Modelling dispersal of metals from a copper smelter at Rouyn-Noranda (Québec, Canada) using peatland data

Abstract

Copper, Pb and Zn levels in surface growth sampled from 37 peat hummocks (ombrotrophic) occurring in peatlands around a smelter in western Québec show that metal levels decrease exponentially with increasing distance from the smelter. The spatial pattern of metal in peat forms a circular map pattern, centred on the smelter and skewed by the predominant wind direction. An empirical model fitted to the data provides an estimate of the rate of concentration decrease with radial distance, and the background metal level far away from the smelter. For Cu, Pb and Zn, the smelter-related anomaly is statistically indistinguishable from background levels at about 50 km from the smelter. Using approximate measurements of peat accumulation rate and bulk density of peat, the amount of metal in the smelter-centred anomaly was calculated by integration. The Cu anomaly can account for about 30% of reported emissions in the sampling year (1996–1997); the Pb and Zn anomalies account for about 10 and 26% of reported emissions, respectively. The discrepancy between the peat-derived metal anomaly and the reported emissions may be due in part to various sources of error and bias. The major causes, however, are probably long-range transport of atmospheric emissions, particularly during dry weather periods, and incomplete physical trapping and chemical fixation of metal in the peat hummocks.