U.S. Dept Commerce/NOAA/NMFS/NWFSC/PublicationsNOAA Technical Memorandum NMFS-NWFSC-26Benthic invertebrates and sediment characteristics in freshwater,       beach habitats of the lower Columbia River, 1994-95George T. McCabe, Jr. and Susan A. HintonNational Marine       Fisheries ServiceNorthwest Fisheries Science CenterCoastal Zone       and Estuarine Studies Division2725 Montlake Blvd. E.Seattle WA       98112       
April 1996
U.S. DEPARTMENT OF COMMERCERonald H. Brown, Secretary 
National Oceanic and Atmospheric AdministrationD. James Baker, Administrator

National Marine Fisheries ServiceRolland A. Schmitten, Assistant Administrator for Fisheries 
CONTENTS- ABSTRACT   
- INTRODUCTION      
- METHODS      - Sampling      - Data     Analyses 
  - Benthic     Invertebrates 
  - Sediments   
- RESULTS      - Beach     Nourishment Area O-34.0 
  - Benthic     Invertebrates 
  - Sediments      - Beach     Nourishment Area W-40.9 
  - Benthic     Invertebrates  
  - Sediments      - Beach     Nourishment Area W-43.8 
  - Benthic     Invertebrates 
  - Sediments      - Beach     Nourishment Area O-44.0 
  - Benthic     Invertebrates 
  - Sediments      - Beach     Nourishment Area W-45.0 
  - Benthic     Invertebrates  
  - Sediment s      - Beach     Nourishment Area O-45.1 
  - Benthic     Invertebrates  
  - Sediments      - Beach     Nourishment Area O-47.8 
  - Benthic     Invertebrates 
  - Sediments      - Beach     Nourishment Area O-57.0 
  - Benthic     Invertebrates 
  - Sediments      - Beach     Nourishment Area W-70.1 
  - Benthic     Invertebrates  
  - Sediments      - Beach     Nourishment Area O-75.8 
  - Benthic     Invertebrates 
  - Sediments      - Grain     Size/Corophium spp. Relationship   
- DISCUSSION   
- ACKNOWLEDGMENTS   
- CITATIONS   
- APPENDIX 
ABSTRACT
In 1994 and 1995, we studied benthic invertebrates and sediment characteristics in freshwater, beach habitats (i.e., intertidal beaches and adjacent shallow subtidal habitats) at 10 areas of the lower Columbia River between River Kilometers 53 and 122. All 10 areas had been used in the past for the disposal of dredged material pumped from the bottom of the navigational channel. The disposal of dredged material in a narrow band (about 30 m wide) onto beaches in the lower Columbia River is commonly referred to as beach nourishment. The main goals of the study were to describe the benthic invertebrate communities at the beach nourishment areas and examine the relationship between sediment median grain size and standing crops of the amphipods Corophium spp., which are seasonally important in the diet of juvenile salmonids.

Benthic invertebrate and sediment samples were collected at the 10 beach nourishment areas in July and October 1994 and January and April 1995 with polyvinyl chloride (PVC) coring devices. The 10 areas were designated Beach Nourishment Areas O-34.0, W-40.9, W-43.8, O-44.0, W-45.0, O-45.1, O-47.8, O-57.0, W-70.1, and O-75.8. The "O" and "W" refer to Oregon and Washington, and the succeeding number refers to the approximate location in river miles from the mouth of the river. Mean numbers of taxa/categories (by month) collected in the beach nourishment areas were generally low, ranging from 2 to 8. Major benthic invertebrate taxa collected in the 10 beach nourishment areas included nemerteans, oligochaetes, Fluminicola virens, Corbicula fluminea, Corophium salmonis, Corophium spinicorne, Chironomidae larvae, and Ceratopogonidae larvae. With the exceptions of Beach Nourishment Areas O-47.8 and O-75.8, total densities (i.e., standing crops) of benthic invertebrates in the beach nourishment areas were not significantly different (P > 0.05) between the 4 months. Densities of Corophium spp., most of which were C. salmonis, were not significantly different (P > 0.05) between months, except at Area O-75.8. In all areas except Area O-45.1, total benthic invertebrate and Corophium spp. densities were significantly higher (P < 0.05) at sampling stations 30 m from the high tide mark on the beach than at stations 15 m from the high tide mark. Densities of Corophium spp. varied widely within and between areas, with densities at individual stations ranging from 0 to more than 82,000 organisms/m2. The regression relationship for median grain size and Corophium spp. density was significant (P < 0.05); however, median grain size was a poor predictor of Corophium spp. density, explaining only 5% of the variation in Corophium spp. density (transformed).

