Spatial Characteristics And Influencing Factors Of Methane Fluxes In Small Lakes

Lakes are an important source of atmospheric methane(CH₄)and have an important contribution to regional climate change.At present,the research on CH₄emissions in the Yangtze River Delta region is concentrated in large lakes such as Taihu Lake and Chaohu Lake,and there is a relative lack of small-scale lake research samples,which brings great uncertainty to the quantitative estimation and prediction of climate change of regional greenhouse gas emissions.This study takes Dalian Lake,a typical small shallow lake in the Yangtze River Delta,as the research object.In the summer of 2021,based on the thin boundary layer model,the spatial distribution of CH₄diffusion flux at the water-air interface in Dalian Lake and its influencing factors were studied.It aims to provide data support for the estimation of lake greenhouse gas emissions and regional water environment protection.The results of the study are as follows:(1)Dalian Lake was the"source"of regional greenhouse gas emissions,and the CH₄diffusion flux at the water-air interface ranged from 0.81?mol/(m²·h)to 24.72?mol/(m²·h),which was at the average level of CH₄emission in subtropical lakes.Compared with large subtropical shallow lakes such as Taihu Lake and Chaohu Lake,CH₄fluxes belong to the same order of magnitude,and small lakes have large CH₄emission potential.(2)There is spatial differentiation of CH₄emissions in Dalian Lake.The CH₄flux in Dalian Lake increases gradually from the center of the lake to the surrounding area.The CH₄flux on the shore is higher than that in the lake area,and the high values were concentrated in the southwest estuarine area and the northern marsh area,where the CH₄fluxes were 15.88?mol/(m²·h)and 24.72?mol/(m²·h),respectively.CH₄ emission is higher in marshes than in estuaries.Comparison of CH₄fluxes in different lakes was as follows:marsh area>estuary area>coastal area>central lake area, indicating that the contribution of CH₄flux in the swamp area inside the lake is higher than that of the river inlet of the exogenous pollution input,which is the most important source of CH₄flux of the lake.(3)From the perspective of the relationship between environmental factors and CH₄emissions,,the CH₄flux of Dalian Lake was significantly positively correlated with air temperature,₄⁺-N,₃^--N and redox potential,and significantly negatively correlated with humidity,wind speed,air pressure,water temperature and dissolved oxygen.The marshes area are the focus areas of CH₄emissions,and water temperature,redox potential dissolved oxygen and₃^--N are the main reasons for their high CH₄emissions.In the high CH₄flux estuarine region,temperature and dissolved oxygen are important influencing factors.TOC,TP and TN are not related to CH₄fluxes,and nutrients in water mainly affect the emission of CH₄in lakes in the form of nitrate nitrogen and ammonia nitrogen inorganic salts.(4)According to the leading reasons for the difference in CH₄flux in different lake areas,eutrophication of water is the main influencing factor of CH₄emissions in The whole lake of Dalian Lake;in the marshes area,the physical and chemical properties of the water body represented by p H value and dissolved oxygen have the greatest impact on CH₄emissions;in the estuary area,the input of external pollution is the main influencing factor of CH₄emissions;in the center of the lake,the atmospheric environment changes represented by atmospheric pressure and humidity are important factors affecting the changes of CH₄emissions in the region The near-shore area is subject to algal imports from surrounding villages,and eutrophication of water bodies is the main influencing factor.In summary,the CH₄flux of Dalian Lake is closely related to the impact of human activities,and the non-point source and point source pollution control of water bodies in farmland and villages can effectively alleviate eutrophication of water bodies and reduce the emission of CH₄from lakes.