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relative abundance (or 16.8 organisms/ft..2), 14.6 relative abundance (or \ <br />50.5 organisms/ft.2) and 11.6X relative abundance (or 34.5 organisms/ft.2) • J <br />at stations 1, 2 and 3 respectively. <br />The third most abundant major group of aquatic macroinvertebrates <br />found is the samples was Diptera (true flies). This group represented <br />33.7X, 33.1X, and 39.2X of the mean total density at stations 1, 2 and 3, <br />respectively. Of the six dipteraa families, midges (or family Chironomidae) <br />were the most abundant group. <br />Total mean densities at stations 1, 2, and 3 were 124.0, 346.2 and <br />298.7, respectively. Although subjective observations of the mean <br />densities suggested that the macroinvertebrate densities were drastically <br />different, statistical comparisons exhibited few significant values. <br />Overall densities (mean numbers of total organisms/ft2) at each <br />station were compared using Student's "t". Of the three comparisons, <br />only stations 1 and 2 exhibited significantly different densities (p< <br />0.025). Differences between stations 1 and 3 or 2 and 3 were not signifi- <br />cant at either the SX or lOX levels, respectively. From the data it is <br />apparent that although the number and kinds of taxa varied very Little <br />between stations the total mean densities were noticeably different. <br />Chemical and physical parameters measured and/or observed at the <br />stations are summarized in Table 5. The stations appeared to be similar <br />in most chemical and yhysical characteristics. The only exception was <br />that the substrate at Station 1 was comprised of Saud and gravel, while <br />stations 2 and 3 contained much less sand. Additional chemical/physical <br />measurements taken in 1976-1977 by U.S. Geological Survey (1977) are <br />shown is Table 6. Based on these measurements, the lower Dort ion of the <br />Williams Fork River appears to exhibit relatively good water Quality <br />conditions. <br />6 <br />