Continental Patterns in River Photosynthesis and Respiration

I am currently a data scientist at the USGS Office of Water Information. My research extends what I began as a postdoc at both the University of Wisconsin-Madison and the USGS Office of Water Information. I am assessing patterns in river metabolism (photosynthesis and respiration) across the continental United States. The working group for this project is supported by the USGS Powell Center. We want to know:
(1) How can we leverage long-term, high-resolution data records to improve estimates of river metabolism?
(2) How do seasonal patterns in metabolism vary across the continent with climate, water quality, and land use?
(3) What is the contribution of stream metabolism to the continental carbon budget?

River Solute Loads and Trends

As a postdoc with Bill McDowell at the University of New Hampshire, I led the development of an R software package to (A) improve researchers' estimates of solute fluxes in rivers and (B) simplify the user experience in making those estimates. The package, called loadflex, is now publicly available on GitHub. The package implements several methods for estimating fluxes, including the relatively new "composite method", and contains new improvements to the composite method including the first algorithm to quantify uncertainty in that method. A description of loadflex and an example application to water quality data from the Lamprey River in New Hampshire are now published in Ecosphere.

Ecological Stoichiometry

As a member of a working group within the Woodstoich III program, I collaborated on a meta-analysis of how species differ globally in their response to fertilization by nitrogen and CO2. Participants in Woodstoich III were united by our shared in1terest in nutritional geometry and ecological stoichiometry, two conceptual frameworks that link what organisms are made of - carbon, phosphorus, etc. - with what they can do - grow, obtain resources, escape predators, and so on. My group's manuscript from that project has been published at Oikos.

Nutrient Kinetics and Dynamics

As a postdoc with Jim Heffernan at Duke University, I used well-founded ideas about how biota operate to generate specific hypotheses about how and why nutrient concentrations vary over time in the environment. In particular, I asked, What are the implications of organisms' flexible stoichiometry (ratios of elements within their biomass) and diverse kinetics (rates of nutrient uptake, as a function of external concentrations) for temporal patterns in nutrients? Although my own bias is toward considering freshwater aquatic systems, especially streams, in thinking about these questions, many of the hypotheses I generated will apply usefully to other ecosystems including lakes, oceans, and - to the extent that we can measure nutrients at high temporal resolution in more complex matrices - also in sediments, soils, grasslands, and forests.

In a modeling experiment now published in The American Naturalist, I found that changes in just a few species traits can lead to measurable changes in the temporal relationship between a pulsed input of carbon (C) and the resulting pulse in phosphorus (P) uptake. Here are some of the patterns you might see, given two resource scenarios (A and B) and variation in one of seven traits (colored lines in C and D). Click for higher resolution:

Figure 7 in Appling & Heffernan 2014
Now, using data from in-situ oxygen and nitrate sensors in headwaters of the Lamprey River Watershed in New Hampshire, I am working with Bill McDowell, Jim Heffernan, and others to study the biological and physical controls on diel nitrate cycles in real aquatic systems. These sensor data allow us to empirically test hypotheses from our theoretical work (above). Here is an example of the patterns we are seeing in one small tributary to the Lamprey River, New Hampshire:

Connectivity and Floodplain Function

Floodplains are productive, biodiverse, and highly dynamic ecosystems; I find them fascinating in their own right and as a way of understanding how physical transport between and within ecosystems (i.e., connectivity) affects ecosystem function. In my dissertation I explored the overarching question, How does connectivity between a floodplain and its river alter the transport, transformation, and accumulation of nitrogen (N) and carbon (C)?  

Specifically, I looked at the effects of connectivity and related processes on (1) N accumulation in floodplain soils during succession, (2) the spatial distribution of soil properties, including C and N storage and denitrification, across and within a Montana floodplain, and (3) the delivery of organic C to subterranean aquatic organisms in the sand-and-cobble matrix underlying that floodplain. A recurring theme in my findings was that connectivity between the river channel and floodplain is essential to numerous floodplain functions, including the carbon storage and denitrification potential mapped below and published here:

Research and Office Map

I have worked at many scales, from local field studies to global syntheses. Here are some of the institutions and field sites I've called home: