Ecosystem health assessment: methods and directions

Abstract

Ecosystem supplies many services to human being on two aspects, the natural resources and living environment. Ecosystem service is the basis for the survival and development of human society. Meanwhile, an ecosystem could only supply long-term services when it kept the integrality of structure and function, and had the ability to resist disturbance and the resilience.Therefore, Ecosystem health could ensure ecosystem services, and is the prerequisite for sustainable development of human society. Ecosystem health refers to the stability and sustainability of an ecosystem. That is, the ability of an ecosystem to maintain its organization, self-adjustment, and resilience on time. It can be defined according to vigor, organization, and resilience. The many results of human activities are the main impacts to ecosystem heath. For example, sewage effluence, non-point source pollution, over-fishery, wetland cultivation, soil erosion, invasive species, irrational water use are the main reasons in aquatic ecosystems. Ecosystem health assessment needs to determine indices based on its functions and processes,especially the resilience after disturbance, which includes the integrity, adaptability and efficiency However, ecosystem health assessment is still in the process of experiment and developing. It is necessary to review the present results on time, and put forward the future directions in order topromote the development of ecosystem health assessment. Indicator taxa and indices are the two methods of ecosystem health assessment. However, it should be careful in selecting indicator taxa. The sensitivity and reliability of taxa need to be considered simultaneously, which means we should know how high or low the taxa are in indicating the ecosystem. Indicator taxa selected at present mainly include, plankton, benthic invertebrates, fishes, and the integration of organisms on different levels in aquatic ecosystems. Parameters on two aspects can be chosen in establishing the indices for ecosystem health assessment. The inner indices of ecosystem, including those in ecotoxicology, epidemiology, and ecosystem medicine, and the integration of indicators on different scales. And the outer indices of ecosystem, for example, the social and economic indices. However, the other indices are also possibly useful in ecosystem health assessment, for example, the landscape pattern, and land use change. Almost all the types of ecosystems have been assessed by now. However, ecosystem health assessment is still a new research field that disputes existed on its concept, indicator taxa and indices, which is what we should do in the future to promote the assessment. Future direction of ecosystem health assessment is to integrate economics, social science and health science with quantitative biological approaches. The aim of ecosystem health assessment is not to diagnose sickiiess, but to define an expected state of the ecosystem and the threshold to disturbance, and implement effective ecosystem management under the constrains of culture, moral, policies, laws and regulations.