| Description |
This thesis examines trace elements as environmental fingerprints in groundwater, surface water, and sediment. Whereas some of the fingerprints examined here are affected by chemical partitioning equilibria, others are not; but all are affected by distance of transport from source to receptor. The trace element forensics in this thesis are divided into four contexts: 1) mechanisms mobilizing arsenic in groundwater; 2) source identification of particulate metals (PM); 3) differentiating mining versus nonmining sourced PM in lacustrine sediment; and 4) reconstruction of the mid-Holocene páramo paleoclimate. We examined covariates associated with arsenic concentrations exceeding the US Environmental Protection Agency (EPA) maximum contamination level for groundwater in the western, central, and eastern US regions via Classification and Regression Trees (CART). Regional CART models suggested that arsenic mobilization in the western US is driven by climate as well as pH, whereas arsenic mobilization in the eastern US is driven by dissolved iron (representative of reducing conditions) and pH. PM loads and lead (Pb) isotopes were used to differentiate mining and nonmining sourced contaminants in the seven main tributaries of the San Juan River, US. PM loads within some tributaries varied with runoff category, indicating that for these watersheds, different runoff categories tapped different PM sources within the watershed. Signatures of tributary PM, including enrichment factors, Pb isotopes, color, and particle size were iv used to tie layers in a San Juan River sediment core to upstream tributary sources. Approximately 10% of the overall PM deposited in the sediment core was attributed to mining sources, whereas approximately 80% of the overall PM reflected a mixture of mining and nonmining sources. In order to understand the timing and extent of a Holocene warm/dry event in the páramo vegetation of the Ecuadorian Andes, a lake sediment core from Tres Lagunas, Ecuador was collected and processed for trace element concentrations, pollen, magnetic susceptibility, and charcoal. The lake record corroborated the presence of a warm/dry period, consistent with other cores from the region; but it suggested a shorter period of warm and dry climate where the intensity was not sufficient to cause the lake to dry. |
