Sources of sediment in tidal flats off Zhejiang coast, southeast China

The growth of tidal flats off Zhejiang coasts in southwestern China has provided substantial areas for local agriculture and construction activities. To evaluate modern and future development of tidal flats in the region, a good understanding of sediment sources is necessary. Previous research has concluded that the Changjiang (Yangtze) River is the dominant supplier of sediments to this part of the southeast Chinese coast, despite the fact that sediment delivery from this source has been decreased markedly in the past two decades. In this study, we investigated the sources of tidal flat sediments, and the magnetic and geochemical properties of recent tidal flat sediments along the Zhejiang coast were compared with those discharged from rivers. Magnetic and geochemical properties of the tidal flat samples reveal statistically distinct sediment provenance groups. The magnetic and geochemical scatter plots show that the suspended sediment samples are naturally divided into two different groups, one including the Changjiang River and Qiantang River material, and the other including the Jiaojiang, Oujiang, and Feiyun Rivers that located in the central and southern parts of the study areas. At last, a binary source of tidal flat sediments along the Zhejiang coast was determined, with the substantial majority originating from local rivers, while a much smaller proportion emanates from the Changjiang River to the north. We conclude that the sediment contribution of the Changjiang River to tidal flat development in the region has been markedly overestimated, with important implications for management.