Influence of Organic Matter on the Transport of Mineral Colloids in the River-Sea Transition Zone

The River-Sea Transition Zone has a significant impact on marine ecosystems, especially at present, due to increased anthropogenic pressure on rivers. The colloidal form of river runoff has not been practically studied, unlike the dissolved and suspended one, but this form is particularly important for the transport of river substances. The mechanisms of substance transfer were studied using model systems (colloidal clay, Fe(OH)3 sol), particle aggregation was estimated by changes in optical density, turbidity and particle size. The influence of the nature of dissolved organic matter (DOM) and salinity on colloid transport was studied. It was found that humic substances (HS) (recalcitrant DOM) stabilize mineral colloids with increasing salinity, while their interaction with chitosan (labile DOM) promotes flocculation and further precipitation in the mixing zone. In natural conditions, labile DOM can be released during viral lysis of bacteria or salt stress of biota. It was shown that clay particles modified with HS are flocculated more effectively than pure clays. HS can facilitate the transport of Fe(OH)3 into the outer part of the mixing zone even in the presence of flocculants. The flocculation mechanism and modern views on this process are considered.