1. Dep. of Bioscience; Aarhus Univ.; Vejlsøvej 25 8600 Silkeborg Denmark
2. Dep. Aquatic Ecosystem Analysis, Helmholtz Centre for Environmental Research (UFZ); Brückstr. 3a 39114 Magdeburg Germany
3. Dep. of Agroecology; Aarhus Univ.; Blichers Allé 20 8830 Tjele Denmark
4. Dep. Environmental and Biochemical Sciences; The James Hutton Institute; Craigiebuckler Aberdeen AB158QH Scotland UK