西太湖区域水环境容量分配及水质可控目标研究

西太湖流域产业、人口集聚,水环境污染一直以来是该区域经济可持续发展的制约因素之一,利用2010年的监测数据对西太湖主要入湖河流及湖体的水环境状况进行了分析,通过对研究区域工业点源、城镇和农村生活源、农田面源和畜禽水产污染源排污的分布情况调查,并计算了入河污染物量;利用构建的西太湖区域水量水质数学模型,估算了区域水环境容量,依据水环境功能区的水质目标与水域面积分配到了各市/区,在充分调查现有与规划的各类型污染源总量控制工程措施的基础上,量化出具有空间分布的流域污染削减率,并提出水质可控目标。结果表明:太湖湖体受总氮污染影响总体水质劣于Ⅴ类,研究区域主要入湖河流基本处于Ⅳ类,氨氮超标最严重;进入水体的COD为25 410.2 t/a,氨氮2 795.4 t/a,总氮4 646.4 t/a,总磷313.8 t/a,其中城镇生活源污染物入河量所占的比例最大,各类污染物均在35%~50%,尤以宜兴市和常州武进区负荷较大;各控制单元进入水体的污染物量基本都超过了水环境容量,近期各市/区COD、氨氮、总氮和总磷的削减率分别为8.0%~56.0%,8.0%~62.1%,6.0%~41.8%,8.0%~59.9%,远期污染物削减率更高;最终通过模型推算,定出西太湖湖体各污染因子的可控目标,2015年,COD、氨氮、总氮和总磷分别为4.50、0.80、3.50和0.08 mg/L,2020年进一步达到4.50、0.60、3.00和0.07 mg/L,为西太湖总量控制提供科学依据。

STUDY ON ALLOCATION OF WATER ENVIRONMENTAL CAPACITIES AND WATER QUALITY CONTROLLABLE TARGET IN WESTERN TAIHU BASIN

Water pollution is a serious problem in the Taihu Basin. The key problems for water environment improvement in the future are as follows: (1) the total amount of pollutants into the lake remarkably exceeds the water environmental capacity of the lake, (2) there remains a high Cyanobacteria biomass in the lake, and (3) the industrial structure transition and upgrading along the lake are very slow-moving. As industry and population increase rapidly, the pollution of water environment has been a main factor influencing the sustainability of economic development in the Western Taihu Basin. Water environmental problems of main inflowing rivers were analyzed according to the monitoring data of 2010. Through the investigation on the distribution of the industry pollution source, urban and rural sewage source, agricultural and breeding pollution source in studied region, total amount of pollutant drainage into the rivers was calculated. After 2007, the State Council ratified Master Plan of Integrated Regulation of Water Environment of Taihu Basin and Water Function Zoning of Taihu Basin, embarking the comprehensive treatment of water environment in the basin. In this context, water quantity and quality model have been established to predict regional water environmental capacities. Based on the water function and water areas, the water environmental capacities were assigned to every county or district. After the implementation of the existing and planned engineering measures, a spatial and temporal reduction rates for pollution load and a controllable target were proposed. The results indicate that the water quality in the Taihu Lake was worse than Grade V, aand was mainly influenced by TN, and the index could only reach Grade IV in rivers and influenced mainly by NH₃-N. The western Taihu Basin has a total pollution load of 25 410.2t/a COD, 2 795.4 t/a NH₃-N, 4 646.4 t/a TN, and 313.8 t/a TP. The urban sewage source has the largest pollution load contribution with the proportion of 35%~50%. The pollution load in Yixing and Wujin were bigger than the other two. Forecasted pollution discharge into river for most of the water exceeds the water environment capacity. Recently, reduction rate of COD, NH₃-N, TN and TP are 8.0%~56.0%, 8.0%~62.1%, 6.0%~41.8%, 8.0%~59.9%, respectively, and are expected to be higher in future. Using the simulation result of the model, an average COD, NH₃-N, TN and TP value of 4.50, 0.80, 3.50 and 0.08 mg/L are proposed as the water quality controllable target for 2015 in the western Taihu Lake, furthermore, the value achieves to 4.50, 0.60, 3.00 and 0.07 mg/L in 2020. The study provides the technical support and the scientific basis to water pollution control in western Taihu Lake.