三峡工程运行后洞庭湖水环境变化及影响分析

以入湖水系、湖体、出湖口为研究区域,基于20多年的监测数据,运用水质单因子评价、综合营养状态指数(∑TLI)等评价方法,系统地分析了洞庭湖水文、水质、营养化状态的时空变化规律,探讨三峡工程运行后洞庭湖水环境变化及原因。结果表明:(1)洞庭湖入湖水量及沙量均明显降低、水位变幅减小。(2)透明度(SD)、总氮(TN)、总磷(TP)、浮游植物等指标的时空分异特征较为明显,4个指标年均值均总体呈上升趋势,其中,SD、浮游植物种类数量及密度自三峡工程运行后变化尤为明显。西洞庭湖的SD高于南洞庭湖,东洞庭湖的SD最低。ρ(TP)在湖体最高,ρ(TN)则在湖体最低。(3)入湖水系水质最好,出湖口水质最差。入湖水系水质一直维持在Ⅱ～Ⅲ类之间,水质良好;出湖口、湖体水质自三峡工程运行后以Ⅳ～Ⅴ类为主,变劣趋势明显。湖体富营养化日趋严重,东洞庭湖的富营养程度稍高于西洞庭湖和南洞庭湖。(4)初步认为:洞庭湖水文水动力环境条件的变化,整体上对水质产生一定的不利影响,对湖体富营养化有一定的促进作用。

CHANGES OF WATER ENVIRONMENT IN DONGTING LAKE AND ITS IMPACT ANALYSIS AFTER THE THREE GORGES PROJECT OPERATION

Taking the upstream rivers, lake body and outlet as the study area, temporal and spatial variations of hydrology, water quality and trophic level in Dongting Lake were analyzed by using ngle factor assessment of water quality and trophic state index(∑TLI),which could be investigated changes of water environment in Dongting Lake and its impact analysis after the Three Gorges project operation based on monitoring data for more than 20 years. The results showed that runoff and sediment into Dongting Lake were decreased significantly. Temporal and spatial characteristics of transparency(SD), total nitrogen(TN), total phosphorus(TP) and photoplankton densitywere obvious. Annual average of four environmental parameters showed increasing trend generally, and changes of SD and density and species of photoplankton were more obvious after the Three Gorges project operation. SD in west Dongting Lake was higher than that in south Dongtinglake, and SD in east Dongting lake was lowest. TP concentration was highest in lake body, while TN concentration was lowest in lake body. Water quality in upstream rivers was better than that in lake body, and it was worst in lake outlet. Water quality in upstream rivers was good and maintained class Ⅱ～Ⅲ, however, water quality in lake body and outlet deteriorated obviously and kept in class Ⅳ～Ⅴ mainly after the Three Gorges project operation. Lake eutrophication was increasingly serious. The trophic level in East Dongting Lake was slightly higher than that in West and South Dongting Lake. After the Three Gorges project operation, runoff and sediment declined, SD increased, water change cycle extended, water environmental capacity decreased, pollutants (nitrogen and phosphorus) concentration increased, above factors had some adverse effects on water quality and increased the degree of lake eutrophication.