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Mineral nitrogen transformations in and under seasonal snow in a high‐elevation catchment in the Rocky Mountains, United States
Author(s) -
Williams Mark W.,
Brooks Paul D.,
Mosier Arvin,
Tonnessen Kathy A.
Publication year - 1996
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/96wr02240
Subject(s) - snowpack , snow , soil water , nitrification , snowmelt , mineralization (soil science) , environmental chemistry , ammonium , nitrate , hydrology (agriculture) , nitrogen , environmental science , chemistry , geology , soil science , geomorphology , geotechnical engineering , organic chemistry
In an effort to understand sources of nitrate (NO 3 − ) in surface waters of high‐elevation catchments, nitrogen (N) transformations in and under seasonal snow were investigated from 1993 to 1995 on Niwot Ridge, an alpine ecosystem at 3,500 m located in the Colorado Front Range of the Rocky Mountains. Ammonium (NH 4 + ) and NO 3 − labeled with 15 N applied as nonconservative tracers to the snow showed no evidence of nitrification in the snowpack. Furthermore, NH 4 + movement through the amended snowpack was highly correlated with a conservative chloride tracer ( r 2 = 0.99). In an unamended snowpack NH 4 + concentrations in meltwater before contact with the ground were highly correlated with NO 3 − concentrations ( r 2 = 0.98), which is consistent with no nitrification in the snowpack. The isotopically labeled 15 NH + 4 applied to the snowpack was found in underlying soils, showing that NH 4 + released from snow can be rapidly immobilized. Resin bag (mixed‐bed ion‐exchange resins) measurements (n = 22) showed that 80% of the mobile inorganic N in unamended subnivial soils was NO 3 − . Measurements of KCl‐extractable inorganic N from surface soils showed that highest values were prior to the initiation of snowmelt and lowest values were during the growing season. The natural δ 15 N abundance of unamended soils was negative and ranged from −12 to −2, suggesting that atmospheric deposition of δ 15 N‐depleted N is an important component of N cycling in these alpine soils. These results suggest that soil mineralization under seasonal snow, rather than snowmelt release of NO 3 − , may control NO 3 − concentrations in surface waters of high‐elevation catchments.