| Water environmental capacity refers to the maximum loading of a certain pollu-tant that water body is able to bear under a specified environmental goal. Water envi-ronmental capacity reflects the bearing capacity of water body to pollutants underspecific functional condition. It is the key parameter of the total quantity control ofpollutants in environmental management. The determination of water environmentalcapacity is the basis of the implement of the total quantity control of water pollutantsand an important step to protect the basin water environmental safety and to promotethe sustainable development of the economy and society in the basin region.Chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) are two im-portant indices to implement water pollutant total quantity control during the12thFive-Year Plan of our country. In this paper, the situations of water pollution and pol-lution sources of the mean stream of Songhua River in Jilin province were analyzed.Also, the environmental capacity of the mean stream of Songhua River in Jilin prov-ince were accounted in different water seasons and sections using riverone-dimensional water quality model. In addition, Gini coefficient method was usedto evaluate the fairness of the accounting results of the initial environmental capacity.The allocation scheme was adjusted according to the evaluation results prior to thefinal allocation scheme was determined.The assessment results of water pollution situation indicated that the water qual-ity situation of the mean stream of Songhua River in Jilin province was improvedgradually with the continuous enhancement of the standard achieved rate, while thepollution of the branches of this river still remained serious. According to the resultsof the pollution source analyses, the major source of COD pollution was the non-pointsource while the point source was the major cause of NH3-N pollution. From the re-spect of city section, it is seen that the quantity of COD and NH3-N entering the river was the largest in Changchun city section among the three riverside city sections, fol-lowed by the Jilin city section, and the quantity was the smallest in Songyuan citysection. The results of non-point source loading accounting using two different meth-ods indicated that the output coefficient method underestimated the loading while theback calculation using measured data was relatively reasonable.The results of environmental capacity accounting showed that the COD waterenvironmental capacity in the main stream of Songhua River downstream the Feng-man cross section, Jilin Province was62.96×104tons per year while NH3-N waterenvironmental capacity was2.64×104tons per year. The water environmental capac-ity of the river was fairly large. The COD water environment capacity in the high wa-ter period took up60.2%of the annual capacity, while that in the average and lowwater period took up24.1%and15.8%, respectively. The NH3-N water environmentcapacity in the high water period took up61.5%of the annual capacity, while that inthe average and low water period took up24.3%and14.3%, respectively. The waterenvironmental capacity of both substances were characterized as high>average>lowwater period. The COD water environmental capacity in Jilin, Changchun and Song-yuan city section took up34.6%,47.1%and18.3%of the total river section, with thecharacterization of Changchun>Jilin>Songyuan. The NH3-N water environmental ca-pacity in Jilin, Changchun and Songyuan city section took up44.6%,40.5%and14.9%of the total river section, with the characterization of Jilin>Changchun> Song-yuan. The residual environment capacities in all three city sections were rather small.The residual environment capacity of NH3-N in the high water period in Changchuncity section was below zero, indicating an urgent requirement of reducing the quantityof a NH3-N entering the river in that section.Gini coefficient method was used to evaluate the fairness of the calculating en-vironment of the initial environmental capacity, with the population, gross domesticproduct, administrative area and water resources quantity as assessment factors. Theresults showed that the Gini coefficient of the administrative area vs. COD environ-ment capacity exceeded the reasonable range and that the average Gini coefficient of each factor vs. NH3-N environmental capacity was relatively high. Therefore, we re-allocated the environmental capacity of the investigated rive section in the context ofkeeping the total environmental capacity fixed.Through an adjustment of the allocation coefficient weight of each assessmentfactor, we calculated the Gini coefficient and determined the optimized allocationscheme. The results of COD environment capacity allocation were21.34×104tonsper year for Jilin city section,25.99×104tons per year for Changchun city sectionand15.62×104tons per year for Songyuan city section. The results of NH3-N envi-ronment capacity allocation were0.89×104tons per year for Jilin city section,1.09×104tons per year for Changchun city section and6.6thousand tons per year forSongyuan city section. The environment capacity was reduced by0.45×104tons peryear for COD and reduced by0.29×104tons per year for NH3-N in Jilin city section;the environment capacity was reduced by3.67×104tons per year for COD and in-creased by0.02×104tons per year for NH3-N in Changchun city section; the envi-ronment capacity was increased by4.12×104tons per year for COD and increased by0.27×104tons per year for NH3-N in Songyuan city section. To implement the opti-mized allocation scheme, the controlling concentration in some of the cross sectionswere adjusted, with the extent less than20%of the limit of the water quality standard.The adjusted concentration in each cross section was less than the limit of the waterquality standard, indicating the optimized allocation scheme was feasible. Thisscheme provided scientific basis for the improvement of the fairness of the economicand social development in the basin region. |
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