Sediment-Overlying Water Relationships Affecting Wintertime Dissolved Oxygen Conditions in the Big Eau Pleine Reservoir, Wisconsin.
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS ENVIRONMENTAL LAB
Pagination or Media Count:
Effects of sediment disturbance and associated chemical oxygen demand on dissolved oxygen DO depletion were evaluated during the winters of 1989- 1990 in the Big Eau Pleine Reservoir. As part of this effort, historical DO data, sediment physical and chemical composition, net sedimentation rates, and water quality characteristics were examined. DO depletion and anoxia in the winter develop rapidly in the headwaters in association with drawdown conditions and low inflows from the Big Eau Pleine River. DO depletion also occurs near the dam of the reservoir. Entrainment of anoxic water from the headwaters and its downstream movement during the winter are promoted by continued withdrawal from the reservoir. Three distinct zones of sedimentation erosional, accumulation, and transport zones were identified, based on the moisture content of the surficial sediment. Sediments in the erosional zone occupied 60 percent of the reservoir surface area and exhibited low moisture content, high sediment density, and low net sedimentation rates. Physical composition of erosional zone sediments varied greatly at different times of the year, indicating deposition, disturbance andor resuspension, and removal of sediment. The erosional zone was within the region of average winter drawdown 1,128 ft MSL. This suggested that winter drawdown may be an important factor in sediment disturbance and longitudinal transport toward the dam. The accumulation zone was located in the basin near the dam and occupied only 2 percent of the reservoir surface area. Sediments in this zone exhibited a higher moisture content, lower sediment density, and higher net sedimentation rate, indicating sediment focusing.
- Hydrology, Limnology and Potamology