Comparative Study Of Total Amount Control Method Based On Environmental Capacity

The total quantity control of pollutants has become a useful measure in water quality management in China.The type that used frequently in total quantity control was target gross control which ignored the relationship between pollutant discharge and water quality.The capacity gross control,based on environmental carrying capacity that calculated through the relationship between the pollutant and water quality,was widely concerned by researchers for the diversity in method selecting and the scientificity in calculation.However,the capacity gross control was still abandoned in application for the complexity of calculation,the high requirement of data,and the difficulty of method screening.In this study,two environmental capacity estimation methods(load duration curve,the WASP model)and two permit discharge load allocation techniques(proportional allocation,comprehensive allocation)were applied in East Tiaoxi watershed,to compared and discussed the applicability of methods and techniques in capacity gross control.Some principles for method selecting and watershed scale water target management in the future were got synchronously.The results are shown as follows:(1)The Self-organizing maps and export coefficient method were employed to assess water quality environment and to estimate pollutant discharge load.The results showed that the areas with the high concentration of ammonia(NH3-N)were Deqing,the middle and lower reach of Ling’an,and middle reach of Yuhang.The pollutant discharge load of watershed showed that the amount of COD,NH3-N,total nitrogen(TN),total phosphorus(TP)reached 15053 t/a,1405 t/a,3980 t/a,470 t/a,respectively.The discharge of point source only concentrated in some place.However,the emission of non-point sources increased from upstream to downstream and from tributaries to the main stream.According to water quality assessment and the distrubition of pollutant discharge load,NH3-N was identified as the critical index in water quality management and Deqing was identified as the priority control area.(2)The load duration curve and the WASP model were used to estimate the environmental carrying capacity of NH3-N for the priority control area.With the water quality goal of grade Ⅲ,the environmental carrying capacity calculated by load duration curve from high flow interval to low flow interval were 2280t/a、735t/a、367t/a、175t/a.3 2t/a,respectively.Under the extremum limit condition,the environment capacity of NH3-N in the priority control area estimated by WASP was only 190 t/a in 2014 hydrological condition.The environmental carrying capacity estimated with different methods showed significant correlation in the same hydrologic year.The estimation results showed the similarity in seasonal variation either.However,because of the differences in the method mechanism and the control targets,there still had differences between the water environmental carrying capacity of the two methods.The carrying capcity was larger calculated by WASP model than that of the load duration curve in the same situation.(3)Based on the water environmental carrying capacity estimated by WASP model,the proportional allocation and the comprehensive allocation methods were carried out.In order to assess the feasibility of two allocation methods,the water quality improvement and the gini coefficient were evaluated.The results showed that the permit discharge load among regions and pollution sources were differed in different allocation methods.The water quality of main sites was effectively improved with both allocation methods.Comparing with the proportional allocation,the comprehensive allocation was much better in fairness but more complex in operation.