The Effects of Organic Matter Amendments on Greenhouse Gas Emissions from a Mitigation Wetland in Virginia’s Coastal Plain

Abstract

There is concern that widespread restoration and/or creation of freshwater wetlands may present a radiative forcing hazard because of the potential for methane (CH4) emissions. Yet data on greenhouse gas (GHG) emissions from restored wetlands are sparse and there has been little investigation into the GHG effects of amending wetland soils with organic matter (OM), a practice used to improve function of mitigation wetlands in the Eastern United States. In this study we measure GHG emissions across an OM gradient at the Charles City Wetland (CCW) in Charles City County, Virginia. We found soils heavily loaded with OM emit significantly more CO2 than those that have received little or no OM. CH4 emissions from CCW are low compared to reference wetlands and show no relationship with the loading rate of added OM or total soil carbon. We conclude that adding moderate amounts (< ~150 kg m−2) of OM to the CCW does not greatly increase GHG emissions, while the addition of high amounts of OM produces additional CO2, but not CH4. CH4 flux is highest under flooded conditions during warmer months but it still a modest contribution to global warming potential compared to soil CO2 flux.