Our paper aims at identifying factors that determine seasonal changes in streamwater chemistry in three catchments with different land use (woodland, agricultural, mixed-use) in the Carpathian Foothills in southern Poland. The study involved weekly and biweekly water sampling in the 2003 and 2004 hydrological years and the analysis of specific conductivity (SC), pH, main ions, and nutrients. R-mode factor analysis was used to identify four factors: (i) streamflow, (ii) climate seasonality, (iii) water circulation, and (iv) nitrification processes. Despite the fact that the same environmental factors were identified in all three catchments, some factors produce a different type of ion response in different types of catchments. The streamflow factor produces the same changes in geologically controlled parameters (SC, main ions) in all catchments but different changes in nutrient concentrations in the woodland and agricultural catchments. In the woodland catchment, nutrients come primarily from diffuse sources (soil flushing), while in the agricultural catchment, nutrients come primarily from point sources (sewage) as result of unregulated wastewater management. The climate factor primarily controls the concentrations of nutrients. High temperatures during the vegetation season usually correlate with increases in nutrient concentrations, especially that of PO^{3-}_{4}. This atypical phenomenon is seldom reported in the literature, especially in relation to woodland catchments. The third factor is associated with water circulation in the catchment under different hydrological conditions – during flood events and during low-flow periods. The fourth factor is most likely associated with nitrification processes.