A Study On The Ecosystem Health Assessment Of Eastern Shallow Lakes

The healthy lake is the important material basis and the effective guarantee for the human existence and the social economic development. As China’s most concentrated distribution and most representative area of freshwater lakes, Eastern shallow lakes are facing series of environmental problems such as the lake eutrophication aggravating circumstances, frequent outbreaks of Cyanobacterial blooms, lake water ecological function degradation, due to excessive exploitation and utilization. And those problems seriously threat the social and economic sustainable development and people’s health. The past scholars’ research work on Eastern shallow lake ecosystem health is fragmented, and also lack of systematic investigation. Therefore, carrying out lakes’ ecosystem health research in this area has advantage to implement scientific management for the lake ecosystem.Taking 24 typical lakes in Hubei province for example, the author carried out the investigation and analysis, including the natural environment, present water environment quality, status survey of aquatic biological communities of eastern shallow lakes at the regional level. This paper screened and established a multi-factor evaluation system which is related to healthy aquatic ecosystems by principal component analysis and correlation analysis method. The weight of index was calculated by hierarchy analysis and fuzzy mathematics. Then assessment standard was determined. A multilevel fuzzy comprehensive evaluation model was established. A complete shallow lake ecosystem health evaluation was formed the typical lake ecosystem in the study area was assessed. The main conclusions are as follows:⑴ By analysizing water quality of the study regional lake, it can be found that most lakes are polluted by nitrogen and phosphorus, and their concentration are higher than Ⅲ surface water quality standard, pollution is more serious. Whlie the concentration of COD is lower, lakes are lightly polluted by organic pollution. The results of eutrophication evaluation show that most lakes in the study area are in different degree of eutrophication, and Lake ZhongXiangNan is in a serious state of eutrophication. The results of aquatic life situation analysis show that there exist large differences in coverage of aquatic plants, part of the lake aquatic plants are disappeared it changed form grass type into the algae. The dominant species of phytoplankton are green algae, diatoms and cyanobacteria, generally speaking, phytoplankton diversity index is low. Whlie the dominant species of zooplankton is rotifer. And the dominant species of benthic animals are aquatic insects, oligochaetes, mollusks, benthic fauna diversity index is low.⑵ The lake water ecosystem health evaluation index system was screened and builded, including nine indicators-TN, TP, CODMn, the total biomass of zooplankton, benthic animal density, aquatic plant coverage, chlorophyll a, lake recharge coefficient, lake water. the system was divided in five evaluation standard levels, including morbid, unhealthy, sub-health, healthy, very healthy. A multilevel fuzzy comprehensive evaluation model was established. A evaluation system including index system, index weight, assessment standard and assessment model was formed.⑶ The results of Lakes health assessment show that the healthy state of lake Hai-Kou, DongXiCha, and BaoXie are healthy. Lake ZhangDu, YeZhu, Lu, BaoAn, XiLiang, Wang,Chong, TongJia, SanShan are sub-healthy. Lake Ce is unhealthy. While lake Hou, ZhongXiangNan, ZhuPo, NiuLang, DaYe, ShangJin, Yu, Chang are morbid.⑷ The results of lakes ecosystem health evaluation show that lakes in study area are subject to different degrees of ecological disturbances. The ecosystem health is poor in general. The overall trend showed that the water ecosystem health of wetland area lakes which located in the outskirts, small and medium sized lakes which only have the function of regulating, and large lakes which have strong ability to purify is good. While the water ecosystem health of micropolis lakes which have been serious disturbed by human activities and small, medium sized suburban lakes which only have the function of industrial and agricultural water, breeding, tourism is relatively poor. The main factors influencing the study area lakes ecological health are external stress strength of system, poor water quality, and high load of total nitrogen. The structure stability of system bad, vegetation coverage is low, and species diverity is poor. The result of lake ecosystem health assessment is consistent with analysis result of lake water quality, eutrophication, aquatic organisms.The lake ecosystem health assessment system and the result of lake ecosystem health assessment of this paper have important practical implications for the follow-effective management of the study area lakes.