reference site

[EPT is Ephemeroptera, Plecoptera, and Trichoptera]

 

Site

 

1

2

3

4

5

6

7

8

10

11

12

12 (duplicate)

Number of taxa (family richness)*1*

38

45

41

45

34

28

48

34

41

41

34

34

Family biotic index*2*

83

107

114

80

91

84

102

103

74

71

76

81

Scraper/(filterer + scraper) abundances*1*

107

90

129

135

135

135

135

135

135

68

105

27

EPT/(Chironomidae + EPT) abundances*1*

93

31

0

161

24

33

80

0

18

52

166

153

Contribution of dominant family*1*

149

316

328

236

230

310

180

94

397

480

245

195

EPT index*1*

100

133

0

33

33

33

67

0

33

67

67

67

Community loss index*3*

2.1

1.8

2.0

1.6

2.3

3.1

1.4

2.0

1.9

1.9

2.3

2.2

Shredder/total abundances*1*

37

0

0

77

20

0

243

82

0

16

0

0

 

 

 

Site

 

13

14

15

16

16 (duplicate)

17

18

19

20

21

22

23

24

25

27

Number of**taxa (family richness)*3*

31

59

31

31

55

45

45

34

31

52

28

62

31

52

48

Family biotic index*4*

71

90

88

82

84

74

81

80

90

97

75

88

71

91

78

Scraper/(filterer + scraper) abundances*1*

135

90

135

135

135

135

135

135

101

135

135

135

135

135

114

EPT/(Chironomidae + EPT) abundances*1*

36

140

83

0

121

91

148

136

163

91

182

113

121

116

113

Contribution of dominant family*1*

527

217

237

247

175

275

212

235

493

224

282

185

455

160

304

EPT index*1*

33

100

33

0

33

33

33

33

33

67

33

67

33

133

67

Community loss index*5*

2.7

1.1

2.7

2.6

1.2

1.5

1.6

2.4

2.6

1.4

3.3

1.0

2.7

1.5

1.6

Shredder/total abundances*1*

0

174

104

21

118

62

0

0

0

785

0

157

21

186

58

Biological condition scores for the Boeuf River Basin sites ranged from 15 to 42, compared to 48 for the reference site (table 16). Scores normalized to the reference score (ratios of Boeuf River Basin scores to the reference score) ranged from 31 to 88 percent. Based on these scores most Boeuf River Basin sites would be in the "moderately impaired" category and two sites would be classified in the "non-impaired" category (Plafkin and others, 1989). However, substantial uncertainty exists in the biological condition category rating because of differing drainage areas, sampling methods, and sampling season between the reference site and sites in the Boeuf River Basin. The biological condition categories presented provide a general and relative assessment of the macroinvertebrate communities at the Boeuf River Basin sites. 

A comparison of individual metrics, biological condition scores, normalized total scores, and the biological condition category for the duplicate samples indicated that substantial differences could occur between duplicate samples. However, these differences did not result in differences in the biological condition category (table 16). The results for the duplicates from site 12 generally were similar, but results for the duplicates from site 16 often were substantially different (table 17). Relative percent differences between metrics and scores for samples from site 12 ranged from 0 to 118 percent, and usually were less than 20 percent. Relative percent differences for samples from site 16 ranged from 0 to 200 percent and usually were greater than 50 percent. The greater similarity of the duplicates from site 12 relative to the duplicates from site 16 may be a function of the larger number of individuals counted and identified at site 12 (201 and 156) than at site 16 (101 and 108) (table 13).

Physical habitat scores for Boeuf River Basin sites ranged from 14 to 83 out of the possible 135 points (table 18). Most sites were considered to have poor habitat related to bottom substrate available cover, embeddedness, and flow and were considered to have poor or fair habitat related to most other factors. The score for the reference site as rated from documented data (Bennett and others, 1987) was 92. Most habitat factors at the reference site were considered good to excellent; only embeddedness was considered poor. Scores for the Boeuf River Basin sites ranged from 15 to 90 percent of the reference site score (table 18). 

Physical habitat can have a strong influence on biological communities. Part of the variation in biological condition scores for the Boeuf River Basin sites and the reference site was explained by the physical habitat scores (Spearmans rho=0.31, one-sided p-value = 0.051; fig. 9). In general, sites with the lowest habitat scores had the lowest biological condition scores (for example, sites 5, 6, 13, and 24). However, a considerable amount of variability in the biological condition scores was not explained by the habitat scores and some sites with low habitat scores were among those with the highest biological condition score totals (for example, sites 1, 25, and 27).

