HR: 08:30h
AN: H41J-03    [Abstracts]
TI: Isotopes of Dissolved Copper and Zinc in Stream Waters
AU: * Borrok, D M
EM: dborrok@utep.edu
AF: University of Texas at El Paso, Department of Geological Sciences, El Paso, TX 79968, United States
AU: Nimick, D A
EM: dnimick@usgs.gov
AF: U.S. Geological Survey, 3162 Bozeman Ave., Helena, MT 59601,
AU: Wanty, R W
EM: rwanty@usgs.gov
AF: U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, United States
AU: Ridley, W I
EM: iridley@usgs.gov
AF: U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, United States
AB: A variety of biological and geochemical processes control the cycling and availability of Zn and Cu in stream waters. It is likely that these mechanisms result in distinctive mass dependent fractionations of the stable isotopes of dissolved Zn and Cu. The relative abundances of these isotopes may elucidate biogeochemical reactions impacting stream water chemistry and/or fingerprint the sources of these metals in natural waters. Stream waters from six historic mining districts located in the United States and Europe were examined for their relative abundances of dissolved Zn and Cu isotopes. Isotopic signatures were measured as a function of time to determine whether changes in biogeochemistry were recorded over well-defined diel (24-hour) metal cycles. Average δ⁶⁶Zn and δ⁶⁵Cu values for the streams varied from +0.02 to +0.46 ‰ and -0.7 to +1.4 ‰, respectively, demonstrating that Zn and Cu isotopic signatures are heterogeneous in the measured streams. There appears to be no correlation between the isotopic signatures for Zn and stream water parameters (pH, Zn-speciation, organic content, flow rate, etc.). Hence, we suspect that differences in the Zn isotopic composition among the metal source materials strongly influenced the measured Zn isotopic signatures of the stream waters. Cu isotopic data was limited to just three streams, and the source(s) of Cu isotopic variation remain unclear. In most of the streams isotopic changes were not determined for Zn or Cu within the resolution of our measurements over diel cycles. However, diel changes in Zn isotopes were recorded in a single dataset where the fluctuation of dissolved Zn was the greatest. We calculate a separation factor of 0.35 ‰ between the dissolved and solid Zn reservoirs in this stream with the solid Zn reservoir preferring the lighter Zn isotope. Although several explanations for the diel variation in Zn isotopes are possible, we speculate that the preference for the lighter isotope may reflect metabolic uptake by microorganisms.
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0461 Metals
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1800 HYDROLOGY
SC: Hydrology [H]
MN: 2007 Fall Meeting