1. Environmental Change Assessment Group, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
2. Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden,
3. Departmento de Edafologia y Quimica Agricola, Faculty of Biology, University of Santiago de Compostela, E-15706 Santiago de Compostela, Spain