Simulation of eutrophication in a reservoir by CE-QUAL-W2 for the evaluation of the importance of point sources and summer monsoon

Kim D, Kim Y, Kim B. Simulation of eutrophication in a reservoir by CE-QUAL-W2 for the evaluation of the importance of point sources and summer monsoon. Lake Reserv Manage. 35:64-76. Water quality was modeled by a 2-dimensional model (CE-QUAL-W2) in a reservoir (Lake Uiam, Korea) receiving nutrients from both nonpoint sources and point sources. Due to the summer monsoon climate and the aggregated seasonal precipitation pattern, the phosphorus export from nonpoint sources is severely concentrated in the rainy season. For several decades, a sewage treatment plant (STP) on the shore of the lake has been releasing effluent, which was suspected as the major cause of eutrophication. However, the total annual phosphorus loading from the STP was smaller than the loadings from nonpoint sources, which aroused skepticism about the effectiveness of an additional chemical P-removal process in the STP as a eutrophication control strategy. The result of scenario simulations in this study showed that P reduction in the STP effluent from 0.9 mg/L to 0.1 mg/L would effectively reduce the chlorophyll a concentration in the lake by 62%. According to the results of the simulation, the addition of a chemical P-removal process was suggested to the municipal government and was installed in 2012. After the process, the chlorophyll a concentration in the lake decreased as predicted in the simulation. The effect of phosphorus loading can have quite different effects on phytoplankton growth depending on the runoff pattern and hydrological characteristics of the receiving water bodies. Flow rate and nutrient loadings are very dynamic, far from a steady state, in the summer monsoon regions, which may be a unique limnological feature of East Asian countries.