The contribution of middle and small rivers to the distal mud of subaqueous Changjiang delta: Results from Jiaojiang river and Oujiang river

Source, transportation and fate of marine sediment are among the crucial questions in oceanographic sedimentology. As well known, the materials of so called Zhe-Min coastal mud are mainly derived from the Changjiang River as well as the medium and small rivers throughout Zhejiang and Fujian Provinces. However, we still have little knowledge on the quantitative contribution of those medium and small rivers to that mud zone, probably due to the lack of suitable tracers. Using grain-size end member and clay minerals as tracers, this paper aims to 1) evaluate the efficiency of two tracers comprehensively, and 2) quantify the individual contribution of Jiaojiang River and Oujiang River. An end member model was used to analyze the grain size data of surficial sediment samples and4 end members were identified. End-member 1 is attributed to the Changjiang River input. End-member 2 is caused by the input of small rivers, such as Jiaojiang River and Oujiang River. End-member 3 is associated with the input from the south part of study area and probably indicates a possible transport towards the north. End member 4 is possibly transported from the residual sandy area. Furthermore, the graph of standard deviation values of grain-size content against grain-size classes of six cores in the mud area reveals characteristic populations of grain-size. It shows that all cores have a common characteristic population (primary peak) of grain size between 3.91 to 9.29 μm, which is associated with the fine particles suspended from the Changjiang River delta and perhaps indicates that the overall study area is affected by Changjiang River. Based on a matrix method model, data of clay minerals contents are used to evaluate the quantitative contribution of Changjiang River, Jiaojiang River and Oujiang River to the coastal muds. Due to the dependence of the clay minerals on the grain-size, the results merely reflect the contribution of fine particles less than 2μm. In comparison, the end members of grain-size are better tracers which include the entire level of fraction to simultaneously solve both of problems about “source and quantification” in a relatively closed system. Therefore, the end-member analysis of grain size is expected to play a significant role in the future.