[Effects of enclosure aquaculture of hairy crab on CO2 and CH4 emission in Yangcheng Lake wetland].

Enclosed aquaculture of hairy crab is an important intensive aquaculture model in freshwater lakes of China. However, there remains a lack of systematic understanding regarding its impact on greenhouse gas emissions and the underlying mechanisms. In this study, we investigated the effects of enclosed aquaculture on CO2 and CH4 concentration, diffusion flux and the key regulatory factors by field observation in Yangcheng Lake during the breeding and non-breeding periods, combined with headspace equilibrium gas chromatography method and molecular biological technique. The results showed that Yangcheng Lake was a net emission source of atmospheric CO2 and CH4, with significant spatial and temporal heterogeneity in emission intensity. During the breeding period, the CO2 emission of breeding area, non-breeding area, and drainage area were 152.16, 81.59, and 71.19 μmol·L-1, while CO2 diffusion fluxes were 204.32, 61.59 and 41.72 mg·m-2·h-1, respectively. CO2 diffusion flux in the breeding area was significantly higher than that in the non-breeding and drainage area. During the non-breeding period, CO2 emission in the three areas were 68.86, 59.51, and 101.92 μmol·L-1, while CO2 diffusion fluxes were 7.04, 14.51, and 69.74 mg·m-2·h-1, respectively, with the drainage area being the strongest emission source. The CH4 concentration and diffusion fluxes exhibited a pattern of drainage area > breeding area > non-breeding area in both periods, indicating that the drainage area was the area with the highest CH4 emission throughout the year. Random forest analysis and structural equation modelling revealed that Chl-a, pH, dissolved organic carbon and total nitrogen were key factors regulating CO2 emission, while CH4 emission were primarily driven by dissolved organic carbon, NH4+-N and the mcrA/pmoA ratio. In conclusion, hairy crab breeding activities significantly enhanced greenhouse gas emission, and thus the drainage system should be considered in the greenhouse gas assessment.