Annual methane and nitrous oxide emissions from rice paddies and inland fish aquaculture wetlands in southeast China.

Inland aquaculture ponds have been documented as important sources of atmospheric methane (CH 4 ) and nitrous oxide (N 2 O), while their regional or global source strength remains unclear due to lack of direct flux measurements by covering more typical habitat-specific aquaculture environments. In this study, we compared the CH 4 and N 2 O fluxes from rice paddies and nearby inland fish aquaculture wetlands that were converted from rice paddies in southeast China. Both CH 4 and N 2 O fluxes were positively related to water temperature and sediment dissolved organic carbon, but negatively related to water dissolved oxygen concentration. More robust response of N 2 O fluxes to water mineral N was observed than to sediment mineral N. Annual CH 4 and N 2 O fluxes from inland fish aquaculture averaged 0.51 mg m −2 h −1 and 54.78 μg m −2 h −1 , amounting to 42.31 kg CH 4 ha −1 and 2.99 kg N 2 O-N ha −1 , respectively. The conversion of rice paddies to conventional fish aquaculture significantly reduced CH 4 and N 2 O emissions by 23% and 66%, respectively. The emission factor for N 2 O was estimated to be 0.46% of total N input in the feed or 1.23 g N 2 O-N kg −1 aquaculture production. The estimate of sustained-flux global warming potential of annual CH 4 and N 2 O emissions and the net economic profit suggested that such conversion of rice paddies to inland fish aquaculture would help to reconcile the dilemma for simultaneously achieving both low climatic impacts and high economic benefits in China. More solid direct field measurements from inland aquaculture are in urgent need to direct the overall budget of national or global CH 4 and N 2 O fluxes. [ABSTRACT FROM AUTHOR]