1. a Natural Resources Area, CIRCE Research Institute , University of Zaragoza , María de Luna s/n, Zaragoza , 50018 , Spain Phone: Fax:
2. b Campus Tafira Baja s/n , University of Las Palmas de Gran Canaria , Las Palmas , Spain
3. c Water Department , Canary Islands Institute of Technology (ITC) , Playa de Pozo Izquierdo s/n. Sta. Lucía, Las Palmas , Spain