Browsing by Author "Pennino, Amanda"

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    Catchment Structure Regulates Hydrodynamic Drivers of Chemical Weathering in Shallow Forest Soils
    Pennino, Amanda (Virginia Tech, 2023-06-12)
    Determining where, when, and how subsurface flow affects soil processes and the resulting arrangement of soil development along flow paths is challenging. While hydrologic regime and soil solution acidity are known to influence weathering rates and soil transformation processes, an integrated understanding of these factors together is still lacking. This dissertation explores the effects of subsurface flow on the mobility and distribution of dissolved organic carbon (DOC) and base cations to explain spatial patterns in chemical weathering in a forested headwater catchment. In the first chapter, relationships between hydrologic behavior, fluxes of weathered elements, and the extent of soil elemental loss across landscape positions are established. The second chapter investigates what specific groundwater behavior best explains spatial patterns in solution DOC concentrations during storm events. Lastly, in the third chapter, near surface saturation dynamics are examined to determine when and where DOC mobilization might be enhanced by subsurface flow. Results show that weathering extent was greatest in the upper reaches of the catchment, where O horizon saturation frequency and DOC concentrations are highest. Annual base cation fluxes, which were also greatest in these positions, could indicate where weathering is likely still enhanced. Additionally, while O horizon saturation occurred across the catchment, spatial differences in DOC concentrations suggest there are other sources of acidity to groundwater solutions other than just leaching from O horizons. Shallow organic soils, near bedrock outcrops at the top of the catchment is likely this additional C source, in which drainage water is transported downslope to nearby mineral soils when water tables are high and hydrologic connectivity between soils is increased. Spring and fall storm events were identified as times when groundwater most frequently reached O horizons during the snow-free year, providing insight into the timing of these processes throughout the year. This dissertation highlights how catchment structure mediates DOC flushing events, which in turn, influences the spatial architecture of soil development and chemical weathering processes across the landscape.
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    Forest catchment structure mediates shallow subsurface flow and soil base cation fluxes
    Pennino, Amanda; Strahm, Brian D.; McGuire, Kevin J.; Bower, Jennifer A.; Bailey, Scott W.; Schreiber, Madeline E.; Ross, Donald S.; Duston, Stephanie A.; Benton, Joshua R. (Elsevier, 2024-10)
    Hydrologic behavior and soil properties across forested landscapes with complex topography exhibit high variability. The interaction of groundwater with spatially distinct soils produces and transports solutes across catchments, however, the spatiotemporal relationships between groundwater dynamics and soil solute fluxes are difficult to directly evaluate. While whole-catchment export of solutes by shallow subsurface flow represents an integration of soil environments and conditions but many studies compartmentalize soil solute fluxes as hillslope vs. riparian, deep vs. shallow, or as individual soil horizon contributions. This potentially obscures and underestimates the hillslope variation and magnitude of solute fluxes and soil development across the landscape. This study determined the spatial variation and of shallow soil base cation fluxes associated with weathering reactions (Ca, Mg, and Na), soil elemental depletion, and soil saturation dynamics in upland soils within a small, forested watershed at the Hubbard Brook Experimental Forest, NH. Base cation fluxes were calculated using a combination of ion-exchange resins placed in shallow groundwater wells (0.3 – 1 m depth) located across hillslope transects (ridges to lower backslopes) and measurements of groundwater levels. Groundwater levels were also used to create metrics of annual soil saturation. Base cation fluxes were positively correlated with soil saturation frequency and were greatest in soil profiles where primary minerals were most depleted of base cations (i.e., highly weathered). Spatial differences in soil saturation across the catchment were strongly related to topographic properties of the upslope drainage area and are interpreted to result from spatial variations in transient groundwater dynamics. Results from this work suggest that the structure of a catchment defines the spatial architecture of base cation fluxes, likely reflecting the mediation of subsurface stormflow dynamics on soil development. Furthermore, this work highlights the importance of further compartmentalizing solute fluxes along hillslopes, where certain areas may disproportionately contribute solutes to the whole catchment. Refining catchment controls on base cation generation and transport could be an important tool for opening the black box of catchment elemental cycling.
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    Women in Soil Science: Growing Participation, Emerging Gaps, and the Opportunities for Advancement in the USA
    Vaughan, Karen; Van Miegroet, Helga; Pennino, Amanda; Pressler, Yamina; Duball, Chelsea; Brevik, Eric C.; Berhe, Asmeret Asefaw; Olson, Carolyn (2019-09)
    The soil science discipline has undergone significant changes since its establishment in the 1900s; from strong connections with agronomy to a broader focus on ecosystems, earth, and environmental sciences while also during this period experiencing a notable increase in diversity among soil scientists. In this review, we explore soil science from the perspective of gender demographics and disciplinary foci of soil scientists. We examine graduate student enrollment metrics; employment information in academia, the federal government, and the private sector; and membership data from SSSA to gain deeper insight into these changes and the implications for the future of soil science. Women earn nearly half of the advanced soil science degrees. The number of women pursuing soil science careers has also increased, albeit less markedly, as women now comprise 24, 26, and 20% of the soil scientists in academic faculty positions, federal agencies, and private industry, respectively. However, there is reason for concern that women linger in intermediate levels of employment, and further attrition occurs along the career ladder with only similar to 18% of the highest employment levels held by women; even fewer reach executive leadership levels in any sector. The growing participation of women in soil science is further reflected in a nearly 45% increase in female membership and meeting attendance in SSSA over the past decade, but recognition of their accomplishments and their presence in SSSA leadership positions remains low. We provide recommendations toward greater inclusion and gender diversity as this represents an important pathway to grow and innovate our science.