Characteristics and Influence Factors of CO₂ Flux at Water-Air Interface of Typical Lake in the Taihu Lake Basin

At present,there are relatively few observations of greenhouse gas fluxes in lakes,especially shallow lakes,with a lack of continuity and long-term monitoring data,leading to highly uncertain in the characteristics of water-air interface exchange flux.To further identify the role and influencing factors of lakes in the carbon cycle,and to support research on the mechanism of lake carbon cycle,this study employed the eddy covariance method,a primary international approach for flux observations,to carry out long-term direct observations of water-air interface CO₂ fluxes in the Gehu Lake,a typical shallow lake in the Taihu Lake Basin.Based on the observation data from 2023 to 2024,the multi-timescale changes characteristics of CO₂ flux in the Gehu Lake and their correlations with indicators such as pH,temperature,algal density,nitrogen and phosphorus nutrients were analyzed,and the sources of organic matter,a key influencing factor of CO₂ flux,were further analyzed.The results showed that on an annual scale,the CO₂ flux in the Gehu Lake was 0.03 μmol/(m²·s),with an overall release of CO₂ in summer and autumn,reaching a peak emission of 32.6 gC/m² in July,while CO₂ was absorbed in winter and spring,reaching a peak absorption of -28.4 gC/m² in February.During spring,summer,and autumn,the lake generally acted as a carbon sink during the daytime and a carbon source at night,with the absorption peak occurring between 10:00 and 15:00,and the emission peak between 20:00 and 06:00.The diurnal variation of CO₂ flux was relatively weak in winter.CO₂ flux showed positive correlations with temperature,pH,total phosphorus,and algal density,and was significantly correlated with organic pollution indicators such as permanganate index.The concentrations of organic indicators,phosphorus nutrients,and algal density were significantly higher in summer and autumn than in winter and spring.Analysis showed that the dissolved organic matter was mainly released from sediments,and the activities of algae,bacteria,and microorganisms,with some influence from exogenous inputs.For every 10% decrease in water temperature,total phosphorus,phosphate,algal density and permanganate index was associated with a 24.6%,2.4%,3.7%,7.4%,and 25.6% decrease in CO₂ flux,respectively.