Paleohydrological changes over the last 4000 years in the middle and lower reaches of the Yangtze River: Evidence from particle size and n -alkanes from Longgan Lake

We have reconstructed the history of late-Holocene paleohydrological changes in the middle and lower reaches of the Yangtze River using grain size and n-alkane data from a sediment core retrieved from Longgan Lake. We employ changes in the grain size distribution to reflect the water level in the floodplain lake, with a higher percentage of the finer fraction indicating higher water level and vice versa. The n-alkane molecular distribution, average chain length (ACL), and P aq ratio (C 23 +C 25 )/(C 23 +C 25 +C 29 +C 31 ) are used to reflect mainly vegetation composition that is also sensitive to water depth. Our results reveal that the lake water level was relatively low and gradually increased from 4 to 2.7 ka. The period from 2.7 to 1.2 ka exhibited the highest late-Holocene lake water level in this region. The water level then decreased toward the present. This paleohydrological reconstruction agrees with existing paleoclimate reconstructions of the middle and lower reaches of the Yangtze River, confirming that the intensity of Asian monsoon rains is an important factor in affecting paleohydrological changes in this region.