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Uferfunk - Aggregate formation, stability and turnover in bank- and floodplain soils of the tidal River Elbe

Leitung:Prof. Dr. Georg Guggenberger, Prof. Dr. Sandra Spielvogel (CAU Kiel), Dr. Jannis Florian Carstens
Bearbeitung:Jan Jagode

Tidal rivers like the Elbe and their estuaries are of significant importance for both overseas cargo transport as well as their diverse and sensitive ecosystems. Reliably understanding the system which is influenced by varied hydrodynamical, environmental and anthropogenic factors would allow for providing sound advice supporting both waterway bound navigation, as well as ecological development and maintenance. To address these topics, we work in close cooperation with the Federal Institute for Hydrology (Bundesanstalt für Gewässerkunde) in Koblenz.

Whereas the processes of soil structure formation and aggregate hierarchy development of various terrestrial and aquatic ecosystems are well known, the transition zone in between is still insufficiently understood. There is a lack of knowledge concerning initial aggregate formation, aggregate stability and aggregate turnover in semisubhydric and semiterrestric soils of mudflats and crude marshes with their characteristically changing redox conditions as well as the further buildup of a more complex soil architecture and its stability in the transition to more developed riverbank and flood plain soils.

Iron minerals and the associated soil organic C (SOC), which play a key role in the stability of soil aggregates, are notably sensitive to alternating redox conditions. Under oxidizing conditions, Fe(III) oxides such as goethite constitute one of the most important types of inorganic binding agents for the formation of soil aggregates, which has been the focus of intense research for decades. Under anoxic conditions, Fe(III) oxides are subjected to reductive dissolution by micro-organisms. This process can result in the destruction of microaggregates, for instance via the dispersion of clay particles that were formerly bound together by Fe(III) oxides. Moreover, organic C that was associated with the oxides can be released into the soil solution. Therefore, it can become subjected to microbial degradation more easily accelerating the loss of soil organic C, fostering the siltation of soil.

In terms of aggregate stability, the key question is to what extent Fe(II) minerals can function as binding agents for soil particles. Despite the significant potential of these minerals for soil structure stabilization under reducing conditions, knowledge on the respective processes remains extremely scarce. Besides promoting aggregate formation, Fe(II) minerals may play an important role for the stabilization of soil organic C released by the reductive dissolution of Fe(III) oxides and thereby reduce the emission of greenhouse gases.