Subsurface characterization of methane production and oxidation from a New Hampshire wetland

Abstract

We measured the carbon isotopic composition of pore water carbon dioxide from Sallie’s Fen, a New Hampshire poor fen. The isotope profiles are used in combination with a one‐dimensional diffusion–reaction model to calculate rates of methane production, oxidation and transport over an annual cycle. We show how the rates vary with depth over a seasonal cycle, with methane produced deeper during the winter months and at progressively shallower depths into the summer season. The rates of methane production, constrained by the measured δ13Cdic profiles, cannot explain high methane emission during the summer. We suggest that much of the methane produced during this time comes either from the unsaturated peat, or from the top 1–3 cm of saturated peat where episodic exchange with the atmosphere makes it invisible to our method.

Modelling methane emissions from natural wetlands by development and application of the TRIPLEX-GHG model

“…The underestimation of CH 4 emission pulse may be partly due to, on the one hand, external environmental triggers and CH 4 contribution from microbial mat systems during summer not being included in the model (Shoemaker and Schrag, 2010;Tian et al, 2010). On the other hand, the ebullition events of short duration, which are often recorded as very high fluxes in the observation, are hard to reproduce (Moore et al, 2011), since some dependent factors (e.g.…”

Spatial and temporal patterns of CH<sub>4</sub> and N<sub>2</sub>O fluxes in terrestrial ecosystems of North America during 1979–2008: application of a global biogeochemistry model

“…For the simulated CH 4 peak while rarely shown in observations, it might due to the low sampling frequency of field work. The underestimation of CH 4 emission in Sallie's fen might be due to either the external environmental trigger which are not included in the model (Tokida et al, 2007;Shoemaker and Schrag 2010), or the contribution to CH 4 from the microbial mat systems during summer season (Shoemaker and Schrag, 2010). Harrison, 1973;Joergensen, 1985;Linton and Buckee, 1977;Lamb and Garver, 1980;Nagai et al, 1973;O'Neill and Wilktnson, 1977;Ferenci et al, 1975 Km CH 4 Oxidsoil (g C m −3 ) 10 0.33-19.…”

Quantification and Controls of Wetland Greenhouse Gas Emissions

“…There are, however, some limitations of these data. First, bulk soil C contributions to wetland CO 2 and CH 4 are likely to be derived from decomposing surface soil or peat horizons -decades to centuries old -where oxygen and other biogeochemical gradients are steepest (Clymo and Pierce, 1995;Shoemaker and Schrag, 2010). These same layers are likely to differ only slightly in their 14 C signature from contemporary atmospheric (modern) C due to the vertical accretion of wetland soils, and therefore the bulk C signal may be obscured.…”