Development of soil properties in a riverine floodplain with time – results from a chronosequence study in the National Park Donau-Auen in Austria

Recently, we established a chronological framework for fluvial deposits along a soil sequence at the Danube River near Vienna, Austria, using optically stimulated luminescence (OSL) dating. We identified fluvial deposits from different time periods ranging from the early last millennium BC to the 18 th century AD. We bridged the gap from the 18 th century AD to the present with fallout 137 Cs dating, and developed a chronofunction model relating Fe oxide crystallinity (Feo/Fed) to deposition age along the studied soil sequence model relating Fe oxide crystallinity (Feo/Fed) to deposition age. This model allows age estimation of soil layers using routinely measured pedological characteristics (Feo/Fed). We examined specifically the build-up of soil organic matter, the redistribution of phosphorus among biogeochemical pools and the retention of pollutants related to soil development. We found rapid C accumulation during the initial 100 years of soil formation, with rates exceeding those in northern peatlands by an order of magnitude. We showed that floodplain land use strongly affects soil C sequestration and pool allocation, and found that the distribution of different C pools reaches a steady state within less than a century. Our results demonstrate that continually rejuvenated soils on riverine floodplains are strong C sinks, but also show that intensive cultivation severely compromises their high C sequestration potential. The youngest soils were dominated by calcium-associated phosphorus (CAP), in less than 100 yrs of pedogenesis, CAP markedly decreased and organic phosphorus (OP) increased, and in less than 180 yrs, OP reached CAP levels. Adsorption properties of the floodplain soils changed, governed specifically by OC accumulation and Feoxide and hydroxide accumulation with time. The soil retention capacity for Cd and Cu increased with increasing soil age.