HR: 0830h
AN: B21D-0740    [PDF]
TI: Bedrock Nitrogen and Hydrothermal Ammonium in Yellowstone National Park, WY, USA
AU: * Holloway, J M
EM: jhollow@usgs.gov
AF: US Geological Survey, 3215 Marine St., Boulder, CO 80303
AU: Bohlke, J K
EM: jkbohlke@usgs.gov
AF: US Geological Survey, 431 National Center, Reston, VA 20192
AU: Nordstrom, D K
EM: dkn@usgs.gov
AF: US Geological Survey, 3215 Marine St., Boulder, CO 80303
AB: High ammonium concentrations in some of the hot springs of Yellowstone National Park (up to 880 mg L$^{-1}$ as N at Washburn Hot Springs) have been attributed to leaching of sedimentary rock by hydrothermal solutions. However, relatively little is known about the direct relationship between rock geochemistry in volcanic centers and nitrogen in thermal waters. For this study, a suite of core samples from US Geological Survey drill holes in Yellowstone National Park were characterized for nitrogen and carbon in different lithologies. These data were related to the aqueous geochemistry and $\delta^{15}$N-NH$_{4}$$^{+}$ of thermal waters in different hot spring basins in the park to better understand the water-rock interactions. Core samples selected for study included tuff, water-reworked volcanic sediments, glacial sediment, lacustrine sedimentary rock, and marine sedimentary rock. Substantial amounts of nitrogen were present in all bedrock types, with the highest nitrogen concentrations measured in marine sedimentary rocks (430-830 mg N kg$^{-1}$) from Y10, which is located at Mammoth Hot Springs. Although the underlying bedrock has elevated nitrogen concentrations, hydrothermal ammonium concentrations at Mammoth Hot Springs are relatively low (~1 mg L$^{-1}$ as N). These solutions are buffered by carbonate (pH $>$8) and may have lost some N by volatilization as ammonia gas. Thermal waters in Norris Geyser Basin are acid to circumneutral with ammonium concentrations ranging from $<$0.03 to 80 mg L$^{-1}$ as N. Nitrogen in tuffs (400-620 mg N kg$^{-1}$) from drill holes Y9 and Y12 at Norris Geyser Basin may be present as a result of ammonium partitioning from solution to zeolites or other secondary minerals. Thermal waters sampled at Mammoth, Norris, and other geyser basins in the park varied widely in ammonium concentrations and isotopic compositions ($\delta^{15}$N), from $<$0.3 to 450 mg L$^{-1}$ as N and -5 to +25$\permil$, respectively. The isotope data are interpreted to reflect multiple processes, including leaching of nitrogen from sedimentary sources, partitioning of ammonium from solution to secondary minerals, with fractionations resulting from boiling and steam distillation of ammonia gas.
DE: 1030 Geochemical cycles (0330)
DE: 1040 Isotopic composition/chemistry
DE: 1831 Groundwater quality
DE: 4845 Nutrients and nutrient cycling
DE: 8424 Hydrothermal systems (8135)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting