BENTHIC MACROFAUNAL COMMUNITY STRUCTURE IN OCEAN DREDGED
MATERIAL DISPOSAL SITES IN LOUISIANA: PRELIMINARY ANALYSIS
by
David A. Flemer, James Patrick, Jr.,
James R. Clark1
Ecotoxicology Branch
U.S. Environmental Protection Agency
Environmental Research Laboratory
Gulf Breeze, FL 32561
Barbara F. Ruth2
Technical Resources, Inc.
Environmental Research Laboratory
U.S. Environmental Protection Agency
Gulf Breeze, FL 32561
Charles M. Bundrick
Institute for Statistical and
Mathematical Modeling
University of West Florida
Pensacola, FL 32514
Gary Gaston
University of Mississippi
Department of Biology
Shoemaker Hall
University, MS 38677
Submitted to:
Susan McKinney
U.S. Environmental Protection Agency
Region VI
Dallas, TX 75202
Final Report: November 1994

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Present Affiliation:
'Dr. James R. Clark
Environmental Toxicology Division
Exxon Biomedical Sciences, Inc.
Mettlers Road, CN2350
East Millstone, NJ 08875-2350
2Barbara F. Ruth
Florida Department of Environmental Protection
Northwest District
760 Governmental Center
Pensacola, FL 32501
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EXECUTIVE SUMMARY
An analysis of the benthic macrofaunal community structure following dredged material
disposal was conducted during October 1991 at three dredged material locations in the northern
Gulf of Mexico. Dredged channels and adjacent reference and disposal sites were located on the
Gulf of Mexico-side of the passes of the Freshwater Bayou, Mermentau River, and Atchafalaya
River systems on the Louisianian coast. Dredged channels and associated reference and disposal
sites were oriented approximately at right angles to the shoreline. Reference and disposal sites at
each study area were divided into parallel and approximately equally-sized sectors, including
nearshore, middepth and offshore sectors. The purpose of the study was:
1.	to compare benthic macrofaunal community composition and taxon abundance
between reference and disposal sites and assess for possible gross effects of dredged
material disposal on benthic macrofaunal recolonization and recovery;
2.	to characterize sampling variance as guidance for possible future studies on effects of
dredged material in comparable habitats; and,
3.	to characterize the sediments for potential toxic contaminants.
Prior to this study, disposal of dredged material last occurred at the Mermentau River in
June/July 1987, Freshwater Bayou in September/October 1990, and Atchafalaya River in May
1991. The study was requested by the EPA Region VI.
The ecological effects component of the investigation was limited because it did not
include a pre-dredged material disposal assessment of benthic community composition as a
reference. Inferences about causes of differences in benthic macrofaunal community structure
were limited to a qualitative assessment. However, the analysis formed the basis for future
sampling strategies, including a statistical power analysis, and an assessment of current benthic
macrofaunal ecological status of reference and disposal sites, and the probable role of toxic
chemicals as determinants of community structure.
The total number of taxa collected from reference (N = 21) and disposal (N = 21) sites at
the Atchafalaya River, Freshwater Bayou, and Mermentau River study areas was 38 and 40, 21
and 18, and 14 and 17, respectively. The opportunistic polychaetes, Mediomastus californiensis
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(reference x = 40.8 and disposal x = 40.7/0.05 m2) and Paraprionospio pinnata (reference x =
14.0 and disposal x = 10.5) greatly dominated abundance at the Atchafalaya River and
Freshwater Bayou reference and disposal sites, respectively. All benthic animal densities are
referenced to 0.05 m2 unless specified otherwise. Differences in abundance between sites of
these highly dominant species on average were not significant (P > 0.05) but significant
differences in abundance were noted within (i.e., N = 7 at all nearshore, middepth, and offshore
stations) and among some reference and disposal stations. P. pinnata averaged 12.2 and 8.4
organisms at Atchafalaya River reference and disposal sites and M. californiensis averaged 6.2
and 1.2 organisms at Freshwater Bayou reference and disposal sites, respectively. These means
differed significantly (P s 0.05: significance level used unless specified otherwise) between sites
within study areas, and significant differences were observed within and among some reference
and disposal stations. No other taxa differed significantly in abundance at Freshwater Bayou
between sites, but at the scale of individual stations, seven other much less abundant taxa
differed significantly within and among some stations at reference and disposal sites.
Other less abundant taxa (x > 5.0 organisms/0.05 m2 at a reference or disposal site) at the
Atchafalaya River reference and disposal sites included the polychaetes, P. ambigua,
Spiochaetopterus oculatus, and Glycinde solitaria, the bivalve, Mulinia lateralis, the nemertean,
Nemertea sp. A., and unknown oligochaetes. Abundance of a nemertean, Oligochaeta, and a
much less abundant taxa (x ^ 5.0 organisms/0.05 m2), Polydora sp., were significantly greater at
the reference site. Abundance of Streblospio benedicti, another much less abundant taxa, was
significantly greater at the disposal site. Overall, abundance of 10 of 17 taxa, whose mean
abundance was greater than 1.0 organism/0.05 m2, differed significantly within and among some
stations at reference and disposal sites.
The polychaete, P. pinnata, dominated abundance at the Mermentau River (reference x =
51.2; disposal x = 113.5). The difference in abundance was significant. The less abundant taxa,
P. ambigua, averaged 5.8 and 1.0 organisms at disposal and reference sites; the difference was
significant. Three additional less abundant taxa, G. solitara, unknown Nemertea, and Magelona
sp., were significantly more abundant at the disposal site, and the polychaete, Cossura soyeri,
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was significantly more abundant at the reference site. Abundance of individual taxa at all three
study areas did not show an apparent graphical correlation with hydrographic factors, sediment
particle size, and sediment organic contaminant or metal concentrations.
The pattern in average abundance and average taxa richness differed substantially
between sites at all three study areas. At the Freshwater Bayou, abundance averaged 10.0, 25.6,
and 44.4 individuals at the combined reference and disposal nearshore, middepth, and offshore
locations. For these same locations, taxa richness averaged 3.3, 5.5, and 7.4. For both response
parameters, the nearshore averages differed significantly from both middepth and offshore
averages but the middepth and offshore averages did not differ significantly. Differences in
response parameters showed no apparent graphical relationship to sediment particle size (e.g., %
sand) and sediment chemical contaminant concentrations or hydrographic factors.
Significant statistical interactions in average abundance and taxa richness between sites
and station locations at the Atchafalaya and Mermentau Rivers required a post hoc analysis to
appropriately distinguish differences. Abundance averaged 144.3 and 51.6, and 92.7 and 176.1,
at Atchafalaya River nearshore and middepth reference and disposal stations, respectively.
Differences were statistically significant. Offshore reference and disposal sites averaged 91.3
and 85.0 organisms; this difference was not significant. Taxa richness difference which
averaged 11.9 at the Atchafalaya River nearshore reference and 6.1 at the nearshore disposal
station was significant. Significant differences were also observed among non-paired stations.
Differences in benthic community structure showed no apparent relationship to measured
sediment properties and hydrographic factors.
Abundance averaged approximately two to three times more individuals at disposal than
reference stations at the Mermentau River study area (e.g., offshore reference and disposal
stations averaged 44.0 and 136.3 organisms, respectively), and all disposal station averages were
significantly greater than reference station averages which was the basis for discounting the
importance of statistically significant (P s 0.043) main effects and station location interactions.
Taxa richness averaged 4.3 and 9.8 at middepth reference and disposal stations; differences were
statistically significant. Although not significant, average taxa richness at nearshore and offshore
disposal stations tended to average higher values than comparable reference stations.
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Differences in community structure occurred between sites and among some stations
within sites at the Atchafalaya River where measured sediment and hydrographic factors were
relatively homogenous. The more sandy disposal compared to reference site at the Mermentau
River was associated with higher abundance and numbers of taxa. Abundance and taxa richness
at the Freshwater Bayou was associated with the depth gradient and not with measured reference
and disposal sediment and hydrographic factors.
The consistent pattern of no significant differences in average abundance and taxa
richness between reference and disposal sites at the Freshwater Bayou, after approximately one
year since dredged material disposal, suggests no gross long-term sustainable effects on benthic
macrofaunal community structure due to disposal activities. The higher average abundance and
trend for higher taxa richness at the Mermentau River disposal site could be the result of natural
factors and not necessarily the result of dredged material disposal, especially with a four year
period since disposal activities last occurred.
Although differences were detected in community structure between reference and
disposal sites at the Atchafalaya River study area, significant differences in average abundance
and taxa richness between paired reference and disposal stations occurred only at the nearshore
location. Four of five individual taxa showed significantly greater abundance at reference sites.
The significant difference in abundance of the dominant species, P. pinnata, occurred only at the
nearshore stations. Since dredged material disposal occurred only five months prior to this study,
disposal effects in this case were not improbable as suggested for the Freshwater Bayou.
However, if the measured differences are the result of dredged material disposal, we suggest that
the magnitude is not large compared to the known seasonal and interannual variability of
members of benthic macrofaunal communties reported in the literature.
The addition of the seventh replicate sample per station seldom added a new taxon to the
inventory. In most cases, four or five replicates captured all but probably the most rare species.
The sampling power analysis revealed that approximately 25 to 50 replicate samples would be
required to achieve an accuracy of the mean for abundance +/-10%. The need for this level of
accuracy should-be determined on a case by case basis because of the obvious high cost for this
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level of sampling. Relaxation of the accuracy requirement to 20% substantially reduced the
number of samples required to achieve a significant P-value s 0.05.
We recommend application of the Before-After-Control-Impact (BACI) study design in
future environmental assessment studies of dredged material disposal. The design incorporates
more appropriate temporal sampling and replicated control sites. Other study design
recommendations are provided in the report. The BACI approach may involve a degree of
indeterminacy that should be addressed in future research.
Keywords: Dredged material disposal, dredged material effects, benthic macroinvertebrates,
Louisiana coast.
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INTRODUCTION
"The variability of nature is legend. In simple terms, variations in biological populations
and rates of processes in time and space constitute statistical noise from which the pollution
effects must be deciphered" (Boesch, 1984).
Dredged material disposal in coastal waters is of ecological concern because of potential
direct and indirect effects from physical smothering of benthic communities and changes in water
and sediment quality (e.g., exposure of organisms to toxic chemicals and possible food web
biomagnification of toxic chemicals.) Related concerns involve physical changes in the
hydrographic regime and physical disruption of benthic habitats (e.g., changes in grain size and
disruption of the biogeochemical integrity of sediments [Cronin, 1967; Kirby et al., 1975,
Probert, 1984]). Much has been learned concerning biological effects of dredged material
disposal in open waters, especially since inception of the Corps of Engineers Dredged Materials
Research Program of the Waterways Experiment Station in 1973 (Kirby et al., op cit).
Additional information has been acquired from site-specific studies performed to support
Environmental Impact Statements under EPA's designation of ocean dumping site program.
Most early work on effects of dredged material disposal and other sources of sediments
on aquatic biota was conducted in freshwaters. Wilson (1957) and Cordone and Kelley (1961)
reviewed some of the many studies of effects of sediments on aquatic life in freshwater streams
and rivers. In the marine environment, Ingle et al. (1955) studied chemical effects of dredging in
Mobile Bay, AL. Lunz (1938), working in coastal South Carolina, found that oyster mortality
occurred only when organisms were smothered with silt; otherwise, no important physiological
damage was detected due to dredged material placement. In a field study in coastal Louisiana,
Mackin (1961) also showed that oysters tolerated silt concentrations from 5 to 700 mg liter'1
Markey and Putnam (1976) concluded that no benthic community effects from dredging were
apparent in the Gulfport Ship Channel six weeks after maintenance dredging operations. As part
of a comprehensive field study on effects of overboard disposal of dredged materials in upper
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Chesapeake Bay, Flemer et al. (1968) described short-term decreases in abundance of two
benthic species (e.g., a hydrobid snail and the isopod, Cyathura polita). Reference samples were
collected approximately one month (September 1966) prior to dredge material disposal (October
1966) and compared with samples collected approximately one month after dredge material
disposal (December 1966). However, Pfitzenmeyer (1970) reported for the same area that
recovery in the disposal area of benthic macroinvertebrates approximated that prior to dredging
operations one year later. In the early 1950 s, Ingle (1952) concluded that local habitat variability
required that each dredging and disposal operation warranted separate environmental impact
consideration. This approach continues as current policy within the U.S. EPA.
Early laboratory studies found species-specific effects of fine sediments on benthic
animals. Loosanoff and Tommers (1948) reported reduced mollusc pumping rates in molluscs
with additions of small quantities of silt. In contrast, Chiba and Oshima (1957) worked with
three species of marine pelecypods and reported very little effect with low concentrations of
inorganic particles. Silt and clay particles less than 0.75 g liter1 (actual sediment concentrations
not given but presumed to be in the low milligrams liter"1 range) showed no significant
developmental effects to the straight hinge stage of the hard clam, Mercenaria mercenaria
(Davis, 1960) compared to seawater controls . Normal development decreased progressively at
successively higher silt and clay concentrations.
In addition to early work on effects of dredging and disposal operations on biota in the
Gulf of Mexico, considerable background information exists on the distribution, abundance,
trophic structure, and seasonality of benthic communities and characterization of sediment
physical properties and concentration of contaminants. Much of this work was sponsored in
response to concerns about changes in salinity (brine) and associated water quality factors (e.g.,
hypoxia, toxic chemicals) following discharge from leaching of salt domes used for oil storage
(e.g., Gaston et al., 1985; Gaston and Edds, 1994; Gaston, 1985; Giammona and Darnell, 1990;
DeRouen et al., 1983; Parker et al., 1980). Gaston and Edds (1994) presented evidence that
changes in hydrographic conditions in concert with hypoxia were major determinants of benthic
macroinvertebrate community structure at the West Hackberry coastal Louisiana brine disposal
site.
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Numerous ecological studies, including benthic macroinvertebrate surveys, have been
conducted in the northern Gulf of Mexico (e.g., Oetking et al., 1979; Ward et al., 1979) in efforts
to identify effects of oil drilling and production on coastal environments. Nearshore coastal
studies have characterized hydrographic and eutrophic conditions (Rabalais et al., 1986;
Rabalais, 1992) and sedimentological conditions (Jones and Williams, 1979) that provide
additional evidence of the importance of these factors to the survival and development of coastal
marine benthic communities. Estuarine environmental monitoring programs conducted by EPA
(Summers et al., 1993a and b) and NOAA (1992) provide a broad range of environmental data.
Such information helps form a basis for a priori expectations of seasonal distribution and
abundance of benthic macroinvertebrates by sediment type for many areas in estuaries and on the
shelf of the northern Gulf of Mexico.
Environmental concerns about dredged material disposal and other water quality issues
resulted in legislation such as the Clean Water Act of 1972 and the Marine Protection Research
and Sanctuaries Act of 1972 (also known as the Ocean Dumping Act). Section 404 of the Clean
Water Act authorizes the U.S. Environmental Protection agency (EPA) and the U.S. Army Corps
of Engineers (COE) to jointly regulate the disposal of dredged and fill materials in bays, harbors,
estuaries, rivers and lakes (waters of the U.S.). The Ocean Dumping Act authorizes the EPA and
the COE to jointly regulate the disposal of dredged materials in the open ocean (seaward of the
baseline). The COE uses the EPA regulations to determine the suitability of dredged material for
ocean disposal.
Because of the nature of the sediments, relatively shallow coastal waters, and commercial
shipping and recreational boating, the state of Louisiana has a continuing need for dredge and
disposal operations (U.S. EPA 1990a,b,c). As part of EPA's environmental evaluation process
and site monitoring responsibilities, a comparison of the benthic community structure at three
Ocean Dredged Material Disposal Sites (ODMDS) located in the coastal Louisiana nearshore
waters was conducted as an initial step in the environmental assessment of effects of disposal of
dredged material adjacent to deepened channels connecting the open Gulf waters to the intra-
coastal waterway. The three sites are located in the vicinity of the Mermentau River, Freshwater
Bayou and near the mouth of the Atchafalaya River (Figures 1 & 2).
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The purpose of the study was: 1. to compare benthic macrofaunal community
composition and taxon abundance between reference and disposal sites and assess for possible
gross effects of disposal of dredged material on benthic macrofaunal recolonization and recovery;
2. to characterize sampling variance as guidance for possible future studies on effects of dredge
material disposal in related habitats in the northern Gulf of Mexico; and 3. to characterize the
sediments for potential toxic contaminants (see Moore et al., 1994; Appendix I).
BACKGROUND AND RATIONALE
An opportunity to conduct the study occurred during October 1991. The study occurred
after dredged material had previously been disposed in each of the study areas. Elapsed time
since last disposal differed among the three study areas. Prior to this study, the most recent
dredged material disposal at the study areas occurred as follows: Atchafalaya River-May 1991;,
Freshwater Bayou— September/October 1990; and Mermentau River-June/July 1987.
Without pre-disposal data, a rigorous comparison of effects of dredged material disposal
was not feasible as typically done in "before and after" environmental studies. Thus, our
approach was necessarily modified. Benthic marine soft sediment macrofaunal communities are
known generally to be patchy in distribution and variable in time (Pearson and Rosenberg, 1978)
and this has been documented for the northern Gulf of Mexico nearshore coastal waters (Gaston
and Weston, 1983). Therefore, we had no plausible basis to assume a high degree of
"equivalency" between reference and disposal site benthic macrofaunal community structure. In
the northern Gulf of Mexico, warm season benthic macrofaunal recolonization is known, in at
least one case, to be well developed after about five months (Gaston et al., 1985). If this is
generally the pattern, then changes in community structure at greater intervals of time will be
difficult to ascribe to a perturbation such as dredged material disposal, unless the perturbation
has a frequency less than approximately five months and occurs during the warm season.
Considering the above perspective, we applied an ANOVA model in an exploratory
manner in the sense of Heck and Horwitz (1984) to examine spatial variability in benthic
macrofaunal community structure, not in the sense of formal hypothesis testing with resultant
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causal inferences. Quantification of ecological variability is a first step in the description of the
range of states possible for components of ecological communities (Duarte, 1991). We discuss
significant differences in response parameters in the context of natural variability and
recolonization rates. Where plausible, we speculate on the relationship of measured differences
in community structure that might be attributed to dredged material disposal. Assessment of
effects of dredged material disposal at the Atchafalaya River study area should be more directly
related to disposal activities than is the case for the other two study areas because of the relatively
short time of five months since last disposal. However, the lack of pre-disposal information
remains a cardinal limitation to causal inferences in the sense of a formal field experiment for all
three study areas. Given the above limitations, we believe that gross differences in response
parameters between reference and disposal sites can provide provisional information concerning
possible effects of dredged material disposal.
DESCRIPTION OF STUDY SITES
All three study areas are located in the nearshore shallow coastal zone of Louisiana
(Figure 1). Detailed environmental characterizations are provided in separate Draft
Environmental Impact Statements (U.S. EPA, 1990 a, b, c). Generally, sediments in the channels
and disposal sites for all three study areas are dominated by silts and clays with some textural
variability (U.S. EPA, 1990 a, b, c).
Atchafalaya River Site
The Atchafalaya River Bar Channel provides ship access to Morgan City, LA, the Gulf
Intercoastal Waterway, and the Bayous Chene, Boeuf, and Black from the Gulf of Mexico
(Figure 2). The proposed Ocean Dredged Material Disposal Site (disposal site) is 30.8 km (19.1
miles) long and 0.8 km (0.5 miles) wide. The center of the proposed site is approximately 26 km
(16 miles) from the mainland shore. The proposed site has an average depth of approximately
5.0 m (16 ft) and a total area of approximately 2480 ha (9.57 square miles). The reference site
with dimensions approximately similar to that of the disposal site is located parallel just west of
the dredged channel (Figure 2). The dredged material generally consists of approximately 45%
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silt, 45% clay, and 10% fine-grained sand with some temporal and spatial variability (U.S. EPA
1990a).
Freshwater Bayou Site
The Freshwater Bayou disposal site is used approximately once every three years to
receive material dredged from the Freshwater Bayou Channel located approximately 23 km (13.5
miles) southwest of Intercoastal City, LA. The channel is 76 m (250 ft) wide and 5.6 km (3.5
miles) long (Figure 2). The disposal site is 610 m (2000 ft) wide, 5.6 km (3.5 miles) long, and
runs parallel to the channel on its west side. A reference site of dimensions similar to the
disposal site is located on the east side of the channel (Figure 2). The 343 ha (848 acre) disposal
site begins at the shoreline at the mean low tide mark and extends seaward approximately
perpendicular to the shoreline for 5.6 km. Seawater depth at the seaward boundary is 4.9 m (16
ft). A hydraulic pipeline dredge was used to deposit dredged material at a minimum distance of
458 m (1500 ft) west of the centerline. An average of 0.92 X 106m3(1.2 X 106 cubic yds) of
dredged material is disposited at the disposal site from a hydraulic cutterhead dredge. Channel-
dredged sediment consists of a mixture of sand, silt and clays; silts and clays comprise about
88% and fine-grained sands make up the remainder (U.S. EPA, 1990b). Mermentau River Site
The Mermentau River disposal site is also used approximately once every three years to
receive material dredged from the Mermentau River-Gulf of Mexico Navigation Channel,
located approximately 6.4 km (4 miles) south of the town of Grand Cheniere, LA (Figure 2). The
channel is 60 m (200 ft) wide and 2.0 km (1.25 miles) long. The disposal site is approximately
1.6 km (1.0 mile) long, 0.8 km (0.5 miles) wide, and runs parallel to the channel on its west side.
The reference site is approximately similar in size to the disposal site and lies just to the east of
the channel (Figure 2). The 135 ha (335 acre) disposal site starts at 0.6 km (0.4 mile) and
extends to approximately 2.2 km (1.4 miles) offshore with depths ranging from 1.2 to 4.3 m (4 to
14 ft). Approximately 382.5 X 103 m3 (500 X 103 cubic yds) are disposed of in the disposal site
from a hydraulic cutterhead dredge. Specific information on sediment grain-size was not located,
but sand apparently comprises about 5% of the sediment west of the channel and sediments are
generally similar inside and outside of the channel (U.S. EPA, 1990 c). The Mermentau River
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Channel was currently dredged in June/July of 1987; however, all material was used for
beneficial use projects with no disposal on the disposal site.
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METHODS AND MATERIALS
BENTHIC COMMUNITY
Field Sampling: Field operations and sample processing were conducted from the U.S.
EPA Ocean Survey Vessel, Peter W. Anderson. Field sampling was conducted from a small
support boat rigged with a boom and winch assembly. Sampling at the study areas occurred over
the following days in October 1991, following some months-to-years after placement of dredged
material at the respective disposal sites: Atchafalaya River (October 16), Freshwater Bayou
(October 17) and Mermentau River (October 18). Each disposal site was divided into three
segments or zones, representative of most landward and shallow areas (nearshore), middle region
(middepth) and deepest offshore areas (offshore)(Table 1). A sampling station was established
approximately near the center-point of each zone (i.e., projected as a rectangle) based on Loran C
coordinates and verified in the field by channel marker buoys. Zones corresponding to those in
the disposal site were established in each reference site located within "study areas" (Figure 2).
For consistency of terminology, the three channel reference and disposal locations (e.g.,
Mermentau River, Freshwater Bayou and Atchafalaya River) are referred to as study areas.
Reference and disposal locations within each study area are referred to as respective reference
and disposal sites and sampling locations within reference and disposal sites are indicated by
their respective depth location (e.g., nearshore reference station).
Ten 0.05 m2 random benthic grabs were made at each reference and disposal site at
approximately the center-point of each depth zone (e.g., offshore disposal station), respectively,
with a modified Ponar sampler similar to that used in the EPA-EMAP Program (Summers et al.,
1993). Station locations were determined by previously mapping station coordinates and
confirming field location by comparing mapped coordinates with channel buoy markers. The
sampler collects approximately the top 10 cm of sediment in fine sediment regimes and varying
depths in more course materials. The general sampling area occupied a square of approximately
20 m on a side. An additional series of benthic grabs was taken at each sampling location within
a depth zone to provide sediment for analysis of grain size and percent organic matter. Sediment
grabs were sub-sampled with a Teflon-coated spoon to provide approximately one cup of
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sediment collected from the center of the ponar to a depth of about 5 cm. Sediment samples
were composited into a one-liter polycarbonate jar with Teflon liner. While on station, but prior
to sediment collection, bottom water temperature, salinity, pH, and dissolved oxygen were
obtained with a HydroLab Surveyor II®. Water depth was measured with marked line and
counter-weight.
A total of 180 benthic community samples (10 samples per sampling depth, e.g.,
nearshore station X 6 zones per study site X 3 study areas) was processed in the field. The entire
contents of the ponar grab were wet-sieved through a 0.5 mm mesh. Material retained on the
sieve was immersed in 0.3% propylene phenoxytol (a relaxant) for 2 to 5 min, then preserved in
10% buffered formalin containing Rose Bengal stain, and stored for transport to the ERL/Gulf
Breeze. At the laboratory, samples were transferred to 60% isopropanol before sorting and
taxonomic identification.
Biological analyses: Seven samples were selected randomly from the 10 samples
collected in the field at each reference and disposal station. Samples were sorted into major
taxonomic groups (Class or Order) with 10 X binocular dissection microscopes, identified to
lowest possible taxa (species where possible) and enumerated. Data were entered into SAS data
files for statistical analyses (see below).
Sediment particle size: Three replicate sediment subsamples from each channel reference
and disposal sampling station were wet-sieved through a 63 //m mesh sieve to separate sands and
silt/clay fractions (Folk, 1980). Each fraction was: dried at 100°C for 12 hr, cooled in a
desiccator, and weighed to determine percent sand/silt and clay. Whole sediment samples were
burned at 550°C to determine weight loss on ignition to estimate organic carbon.
Chemical analyses: Chlorinated hydrocarbon pesticides and polychlorinated biphenyls
(PCBs): A Hewlett-Packard Model 5890 gas chromatograph equipped with a 63Ni electron-
capture detector was used (see Moore et al., 1994, for details; Appendix I). Sediments were air-
dried, weighed and extracted with a 20% (v/v) acetone and petroleum ether and then centrifuged
(1600 x g) and solvent extracts extracted with 2.0% (v/v) aqueous sodium sulfate. After phase
separation, the solvent was transferred to a concentrator tube, and the aqueous wash was repeated
two more times. Sample extracts from the three aqueous washes were combined and
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concentrated to 1 ml on a nitrogen evaporator in preparation for a Florisil cleanup. Samples were
shaken with 500 ml of mercury to remove sulfur before gas chromatographic analysis. Clean-up
columns were prepared by adding 3 g of PR-grade Florisil and 2 g anhydrous powdered sulfate to
a Chromaflex column and rinsed with 10 ml of hexane. Sediment extracts were transferred to the
column with two additional 2-ml volumes of hexane. Pesticides and PCB's were eluted with 20
ml of 5% (v/v) diethyl ether in hexane. Dieldrin and endosulfan were eluted with 20 ml of 10%
(v/v) isopropanol in isooctane. Separations were performed by using a 30-m (0.32 mm i.d.)
RTX-5 and RTX-1 fused silica capillary column. The helium carrier gas flowed at 1.5 ml/min,
column temperature was operated at 50°C (held for 2 min), ramped 10°/min to 150°C, and then
2°/min to 260°C (held for 3 min). Inlet temperature was 250°C; and detector temperature was
350°C. Makeup gas was 10% methane in argon flowing at 60 ml/min. Pesticides were analyzed
with external standards; all standards were obtained from the EPA pesticide repository, Las
Vegas, Nevada.
Petroleum hydrocarbons: Analyses were performed on a Perkin-Elmer gas
chromatograph (GC) equipped with a flame ionization detector (see Moore et af., 1994, for
details; Appendix I). Sediment extracts (Warner, 1976) were injected into the GC and
separations were performed by using a fused silica capillary column. Helium carrier gas was
used at a flow rate of 1.5 ml min'1. Other GC parameters were: oven temperature programmed
from 50°C (hold for 2 min) at a rate of 20° min"1; injector temperature was 250°C, and detector
temperature was 350 °C. Androstane was obtained from Sigma Chemical Co., St. Louis, MO,
and used as an internal standard to quantify petroleum hydrocarbons.
Heavy metals: One to two grams of sediment were weighed and placed into a 40-ml
reaction vessel. Five milliliters of concentrated nitric acid were added and the samples digested
for 2 to 4 h at 90°C in a tube heater. Digestion was continued, with vessels capped, for 48 h at
70°C. After digestion, samples were transferred to 15-ml tubes and a 5-ml aliquot was diluted to
10 ml for aspiration into a Jarrell-Ash AtomComp 800 series inductively-coupled argon-plasma
emission spectrometer (ICP). This instrument acquires data for 15 elements simultaneously. No
detectable residues could be found in method blanks. A solution of 10% nitric acid/distilled
water was aspirated between samples to prevent carryover of residues from one sample to the
10

