Graduate Thesis Or Dissertation
 

Drift, wood, and grazing cattle : macroinvertebrates in managed streams

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  • The importance of active-entry drift at a community-scale was evaluated by testing whether the placement of wood in streams affected the abundance of Baetis spp. mayflies in drift. Baetis were chosen because they use drift as a behavioral strategy and are important in salmonid diets. The density of woody debris was manipulated in a divided concrete diversion channel by building a debris jam on one side and leaving the other side free flowing. Although the drift density (as measured by Baetis/unit volume) was almost equal between the two channels, more Baetis were retained in the channel with woody debris due to the slower flow rate. While possibly an important behavioral strategy, active-entry by the insects does not appear to be a factor in community-scale macroinvertebrate drift dynamics. The diversion channel results were tested against samples from Badger, Hoffman and Trout Creeks in the Ochoco National Forest. The results of these field tests were inconclusive because of a depression in the number of Baetis in the system apparently as a result of the presence of grazing cattle. Baetis exhibited a complex relationship to wood. Nonmetric Multidimensional Scaling (NMS) ordinations of samples taken from wood and from gravel benthos showed little difference in Baetis response to substrate type. The possible changes in macroinvertebrate assemblages resulting from the presence of cattle in the stream were explored using survey data from Badger Creek as well as benthic samples taken from two comparable reaches of stream, one with cattle and one without. Ordinations of these data indicate dramatic differences in community composition which suggest that the cattle have a greater effect on macroinvertebrate drift than does the presence or absence of wood in the system.
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file details ReedTL1996.pdf 2017-10-19 公开 下载