Methane in sulfate-rich and sulfate-poor wetland sediments

Abstract

Wetlands of northern Belize provide a unique opportunity to study methane production and emissions from marshes dominated by identical species (Typha domingensis, Cladium jamaicense) and genus (Eleocharis spp.), but differing substantially in the amount of sulfates present in the sediments. Some marshes occur on limestone marls rich in gypsum (CaSO₄) while others are underlain by alluvial sands poor in sulfates. Concentrations of methane and sulfates in the sediment interstitial water are one or more orders of magnitude different for these two geological substrata averaging 139.2 and 14.9 μM of CH₄, and 0.08 and 11.53 mM of SO₄ ⁻² 2 on alluvial sands and limestone respectively. The amount of methane found in the internal atmosphere of plants from alluvial sands is significantly higher (6.3 μM) than in plants from limestone (0.19 μM). The average methane emissions measured in wetlands located on alluvial sands were 25.2 mg m⁻² h⁻¹ while emissions from marshes on limestone were only 2.4 mg m⁻² h⁻¹. These values extrapolated for the entire year and the respective wetland areas resulted in the estimate of total CH4 emissions from northern Belize of 0.066 Tg per year.