ARE ION-EXCHANGE PROCESSES IMPORTANT IN CONTROLLING THE CATION CHEMISTRY OF SOIL AND RUNOFF WATERS

Soil- and stream water elemental concentrations from a subcatchment in the Lake Gardsjon area have been used to evaluate the importance of i on exchange processes on the transport of cations to aquatic ecosystem s. The importance of cation exchange processes in the upper organic an d upper B soil horizons was demonstrated using lysimeter water data fr om a recharge area and soil water flow simulated with SOIL model durin g winter rain events with high sea-salt concentration. The importance of the hydrological conditions, such as water flow and water pathway, silicate weathering and the ion exchange of Al with Hf on the streambe d materials in controlling cation concentrations in soil and stream wa ters are also discussed. With the SAFE model, the contribution of cati ons from ion exchange by depletion of base cations from the exchange m atrixes compared to from weathering was also assessed. SAFE calculatio ns indicate that the release rate of base cation by ion exchange to ru noff water has decreased since 1945 and is very low, approx. 0.1 keq/h a per year, at present time as a result of soil acidification due to S and N inputs.