IMIS

We used a kinetic method (Postma 1993) in which iron oxide reactivity is represented as a reactive continuum, and compare results of a freshwater, an estuarine and a deep-sea sediment to traditional, single-step extraction results. Depth profiles were derived using both approaches. The traditional extraction methods have sufficient resolving power to reveal concentration differences of reactive iron oxides between samples from deep-sea, estuarine and freshwater sediments, but result in homogeneous depth profiles for iron oxide composition in the latter two sediments. The reactive continuum approach resulted in heterogeneous depth profiles of initial iron oxide reactivity and reactivity distribution for estuarine and freshwater sediments, thereby revealing differences in iron oxide composition. Due to low concentrations of reactive iron oxides the reactive continuum approach was not applicable in deep-sea sediments. Reactivities were independent of sediment surface area and the load of reactive iron oxides.