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D.E. Armstrong

Publications and source records attributed to D.E. Armstrong.

4 recordsLinked to original sources
USGS2008

Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5 mg L-1. These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.

Environmental Pollution↗
USGS2005

Trace metal concentrations in shallow ground water

Trace metal clean sampling and analysis techniques were used to examine the temporal patterns of Hg, Cu, and Zn concentrations in shallow ground water, and the relationships between metal concentrations in ground water and in a hydrologically connected river. Hg, Cu, and Zn concentrations in ground water ranged from 0.07 to 4.6 ng L −1 , 0.07 to 3.10 μg L −1 , and 0.17 to 2.18 μg L −1 , respectively. There was no apparent seasonal pattern in any of the metal concentrations. Filtrable Hg, Cu, and Zn concentrations in the North Branch of the Milwaukee River ranged from below the detection limit to 2.65 ng Hg L −1 ,0.51 to 4.30 μg Cu L −1 , and 0.34 to 2.33 μg Zn L −1 . Thus, metal concentrations in ground water were sufficiently high to account for a substantial fraction of the filtrable trace metal concentration in the river. Metal concentrations in the soil ranged from 8 to 86 ng Hg g −1 , 10 to 39 μg Cu g −1 , and 15 to 84 μg Zn g −1 . Distribution coefficients, K D , in the aquifer were 7900,22,000, and 23,000 L kg −1 for Hg, Cu, and Zn, respectively. These values were three to 40 times smaller than K D values observed in the Milwaukee River for suspended particulate matter.

Ground Water↗
USGS1990

Carbon dioxide retention and carbon exchange on unsaturated Quaternary sediments

Retention of CO 2 on three air-dried and partly water-saturated glacial and eolian sediments was measured at 20°C for a range in, P CO 2 that commonly occurs in unsaturated zones. Ratios of the relative losses of CO 2 and 14 CO 2 from a surrogate atmosphere overlying the sediments were 1:1 for the dry condition. For the wet condition, those relative losses were generally ⪯ 1:2, indicating bicarbonateion formation and C-isotope exchange. Mass losses of CO 2 per surface area of sediment were similar for dry and wet conditions; however, CO 2 losses for the wet condition were 8 to 17 times greater than losses predicted by calcite equilibria. Occurrence of this comparatively large reservoir of immobile, exchangeable C in unsaturated zones can cause alteration of the C-isotope composition of soil CO 2 and of dissolved inorganic C in interstitial water, and needs to be considered when modeling 14 CO 2 movement in the unsaturated zone or when interpreting radiocarbon ages of infiltrating water.

Geochimica et Cosmochimica Acta↗