Controls on Stream Water Dissolved and Particulate Mercury within Three Mid-Appalachian Forested Headwater Catchments

This dissertation examines streamwater dissolved and particulate mercury dynamics (Hg D and Hg P, respectively) to gain an improved understanding of factors that control Hg transport from the terrestrial to stream environment. The three study sites, Piney River, Staunton River, and Paine Run, are each forested, headwater systems situated within Shenandoah National Park, VA, and are distinguished by chemical (acidic to neutral pH) and physical soil (sands to clays) characteristics. At each of the three sites, streamwater Hg D , Hg P , dissolved organic carbon (DOC) concentrations, turbidity, as well as suspended sediment at one location, were evaluated over a range of discharge conditions within an 18-month period with a focus on frequent sampling during high-flow periods. Total Hg streamwater export ranged from 1.26-3.71 µg m -2 yr -1 , representing 4-190f the Hg deposited through atmospheric deposition. Hg fluxes were dominated by the particulate fraction at each site. Brief high-flow rainfall/snowmelt events, corresponding to approximately 10f the time, were found to export the majority (80%) of the annual Hg flux. Hg D was strongly coupled with DOC at all sites confirming the known association with organic carbon. Both soil solution chemistry as well as soil particle size distribution were found to be controlling factors on the mobilization of Hg D. More acidic systems mobilize less aromatic DOC, which relates to less Hg per unit DOC. Soil composition was also found to influence Hg D export, with coarse sandy soils having a lesser capacity to retain Hg and keep it out of solution resulting in more Hg per unit DOC. Soil organic matter content appears to be a first-order determinant of the amount of Hg per unit iii organic carbon based on all available stream data, which include locations throughout the U.S. and Sweden. Hg P was strongly positively correlated with the organic fraction of suspended sediment, and due to a consistent organic fraction of the suspended solids, was also well correlated with total suspended sediment (TSS). Stream turbidity measured with an in situ sonde also had a strong correlation with TSS, enabling commutative association with Hg P . Turbidity-Hg P relationships established for each site allowed for improved quantification of Hg P mass fluxes.

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