Holocene Nile Delta sea-level fluctuations and its impact on environment——with special reference to the Changjiang River Delta

The Holocene sea-level rise of the Nile Delta is reconstructed on the basis of radiocarbon dates that are derived from 33 peat samples and 65 lagoon samples obtained from many boreholes located in the lower delta plain.The result indicates that the lagoonal curve is more reliable than that of the peat curve,the latter is much influenced by the sediment compact.The result also shows that the sea level was about 10 m below the present during 7 000 a B.P.,about 5 m below the present in 5 000 a B.P.,and was nearer to the present in 2 000 a B.P.Affected by the paleotopography and regional subsidence of the study area,the largest impact from transgressive intensity and scope tends to occur in the northeastern Nile sector.This influence becomes progressively reduced toward the central and northwestern Nile sectors.A vast Nile Delta Plain dominated by lagoon-sand beach and fluvial plain system had began to build at about 7 000 a B.P.,when rise in sea level started to decelerate and deltaic sedimentation rate overwhelmed the sea contribution.As sea level tends to be stabilized in Late Holocene,human activity,such as reclamation and channelisation,induces environmental deterioration,represented by largely shrunken lagoonal system.A comparable example of the Changjiang Delta is cited in the present study.It is shown that the Holocene Changjiang sea level did not fluctuate coincidentally as the Nile,much likely due to the differences of regional subsidence between the two regions.The fertile delta plain that was formed by the delta-coast construction at about 7 000 a B.P.induced the Neolithic civilization.However,intensifying human activity since 2000 a B.P.also has aggravated the delta-coast environment.Many lakes and drainage networks are diminishing.