Ground Water

Kristina LoenWei Zheng

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

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

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)

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

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

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

at

aSOSRR

Re24 )(

TIC

CH

at

aTICCRR

4

)(

COOCH

CHTICCOOCH

a

aaa

t

COOCHATR

3

43ln)( 3

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

Inorganic compounds

/shell

With increase Ca,

Mg

Reduction of Fe-oxides

Dry Deposition

/Earlier Inundation

Dry Deposition in Pyrite

Oxidation

Fe-oxide reduction/sulfate

reduction/increase in methane

Degrade/Oxidation Organic Matter

release

Transport organic

matter from surface to

aquifer

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

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

Average -4.5kJ/mol,

adequate for ATP synthesis

High

Low

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

Questions?