Soil water chemistry dependence on water pathways and turnover

Water flow and transit in the soil are important to water supply and transport of chemical compounds. Flows through forested till soils are by vertical percolation in the upslope areas, groundwater flows along the slope to discharge in downslope sites. The flow is divided into slow and fast parts both in the unsaturated percolation and the saturated groundwater. Soil development influences the flow and in coarse grained and well drained soils groundwater flow is stable but in finer grained physically stratified soils, variations in flow are considerable. Large flows occur in the upper soil layers and small flows in deep layers. Chemical composition of soil water varies in a similar way. In the upper layers, water is more acid and has a lower content of base cations compared to deeper layers. In downslope areas discharging deep groundwater contributes to less acidic conditions also in the upper soil layers. This discharge and a dominating lateral water flow in the upper layers partly protect deep layers from acidification which is emphasised by slow water turnover in these layers.