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<br />.~ ''II':: ._, <br />Iu...;: <br /> <br />I <br /> <br />On the whole there appeared to be abundant ni trogen and phosphorus, <br />as well as other nutrients available for algal growth. However, with <br />the exception of the sample collected at Masters during October, the <br />addition of nutrient to the water stimulated algal growth. The sample <br />that showed no additional growth when more nutrient was added would <br />indicate that luxury amounts of nutrient were available. This is what <br />had been expected from all samples prior to performing the algal assays. <br />However, the results of the assays would indicate that nutrients could <br />be limiting at times. Even if nutrient limitation should occur, it <br />is obvious that a large algal standing crop would develop first. The <br />algal standing crop would be likely to be mafntained at a high level. <br /> <br />Algal growths in excess of the maxima obtained during these assays have <br />been observed in several mainstem reservoirs on the North Platte River <br />in southern Wyoming (USGS, 1976). These occur during what appears to <br />be an annual bloom of the blue-green alga Aphanizomenon sp. during late <br />August or early September. These North Platte Reservoirs appear to <br />exhibit a temperature regime similar to that obtained in the previously <br />described temperature simulation; however, the maximum temperature is <br />somewhat lower than that projected for the Narrows Unit. The North <br />Platte Reservoirs experienced some oxygen depletion in the deeper <br />waters during 1975, but there was no evidence of an oxygen,deficit <br />(USGS, 1976). These reservoirs are extensively used for recreation. <br /> <br />Concurrent with the collection of water samples during August, artificial <br />substrate samplers were placed in the river at each of the two above <br />described stations. These consisted of bark samplers for invertebrate <br />sampling and microscope slides for algal sampling. Organisms collected <br />were identified and standard diversity indices (SOl) were calculated. <br /> <br />At both stations the number of invertebrates collected was low. The <br />samplers on several occasions were observed to be buried in the bed <br />material, which consisted primarily of sand and gravel. The stream <br />bed undoubtedly limits invertebrate productivity. <br /> <br />At the Masters station invertebrates consisted of caddisfly, tendipid, <br />and mayfly larvae. The SOI's calculated from the two samples at this <br />station were 1.9 and 1.5. Only one of the two samplers was recovered <br />at the downstream station. Invertebrates in this sample comprised <br />only caddisf1y and tendipid larvae. The SDI on this sample was 1.0. <br /> <br />22 <br />