Wednesday, August 5, 2009
Exhibit Hall NE & SE, Albuquerque Convention Center
Kurt M. Chowanski, Instaar LTER, University of Colorado Boulder, Nederland, CO, Timothy Kittel, Institute of Arctic and Alpine Research, University of Colorado at Boulder Boulder, Boulder, CO, Isabel W. Ashton, Northern Great Plains Network Inventory and Monitoring Program, National Park Service, Rapid City, SD and Mark Williams, Department of Geography, University of Colorado, Boulder, CO
Background/Question/Methods Soil temperature is one of the key determinants of carbon flux, nutrient availability, decomposition rates, and primary productivity. Global climate models predict that as air temperatures rise there will be a corresponding increase in soil temperature, a longer snow-free season, and an increase in soil freezing events. For ecosystems where temperature is a primary limitation to growth and metabolism, like boreal, arctic, subalpine, and alpine regions, increases in soil temperature are expected to increase N mineralization and subsequent nitrate and ammonium runoff, increase respiration and the release of CO2, and alter plant community composition. Despite the large potential changes caused by alterations in soil temperature, spatial and temporal variations in soil temperatures are not as well documented as changes in air temperature and precipitation. Here, we examine whether soil temperatures in seasonally snow-covered areas correlate with air temperatures over an elevational gradient spanning montane forests to high alpine in the Front Range of the Colorado Rockies, Niwot Ridge LTER. Soil and air temperature, soil moisture and precipitation were measured at 3 locations spanning this gradient since the mid 1980s. Degree days were calculated using a base of 0C. Spatial variation in soil temperature was examined by measuring hourly temperatures at 19 locations using dataloggers buried 5 cm from 2004-2008. Snow depth above the soil temperature loggers was measured approximately biweekly for the same period.
Results/Conclusions This area is typified by short growing seasons where the snow free period typically lasts less than 4 months. Soil temperature remained at or below freezing when there is snow cover. At several locations, we found a trend of increasing soil temperature over time. Across the elevational gradient, air and soil temperature were directly correlated in areas of low snow accumulation, while in areas with high snow accumulation air and soil temperature were correlated only during the summer months. Our results suggest that predicted increases in air temperature will have an effect on soil temperature driven by changes in the duration and extent of snowpack. To better understand future changes, it is critical to have a better understanding of how soil temperatures affect carbon and nitrogen cycling, and plant community composition.
