Research Philosophy

I am an ecohydrologist with a B.A. and an M.S. in ecology and a Ph.D. in hydrogeology.  My research is focused on the nexus of three concepts: hydrological connectivity, geological controls on physical and chemical hydrology, and hydrological controls on ecosystem structure and function.  Specifically, my research is focused on:

  • delineating flowpaths and quantifying fluxes along flowpaths within hydrological landscapes,
  • quantifying how these fluxes control the physical and chemical characteristics of surface water and shallow groundwater in ecosystems embedded within these hydrological landscapes, and
  • quantifying how the physical and chemical characteristics of the surface water and shallow groundwater control the structure and function of ecosystems embedded within these hydrological landscapes.

I pursue these efforts in a variety of surface-water and shallow-groundwater environments, including depressional wetlands, headwater streams and mainstem rivers, and mangroves and lagoons. My research is focused within the hydrological sciences, but often extends into the ecological sciences and occasionally has sociopolitical implications.  This is far too broad a research agenda for a single individual to fulfill.  Therefore, collaboration is essential to my success.

Some selected projects are briefly described below.

The Role of Groundwater-Controlled Thermal Reugia in Supporting Juvenile Salmonid Habitat, Kenai Peninsula, Alaska

This is a collaborative project that brings together principle investigators from Alaska Department of Fish & Game/Kachemak Bay Research Reserve, Smithsonian Environmental Research Center, Baylor University, and the University of South Florida. This project builds on previous work to gain an understanding of how wetlands associated with headwater streams on the lower Kenai Peninsula contribute to juvenile fish habitat. The previous work investigated the relationship between wetlands in differing geomorphic settings, headwater stream habitat, and aquatic fauna. This project is expanding that knowledge to include an understanding of the hydrologic relationships between the wetlands and streams. All results will be attributed to the Kenai Lowlands Wetland Management Tool, a GIS-based resource used by planners, managers, and residents.

Many colleagues are collaborating on this project, including but not limited to Coowe Walker (Alaska Department of Fish & Game/Kachemak Bay Research Reserve), Dennis Whigham (Smithsonian Environmental Research Center), and Ryan King (Baylor University). Jason Bellino is one of my current M.S. students working on this project.

Funding has been provided by the U.S. Environmental Protection Agency.

Balancing the Needs of Human and Natural Systems through the Sustainable Development of Water Resources: A Case Study on the Costa Alegre, Mexico

This is an international collaborative effort that brings together principle investigators, students, and volunteers from the University of South Florida; the University of Nevada, Reno; California State University, Channel Islands; the Universidad de Guadalajara; the Great Basin Institute, and the Patel Center for Global Solutions. This project combines graduate and undergraduate teaching, research, and community service with on-the-ground natural resource conservation and community outreach efforts.

This project combines research, teaching, and community service with on-the-ground water-supply planning and infrastructure, natural-resource conservation, and community-outreach efforts. The overall objective is to provide current scientific information regarding the hydrological carrying capacity of the basin for the purpose of informing local and regional resource land-use planning and decision-making. Ongoing scientific studies integrate hydrology, plant ecology, aquatic ecology, and fisheries biology with citizen science, promoting a long-term natural resource and community development program for the region.

The project is ongoing, with principle investigators leading students and volunteers on regular field trips. Courses will be taught annually in spring, and volunteer efforts will be run throughout each year. Potential students should visit the course website.

Many colleagues are collaborating on this project, including but not limited to Kai Rains (Three Parameters Plus, Inc.), Jerry Keir (Great Basin Institute), Sudeep Chandra (University of Nevada, Reno), and Michael Marchetti (California State University, Channel Islands). Christina Stringer is one of my current Ph.D. students working on this project.

In 2007, the project was funded by Earthwatch volunteer and university student participation fees. In 2008, the project is being funded by university student participation fees, with university student participation fees partially offset by small grants to student participants from the UR USF--Office of Undergraduate Research and the American Water Resources Association. Currently, additional funding is being sought to maintain and expand the program and to therefore ensure ongoing and continued success if the on-the-ground water-supply planning and infrastructure, natural-resource conservation, and community-outreach efforts.
 

The Role of Headwaters in Maintaining the Integrity of Downstream Waters

Perhaps my highest-impact effort to date has been in providing links between science and policy in the ongoing debate over the definition of “Waters of the United States” subject to federal regulation under the Clean Water Act.  Two recent US Supreme Court rulings have called this definition into question.  In 2001, the Court explored Clean Water Act protections for isolated, intrastate, non-navigable waters in Solid Waste Agency of Northern Cook County v US Army Corps of Engineers (2001) (SWANCC).  Five years later, the Court further explored Clean Water Act protections for tributaries and adjacent wetlands in Rapanos v United States and Carabell v United States, which were ultimately consolidated into Rapanos v United States (2006) (Rapanos).

