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1995] MACROINVERTEBRATES OF THE GREEN RIVER 221 1.00 0.75 V o B '" is "t:l50 B o :a J: 0.25 . . . . 0.00 0.00 . ... ...... . . ... . . . 0.25 0.75 1.00 0.50 Original Distance Fig, 4, Comparison of original dissimilarity matrix and implied matrix from the dendrogram. c. organic matter found in the sediment are pri- mary factors determining which species will be present in a particular area (Brinkhurst and Cook 1974). We identified our specimens only to class level. Oligochaete densities in nonpol- luted lakes are lower than those in organically polluted waters. Densities in Mirror Lake ranged trom 30,000 to 33,000/m2 (Strayer 1985), Jonasson and Thorhauge (1976) reported oligo- chaete densities in Lake Esrom, Denmark, of 6000-12,000/m2, Brinkhurst and Cook (1974) found that densities of the three most common tubificids in the more polluted areas of Toronto Harbor ranged from 51,000 to 197,000/m2. Oligochaete densities in nonpolluted lotic sys- tems tend to be lower, Grzybkowska and Witczak (1990) report oligochaete densities in the lower Grabia River, Poland, ranging trom llO to 900/m2, and Palmer (1990) reports den- sities from 5000 to 15,000/m2 in Goose Creek, VA. Densities from polluted lotic systems can approach 200,000/m2 (Koehn and Frank 1980). Oligochaete densities in the seasonally in- undated wetland June sample (87,l50/m2) and river backwater August sample (164,73l!m2) are comparable to values observed in polluted systems described above. Densities from both ephemeral side channel samples (2728 m2 and 12,796/m2) and both river channel samples (3426/m2 and ll,182/m2) are comparable to those in Goose Creek (Palmer 1990), In general, t oligochaete densities in our study were higher in habitats with the least amount of water flow (seasonally inundated wetland and river back- water habitat types). Terrestrial vegetation invades wetlands during dry periods, and when the water returns the following spring, decaying vegetation forms a rich food base. Backwater habitats retain fine particles, including detri- tus, being transported by the river; as summer progresses, this creates an enriched food base, These factors are the likely reason for the con- vergence oligochaete densities in these two hab- itats with those in organically polluted systems. Ceratopogonidae The study of ceratopogonids has mainly centered on adults because of their economic importance (Davies and Walker 1974). Larvae inhabit a variety of habitats including tree holes, leafpacks, and pitcher plants, but are usu- ally most numerous in shallow areas of streams, lakes, and ponds (Bowen 1983). Aquatic forms are mostly predaceous (Merritt and Cummins 1984), but several species are mown to consume algae and plant debris (Kwan and Morrison 1974). Corkum (1990) investigated streams associ- ated with different land-use types in south- western Ontario and found densities of 501m2 in "forested" sites, 480/m2 in "mixed" sites, and 5300/m2 in "farmland" sites. Adamek and Sukop (1992) found maximum densities of only