水生态评价方法探索——以汉江中下游为例

Research on aquatic ecological assessment method:case of middle and lower reaches of Hanjiang River

水生态评价是水生态保护与管理的基础和抓手,但中国在水生态评价方法方面基本处于起步阶段,亟需研究和完善,尤其是水生态评价和以物理化学指标为主的常规水质评价之间关系的处理更是处于空白状态。在充分研究和汲取美国、欧盟等发达国家或组织在水生态评价方面的先进理念基础上,以汉江中下游为例开展了水生态评价方法探索,将以物理化学指标为主的常规水质评价和水生生物指标评价相融合,提出了适于我国的水生态评价方法的基本思路及框架。研究成果包括:(1)提出了将常规水质评价基本单位——监测断面改为水体单元(或称评价单元),为常规的水质指标及拟增的水生生物指标等提供了共同载体;(2)提出了水生生物指标筛选的3条原则“生态代表性、压力敏感性、监测便捷性”;(3)提出了以水体功能是否满足为首要原则,以物理化学指标、水生生物指标为核心,以水文、栖息地等指标作为原因解析指标的水生态评价方法。应用所提出的方法对汉江中下游水生态状况进行了评价,评价结果表明:汉江中下游兴隆水库至汉口江段水生态环境已严重受损,其最突出的水生态问题为枯水期硅藻水华频发及底栖动物群落完整性显著下降,原因在于总磷、总氮、高锰酸盐指数的升高和大坝修建等因素引起的纵向连通性下降、流速减缓、泥沙减少;河流总磷Ⅲ类标准限值0.20 mg/L已不适用于汉江中下游水生态保护的需要,建议执行更严格的总磷控制标准,并适当从严控制总氮浓度和耗氧有机污染。

The aquatic ecological assessment is the foundation and the starting point for aquatic ecological protection and management.However,China′s aquatic ecological assessment methods are basically in the initial stage,especially the relationship between aquatic ecological assessment and conventional water quality assessment based on physical and chemical indicators is in a blank state,which need to be studied and improved.Therefore,on the basis of fully absorbing the advanced ideas of the United States,the European Union and other developed countries or organizations in aquatic ecological assessment,taking the middle and lower reaches of the Hanjiang River as an example,this paper puts forward a basic idea and framework of the aquatic ecological assessment method of surface water in China.The research results include:(1)changing the basic unit of monitoring section in conventional aquatic quality assessment into water body unit(or assessment unit),providing a common carrier for the conventional physical and chemical indicators and aquatic biological indicators and physical habitat indicators.(2)putting forward the three principles of screening rules for the aquatic biological indicators in aquatic ecological assessment such as ecological representativeness,pressure sensitivity and monitoring convenience.(3)proposing a water ecological assessment method that takes fulfilling function of water body as essential principle,physical and chemical indicators and aquatic biological indicators as the core,and hydrology,habitat and other indicators as cause analysis indicators.This method was applied to evaluate the ecological status in the middle and lower reaches of the Hanjiang River.The results showed that the ecological environment in the reach from Xinglong Reservoir to Hankou had been seriously impaired.The most prominent assessment ecological problems were the frequent occurrence of diatom blooms in the dry season and the significant decline in the integrity of benthic animal communities.The reasons were high concentrations of pollutants such as total phosphorus and total nitrogen,and the decrease of longitudinal connectivity and flow velocity caused by dam construction.The standard of 0.20 mg/L of TP(the class III standard limit in the river)was no longer applicable to water ecological protection in the middle and lower reaches of the Hanjiang River.It was recommended to strictly control the concentration of TP,TD and oxygen consuming organic pollution.