McMurdo LTER Hypotheses for MCM-IV

Overarching Hypothesis Climate warming in the McMurdo Dry Valley ecosystem will amplify connectivity among landscape units leading to enhanced coupling of nutrient cycles across landscapes, and increased biodiversity and productivity within the ecosystem.

Climate warming may be manifested as a slow press of warmer summers as ozone depletion is ameliorated, upon which transient pulse events of high summer flows and katabatic winds will be overprinted

Working Hypotheses

H1. Pulse events (wind and melt) increase hydrological and biological connectivity across landscape units.

Floods produced by warming events and katabatic windstorms of increased magnitude and/or frequency will accelerate movement of biota and nutrients across the dry valley landscape. Large pulses in melt water should enhance connectivity by increasing habitat suitability for microalgae and invertebrates and effectively expanding the range of many taxa. Movement of specific organisms with water and wind-blown material should resemble source pools within a given valley because the valleys are aligned with prevailing winds

H2. Summer pulses of liquid water produce transient moist habitats with altered biological diversity and ecological complexity.

If dry valley invertebrate and bacterial communities respond in opposite ways to saturation, then the most complex communities (i.e., those characterized by moderate levels of bacterial, cyanobacterial and invertebrate diversity) may occur in the ecotones between saturated sediments and arid soil environments. If warm climates enhance hydrologic connectivity by expanding the saturated zones, these ecotones between wet sediment and dry soil environments may also be expanded, thus contributing to more biological complexity within the dry valley landscape.

H3. Increased connectivity enhances rate, variance and the coupling of biogeochemical processes across the landscape

In streams, high flows may cause scouring of cyanobacterial mats from the streambed and contribute to high organic matter and nutrient loading to lakes. In soils, high melt years are associated with changes in soil communities and the mobilization of salts. Increased snow patch and permafrost melting during warm years would also increase solute and nutrient fluxes into the stream and lakes and de-salt the soils.

H4. The emergence of wetted habitats varies with local geography (i.e., slope, aspect, elevation and geomorphology) and history of landscape development.

The elevational and longitudinal gradients characterizing the local physical geography will constrain development of newly or intermittently wetted habitats resulting from increased frequency of summer warming events and increased hydrological connectivity. Habitat suitability varies greatly along both gradients in both soils and streams. With warmer summer conditions, some currently closed basin lakes may become flow through lakes like Lake Miers. This change would be expected to influence the connectivity of the lake microbial communities.

Read more details in our 2010 research proposal