Response to Comment on 'Sphagnum Mosses from 21 Ombrotrophic Bogs in the Athabasca Bituminous Sands Region Show No Significant Atmospheric Contamination of 'Heavy Metals''

摘要

Lead concentrations had been measured in three samples collected from each of 21 peat bogs, and the values averaged. These values are now shown for individual moss samples as a function of distance from the midpoint between the two upgraders (Figure la). Note that seven sites, representing 21 moss samples, are within 20 km of the midpoint between the two upgraders, not five sites (and 15 samples) as claimed by Blais and Donahue. As a point of reference, the horizontal dashed line indicates the natural "background" Pb concentration for ancient, preanthropogenic peat samples from Etang de la Gruere (EGR), an ombrotrophic bog in the Jura Mountains of Switzerland. Peat formation at the EGR bog began nearly 15 000 years ago, and it represents the longest record of continuous peat accumulation in the northern hemisphere. These peat samples, dating from the mid-HoIocene (～6000-9000 years old), represent the lowest Pb concentrations found in this profile since peat formation began during the Late Glacial, and contain 0.28 ± 0.05 mg/kg Pb; n = 17. Notice that some of the contemporary moss samples collected from the ABS region approach the background concentrations for ombrotrophic (ie., rain-fed) peat dating from the mid-Holocene. Except for one site (site 12, which is adjacent to an open pit mine, as shown in Figure 1 of Shotyk et al.), all of the ABS region moss samples are within a factor of 5 of the background Pb concentration for peat from EGR. In contemporary moss samples, comparable Pb concentrations have been reported for specimens from southernmost South America and Antarctica. However the moss data from the ABS region is viewed, the Pb concentrations are low.