Diel%redox%changes%of%% Rio%Agrio,%Argen4nasainieid/geochem/talks/Wrage-Diel-r… · Study%area...
Transcript of Diel%redox%changes%of%% Rio%Agrio,%Argen4nasainieid/geochem/talks/Wrage-Diel-r… · Study%area...
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Diel redox changes of Rio Agrio, Argen4na
Jackie Wrage
NDSU Geochemistry December 11, 2014
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Outline
• Background • Introduc4on • Study • Results • Conclusion • Further Research
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Where are we?
• Copahue Volcano • Stratovolcano • Ac4ve volcano:
– Been erup4ng since 2012 – Latest: 4th of July, 2014
• Name means “sulphur waters” in indigenous Mapuche
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Study area Rio Agrio river: • Naturally acidic, starts at acid
hot springs at the top of Copahue Volcano
• Owes acidity to influx of vola4les (SO4, HCl, & HF)
• Enters Glacial Lake Caviahue • Con4nues down to waterfall:
Salto del Agrio • Lower Rio Agrio
• Increasing pH downstream
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Diel redox changes of the Rio Agrio
• Diel: Chemistry changes that occur within 24 hours (day to night differences)
• Redox: Chemical reac4ons in which atoms have their oxida4on states changed
• I used data from Parker et al. (2008) at the sampling point of Salto del Agrio, a waterfall with pH of 3.2
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Data
Diel varia4ons of total dissolved Fe2+ and Fe3+
(Parker et al. 2008)
Element analysis from Parker et al. (2008). Concentra4on in mmol.
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The study
• Many studies done here, found that concentra2on and specia2on of Fe changed from day to night
• Why?
• Does this affect redox state of river?
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Why?
• Iron has 2 valence states: 3+ and 2+ – Fe3+ is oxidized state (ferric) – Fe2+ is reduced state (ferrous)
• Studies have shown that in hyperacidic rivers (like Rio Agrio), photoreduc1on during the day causes the increase in Fe2+ and decrease in Fe3+
• Photoreduc4on: A reduc4on reac4on that takes place in the presence of light
This reac2on occurs in the UV to near UV region of Electromagne2c Spectrum (200-‐450 nm) & is max with pH of 2-‐4
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Summary of diel Fe specia4on
• Fe3+ increases at night – open to atmosphere, oxidizing environment
• Photoreduc4on during the day decreases Fe3+ and increases Fe2+
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Does this effect the redox state? Using PHREEQ-‐C:
• I simulated photoreduc4on by changing the ra4o of Fe species in the Salto del Agrio input file
• Used average element concentra4ons through 24 hours
• Ran 9 solu4ons to determine Eh (redox state)
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Results
0.2
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0.4
0.5
0.6
0.7
0.8
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1
0 1 2 3 4 5 6 7 8 9 10
Eh
Solu1on
Eh changes from day to night • Eh varied from 0.727 to 0.767
• Not a great difference
• Increased slightly at night
• Trend matched concentra4on of Fe3+ because it’s the more oxidized species
Graph of diel Eh changes (Blue box represents nighkme values)
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Conclusion
• Although the Fe specia4on and concentra4on varied throughout the day, it did not effect the redox state of the en4re river
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Further Research
• Rio Agrio is a modern analog to the Mar4an environment and possibly early Earth
• Understanding interac4ons between organic & inorganic processes is important to astrobiology
• Fe-‐oxidizing bacteria are present in the Rio Agrio, studying their effect on the river chemistry can have important implica4ons
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References
Parker, S., Gammons, C., Pedrozo, F., and Wood, S. (2008) Diel changes in metal concentra4ons in a geogenically acidic river: Rio Agrio, Argen4na. Jornal of Volcanology and Geothermal Research 178. 213-‐223.
Gammons, C., Nimick, D., Parker, S., Snyder, D., McCleskey, B., Amils, R., and Poulson, S. (2008) Photoreduc4on fuels biogeochemical cycling of iron in Spain’s acid rivers. Chemical Geology 252. 202-‐213.
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Ques4ons?