Using eutrophication and ecological indicators to assess ecosystem condition in Poyang Lake, a Yangtze-connected lake

Abstract

Poyang Lake, the largest freshwater lake in China, has been facing shrinkage and environmental problems in recent years, making it imperative to assess the status of its ecosystem. In this study, such an assessment was conducted based on the trophic status index, phytoplankton biomass, the ratio of zooplankton biomass to phytoplankton biomass, eco-exergy, structural eco-exergy, and ecological buffer capacity to total phosphorus for phytoplankton. First, the spatial and temporal variations of the ecosystem status in Poyang Lake were assessed based on these six indicators. Then, cluster analysis was utilized to classify the 15 sites based on the various indicators and to identify the most influential indicators. The results showed that the ecological status of Poyang Lake was affected not only by eutrophication but also by hydrological characteristics. All of the 15 sites had deteriorated to a certain degree. An analysis of the relative spatial ecological status showed that the status of the water in the rivers was superior to the status of water in the central lake. Furthermore, the relative ecological status was found to be best in summer and second best in autumn with ecological status deteriorating in winter. There was no significant correlation between eco-exergy and trophic status index, but a very strong relationship was found between eco-exergy and macrozoobenthos biomass with an R2 of 0.92, indicating that macrozoobenthos contributed greatly to the eco-exergy.

Assessing Aquatic Ecological Health for Lake Poyang, China: Part I Index Development

“…Given the connotation of ecosystem health [24], characteristics of Lake Poyang [18,20,25] and previous assessments [8,11,12], natural indicators were divided into three subject areas for measuring physical, chemical, and biological integrity.…”

“…Nutrition conditions were represented by the nutrient indictor of trophic level indices (TLI). TLI had been used in assessing the ecological status of Lake Poyang to examine the ability of the ecosystem to resist external perturbations [11]. Organochloride pesticides (OCPs) including HCH, DDT were highly concerned pollutant in China.…”

“…Phytoplankton (algae) was the primary producer and responded quickly to water chemistry and environmental quality. Blue-green algae bloom was one of the most visible indicators of impaired water quality and presented harmful socioeconomic and ecological effects [11]. Diversity and composition indices including ratio of blue algae biomass and Berger-Parker index (percentage of the most-dominant taxa) were constructed to measure the health condition of phytoplankton (the supplementary material).…”

“…LP-EHI also went beyond the biophysical realm to include a number of human socio-economic factors, with which there are more concerns on analysis of the linkages between the human pressures and response on ecosystem, and have been explicitly avoided by conventional science [7,11,[59][60][61]. Indeed, effective diagnosis requires an exploration for, and identification of, most critical of these links of human alterations and societal responses.…”

Assessing Aquatic Ecological Health for Lake Poyang, China: Part II Index Application

“…Unfortunately, the hydrological characteristics of the lake have changed during the past decade, and the duration of extreme low or high water events have increased, thereby affecting wetland landscapes [10], water quality [2,11], and aquatic habitats [12][13][14]. However, these changes were seldom discussed in previous studies [15,16]. Based on the developed ecosystem health index for Lake Poyang (LP-EHI) in Part I, which holistically incorporated the lake's characteristics, a comprehensive and objective ecological assessment can be achieved.…”