Natural variability in N export from headwater catchments: snow cover controls on ecosystem N retention
✍ Scribed by Paul D. Brooks; Don H. Campbell; Kathy A. Tonnessen; Kristi Heuer
- Book ID
- 101284290
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 139 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0885-6087
No coin nor oath required. For personal study only.
✦ Synopsis
The causes of natural variability in catchment scale N export need to be understood and quanti®ed before the eects 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 ¯ush 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 ¯ush 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 CO 2 ¯ux 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 identi®ed a strong, linear relationship (r 2 0 . 68) between catchment scale N retention and winter snow cover, consistent with subnivean, soil based controls on the mobile N pool identi®ed 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 eect of winter snow cover on the fate of both atmospheric and soil N needs to be considered when evaluating potential the eects of increased N deposition on either terrestrial or aquatic ecosystems in seasonally snow-covered watersheds. In these systems, changes in surface water chemistry are likely to occur in high deposition, snow-covered sites during low snow years before terrestrial vegetation is aected.