Because of the temporal and spatial variation in materials 

 deposited and subsequent temporal changes at the mound apex from 

 erosion, it was more appropriate to group samples by sediment type 

 for comparison rather than by station location alone. For most 

 historical surveys there was at least some grain size and sediment 

 contaminant data. Some of these data have been published; the 

 large amount of data collected by the EPA as part of "Operation 

 Dumptrack" is available only as a paper printout. 



Although a variety of sampling plans was used in the 

 different studies (Figures 4-2 and 4-3) , the site center, edges, 

 and a reference site on fine sand east of the disposal mound were 

 sampled on each occasion. Some of the characteristics of the 

 invertebrate assemblages at the center and reference site are 

 summarized in Table 4-1 and reviewed below. 



Number of individuals ; At the site center a small number 

 of individuals were found during active disposal operations. 

 Numbers rose to around 300 per 0.1 m 2 during the first year of 

 recovery and remained at these levels through 1975. Numbers at the 

 reference station were about five times higher, but more than half 

 of the individuals represented were Ampelisca aqassizi . 



In 1987, the lowest density of individuals was 598 on 

 sandy substratum. Full recovery in numbers had occurred on dredged 

 material on the edges of the disposal site by 1987. 



Number of species : At the site center, the number of 

 species was 26 per sample after one year of recovery. This high 

 diversity (relative to the small number of individuals present) was 

 due to the heterogeneity of sediment texture, resulting in a 

 mixture of species normally found on a number of different 

 substratum types. Mean species number was higher at the reference 

 station where the subdominants of the Ampelisca community make up 

 a stable, possibly biologically-accommodated assemblage. Most of 

 the increase in species numbers from the 1987 samples was due to 

 improved taxonomy rather than the use of a smaller sieve size. 

 With the exception of one coarse sand sample (Station 7) , there was 

 no difference between the number of species in samples from center, 

 edge, and reference areas in 1987. 



Ampeliscid density : In each survey, dense populations of 

 Ampelisca aqassizi (amphipod crustacean) were found adjacent to the 

 disposal site. While shallow water Ampelisca species are subject 

 to large fluctuations in density, A^ aqassizi remains dominant over 

 wide areas through replacement of the adult population once a year. 

 Small scale variation in density within beds (observed by divers) 

 as well as predator foraging can be invoked to explain the high 

 variance seen in Table 4-1. 



A. aqassizi had not recolonized the center or edges of 

 the disposal site by 1975; it was not altogether surprising that 



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