Temporal dynamics of pore water concentrations of Cd, Co, Cu, Ni, and Zn and their controlling factors in a contaminated floodplain soil assessed by undisturbed groundwater lysimeters Sabry M. Shaheen a, b , Jörg Rinklebe b, * , Holger Rupp c , Ralph Meissner c a University of Kafrelsheikh, Faculty of Agriculture, Department of Soil and Water Sciences, 33 516 Kafr El-Sheikh, Egypt b University of Wuppertal, Department D, Soil- and Groundwater-Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany c Helmholtz Centre for Environmental Research e UFZ, Department of Soil Physics, Lysimeter station Falkenberg, Dorfstr. 55, 39615 Falkenberg, Germany article info Article history: Received 27 November 2013 Received in revised form 16 April 2014 Accepted 23 April 2014 Available online xxx Keywords: Flooding periods Redox potential Metals Wetland soil abstract We aimed to assess the dynamics of pore water concentrations of Cd, Co, Cu, Ni, Zn and their controlling factors (E H , pH, DOC, Fe, Mn, and SO 4 2 ) in a contaminated floodplain soil under different flood-dry-cycles. Two parallel undisturbed groundwater lysimeters (mean values presented) were used for long term (LT; 94 days) and short term (ST; 21 days) flood-dry-cycles. Reducing conditions under LT lead to low E H and pH, while DOC, Co, Fe, Mn, and Ni increased. Cadmium, Cu, Zn, and SO 4 2 increased under oxidizing conditions during ST. Cobalt and Ni revealed a similar behavior which seem to governed by E H /pH, Mn, Fe, and DOC. Cadmium, Cu, and Zn reveal a similar fate; their dynamics were affected by E H /pH, DOC, and SO 4 2 . Our findings suggest that a release of Cd, Cu, Co, Fe, Mn, Ni, and Zn under different flood-dry-cycles can assumed what might create potential environmental risks in using metal-enriched floodplain soils. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Soil contamination by potentially toxic metals (PTMs) is of serious environmental concern. Many floodplain soils are polluted with PTMs world-wide. For instance soils along the Elbe River (Germany) are contaminated mainly because wastes originating from different industrial activities during the last centuries were discharged into the river (e.g., Overesch et al., 2007; Rinklebe et al., 2007; Shaheen and Rinklebe, 2014). Elevated levels of PTMs, including Cd, Co, Cu, Ni, and Zn in riverine acidic soils may increase the solubility and leaching of these metals resulting an adverse impact on the agricultural environment (Hobbelen et al., 2004; Yang et al., 2013). The release of many PTMs is a concern for floodplain ecosystems and for surface- and groundwater quality since these elements might be released from soil solid phase to soil solution particularly under different flood-dry-cycles, and thus, they can be transferred to the ecosystem and food chain, thereby posing a hazard to environment and human health. Therefore, to elucidate the dynamics and release kinetics of PTMs including their controlling factors in floodplain soils is highly relevant and challenging at the same time. The results are required to answer both scientific and practical questions regarding protection of groundwater and plants, sustainable management of soils or explain the pathways of environmental harmful substances (Wennrich et al., 2012). Wetlands are characterized by a highly dynamic and variable hydrological regime, which have considerable impacts on the metal mobilization (Reddy and DeLaune, 2008). Dynamics of redox- sensitive processes is of large importance for flooded soils as the location of the oxiceanoxic interface is subject to change due to fluctuating water table levels (Du Laing et al., 2009a). Dynamics and release of PTMs in floodplain soils is determined by a complex of effects as metal concentrations, redox potential (E H ), pH, adsorp- tion/desorption processes, the presence of iron (Fe) and manganese (Mn) oxides, organic matter (OM), and total sulfur (S t )(Rinklebe and Du Laing, 2011; Rupp et al., 2010). According to the state-of-the-art of soil science in floodplains, we hypothesized that the periodic inundation of floodplain soils affects the dynamics of PTMs due to changes of E H /pH-values, dissolved organic carbon (DOC), and the chemistry of Fe, Mn, and S. Despite a number of scientific investigations, our knowledge regarding specific mechanisms prevailing at floodplain soils and resulting approaches for the purposefully control of the mobility and dynamics of PTMs under different flood-dry-cycles is lacking. * Corresponding author. E-mail address: rinklebe@uni-wuppertal.de (J. Rinklebe). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2014.04.035 0269-7491/Ó 2014 Elsevier Ltd. All rights reserved. Environmental Pollution 191 (2014) 223e231