NSF Award
2423066
Streams and rivers carry distinctive compositions of dissolved chemicals that affect aquatic ecosystems and determine the suitability of the water for human uses. This chemical composition results from the reaction of rainfall and snowmelt with the materials in the Critical Zone: the rocks, soil, and biosphere at or near the Earth’s surface. Urban and suburban landscapes are underlain by extensive sanitary-sewer infrastructure of varying age and condition, which may also contribute to the dissolved chemicals entering stream water. This project will develop a semi-quantitative conceptual model to predict how exchanges with sanitary sewer infrastructure occur and their impacts within stream network. Using data sources from urban watersheds within the Atlanta metropolitan area as a test site, this project will produce maps of sewer infrastructure conditions and examine how these are associated with water-quality impacts. The research will yield new knowledge to support urban-watershed managers in their decision-making about sanitary-sewer rehabilitation. This project will advance STEM (Science, Technology, Engineering, and Math) education by supporting students at Georgia State University, a primarily Black university. The project will also support research experiences for high-school students through an internship program in the Atlanta Public Schools. Accordingly, there will be significant STEM education and training for students from groups that have been historically underrepresented in scientific research.<br/><br/>Longitudinal patterns of solute chemistry within baseflow represent the spatial and temporal integration of chemical weathering and biogeochemical reactions within the Critical Zone, and the water-flow paths that transport those reaction products from land to stream. In urbanized areas, these processes and patterns are strongly influenced by anthropogenic infrastructure, including sewer networks that span thousands of miles within individual cities. This research will develop a semi-quantitative conceptual model to examine the functional relationship between urban sewer infrastructure and the dissolved solute load within urban streams. The model aims to index the groundwater-mediated, source-versus-sink behavior of sewer infrastructure within delineated contributing areas of urban watersheds, then link this index to observed trends and transitions in baseflow chemistry within and between stream reaches draining those areas. The research will occur in a group of variably urbanized watersheds in the Atlanta Metropolitan area. Data collection includes (1) longitudinal sampling of stream baseflow and analysis of dissolved solute concentrations;(2) observations of depth to groundwater within an array of wells and via ground-penetrating radar; and (3) compilation of publicly accessible spatial data representing landscape characteristics and the age, installation, and material composition of sewer infrastructure. These data will be used to develop probabilistic indices of sewer infrastructure failure and groundwater inundation, and to define watershed-specific probability distributions of source versus sink behavior of the sewer infrastructure. Correlation analysis will examine functional relationships with longitudinal trends in dissolved solute concentrations and loads during baseflow conditions. The model could be generalized to other urban watersheds and enable delineation of the characteristics of sewer infrastructure that disproportionately affects biogeochemical cycling and dissolved solute loads in urban streams. The project will leverage the existing Urban Critical Zone cluster, expanding to an urban area with similar geology and physiography while providing water quality observations in a sub-tropical, lower-latitude city.<br/><br/>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.
