Greenhouse gas (CO2, CH4, H2O) fluxes from drained and flooded agricultural peatlands in the Sacramento-San Joaquin Delta

The Sacramento-San Joaquin Delta in California was drained and converted to agriculture more than a century ago, and since then has experienced extreme rates of soil subsidence from peat oxidation. To reverse subsidence and capture carbon there is increasing interest in converting drained agricultural land-use types to flooded conditions. Rice agriculture is proposed as a flooded land-use type with CO2 sequestration potential for this region. We conducted two years of simultaneous eddy covariance measurements at a conventional drained and grazed degraded peatland and a newly converted rice paddy to evaluate the impact of drained to flooded land-use change on CO2, CH4, and evaporation fluxes.We found that the grazed degraded peatland emitted 175–299 g-C m−2 yr−1 as CO2 and 3.3 g-C m−2 yr−1 as CH4, while the rice paddy sequestered 84–283 g-C m−2 yr−1 of CO2 from the atmosphere and released 2.5–6.6 g-C m−2 yr−1 as CH4. The rice paddy evaporated 45–95% more water than the grazed degraded peatland. Annual photosynthesis was similar between sites, but flooding at the rice paddy inhibited ecosystem respiration, making it a net CO2 sink. The rice paddy had reduced rates of soil subsidence due to oxidation compared with the drained peatland, but did not completely reverse subsidence.

► We compared CO2, CH4, and H2O fluxes from a flooded rice paddy and drained peatland. ► The drained peatland was a net source and the rice paddy a net sink for atmospheric CO2. ► Considering CH4 flux, the rice paddy had a smaller net carbon greenhouse gas effect. ► The rice paddy evaporated 45–95% more water than the drained peatland. ► Subsidence at the rice paddy was about half that of the drained peatland.