Effects of environmental change on carbon and nitrogen Fluxes in Antarctic Terrestrial Ecosystems (FATE)

Problem definition
Terrestrial ecosystems in the higher latitudes of the Maritime Antarctic, in contrast with those of the high Arctic, are structurally simple with only two trophic levels well developed: primary producers and decomposers. These ecosystems are largely oligotrophic. Nitrogen and other minerals are mostly imported from the marine ecosystem (by sea spray, precipitation, marine birds and mammals). Temperature is the key factor controlling the cycling of carbon and nitrogen. As temperature increases so will water availability (through both increased snow melt and precipitation), primary production (via increased water availability) and carbon and nitrogen recycling (via increased rate of decomposition). The import of nitrogen from marine sources will increase with increased precipitation. Soil formation processes will also become more important. It is predicted that functional group diversity will increase.
We hypothesise that, as a result of the increasing temperatures in this region, terrestrial ecosystem structure and processes will become more complex and will ultimately develop increasing similarity with counterparts currently found in lower latitudes.

Objectives

1. To measure C, N, O isotopic ratios of organic matter of known origin and identify organic biomarkers indicative of terrestrial and marine ecosystems, in order to describe the origin, diagenesis and transport pathways of organic matter in the terrestrial ecosystem.
2. To quantify the imports of carbon and nitrogen from the marine ecosystem into the terrestrial ecosystem and identify the role of snow/ice in their storage and subsequent release.
3. To use stable isotope analyses and identified biomarkers to quantify rates of decomposition and describe fluxes of organic matter through key trophic elements of the terrestrial food chain.
4. To identify the influence of elevated temperature on decomposition and the transport of carbon and minerals.

Approach
We will execute comparative studies of terrestrial ecosystems at three different latitudes in the region of the Antarctic Peninsula (Rothera (68°S), Signy Island (61°S), Falkland Islands (52°S)), using this environmental gradient as a proxy for predicted temperature increase. Besides a baseline description of the structure of the terrestrial ecosystems, we will focus on carbon and nitrogen fluxes, and their relationship to temperature. To achieve this we will: (1) measure stable isotope ratios of organic matter (C, N, and O) of different biotic elements of the ecosystem, (2) identify key organic molecules as biomarkers to trace trophic interactions and (3) perform field manipulations, using open-top chambers to increase the temperature artificially with 2-3 °C by which to examine the impact of temperature enhancement on nutrient cycling, rate of decomposition and species diversity.

International co-operation
British Antarctic Survey, UK; Department of Agriculture, Falkland Islands Government, Port Stanley Falkland Islands; University of Antwerp, Belgium.
 

Some results

Open-Top Chambers (OTC) are warming the soil and air, since the Antarctic summer of 2003. These OTC have been placed at sites along a latitudinal gradient from the Falkland Islands to Adelaide Island. During the summer months, the increase in temperature has been almost 1.0 °C.

Over the last three years we have been collecting soil arthropods to monitor the effects of this temperature increase on the community compositions. When you sample from north to south, the number of species drop but the abundance of species increases several times. The most abundant species in the Antarctic are the springtail Cryptopygus Antarcticus and the Oribatid mite Alaskozetes Antarcticus.

The respriration rate of these soils increases with increasing temperature. During the summer of 2004-2005 and 2005-2006 we have been measuring the soil respiration rate inside and outside the OTC. The field measurements also indicate that the OTC treatment is raising the CO₂ flux from the soil.