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next. Standards in 10% nitric acid were used to calibrate the instrument initially and adjustments
were made when necessary. Concentrations were reported in two significant figures as our
method allowed, and were not corrected for percentage recovery. Standard solutions of metals
were obtained from J. T. Baker Chemical Co., Phillipsburg, NJ, and were Instra-Analyzed
quality.
For all chemical analyzes, reagent and glassware blanks were analyzed to verify that the
analytical system was not contaminated with chemical residues that could interfere with
quantitation (Moore et al., 1994; Appendix I).
Statistical Procedures-- Data were transferred to computer disk for statistical summary
and analyses using SAS software (SAS, 1989a and b). Average total numbers of organisms per
0.05	m2 or abundance, average total number of taxa per 0.05 m2 or taxa richness and dominant
taxa were used as response variables. This unit area quantification is used in this paper unless
otherwise specified.
Statistical analyses included a Two-Way Analysis of Variance (ANOVA, Sokal and
Rohlf, 1981) between reference and disposal sites and among sampling depths. If statistically
significant differences (P ^ 0.05) among stations were indicated by ANOVA, Tukey's
Studentized Range Test was used to test for differences among stations. Before ANOVA
procedures were used, the number of organisms in each sample was log-transformed [i.e., log (x
+ 1)] to stabilize variance and improve normality. The number of taxa in each observation was
transformed by taking the square root. A note of clarification~we used the ANOVA as an
exploratory technique to measure variation within and between reference and disposal sites. The
field analysis does not control all potentially important exogenous variation and environmental
heterogeneity between reference and disposal sites. Therefore, we emphasize the correlational
aspect of the analysis vs a controlled experiment in the classical sense.
Rare taxa were qualitatively compared by grouping taxa into geometric classes by number
of individuals by station for each reference and disposal site. Scale of geometric classes was 2 X,
1.e.,	Class I = 1 individual, Class II = 2 to 3 individuals and Class III = 4 to 7 individuals, etc.
This analysis facilitated comparative scaling among samples which contained different numbers
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of individuals (Gray and Pearson, 1982). The accuracy of average density estimates for each
station for reference and disposal sites was calculated using sample variance (Eckblad, 1991).
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RESULTS
HYDROGRAPHY-SEDIMENT
Atchafalaya River
Water depths increased slightly in a seaward direction in reference and disposal sites from
1.9 and 1.1 (e.g., nearshore station) to 3.3 and 3.5 m, respectively (offshore station; Table 2).
Bottom water salinities differed little in magnitude between reference and disposal sites among
stations (Table 2) but increased with distance from shore (e.g., salinities were 8.0 and 9.5%o in
reference and disposal sites of the nearshore stations and 24.4 and 25.8%o in reference and
disposal sites of the offshore stations). Bottom water temperatures ranged between 22.9 and
23.7°C, and small differences (e.g., equal to or less than 0.3°C) were measured between
reference and disposal sites with little difference recorded over the salinity gradient. Dissolved
oxygen concentrations ranged between 6.2 and 7.5 mg liter"1 with small differences, typically less
than 0.6 mg liter'1, noted among stations in reference and disposal sites (Table 2). Unusually
high pH values of 8.6 to 8.8 were recorded for the nearshore stations at salinities of 8.0 to 9.5%o
and low values of 7.4 were observed at salinities of 24 to 26%o. Nominal differences of 0.2 pH
units or less were noted between reference and disposal sites.
Sediment particle size was highly variable along the depth gradient for reference and
disposal sites and moderately variable at comparable sampling depths between reference and
disposal sites (Table 2). At nearshore stations, reference and disposal sites were characterized by
course (sand) particle sizes of 60.0 and 56.6% and this size category decreased to 1.9 and 9.8% at
reference and disposal middepth stations, stations with the largest differences in percent sand
between reference and disposal sites. Offshore stations in reference and disposal sites both
contained 3.4% sand. Weight loss on ignition (WLOI) ranged between 2.2 and 6.6% of sediment
mass. Small differences in WLOI of 0.5 to 1.3% were measured between reference and disposal
stations. Nearshore reference and disposal stations were characterized by lowest values of WLOI
(reference = 2.2 and disposal site = 3.5%). Highest values occurred at middepth stations and
values in reference (6.6%) and disposal middepth stations (6.1%) approximated each other.
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Freshwater Bayou
Water depths increased from 1.6 and 1.7 m in the reference and disposal sites at nearshore
stations to 4.0 and 3.0 m at offshore stations (Table 2). Salinities ranged between 26.0 and
27.2%o with small differences (< 0.2%o) between reference and disposal sites. Highest salinities
were measured at reference and disposal offshore stations (e.g., 27.2%o). Differences in bottom
water temperatures were equal to or less than 0.2°C among all stations. Water temperatures
ranged from a low of 21.7 at the nearshore disposal station to 22.8°C at the offshore reference
station. Dissolved oxygen ranged between 6.6 and 6.8 mg liter'1 among all stations.
Percent sand decreased in a seaward direction (Table 2) and variability was especially
prevalent at the middepth stations. Values ranged from 3.0 to 4.5 at reference and disposal
nearshore stations (Table 2) to 3.1 to 24.8 at middepth stations. Shell fragments were abundant
at this site and resulted in the unusually high variability and large particle size. Offshore stations
were characterized by percent particle sizes indicative of fine mud with 99+% less than 63 |im.
Percent WLOI ranged from 6.7 to 11.6 with highest values recorded for offshore stations.
Differences in WLOI for stations at comparable depths between reference and disposal sites were
moderately variable. For example, percent WLOI was 9.1 and 6.7% at nearshore reference and
disposal stations. Differences approximated 0.5 and 0.8% for stations located at middepth and
offshore reference and disposal sites (Table 2).
Mermentau River
Water depths ranged between 1.5 and 2.0 m, 1.8 and 3.0 m, and 2.6 and 3.7 m at
reference and disposal stations. Salinities approximated 30.5%o for all stations. Water
temperatures ranged from 22.0 to 22.5°C among all stations. The concentration of dissolved
oxygen ranged from 5.9 to 6.9 mg liter"1 for all stations. The pH values for reference and
disposal sites closely approximated each other with values for the study area ranging between 8.0
and 8.3 and differences between reference and disposal sites being less than 0.2.
Percent particles greater than 63 nm was quite variable between reference and disposal
sites (Table 2). Values for the nearshore stations ranged between 17.5 (reference) and 40.8
(disposal site), middepth stations ranged between 6.7 (reference) and 10.9 (disposal site) and at
14

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offshore stations values ranged between 0.9 (reference) and 12.2% (disposal site). Values for
percent WLOI were moderately variable with nominal differences among stations.
CHEMICAL RESIDUES
Selected Chlorinated Hydrocarbon Pesticides & PCBs: No chemicals in these classes
were detected in sediments at the Mermentau River or Atchafalaya River study areas above
detection limits of 0.010 /ig g"1 wet wt (see Table 3 for chemicals analyzed and their percent
recovery). The pesticide, DDE (P,P') (0.026 fxg g"1 wet wt) was detected in sediments at the
Freshwater Bayou nearshore disposal site, and this pesticide occurred in sediments at the offshore
reference site at a concentration of 0.036 /ug g"1 wet wt. Hexachlorobenzene (0.018) and
methoxychlor (0.047 /ug g'1 wet wt) occurred in sediments at the offshore reference site. Only
four samples out of a total of 324 contained chemical contaminant concentrations above
detection limits [ e.g., 18 chemicals screened X 3 study areas X 2 sites/study area (i.e., reference
and disposal sites) X 3 depth zones/site = 324],
Petroleum hydrocarbons: Petroleum hydrocarbons were not detected in any sediment
sample above 1.0 /j.g g"1 wet wt, the method detection limit.
Heavy metals: Concentrations of selected heavy metals approximated each other between
reference and disposal sites (Tables 4). Concentrations of these metals from different water
depth zones (e.g., Atchafalaya nearshore reference) were similar except for chromium and
copper. Metal concentrations were lower in nearshore than in offshore samples at both
Mermentau River disposal site and its reference site, and in the Atchafalaya River disposal and
reference sites.
MACROFAUNAL DISTRIBUTION AND ABUNDANCE
Atchafalaya River
Reference and disposal sites contained 38 and 40 taxa of which sites shared 29 taxa in
common (Table 5). Of five molluscan taxa, only the bivalve, M. lateralis, occurred at both sites.
Among 10 arthropod taxa, only three co-occurred at both sites (e.g., Balanus sp., Oxyurostylis
smithi, and the free-living pinnixid, Pinnixia sayana). Annelids dominated taxa richness;
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nineteen of 27 annelids co-occurred at both sites. The more abundant taxa usually occurred at all
three stations within a site and they occurred 15 out of 21 samples (Table 6). Seven taxa
occurred at nearshore, middepth, and offshore stations of both reference and disposal sites. Less
abundant taxa (e.g., less than 2 individuals/0.05 m2) frequently occurred at only one or two
stations at a site.
There was very little difference in average taxa richness/0.05 m2 at the reference site (x =
13.1; sd = 2.83) compared to the disposal site (x = 11.5; sd = 4.88; Table 7). Treatment, within
treatment and interactions were all statistically significant (Table 8), thus we applied Tukey's test
to examine station location differences between and within treatments. Average taxa richness at
the nearshore reference station (x = 11.9) was nearly twice that of the nearshore disposal station
(x = 6.1). This was the only case of a significant difference (P s 0.05) between paired reference
and disposal stations. Average taxa richness of 16.0 at the offshore disposal station was the
maximum value for the study area and was significantly greater than averages at the nearshore
reference and disposal, and middepth reference stations (Table 8).
Little difference in overall average abundance/0.05 m2 between reference (x = 109.4; sd =
39.05) and disposal sites (x = 104.2; sd = 77.75) sites (Tables 7) was evident, but differences in
abundance within sites and among stations between sites were detected. Abundance averaged
approximately three times fewer individuals at the nearshore disposal (x = 51.6) compared to the
nearshore reference (x = 144.3) station (Tables 9). Differences were significant (Ps 0.05). The
difference in abundance was due primarily to high numbers of the polychaete, Mediomastus
californiensis, at the nearshore reference station (x = 81.1; Table 10) compared to those at the
nearshore disposal station (x = 30.3). The polychaete, Pseudoerythoe ambigua, ranked 2nd and
3rd in abundance at disposal and reference sites but abundance was not significantly different (P
> 0.05) between sites. Average abundances of P. pinnata and an unknown nemertean were
significantly greater (P^ 0.05) at the reference than at the disposal site (e.g., 12.2 vs 8.4 and 9.2
vs 8.8), respectively; Table 10). Five other taxa (i.e., Polydora sp., Paraprionospio pinnata,
Spiochaepterus oculatus, unknown Nemertea, and unknown Oligochaeta; Table 10) contributed
16

