[1] Univ Northampton, Sch Sci & Technol, Northampton NN2 6JD, England
[2] Rhodes Univ, Dept Geog, ZA-6140 Grahamstown, Eastern Cape, South Africa
[3] Jozef Stefan Inst, Dept Environm Sci, Ljubljana 1000, Slovenia
[4] Univ Western Australia, Dept Civil Environm & Min Engn, Crawley, WA 6009, Australia