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Snowpack controls on soil nitrogen dynamics
in the Colorado alpine
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Paul D. Brooks, Mark W. Williams,
and Steven K. Schmidt
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| Experiments were conducted before and during spring snowmelt in 1993 and 1994 at Niwot Ridge in the Colorado Front Range to assess the degree of interaction between inorganic nitrogen (N) deposited in seasonal snowpacks and soil N pools in alpine environments. Soils typically froze in early winter with minimum soil temperatures inversely related to the depth of early season snowpacks. Minimum soil temperatures under late-accumulating, shallow snowpack reached –10 to –14°C, while soils under deeper, earlier snowpacks reached minimum temperatures of –5 to –6°C. Mineralization and nitrification inputs to the soil inorganic N pool were an order of magnitude higher than snowmelt inputs and were controlled by the timing and depth of snowpack accumulation. Ion exchange resin bags located at the soil surface indicated that the actual N inputs any location were highly variable. About 90% of isotopically labeled 15NH4+ applied to the snow surface before melt was recovered in soil pools. Nitrogen mineralization in 1994 was generally higher (1712-1960 mg N m-2) and exhibited relatively little spatial variability (CV 0.04-0.26) under deeper, earlier accumulating snowpacks. In contrast, N mineralization under shallower, late-accumulating snowpacks was lower (511-1440 mg N m-2) and much more variable (CV 0,42-0.83). The lowest nitrification rates were found under deep/early snowpacks (8-18% of mineralized N); the highest were found under shallow/late snowpacks (16-58% mineralized N). These results indicate the timing and depth of snowpack accumulation plays a key role in nitrogen cycling in alpine ecosystems and may control inorganic nitrogen export to surface waters. | |||||||||||
Biogeochemistry of Seasonally Snow-Covered
Catchments (Proceedings of a Boulder Symposium, July 1995). IAHS Publ.
no. 228, 1995
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