基于风险源体—受体—响应系统的控制单元水环境综合风险评价

The water environmental risk evaluation of watershed control units based on the risk source-acceptor-response framework

随着控制单元在全国的推广,风险防范型优先控制单元缺少相应的理论支撑。基于控制单元水环境风险特点,提出了源体—受体—响应综合评价体系,根据指标特性,采用熵值法、模糊层次分析法计算权重系数,通过综合风险评价确定各控制单元的风险等级,并定义高风险控制单元为风险防范型优先控制单元、中风险控制单元为优先预警单元。研究筛选五大类20个指标构建三级水环境风险评价体系,通过对太湖流域(浙江片区)13个县市35个控制单元风险评估表明:1 4个位于下游的控制单元为风险防范型优先控制单元;2 17个为优先预警单元,除嘉善县均为优先控制单元外,涵盖其余12县市。研究成果可为风险防范型控制单元提供重要的理论依据。

Small areas within watersheds, known as control units, have been designated in China to improve water resources management, and the definition of these control units is a government priority. As yet, there is no consensus on how to identify ＂risk defensive priority＂, ＂water quality maintained priority＂ and ＂water quality improved priority＂ control units. Hence, the definition of risk defensive priority control units was the focus of this study. The risk source- acceptor-response framework was applied to establish a comprehensive water environment risk evaluation system with quantitative and qualitative indexes. Different methods were used to calculate the weighting coefficient for each type of index： for the quantitative index, the coefficient was determined using the entropy value method; for the qualitative index, the coefficient was determined using a fuzzy hierarchy analysis method. Finally, the risk level for each control unit was ascertained by calculating the risk scoring, and four levels of risk were established： ＂high＂, ＂medium＂, ＂low＂ and ＂extremely low＂. The high-risk units were defined as risk defensive priority control units, and the medium-risk units were defined as early warning units. A case study of the Zhejiang province in the Taihu watershed was conducted using 2011 data. Five categories of risk and 20 indexes were selected to construct the three-level water environmental risk evaluation system. In all, 35 control units were dispersed across 13 counties of the research area. Four high-risk （risk defensive priority） control units were identified, which were located in the downstream portion of the basin, including all of Jiashan County and part of Pinghu County. These units suffer from ＂self-contamination＂ risk and from ＂upstream accumulated pollution＂ risk, and should receive much remedial attention. In addition, 17 medium-risk （early warning） control units were identified, which were distributed in 12 towns （excluding the town of Jiashan County）. In conclusion, it is feasible to identify risk defensive priority units and early warning units by distinguishing their risk rankings. This study provides an important theoretical benchmark for objective definition of risk defensive priority control units.