CAREER: Balancing the global alkalinity cycle by improving models of river chemistry

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The water flowing in a river today is largely composed of rainwater that fell in the past and traveled underground before arriving at the river channel. The amount of time this transit takes is also the amount of time available for chemical reaction to occur. At the same time, the exact path that rain takes through watersheds - whether through shallow soils or deep, fractured bedrock - influences which reactions occur and at what rates. Consequently, observations of river water chemistry can be described equally well by models that attribute all variation to changes in either flow paths or flow rates. This ambiguity is problematic as the predicted effects of climate change on water resources are different depending upon the exact processes governing flow and reaction. To provide new insights into the controls on river water chemistry, this project will develop new approaches for analyzing variations in chemistry over time to separate the effects of flow paths from flow rates. The project will engage undergraduate students through an engineering design course, internships, and public outreach on local water quality issues.This work will leverage the information content of time-series data to constrain the coupled timescales of subsurface water transit and solute acquisition. To avoid some of the assumptions embedded in past work, non-parametric approaches will be used to infer geochemical kinetics and solute generation mechanisms. After being validated against 2-D numerical and analog experiments, the analysis approach will be used to elucidate the role of Critical Zone structure in the climate-weathering feedback as well as account for the non-linear behavior of trace element and isotopic proxies to improve mixing models. The results of these applications will be used to inform a new global analysis of weathering processes and their implications for planetary habitability with a timescale-agnostic framework for comparing terrestrial and marine systems. To lower barriers to collecting time-series data, undergraduate engineering design teams will develop a design-for-purpose autosampler. To help engage more undergraduate students in geoscience research, the project will develop a new, outreach-based course on local water quality issues.This project is co-funded by the Hydrologic Sciences and Geobiology & Low-Temperature Geochemistry programs.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.