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?