Spatiotemporal variability in stream chemistry in a high-elevation catchment affected by mine drainage

Abstract

This study examined solute dynamics on both spatial and temporal (seasonal, 24 h) scales in a high-elevation stream affected by drainage from abandoned metal mines. Peru Creek is located along the Continental Divide in the US Rocky Mountains, and the hydrologic cycle is dominated by melting of snow. Spatially, tributary inflows produced order-of-magnitude concentration changes along Peru Creek; these were due to dilution and concentration, and also to precipitation of solids. Seasonally, the concentration of most solutes increased as snowmelt diminished. Concentrations of Al, Fe, Cu and Zn, at times affected by instream processes, increased the most, by factors of 2.1–12.8. Ca, Mg, and SO 4 2−, which approximated conservative behavior, increased by factors of 1.7–2.2. Si, Na and K, which were unaffected by mine drainage, increased less, by factors of 1.1–1.6. Concentrations of NO 3 − decreased slightly during the snowmelt season. Hydrologic, photochemical and biological processes were active on the 24 h timescale and produced daily concentration variations of up to 40%. Accurate predictions of solute concentrations, which rely on knowledge of processes that produce natural cycling, are crucial in developing models of toxicity and pollutant loading.