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<br />Iq95 wol~ <br /> <br />Great Basin Naturalist 55(3), @ 1995, pp, 213-224 <br /> <br />78 L./t5 <br /> <br /> <br />SOFT SEDIMENT BENTHIC MACRO INVERTEBRATE COMMUNITIES <br />OF THE GREEN RIVER AT THE OURAY NATIONAL WILDLIFE <br />REFUGE, UINTAH COUNTY, UTAH <br /> <br />.t Eric R. Wolzl and Dennis K. Shiozawa2,3 <br /> <br />ABSTRACT.-Benthic macroinvertebrates from four habitat types (river channel, ephemeral side channel, river back- <br />-~ water, and seasonally inundated wetland) were examined from the Green River at the Ouray National Wildlife Refuge, <br />Uintah County, UT, June-August 1991. Four major taxa (Nematoda, Oligo chaeta, Diptera: Ceratopogonidae, and <br />Chironomidae) were quantified. Cluster analysis of densities showed that habitat types with comparable flow conditions <br />were the most similar. Highest to lowest overall benthic invertebrate densities of the four habitats were as follows: <br />ephemeral side channel, river backwater, seasonally inundated wetland, and river channel. Nematodes were the most <br />abundant taxon in all habitat types and sample dates except the August sample of the river channel and river backwater <br />and the July sample of the seasonally inundated wetland, <br /> <br />Key words: benthic macroinvertebrates, Nematoda, Oligochoota, Ceratopogonidae, Chirorwmidae, river benthos, wetland, <br />benthos, Green River. <br /> <br />. <br />. ~ <br /> <br />In 1962 Flaming Gorge Dam was completed <br />on the Green River in northeastern Utah. This, <br />in addition to dikes constructed along the river's <br />course and the introduction of nonnative fishes, <br />has altered natural conditions such that many <br />native fishes have reached the brink of extinc- <br />tion and are now listed as endangered species. <br />Grabowski and Hiebert (1989) studied the <br />Green River below Flaming Gorge Dam and <br />noted the importance of backwaters as nursery <br />habitats to introduced and native fishes. They <br />found the most important food items to be ben- <br />thic macroiI;lvertebrates, predominantly chiro- <br />nomid larva~. Their investigation was confined <br />to two habitats: the main channel and river <br />backwaters.'We also studied benthic commu- <br />nities of the river channel and backwater habi- <br />tats and two additional habitats-seasonally <br />inundated wetlands and ephemeral side chan- <br />nels, No published information exists about <br />the commu~ity structure of benthic macro- <br />invertebrates in these latter two habitat types. <br />Benthic jnvertebrates of large rivers are <br />poorly known. Difficulty in sampling, the <br />amount of time needed to process samples, <br />identification of specimens after collection, <br />and heterogeneity of habitats make study diffi- <br />cult and often expensive, Studies of riverine <br />systems have utilized divergent methodologies. <br /> <br />. <br />. <br /> <br />lChadwick & Associates, Inc., Littleton, CO 80120. <br />2Department of Zoology, Brigham Young University, Provo, UT 84602 USA. <br />3Author to whom correspondence should be addressed. <br /> <br />Some studies randomly sample an entire river <br />cross section and do not attempt to quantifY dif- <br />ferent river habitat types (Grzybkowska 1989, <br />Grzybkowska et al. 1990, Munn and, Brusven <br />1991), Other studies have been directed toward <br />specific river habitats such as riffles (Rader <br />and Ward 1988, Morgan et al. 1991), floodplains <br />(Gladden and Smock 1990), or tailwaters of re- <br />servoirs (SWink and Novotny 1985). Relatively <br />few have simultaneously studied multiple <br />habitat types in a single river system (Beckett <br />et al. 1983, Grabowski and Hiebert 1989). <br />Our purpose was to determine densities <br />and community assemblages of the major ben- <br />thic macroinvertebrates in four Green River <br />habitats: river channel, ephemeral side channel, <br />river backwater, and seasonally inundated wet- <br />land. Benthic samples were taken from June <br />through August 1991, in the Green River at the <br />Ouray National Wildlife Refuge, Uintah County, <br />UT, USA. <br /> <br />STUDY SITES <br /> <br />The Green River originates in Wyoming and <br />flows south through eastern Utah to its conflu- <br />ence with the Colorado River (Fig. 1). It adds <br />more volume to the Colorado River system than <br />any other tributary. In eastern Utah, at river km <br />404, the Green River enters the Ouray National <br /> <br />213 <br />