The Critical Zone is where much of the world’s surface water is generated, and processes within the CZ play a large role in determining the flux and composition of stream waters, including “water quality.” The flow of water through the landscape and its chemistry are intimately related, as water takes multiple pathways depending on the structure of the Critical Zone, in turn influencing the type and extent of reaction experienced along the path. New data now available with Critical Zone observing networks represent an opportunity to “look inside” hydrobiogeochemical systems and gain insight into water pathways, transit time scales and reactions that control biogeochemical fluxes.
Lin Ma(UTEP), Nicole Fernandez (IPGP, Cornell), Fabiola Levy (UP)
Relationships between variations in stream discharge and solute concentrations (C-Q relations) contain information about multiple Critical Zone processes, from hydrologic flow paths to weathering reactions to transport and reaction time scales. Variations in stream export are a dynamic integrator of Critical Zone processes. A typical stream system may show large variations in discharge with only modest variations in the concentration of solutes, with interesting implications for solute fluxes. As an example, a system that shows factor of ten variation in discharge (Q) but only factor of two variation in concentration of a given solute (C) has a factor of five variation in solute flux, and this can occur over short time scales. Where does this five-fold increase in solute flux “come from”, and what does that tell us about the fluid flow and geochemical reactions that take place within the Critical Zone, and how they vary with time?
We are using a network of Critical Zone sites in France and the US to gather data and test hypotheses. They include sites instrumented with the River Lab high frequency measuring and sampling system developed under the CRITEX program. The River Lab permits continuous automated measurement and sampling at ca. 30 minute intervals, enabling new insight into the nature of hydrochemical variability.
The main support for the project is from ANR under the French program “Investissements d’avenir”. Additional funding includes support from the Chateaubriand Fellowship program of the Embassy of France. Closely related work on the Critical Zone is supported by the grants to PI Derry from the U.S. National Science Foundation.
More detailed information about the project is here.
Jean Marcais (IPGP, INRAe), Sylvain Pasquet (IPGP)
