Variation characteristics of algae density and water environment factors in Lake Nansi before and after division of the water transfer

为探究大规模调水输入背景下南四湖生态环境演变特征，采用多种非参数统计方法综合分析2010—2020年南四湖藻密度、总氮（TN）、总磷（TP）、氨氮、叶绿素a（Chl.a）、五日生化需氧量（BOD5）、高锰酸盐指数（CODMn）年际年内变化规律和影响因素.结果表明：2010—2020年南四湖上、下级湖水质综合污染指数年均值范围分别为0.759~0.945、0.719~0.926，水质总体逐渐改善，但TN单项污染指数存在超标现象，主要可能与入湖河流中高浓度氮输入有关.受南水北调东线工程运行初期与严峻旱情的影响，南四湖藻密度、TP、氨氮、Chl.a在2013—2015年发生突变，随后均呈增加趋势.南水北调东线工程的运行对南四湖藻密度的年内波动影响强烈，调水工程运行后每年10月份出现峰值，其中2016年上级湖藻密度高达520.0×104 cells/L.湖区藻密度不仅与氮磷质量比（TN/TP）、TP、CODMn、Chl.a呈显著相关，还与降雨、水温密切相关.在南四湖生态环境保护治理过程中，应强化关键水质指标的污染监管与治理，完善调水方案和水生态危机应急管理办法.;In order to explore the characteristics of algae density and its water environment factors in Lake Nansi under context transfer, non-parametric statistical methods are used comprehensively analyze inter-annual intra-annual distribution trends key (total nitrogen(TN), total phosphorus(TP), ammonia nitrogen, chlorophyll-a, BOD5, CODMn). The results show annual average comprehensive pollution index quality fluctuates range 0.759-0.945, 0.719-0.926 upper lower lakes from 2010 2020, but TN still exceeds standard, which was mainly related high input nitrogen into lake. TP, chlorophyll-a had a sharp turning during 2013-2015 because drought early operation South-to-North Water Transfer Project. indicators all increased afterward. east route Project has strong impact on fluctuation density. peak value occurs October when 520.0×104 cells/L lake 2016. Algae not only significantly ratio phosphorus, CODMn, chorophyll-a, also closely rainfall temperature. In process environmental protection management Nansi, supervision needs be strengthened. diversion ecological crisis should improved.