Geochemical Behavior And Influencing Factors Of Particulate Inorganic Carbon In The Wujiang Cascade Reservoirs

The biogeochemical cycle of carbon in river ecosystems is a key link in the global carbon cycle.The construction of cascade hydropower stations has profoundly affected the migration and transformation of various forms of carbon in rivers,and caused ecological and environmental problems such as eutrophication of reservoirs and greenhouse gas emissions.At present,there are abundant studies on particulate organic carbon(POC),dissolved organic carbon(DOC)and dissolved inorganic carbon(DIC)in dammed rivers,but there are relatively few studies on particulate inorganic carbon(PIC),which affects the understanding of the biogeochemical cycle of river carbon.Therefore,taking the cascade reservoir group of Wujiang as the research object and combining the field and indoor results,the influencing factors and the mechanism of the temporal and spatial changes of the PIC and ¹³C_PIC cascade reservoirs are discussed.The research helps to understand the carbon cycle of cascade reservoirs.At the same time,it provides theoretical support for the establishment of ecological environment protection measures for dammed rivers.The main conclusions are as follows:1.The PIC content in the study area ranged from 2.10 to 134.09?g·L^-1,with an average value of 23.02?g·L^-1,showing significant seasonal difference(F=2.96,p<0.05)and spatial difference(F=3.29,p<0.05).The PIC content of the incoming water was the highest,and the content of the reservoir water was the same as that in the reservoir discharge.PIC content was the highest in summer(July),the lowest in winter(January),and the same in spring and autumn(April and October).In different layers of the reservoir profiles,the PIC content in the upper layer(0?5 m)is the highest,the middle layer(10?25 m)is the second,and the lower layer(30?60 m)is the lowest.The PIC content of water in the reservoir profiles also showed obvious seasonal difference,the PIC content was the highest in summer and the lowest in winter,and the content was the same in spring and autumn.2.The?¹³C_PIC of the study area was between-13.01?-2.85‰,with an average value of-7.56‰,showing significant seasonal difference(F=4.13,p<0.01)and no significant spatial difference.The water?¹³C_PIC in the reservoir is more negative.The incoming river?¹³C_PIC is equivalent to the reservoir discharge.In terms of season,?¹³C_PIC is greater in autumn than in spring,greater in summer than in winter.?¹³C_PIC in the section of water body in the reservoir area had significant seasonal difference(F=11.58,p<0.01),and the spatial difference under different strata was not significant.In terms of season,?¹³C_PIC in different layers of reservoir profiles is higher in autumn than in spring,higher in summer and greater in winter.3.Algal phytoplankton is closely related to the geochemical behavior of PIC.Photosynthesis and respiration are the main factors controlling the content change of PIC.Among them,the upper layer photosynthesis in the reservoir section improves the p H of the water,and the calcium carbonate saturation index(SIc)increases,which drives the conversion of DIC to PIC,and the PIC content is relatively high.Lower respiration reduces water p H,reduces SIc,promotes PIC dissolution,and reduces PIC content.4.PIC of reservoir water body may always exist in the process of carbon isotope exchange with DIC.This process is carried out by calcium carbonate precipitation-dissolution dynamic equilibrium.This provides a new interpretation Angle for the composition of PIC isotope with negative overall.