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Mid-Continent Resources'Stream Impairment Study 8 <br /> Results for the H}alella exposures are summarized in Table 3. Raw test data are provided <br /> in Appendix 3. The sediments ranged from sand to rich organic material with indigenous species <br /> present. Sites 4 through 7 were characterized as sandy and dense. Site 1 and the laboratory control <br /> were primarily sand. Sites 2 and 3 were black with a mixture of organic matter and fine sediment. <br /> There was a slight shift from sand to clay in sites 4 through 7 during the low flow period. <br /> Site 1, the field control on Dutch Creek was used as the reference control in calculations due <br /> to unsatisfactory results from the laboratory control (Site 8). It is felt that low survivorship and <br /> weights in this sediment were due to an artificial substrate not conducive to amphipod survival. <br /> During the high flow period, Site 2, 3, 5, and 7 showed statistically significant differences in <br /> survival and growth when compared to the control samples. Sites 2, 3, remained toxic during the low <br /> flow period. In addition, sediments from Sites 4, 6, and 7 produced a toxic response which resulted <br /> in statistically higher mortalities than in the control sediments. Acute effects were most evident in <br /> the spring. Growth effects were the most obvious in the fall sediments. <br /> BenlliicMacroitwerlebrates. Macroinvertebrate data are summarized in Table 4 with all data <br /> presented in Appendix 4. Overall, the highest numbers of animals were collected in the spring due <br /> mostly to large numbers of Chironomids at Stations 2 and 3. Animal numbers were comparatively <br /> smaller and relatively similar during the two periods at the other stations. <br /> The high dominance of the chironomids at Stations 2 and 3 ranged from 65-96% of the total <br /> population. By comparison, chironomids made up only 15-48% of the population at the other <br /> stations. The lowest numbers were in the control stations. This dominance at Stations 2 and 3 was <br /> reflected in low diversity indices. With the exception of Stations 2 and 3, the Shannon-Weaver <br /> diversity was similar at all of the stations and remained consistent between the two sampling periods. <br /> The numbers of EPT taxa were highest at Stations 1, 6, and 7 during both periods. Shredders <br /> and animals expected to feed on plant matter increased with lower elevation during the spring. This <br /> may reflect environmental conditions which delay algal growth at higher elevations due to <br /> temperatures and/or nutrient levels. Effects of ice scouring at higher elevations may also account for <br /> this observation. <br /> When the BCI was compared, Stations 2, 3, and 4 showed the lowest biological potential <br /> during both periods. During high flow periods, the remaining stations appeared to be relatively close <br /> to reaching their full potential. During the fall, only stations 1 and 6 were at the highest levels with <br /> Stations 5 and 7 at slightly lower levels. <br /> The SeaCrest Group <br />