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significantly more individuals to reference than to disposal sites. Nine and eight taxa,
respectively, differed in average abundance within reference and disposal stations. Abundance at
the middepth disposal station averaged 1.9 times (x = 176.1) that of the middepth reference
station (x = 92.7); the difference was significant (P ^ 0.05). Again, the polychaete, M.
californiensis, accounted for much of the difference in abundance (e.g., middepth disposal
station--x = 84.3 and middepth reference- x = 27.7).
Sample size was adequate to capture most taxa at stations within this study area based on
"species area curves" (e.g., middepth disposal station; Figure 3). At this station twenty taxa were
collected with three replicate samples compared to 21 taxa with six replicate samples.
A relatively large percentage of taxa contained only a few individuals (Figure 4; Table
10). The general pattern of percent taxa and abundance group was approximately similar
between Atchafalaya reference and disposal sites (Figure 4).
Freshwater Bayou
Only a small numerical difference was noted in taxa richness between reference (21 taxa)
and disposal sites (18 taxa). Thirteen taxa occurred in common between sites (Table 5).
Molluscs contributed only two species, the bivalve, Mulinia lateralis, and the snail, Nassarius
vibex. Four crustacean taxa were present (Balanus sp., Corophium sp., a paguridian and a
pinnixid crab). Annelids dominated taxa richness with 14 taxa (most identified to species level);
polychaetes contributed 13 taxa and the Class, Oligochaeta, may have contributed more than one
species. Of the more abundant taxa, five co-occurred at all stations at both the reference and
disposal sites (Table 6). The polychaete, P. ambigua, occurred at all three reference sites but
only occurred at the middepth and offshore disposal stations. The polychaete, P. pinnata,
occurred in 20 and 21 samples out of a total of 21 samples at the reference and disposal sites,
respectively, whereas M. californiensis only occurred in 15 and 7 samples out of a possible total
of 21 samples at these sites (Table 6). The next most frequently occurring taxa, P. ambigua, was
present in only 10 samples at both reference and disposal sites.
The overall average taxa richness/0.05 m2 at the Freshwater reference (x = 5.5; sd = 3.30)
and disposal sites (x = 5.2; sd = 2.28; Table 7) closely resembled each other and differences were
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not statistically significant (P = 0.896). Taxa richness averaged 3.3, 5.5 and 7.4 at the combined
reference and disposal nearshore, middepth, and offshore stations, respectively (Table 7). The
combined average of 3.3 was significantly (P ^ 0.05) less than averages of 5.5 and 7.4 but the
average of 5.5 and 7.4 were not significantly different (Table 8). Abundance averaged 28.8 (sd =
32.46) and 24.5 (sd = 21.21) per 0.05 m2 at the Freshwater reference and disposal sites (Table 7).
Sampling variation was too large to detect a significant difference. Abundance averaged 10.0,
25.6, and 44.4 at combined reference and disposal sites at nearshore, middepth and offshore
stations, respectively (Table 9). The polychaetes, P. pinnata and M. californiensis, contributed
most to the increased abundance of the combined middepth compared to the combined nearshore
stations, and the polychaetes, P. pinnata and Pseudoeurythoe ambigua, enriched the abundance
at the combined offshore stations compared to the combined middepth stations (Table 11). The
combined average of 10.0 differed significantly (P s 0.05) from both the combined average 25.6
and 44.4, but the values of 25.6 and 44.4 were not significantly different primarily because of the
high variance associated with the mean of 44.4 (Table 9). Average abundance of the polychaete,
M. calif orniensis, was greater (x = 6.2) at the reference site than at the disposal site (x = 1.2); the
difference was significant. The reverse pattern was observed for the polychaete, P. ambigua,
where abundance averaged 3.4 and 1.9 individuals/0.05 m2 at the disposal and reference sites;
differences were significant. Average abundance of most taxa differed significantly among one
or more stations within and between reference and disposal sites (Table 11).
Moderate differences were detected in species-area relationships among stations at both
freshwater reference and disposal sites (Figure 3). Three samples captured 12 of a total of 13
taxa at the middepth disposal site, whereas four samples were required to capture 17 of 18 taxa at
the Freshwater offshore reference site.
Abundance Groups I-IV differed greatly in percent taxa between Freshwater nearshore
reference and disposal stations (Figure 4). The nearshore disposal station contained half of the
taxa in Abundance Group I compared to none at the nearshore reference station. Percent taxa in
abundance groups between middepth reference and disposal sites approximated each other. The
offshore disposal station contained more taxa in Abundance Groups VI through VIII than the
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comparable reference station. The reference and disposal sites differed considerably in the
overall pattern of percent taxa for each abundance group.
Mermentau River
The disposal site contained more taxa (17) than the reference site (14) (Table 5).
Polychaetes dominated taxa richness with 11 taxa. Polychaete taxa contributed seven and 10
taxa at reference and disposal sites, respectively; co-occurrence was limited to six taxa.
Arthropods and molluscs were limited to three (i.e., Balanus sp., Corophium sp., and P. sayana)
and one taxa (i.e., M. lateralis), respectively. Three rhyncocoels (Cerebratulus lacteus, Micrura
sp., and Nemertea sp. A) occurred at reference and disposal sites. Five taxa (Glycinde solitaria,
P. pinnata, P. ambigua, Balanus sp., and Nemertea sp. A) co-occurred at all three reference and
disposal stations (Table 6). The numerically dominant species, P. pinnata, was present in all
samples (N = 42 samples).
Taxa richness per 0.05 m2 averaged 4.7 (sd = 1.65) at the reference site and 7.0 (sd =
2.36) at the disposal site (Table 7). A significant interaction between main effects and station
locations (Table 8) complicated analysis. Average taxa richness at the middepth disposal station
(x = 9.0) approximated twice that of the reference (x = 4.3) station; the difference was significant
(P < 0.05). Taxa richness differed little between nearshore and offshore paired reference and
disposal stations. Taxa richness at the nearshore reference station (x = 4.0) was only slightly
more than one half that of the offshore disposal site (x = 7.0 station; Table 8). The difference
was significant (P ^ 0.05).
Abundance per 0.05 m2 averaged 57.9 (sd = 19.85) at the Mermentau reference site but
increased by two-fold to 131.0 (sd = 24.31) at the disposal site (Table 7). The polychaete, P.
pinnata, dominated abundance at both reference (x = 51.2) and disposal (x = 113.5) sites (Table
12). Analysis of average abundance was complicated by a significant statistical interaction
between main effects and stations (P = 0.049; Table 9). However, we judged the interaction to
be unimportant because of the large magnitude of differences in abundance between reference
and disposal site stations noted above (Table 9). Six of seven relatively abundant taxa (i.e., mean
abundance > 1.0 organism/0.05 m2) were significantly more abundant at the disposal site (Table
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12). Only one taxa, Cossura soyeri, averaged more individuals at the reference (2.6) than at the
disposal site (2.4). Three of seven relatively abundant taxa were distributed with significant
differences in abundance among reference and disposal stations (i.e., P. ambigua, Magelona sp.,
and C. soyeri).
Two samples were required to detect eight taxa, and four samples only increased the total
to nine taxa at the Mermentau nearshore reference station. The latter was representative of other
stations with only small differences noted in this relationship between reference and disposal
sites (Figure 3).
Percent taxa in Abundance Groups II and V differed somewhat between reference and
disposal sites (Figure 4). Abundance Groups V-X approximated each other closely. Overall, the
abundance patterns between reference and disposal sites were approximately equal.
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DISCUSSION
Analysis of differences in benthic community structure is one of the mainstays for
detecting and monitoring the biological effects of marine pollution (Warwick and Clarke, 1993).
Although temporal sampling was not possible in this study, spatial variability in response
parameters was the central focus. We measured variability in benthic macrofaunal community
structure (i.e., mostly species) at the scale of reference and disposal sites and within sites. At the
scale of individual stations, or within site variability, we initially planned to focus on comparison
of paired reference and disposal stations as the smallest scale resolution on the assumption that
they would represent more ecologically comparable habitats than more distant non-paired
stations. The presence of a water column depth gradient from shore seaward suggested the
relevance of this assumption. Sediment particle size data by visual inspection were not highly
consistent between paired stations (Table 2). Thus, sediment particle size variability was of
limited value as an explanatory factor in community composition and taxa abundance, except
possibly at the Mermentau River study area.
Large temporal variability typical of soft sediment benthic macrofaunal communities
often results in benthic populations appearing very "noisy" (e.g., Franz and Harris, 1988; Gaston
and Weston, 1983). These populations often show a marked lack of concordance in their
temporal trajectories from one place to another. This contributes to high spatial variance. The
consequence is that considerable statistical interaction occurs between changes in average
abundances from time-to-time and from place-to-place (Underwood, 1994). Statistical
interaction in the ANOVA model was characteristic in community level response parameters
(i.e., average taxa richness and abundance) at the Atchafalaya and Mermentau River study areas.
Taxa collected in this study correspond closely to those identified in other near-coastal
and estuarine waters of the northern Gulf of Mexico, especially coastal Louisiana (Gaston and
Weston, 1983; Gaston and Nasci, 1988; Giammona and Darnell, 1990; Gaston and Edds, 1994).
Wright et al. (1978) reported similar dominant taxa present at stations in 10 to 15 m waters at a
dredged material disposal site in the Gulf of Mexico offshore of Galveston Bay, TX. Many
dominant benthic macrofauna in our study co-occur in Hillsborough Bay, an arm of Tampa Bay,
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FL (Santos and Simon, 1980). Gaston and Weston (1983) reported that the phoronid, Phoronis
sp. A (later confirmed as P. muelleri), was a dominant species at the West Hackberry brine
diffuser site in approximately 10 m of water during March through July 1981, but failed to repeat
a population erruption in 1982. Phoronis sp. (probably P. muelleri) occurred in only one sample
at each of the Atchafalaya River reference and disposal sites and in only one reference sample at
the Freshwater Bayou study area. Presence was only at offshore stations which suggests that this
taxa is adapted to a more marine than an estuarine habitat.
The total number of taxa in our three study areas ranges from relatively low values of 14
to 17 (more typical of oligohaline areas; e.g., St. E-2, Calcasieu Lake-Gaston and Weston, 1983)
in reference and disposal sites at the Mermentau River study area to moderately high numbers of
38 and 40 taxa in reference and disposal sites at the Atchafalaya River study area. The higher
r
number of taxa approximates values reported for fall samples collected at the West Hackberry
Strategic Petroleum Reserve Site Brine Disposal Area (Gaston and Weston, 1983), the Texas
coastal shelf off Corpus Christi (Flint and Holland, 1980) and somewhat less (e.g., 65 vs 40) than
Parker et al. (1980) reported for Weeks Island Brine Disposal Site located 44 km (26 miles) south
of Marsh Is., LA. A trend was noted for higher average taxa richness to occur at the offshore
stations at all three study areas, probably a reflection of higher salinities (Carriker, 1967) and
reduced sediment disturbance due to wave action.
Many species in the present study, especially the dominant polychaetes, e.g.,
Mediomastus californiensis, Paraprionospio pinnata, Pseudoeurythoe ambigua, and the bivalve,
Mulinia lateralis, are considered opportunists because they frequently are first-colonizers
following natural and anthropogenically-initiated disturbances (Grassle & Grassle, 1974; Santos
& Simon, 1980; Boesch & Rosenburg, 1981; Pearson and Rosenberg, 1978). Opportunistic
benthic macrofauna are characterized by high reproductive potential, and many have planktonic
dispersal mechanisms that contribute to rapid population build-up often followed by rapid
population declines. Natural disturbance includes physical factors such as major freshets, e.g.,
Tropical Storm Agnes in June 1972, Chesapeake Bay, and biotic interactions (e.g., predator
effects, competition and adult/larval interactions); and human disturbance includes dredge
material disposal, release of toxic chemicals, and hypoxic events in overlying waters and
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sediments typically associated with nutrient over-enrichment. Presumably, varying degrees of
interaction occur between natural and anthropogenic stressors and among each source class
which complicates assessment of strictly anthropogenic effects (e.g., brine vs hypoxia; Gaston et
al., 1985).
Total average abundance per meter square (extrapolated from 0.05 m2) in our study
averaged 580 to 480 individuals in the reference and disposal sites at the Freshwater Bayou study
area. Abundance averaged 2,180 and 2,080 at the reference and disposal sites at the Atchafalaya
River study area and averaged 1,160 and 2,620 at reference and disposal sites at the Mermentau
River study area. Mean densities for the Freshwater Bayou are lower than most values reported
in the literature for soft sediments in the northern Gulf of Mexico (e.g., Weston and Gaston,
1982; Gaston and Weston, 1983). These low densities correspond more closely to those reported
for the upper Calcasieu Estuary (Gaston and Nasci, op. cit.) and the June sampling of the
Gulfport, MS, dredge material disposal site (Markey and Putnam, 1976). Mean densities of one
to two thousand individuals/m"2 range are not uncommon for the fall season in the northern Gulf
of Mexico. Abundance of benthic macrofauna averaged over an 18-month study on the Texas
shelf in 22 m depth approximated 1,000 m"2 (see Figure 2; Flint and Holland, 1980). Differences
in water depth and large expanse of Texas coastline adds considerable uncertainty to the
comparison.
Community level response variables, average taxa richness and abundance, did not differ
significantly between reference and disposal sites at the Freshwater Bayou study area.
Significant differences in these response variables occurred only between combined paired
stations, e.g., between nearshore reference and disposal stations, and their middepth and offshore
counterparts (Tables 8 & 9). This response pattern was unique to the Freshwater Bayou, and we
see little reason to ascribe the effects of dredged material disposal to this response pattern.
Of nine most abundant taxa at the Freshwater Bayou study area, only two, the
polychaetes, (Mediomastus californiensis and Pseudoeurythoe ambigua) showed significant
differences (P s 0.05) between reference and disposal sites. Abundance of M. californiensis was
significantly less (P s 0.05) at the disposal compared to the reference site (x = 6.2 vs 1.2).
Abundance of P. ambigua was significantly greater at the disposal vs reference site (1.9 vs
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3.4)(Table 11). Abundance of several taxa, including M. californiensis and P. ambigua, differed
significantly within and among reference and disposal stations. The magnitude of the differences
among stations generally was as large within sites as between sites. The magnitude of
differences in abundance is within natural variability for the northern Gulf of Mexico. Thus, if
the differences, in fact, are caused by dredged material disposal, the magnitude appears to be
nominal.
The pattern of increased abundance of benthic macrofauna from nearshore to offshore at
the Freshwater Bayou study area is not explained by measured physical sediment or hydrographic
factors nor by measured chemical contaminants. It appears that unidentified environmental
gradients and possibly biotic interactions explain major features of the distribution and
abundance of the benthic macrofauna at Freshwater Bayou. Further work is required to explain
these findings.
The Mermentau River study area showed greatest relative differences between reference
and disposal sites in average abundance and taxa richness compared to the other two study areas.
The disposal site samples averaged significantly higher abundance than did the reference site, an
unanticipated response. Differences in average taxa richness were less striking than average
abundance; however, nearshore and middepth reference values for taxa richness averaged
approximately one half of the middepth and offshore disposal values (e.g., 4.0 and 4.3 vs 9.0 and
7.0).
Individual taxa at the Mermentau River study area averaged significantly higher
abundances in five out of six comparisons of dominant taxa at the disposal compared to the
reference site, as would be expected based on the response variable, average abundance.
Differences in percent sand among paired stations at this study area were consistently greater
than those measured for other study areas, except for the single large difference due to shell
fragments measured at the middepth Freshwater disposal station (Table 2). Abundance data for
individual taxa at the Mermentau disposal site were more variable on average than at the
reference site. The relatively high particle size variability was consistent with the benthic
macroinvertebrate variability. Other measured environmental factors do not clarify the benthic
macrofaunal distributional patterns observed at this study site.
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The Mermentau River study area last received dredged material in June/July 1987, an
interval considerably longer than at the other two study areas. This longer time interval adds
considerable uncertainty to causal inferences regarding effects of disposal of dredged material. It
is not clear why this study area contained fewer taxa than the two other study areas or the
enhanced abundances of taxa at the disposal site. More frequent sampling could determine
whether the increased abundance detected at the disposal site was within the longterm seasonal
excursion characteristic of the study area. A speculative possibility is that the timing and
magnitude of disturbance from dredged material disposal at this study area acted as an
"intermediate disturbance" which would increase the number of species and their abundance
(Sousa, 1984).
In contrast to Freshwater Bayou, analysis of average taxa richness and abundance of taxa
at the Atchafalaya River study area was complicated by statistical interaction of main and within
site effects. Average abundance was greater by approximately a factor of three and significant (P
^ 0.05) at the nearshore reference compared to the nearshore disposal station. Average
abundance at the middepth disposal station was approximately twice that of the middepth
reference station and the difference was significant (P ^ 0.05). Average abundance at offshore
reference and disposal stations approximated each other. Variability (i.e., variance) in average
abundance within sites was often as large as that between sites. Average taxa richness was
significantly smaller at the Atchafalaya River nearshore disposal station compared to all other
stations, and this response variable was significantly larger at the offshore disposal station than at
the nearshore and middepth reference, and nearshore disposal stations. These differences do not
show a consistent association between reference and disposal sites or within measured
environmental variables, e.g., percent sand or sediment chemical contaminant data. Evidence of
recolonization by macrofauna of marine soft sediments in the northern Gulf of Mexico suggests
that recolonization should be well developed within about five months (Gaston et al., 1985). The
"patchy" nature of community level indicators of recolonization masked possible effects of
dredged material disposal at this study area.
The distribution and abundance of individual taxa at the Atchafalaya River study area
indicated that average abundance was significantly greater at the reference site compared to the
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disposal site in four out of five comparisons where differences were statistically significant
(Table 10). However, the differences were usually less than a factor of two. Variability within
reference and disposal sites usually was as large as variability between sites which would
minimize whole-site differential effects of dredged material disposal on taxa abundance. These
data confirm that statistically significant differences in abundances were registered at the disposal
compared to the reference site on selected individual taxa. These differences could be plausibly
ascribable to dredged material disposal. However, we believe that the magnitude of the
differences is not large compared to other stations in this study and in the literature.
We examined several aspects of sampling variability to assist in interpretation of our
results and provide a better basis for determining future sampling requirements should further
assessments be conducted for these study areas. It appears that four to five samples captured 90
to 95% of the taxa at all three study areas. At a disposal site offshore of Galveston Island, the
species-area curve suggested the "plateau" was not reached for several sites with 10 replicate
samples (Wright et al., 1978; Harper, 1977). Variability of all response variables in our study
was relatively high for most stations. The coefficient of variability often approximated 50 to
100% and occasionally higher values were measured.
We estimated with the power analysis that frequently 25 to 50 samples would be required
to achieve an accuracy of mean abundance of ± 10%, and in several cases one to several hundred
samples would be required to achieve this level of accuracy (Figure 5; Table 13). Relaxation of
accuracy to to 20% reduced the number of samples by approximately a factor of four in most
cases. This level of quantitation would still pose a burden on most sampling programs. In the
Galveston disposal study cited above, instances occurred where over 1,000 samples would be ,
required to achieve a standard error equal to 20% of the mean. Wright et al. (1978) stated that
variability not compensated for by an adequate sample size may have obscured some effects and
indicated changes when none occurred. In areas where sampling variability is especially high,
suggestive of patchy distribution, it would be desirable to stratify the sampling effort in future
assessments and focus sampling effort on the "hot-spot" areas. Ecological variability has
routinely constrained the ability to ascribe significant differences to cause or distinguish
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differences due to chance in environmental assessments of effects of human disturbance on
ecosystems (Boesch, 1984).
Reference and disposal site sediment chemical data from the three study areas resembled
each other quite closely in most cases. Few of the chlorinated hydrocarbon pesticide
concentrations were above detection limits. Polychlorinated biphenyls (PCB's) were not detected
in any of the samples. Concentrations of trace metals,measured in the sediments were within the
ranges of contaminants reported for northern Gulf estuaries (NOAA, 1991; Summers et al., 1993
b). Chromium and copper were lower in nearshore samples than in samples from offshore at
both Mermentau River disposal and reference sites. Available data on particle size and organic
carbon for this study area provide little insight into the differences in concentrations of
chromium and copper. Bulk sediment concentrations of trace metals were not unusually high
compared to similar fine-grained coastal/estuarine sediments in the Northern Gulf estuaries
(Brecken-Folse and Duke, unpublished report, and NOAA, 1991). However, bulk sediment
concentrations typically do not allow useful estimates of biologically available metals without
additional sediment chemistry (e.g., acid volatile sulfide concentration; Di Toro et al., 1990).
Ecosystem Dynamics and The Illusion of Ecosystem Recovery
Classical environmental science definition of ecosystem recovery is the return of a system
to its pre-existing state (i.e., structurally, metabolically, and dynamically; Landis et al., 1993).
The question at hand is what criteria will reliably allow the determination of disturbance and
recovery? The answer to this question is not as straightforward as traditionally perceived.
Evidence exists that ecological disturbance is expressed at various hierarchical levels (e.g.,
biological organizational scale—species vs population vs community and process scale—spatial
and temporal patterns; Pickett et al., 1989). One consequence is that an arbitrary conversion of
disturbance to non-disturbance may simply occur by shifting the scale of observation. For
example, we detected, in some cases, significant differences at the scale of stations but not at the
scale of sites. A biological scale-shift might involve simply changes in taxonomic resolution
between reference and disposal sites. A possible remedy is to use higher taxonomic levels than
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species where adequate reference locations are unavailable or the taxonomy is impractical to
resolve to comparable units (Warwick, 1993).
Many biotic and abiotic factors govern the composition of an ecosystem prior to and after
a disturbance event. For benthic macrofauna, substrate type, changes in biogeochemical
processes (e.g., indicated by redox profiles), "founder effect" or which species arrives and
colonizes first after a stress, changes in the water current field, changes in exposure to toxic
organic contaminants and metals, and the patchy nature of the recruitment process are but a few.
Since each of the initial conditions is likely to be different from those that lead to the original
system, it is very improbable that the so-called recovered system will be identical to the pre-
disturbance state. Besides being statistically significant, by what criteria do we measure
departure from the identical state and what importance do we attach to the differences? This
question reinforces the idea that statistically significant differences need to be interpreted
ecologically. The apparent recovery or movement of the disturbed system towards the reference
or pre-disturbed state may be an illusion, because the systems may be moving in opposite
directions and simply pass by similar endpoints during certain time intervals (see Figure 10 in
Landis et al., 1993). Of course, if variance increases in the measurement parameters in reference
or disturbed system, then the ability to detect a statistically significant effect between the
reference and disturbed system would decrease at comparable sampling efforts. Additional
theoretical complications may arise from complexity in nonlinear ecological systems (Hastings et
al., 1993). There are strong theoretical reasons that recovery to a reference state may be highly
unlikely because of small, often unmeasurable initial conditions (May and Oster, 1978). What is
needed is a framework that allows unambiguous definitions of disturbance and the object being
disturbed. The concept of "minimal structure" appears to provide greater generality and
objectivity in applying the concept of disturbance to ecological systems. Pickett et al. (1989)
provide an explanation of this concept. These brief comments are meant to raise awareness that
ecological "impact" assessment has many dimensions that may be unaddressed by simple
empirical comparisons of a few structural indicators of community change. Most of the issues
raised are still under active research and further clarification will depend on research progress.
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In our study, we did not find many indications of gross effects even though numerous statistically
significant effects were detected.
Recommendation for Improvement in Sampling Design
In recent years, environmental impact assessment has made considerable improvement in
sampling strategies designed to test hypotheses regarding effects of putative environmental
stressors (Eberhardt and Thomas, 1991; Underwood and Peterson, 1988). Progress is still
limited by theoretical uncertainties discussed under the section on Illusion of Ecosystem
Recovery. A complete rationale for the subject at hand could involve a monograph level
presentation (e.g., Green, 1979) which is beyond the scope of this paper. Our purpose here is to
provide a brief description for conceptual improvement in future studies designed to assess the
extent and magnitude of ecological effects of dredged material disposal on benthic macrofaunal
communities in the three study areas reported herein. The approach is generalizable to other
forms of ecological disturbance and other coastal ecosystems.
Ideally, one would like to employ an "experimental" design that optimized on the
identification of causal relations between effects and probable cause (s). More generally, an
approach that might reliably detect environmental disturbance and distinguish between natural
variability and human influence is known as the BACI (Before-After-Control-Impact) approach
(Underwood, 1991, and Underwood, 1994). Implicit in the approach is the need for an initial
synthesis or scoping of ecosystem structure and function (i.e., scaled process focus) to determine
what ecological information is relevant to the presumed problem. For example, the spatial extent
of the disposal area (i.e., will the deposited dredged material be spatially homogenous in texture
and will the depth of deposited material be reliably estimated?) should be estimated. Precise
answers may not be possible, but an awareness of the need to estimate relevant answers to such
questions is critical.
The ability to conduct pre-disposal sampling is very important to environmental
assessment projects. The likelihood of local differences in benthic macrofaunal community
structure to occur, especially prior to dredged material disposal, reinforces the need for such
information. For example, suppose the response variables used to assess ecological change
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already were an order of magnitude larger at the disposal site compared to the reference site at
initiation of dredged material disposal. The effect might be to reduce the quantitative value of
the variables to that of the reference area. An effect would have occurred, but it would be
undetected without pre-disposal information available from reference and disposal sites.
The BACI approach recommends multiple reference areas to increase discriminating
power even when only a single treatment site is available. In the present study, we sampled only
one reference site per study area. The papers by Underwood (op cit) describe the utility of
temporal sampling that helps detect effects of exogenous factors that can confound interpretation
of results. Elements of the BACI approach were used in the studies on brine effects at the West
Hackberry site (Gaston and Weston, 1983).
Future work should randomly sample each depth zone instead of randomly sampling a
central location within each depth zone (e.g., nearshore reference station). This would provide a
more appropriate estimate of spatial variability in the response variables for comparison and
minimize problems of spatial pseudoreplication (Hurlburt, 1984). Problems of temporal
pseudoreplication should also be addressed (Stewart-Oaten et al„ 1986). Non-parametric
multivariate analyses should be considered, especially when data transformations are unable to
satisfy parametric statistical assumptions. Categorical presence/absence data necessitate non-
parametric statistical analyses (Clarke, 1993; Warwick and Clarke, 1993). A variance test for
species associations looks promising for future community level analyses (McCulIoch, 1985).
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SUMMARY
Overall, the evidence was weak to support the hypothesis that gross differences in benthic
macrofaunal community structure were present and that the differences were associated with
dredged material disposal. The numbers of taxa present at these Atchafalaya River, Freshwater
Bayou, and Mermentau River reference and disposal sites were: 38 and 40, 21 and 18, and 14 and
17, respectively. The opportunistic polychaetes, Mediomastus californiensis, Paraprionospio
pinnata, and another polychaete, Pseudoeurythoe ambigua, dominated abundance at the
Atchafalaya River and Freshwater Bayou study areas (i.e., average abundance > 5.0 individuals
0.05 m"2 in, at least, either a reference or a disposal site). Other abundant taxa at the Atchafayala
River study area included the polychaetes, Spiochaetopterus oculatus and Glycinde solitaria, the
bivalve, Mulitiia lateralis, and the rhyncocoele, Nemertea sp. A. The two polychaetes, P.
pinnata and P. ambigua, dominated abundance at the Mermentau River study area.
Distribution and abundance of benthic macrofauna at the Freshwater Bayou study area
differed substantially from that of the other two study areas. Reference and disposal sites at the
Freshwater Bayou study area did not differ significantly from each other in average abundance
and taxa richness. However, the combined abundance of nearshore reference and disposal sites
(x = 10.0) differed significantly from the combined middepth (x = 25.6) and offshore sites but
the middepth and offshore sites did not differ significantly. A similar significance pattern was
observed for taxa richness. Of the two dominant taxa that differed significantly between sites,
abundance of the polychaete, P. ambigua, was greater at the disposal site but abundance of
another polychaete, M. californiensis, was greater at the reference site. Measured sediment
physical properties (e.g., particle size) and organic contaminants and metals provided no clues to
explain the distributional pattern and abundance of the individual benthic macrofaunal taxa.
At the Atchafalaya study area, variability in taxa richness and numerical abundance
within and among some reference and disposal stations suggests lack of a consistent increase or
decrease in these parameters at reference and disposal sites. Four out of a total of 17 numerically
abundant taxa at the Atchafalaya River reference site averaged significantly more individuals
than occurred at the disposal site. The polychaete, Streblospio benedictii, was the only species to
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average significantly more individuals at the disposal than at the reference site. Variability in
abundance within and among reference and disposal stations was high which indicated a lack of
consistency in individual taxa abundance at the physical scale of stations employed in this study.
The lack of consistency suggests that the possible differential influence of dredged material
disposal on selected individual benthic macrofaunal taxa cannot be ruled out. However, the
overall magnitude of these differences appeared relatively small between reference and disposal
sites. Benthic macrofaunal response patterns did not correlate with the measured sediment
physical factors, hydrographic factors or sediment chemical constituents.
Five of seven relatively abundant taxa averaged significantly more individuals at
Mermentau River disposal than at the reference site. Average numerical abundance was greater
at the disposal site. Taxa richness showed a statistically significantly higher value at the
middepth disposal station than at the middepth reference station. This parameter did not differ
significantly between the other paired reference and disposal stations. Although the response
parameters were generally consistent between reference and disposal sites, we believe further
work would allow more informed judgement of potential effect or lack thereof.
The addition of the seventh replicate sample per station seldom added a new taxon to the
inventory. In most cases, four or five replicates captured all but probably the most rare species.
The sampling power analysis revealed that approximately 25 to 50 replicate samples would be
required to achieve an accuracy of the mean for abundance at +/-10%. The need for this level of
accuracy should be determined on a case-by-case basis because of the obvious high cost for this
level of sampling. Relaxation of the accuracy requirement to 20% substantially reduced the
number of samples required to achieve a significant P-value $ 0.05.
ACKNOWLEDGMENTS
The following individuals are thanked for their laboratory and field assistance in the
project: Barbara Albrecht, Brian Dorn, Diane Folse, John Harmuth, Courtney Head, Guy
Herring, Rob Holbrook, Andrew Kelly, Vicki Kramer, Shannon Phifer, Bob Quarles, Sean
Stangeland, Roman Stanley, David Whiting, and Ruth Yoakum. Wallace T. Gilliam provided
the gas chromatographic and mass spectral analyses of sediment samples. Captain Dwight Paine
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and crew of the Ocean Survey vessel Peter W. Anderson exhibited a high degree of
professionalism through their assistance in making the field work a success. Maureen Stubbs
and Valerie Coseo are thanked for typing the manuscript. George W. Ryan assisted with some of
the preliminary statistical analyses. Tom Poe and Steve Embry provided the graphical support.
Andrew McErlean, Larry Goodman, C. McKenney, John Valentine and Linda Mathies are
thanked for helpful comments on the manuscript. Mention of trade names or commercial
products in this report does not constitute endorsement by the U.S. Environmental Protection
Agency.
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(Draft). U.S. EPA Region VI, Dallas, TX. EPA/906/07-90-008.
U.S. EPA 1990c. Mermentau River Ocean Dredged Material Disposal Site Designation. EIS
(Draft). U.S. EPA Region VI, Dallas, TX. EPA/906/05-90-004.
Ward. C.H., M.E. Bender and D.S. Reish, eds. 1979. The Offshore Ecology Investigations.
Effects of oil drilling and production in a coastal environment. Rice University Studies
65 (Nos. 4 and 5), Houston, TX.
Warner, J.S. 1976. Determination of aliphatic and aromatic hydrocarbons in marine organisms.
Analytical Chemistry 48 (3): 578-583.
Warwick, R.M. 1993. Environmental impact studies on marine communities: Pragmatical
considerations. Aust. J. Ecol. 18: 63-80.
Warwick, R.M. and K.R. Clarke. 1993. Comparing the severity of disturbance: A meta-analysis
of marine macrobenthic community data. Mar. Ecol. Prog. Ser. 92: 221-231.
Weston, D.P., and G.R. Gaston. 1982. Benthos, Chapter 5. pp. 5-1 to 5-86. In: L.R. DeRouen,
R.W. Hann, D.M. Casserly and C. Giammona, eds. West Hackberry Brine Disposal
Project Pre-Discharge Characterization. DOE, Washington, DC.
Wilson, J.N. 1957. Effects of turbidity and silt on aquatic life. Biological Problems in Water
Pollution. U.S. Dep. Health Educ. and Welfare. Robert A. Taft Sanitary Engineering
Center, p. 235-239.
Wright T.D., D.B. Mathis and J.M. Brannon. 1978. Aquatic disposal field investigations,
Galveston, Texas, Offshore Disposal Site. Evaluative Summary, Technical Report D-77-
20, Office, Chief of Engineers, U.S. Army, Washington, DC, 89 pp. (NTIS No. AD-
A061844).
40

-------
'Mississippi River
New Orleans £
• (Morgan City
1	Atchafalaya Bayou Site
2	Freshwater Bayou Site
3	Mermentau River Site
94°	93°	92° f
N	Atchafalaya River
¦ 30°
Port Arthur

_ • . .


.t-.
• "»,H - , .
/•Lake.
Dharles
n
n o-\

II1; ¦' "! ll:l l""!
Gulf of
Mexico
80 Kilometers
"¦i
50 Miles
Figure l. Map of the study areas for benthic macrofaunal community analyses.
41

-------
Figure 2. Map of individual study sites including Mermentau River, Freshwater Bayou and
Atchafalaya River showing sampling locations.
42

-------
Atchafaiaya River
yermillion
Bay
Morgan City 0'
Marsh
Island
Au Fer
Jsland
0	16 32 Kilometers
1	I	1
0	10 20 Miles
Atchafaiaya Rrver
Gulf of
Mexico
i	
OUMDS
O Reference Site
Area
* ODMDS
O Reference Site
5 Miles
29°30' -
Gulf of
Mexico
EPA/RL#94011 -01

-------
Figure 3. Representative taxa - area curves showing cumulative number of taxa with increased
number of replicate samples from given station.
43

-------
24
22
20
18
16
14
12
10
8
6
4
2
0
Representative Species-Area Curves
• • • Atchafalaya disposal—Middepth
b-g-g Freshwater disposal-Middepth
a-a-a Freshwater reference—Offshore
T	1	1	1	T
1	2	3	4	5
Replicate
T"
6
7

-------
Figure 4. Relationship between percent taxa of benthic macroinvertebrates and abundance group
(I = 1 individual, II = 2 to 3 individuals, III = 4 to 7 individuals, IV = 8 to 15 individuals, etc.).
Results for reference and disposal sites are shown separately.
44

-------
REFERENCE SITES
50 n
Stations
] Mermentau
~§ Freshwater
I I Atchafalaya
Abundance Group
EPA/RL#94011 -04

-------
Stations
] Mermentau
Freshwater
I I Atchafalaya
DISPOSAL SITES
Abundance Group
EPA/RL#94011 -05

-------
Figure 5. Number of samples required to sample benthic macroinvertebrates within a certain
percent accuracy of the mean at P = 0.05.
45

-------
500
450
400
350
300
250
200
150
100
50
0
I i i i i i i i i
0
EPA/RL#94011 -03
I | I I I I I I I I I | I I I I I I I I I | I I I I I I I I I | I I I I I I I I I |
10	20	30	40	50
Accuracy of Mean (±%)
Freshwater Bayou Stations
-f- Ref. Nearshore ~ Disp. Nearshore
| Ref. Middepth O Disp. Middepth
A Ref- Offshore
Freshwater Bayou Disposal Offshore
Station & Atchafalaya River Disposal
Nearshore & Mid-depth Stations.
All Mermentau River Stations & All
Atchafalaya River Reference Stations &
Disposal Offshore Station.

-------
Table 1. Latitude and longitude coordinates for Louisiana benthic community
analysis sampling locations.
Site Station

Disposal
Reference
Atchafalaya Nearshore
N
29° 19'25"
29° 19'58"

W
91°25'28"
91 °26'07"
Midsection
N
29° 16'09"
29° 16'36"

W
91 °28'29"
91 °29'00"
Offshore
N
29° 13'58"
29° 12'59"

W
91°31'16"
91 °32'25"
Freshwater Nearshore
N
29°30'50"
29°30'53"

W
92°21' 19"
92°20'56"
Midsection
N
'29o30'H"
29° 30'14"

W
92°21,4I"*
92°20'58"
Offshore
N
29°28'48"
29°28'31"

W
92° 19'59"
92° is'io"
Mermentau Nearshore
N
29°42'22"
29042-17"

W
93°08'17"
93°07'05"
Midsection
N
29°41'05"
29°41'05"

W
93°08'01"
93°07'ir
Offshore
N
29°4I'49"
29041-53"

W
93°07'35"*
93°07'00"*
* Loran malfunction probable

-------
Table 2. Louisiana Benlhic Community Analysis Physical Parameters










% weight



SAL
TEMP
DO

DEPTH
PARTICLE SIZE
loss on
CHANNEL
SITE
STATION
(ppt)
ro
(mg/liter)
pH
(m)
%>63^m
%<63^m
ignition
Atchafalaya
Reference
Nearshore
8.0
23 5
7.0
8.6
1.9
60.01
39.99
2 22
Atchafalaya
Disposal site
Nearshore
9.5
23.7
7.5
88
I.I
56.65
43.35
3.50
Atchafalaya
'Reference
Middepth
17.6
23 3
6.2
8.8
2.1
1 89
98.11
6 62
Atchafalaya
Disposal site
Middepth
19.1
23.3
6.3
8.3
2.0
9.84
90.16
6.10
Atchafalaya
Reference
Offshore
24.4
22.9
6.3
74
3 3
3.37
96.63
5.48
Atchafalaya
Disposal site
Offshore
25.8
22.9
6.5
7.4
3.5
3.43
96.57
5.98
Freshwater
Reference
Nearshore
26.5
21.8
6.7
8.1
1.6
2.97
97.03
9 12
Freshwater
Disposal site
Nearshore
26.6
21.7
6.7
8.0
1.7
4.46
95.54
6.74
Freshwater
Reference
Middepth
26.0
22.0
6.8
79
2.5
3.11
96 89
7.53
Freshwater
Disposal site
Middepth
26.2
22.1
6.7
79
2.3
24.75
75.25
6.98
Freshwater
Reference
Offshore
27.2
22.8
6.7
00
40
0 49
99.51
11.63
Freshwater
Disposal site
Offshore
27.2
22.6
6.6
8.1
30
0 55
99.45
10.81
Mermentau
Reference
Nearshore
30 6
22.3
6.6
8.2
1.5
17 55
82.45
5.84
Mermentau
Disposal site
Nearshore
30.5
22.5
6.3
8.0
2.0
40.79
59.21
5.37
Mermentau
Reference
Middepth
30.5
22.0
5.9
8.2
1.8
6.74
93.26
8.20
Mermentau
Disposal site
Middepth
30.5
22.2
6.7
8.2
3.0
10.91
89.09
641
Mermentau
Reference
Offshore
30 5
22.0
6.3
8.3
2.6
0 92
99.08
9 73
Mermentau
Disposal site
Offshore
30.5
22.0
69
8.2
3.7
12.15
87 85
6.50

-------
Table 3. Average percentage recovery of selected chlorinated pesticides and PCB spiked on samples of sediment.
Method detection limits are also shown (From Moore et al. 1994).
Spike	Average Percentage	Method
Concentration	Recovery and	Detection Limit
Compound	(ng/g)	N Standard Deviation (ug/g wet weight)
Aldrin
0.10
3
76 ± 2.0
0.010
BHC Isomers




Alpha
a


0.010
Beta
a


0.010
Gamma (lindane)
0.10
4
25 ± 3.7
0.010
Chlordane (alpha)
0.10
12
55 ± 18
0.010
Chlorpyrifos (Dursban)
a


0.010
DDE (P,P')
0.10
11
91 ± 14
0.010
DDD (P,P')
0.10
6
71 ± 5.3
0.010
Dieldrin
0.10
11
87 ± 15
0.010
Endrin
a

a
0.010
Endosulfan I
0.10
11
82 ±21
0.010
Endosulfan II
0.10
12
96 ± 7.0
0.010
Endosulfan Sulfate
a


0.010
Heptachlor
0.10
3
76 ± 2.0
0.010
Heptachlor epoxide
0.10
3
67 ± 1.0
0.010
Hexachlorobenzene
0.10
3
68 ± 2.6
0.010
Methoxychlor
a


0.010
Mirex
0.10
12
87 ± 6.4
0.010
PCBs"
0.10
11
88 ± 4.7
0.010
Toxaphene
a


0.010
ND = Not detected
" Analytes were not spiked for recovery.
b Percentage recovery was based on specific congener analysis.

