Mineral nitrogen transformations in and under seasonal snow in a high- elevation catchment in the Rocky Mountains, United States

Mark W. Williams, Paul Brooks, Arvin Mosier, Kathy A. Tonnessen

Research output: Contribution to journalArticle

103 Citations (Scopus)

Abstract

In an effort to understand sources of nitrate (NO3/-) 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 (NH4/+) and NO3/- labeled with 15N applied as nonconservative tracers to the snow showed no evidence of nitrification in the snowpack. Furthermore, NH4/+ movement through the amended snowpack was highly correlated with a conservative chloride tracer (r2 = 0.99). In an unamended snowpack NH4/+ concentrations in meltwater before contact with the ground were highly correlated with NO3/- concentrations (r2 = 0.98), which is consistent with no nitrification in the snowpack. The isotopically labeled 15NH4/+ applied to the snowpack was found in underlying soils, showing that NH4/+ 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 NO3/-. 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 δ15N abundance of unamended soils was negative and ranged from -12 to -2, suggesting that atmospheric deposition of δ15N- 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 NO3/-, may control NO3/- concentrations in surface waters of high-elevation catchments.

Original languageEnglish (US)
Pages (from-to)3161-3171
Number of pages11
JournalWater Resources Research
Volume32
Issue number10
DOIs
StatePublished - Oct 1996
Externally publishedYes

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Rocky Mountain region
snowpack
Snow
snow
Catchments
Minerals
Nitrogen
catchment
minerals
Soils
mountain
nitrogen
snowmelt
mineral
soil
Nitrification
nitrification
resin
Surface waters
tracer

ASJC Scopus subject areas

  • Aquatic Science
  • Environmental Science(all)
  • Environmental Chemistry
  • Water Science and Technology

Cite this

Mineral nitrogen transformations in and under seasonal snow in a high- elevation catchment in the Rocky Mountains, United States. / Williams, Mark W.; Brooks, Paul; Mosier, Arvin; Tonnessen, Kathy A.

In: Water Resources Research, Vol. 32, No. 10, 10.1996, p. 3161-3171.

Research output: Contribution to journalArticle

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abstract = "In an effort to understand sources of nitrate (NO3/-) 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 (NH4/+) and NO3/- labeled with 15N applied as nonconservative tracers to the snow showed no evidence of nitrification in the snowpack. Furthermore, NH4/+ movement through the amended snowpack was highly correlated with a conservative chloride tracer (r2 = 0.99). In an unamended snowpack NH4/+ concentrations in meltwater before contact with the ground were highly correlated with NO3/- concentrations (r2 = 0.98), which is consistent with no nitrification in the snowpack. The isotopically labeled 15NH4/+ applied to the snowpack was found in underlying soils, showing that NH4/+ 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 NO3/-. 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 δ15N abundance of unamended soils was negative and ranged from -12 to -2, suggesting that atmospheric deposition of δ15N- 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 NO3/-, may control NO3/- concentrations in surface waters of high-elevation catchments.",
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