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DISCUSSION AND CONCLUSIONS <br />Macroinvertebrate counts exhibited generally high variability. The high standard deviations of <br />mean macro invertebrate counts could be due to several factors, including variable distribution <br />of insects on the stream bottom, sampling method, and bottom condition during the week(s) <br />prior to sampling. Distribution and density of aquatic insects in the substrate is strongly related <br />to the condition of the stream bottom, and particularly to the particle size of the sediments. A <br />stream bottom covered with cobbles should provide excellent habitat if adequate food is <br />present and water quality is acceptable. This is because the spaces between the rocks is large <br />enough to afford free movement of insects, yet provide protection from the current. As the <br />size of rocks increases toward boulder size, surface area decreases, and suitable space <br />affording protection from current and predators diminishes. Likewise, as the stream sediment <br />size decreases toward gravel - and sand -sized particles, there is less interstitial space for aquatic <br />insects. <br />When samples were collected, it was apparent that some replicates had large numbers of <br />insects, while other replicates collected a short distance away had noticeably smaller numbers. <br />We attempted to sample within cobble areas, but even so, this did not always produce <br />consistent numbers of insects collected. Theoretically, given the predominance of bcalders in <br />the substrate, it would have been desirable to use a larger diameter sampler barrel so that it <br />wouldn't have been so necessary to pick and choose a spot between the boulders to sample, <br />although this would have forced the person collecting the samples to deal with large rocks that <br />would have been difficult to handle. The size of our sampler undoubtedly introduced a bias <br />toward sampling insect populations living in the cobbles. It is difficult to assess the effect that <br />sampling even a slightly larger or smaller rock size (within the cobble - small boulder range) <br />would have on insect density. <br />A certain "patchiness" of insect populations may occur for reasons not apparently associated <br />with substrate size. Such factors may include depth, current velocity, and other environmental <br />causes. The March samples were collected a week or so after water levels began to rise at the <br />beginning of spring runoff. Some locations in the river bottom produced no insects, and we <br />concluded that such places might have been dry during the winter. In these instances, we <br />moved our replicate sample spots to deeper places in the channel where we did collect insects, <br />but some of the variability in the March samples might be due to this seasonal effect. At some <br />places in August, both upstream and downstream of the discharge, we noticed that boulders <br />along the stream bank were covered with Trichopteran cases near the water's edge. In other <br />places the cases were rare, and it was not obvious what the reasons for the decrease in density <br />were. <br />In general, macroinvertebrate numbers were moderately high. Chironomids and Trichopterans <br />were the two groups that had the highest densities and seemed to show the most apparent <br />differences in density between locations upstream and downstream of the discharge. These two <br />groups also had the greatest effect on the EPT /C ratios. Because Chironomids are more <br />20 <br />