Comparative study of methane dynamics between a productive fen and a shallow lake in a subarctic palsa mire complex, Northern Sweden
Abstract
Land-atmosphere carbon exchanges, with a focus on methane emissions, have been monitored continuously since late May 2012 over a subarctic palsa mire which is underlain by discontinuous permafrost (Stordalen Mire, Northern Sweden, 68°20'N, 19°03'E). This dynamic landscape is a mix of dry palsa mounds elevated by permafrost, water-saturated areas with deep summer active layers, fen areas without permafrost, and open water areas. Using high frequency eddy covariance (EC) measurements, we take an ecosystem-scale approach to analyze emissions from different surface types and integrate the effect of landscape heterogeneity on methane dynamics. Early results from the EC tower situated at the shore of the wettest part of the mire, bordered by a shallow lake, show significant differences depending upon the dominant air flow. Thanks to a stable bimodal east-west wind direction, we are able to clearly distinguish methane emissions between the vegetated productive fen and the lake. The two surfaces present different analytical challenges due to different vertical turbulent transport in the boundary layer. Measurements indicate much higher methane fluxes from the wetland quadrant during the early growing season: average emissions of 6.5 mg.m-2.h-1 over the fen are four times higher than those observed from the lake (1.5 mg.m-2.h-1). Methane release increased during the summer season in both cases. The fen and lake results are consistent with previous studies and local, ongoing chamber measurements conducted at the mire. However, the minimal contribution of the lake to total emissions is unexpected given recent publications about arctic emissions. The role of open water areas on methane dynamics is still an open question, and the low fluxes we observe might be due to cooler sediment temperatures early in the ice free season. A second EC tower will be operational from late summer 2012, with a methane flux footprint comprising dryer and barely thawed vegetated areas. Permafrost in the area is expected to further degrade, therefore, the fen is likely to represent a possible future state of the mire, that is to say a stable large methane source.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.B31D0459J
- Keywords:
-
- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0426 BIOGEOSCIENCES / Biosphere/atmosphere interactions;
- 0497 BIOGEOSCIENCES / Wetlands