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February 15th, 2004

High-elevation climate change: A new model for ecosystems

Tim Seastedt, Bill Bowman, Nel Caine, Diane McKnight, Alan Towsend, and Mark Williams (Niwot Ridge LTER PIs) published a key conceptual paper, "The Landscape Continuum: A Model for High-Elevation Ecosystems," in volume 54, no. 2 of Bioscience. Their paper employs a new conceptual model that links terrestrial ecosystems to each other and to aquatic ecosystems.

At the Niwot Ridge LTER Colorado Rocky Mountain Front Range site, the researchers have documented an increase in precipitation of more than 10 millimeters per year for the last 50 years. This increase has affected the physical processes of alpine lakes; lake-ice thickness measured in late March over a 20-year interval shows a marked decline, while temperatures over this interval have remained statistically unchanged. The changes in ice thickness are best explained by increased winter precipitation (about 1% per year), which leads to increased flows into the lakes. Greater volumes of water hold greater quantities of energy, and thus ice thickness in late winter is reduced. They have also detected an increase in inorganic nitrogen deposition from the atmosphere of 0.3 kilograms per hectare per year between 1984 and 1996. In contrast to the terrestrial ecosystems in alpine areas, which are relatively stable, lake ecosystems in the same areas are undergoing rapid changes in benthic primary production and in diatom species composition. In order to provide a conceptual framework for understanding and predicting how high-elevation systems will respond to climate change, they integrated and augmented previous conceptual models to develop a new model, which suggests that high-elevation lakes and tree line, which functions as a windbreak and collects snow, particulates, and nutrients, are the locations that experience the first negative impacts of anthropogenic materials scavenged from the atmosphere.