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<br />Great Basin Naturalist 55(3), @ 1995, pp, 213-224
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<br />78 L./t5
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<br />SOFT SEDIMENT BENTHIC MACRO INVERTEBRATE COMMUNITIES
<br />OF THE GREEN RIVER AT THE OURAY NATIONAL WILDLIFE
<br />REFUGE, UINTAH COUNTY, UTAH
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<br />.t Eric R. Wolzl and Dennis K. Shiozawa2,3
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<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,
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<br />Key words: benthic macroinvertebrates, Nematoda, Oligochoota, Ceratopogonidae, Chirorwmidae, river benthos, wetland,
<br />benthos, Green River.
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<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.
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<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.
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<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.
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<br />STUDY SITES
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<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
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