1. ALTERRA; Wageningen Univ. and Research Centre; Droevendaalsesteeg 4 6708 PB Wageningen the Netherlands
2. Dep. of Environmental Sciences, Soil Physics, Ecohydrology and Groundwater Management Group; Wageningen Univ. and Research Centre; Droevendaalsesteeg 4 6708 PB Wageningen the Netherlands
3. Lab. for Physical Chemistry and Colloid Science; Wageningen Univ. and Research Centre; Dreijenplein 6 6703 HB Wageningen the Netherlands
4. Faculty of Science and Technology; Twente Univ.; Langezijds LA 1727, P.O. Box 217 7500 AE Enschede the Netherlands