Plant communities in relation to flooding and soil contamination in a lowland Rhine River floodplain Aafke M. Schipper a, * , Kim Lotterman a, b , Rob S.E.W. Leuven a , Ad M.J. Ragas a , Hans de Kroon c , A. Jan Hendriks a a Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Environmental Science, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands b Bureau Natuurbalans e Limes Divergens, P.O. Box 31070, 6503 CB Nijmegen, The Netherlands c Radboud University Nijmegen, Institute for Water and Wetland Research, Department of Experimental Plant Ecology, P.O. Box 9010, 6500 GL, Nijmegen, The Netherlands Multiple contaminants and periodic flooding may pose cumulative stress to plants in lowland floodplains. article info Article history: Received 26 May 2010 Received in revised form 27 August 2010 Accepted 6 September 2010 Keywords: Canonical correspondence analysis (CCA) Heavy metals Multiple stress Stress ecology Vegetation abstract Using canonical correspondence analysis (CCA), relationships were investigated between plant species composition and flooding characteristics, heavy metal contamination and soil properties in a lowland floodplain of the Rhine River. Floodplain elevation and yearly average flooding duration turned out to be more important for explaining variation in plant species composition than soil heavy metal contami- nation. Nevertheless, plant species richness and diversity showed a significant decrease with the level of contamination. As single heavy metal concentrations seemed mostly too low for causing phytotoxic effects in plants, this trend is possibly explained by additive effects of multiple contaminants or by the concomitant influences of contamination and non-chemical stressors like flooding. These results suggest that impacts of soil contamination on plants in floodplains could be larger than expected from mere soil concentrations. In general, these findings emphasize the relevance of analyzing effects of toxic substances in concert with the effects of other relevant stressors. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction During the past century, large amounts of sediment-bound heavy metals have been deposited on the lowland floodplains of the Rhine River (Middelkoop, 2000). As a result, heavy metal concentrations in the floodplain soils commonly exceed environ- mental quality standards, indicating potential toxicological risks for the organisms in these floodplains (Leuven et al., 2005). Although effects for invertebrate fauna seem mostly limited (De Jonge et al., 1999; Hobbelen et al., 2006; Ma, 2004; Notten et al., 2005; Schipper et al., 2010; Schipper et al., 2008b), several studies conclude that contamination levels may be high enough to induce adverse effects in vertebrates, including protected top predator species (Kooistra et al., 2001; Schipper et al., 2008a; Van den Brink et al., 2003; Wijnhoven et al., 2006). However, whereas potential impacts on animals have been studied extensively, little attention has been paid to plants. Plants may be very sensitive to surpluses of partic- ular trace elements, with certain sensitive species showing signs of toxicity already at low heavy metal concentrations (Balsberg- Påhlsson, 1989; Kabata-Pendias and Pendias, 2001). This suggests that potential impacts of heavy metal contamination on the plant communities in the lowland Rhine River floodplains are not unlikely. In general, potential effects of toxicants on biota are difficult to verify under field conditions (Chapman et al., 2002; Klok and Kraak, 2008). Obviously, under field conditions a wide variety of abiotic factors (e.g., physicalechemical conditions) and biotic processes (e.g., competition) jointly determine the presence and abundance of species (Ter Braak, 1987). Hence, the absence of species from contaminated sites does not necessarily reflect exclusion due to toxicity (Chapman et al., 2002). This implies that a simultaneous analysis of all relevant environmental factors is needed both to distinguish potential effects of soil contamination from the influ- ences of other environmental factors and to place the effects of contamination in a realistic perspective (Loos et al., 2010; Van Straalen, 2003; Van Straalen and Van Gestel, 2008). For plants in floodplains, periodical flooding is generally considered an environmental factor of major importance (Huber et al., 2009; Van de Steeg and Blom, 1998; Van Eck et al., 2004; Voesenek et al., 2004). Flooding fills the soil pores with water, * Corresponding author. E-mail address: a.schipper@science.ru.nl (A.M. Schipper). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2010.09.006 Environmental Pollution 159 (2011) 182e189