2015~2020年洞庭湖水质变化及驱动因子分析

Water Quality Variations and Driving Factors in Dongting Lake Before and After the Operation of the Three-year Action Plan

为了分析2015~2020年(即湖南省政府开展了《洞庭湖生态环境专项整治三年行动计划(2018-2020年)》前后)洞庭湖水质变化趋势及其关键驱动因子,选取总氮(total nitrogen,TN)、总磷(total phosphorus,TP)、高锰酸盐指数(chemical oxygen demand,CODMn)和氨氮(NH3-N)4项水质指标,分析了洞庭湖水质年际变化趋势及行动计划前后的水质特征;并通过水体污染指数w和综合污染指数γ评估了洞庭湖水质污染水平;最后结合水位、入湖径流等水文指标和污水处理率、畜禽排泄量等人为指标,深入揭示不同时期影响湖泊水质的关键驱动因子。结果表明:(1)研究期间,TN、TP和NH3-N浓度均呈显著下降趋势(显著性水平p<0.05),且在行动计划后期间3个水质指标浓度均显著降低。洞庭湖水质污染程度在空间上表现为东高西低的空间分布特点,东、南和西洞庭湖的综合污染指数分别为0.86、0.78、0.78。(2)水位、入湖流量、入湖泥沙量呈年际波动趋势;泥沙沉积量显著增加,由-1528.2×10^(4) t/a增至1211.7×10^(4) t/a。(3)畜禽排泄量、施肥量、污水处理率、水位和泥沙沉积量是影响洞庭湖水质变化的关键驱动因子。建议后续湖泊管理中继续加强外源污染物管控,同时合理改善洞庭湖水文条件,加强水文连通性。

We studied the variations of water quality and its related driving factors of Dongting Lake from 2015 to 2020.Four water quality indicators were selected,including TN,TP,CODMn and NH3-N,to analyze the lake water quality variations before and after the operation of the Three-year Action Plan.Water pollution index w and composite pollution indexγwere calculated to assess the water quality pollution level of the lake.The driving mechanism of water quality variations was studied combining with four hydrological indicators,namely water level,inlet flow,inlet sediment volume and sedimentation,and four anthropogenic indicators of sewage treatment rate,livestock excretion,fish production and fertilizer application.The results showed that:(1)During the study period,the water quality of Dongting Lake showed an improving trend(p<0.05).The TN,TP and NH3-N concentrations showed a significant decreasing trend,which were significantly reduced after the Action Plan.The composite pollution indices of Dongting East,Dongting South and Dongting West were respectively 0.86,0.78,0.78,and the pollution level of Dongting Lake was much higher in the eastern than in the western lake basin.(2)The water level,inlet flow,and inlet sediment volume were relatively stable,while sediment deposition rises significantly from-1528.2×10^(4) t/a to 1211.7×10^(4) t/a.(3)Livestock excretion,fertilizer application,sewage treatment rate,water level,and sediment deposition were the vital driving factors influencing the change of water quality.It was recommended that subsequent management be consistently strengthened to control the exogenous nutrients.Meanwhile,the hydrological conditions of Dongting Lake should be improved to enhance its hydrological connectivity.