Interpretation of the environmental change of Dongting Lake, middle reach of Yangtze River, China, by Pb-210 measurement and satellite image analysis

The present study examined the recent environmental history of the Dongting Lake, located in the middle Yangtze River region, central China. The sedim ent was recovered by 22 vibrocores in different lake sectors, primarily cha racterizing subaqueous delta and bay subfacies. High sedimentation rates, r evealed by Pb-210 measurement in different subfacies of the lake, ranged fr om 0.77 to 2.33 cm/year. These rates equate to deltaic sedimentation associ ated with mobile channels resulting from Yangtze flood events. Satellite im ages confirm that the Dongting Lake does not contain the biggest Yangtze fl oods. Moreover, comparative bathymetric surveys verify that the Dongting La ke has lost almost two-thirds of its total area in the past century, due pr imarily to siltation by Yangtze sediment. In the late 19th century, a major flood-induced channel avulsion resulted in the coupling of the 'Four-Tribu tary' subbasin to the Dongting Lake, causing a massive increase in the sedi ment supply into the lake since then. Hydrological data demonstrate that ab out 83% of the lake's annual sediment influx are derived from the Yangtze. In addition, pressures from a growing population and associated human activ ities, such as reclamation, embanking, aquaculture, slope modification and deforestation, are compounding the loss of the lake surface area and associ ated storage capacity. (C) 2001 Elsevier Science B.V. All rights reserved.