달방댐 3개 유입수의 연평균 총인 농도는 달방골, 서 학골 및 신흥골이 각각 7.7, 19.1 및 40.0 mgP/m3이었으며 신흥골 유입수가 상대적으로 높았다. 초기 강우시에는 유입수량 증가에 따라 총인 농도가 모두 증가하는 양의 관계를 보여주고 있으나 뒤이어 계속해되는 두번째 강우에서는 유입수량 증가와 크게 관련이 없는 것으로 나타났다. 강우가 집중되었던 1994년 10월 12일에 달방골 유입수의 초기 강우시 총인농도는 97.8 mgP/m3 이였으며, 서학골 유입수는 190 mgP/m3, 신흥골 유입수는 1,336 mgP/m3로 매우 높았다. 달방댐 표층(0~5m 평균)의 총인 농도는 1994년부터 점차 증가되어 1994년과 1995년 10월의 농도가 각각 26.0과 50.0 (3회 측정치 평균) mgP/m3으로 조사되었다. 달방댐에 유입되는 전체 총인 부하량은 각각 236.9 kgP/yr으로 계산되었으며 우기인 10월과 11월에 유입 되는 부하량이 전체 부하량의 71.0%인 167.8 kgP/yr이었다. 유역전체로 볼 때 신흥골 유역으로부터 부하되는 인부하량이 64.1%로 많은 것으로 나타났다. 인 발생부 하량은 2,216 kgP/yr로 계산되었으며, 유역에서 발생된 인이 호수까지 도달되는 도달율은 10.7%이었다. 본 연구결과 호수 수질을 관리하기 위해서는 강우, 특히 초기 강우시에 유입되는 오염물질의 양을 줄여야 할 것으로 사료된다. 이를 위해서는 유역에 산재해 있는 비점오염원인 가축 배설물과 농경지로부터 유출되는 인부 하량을 감소시킬 수 있는 방안이 수립되어야 할 것으로 보인다.

This study was conducted to investigate the ratios of phosphorus release to COD uptake, phosphorus release to nitrate removal, and phosphorus uptake to phosphorus release by DNPAOs(denitrifying phosphate accumulating organisms). In case I～IV, influent 1 were fed with synthetic wastewater with influent 2 NO3--N injection to anoxic zone and the case V were fed with municipal wastewater with side stream oxic zone instead of influent 2 NO3--N injection. As a result, the ratio of phosphorus release to carbon uptake was increased in accordance with nitrate supply. The DNPAOs simultaneously took up phosphate and removed nitrate from the anoxic reactor. In case I～IV, with above 20 mg/L of sufficient NO3--N supply, phosphate was taken up excessively by the DNPAOs in anoxic condition. The large amount of both uptake and release of phosphorus occurred above 20 mg/L of nitrate supply, achieving the ratio of phosphorus uptake to phosphorus release to be 1.05. In case V, phosphate luxury uptake was not occurred in system due to 6.98 mg/L of insufficient NO3--N supply and the ratio of phosphorus uptake to phosphorus release was 0.98. Consequently, if nitrate as the electron acceptor was sufficient in anoxic zone, the ratio was found to be high.

The purpose of this study is to evaluate and to predict of eutrophication in lakes by using Vollenweider- OECD model and total phosphorus concentration and inflow rate which were measurded in 1993～2001. The results of study were as follows. The annual total phosphorus loading from the watershed was calculated to be 55～195tP/yr at lake Soyang, 221～466tP/yr at lake Taechong, 123～278tP/yr at lake Andong, 57～109tP/yr at lake Seomjin. These are discharged, for the most parts, from population and fishfarm facility. TP loading on the surface area at lake Soyang was 3.01gP/㎡/yr, 2.82gP/㎡/yr, 2.84gP/㎡/yr, 3.03gP/㎡/yr, 2.34gP/㎡/yr, 1.78gP/㎡/yr, 0.91gP/㎡/yr, 0.89gP/㎡/yr, 0.86gP/㎡/yr, lake Taechong was 6.71gP/㎡/yr, 7.25gP/㎡/yr, 7.24gP/㎡/yr, 6.53gP/㎡/yr, 6.50gP/㎡/yr, 7.06gP/㎡/yr, 7.04gP/㎡/yr, 4.05gP/㎡/yr, 3.44gP/㎡/yr and TP loading on the surface area of lake Andong, lake Soemjin were 5.39gP/㎡/yr, 4.47gP/㎡/yr, 4.56gP/㎡/yr, 4.45gP/㎡/yr, 3.33gP/㎡/yr, 2.38gP/㎡/yr, 2.53gP/㎡/yr, 2.46gP/㎡/yr, 2.54gP/㎡/yr, 4.09gP/㎡/yr, 4.10gP/㎡/yr, 3.98gP/㎡/yr, 3.73gP/㎡/yr, 2.80gP/㎡/yr, 3.46gP/㎡/yr, 3.22gP/㎡/yr, 2.19gP/㎡/yr, 2.13gP/㎡/yr respectively. The tropic states of four lakes can be assessed as eutrophy because phosphorus loading exceeds the critical phosphorus loading by Vollenweider-OECD model.

Phosphorus and nitrogen loadings from the main tributaries into the Nakdong River were estimated by measuring phosphorus and nitrogen concentration in the main tributaries, Nakdong River(Kangjung), Kumho River, Heichun, Hwang River, Nam River, Milyang River, and Yangsanchun from May 1994 to October. Total phosphorus concentration of Kumho River was vary high, average 1.0 ㎎P/ℓ. The other rivers were the range 0.05∼0.15 ㎎P/ℓ. Total nitrogen concentration of Kumho River was vary high, average 6.27 ㎎N/ℓ. The other rivers were the range 1.5∼3.0 ㎎N/ℓ. The phosphorus loading from Kumho River, Nakdong River(Kangjung), Nam River, Milyang River, Hwang River, Yangsanchun, and Heichun were calculated to be 1,108, 603, 198, 57, 34, 23, and 21 tP/yr, respectively. Therefore, the loading from Kumho River accounted for 45 % of total loading, 2,042 tP/yr. The nitrogen loading from Nakdong River (Kangjung), Kumho River, Nam River, Milyang River, Hwang River, Heichun, and Yangsanchun were calculated to be 12,636, 7,411, 2,611, 1,523, 779, 608, and 391 tN/yr, respectively. Therefore, the loading from Nakdong River(Kangjung) and Kumho River accounted for 50 % and 30% of total loading, 25,959 tN/yr, respectively.