拉萨河河流健康评价指标体系构建及应用

为全面反映拉萨河干流生态环境现状,基于拉萨河特征和国内外研究构建了包含水文、水质、生物、生境、服务功能5个要素12个指标的河流健康评价指标体系,提出了赋值标准,并在拉萨干流进行了应用。评价所用数据来自资料收集、文献调研、现场监测和调查。评价结果显示拉萨河干流整体处于较为健康状态,且上游健康状况优于中下游。上游河段枯水期水质达到I类水功能区水质目标,丰水期氨氮含量未达到I类水功能区水质目标,总达标率为50%,赋50分,其余指标赋值大于75分;中游河段受水电站运行和灌溉引水影响,流量过程变异程度、河流连通阻隔状况、大型底栖无脊椎动物科级耐污指数赋值较低,分别为0分、25分和45分,生态基流保障度、外来鱼类入侵率、河道稳定性指标较上游变差,赋值在50—75分之间,其余指标赋值大于75分;下游河段流量过程变异程度、外来鱼类入侵情况赋值为0分,河流连通阻隔状况与中游相同为25分,大型底栖无脊椎动物科级耐污指数赋45分,河道稳定性赋68分,其余指标赋值大于75分。从河流健康角度分析,未来拉萨河流域管理应重点关注上游湿地面源问题、中下游水利水电工程的综合效应、人类聚集区鱼类入侵等问题。

Construction and application of health assessment index system for Lhasa River

To reflect comprehensively the health statement of the Lhasa River main stream, a river health evaluation index system including 14 indexes involving hydrological water resources, water quality, biology, habitat, and service functions was constructed based on the characteristics of the Lhasa River and domestic and foreign research. The health evaluation index system was applied to the Lhasa River. The data used in the evaluation came from data collection, literature research, and field monitoring and investigation. The evaluation results showed that the Lhasa River is generally in a relatively healthy state, and the health statement of the upper reaches was better than the middle and lower reaches. The water quality of the upper reaches fulfilled the requirement of a Class I water function area during the dry season; however, in the wet season, ammonia nitrogen content exceeded the concentration limit prescribed for a Class I water function area. The total water qualification rate was 50% and scored 50. The remaining indexes of the upper reaches scored more than 75. Affected by hydropower stations and irrigation projects, the degree of variation in the flow process, river connectivity barrier, and family biotic index scored 0, 25, and 45 respectively in the middle reaches; ecological base flow security degree, invasive percentage of exotic fish, and river stability scored between 50 and 75; the other indexes of midstream scored over 75. Degree of variation in the flow process and invasive percentage of exotic fish scored 0 for downstream; river connectivity barrier scored 25; family biotic index scored 45; river stability scored 68; the other indexes of the lower reaches scored more than 75. From a river health perspective, the future management of the Lhasa River basin should focus on non-point source pollution from wet land, the comprehensive effect of hydropower station and irrigation projects, and the invasion of the river by exotic fish.