Anthropogenic and climate-driven environmental change in the Songnen Plain of northeastern China over the past 200 years

Abstract

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.