Working in response to SWANCC and in parallel with Rapanos, Dr. Tracie-Lynn Nadeau and I co-edited a Featured Collection of the Journal of the American Water Resources Association addressing the roles played by headwater streams and adjacent wetlands in maintaining the integrity of downstream navigable-in-fact waters.  In the first month following publication, the introductory and synthesizing papers were downloaded from the publishers’ website nearly 1,000 and 500 times, respectively.  As of June 18, 2008, ~16 months following publication, the 10 papers that comprise the Featured Collection were listed as the numbers 1-7, 9-10, and 14 most popular papers in the Journal of the American Water Resources Association, based on the number of full-text downloads over the previous 12 months.  The US Environmental Protection Agency distributed ~1000 copies of the full Featured Collection to key policymakers throughout Washington, DC, and posted products from the synthesizing paper and a link to the full Featured Collection as the first and second items listed under “Relevant Studies” on the website that provides information regarding "Waters of the United States".  For these efforts, Dr. Nadeau and I shared a US Environmental Protection Agency Level I Scientific and Technological Achievement Award in 2007, which was awarded in recognition that our research is of national significance and is represents a major scientific achievement within our field of study.

Specific issues raised in Rapanos remained unresolved due to the relative timing of the Featured Collection and the issuance of the Rapanos decision.  Most important were the meanings of the so-called Scalia and Kennedy Standards, two suggested standards by which the geographic extent of “Waters of the United States” could be defined.  By the Scalia Standard, waters of the US extend beyond navigable-in-fact waters to include “relatively permanent, standing or flowing bodies of water”.  By the Kennedy Standard, waters of the US include waters that “possess a ‘significant nexus’ to waters that are or were navigable in fact, or that could reasonably be so made”.  Leibowitz et al. (2008) responded by interpreting the Scalia and Kennedy Standards within the established scientific context, then proposing specific metrics by which the Scalia and Kennedy Standards could be assessed for a given water or class of waters.

Many colleagues have collaborated on this project, including but not limited to Tracie-Lynn Nadeau, Scott Leibowitz, Jim Wigington, Donna Downing (U.S. Environmental Protection Agency) as well as the many authors who gave their time and energy in writing papers for the Featured Collection.

The Role of Hydrological Processes in Maintaining Ecosystem Structure and Function in Mangroves

Hydrological processes have a dominant impact on the structure and function of wetland ecosystems, including coastal wetland that in the tropics are dominated by mangroves. Globally, mangroves have been impacted by a variety of activities that result in significant modifications of the original hydrologic conditions. Mangrove systems comprise ~2,500 km2 of south Florida and many are located in the Indian River Lagoon, a series of connected estuaries that extends ~250 km along the east coast of Florida. Most of the mangrove systems in the Indian River Lagoon have been ditched and impounded for mosquito control but are still hydrologically linked by surface water and groundwater pathways to the Indian River Lagoon. Our study site is a mosquito impoundment located on a carbonate barrier island near Ft. Pierce, Florida. A consequence of mangrove alterations has been the development of a complex matrix of vegetation within the impoundment that ranges from high salinity salt pannes in which no mangrove trees grow to areas adjacent to open water that support tall mangroves.

Our research focusses on the relationships between hydrological processes and ecosystem structure and function of these mangroves. Our overall objectives are to understand the relationships between hydrologic conditions at a range of scales from small-scale processes associated with nitrogen, the nutrient that limits the growth of mangroves at this site, cycling to the relationship between surface and subsurface hydrology and the distribution, structure and function of different variants of vegetation. Dominant mangroves at the study site are Rhizophora mangle (Red mangrove), Avicennia germinans (Black mangrove), and Laguncularia racemosa (White mangrove).

Many colleagues are collaborating on this project, including but not limited to Dennis Whigham and Ilka Feller (Smithsonian Environmental Research Center), Jos Verhoeven (University of Utrecht), and Riks Laansbrok (Netherlands Institute of Ecology). Christina Stringer and Bruce LaFrenz are two of my current Ph.D. students working on this project.

Funding has been provided by the Smithsonian Marine Station at Ft. Pierce.

Hydrology of Clay Storage Areas

The phosphate industry owns or has mineral rights to more than 440,000 acres of land in northern and central Florida, approximately 25% of which are river or wetland habitats. Following mining, approximately 40% of the land is covered with clay settling areas, which are steep-sided, high-walled reservoirs as large as one square mile, filled with supersaturated clay separated from the phosphate and sand during processing. Potentially, hundreds of thousands of acres of land in northern and central Florida could someday be covered by clay settling areas. It takes decades for the clays to dewater sufficiently to support even light land uses. Therefore, clay settling areas are the most conspicuous and development-limiting landforms remaining after phosphate mining.

