Nitrous Oxide Emissions from Soils in Louisiana’s Atchafalaya River Basin

Abstract

The Atchafalaya River Basin functions as a net sink for nitrogen delivered by the Mississippi and Red Rivers. Continued influx of river-borne sediment drives rapid habitat change on the floodplain, and lakes are transitioning to seasonally flooded baldcypress swamps and bottomland hardwood forests. As flooding regimes change, leading to more intermittent wet and dry cycles, soil conditions become more conducive to incomplete denitrification resulting in increased N2O emissions. The objective of this laboratory study was to determine if sediments in the Basin are potential sources of N2O emissions, and if emission rates differ among habitats types. Results indicate that potential N2O emission rates are low, and differ by habitat type. Lake sediments had the highest potential denitrification rates (53.68 g N2-N ha−1d−1), while baldcypress sediments had the highest potential N2O emissions (2.31 g N2O-N ha−1d−1). Unflooded bottomland hardwood sediments had very low denitrification potential and were not a source of N2O emissions, but emissions of both N2 and N2O increased after bottomland hardwood sediments were flooded. These results suggest that overall N2O emissions are low, but management strategies aiming to improve water quality and reduce greenhouse gas emissions should consider each habitat separately when modeling nitrogen removal within large floodplains.