Acid Mine Drainage (AMD) originating from abandoned hardrock mines characteristically has high concentrations of potentially toxic metals, such as Cu, as well as dissolved and particulate forms of Al and Fe. Interaction of dissolved organic carbon (DOC) with particulate Fe and Al oxides has been previously shown to cause its chemical fractionation. DOC chemical characteristics may also vary among watersheds and can be influenced by vegetation, climate, geology, and hydrology. This study examined the relative importance of source and fractionation on DOC characteristics in three watersheds (Upper Snake River, Colorado Gulch, and St. Kevin’s Gulch). Specifically, the fulvic acid (hydrophobic) fraction of DOC was isolated from the AMD impacted and pristine tributaries as well as below the confluence. All three watersheds are located in high alpine ecosystems (2500 – 3000m AMSL) with wetlands and boreal forests present. Optical properties including SUVA254 and the fluorescence index (FI) were examined. SUVA254 results showed differences between the AMD impacted tributaries (0.53 – 3.52 L mg-1 m-1), non-AMD impacted tributaries (0.77 – 4.88 L mg-1 m-1), and their respective confluences (0.58 – 3.30 L mg-1 m-1). Fluorescence index (FI) values showed differences between the three watersheds (1.11 – 1.74). SUVA254 and FI suggest that variability in fulvic acid optical properties within the watersheds result from both seasonal changes in sources and DOC fractionation by metal oxide precipitation. Solute-loss calculations showed that DOC and hydrous iron and aluminum oxides behave non-conservatively. Characterizing fulvic acid compositional variability throughout any given AMD impacted watershed may provide a better understanding of aquatic metal toxicity, given the observed relationship between metal binding strength and optical properties. This information may assist in the parameterization of modeling programs, such as biotic ligand models, for application to AMD-impacted watersheds.

DOC variability and characteristics in alpine watersheds

249th National Meeting (2015)

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