Hydrogeographic investigation of the east coast lagoon: Hwajinpo Lake

Physicochemical factors, plankton biomass, and sediment were measured from 1998 to 2000 at two months interim in a eutrophic shoreline Lake, Hwajinpo, in Korea. The lake is isolated from the sea by a narrow sand hill. Coastal zone is well vegetated with floating leaved marine plants. The lake basin is divided into two sub-basins by a shallow ridge. It has disturbance of seawater by stormy waves. Stable chemoclines are made by salinity variations at depth of 1 m around the year. Dissolved Oxygen was often very low ( 1 mgO2/L) at hypolimnion. Temperature reverse were detected in November. Nitrate and Ammonium concentrations were also very low ( 0.1 mgN/L), while TN was usually 2.0~3.5 mgN/L. In general, TN/TP was lower than the Redfield ratio. Transparency was 0.2~1.7m, and COD, TP, and TN of sediment were 3.1~40.3 mg O2/g, 0.91~1.39 mgP/g, and 0.34~3.07 mgN/g, respectively. Phytoplankton chlorophyll-a concentrations were mostly over 40 mg/m3 . Two basins showed different phytoplankton groups with Oscillatoria sp., Trachelomonas sp., Schizochlamys gelatinosa, and Anabaena spiroides dominant in South basin, and with Trachelomonas sp., Schroederia sp., Schizochlamys gelatinosa, and Trachelomonas sp. dominant in the North basin. The seasonal progression of phytoplankton was quick, probably because of unexpected variations in physical environments, such as salinity, turbidity, wind, and light.