Indicators And Methods Of Ecosystem Health Assessment In Daliao River Estuary

Estuaries are major corridors between drainage basins and the sea where land and sea interact intensively. Due to the mixing of river runoff and tide flow, estuarine ecosystems show remarkable regional characteristics with complexity in environment and species structure. Along with the high-speed economic and social development, millions of tons of pollutant are discharged into rivers. Unfortunately, estuarine ecosystems located at the downstream ends of drainage basins, frequently suffer significant environmental pollution and ecological degradation, consequently causing serious threaten for estuarine health. Estuarine health assessment, providing realistic significance in pollution control and ecological restoration, recently becomes one of the hotpots in the fields of international ecological environment.So far, ecosystem health is still in a preliminary stage with a lack of well-developed methodology in evaluation index system and method. Furthermore, studies on estuarine health assessment are rarely reported. This paper aims to establish an integrated index system,to determine an aggregation of evaluation standards, to calculate the index weights through analytical hierarchy process and to propose an evaluation method based on a fuzzy comprehensive evaluation model. Ultimately, the practicability of the above methodology is verified with Daliao River estuary health assessment as a case study.In terms of monitoring data collected from Daliao River estuary in dry season, medium season and abundant season between 2009 and 2010, a set of candidate index system covering water quality, biological features and physical habitat quality was established. Then the principal component analysis and correlation analysis were performed for indicator screening. Combined with expert judgment, 11 significant indicators including COD_Mn, SS, NH₃-N, TN, TP, Chl-a, zooplankton diversity index, B-IBI, DO, sediment grain size and water depth were selected to build the evaluation index system. After the index system for health assessment was established, AHP was employed in this study to calculate the weights of each indicator and of total hierarchical aggregation integrating the expert judgment. It could be perceived that water quality played a decisive role in estuarine health condition because of its crucial status and significant contribution. Finally, fuzzy comprehensive evaluation model was applied to identify the final health level in terms of maximum membership principle.Results showed that the health status of Daliao River estuary showed a deterioration trend from the river mouth to upper reaches, where the seasonal variation presented a trend that the health condition of medium season was in the best level, followed by abundant season and dry season. Considering the large load of various pollutants especially nutrients and organic compounds from the upper Hunhe River and Taizi River, as well as the widespread pollution from the overuse of fertilizers and pesticides in agricultural zones in upper Daliao River drainage basin, water pollution problem in the upper reaches was prominent. Besides, increasingly serious water pollution had aroused the decline of biodiversity compared to the lower reaches of Daliao River estuary. As a result, it could be concluded that upper reaches was in sick state. During the transport process of pollutants from upper reaches to the river mouth, accompanied by the impact of tidal action, water pollution condition was mitigated and the water quality showed signs of improvement. In addition, the massive quantities of saltwater rushing into river channel could further bring about abundant DO, resulting in increased biodiversity. It was obvious that the health status in lower reaches especially near the river mouth was much better than the upper reaches. With regard to the comprehensive health assessment results in various seasons, fairly poor water quality was the major factor resulting in sick estuarine health level in dry season. Comparatively, the health status in medium season was the best of all. Nevertheless, the deterioration of physical habitat quality attributing to remarkable declination of DO concentration restricted the estuarine health level. As for the abundant season, the discharge of water from the reservoir of upper reaches caused severe water pollution, leading to a poor health level. This paper applied the ecosystem health theory to estuarine complex ecosystem characterized by its complexity and uncertainty, and provided an objective and scientific tool for health assessment in estuaries through the combination of AHP and fuzzy mathematics theory. In spite of some shortages on data availability, result credibility and standard setting existing in the methodology, the methodology presented in this paper strived to reflect a relatively comprehensive and objective estuarine health condition and seasonal variation. It can be taken for granted that our study on the theory and method of estuarine health assessment is valuable for the future application.