-------
Table 4. Concentration of selected metals in three replicate sediment samples from Atchafalaya River, Freshwater
Bayou and Mermentau River dispersal and reference sites.
Concentrations in ^g/g wet weight
Sediment Location
Depth
<
-------
Table 5. List of taxa with presence (X) or absence (-) at reference and dredge disposal sites.
Taxa
Atchafalaya
Freshwater
Mermentau
Reference
Disposal
Reference
Disposal
Reference
Disposal
ANNELIDA
Amphareie americana
X
X
.
.

.
Cossura soyeri
X
X
X
X
X
X
Diopatra cuprea
X
X
_
_
. •
_
Glycinde solitaria
X
X
.
.
X
X
Hesionidae (LPIL)
_
X
.
.
.
_
Lepidaslhenia sp.
X

X
X
.
.
Magelona cf. phyllisae
X
X
.
_
X
X
Mediomastus califomiensis
X
X
X
X
X
X
Neanthes micromma
.
X
X
X
.
X
Ncanthcs sp.
_
X
.
.
.
.
Onuphis emcrita oculatus
.
X

.
_
.
Ouenia (usifomies
X
X
.
.
_
.
Parandalia sp.
X
X
.
X
_
.
Parapnonospio pinnata
X
X
X
X
X
X
Pectinaria gouldii
X
.

.

_
Phyllodoce arena
X
X
.
.

_
Podariiopsis levifusina
X
X
X
X
.

Poly chaste sp A
.
_

.
.
X
Polychaete sp. B
X

X
.

_
Polychaete sp. C
X
.
.
.
.
_
Polydora sp.
X
X
' .
.
.
_
Prionospto sp.
X
X
X
X
X
.
Pseudoeurythoe ambigua
X
X
X
X
X
X
Sigambra tcntaculata
X
X
X
X
.
X
Spiochaetoptems oculatus
X
X
.
X
.
X
Streblospio benedicti
X
X
X
.

_
Olieochaeta (LPIL)
X
X
-
-
-
-
-------
Table. 5 (continued)
Taxa
Atchafalaya
Freshwater
Mermentau
Reference
Disposal
Reference
Disposal
Reference
Disposal
ARTHROPODA
Balanus sp.
X
X
X
X
X
X
Callianassa sp.
X
.
.
.
.

Corophium sp.
X
.
X
.
X
_
Edotea numtosa
.
X
.

.

Ischyrocendae (LPIL)

X
.
.
.
.
Melita sp.

X

.
.
.
Oxyurosnlis sniithi
X
X
.
.
.
.
Pagundae (LPIL)
.
_
.
X
.
.
Pinnixa sayana
X
X
X
X

X
Xanthidae (LPIL)
.
X
_
.
_
.
MOLLUSCA
Mulinia lateralis
X
X
.
X
X
X
Nassarius vibex

X
X
.

.
Nucutana acuta
X
.
.
_


Rangia cuneata
X
_
_
.
_

Telhna texana
X
.
.
.
_
.
RHYNCOCOELA
Cerebratulus lacteus
X
X
X
.
X
X
Linens sp.
.
X
_
.
.
.
Micrura sp.
X
X
X
X
X
X
Nemertea sp. A (LPIL)
X
X
X
X
X
X
ECH1NODERMATA
Microphioplwlis atra
_
X
_
.

.
PHORONIDA
Phoronis sp.
X
X
X
.
.
.
HEMICHORDATA
Enteropneusta (LPIL)
X
X
X
X
.
.
HOLOTHUROIDEA
Holothuroidea (LPIL)
X
X
X

X
X
PLATYHELMITHES
Styloclius ellipticus
X
X
-
-
-
-
-------
Table 6. Species list by study area and site (reference and disposal) showing frequency of occurrence (Fq, location of occurrence by relative
distance from shore: Loc, N =
nearshore. M
= middepth, O =
offshore), mean abundance (x) and standard deviation (sd) for 21 samples
(0 05m! sample) per channel.










Reference


Disposal



Species
Fq
Loc
%
sd
Fq
Loc
X
sd



ATCHAFALAYA RIVER




Annelida








. Ampharete amencana
8
N.O
0.7
1.10
5
N.O
0.7
1.98
Cossura soyeri
13
N.M.O
2.0
2 92
6
N.M.O
1 2
2.09
Diopatra cnprea
3
N.M.O
02
051
5
M
08
1.69
Gtyeinde solitana
19
N.M.O
5.4
4.62
15
N.M.O
3 2
3.19
Hesionidae (LPIL)




1
O
0 1
0.38
Lepidasthenia sp.
1
O
0 1
0.75




Magehma cf. phyllts
2
.0
0.1
0.78
1
O
0.1
0 38
Medtomastus califnrniensis
21
N.M.O
40.8
33.48
21
N.M.O
40.7
50.43
Neanthes micromma




4
O
0.2
0.76
Neanthes sp.




3
N
0.1
0.42
Onuphis emerita oculatus




1
O
0.1
0.38
Owenia fustformes
6
N.O
04
0 93
12
M.O
1.7
2 07
Parandalia sp
12
M,N,0
1.7
2.58
2
N
0.1
0.49
Paraprionospio pmnata
21
N.M.O
12.2
5.67
14
M.O
8.4
7 55
Peclinaria gouldii
1
N
0.1
0.76




Phylludnce arenae
2
N.M
0.1
0.36
1
O
0.1
0.38
Podarkiopsts levtfusina
2
0
0.1
0.49
1
O
0.1
1 57
Polychaete sp. C (LPIL)
1
O
0 1
0 38




Polychaete sp. B (LPIL)
1
M
0.1
0.38




Polvdora sp.
7
N.M.O
2.0
4 96
2
M.O
0.1
0.30
Prinnospio sp.
2
0
0.2
1.33
3
O
0.2
0 95
Pseudneurythoe ambigua
19
N.M.O
98
7 82
13
M.O
10.7
13 32
Sigambra tentaculata
9
M,0
1 3
200
8
M.O
1.6
2.48
Spiochaetoptens oculatus
20
N.M.O
72
8.15
13
M.O
7.0
10.06
Streblospio benedtcti
2
N
1.4
5.51
7
N
2.5
4.35
Oligochaeta (LPIL)
16
N.M.O
4.0
4.09
11
N.M.O
2.0
3.42
Arthropoda








Balanus sp
1
N
0.1
0.38
6
N.M.O
0.3
0.43
Callianassa sp.
1
N
0.1
0.38




Corophium sp.
1
N
0.2
1.89




Edntea montosa




1
N
0 1
0 75
Ischyroceridae (LPIL)




1
O
0.1
0 38
Melila sp.




1
M
0.1
0.38
Oxyurastylis smithi
3
N.O
0.2
0.43
3
O
0.2
0.79
Pinnixa sayana
3
M.O
02
0.43
2
M.O
0.1
0 36
Xanthidae (LPIL)




1

0 1
0.38
Mollusca








Mulinia lateralis
17
N.M.O
5.5
5.69
19
N.M.O
7.1
5.74
Nassarius vtbex




1
O
0 1
0 38
Nuculana acuta
2
0
0.1
0 49




Rartgia cuneata
1
N
0.1
0.38




Tellina texana
1
N
0.1
0.38




Rhyncocoela








Cerebratulus lacteus
1
M
0.1
0.38
4
N.M
0.2
0.47
Linens sp.




1
O
0.1
0.38
Micrura sp.
15
N.M.O
1.2
1 14
11
N.M.O
0.8
0 89
Nemertea sp. A (LPIL)
21
N.M.O
92
5.32
18
N.M.O
88
8.39
Echinodermata








Microphinpholis atra




5
M.O
0.4
1.01
-------
Table 6, continued
Species
Fq
Reference
Loc
X
sd
Disposal
Fq
Loc
X
sd
Phoronida



f




Phoronis sp
1
O
0 1
0.38
1
O
0.1
0.38
Hemichordala








Enteropneusta (LPIL)
13
M,0
2.1
2.52
12
M.O
4.1
590
Holothuroidea








Holothuroidea (LPIL)
5
M,0
0.6
1.29
4
M
0.2
0.40
Platyhethminthes








Stylochus ellipticus
1
N
0.1
0.38
2
N.M
0.2
0.83



FRESHWATER BAYOU




Annelida








Cosstira soyeri
9
M.O
0.9
1.46
8
N.M
0.8
1.40
Lepidasthenia sp.
3
O
0.1
0.53
1
O
0 1
0 38
Mediomastus califomiensis
15
N.M.O
62
8 69
7
N.M.O
1 2
1 95
Neanlhes micromma
4
M.O
0.2
0.47
3
M.O
0.2
0.61
Parandalia sp.




1
N
0 1
0.38
Paraprionospio pinnata
20
N.M.O
13.9
24.64
21
N.M.O
10.5
9.81
Podarkiopsis levifiisina
4
M.O
04
1.22
2
O
0 1
0.79
Polychaete sp. B (LPIL)
2
0
0.1
0 49




Prionospio sp.
1
0
0.2
1.51
3
M.O
0.2
0.84
Pseudoeurythoe ambigua
10
N.M.O
1.9
3.02
10
M.O
34
5.49
Sigambra tentaculata
7
M.O
0.7
1.19
' 7
M.O
0.9
1.69
Slreblospio benedicti
1
M
0.1
0.38




Spwchaetnpterus oculaius




1
M
0.1
0.38
Arthropoda








Balanus sp.
7
N.M.O
0.5
0.87
9
N.M.O
1.9
3.98
Corophium sp
1
0
0 1
0 38




Paguridae (LPIL)




1
M
0.1
0.38
Pinnixa sayana
3
0
0.4
1.46
3
O
0.1
0.53
Mollusca








Muhnia lateralis




1
M
0.1
0.76
Nassarius vibex
1
0
0.1
0.38




Rhyncocoela








Cerebrululus lacteus
2
0
0 1
0.49




Micrura sp.
9
N.M.O
0.9
1.81
11
N.M.O
1.3
1 90
Nemertea sp. A (LPIL)
9
N.M.O
0.6
0.87
12
N.M.O
27
7.93
Phoronida








Phoronis sp.
1
0
0.1
0.38




Hemichordata








Enteropneusta (LPIL)
7
M.O
1.3
2.80
5
N
06
1.77
Holothuroidea

)






Holothuroidea (LPIL)
1
0
0.1
0.86




-------
Table 6, continued
Species
Reference
Fq
Loc
X
sd
Disposal
Fq
Loc
X
sd



MERMENTAU RIVER




Annelida









Cossura soyeri
20
N,M,0
2.6
1.66

14
M.O
2.4
2.34
Glycinde solitana
5
N.M.O
03
0.56

17
N.M.O
1.8
1.67
Magelona cf. phyllhea
2
N.O
0 1
0.30

8
M.O
08
1.67
Mediomamus califoriuensis
3
N,0
0.1
0.43

4
M.O
0.3
0.90
Neanthea micromma





1
O
0.1
0.38
Paraprionnspio pinnata
21
N.M.O
51.2
20.35

21
N.M.O
113.5
20.78
Polychaete sp.A





1
M
0.1
0.38
Prionospio sp
1
M
0.1
0.38





Pseudoeurythoe ambigua
15
N,M,0
1.0
0.95

18
N,M,0
5 8
5 14
Sigambra tentaculala





9
N.M.O
0.6
0.86
Spiochaetopterus oculatus





1
M
0.1
0.38
Arthropods









Balamis sp.
12
N.M.O
1.3
1 83

14
N.M.O
2.3
4.46
Corophmm sp.
1
N
0.1
0.38





Pinnixa sayana





1
O
0.1
0.38
Mollusca









Mulinta lateralis
1
N
0.1
0.38

1
N
0 1
0 38
Rhyncocoela









Cerebralulus lacteus
3
M.O
0.1
0 43

10
N.M.O
0.6
0.68
Micrura sp.
2
0
0.1
0 78

3
N,M
01
0.43
Nemertea Sp. A (LPIL)
12
N.M.O
0.8
0.77

17
N.M.O
1.9
1 53
Holothuroidea









Holothuroidea (LPIL)
1
0
0.1
0.38

4
M.O
0.7
2.20
-------
Table 7. Mean (x) of abundance and taxa richness per 0.05m! standard deviations
(sd) for each reference and disposal site within study areas
Mean Taxa Richness
Channel Station
N
Reference
x sd
Disposal
% sd
Atchafalaya
Nearshore
Midsection
Offshore
7
7
7
11.9 -
11 9
15 7
2.12
2.19
2.43
6.1
12.4
16.0
1.95
360
2.16
Overall
21
13.1
2.83
11 5
4 88
Freshwater
Nearshore
Midsection
Offshore
7
7
7
3.3
5.0
8.3
1.38
2.58
3.55
3.3
60
64
0.76
2 45
1.99
Overall
21
5.5
3.30
52
2.28
Mermentau
Nearshore
Midsection
Offshore
7
7
7
4.0
4.3
5.9
2.00
0.95
1.35
4.9
90
7.0
1.77
1.73
1.53
Overall
21
47
1.65
70
2.36
Mean Abundance
Channel Station
Reference Disposal
N T sd
X
sd
Atchafalaya
Nearshore
Midsection
Offshore
7
7
7
144.3
92.7
91.3
29 84
40.84
19.91
51.6
176 1
85.0
30.75
94.35
24.54
Overall
21
109.4
39 05
104.2
77.75
Freshwater
Nearshore
Midsection
Offshore
7
7
7
9.7
32 6
44.0
6.60
21.04
48.11
10.3
18.6
44.7
7.89
12.16
23.15
Overall
21
28.8
32.46
24.5
21.21
Mermentau
Nearshore
Midsection
Offshore
7
7
7
61.4
68.1
44.0
14.70
18.88
19.44
119 3
137.6
136.3
26.47
22.83
22.46
Overall
21
57.9
19.85
1310
24.31
-------
Table 8. Results of two-way ANOVA's for taxa richness for the Atchafalaya River. Freshwater Bayou,
and Mermentau River study areas. Main effects were Silfi (Reference site, RS; Disposal Site. DS) and
Station Location (Nearshore, N: Middepth. M: and Offshore, 0). Tukey's post hoc analysis was used to
compare a) main effect means when effects were significant and interaction was not and b) Site by
Station Location means when a significant interaction occurred Means followed by the same letter are
not significantly different (alpha = 0.05) Standard deviation are in parentheses ().

