Research Interests
I am interested in ecosystem scale patterns that occur predictably because of the Earth's rotation. Primarily I study patterns that occur daily, though I am also interested in seasonal and tidal patterns. I am most interested in temporal biogeochemical patterns , and I investigate these processes at many different levels, from whole-stream chemical concentration changes to circadian cycling of proteins within cells. Most of my experience has been in streams and rivers. However, if questions about circadian drivers of ecosystem function arise in drier or saltier places in the future, then I will gladly go there to study them. My work in aquatic systems has also given me a strong interest in water quality and the impacts of nutrients on the eutrophication of receiving water bodies.
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My dissertation examines the extent and causes of diel nitrate concentration patterns in rivers around the US. I use publicly available in-situ nitrate time-series to look at the total variation in nitrate concentration in rivers at this time scale, and compare these concentrations to biological activity in the stream channel. Using a method called Empirical Mode Decomposition, I isolate diel signals from complex signals, such as the ones pictured adjacent. Then I compare changes in concentration that likely arise from biology to those arising from other factors, such as hydrology or people. I also use experiments to determine if nutrient limitation can alter the timing of nutrient uptake by aquatic organisms, which may change the concentration patterns they create within the stream.
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Additionally during my PhD I researched the causes of landscape patterning in Big Cypress National Preserve in Florida. This area is a karst landscape with regularly spaced depressions etched into the underlying bedrock. These depressions hold water longer than the surrounding uplands, and support trees that grow taller, resulting in an apparent domed shape (hence their name, "cypress domes"). Regular patterns in nature can arise from positive and negative feedback operating at various scales, so, along with others in my research team, I tested the hypothesis that the trees themselves have created these domes by preferentially dissolving bedrock in the cypress domes. I used a mass balance of calcium and phosphorus entering, exiting, and existing on the landscape to estimate how long this landscape may have taken to form - a clue as to what mechanisms could have possibly created such a strikingly patterned wetland.
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Prior to graduate school, I studied the circadian cycles of plants on a molecular level. I investigated how Arabidopsis thaliana protein abundance in cells changes over the course of a day. Specifically, I traced a protein called ubiquitin that, among other functions, plays a role in the degradation of proteins within a cell. By studying when ubiquitin binds to other proteins over a circadian cycle, I determined when different proteins are degraded and removed from a cell. This knowledge helps in understanding how the plant circadian clock regulates itself and other cellular functions.
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As an undergraduate, I examined the hydrogen isotopic composition of organic molecules in soil and leaf extracts along a mountain gradient in New Zealand. As mountains force humid air masses up in elevation, water vapor condenses into rain. Because water that contains deuterium (heavier hydrogen, with an extra neutron) condenses slightly faster than water that doesn't, the average isotopic weight of hydrogen at the base of mountains should be heavier than that at higher elevations. My study field-tested this hypothesis and found that isotope compositions in different forms of organic matter did relate to elevation. Because hydrogen atoms can get preserved in fossils for eons, hydrogen isotopes in fossils present an opportunity to reconstruct Earth's topography as much as hundreds of millions of years ago.
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