Complex terrain, flowpaths, and biogeochemistry of water in the H.J. Andrews Experimental Forest

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Understanding the impacts of natural and anthropogenic perturbations on catchment function requires improved understanding of fundamental controls on hydrology and streamwater solute fluxes. Isotopic and trace element tracers can provide important information about solute sources, biogeochemical processes, and hydrologic pathways. Here, the spatial and temporal dynamics of streamwater chemistry were examined across the H.J. Andrews LTER. Contrasting behavior is observed in stormflow solute chemistry across small watersheds ranging from 100 to 300 ha in size, in terms of nutrients, weathering-derived solutes, and precipitation-derived solutes.  Analyses of long-term stream chemistry data also highlight differences in solute-discharge patterns, with some catchments reflecting weathering-derived solute dilution with increasing discharge and others displaying chemostatic behavior, implying longer fluid residence times.  During a storm event, changing Ge/Si and ⁸⁷Sr/⁸⁶Sr reflect changing water sources from groundwater-dominated to shallower flowpaths in the watersheds that display dilution behavior.  Ongoing work is identifying shallow and deep soil weathering reactions and their associated Ge/Si and ⁸⁷Sr/⁸⁶Sr ratios in order to construct quantitative mixing models of the components of stormflow water.