All 10 beach nourishment areas supported substantial standing crops of Corophium spp. at times, particularly at stations along the 30-m transects. Since Corophium spp. are important prey for juvenile salmonids, and juvenile salmonids migrate along the beach nourishment areas, it is important to insure that Corophium spp. populations in these areas are not adversely impacted. 
INTRODUCTION
Relatively little is known about benthic invertebrate communities in freshwater, beach habitats of the Columbia River downstream from Bonneville Dam, the lowermost dam. Benthic invertebrate communities in the Columbia River downstream from River Kilometer (RKm) 50 have been studied more than upstream populations (e.g., Durkin and Emmett 1980; Durkin et al. 1981; Holton et al. 1984; Emmett et al. 1986; Hinton et al. 1990, 1995). Upstream from RKm 50, benthic invertebrate studies have been limited generally to short-term or geographically limited studies (e.g., Blahm and McConnell 1979, Blahm et al. 1979, McCabe and Hinton 1990, McCabe et al. 1990). Sanborn (1975) sampled the benthos of four areas in the Columbia River between RKm 29 and 167 in 1973-74. McCabe et al. (1993b) studied the benthos in eight areas of the lower Columbia River between RKm 46 and 211 during four surveys; all sampling was conducted in channel areas with mean depths greater than 5 m.

In 1994 and 1995, we studied benthic invertebrates and sediment characteristics in shallow, freshwater habitats (i.e., intertidal beaches and adjacent shallow subtidal habitats) at 10 areas of the lower Columbia River between River Kilometers 53 and 122 (Fig. 1). All 10 areas had been used in the past for the disposal of dredged material pumped from the bottom of the navigational channel. The lower Columbia River is an important shipping channel in the Pacific Northwest, requiring the maintenance of a navigational channel from the mouth of the river to Portland, Oregon. Annually, the U.S. Army Corps of Engineers (COE) is responsible for removing and disposing of almost 6.9 million m3 of material from the bottom of the navigational channel. The dredged material is disposed of at three types of sites: in water, upland, and in shoreline (beach) areas. The third type, disposal of dredged material in a narrow band (about 30 m wide) onto beaches in the lower Columbia River, is commonly referred to as beach nourishment. Habitats affected by beach nourishment typically include both intertidal and shallow subtidal habitats.

Because the lower Columbia River is presently designated as critical habitat for endangered Snake River Pacific salmon (Oncorhynchus spp.), the COE is required to complete biological assessments of the 10 areas prior to any future disposal of dredged material in these areas. Benthic invertebrates, particularly the amphipod Corophium salmonis, found in intertidal and shallow subtidal habitats of the Columbia River estuary are seasonally important in the diets of juvenile salmonids (McCabe et al. 1983, 1986; Kirn et al. 1986). Muir and Emmett (1988) found that C. salmonis and C. spinicorne were the dominant prey for juvenile salmonids collected during the spring of 1984 at Bonneville Dam.

The overall goal of the present study was to describe the benthic invertebrate communities at the 10 beach nourishment areas. Specifically, we assessed benthic invertebrate species composition, standing crops, diversity, and equitability. We also examined the relationship between sediment median grain size and standing crops of Corophium spp. The information in this manuscript was originally presented in a final report to the COE. Because of the lack of data on benthic invertebrates in freshwater, beach habitats of the lower Columbia River, we present the same data in this publication to make it available to a larger audience. 
METHODS 
Sampling

Benthic invertebrate and sediment samples were collected at the 10 beach nourishment areas in July and October 1994 and January and April 1995 (Fig. 1). At Beach Nourishment Area O-75.8, samples were actually collected on 1 August 1994, instead of in July. In addition, about 274 m (900 ft) of the upper end of Beach Nourishment Area O-74.5 is included with Beach Nourishment Area O-75.8. Each area is identified by an "O" or a "W," followed by a number. The "O" and "W" refer to Oregon and Washington, and the succeeding number refers to the approximate location in river miles from the mouth of the river (see U.S. Army Corps of Engineers 1991 for detailed navigational charts of the 10 beach nourishment areas).

