James T. Oris | Geology Reports

USGS2009

Mercury flux to sediments of Lake Tahoe, California–Nevada

We report estimates of mercury (Hg) flux to the sediments of Lake Tahoe, California–Nevada: 2 and 15–20 µg/m 2 /year in preindustrial and modern sediments, respectively. These values result in a modern to preindustrial flux ratio of 7.5–10, which is similar to flux ratios recently reported for other alpine lakes in California, and greater than the value of 3 typically seen worldwide. We offer plausible hypotheses to explain the high flux ratios, including (1) proportionally less photoreduction and evasion of Hg with the onset of cultural eutrophication and (2) a combination of enhanced regional oxidation of gaseous elemental Hg and transport of the resulting reactive gaseous Hg to the surface with nightly downslope flows of air. If either of these mechanisms is correct, it could lead to local/regional solutions to lessen the impact of globally increasing anthropogenic emissions of Hg on Lake Tahoe and other alpine ecosystems.

California, Nevada↗

USGS1996

The role of water ventilation and sediment ingestion in the uptake of benzo[A]pyrene in gizzard shad ( Dorosoma cepedianum )

The objective of this study was to determine whether sediment ingestion or water ventilation was the primary route of uptake for benzo[ a ]pyrene (B a P) in the gizzard shad ( Dorosoma cepedianum ), a detritivorous fish. Two experiments were conducted in which fish were exposed to sediments spiked with 1 μg/g B a P. In the first experiment, fish were prevented from feeding by esophagus ligation. In the second experiment, 20 nonligated fish and 30 ligated fish were added to the aquarium. The nonligated fish roiled the water as they fed. Fish were collected 4, 8, 15, and 22 d after the experiments began. Gizzard shad metabolize B a P; therefore, the concentrations of B a P equivalents (parent B a P plus metabolite) were determined. Concentrations of B a P equivalents were significantly greater in the ligated fish in experiment 2 relative to those in experiment 1. In contrast, the concentration of B a P equivalents in the ligated fish in experiment 2 was not significantly different than that in the nonligated fish. Our results suggest that ventilation of turbid water may be a significant source of B a P for gizzard shad. Sediment ingestion, however, does not appear to significantly influence the total body concentration of B a P equivalents in gizzard shad.

Environmental Toxicology and Chemistry↗