Effects of colloids on metal transport in a river receiving acid mine drainage,upper Arkansas River,Colorado, U.S.A. |
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| Affiliation: | 1. Programa de Pós-Graduação em Ciência, Inovação e Modelagem em Materiais, Laboratório de Materiais e Meio Ambiente, LAMMA, Universidade Estadual de Santa Cruz – UESC, Rodovia Jorge Amado, km 16, CEP 45662-200, Ilhéus, BA, Brazil;2. Universidade Feevale, RS 239, 2755, CEP 93352-000, Novo Hamburgo, RS, Brazil;1. School of Earth, Atmosphere and Environment, 9 Rainforest Walk, Monash University, Clayton, VIC 3173, Australia;2. School of Chemical Engineering, The University of Queensland, Level 3, Chemical Engineering Building (74), St Lucia, QLD 4072, Australia;1. KU Leuven, Department of Earth and Environmental Sciences, Kasteelpark Arenberg 20 bus 2459, 3001 Leuven, Belgium;2. Alterra, Wageningen University and Research Centre (WUR), P.O. Box 47, 6700 AA Wageningen, The Netherlands;3. Wageningen University, WUR, Department of Soil Quality, P.O. Box 47, 6700 AA Wageningen, The Netherlands;1. Department of Biology, The University of Akron, Akron, OH, USA;2. Integrated Bioscience Program, The University of Akron, Akron, OH, USA;3. Department of Geosciences, The University of Akron, Akron, OH, USA;4. Department of Civil Engineering, The University of Akron, Akron, OH, USA;1. Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Jordi Girona 18-26, 08034 Barcelona, Catalonia, Spain;2. LBNL Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA;3. National Institute for Laser, Plasma and Radiation Physics, Atomistilor Str. 409, P.O. Box MG-36, Magurele, 077125 Bucharest, Romania |
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| Abstract: | Inflows of metal-rich, acidic water that drain from mine dumps and tailings piles in the Leadville, Colorado, area enter the non-acidic water in the upper Arkansas River. Hydrous iron oxides precipitate as colloids and move downstream in suspension, particularly downstream from California Gulch, which has been the major source of metal loads. The colloids influence the concentrations of metals dissolved in the water and the concentrations in bed sediments. To determine the role of colloids, samples of water, colloids, and fine-grained bed sediment were obtained at stream-gaging sites on the upper Arkansas River and at the mouths of major tributaries over a 250-km reach. Dissolved and colloidal metal concentrations in the water column were operationally defined using tangential-flow filtration through 0.001-pm membranes to separate the water and the colloids. Surface-extractable and total bed sediment metal concentrations were obtained on the <60-μm fraction of the bed sediment. The highest concentrations of metals in water, colloids, and bed sediments occurred just downstream from California Gulch. Iron dominated the colloid composition, but substantial concentrations of As, Cd, Cu, Mn, Pb, and Zn also occurred in the colloidal solids. The colloidal load decreased by one half in the first 50 km downstream from the mining inflows due to sedimentation of aggregated colloids to the streambed. Nevertheless, a substantial load of colloids was transported through the entire study reach to Pueblo Reservoir. Dissolved metals were dominated by Mn and Zn, and their concentrations remained relatively high throughout the 250-km reach. The composition of extractable and total metals in bed sediment for several kilometers downstream from California Gulch is similar to the composition of the colloids that settle to the bed. Substantial concentrations of Mn and Zn were extractable, which is consistent with sediment-water chemical reaction. Concentrations of Cd, Pb, and Zn in bed sediment clearly result from the influence of mining near Leadville. Concentrations of Fe and Cu in bed sediments are nearly equal to concentrations in colloids for about 10 km downstream from California Gulch. Farther downstream, concentrations of Fe and Cu in tributary sediments mask the signal of mining inflows. These results indicate that colloids indeed influence the occurrence and transport of metals in rivers affected by mining. |
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