Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Changes in the Environment and Ecology at Toolik Lake, Alaska
John E. Hobbie1
1The Ecosystems Center, Marine Biological Laboratory, 67 Water Street, Woods Hole, MA, 02543, USA, Phone 508-289-7470, Fax 508-457-1548, jhobbie@mbl.edu
Toolik Lake, on the North Slope of Alaska, is the site of a long-term ecological study of tundra, lakes, and streams that is now in its 28th year. It is expected that funding from the U.S. Long-term Ecological Research program will continue for decades more. Data collected include climate, thickness of active layer, water and soil temperatures, species and abundance of vegetation, primary production and chemistry in tundra, streams, and lakes, species and abundance of stream and lake invertebrates and fish, and growth of stream fish. Long-term experimental manipulations include warming, shading, and fertilizing four types of tundra, fertilizing streams and lakes, and changing the predation pressure from fish at the top of the trophic cascade. Simulation models based on mechanistic or process understanding are used to forecast and hindcast ecological response to changes in CO2 concentrations, air temperature, and soil moisture.
The increase in air temperature of several degrees centigrade over the past decades in northern Alaska is well documented. Most of this is in winter-time temperatures. Permafrost temperatures have risen but some of the rise is due to changes in depth of snow. At a depth of 20 m, where the annual variation is damped out, the permafrost temperature is still –5°C so there is no thawing. The long-term response of the vegetation is subtle and has only in recent years begun to emerge from the variability across the landscape. The trend is for an increase in the abundance of shrubs, such as dwarf birch. The chemistry of streams and lakes is also changing; the alkalinity has doubled in the past decade. The most likely cause is increased total weathering of glacial till as the depth of the thawed layer increases slightly and material frozen for 10,000 years is exposed.
Long-term experiments with low-lying tundra vegetation give even more dramatic results. An increase of 5°C in air temperature led to the dominance of birch that reached a height of more than a meter. Similar results with fertilizer treatments indicate a possible link to rates of nutrient cycling. Long-term measures of fish growth in streams reveal that this population of arctic grayling is close to its upper limit of temperature for survival. If summer temperatures continue to increase, the grayling will burn more calories than they can collect in their food, they will lose weight during the summers (which happens in warm summers now), and will be unable to reproduce the following spring. If warm summers become more frequent, the population will not reproduce and may die out.
Models of tundra carbon are based on processes of photosynthesis and nitrogen cycling and calibrated to the long-term experimental data. The projection for the next century is that there will be a relatively small increase in carbon stored in soils and vegetation.
In conclusion, even in the Arctic tundra where the first ecological changes to climate change are expected, the response of the environment and ecosystems is slow and difficult to measure even over three decades. A number of intensive study sites must be established in addition to the three or four already in existence.
Abstract Categories: Changes on Land
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