Ecological indicators for assessing freshwater ecosystem health

The paper presents the structural, functional and system-level symptoms of four chemical stresses, acidification, copper, oil and pesticide contamination in freshwater ecosystems. Exergy, structural exergy and zooplankton buffer capacity were used as ecological indicators for the measurement of ecosystem-level responses to the four chemical stresses. The results showed that the changes in ecosystem level were highly related to the changes in structure and function of the studied ecosystems and these changes indicated the effects of chemical stress on freshwater ecosystem health. Exergy, structural exergy and zooplankton buffer capacity followed the significant decline of zooplankton biomass, Bz/Bp ratio, species richness or diversity and resource use efficiency, caused by chemical stress. A slight change in structure and function of local ecosystems, was accompanied by unchanged or slightly changed exergy, structural exergy and zooplankton buffer capacity. The results lead to a set of comprehensive ecological indicators for assessing the impacts of chemical stress on freshwater ecosystem health, including structural, functional and system-level indicators. These indicators were successfully applied to assess the health of a lake ecosystem.