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The Hubbard Brook Ecosystem Study: Biogeochemistry of Lead in the Northern Hardwood Forest¹

ABSTRACT

The average annual Pb input to the northern hardwood forest at the Hubbard Brook Experimental Forest in central New Hampshire was 266 g ha^–1 year^–1 based on 4 years of records. Lead output via streamwater and eroded particulate matter was 5.0 and 1.1 g ha^–1 year^–1, respectively. Lead concentration in precipitation averaged 22 µg liter^–1 and showed a significant decline over the 4 sample years (1975–1978).

Lead input to the ecosystem via meteorological vectors is accumulated in the forest floor. Total current Pb content of the forest floor was 8.6 kg ha^–1 and showed no significant differences along the elevation gradient of the watershed (400–800 m). Lead concentration in the forest floor was maximum on the ridge due to a minimum forest floor mass relative to the rest of the watershed. Within the forest floor, maximum Pb concentration is in the fermented (F) layer.

Total Pb content of the forest biomass (stems 10 cm dbh) was 1,248 g ha^–1. Lead concentration in the biota was in the following order: lichens (213 µg g^–1) > mosses (190 µg g^–1) > tree twigs (26 µg g^–1) > roots (20 µg g^–1) > bark (19 µg g^–1) > leaves (7 µg g^–1) = bracket fungi (7 µg g^–1) > wood (0.7 µg g^–1).

Disturbance of the forest ecosystem through harvest cutting, other than through increased runoff, increased erosion, and transport of particulate matter, does not alter the biogeochemistry of Pb and does not result in increased mobility and export of Pb due to gross or subtle alterations of the behavior of Pb in the ecosystem.

Key Words: air pollution • forests

¹ Funded by the National Science Foundation through a grant to F.H. Bormann at Yale Univ. (Grant nos. DEB-76-10543 and DEB-78-10718). This project is part of the Hubbard Brook Forest Ecosystem Study.

² Associate Dean and Professor of Forest Pathology, and Lecturer and Research Associate, respectively, Sch. of Forestry and Environ. Studies, Yale Univ., New Haven, CT 06511.

Received for publication June 9, 1980.

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