Abstract

The spatial and temporal trends of water qualities in Lake Soyang was statistically analyzed in this study. The water qualities include nutrients, ionic contents and chlorophyll-a (Chl-a) measured during 1993${\sim}$2000. The rainfall intensity and runoff from the catchment appeared to play an important role in water quality trends in the lake. According to seasonal Mann-Kendall test, conductivity, TP, and Ctl-a did not show any trends of increase or decrease over the 8 year period, while TN declined slightly. It was found that the variation of TP was a function of interannual inflow and rainfall. In the analyses of spatial trend, conductivity, based on the mean by site, showed a downlake decline over the eight year period. Minimum conductivity was found in the headwaters during summer monsoon of July to August and near the dam during October. This result indicates a time-lag phenomenon that the headwater is diluted by rainwater immediately after summer monsoon rain and then the lake water near the dam is completely diluted in October. During summer period, TP and TN had an inverse relation with conductivity values. Concentrations of TP peaked during July to September in the headwaters and during September in the downlake. Also, TN increase during the summer and was more than 1.5 mg/L regardless of season and location, indicating a consistent eutrophic state. Values of Chl-a varied depending on location and season, but peaked in the midlake rather than in the headwaters during the monsoon. Regression analyses of log-transformed seasonal Chl-a against TP showed that value of $R^2$ was below 0.003 in the premonsoon and monsoon seasons but was 0.82 during the postmonsoon, indicating a greater algal response to the phosphorus during the postmonsoon. In contrast, TN had no any relations with Chl-a during all seasons.

본 연구는 1993년부터 2000년까지 소양호의 총인, 총질소, 전기전도도, 엽록소의 시${\cdot}$공간적 경향을 통계기법을 적용하여 파악하였다. 호수내의 수질특성은 연간강우량 및 수계의 유입량에 의해 변동되었으나, 변동 정도는 조사지역에 따라 역동적인 차이를 보였다. 맨-켄달검정법 (Mann-Kendall test)으로 연별 수질변화를 분석한 　결과,　전기전도도, 총인, 엽록소-a는 8년 동안 모든 지점에서 증가 및 감소 경향이 없으나 TN은 극히 미약하게 감소하는 경향을 보였다. 총인은 유입량 및 강우에 의해 결정되는 것으로 밝혀졌다. 공간적 분석결과에 따르면, 전기전도도는 호수내 상류에서 하류로 감소하는 경향을 보였고 장마중 상류에서는 집중 강우동안 최소값을 보이고 하류에서는 수체류　현상으로 10월에 최소값을 나타냈다. 총인 및 총질소는 장마중에 최대값을 나타내면서 전기전도_도의 변화 양상과 역관계를 나타냈다. 호수내 1차 생산력의 척도로서 측정된 엽록소-a의 농도는 영양염류의 농도 및 계절에 따라 큰 차이를 보였다. 계절별 총인에 대한 엽록소 농도의 회귀 분석결과에 따르면, 장마 전 및 장마 중에는 $R^2$값이 0.003이하이지만 장마후 $R^2$값은 0.82로서 조류생장이 인의 농도에 의해 결정되는 것을 확인하였다. 반면 질소의 농도는 계절에 상관없이 엽록소의 농도와 극히 미약한 관계를 보였다.

Keywords

• Nutrients;
• Conductivity;
• Rainfall;
• Inflow;
• Chlorophyll-a;
• Lake Soyang