SPATIAL VARIATION OF ACTIVE HEAVY METALS IN INTERTIDAL SEDIMENTS OF THE YANGTZE ESTUARY

Concentrations of active heavy metals(available to hydroxylamine hydrochloride-25% acetic acid) were determined in surface sediments and sediments between 0~20 cm depths from the intertidal zone of the Yangtze Estuary,China.It was found that the percentage of active heavy metal concentrations in the total was Cu 26%,Pb 36%,Fe 7%,Mn 49%,Zn 32%,Cr 14% and Al 1.6% respectively in the intertidal sediments.No pollution of Cr was found in the sediments and the pollution level of other metals lied between the mid to lower ranges.Except for Zn and Cr,the concentrations of other active heavy metals in sediments in the summer were significantly lower than the spring,mainly because of the summer storm resulting in large number of fine sediment and its associated heavy metals away from the tidal flats into the estuary water.Influenced by the sewage discharge from point sources and particle size of sediments,active heavy metals appeared to be enriched in sediments of Xupu,Gulu and Pudongjichang distributed in south bank of the Yangtze Estuary and the high tidal flat along a same transect.In core sediments,active heavy metals showed surface or sub-surface enrichment.The geochemical actions of Cu and Pb in coastal intertidal sediments were mainly controlled by the redox conditions near the river mouth.While in sediments with weak hydrodynamic conditions and being polluted by heavy metals,vertical distributions of Cu,Pb were mainly controlled by the variation of organic matter contents.