 

9. Relation of biological condition score to habitat score.

 

 

16. Comparison of biological condition scores for samples collected from sites in the Boeuf River Basin to a reference site

[EPT is Ephemeroptera, Plecoptera, and Trichoptera; N/A is not applicable; NI is non-impaired; MI is moderately impaired]

 

 

Site

 

Reference

1

2

3

4

5

6

7

8

10

11

12

12 (duplicate)

13

Number of taxa (family richness)

6

0

3

3

3

0

0

3

0

3

3

0

0

0

Family biotic index

6

3

6

6

3

6

3

6

6

3

3

3

3

3

Scraper/(filterer + scraper) abundances

6

6

6

6

6

6

6

6

6

6

6

6

3

6

EPT/(Chironomidae + EPT) abundances

6

6

3

0

6

0

3

6

0

0

3

6

6

3

Contribution of dominant family

6

6

0

0

3

3

0

3

6

0

0

3

3

0

EPT index

6

6

6

0

0

0

0

0

0

0

0

0

0

0

Community loss index

6

3

3

3

3

3

3

3

3

3

3

3

3

3

Shredder/total abundances

6

6

0

0

6

0

0

6

6

0

0

0

0

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Biological condition score (total)

48

36

27

18

30

18

15

33

27

15

18

21

18

15

Normalized total score (percent ofreference score)

N/A

75

56

38

63

38

31

69

56

31

38

44

38

31

Biological condition category

NI

MI

MI

MI

MI

MI

MI

MI

MI

MI

MI

MI

MI

MI

 

 

 

Site

 

Reference

14

15

16

16 (duplicate)

17

18

19

20

21

22

23

24

25

27

Number of taxa (family richness)

6

3

0

0

3

3

3

0

0

3

0

3

0

3

3

Family biotic index

6

6

6

3

3

3

3

3

6

6

3

6

3

6

3

Scraper/(filterer + scraper) abundances

6

6

6

6

6

6

6

6

6

6

6

6

6

6

6

EPT/(Chironomidae + EPT) abundances

6

6

6

0

6

6

6

6

6

6

6

6

6

6

6

Contribution of dominant family

6

3

3

3

6

3

3

3

0

3

3

3

0

6

3

EPT index

6

6

0

0

0

0

0

0

0

0

0

0

0

6

0

Community loss index

6

3

3

3

3

3

3

3

3

3

3

3

3

3

3

Shredder/total abundances

6

6

6

0

6

6

0

0

0

6

0

6

0

6

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Biological condition score (total)

48

39

30

15

33

30

24

21

21

33

21

33

18

42

30

Normalized total score (percent ofreference score)

N/A

81

63

31

69

63

50

44

44

69

44

69

38

88

63

Biological condition category

NI

NI

MI

MI

MI

MI

MI

MI

MI

MI

MI

MI

MI

NI

MI

 

17. Relative percent difference values for metrics and scores associated with duplicate samples

[EPT is Ephemeroptera, Plecoptera, and Trichoptera]

 

Site 12

Site 16
Number of taxa (family richness)
0

56
Family biotic index
6

1
Scraper /(filterer + scraper) abundances
118

0
EPT/(Chironomidae + EPT) abundances
9

200
Percent contribution of dominant family
22

34
EPT index (family)
0

200
Community loss index
4

67
Shredder/total abundance
0

143
Biological condition score (total)
15

75
Normalized total score
15

76

  

18. Physical habitat score assessment of the Boeuf River and its tributaries

Site

number

Bottom

substrate

available

cover

score(0-20)

Embed-

dedness

score

(0-20)

Flow

score

(0-20)

Channel

alteration

score

(0-15)

Bottom

scouring

and

deposition

score

(0-15)

Run/bend

ratio

score

(0-15)

Bank

stability

score

(0-10)

Bank

vegeta-

tive

stability

score

(0-10)

Stream-

side

cover

score

(0-10)

Habitat

score

(0-135)

