Observations Emerging from a Network of Critical Zone Observatories: Shale Weathering at the Susquehanna-Shale Hills Observatory

The Critical Zone supports ecosystems by providing clean water and healthy soil. However, humans are running a global chemical experiment by pumping carbon into the atmosphere, dissolving bicarbonate into the ocean, dissolving acids, metals, and organics into terrestrial water, and contaminating, leaching, and washing away the soil. We need to be able to model development of the Critical Zone to predict how human perturbations will affect soil resources in the future and to interpret past climate, landscapes and ecosystem evolution by studying paleosols. However, Critical Zone science crosses disciplines and scales of space and time. For scientists from these disciplines to work together requires collaborative field sites and community models which enable the prediction of processes across scales of space and time as well as across gradients in environmental variables. The three Critical Zone Observatories (CZO) and the Critical Zone Exploration Network (CZEN) are now providing sites for collaborative research to test the rates of processes across environmental gradients. One CZO, the Susquehanna-Shale Hills Observatory, anchors a set of weathering studies that explores the effects of climate and shale composition on weathering rates of this lithology. Weathering sites are chosen for investigation as a function of hydrologic flow path from one-dimensional flow (ridgetop), to two-dimensional flow (planar hillslope), to three-dimensional (convergent or divergent hillslope). The rates of weathering are compared for present-day (using porefluid chemistry) and when integrated over the exposure age of the soil (using chemistry of the solid profile).