Methanogenesis, Redox and Carbon Isotope Biogeochemistry: Georgetown Lake,

MontanaMaster Thesis Project, Tyler Johnston

Department of Chemistry and Geochemistry, Montana Tech

Overview• Field Area and History• Previous Work

– Conclusions Made– Concerns

• Objective of Current Work• Methods

– Methane Identification• GC-MS• CRDS

• Results– Water Column– Sediment– C speciation

• Conclusions• Recommendations

Google Earth image of the Georgetown Lake area showing the Pintlar & Flint Creek ranges, Discovery Ski Area and Anaconda, MT

Comers Pt Site

Adapted from Gammons et al. in press

History of Georgetown Lake• Flint Creek dammed in

1899 - power for mining operations in Philipsburg, Anaconda, and the surrounding areas.

• The new dam flooded the Georgetown flats, which was primarily grazing pasture, creating Georgetown Lake.

Previous Work• In 1977 EPA report classified

Georgetown Lake as an eutrophic (excess nutrient loads)

• 9th out of 15 lakes studied (15 being most eutrophic)

• Analysis determined lake water was nitrogen limited

• Estimated 4250 kg/year phosphorus loading

• Several more studies have been conducted in order to determine sources of nutrient loading– Groundwater, septic tanks, surface

run off (fertilizers, detergents), surface and submarine springs, lake sediment

So, what is eutrophication?• Eutrophication - a water

body becomes loaded in excess nutrients causing blooms of algae and plant growth.

• Decay of excess organic matter via respiration, lowers dissolved oxygen to levels lethal to aquatic life.

Previous Work cont.

• Deep water and sediment become anoxic during winter ice cover.

• Apparent redox boundary allows for the formation of reduced species.

• NH4+ found in large quantities in bottom water

(up to 3.3 mg/L)

• H2S gas produced by sulfate reducing bacteria (up to1.2 mg/L)

SO42- + 2 CH2O + 2 H+ H2S + 2 CO2 + 2 H2O

Org C

Previous Work Cont.

• A more recent study by Stafford of the U of M (2013) found Georgetown Lake is becoming less eutrophic.

• Nutrient loading had greatly decreased since last comprehensive study in 1980’s– Phosphorus has now become a limiting nutrient

• Suboxic conditions are still present even with decreased nutrient loading

Adapted from NSF proposal in review (S. Parker, C. Gammons, J. Dore, E. Boyd)

Transition from open water to ice-cover is accompanied by a dramatic change in geochemical structure.• Persistent anoxic conditions threaten GTL fisheries• High potential for release of toxic and greenhouse gases during ice break up

and spring turnover

Reason for this study

A: GT-1Dam

DIC concentration, mmol/L

0 1 2 3 4 5

13 C

-DIC

, ‰

-9

-6

-3

0

3

Nov 2010Jan 2011Feb 2011March 2011April 2011May 2011June 2011Aug 2011

B: GT-2 Comer's

DIC concentration, mmol/L

0 2 4 6 8 10

Nov 2010Jan 2011March 2011April 2011May 2011June 2011Aug 2011

From Henne, 2011

Produces isotopically light CH4 and heavy CO2

Objectives• To identify and quantify

methane production in the waters of GTL.

• Use carbon stable isotopes to identify carbon cycling in GTL.

• Estimate quantity of CH4 released from GTL to the atmosphere with ice-off.

Methods• Sampling of the vertical water column was

conducted from Jan. 2013 to March 2014.• Measured: pH, Temp, Conductivity, ORP

and DO• Water was pumped to the surface from

~2ft intervals for analysis– Alkalinity, Ammonia, Sulfide, Anions,

Methane, DIC/DOC, Carbon isotopes,, TPC, and Water isotopes.

• Sediment cores were taken in Sept. and Dec. 2013

• Gas samples were gathered from ebullition by disturbance of sediment

CH4 Methods• CH4 analysis by GC-MS (EI) or CRDS

analyzer • Samples were gathered vertically

throughout water column• Water was pumped to the surface and

collected in125 mL glass serum bottles.• Analysis by CRDS was done on septum

capped vial.

Analyze CH4 in gas bubble

Methane Identification by GC-MS• Initial column did not resolve

methyl cation peak (m/z 15 CH3+)

• Switched to mole sieve column which resolved methyl cation peak.

