Reservoir CO_2 evasion flux and controlling factors of carbon species traced by δ~(13)C_(DIC) at different regulating phases of a hydro-power dam

摘要

As the world largest hydropower reservoir, the Three Gorges Reservoir (TGR) significantly impacted on the carbon cycle since reservoirs are sources of carbon sink This study was carried out to investigate the effects of damming on the carbon cycle. delta C-13(DIC) and delta C-13(DOC) were used to trace the origin of dissolved organic (DOC) and inorganic carbon (DIC). The estimated CO2 evasion flux in two regulating phases (discharge and recharge) with averages of 111 mg/m(2) h and 264 mg/m(2 )h, respectively. At the basin scale, average CO2 flux was about 188 mg/m(2 )h and varies from -158 mg/m(2) h to 1092 mg/m(2) h. The highest average pCO(2) (1294 ppmv) was observed during the discharge period, which was oversaturated than atmospheric equilibrium value; hence, the TGR act as a considerable sink of atmospheric carbon. The delta C-13(DIC) varies from -8.95 parts per thousand to 0.00 parts per thousand with mean - 1.87 parts per thousand; these enrich isotope values indicated that metabolic process (photosynthesis and respiration) and the rapid kinetics of carbonate weathering by soil CO2 control the pCO(2). The low pCO(2) of reservoir water caused the rapid dissolution of CO2 from the atmosphere during the recharge period. The delta C-13(DOC) varies between - 30.64 parts per thousand to -23.05 parts per thousand, which is similar to the values of C-3 vegetation; thus, the source of DOC would be the degradation of soil organic matter. Overall, this study revealed the delta C-13(DIC) signature coupled with soil CO2 dissolution and admixture of atmospherically equilibrated waters resulting in the sink of atmospheric CO2 of the reservoir and impoundment of the dam alters the carbon cycle and aquatic carbon budget in TGR. The findings of this study provide a global image on the contribution of reservoirs to the carbon cycle and aquatic carbon budget Coupling with isotope signatures and elemental concentrations, investigation of the biogeochemical cycle of the carbon can be effectively traced. (C) 2019 Elsevier B.V. All rights reserved.