| In recent years,the environmental problem about cross-regional impact of pollution transport has become the attention of the government and even the public.A mechanism of joint prevention and control of regional air pollution has been suggested based on related research.Analogous to air pollution,the cross-regional transmission impact also exists in the field of water pollution.And because if the propagation of water pollutants in a river from upstream to downstream,the responsibility of cross-regional transport should not be ignored.However,there has been little consideration about systematic clarification of the responsibility of regional water pollution,especially the responsibility of transportation between many administrative area.The existing mechanism of watershed ecological compensation is still hard to solve the problem of "responsibility of transport".Under this circumstance,this paper builds a regional SWAT-Markov Chain model system,based on the data on the monitor of surface water hydrology flow and surface quality,topography,rainfall and climate etc.This model system uses coupling mechanistic regional model and advanced statistical model building methods.Using Nenjiang river basin as an example,this paper simulated the water pollution transport data within the Nenjiang river basin as well as cross-province and cross-city.The method for calculating the matrix of pollution responsibility was further developed.Based on this,we defined the relationship of responsibility taken by the upstream,downstream,and different administrative regions in the Nenjiang River Basin.The method may provides a feasible technical framework for cross-border or cross-regional water ecological compensation research,especially will be applicated in Yangtze River Economic Belt in the future,thus could greatly enrich the theory and practice of water ecological compensation in China.This paper firstly constructs the SWAT model for Nenjiang,which has been divided into 146 subbasins.The SWAT-CUP software is used to analyze the sensitivity of the parameters of the model,and for calibration and validation.The result shows that the simulated value of the calibrated model fits quite well with the actual observed data.In terms of monthly flow index,the ENS efficiency coefficient of the simulated values are within very good grade,with the coefficient reaching above 0.75.In terms of water pollution overload,its ENS efficiency coefficient is within good range,with the coefficient reaching 0.65.The validated model has larger relative error bar,but the overall assessment is still within acceptable range.Overall,our SWAT model produced reasonably good results after assessed by various indices,reflecting the good simulation effect of our model with high sensitivity.Based on the output of the SWAT model of the Nenjiang river basin,we build river basin confluence relationship matrix P and pollution transport efficiency matrix RC.We applied the Markov Chain method to calculate the N×N matrix H of river basin pollution transportation,then further calculation obtains the characteristics of water pollutant transportation in river basin across provinces and cities.The result shows that there is a significant cross-regional transportation characteristic of water pollutant NH3-N between upstream and downstream of river basins.In terms of provinces,the contribution of pollution transportation for Heilongjiang Province and Inner Mongolia autonomous region in Nenjiang River Basin are 50.25%and 49.75%respectively.In terms of cities,the pollution contribution to load flux at the outlet of river basin for Hulunbeier city and Qiqihar city in Nenjiang River Basin are 45.95%and 41.68%.Based on the simulation results on the characteristics of water pollution transportation in Nenjiang,combining objective requirement of the water function zone,this paper calculated the N×N matrix H’ of water pollution responsibility.On the level of river course or subbasin,it is the other river courses from far away that is responsible for the water quality in various essential points along the river to fail to meet the standards.Although some river course are in the upper stream of a river basin,its pollution emission can still have huge influence on the water quality at many other points in the river basin via river transporting network,for example subbasin 17 and 18.On the level of province,although the pollution transportation contributions of both two provinces of Nenjiang are similar,the main responsibility for not meeting standard is from Heilongjiang Province,with 64.67%contribution.On the level of cities,the pollution responsibility mainly comes from Qiqihar city,with 58.82%contribution.Finally,this paper defines the "fairness and efficiency problem"that is widely scrutinized in pollution control,based on the responsibility and contribution of water pollution transportation.The responsibility of water pollution transportation index is defined to represents the fairness of environmental protection,the contribution of water pollution transportation index is defined to represents the efficiency of environmental protection.The PMAs is then selected based on "fairness-efficiency"analysis.The identification of PMAs in the paper could provides basis for the division of priority control units in "14th Five-Year Water Pollution Prevention and Control Plan" in Songhua River Basin,and could also provides methodological reference for other watersheds.At last,different pollution control scenarios are set up to simulate the improving effect on water quality,an optimization model that comprehensively reflects responsibility and contribution of pollution transportation was constructed and solved by LINGO software.When the reduction of total pollution load in the basin achieves the target(7%),the improving rate of the water quality could reach 7.49%under the premise of improving efficiency and responsibility.The Water quality improvement efficiency is up to 1.07,which means moderate efficient. |
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