Change in the sedimentary environment of Wanquan River Estuary, Hainan Island, China

Abstract

210Pb geochronology and sediment core profiles of organic carbon, total sulfur and organic carbon isotope (δ13C) values were used to reconstruct the local environmental history of the Shamei Lagoon, located in the Wanquan River Estuary, eastern Hainan Island, China. Total sulfur and δ13C values decreased upwards in the top 30 cm of a sediment core that spanned the last 200 years of deposition. Total sulfur concentration and δ13C values respectively decreased upward from 1.92% to 0.36%, and −20.63‰ to −23.64‰ The C/S ratio in the 19th century and earlier was relatively stable in the range of 0.47–0.80, and there was a positive correlation between organic carbon and total sulfur. Since around 1900 AD, the C/S ratio increased rapidly to a maximum of 3.94, but no simple correlation was found between organic carbon and total sulfur during this more recent period. These results indicated that before 1800 AD, the lagoon had a fully marine character, and the location of today’s Wanquan River Estuary was an open embayment. From 1800 to 1900, the salinity of Shamei Lagoon decreased noticeably. The amount of seawater which could enter the lagoon decreased gradually as the Yudai spit grew. Today, seawater scarcely affects the lagoon; it is essentially a freshwater basin.