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Sorption of heavy metals to organic matter and mineral soil constituents can hardly be separated experimentally. Here we studied the retention capacity of organic matter and minerals from soils in a long-term field experiment in which the organic carbon content had been altered, but the mineral phase had remained constant over time. The sorption of Cu, Cd and Zn showed a non-additive contribution of soil organic matter and minerals to the sorption capacity of soil. Sorption on organic matter exceeded mineral sorption from 6 to 13 times. This is the first time that sorption to soil organic matter is quantified in bulk soils.

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[1] The importance of wetlands in the global C budget has been recognized in recent years, and the high biomass productivity of riverine floodplains is widely acknowledged. However, soil C dynamics in these ecosystems are still poorly understood and rarely quantified. In this study, we quantify organic C accretion and examine changes of organic matter pools across an age gradient of riverine floodplain soils under different land uses in a warm temperate climate. We find rapid C accumulation during the initial 100 years of soil formation, with rates exceeding 100 g m À2 a À1 . We show that floodplain land use strongly affects soil C sequestration and organic matter pool allocation and find that the distribution of different soil organic matter pools reaches a steady state within a few decades of soil development. 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.Citation: Zehetner, F., G. J. Lair, and M. H. Gerzabek (2009), Rapid carbon accretion and organic matter pool stabilization in riverine floodplain soils, Global Biogeochem. Cycles, 23, GB4004,

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This study investigated the effect of different farming practices over long time periods on the sorption‐desorption behavior of Cu, Cd, and Zn in soils. Various amendments in a long‐term field experiment over 44 y altered the chemical and physical properties of the soil. Adsorption isotherms obtained from batch sorption experiments with Cu, Cd, and Zn were well described by Freundlich equations for adsorption and desorption. The data showed that Cu was adsorbed in high amounts, followed by Zn and Cd. In most treatments, Cd ions were more weakly sorbed than Cu or Zn. Generally, adsorption coefficients KF increased among the investigated farming practices in the following order: sewage sludge ≤ fallow < inorganic fertilizer without N ≈ green manure < peat < Ca(NO3)2 < animal manure ≤ grassland/extensive pasture. The impact of different soil management on the sorption properties of agricultural soils for trace metals was quantified. Results demonstrated that the soil pH was the main factor controlling the behavior of heavy metals in soil altered through management. Furthermore, the constants KF and n of isotherms obtained from the experiments significantly correlated with the amount of solid and water‐soluble organic carbon (WSOC) in the soils. Higher soil pH and higher contents of soil organic carbon led to higher adsorption. Carboxyl and carbonyl groups as well as WSOC significantly influenced the sorption behavior of heavy metals in soils with similar mineral soil constituents.