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Cores (15 to 40 cm of depth) were collected from 11 lakes of the Songnen Plain in northeastern China to reconstruct changes in potentially harmful trace element (PHTE) inputs as tracers of human activities. In each profile, most PHTE enrichment factors do not differ significantly from the pre-industrial values (EF 1.5), except for Cd (EF = 2-5.5). This shows that detrital material accounts for a large part of the PHTE supply to the Songnen Plain lakes. Radiometric dating of the cores (

Multi-proxy records (pollen, particle size, loss on ignition, C:N ratios and radioisotopes, 210Pb and 137Cs) of natural and anthropogenic environmental change are reported for sediment cores from three lakes in the Songnen Plain of northeastern China. These data provide high-resolution records of vegetation history and catchment dynamics for the region over the past 200 years. Records show that vegetation initially responded to a cooler and drier climate during the Little Ice Age with high values of Pinus, Ephedra and Amaranthaceae and low values of Cyperaceae. As anthropogenic activity increased in northeastern China, Pinus gradually declined while broad-leaved deciduous vegetation increased in the region from 1900 CE. Aquatic taxa also increased from 1900 CE as the wetlands responded to changing lake water levels and agricultural activities. Land policy implementation had a profound impact on the vegetation with arboreal pollen in Keqin and Hongyan lakes declining from 1900 CE as marginal land was reclaimed, and agricultural activities increased. Vegetation diversity increased as agricultural activities caused environmental disturbance, with pollen taxa indicating human disturbance including Humulus, Polygonum and Xanthium. Silt and organic content increased and C:N ratios declined after 1940 CE as erosion in the catchment and productivity in the lakes increased. Re-vegetation strategies introduced in the late 1990s caused an increase in arboreal taxa in the pollen record. This multi-proxy palaeoenvironmental study improves understanding of the long-term relationship between natural and anthropogenic environmental change in northeastern China.

Dust deposition in north-eastern Canada was estimated from the geochemical signature of a boreal peat bog from the James Bay lowlands. The rare earth elements and other lithogenic elements, as well as Nd isotopes were measured by Q-ICP-MS, ICP-OES and MC-ICP-MS, respectively along a 4.20 m peat core covering the last 7000 years. A principal component analysis performed on the geochemical dataset shows that REEs display the same chemical behavior as other lithogenic elements such as Al and Ti, which suggests that they are immobile in the peat column and can be used as tracers of dust deposition. After 4000 cal yr BP, peaks in dust deposition associated with greater variability in testate amoebae assemblages and plant macrofossil composition as well as a change in ɛNd values are observed. Between 7000 and 4100 cal yr BP, the ɛNd values varied from −36 to −29, while they gradually increased from 4100 cal yr BP until 1500 cal yr BP, suggesting proportionally less dust from local source(s) is deposited in favor of more regional source(s). From 1500 cal yr BP, ɛNd values remained relatively stable around −15 and −12. Most of the dust peaks correspond to documented cold and dry periods likely linked to intrusion of arctic air masses. A migration of the polar front might explain the more frequent intrusion of Arctic air masses in the region and the greater variability in the LG2 record over the last 4000 years.

The recent history of atmospheric As, Cd, Ni, Pb and Zn deposition and the stable Pb isotope signatures were reconstructed from short cores collected at three peat bogs along the St. Lawrence Valley (SLV). The onset of industrial activity was recorded around 1810–1850 AD. As, Cd, Pb and, to a certain extent, Ni deposition rates reached maxima between 1940 and the early 1970s. Trace metals likely originated from coal-burning and ore smelting between 1850 and 1950 AD, and were replaced thereafter, at least in the case of Pb, by the combustion of leaded gasolines until the mid-1980s. Trace metal contents and accumulation rates were greater in the two cores recovered from the southwestern SLV than further northeast, as expected from their proximity to urban and industrial centers of eastern Canada and the U.S. Mid-West and the direction of the prevalent winds. A rapid decrease in metal accumulation rates since the 1970s suggests that mitigation policies were effective in reducing atmospheric metal emissions. Nevertheless, metal accumulation rates and stable Pb isotope signatures have not yet returned to their pre-industrial values.