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19951 MACROINVERTEBRATES OF THE GREEN RIVER 219 the August river channel and river backwater habitats and the July wetland sample. Oligochaetes were present in all habitat types and on all sample dates. Densities ranged from a low of 2728/m2 in the June ephemeral side channel sample to a high of 164,7311m2 in the July river backwater sample (Tables 2-5), The lowest abundance of Ceratopogonids was observed in the July river backwater sam- ple (961m2). Their density was 136X greater in the river channel August sample (13,026/m2; Tables 2-5). Ceratopogonids were absent from both June and July samples of the seasonally inundated wetland and the ephemeral side channel. Ninteen chironomid genera were collected during this study. Fourteen genera were found in the July seasonally inundated wetland sam- ples, and five genera occurred in the August river channel and river backwater samples. Seven genera occurred in only one habitat or on only one date. Six genera were found in the seasonally inundated wetland habitat only, and four occurred only in the river channel. No chi- ronomid genus was unique to the ephemeral side channel or the river backwater. The genus Polypedilum was collected in all habitat types and on all sample dates. Total chironomid densi- ties were least (903/m2) in the June sample of the seasonally inundated wetland and greatest (31,125/m2) in the July river backwater sample (Tables 2-5). Unidentifiable early instars were collected in all habitat types and in all sample periods and comprised 86% of the river chan- nel sample in August. The most common nmc- tional group category of the Green River chi- ronomids was collectors followed by predators and shredders. Specific functional group and Green River habitat association for each genus are presented in Table 6. Other insects found in the samples are list- ed in Table 7. Density estimates would not be valid for these taxa because of their ability to avoid the core sampler. Cluster Analysis The UPGMA cluster analysis of the benthic invertebrate communities in each habitat type and sample date indicated that sites with similar flow conditions tended to cluster together (Fig. 3). A matrix comparison of original distances calculated using the Bray-Curtis coefficient with distances implied from the dendrogram is presented in Figure 4. Correlation between the two was high (R = .907), implying that the dendrogram is an accurate representation of TABLE 7, Other insects encountered iu the Green River ecosystem, June-August 1991. River Ephemeral River Seasonally inundated channel side channel backwater wetland Taxon July August June July July August June July August Coleoptera Hydrophilidae (larvae) X Diptera Chironomidae (pupae) X X X X X Empididae (larvae) X X Simuliidae (larvae) X . Ephemeroptera Baetidae Baetis (nymph) X X X X X Callibaetis (nymph) X t Caenidae Caenis (nymph) X X X Tricorythidae Tricorythodes(nymph) X Hemiptera Corixidae X X X Odonata Coenagrionidae Ischnura (nymph) X X Gomphidae (nymph) X Plecoptera Perlodidae (nymph) Isoperla X