Application of fuzzy mathematics in health assessment of estuarine ecosystem

To protect and restore the estuarine ecosystem, it is very important to evaluate estuarine ecosystem health. A comprehensive multi-index evaluation model of estuarine ecosystem health was investigated in this paper by using the relevant theories of comprehensive evaluation and fuzzy mathematics. Considering synthetically the dependencies and constrains among the influencing factors, a new evaluation index system for estuarine ecosystem health was developed with twelve indices of physical chemistry, ecology and economy. Then, the membership degree of every index was analyzed to obtain a fuzzy matrix. Weight of every index was determined by the analytic hierarchy process (AHP). Finally, a composite index of estuarine ecosystem health could be obtained based on fuzzy transformation. The Yangtze River estuary was chosen as an example to apply the proposed evaluation model. The evaluation result showed that the healthy conditions of the Yangtze River estuary were becoming worse from 2001 to 2005. With further analysis, main factors affecting the ecosystem health of the Yangtze River estuary were increase of pollutant discharge, decrease of suspended solid and decrease in biodiversity. This model is reliable and it can be applied for dynamic evaluation of estuarine ecosystem health.