A clay-specific mineralogical approach to the dynamics of agricultural runoff through a wetland site in a watershed in Sheldon, VT.

Modernized agricultural land use and corresponding fertilizer usage are common throughout the Lake Champlain watershed in Northwestern Vermont. Fertilizers contribute to eutrophication of lake waters, harming and altering the environment. Eutrophication events render the water toxic, reduce oxygen levels, and are becoming more frequent. In Sheldon, VT, a slope downhill from an agricultural field leads to a wetland flanked by Hungerford Brook, a tributary stream that feeds into the lake. For this project, core samples of the soil were taken from the wetland portion of the Hungerford site. A previous project for a Geochemistry class had sampling performed at this site for mineralogical identification of the soils, but the constraints of the project produced mixed results. Therefore, a more detailed process of data collection in addition to a focus on the mineralogical behavior of clays were included in this project. Understanding the behaviors of the clays can provide important insight into their interactions with pollutants being carried from runoff sourced from the adjacent agricultural site. This information has the potential to be valuable to remediation, and an improved understanding into minerals affected runoff dynamics. Clay fractions were created to separate primary and secondary minerals, so that they could be identified individually via x-ray diffraction (XRD). In addition to XRD, clays were identified through other techniques such as drying, oven heating, and ethylene glycol treatment. Primary minerals consist of feldspars, phyllosilicates, calcite, and serpentine, while secondary minerals include sepiolite, smectite, illite, and kaolinite. The preliminary mineralogical results yield insight into the sourcing for secondary minerals regarding their corresponding parent minerals and their depositional environment at incremental depths. Understanding the mineralogical behavior of clays in buffer zones through which contaminated water flows into tributary streams is imperative to predict interactions with fertilizers in respect to their mobility and stability