MERCURY IN SOILS ALONG A N/S TRANSECT IN ALASKA

Mercury concentrations and Hg mass gain in soils were determined form soil samples collected along a 1020 km N/S transect from Prudhoe Bay to Prince William Sound, Alaska. Mercury and organic carbon content were determined in the O and A soil horizons and subsurface soils from 177 sites spaced approximately 8 km apart. Here the subsurface samples are considered to be the deepest sample collected regardless of whether the field horizon was B or C. Mercury analysis was carried out by cold-vapor atomic absorption. Organic carbon in soil was calculated as the difference between total and inorganic carbon. Fractional mass gain or loss (t) of Hg was calculated as the ratio of Hg to Ti concentration in the soil and the ratio of Hg to Ti concentration in the subsurface. Concentration of Hg range from 0.02 – 0.26 and 0.01– 0.21 ug/g in the O, A horizons, and <0.1 – 0.30 ug/g in the subsurface. The median Hg concentration, 0.10 ug/g, for the O-horizon samples is significantly higher than the A-horizon or subsurface median concentrations of 0.05 and 0.04 ug/g, respectively. Concentrations of Hg in the O, A, and subsurface samples were found to increase as the transect passed through the Brook Range and the Alaska Range foothills. Although the subsurface samples typically had lower Hg concentration than the O or A horizon samples, the highest Hg concentration (0.30 ug/g) was found in a subsurface sample in the Alaska Range foot hills. The Hg concentration in the O and A horizons was positively correlated with both soil organic carbon content and the subsurface Hg concentration. Concentration profiles and mass gain of Hg in the O horizons along much of the transect may reflect atmospheric Hg deposition, however, geogenic Hg likely accounts for the increase in Hg concentration in O and A horizons through the Alaska Range.