Transcript Organic Carbon Dynamics in Soils, and its Impact on Global Carbon

Organic Carbon Dynamics in Soils, and
its Impact on Global Carbon Cycling
Aparna Raghu
Advisor: Professor Satish Myneni,
Environmental Geochemistry Group,
Geosciences
Background: Organic Carbon Dynamics in the Pine Barrens
Photochemical reactions
cause some fractions of
the DOM to precipitate
out as floc
Carbon Compounds
from decomposed
leaves
Pine Barrens Stream
contains dissolved organic
matter (DOM) from the soil ,
decomposed leaves etc.
Minerals in the
Stream Bed adsorb
to certain organic
functional groups
from the DOM
Carbon Compounds
Leached from forest
soil
Key Questions:
How do the mineral-organic precipitates compare to floc
formed naturally from the DOM?
How do different minerals compare in ability to adsorb to
organic compounds?
How does pH affect the adsorption of organic compounds
to minerals?
Interactions of Minerals and Organic Compounds:
Possible Sorption Mechanisms
*
*
*
Philippe et al
2014
1553
New Floc IR
Spectrum
1051
1158
1340
1400
1565
IR Studies of DOM: Overview
1700
-1800
-As. C=O stretch from carboxylic
acids
around -As. C=O stretch from amides
1650
(Amide I)
-As. C=O stretch from strong COOmetal complex
around -Benzene two quadrant stretch
1600
-As. C=O stretch from weak COO/metal complex
1723
around - NH in plane bend/CN stretch
1550
(Amide II)
-As. C-O stretch from COOaround -Sym. C-O stretch from COO1400
-NU bend/CN stretch (Amide III)
around •In plane C-O stretching
1350
Wavenumbers (cm-1)
As. = Asymmetric
Sym. = Symmetric
around •C-O-H vibrations (carbohydrates)
1250
•Out of phase C-C-O stretching
(carbohydrates)
Results from Adsorption Experiments
New DOM
New Floc
Boehmite
Kaolinite
Goethite
Calcite pH7
1800
1700
1600
1500
Wavenumbers (cm-1)
1400
1300
1200
Effects of pH on Adsorption: Explaining the
Boehmite Peak Splitting : 1650
Full Double Bond
Character
1720 cm-1
Least Double
Bond Character
1570-1600 cm-1
1565
Mostly Double
Bond Character
1650 cm-1
M+
1540
1650
Effects of pH on Adsorption: Explaining the
Boehmite Peak Splitting : 1540
Full Double Bond
Character
1720 cm-1
Least Double
Bond Character
1570-1600 cm-1
1565
Mostly Single
Bond Character
1540
M+
1540
1650
Comparing Iron and Kaolinite Flocs to Boehmite Floc
Boehmite Boehmite Boehmite Kaolinit Kaolinite Kaolinite Iron Iron Iron
pH 4
pH 7
pH 9
e pH 4 pH 7
pH 9
pH 4 pH 7 pH 9
1645
1645
1650
1625
1565
1575
1650
1658 1642 1634
1538
1536
1573 1553 1551
1596
1580
1540
Boehmite pH 9:
Peaks at 1650
and 1540
Key:
Strong
Shoulder/weak
1650
Kaolinite pH 7
and 9: Peaks at
1650 and 1537
Iron pH 7 and 9:
Peaks at 1635
and 1550
Comparing Calcite Floc to Boehmite Floc
Calcite pH Calcite pH Boehmite Boehmite Boehmite
7 floc
9 floc
pH 4
pH 7
pH 9
1670
1670
1625
1620
1555
Key:
Strong
Shoulder/weak
1540
Calcite: Peak at
1625, Shoulder
at 1550
1645
1645
1650
1625
1565
1575
Boehmite pH 4
and 7: Peak at
1570, Shoulder at
1645
1580
1540
Boehmite pH 9::
Peaks at 1540 and
1650
Comparing Calcite Floc to Boehmite Floc
Calcite
Boehmite
Less Double Bond
Character: 1625
Ca 2+
Less Single Bond
Character: 1550
Ca 2+
More Double Bond
Character: 1650
Al 3+
More Single Bond
Character: 1540
Al 3+
Conclusions and Future Experiments
•Mineral adsorption of DOM relies on interactions with carboxylic acid moieties in the
DOM
• Adsorption of DOM may also involve amides, alcohols, and other carbonyl
groups
• Shifts in Carboxylate Stretches in the Infrared Spectra can be attributed into
strength of complexing interactions
•Adsorption mechanisms vary with pH
• At lower pH values, the carboxylate anion exists mainly in the uncomplexed
form, whereas at higher pH values, we see the complex forming
•Future Flow Through Experimentation may allow us to see how organic matter
interacts both directly with mineral surfaces and with itself as additional layers are
formed
The Summer Research
Experience
Filtratration of soil sample extractions
for Mass Spectrometry
Samples covered with foil to
prevent photochemical reactions
Our Beloved Infrared Spectrometer
Collecting Soil Cores for
Organohalogens Project
Acknowledgements
I would like to thank Professor Satish Myneni and Dr. Sarah Jane White for providing
their expertise and support throughout the summer.
I would also like to thank Chris Habermann for being a fantastic lab partner and
Rebecca Lowy, Justin Mehl, and Lydon Kersting for being wonderful friends and
mentors in the lab (and for letting us use the IR machine, even when you had samples
to run!).
Finally, I would like to that Princeton Environmental Institute for supporting my
research.