Arctic LTER: Goals and Results

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John Hobbie
George Kling
Chris Luecke
Gus Shaver
Anne Giblin
Donie Bret-Harte

The goal of the Arctic LTER is to predict the future ecological characteristics of Arctic Alaska based upon our knowledge of the controls of ecosystem structure and function as exerted by physical setting and geologic factors, climatic factors, biotic factors, and the changes in fluxes of water and materials from land to water.

The site lies at 68oN in the foothills of the Brooks Range, in tundra vegetation of sedges and grasses mixed with dwarf birch and low willows. The tundra, streams, and lakes at the site have been undisturbed and unchanged for more than 5,000 years; caribou and moose move freely over this region pursued by wolves and grizzly bears. Populations of lake trout, char, and Arctic grayling are in a pristine state, often dominated by very large and very old individuals. This allows the analysis of relationships in plants and animal communities in an ecosystem unaffected by a legacy of human use.

The climate of northern Alaska has changed remarkably over the past 34 years; the 0.7oC per decade increase in temperature could result in much more than the 3-5o total change predicted by GCM models for a doubling of CO2. Based on several types of observations, there appears to be a biotic response to this regional warming. The nature of this response, its controls, and its long-term implications are under investigation through:
1. Long-term monitoring and surveys of natural variation of terrestrial and aquatic ecosystems in space and time show definite, but very slow, changes. Plant communities are becoming more shrubby, the active layer (annual thaw layer) above the permafrost is becoming thicker as evidenced by stream and lake chemistry, stream nitrate concentration is increasing, an increase in drought frequency has caused disruption in the stream fish habitat with resulting major decrease in the top predators, and the snow-free period is lengthening.
2. Long-term experimental manipulation of terrestrial and aquatic ecosystems show very slow recovery of lakes from nutrient fertilization, and show a rapid response to heating and fertilization of tundra that is similar to the changes happening very slowly in the natural systems.
3. Synthesis of results and predictive modeling at ecosystem and watershed scales. A model of terrestrial primary productivity can be applied across a wider range of PanArctic tundra than exist at the LTER site. An Ensemble Kalman Filter was used to assimilate eddy covariance data into a simple model of Net Ecosystem Production. Stable isotopes of mycorrhizal fungi and plants indicate the strong importance of these fungi in moving N from the abundant organic pools to the plants. Synthesis of lake data show that annual temperature changes are not correlated with average air temperature, wind, or solar radiation but are related to the number of wind or cooling events.