浅水湖泊冬季温室气体浓度与通量的变化特征及影响因素

Inland waters are important natural emission sources of atmospheric carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). In order to reveal the dissolved greenhouse gas (GHG) concentrations and their diffusive fluxes in a shallow lake, we investigated the winter (January to February 2022) greenhouse gas in Changdang Lake, a shallow lake in the upper Taihu Lake Basin. We used the headspace equilibrium-gas chromatography (GC) method to measure the GHG concentrations and emission fluxes in surface water. Analysis of variance (ANOVA) and multiple stepwise regression analysis (MSRA) were used to explore the spatial distribution characteristics and the main factors influencing dissolved GHG concentrations and emission fluxes in the Lake and its main inlet and outlet rivers. The results showed that the mean dissolved CO₂, CH₄ and N₂O concentrations in Changdang Lake in winter were (40.49±14.18) μmol/L, (0.86±1.92) μmol/L, and (18.43±8.44) nmol/L, respectively. The mean diffusive fluxes were (49.99±69.49) μmol/(m²·h), (1.28±2.64) μmol/(m²·h), and (12.01±14.37) nmol/(m²·h), respectively. From the perspective of spatial distribution, CO₂ fluxes in Changdang Lake were higher than those in the inlet and outlet rivers, while dissolved CH₄ and N₂O concentrations and their fluxes in the lake were significantly lower than those in the inlet and outlet rivers. Statistical analysis showed that CO₂ emission was mainly affected by water temperature, electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP) and chlorophyll a (Chla) concentrations. CH₄ emission was mainly affected by pH, peroxynitrite index (COD_Mn), EC and DO concentration, and N₂O emission was mainly affected by pH, DO, TN and TP concentrations. The cumulative emission fluxes of CO₂, CH₄ and N₂O from the Changdang Lake in winter were 47.51 kg/hm², 0.44 kg/hm² and 0.01 kg/hm², respectively, and the total GHG emission was estimated to be 545.57 t (in terms of CO₂ equivalent) combined with the lake area. Our findings suggest that winter GHG emissions from Changdang Lake show obvious spatial heterogeneity and are affected by water environment conditions, exogenous nutrient inputs, and human activities in different regions. This study highlights the importance of winter GHG emissions from shallow lakes to the GHG balance of inland waters, which can provide important support for accurate estimation of global and regional lake greenhouse gas emissions.