Greenhouse gas emissions from managed freshwater wetlands under intensified aquaculture

Wetlands are important niches for aquatic organisms and biodiversity as well as for organic carbon sequestration. However, wetlands are frequently managed for aquaculture production, which jeopardized their ability to act as a natural carbon sink. In this experiment, greenhouse gases (GHG) including CO2, CH4 and N2O fluxes at the water-air interface, were monitored on a daily and monthly basis in four aquaculture wetlands: a natural wetland (NW), an enclosure wetland for intensive aquaculture (EWIA), a constructed wetland made from reclaimed paddy land for intensive aquaculture (CWIA), and a constructed wetland made from reclaimed paddy land for extensive aquaculture (CWEA). As a result, annual GHG fluxes for CWEA, CWIA, EWIA and NW wetlands averaged 0.81, 1.06, 2.43 and 1.12 kg N2O-N ha−1, 23.83, 457.08, 1,360.27 and 38.29 kg CH4-C ha−1, 1,321.32, 1,877.04, 2,246.79 and 1,305.48 kg CO2-C ha−1, respectively. Also, the highest yearly global warming potential (GWP) for EWIA, which was 60.02 t CO2-eq ha−1, was roughly ten times greater than that of NW, which was 6.04 t CO2-eq ha−1. Furthermore, the GHG emission intensity per unit of production ranged from 1.21 (CWEA) −5.30 (EWIA) kg CO2-eq kg−1, with EWIA having the highest N2O and CH4 emission factors per unit of aquaculture output at 0.34 g N2O kg−1 and 0.19 kg CH4 kg−1. The study also revealed that feed quantity and water parameters positively linked with GHG emissions, suggesting that improving human management and water environmental quality could achieve large mitigation for both natural and artificial aquaculture wetlands. Given the high heterogeneity of GHGs emissions in aquaculture wetlands, future research should conduct long-term continuous automatic monitoring of aquaculture wetlands to understand the patterns of GHGs emissions and their responses and mechanisms to human management.