• Sample precision in duplicate samples was poor, ranging between 5-20%

CH4 (mol)0.00 0.04 0.08 0.12

Peak area

0.0

5.0e+5

1.0e+6

1.5e+6

2.0e+6

y=(4.615·105)·ln(x)+2.683·106

R2=0.999

Sample calibration curvePeak area for m/z 15, CH3

+

Sample GC-MS results

RT: 0.00 - 9.08

0 1 2 3 4 5 6 7 8 9Time (min)

0

50

100

0

50

100

0

50

100

Rela

tive A

bundance

0

50

100

0

50

1002.80

4.27

5.792.97 5.451.48 3.98 7.81 8.146.52 7.120.26 2.00RT: 5.79MA: 437457

5.83

6.432.79 4.29 8.12RT: 2.80MA: 5243006

1.48 4.003.05 4.32 6.634.95 7.156.25 7.960.18 8.762.68RT: 4.27MA: 6116147

2.97 5.454.54 6.89 7.826.522.78 8.380.17 0.77 3.41RT: 7.81MA: 114691

8.048.31

2.814.24 4.312.970.36 2.281.38 7.126.135.65

NL:1.95E6

TIC MS mix_std-1-02-14_10

NL:9.65E4

m/z= 14.50-15.50 MS mix_std-1-02-14_10

NL:1.89E6

m/z= 31.50-32.50 MS mix_std-1-02-14_10

NL:1.42E6

m/z= 27.50-28.50 MS mix_std-1-02-14_10

NL:7.20E3

m/z= 43.50-44.50 MS mix_std-1-02-14_10

CH4 as CH3+ ion

O2

N2

CO2

TIC; 20 μL of standard mixture

(A)

(B)

(C)

(D)

(E)

CH4 using CRDS• CH4 using Cavity Ring-Down

Spectrometer.• CH4 measured for

interference correction with CO2 for δ13C.

• Original CH4 calculated based temperature, cavity volume & pressure, molar volume

CH4 (M)0 500 1000 1500

CH

4 pe

ak a

rea

0

10000

20000

30000

40000

y=20.2*x+48.7R2=0.9998

All points are duplicate determinations

Calibration of CRDS for CH4 analysis

Results

DateJan Mar May Jul Sep Nov Jan Mar

CH

4 (M)

0

300

600

900

1200

1500

GC-MSCRDS

2013 2014

ice ice

CH4 concentration over the sampling visits to the GT-2 site

Results

DateJan Mar May Jul Sep Nov Jan Mar

OR

P (m

V)

-150

0

150

300

450

DO

(mg/L)

0

2

4

6

ORPDO

2013 2014

ice ice

Dissolved oxygen near bottom at GT-2 and oxidation-reduction potential

Results

DO (mg/L)

0 2 4 6 8 10 12

De

pth (m

)

0

1

2

3

4

5

6

Temp (oC)

0 1 2 3 4 5

SC (S/cm)

150 225 300 375

pH

6.0 6.5 7.0 7.5

ORP (mV)

100 200 300 400 500

NH3-NH4+(N-mg/L)

0 1 2 3 4 5 6

CH4 (M)

0 200 400 600 800

Sulfide (S-mg/L)0.0 0.2 0.4

C-DIC (‰)

-6 -5 -4 -3 -2 -1 0

13C-DOC (‰)-32 -30 -28 -26

DIC (mg/L)0 25 50 75 100125150

De

pth (m

)

0

1

2

3

4

5

6

DOC (mg/L)2.0 2.2 2.4 2.6

ICE ICE ICE ICE ICE ICEA B C D E F

TempDO

SC

pH

NH3

ORP

Sulfide

CH4

DOC

DIC DIC

DOC

Depth profiles for the GT-2 site in Feb. 2013

Microbe populations under ice cover (from Apr. 2013); densities increase near the redox boundary.

Adapted from NSF proposal in review (S. Parker, C. Gammons, J. Dore, E. Boyd)

Possibly a result of increase spectrum of nutrients allowing broader range of “niches” for greater species diversity and ecological success.

Results

DO (mg/L)4 6 8

De

pth (m

)

0

2

4

6

Temp (oC)17.8 17.9 18.0

Temp

DO

pH7.0 7.5 8.0 8.5

SC (S/cm)176 180 184 188

ORP (mV)0 100 200 300 400

SO42- (mg/L)

3.0 3.2 3.4

pHSC

SO42-

ORP

13CDIC (‰)

-4.0 -3.5 -3.0 -2.5

13CDOC (‰)-29.6 -28.8 -28.0 -27.2

DOC

DIC

DIC (mg C/L)20 22 24 26

DOC (mg C/L)2.0 2.4 2.8

CH4 (M)0 20 40 60

DOC

DIC

CH4

18OH2O (‰)

-13.8 -13.5 -13.2 -12.9

De

pth (m

)

0

2

4

6

dDH2O (‰)

-114.4 -113.6 -112.8

A B C D E F G

Depth profiles for the GT-2 site in Sep. 2013

Results

Depth profiles in shallow sediment cores from the GT-2 site.

A to C are from Sep. 2013

Organic C concentration at top of core is less than deeper. Suggests processing of C and return to lake (atmosphere?).

