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 , Chemistry and Geochemistry Dept., Montana Tech Garrett Smith, MS student in Geochemistry now of MBMG, Montana Tech Chris Gammons, Geological Engineering, Montana Tech Simon Poulson, Geological Sciences & Engineering, U. Nevada ‐ Reno Ric Hauer, Flathead Lake Biological Station, Univ. Montana ‐ Missoula Brian Kuhn & Montana Tech field Hydrogeology class Funding: NSF, Hydrological Sciences, Grant # 0739054 Smith et al ., Geochim. Cosmochim ., doi:10.1016/j.gca.2011.07.033 .

Where is Nyack? to W. Glacier • Floodplain aquifer on US 2 the M. Fork of Flathead River • ~80 m 3 s ‐ 1 mean annual flow in river. • ~9 km long

Nyack Floodplain Research Natural Annual flood Area zone ALLUVIAL AQUIFER Biocomplexity Project – FLBS Microbial Observatory – UM Biosciences/Geosciences 20 yr flood zone Salmonid Rivers Observatory Network 5 yr flood zone (SaRON) ‐ UM, WSC, Moscow St. Univ. Stable isotopes as tracers of ground water processes – MT Tech Courtesy: J. Stanford

Courtesy: M. Wright Courtesy: M. Wright

What processes are important in introduction, transport and consumption of O 2 across a floodplain system? O 2 b. O 2 c. O 2 d. a. O 2 O 2 O 2 O 2 e. H 2 H 2 O a) Advection from recharge source area b) Advection from infiltration during storms/snowmelt c) Diffusion from vadose zone d) Leakage of O 2 from roots of plants e) Isotope exchange/radiolysis of water?

Oxygen dynamics near recharge o Site and location of wells sampled o Movie transect near head of floodplain

O 2 at Movie 50 m About 80% of the O 2 entering from the river is used in the first 100 m. 3.26 Fork of MFFR O 2 + CH 2 O  CO 2 + H 2 O 3.58 8.86 2.57 16 O 16 O 3.02 2.41 4.51 16 O 17 O 4.21 3.18 6.10 16 O 18 O 6.13 5.91 7.35 δ 18 O ‐ DO 7.95 8.49 Respiration Flood channel 9.30 N Data from Aug. 2008 (mg O 2 /L)

 18 O ‐ DO vs. DO Conc. Across Movie Transect 34 Jan 2009 Aug 2008 32 Aug 2008 river 18 O-DO (‰, VSMOW) Oct 2008 Oct 2008 river May 2009 30 Jul 2009 Jul 2009 river 28 26 DO in equil. with air  24 Atmos. O 2 Diel variations in stream 22 0 20 40 60 80 100 120 Dissolved oxygen (% sat)

DO Dynamics for All Wells

Other Wells in Valley (Aug. 2008) δ 18 O 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

DO (  mol L -1 ) 0 100 200 300 400 Floodplain wells show a 34 (a) Movie different fractionation 32 Aug. 2008  = 0.996  =0.996 Oct. 2008  = 0.998 pattern for  18 O ‐ DO. Jan. 2009 NC May 2009  = 0.995 30 Jul. 2009  = 0.997 Aug. 2099  = 0.995 Is this some kind of 28 reverse fractionation 26 process that defies DO equilibrium with air 24 Air the laws of  18 O-DO (‰) 22 thermodynamics? (b) Floodplain 25 DO equilibrium with air Air 20 1.0028 Aug. 08 Aug. 08-MFFR Oct. 08 15 Oct. 08-MFFR Jan. 09 Jan. 09-MFFR 10 May 09 May 09-MFFR Jul. 09 1.010 Jul. 09-MFFR 5 Aug. 09 Aug. 09-MFFR 0 0 100 200 300 400 DO (  mol L -1 )

What processes are important in introduction, transport and consumption of O 2 across a floodplain system? O 2 b. O 2 c. O 2 d. a. O 2 O 2 O 2 O 2 e. H 2 H 2 O a) Advection from recharge source area b) Advection from infiltration during storms/snowmelt c) Diffusion from vadose zone d) Leakage of O 2 from roots of plants e) Isotope exchange/radiolysis of water?

Diffusion of O 2 from vadose The addition of O 2 by diffusion from the vadose zone and by advection from upgradient along the flow path were compared.

Diffusion of O 2 from vadose Based on O 2 gradients between vadose and groundwater approximately 425 kg O 2 /day enters this portion of the aquifer. Based on the concentration and hydraulic properties of the aquifer about 51 kg O 2 /day is advected through the area. Data from Aug. 2008

Can diffusion across the air ‐ water interface lead to the low δ 18 O ‐ DO values observed down the floodplain? O 2 b. O 2 c. O 2 d. a. O 2 O 2 O 2 O 2 e. H 2 H 2 O

Modeling the change in δ 18 O ‐ DO during diffusion suggests that this could be the source of the light DO. Unsaturated zone DO conc.  δ 18 O ‐ DO  Capillary fringe Advection  Saturated zone (b) 32 y=0.052x+25.2 R 2 =0.61 18 O-DO (‰) This also suggests that there 24 should be a change in δ 18 O ‐ DO y=-0.0017x+21.5 16 R 2 =0.20  behavior down the floodplain. 8 0 40 80 1500 3000 4500 Distance from MFFR at Movie (m)

DO (  mol L -1 ) 0 50 100 150 200 0 50 100 150 200 0 0.00 (a) (c) 10 yr 1 min 50 yr 0.05 200 5 min 200 yr 0.10 25 min 400 0.15 45 min 0.20 Depth (cm) Depth (cm) 600 0 0.00 (b) (d) 0.05 10 yr 200 1 min 0.10 400 0.15 50 yr 200 yr 5 min 25 min 45 min 0.20 600 -5 0 5 10 15 20 25 -6 0 6 12 18 24  18 O-DO (‰) Modeled DO concentration and isotope composition based on Fick’s 2 nd Law

This suggests that isotopically lighter groundwater down the floodplain will be older. 28 24  18 O-DO (‰) 20 16 12 R 2 =0.70 8 0 2 4 6 8 10 12 3 He-T age, yr 90% of 2 yr water with 10% of 35 yr water results in a 10 yr age for the sample.

The other question is whether plant roots could “leak” enough O 2 to the surrounding saturated zone to change the δ 18 O ‐ DO O 2 b. O 2 c. O 2 d. a. O 2 O 2 O 2 O 2 e. H 2 H 2 O

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 O 2 . 78 23.0 6 DO% 76 22.5 5 74 22.0  18 O-DO (‰) SWL (cm) DO % sat 4  18 O-DO 72 21.5 70 3 21.0 68 2 20.5 Level 66 64 20.0 1 15:00 19:00 23:00 03:00 07:00 11:00 15:00 19:00 23:00 03:00 07:00 Time

Summary: • Over short distances, near recharge, we observed high rates of respiration consuming O 2 , increasing δ 18 O ‐ DO. • Areas farther from direct recharge have slower rates of respiration (limited by org. C & O 2 ?); decreasing δ 18 O ‐ DO. • Diffusion from the vadose may contribute as much or more O 2 to the aquifer as does advection. • Some of the Nyack groundwater is older than previously thought.

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