运用水质指数法评价南水北调中线水源地丹江口水库水质

丹江口水库是南水北调中线工程水源地，水库水质的好坏直接影响工程效益的发挥. 根据2005年雨季和枯季的水质监测数据，参照GB3838-2002中Ⅱ类水质标准，将21项水质监测指标分为难处理的毒性指标(ρ(As)，ρ(Hg)，ρ(Cd)，ρ(Cr)，ρ(Pb)和ρ(Se))、易净化的污染指标(pH，ρ(DO)，I_Mn，ρ(BOD₅)和ρ(NH₃-N))及其他指标(ρ(DP)，ρ(DIN)，ρ(F-)，ρ(Cl-)，ρ(SO₄2-)，ρ(NO₃--N)，ρ(Cu)，ρ(Zn)，ρ(Fe)和ρ(Mn))3类，首先计算单项水质指数，然后分类别计算分类指数，最后得到综合水质指数(WQI). 结果表明:①重金属Hg，Se，Cd和Pb危及库区水质安全；②易净化污染指标及其他指标的WQI值小于20，但氮已对水质构成极大威胁；③水库水质在枯季好于雨季；④水质空间格局为汉江库区好于丹江库区，丹江库区好于库区下游. 对于水源地，在评价有毒重金属时应结合地表水环境标准和饮用水标准. 另外，就污染物成因及水资源保护措施进行了初步探讨. 

Assessing the Water Quality in the Water Source Area of the Middle Route of the South to North Water Transfer Project (Danjiangkou Reservoir) Using A Water Quality Index Method

Danjiangkou Reservoir is the water source area of the Middle Route of the South to North Water Transfer Project. Thus, its water quality is of great importance. Based on the data from 2005, water qualities parameters were grouped into 3 types, i.e. poisonous metals (ρ(As), ρ(Hg), ρ(Cd), ρ(Cr), ρ(Pb) and ρ(Se)), easily purified (pH, ρ(DO), I_Mn, ρ(BOD₅) and ρ(NH₃-N)) and others (ρ(DP), ρ(DIN), ρ(F-), ρ(Cl-), ρ(SO₄2-), ρ(NO₃--N), ρ(Cu), ρ(Zn), ρ(Fe) and ρ(Mn)). Firstly, water quality index for every single parameter wascalculated, then the grouped indexes were calculated for the three types, and finally the integrated water quality index (WQI) was obtained. The results demonstrate: ① heavy metals Hg, Se, Cd and Pb endanger the water quality security in the reservoir area; ② the easily purified and other pollutants belong to Level Ⅱ of the national standard for surface waters (WQI<20), while nitrogen is seriouslyendangering water quality security; ③ water quality in the dry season is better than that in the wet season; ④ water quality in the Hanjiang reservoir is better than that in the Danjiang reservoir, and water quality in the Danjiang reservoir is better than that in the downstream of the Dam. Surface water standard and drinking water standard should be integrated to evaluate poisonous heavy metals in the water source areas. Additionally, preliminary analysis on the source of the pollutants and water quality conservation strategies are discussed.