The results of the watershed position ANOVA tests revealed statistically significant differences in salinity and Na+ between the three watershed positions.  Both USC and MSC contain land use types suspected to be major sources of pollution. USC comprises a built-up area, which includes part of the Lusaka city CBD and an industrial area (point sources of pollution). These locations discharge drainage containing high amounts of dissolved salts and cations, such as Na+. However, apart from receiving runoff with high salinity levels from USC, MSC introduces diffuse sources of pollution from commercial farmland. As runoff proceeds downstream to DSC, sources of emission for salts and Na+ decrease. Loading of colloidal material is also reduced by coagulation, which is enhanced by dissolved organic matter (Wilkinson et al., 1997; Ma et al., 2001; Ma & Liu, 2002), resulting in the comparatively low salinity and Na+ levels observed under DSC.