Research On Effluent Trading Decision Of Dagu River Basin From The Perspective Of Relationship Between Water Resources And Water Environment

In some sections of rivers in China,there are considerable quantities of Class IV to inferior V water bodies.Water supply security is threatened and the needs of water environment for ecological restoration cannot be satisfied.Therefore,water quality management is imperative.Effluent trading system can optimize the allocation of discharge permits and promote the flow of permits to high-efficiency users.Thus,effluent trading can effectively reduce the pollution treatment cost,and realize the balance of economic,social and environmental benefits.Effluent trading system includes subsystems of social economy,water environment,water resources market.These subsystems relate to each other.The existing researches on effluent trading mainly focus on the design of single subsystems and related factors,ignoring the correlations among different subsystems and their typical factors.Thus,they fail to reveal the interaction mechanisms of typical factors.As a result,the principle and basis of decision-making is not yet clear,leading to the lack of decisionmaking.And it is not conducive to the collaborative improvement of subsystem functions.In addition,watershed process simulation,mechanism study,strategy optimization and decision-making are interrelated.The construction of "simulation-mechanical-strategyscheme" architecture can improve the scientificity and effectiveness of decision-making schemes.However,few researches on effluent trading pay attention to systematic decisionmaking,failing to reflect the holistic characteristics of decision-making process.In this study,the Daguhe Basin in Qingdao,Shandong Province is selected as the study area.The key pollutant,chemical oxygen demand,is deemed as water quality factors for effluent trading.Based on the comprehensive consideration of water quality,water resources status and management rules in the watershed,the elaborate constraints that simulate regional characteristic mechanism are constructed.Coupled with SWAT simulation model and twostage stochastic bi-level programming method,the uncertain effluent trading model is constructed to analyze the mechanism of single and interactive effect of water resources and water environment typical factors.The decision analysis of effluent trading is carried out based on the main line of "simulation-mechanism-strategy-scheme".The main results include:(i)The effects of hydrological year type on effluent trading system have been analyzed.The hydrological year type has obvious influence on total water consumption,pollution loading and trading market vitality.There is no trade in special wet years,while the trading market of other hydrological year type(dry and normal years)is active.With the increase of runoff,the total water consumption and pollution loading of the system increase.(ii)The single influence of typical factors of water resources subsystem(water-saving percentage,ecological water allocation)on trading system has been revealed.As for the water-saving percentage,the total water consumption decreases with the increase of watersaving percentage.The amount of water saving mainly flows to the non-polluting fishery users.With the increase of water-saving percentage,the pollution loading decreases and the trading amount shows a downward trend.The system benefits decrease with the increase of water saving percentage.As for the factor of ecological water allocation,with the increase of ecological water allocation,the total water consumption decreases,and the comprehensive benefits decrease.With the increase of ecological water allocation,the trading would occur in more hydrological year types.However,ecological water allocation strengthens the regional water consumption limit,effluent trading would be curbed.The results imply that the subsystem of water resources has obvious influence on the subsystem of water environment.(iii)The single influence of typical factors of water environment subsystem(pollutant reduction percentage,initial allocation method of pollutant discharge permits)on trading system has been revealed.As for the pollutant reduction percentage,with the increase of pollutant reduction percentage,the pollution loading of the unit production scale of pollution source decreases,leading to the increase of the production scale and water consumption of livestock.With the increase of pollutant reduction percentage,the system pollution loading decreases and the trading amount decreases,but the system comprehensive benefit increases.The water environment subsystem has a significant impact on the water resources subsystem.As for the initial allocation method of discharge permit,method U takes the maximum benefit of the watershed as the target orientation,method L focuses on system equity,and method M follows the principle of benefit and fair distribution.The total water consumption,pollution loading and system benefit are the highest under target U,and the lowest under target L.Under method U,there is no need for trading in the system.Under method L and method M,the trading market is started,and the effluent trading market under method L is most active.(iv)The interaction of typical factors of water resources and water environment subsystem on trading system has been analyzed.The water-saving percentage enhances the influence of pollutant reduction percentage on total water consumption and benefits.The increase of pollutant reduction percentage reduces the pollution loading of the system,but the total water consumption and system benefits would increase.With the increase of watersaving percentage,the amount of available water resources increases and the limit of water consumption decreases.After the increase of pollutant reduction percentage,the production scale,water consumption and system benefits of users are further improved.The interaction between ecological water allocation and pollutant reduction percentage on pollution loading and benefis is obvious.The increase of pollutant reduction percentage reduces the loading of pollutant and increases the total benefits.With the increase of ecological water allocation,the system water restriction degree increases.The pollution loading is further reduced and the increase range of benefit is reduced.The effect of pollutant reduction percentage on pollution loading reduction is enhanced,while the effect on benefit increase is weakened.(v)The strategy of effluent trading system has been selected.Based on the TOPSIS analysis(Technique for Order Preference by Similarity to Ideal Solution),considering system benefit,ecological water allocation,total water consumption,pollution loading,benefit per unit of water consumption and benefit per unit of pollution loading,the optimal strategy is W5P5E5 L.It means water-saving percentage,pollutant reduction percentage and ecological water allocation should be at the highest level,and the initial allocation method should aim at the maximum satisfaction of users.Effluent trading planning in watershed should take into account the interaction between water resources and water environment subsystems,vigorously carry out measures such as fair distribution of discharge permits,water saving,pollutant reduction and ecological water replenishment.It can jointly promote the optimization and improvement of water resources and water environment,so as to realize the sustainable development of social economy and water resources system in Daguhe Basin.(vi)The decision scheme of effluent trading system under the optimal strategy has been obtained.Regarding the industrial scale,Laixi has the largest area,Pingdu takes second place.Livestock in Laixi has the largest scale,Jiaozhou takes second place.Laixi would have the biggst breeding area,followed by Jiaozhou,Pingdu and Jimo.In terms of water resources allocation scheme,Laixi has the most amount of water,followed by Pingdu and Jiaozhou.In terms of industry,fishery gets the lion’s share of water,and industries is the least.In terms of users,Laixi fishery and crop farming are the largest water users.As for the water-saving scheme,the crop farming should plan the largest scale of water-saving.As for pollution loading allocation,livestock in Laixi has the most amount of COD discharge loading,followed by livestock in Jiaozhou.They are the main sources of COD discharge.As for the pollutant reduction scheme,the user with the highest pollutant reduction is livestock and in Laixi.As for the effluent trading scheme,livestock in Laixi is the main buyer of discharge permits,while other users are sellers.Livestock in Laixi holds the most pollutant discharge permits after trading,followed by livestock in Jimo.As for the ecological water allocation scheme,Jiaozhou has the most ecological water,followed by Jimo and Pingdu.In terms of system benefits,the benefit of Laixi is the highest in the region,planting industry has the highest benefit in the industry.Among the users,Jimo fishery benefits are the highest.