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iJ'J0018 Photo Plate 8 The sedimentllt,ion of coarse-bedded streams often reduces fish food production drastically. 'Por example, comparing the top left and top right photos, the extra sedimentation has reduced productivity by 75%. The sediment eliminates the habitat that would ordinarily be used by animals like aquatic insects. The middle photo shows a 95% drop in productivity because sand and fine gravel have replaced the existing plant beds. The bottom photo shows a similar loss where sands and fine gravels buried the original moss covered rocks. Macroinvertebrates Stream Health monitoring frequently includes the aquatic macroinvertebrate community for measures of diversity and productivity. Macroinvertebrates are valuable because many species are sensitive to pollution and respond quickly to it. Bottom fauna tend to have complex life cycles and die off if conditions are outside tolerance limits; many species have an attached or , sessi le form and cannot migrate to avoid the stress. For example, small, changes in water temperature, oxygen levels, dissolved metals, industrial solvents, organic poisons, nutrients, and other dissolved materials often kill off the more sensitive species. Certain 'insect groups, including mayflies, stoneflies, and caddisflies, need clean water conditions and can be used as indicators to help assess water pollution. Unfortunately, the laboratory analysis of macroinvertebrates for diversity and productivity is both time consuming and expensive. A way to avoid the expense is to use Tarzwell Substrate Ratios. This method provides a fairly simple way to indirectly measure productivity by visually matching substrate conditions with a list of previously defined categories. The change in productivity is then inferred by the change from one kind of substrate to another. The key is that sedimentation fills in the nooks and crannies used by macroinvertebrates. For chemical impacts, and for advance warning purposes, the aquatic forms of mayflies, stoneflies, and caddisflies make good indicators because they are generally sensitive to chemical and organic pollution. Some common families of the most sensitive groups also live on the more exposed rocks in the faster part of the stream. By picking a few fist-sized rocks from these fast water habitats and checking for these groups, we can quickly decide if chemistry is likely to be a problem or not. There is no intent here to replace detailed macroinvertebrate studies with this simple technique, but there are times when such a screen is both appropriate and cost effective. Yhat makes this technique work is that mayfly and stonefly nymphs and many caddisfly larva (with characteristic cases) are easy to identify with a simple hand lens. The drawings on Page 11 provide some keys for identification. Text Page 8 :~ ;e