My research focuses on improving our understanding of how water and conservative solutes move through soils, hillslopes, and low-order catchments. Specific processes I focus on include infiltration, groundwater recharge, streamflow generation, and the advective-dispersive transport of solutes at pedon to small-catchment scales. My research includes field-based observational studies, laboratory- and field-based manipulative experimentation, and application of various flow and transport modeling techniques. I utilize stable-isotopes of water (2H and 18O)—introduced through active experimentation, or observed in natural precipitation and outflow—to trace geographic sources of water and to quantify time-scales of water transport through the subsurface. My work also involves the development of new techniques for measuring the abundance of these isotopes in natural waters.

Currently I am particularly interested in performing field studies and laboratory experiments aimed at quantifying distributions of transit times that water and conservative solutes require to move though soils, hillslopes, and catchments. The motivating question is “what is the distribution of ages (exit time – entry time) of water molecules that are discharged from landscapes into surface water bodies, and how are those age distributions controlled by ecological, geomorphic, and pedologic features of the landscape?” These age distributions, or transit time distributions, provide an integrated metric of the hydrological transport behavior of the landscape. They are very interesting for purposes of inter-site comparison, and in some cases for predicting differences in stream-water chemistry among catchments.

I welcome inquiries from students with interests in surface and/or groundwater hydrology that may be considering graduate studies.

Current Research Interests Include:

1) Field studies and laboratory experiments aimed at quantifying distributions of transit times that water and conservative solutes require to move though soils, hillslopes, and catchments. The motivating question is “what is the distribution of ages (exit time – entry time) of water molecules that are discharged from landscapes into surface water bodies, and how are those age distributions controlled by ecological, geological, geomorphic, and pedologic features of the landscape?” These age distributions, or transit time distributions, provide an integrated metric of the hydrological transport throughout the entire landscape. They are very interesting for purposes of inter-site comparison, and in some cases for predicting differences in stream-water chemistry among catchments. I am also interested in applying similar methodologies in an attempt to quantify transit time distributions of water that flows through trees and eventually back into the atmosphere. I am involved with ongoing collaborative projects at the Landscape Evolution Observatory at the University of Arizona – Biosphere 2 that investigate these transport timescales. I am interested to pursue new projects in this topic area with graduate students at Georgia State University, in relatively undisturbed landscapes or in urban/suburban environments. North Georgia is an outstanding region to pursue these questions, because there are four different physiographic provinces—with contrasting geology, soils, and vegetation—within a 150-mile radius of Atlanta (and, of course, the urban environment of Atlanta).

2) Discerning the impacts of meteorological variability and climatic change on water balance partitioning in diverse landscape. I maintain an interest in how weather variability we experience at daily to monthly time scales, and climate change that has happened, or is projected to occur, will alter the way precipitation is partitioned between evapotranspiration, groundwater recharge, and streamflow generation. This area of research is fundamental for intelligent use of water resources. Water supply has typically been a concern of arid western states, while water quality has been more of an imperative in the humid eastern US. That paradigm will continue to change throughout the 21^st century, as the human population continues to grow, irrigated agriculture expands in eastern states, and the energy sector demand for water rises concomitantly. Surface water allocations in many parts of the southeast are already strained. Enhanced utilization of groundwater resources is likely to continue. Hydrological scientists have a large role to play in informing the public about how our rainfall gets partitioned between subsurface storage and evapotranspiration back to the atmosphere. In particular, there are significant advances to be made in quantifying groundwater recharge fluxes in the piedmont and upper coastal plain regions, where the vadose zone is vertically expansive and spatially heterogeneous. Climate impacts on the vadose zone water balance was a focal point of my past research, and I want to continue working in this area with students at GSU.

3) Novel applications of stable-isotope tracers in hydrological science. Stable isotopes of hydrogen and oxygen continue to be imperative tools in hydrological science for understanding geographic origins and travel times of water flows. Laser spectroscopic analyzers now make possible rapid analysis of very large sample loads, and new field-based sampling methodologies show promise for advancing our ability to monitor water fluxes with unprecedented spatial and temporal resolution. My new laboratory at GSU is equipped with a Los Gatos Research IWA-45EP laser spectrometer that would be available for use by graduate students and post-docs. There are exciting possibilities for applying these new approaches in the areas of research described above, and for investigating the hydrology of human-altered environments—for example, for determining the effects and efficacy of green infrastructures. I encourage students with interests in these applications to contact me about possible research opportunities.