Sediment record of abrupt environmental changes in Lake Chenpu, upper reaches of Yellow River Basin, north China

Lake Chenpu is located in the western part of Hetao Basin approaching the Ulan Buh Desert in the upper reaches of the Yellow River in northern China. An 84 cm sediment core was collected from the center of the lake. Geochronology radiometric method using Pb-210 was subsequently used to date the short sediment core in the hope that it would reflect environmental changes over the past 150 years. Principal component analysis and the variation of the grain-size standard deviation were used to identify latent factors and extract environmentally sensitive grain-size components in sediment. Then a combination of sensitive grain-size parameters, magnetic susceptibility, total organic matter (TOC), and total nitrogen (TN) was used to reconstruct the recent lake environmental sequence. The result showed that the lake has seen increasing salinization and swampiness over the past 150 years. Further, sensitive grain-size parameters displayed several abrupt environment changes, i.e. 1850 AD, 1920 AD, and 1980 AD, which are supported by written records. In the 1850s, the yellow clay content increased dramatically, and that of silt declined. Magnetic susceptibility and C/N values increased significantly, as indicated by flood action. In the 1920s and the 1980s, dust-sand activity was recorded twice in the lake sediments with a markedly higher value of 16-32 mu m and average grain size (C2). Grain size and other environmental proxies showed the period after the mid-1990s to be mainly dominated by wind-sand activity and anthropogenic impacts, which marked by obviously increasing grain-size coarse, carbonate content, TOC, and TN values. The results show that the lake sediments provide a dependable archive for studying the environmental history of the lake.