Soils and vegetation as a record of anthropogenic pollutants: Mn in the Shale Hills CZO

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It is well known that metals are emitted to the air by human activities and subsequently deposited to the land surface. Current regulations in the U.S.A. require that air emissions be monitored; however, past inputs to the land surface are largely unknown. Soils record natural and anthropogenic fluxes to the Earth?s surface, including atmospheric deposition, and can therefore be analyzed using mass balance models to constrain inputs and outputs. In work started at the Penn State Susquehanna Shale Hills Critical Zone Observatory (CZO), the investigator has demonstrated that atmospheric inputs have contaminated soils with Mn in Pennsylvania. Specifically, over half the Mn in the soil in the CZO was most likely added by atmospheric deposition from industrial sources over the last 200 years. Investigation of published soil databases shows that Mn contamination is widespread but highly localized in many industrialized areas in the U.S.A. and Europe. These results emphasize that atmospheric transport is now a critical component of the global Mn cycle. In this project, the investigator is working to understand how Mn moves from atmospheric deposition through the soil and vegetation and into stream water. Mn is important in impacting ecosystem processes because of its high reactivity and because its compounds are redox-sensitive. Mn is essential for photosynthesis and enzymatic function but can also be toxic to forests and humans in high amounts. Additionally, Mn-oxides can sequester large concentrations of heavy metals, can affect mobility of contaminants, and can impact biotic function in soils. This project will 1) quantify concentrations of Mn in CZO vegetation; 2) examine the reservoirs of Mn in the CZO using state-of-the-art spectroscopic techniques; 3) develop models of Mn cycling in the soils; and 4) continue to mine and synthesize data from published literature to test the hypothesis of widespread Mn contamination of topsoils in industrialized regions. The proposed work will contribute to collaborative efforts to study regolith weathering at the NSF-funded Shale Hills CZO, which has supported 18 students and 17 faculty across multiple disciplines. The project will support doctoral student Beth Herndon. The researchers will also begin to collaborate with a Pennsylvania State University professor of Curriculum and Instruction to improve the Earth science curriculum and develop outreach activities for K-8 students in a nearby school district.