SLIDE 1
Sources of DO Supporting Microbial Activity In Groundwater: Nyack Aquifer
Marissa Dar Marissa Darvis is De
- Dept. of
- pt. of Chemistry & Geoc
Sources of DO Supporting Microbial Activity In Groundwater: Nyack - - PowerPoint PPT Presentation
Sources of DO Supporting Microbial Activity In Groundwater: Nyack - - PowerPoint PPT Presentation
Sources of DO Supporting Microbial Activity In Groundwater: Nyack Aquifer Marissa Dar Marissa Darvis is De Dept. of pt. of Chemistry & Geoc Chemistry & Geochemistry hemistry Montana T Montana Tech Acknowledgements Steve Parker ,
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SLIDE 3
Where is Nyack?
- Floodplain aquifer on
the M. Fork of Flathead River
- ~80 m3 s‐1 mean annual
flow in river.
- ~9 km long
to W. Glacier US 2
SLIDE 4
Annual flood zone 5 yr flood zone ALLUVIAL AQUIFER
20 yr flood zone
Nyack Floodplain Research Natural Area
Courtesy: J. Stanford
Biocomplexity Project – FLBS Microbial Observatory – UM Biosciences/Geosciences Salmonid Rivers Observatory Network (SaRON) ‐ UM, WSC, Moscow St. Univ. Stable isotopes as tracers of ground water processes – MT Tech
SLIDE 5
Courtesy: M. Wright Courtesy: M. Wright
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What processes are important in introduction, transport and consumption of O2 across a floodplain system?
a) Advection from recharge source area b) Advection from infiltration during storms/snowmelt c) Diffusion from vadose zone d) Leakage of O2 from roots of plants e) Isotope exchange/radiolysis of water?
O2
O2 O2
a.
O2
b.
O2 c. O2
d.
O2 H2 H2O
e.
SLIDE 7
Oxygen dynamics near recharge
- Site and location
- f wells sampled
- Movie transect
near head of floodplain
SLIDE 8
O2 at Movie
About 80% of the O2 entering from the river is used in the first 100 m.
Flood channel Fork of MFFR
8.49 7.95 7.35 6.13 4.21 4.51 2.57 3.58 3.26 8.86 3.02 6.10 2.41 3.18 5.91
50 m
9.30
N
Data from Aug. 2008 (mg O2/L)
O2 + CH2O CO2 + H2O
16O16O 16O17O 16O18O
δ18O‐DO Respiration
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18O‐DO vs. DO Conc. Across Movie Transect
Dissolved oxygen (% sat)
20 40 60 80 100 120
18O-DO (‰, VSMOW)
22 24 26 28 30 32 34
Jan 2009 Aug 2008 Aug 2008 river Oct 2008 Oct 2008 river May 2009 Jul 2009 Jul 2009 river
- Atmos. O2
DO in equil. with air Diel variations in stream
SLIDE 10
DO Dynamics for All Wells
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Other Wells in Valley (Aug. 2008)
δ18O LDO (%) LDO (mg/L)
HA-11 20.23 20.8 2.03 HA-19 7.40 11.3 1.11 Sgt E 18.52 19.8 1.89 Sgt N 16.79 20.4 1.96 Sgt S 16.19 13.4 1.31 Cabin 10.72 43.6 4.53 HA-7 12.96 41.0 4.28 HA-6 13.05 59.5 6.22 Chris A 18.50 46.8 4.65 HA-5 15.29 64.6 6.52 Twin Crossing 22.79 59.3 6.14 Twin SB 22.14 66.1 7
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Floodplain wells show a different fractionation pattern for 18O‐DO.