ATCHAFALAYA

Source
d.f
F

P
R/DS
SL
R/DS x SL
1
2
2
6 76
27 59
9 20

0.0134
00001
0.0006
Results of Tukey's Test. Means (x) and standard deviation (sd) are given; N = 7.



Site


Station
N
RS
II.9h
(2.12)
DS
6 1'
(195)

Location
M
11.9"
(2.19)
12 4*
(3.60)


O
I5.7*"
(2.43)
16 0*
(2.16)


FRESHWATER

Source
d.f.
F
P

R x DS
SL
R/DS x SL
1
2
2
0.02
11.80
1 13
0.8959
00001
0.3345

Results of Tukey's Test. Means (x) and standard
deviation (sd) are given; N = 14
Station

X
sd

N
M
O

3.3*
5 5"
7.4"
1.06
2.47
2 92



MERMENTAU

Source
d.f.
F
P

R/DS
SL
R/DS x SL
1
2
2
18.04
8.11
4 49
00001
0.0012
00182

Results of Tukey's Test: N = 7.

Site


Station
N
RS
40=
(2.00)
DS
49*
(1.77)

Location
M
4.3C
(0.95)
9.0"
(1.73)


O
5.9"
(1.35^
7.0lb
(1.53)
-------
Table 9. Results of two-way ANOVA's for the Atchafalaya River, Freshwater Bayou, and Mermentau River study
areas. Main effects were 2il£ (Reference site. RS; and Disposal Site, DS) and Station Location (Nearshore. N;
Middepth. M: and Offshore, O). Tukey's post-hoc analysis was used to compare a) main effect means when main
effects were significant and interaction was not and b) Site by Station Location means when a significant interaction
occurred. Means followed by the same letter are not significantly different (alpha = .05)	
ATCHAFALAYA
Source
sLL
E
E
R/DS
SL
R/DS x SL
1
2
2
2.30
2 08
12.08
0 1381
0.1391
0.0001
Results of Tukey's Test. Means (x) and
standard deviation (sd) are given: (N = 7).

Site


Station N
RS
144.3"
(29 84)
DS
51.5C
(3075)

Location M
92.7*
(40.84)
176.1*
(94.35)

0
91 3*
(19.91)
85.0"
(24.54)

FRESHWATER

Source
d.f.
E
E
Rx DS
SL
R/DS x SL
1
2
2
0.37
12.13
1.42
0 5450
0.0001
0.2554
Results of Tukey's Test (N = 14).



Station Location

X sd

N
M
O

100a
25.6"
44.4"
6.99
18.04
36.27
MERMENTAU

Source
sLL
£
E
R/DS
SL
R/DS x SL
1
2
2
78.60
2.35
3.28
00001
0 1095
0.0491
Results of Tukey's Test (N = 7).
Site


Station N
RS
61.4"
(14.70)
DS
119.3*
(26.47)

Location M
68.1"
(18.88)
137.6"
(22.83)

0
44.0"
136.3'

(19 44)
(22.46)
-------
Table 10. Average abundance per 0.05m'. standard deviation ( ). and relative abundance [ 1 of benthic macrofauna (density >1 at. at least, one station) for the
Atchafalaya River study area. Nearshore (N). Middepth (M). and Offshore (0) stations and overall mean (x) by site for individual taxa are provided Means
followed by similar letters are not significantly different (alpha = 0 05) based on ANOVA and Tukey's test.
Taxa
Reference Station
Disposal Station
N
M
O
X
N
M
O
X
Ampharele amertcana
0 3*
(0.49)
[12]
0.01
1.9'
(121)
[13]
0.7'
(1.10)
[161
0.1*
(0.38)
[9]
00*
1.9'
(3 24)
[131
0.7'
(1 98)
[16]
Cuss lira soyen
0 1"
(0.38)
[131
2.1'
(1 21)
[81
3 6'
(4.47)
[9]
1.9*
(2.92)
[I0|
0.0"
0.0"
3 6'
(2.15)
[9]
1 2'
(2.09)
[131
Diopalra cuprea
o r
(0 38)
[13]
0.3"
(0.76)
[14]
0 1"
(0.38)
[16]
0 2*
(0.51)
[19]
0 0"
2.4'
(2 22)
[9]
0 0"
0 8'
(1.69)
[14)
Glycinde solitaria
5.9'
(3 72)
[61
7 3'
(6.18)
[61
30"
(2.83)
[11]
5 4'
(4.62)
[7]
l.l*
(1 46)
[5]
5.6*
(3.69)
[7]
3.1*
(2.58)
[12]
3.2'
(3.19)
[8]
Mediomastus califomiensis
81.P
(2028)
[11
27 T"
(18.07)
[11
I3.6cjd
(5.86)
[3]
40.8'
(33.48)
[1]
30 3**'
(23.46)
[1]
84 3*"
(65.45)
[1]
7.4d
(2.88)
[4]
40.7'
(50.43)
[1]
Micura sp.
1.7*
(1.60)
[10]
0.7*
(0.49)
[12]
1.3'
(0.95)
[14]
1 2*
(1.14)
[15]
0.7*
(0 76)
[6]
0 4'
(0.79)
[13]
l.l*
(1.07)
[14]
0.8'
(0 89)
[14]
Mulinia lateralis
9.0"
(4 83)
[3]
I.0"
(1.16)
[101
6.6'"
(6.63)
[4]
5.5'
(5.69)
[6]
8.6'
(5.97)
[2]
8 7*
(6.63)
[6]
4.0**
(3.70)
[7]
7 P
(5.74)
[5]
Paraprionospio pinnala
6.9"
(4 74)
[5]
13.9*
(5.15)
[2]
160*
(2.24)
[2]
12.2'
(5.67)
[2]
0.0*
12.71"
(6.70)
[5]
12 4'
(4.72)
[2]
8 4'
(7 55)
[4]
Polydora sp.
O.P
(0.38)
[13]
0.1"
(0.38)
[15]
5.4'
(7 74)
[6]
1.9"
(4.96)
[10]
0.0"
0.1"
(0.38)
[14]
0.1"
(0 38)
[15]
0.1'
(0 30)
[18]
Pseudoeurothoe ambigiia
1.7*
(1.77)
[10]
10.6'
(7.46)
[4]
16.9'
(3.58)
[1]
9.8*
(7.82)
[31
0.0*
16 6*
(16 35)
[4]
15.4'
(11.13)
[1]
10.7'
(13.32)
[2]
Sigambra tentaulata
0.0*
0.3'
(0.48)
[14]
3.7'
(1.80)
[8]
1.3'
(2.00)
[14]
0.0*
0 P
(0.38)
[14]
4.6'
(2.15)
[61
1 6'
(2.48)
[12]
Spiochaetopterus oculatus
5 9tb
(3.71)
[6]
13.4**
(11.41)
[3]
.3"'
(1.38)
[12]
7.9s
(8.15)
[51
O.ff
17.P
(11.78)
[3]
3 9**
(3.13)
[81
70*
(10.06)
[61
Streblospio btncdtcli
4 3'
(9.32)
[8]
0.0"
0.0"
1.4'
(5.51)
[13]
7.4"
(4 50)
[3]
00"
0.0"
2 5'
(4 35)
[9]
Unknown Enteropneusta
0.0*
2.6*
(1.51)
n
3 9*
(3.31)
[7]
2.1*
(2.52)
[9]
0.0*
3.P
(3 44)
[8]
9.1"
(7.34)
[3]
4.1'
(5.90)
[7]
Unknown Holothuroidea
0.0"
1 6'
• (1 90)
[9]
0 P
(0 38)
[1.6]
0 6'
(1 29)
[17]
0.0*
0.6'
(0.53)
[12]
0.0*
0 2'
(0.40)
[17]
Unknown Nemertea
12 4**
(5.44)
[21
9.4'*
(5.61)
[5]
6.1"
(3 24)
[5]
9.2*
(5 33)
[4]
1.7'
(1 89)
[4]
17.7'
(7.87)
[2]
70**
(3.79)
[5]
8.8'
(8.39)
[31
Unknown Oligochaeta
80*
(4.58)
[41
0 6C
(1 13)
[13]
3.1**
(0.69)
[10]
*3.9*
(4.10)
[8]
0.3C
(0.49)
[7]
2.4"
(3.26)
[9]
3.3"
(4.31)
[11]
2.0'
(3 42)
[10]
-------
Table 11. Average abundance per 0.05m2, standard deviation (sd) and relative abundance [ ] of benthic macrofauna (density > 1 0 at. at least,
one station) for the Freshwater Bayou study area. Nearshore (N), middepth (M) and offshore (0) stations and overall mean (x) by site for
individual taxa are provided. Means followed by similar letters are not significantly different (alpha = 0.05) based on ANOVA and Tukey's
test.
Taxa
Reference Site
Station
Disposal site
Station
N
M
O
X
N
M
O
X
Balanus sp.
0.4'
(1.13)
[5]
0.6'
(0.79)
[6]
0 6'
(0.79)
[6]
0.5d
(0.87)
[8]
3.7"
(6 40)
[1]
1 7"
(2 06)
[4]
0.1'
(0 38)
[8]
1 9*
(3 98)
[3]
Unknown Nemertea
0.6'
(0.55)
[4]
0.7'
(1.25)
[5]
0.6*
(0.79)
[6]
0.6d
(0.87)
[8]
1.0"
(1.00)
[3]
1 1'
(0 90)
15]
5.9"
(13.78)
[3]
1.9"
(3 98)
[3]
Cossura soytri
0.0*
[7]
2.0'
(2.00)
[3]
0.6C
(0.79)
[6]
0.9"
(1.46)
[6]
0.1'
(0.38)
[6]
2 3"
(160)
[3]
Off
[9]
0 8"
(1 40)
[8]
Micrura sp.
0.4*
(0.53)
[5]
0.P
(0.38)
[9]
2.1"
(2.79)
[4]
0.9"
(1.81)
[5]
0.3*
(0.49)
[5]
0.4'
(0.79)
[7]
3.lh
(2.27)
[4]
1 3d
(1 90)
[5]
Paraprionospio pinnata
3.0*
(3.21)
[2]
12.9"
(8.44)
[2]
26.0"
(40 41)
[1]
14.C
(24.65)
[1]
3.61
(2.30)
[2]
8 1"
(6 59)
[11
19.7"
(10.52)
[1]
I0.5d
(981)
[1]
Sigambra tenlaculara
0.0*
[7]
0 3"
(049)
[7]
1 9"
(146)
[5]
0.7"
(1.19)
[71
0.0*
[6]
0 3"
(0.76)
[8]
2.6"
(0 76)
[5]
1 0s
(1.69)
[7]
Unknown Enteropneusta
0.0*
[7]
0.3"
(0.76)
[7]
3.6"
(4.04)
[3]
1.3d
(2.80)
[4]
0.1'
(0 38)
[6]
0.1"
(0.38)
[9]
1.6"
(2.94)
[6]
0 6"
(1 77)
[91
Mediomastus califomiensis
4.3*
(3.25)
[1]
14.3*
(10.86)
[1]
o.r
(0.38)
[9]
6.2d
(8.69)
[2]
1.0*
(1 91)
[3]
2.4"
(2 37)
[2]
or
(0.76)
[7]
1.2'
(1.95)
[6]
Pseudoeurythoe ambigua
I.0"
(2.24)
[3]
0.9"
(1.07)
[4]
3.9*
(4.18)
[2]
1.9^
(3.02)
[3]
0.0"
[7]
0.9"
(1.22)
[6]
9.4'
(5 97)
[2]
3.4*
(5 49)
[2]
-------
Table 12 Average abundance per 0.05m! standard deviation (sd> and relative abundance [ ] of benthic macrofauna (density > 1.0, at least, one station) for the Mermentau River study area. Nearshore (N), middepth (M)
and offshore (0) stations and overall mean (x) by site for individual taxa are provided. Means followed by similar letters are not significantly different (alpha = 0.05) based on ANOVA and Tukey's test
Taxa

Reference Site


Disposal Site
Station
Station

N
M
O
X
N
M
O
X
Balanus sp.
1.6*
1.6*
0.9*
l.3c
0.6"
2 6'
3.7'
2.3-

(2 57)
(1.90)
(0.69)
(1.83)
(0.79)
(2 76)
(7 23)
(4.46)

[2]
[31
[4]

[5]
[51
[31

Glycinde solitaria
0 I*
0.3'
0.4'
0.3'
1.3"
2 7'
1 3'
1.8'

(0 38)
(0.76)
(0.53)
(0.56)
(1.38)
(2.29)
(0 76)
(1.67)

[61
[6]
[51

[4]
[41
[61

Unknown
0.6*
0.6'
1.1'
0.8C
2.3"
1.6'
1.7'
l.9r
Nemeitea
(0.79)
(0.79)
(0.69)
(0.77)
(2 06)
(1.40)
(IN)
(1.53)

[51
[51
[31

[3]
[81
[5]

Pseudoeryihue ambigua1
0.4"
1.4'
1 l"
1.01
4.6"
8.9*
4.0"
5.8'

(0 53)
(1.27)
(0.69)
(0.95)
(5.09)
(5.98)
(3.16)
(5 14)

[41
[41
[31

[2)
[21
[21

Magelona s\>.
0.1"
0.0"
0.1"
0.1'
0.0"
2.3'
0.1"
0.8'

(0.38)

(0.38)
(0.30)

(1.80)
(0.38)
(1.47)

[61
[71
[61

[71
[61
[71

Cossura soyerr
1.6'
3.7*"
2.4"
2.6*
o.o"
5 4'
1.9*
2.4'

(1.13)
(2.06)
(0.98)
(1.66)

(1.72)
(1.22)
(2 58)

[21
[21
[21

[71
[31
[41

Paraprionospto ptnnata
56.4'
60.3'
36.9*
51.2'
109.3"
109 4"
121.7"
113.5'

(16.09)
(20 34)
(18.43)
(20.35)
(24.32)
(17 58)
(20 52)
(20.78)

[11
[11
[11

[¦I
[11
[11

1 Significant zonal effects, therefore, tested with Turkey's test.
2 Significant interaction between treatments (R & DS) and depth zones, therefore tested with Tukey's test.
-------
Table 13 Accuracy of the sample mean ± 9J
o. for estimating theoretical population mean based on seven replicates, and coefficient of variation (%) for each Ocean Dredged Disposal Site and Reference area station

Equation used to derive estimates (Eckblad, 1991):










Accuracy = (coefficient of variationHt-value)
/ sample size











Note: t-value taken from i-distribution table with 0.05 level of significance and six degrees of
freedom.










