Distribution and speciation of Cu, Pb, and Fe along the mae klong river, and their variations during estuarine Mixing

Abstract

Rivers transport metals to the ocean in dissolved, colloidal and particulate forms. In estuaries, where river-water and seawater of different compositions are mixed, changes in physic-chemical conditions occur. As the result, the relative contributions of the various chemical species of any elements to these forms can be modified considerably. It is important therefore to understand the effects of estuarine processes on metal behavior for predicting the geochemical behavior of each individual element as well as the role of estuaries in the mass balance between river and ocean. In this study, the concentration of iron, copper and lead, both in the forms of dissolved and particulate, were analyzed. Water samples were collected along the Mae Klong River and its estuary during dry and wet seasons in 1986. Laboratory investigations of estuarine mixing behavior of the there metals were also performed in both seasons. In addition, water samples were collected from the reservoirs of the Vachiralongkorn, the Srinakarindra, and the Khao Laem dams during each field sampling. The relationships between the dissolved and particulate forms of the three metals with salinity indicates that during mixing of seawater with freshwater, these metals show non-conservative behavior in both seasons. The non-conservative behavior is characterized by the removal of dissolved form by the flocculation of oxides and/or hydroxides of iron which consequently leads to coprecipition of copper and lead with the iron floes. The removal processes occur at salinities between 2-15 °/00. In addition, the presence of dissolved organic ligands and phosphate is likely to affect the removal processes of the three metals. There is seasonal variation of the removal processes probably because of the differences in volume of freshwater, composition and quantity of the suspended particulate matters carried by the Mae Klong River in each season. The results of laboratory investigations do support the results of the field investigations.