Hydrogeochemical characteristics of major estuaries in eastern China: physicochemical indicators and soluble element concentrations of river water

Abstract：Hydro-physicochemical properties and element concentrations of rivers constitute key indicators related to water functions. Chemical flux through river to sea has important impact on marine ecosystem. This paper presents pH values, electric conductivities and soluble concentrations of major and trace elements in river water sampled at the lower position or estuaries of 33 rivers. It is demonstrated that pH values, electric conductivities and soluble concentrations of major and trace elements in most rivers of northern China are much higher than those in rivers of southern China, which is consistent with climate change from north to south. The soluble concentrations of major elements in river water are associated with the zoning of soil type and soil chemical distribution pattern from north to south. However, anomalous content of major elements and physicochemical indexes in some rivers may be influenced by the mixture of sea water with fresh water. It is found that trace element concentrations in some rivers are anomalous in comparison with the concentrations in other rivers of the same region. Such a phenomenon may be attributed to (1) special geological and geochemical background of drainage areas; and (2) anthropogenic activity and pollution. It is inferred that the lower concentrations of soluble Na, Ca, K, Zn, Se in flood season are caused by dilution under higher precipitation, whereas the higher concentration of Al, REE, Fe and some other elements may be the consequence of containing lots of micro-particulates and colloids derived from soil through surface current.