Gannan Small Watershed In Water Of Dissolved Rare Earth Elements Geochemistry And Trace Element Compositions

River is a major component of the global surface water and it plays an important role during the cycles of the chemical elements. The chemistry of river waters reveals the nature of weathering in a basin-wide scale and helps us understand the exogenic cycles of elements in the continent-river-ocean system. In particular, geochemical investigation of large river gives important information on the biogeochemical cycles of the elements, chemical weathering rates, physical erosion rates and CO₂ consumpti -on during the weathering of the rocks within the drainage basin. Its importance has led to a number of detailed geochemical studies on some of the world's large and medium-size river systems.In this paper the upper reaches of Ganjiang River in the southern Jiangxi Province has been selected as the object of study. By making use of trace element geochemical approaches, we discuss the relations between the water chemical characteristics of the rivers and human activities, climate, topography, and lithological character and tracing investigations, both in time and space, are conducted on the processes of cycling of chemical substances(heavy elements), we also study the concentration,distribution,mechanism of the fractionation and its influencing factor.Through studying the DREE and trace elements of river water in the southern Jiangxi Province, some conclusions are drawn as follows:(1) In the process of chemical weathering the rare-earth elements (REEs) are relatively inert with respect to their behavior and therefore they are ready to transport and tend to be retained in the weathering crust. It is found that only a little amount of REE enters river water in the form of dissolved species. So the dissolved REE in river water are extremely low. The shale-normalized river water-dissolved REE distribution patterns of the Ganjiang River in the southern Jiangxi Province are not flat and the HREEs are relatively slightly enriched, showing obvious Ce negative anomaly and Eu positive anomaly.(2) The pH of river water is the most important factor controlling the concentrations of river water-dissolved REE. In addition, the ions strength of water, in organic complex anions (HCO₃^-), metallic oxide colloidal particulates and biological processes would all exert a great influence on the behavior of REE. The high pH values and high ion concentrations of the Ganjiang River in the southern Jiangxi Province are a main factor leading to the lower concentrations of dissolved REE in the river water columns.(3) The distribution patterns of Ganjiang River in the southern Jiangxi Province represented obvious Ce negative anomaly and Eu positive anomaly, which corresponded the Ce positive anomaly and Eu negative anomaly of the topsoil with the same background, and middle and heavy REEs enriched, which may resulted from the exist of yttrosynchysite which enriched in heavy REEs and was weathered easily.(4) The study of the heavy metal of Ganjiang River in the southern Jiangxi Province indicates that the concentration of the heavy metal is low ,which reveals the small strength of human activities. Further more, the pH influences the concentration of the dissolved ion, and high pH can make the dissolved heavy metals absorbed more easily, which lead low concentration of the heavy metals.