The effects of the clay settling areas on water resources are largely unknown. To be sure, annual rainfall is captured by the clay settling areas. However, the fate of this rainfall and the original processing water still contained within the clay settling area is unclear. Does it recharge the underlying surficial aquifer and flow to nearby wetlands and streams? Does it recharge the underlying Floridan aquifer from which many Floridians derive their water? Or does it simply evaporate back to the atmosphere and not become available for any beneficial use? This four-year project is designed to address these and other fundamental questions of hydrological and ecological importance in Florida and other phosphate mining districts around the world.

Many colleagues are collaborating on this project including Mark Stewart (USF Geology), Mark Ross (USF Civil & Environmental Engineering), and Ken Trout (USF Civil & Environmental Engineering). Kathryn Murphy, Mike Kittridge, and Natalie Pechenik are three of my M.S. students who have worked or are currently working on this project.

Funding is being provided by the Florida Institute of Phosphate Research.

Geological Control of Ecological Structure and Function in Vernal Pool Wetlands

Vernal pools are depressional features that are inundated for portions of the wet season, then drain and dry in the late wet and early dry seasons. They occur as small, poorly-drained depressions perched above an impermeable or very slowly permeable soil horizon or bedrock. These wetlands typically range in size from 50 m2 to 5000 m2, with some functioning vernal pools being as small as 30 m2. Vernal pools usually have maximum water depths less than 1.0 m. They represent small yet complete ecosystems that are aquatic islands surrounded by uplands. Vernal pools occur in southern Oregon, northern Baja California, throughout California, and in other Mediterranean-type climates of the world.

Vernal pools are best known for the biological functions that they perform. Vernal pools are among the last remaining California ecosystems still typically dominated by native flora. Many vernal pool floral and macroinvertebrate species are endemic, and some vernal pool floral and macroinvertebrate species are federally-listed threatened and endangered species and/or state-listed endangered and rare species. Thus, vernal pools are critical components of regional biological conservation efforts. However, vernal pools are rapidly being lost to agricultural or urban land uses. For example, estimates based on soil maps, the presence of relict vernal pools, and inference suggest that 60 to 90 percent of the original vernal pool area in California has been lost to agricultural or urban land uses.

Hydrology is the primary forcing function in most wetlands, and is particularly critical in vernal pools. Vernal pool flora are sensitive to variations in inundation duration, while vernal pool macroinvertebrates are sensitive to variations in inundation duration, salinity, and possibly several other water chemistry constituents (e.g., pH, dissolved oxygen, and nutrients). It is therefore surprising that few studies of vernal pool hydrogeology and biogeochemistry have been conducted.

Vernal pools occur on many geologic surfaces. However, in all cases vernal pools are underlain by impermeable or very slowly permeable layers such as hardpans (e.g., silica-cemented duripans), clay-rich soils, mudflows or lahars, or bedrock. This study is focused on vernal pools on hardpans and clay-rich soils, the most common types of vernal pool in the Central Valley of California. Our global hypothesis is that geological processes determine hydrogeological, biogeochemical, and biological structure and function in vernal pools. Many parallel and complimentary studies are being conducted under this global hypothesis.

Many colleagues have contributed to this project, including but not limited to Graham Fogg (UC Davis), Thomas Harter (UC Davis), Randy Dahlgren (UC Davis), and Bob Williamson (UC Davis). Currently, much of the work is being conducted by Bob Williamson (UC Davis).

Funding has been provided by the California Department of Transportation.

The Role of Reconnecting Channels and Floodplains in the Restoration of Hydrological and Biological Structure and Function in Riverine Ecosystems

Greater than 50 percent of the wetlands in the conterminous United States have been lost or severely degraded due to conversion from natural to agricultural or urban land uses. Estimates of loss or severe degradation exceed 90 percent for all wetland types in California and 95 percent for riparian systems in the Sacramento Valley of California. Similar trends have been reported throughout the world. Thus, restoration and management are considered critical components of wetland and riparian system conservation efforts in the United States and throughout the world.

Hydrology is the primary forcing function in wetland and riparian systems and is the critical element in wetland and riparian system restoration and management efforts. Hydrology is particularly critical in riparian systems since it is the primary mechanism by which mass and energy are transported between uplands and downstream environments; it is the primary control on the pathways and rates of biogeochemical processing of dissolved and particulate matter; it provides multidimensional environmental gradients that support diverse metazoan populations which serve as critical pathways and mechanisms by which energy is transferred in riparian food webs; and it plays critical roles in vegetation recruitment and persistence. Unfortunately, very little is known about the hydrological and related biological effects of river restoration efforts.

