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David J. Manthorne

Publications and source records attributed to David J. Manthorne.

4 recordsLinked to original sources
USGS2010

Historical deposition of mercury and selected trace elements to high-elevation National Parks in the Western U.S. inferred from lake-sediment cores

Atmospheric deposition of Hg and selected trace elements was reconstructed over the past 150 years using sediment cores collected from nine remote, high-elevation lakes in Rocky Mountain National Park in Colorado and Glacier National Park in Montana. Cores were age dated by 210 Pb, and sedimentation rates were determined using the constant rate of supply model. Hg concentrations in most of the cores began to increase around 1900, reaching a peak sometime after 1980. Other trace elements, particularly Pb and Cd, showed similar post-industrial increases in lake sediments, confirming that anthropogenic contaminants are reaching remote areas of the Rocky Mountains via atmospheric transport and deposition. Preindustrial (pre-1875) Hg fluxes in the sediment ranged from 5.7 to 42 μg m −2 yr −1 and modern (post-1985) fluxes ranged from 17.7 to 141 μg m −2 yr −1 . The average ratio of modern to preindustrial fluxes was 3.2, which is similar to remote lakes elsewhere in North America. Estimates of net atmospheric deposition based on the cores were 3.1 μg m −2 yr −1 for preindustrial and 11.7 μg m −2 yr −1 for modern times. Current-day measurements of wet deposition range from 5.0 to 8.6 μg m −2 yr −1 , which are lower than the modern sediment-based estimate of 11.7 μg m −2 yr −1 , perhaps owing to inputs of dry-deposited Hg to the lakes.

Atmospheric Environment↗
USGS2007

Rocky Mountain Snowpack Chemistry at Selected Sites, 2004

During spring 2004, the U.S. Geological Survey in cooperation with the National Park Service and the U.S. Department of Agriculture, Forest Service collected and analyzed snowpack samples for 65 sites in the Rocky Mountain region from New Mexico to Montana. Snowpacks were sampled from late February through early April and generally had well-below-average- to near-average snow-water equivalent. Regionally, on April 1, snow-water equivalent ranged from 50 to 89 percent. At most regional sites monitored during 1993-2004, snowpack ammonium, nitrate, and sulfate concentrations for 2004 were lower than the 12-year averages. Snowpack ammonium concentrations in the region were lower than average concentrations for the period at 61 percent of sites in the region, but showed a new pattern compared to previous years with three of the four highest 2004 concentrations observed in northern Colorado. Nitrate concentrations in 2004 were lower than the 12-year average for the year at 53 percent of regional sites, and typically occurred at sites in Wyoming, Idaho, and Montana where powerplants and large industrial areas were limited. A regional decrease in sulfate concentrations across most of the Rocky Mountains (with concentrations lower than the 12-year average at 84 percent of snowpack sites) was consistent with other monitoring of atmospheric deposition in the Western United States. Total mercury concentrations, although data are only available for the past 3 years, decreased slightly for the region as a whole in 2004 relative to 2003. Ratios of stable sulfur isotopes indicated a similar regional pattern as observed in recent years with sulfur-34 (d34S) values generally increasing northward from northern New Mexico and southern Colorado to northern Colorado, Wyoming, Idaho, and Montana.

Open-File Report↗
USGS2004

Rocky Mountain Snowpack Chemistry at Selected Sites, 2002

During spring 2002, the chemical composition of annual snowpacks in the Rocky Mountain region of the Western United States was analyzed. Snow samples were collected at 75 geographically distributed sites extending from New Mexico to Montana. Near the end of the 2002 snowfall season, the snow-water equivalent (SWE) in annual snowpacks sampled generally was below average in most of the region. Regional patterns in the concentrations of major ions (including ammonium, nitrate, and sulfate), mercury, and stable sulfur isotope ratios are presented. The 2002 snowpack chemistry in the region differed from the previous year. Snowpack ammonium concentrations were higher at 66 percent of sites in Montana compared to concentrations in the 2001 snowpack but were lower at 74 percent of sites in Wyoming, Colorado, and New Mexico. Nitrate was lower at all Montana sites and lower at all but one Wyoming site; nitrate was higher at all but two Colorado sites and higher at all New Mexico sites. Sulfate was lower across the region at 77 percent of sites. The range of mercury concentrations for the region was similar to those of 2001 but showed more variability than ammonium, nitrate, and sulfate concentrations. Concentrations of stable sulfur isotope ratios exhibited a strong regional pattern with values increasing northward from southern Colorado to northern Colorado and Wyoming.

Open-File Report↗