陕北无定河水环境容量研究

目的定量研究无定河水环境功能受控区域内所能受纳的污染物最大数量(水环境容量),为寻找水环境容量控制下的区域发展对策提供依据。方法基于满足河流水质要求,以相邻两个排污口为分界线,将河流概化为多个河段,以沿河排污口所能容纳的污染物排放量为控制目标,建立一维水环境容量计算模型。结果在75%逐月流量和最枯月平均流量以及90%逐月流量3种不同水文条件下,COD环境容量分别为6 070.67 t/a,5 276.24 t/a,5 116.37 t/a,NH3-N环境容量分别为259.95 t/a,220.15 t/a,217.44 t/a。结论以偏枯频率年P=75%枯水期平均流量计算获得的年水环境容量作为水污染排放总量控制目标时,既对当地水污染物的排放起到了良好的限制作用,也对地区经济发展留有一定的拓展空间。从2007年现状排污量来看,COD排放量略大于水环境容量,而NH3-N排放量远超过水环境容量,削减率约为73.11%。对无定河实行严格的污染总量控制显得十分重要。

Estimation of water environmental capacity for the Wuding River in Northern Shaanxi Province

Aim To estimate the water environmental capacity for the different water functional areas in the Wuding River in order to promote the pollution control and provide measures of local development in the Wuding River Basin.Methods In order to meet the environmental requirements of water quality for rivers,the river was divided into several reaches marked by different sewage discharge ports.Taking into account of the dilution and degradation of pollution substance along the stream,it suggested that the water environmental capacity should be estimated according to the environmental quality standard of the surface water.The concentration of water pollutant should be less than its threshold value of environmental quality standard.Then,an estimation method of water environmental capacity is derived.It further considered that water environmental capacity for a stream should be added by reach′s value together.Results On the basis of the three hydrological conditions including monthly flow and average low monthly flow by typical years with the probability of 75%,and monthly flow by typical years with the probability of 90%,the water environmental capacities of COD are estimated to be 6 070.67 t/a,5 276.24 t/a,5 116.37 t/a,respectively,and the water environmental capacities of NH3-N are estimated to be 259.95 t/a,220.15 t/a,217.44 t/a,respectively.Conclusion In general,it is reasonable to control water pollutant discharged into the river using the calculated results of water environmental capacity under condition of average instream flow from the typical years with the probability of 75%.Compared with the actual discharged volume of 2007,the current discharged volume of COD is a bit more than its water environmental capacity but the current discharged volume of NH3-N is largely more than its water environmental capacity.Therefore,it is very important to control the pollution from COD and NH3-N by effective measures.