Speciation studies of iron in a river water system entering brackish and estuarine water zone

Speciation studies of iron in a river water system will be reviewed. By use of an automatic monitoring station and a portable voltammetric system, speciation studies of iron has been carried out in the transition zone where river water enters the brackish and estuarine water. The measurements have been carried out in the zones where the river system of Leirelva and Nidelva enters the fjord water in Trondheim Norway. The study of iron has been carried out both in the water and the upper river sediments fraction (10 cm). In the water samples, a working electrode (d = 6 mm) of solid dental amalgam electrode was used together with an Ag/AgCl/KCl (3 M) reference electrode, and a platinum counter electrode. In the river sediments, the electolabile fraction of iron was measured by use of a silver-copper micro electrode. ICP-MS measurements were included to get information about the total amount of iron in the different fractions. In the water system the observed electrolabile iron concentration in the various zones was studied as function of the salinity, and in the sediments the iron concentration was studied both as a function of the salinity in the water and the level of depth. Variations in the electrolabile iron concentration in the water fraction on short and long time scale is discussed due to seasonal variation in temperature and precipitation. Preliminary results indicates that there is a clear correlation between the electrolabile iron content in the river water as function of salinity, and an increasing amount of non-electrolabile iron in the suspended matter and sediments with increasing salinity.