Photochemical degradation of dissolved organic matter in arctic surface waters by Collin Patrick ...

207 Pages·2015·4.13 MB·English

by  William F. Defliese

Photochemical degradation of dissolved organic matter in arctic surface waters

by

Collin Patrick Ward

A dissertation submitted in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
(Earth and Environmental Sciences)
in the University of Michigan
2015

Doctoral Committee:

Assistant Professor Rose M. Cory, Chair
Professor Joel D. Blum
Associate Professor Gregory J. Dick
Professor George W. Kling
Emeritus Professor Philip A. Meyers
© 2015 Collin P. Ward
Dedication
To Kiffy, Uncle Pat, and Lebold - thanks for the good times

ii
Acknowledgements

It is practically impossible to acknowledge all the folks and organizations that deserve
credit for helping me complete this dissertation, but here it goes. First, thanks to my advisor Rose
for the endless patience, insight, and enthusiasm over the years. Despite that the music and food
scene does not compare to north cackalacky, moving with your lab to Ann Arbor was one of the
best decisions I’ve made over the past five years. It’s been an honor to help establish the aquatic
geochemistry lab at UM, and I am excited for the future of your lab. My committees at UNC and
UM were very different, each with its strengths that helped me a great deal. At UNC, Drs.
Surratt, Weinberg, and Whalen challenged me to focus on the details that comprise a robust
experimental design. At UM, Drs. Blum, Dick, and Meyers pushed me to think about my
research more broadly, which has changed the way I think about Earth’s processes and history.
George served on both committees, and consistently went above and beyond the expectations as
a committee member. Thank you for teaching me how to stay organized and be critical of my
work. Byron didn't serve on either committee, but provided lots of input over the years. He also
has an unparalleled passion for baseball, which I admire.
Thanks to all the current and former students and technicians in the Cory, Kling, and
Crump Labs. Namely, Harrold and Jason have been there since the beginning and I'm deeply
thankful for their friendship and support over the years. Thanks to Rachel Sleighter at ODU for
teaching me high resolution mass spectrometry and patiently answering my questions. The same
can be said about Sarah Burton at EMSL, who taught me how to acquire and analyze NMR
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spectra. The logistical support at Toolik was extremely helpful throughout my three field
seasons. Thanks to Anne Hudon for helping me transfer to UM and being an excellent resource.
Thanks to the friends I've made over the past five years and my apologies to the old
friends that I’ve lost touch with. I was very fortunate to be surrounded by a great group of folks
in NC. Thanks to everyone at the cradle, the underground, and everlaughter. I'm really happy for
you Tracey Jones. Thanks to Will, Tommy, and DC for the bike rides and epic racquetball
matches. Thanks to Amanda and Carlos, and Katie and Mike for living in Durham so we could
come visit and explore together. Thanks to all my classmates at UNC and UM for talking
through all the small, inevitable roadblocks. My soccer teams in NC and MI provided a much
needed stress relief after work. Thanks to Yo and Ryan in Columbus for being good friends and
mentors.
Many thanks to my parents for their encouragement and support, even though the route I
have taken is unfamiliar and probably very confusing for them. Thanks to my brothers for
providing different perspectives on life - it's important to hear multiple voices. Thanks to my
extended family for being so incredibly supportive and loyal. The same can be said about Katie's
family, who has consistently demonstrated their support since the day we met. Finally, thanks to
Katie for joining me on this adventure. We've experienced every emotion possible, including
many that we didn't want to, but it's fair to say that we've learned a lot about each other and how
we think the world works (or should work). I look forward to continuing this adventure with you,
and thanks for encouraging me to adopt lenny - he's pretty cool.

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Table of Contents

Dedication ii
Acknowledgements iii
List of Figures ix
List of Tables xi
List of Appendices xii
Abstract xiii
Chapter 1: Introduction 1
1.1 The role of dissolved organic matter (DOM) in the global C cycle 1
1.2 Characterizing the chemical composition of DOM 2
1.3 Controls on the photochemical degradation of DOM 4
1.4 How will a changing Arctic alter DOM composition and degradation 9

Chapter 2: Insights into the complete and partial photo-oxidation of black carbon in
surface waters 21
2.1 Abstract 21
2.2 Introduction 22
2.3 Methods 25
2.3.1 Production and elemental composition of precursor and charred biomass 25
2.3.2 Particulate and dissolved BC treatments 26
2.3.3 Light absorption of the pBC and dBC treatments 27
2.3.4 Photo-oxidation Experiments 27
2.3.4.1 Photochemical O₂ consumption and CO₂ production 28
2.3.4.2 Effect of sunlight on dBC chemical characterization 29
2.4 Results 32
2.4.1 Elemental composition of precursor and charred biomass 32
2.4.2 Filter separation of pBC and dBC treatments 33
2.4.3 Light absorption and photo-oxidation of pBC vs. dBC 33
2.4.4 Effects of sunlight on the chemical characterization of dBC 35
2.5 Discussion 37
2.5.1 Characterization of BC 37
2.5.2 Photochemical reactivity of dBC 39
2.5.3 Environmental implications: photochemical fate of BC 42
2.6 Acknowledgements 45

