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 CO₂from 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.