The chemical composition of surface water and groundwater is subject to constant changes, which result primarily from meteorological factors (for instance, size and intensity of atmospheric precipitation), hydrological factors (for instance, the degree of hydration of the mountain massif and changes in river flows), and geological-lithological factors (the type of bedrock). The aim of the present research was to examine the hydrological and chemical regime of surface and underground waters in the Bystra and Sucha Woda mountain stream catchments. Between December 2013 and December 2016, 77 series of measurements were collected at the rhythm of twice a month (n = 611 water samples) from 8 sites, which represented both surface waters (watercourses, ponds) and underground waters (karst springs). The studied area possesses very distinct geological duality. The southern part is a crystalline region, and the northern part is made up of sedimentary rocks. During the field studies, the following have been measured: water levels of the watercourses, flow rates, and physicochemical characteristics of water, such as electrical conductivity, pH and water temperature. At the same time, water samples were collected for laboratory analyses, which included general mineralization and concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃⁻, SO₄²⁻, Cl⁻, NH₄⁺, PO₄³⁻, NO₃⁻, Li⁺, Br⁻i F⁻ions. The geological structure had the greatest impact on the chemical composition of waters in the Bystra stream and Sucha Woda stream catchments. The waters representing the crystalline region were characterized by significantly lower total mineralization, lower specific electrical conductivity, and lower ion concentration than water in the crystalline-sedimentary (karst) region. The average value of total mineralization in the crystalline region was 14.3 mg · dm⁻³, and in the crystalline-sedimentary region – 81.2 mg · dm⁻³. The waters in the crystalline region were characterized by a demonstrably lower pH (average pH of 6.5) than the water in the karst region (average pH of 7.7). Low values of mineralization, electrical conductivity and concentration of main ions were accompanied by increased flows during the summer and autumn. In all the waters subjected to testing, there was also a marked decrease in the value of these parameters during the spring thaw. In the feeding of streams and karst springs during this time, slightly mineralized melt-waters had their significant share. In spring, there was also the greatest variation in the chemical composition of the studied waters. This variability was clearly lower in the lower Bystra karst spring than in the Goryczkowa karst string. It was most likely related to a different rate of melt-water inflow to the two karst springs. In all the tested waters, the highest values of total mineralization, electrical conductivity and concentration of main ions occurred during the winter low discharge, which resulted from the predominance of underground feed in the river’s runoff. In all the studied waters, a clear decrease in NO₃⁻ concentration was observed during the summer and autumn months. Most probably, this was associated with increased NO₃⁻ uptake by plants during the growing season. In the waters of streams draining the crystalline part of the Bystra stream catchment there was clearly lower nitrate concentration than in the Bystra stream waters draining the crystalline-sedimentary (karst) part. The chemical composition of the Bystra stream water, draining the crystalline-sedimentary (karst) part of the catchment, was strictly dependent on the chemical composition of groundwater from the Goryczkowy and lower Bystra karst springs.
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