ground water
DESCRIPTION
Ground Water. Geochemistry at Sulfate Reduction- Methangenesis Transition Zone in an Anoxic Groundwater. Kristina Loen Wei Zheng. Introduction. Groundwater important of drinking Pollution industry/agriculture: near surface abandoned, obtained from deeper anoxic aquifers. - PowerPoint PPT PresentationTRANSCRIPT
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Ground Water
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Kristina LoenWei Zheng
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Groundwater important of drinking Pollution industry/agriculture: near surface
abandoned, obtained from deeper anoxic aquifers.
Anoxic redox processes important for water quality in deep aquifers
Anoxic RØMØ aquifer: inorganic geochemical processes+microbiologically mediated redox processes+thermodynamics
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This Study Focus: geochemistry of Fe-oxide
reduction/sulfate reduction/methanogenesis mediated by microorganisms.
Shallow marine sand rather dune sand of RØmØ
High flow rate, different infiltration composition, lithologically less homogeneous
Useful interpreting other anaerobic aquifer
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Northern Zealand, Denmark 10m deep phreatic postglacial sandy
aquifer, lower 7-8m occasional gravely, with pebbles; upper 2-3m homogeneous eolian sand with occasional paleosols.
Porosities 25-30%, Hydraulic conductivity 1.3×10-4 m/s
Groundwater table 1.2mbs (meter below surface)
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Groundwater: stainless steel drive point piezometers
H2 sampling: a bundle of 10mm PVC with 20mm disc-shape 20μm nylon screen, field measure: bubble stripping (Chapelle & McMahon 1991)
Methane: syringe, injected pre-weighted 13ml evacuated blood vial, frozen below -18°C
Others(anions, acetate,formate): filtered anaerobically through 0.2μm filter, 5ml polypropylene vials, frozen below -18°C
pH, O2, conductivity: field measured.
Alkalinity: Gran titration
Fe2+ , H2S: spectrophotometric
In Lab: Cation-AAS; Anion-ion chromatography; methane-gas chromatography; acetate/formate: ion exclusion chromatography
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Radiotracer Rate: 50mmID, 1.5mm thick, stainless steel tubing ; After retrieval core, 1mm holes and 12.5~25uL radiotracer injected, interval of 10~12cm. Incubation
CO2 reduction-H14 CO3- 22h
Acetate -14 CH3COONa 14h Sulfate reduction-H2
35 SO4 18h incubation ended by freezing cores to -50°C
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α=1.06 (SRR-Sulfate Reduction Rate)(Jakobsen&Postma 1994)
α=1.08 (Hansen, 1998) (CO2 Reduction Rate)
α=1.08 (Acetate Turnover Rate)
sulfate
Sd
ataSOSRR
Re24 )(
TIC
CH
ataTIC
CRR
4
)(
COOCH
CHTICCOOCH
a
aaa
tCOOCHATR
3
43ln)( 3
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Sediment Parameters: Fe, Organic and Inorganic carbon, Sulfide
as AVS (Acid Volatile) and CRS (Chromium Reducible)
Sediment bound organic carbon: non acid desorbable sedimentary organic
carbon (NADSOC) Inorganic carbon=TC-NADSOC-ADSOC
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Inorganic compounds
/shell
With increase Ca,
Mg
Reduction of Fe-oxides
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Dry Deposition
/Earlier Inundation
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Dry Deposition in Pyrite
Oxidation
Fe-oxide reduction/sulfate
reduction/increase in methane
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Degrade/Oxidation Organic Matter
release
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Transport organic
matter from surface to
aquifer
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Na+ slightly delayed in terms of vertical transportation
Ion exchange affect cations, also affect Ca2+,
Mg2+ , K+
Mg2+ displace Ca2+
Ca2+ affected by dissolution of calcite, ion exchange release Ca2+ , precipitate Ca2+
Al3+ not affected by ion exchange
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Sulfate reduction rate highly correlated with where sulfide found in sediment
AVS (Acid Volatile Sulfur) only in 5~6 mbs, transform of AVS to CRS (Chromium Reduced Sulfur)
Sulfate reduction rate extremely small, sulfate input higher, so sulfate reduction took place in large volume of sediment.
Organic matter low
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Average -4.5kJ/mol,
adequate for ATP synthesis
High
Low
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Similar to RØmØ aquifer, but 1)No pool AVS below sulfate reducing zone,
indicating enough sulfide for conversion, related to higher measurable sulfide concentration
2) H2 level high enough to sustain methanogenesis, removing need for stagnant microniches.
3)Data indicating influx organic matter from soil, sustaining redox processes in system
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Questions?