Geology topics
Publications and source records attributed to E.V. Axtmann.
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The effect of tributary inflows on metal concentrations in <63-μm sediments and benthic insects was examined on two scales (380 km and <2 km) in a river impacted by mining. A dilution−mixing model effectively described large-scale dispersion of Cd, Cu, and Pb in the sediments of the river. Input of metal from contaminated flood plains may introduce additional contamination in the middle reaches of the river. Intensive sampling around the confluences of two tributaries showed that there were significant, localized decreases in some metal concentrations immediately downstream of the inflows. Sediment metal concentrations 1 km below the inflows returned to values within the range predicted by the dilution−mixing model. Metal concentrations in benthic insects exhibited spatial patterns similar to those of the sediments, indicating that biological exposures to metals are at least partially dependent on the physical processes controlling the dispersion of sediment-bound metals. Tributary inflows introduce variability in metal contamination on different spatial scales that must be considered when assessing ecological risks in contaminated rivers. In addition to large-scale dilution of contaminants, smaller areas of reduced metal exposure occur near tributary inflows. These may shelter metal-sensitive taxa from severe metal contamination in the mainstem.
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Water, bed sediment, and biota were sampled in streams from Butte to below Missoula as part of a program to characterize aquatic resources in the upper Clark Fork basin of western Montana. Sampling stations were located on the Clark Fork and major tributaries. Water-quality data were obtained periodically at 16 stations during October 1994 through September 1995 (water year 1995). Data for twelve bed-sediment and eleven biological stations were obtained in August 1995. The primary constituents analyzed were trace elements associated with mine tailings from historical mining and smelting activities. Water-quality data include concentrations of major ions, trace element, and suspended sediment in stream samples collected periodically during water year 1995. Daily values of streamflow, suspended- sediment concentrations in the fine-grained and bulk fractions. Biological data include trace- element concentrations in whole-body tissue of aquatic benthic insects. Quality-assurance data are reported for analytical results of water, bed sediment, and biota. Statistical summaries of water-quality, bed-sediment, and biological data are provided for the period of record at each station since 1985.
We evaluated the effect of metal associated with the gut content in immature aquatic insects (larvae and nymphs) on spatial and interspecific comparisons of whole-body metal concentrations. Four species, common to cobble-bottom rivers and streams, were collected along an established contamination gradient in the Clark Fork River, and from tributaries of the Clark Fork. Metal concentrations were determined in the gut and its content and in the insect body. Whole-body metal concentrations were higher and more variable as a result of gut content. The positive bias produced by the gut content did not alter interpretations of site contamination in most cases. Interspecific comparisons of metal bioaccumulation also were not greatly affected by the presence of gut content. The influence of gut content was specific for metal, species, and site. Feeding habit, gut size, and metal bioaccumulation in the body affected the relative contribution of the gut and its content to metal concentrations in the whole insect.
Water, bed sediment, and biota were sampled in streams from Butte to below Missoula as part of a program to characterize aquatic resources in the upper Clark Fork basin of western Montana. Water- quality data were obtained periodically at 16 stations during October 1993 through September 1994 (water year 1994); daily suspended-sediment data were obtained at six of these stations. Bed-sediment and biological data were obtained at 11 stations in August 1994. Sampling stations were located on the Clark Fork and major tributaries. The primary constituents analyzed were trace elements associated with mine tailings from historical mining and smelting activities. Water-quality data include concentrations of major ions, trace elements, and suspended sediment in samples collected periodically during water year 1994. Daily values of streamflow, suspended-sediment concentration, and suspended- sediment discharge are given for six stations. Bed- sediment data include trace-element concentrations in the fine and bulk fractions. Biological data include trace-element concentrations in whole-body tissue of aquatic benthic insects. Quality-assurance data are reported for analytical results of water, bed sediment, and biota. Statistical summaries of bed sediment, and biological data are provided for the period of record at each station since 1985.
Historic discharges from the mining and smelting complex at the head-waters of the Clark Fork River have resulted in elevated Ag, Cd, Cu, Pb and Zn concentrations in the <60 μm fraction of both bed and flood-plain sediments of the river. Processes affecting the trends in longitudinal distributions of these metals were investigated by repeated sampling over a 380 km river reach between August 1986 and July 1989. At the most upstream site, bed-sediment metal concentrations were enriched 18–115 times above least enriched tributaries, depending on the metal. All metals decreased exponentially with distance downstream away from mining. The exponential model predicts that elevated metal concentrations should occur over 550 km downstream, in Lake Pend Oreille. Longitudinal trends, obvious on a scale of hundreds of kilometers, were obscured by small-scale spatial variability when shorter stretches of the river were considered. Longitudinal dispersion appeared to be controlled largely by physical dilution with less-contaminated sediments. Evidence suggests that erosion of contaminated flood-plains contributes to metal contamination in the bed sediments. Tributary input appeared to have little influence on the large-scale, downstream distribution of metals; however, it did contribute to local variability in bed-sediment metal concentrations. Association of metals with specific mineral grains, as well as variability in total organic C and Fe concentration, appeared also to contribute to variability. Some year-to-year variability in bed-sediment metal concentrations was observed, however, trends in longitudinal dispersion were not significantly different between at least two of the years sampled.