Apportioning atmospheric pollution to Canadian and American sources in Kejimkujik National Park, Nova Scotia, using Pb isotopes in precipitation (original) (raw)
Related papers
Geochimica et Cosmochimica Acta, 2000
Elemental concentrations of Al, Ba, Cd, Cu, Mg, Mn, Pb, Rb, Sr, and Zn, as well as Pb and Sr isotopic compositions were determined in samples of snowpack obtained along two main transects from the province of Quebec (Canada); one north-south (between 47°N and 55°N; 1994) and the other within the St. Lawrence Valley (1997). Median enrichment factors (relative to upper crustal abundances) for Cd, Cu, Mn, Pb and Zn for all samples range from Ϸ300 to Ϸ42,000 and are indicative of an anthropogenic origin. Pb isotope ratios for snow samples retrieved in 1994 are highly variable ( 206 Pb/ 207 Pb ϭ 1.148 to 1.193) and are characterized by the most radiogenic Sr isotope values ( 87 Sr/ 86 Sr Ն 0.710). In contrast, the Pb and Sr isotope results for 1997 snow samples collected along the St. Lawrence Valley (below latitude 47°N), yield the most radiogenic Pb isotope ratios ( 206 Pb/ 207 Pb ϭ 1.180 to 1.190) and 87 Sr/ 86 Sr ratios between 0.708 and 0.710. The former indicate that the atmospheric pollution in this region of Quebec is dominated by a mixture of anthropogenic emissions from U.S. ( 206 Pb/ 207 Pb Ϸ 1.20) and Canadian ( 206 Pb/ 207 Pb Ϸ 1.15) sources. Pb isotope ratios ( 206 Pb/ 207 Pb ϭ 1.160 to 1.180) for 1997 samples collected north of latitude 47°N indicate input of an additional anthropogenic component, possibly that of Eurasian pollution being transported over the high Arctic during the winter season.
Atmospheric Environment, 2003
The Pb isotopic composition and trace metal concentrations of epiphytic lichens collected from tree branches within northwestern North America are reported here, with a latitudinal coverage extending from the Beaufort Sea (Arctic circle) to the Canada-USA border. Overall, the trace metal concentrations and Pb isotope compositions correlate with latitudinal position, since lichens retrieved north of latitude 60 N are characterized by low enrichment factors (EF) (mainly between 10 and 30) for heavy metals (i.e. Pb, Zn) and radiogenic 206 Pb/ 207 Pb isotope values (B1.170-1.180). Samples collected further south are characterized by higher EF for heavy metals and much lower Pb isotopic compositions (i.e. 206 Pb/ 207 Pbp1.150). Lichens retrieved in the immediate vicinity of major urban centers (i.e. Calgary, Alberta and Victoria, British Columbia) record distinct Pb isotopic values compared to the regional signal measured in adjacent (remote) samples. The total variation defined by the Pb isotopic compositions of the lichens may be attributed to the mixing of atmospheric particulates and aerosols derived from at least four end-member components, three anthropogenic and one natural. The latter is the predominant signal recorded in lichens retrieved north of 60 N, and is similar in Pb isotopic composition to a natural component identified in aerosols collected during the autumn season of 1994 at Alert (Canadian High Arctic). In contrast, samples collected further south reflect in-part mixing between Canadian and USA anthropogenic sources of atmospheric Pb. The third (unradiogenic) anthropogenic end-member most probably represents atmospheric emissions originating from one of the world's major Zn/Pb smelters located at Trail, British Columbia. r
Geochimica et Cosmochimica Acta, 2010
A peat core from an ombrotrophic bog documents the isotopic evolution of atmospheric Pb in central Ontario since AD 1804 ± 53 ( 210 Pb dating). Despite the introduction of unleaded gasoline in the mid-1970's, the ratio 206 Pb/ 207 Pb in atmospheric deposition has not increased as expected, but rather continues to decline. In fact, snowpack sampling (2005 and 2009) and rainwater samples (2008) show that the isotopic composition of atmospheric Pb today is often far less radiogenic than the gasoline lead that had been used in Canada in the past. The peat, snow, and rainwater data presented here are consistent with the Pb isotope data for aerosols collected in Dorset in 1984 and 1986 which were traced by Sturges and to emissions from the Noranda smelter in northern Quèbec, Canada's largest single source of atmospheric Pb. Understanding atmospheric Pb deposition in central Ontario, therefore, requires not only consideration of natural sources and past contributions from leaded gasoline, but also emissions from metal smelting and refining.
