Organic Matter and Mineral Interactions Modulate Flocculation Across Arctic River Mixing Zones

Abstract

AbstractThe focus of this study is organic matter changes and suspended particle and colloid behavior in riverine and marine water mixing zones. Laboratory experiments demonstrated that salinity, clay mineral type, and the nature of dissolved organic matter (DOM) have a strong influence on mineral suspension stabilities (clays, carbonates, and ferric hydroxide), which represent the main fractions of particulate and colloidal matter riverine export. Clay mineral modification by humic acids stabilizes suspensions under increasing salinity, resulting in greater export of particles to coastal zones. Simultaneously, modified particles are more efficiently aggregated by a flocculant than nonmodified particles. Field investigations were conducted in Arctic river mixing zones, providing new information about colloid matter and colloid organic carbon distributions in the mixing zones, which agreed well with laboratory studies. The ratio between colloid organic carbon and suspended matter may prove a useful criterion to distinguish effective flocculation zones. Arctic River DOM fluorescence suggests dominance of terrigenous humic substances in mixing zones as well as coprecipitation by coagulation and flocculation. Our findings may reconcile reports of nonconservative behavior of DOM previously reported in the mixing zone at salinities of less than 12. We suggest that there is a flocculation mechanism in the estuarine mixing zone, which implies the presence of natural active substances, released during microorganism viral lysis (viral shunting).