The Bay Ecosystem Health Assessment Based On Variable Fuzzy Evaluation Model

Human activities such as overfishing, coastal development and pollution have altered bayecosystems and eroded their capacity to provide benefits now and in the future. A systematicdiagnosis of bay ecosystem health for sustainable ecological management is urgently needed.Sustainable management aimed at maintaining the flow of a broad range of benefits from the bayalso requires a comprehensive and quantitative method to measure and monitor the health of bayat the level of ecosystem.A variable fuzzy evaluation model is introduced for the comprehensive evaluation of bayecosystem health. According to the environmental pollution conditions and ecosystemcharacteristics of bay, an integrated index system comprising water, sediment environment,residual toxicity in organisms and marine biota were created for evaluation of bay ecosystemhealth. The judgment criteria regarding the level of bay ecosystem health could be roughlyclassified as “excellent, good, moderate, poor, and bad”. The five levels could be furthersub-classified into13ranks. Ecosystem health assessment of Dongshan Bay in spring andautumn based on variable fuzzy evaluation model was presented in this paper.The results showed that the score of ecosystem health index for Dongshan bay was2.36inspring and2.44in autumn, respectively. The status of Dongshan bay ecosystem health could begenerally classified as “between good and moderate, mostly good”, with better level in springthan in autumn. In more detail, the scores of ecosystem health index ranged from2.31to2.47and all stations were classified as“between good and moderate, mostly good” in spring. Inautumn, the scores of ecosystem health index ranged from2.29to2.74. Only three stations(D11、D13and D14) were classified as “between good and moderate, mostly good” and the otherstations were classified as “between good and moderate, mostly moderate”. Several factorsshowed their positive effects on the ecosystem heath status, such as heavy metals in seawater,sediment and organism, oil in seawater and sediment, zooplankton biomass, phytoplankton cellsdensity and diversity as well as benthos diversity. The scores of health index for these indicatorswere all lower than1.5in spring and autumn. However, the health status of the ecosystem waspotentially made to change to “between good and moderate, mostly moderate” by the negativefactors including fish eggs and larva density (average score of heath index in spring and autumnwas4.95), nutrition level (the score of heath index in autumn was4.47), and benthos biomass (the score of heath index in spring was3.59). The scores of health index for these threeindicators were all higher than3.5.Case study indicated that the ecosystem health assessment based on variable fuzzyevaluation model also provides a standardized and quantitative approach for measuring overallhealth condition of bay ecosystems, which can perform well and accurately evaluate thecomprehensive status of the bay ecosystem heath through the change of variable modelparameters (the criterion and distance parameter, α and p), combining the linear and nonlinearmodels. Therefore, the model result is more reliable than before.