Concentration-Discharge Behavior of Contaminants in a Stream Impacted by Acid Mine Drainage

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Acid mine drainage (AMD) is a common byproduct of mining that has severely degraded many streams world-wide.In coal mining, AMD occurs when pyrite contained in coal is exposed to water and air during mining activities and oxidized to release high concentrations of sulfate, metals, and acid into water bodies.Controls on concentrationdischarge (CQ) relationships of solutes in AMD-impacted streams remain unclear due to the complicated nature of acid mine drainage systems.For example, streams may receive inputs from multiple sources including runoff, outflow from constructed treatment systems, and abandoned mines that bypass these systems to continue to contaminate the streams.It is important to understand the CQ relationships of contaminants in AMDimpacted streams in order to elucidate contaminant sources and to predict effects on aquatic ecosystems under different flow regimes.Here, we study the CQ behaviors of acid, metals, and sulfate in an AMD-contaminated watershed in northeastern Ohio where a treatment system has been installed to remediate water draining from a mine pool into the stream.The treatment system includes a series of limestone channels and settling ponds designed to increase drainage pH and promote precipitation of Fe-and Mn-oxides.Stream chemistry was measured in samples collected approximately once per day from March through November and hourly during select storm events.Stream flow was measured continuously at the watershed outlet.Contaminant concentrations in the stream generally decreased with increasing stream discharge due to inputs from the treatment system that only occurred at high flow.A decrease in pH from March (~6) through November (~3) was concurrent with a decrease in stream discharge and declining inputs from the treatment system.Correspondingly, AMD-derived contaminants (Fe, Mn, Al) increased in concentration from March through November.These trends reflect mixing of contaminated baseflow and intermittent inputs from the treatment system, indicating that the treatment system is only effective at neutralizing v TABLE OF CONTENTS……………………………………………………………………………………………………v LIST OF FIGURES………….……………………………………………………………………………………………..

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