The ecology of pulse events: insights from an extreme climatic event in a polar desert ecosystem

Abstract

Abstract. Climate change is occurring globally, with wide ranging impacts on organisms and ecosystems alike. While most studies focus on increases in mean temperatures and changes in precipitation, there is growing evidence that an increase in extreme events may be particularly important to altering ecosystem structure and function. During extreme events organisms encounter environmental conditions well beyond the range normally experienced. Such conditions may cause rapid changes in community composition and ecosystem states. We present the impact of an extreme pulse event (a flood) on soil communities in an Antarctic polar desert. Taylor Valley, McMurdo Dry Valleys, is dominated by large expanses of dry, saline soils. During the austral summer, melting of glaciers, snow patches and subsurface ice supplies water to ephemeral streams and wetlands. We show how the activation of a nonannual ephemeral stream, Wormherder Creek, and the associated wetland during an exceptional high-flow event alters soil properties and communities. The flow of water increased soil water availability and decreased salinity within the wetted zone compared with the surrounding dry soils. We propose that periodic leaching of salts from flooding reduces soil osmotic stress to levels that are more favorable for soil organisms, improving the habitat suitability, which has a strong positive effect on soil animal abundance and diversity. Moreover, we found that communities differentiated along a soil moisture gradient and that overland water flow created greater connectivity within the landscape, and is expected to promote soil faunal dispersal. Thus, floods can 'precondition' soils to support belowground communities by creating conditions below or above key environmental thresholds. We conclude that pulse events can have significant long-term impacts on soil habitat suitability, and knowledge of pulse events is essential for understanding the present distribution and functioning of communities in soil ecosystems.

The spatial structure of Antarctic biodiversity

“…Water availability is regarded as the most important abiotic stress influencing Antarctic terrestrial communities (Kennedy 1993, Howard-Williams et al 2010, Nielsen et al 2012. At the broadest scales, this is illustrated by the substantial decline in cryptogamic vegetation abundance and areal extent from the maritime regions of the Scotia arc to the southern part of the Antarctic Peninsula (Smith 1972, V. R. Smith 1988, Peat et al 2007).…”

“…Two events reactivated nonannual ephemeral streams and generated greater water flow across the land surface. These warming events increased soil moisture, altered soil invertebrate community composition and soil and stream chemistry, as well as increasing lake levels, with many of these effects still apparent the following summer season , Nielsen et al 2012.…”

Physiological mechanisms used by fish to cope with salinity stress

“…In addition to such gradual climate-induced salinity changes, severe and acute salinity stress results from extreme pulsatory climate events (tsunamis, hurricanes, etc. ), which are predicted to increase in frequency and severity (Nielsen et al, 2012). Such events can cause large and sudden increases or decreases in habitat salinity, e.g.…”

Local and regional influences over soil microbial metacommunities in the Transantarctic Mountains

“…Understanding how ecological context influences local and regional controls over soil microbial diversity (Dumbrell et al 2009, Caruso et al 2011, Soininen 2012) is imperative for Antarctic soils because these relatively simple ecosystems may be particularly sensitive to climate change (Nielsen and Wall 2013). Antarctic soils are predicted to become warmer and wetter (Bracegirdle et al 2008), and an increased frequency of pulse melt/flood events (IPCC 2007) will likely alter the temporal and spatial distribution of liquid water, which can significantly affect soil ecological processes , Nielsen et al 2012, Nielsen and Wall 2013. Therefore, it is essential to resolve the influences of local and regional controls over soil microbial community composition, which may allow us to predict how Antarctic terrestrial ecosystems will respond to climatic shifts.…”