Variations in CH4 and N2O Exchange Fluxes at the Water-Air Interface and Their Influencing Factors in Genggahai Lake in the Northeastern Qinghai-Xizang Plateau from July to September
Lakes in Qinghai-Xizang Plateau(QTP)account for more than 50%of the total lake area in China.However,due to the lack of fixed-point monitoring data from a variety of lakes,considerable uncertainty exists in CH4 and N2O exchange mechanism in QTP lakes.Here we present CH4 fluxes(FCH4)and N2O fluxes(FN2O)at the water-air interface in Genggahai Lake(GGH Lake),a shallow macrophytic lake in northeastern QTP.The FCH4 and FN2O were observed continuously during daytime from July to September in 2021 based on the floating chamber-gas chromatography method.In combination with meteoric data within the watershed,and the GGH lake water environmental parameters,the spatial-temporal change characteristics of FCH4 and FN2O and their influencing factors were analyzed.The results showed that the average daily FCH4 was 0.557 mg/(m2·h),and the GGH Lake was a source of atmospheric CH4;and the average daily FN2O was-0.100 μg/(m2·h),and the GGH Lake was a weak sink of atmospheric N2O.Because the distribution of aquatic plants species is different,there are differences in the FCH4 at the water-air interface in these different aquatic plants growth area.Among these areas,the FCH4 was the highest in yellow moss distributed area,whereas in none aquatic plants distributed area,the FCH4 was the lowest.Probably influenced by pollutant loads,variations in FN2O showed great spatial heterogeneity.The fecal discharge zone is a hotspot area for N2O.Affected by atmospheric temperature,the peak of FCH4 mainly occurred in 15:00.The daily variation in FN2O was likely influenced by the photosynthesis of submerged aquatic plants.During photosynthesis,the submerged plants release O2 to the waterbody,which caused the pH increasing.Then denitrification and microbial activities in the lake sediment were inhibited,resulted in the significantly negative correlationship between FN2O and pH and ORP.Due to the relatively lower local air pressure in the QTP,the contents of DOin the waterbody and the oxidation of CH4 were weakened.Meanwhile,the solubility of CH4 in the waterbody was also reduced.These processes caused a significantly higher CH4 flux in the QTP lakes than that in lakes of eastern China.Furthermore,because of the weak human activities and exogenous pollution,the FN2O in the QTP lakes were lower than those in the lakes of eastern China.
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万方数据
