DISRUPTION OF NUTRIENT POOLS AND TRANSPORT OF HEAVY-METALS IN A FORESTED WATERSHED NEAR A LEAD SMELTER

A 1 yr study was initiated in March 1974 to measure the distribution and investigate the effects of the heavy metals Pb, Cd, Zn and Cu on a forested ecosystem (Crooked Creek Watershed) located near a Pb smelter in southeastern Missouri [USA]. Atmospheric discharges of heavy metal particulates have impacted the watershed since 1968. Recent annual deposition rates of particulate Pb, Cd, Zn and Cu measured within 0.4 km from the smelter were 103, 0.72, 6.4 and 2.1 g/m2, respectively. Sampling stations were established at 0.4-, 0.8-, 1.2- and 2.0- km intervals along a centrally located transect on the watershed. The transect was located on the leeward side of the smelter stack and in line with the prevailing wind direction. Extremely high metal concentrations in soil and vegetation along the transect reflected the long-term impact of emissions on the watershed. Two stages of ecosystem disruption on Crooked Creek Watershed were found: an initial stage (1.2-2.0 km from the stack) characterized by an accumulation of O2 litter with no measurable effects on soil-litter biota, and an advanced stage (0.4-0.8 km from the stack) characterized by depletion of soil and litter nutrient pools with evidence of depressed decomposer communities and nutrient translocation. Disruption of nutrient cycling mechanisms may serve as an early indicator of ecosystem stress in response to chemical contamination.