The influence of hydrochemistry on methane emissions from two contrasting Northern Wetlands

Methane emissions from an acidic bog and a forested swamp in north Wales, U.K., were measured over a 12 month period. Along with the emission, hydrochemistry (DOC, SO^2-₄ and NO3^-₃) and physical factors (temperature, water table level) were determined. At the bog site, the methane emission ranged from 0.15 mg m^-2 day^-1 to 6.39 mg m^-2 day^-1, having two peaks in spring and late summer. In contrast, high emission was observed in October (38.95 mg m^-2 day^-1) and November (75.37 mg m^-2 day^-1) at the swamp site, which is concurrent with leaf litter production and high DOC concentrations. During the remaining months, the flux varied between -1.33 mg m^-2 day^-1 and 3.05 mg m^-2 day^-1. Correlation analyses showed that the methane emission from the acidic bog had a positive correlation with soil temperature, and negative correlations with sulfate and nitrate concentrations in the pore-water. However, a correlation with water table level was absent. Methane emission from the swamp exhibited a negative correlation with sulfate concentration. Our results confirm that methane emissions vary substantially between different types of wetlands, and suggest that under certain conditions, hydrochemistry may be a more critical controlling variable for methane emissions than temperature and water table level.