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.
Normal 0 false false false EN-US X-NONE X-NONE Many soils around the globe are contaminated with metals due to inputs from anthropogenic activities; however, the long-term processes that retain these metals in soils or flush them into river systems remain unclear. Soils at the Susquehanna Shale Hills Observatory (SSHO), a Critical Zone Observatory in central Pennsylvania, USA, are enriched in manganese (Mn) due to past atmospheric deposition from industrial sources. Soils at the SSHO record the legacy of industrial Mn inputs from the numerous iron furnaces operating regionally during the mid-19th century and the widespread industrialization of PA into the 20th century. The purpose of our research was to investigate what factors contribute to both Mn retention in soils and release into streams and rivers. We hypothesized that vegetation takes up and stores large quantities of Mn, slowing its loss from watersheds. To address this hypothesis, we 1) quantified Mn concentrations in green foliage and leaf litter; 2) built mass balance models describing the cycling of Mn through trees at SSHO and in greenhouse mesocosm experiments; 3) determined major Mn species in the soil-plant system using spectroscopic techniques, and 4) evaluated historical trends in Mn concentrations in the Susquehanna River (1957-2010). With this research, we established that soils, vegetation, and water systems in Pennsylvania remain enriched in Mn despite decreasing levels of atmospheric Mn deposition that have fallen with the decline of the iron and steel industries. Furthermore, we found that impacted ecosystems slowly release accumulated Mn from soils and vegetation into rivers. Specifically, trees take up dissolved Mn from the soil and store it in biomass for years to decades. The soluble Mn that is stored in biomass is oxidized and immobilized as Mn-oxides in the soil during biomass decomposition. The continuing process of uptake, storage, and oxidation of Mn in vegetation leads to long-term retention of Mn within impacted ecosystems, and Mn is only slowly leaked from soils and vegetation into rivers. Overall, biological cycling increases Mn retention in ecosystems impacted by industrial inputs and concentrates the Mn into soils with high soil organic matter before the Mn is lost from the catchment. These results emphasize that vegetation acts as a capacitor that concentrates Mn inputs in the temperate catchment investigated here. This research spurred two additional, complementary projects. First, sources of atmospheric addition to SSHO soils were identified using lead isotopes. Lead, like Mn, is enriched in surface soils at SSHO, and its isotopic signature was found to be consistent with coal burning in western Pennsylvania in the late 19th / early 20th centuries. Second, Mn inputs to soils were quantified in the vicinity of an operating ferromanganese refinery in Ohio, and the magnitude of Mn enrichment in soils was found to decline as a function of distance from the refinery. This work involved substantial collaboration with meteorologists to synthesize observations of Mn enrichment in soils with atmospheric dispersion models. This collaboration resulted in a more accurate quantification of Mn inputs to soils over time and will encourage future model integration between disciplines. Together, these studies highlight the continuing legacy of metal contamination in industrialized areas, and underscore the need to evaluate metal enrichment and transport processes in impacted systems. This grant supported research training for two female graduate students at Penn State, generating one PhD dissertation, one MS thesis, four manuscripts (to date), and numerous presentations at scientific conferences. Additionally, this grant supported training four undergraduate students in methods of sample collection and processing.
