1. Department of Ecology and Natural Resource Management; Norwegian University of Life Sciences; P.O. Box 5003 Ås 1432 Norway
2. Instituto Nacional de Pesquisas da Amazônia; Av. André Araújo 2.936 Manaus AM CEP 69.067-375 Brazil
3. Faculty of Environment and Natural Resources; University of Freiburg; Tennenbacherstrasse 4 Freiburg 79106 Germany
4. Biogeochemistry Dep.; Max Planck Institute for Chemistry; Hahn-Meitner Weg 1 Mainz 55128 Germany