Remote Sensed Analysis Of The Suspended Sediment Variations From The Yangtze Estuary To Zhejiang-fujian Provincial Coastal Waters

Suspended Sediment Concentration?SSC?is one of the important parameters of water environmental assessment in the coastal sea area,which can provide important basis for the development and evolution of estuarine delta,the water quality of coastal zone and the evolution of estuarine ecological environment.In recent years,the construction of numbers of dams in the Changjiang River basin,especially large dams on the mainstream,leads to the sediment supply dramtically decrease to the Yangtze Estuary and adjacent waters,but also the impact on the transportion of sediment into the sea,what would happen to the adjacent waters when the sediment source decreased?Whether it will lead to changes of suspended sediment suspended field transporting to the sea,thus affecting the characteristics and space-time changes of transportion to Zhejiang and Fujian provincial coastal waters.In this paper,the research focuses on the spatial and temporal variations of the suspended sediments from the Yangtze Estuary to Zhejiang-Fujian provincial coastal sea by employed the satellite remote sensing technology and provenance tracing method to carry out in-depth investigation Based on the satellite data and in-situ data,the temporal and spatial changes and the diffusion patterns of the surface sediments to transport to Zhejiang and Fujian provincial coastal after the Yangtze Estuary sedimentation significantly reduced were analyzed,which has great significant to explore the new pattern sediment reduction along the coast of Zhejiang and Fujian provincial coastal and analyze the new changes of coastal ecological environment.Based on the satellite remote sensing technology,a reliable model was established according to in-situ measurements in different seasons in 2014 to extract SSC from the Terra-Moderate Resolution Imaging Spectroradiometer images from year 2000 to 2015.The suspended sediment in the Yangtze Estuary and the adjacent waters were retrieved to observe the sediment transport to the offshore sea,revealing the temporal and spatial characteristics and the recent trend of the suspended sediment transport along the Zhejiang-Fujian coast.Based on the results of these analyses,the SSC transport mechanism was also studied.The results revealed that:in the spatial change,the suspended sediment in the Yangtze Estuary descends to the north and the south,but mainly transported to the southeast direction,formating a continuous coastal suspended sediment strip along the shore from the Yangtze Estuary to the Minjiang River.At the same time,the suspended sediment spreads out to the sea at the east of 122.5°E,and the concentration of suspended sediment in the surface ofthe sea is rapidly reduced.In years changes,during the period of 2000?2002,the sediment concentration from the Yangtze Estuary to the Minjiang River estuary changed little;Since 2003,the Yangtze Estuary sediment suddenly reduced,its south of the coastal waters of suspended sediment concentration also will be reduced.Driven by the monsoon and coastal ocean currents,the transportation of the suspended sediment from the Yangtze Estuary to south coast has obvious seasonal variation.In spring,the suspended sediment transported as a strip from the Yangtze estuary to Zhejiang and Fujian provincial coastal;late spring,the transport of suspended sediment is interrupted at the Wenling coastal waters in Zhejiang Province.In summer,a large number of suspended sediment stranded in the Yangtze Estuary and Hangzhou Bay,the interruptions were obvious.In autumn,a continuous coastal suspended sediment strip gradually formed between mid-October and late November.From the inversion of the results for 16 consecutive years and the Yangtze River,Qiantang River,Yongjiang River,Oujiang River and Minjiang River and other rivers per year into the sea sediment load show that the Yangtze Estuary into the sea sediment is precipitation origin of suspended sediment in Zhejiang and Fujian provincial coastal area.Futhermore,in order to verify the reliability of the remote sensing image and sediment data,paper also analyzes the source,diffusion range and migration direction of the sediment from the perspective of source tracing to complement the suspended sediment transport with remote sensing.The results show that the suspended matter from the Yangtze Estuary has a great contribution to the suspended matter along the coast of Zhejiang and Fujian province,whether from the perspective of constant elements,E.g,Fe₂O₃/Al₂O₃?TiO₂/Al₂O₃ and TiO₂/Fe₂O₃?TiO₂/Al₂O₃,or fom the rare earth element source discrimination chart analysis of ?Ce??Eu???LREE/?HREE?UCC??Ce??Gd/Lu?UCC??La/Lu?ucc??La/Sm?UCC??Gd/Yb?UCC?LREE?HREE show the same results.At the same time,according to the remote sensing data set of suspended sediment transport in the Yangtze Estuary,as a result of the sudden decline in sediment appeared in the Wenling coast,according to this,the monthly average of suspended sediment is calculated and plotted its change curve.Its annual data analysis confirmed that with the Yangtze River into the estuary of the sediment was significantly reduced,sediment concentration in Zhejiang and Fujian coastal waters is also affected.In recent years,under the influence of reducing suspended sediment from the river basin into the estuary,the continuous suspended sediment strip in winter was broken off ahead in spring and delayed recovery in the autumn.The year 2003 when three Gorges Reservoir began to run became a turning point.The sustained influence of this effect will change the hydrological and suspended sediment field along the Zhejiang and Fujian provincial coastal,and require continuous observation and research.