270209 PR Environmental chemistry lab course including scientific fieldwork (2012S)

The extremely low concentrations of iron in surface seawater limit biological productivity in large areas of the world ocean. Due to the very low solubility of Fe(OH)3 in seawater, dissolved Fe tends to precipitate and has a relatively short residence time in the surface ocean. Continental weathering of silicates, and, subsequently, river input of dissolved weathering products is one of the possible sources of iron to the ocean, with the constraint that the river-borne iron input is controlled by estuarine sedimentation processes. It is well accepted that the vast majority of dissolved Fe in river water exists as colloid particles (mainly hydrous ferric oxides and iron-binding humic substances). Aggregation of these colloids, due to the major change in ionic strength upon mixing of river water with seawater, causes a massive removal of the Fe in the estuarine mixing zone. However, this removal is not necessarily complete. Iron may exhibit different behaviours depending on a number of variables. Geographic position, size, and types of vegetation cover and land use of a given river basin are critical factors influencing both, riverine DOM (dissolved organic matter) quality, and the riverine iron transport from land to the sea. In the framework of the lab course, natural iron-binding chelating ligands will be isolated from river water.