Effects Of Water Level Fluctuations On The Littoral Macroinvertebrates Of West Point Reservoir

The water level of West Point Reservoir is lowered 3 m from October to May for flood control purposes, exposing about 2,900 ha oflittoral zone. The effects of water level fluctuations on the benthic organisms inhabiting this zone were determined from samples taken at 2 bottom contours; the contour exposed during winter drawdown and the contour just below the winter drawdown that remained permanently inundated. During May and July, fewer organisms (P < 0.05) were collected from the contour exposed during drawdown than from the contour never exposed. By August there were no differences (P > 0.05) in the number of organisms inhabiting both contours, indicating that the community had recovered after about 4 months of inundation. Soil particle size analysis showed a smaller percentage (P < 0.05) of silt and clay and a larger percentage (P < 0.05) of sand in the contour exposed during winter drawdown than the contour that remained permanently inundated. Continued annual fluctuation of the water level is expected to cause further deterioration in soil composition of the exposed littoral areas, leading to lower production of benthic fish-food organisms.

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