1. Dep. of Agroecology, Faculty of Science and Technology; Aarhus Univ.; Blichers Allé 20, P.O. Box 50 DK-8830 Tjele Denmark
2. Costa Rica Institute of Technology (TEC); Cartago 30101 Costa Rica
3. Dep. of Civil Engineering; Aalborg Univ.; Sofiendalsvej 11 DK-9200 Aalborg SV Denmark
4. Dep. of Soil, Water and Environmental Science; Univ. of Arizona; 1177 E. 4th St. Tucson AZ 85721