Methane Flux Heterogeneity and Driving Mechanisms in Wetland Ecosystems

Wetlands are significant contributors to global methane (CH₄) emissions, a critical driver of climate change. However, the spatial heterogeneity of CH₄ fluxes and the underlying mechanisms within these wetland ecosystems remains largely unexplored. This study examines the heterogeneity of CH₄ emissions from different types of wetlands in Estonia and California, USA. The studied wetlands include free surface water treatment wetlands, recently restored peatlands in Estonia and three different restored wetlands in California that differ from each other in salinity level, tidal influence, vegetation, and restoration year. All studied sites except the free surface treatment wetlands are equipped with eddy covariance stations for continuous CO₂, H₂O, and CH₄ measurements (open path LI-7500 and LI-7700 analyzers, LICOR Biosciences). Spatial heterogeneity in methane flux was assessed through static chamber measurements using a LI-7810 trace gas analyzer (LICOR Biosciences). Chamber measurement surveys revealed significant variations among gas measurement points within the eddy tower footprint. Additional parameters such as LAI, water pH, electrical conductivity, dissolved oxygen concentration, temperature, turbidity, salinity, water level, and dissolved gas concentration (dCO₂ and dCH₄; analyzed in the lab with GC-2014, Shimadzu) were measured from each sampling spot. After measurements, we collected surface sediment samples for soil TN, TOC, TIC, DOC, DIC, and DN analyses. Our results indicate significant variation in CH₄ fluxes and soil C and N content within different sampling points and in different ecosystems. In the constructed wetland in Estonia, biweekly measurements from twelve distinct points over two years revealed significant heterogeneity in CH₄ fluxes, with peak emissions ranging from 144 mg m^-2 d^-1 to 254.4 mg m^-2 d^-1 observed from specific chamber measurement plots. In contrast, the restored peatland showed a lower range of CH₄ emissions (0.096 mg m^-2 d^-1 to 34.6 mg m^-2 d^-1) observed from six measurement plots. The preliminary measurements conducted in California wetlands also showed a large variation within and between the sites. These findings highlight the complex nature of CH₄ flux heterogeneity in wetlands and the critical need for site-specific management strategies. Accurately quantifying and understanding these variations is essential for refining CH₄ budgets and developing effective mitigation strategies for greenhouse gas emissions from wetland ecosystems.