Most ecosystems are impacted by human activities to some degree, but this can vary considerably beteween locations. For example, cities differ in their impacts on streams and rivers depending on age, storm water infrastructure, amount of green space, and other factors of the built environment. Natural factors such as climate (temperature and precipitation) and geology also affect how different cities influence water quality and quantity at different times of the year. In this project, differences in urban impacts on carbon inputs and outputs in streams will be evaluated across cities in the U.S. that have different urban and climate contexts. This research is critical for understanding ecological patterns and processes in urban streams. Broader impacts of the work will include training opportunities for undergraduate and graduate students and postdoctoral scholars, workshops, and an innovative training and internship program for high school students.This study will take a novel approach to jointly consider how the human and ecological dimensions of ecosystem ecology interact to control the quality, quantity, and timing of dissolved organic carbon (DOC) the largest flux of carbon in streams entering watersheds across the continent. This project will assess how urbanization affects DOC, focusing on how urbanization affects stream ecosystems in regionally-specific ways. Researchers will test the hypothesis that human activities introduce novel sources of DOC and affect the spatial and temporal scales and variability of ecological processes in different geographies and urban contexts. The hypothesis will be tested using a comparative approach to understand urban effects on DOC in five urban study areas Miami, FL, Boston, MA, Atlanta, GA, Salt Lake City, UT, and Portland, OR. Extensive synoptic sampling of DOC concentrations and quality will be combined with intensive sensor networks to develop a multi-scale understanding of the quantity and quality of DOC in urban systems. Spatial statistics and time-series analyses will identify key spatio-temporal characteristics of human development (e.g., wastewater infrastructure, housing density) and biophysical factors (e.g., discharge, precipitation, canopy cover) that control the concentration, characteristics, and bioavailability of DOC.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.