Spatial Patterns of Stream Alimentation in Lowland Areas of Nw Poland a Hydrochemical and Geostatistical Analysis

Areas of the Last Glaciation in northern Poland differ widely as to the conditions controlling the formation of river runoff and solute loads. The aim of the research was to identify chief mechanisms of stream alimentation in this area depending on the scale of a catchment. The analysis rested on data from hydrochemical profiling. Three types of systems were found to occur: in spring-head catchments with areas of the order of 10 km, in small catchments (10 km), and in medium-sized ones (10–10 km). The first is connected with the mixing of soiland groundwater, the second, with the mixing of waters from relatively homogeneous subcatchments, and the third, with the mixing of groundwater from various water-bearing horizons. In headwater catchments, river waters reach a new physico-chemical equilibrium at a distance of 20– 40 m; in small catchments, two nested autocorrelation structures (150 and 400 m) reflect the sequence of land cover changes and distances between main tributaries; in medium-sized catchments, river waters demonstrate similarity at a distance of between 300 and 450 m and 1.2 km; it is controlled by the sequence of successive valley reaches of different origins (melt-out basins & ravines).The reported analysis justifies the hypothesis that in the areas of northern Poland covered by the Last Glaciation it is possible to identify the zones and forms of channel alimentation on the basis of hydrochemical interpretation of runoff recorded in gauging profiles only in the case of small catchments no larger than n × 10 km. In larger catchments, it is only possible to differentiate between ‘new water’ (direct fall of precipitation on the channel and the overland flow) and ‘old water’, composed of a mixture of soil water and the alimentation from various waterbearing horizons