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Three mayfly genera were dominant or subdominant throughout the ~~ <br />survey; Rithrogena sp. (family Heptageniidae), Ephemerella sp. (family <br />Ephemerellidae), and Baetis sp. (family Baetidae). All three genera are <br />collectors-gatherers and scrapers of detritus and diatoms, while some <br />Ephemerella species are also herbivores which eat filamentous algae (Edmunds <br />1978). <br />RithroReaa sp, was dominant at Stations 1 and 2, while Baetis sp. <br />was subdominant at Stations 1 and 3 in March. Ephemerella sp. was the <br />most abundant organism collected at Station 1 in June and was second is <br />abundance at Station 3. <br />True flies comprised approximately 16 percent of the total organisms <br />collected during this survey and were the third most dominant group. <br />The highest mean relative abundance for flies was approximately 29 percent <br />in June, while the lowest mean relative abundance, 10 percent, occurred <br />is September. Fly densities varied from a high of approximately <br />158 organisms/ft2 in March to a low of approximately 15 organisms/ft2 <br />in June. Flies were present at all three stations. _ <br />The dominant fly larvae belonged to the family Chironomidae, which •~ <br />ate commonly known as midges. The midge, Cricotopus sp., is a collector- <br />gatherer and shredder-herbivore of detritus and algae (Coffman 1978). <br />The only time that Cricotopus sp. was dominant was in March. This <br />midge was the most abundant organism at Station 3 and was subdominant at <br />Station 2. <br />Ia general, species diversity values were highest in November and <br />lowest in Juae. Mean species diversity values ranged between 2.5 <br />(Station 3, June) and 3.5 (Station 2, March; Station 3, November). The <br />mean value for the entire year was 2.95. According to Wilhm and <br />Dorris (1968), values from 1 to 3 indicate moderate pollution; values <br />above 3 indicate clean water areas. The year's mean species diversity <br />of 2.95 suggests that this stretch of the Williams Fork River represents <br />a favorable environment for macroinvertebrates. <br />The macroinvertebrates collected throughout this study were almost <br />entirely taxa that are intolerant or facultatively tolerant of organic <br />pollution. Composition, moderately high densities, and diversities ~~ <br />indicate a stream of moderate to good quality for macroinvertebrate <br />life. <br />8 <br />