This heavy metal
contamination, with Cd and Zn for example, has accumulated
in the topsoil and leaches towards the surface water system
by different pathways, namely overland flow and subsurface
drainage, especially during periods with high groundwater
levels and high discharge rates (Rozemeijer and Broers,
2007). The contamination of surface water due to leaching of
contaminants already present and adsorbed to the soil on a large-scale is sensitive to changes in the location and
dynamics of the water table, drainage and stream discharge
fluxes (Bonten et al., in preparation).