Behaviour and speciation of dissolved selenium in estuarine waters

Abstract

THE behaviour of chemical species in estuaries¹ is important for several reasons. The extent of any modification of the riverborne flux of dissolved materials to the open sea, as a result of interactions during the mixing of fresh and saline waters, is of fundamental geochemical significance. Knowledge of the pathways of element transference in estuaries is needed to predict effects of waste inputs and other modifications of estuarine conditions. It is also in the estuarine zone that the limitations of the determination and modelling of chemical speciation become most acute, because of the wide range of major compositional variables and the importance of kinetic factors. Among the major problems is the uncertainty as to the true redox potentials of natural waters and the factors which can lead to the presence of thermodynamically unstable oxidation states. Recent work^2,3 on selenium in seawater has indicated that the redox speciation of this element shows some differences from that predicted for an equilibrium system. We give here results of measurements of selenium in some river and estuarine waters of the Solent area. Available Se(IV) was detected in chalk streams but always accounted for less than 10% of the total dissolved selenium. Dissolved forms of selenium behaved essentially conservatively during estuarine mixing of chalk stream inputs.