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<br />Table 4. Range of the mean number of chironomids from investigations of
<br />various habitats in the Upper Colorado River Basin. 1/ l/
<br />
<br />Habitat Range of the mean number of organisms/m2
<br />
<br />Main Channel
<br />
<br />20
<br />
<br />4,150
<br />31,125
<br />
<br />Backwaters
<br />
<br />83
<br />
<br />Floodplain Habitats
<br />
<br />o
<br />
<br />23,055
<br />
<br />1/ The mean number of chironomids were obtained from the following studies:
<br />Grabowski and Hiebert (1989); Cooper and Severn (1994a), b, c, d, and e;
<br />Wolz and Schiozawa (1995). The main channel, backwaters, and floodplain
<br />habitats contained primarily sand and silt at the sites sampled so
<br />chironomids were used as a measure of relative abundance of benthic
<br />macroinvertebrates. The number of samples taken, sampling gear used,
<br />seasons (late spring and summer) and years of sampling differed so ranges
<br />are used to illustrate the relative productivity of chironomids.
<br />
<br />l/ Most (4) of the investigations were made on the Green River. However the
<br />data include two investigations on the Colorado River and one
<br />investigation on the Gunnison River, a major tributary of the Colorado.
<br />
<br />##########
<br />
<br />productive in chironomid production than the main channel. Another study
<br />evaluated macroinvertebrate densities in the main channel, side
<br />(ephemeral) channel, and two types of backwater habitats in the middle
<br />Green River, downstream of Vernal, Utah. The numbers of chironomids in
<br />the main channel ranged between 3,500 and 4,200 organismsfm2, the range
<br />for the side (ephemeral) channel was between 2,300 and 8,100, in one large
<br />backwater (basically a riverside lagoon) the range of chironomids was
<br />between 9,000 and 23,000, and in the other backwater, the range was
<br />between 22,800 and 31,100 organisms/m2 (Appendix 2; Wolz and Shiozawa
<br />1995). Four baseline studies were conducted of wetland habitat sites in
<br />bottomlands of rivers in the Upper Basin. The wetland at Escalante Ranch
<br />along the middle Green River, upstream from Jensen, Utah, produced a mean
<br />of 17 chironomids/m2 in the main channel, 17 organisms/m2 in a backwater,
<br />and 31 organisms/m2 for an open water wetland (Appendix 2; Cooper and
<br />Severn 1994b). At another wetland site, Cooper and Severn (1994a)
<br />reported a mean of 11 chironomids/m2 in the main channel of the Colorado
<br />River immediately upstream from Moab, Utah, 4 in a backwater site and 11
<br />in an open water wetland. The Gunnison River at the Escalante State
<br />Wildlife Area, about five miles downstream from Delta, Colorado, contained
<br />a mean of about 496 chironomids/m2, a backwater contained 1,141 and an
<br />open water wetland contained 1,092 (Appendix 2; Cooper and Severn 1994c).
<br />The mean number of benthic chironomids/m2 in a floodplain depression (Old
<br />Charley Wash) was 33, 21 in a backwater, and 10 from the channel of the
<br />middle Green River adjacent to the floodplain on the Ouray National
<br />Wildlife Refuge, Utah (Cooper and Severn 1994d) .
<br />
<br />The mean number of aquatic organisms (combined species) collected in five
<br />1.85 cm bottom cores from backwaters in the lower Green River varied
<br />between 65,200 and 562,200 organisms/m2, depending upon the site and date
<br />of collection (Nance 1997).
<br />
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