年均值法和频次法对水功能区达标评价影响分析

水功能区达标评价是落实最严格水资源管理制度和水污染防治重要抓手。年均值法和频次法是水功能区达标评价两种主要方法。以太湖流域平原河网区S市W区2013～2017年64个水功能区水质数据为例,比较了两种方法区域水功能区达标评价结果差异。结果表明:(1)年均值法评价区域水功能区达标率高于频次法,双因子(CODMn和NH3-N)、三因子(CODMn、NH3-N、TP)年均值法达标率分别高于频次法18%、24%;(2)CODMn、NH3-N、TP单项因子评价年均值法达标率分别高于频次法11%、12%、14%;(3)两种方法评价结果差异的水功能区占功能区总量的41%,多次出现两种评价方法结果差异的水功能区主要分布在水流不畅易发生滞流的水域,水体污染源和降水可能是影响评价结果的主要因素。选择达标评价方法时应综合考虑水功能区水质变化特征、水生态系统对水质响应关系、水质评价结果的历史连贯性和实际管理可行性等多方面因素。

Influence of Annual Averaging Method and Exceeding Frequency Method on Water FunctionArea Compliance Evaluation

Water function area compliance evaluation plays a vital role in implementing the strictest water resources management system andwater pollution control. Annual Averaging Method (AAM) and Exceeding Frequency Method (EFM) are the two main methods for waterfunction area compliance evaluation. Water quality data of sixty-four water function areas during 2013-2017 were selected to investigatethe difference between two methods in W district of S city from the plain river network of the Taihu Basin. The results show that regionalcompliance rates of AAM are 18% and 24% higher than those of EFM respectively, based on two factors (CODMn and NH3-N) and threefactors (CODMn, NH3-N, TP). Regional compliance rates of AAM are 11%, 12% and 14% higher than those of EFM for CODMn, NH3-N, TPas being single factor. The number of water function areas with different evaluation results occupy 41% of all of the water function areas.Those water function areas without the same evaluation results are mainly distributed in the area where streamflow is often sluggish andprone to be standstill. Water pollution source and rainfall might be the key factors affecting the assessment results. Comprehensiveconsideration of water quality characteristics, the response of aquatic ecosystem on water quality, historical consistency of evaluationoutcomes and practical management feasibility should be taken carefully when choosing compliance evaluation method.