Mechanisms and Influencing Factors of N2O Emission from the Cascade Reservoirs of the Wujiang Watershed During Mixing Period Stratification Period
The construction of dams has profoundly altered the biogeochemical cycling processes of nutrient elements,attracting increasing attention towards its effects on the nitrogen biogeochemical cycling processes and the release of greenhouse gas N2O.This study investigated four cascade reservoirs of Wujiang Watershed during the non-thermal stratification period(Winter).Dissolved N2O concentrations and nitrogen species were analyzed to elucidate N2O production mechanisms and influencing factors.The findings indicated that the Hongjiadu,Dongfeng,Suofengying,and Wujiangdu Reservoirs act as N2O emission sources with oversaturated concentrations.Their mean N2O emission fluxes were(0.48±0.07),(0.34±0.04),0.35 and(0.91±0.76)μmol/(m2·h),respectively,which were at a moderate level compared to other lakes/river systems globally.It was demonstrated that N2O primarily originated from nitrification processes during the non-thermal stratification period.Notably,deeper layers of the eutrophicated Wujiangdu Reservoir were predominantly influenced by the nitrification-denitrification coupling process and denitrification,which resulted in the high level of N2O concentration.Consequently,these high dissolved N2O concentration emerged as the significant N2O emissions sources through the discharge water with the hydropower operation.In addition,it was found that the production of N2O in reservoirs was indirectly influenced by the reservoir characteristics,e.g.,reservoir type and age.In comparison with other studies,the reported EF5r from IPCC may significantly overestimate the emission potential of the studied reservoirs.This study contributes valuable insights for evaluating N2O emissions in cascade reservoir systems and understanding the spatiotemporal nitrogen dynamics with the influence of cascade reservoirs.
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