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. (C) 2012 Elsevier B.V. All rights reserved.