Chain Reaction

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Soil plots in a reactivated wetland (summer 2008-09).

MCM scientists are contributing to the recognition that ecosystem responses to climate change are not necessarily gradual or directional, especially in low diversity ecosystems where harsh environmental conditions dominate (Fig. 1). For example, in soil ecosystems in the McMurdo Dry Valleys in Antarctica there are only a few soil nematode species, compared to the hundreds in a temperate soil sample, and the dominant nematode in the dry valley soils contributes disproportionably to soil carbon turnover. As a result, episodic increases or decreases in soil moisture may be amplified, causing a large change in ecosystem function because of the sensitivity of the dominant nematode species, rather than driving a shift in the community composition with other nematode species becoming more active.

Overall, the anticipated climate transitions in the Dry Valleys provide an excellent opportunity to examine contemporary patterns in ecological connectivity and predict how these patterns may change in the future. The reasons that measurements of rates of change and connectivity across the landscape are facilitated in the MDV are several:

  1. Landscapes are old (>106 years) with little direct anthropogenic impact
  2. Food webs are simple with low diversity of metazoan taxa (there are no vascular plants or vertebrates)
  3. Although considered a desert, the MDV contains a massive amount of water as ice
  4. Summer temperatures hover near 0°C and moderate summer warming can greatly increase hydrologic connectivity (through pulsed flood events and gradual increase in glacier melt)

Our past studies have shown the influences of a decadal cooling trend and intense seasonal warming events (Doran et al. 2002b; Foreman et al. 2004). Based on these observations we predict that the ecological impacts of sustained warming will be mediated by changes in hydrologic and wind-driven connectivity. Our conceptual model of changes in connectivity (Fig. 2) provides a basis for developing new models of MDV dynamics under a warming climate that will be relevant to many low diversity ecosystems worldwide.

Conceptual model of climate driven presses and pulses in the MDV ecosystem. Influences of presses (grey line) are a linear function of duration and magnitude whereas pulses (events represented as variability in the black line) influence climate disproportionally to their duration. Pulses and presses can elicit non-linear responses from ecosystems depending upon initial conditions and nature (sign, magnitude, duration) of the changes. For example, in the MDVs a long-term cooling press limited meltwater generation and streamflow, decreasing productivity in lake and soil biota over a decadal time scale. In contrast, the warm windy summers of 2001-02 and 2008-09 enhanced hydrological connectivity, offsetting previous changes from a decade of cooling. Climate models predict that the role of pulses in driving the behavior of the MDV ecosystem will increase in the immediate future.
For further reading: 
Foreman, C. M., B. Sattler, J. A. Mikucki, D. L. Porazinska, and J. C. Priscu (2007), Metabolic activity and diversity of cryoconites in the Taylor Valley, Antarctica, J. Geophys. Res., 112, G04S32, doi:10.1029/2006JG000358.
Fountain, A. G., T. H. Nylen, M. Tranter, and E. Bagshaw, (2008), Temporal variations in physical and chemical features of cryoconite holes on Canada Glacier, McMurdo Dry Valleys, Antarctica, J. Geophys. Res., 113, G01S92, doi:10.1029/2007JG000430.
Tranter, M., A. G. Fountain, C. H. Fritsen, W. B. Lyons, J. C. Priscu, P. J. Statham, and K. A. Welch (2004), Extreme hydrochemical conditions in natural microcosms entombed within Antarctic ice, Hydrol. Processes, 18, 379-387.
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