Geochimica et Cosmochimica Acta, 2000
Concentrations of Al, Ba, Cd, Cu, Mg, Mn, Pb, Rb, Sr, and Zn, as well as Pb and Sr isotopic compositions were determined in samples of snowpack obtained during the 1998 winter season from northeastern North America. Median enrichment factors, relative to upper crustal abundances, for Cd, Cu, Mn, Pb, and Zn for all samples range from ca. 50 to 36,000 and are indicative of an anthropogenic origin. The Pb isotope ratios correlate with geographic location because snowpack from eastern Ontario and the northeastern USA are characterized by the most radiogenic 206 Pb/ 207 Pb ratios (ca. 1.18 -1.19), and these decrease systematically in an easterly direction towards the Atlantic coast (ca. 1.16). The Pb isotope data for the 1998 samples of snowpack indicate that atmospheric pollution in this region of North America is dominated solely by a mixture of anthropogenic emissions from US ( 206 Pb/ 207 Pb ca. 1.20) and Canadian ( 206 Pb/ 207 Pb ca. 1.15)
2009
Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20°latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the 206 Pb/ 207 Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot ( 206 Pb/ 207 Pb vs. 208 Pb/ 206 Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.
Geophysical Research Letters, 2005
1] Atmospheric Pb contamination was studied using snow and ice from the Canadian arctic. Forty-five samples representing the past ten years of snow accumulation on Devon Island contain an average of 45.2 pg/g of Pb but only 0.43 pg/g of Sc. The average ratio of Pb to Sc (105) is far greater than that of soil-derived dust particles (in the range 1 to 5) which indicates that ca. 95 to 99% of recent Pb is anthropogenic. Isotopic analyses ( 206 Pb, 207 Pb, 208 Pb) confirm that anthropogenic sources continue to dominate atmospheric Pb inputs. Unlike snow from Greenland which receives Pb predominantly from the U.S. ( 206 Pb/ 207 Pb % 1.2), snow from Devon Island is less radiogenic ( 206 Pb/ 207 Pb % 1.15). There are pronounced seasonal variations, and the snow samples containing the greatest Pb enrichments are from winter when the Arctic is dominated by air masses originating in Eurasia. While the elimination of gasoline lead additives in Europe, North America and Japan has helped to reduce Pb emissions during the past two to three decades, aerosols in the Arctic today are still highly contaminated by industrial Pb.
Water, Air, and Soil Pollution, 2005
The forest floor at high elevation spruce-fir sites from southern Vermont, U.S. to the Gaspé Peninsula, Québec, Canada was sampled and analyzed in 1979 and re-sampled and analyzed in 1996 to study temporal changes in the impacts of atmospheric pollutants. We determined organic matter mass, pH, and concentrations of Al, Ca, Fe, K, Mg, Na, Cd, Cu, Hg, Pb, and Zn for the litter (L = fresh litter plus Oi horizon) and fermentation plus humic horizons (F + H) (= Oe plus Oa horizons) of the forest floor. There were no trends for Al or Fe concentrations in the 1979 or 1996 L along the transect. Several sites had significantly lower Al and Fe values in 1996 than in 1979, likely indicating less mineral soil in the 1996 samples. The 1996 concentrations of Ca in L increased along the transect from 0.22% dry weight (dw) in Vermont to 0.60% dw in Québec. Concentrations of Mg in L were relatively constant along the transect. Neither Ca nor Mg changed at sites from 1979 to 1996, indicating unchanged base status. Concentrations of Cd did not vary spatially along the transect but decreased at all sites from 1979 to 1996. Cu and Zn did not vary spatially or with time. In 1979, the concentration of Hg in L ranged between 150 and 300 µg kg −1 dw, with no spatial gradient. By 1996, Hg concentrations were 25 to 50% lower in L, with decreases generally proportional to the concentration in 1979. The concentration of Pb in 1979 L decreased significantly from 200 mg kg −1 dw in southern Vermont to 60 mg kg −1 dw in Québec. By 1996, the Pb concentration in L ranged between 32 and 66 mg kg −1 dw with no spatial trend along the transect. Decreases in Pb concentrations at sites were proportional to the absolute value in 1979. The concentrations of Cd, Hg, and Pb have declined in litter from 1979 to 1996, indicating a decline in atmospheric deposition. Higher Hg and Pb accumulation rates to the southwest are suggested for the past as indicated by (F + H) concentrations and inventories of Hg and Pb. The decline of Pb in L is consistent with the decreased use of leaded gasoline starting in the 1970s; the declines in Cd and Hg probably reflect lower emissions over the same period. Declining concentrations of Cd, Hg, and Pb in L parallel those documented in recent lake and peat sediments in the northeastern United States.
Peat bogs in northern Alberta, Canada reveal decades of declining atmospheric Pb contamination
Geophysical Research Letters, 2016
Peat cores were collected from six bogs in northern Alberta to reconstruct changes in the atmospheric deposition of Pb, a valuable tracer of human activities. In each profile, the maximum Pb enrichment is found well below the surface. Radiometric age dating using three independent approaches (14 C measurements of plant macrofossils combined with the atmospheric bomb pulse curve, plus 210 Pb confirmed using the fallout radionuclides 137 Cs and 241 Am) showed that Pb contamination has been in decline for decades. Today, the surface layers of these bogs are comparable in composition to the "cleanest" peat samples ever found in the Northern Hemisphere, from a Swiss bog~6000 to 9000 years old. The lack of contemporary Pb contamination in the Alberta bogs is testimony to successful international efforts of the past decades to reduce anthropogenic emissions of this potentially toxic metal to the atmosphere.