MECHANISMS REGULATING GREENHOUSE GAS EMISSIONS AND SOIL CARBON STORAGE IN MID-ATLANTIC COASTAL PLAIN WETLANDS

Abstract

Wetlands are key components of the global carbon (C) cycle, storing significant amounts of C while emitting methane (CH4), a greenhouse gas. As wetland restoration emerges as a potential climate mitigation strategy, understanding the factors that influence wetland greenhouse gas exchange across land uses is essential for aligning management with ecology and biogeochemistry. This dissertation investigates variability in soil organic carbon (SOC) storage and CH4 flux in mid-Atlantic Coastal Plain wetlands, focusing on the roles of hydrology, vegetation, and land-use history in shaping underlying ecosystem processes.In Chapter 1, I surveyed SOC stocks across neighboring least-disturbed wetlands with similar vegetation and hydrogeomorphology and found substantial variation. Hydrologic regimes and relative topography partially explained variability, highlighting the importance of landscape heterogeneity in determining wetland C storage capacity. In Chapter 2, I measured CH4 fluxes across five dominant vegetation patch types in a freshwater wetland using a multi-scale approach. I found that vegetation patches had distinct CH4 signals throughout the growing season, likely driven by differences in the mechanisms that regulate fluxes. The magnitude of the CH4 source was linked to patch identity, suggesting that CH4 fluxes were properties of patch types, and that a patch-explicit representation may be needed for modeling and estimating wetland greenhouse gas exchange. In Chapter 3, I explored the temporal dynamics of CH4 flux across wetlands with different land-use histories, identifying key biophysical drivers at multiple time scales. I found that after two decades, CH4 dynamics in a restored wetland appeared to have converged with those at a natural wetland and diverged with those at a cultivated former wetland. Together, these findings demonstrate the importance of acknowledging and accounting for the inherent variability and context-specificity in wetland C dynamics and suggest that wetland management and restoration for climate mitigation requires a detailed understanding of wetland ecosystem processes.