Geochemistry of Trace Metals from Chinese River/Estuary Systems: An Overview

Based on the data from extensive estuarine studies over 10 years (1983-93), the present work provides an overview of the geochemical features of large Chinese river/estuary systems. Elevated concentrations of major elements are observed in Chinese rivers from north to south, which is attributed to intense weathering and erosion over the drainage basins. Trace metal levels in Chinese rivers are relatively low and similar to those from large and less disturbed world aquatic systems (e.g. Amazon and Orinoco). In the estuaries, particulate elements show stable distributions in the mixing zone especially when absolute concentrations are normalized to aluminium and/or scandium. Dissolved trace metals may have either conservative and/or active (non-conservative) distributions or both in Chinese estuaries. Wherever non-conservative distributions are observed, trace elements may be remobilized and/or scavenged from solution depending upon river discharge, sedimentary dynamics and element. Biological uptake and regeneration of trace metals becomes more important in high salinity areas further offshore the riverine effluent plumes than inside. Correlation of heavy metals with grain size and operational chemical forms reveals a high proportion of elements associated with the fine size fraction compared to total sediments and elevated labile fractions in bottom sediments in anthropogenically disturbed systems. Finally, an estimate is made towards the chemical flux of trace metals to the ocean through Chinese estuaries.