HR: 1330h
AN: C42A-1012    [PDF]
TI: Nitrogen Dynamics Along the Western Slope of the Sierra Nevada, California
AU: * Sickman, J O
EM: jsickman@uno.edu
AF: Department of Geology and Geophysics, University of New Orleans, New Orleans, La 70148 United States
AU: Miller, A E
EM: amy@icess.ucsb.edu
AF: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, Ca 93106 United States
AU: Melack, J M
EM: melack@lifesci.ucsb.edu
AF: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, Ca 93106 United States
AU: Schimel, J P
EM: schimel@lifesci.ucsb.edu
AF: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, Ca 93106 United States
AU: Meixner, T
EM: tmeixner@mail.ucr.edu
AF: Department of Environmental Sciences, University of California, Riverside, Riverside, Ca 92507 United States
AB: Along the western slope of the Sierra Nevada, elevation ranges from 200 to 4000 meters over a distance of less than 25 km. Biomes along this gradient range from chaparral, through mixed conifer and Giant Sequoia forests to alpine fell fields. Rates and forms of N loss from these biomes vary considerably. In middle elevation oak and mixed conifer forests, dissolved organic nitrogen (DON) is the dominant form of N in catchment outflow ($>$95%) and, on an annual basis, is less than or about equal to inorganic N loading (DIN)(ca. 4 kg/ha/yr). In catchments near the elevation extremes, DIN export is significant and, when combined with DON losses, catchment N-losses balance or can exceed inorganic N loading. DIN export from Sierra Nevada catchments is generally confined to hydrologic flushing periods during seasonal transitions (e.g., transitions from dry summers to fall rains, and from winter to spring snowmelt). In alpine catchments nitrate pulses typically range from 5-20 uEq/L, while in middle elevation catchments nitrate levels are less than 1 uEq/L. Nitrate concentrations during first flush storms in chaparral catchments can exceed 500 uEq/L and may be related to elevated dry deposition of N (~10 kg/ha/yr). These observations suggest: (1) forested ecosystems in the Sierra Nevada are generally more N-retentive than alpine or chaparral systems (2) ecosystems at elevational extremes are less N-retentive and may be more sensitive to changes in N deposition rates and 3) abrupt seasonal transitions may be a common mechanism controlling nitrate losses in alpine and chaparral ecosystems.
DE: 1615 Biogeochemical processes (4805)
DE: 1803 Anthropogenic effects
SC: Cryosphere [C]
MN: 2003 Fall Meeting