Sulfate Distribution In Modern Tidal Flat At The Yangtze Coast And Its Implication For The Holocene Evolution Of Sedimentary Environment

Sulfate reduction plays an important role in the mineralization processes of organic matter at the Yangtze coast and it is the key step of the sulfur cycle. Sulfur biogeochemistry is closely related to the cycle of Fe, Mn and C. The coastal wetland, a typical transitional zone, is a multifunctional and complex ecosystem between land and ocean, as well as a significant and active sulfate reduction zone. Therefore, it is important to develop researches on the characteristic of sulfate reduction in the sediments of wetland. In this paper, Sulfate ions and chloride ions were determined and analysed along the tidal flat from the northern and eastern coasts of Chongming island (Beipugang, Beiqiyao and Tuanjiesha), Changjiang River mouth and northern coast of Hangzhou Bay (Fengxian), and sediments in a Holocene core SL67. This study aims to examine the distribution of sulfate reduction zone in modern tidal flat depositions and Holocene core, therefore to rebuild a high-precision sea-level curve.The results revealed that (1) Sulfate content is the greatest in the upper tide flat sediments and in the phragmites australis zone.(2) Sulfate reduction zone is generally distributed in the high salt marsh and the upper mid tidal flat, while the sulfate consumption zone is distributed in the mid and low tidal flat.(3) The relationship between ASO42-and Cl-shows sulfate in the intertidal sediments is consumed, while it shows a good conservative in the low tidal flat sediment. The conservative in upper tidal flat is more complex than the two others, which may due to the active sulfur biogeochemical processes.(4) The sulfate distribution rules in the modern tidal flats were similar to the transgressive sediment:the SO42-and ΔSO42-concentration were higher in salt marsh sediment and the upper tidal flat sediment. In the regressive sediment, the SO42-and ΔSO42-concentration were higher in intertidal and low tidal flat, which may caused by the early diagenesis of the underlying strata and freshwater leaching from the top.