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October 27, 2003
Seattle, Washington, USA

The Effects of Soil Moisture on Carbon Processes in Upland and Lowland Tundra Ecosystems

Faith A. Heinsch¹, John S. Kimball², Sinkyu Kang³, Hyojung Kwon⁴, Walter C. Oechel^5
1NTSG/College of Forestry and Conservation, The University of Montana, 32 Campus Drive, Missoula, MT, 59802, USA, Phone 406-243-6218, Fax 406-243-4510, faithann@ntsg.umt.edu
²Flathead Lake Biological Station, The University of Montana, 311 BioStation Lane, Polson, MT, 59860, USA, Phone 406-982-3301, Fax 406-982-3201, johnk@ntsg.umt.edu
³NTSG/College of Forestry and Conservation, The University of Montana, 32 Campus Drive, Missoula, MT, 59802, USA, Phone 406-243-6263, Fax 406-243-2434510, kang@ntsg.umt.edu
⁴Global Change Research Group, San Diego State University, Department of Biology, PS-240, 5500 Campanile Drive, San Diego, CA, 92182, USA, Phone 619-594-6613, Fax 619-594-7831, hkwon@sciences.sdsu.edu
⁵Global Change Research Group, San Diego State University, Department of Biology, PS-240, 5500 Campanile Drive, San Diego, CA, 92182, USA, Phone 619-594-6613, Fax 619-594-7831, oechel@sunstroke.sdsu.edu

Global climate change, in the form of increasing temperatures, melting permafrost, longer growing seasons and altered precipitation and hydrologic drainage patterns is leading to dramatic changes in the Arctic, while the full implications of such changes on regional terrestrial carbon cycle dynamics is unknown. We use a terrestrial ecosystem process model and eddy covariance flux network measurements to investigate spatial patterns and temporal variability in vegetation net primary production (NPP), soil heterotrophic respiration and net CO₂ exchange of lowland and upland tundra communities on the Alaska North Slope. In particular, we investigate the sensitivity of these processes to ground water depth and soil moisture and the potential effects of altered drainage and precipitation on the regional carbon cycle under a changing climate.

Our results indicate that the regional carbon budget is highly sensitive to variations in ground water depth. Drying soils yield marked increases in soil heterotrophic respiration, increased N cycling and a decrease in soil C storage even though increased N cycling and associated soil nutrient availability under drier soil conditions yields higher NPP and increased C sequestration by vegetation. In lowland tundra, however, we find evidence that decreases in ground water depth and soil moisture can lead to moisture stress, decreasing both vegetation productivity and soil microbial activity. Our results indicate that the capacity of the tundra as a net source or sink for atmospheric CO₂ under current and projected future warming will depend largely on precipitation and soil hydrological impacts to soil respiration. Warming with increased or no net change in soil moisture will likely lead to increased NPP, relatively stable soil carbon pools and net C sequestration, while regional warming and drying will likely lead to increased soil respiration and net C losses.

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