Arctic and Alpine Research (in press)
Alisa J. Bieber
Mark W Williams
Mark J. Johnsson
Thomas Davinroy
Department of Biology
Bryn Mawr College
Department of Geography and
Institute of Arctic and Alpine Research
University of Colorado, Boulder
Department of Geology
Bryn Mawr College
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.