Drought changes the dynamics of trace element accumulation in a Mediterranean Quercus ilex forest J. Sardans * , J. Pen ˜uelas Unitat d’Ecofisiologia CSIC-CEAB-CREAF, CREAF (Centre de Recerca Ecolo `gica d’Aplicacions Forestals) Edifici C, Universitat Auto `noma Barcelona, 08193 Bellaterra, Barcelona, Spain Received 20 June 2006; received in revised form 3 October 2006; accepted 6 October 2006 Drought increased biomass concentrations of As and Cd and favors exportation of some trace elements to continental waters in a Mediterranean forest. Abstract We conducted a field drought manipulation experiment in an evergreen oak Mediterranean forest from 1999 to 2005 to investigate the effects of the increased drought predicted for the next decades on the accumulation of trace elements that can be toxic for animals, in stand biomass, litter and soil. Drought increased concentrations of As, Cd, Ni, Pb and Cr in roots of the dominant tree species, Quercus ilex, and leaf Cd con- centrations in Arbutus unedo and of Phillyrea latifolia codominant shrubs. The increased concentration of As and Cd can aggravate the toxic capacity of those two elements, which are already next or within the levels that have been shown to be toxic for herbivores. The study also showed a great reduction in Pb biomass content (100e135 g ha 1 ) during the studied period (1999e2005) showing the effectiveness of the law that prohibited leaded fuel after 2001. The results also indicate that drought increases the exportation of some trace elements to continental waters. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Arsenic; Aluminum; Cadmium; Climate change; Holm oak; Jasmine box; Lead; Mediterranean forest; Quercus ilex; Strawberry tree; Trace elements 1. Introduction In Mediterranean ecosystems the most serious effects of climate change (IPCC, 2001; Pen ˜uelas et al., 2005) are expected to be related to increased drought, since water stress is already the principal constraint in the world’s Mediterranean environments (Specht, 1979; Mooney, 1989). In the Mediterra- nean Basin precipitation is already either exhibiting a long- term downward trend, principally in the dry season (Kutiel et al., 1996; Esteban-Parra et al., 1998), or showing no signs of significant change (Pin ˜ol et al., 1998; Pen ˜uelas et al., 2002; Pen ˜uelas and Boada, 2003). Nevertheless, in all cases a rise in the evapotranspiration potential has led to increased aridity (Pin ˜ol et al., 1998), because temperatures in the Med- iterranean Basin have risen significantly (Kutiel and Maheras, 1998; Pen ˜uelas et al., 2002; Pen ˜uelas and Boada, 2003). As well, other increasingly intrusive anthropogenic disturbances are occurring in Mediterranean areas in recent decades; the number and intensity of sources of trace elements (rubbish tips, smelter stacks, fertilizers, waste incineration, vehicle ex- haust, and sewage sludge) have increased, thereby increasing overall concentrations of environmental trace elements (Koch and Rotard, 2001; Pen ˜uelas and Filella, 2002; Sardans and Pen ˜uelas, 2005a). Interactions between the predicted drought and trace ele- ment pollution and accumulation in Mediterranean ecosystems will have to be studied if we are to fully appreciate the real impact of climate change on ecosystems. Some experiments have shown that recent climate changes have had a strong im- pact on pollution pathways in Arctic ecosystems (Macdonald * Corresponding author. Tel.: þ34 93 581 18 77; fax: þ34 93 581 41 51. E-mail address: j.sardans@creaf.uab.cat (J. Sardans). 0269-7491/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2006.10.008 Environmental Pollution 147 (2007) 567e583 www.elsevier.com/locate/envpol