Station locations (latitude and longitude) were established using the Global Positioning System, which also allowed stations to be easily reoccupied (Appendix Table). In each area, samples were collected along two parallel transects that were located about 15 m and 30 m, respectively, from the high tide mark on the shore. The number of sampling stations along each transect in the 10 disposal areas varied depending upon the length and habitat diversity of the area (Table 1). Odd-numbered stations were located along the 15-m transect, and even-numbered stations along the 30-m transect. At Beach Nourishment Areas O-34.0 and O-57.0, two stations outside of the disposal areas were sampled to provide information about benthic invertebrates in undisturbed habitats. 

Eleven core samples were taken at each of 96 stations (Fig. 1). Samples were collected with a polyvinyl chloride (PVC) coring device with an inside diameter of 3.85 cm, a penetrating depth of 15 cm, and a 174.6-cm3 sample volume (Appendix Fig.). Samples were collected by commercial divers at depths greater than 0.9 m. Ten core samples from each station were placed in labeled jars and preserved in a buffered formaldehyde solution (>4%) containing rose bengal, a protein stain. In the laboratory, samples were washed with water through a 0.5-mm screen. All benthic invertebrates were sorted from each sample, identified to the lowest practical taxon, counted, and stored in 70% ethanol. The 11th benthic sample from each station was placed in a labeled plastic bag and refrigerated for analysis of grain size, percent silt/clay, and percent volatile solids by the COE North Pacific Division Materials Laboratory, Troutdale, Oregon.
Data AnalysesBenthic Invertebrates Benthic invertebrate data were analyzed by station to determine species composition, densities (by taxon and total), and community structure (diversity and equitability). The Shannon-Wiener function (H) was used to determine diversity (Krebs 1978). Diversity is expressed as 
where pi = ni/N (ni is the number of individuals of the ith taxon in the sample, and N is the total number of all individuals in the sample) and s = number of taxa. Equitability (E) was the second community structure index determined; E measures the proportional abundances among the various taxa in a sample (Krebs 1978) and ranges from 0.00 to 1.00, with 1.00 indicating all taxa in the sample are numerically equal. Equitability is expressed as
E=H/log2s
where H = Shannon-Wiener function and s = number of taxa. Both H and E were calculated for each sampling station.

At each of the 10 beach nourishment areas, total benthic invertebrate densities, Corophium spp. densities, H, and E were each compared between transects (15- and 30-m) and months using two-way analysis of variance (ANOVA) (Ryan et al. 1985); densities were transformed (log10(density + 1)) prior to running ANOVA. Means from the 10 samples at each sampling station provided the basic data entries for all statistical tests. 

SedimentsTwo-way ANOVA was used to compare median grain size between transects (15- and 30-m) and months. One high outlying value for median grain size (Area W-45.0, Station 5, July 1994) was removed prior to using ANOVA. Percent silt/clay and percent volatile solids values were compared using the Kruskal-Wallis test (Ryan et al. 1985) because of the non-normal distribution of the data. 

The relationship between median grain size and Corophium spp. density was investigated by plotting the data from all 10 beach nourishment areas and then using linear regression. Corophium spp. densities were transformed (log10(density + 1)) prior to using regression. One regression was computed using data from all 4 months. The data were combined in this manner because overall there were no significant differences (P > 0.05) in Corophium spp. density or median grain size between months.
RESULTS 
Beach Nourishment Area O-34.0

Benthic InvertebratesAt Beach Nourishment Area O-34.0, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) (Table 2.); the lowest mean density occurred in July 1994 (14,113 organisms/m2) and the highest in January 1995 (29,246 organisms/m2) (Table 3). Benthic invertebrate densities were significantly different between the 15- and 30-m transects (P < 0.05), with the highest densities occurring at stations along the 30-m transect (Tables 2 and 3). In the undisturbed area outside of the beach nourishment area (Stations 1 and 2), mean benthic invertebrate densities were lower than those in the beach nourishment area in all months (Table 3). No statistical analysis was performed because only two stations were sampled in the undisturbed area.

