A common observation is that the chemistry of stream waters varies with discharge, something that is seen both in event-driven small watersheds and the seasonal monsoon variations in large rivers. Isotopic tracers indicate that the source of the solutes varies as well. These observations indicate that the flow paths and reaction networks vary with time and hydrologic conditions in the Critical Zone. To unravel this complex behavior we are using a new generation of hydrologic models that permits the estimation of the non-steady state transit time distributions in a watershed. We seek to couple this information with the chemical and isotopic information interpreted through reactive transport modeling. The constraints from the hydrologic, chemical and isotopic approaches can tell us about how and why water chemistry and quality vary within a system and how this may vary with moficiations in hydrologic forcing under changing climate.
We are using observations and sampling from OZCAR and CZO sites (France, North America) to obtain high frequency event based sampling for discharge (Q), concentration (C) and isotope ratio (R) data to generate detailed C-Q-R patterns that contain unique information about flow and reaction networks in watersheds.