Spatial variations in diffusive methane fluxes and the role of eutrophication in a subtropical shallow lake

Shallow lakes account for most of the diffusive CH₄ emissions from global lakes, and they also suffer from eutrophication worldwide. Determining the effect of eutrophication on diffusive CH₄ fluxes is fundamental to understanding CH₄ emissions in shallow lakes. This study aimed to investigate the spatial variations in diffusive CH₄ fluxes and explore the role of eutrophication in Lake Chaohu, a large and shallow eutrophic lake in the lower reaches of the Yangtze River. A one-year field observation was carried out to examine CH₄ concentrations in the sediment and water and the diffusive fluxes of CH₄ across the sediment-water interface (F_s-w) and water-air interface (F_w-a). Both F_s-w (0.306-1.56 mmol m^-2 d^-1) and F_w-a (0.097-0.529 mmol m^-2 d^-1) were upward and showed significant spatial heterogeneity and were significantly positively correlated. Parameters related to eutrophication had significant positive relationships with F_w-a, and the total phosphorus distribution in the water explained the greatest proportion of the spatial variation in F_w-a. Distance to shore and water depth were inversely correlated with F_w-a and modified the effects of eutrophication. Overall, the results provide direct evidence of the key role of eutrophication in shaping the spatial distribution of diffusive CH₄ fluxes and a scientific basis for predicting changes in CH₄ emissions with future eutrophication changes in shallow lakes in subtropical zones.