Water quality assessment and spatial-temporal variation analysis in Erhai lake, southwest China

For the implementation of lake ecological protection, understanding the water pollution status and spatio-temporal variation of water quality has become the most important thing for water safety in the basin. To analyze the water quality in recent years, water quality data in Erhai lake from 2013 to 2017 were first collected from typical nine monitoring stations. Based on the comprehensive water quality index (WQI) method, the temporal and spatial variation characteristics of water quality in Erhai lake were analyzed, and the main factors affecting water quality in Erhai lake were explored. The results indicated that the water quality of Erhai lake was worse than its target water quality, and total nitrogen (TN) and total phosphorus (TP) exceeded the Class II standards (TN: 0.5 mg L-1, TP: 0.025 mg L-1) of China's Environmental Quality Standard for Surface Water (GB3838-2002). In terms of changes across seasons, the overall lake water quality in the dry season was better than that in the wet season, and TN and TP reached the peak value in September. In terms of spatial distribution, water quality of the northern area was better than that of the southern area in the dry season, whereas water quality of the southern area was better than that of the northern area in the wet season. At present, Erhai lake is at a critical turning point of water eutrophication, and its nutrition status is mainly affected by both nitrogen and phosphorus. The pollution load from the land area is the main factor affecting the deterioration of Erhai lake. Our results can provide a scientific basis for the treatment of the water environment of Erhai lake.