When
Monday, September 14, 2026, at 10:00 a.m.
Bryn Stewart
Assistant Professor
Department of Hydrology & Atmospheric Sciences
University of Arizona
"Using Critical Zone Science to Understand Watershed Processes and Stream Water Quality"
Harshbarger 118A-A1
ABSTRACT
Streams integrate complex and interrelated processes that occur in the Critical Zone, or the outer layer of Earth that provides life-sustaining resources like clean water and fertile soil. Critical Zone processes, including biogeochemical reactions and hydrological processes, govern the production and export of chemical solutes at the terrestrial-aquatic interface, shaping the water quality of our streams and rivers. However, it is difficult to directly observe and measure these processes, limiting our understanding of the Critical Zone. In this talk, I will demonstrate the use of field observations and watershed-scale reactive transport modeling to understand how different hydrological and biogeochemical processes, especially those at shallow and deep subsurface depths, shape the dynamics of stream chemistry. Moreover, I will demonstrate how stream chemistry dynamics mirror the chemistry of different subsurface flow paths under distinct flow conditions. This Shallow and Deep hypothesis concept further explains near-universal export patterns of many solutes in streams spanning gradients of climate, vegetation and geology across the continental US. My current and future research interests focus on understanding and predicting the impacts of extreme events (e.g., storms, heatwaves) on Critical Zone processes and water quality across diverse landscapes and across a range of spatial and temporal scales.
ABOUT THE SPEAKER
Bryn Stewart is an assistant professor in the Department of Hydrology and Atmospheric Sciences at the University of Arizona. Bryn is a watershed and Critical Zone scientist whose research explores how hydrologic and biogeochemical processes respond to external influences and control water quantity and quality. Their work combines field observations, large-scale datasets, watershed-scale reactive transport models and data-driven models to investigate patterns and processes in biogeochemical cycling and water quality dynamics. Bryn earned a BS in chemical engineering and PhD in environmental engineering and biogeochemistry from the Pennsylvania State University. Before joining the University of Arizona, Bryn worked as a postdoctoral fellow in environmental science and engineering at the California Institute of Technology.