Phosphorus Dynamics in an Arkansas Reservoir: The Importance of Seasonal Loading and Internal Recycling

摘要

DeGray Lake, a large U. S. Army Corps of Engineers impoundment on the Caddo River in south-central Arkansas, receives the majority of its material loads during fall, winter, and spring, when flows are highest. During summer stratified months, when loads are minimal, anoxic conditions develop in the upstream portion of the hypolimnion. Longitudinal differences in water-column phosphorus and iron concentrations indicate that processes occurring in this region of the lake play an important role in determining the fate and ultimate impact of materials input from the river. Headwater sediments, which store allochthonous loads during fall, winter, and spring, act as a source for phosphorus and iron during anoxic periods. Deepening of the thermocline in late summer leads to losses of phosphorus and iron. These occurrences are also suggested by changes in the chemical compositions of sedimenting material collected in sediment traps. This study represents one part of an effort to better define the impacts of Corps reservoir design and management on water quality. (Author)