Abstract
The three-year field investigation in hypertrophic Lake Teganuma and laboratory studies were conducted to evaluate the rates of nitrogen and phosphorus eliminated from the lake water.
T-N concentrations in the lake water decreased gradually from the mouth of the Ohori River entering the lake to the outlet of the lake. T-N concentrations in the surface sediments decreased in the mouths of the Ohori River and the Otsu River and leveled off constant values in the downstream of the lake. T-P concentrations in the lake water and surface sediment in Kaminuma, upperstream of Lake Teganuma, decreased remarkably along the flow of water from the inlet to the outlet and leveled off in Shimonuma, downstream of Lake Teganuma.
A three-year nutrient budget indicated that retention coefficients of nitrogen and phosphorus in lake water defined by Vollenweider were 0.34-0.38 and 0.44-0.56, respectively. Phosphorus eliminated apparently from lake water was shifted to sediment phosphorus particularly in Kaminuma. The horizontal distribution of nitrogen in the surface sediments and the laboratory study on denitrification rate in sediment-water systems suggested that a large portion of loss of nitrogen in lake water was caused by denitrification particularly in the sediment-water interface.
