Plant Species and Hydrology as Controls on Constructed Wetland Methane Fluxes

Abstract

Core IdeasWetland plant species and site hydrology affect methane fluxes.Plant species effects were clearer under stable hydrology in mesocosm experiments.Species was not as important as the long‐term saturation pattern under variable field hydrologic conditions.Plants which emit methane under isolated mesocosm conditions do not necessarily do so under field conditions.Water table height and fluctuation may be a more dominant control over methane fluxes in wetland soils.Wetlands are the largest natural source of atmospheric methane (CH4), a potent greenhouse gas. Hydrology and species composition are important controls on wetland CH4emissions. Few studies target interactive effects on CH4fluxes, but rather study variables in isolation. Therefore, we asked: How do hydrology and plant species interact to affect CH4fluxes from wetland soils? We measured CH4fluxes under stable water tables in mesocosms planted withAsclepias incarnataL. and mesocosms planted withAlisma trivialePursh. We then tested the interactive effects in saturated and unsaturated restored field locations by measuring CH4fluxes from the plants and the surrounding soil. In mesocosms, CH4fluxes fromA. incarnatawere 8‐fold greater than fluxes from control (no plant) orA. trivialemesocosms.Alisma trivialemesocosms had higher CO2to CH4ratio (less methanogenic dominance) than control mesocosms but did not differ significantly fromA. incarnatamesocosms. In the field, hydrology was the dominant control of CH4flux; both plant species produced approximately 10‐fold more CH4in saturated plots than in unsaturated plots. Incorporating hydrology and species composition into modeling will better predict CH4fluxes from wetland soils, which in turn could aid in designing restored wetlands that offset greenhouse gas emissions.