HR: 17:15h
AN: H32G-06    [PDF]
TI: The Effect of Biogeochemical and Hydrologic Processes on Nitrogen in Stream Water Originating From Coal-Bed Methane Supply Wells
AU: * Smith, R L
EM: rlsmith@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St. Suite E-127, Boulder, CO 80303 United States
AU: Repert, D A
EM: darepert@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St. Suite E-127, Boulder, CO 80303 United States
AU: Hart, C P
EM: cphart@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St. Suite E-127, Boulder, CO 80303 United States
AB: Water obtained from coal-bed methane (CBM) wells typically contains a variety of reduced chemical constituents, including methane, metal ions, particulate and dissolved organic carbon, and ammonium. In many locales in Wyoming and Montana, CBM water is disposed via discharge to stream channels and reservoirs. Though it is likely that biogeochemical and hydrologic processes will result in major changes in the chemical composition of these waters with subsequent downstream transport, few studies have actually examined these water quality changes or their ecological impacts. A field study was conducted in the Powder River Basin, WY to document changes in solute composition within stream channels below discharge points of CBM water. Particular emphasis was placed on nitrogen and nitrogen cycling processes. Concentration ranges in discharge water were: DOC, 200-350 $\mu$M; alkalinity, 40-50 meq/L; specific conductance, 3.3-4.0 mS/cm; ammonium, 350-400 $\mu$M; and pH, 7.2-7.3. Ammonium concentrations decreased with transport distance via nitrification, with subsequent increases in nitrite and nitrate. Within a single discharge channel, nitrite concentrations increased with travel distance, peaking at $>$100 $\mu$M at 100-200 m, but also exhibited a strong diel pattern that was inversely related to incident light. Nitrite production/consumption processes differed significantly within in-stream incubation chambers, depending upon location relative to the CBM discharge point and time of day. In the main channel, subject to several CBM discharge points, diel nitrite concentrations were more constant at a fixed station, but did increase with distance downstream. Main channel total inorganic nitrogen remained relatively constant ($\sim$400 $\mu$M N) with distance ($>$5 km), suggesting little net nitrogen removal. The results of this study suggest that CBM discharge can serve as a significant source of dissolved nitrogen to western watersheds, with oxidative processes resulting in nitrate and nitrite concentrations greatly in excess of current drinking water limits.
DE: 0400 Biogeosciences
DE: 1803 Anthropogenic effects
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting