THE HYDROPHOBIC FRACTION OF ORGANIC-MATTER IN THE KRKA RIVER ESTUARY

Surface active substances have been studied in the Krka River Estuary using an a.c. polarography method and various fractionation procedures. Total surface substances (SA(T)) were separated into (particulate) heterodispersed and dissolved fractions by filtration. The dissolved fraction was separated into hydrophobic basic and neutral components, hydrophobic acid and hydrophilic components by sorption on to XAD-8 resin. The content and the composition of SAT varied seasonally, depending on the biological activities taking place in the Krka River Estuary. The accumulation of SA(T)), with hydrophobic properties, occurred at the fresh/saline water interface along the vertical profile. Daily changes in the form of the surface active substances along the vertical profile were observed. The formation of the heterodispersed fraction, especially observable in the upper freshwater layer and at the halocline, resulted in the change of physico-chemical properties of surface active substances. Organic matter appeared mainly in a dissolved form in the deeper saline water layer, showing negligible oscillations. The electrochemical characterization of the fractionated SAT indicated that strong hydrophobicity of the surface active substances under natural pH conditions could be attributed to the significant contribution of the heterodispersed fraction of the organic material, which is the most reactive part of the surface active substances in the Krka River Estuary. The dissolved fraction of the surface active substances, prevailing in the deeper saline water layer, exhibited either hydrophilic or conditionally hydrophobic properties, depending on pH and ionic strength of the medium.