In the 1970s, the U.S. Congress passed legislation restricting the sal
e of gasoline with alkyl-lead additives. In the intervening years, the
amount of lead (Pb) consumed in gasoline has declined sharply, result
ing in lower rates of atmospheric Pb deposition. At the Hubbard Brook
Experimental Forest (HBEF) in New Hampshire, the input of Pb in precip
itation has declined by 97% between 1976 and 1989. The purpose of this
paper is to evaluate the long-term response of forest and associated
aquatic ecosystems to these declining inputs of Pb. Lead continues to
accumulate in the forest ecosystem of the HBEF, in spite of lower inpu
ts, due to extremely low losses in drainage water. However, between 19
77 and 1987 the Pb content in the forest floor declined by 29%. Lead n
ow appears to be accumulating in the mineral soil. The stratigraphy of
Pb in sediment from a nearby lake shows continued Pb deposition, thou
gh at a declining rate. Much of our understanding of the long-term pat
terns of lead accumulation in ecosystems has been shaped by paleoecolo
gical studies, in which inputs of lead are assumed to be irreversibly
retained. Using a regression model and historical information concerni
ng Pb consumption in gasoline, we estimated Pb inputs to the HBEF ecos
ystem during the period 1926-1989. Based on this analysis and our fiel
d observations, it is clear that Pb mobility at the HBEF is greater th
an previously reported: approximate to 30% of the total atmospheric Pb
input between 1926 and 1987 was not retained in organic soils or pond
sediments. The potential for Pb pollution in drainage water may there
fore be greater than suspected in regions with continued high rates of
atmospheric Pb deposition.