三峡大坝建成后长江河流表层沉积物中有机物组成与分布特征

利用气相色谱法对2009年长江河流(干流和主要支流)表层沉积物样品中的正构烷烃(n-alkanes)和脂肪酸(fatty acids)进行测定和分析,结合粒度、OC%、δ13C等参数,研究样品中有机质的组成和分布特征,并对其来源及影响因素,特别是三峡大坝对其的影响进行了初步分析.结果显示,长江表层沉积物粒度组成主要以粉砂(45.8%)和砂(41.4%)为主,OC%值为0.08~1.99%, OC 的δ13C值为-31.9‰~-21.4‰.正构烷烃含量以干重计为0.71~13.69 μg/g,以OC计为0.05~1.99mg/g.脂肪酸含量以干重计为2.77~32.52μg/g,以OC计为0.16~40.58mg/g,其中饱和脂肪酸含量最多,含量最少的是支链脂肪酸.水动力分选、粒径是控制支流沉积有机质含量与分布的重要因素.干流中下游较上游具有丰富的水生植物源贡献,并且降解程度低.三峡大坝对陆源有机质的输送和改造具有重要影响.

Composition and distribution of organic matter in the surface sediments of the Changjiang River in Post-Three Gorges Dam period

n-alkanes and fatty acids (FA) were analyzed in the sediment samples collected in 2009 from the Changjiang River (main streams and tributaries) by gas chromatography. Combined with general geochemical parameters, e.g. grain size, organic carbon content, stable carbon isotopes etc. The characteristics of composition and distribution of organic matters were investigated. The variation of sources and control factors, especially the influence of Three Gorges Dam(TGD) were also evaluated initially. The result showed that the surface sediment matters were composed of silt (45.8%) and sand(41.4%); the content of OC% ranged between 0.08% to 1.99%; and δ13C of the OC varied -31.88‰ to -21.41‰ which were close to the signature of continental C3 vegetation. Total n-alkanes concentration varied from 0.71 to 13.69μg/g(dry weight), or from 0.05 to 1.99mg/gOC. Fatty acids (FA) concentration, from 2.77 to 32.52μg/g (dry weight), or from 0.16 to 40.58mg/gOC, the maximum was saturated FA and the minimum was branched FA compounds. Hydrodynamic sorting and grain size took an important role in the concentrations and distribution of organic matter in tributaries of the Changjiang. Compared to the upper reach of mainstream, middle and low reaches were rich in aquatic plants, and less degraded. TGD had a significant influence on the transportation and transformation of terrestrial OM in the Changjiang River system.