This project will advance knowledge of urban critical zone processes through a Critical Zone (CZ) Cluster spanning four cities on the U.S. East Coast: Philadelphia, Baltimore, Washington, DC, and Raleigh. These cities were developed along the Fall Zone, a region of steep rivers incised into crystalline Piedmont bedrock upstream of the Atlantic Coastal Plain. The north-south gradient of this urban cluster is associated with climatic trends and with a gradient in age from older and denser development in Philadelphia and Baltimore to newer and sparser development in Raleigh.

We will address the following questions: (1) How does urbanization in a temperate, Eastern seaboard landscape result in a shift from a supply-limited to a transport-limited regime governing solute export? (2) How does the underlying structure of the CZ along the Piedmont-Coastal Plain transition interact with urbanization to affect export fluxes? (3) How do chemical and hydrological dynamics associated with urbanization affect material export along the latitudinal gradient from Philadelphia to Raleigh?

Research methods will include development of a watershed-scale geochemical-hydrological model as a framework for data collection, assimilation, and prediction; geophysics for subsurface mapping; land cover/land use data analysis; soil and rock core chemical analysis; soil gas sampling; stream and well sampling for solutes; and analysis of sediment concentrations and yields. We will construct a new conceptual model of solute movement from the land surface through the subsurface to streams, constrained by geologic and geomorphic architecture and the overprinting of urban development. This project will train 7 undergraduates per year, 7 graduate students, and 1 post-doctoral associate.

Project participants will work with high school science teachers to identify topics for a CZ instructional module and a teacher professional development program. A regional CZ Citizen Science Interest Group will be convened to identify opportunities to adopt CZ project protocols in local programs and to contribute to CZ project research. The project engagement plan includes hosting open quarterly science meetings and establishing a visiting scholar fund to support scientific exchange with other CZ cluster sites.