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Study on the geochemical characteristics of the surface sediments from the Yangtze River estuary under the 2011 sharp turn from drought to flood in middle and lower Yangtze

HU Li-min;SHI Xue-fa;WANG Guo-qing;QIAO Shu-qing;YANG Gang;GAO Jing-jing;BAI Ya-zhi;Key Laboratory of State Oceanic Administration for Marine Sedimentology & Environmental Geology,First Institute of Oceanography, State Oceanic Administration;Faculty of Earth Sciences, China University of Geosciences;  
The geochemical characteristics of major elements, trace elements and organic carbon and their influential factors were analyzed for the surface sediment samples from the Yangtze River estuary under a sharp turn from drought to flood in 2011 in the Yangtze River, then further to evaluate the impact of this sharp turn event on the sedimentary geochemical province. The results showed that the sediment grain-size turned to coarser in flood season, especially in the southern river mouth to the front delta. The decreased major elements in flood season were Al2 O3, K2 O, Na2O, whereas the increased components of TFe2 O3, CaCO3, CaO, TiO2, Mn and P. The correlation between major elements and clay is more significant in the drought season, the inconsistent relationship between major component and grain-size was observed in S4 from the southern transect. This could be related to the fluvial input and specific depositional hydrodynamic setting. The trace elements in most sediment samples showed an increase during flood season, revealing the impact of coarser grain-size and increased flux of fluvial input. The correlation between TOC and TN in the drought and flood periods showed good positive relation, but with higher C/N ratios in the flood season showing higher terrigenous contributions. Even though, the lower C/N ratios should be ascribed to the source pool of organic matter, the input of soil organic matter and degradation of microorganisms. The distribution of variables on the loading plot showed more scattered in the flood season, reflecting the decreased control of grain-size on the element association and increased riverine input. Based on the sample scores, the geochemical province of the estuarine samples showed little variation during the sharp turn from drought to flood.
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