Reservoirs form stagnant water bodies due to their hydraulic properties. Thus, water quality problems such as eutrophication and algal bloom can occur. In the Okjung reservoir, algae growth may also occur due to changes in nutrients and various environment factors. Therefore, it is necessary to suppress algae growth and occurrence through water quality management, including meteorological and hydrological status.
The purpose of this study was to find out the meteorological and hydrological status and the trend through the results of the water quality monitoring network of Okjung reservoir. By analyzing the water quality and algae, we tried to find out the spatial and temporal distribution of Okjung reservoir. In addition, statistical analysis was performed to find out factors influencing algae growth.
As a result of the water quality monitoring network, the T-N and T-P concentrations showed different trends in the results of the river and lake measurement networks. The concentration change in the river monitoring network was greater than that in the lake because it was affected by rainfall directly. T-P, TOC, and COD showed similar tendencies because particulate phosphorus flow into water body with pollutants due to rainfall.
The water samples were collected from three points in the river and five points in the lake in 2017 and 2018. Water quality factors such as SS, organic factors and nutrients were found to be affected by inflow due to changes in rainfall. In particular, the concentration change of the upstream inflow was affected by the rainfall from the non-point source of pollution. T-P came in the form of particulate phosphorus and was unable to move relatively far, and the concentration near the upstream inflow river was high. On the other hand, T-N came in the form of dissolved nitrogen and as it accumulates after moving, it showed a higher concentration near the dam than the inflow river. N/P ratio was observed to be P-limited condition in both the monitoring network and the water quality analysis. As a result of the TSIKO, most of the analysis was found to be a mesotrophic condition. The phytoplankton community was found to be mainly composed of diatoms during the study period.
Principal component analysis of 2017 and 2018 identified 4 component that explained 74.6% and 78.3% respectively. In 2017, these components were attributed to change of meteorological and environment factor(40.4), growth of phytoplankton by inflow of organic matter and particulate phosphorus(17.0%), concentrated precipitation in the summer(11.2%), environmental changes causing growth of cyanobacteria(8.0%). In 2018, these components were attributed to change of meteorological and environment factor(34.7%), growth of phytoplankton by inflow of phosphorus(21.6%), environmental changes causing growth of cyanobacteria(12.0%), meteorological condition(9.9%). As a result of the cluster analysis, clusters were classified based on location characteristics in 2017.In 2018, clusters were classified into stream and lake sites but there was no distinction between lake sites.
As a result of this study, T-P management is necessary because it acts as a limiting nutrient among water quality factors. And the upstream inflow river has a large change in the concentration of nutrients and organic matters entered as the flow rate changes. Therefore, it is necessary to control the growth of algae by managing the water quality of upstream inflow river.