THE MONTHLY IMPACT OF NONPOINT SOURCES TO HOEDONG LAKE, KOREA

Lake Hoedong, located in the south of Korea peninsula, is a small, sha llow, eutrophic lake, which is an important water supply source for th e city of Pusan. Although point sources are discharged after secondary treatment, there has been a steady deterioration of lake water qualit y. Removal of point sources alone may produce no measurable improvemen t in the lake condition because of nonpoint sources. So the objectives of this paper are to quantify the nonpoint sources and to assess the impact to the lake. Nutrient inputs from point sources are unlikely to have been altered significantly, but nonpoint nutrient inputs have gr eat monthly variation. Contribution of nonpoint sources to the externa l input of total phosphorus is almost 67% in the wet season and 19% in the dry season. Assuming that a substantial nonpoint source reduction is made by the Hoedong Lake basin, we attempt to estimate the effect of the lake water quality by mass balance equation. The nonpoint sourc e impact to Hoedong Lake water quality is more than 60% in the wet sea son.