Diffusive methane emissions from temperate semi-intensive carp ponds

Abstract

Manuring and supplementary feeding are common practices used to sustain high fish production in temperate semi-intensive carp ponds. However, the low use efficiency of added nutrients and organic matter may cause carp ponds to be ‘hot spots’ of methane (CH4) production and emission. Surface CH4 concentrations were measured and diffusive CH4 flux was estimated using a wind-based transboundary layer model in 3 nursery and 3 main carp ponds with different feeding rates and organic loading during 1 growing season. Mean (±SD) concentrations of CH4 were 1.3 ± 0.9 µM and 0.8 ± 0.8 µM in nursery and main ponds, respectively. All ponds were sources of CH4, with diffusive CH4 fluxes of 9.1 ± 6.8 mg C m-2 d-1 in nursery ponds and 6.4 ± 6.9 mg C m-2 d-1 in main ponds. Lower CH4 concentration and diffusive flux in the main ponds were probably due to bioturbation caused by the larger carp and consequent oxidation of the sediment. Seasonal dynamics of CH4 were mainly related to temperature. Methane concentration and diffusive flux levels recorded in this study were within the range of those reported in natural water bodies worldwide. Our results provide information on the role of carp aquaculture in greenhouse gas emission in temparate regions.