Sedimentary lead pollution history: Lead isotope ratios and conservative elements at East Taihu Lake, Yangtze Delta, China

摘要

In 2009, two short sedimentary cores (DJZ and DQG) were collected from the East Taihu Lake at the lower Yangtze River Basin using a gravity corer. Lead isotopes and metals including Pb, Al, Fe, and Ti were measured. Radio nuclides including ~(210)Pb and ~(137)Cs were also analyzed for dating of the sediments at both cores. The averaged sedimentation rate at DQG site was 0.32 cm/a since the early 1960s, while at DJZ it was at least 1 cm/a. Significant decline of ~(206)Pb/~(207)Pb ratios were observed in DQG from the deeper sediments to near-surface sediments, indicating increased anthropogenic lead load to the lake sediments due to human impact since the 1970s. The uppermost sediments' lead contents were 2.3 times of those before the 1950s. Trends of anthropogenic lead in both cores inferred from a lead isotope mixing model were found to be similar to those from Al, Fe, and Ti normalization methods. Ti was found to be the best passive tracer element, highly in accordance with Pb isotope mixing model results. In DQG, anthropogenic lead increased sharply since the 1970s and reached a maximum in 2000s (28 mg/kg from lead isotope mixing model), while at DJZ the highest value was 20 mg/kg. These results revealed significant anthropogenic lead influx into the lake caused by human activities, in good agreement with the economic development in the past three decades in China.