汉江中下游生态系统健康评价指标体系构建及其应用

水利工程建设影响了河流生态系统健康。为探究梯级水库、跨流域调水等水利工程建设对长江流域河流生态系统健康的影响,以汉江中下游为例,采用频次分析法和相关性分析法对评价指标进行筛选,用最小二乘法和熵系数法相结合的综合权重模型确定各评价指标权重,从整体性、稳定性及可持续性3个方面构建了河流生态系统健康评价指标体系,并利用赋分法进行河流健康评价。结果表明,汉江中下游河流健康评价指标体系包含流量过程变异程度、输沙量变化、河流连通性、富营养化状况、鱼类物种数等11个指标。评价结果显示汉江中下游河流生态健康状况表现出较强的空间异质性,且健康状况逐年降低。靠近丹江口水库的区域较好,越往下游越差。

Establishment and application of the index system for health assessment of the middle and lower reaches of the Hanjiang River

River ecosystem is one of the most important natural ecosystems. It plays a vital role in the exchange of material, energy and information. Humans have been altering natural rivers for different purposes such as navigation, irrigation, flood control, and power generation. While great social and economic benefits are achieved, these projects can cause ecological problems such as eutrophication, black and odorous water, and insufficient eco-flow. The problems of river ecosystem health as a result of human activities have drawn great attention. Questions remained unclear regarding river management. One is the method to evaluate river health condition affected by humans. The other is to minimize the adverse impact of water conservancy and hydropower projects on river ecosystem. In this study, a river health evaluation method was proposed from the perspective of ecosystem integrity, stability, and sustainability. The proposed method is based on the harmony theory, the comprehensive weight model combined with the least squares method, and the entropy coefficient method. A new framework for assessing river health was developed from the perspective of harmony and health between hydraulic engineering and the river ecosystem. As a case study, the method and framework were applied to the middle and lower reaches of the Hanjiang River, an important tributary of Yangtze River, China. The health status of the river ecosystem and crucial drivers were evaluated. The results indicated that:(1) a total of 11 indicators including sediment transport, river connectivity, eutrophication status, fish biological integrity index, etc. contributed to the index system for health assessment of the studied site; (2) the ecological environment of Hanjiang water was generally poor and change gradually along the river. River health levels were generally "healthy" in the upstream, mostly "sub-healthy" in the midstream, and "unhealthy" in the downstream. This indicates that pollution in Hanjiang River was more serious in the downstream; (3) the physical attributes of the river were altering to that of a lake due to an increasing number of cascaded dams and inter-basin water transfer projects. The speed of such a change scales with the extent of hydraulic engineering intervention. This study will serve as an important reference for basin management in Hanjiang River.