CHEMICAL SPECIATION IN SILVER BOW AND BLACKTAIL CREEKS: IMPLICATIONS FOR BIOAVAILABILITY AND RESTORATION

Silver Bow and Blacktail Creeks, contaminated with toxic elements from mining, present a need for remediation and restoration. Trace elements are present in elevated concentrations, particularly copper. Determining element speciation will allow informed consideration of effective restoration strategies, by providing a foundation for assessing bioavailability and toxicity. The three goals are: determine how speciation varies between seasons and sites in four impacted sites from the greater Butte Area One, an impacted downstream site known as Santa, and a control site on Upper Blacktail Creek known as Blacktail; how these variations influence bioavailability and toxicity; and what causes these variations. Total concentration measurements of these elements exist for every season since November 2015, whereas speciation calculations are lacking. The complete aqueous chemistry needed for speciation calculations is considered: pH, dissolved oxygen, conductivity, temperature, major cations, major anions, dissolved organic carbon, dissolved inorganic carbon, and trace elements. The chemical speciation program EQ3 produced all speciation data for As, Cu, Fe, Ba, Zn, and Mn, all contaminants released by mining activities, for five seasonal sampling trips. Variations in pH values and contributions of tailings-contaminated waters conceivably influenced seasonal and geographical changes in bioavailability and toxicity. Photosynthetic activity acted as the primary influence on seasonal variations in bioavailability for all elements except barium and arsenic. Barium’s bioavailability and toxicity stayed relatively consistent between seasons and sites, whereas competition with phosphate plausibly created seasonal variations in arsenic toxicity. Copper carbonate complexes predominated through the year at most sites, and as a result, copper had a low bioavailability there. Inflow of tailings-contaminated groundwater drove most spatial variations in bioavailability and toxicity for zinc, copper, and iron during all months except May 2016 and August 2016. During August 2016, phosphate differences between sites acted as a major influence on geographical variations in bioavailability and toxicity for all speciated elements. Overall, this study has provided a foundation for restoration projects by discovering and explaining geographic and seasonal variations in chemical speciation