| Under the condition that the point source pollution has been gradually controlled, the non-point source pollution becomes the major cause of water eutrophication. Tangpu Reservoir is the important drinking water source for3million people in Yushao Plain, located in the upstream of Xiaoshun River, one of the major tributaries of Cao'E River. Since its operation for more than ten years ago, most of the water quality indexes of the reservoir and the tributaries meet Grade I of environmental guideline of national quality standards for surface waters, China (GB3838-2002). However, the concentration of Total nitrogen (TN) has always been in high level, ranging from Grade IV to worse than Grade V. Aiming at the status aqo of heavy TN pollution in Tangpu Reservoir Watershed, this paper carried out the research on the quantitative source apportionment and control of TN. The major contents include water environmental capacity calculating, partition of the contributions of surface water and base flow, source apportionment of surface water pollution, and the allocation of water environmental capacity, etc. The major results are as follows:Applied Dillion Model to calculate the water environmental capacity of TN in Tangpu Reservoir. T With the goal of TN concentration reaches Grade ?, in conditions the inflows equal to90%,75%and50%guarantees of annual runoff volumes, the water environmental capacities were402ton,580ton and679ton, respectively.Applied ReNuMa model in the simulation of hydrological process and TN load in Tangpu Reservoir Watershed. Domestic pollution source, surface water source and base flow source accounted for11.1±1.1%,34.3±8.9%and54.4±10.4%to annual TN inputs to reservoir, while irrigated land, dry land, garden, forest, shrub land, grass land, waters and construction land contributed for16.9±1.5%,10.6±0.4%,6.4±0.1%,38.9±2.6%,13.4±0.2%,0.2±0.01%,2.0±0.3%and11.6±0.7%, respectively. The results of scene simulations showed that the highest reducing rate of TN was22.1%by means of land use conversion, explaining the reason for TN concentration was always in high level even if many pollution control measurements had been putting into practice in the past ten years.Established a universal yet simple series of methodologies for quantitative source apportionment of TN according to the regions and pollution sources in watershed scale. Firstly, the contributions of domestic pollution source, surface water source and base flow source to riverine TN was quantitatively separate by means of digital filtering and statistical method. And then, the export coefficients of various landuses were solved by modern optimization algorithm of genetic algorithm. Domestic pollution source, surface water source and base flow source accounted for6.9±1.3%,28.2±2.7%and64.9±4.0%to annual riverine TN. In consideration of the time lag of base flow source pollution, the TN pollution level in this watershed would not be decreased in near future. This conclusion was coinciding with the scene simulation results of ReNuMa model. The annual export coefficients of irrigated land, dry land, garden, forest, shrub land, grass land, waters and construction land were15.48±1.49kg.hm-2,3.74±0.36kg.hm-2,9.74±0.93kg.hm-2,2.03±0.19kg.hm-2,12.59±1.21kg.hm-2,11.73±1.13kg.hm-2,16.88±1.63kg.hm-2and11.75±1.14/kg.hm-2, respectively.The fair allocation of water environmental capacity and the confirmation of reduction responsibility were the core issues after the processes of non-point source pollution had been quantified. GiNi coefficient method had been widly applied in the field. However, the traditional GiNi coefficient method was based on two dimensional plane. In order to deal with this problem, we established a water environmental capacity allocation model based on multi-dimensional GiNi coefficient method, making an advance in water environment capacity allocation. In order to expand the application of this model, a softwere was developed.Formulated a TN reduction program according to regions and sources in watershed scale. In consideration of the time lag of base flow source pollution, proposed a concept namely "realistic allocatable water environmental capacity", which was the realistic water environmental capacity minus the portion of base flow source. In conditions the inflows equal to90%,75%and50%guarantees of annual runoff volumes, the realistic allocatable water environmental capacity were-30ton,148ton and247ton, respectively. With the goal of TN concentration reaches Grade ?, and in conditions the inflows equal to50%guarantees of annual runoff volumes, the total reduction amount of TN was-68.5ton, accounted for-30.9%of the surface source TN. In according to the Water environmental capacity allocation system based on multi-dimensional GiNi coefficient method, regions of Wangyan, Zhuxi, Gulai, Jidong, Wangtan and Pingshui in the watershed should reduce for2.4ton,2.6ton,-2.5ton,-20.3ton,-37.2ton and-13.5ton, respectively, and accounted for27.5%,21.2%,-4.0%,-35.2%,-63.1%and-59.9%to the total reduction amount, respectively. Finally, measurements for TN reduction in according to different regions and sources were proposed. |
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