The mean numbers of taxa/categories collected in both the beach nourishment area and the undisturbed area were similar for each month, ranging from seven to eight (Table 4). Major benthic invertebrate taxa collected in the beach nourishment area included nemerteans, oligochaetes, the bivalve Corbicula fluminea, Corophium salmonis, and Chironomidae larvae (Table 5). Summaries by station for all months and beach nourishment areas are available upon request from National Marine Fisheries Service, Northwest Fisheries Science Center, Point Adams Biological Field Station, P.O. Box 155, Hammond, OR 97121.

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-34.0; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect compared to stations along the 15-m transect (Tables 2 and 5). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 464 organisms/m2 in January 1995 to 5,377 organisms/m2 in April 1995. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 5,772 organisms/m2 in July 1994 to 34,237 organisms/m2 in January 1995 (Table 5). Densities of Corophium spp. also varied spatially along each transect (Fig. 2). Mean densities of Corophium spp. along the 15-m transect in the undisturbed area (Station 1) outside of the beach area were higher than mean densities at stations along the 15-m transect in the beach nourishment area (Table 5). With the exception of October 1994, mean densities of Corophium spp. along the 30-m transect in the undisturbed area (Station 2) outside of the beach area were lower than mean densities at stations along the 30-m transect in the beach nourishment area.

Diversity (H) was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-34.0 (Table 2). Mean H values ranged from 1.19 in April 1995 to 1.72 in July 1994 (Table 4). Equitability (E) was not significantly different (P > 0.05) between months; however, it was significantly higher (P < 0.05) at stations along the 15-m transect (mean = 0.69) than at stations along the 30-m transect (mean = 0.50) (Tables 2 and 4). Diversity and Equitability did not follow any consistent monthly pattern in comparisons between the beach nourishment area and the undisturbed area outside of the beach nourishment area (Table 4).

Sediments Median grain size was not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-34.0; however, it was significantly higher (P < 0.05) at stations along the 15-m transect (mean = 0.39 mm) than at stations along the 30-m transect (mean = 0.26 mm) (Table 6). Mean median grain size in the beach nourishment area ranged from 0.31 mm in January 1995 to 0.33 mm in the other 3 months. Both percent silt/clay and percent volatile solids did not vary significantly between months (Kruskal- Wallis, P > 0.05). Mean percent silt/clay ranged from 7.2% in July 1994 to 10.0% in April 1995, and mean percent volatile solids ranged from 0.8% in January and April 1995 to 1.3% in July 1994 (Table 6). At stations along the 15-m transect in the beach nourishment area, percent silt/clay and percent volatile solids were significantly lower (Kruskal-Wallis, P < 0.05) than at stations along the 30-m transect. Mean median grain size was lower in the undisturbed area outside of the beach nourishment area compared to the beach nourishment area (Table 6). No statistical analysis was performed because only two stations were sampled in the undisturbed area. With the exception of July 1994, mean percent silt/clay values in the undisturbed area outside of the beach area were lower than mean values in the beach nourishment area. Mean percent volatile solids were 2.0% or less for both the undisturbed area and the beach nourishment area (Table 6).
Beach Nourishment Area W-40.9
Benthic Invertebrates

At Beach Nourishment Area W-40.9, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) (Table 7); the lowest mean density occurred in July 1994 (9,635 organisms/m2) and the highest in January 1995 (25,426 organisms/m2) (Table 8). Benthic invertebrate densities were significantly different between the 15-m and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transect (Tables 7 and 8).

The mean numbers of taxa/categories collected in the beach nourishment area were similar for each month, ranging from six to seven (Table 9). Major benthic invertebrate taxa collected in the beach nourishment area included nemerteans, oligochaetes, Corbicula fluminea, and Corophium salmonis (Table 10). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area W-40.9; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect compared to stations along the 15-m transect (Tables 7 and 10). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 143 organisms/m2 in July 1994 to 9,879 organisms/m2 in January 1995. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 10,050 organisms/m2 in July 1994 to 30,609 organisms/m2 in January 1995 (Table 10). Densities of Corophium spp. also varied spatially along each transect (Fig. 3).

