Solute Transport at Low Flow in an Acid Stream in Appalachian Ohio

ISSN： 0049-6979

Source： Water, Air, and Soil Pollution, Vol.144, Iss.1, 2003-01, pp. : 195-222

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Abstract

The spatial variability in chemical composition of water and sediments along Snow Fork, a stream draining 70 km² of southeastern Ohio, was investigated under low-flow conditions. The stream is affected by acid mine drainage (AMD) beginning at Essex Mine, an abandoned mine opening, and extending 23 km downstream to the confluence with Monday Creek. Volumetric discharge and changes in stream water and sediment metal concentrations were examined to identify chemical interactions and processes controlling the transport and fate of metal contaminants. The stream loses water to the groundwater system in some sections. The water loss probably occurs through fractures connecting the stream to underlying underground coal mines. Mass balance (loading) and mineral saturation index calculations were used to identify metal sources and sinks. Dissolved metal loading increases downstream along the length of Snow Fork, despite the precipitation of metals as hydroxides in the streambed, indicating multiple groundwater sources of AMD along the flow path. Relatively high dissolved metal concentrations and low sediment metal concentrations occur where the pH is low, indicating that local sediment-water interaction dominates mass transfer between sediments and water. Calculated mineral saturation indexes indicate that aluminum and iron hydroxides precipitate in some stream segments and dissolve in others. X-ray diffractograms of sediments show two distinct mineral groups. Amorphous or weakly crystalline minerals dominate one group found near the stream headwaters near the underground mine. Crystalline mineral phases dominate the sediments downstream. These diffractograms contain the primary peaks for quartz, kaolinite and illite all of which constitute the local sandstones, shales or underclay. Peaks of amorphous phases of iron and manganese, if present, are obscured. The implications of these findings are that the transport of metals in sediments may be as important as dissolved metal transport in estimating the overall stream load, particularly if downstream sources of AMD may remobilize metals from soluble precipitates.