近30年长荡湖和滆湖水环境演变趋势

Trend of Water Environment Change in Lake Changdang and Lake Gehu in the Last 30 Years

为探究太湖流域中型湖泊水质时空分布规律及演变趋势,以太湖流域上游长荡湖和滆湖为研究对象,基于近期调查并结合历史文献资料分析其演变特征。2017~2019季度监测结果显示:两湖主要污染物为总氮(TN,劣V类)、总磷(TP,Ⅲ类~Ⅴ类)和高锰酸盐指数(COD_(Mn),Ⅱ类~Ⅳ类),水体营养水平介于轻度~中度富营养之间。通过文献调研,并结合遥感解译,分析了两湖1990~2019年TN、TP变化情况及其与社会经济发展因素的关系,结果表明:(1)1990~2005年,两湖水质持续恶化,综合水质类别由Ⅲ类变为劣V类;(2)2006~2014年,两湖水质波动较大,此阶段主要受一系列生态修复政策(包括围网拆除、湖区餐饮业整治、入湖氮磷削减示范工程等)影响;(3)2017~2019年,两湖TN和TP浓度处于较高水平。水生植物物种丰度和覆盖度急剧下降。尤其是滆湖,2016年后沉水植物近乎消失,主要优势种由沉水植物黄丝草演变为现在的挺水植物芦苇。相关性分析显示:农业面源污染、城镇化、工业化以及水产养殖是两湖富营养化的主要原因,但两湖TN、TP与围网面积二者间并无显著性相关关系。现阶段长荡湖和滆湖富营养化的治理应遵循“控源—削减—修复”的原则,推进农村生活污水以及畜禽养殖废水达标排放,加大湖滨带保护力度,实施生态修复,构建草型生态系统。

Spatio-temporal heterogeneity and succession patterns of water quality were examined in Lake Changdang and Lake Gehu based on quarterly survey from February 2017 to November 2019 and historical data.The results showed that the main pollutants were total nitrogen(TN,inferior grade V),total phosphorus(TP,between grade Ⅲ and grade V) and permanganate index(COD_(Mn),between grade Ⅱ and grade Ⅳ).In general,the trophic status of Lake Changdang and Lake Gehu were between light eutrophication and moderate eutrophication.The evolution trend analyzed of TN and TP and their relationship with social economic development factors were also analyzed based on literature research and remote sensing interpretation.The water quality of the two lakes continued to deteriorate,and the comprehensive water quality deteriorated from grade Ⅲ to grade V from 1990 to 2005.The water quality of the two lakes fluctuated greatly from 2006 to 2014.At this stage,it was mainly affected by a series of ecological restoration policies of Changzhou government(including the removal of the Seine net,the renovation of the catering industry in the lakes,the reduction of nitrogen and phosphorus).TN and TP concentrations was maintained at a relatively high level from 2017 to 2019.The species abundance and coverage of aquatic plants decreased sharply.After 2016,submerged plants in Lake Gehu almost disappeared,and the main dominant species changed from submerged plant Phragmites australis to emergent plant Phragmites australis.The significant positive relationships were calculated between TN or TP and social economic development factors through Spearman correlation analysis,while agricultural non-point source pollution,urbanization,industrialization and aquaculture were the main reasons for eutrophication.But enclosed aquaculture was not the decisive factor for eutrophication in Lake Changdang and Lake Gehu.So the eutrophication managements of Lake Changdang and Lake Gehu should follow the principles of “source controlling-reduction-restoration”.Furthermore,it is necessary to promote rural domestic sewage and livestock wastewater discharge standards,strengthen the protection of lakeshore zone and implement ecological restoration.