Methane Fluxes and Drivers in a Coastal Freshwater Forested Wetland: From the Soil to the Canopy

Methane (CH 4) emissions from wetlands represents~ 32% of the global total, and some coastal wetlands have recently been found to exhibit very high CH 4 emission rates. Yet, the mechanisms responsible for these emissions and their broader representativeness remain unknown. Here we report five years of CH 4 fluxes (2012-2016, using the eddy-covariance approach) from a coastal freshwater forested wetland in North Carolina, USA. Over the five years, CH 4 fluxes ranged from 16.3 to 54.7 gC m-2 yr-1. Variations in the CH 4 time series strongly co-varied with sap flux and gross primary productivity at the diurnal scale, water table depth at the synoptic scale and soil temperature at the diurnal and synoptic scale. In a suite of laboratory studies on soil CH 4 production, hummock-hollow microtopography was identified as an important mediator of CH 4 fluxes, with 3-5 times the potential CH 4 production in …