近50a洱海水环境演变特征及其主要驱动因素

Trend and driving factors of water environment change in Lake Erhai in the last 50 years

基于19712020年近50年洱海湖区主要水质指标的监测数据,采用M-K检验和GAMs模型定量解析了洱海水质的年际变化趋势,采用多元回归法综合分析了洱海水环境演变的驱动因素。结果表明,近50年来,在流域发展与湖泊保护双轮驱动的作用下,洱海水质年际波动明显,主要水质指标浓度也呈现出多个显著变化的趋势过程。1980s初至1985年间水质指标浓度显著上升,主要与流域南部城镇化发展有关;19861980s末显著下降,与南部截污干渠(管)建设密切相关;1990s末至2003年间显著上升,主要与南部城镇工业发展、农业种植结构调整等重要发展策略有关;20042008年间显著下降,主要与中心城区截污治污、环洱海湖滨带修复等重要工程实施有关。在此期间洱海发生过两次较为严重的规模化藻华事件,1996年在水质优良的情况下洱海首次发生蓝藻水华,这与长期低水位运行、网箱养鱼和银鱼引种等导致湖泊生态系统严重受损密切相关;2003年在水质污染加重、生态系统尚未恢复情况下洱海再次发生蓝藻水华。2次藻华事件也改变了流域发展政策,对洱海的科学认识和保护治理力度不断加大,特别是2016年以来高强度的湖泊保护工作,促使洱海氨氮、总氮、总磷、透明度等主要指标均呈现向好的趋势。然而,值得注意的是,近10年洱海COD Mn浓度仍在显著升高,且TLI(COD Mn)加权占比由1992年的6%增加至2020年的17%,说明COD Mn对洱海富营养化的影响逐渐增加,这将是未来洱海保护工作重点关注的方向。

This paper is based on the long-term monitoring data of Lake Erhai from 1971 to 2020.Temporal trends of TN,TP,NH 3-N,SD,COD Mn and Chl.a were quantified using M-K test methods and GAMs models.Combined with multiple linear regression,relationships between water quality parameters and driving factors were analysed.The results showed that in the past 50 years,under the dual drive of watershed development and lake protection,the water quality of Lake Erhai fluctuated significantly from year to year,and the concentration of key water quality indicators also showed a series of significant change trends.The trend of the concentration of key indicators increased significantly from the early 1980s to 1985,while a decrease occurred in 1986-1989,corresponding to the development of urbanisation and the construction of main sewers in the south of the basin.Between the late 1990s and 2003,the concentration of the main indicator increased significantly again,related to factors such as the development of southern cities and industries,and the adjustment of the structure of agricultural planting.Then,the local government took some constructive measures to combat the deterioration of water quality,such as sewage treatment and ecological restoration of the lakeshore.During this period,Lake Erhai experienced two severe algal blooms.In 1996,a Herba houttuyniae bloom occurred,although the overall water quality was in the second phase,which was closely related to long-term low water operations,cage fish farming and the introduction of whitebait fish.In 2003,the second algal bloom occurred due to increased water pollution and an unrestored ecosystem.Two algal blooms threatened the sustainable ecosystem functions of Lake Erhai,which motivated the implementation of subsequent social policies and lake protection strategies.In particular,high-intensity lake protection since 2016 has contributed to the positive trend of Lake Erha s key indicators.However,it is worth noting that the COD Mn concentration still increased significantly in the last decade,and the contribution of TLI(COD Mn)to TLI(Σ)increased from 6%in 1992 to 17%in 2020.This indicates that the influence of COD Mn on the eutrophication of Lake Erhai is gradually increasing,which will be the focus of future protection of Lake Erhai.