Ratio of

habitat

score at

 site to

reference

site

 score

(percent)
Reference
13

5

15

15

14

7

10

5

8

92

100

1

3

3

6

3

3

4

5

6

5

38

41

2

3

6

4

3

2

6

6

6

5

41

45

3

6

2

8

2

2

2

5

9

5

41

45

4

12

12

5

5

5

2

1

4

5

51

55

5

1

2

1

1

1

2

1

2

3

14

15

6

2

1

3

1

2

4

5

6

5

29

32

7

4

3

4

8

8

2

6

9

8

52

57

8

16

16

5

10

10

3

5

8

8

81

88

10

3

3

6

6

6

6

2

8

5

45

49

11

4

5

5

3

4

4

3

6

5

39

42

12

4

5

5

7

4

3

8

8

8

52

57

13

2

2

2

2

2

4

4

3

4

25

27

14

12

6

4

4

4

4

5

8

9

56

61

15

8

10

4

6

7

5

5

8

6

59

64

16

5

10

5

8

12

3

5

5

8

61

66

17

10

10

2

5

5

4

2

2

6

46

50

18

4

2

3

6

3

3

5

6

9

41

45

19

10

1

2

11

11

3

9

10

8

65

71

20

5

5

11

3

4

7

8

8

5

56

61

21

5

3

5

8

8

3

2

6

6

46

50

22

18

12

8

10

10

8

4

8

5

83

90

23

14

8

5

8

8

6

5

6

9

69

75

24

2

1

1

1

1

1

3

9

6

25

27

25

3

2

3

3

4

3

2

5

5

30

33

27

4

4

5

4

6

3

2

5

5

38

41

19. Correlations between water quality and biological condition scores

[Spearman's rho correlation values can range from 0 to 1 or 0 to -1. Negative values indicate an inverse relation. A value of 0 would indicate no correlation between the water-quality factor and the biological condition score, whereas a value of 1 or -1 would indicate perfect correlation. p is one-sided probability value from a t-test]

 

Spearman'srho

p

Specific conductance

0.03

0.44

Dissolved oxygen

-0.40

0.02

Turbidity

-0.15

0.22

Suspended solids

-0.34

0.04

Dissolved nitrite plus nitrate

-0.10

0.32

Total ammonia

-0.03

0.44

Total ammonia plus organic nitrogen

-0.21

0.15

Total phosphorus

-0.29

0.14

Dissolved orthophosphorus

0.25

0.11

Water quality (table 2) also can influence biological communities. Biological condition scores were correlated most strongly (table 19) with dissolved oxygen concentrations (Spearmans rho = -0.40, one-sided p-value = 0.02) and suspended solids concentrations (Spearmans rho = -0.34, one-sided p-value = 0.04). There does not appear to be a meaningful and consistent relation between dissolved-oxygen concentration and the biological condition scores for these data (fig. 10); in general, relatively low and relatively high biological condition scores are found through much of the range of dissolved-oxygen concentrations. However, many of the lowest scores are associated with sites that had the highest dissolved-oxygen concentrations and many of the highest scores are associated with sites that had slightly lower oxygen concentrations. At sites where suspended solids concentrations were less than about 125 mg/L biological condition scores were quite variable, ranging from 15 to 42 (fig. 11). At sites where suspended solids concentrations were greater than about 125 mg/L biological condition scores were less variable, typically ranging from 15 to 24. Two sites had suspended solids concentrations exceeding 250 mg/L and biological condition scores exceeding 29. Other water-quality characteristics (specific conductance, turbidity, nitrite plus nitrate, ammonia, ammonia plus organic nitrogen, total phosphorus, and orthophosphorus) compared with biological condition scores were less strongly correlated (absolute values of rho ranged from 0.03 to 0.29) with the scores.

SUMMARY

Water-quality and biological samples were collected at 27 sites in the Boeuf River Basin between November 1994 and December 1996. Single water-quality samples were collected at 25 ambient monitoring sites during periods of seasonal low flow; one of these sites was the same site sampled downstream from a forested area during storm events. Storm runoff samples were collected at two sites (one draining a cotton field, one draining a forested area) using automatic samplers during 11 storm events. Ten water-quality samples were collected at one site during the draining of a catfish pond. Benthic macroinvertebrate community samples were collected and habitat was measured at the 25 ambient sites. Collection and measurement occurred on the same date that the water-quality samples were collected.

Water-quality samples from the 25 ambient sites (which were at locations where recent bank, substrate, or channelization disturbances were not evident) indicate that streams in the Boeuf River Basin typically are turbid and nutrient enriched during the late fall during periods of relatively low flow. For example, most suspended solids concentrations ranged from about 50 to 200 mg/L, most total nitrogen concentrations ranged from about 1.1 to 1.8 mg/L, total phosphorus typically ranged from about 0.25 to 0.40 mg/L. These concentrations appear to be slightly higher than typical spring and summer sample concentrations from the Mississippi Alluvial Plain.

