[Characteristics and Influencing Factors of CH₄ Emissions in Small Artificial Lakes in Mountainous Area]

Small lakes serve as a substantial source of global CH₄ emissions. With the growing human demand for water resources， a significant number of small artificial lakes， either created or modified by humans， have emerged and are now widely distributed. However， the dynamics of CH₄ emissions and the underlying regulatory mechanisms in these artificial water bodies remain inadequately understood. This study selected 33 small lakes with diverse functions located in the metropolitan area of Chongqing as research subjects， systematically investigating the spatiotemporal dynamics of CH₄ concentrations and fluxes， as well as their emission pathways through seasonal sampling and analysis. It further evaluated the CH₄ production potential of lake sediments and clarified the impact of changes in utilization patterns， driven by human activities， on CH₄ emissions from these small artificial lakes. The results revealed that the CH₄ concentrations in the 33 artificial lakes varied from 104 to 10 234 μmol·L^-1， with the majority of the lakes exhibiting super-saturation. The total CH₄ fluxes ranged from -28 to 14 386 μmol·（m²·d）^-1， with an average of （1 469 ± 1 678） μmol·（m²·d）^-1， confirming these artificial lakes as net sources of atmospheric CH₄. From the perspective of social functions and utilization patterns， landscape and aquaculture lakes typically exhibited much higher CH₄ concentrations and fluxes， serving as significant emission hotspots. In contrast， most irrigation lakes located in agricultural landscapes showed moderately lower CH₄ concentrations and fluxes. Lakes designated for drinking water supply presented the lowest emissions， acting as minimal CH₄ emitters. These findings suggest that the utilization patterns may have significantly influenced CH₄ fluxes in these small artificial lakes. Particularly， urban development and aquaculture activities significantly heightened the risk of small artificial lakes evolving into stronger sources of CH₄ emissions. From an emission pathway perspective， the CH₄ diffusion flux could contribute over 85% to the total flux in drinking-water-type lakes， which was significantly higher than those observed in irrigation-type （69%） and aquaculture-type lakes （61%）. Landscape lakes exhibited a much lower contribution of diffusive flux to the total flux， accounting for only 42%， while bubbling flux constituted 58%. The altered utilization mode substantially modified the primary pathways of CH₄ emissions from these small artificial lakes. Furthermore， the rates of CH₄ production from sediments were highest in the landscape and aquaculture-type lakes， followed by irrigation lakes， and lowest in drinking-water lakes. These variations can primarily be attributed to differences in organic carbon content and microbial activity within the sediments， which are shaped by distinct utilization patterns. Correlation analysis revealed that the accumulations of organic carbon and nutrients in water were factors determining the variations in CH₄ fluxes among different functional types of artificial lakes. However， the predominant controlling factors for CH₄ emissions differed across different types of lake. Specifically， in drinking-water-type and irrigation-type lakes， CH₄ fluxes were significantly influenced by organic carbon loads， whereas in landscape and aquaculture-type lakes， they were predominantly driven by nutrient accumulation. This study emphasized that continuous nutrient enrichment in waters and sediments， driven by human activities， has significantly increased the risk of CH₄ emissions from small artificial lakes and altered the primary controlling factors. Consequently， to accurately evaluate the contribution of small lakes to global greenhouse gas emissions， it is imperative to develop an adaptive prediction model that incorporates patterns of human utilization.