My research focuses on the complex interactions and constraints that govern the evolution of natural landscapes, including surfaces of other planets. This research combines field studies, theory, simulation modeling, and quantitative analysis. Field studies have included evolution of channels in badlands, the natural regime and man’s influence on the Colorado River in the Grand Canyon, and the role of groundwater sapping in erosion of sandstone canyons in the southwest U.S..


My general field of interest is low-temperature aqueous geochemistry, encompassing problems in water-rock interactions, kinetics of geochemical reactions, and evolution of groundwater chemistry in various hydrogeological environments. My research includes elements of field studies, laboratory experimentation, and theoretical modeling. One research project is focused on the fate and transport of bacteria and organic contaminants in groundwater and is a collaborative effort with Messrs. Mills and Hornberger.


My biogeochemical research includes investigations on the natural and anthropogenic controls on chemical cycles at the watershed, regional and global scales.  I started first with trace metal biogeochemistry of the coastal ocean, and then expanded to investigations on the increased acidification of the atmosphere, soils and fresh waters.  My current research focuses on beneficial and detrimental effects of reactive nitrogen as it cascades between the atmosphere, terrestrial ecosystems and freshwater and marine ecosystems.  My most recent work examines how to maximize the use of nitrogen for


My research spans oceanography, climate and biogeochemistry, with an emphasis on numerical models, remote sensing, and data analysis. I am interested in how the global carbon cycle and ocean ecology respond to natural and human-driven climate change signals such as ocean warming, sea-ice loss, and ocean acidification due to the invasion of carbon dioxide from fossil fuel burning.


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Prior to retirement in May 2018, my primary teaching interests were physical geology, landscape evolution, petrology, economic ore deposits, and environmental geology. I am also interested in the geology of Virginia and the tectonic evolution of the state and mid-Atlantic region, as well as the geology and ecology of US National Parks.


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