Gila Merschel

• Rivers transport large amounts of dissolved and suspended particulate material from their catchment area to the oceans and are a major source of trace metals to seawater. The Amazon River is the world’s largest river and supplies approximately 15% of the global freshwater flux to the oceans. However, the behavior of trace elements, especially particle-reactive elements such as the rare earth elements, within this river as well as in the estuary is not well constrained and rather little is known about their transport mechanisms. This thesis presents major and trace element distributions as well as Nd and Hf isotope data of river water samples from the Amazon Basin. The Amazon River and most of its major tributaries were sampled during seasons of high and low discharge. Samples were separated into suspended particulate and dissolved load prior to analysis to investigate transport properties of particle-reactive elements along the sampled river transect. Ultrafiltration techniques were applied to selected samples to investigate specific transport mechanisms of particle-reactive elements in the colloidal – truly dissolved load. The geochemistry of the Amazon River is mainly controlled by its tributaries draining the Andes, whereas tributaries draining the Precambrian shields and Amazonian lowlands only have a minor influence. The Andean tributaries supply large amounts of inorganic (nano-) particles and colloids that significantly influence the geochemistry of the Amazon River. Large differences in composition of the particulate, nanoparticulate and truly dissolved load could be traced by major and trace element chemistry in the Amazon River and its major Andean tributary, the Rio Solimões. In contrast, the geochemistry of tributaries that drain the Amazonian lowlands and Precambrian shields is dominated by the presence of organic (nano-) particles and colloids. In these rivers, a constant exchange between the truly dissolved, nanoparticulate and particulate load occu