Paul D. Brooks Arvin Mosier Kathy A. Tonnessen Mark W. Williams 1996 <p><span>In an effort to understand sources of nitrate (NO</span>₃⁻<span>) 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</span>₄⁺<span>) and NO</span>₃⁻<span><span>&nbsp;</span>labeled with<span>&nbsp;</span></span>¹⁵<span>N applied as nonconservative tracers to the snow showed no evidence of nitrification in the snowpack. Furthermore, NH</span>₄⁺<span><span>&nbsp;</span>movement through the amended snowpack was highly correlated with a conservative chloride tracer (</span><i>r</i>²<span><span>&nbsp;</span>= 0.99). In an unamended snowpack NH</span>₄⁺<span><span>&nbsp;</span>concentrations in meltwater before contact with the ground were highly correlated with NO</span>₃⁻<span><span>&nbsp;</span>concentrations (</span><i>r</i>²<span><span>&nbsp;</span>= 0.98), which is consistent with no nitrification in the snowpack. The isotopically labeled<span>&nbsp;</span></span>¹⁵<span>NH</span>⁺₄<span>applied to the snowpack was found in underlying soils, showing that NH</span>₄⁺<span><span>&nbsp;</span>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</span>₃⁻<span>. 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</span>¹⁵<span>N abundance of unamended soils was negative and ranged from −12 to −2, suggesting that atmospheric deposition of δ</span>¹⁵<span>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</span>₃⁻<span>, may control NO</span>₃⁻<span><span>&nbsp;</span>concentrations in surface waters of high-elevation catchments.</span></p> application/pdf 10.1029/96WR02240 en American Geophysical Union Mineral nitrogen transformations in and under seasonal snow in a high-elevation catchment in the Rocky Mountains, United States article