Plant Species and Hydrology as Controls on Constructed Wetland Methane Fluxes

Wetlands are the largest natural source of atmospheric methane (CH4), a potent greenhouse gas. Hydrology and species composition are important controls on wetland CH4 emissions. Few studies target interactive effects on CH4 fluxes, but rather study variables in isolation. Therefore, we asked: How do hydrology and plant species interact to affect CH4 fluxes from wetland soils? We measured CH4 fluxes under stable water tables in mesocosms planted with Asclepias incarnata 1. and mesocosms planted with Alisma triviale Pursh. We then tested the interactive effects in saturated and unsaturated restored field locations by measuring CH4 fluxes from the plants and the surrounding soil. In mesocosms, CH4 fluxes from A. incarnata were 8-fold greater than fluxes from control (no plant) or A. triviale mesocosms. Alisma triviale mesocosms had higher CO2 to CH4 ratio (less methanogenic dominance) than control mesocosms but did not differ significantly from A. incarnata mesocosms. In the field, hydrology was the dominant control of CH4 flux; both plant species produced approximately 10-fold more CH4 in saturated plots than in unsaturated plots. Incorporating hydrology and species composition into modeling will better predict CH4 fluxes from wetland soils, which in turn could aid in designing restored wetlands that offset greenhouse gas emissions.