HR: 09:15h
AN: A51A-06    [PDF]
TI: Export of Atmospherically Derived Nitrogen in the Tampa Bay Watershed
AU: * Pollman, C D
EM: cpollman@att.net
AF: Tetra Tech, Inc., 408 W. University Ave., Suite 301, Gainesville, FL 32601 United States
AB: Several approaches are used to place bounds on likely fluxes of nitrogen to Tampa Bay, Florida that ultimately are derived from atmospheric deposition to the watershed. One approach compares ion ratios of total N and Cl in a number of north Florida watersheds to ratios in atmospheric deposition. Atmospheric deposition ion ratios were calculated based on wet deposition measured at NADP/NTN sites in north and central Florida and dry deposition estimates developed by Poor et al. (2003). Two key assumptions are inherent in the analysis: Cl is conservative (no sources other than atmospheric deposition contribute significantly to riverine Cl fluxes; nor are there significant sinks for Cl within the watershed other than surface runoff and groundwater recharge), and the only source of nitrogen is atmospheric deposition. This approach thus defines a minimum degree of N retention. Samples with K concentrations greater than 15 microequivalents per liter were screened to remove agricultural influences on nutrient export, resulting in average N retention estimates ranging from 41 to 81%. The data base analyzed included 22 different stream stations in Florida that are part of the USGS NASQAN stream water chemistry data base. Other approaches are based on simplified watershed mass balances computed from NASQAN flow and water quality measurements and atmospheric fluxes based on NADP wet deposition fluxes and dry deposition fluxes developed by Poor et al. (2003). For systems where atmospheric inputs of chloride balance riverine export (within +/- 20%), preliminary estimates of minimum N retention based on this approach range from 5 to 94% and likely reflect the limited hydrologic data available to estimate annual fluxes. The third approach is based on a critical examination of existing nutrient budgets for Tampa Bay, and defining the maximum contribution to indirect N loading to Tampa Bay from atmospheric deposition.
DE: 1854 Precipitation (3354)
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
DE: 4845 Nutrients and nutrient cycling
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting