Kent A. Elrick

The relation of stream sediment surface area, grain size and composition to trace element chemistry

Abstract Intensive studies of 17 geographically and hydrologically diverse stream bed sediments provide information on the relation between grain size, surface area, and operationally defined geochemical phases (e.g. Mn oxides, amorphous Fe oxides) to trace element concentrations. Of the size fractions investigated ( 125 μm), each of the various phases contribute to overall sample surface area. For material having mean grain sizes in the very fine sand range and finer (

The effect of membrane filtration artifacts on dissolved trace element concentrations

Abstract Among environment scientists, the current and almost universally accepted definition of dissolved constituents is an operational one-only those materials which pass through a 0.45-μm membrane filter are considered to be dissolved. Detailed laboratory and field studies on Fe and Al indicate that a number of factors associated with filtration, other than just pore size, can substantially alter “dissolved” trace element concentrations; these include: filter type, filter diameter, filtration method, volume of sample processed, suspended sediment concentration, suspended sediment grain-size distribution, concentration of colloids and colloidally-associated trace elements and concentration of organic matter. As such, reported filtered-water concentrations employing the same pore size filter may not be equal. Filtration artifacts may lead to the production of chemical data that indicate seasonal or annual “dissolved” chemical trends which do not reflect actual environmental conditions. Further, the development of worldwide averages for various dissolved chemical constituents, the quantification of geochemical cycles, and the determination of short- or long-term environmental chemical trends may be subject to substantial errors, due to filtration artifacts, when data from the same or multiple sources are combined. Finally, filtration effects could have a substantial impact on various regulatory requirements.

The effect of mining on the sediment - trace element geochemistry of cores from the Cheyenne River arm of Lake Oahe, South Dakota, U.S.A.

Abstract Six cores, ranging in length from 1 to 2 m, were collected in the Cheyenne River arm of Lake Oahe, South Dakota, to investigate potential impacts from gold-mining operations around Lead, South Dakota. Sedimentation rates in the river arm appear to be event-dominated and rapid, on the order of 6–7 cm yr.−1. All the chemical concentrations in the core samples fall within the wide ranges previously reported for the Pierre Shale of Cretaceous age and with the exception of As, generally are similar to bed sediment levels in the Cheyenne River, Lake Oahe and Foster Bay. Based on the downcore distribution of Mn, it appears that reducing conditions exist in the sediment column of the river arm below 2–3 cm. The reducing conditions do not appear to be severe enough to produce differentiation of Fe and Mn throughout the sediment column in the river arm. Cross-correlations for high-level metal-bearing strata within the sediment column can be made for several strata and for several cores; however, cross-correlations for all the high-level metal-bearing strata are not feasible. As is the only element which appears enriched in the core samples compared to surface sediment levels. Well-crystallized arsenopyrite was found in high-As bearing strata from two cores and probably was transported in that form from reducing sediment-storage sites in the banks or floodplains of Whitewood Creek and the Belle Fourche River. It has not oxidized due to the reducing conditions in the sediment column of the Cheyenne River arm. Some As may also be transported in association with Fe- and Mn-oxides and -hydroxides, remobilized under the reducing conditions in the river arm, and then reprecipitated in authigenic sulfide phases. In either case, the As appears to be relatively immobile in the sediment column.

An evaluation of air elutriation for sediment particle size separation and subsequent chemical analysis

Abstract Air elutriation can be used for the separation of sediments into particle size classes for subsequent chemical analysis . Size distributions obtained by elutriation compare with those determined by non‐chetnically dispersed pipet analysis . Contaminant‐free fractions can be obtained for the analysis of Cu, Zn, Pb, Co, Cr, Fe, Mn, Al, Ti, and probably Cd.

Arsenopyrite in the bank deposits of the Whitewood Creek-Belle Fourche-Cheyenne River-Lake Oahe system, South Dakota, U.S.A.

Mining, milling, and processing wastes containing quantities of arsenopyrite were produced around Lead, South Dakota, from 1875 to 1977. Much of this material was discharged into Whitewood Creek, and from there portions of the waste were transported to the Belle Fourche River, thence to the Cheyenne River, and finally to the Missouri River. In 1958, the Missouri River was dammed at Pierre, forming Lake Oahe. Analyses of cores collected from the lake bottom showed the presence of arsenic-rich layers in the bed sediments; substantial portions of the arsenic are due to arsenopyrite in the 8–16 and 16–32 μm size fractions of the sediments. In addition, suspended-sediment samples collected from the Cheyenne River above Lake Oahe contain detectable quantities of arsenopyrite in the 8–16 and 16–32 μm fractions. Solid material collected from the banks and floodplains of the Belle Fourche River and Whitewood Creek contains reduced and oxidized phases. The reduced phases have arsenic maxima in the 16–32 and 32–63 μm size ranges. These fractions also contribute the most arsenic to the samples; the major source being arsenopyrite. The oxidized segments have arsenic maxima in the 63 μm size ranges. The 63 μm fractions contribute the most arsenic to the oxidized samples. This arsenic, despite the oxidized nature of the samples, is associated with arsenopyrite coated with thin iron oxide rinds. It has been calculated that 80% of the arsenic in these deposits is associated with sulfides (in the form of arsenopyrite), while 20% is associated with iron oxides. The arsenopyrite found in the banks and floodplains of Whitewood Creek and the Belle Fourche River are the likely source of the arsenopyrite found in the suspended sediments of the Cheyenne River and in the bed sediment of Lake Oahe.