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ORCID: 0000-0002-5392-5707
All figures and results presented here are my own work, conducted (in R) in close collaboration with several colleagues and mentors.

Ecohydrology

Ecohydrology explores the interonnectedness of biota and the hydrologic cycle through local and global feedbacks. This idea is so intriguing to me!

Plant-water Interactions and Disturbance


The invasive pest, the emerald ash borer, is causing large-scale loss of ash trees in North America, with important consequences for forestry, aesthetics, and ecosystem functioning. For the first chapter of my dissertation, I analyzed the ecohydrologic impacts of forest loss for the unique and beautiful black ash wetlands. We found three main things:

  1. evapotranspiration (ET) limits the amount of water in black ash wetlands, and
  2. ET is uniquely determined by vegetation type and physical structure, but more interestingly,
  3. when black ash is lost, a wetter and more marsh-like ecosystem persists, with implications for an alternative stable state.

You can read about it here.

Co-authors:
Daniel McLaughlin
Rob Slesak
Anthony D’Amato
Brian Palik

Project funded by the Minnesota Environmental and Natural Resources Trust Fund, the USDA Forest Service Northern Research Station, and the Minnesota Forest Resources Council. Additional funding was provided by the Virginia Tech Forest Resources and Environmental Conservation department, the Virginia Tech Institute for Critical Technology and Applied Science, and the Virginia Tech William J. Dann Fellowship.


Wetland Microtopography


Decades of research suggest that microtopography—changes in ground elevation on the order of 10–100 cm—is an important feature of ecosystems, and particularly wetlands, around the world. For example, we know that high points in a wetland (“hummocks”) have greater plant diversity, primary production, and nutrient concentrations than nearby low points (“hollows”). We also know that, under the right circumstances, spatial patterns of microtopography can emerge—a result of feedbacks that develop between biota, soil carbon, and hydrology. These observations, while interesting in their own right, also have important consequences for how we scale from point measurements to ecosystem and global estimates.

I explored black ash wetland microtopography in detail as part of my dissertation work, and with the help of my collaborator, Dr. Atticus Stovall, we used a novel LiDAR method called Terrestrial Laser Scanning (TLS) to analyze the microtopographic pattern, structure, and ecological implications. In particular we:

  1. published the algorithm to extract microtopography from TLS data. You can read about it here.
  2. analyzed the geospatial structure of microtopography and found that it supports a model where plants create their own microtopography. You can read about it here.
  3. related this structure to measured biogeochemical variables

Finally, with the help of many other collaborators, we have recently submitted the first synthesis of wetland microtopography: what it is, why it’s ecologically important, and how it comes to be! Coming soon to a journal near you!

Co-authors:
Atticus Stovall
Daniel McLaughlin
Rob Slesak


Biogeochemistry


In wetland systems like the black ash swamps that we study, the ground surface is covered by an organic layer of peat or muck. The height (or depth) of this layer is a function of the balance between primary production and soil respiration. We commonly observe local high points (“hummocks”) of this organic layer that are occupied by black ash trees, which led us to a hypothesis:

H: black ash trees “create” their own hummocks through an evapoconcentration positive feedback loop, like so:

  1. black ash tree transpiration draws in dissolved nutrients from the surrounding area, which leads to
  2. greater local primary production, which leads to
  3. buildup of root mass/soil organic matter and also greater transpiration, which leads to
  4. nutrient accumulation, and so on.

As part of my dissertation work, I tested this hypothesis by investigating microtopography and wetland biogeochemical variables such as nutrients, vegetative diversity, and primary production. We found evidence supporting the evapoconcentration feedback loop where hummocks were hotspots for soil phosphorus (and the passive evapotranspiration tracer, chloride!), understory diversity, and overstory biomass.

Are plants actively changing their environment to their own advantage? (Could be!) This is a very difficult question to answer, but this research may add another piece of evidence to our growing understanding of the agency of plants.

You can read about it here.  

Co-authors:
Daniel McLaughlin
Rob Slesak
Atticus Stovall


Hydrology

Watershed Hydrochemistry

Since the early days of watershed science, researchers have been fascinated with the concentration-discharge (C-Q) relationships of rivers and streams. The idea is simple enough: how does the chemical concentration of a material (e.g., nitrogen or sediment) change with the amount of water flowing in the river (aka “discharge”)? Perhaps surprisingly, these C-Q relationships can tell us quite a bit about how, when, and where water is routed through, and stored by watersheds.

For my master’s thesis, I analyzed long-term measurements of concentration and discharge for rivers and streams across Florida. I found consistent patterns in C-Q relationships, where the C-Q shape depended entirely on the type of material under consideration (e.g., organically-derived versus rock-derived), implying common hydrologic storage and transport across systems, regardless of size or location. Interestingly, I also found consistent “breaks” in many of the C-Q relationships, implying a watershed switching behavior in the source location for river water (e.g., deep aquifer storage versus shallow soil horizons). This information improves our understanding of the fate and transport of materials through watersheds, with implications for predicting loads to downstream waterbodies.

You can read about it here.

Co-authors:
Matt Cohen

Project funded by the National Council for Air and Stream Improvement, the Florida Forest Service, and the National Institute of Food and Agriculture (NIFA) via CRIS project FLA‐FOR‐ 005284.


Wetlandscape Connectivity


A wetlandscape is a complex of all the wetlands within a drainage network. Most of the time, wetlands in a wetlandscape are disconnected from each other—they are geographically isolated. However, the timing, magnitude, and frequency of connections among wetlands in a wetlandscape has important implications for policy and regulations, ecosystem functioning, and also ecosystem services.

We used high-frequency measurements of wetland stage (i.e., water-level) in geographically-isolated cypress domes in Big Cypress National Preserve in southwest Florida to develop a simple methodology for extracting:

  1. elevation thresholds of wetlandscape connectivity,
  2. frequencies and timings of wetlandscape connectivity (i.e., when and how often are the wetlands connected to each other), and
  3. magnitudes of hydrologic exchange among wetlands

You can read about it here

Co-authors:
Daniel McLaughlin
Matt Cohen
Carlos Quintero Jim Heffernan