18O-DO (‰)
22 24 26 28 30 32 34
DO (mol L-1)
100 200 300 400
- Aug. 08
- Aug. 08-MFFR
- Oct. 08
- Oct. 08-MFFR
- Jan. 09
- Jan. 09-MFFR
May 09 May 09-MFFR
- Jul. 09
- Jul. 09-MFFR
- Aug. 09
- Aug. 09-MFFR
DO (mol L-1)
100 200 300 400 5 10 15 20 25
DO equilibrium with air DO equilibrium with air Air Air
(a) (b) 1.010 1.0028 Movie Floodplain
- Aug. 2008 = 0.996
- Oct. 2008 = 0.998
- Jan. 2009 NC
May 2009 = 0.995
- Jul. 2009 = 0.997
- Aug. 2099 = 0.995
=0.996
Is this some kind of reverse fractionation process that defies the laws of thermodynamics?
SLIDE 13
What processes are important in introduction, transport and consumption of O2 across a floodplain system?
a) Advection from recharge source area b) Advection from infiltration during storms/snowmelt c) Diffusion from vadose zone d) Leakage of O2 from roots of plants e) Isotope exchange/radiolysis of water?
O2
O2 O2
a.
O2
b.
O2 c. O2
d.
O2 H2 H2O
e.
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Diffusion of O2 from vadose
The addition of O2 by diffusion from the vadose zone and by advection from upgradient along the flow path were compared.
SLIDE 15
Diffusion of O2 from vadose
Based on O2 gradients between vadose and groundwater approximately 425 kg O2/day enters this portion of the aquifer. Based on the concentration and hydraulic properties
- f the aquifer about 51
kg O2/day is advected through the area.
Data from Aug. 2008
SLIDE 16
O2
O2 O2
a.
O2
b.
O2 c. O2
d.
O2 H2 H2O
e.
Can diffusion across the air‐water interface lead to the low δ18O‐DO values observed down the floodplain?
SLIDE 17
Modeling the change in δ18O‐DO during diffusion suggests that this could be the source of the light DO.
Saturated zone Unsaturated zone Capillary fringe DO conc. δ18O‐DO Advection
Distance from MFFR at Movie (m)
40 80 1500 3000 4500
18O-DO (‰)
8 16 24 32 y=-0.0017x+21.5 R2=0.20 y=0.052x+25.2 R2=0.61
(b)
This also suggests that there should be a change in δ18O‐DO behavior down the floodplain.
SLIDE 18
DO (mol L-1)
50 100 150 200
Depth (cm)
0.00 0.05 0.10 0.15 0.20 1 min 5 min 25 min 45 min
18O-DO (‰)
- 5
5 10 15 20 25 0.00 0.05 0.10 0.15 0.20 1 min 5 min 25 min 45 min
(a) (b)
50 100 150 200
Depth (cm)
200 400 600
- 6
6 12 18 24 200 400 600 10 yr 10 yr 50 yr 50 yr 200 yr 200 yr
(c) (d)
Modeled DO concentration and isotope composition based on Fick’s 2nd Law
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This suggests that isotopically lighter groundwater down the floodplain will be older.
3He-T age, yr
2 4 6 8 10 12
18O-DO (‰)
8 12 16 20 24 28 R2=0.70
90% of 2 yr water with 10% of 35 yr water results in a 10 yr age for the sample.
SLIDE 20
O2
O2 O2
a.
O2
b.
O2 c. O2
d.
O2 H2 H2O
e.
The other question is whether plant roots could “leak” enough O2 to the surrounding saturated zone to change the δ18O‐DO
SLIDE 21
Results from a shallow well in the Silver Bow Creek floodplain next to a large stand of Willows has shown a daily change in dissolved O2.
Time
15:00 19:00 23:00 03:00 07:00 11:00 15:00 19:00 23:00 03:00 07:00
DO % sat
64 66 68 70 72 74 76 78
18O-DO (‰)
20.0 20.5 21.0 21.5 22.0 22.5 23.0
SWL (cm)
1 2 3 4 5 6 Level 18O-DO DO%
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Summary:
- Over short distances, near recharge, we observed
high rates of respiration consuming O2, increasing δ18O‐DO.
- Areas farther from direct recharge have slower
rates of respiration (limited by org. C & O2?); decreasing δ18O‐DO.
- Diffusion from the vadose may contribute as much
- r more O2 to the aquifer as does advection.
- Some of the Nyack groundwater is older than
previously thought.
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