TY - JOUR
T1 - Natural variability in N export from headwater catchments
T2 - Snow cover controls on ecosystem N retention
AU - Brooks, Paul D.
AU - Campbell, Don H.
AU - Tonnessen, Kathy A.
AU - Heuer, Kristi
PY - 1999/10
Y1 - 1999/10
N2 - The causes of natural variability in catchment scale N export need to be understood and quantified before the effects of increased N deposition in high elevation catchments can be evaluated. This study evaluates controls on the size of the leachable soil N pool concurrent with the spring hydrologic flush that is primarily responsible for the transport of N to surface water. In high elevation catchments in the western United States, sources of N during this snowmelt flush include both atmospheric N deposition stored in the snowpack until melt and mobile soil N pools, and sinks are dominated by biogeochemical processes that occur in soil under snow cover. Because soil processes may serve either as a source or sink for N, controls on the amount of inorganic N leached from soil during the snowmelt period were evaluated in the major landscape types in four catchments in Colorado. Measurements of leached N were inversely related to measurements of over-winter CO2 flux at all sites, indicating that N was immobilized in soil heterotrophic biomass. Because over-winter soil heterotrophic activity is controlled primarily by the depth and timing of snow accumulation, the importance of these plot scale measurements to catchment scale N export were evaluated using a long-term record of winter precipitation, N deposition, and N export from Loch Vale in Rocky Mountain National Park. This data set identified a strong, linear relationship (r2 = 0·68) between catchment scale N retention and winter snow cover, consistent with subnivean, soil based controls on the mobile N pool identified at the plot scale. These results indicate that the winter snow pack is the major control both on hydrologic N export and on soil source/sink relationships for N concurrent with this transport mechanism. The effect of winter snow cover on the fate of both atmospheric and soil N needs to be considered when evaluating potential the effects of increased N deposition on either terrestrial or aquatic ecosystems in seasonally snow-covered watersheds. In these systeems, changes in surface water chemistry are likely to occur in high deposition, snow-covered sites during low years before terrestrial vegetation is affected.
AB - The causes of natural variability in catchment scale N export need to be understood and quantified before the effects of increased N deposition in high elevation catchments can be evaluated. This study evaluates controls on the size of the leachable soil N pool concurrent with the spring hydrologic flush that is primarily responsible for the transport of N to surface water. In high elevation catchments in the western United States, sources of N during this snowmelt flush include both atmospheric N deposition stored in the snowpack until melt and mobile soil N pools, and sinks are dominated by biogeochemical processes that occur in soil under snow cover. Because soil processes may serve either as a source or sink for N, controls on the amount of inorganic N leached from soil during the snowmelt period were evaluated in the major landscape types in four catchments in Colorado. Measurements of leached N were inversely related to measurements of over-winter CO2 flux at all sites, indicating that N was immobilized in soil heterotrophic biomass. Because over-winter soil heterotrophic activity is controlled primarily by the depth and timing of snow accumulation, the importance of these plot scale measurements to catchment scale N export were evaluated using a long-term record of winter precipitation, N deposition, and N export from Loch Vale in Rocky Mountain National Park. This data set identified a strong, linear relationship (r2 = 0·68) between catchment scale N retention and winter snow cover, consistent with subnivean, soil based controls on the mobile N pool identified at the plot scale. These results indicate that the winter snow pack is the major control both on hydrologic N export and on soil source/sink relationships for N concurrent with this transport mechanism. The effect of winter snow cover on the fate of both atmospheric and soil N needs to be considered when evaluating potential the effects of increased N deposition on either terrestrial or aquatic ecosystems in seasonally snow-covered watersheds. In these systeems, changes in surface water chemistry are likely to occur in high deposition, snow-covered sites during low years before terrestrial vegetation is affected.
KW - Catchment biogeochemistry
KW - Headwater catchments
KW - Nitrogen cycling
KW - Nitrogen saturation
KW - Snow cover
KW - Snowmelt
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U2 - 10.1002/(sici)1099-1085(199910)13:14/15<2191::aid-hyp849>3.0.co;2-l
DO - 10.1002/(sici)1099-1085(199910)13:14/15<2191::aid-hyp849>3.0.co;2-l
M3 - Article
AN - SCOPUS:0033208394
VL - 13
SP - 2191
EP - 2201
JO - Hydrological Processes
JF - Hydrological Processes
SN - 0885-6087
IS - 14-15
ER -