Research Interests

I am interested in ecosystem scale spatial patterns and temporal patterns that happen predictably due to Earth's rotation and revolution. I am particularly interested in patterns that occur daily, though I am also interested in seasonal and tidal patterns as well. I believe that the study of the propagation of individual circadian processes to ecosystem-scale ecological properties (or circadian ecology) has much to offer that will help illuminate questions of how ecological processes scale. I incorporate many methodologies into my research, from field sensor deployments, to experimental manipulations, to theoretical modeling. 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.

My dissertation examined the extent and cause of diel nitrate concentration patterns in rivers around the US. I used publicly available in-situ nitrate time-series to look at the total variation in nitrate concentration in rivers at this time scale, and compared these concentrations to biological activity in the stream channel. I characterized timing of nitrate variation across the timeseries to characterize streams as more likely dominated by autotrophic signals (such as the stream to the right, because of it's unique time signature) or dissimilatory processes. Additionally, using a method called Empirical Mode Decomposition, I isolated diel signals from complex signals, such as the one pictured adjacent. Then I compare changes in concentration that likely arise from biology to those arising from other factors, such as hydrology or people.

A secondary project during my dissertation research used experiments to determine if nutrient limitation can alter the timing of nutrient uptake by aquatic organisms. Under normal circumstances, the mechanisms that move nitrate out of the water and into the cell work mostly during daylight when photosynthesis is occurring and new biomass is being created. In a river, this behavior by thousands of organisms can cause the measured concentration of nitrate to decrease during the day. Theoretically, it had been hypothesized that if nitrate becomes more scarce, the nitrate-accessing mechanisms may keep going even after the sun sets, so that there is more time to acquire enough of this necessary nutrient. With nitrate being taken out of the water night and day, the concentration that we measure may barely change between day and night. I used a mesocosm experiment to test this hypothesis. I measured rates of uptake both day and night, and found that the mesocosms that were nitrogen-limited had constant uptake, and mesocosms with enough nitrogen had day-night differences. This difference was noticeable even before it was possible to notice different growth rates, meaning that this ecosystem behavior may be able to be used as an early indicator of eutrophication status.

During my postdoctoral research, I am asking the question "How can we most efficiently reduce nutrient loading from large catchments?" I am using the US EPA's Watershed Management Optimization Support Tool (WMOST), which is used by managers to find the most cost-effective strategies to reduce nutrient loading out of a small watershed (e.g. HUC12s), and I am finding ways to scale this type of support to larger catchments (e.g. HUC6s). With case studies in the Upper Connecticut river basin, the Puget Sound watershed and the Kansas River river basin, I am creating a robust support tool that compiles information about baseline nutrient loading, Best Management Practice (BMP) implementation across watersheds, costs of BMPs, and landcover and soil type into an optimization problem that can be quickly solved to offer insight into which BMPs are best implemented where, and what the overall cost is expected to be to reach loading targets. The goal is to create a user-friendly, efficient, and robust tool that can be made publicly available to watershed planners.

Photo Credit: Chelsea Clifford

In the first year of my PhD, I explored an alternate dissertation path that would have investigated how nutrient limitation might cause self-organization of spatial patterns 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. When faced with the choice of over which dimension I wanted to study patterns for my dissertation, I chose time over space, but I believe that many of the underlying theories of pattern formation are true irrespective of dimensionality.

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.

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 (a heavier hydrogen that has 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.