Determination of Optimum Water Intaking Depth Based on Phytoplankton Distribution in Unmun Reservoir

식물플랑크톤 분포도에 따른 운문호의 선택취수 수심 결정

The purpose of this study was to determine the optimum water intaking depth for water treatment plant based on the changes of phytoplankton distributions in Unmun reservoir. Sampling was carried around of intaking tower near the Dam site at monthly intervals from February to Ocotber in 1998. Total 79 phytoplankton taxa were observed and they were classified into 4 varieties, 75 species within 51 genera. Diatoms were mainly dominated from February to July. However Rhodomonas sp. was a dominant species in August, and Microcystis ichthyblabe in September and October. Cell density of 122,800 cells/mL in October was the highest, and 415 cells/mL in May was the lowest. The pattern of vertical distribution was similar until May; however, the cell density in the epilimnion was much higher than it in the hypolimnion during the periods with the high water temperature over $20^{\circ}C$ since June. The water depths showing over 5,000 cells/mL ranged from the surface to 9m in June, surface to 6m in September, and on the only surface in October. Based on water temperature and phytoplankton vertical distribution, the depth of 6m appeared to be the optimum intaking depth far water treatment plant: 75.4 to 98.0% of phytoplankton cell densities could be avoided and the temperature over $18.3^{\circ}C$ was preserved to prevent cold water damage for rice growth at the water depth during cyanobacterial blooming period in Unmun reservoir.

식물플랑크톤 군집의 분포 특성에 따른 운모호의 최적 취수수심 검토를 목적으로 1998년 2월부터 10월까지 조사를 실시하였다. 식물플랑크톤 출현종은 7강, 12목, 28과, 51속의 75종, 4변종인 총 79 taxa였다. 2월부터 7월까지는 4월을 제외하고 규조강이 우점종이었으며, 8월은 갈색편모조강의 Rhodomonas sp.가 우점종이었으나 9월과 10월은 남조강의 Microcystis ichthyoblabe가 우점종이었다. 식물플랑크톤 현존량은 10월이 122,800 cells/mL로 가장 많았으며, 5월이 가장 적은 415 cells/mL로 나타났다. 2월부터 5월까지는 수심별 식물플랑크톤의 현존량 변화는 심하지 않았으나, 6월부터의 고수온기에는 표층수를 비롯한 표수층(表水層)의 식물플랑크톤의 양이 해수층(深水層)보다 훨씬 높게 나타났다. 5,000 cells/mL 이상의 현존량을 보인 수심은 6월의 경우 표층수로부터 9m의 범위이며, 9월은 6m까지, 그리고 10월은 단지 표층수에만 국한되었다. 수온과 식물플랑크톤량의 2가지 요인만을 고려한 적정 취수 수심은 전체 수심의 총 식물플랑크톤 현존량을 최소 75.4%에서 최대 98.0%까지 배제하며, 수온은 18.3${\sim}$20.0$^{\circ}C$$ 범위를 나타내는 6m의 수심이 타당할 것으로 판단된다.