SOIL MERCURY ACCUMULATION IN O HORIZONS FROM THE AVERY BROOK WATERSHED, WEST WHATELY, MASSACHUSETTS
Organic horizons at the coniferous site had the highest average THg concentrations (272 ng/g), while the average concentration at the deciduous site was only 189 ng/g. Within the coniferous O horizon the surface Oi horizon had the lowest THg (120 ng/g) while the intermediate Oe horizon had the highest THg (391 ng/g). Total Hg in the lowermost Oa horizon (305 ng/g) was only slightly lower than the Oe. In contrast, THg concentrations in the deciduous O horizons progressively increase with depth from 47 ng/g in the Oi horizon to 215 ng/g in the Oe to 306 ng/g in the Oa. The progressive increase in THg with depth is likely the result of leaching of mercury from the decomposing organic material at the top of the profile and its accumulation in the humus of the lower part of the O horizon. The higher THg concentrations observed under coniferous stands are likely the result of more efficient capture of dry deposition by the coniferous canopy. This could be due to the nature of the surface of the coniferous needles or more likely it is due to the fact that coniferous needles are present throughout the year compared to deciduous leaves that are present only during the growing season.