Collaborative Research: Network Cluster: Urban Critical Zone processes along the Piedmont-Coastal Plain transition

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The Earth’s Critical Zone spans bedrock to treetops. For urban areas, the built environment is an integral but understudied part of the Critical Zone. Soil and rock influence the chemistry of groundwater flowing through the subsurface to streams. Rocks “weather” (chemically change) from the bottom up over long periods, influencing groundwater and stream chemistry. Stream chemistry is critical for freshwater habitat and drinking water quality. In urban areas, human activities alter this geologic foundation, moving earth for construction, burying water and sewer pipes, and applying road salt and fertilizer. Little is known about how above-ground urban processes and below-ground geological processes interact to change weathering and chemistry of groundwater and streams. This project studies the interactions of natural and anthropogenic weathering processes and their effects on water quality, using a cluster of four cities as our laboratory -- Philadelphia, Baltimore, Washington, DC, and Raleigh. The cities are located along the Fall Zone - a geologic transition that creates waterfalls, along the Eastern Seaboard. The cities capture variation in climate, development age, and population density. Research methods include observational and modeling activities that integrated multiple processes in urban Critical Zones. This project will train 7 undergraduates per year, 7 graduate students, and 1 post-doctoral associate. Project participants will work with K-12 teachers to integrate Critical Zone science in the classroom and provide professional development. A regional Critical Zone Citizen Science Interest Group will be convened to adopt project protocols in local programs and contribute to project research. An engagement plan to foster interaction with a broad community of other Critical Zone scientists includes hosting open quarterly science meetings and establishing a visiting scholar fund. Project results will allow policy makers and regulators to incorporate Critical Zone processes into management of water quality and resilient, sustainable, urban development. 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. The project will address the following research 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?; and (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. 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 will be developed. This project will train 7 undergraduates per year, 7 graduate students, and 1 post-doctoral associate. Existing institutional programs will be utilized to recruit underrepresented groups into STEM fields for the project. 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.This project is jointly funded by the Critical Zone Collaborative Network and the Hydrologic Sciences programs in the Division of Earth Sciences and the Environmental Sustainability program in the Division of Chemical, Bioengineering, Environmental and Transport Systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.