Diversity (H) and Equitability (E) were not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area W-40.9 (Table 7). Mean H values ranged from 1.31 in January 1995 to 1.72 in October 1994, and mean E values ranged from 0.58 in January 1995 to 0.76 in July 1994 (Table 9). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area W-40.9; however, it was significantly higher (P < 0.05) at stations along the 15-m transect (mean = 0.37 mm) compared to stations along the 30-m transect (mean = 0.32 mm) (Table 11). Mean median grain size in the beach nourishment area ranged from 0.33 mm in January 1995 to 0.36 mm in October 1994. Percent silt/clay was not significantly different between months (Kruskal-Wallis, P > 0.05), but it was significantly lower at stations along the 15-m transect (Kruskal-Wallis, P < 0.05) than at stations along the 30-m transect. Mean percent silt/clay ranged from 0.8% in July 1994 to 2.8% in April 1995 (Table 11). Percent volatile solids were significantly different between months (Kruskal-Wallis, P < 0.05), but not significantly different between 15-m and 30-m transects (Kruskal-Wallis, P > 0.05). Mean percent volatile solids ranged from 0.4% in January 1995 to 0.8% in October 1994 (Table 11).
Beach Nourishment Area W-43.8
Benthic Invertebrates

At Beach Nourishment Area W-43.8, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) (Table 12); the lowest mean density occurred in July 1994 (3,060 organisms/m2) and the highest in January 1995 (27,273 organisms/m2) (Table 13). Benthic invertebrate densities were significantly different between the 15-m and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transect (Tables 12 and 13).

The mean numbers of taxa/categories collected in the beach nourishment area were similar for each month, ranging from six to seven (Table 14). Major benthic invertebrate taxa collected in the beach nourishment area included nemerteans, oligochaetes, Corbicula fluminea, Corophium salmonis, and Ceratopogonidae larvae (Table 15). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area W-43.8; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect compared to stations along the 15-m transect (Tables 12 and 15). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 154 organisms/m2 in July 1994 to 23,772 organisms/m2 in January 1995. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 988 organisms/m2 in July 1994 to 28,390 organisms/m2 in April 1995 (Table 15). Densities of Corophium spp. also varied spatially along each transect (Fig. 4).

Diversity (H) and Equitability (E) were significantly different (ANOVA, P < 0.05) between months, but not between transects in Beach Nourishment Area W-43.8 (Table 12). Mean H values ranged from 1.03 in January 1995 to 2.09 in July 1994, and mean E values ranged from 0.43 in January 1995 to 0.80 in July 1994 (Table 14). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area W-43.8. Mean median grain size in the beach nourishment area ranged from 0.39 mm in July and October 1994 to 0.41 mm in January 1995 (Table 16). Percent silt/clay was not significantly different between months (Kruskal-Wallis, P > 0.05), but was significantly lower at stations along the 15-m transect (Kruskal-Wallis, P < 0.05) than at stations along the 30-m transect. Mean percent silt/clay ranged from 0.4% in January and April 1995 to 1.6% in October 1994 (Table 16). Percent volatile solids were significantly different between months (Kruskal-Wallis, P < 0.05), but not significantly different between 15-m and 30-m transects (Kruskal-Wallis, P > 0.05). Mean percent volatile solids ranged from 0.3% in January 1995 to 1.1% in July 1994 (Table 16).
Beach Nourishment Area O-44.0
Benthic Invertebrates

At Beach Nourishment Area O-44.0, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) (Table 17); the lowest mean density occurred in October 1994 (2,802 organisms/m2) and the highest in January 1995 (6,826 organisms/m2) (Table 18). Benthic invertebrate densities were significantly different between the 15-m and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transect (Tables 17 and 18).

The mean number of taxa/categories collected in the beach nourishment area in each month was four (Table 19). Major benthic invertebrate taxa collected in the beach nourishment area included oligochaetes, Corbicula fluminea, and Corophium salmonis (Table 20). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-44.0; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect (Tables 17 and 20). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 10 organisms/m2 in October 1994 to 95 organisms/m2 in January and April 1995. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 2,358 organisms/m2 in October 1994 to 9,536 organisms/m2 in January 1995 (Table 20). Densities of Corophium spp. also varied spatially along each transect (Fig. 5).

