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found that nematode densities were greater in silt than in sand. In our study, the highest <br />densities are associated with a low sand content in the substrata. Low densities reported <br />in the June sample of the seasonally inundated wetland may be due to the relatively short <br />time that water had been on the sample site. Of the four major invertebrate groups <br />collected in this study, nematodes accounted for 8% of the invertebrates (by density) in <br />the river channel August sample and ranged to 98 % in the ephemeral side channel June <br />sample with an overall mean of 59%. For the same groups, Palmer (1990), using a <br />3.3cm dia. core and 44-µm mesh, reported that nematodes comprised only 4 - 15 % with <br />a mean of 9%. The high nematode densities and their high percent of total invertebrates <br />that we report may merit further investigation. <br />Oligochaeta <br />Fresh water oligochaetes are a well studied and diverse group of aquatic annelids <br />that are found in every type of estuarine and freshwater habitat. The most common <br />families encountered are Lumbriculidae, Naididae, Tubificidae (Brinkhurst and Gelder <br />1991). They feed mostly on the bacteria found in soft sediments. The amount and <br />quality of organic matter found in the sediment are the primary factors determining which <br />species will be present in a particular area (Brinkhurst and Cook 1974). Since we only <br />identified our specimens to phylum level, the ecology of oligochaetes in the Green river <br />cannot be discussed. Therefore, our discussion will only concern densities. Oligochaete <br />densities in non-polluted lakes are lower than those where pollution is high. Densities <br />in Mirror Lake ranged from 30,000 to 33,000le in Strayers (1985) study of Mirror <br />Lake and Jonasson and Thorhauge (1976) reported oligochaete densities from Lake <br />14