| The longitudinal range-gorge region is the most complex and sensitive area of the global environment.The region is ecological corridor in the southwest of China because of its prominent biodiversity and obvious ecosystem characteristics,and also is economic cooperation corridor between China and ASEAN of "The Belt and Road" strategy.The planning and construction of large hydropower stations in the main stream have threatened the sustainable development of ecological environment in the region.Heavy metal is a kind of persistent pollutant.The interception effect of hydroelectric dams on sediment in the river will make the heavy metal accumulated in the reservoir,which has a huge negative impact on the natural river ecosystem.This has led to a major focus on the ecological health of rivers.Therefore,the study selected Longkaikou reservoir with daily regulation ability of the Jinshajiang river basin and Xiaowan reservoir with annual regulation ability of the Lancang river basin in the longitudinal range-gorge region,collected samples and tested in the laboratory systematically,then analyzed cumulative content of heavy metals in two reservoirs with different capacities,in order to reveal the temporal and spatial distribution of heavy metals in two reservoirs influenced by cascade hydroelectric dams,which not only provides theoretical support for regional ecosystem protection and sustainable exploitation of resources,but also has a practical significance of protecting friendly cooperative partnership in downstream of Lancang river between China and ASEAN and humanistic ecological safety in the lower reaches region of the Jinshajiang river.This paper explored the heavy metal pollution on the response of the cascade hydroelectric dams,assessed the degree of heavy metal pollution in two reservoirs,and compared the similarities and differences of pollution evaluation methods.Its aim is to provide scientific bases for making environmental protection and pollution control policy in reservoir and watershed.The main conclusions are as follows:(1)Distribution law of heavy metals in two reservoirsIn 2015 and 2016,the total content of heavy metals in sediment of Longkaikou reservoir in descending order was dry season,normal season,wet season;while Xiaowan reservoir in descending order was normal season,wet season,dry season in 2015 and normal season,dry season,wet season in 2016.The total content of heavy metals in 2016 of two reservoirs was higher than that in 2015.The overall content of heavy metals in sediment of Xiaowan reservoir increased significantly during wet season in 2015 and normal season in 2016,while the overall changing trend of heavy metals with seasonal variation was relatively gentle in other seasons.In 2015 and 2016,the total content of heavy metals in Longkaikou reservoir was slightly higher in dry season,but Xiaowan reservoir was higher in normal season.Spatially,the total content of heavy metals in upstream of dam was higher than that in downstream.The total content of heavy metals of Longkaikou reservoir was higher than that of Xiaowan reservoir from dry season in 2015 to wet season in 2016,but the normal season in 2016 was just the opposite.The total content of heavy metals in sediment of Longkaikou reservoir was higher than that of Xiaowan reservoir in 2015 and 2016,but the rangeability of heavy metals' content between seasonal and inter-annual are less than Xiaowan reservoir.(2)Pollution assessment of heavy metals and heavy metal pollution on the response of the cascade hydroelectric damsThe results of three pollution assessment showed that:in 2015 and 2016,the pollution degree of heavy metals in normal season was higher than in other seasons;the pollution index of heavy metals in two reservoirs in 2016 were higher than that in 2015,so its overall pollution degree of heavy metals was more serious,especially Cd pollution;in 2015,the pollution index of heavy metals in sediment of Longkaikou reservoir were higher than that of Xiaowan reservoir,so its overall pollution degree of heavy metals was also more serious.However,the condition in 2016 was opposite.The assessment results of geoaccumulation pollution index and potential ecological risk index showed that the pollution coefficient of Cd,Cu and As in two reservoirs was higher in 2015 and 2016,and they were the main ecological risk contribution factors.That was worth further attention for ecological environment management in the watershed.The studies showed that cascade hydroelectric dams make heavy metal pollution appear in various seasons,prolong the time of pollution,and change the occurrence period of heavy metal pollution.(3)Application scope of heavy metal pollution assessment methodsThe results of the actual assessment pollution are showed:when characterizing the pollution degree of single heavy metal element,Nemerow pollution index and geoaccumulation pollution index method are more simple and convenient;when considering the biological toxicity of heavy metals emphatically,potential ecological risk index method is more accurate and effective;when characterizing the overall pollution of various heavy metal elements,compared with the Nemerow pollution index and the potential ecological risk index method,using the comprehensive geoaccumulation pollution index method for evaluating the overall pollution degree is more objective and accurate. |
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