Eutrophication of the lower Nakdong River after the construction of an estuarine dam in 1987

The lower Nakdong River has became a "reservoir-river hybrid" since the con struction of an estuarine dam in 1987. Due to the increased nutrient input from the middle part of the river and a longer hydrologic retention due to the estuarine dam, phytoplankton biomass (chi. a) was increased from 28+/-2 3 mu g/l (1982-87) to 60+/-152 mu g/l (1989-96) while phytoplankton blooms occurred frequently. Nutrient concentrations (mg/l) also increased during t he same period (NO3-N: 0.9 to 2, TN: 1.9 to 3.6, PO4-P (mu g/l): 40 to 200) . Since 1992, Microcystis (blue-green algae) in summer and Stephanodiscus ( diatom) bloom in the winter repeatedly occurred. Steady increase in daily w ater intake at the lower part of the river is also a major cause for the ac celeration of eutrophication.