PhD Students

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Travis Drake


I am interested in the fate of large, globally relevant, stocks of soil carbon that are on the move due to human activities. In particular, I study whether these vulnerable carbon reservoirs leak into the atmosphere as carbon dioxide through rivers and streams and thereby add to the greenhouse effect. My current research is focused on the effect of agriculture on carbon mobilization in watersheds of eastern Democratic Republic of the Congo. To accomplish this, I use a variety of analytical tools to characterize both organic and inorganic carbon in streams draining pristine and impacted catchments. These include 13/14C isotopes, FTICR mass spectrometry, fluorescence, uv-visible absorbance, and bioincubations. With these tools I strive to link the isotopic signature of inorganic carbon with potential organic sources. Underpinning this research is an effort to improve methods of capturing whole watershed processes, since a growing body of work has highlighted headwaters as important vents for respired terrestrial carbon dioxide.

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Sarah Ellen Johnston


I'm interested in drivers of dissolved organic matter composition in northern high latitude aquatic environments, particularly seasonality and changes in vegetation and permafrost thaw input. Using optical measurements, ultrahigh resolution mass spectrometry, and lignin phenol biomarker analyses I investigate the source and transformations of organic matter and the effects of vegetation type and permafrost thaw on organic matter composition in lakes and rivers. I am also interested in using optical measurements (absorbance and fluorescence) as a predictor of lignin concentration in a range of ecosystems to model terrestrial organic carbon contribution in both inland and marine waters. Ultimately I seek to tie optical measurements to compositional measurements to fundamentally assess the drivers of chromophoric and fluorescent DOM in Arctic aquatic ecosystems.