Articles | Volume 12, issue 10
Research article
21 May 2015
Research article |  | 21 May 2015

Vegetation and elevation influence the timing and magnitude of soil CO2 efflux in a humid, topographically complex watershed

J. W. Atkins, H. E. Epstein, and D. L. Welsch

Abstract. In topographically complex watersheds, landscape position and vegetation heterogeneity can alter the soil water regime through both lateral and vertical redistribution, respectively. These alterations of soil moisture may have significant impacts on the spatial heterogeneity of biogeochemical cycles throughout the watershed. To evaluate how landscape position and vegetation heterogeneity affect soil CO2 efflux (FSOIL), we conducted observations across the Weimer Run watershed (373 ha), located near Davis, West Virginia, for three growing seasons with varying precipitation. An apparent soil temperature threshold of 11 °C for FSOIL at 12 cm depth was observed in our data, where FSOIL rates greatly increase in variance above this threshold. We therefore focus our analyses of FSOIL on instances in which soil temperature values were above this threshold. Vegetation had the greatest effect on FSOIL rates, with plots beneath shrubs at all elevations, for all years, showing the greatest mean rates of FSOIL (6.07 μmol CO2 m−2 s−1) compared to plots beneath closed-forest canopy (4.69 μmol CO2 m−2 s−1) and plots located in open, forest gap (4.09 μmol CO2 m−2 s−1) plots. During periods of high soil moisture, we find that CO2 efflux rates are constrained, and that maximum efflux rates occur during periods of average to below-average soil water availability. While vegetation was the variable most related to FSOIL, there is also strong interannual variability in fluxes determined by the interaction of annual precipitation and topography. These findings add to the current theoretical constructs related to the interactions of moisture and vegetation in biogeochemical cycles within topographically complex watersheds.

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Short summary
We wanted to understand how the coupling of water and carbon cycling is affected by landscape position and vegetation heterogeneity within a humid, topographically complex watershed in the Appalachian mountains of West Virginia. Over 3 years (2010-2012), we found that in low-rainfall years, shrubs had a strong effect on the magnitude of soil carbon fluxes but that in high-rainfall years, fluxes were constrained across the watershed. Highest fluxes occurred at below-average soil moisture.
Final-revised paper