Lead Distribution and Fluxes in a High-Elevation Forest in Northern Vermont1
- A. J. Friedland and
- A. H. Johnson2
High-elevation forests receive large amounts of atmospheric lead (Pb) and accumulate it in the forest floor. In order to determine Pb partitioning in a montane, coniferous forest, we analyzed forest floor and mineral soil (Haplorthods and Fragiorthods), and vegetation parts (leaves, twigs, bark, wood) for their Pb content. Soil and stream water were sampled to estimate Pb flux. Mean Pb concentration in trees, in mg kg−1, was root bark (33.0), twigs (28.3), bark (23.0) > root wood (10.4) > foliage (3). wood (3). Total Pb in above-ground biomass (trees + shrubs + herbs) was 0.89 kg ha−1. Lead in the organic horizon (forest floor) was 20 kg ha−1 while Pb in the mineral horizon (E + B) was 63 kg ha−1.
Monitoring of soil water for one year yielded volume-weighted mean Pb concentrations of 3.7, 1.8, 1.1, and 1.0 µg L−1 at 3-, 12-, 25-, and 40-cm depth, respectively. Stream Pb concentration averaged 0.6 µg L−1. We estimated annual Pb input of > 700 g ha−1 yr−1. Estimated output from the forest in stream water was < 12 g ha−1 yr−1. Annual accumulation in the forest floor is approximately 3% of the current forest floor Pb amount. At current accumulation rates, forest floor Pb amount will double in 30 to 40 yr. At current leaching rates, mean residence time of Pb in the forest floor is approximately 500 yr. The ratio of Pb input to output for the forest is 60:1.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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