Assessing the Impacts of Land-Use Change and Ecological Restoration on CH4 and CO2 Fluxes in the Sacramento-San Joaquin Delta, California: Findings from a Regional Network of Eddy Covariance Towers

The Sacramento--San Joaquin Delta in California was drained for agriculture and human settlement circa 1850, resulting in extreme rates of soil subsidence and CO2 emissions due to peat oxidation. As a result of this prolonged ecosystem carbon imbalance where ecosystem respiration exceeded primary productivity, much of the land surface in the Delta now lies 5 to 8 m below sea level. To help reverse subsidence and convert Delta ecosystems from net carbon sources to carbon sinks, land managers have begun converting drained agricultural lands back to flooded ecosystems including wetlands and irrigated rice paddies. However, this comes at the cost of increased CH 4 emissions, a much more potent greenhouse gas than CO2.;To evaluate the impacts of drained to flooded land-use change on the biosphere-atmosphere exchange of CO2 and CH4 in the Delta, I conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land-use types (a rice paddy and two restored wetlands). This research showed that the drained sites were large CO2 and greenhouse gas (GHG) sources. However, this study also found that converting drained agricultural peat soils to flooded rice paddies or wetlands can help reduce or reverse soil subsidence and reduce GHG emissions, despite the potential for considerably higher CH4 emissions. In particular, wetlands offer the greatest potential for reversing subsidence since both restored wetlands were large net carbon sinks. (Abstract shortened by ProQuest.).