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Chapter 3: Chemical composition of dissolved organic matter draining permafrost
soils 63
3.1 Abstract 63
3.2 Introduction 64
3.3 Methods 68
3.3.1 Study site 68
3.3.2 Experimental design 69
3.3.3 Whole water DOM vs. solid phase extraction DOM 70
3.3.4 DOC concentration and optical characterization 70
3.3.5 Fourier transform ion cyclotron resonance mass spectrometry 72
3.3.6 Principal component analysis of whole water and SPE DOM 73
3.3.7 Solid-state 13C NMR analysis of SPE DOM 73
3.3.8 Bacterial respiration, production, and growth efficiency 74
3.4 Results 75
3.4.1 DOC concentration and water chemistry of soil leachates 75
3.4.2 Optical characterization of DOM in whole water leachates 76
3.4.3 FT-ICR MS characterization of whole water DOM 77
3.4.4 Optical characterization of solid phase extraction (SPE) DOM 80
3.4.5 FT-ICR MS Characterization of SPE DOM 80
3.4.6 The effects of salt ions and isolation on FT-ICR MS characterization of
DOM 82
3.4.7 13C NMR Characterization of SPE DOM 83
3.4.8 Principal component analysis of whole water and SPE DOM 84
3.4.9 Dark bacterial respiration rates of organic mat and permafrost DOM 86
3.5 Discussion 87
3.5.1 FT-ICR MS reproducibility and the effects of interfering species,
isolation, and instrumentation on DOM chemical composition 87
3.5.2 Compositional differences between organic mat and permafrost DOM 90
3.5.3 Bacterial degradation of DOM draining arctic permafrost soils 91
3.5.4 Conclusions and implications 93
3.6 Acknowledgements 95

Chapter 4: Complete and partial photo-oxidation of DOM draining permafrost soils 115

4.1 Abstract 115
4.2 Introduction 116
4.3 Methods 119
4.3.1 Experimental Design 119
4.3.2 Effect of sunlight on the chemical composition of organic mat and
permafrost DOM 120
4.3.2.1 Effect of sunlight on the light absorbing and emitting fraction
of organic mat and permafrost DOM 120
4.3.2.2 Effect of sunlight on high resolution mass spectra of organic
mat and permafrost DOM 122
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4.3.2.3 Effect of sunlight on 13C NMR spectra of organic mat and
permafrost DOM 123
4.3.3 Measurement of complete and partial photo-oxidation 123
4.4 Results 124
4.4.1 Photo-mineralization and photo-oxidation of organic mat and permafrost
DOM 125
4.4.2 The effects of sunlight on the light-absorbing and emitting fractions of
organic mat and permafrost DOM 125
4.4.3 High resolution mass spectra of organic mat and permafrost DOM 126
4.4.4 The effect of sunlight on high resolution mass spectra of organic mat
and permafrost DOM 127
4.4.5 The effect of photo-degradation on function group distribution 129
4.5 Discussion 130
4.5.1 The effects of sunlight on the bulk chemical composition of DOM 130
4.5.2 Photo-mineralization of organic mat and permafrost DOM: evidence for
photo- decarboxylation 131
4.5.3 Photo-oxidation of organic mat and permafrost DOM: evidence for
partial photo-oxidation 133
4.5.4 Conclusions and implications 134
4.6 Acknowledgements 138

Chapter 5: Apparent quantum yield spectra for the photo-mineralization of dissolved
organic matter 159

5.1 Introduction 159
5.2 Methods 160
5.2.1 General approach 160
5.2.2 DOM sources 160
5.2.3 Quantifying the rate of photochemical mineralization 161
5.2.4 Quantifying light absorption by the water column and CDOM 162
5.2.5 Calculation of apparent quantum yield (Φ ) for the photo-mineralization
λ
of DOM 163
5.2.6 Optical proxies for DOM chemical composition 163
5.3 Results 164
5.3.1 Reproducibility of waveband subtraction method 164
5.3.2 Trends in Φ and light absorption and emission between DOM sources 164
λ
5.4 Discussion 165
5.4.1 Comparison of measured Φ spectra to previously reported Φ spectra 165
λ λ
5.4.2 Aromatic C content vs. light exposure history as an important control for
the susceptibility of DOM to photo-mineralization 166
5.5 Acknowledgements 168

Chapter 6: Conclusion 179

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6.1 Controls on the complete and partial photo-oxidation of DOM in arctic surface
waters 179
6.2 Future work: implications for the aquatic C cycling 183

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List of Figures

Figure

1.1 Conceptual model for the controls on the composition and degradation of DOM in sunlit
surface waters 14
1.2 Van Krevelen diagram showing compound classes defined by the atomic ratios of major
biomolecules 15
1.3 Conceptual framework for the oxidation of DOM by sunlight 16
2.1 Absorption spectra of the pBC and dBC treatments 46
2.2 Effect of sunlight on the dissolved O and CO concentrations in the dBC and pBC
2 2
treatments 47
2.3 Mass balance analysis of the complete and partial photo-oxidation of dBC treatments 48
2.4 Effect of sunlight on EEMs of the dark control and light exposed dBC treatments 49
2.5 Van Krevelen diagrams for formulas assigned via FT-ICR MS analysis of the dark control
(A and B) and light exposed dBC treatment (C and D) 50
2.6 Van Krevelen diagrams showing formulas degraded and produced by sunlight 51
2.S1 Particulate BC concentration vs. absorption at 350 nm 52
2.S2 Comparison of natural to simulated sunlight 53
2.S3 Particulate and dissolved BC concentrations 54
3.1: Experimental design for leaching and isolating DOM 96
3.2: Mass spectra of whole water and solid phase extraction (SPE) organic mat and
permafrost DOM 97
3.3: Linear correlations between FT-ICR MS peak intensities of experimental replicates 98
3.4: Peak distribution at nominal m/z 503 99
3.5: Van Krevelen diagrams demonstrating differences between DOM fractions and sources 100
3.6: Functional group distributions of DOM 101
3.7: Principal component analysis bi-plot 102
3.8: Van Krevelen diagrams of formulas enriched in DOM 103
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