Atchafalaya River
Mermentau River
Freshwater Bayou

Reference
Disposal
Reference
Disposal
Reference
Disposal

Accuracy
±%
CV
(%)
Accuracy
± %
CV
(%)
Accuracy
±%
CV
(%)
Accuracy
±%
CV
(%)
Accuracy
±%
CV
<%)
Accuracy
±%
CV
<%)
Nearshore
152
(20.7)
43.8
(59 6)
176
(23 9)
16 3
(22.2)
49.9
(67 9)
56.3
(76 7)
Mid-depth _
32.3
(44 0)
39.3
(53.6)
20 3
(27 7)
12.2
(16.6)
47.4
(64.6)
48.1
(65 5)
Offshore
160
(21 8)
21 2
(28 9)
32.5
(44 2)
12.1
(16.5)
80.3
(109 3)
38 0
(51.8)
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APPENDIX I
CHEMICAL ANALYSES OF SEDIMENT FROM THREE OCEAN DREDGED MATERIAL
DISPOSAL SITES AND REFERENCE SITES IN MERMENTAU RIVER, FRESHWATER
BAYOU AND ATCHAFALAYA RIVER, LOUISIANA
by
Analytical Chemistry Team
Ecotoxicology Branch
James C. Moore, Team Leader
E.M. Lores and Jerrold Forester
U.S. Environmental Protection Agency
Environmental Research Laboratory
Sabine Island
Gulf Breeze, FL 32561
Submitted to
Susan McKinney
U.S. Environmental Protection Agency
Region VI
6W-QM 1445 Ross Avenue
Dallas, Texas 75202
Final Report: November 1994
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ABSTRACT
Sediments from Mermentau River, Freshwater Bayou and
Atchafalaya River, Ocean Dredged Material Disposal Sites, and
sediments from reference sites near these disposal sites were
chemically analyzed for selected heavy metals, pesticides, PCBs,
and petroleum hydrocarbons. Residues of PCBs or petroleum
hydrocarbons were not detected in any sediment sample. Some
chlorinated-hydrocarbon pesticides were detected at concentrations
near the detection limit in Freshwater Bayou Ocean Dredged Material
Disposal Site (ODMDS) and its nearby reference site, but none were
found in Mermentau River ODMDS, in its nearby reference site, nor
in Atchafalaya River ODMDS or its reference site. All sediment
samples contained residues of some heavy metals. Concentrations of
heavy metals in reference sediment samples were similar to
concentrations in sediments from the disposal sites.
ii
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INTRODUCTION
Chemical analyses were performed on sediment from three
dredged materials disposal sites and reference sites located near
the disposal sites. Each disposal area and reference site was
divided into three segments representing shallow, mid-depth and
deepest depth of the disposal area with corresponding reference
stations outside the disposal area with similar depths. Sediments
from one sampling station of each area were sampled and chemically-
analyzed for selected chlorinated pesticides, PCBs, selected heavy
metals and petroleum hydrocarbons. Chemical analyses for
pesticides and petroleum hydrocarbons were performed by using a
capillary-column gas chromatographs equipped with an electron-
capture detector and flame-ionization detector respectively.
Inductively coupled argon plasma emission spectroscopy was,used to
analyze sediments for heavy metals.
1
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METHODS OF CHEMICAL ANALYSES
A. Chlorinated Hydrocarbon Pesticides
Sediments were air dried and blended as necessary, then
weighed into 150-mm by 25-mm screw top test tube with teflon liner.
Twenty milliliters of 20% (v/v) acetone in petroleum ether were
added and then the samples were tumbled on a rotorack at 60-90 rpm
for 30 minutes. Samples were then centrifuged (1600 x g) for 10
minutes. The solvent extracts were transferred to an oil sample
bottle containing 50 mC of 2.0% (v/v) aqueous sodium sulfate and
gently shook for one minute. After the two phases separated the
solvent was transferred to a 25 mf-concentrator tube and the aqueous
wash was repeated two more times. Sample extracts from the three
aqueous washes were combined and concentrated to 1 mf on a nitrogen
evaporator in preparation for Florisil cleanup. Samples analyzed
with electron-capture detectors were shaken with 500 of mercury
to remove sulfur before gas chromatographic analysis. Cleanup
columns were prepared,by adding 3 g of PR-grade Florisil (stored at
130°C) and 2 g of anhydrous sodium sulfate (powder) to a 200-mm by
9-mm i.d. Chromaflex column (Kontes Glass Co., Vineland, NJ) and
rinsing with 10 ml of hexane. Sediment extracts were transferred
to the column with two additional 2-ml volumes of hexane.
Pesticides and PCBs were eluted with 20 ml of 5% (v/v) diethyl
ether in hexane. Dieldrin and Endosulfan were eluted with 20 ml of
10% (v/v) isopropanol in isooctane.
2
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Pesticides were analyzed with external standard methods. All
standards were obtained from the EPA pesticide repository.
Analyses were performed on a Hewlett-Packard Model 5890 gas
chromatograph equipped with a S3Ni electron-capture detector.
..Separations were performed by using a 30-m (0.32 mm i.d.) RTX-5 and
RTX-1 fused silica capillary column. Other gas chromatographic
parameters were: helium carrier gas flowing 1.5 mf/min; column
temperature, 50°C (hold for 2 min),10o/min to 150°C, 2°/min to 260°C
(hold for 3 min); inlet temperature 250°C; and detector
temperature, 350°C; 10% methane irj argon makeup gas flowing at 60
mf/min.
B. Heavy Metals
One to two grams of sediment were weighed and placed into a
40-ml reaction vessel. Five milliliters of concentrated nitric
acid were added and the samples digested for 2 to 4 h at 90°C in a
tube heater. Digestion was continued, with vessels capped, for 48
h at 70°C. After digestion, samples were transferred to 15-ml
tubes and a 5-ml aliquot was diluted to 10 ml for aspiration into
a Jarrell-Ash AtomComp 800 Series inductively-coupled argon-plasma
emission spectrometer (ICP). This instrument acquires data for 15
elements simultaneously. No detectable residues could be found in
method blanks. A solution of 10% nitric acid/distilled water was
aspirated between samples to prevent carryover of residues from one
sample to the next. Standards in 10% nitric acid were used to
calibrate the instrument initially and adjustments were made when
3
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necessary. Concentrations were reported in two significant figures
as our method allowed, and were not corrected for percentage
recovery.
C. Petroleum Hydrocarbons
Ten grams of sediment were weighed into culture tubes and
extracted as described by J.S. Warner (1976). Sample extracts were
concentrated to approximately 0.50 ml for gas chromatographic
analyses. Analyses were performed on a Perkin-Elmer gas
chromatograph (GC) equipped with flame ionization detectors (FID).
Separations were performed by using a 30-m, 0.32-mm i.d. RTX-5
fused silica capillary column. Helium carrier gas was used at a
flow of 1.5 ml/min. Other gas chromatographic parameters were:
oven temperature programmed from 50°C (hold for 2 min) at a rate of
20°/min to 315°C (hold for 5 min); injector temperature was 250°C
and detector temperature was 350°C.
Quality Assurance of Chemical Analyses
All standards used for quantitations of pesticides were
obtained from EPA's repository in Las Vegas, Nevada. Standard
solutions of metals were obtained from J.T. Baker Chemical Co.,
Phillipsburg, NJ, and were Instra-Analyzed quality. Androstane was
obtained from Sigma Chemical Company, St. Louis, MO, and was used
as an internal standard to quantify petroleum hydrocarbons.
Reagent and glassware blanks were analyzed to verify that the
analytical system was not contaminated with chemical residues that
could interfere with quantitations.
4
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RESULTS AND DISCUSSION
Detection limits for chlorinated hydrocarbon pesticides and
PCBs are shown in Table 1 along with recovery efficiencies for
these compounds. Some compounds were volatile and could not be
recovered efficiently as shown by low recovery. Tables 2 and 3
show results of chlorinated hydrocarbon pesticide and PCBs
analysis. No residues of these compounds were detected in
sediments from Mermentau River ODMDS and nearby reference site or
in Atchafalaya Bayou ODMDS and its reference site. One sediment
sample from Freshwater Bayou ODMDS and one sample from its
reference site had detectable concentrations of pesticides (Table
3) . Since these concentrations were near the method detection
limit and are subject to unknown interferences at these low
concentrations, these compounds may be falsely identified by the
electron-capture detector.
Concentrations of selected heavy metals are shown in Tables 4,
5, and 6. Concentrations of metals in sediment from the disposal
sites were similar to concentrations of metals in their reference
sites. Concentrations of metals in sediment samples from different
depths were similar for most metals except for chromium and copper.
Concentrations of these metals were lower in nearshore samples than
in samples from offshore at both Mermentau River disposal site and
its reference site, and in Atchafalaya River ODMDS and its
reference site.
Petroleum hydrocarbons were not detected in any sediment
sample above 1.0 t^g/g wet weight, the method detection limit.
5
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REFERENCE
Warner, J.S. 1976. Determination of Aliphatic and aromatic
Hydrocarbons in Marine Organisms. Analytical Chemistry, 48,
No. 3, 578-583.
6
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Table 1. Average percentage recovery of selected chlorinated pesticides and PCB spiked on
samples of sediment. Method detection limits are also shown.
Spike	Average Percentage	Method
Concentration	Recovery and	Detection Limit
Compound	if^g/g)	N	Standard Deviation	g/g wet weight)
Aldrin
O
H-1
O
3
76
±
2.0
0.010
BHC Isomers






Alpha
a




0.010
Beta
a




0 . 010
Gamma (1indane)
0 .10
4
25
+
3.7

0. 010






Chlordane (alpha)
0.10
12
55
+
18
0 . 010
Chlorpyrifos (Dursban)
a




0.010
DDE (P,P')
0 .10
11
91
+
14
0 . 010
DDD (P,P")
0 .10
6
71
+
5.3
0.010
Dieldrin
0.10
11
87
+
15
0.010
Endrin
a

a



0.010






Endosulfan I
0.10
11
82
±
21
0.010
Endosulfan II
0 .10
12
96
+
7.0
0 . 010
Endosulfan Sulfate
a




0.010
Heptachlor
0.10
3
76
+
2 . 0
0 .010
Heptachlor epoxide
0 .10
3
67
±
1.0
0 . 010
Hexachlorobenzene
0 .10
3
68
+
2.6
0.010
Methoxychlor
a




0. 010
Mirex
0.10
12
87
+
6.4
0.010
PCBsb
0 .10
11
88
+
4.7
0.010
Toxaphene
a




0.010
ND = Not detected
a Analytes were not spiked for recovery.
b Percentage recovery was based on specific congener analysis.
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Table 2. Concentration (in ng/g wet weight) of selected chlorinated pesticides and PCBs
in replicate samples of sediment from Atchafalaya River ODMDS and a nearby-
reference site.
Atchafalaya	Atchafalaya
River ODMDS	Reference Site
Replicate	ABC	ABC
Aldrin
ND
ND
ND
ND
ND
ND
BHC Isomers






Alpha






Beta






Gamma (1indane)
ND
ND
ND
ND
ND
ND
Chlordane (alpha)
ND
ND
ND
ND
ND
ND
Chlorpyrifos (Dursban)
ND
ND
ND
ND
ND
ND
DDE (P,P')
ND
ND
ND
ND
ND
ND
DDD (P,P1)
ND
ND
ND
ND
ND
ND
Dieldrin
ND
ND
ND
ND
ND
ND
Endrin
ND
ND
ND
ND
ND
ND
Endosulfan I
ND
ND
ND
ND
ND
ND
Endosulfan II
ND
ND
ND
ND
ND
ND
Endosulfan Sulfate
ND
ND
ND
ND
ND
ND
Heptachlor
ND
ND
ND
ND
ND
ND
Heptachlor epoxide
ND
ND
ND
ND
ND
ND
Hexachlorobenzene
ND
ND
ND
ND
ND
ND
Methoxychlor
ND
ND
ND
ND
ND
ND
Mirex
ND
ND
ND
ND
ND
ND
PCBs
ND
ND
ND
ND
ND
ND
Toxaphene
ND
ND
ND
ND
ND
ND
ND = Not detected, see Table 1 for detection limits.
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Table 3. Concentration (in /ug/g wet weight) of selected chlorinated pesticides and PCBs in
samples of sediment from Freshwater Bayou ODMDS, and a nearby reference site.
Freshwater Bayou	Freshwater Bayou
ODMDS	Reference Site
Replicate	ABC	ABC
Aldrin
ND
ND
ND
ND
ND
ND
BHC Isomers






Alpha






Beta






Gamma (lindane)
ND
ND
ND
ND
ND
ND
Chlordane (alpha)
ND
ND
ND
ND
ND
ND
Chlorpyrifos (Dursban)
ND
ND
ND
ND
ND
ND
DDE (P,P')
0.026
ND
ND
ND
ND
0.036
DDD (P,P1)
ND
ND
ND
ND
ND
ND
Dieldrin
ND
ND
ND
ND
ND
ND
Endrin
ND
ND
ND
ND
ND
ND
Endosulfan I
ND
ND
ND
ND
ND
ND
Endosulfan II
ND
ND
ND
ND
ND
ND
Endosulfan Sulfate
ND
ND
ND
ND
ND
ND
Heptachlor
ND
ND
ND
ND
ND
ND
Heptachlor epoxide
ND
ND
ND
ND
ND
ND
Hexachlorobenzene
ND
ND
ND
ND
ND
0.018
Methoxychlor
ND
ND
ND
ND
ND
ND
Mirex
ND
ND
ND
ND
ND
0.047
PCBsb
ND
ND
ND
ND
ND
ND
Toxaphene
ND
ND
ND
ND
ND
ND
ND = Not detected, see Table 1 for detection limits.
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Table 4. Concentration of selected metals in three replicate sediment samples from Mermentau
River ODMDS, Louisiana, and a nearby Reference Site.
Concentrations in £*g/g wet weight
Sediment
Location
Deoth
Asa
Cd
Cr Cu
Hg
Ni
PbA
Se
Zn
Mermentau
Nearshore
21
ND
5.8 5.5
ND
14
14
ND
29
River ODMDS
Mid-depth
34
ND
12 11
ND
22
20
ND
35

Offshore
33
ND
11 12
ND
22
20
ND
36
Reference
Nearshore
39
ND
13 11
ND
24
19
ND
34
Site
Mid-depth
41
ND
15 13
ND
25
20
ND
30

Offshore
59
ND
20 15
ND
31
28
ND
3$


Method
Detection Limit in
ua/cr
wet weiaht




2.5
0.15
0.50 0.25
0.50
0.60
2.5
2.5
0.15
ND = Not detected.
A Usual background correction techniques could not be applied because of the intense
interference; therefore, without subtracting background, lead and arsenic may be present but
not in quantities greater than these shown.
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Table 5. Concentration of selected metals in three replicate sediment samples from
Freshwater Bayou ODMDS, Louisiana, and nearby Reference Site.
Concentrations in /ug/g wet weight
Sediment
Location
Depth
Asa
Cd
Cr
Cu
Hg
Ni
PbA
Se
Zn
Freshwater
Nearshore
29
ND
11
12
ND
21
17
ND
32
Bayou ODMDS
Mid-depth
31
ND
11
12
ND
24
24
ND
42

Offshore
52
ND
18
17
ND
32
28
ND
37
Reference
Nearshore
49
ND
17
14
ND
27
24
ND
32
Site
Mid-depth
50
ND
18
17
ND
30
27
ND
39

Offshore
43
ND
14
13
ND
28
28
ND
37
i
ND = Not detected; see Table 4 for detection limits.
A Usual background correction techniques could not be applied because of the intense
interference; therefore, without subtracting background, lead and arsenic may be present but
not in quantities greater than these shown.
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Table 6. Concentration of selected metals in three replicate sediment samples from
Atchafalaya River ODMDS, Louisiana, and a nearby Reference Site.
Concentrations in ng/g wet weight
Sediment
Location
Depth
Asa
Cd
Cr
Cu
Hg
Ni
PbA
Se
Zn
Atchatalaya
Nearshore
11
ND
3.8
4.0
ND
10
7.5
ND
16
River ODMDS
Mid-depth
34
ND
11
14
ND
22
18
ND
31

Offshore
34
ND
11
12
ND
21
20
ND
31
Reference
Nearshore
11
ND
4 . 5
4.4
ND
11
6 . 8
ND
13
Site
Mid-depth
42
ND
14
18
ND
29
23
ND
43

Offshore
25
ND
10
10
ND
20
16
ND
28
t
ND = Not detected; see Table 4 for detection limits.
A Usual background correction techniques could not be applied because of the intense
interference; therefore, without subtracting background, lead and arsenic may be present but
not in quanities greater than these shown.
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