A soil carbon proxy to predict CH4 and N2O emissions from rewetted agricultural peatlands

The temporal and spatial variations in greenhouse gas (GHG) emission estimates in wetlands impede our ability to predict and upscale total emissions; thus, a scalar parameter is needed to predict GHG emissions. We investigated the importance of soil organic carbon (SOC) in the prediction of methane (CH4) and nitrous oxide (N2O) emissions in rewetted agricultural peatlands, positing that both CH4 and N2O production are explained by the quantity and turnover of SOC. Field CH4 and N2O fluxes, along with other edaphic and environmental variables, were monitored in rewetted peatlands with a range of SOC (6%, 11%, and 23%) that were recently converted from row crops to flooded rice cultivation to reverse soil subsidence. Nitrogen (N) fertilization reduced annual CH4 emission by 77.2% in the 6% C field, but this effect was not found in other fields. Annual N2O emissions were not affected by N fertilization and averaged 8.9, 5.2, and 1.9 kg N2O-N ha−1 for the 6%, 11%, and 23% C fields, respectively. SOC was the dominant factor controlling both CH4 and N2O emissions. The annual emission for both CH4 and N2O was accurately described by a decaying power regression with increasing SOC contents (R2 > 0.49). This relationship was also observed after splitting total annual emission of CH4 and N2O into growing and fallow seasons. Nitrogen fertilization and the seasonality in CH4 and N2O emissions did not change the relationships. The inverse correlation between SOC and CH4 and N2O emissions was likely caused by different chemical composition of SOC in various soils. Our results suggest that SOC can be a potential proxy to predict CH4 and N2O emissions in rewetted peatlands to better define GHG predictions of wetland restoration efforts.