关键词: 气候变化, 水环境, 湖泊富营养化, 洱海, 大理地区

Abstract:

In this study, we characterized the climatic changes and their impacts on lake eutrophication in Erhai Lake and assessed the relationships between air temperature, precipitation amount, and trophic status index of the lake using the climate data collected from 12 monitoring stations in Dali of Yunnan Province, and water quality monitoring data of Erhai Lake from 1989 to 2019. During this time, the annual mean air temperatures showed a fluctuating upward pattern which clearly indicated a warming trend with the largest temperature increases in the wintertime; meanwhile, the annual precipitation amount showed a fluctuating downward tendency with the most substantial declines in autumns. Comprehensive trophic status index, total nitrogen, total phosphorus, and permanganate index levels increased, while levels of water transparency declined. The changes in overall water quality were characterized by two distinct stages: before 2003, the comprehensive trophic status index, total nitrogen, total phosphorus, and permanganate index levels increased rapidly, while water transparency measured by Secchi Depth declined; after 2003, these same indices were relatively stable with minor fluctuations. We found that the comprehensive trophic status index of Erhai Lake was positively correlated with the annual mean air temperatures, but negatively correlated with the annual precipitation amount. Total nitrogen and water transparency levels showed a distinct correlation with both the annual mean air temperatures and precipitation. Total phosphorus was correlated clearly with the average winter air temperature, and the permanganate index levels correlated with the mean summer/winter air temperatures, respectively. In terms of monthly changes, both the water pollution index and comprehensive trophic status index increased substantially between June and October from 2015 to 2019, indicating water quality during the dry season was significantly better than during flood season. In summary, the comprehensive trophic status index of Erhai Lake increased continuously due to rising air temperatures, and reduced precipitation and lake inflow from 1989 to 2019, and the intensification of lake eutrophication has not improved and the water environmental condition of Erhai Lake remains relatively fragile.

Key words: climate change, water environment, lake eutrophication, Erhai Lake, Dali area