非点源污染河流水环境容量的不确定性分析

基于河流一维水环境容量计算模型和实测水文水质参数的统计分析,应用MonteCarlo模拟方法,分析模型各输入参数的灵敏度以及水环境容量值的概率分布,建立了非点源污染河流水环境容量的分期不确定性分析方法.本方法表达了由于获取的河流系统信息不确定性和非点源污染发生的随机性引起的水环境容量计算结果不确定性,给出了不同水文期在不同可信度下的河流水环境容量,为实现非点源污染的总量控制提供了可靠的基础.应用本方法,对长乐江的总氮水环境容量进行了不确定性分析.结果表明,根据水质控制目标,枯水期、平水期、丰水期中90%可信度的总氮水环境容量分别为487.9、949.8、1392.8kg·d-1,其中稀释容量是各水文期水环境容量的主要组成部分.据此,各水文期流域内的总氮现状入河量需削减1258.3～3591.2kg·d-1,丰水期是削减量最大的时期.不确定性分析方法计算得到的水环境容量是基于非点源污染河流水文水质状况的实际变化,这相对于按某一设计流量来确定水环境容量的常规方法更为科学、合理,拓展了水环境容量的研究思路和方法.

Uncertainty Analysis of Water Environmental Capacity in the Nonpoint Source Polluted River

Based on the one-dimension model for river water environmental capacity (WEC) and the statistical analysis of the measured hydrological and water quality variables, a uncertainty analysis method for the WEC in nonpoint source polluted river was developed, which included the sensitivity analysis for input parameters of the model and the probability distributions analysis for the WEC using Monte Carlo simulation approach. The method, which described the uncertainty derived from the adopted information of the river system and the randomicity from the occurrence of nonpoint source pollution, could provide different WEC combined with reliabilities for different hydrological seasons. As a case study, the total nitrogen (TN) WEC in the Changle River located in southeast China was calculated using the method. Results indicated that the TN WEC with 90% of reliability were 487.9, 949.8 and 1392.8 kg·d^-1 in dry season, average season and flood season, respectively, and the dilution effect of river water flow accounted for the main content of WEC. In order to satisfy water quality target of the river, about 1258.3-3591.2 kg·d^-1 of current TN quantity that entered into the river should be reduced in watershed, and the largest reducing quantity of TN was occurred during flood season. The uncertainty method, which reflected hydrology and water quality variations in the nonpoint source polluted river, provided a more reliable and efficient method for the WEC calculation.