HR: 14:25h
AN: H33H-04    [Abstracts]
TI: Fate of Arsenic Within the Lower Humboldt River Basin, Nevada, Under High Flow Conditions
AU: * Paul, A P
EM: appaul@usgs.gov
AB: The Humboldt Wildlife Management Area (HWMA) has been identified as a wetland ecosystem in decline because of the dominance of salt-tolerant submergent vegetation, loss of indigenous fauna over time, and episodic bird kills. Previous investigations within the HWMA indicated that certain trace elements, including arsenic, were greater than geochemical background concentrations, and in some cases, exceeded protective ecological criteria established by the U.S. Environmental Protection Agency. From 1998 through 2001, arsenic was characterized within the lower Humboldt River system during high-flow conditions. The lower Humboldt River and associated irrigation drains are the primary sources of surface water for HWMA. Arsenic in surface-water samples occurred primarily as dissolved arsenate with concentrations ranging from 14 to 238 ppb. Arsenic concentrations increased downriver with the highest concentrations occurring in Humboldt Lake waters. Although arsenite concentrations were less than U.S. Environmental Protection Agency ecological criteria, the criterion for the watering of livestock (200 ppb) was exceeded in wetland surface waters near the mouth of the river. Arsenic concentrations in wetland sediments ranged from 19 to 57 ppm. Pore-water collected from these sediments contained arsenic concentrations ranging from 90 to 524 ppb of which 5 to 74 percent was arsenite. The Canadian Interim Sediment Quality Guideline (5.9 ppm) and consensus based toxicity-threshold arsenic concentration (9.79 ppm) were exceeded in all wetland-sediment samples. Arsenic concentrations in surface-water samples collected from the outflow of the Humboldt Sink indicate that arsenic may be flushed from the HWMA wetland ecosystem under high-flow conditions.
DE: 1806 Chemistry of fresh water
DE: 1871 Surface water quality
DE: 1890 Wetlands
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting