Elberling et al. 2004

Elberling B, Jakobsen BH, Berg P, Sondergaard J, Sigsgaard C. 2004. Influence of vegetation, temperature, and water content on soil carbon distribution and mineralization in four High Arctic soils. Arctic, Antarctic, and Alpine Research, 36: 528-538.

These authors examined the carbon pools and carbon dioxide effluxes from four ecosystems at Zackenberg, in north-east Greenland. Their four ecosystems are very similar to the Alexandra Fjord systems of Dryas (CAVM P1), Cassiope (P2), Salix (G3), and Wet Sedge Meadow (W1).

There are two major sources of soil CO2: respiration by plant roots, and microbial respiration. Which of these two processes dominates CO2 production is a matter of some debate, with studies in the 1990s and 2000s indicating either when measuring similar arctic ecosystems. This study does not settle that debate, with estimated ratios of the two processes ranging from 9:1 to 1:9. What is clear is that plants and microbes compete for resources in arctic soils, with considerable variation in both time and space, even among vegetation communities in one valley with a consistent above-ground climate.

These soils include a buried A-horizon, with birch leaves present in pockets of organic-rich former topsoil indicative of surface conditions during the previous climatic mild period approximately 5000 years ago. These pockets of “Ab” create something of a wildcard situation for CO2 evolution, being responsible for a considerable fraction of the measured CO2 efflux at all ecosystems to varying extent.

To measure subsurface concentrations of CO2, these authors extended a probe to a range of depths and connected it to their gas analyzer also used for measuring surface fluxes, much as we have done at Alexandra Fjord. However, their gas analyzer only measures CO2, and they did not allow their probes to equilibrate to subsurface conditions for very long; a few minutes seems to be the usual protocol in this case.

A range of soil parameters were measured, and in general variation between vegetation types in these parameters exceeded variation within. The Cassiope system was the most variable, but also had the most variable Ab layers, which probably accounted for most of the variation. These patterns of variation at all ecosystems, however, suggest that the effects of climate change will not be uniform across the High Arctic, with increased temperatures leading to perhaps increases or decreases in the decomposition of buried organic matter and CO2 effluxes.

Like our own results from Alexandra Fjord, the Salix ecosystem at Zackenberg showed the highest below-ground CO2 concentrations. At Zackenberg, CO2 concentrations in Salix were mostly related to microbial decomposition of organic matter, with reduced soil water content leading to more oxygenation and higher temperatures, both increasing the rate of decomposition. In contrast, the water-saturated Eriophorum system had very high carbon stores and the highest CO2 efflux, but a decrease in water levels here leads to a shift from methane production to CO2 production, rather than a simple increase in one rate.

Overall, this paper provides some results and considerations of high relevance to my own work, especially given the high overlap in the range of ecosystems under consideration and the range of methods employed in their analysis. Their systems are not identical to those I studied; for example, the Dryas system at Zackenberg appears to be considerably drier and with less vegetation cover compared to the system with the same name at Alexandra Fjord.