FULVIC ACID CHARACTERIZATION AND VARIABILITY IN ALPINE WATERSHEDS

Dissolved Organic Carbon (DOC) is a widely known regulator of carbon, source of energy, and binding ligand with metals in freshwater aquatic environments. DOC chemical characteristics may vary among watersheds and can be influenced by vegetation, climate, geology, and hydrology. DOC has two operationally-defined components consisting of hydrophobic acids (HPOA) and hydrophilic acids (HPLA). The HPOA component consists of approximately 40% humic acid and 60% fulvic acid. Acid Mine Drainage (AMD) originating from abandoned hardrock mines characteristically has low pH (<4.0) and high concentrations of Cu, as well as dissolved and particulate forms of Al and Fe. Interaction of DOC with particulate Fe and Al oxides has been shown to cause chemical fractionation. This study examined the relative importance of source and fractionation on DOC characteristics. Three high alpine watersheds (Upper Snake River, Colorado Gulch, and St. Kevin’s Gulch) are included in this research where DOC was characterized from AMD impacted and non-AMD impacted tributaries. Optical properties including SUVA₂₅₄, excitation-emission matrices (EEMs), and the fluorescence index (FI) of the fulvic acid (hydrophobic) fraction of DOC were examined. Differences that are associated with DOC source, season, and aqueous fractionation mechanisms were assessed. SUVA₂₅₄ analysis of fulvic acid showed differences between the AMD impacted (0.53 – 2.68 L mg^-1 m^-1), non-AMD impacted tributaries (0.77 – 3.49 L mg^-1 m^-1), and below their respective confluences (0.58 – 2.93 L mg^-1 m^-1). Fluorescence index (FI) values showed differences between the three watersheds (1.11 – 1.61). EEM plots showed similar patterns for the fulvic acid fluorophores but the maxima and intensity values were variable. SUVA₂₅₄ and FI results suggest that variability throughout the watersheds included in this study result from a shift in sources due to seasonal changes and fractionation mechanisms when AMD impacted water mixes with non-AMD impacted waters. Understanding the significance of fulvic acid variability throughout any given watershed will provide a better understanding of aquatic metal toxicity including parameterization of modeling programs such as the BLM specific to AMD-impacted watersheds.