| The Three Gorges Reservoir Region of the Yangtze River,a crucial component of the Yangtze River Economic Belt that has experienced rapid economic development,now faces issues of changing ecological environment due to the adjustment of the water level in the reservoir region as well as the environmental pollution caused by the economic and social activity.At present,the high-quality development of the Yangtze River Economic Belt is of great significance to realizing the ecological protection and regional development strategies of China.The paper studies the subsystems of water,land,and air,and the compound system formed by the three subsystems,evaluates and predicts the comprehensive risk of heavy metal pollution specific to each of the subsystems as well as the compound system,and proposes corresponding control,prevention,and management measures.The research content and results primarily include the following aspects:(1)Based on the analysis of the sources of heavy metal pollutants in the Three Gorges Reservoir Region,the method of principal component analysis,which is based on information sensitivity,was applied to the water,land,and air subsystems of the reservoir region to quantitatively screen the primary indicators.Indicators with less sensitivity were eliminated by the information sensitivity criteria,which led to the establishment of a comprehensive risk evaluation system of heavy metal pollution of the reservoir region’s subsystems including the water body,the soil of the water-level-fluctuation zone,the atmospheric subsidence,and their compound system.(2)The Jialing River was selected as the research object for the study on the water subsystem.Comprehensive risk evaluation of heavy metal pollution was conducted using the RRM model,the synthetical index method,and the comprehensive risk index system of heavy metal pollution of the water body.A spatial distribution feature map of the comprehensive heavy metal pollution risks of the Jialing River was created using Arc GIS to perform kriging interpolation on the risk evaluation results.The evaluation results uncovered that low-risk and medium-risk river sections accounted for a large proportion,followed by high-risk and extremely high-risk sections.The proportion of each section was43.5%,34.6%,14.3%,and 7.6%,respectively.The low-risk sections are mainly distributed in the Jialing River Basin of the north of Chongqing,and the confluence region of the Jialing River and the Yangtze River was identified as the high-risk region.(3)The Xiangxi River water-level-fluctuation zone was selected as the research object for the study on the subsystem of the soil of the water-level-fluctuation zone.The single-factor and composite-factor pollutant index was computed using the comprehensive pollution index method,which was incorporated into the comprehensive risk evaluation index system of the heavy metal pollution in the soil of the water-level-fluctuation zone.The comprehensive risk evaluation of heavy metal pollution in the soil of the Xiangxi River water-level-fluctuation zone was conducted using the fuzzy comprehensive evaluation method coupled with GIS technology,which led to the creation of the spatial distribution map of the comprehensive soil heavy metals risk of the Xiangxi River water-level-fluctuation zone.The evaluation results showed that the low-risk area accounted for 39.2%,the medium-risk area accounted for 24.5%,the high-risk area accounted for11.2%,and the extremely high-risk area accounted for 6.95%.The upper reaches of the Xiangxi River were identified as low-risk areas,densely-populated areas with active agricultural activities were identified as medium-risk areas,and hotspots where industrial and mining enterprises aggregate,as well as the Xiangxi River estuary were identified as the high-risk areas.(4)Chongqing City was selected as the research object for the study on the atmospheric subsidence subsystem.A comprehensive risk evaluation system of heavy metal pollution in the atmospheric subsidence was developed with three layers of indicators,namely the natural environment factor,human-induced risk factor,and the heavy metal deposition factor.The comprehensive heavy metal risk evaluation of the atmospheric subsidence of Chongqing City was performed using the relative risk model and the comprehensive index evaluation method.A spatial distribution map of the atmospheric subsidence-related heavy metal pollution risk was created using the GIS interpolation technique.The evaluation results showed the regional variance of the atmospheric subsidence-related heavy metal risks in Chongqing’s main urban area and surrounding counties.The mixed commercial-residential-industrial zones showed a relatively high level of risks while commercial-residential zones and regions far away from industrial zones are exposed to relatively low-level risks.Other counties were identified with low-to medium-risk of heavy metal pollution due to the deposition of atmospheric particulates.(5)A hierarchical comprehensive risk evaluation index system of the heavy metal pollution of the water,land,and air compound system of the Three Gorges Reservoir Region was constructed based on the water,land,and air subsystems.The fuzzy evaluation data set and an indicator membership layer was established using the RRM model coupled with the GIS technology.Three maps were created through the interpolation process: the comprehensive risk evaluation results of heavy metal pollution in the water,land,and air compound system of the Three Gorges Reservoir Region and its spatial distribution map,the spatial distribution map of the comprehensive risk of heavy metal pollution in the compound system of the buffer zone along the river in the Three Gorges Reservoir Region,and the comprehensive risk distribution map of heavy metal pollution in the compound system of the districts and counties in the Three Gorges Reservoir Region.It can be concluded from these evaluation results that the spatial distribution of the heavy metal pollution risk in the Three Gorges Reservoir Region had a patch-like distribution,with low-risk and medium-risk areas covering the broadest region,followed by high-risk areas and extremely high-risk areas.Their proportions are 41.36%,21.28%,19.80%,and 17.56%,respectively.The pollution index of the section from the reservoir to Chongqing appeared to be low;the pollution index of the main urban zone of Chongqing appeared to be relatively high;the pollution index tended to reduce from the middle to the downstream section.From the perspective of the proportion of the area of the risk level,the comprehensive risk of heavy metal pollution in the Hubei section of the Three Gorges Reservoir Region appeared to be higher than that of the Chongqing section.(6)A system dynamics predictive model for analyzing the comprehensive risk of heavy metal pollution of the Three Gorges Reservoir Region was developed using the system dynamics method.Four scenario development models,namely a natural development model,an economy-dominant model,a coordinated development model,and an ecological protection model,were built using the simulation method to predict the comprehensive risk value of the heavy metal pollution of the reservoir region’s compound system and its subsystems between 2020 and 2040.From a time-series perspective,the soil of the water-level-fluctuation zone was predicted to have the largest value of heavy metal pollution risk,followed by the compound system,the water subsystem,and finally the atmospheric subsidence subsystem.(7)With regard to the comprehensive prevention,control,and management of heavy metal pollution,the primary prevention and control factors for heavy metal pollutants in The Three Gorges Reservoir Region’s water,land,and air subsystems and the compound system were determined by comprehensive evaluation and the prediction results.From the perspective of regional division,appropriate risk prevention measures were proposed for different regions according to their respective economic development levels.According to the characteristics of the pollution prevention and control factors of each subsystem,comprehensive risk prevention and control measures for heavy metal pollution in the water body,the soil of the water-level-fluctuation,and atmospheric subsidence were proposed.The Three Gorges Reservoir Region was also divided into several sub-zones with different risk prevention and control levels,including the controlled development zone,the moderate development zone,and the ecologically dominant zone.Quantitative prevention and control measures were designed for each type of the development zones. |
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