MEASURING THE TOTAL LEAD SOIL BURDEN IN ORGANIC HORIZONS ALONG AN ELEVATIONAL PROFILE IN THE GREEN MOUNTAIN RANGE OF NORTHERN VERMONT

Over the last two centuries, there has been a dramatic increase in industrial and combustion-related emissions that have released lead (Pb) into our atmosphere and deposited it onto forests of the northeastern U.S. Even with the US completely phasing out leaded gasoline in 1996, high metal burdens remain in the northern Appalachians due to a 50-150 year residence time in remote forest ecosystems.

On the western face of Camel’s Hump, VT, soil samples have been collected every decade since 1980 at stands from 540 to 1159 meters of elevation to assess total Pb burdens in the organic (O) horizon. We used the most recent samples, collected in 2022, to assess O horizon total Pb burdens by acid digestion and ICP-OES (inductively coupled plasma optical emission spectroscopy). Comparing them to published data from 2010, we found that 2022 Pb levels were significantly decreased overall (p=0.0361), and were lower by 11 – 78% in 10/11 stands. There were generally larger decreases at stands > 986 meters of elevation. However, despite lower overall Pb levels, Pb burdens increased with elevation, going from 0.15- 0.36 g/m² in the lower deciduous forest to 0.43 - 2.17 g/m² in the coniferous zone (above 900 meters of elevation), consistent with prior studies. The rate of Pb leaching surpassed the rate of deposition at all but the highest stand; clearly, leaching continues to play an active role in transporting Pb from the O horizon to deeper soil horizons. Further research to confirm our findings and identify mechanisms of Pb transport at elevation (e.g. new sources of pollution, plant-driven cycling) is warranted.