Typically the suspended solids and nutrient concentrations from the ambient sites were lower than concentrations in runoff from the cotton field but higher than concentrations in runoff from the forest area. This indicates that suspended solids and nutrient concentration in the Boeuf River Basin are affected by streamflow and land use.

Samples collected during the storm events at the sites downstream from the cotton field and the forested area indicate that suspended solids, total nitrogen, total ammonia plus organic nitrogen, total phosphorus, dissolved orthophosphorus, and dissolved chloride concentrations were significantly different (p<0.05) during runoff events at the two sites. Dissolved chloride concentrations typically were higher at the site downstream from the forested area. Concentrations of the other constituents typically were higher downstream from the cotton field. The higher suspended solids and nutrient concentrations may result from soil tillage and fertilizer application at the cotton field. Concentrations of sulfate, chloride, suspended solids and some nutrients in samples from the catfish pond generally were greater than concentrations in samples from the cotton field and forest runoff sites and the ambient sites. Total phosphorus, orthophosphorus, and fecal coliform bacteria concentrations from the catfish pond generally were lower than concentrations in the cotton field or forest runoff and ambient-site samples.

Estimated annual yields of suspended solids, nitrogen, and phosphorus were substantially higher from the cotton field than from the forested area. Yields ranged from about 2 to 27 times greater at the cotton field site than at the forested site. 

Biological condition scores for the Boeuf River Basin sites ranged from 15 to 42, compared to 48 for the reference site (table 16). Scores normalized to the reference score (ratios of Basin scores to the reference score) ranged from 31 to 88 percent. Based on these scores most Boeuf River Basin sites would be in the "moderately impaired" category and two sites would be in the "non-impaired" category (Plafkin and others, 1989). However, substantial uncertainty exists in the biological condition category rating because of differing drainage areas, sampling methods, and sampling season between the reference site and sites in the Boeuf River Basin. The biological condition categories presented provide a general and relative assessment of the macroinvertebrate communities at the Boeuf River Basin sites. 

Several metrics that are measurements of the tolerance of individuals and taxa in the benthic macroinvertebrate community and that are used in calculating the biological condition scores indicate that the communities at most sites are composed of more tolerant macroinvertebrates than the community at the reference site. Family biotic index values generally were substantially lower at the reference site than at most sites in the Boeuf River Basin, indicating a less tolerant community at the reference site. Two tolerance related metrics (Ratio of EPT to EPT plus Chironomidae, EPT Index) also indicated a less tolerant community at the reference site. The indication of more tolerant communities suggests that sites are organically enriched or otherwise stressed.

Physical habitat scores for Boeuf River Basin sites indicated that most sites had poor habitat related to bottom substrate available cover, embeddedness, and flow and were considered to have poor or fair habitat related to most other factors. Most habitat factors at the reference site were considered good to excellent; only embeddedness was considered poor. Scores for the Boeuf River Basin sites ranged from 15 to 90 percent of the reference site score.

Physical habitat has a strong influence on biological communities. Part of the variation in biological condition scores for the Boeuf River Basin sites and the reference site was explained by the physical habitat scores. In general, sites with the lowest habitat scores had the lowest biological condition scores. However, a considerable amount of variability in the biological condition scores is not explained by the habitat scores and some sites with low habitat scores are among those with the highest biological condition score totals. 

Biological condition scores also were significantly correlated with dissolved oxygen concentrations and suspended solids concentrations. However, in neither case does there appear to be a meaningful and consistent relation between the water-quality characteristic and the biological condition scores; in general, relatively low and relatively high biological condition scores are found through much of the range of dissolved oxygen and total suspended solids concentrations. However, many of the lowest scores are associated with sites that had the highest dissolved oxygen concentrations and many of the highest scores are associated with sites that had slightly lower oxygen concentrations. Also, many of the sites with the highest scores had lower suspended solids concentrations, while many of the lowest scores are at sites with higher suspended solids concentrations. Other water-quality characteristics (specific conductance, turbidity, nitrite plus nitrate, ammonia, ammonia plus organic nitrogen, total phosphorus, and orthophosphorus) compared with Biological Condition Scores were less strongly correlated with the scores.     

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1.Composite samples collected during storm event of December 16-20, 1996.2.4.99 inches of rain fell during the draining of the pond. Volume was calculated by multiplying rainfall by drainage area of pond.3.Ratio of the study site to the reference site expressed as a percentage.4.Ratio of the reference site to the study site expressed as a percentage.5.Raw value (not compared to reference site as a ratio).