[Methane Emission Characteristics and Its Influencing Factors over Aquaculture Ponds]

Eutrophic aquaculture ponds are important methane (CH₄) sources. In order to quantify CH₄ emission characteristics and its influencing factors over aquaculture ponds, we conducted several intensive observations over two ponds located in Quanjiao County, Anhui Province, in 2018. The ebullition and diffusion flux of CH₄ were measured in two seasons (winter and spring) using the inverted-funnel and bulk diffusion model, respectively. In winter, the CH₄ ebullition flux during the daytime was higher than that at night (almost zero), whereas the diurnal pattern was found to be reversed in spring. Seasonally, the CH₄ ebullition flux over the ponds was significantly lower in winter[3.92 mg·(m²·d)^-1] than in spring[106.94 mg·(m²·d)^-1], while the diffusion flux in winter[2.81 mg·(m²·d)^-1] was slightly higher than in spring[0.87 mg·(m²·d)^-1]. The CH₄ ebullition and diffusion flux can be significantly controlled by natural factors such as water temperature and air pressure. It was revealed that the CH₄ebullition flux in the studied ponds increased exponentially with increasing water temperature, and increased linearly with decreasing air pressure. Furthermore, we found that artificial management measures (i.e., winter drainage and spring manure treatment) could significantly enhance the CH₄ ebullition flux rather than diffusion flux. For instance, the CH₄ ebullition flux was found to increase with water depth decrease during the winter drainage period, while in the spring, the CH₄ ebullition flux could reach as high as 1002.30 mg·(m²·d)^-1 with chicken manure applicated. This study can provide data support for assessing the contribution of small ponds to the global carbon cycle.