Dynamic and high methane emission flux in pond and lake aquaculture

Freshwater aquaculture systems are recognized as significant contributors to atmospheric methane (CH4) emissions, yet accurate quantification remains challenging due to high variability across different aquaculture types and the scarcity of high-frequency observations. To address these gaps, we conducted synchronous in-situ measurements of CH4 emissions from two typical aquaculture types - pond aquaculture and lake aquaculture - in the Yangtze River Delta, China, using the eddy covariance technique, capturing CH4 flux from hourly to annual scales. Our high-resolution measurements revealed a weak diurnal pattern in CH4 flux, although daily mean flux varied considerately at the two systems (lake aquaculture: 0.04 to 6.60 mu g CH4 m- 2 s- 1; pond aquaculture: 0.08 to 15.4 mu g CH4 m- 2 s-1). CH4 flux was significantly higher in the pond aquaculture compared to the lake aquaculture, with the annual mean value of 5.08 mu g CH4 m- 2 s- 1 (120 g CH4-C m- 2 yr- 1) and 1.52 mu g CH4 m- 2 s-1 (36 g CH4-C m- 2 yr- 1), respectively. Further analysis suggested that smaller size of the ponds, combined with higher nitrogen and carbon loadings and elevated chlorophyll-a concentrations, likely contributed to substantial emissions from the pond aquaculture. Ebullition was identified as the primary emission pathway, accounting for 70 % and 60 % of the total CH4 emissions from the pond and the lake system, respectively. While CH4 flux increased significantly with increasing temperature, the flux during the warming phase of the year was lower than during the cooling phase at equivalent temperatures. Additionally, CH4 flux in the pond system was less sensitive to temperature than in the lake system (Q10 for pond: 2.29; Q10 for lake: 5.75), likely due to the compound influence of biotic factors. Our findings underscore the importance of incorporating high-resolution emissions data from diverse aquaculture systems to accurately estimate the CH4 budget of freshwater aquaculture.