Arctic and Alpine Research (in press)

Nitrogen Mineralization in Alpine Talus Fields, Green Lakes Valley, Colorado, USA

Alisa J. Bieber
Department of Biology Bryn Mawr College

Mark W Williams
Department of Geography and Institute of Arctic and Alpine Research University of Colorado, Boulder

Mark J. Johnsson
Department of Geology Bryn Mawr College

Thomas Davinroy
Department of Geography and Institute of Arctic and Alpine Research University of Colorado, Boulder

Abstract

This study reports the first direct evidence of nitrogen (N) mineralization in alpine talus fields. Mineralization and nitrification rates were measured in pockets of fine material in talus slopes of an alpine catchment of the Colorado Front Range, USA in 1996. Rates of both processes were higher in patches with vegetation covering >80% of the surface area than in patches with vegetation covering <20% of the surface area. In the mid to late growing season, net mineralization rates at vegetated sites of 2.49 mg N kg-1 d-1were significantly greater than the 0.39 mg N kg-1 d-1at unvegetated sites (P = 0.03). Net nitrification rates of 1.0 mg N kg-1 d-1 with vegetation were significantly greater than the 0.27 mg N kg-1 d-1 at unvegetated sites (P = 0.01). These rates were comparable to mineralization and nitrification rates reported for well-developed tundra soils on nearby Niwot Ridge. Mineralization and nitrification rates varied inversely with elevation along a transect with a 100 meter elevational change (P = 0.005, P = 0.025). N mineralization and nitrification in talus may help explain elevated levels of nitrate (NO3-) in alpine streams in mid to late summer.