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Research Interests
I am broadly interested in the movement of nutrients through ecosystems, the effect of anthropogenic nutrient loading on the biotic community, and the role that humans and other species play in transforming and retaining nutrients at the catchment scale. I have used a combination of field measurements and manipulations, laboratory experiments, and modeling to explore questions at the interface of biogeochemistry and food web ecology. My current research activities fall under four categories:
 Working with Ben Beall on the RV Blue Heron | 1. Microbial transformations of nitrogen in the Great Lakes. In my postdoctoral research, I am measuring rates and controls of nitrification, denitrification, and N recycling in Lake Superior and Lake Erie. Future research goals include developing a model of coupled biogeochemical cycles in Lake Superior based on sediment redox conditions and biotic nutrient recycling.
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2. Retention of phosphorus in stream ecosystems. I am using data collected during and after an eight-year experimental P addition in a lowland tropical forest headwater stream to quantify P retention though biotic and abiotic mechanisms. I am interested in collecting similar data from other experimentally nutrient-enriched streams as well as utilizing sources of anthropogenic nutrient loading to investigate nutrient retention capacity across a variety of stream ecosystems.
|  Rhodamine dye release in a small stream at La Selva Biological Station, Costa Rica |
 Fishes such as this cichlid have a high P demand and recycle this nutrient at very low rates in low-solute streams | 3. Interaction between stream nutrient loading and benthic food webs.My dissertation research showed that, in naturally high P streams, the entire invertebrate assemblage doubled in P-content due to feeding on P-enriched detritus and algae. Some consumers in high-P streams showed an elevated P-demand, indicating that microevolution can lead to stoichiometric heterogeneity across landscapes. My dissertation research also highlighted the importance of species identity in ecosystem-level nutrient recycling.
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4. Carbon transport and processing in tropical rivers.I analyzed a long-term neotropical stream chemistry dataset to show that seasonal and inter-annual stream acidification is driven by CO2 inputs from soil respiration. We are currently developing a series of experiments to measure the seasonal contribution of in-stream metabolism to this CO2 loading, and to measure the capacity of stream microbes to utilize dissolved organic carbon of different qualities. To put our findings into a broader context of tropical stream geochemistry, I organized an NSF-funded working group on “Carbon Transport and Processing in Tropical Streams and Rivers” and am leading the effort to write a synthesis paper on this topic.
|  Puerto Viejo river, La Selva Biological Station, Costa Rica  Puerto Viejo river during a flood |