This project explores the role of reconnecting a channel and a floodplain in the restoration of hydrological and biological structure and function in a riverine ecosystem. The project is being organized into three linked efforts, the first of which will treat key elements of hydrological and hydrogeological structure and function, the second of which will treat key elements of vegetation structure and function, and the third of which will treat key elements of fisheries structure and function.

The project site is Bear Creek and the adjoining meadow near Dana, California. In 1960, the Soil Conservation Service assisted the previous landowner in a channel improvement project to enhance grazing and farming of the meadow. This project abandoned approximately 3.5 km of existing stream channel, which consisted of a low-gradient, meandering main channel with multiple secondary distributary channels typical of meadows in the area. Straightened main and secondary channels were constructed near the edges of the meadow. Between 1960 and 1999, the straightened channel reaches incised as much as 5 m into the alluvium. The incision led to the near complete loss of floodplain water and sediment storage, a significant lowering of the ground water table, the loss of riparian and meadow plant communities, and the loss of in-stream spawning habitat. Channel incision also led to substantial increases in flood waves and sediment loads delivered to the Fall River.

Based on five years of pre-project surveys of hydrologic and geomorphic conditions, including analyses of remnant channel segments as reference reaches, the current landowner developed a restoration and enhancement design. The project was completed during the summer of 1999. The restored and enhanced channel is designed to carry a bankfull discharge of approximately 200 cfs through a meandering, single-thread channel with slopes that vary from 0.001-0.002. Approximately 2.2 miles of channel were constructed or restored by linking newly-created channel with remnant channel segments. Approximately 42 acres of ponds were excavated in order to fill portions of the incised channel and to provide gravel for the new channel. Approximately 5,000 cubic yards of gravel were used to create more than 8,700 linear feet of riffle habitat. More than 113,000 native plants, including sedges, rushes, grasses, shrubs, and trees were planted on the meadow. Bank stabilization was achieved by planting sod mats, transplanting willows and other riparian shrubs and trees, and installing root wads. Grade stabilization utilized rock weirs.

Many colleagues have contributed to this project, including but not limited to Chris Hammersmark and Jeff Mount (UC Davis) and Solomon Dobrowski (University of Montana).

Funding has been provided by the current landowners, the Cantara Trustee Council, and the Packard Foundation.

The Effects of Reservoir Operations on Shallow Groundwater and Vegetation Distributions in Reservoir-Fringe Ecosystems

Currently, there are more than 75,000 dams greater than six feet in height in the United States, and the reservoirs created by these dams cover approximately three percent of the nation’s land surface. Most reservoirs are managed exclusively for traditional purposes: municipal and irrigation water supply, hydroelectric power, flood control, and recreation. However, there is growing interest in managing these reservoir resources, at least in part, for the maintenance of plant and wildlife habitats. Virtually all of the discussion surrounding this management objective is centered on the downstream effects of reservoir operations on flow regimes, vegetation distributions in the near-channel area, and channel morphology and in-channel fish habitat. Thus, decommissioning reservoirs or otherwise restoring natural flow regimes has been the focus of many recent efforts. This approach, however, does not always clearly result in net ecosystem benefits.

Reservoir construction often leads to the development of new habitats in reservoir-fringe areas such as emergent marshes, wet meadows, scrub-shrub wetlands, and riparian forests. These habitats can be regionally unique and, therefore, can serve as critical habitats for regionally uncommon plant and wildlife species. Decommissioning reservoirs or otherwise altering reservoir operations can restore some channel and floodplain functions but can degrade or eliminate these regionally unique reservoir-fringe ecosystems. Thus, reservoir-fringe ecosystems should be considered in the context of the maintenance of plant and wildlife habitats. This is particularly true for reservoirs that are unlikely to be decommissioned due to their socioeconomic importance and for reservoirs that are located directly upstream from reservoirs or otherwise impaired water courses.

This project explored surface water and groundwater origins and interaction and associated vegetation distributions in riverine and reservoir-fringe systems. The overall objective of this effort was to develop concepts and tools for the planning, implementation, and monitoring stages of river and reservoir management efforts. This project was organized into three linked efforts. In the first effort, the primary sources of the shallow groundwater were identified. In the second effort, the roles of stream discharge, regional groundwater discharge, and reservoir stage in controlling shallow groundwater were characterized. In the third effort, a linked groundwater and vegetation distribution model was presented and used to simulate groundwater and vegetation distributions under different reservoir operations.

Many colleagues contributed to this project, including but not limited to Jeff Mount, Eric Larsen, and Graham Fogg (UC Davis).

Funding has been provided by a cooperative agreement between the United States Bureau of Reclamation and Ducks Unlimited and a gift from the Peter and Nora Stent Fund of the Peninsula Community Foundation.