Diversity (H) and Equitability (E) were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area O-44.0 (Table 17). Mean H values ranged from 1.14 in April 1995 to 1.39 in January 1995, and mean E values ranged from 0.56 in April 1995 to 0.73 in January 1995 (Table 19). Diversity was significantly higher (ANOVA, P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect; however, E was not significantly different between transects. 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months or transects in Beach Nourishment Area O-44.0. Mean median grain size in the beach nourishment area ranged from 0.37 mm in October 1994 to 0.40 mm in January 1995 (Table 21). Percent silt/clay was not significantly different between months or transects (Kruskal-Wallis, P > 0.05). Mean percent silt/clay ranged from 1.3% in July 1994 and April 1995 to 3.4% in October 1994 (Table 21). Percent volatile solids were significantly different between months (Kruskal-Wallis, P < 0.05), but not significantly different between 15-m and 30-m transects (Kruskal-Wallis, P > 0.05). Mean percent volatile solids ranged from 0.4% in January 1995 to 0.6% in July and October 1994 (Table 21).
Beach Nourishment Area W-45.0
Benthic Invertebrates

At Beach Nourishment Area W-45.0, benthic invertebrate densities (total) were not significantly different between months (ANOVA, P > 0.05) (Table 22); the lowest mean density occurred in October 1994 (8,083 organisms/m2) and the highest in January 1995 (15,884 organisms/m2) (Table 23). Benthic invertebrate densities were significantly different between the 15-m and 30-m transects (P < 0.05), with the highest densities generally occurring at stations along the 30-m transects (Tables 22 and 23).

The mean numbers of taxa/categories collected in the beach nourishment area were similar for each month, ranging from six to eight (Table 24). Major benthic invertebrate taxa collected in the beach nourishment area included nemerteans, oligochaetes, Fluminicola virens, Corbicula fluminea, and Corophium salmonis (Table 25). 

Densities of Corophium spp. were not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area W-45.0; however, densities were significantly higher (P < 0.05) at stations along the 30-m transect than at stations along the 15-m transect (Tables 22 and 25). Mean densities of Corophium spp. at stations along the 15-m transect ranged from 245 organisms/m2 in January 1995 to 2,285 organisms/m2 in April 1995. At stations along the 30-m transect, mean densities of Corophium spp. ranged from 4,945 organisms/m2 in July 1994 to 23,347 organism/m2 in January 1995 (Table 25). Densities of Corophium spp. also varied spatially along each transect (Fig. 6).

Diversity (H) was significantly different (ANOVA, P < 0.05) between months, but not significantly different (ANOVA, P > 0.05) between transects in Beach Nourishment Area W-45.0 (Table 22). Mean H values ranged from 1.28 in January 1995 to 2.15 in July 1994 (Table 24). Equitability (E) was not significantly different (ANOVA, P > 0.05) between months or transects (Table 22). Mean E values ranged from 0.53 in January 1995 to 0.78 in July 1994 (Table 24). 

SedimentsMedian grain size was not significantly different (ANOVA, P > 0.05) between months in Beach Nourishment Area W-45.0; however, it was significantly higher (P < 0.05) at stations along the 15-m transect (mean = 0.40 mm) than at stations along the 30-m transect (mean = 0.29 mm) (Table 26). The high outlying value for Station 5 in July 1994 was excluded from the statistical analysis. Mean median grain size in the beach nourishment area ranged from 0.32 mm in April 1995 to 1.94 mm (or 0.35 mm if the outlying value is excluded) in July 1994 (Table 26). Percent silt/clay was not significantly different between months (Kruskal-Wallis, P > 0.05), but it was significantly lower at stations along the 15-m transect (Kruskal-Wallis, P < 0.05) than at stations along the 30-m transect. Mean percent silt/clay ranged from 5.4% in January 1995 to 10.0% in July 1994 (Table 26). Percent volatile solids were not significantly different between months (Kruskal- Wallis, P > 0.05), but they were significantly different between transects (Kruskal-Wallis, P < 0.05). Mean percent volatile solids ranged from 0.6% in October 1994 and January 1995 to 1.7% in July 1994 (Table 26).
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