Trace metal behaviour in a highly stratified Mediterranean estuary: the Krka (Yugoslavia)

Abstract

The distribution of total dissolved trace metals (Pb, Cd, Cu, Ni and Fe) in the Krka River estuary was studied in May 1988 during the high-productivity period. The dissolved metal concentrations in the freshwater end-member are: Pb 0.08 nM; Cd 0.044 nM; Cu 1.78 nM; Ni 2.47 nM; and Fe 24.1 nM. These concentrations are of the same order of magnitude as those observed in unpolluted rivers throughout the world and are in accordance with the carbonate nature of the catchment of the Krka River, which is, further, located in a national park. The trace metals in the plume show low reactivity during estuarine mixing. In contrast to most estuarine data, dissolved trace metal concentrations are generally lower in the river water than in seawater. However, the bottom saline waters of the estuary are inhomogeneous with regard to dissolved trace metal concentrations, which increase with water age. This may be due to degradation of organic matter. There is no clear evidence for accumulation of dissolved trace metals at the freshwater-seawater interface. This is dependent on the physico-chemical properties of the metals involved and may be more readily detected at downstream sites.