The study aimed to determine the linkage between soil exchangeable potassium (K+) concentration and stream water K+ concentration during rainfall and snowmelt events. The research was performed in small catchments with different land use (i.e. woodland, traditional agriculture, experimental agriculture, mixed-use) in the Carpathian Foothills (Poland). All of the studied catchments whose hillslopes were covered with fragipan soils had a markedly lower hydraulic conductivity (Ksat) in the fragipan (Btx) than in the horizons lying above (A and E). These highly permeable horizons determine the K+ influx to streams during most event types except snowmelts with frozen soil. In the woodland catchment, stream water K+ concentrations during events are determined by a high vertical variability in Ksat and exchangeable K+ concentrations in soil profiles. Rapid flushing of K+ from the topsoil Ah horizon with higher Ksat and higher exchangeable K+ concentrations than in the lying lower E horizon resulted in a clockwise hysteresis of K+ in stream water during most events. In the agricultural catchments, changes in stream water K+ concentration during events were determined by distinct differences between soil exchangeable K+ concentrations on hillslopes and in riparian areas. For example, during rainfall events under dry antecedent conditions, exchangeable K+ concentrations in topsoil horizons on hillslopes were distinctly higher than concentrations of exchangeable K+ in riparian area soils. The inflow of alluvial water with a low dose of K+ before the inflow of throughflow from hillslopes with a high dose of K+ thus resulted in wide counterclockwise hystereses for streamwater K+.