Mae Gustin University of Nevada

Transcription

1 Mae Gustin Mae Gustin University of Nevada

2 General -atmospheric Hg and watersheds Atmospheric contribution i from mining i Sources Form Measuring deposition Effect of mining on deposition Local Nevada gold mine example Consideration of vegetation Global Concluding thoughts with respect to California

3 Atmosphere Watershed Considerations Gaseous Elemental Hg >95% Fairly inert Long RT Bidirectional exchange

4 Atmosphere Watershed Considerations Gaseous oxidized mercury -Primary and secondary pollutant Short residence time Water soluble and more bioavailable Is re-emitted emitted after photoreduction

5 Watershed sources Atmosphere Reservoir 5600 Mg Global Transport GOM Hg p Hg 0 oxidation GOM Legacy source Primary Sources Local dry and wet deposition Anthropogenic and Natural Deposition from the global atmosphere pool Lithosphere-Hydrosphere-Biosphere Reservoirs (Mg) Plants Soils x 10 6 Ocean sediments - 3 x Ocean waters x 10 5

6 GOM formation Oxidants involved not understood -Local ground based -Free troposphere Global GOM Hg 0 oxidation GOM Legacy source Primary Sources Local dry and wet deposition Anthropogenic and Natural Lithosphere-Hydrosphere-Biosphere Reservoirs (Mg) Plants Soils x 10 6 Ocean sediments - 3 x Deposition from the global atmosphere pool Ocean waters x

7 Peterson and Gustin 2009 Weiss Penzias et al Figure 5: Twenty-four hour back trajectories for time periods when RGM concentrations were >100 pg m -3 (n = 100). Model start height set at 0.5 times the modeled mixed layer depth.

8 Natural enrichment associated with ore deposits Elemental Hg amalgamation Chapter 1 Mercury Fate and Transport in Global Atmosphere 2009 Pirrone and Mason eds

9 Natural sources of atmospheric Hg Global ~ Mg/y U.S. Coal fired power plants 40 Mg/y Nevada Mines 2 Mg/y Western United States 11.4 to 19.3 Mg/year Gustin et al (2008) Applied Geochemistry

10 Estimated 400 Mg/y Chapter 6 Mercury Fate and Transport in Global Atmosphere 2009 Pirrone and Mason eds

11 Chapter 1 Mercury Fate and Transport in Global Atmosphere 2009 Pirrone and Mason eds

12 What is the form of Hg emitted? Carson River Superfund Site Steamboat Springs Geothermal Area Sulfur Bank Superfund Site Lake Tahoe Basin

13 What happens to Hg emitted in mining Atmosphere Reservoir 5600 Mg Global Transport GOM Hg p Hg 0 oxidation GOM Legacy source Primary Sources Local dry and wet deposition Anthropogenic and Natural Lithosphere-Hydrosphere-Biosphere Reservoirs (Mg) Plants Soils x 10 6 Ocean sediments - 3 x Deposition from the global atmosphere pool Ocean waters x

14 Wet GOM more water soluble Dry All forms of Hg dry deposited GEM GOM PHg

15 Wet deposition

16 What about dry deposition Apply estimated deposition velocities and measured air concentrations in models Deposition velocity GEM to 0.19 cm/s RGM-0.5 to 7.6 cm/s Measure gaseous elemental deposition using micrometeorological methods and field chambers

17 RGM dry deposition Direct measurement using micromet methods difficult Low RGM concentrations (0 to ~200 pg/m3) Low instrument precision (15 ± 9%) Surrogate surfaces

18 Hg uptake by surrogate surface correlates well with GOM concentrations and modeled deposition Lyman et al. 2007;2009, EST Lyman et al., 2007/2009

19 Observations of wet and dry deposition Lyman et al., 2009

20 So how should we determine dry deposition? Which scenario represents reality? Understanding dry deposition is important in RGM Hg Western p Hg US 0 4 NV02 NV99 Deposition (µ µg m -2 ) Seasonal Lyman et al., 2007 Wet Dep. Scenario 1 Scenario 2 Scenario 3 Wet Dep. Scenario 1 Scenario 2 Scenario 3 *Utilizes data from spring, summer, and fall 2005

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22 Field Measurements: Active leach Reclaimed tailings -Characterize Hg concentrations in substrate -Collect data from field for comparison with laboratory data -Measure flux from surfaces not represented in laboratory study Tailings material Old leach pad

23 What happens to Hg emitted in mining Atmosphere Reservoir 5600 Mg Global Transport GOM Hg p Hg 0 oxidation GOM Legacy source Primary Sources Local dry and wet deposition Anthropogenic and Natural Lithosphere-Hydrosphere-Biosphere Reservoirs (Mg) Plants Soils x 10 6 Ocean sediments - 3 x Deposition from the global atmosphere pool Ocean waters x

24 Near major mine adit 1 to 2 ppm Near smaller adit to ppm Away from adit 0.01 to 0.05 ppm

25 Sanders et al fold increase since industrial revolution -regional deposition -global deposition -climate change

26 Deposition to CA watersheds Influenced by global pool Dry deposition important Neither wet nor dry deposition well understood Mining impact to watershed Contributes to global deposition Local deposition Depends on form emitted Re-emission important Plant recycling Continued emission from old mines Reclamation important