HR: 1340h
AN: H53A-1206    [Abstracts]
TI: Mercury Benthic Flux: A Comparison Between 3 Mining-Impacted Water Bodies in the Western United States
AU: * Topping, B R
EM: btopping@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Kuwabara, J S
EM: kuwabara@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Marvin-Dipasquale, M C
EM: mmarvin@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Agee, J L
EM: jlagee@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Kieu, L H
EM: lhkieu@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Flanders, J R
EM: jflander@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Parchaso, F
EM: parchaso@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: The legacy of mining in the Western United States has left an indelible environmental imprint on terrestrial and aquatic systems. On both sides of the Sierra Nevada mountain range (Sierras), mercury was used copiously in the amalgamation of gold and silver. Mercury deposits in close proximity to San Francisco Bay (e.g., the New Almaden mining district) provided much of the mercury for these processes. To evaluate mercury benthic flux, three geographically distinct water bodies were studied: Lahontan Reservoir (NV) on the eastern side of the Sierras, affected by historic gold and silver mining; Camp Far West Reservoir (CA) on the western side of the Sierras, down stream of historic hydraulic gold mining and processing; and South San Francisco Bay (CA), the estuarine component down stream of the New Almaden Mercury Mines. Average benthic flux of total-dissolved mercury was highest in Lahontan Reservoir ($\sim$1400 pmol/m$^{2}$/hr), followed by Camp Far West Reservoir ($\sim$180 pmol/m$^{2}$/hr), and lowest in South San Francisco Bay ($\sim$50 pmol/m$^{2}$/hr). In spite of this wide range of values, and the unique character of each watershed (e.g., forested vs. urbanized), all three systems exhibited quantitatively significant mercury benthic fluxes relative to riverine inputs. That is, areally averaged benthic fluxes (thus, expressed as annual loads) were of similar or greater magnitude relative to riverine loads. System-averaged values of dissolved methylmercury fluxes were similar for South San Francisco Bay (undetectable) and Camp Far West Reservoir (average of $\sim$0 pmol/m$^{2}$/hr; some fluxes undetectable), and only slightly higher in Lahontan Reservoir ($\sim$2 pmol/m$^{2}$/hr). Similarly, system averaged potential rates of methylmercury production (by sulfate-reducing bacteria; as assessed by $^{203}$Hg(II) radiotracer studies) in the surficial sediment were not significantly different among the three locations. However, within-system variability was approximately an order of magnitude in each case. The interactions between bottom sediment and overlying water chemistry appears to consistently play an important role in dissolved-mercury distribution, transport and trophic transfer, and should therefore be considered when numeric targets are developed for remediation and restoration programs.
DE: 4804 Benthic processes/benthos
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1857 Reservoirs (surface)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting