Daily Freeze–Thaw Cycles Affect the Transport of Metals in Streams Affected by Acid Drainage

Abstract

Stream flow rates with seasonal, daily, or hourly cycles due to freezing and thawing can control downstream chemical processes by changing the mixing ratio of reactive flows. The extent of these hydrologic-chemical interactions has not been fully realized yet. This work explored the link between daily freeze-thaw cycles and the fate and transport of metals at a model stream impacted by acid drainage. We characterized hydrological and physicochemical parameters at the confluence between the Caracarani River (pH~8.6) and the Azufre River (pH < 2), in northern Chile. Hourly water depth, temperature, and electrical conductivity monitoring coupled with pH and turbidity measurements revealed that maximum flow rates from thawing of the Azufre River induced characteristic daily drops in pH and turbidity. Shifts in pH controlled the precipitation and dissolution of arsenic-rich iron and aluminum reactive phases. Thus freeze-thaw processes are critical at streams receiving acid drainage where iron and aluminum phases form and are likely to impact the fate and transport of toxic metals in the system. This work highlights the importance of assessing the hydrological controls on flows and mixing ratios when studying the chemical reactivity and fate of contaminants at systems affected by acid drainage.

Response of suspended sediment particle size distributions to changes in water chemistry at an Andean mountain stream confluence receiving arsenic rich acid drainage

“…Hydrological processes determine the fate of dissolved and particle‐bound metals and metalloids due to complex interactions between chemical reactivity and hydraulic features (Droppo, Walling, & Ongley, ; Droppo, ; Guerra et al, ; Liss, Droppo, Flannigan, & Leppard, ; Webster, Swedlund, & Webster, ). However, the role of particle size distributions (PSDs) on trace metal fate has often been overlooked in freshwater systems receiving acid drainage.…”

“…Mixing zones receiving acid drainage are reactive domains where changes of pH and chemical environments favor the formation of metal‐rich suspended solids composed primarily of iron and aluminum oxyhydroxides. Short‐term changes in the mixing ratio between an acid and an alkaline stream dramatically shifted the speciation of arsenic from the particulate to the dissolved phase in a shallow mountain stream receiving acid drainage (Guerra et al, ). A variety of mineral phases can control the fluxes of toxic metalloids such as arsenic throughout the drainage network via settling, resuspension, precipitation/coprecipitation, dissolution, sorption, and desorption (Droppo et al, ; Kretzschmar & Schafer, ; Nordstrom, ; Sodre, Schnitzler, Scheffer, & Grassi, ).…”

Removal of Arsenic Using Acid/Metal-Tolerant Sulfate Reducing Bacteria: A New Approach for Bioremediation of High-Arsenic Acid Mine Waters

“…The Aguas Calientes area is located in the Azufre River sub-basin near the Tacora volcano, in the Lluta River Watershed (LRW) in northern Chile (18 • 4 2− ] (4678 ± 16.9 mg·L −1 ), and a pH less than 2.0 [4,5] due to contributions from hydrothermal springs and acidic metal-rich runoffs.…”

“…In this area, hydrothermal waters emerge with high concentrations of dissolved As (>3 mg·L −1 ), iron (Fe) (>80 mg·L −1 ), and a pH lower than 3 [4,5]. The As occurrence in fluvial waters is linked to the presence of ferric Fe(III)-oxyhydroxide ores, because As is sorbed onto these minerals [6].…”

“…Several groundwaters, sediments and minerals of Northern Chile are enriched in As [2][3][4][5]. Specifically, the Chilean Altiplano has high concentrations of As and sulfate in fluvial waters, seriously affecting the quality of water resources and limiting the use of water for consumption, agricultural, and industrial purposes [4].…”