Biogeochemistry of a Treeline Watershed, Northwestern Alaska

• Published in: Journal of Environmental Quality
• Main Author: Stottlemyer, Robert
• Other Authors: Department of Interior Global Change Program, U.S. Geological Survey Long-Term Ecosystem Studies Program
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2001
• Subjects: Management, Monitoring, Policy and Law; Pollution; Waste Management and Disposal; Water Science and Technology; Environmental Engineering; permafrost; Alaska
• Online Access: http://dx.doi.org/10.2134/jeq2001.1990; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2134%2Fjeq2001.1990; http://onlinelibrary.wiley.com/wol1/doi/10.2134/jeq2001.1990/fullpdf

ABSTRACT Since 1950, mean annual temperatures in northwestern Alaska have increased. Change in forest floor and soil temperature or moisture could alter N mineralization rates, production of dissolved organic carbon (DOC) and organic nitrogen (DON), and their export to the aquatic ecosystem. In 1990, we began study of nutrient cycles in the 800‐ha Asik watershed, located at treeline in the Noatak National Preserve, northwestern Alaska. This paper summarizes relationships between topographic aspect, soil temperature and moisture, inorganic and organic N pools, C pools, CO 2 efflux, growing season net N mineralization rates, and stream water chemistry. Forest floor (O2) C/N ratios, C pools, temperature, and moisture were greater on south aspects. More rapid melt of the soil active layer (zone of annual freeze–thaw) and permafrost accounted for the higher moisture. The O2 C and N content were correlated with moisture, inorganic N pools, CO 2 efflux, and inversely with temperature. Inorganic N pools were correlated with temperature and CO 2 efflux. Net N mineralization rates were positive in early summer, and correlated with O2 moisture, temperature, and C and N pools. Net nitrification rates were inversely correlated with moisture, total C and N. The CO 2 efflux increased with temperature and moisture, and was greater on south aspects. Stream ion concentrations declined and DOC increased with discharge. Stream inorganic nitrogen (DIN) output exceeded input by 70%. Alpine stream water nitrate (NO − 3 ) and DOC concentrations indicated substantial contributions to the watershed DIN and DOC budgets.