Surface properties of suspended solids in stratified estuaries (Krka River estuary and Rhône River delta)

Abstract

Three surface parameters—specific surface area (SSA), heat of wetting (Hw), and cation exchange capacity (CEC)—of estuarine suspended solids were studied in relation to the organic matter (dissolved or particulate). Natural suspended solids were studied in two stratified river mouths—the Krka River estuary and the Rhône River delta. The same studies were performed with model solids, well defined by chemical composition and preparation (controlled pore glass, silanized controlled pore glass and calcite) after exposure to natural water samples from the Krka River estuary. On the basis of the studied parameters, the existence of two types of organic compounds that mediate the surface properties of particulates was indicated: (1) hydrophilic, with high density of functional groups, reactive and degradable, and coinciding with ‘river type organic matter’, and (2) hydrophobic, less reactive and thus more persistent, and coinciding prevalently with ‘marine type organic matter’. Generally, it was found that high Hw values (100–300 μJ cm −2) reflect the influence of surface functional groups that originate primarily from the reactive organics (adsorbed or particulate). An extreme value of Hw (523 μJ cm −2) was found at a location of high biological productivity and high anthropogenic influence.