Org C (mmol/g)28 32 36 40

Se

dim

ent d

ep

th (cm)

0

4

8

12

Inorg. C (mmol/g)0 2 4 6

OCIC

13C (‰)-32 -28 -24 -20 -16

13C-OC

13C-ICLodge poleKinickinick

A B

N/P

0 10 20 30 40

Se

dim

ent d

ep

th (cm)

0

4

8

12

N/S0.0 0.6 1.2 1.8

N/P

N/S

C

Limestone -0.41Bottom plants-9.6 & -11.7

Depth under ice ft

Depth under ice m

pCO2 µatm

HCO3-

µmol/LCO3

2- μmol/L

CO2

μmol/Lfrac

HCO3- frac CO3

2- frac CO2

ε(CO2-

HCO3-)

ε(CO32--

HCO3-) δ13C-CO2

δ13C-

HCO3-

δ13C-

CO32-

δ13C-DIC ‰ VPDB

COM-17-3 0 0.00 3620 1678 0.9 270 0.86 0.0005 0.14 12.1 0.64 -13.3 -1.2 -1.8 -2.9COM-17-6 3 0.91 3516 2032 1.5 253 0.89 0.0006 0.11 12.0 0.63 -14.0 -2.0 -2.6 -3.3COM-17-9 6 1.83 5502 2036 1.0 382 0.84 0.0004 0.16 11.9 0.62 -13.6 -1.8 -2.4 -3.7

COM-17-12 9 2.74 6953 2081 0.8 475 0.81 0.0003 0.19 11.8 0.62 -13.8 -2.0 -2.6 -4.2COM-17-14 11 3.35 8124 2156 0.8 544 0.80 0.0003 0.20 11.7 0.61 -13.5 -1.7 -2.3 -4.1COM-17-16 13 3.96 8221 2386 0.9 545 0.81 0.0003 0.19 11.7 0.61 -13.8 -2.1 -2.7 -4.3COM-17-18 15 4.57 8798 2490 1.0 579 0.81 0.0003 0.19 11.7 0.61 -12.6 -0.9 -1.5 -3.1COM-17-20 17 5.18 20632 3119 0.7 1332 0.70 0.0001 0.30 11.6 0.60 -8.3 3.3 2.7 -0.17

Speciate inorganic C using [DIC], T, pHCalculate fraction inorganic speciesCalculate isotopic separation based on T & speciesUse these to calculate δ13C of each species

What can we learn from the carbon in the lake?

The dissolved CO2 should look like this isotopically (assuming equilibrium).

Mar. 2014 data

13C (‰)

-36 -30 -24 -18 -12 -6

De

pth

(m)

0

2

4

ice

localterrestrial plants

aquatic plants

13C-CO2

Calc13C-DOC Meas

13C-DOC Calc

Calculated C fixation

atm CO2

13C-TPC

Limestone -0.41

Is the dissolved CO2 being used by in lake processes?

How much CH4 actually is released from the lake in the spring when the ice leaves and the lake turns over.

Making some broad assumptions based on measured CH4, lake area, depth of anoxic layer we get about 109 moles (0.02 Tg) CH4 released from the lake at ice-off.

The watershed can oxidize about 107 moles by normal processes in upland soils.

At the dam outlet, an estimated 106 mole of methane enter Flint Creek

Climate change may enhance CH4 production faster than CO2.

Conclusions

• CH4 was found at measurable quantities at the GT-2 site all year round.

• Sediment cores show an active region of diagenetic processing in the top regions of the shallow sediment.

Conclusions• Water in the anoxic zone

showed enrichment of δ13C-DIC due to the production of isotopically heavy CO2 via methanogenesis. Organisms that consume the enriched CO2 near the redox boundary appear to produce enriched δ13C-DOC.

• DOC found in the lake and sediment cores is consistent with a large component of organic carbon from terrestrial sources. White-stem pond weed from GTL

Conclusions• Based on broad estimations

109 mol of CH4 can escape GTL when the lake turns over in the spring. This number reveals that the eutrophic nature of GTL is a source of greenhouse gas.

• The persistent anoxic zone is not only bad for the stability of lake ecosystems, but has the potential of being a source of greenhouse contributing to global climate change.Image taken from Google, shows trapped

methane in ice being lit on fire.

Distance from bottom of ice to 3 mg/L DO level (Stafford, 2013).3 mg/L is Montana chronic DO minimum for salmonoid fisheries.

Comer’s Point site

Recommendations

• Perform sampling over a broader range of sites across the lake to better determine extent of methanogenesis.

• Refine the estimate of the amount of CH4 released after the ice breaks apart.

• Use stable isotopes of carbon to examine diagenic processes throughout the lake water and sediment.

• Use “peepers” to examine pore water chemistry in detail and δ13C-CO2 found in pore water.

• Conduct investigations to types of microbial communities present and how they change with seasonal changes in the physical/chemical composition of lake waters.

Acknowledgements

Dr. Steve Parker

Dr. Doug Cameron

Dr. Chris Gammons

John Wheaton, MBMG

Lynda Bone, RAMP

George Williams

Lydia Johnston

Montana Tech

Chemistry Department

MSE-TA

Questions?