Sedimentary And Geochemical Records Of Climate And Environmental Change For The Chaohu-Hangbu River Catchment In Anhui Province

Lake sediments are the best records for researches of the catchment environmental change. In east China the lower Yangtze River has ever been, for decades, an area influenced strongly by monsoon climate and under high pressure of human activities. Therefore, it is more significant in both theory and reality to choose a representative catchment for studies of the processes and mechanism of the environmental changes based on sediment cores. This paper takes the Chaohu-Hangbu catchment as an example. Two cores covering different time-scales were deeply studied for different purposes. One is, covering the complete Holocene, a drilling core (ACN) in the Hangbu delta plain of the Chaohu lake and the other, spanning the last several decades, is taken from the Longhekou reservoir (ALE) in the upper reaches of Hangbu River. Methods, such as AMS dating, grain-size analysis, magnetic measurements, organic carbon, nitrogen and phosphorus, isotopes of carbon and nitrogen and XRD and XRF analyses, spherical carbon particles (SPC) analysis etc, were alternatively included. Results can be drawn as follows.The lower part of ACN core consists of alluvial-pluvial deposits, indicating that it is formed under conditions of increasing water table of Yangtze River due to the global sea-level uprising during the early time of the Holocene (10.0~8.73kaBP). The middle part (nearly nine meters thick) is lacustrine deposits showing that the paleo-Chaohu lake here lasts from 8.73~2.15kaBP. From then this bay was filled up with the sediments derived from Dabie Mountains and formed as a delta of the Hangbu River.Since ~8.7ka BP seven substages of climate change in this area were divided. They are warming up substage of 8.7~8.3ka BP, cold substage of 8.3~7.4ka BP, most warm and humid substage of 7.4-6.3ka BP, fluctuation substage of 6.3~4.3ka BP, cold substage of 4.3~2.2ka BP, warm and humid substage of 2.2-1.Oka BP, and cool and dry substage since ~1.0ka BP. This framework of climatic change is fundamentally in accordance with the global change during the post-glacial. The Holocene warm period seems to begin at ca 8.5ka BP and to conclude at ca 4.3ka BP, and the Climatic Optimum is from 7.4~6.3ka BP.The ALE core reveals a yearly resolution record over the past 50 years, with a mean sedimentary rate of 2.28cm/a. We built the depth-age model based on the SCP analysis and particle size-to-runnoff comparison. Significantly, the residual value obtained through fit polynary analysis to the percent of coarse sediments (>63um) represents a proxy of rainy season or floods in summer under monsoon conditions. Six substages indicative of the catchment environmental change were grouped through multi-proxes analyses. These substages each are strongly characterized by both the catchment rainfall-to-runoff and the human activities.