Author(s): Tianying Shi; Zhaowei Liu; Hong Zhang; Haoran Wang; Yongcan Chen
Keywords: Shallow Lake; PCLake; Water quality; Simulation; Evaluation
Abstract: The problem of water environment is a long-term challenge for rivers and lakes around the world. Numerical simulation is an important means to comprehensively understand the water environment. Aiming at problems of high pollution load, poor capacity of self-purification and sensitive water environment system of lakes, this study took Xinglong Lake, the largest artificial lake in Chengdu City, Sichuan Province, west of China, as an example, to simulate and quantitatively evaluate the spatio-temporal changes of key water quality factors such as TN, TP, COD and NH3-N, by using integrates historical data, in-situ monitoring and PCLake model. The historical and in-situ spatial data of TN and TP concentrations were water exit>north side>center>south side>inlet, indicating that the self-purification capacity of Xinglong Lake is weak. In terms of time, the PCLake was used to establish a high precision water quality model which is suitable for shallow lakes through initial condition setting, parameter calibration, modeling, model correction and verification. The results showed that compared with the measured values, the model can reflect the dynamic changes of water quality in Xinglong Lake well (RMSE<0.25). The concentrations of 4 water quality factors showed a fluctuating decline from 2016 to 2019, with the decreasing rates of TN(0.28mg/(l∙a)), TP(0.02mg/(l∙a)), NH3-N(0.04mg/(l∙a)), and COD(4.54mg/(l∙a)), respectively. Affected by heavy rainfall, temperature and algal reproduction, the water quality of Xinglong Lake in spring and summer were obviously better than those in autumn and winter. The TN and NH3-N concentration in spring and summer were about 1.5 times and 3 times of that in autumn and winter. TP has little change within a year, and the concentration of COD was the highest in autumn. The comprehensive evaluation showed that the water quality of Xinglong Lake increased from inferior V class to IV class during 2016 to 2019. After 2019, the proportion of water quality below IV class decreased by about 30%, and some of them even reached III class. However, about 12.5% of water quality in the south and outlet of Xinglong Lake still failed to reach IV class. Also, the lake had problems of light eutrophication from 2016 to 2020 and trophic state index (TSI) showed a trend of increasing and then decreasing, reaching a peak in 2018. TSI reduced to less than 50 after 2022.The results provided an effective method for water quality simulation and evaluation of shallow lakes, which can play an important role in water environmental protection and comprehensive management of rivers and lakes.