Eddy Covariance Measured Methane and Carbon Dioxide Fluxes for a Restored Wetland, Sacramento - San Joaquin Delta, California, USA

There is an increase in investment to protect and restore natural wetlands due to environmental benefits such as soil carbon storage, atmospheric carbon sequestration, and in the case of the Sacramento-San Joaquin Delta (SSJ-Delta), subsidence reversal. Although these ecosystems can actively increase stored carbon or limit oxidation of existing soil organic carbon (e.g. peat), anaerobic conditions created by permanent and semi-permanent flooding can result in the release of methane (CH4), a more potent greenhouse gas. In the summer of 2010, continuous eddy covariance measurements of CH4 and carbon dioxide (CO2) were collected from a restored wetland marsh on Twitchell Island in the SSJ-Delta. The eddy covariance instrumentation includes a CSAT3 sonic anemometer(Campbell Scientific, Logan, UT USA) , an open-path CO2/H2O infrared gas analyzer (LI-7500, LI-COR Biogeosciences, Lincoln NE USA) and closed-path tunable diode laser fast methane sensor (FMA or FGGA, Los Gatos Research). From June 22-30, an open-path methane analyzer (LI-7700, LI-COR Biogeosciences) was installed for 2-3 weeks to compare with the closed-path method. Initial results over the growing season, show the wetland’s potential to be a sink for CO2, as maximum daily values are around -10 µmol m-2 s-1. However, CH4 emissions may offset this potential as average CH4 emissions from the open and closed path comparison study were close to 200 nmol m-2 s-1, with peak rates as high as 400 nmol m-2 s-1. Here we present results showing diurnal and seasonal trends of CH4 and CO2 fluxes, which are dependent upon air, leaf, and water temperatures, differences in humidity, and plant stomatal controls, all driven by changes in daily and seasonal variations in solar radiation.