Long‐term simulated water balance and streamflow data for the territory of Poland with high spatio‐temporal resolution were reconstructed for the period 1951–2020 with a daily time step, using the Soil and Water Assessment Tool (SWAT) hydrological model. The spatial structure includes 4,381 sub‐basins and 47,725 hydrological response units. The SWAT model was extensively calibrated and validated following a two‐stage, multi‐site calibration method for 88 gauging stations across Poland. The simulations show satisfactory performance with a median Kling–Gupta efficiency of 0.73 and 0.7 in the calibration and validation period respectively. The model performance exceeded that of its predecessor, the SWAT model of the Vistula and Odra basins. The simulated hydrological data set covers daily water balance components at the sub‐basin level, including precipitation total, snowfall, snowmelt, evapotranspiration (actual and potential), surface runoff, soil water, percolation, groundwater recharge, groundwater flow, tile flow and water yield (all components in mm), and daily streamflow (m³/s) at the reach level. The data set is stored in an online, publicly available research data archive 4TU.Research Data (Marcinkowski, P., Kardel, I., Płaczkowska, E., Giełczewski, M., Osuch, P., Okruszko, T., Venegas‐Cordero, N., Ignar, S. & Piniewski, M (2021). PL‐SWAT‐51_20: a high‐resolution simulated water balance and streamflow data set for 1951‐2020 for the territory of Poland, 4TU.ResearchData. dataset, https://doi.org/10.4121/16843183).

Ewelina Mocior, Bartlomiej Rzonca, Janusz Siwek, Joanna Plenzler, Eliza Placzkowska, Natalia Dabek, Barbara Jaskowiec, Piotr Potoniec, Sylwia Roman, Dominik Zdziebko. Episodes 2015;38:21-30. https://doi.org/10.18814/epiiugs/2015/v38i1/003

To ensure the good chemical status of surface water across Europe, it is necessary to increase research on the comprehensive impact of land use and land cover changes, i.e., deforestation, on the natural environment. For this reason, we used data from 9-year environmental monitoring in the Wüstebach experimental catchment of the TERENO (Terrestrial Environmental Observatories) network to determine the impact of partial deforestation on solute fluxes and stream water ionic composition. In 2013, a partial deforestation experiment was conducted in the study area using a cut-to-length logging method. To this end, two headwater catchments were compared: one partially deforested (22% of the catchment area) and one untreated control catchment. The concentrations of ions in stream water, groundwater, and precipitation were analyzed: Ca²⁺, Mg²⁺, Na⁺, K⁺, Al³⁺, Fe_tot, Mn²⁺, NO₃⁻, SO₄⁻, and Cl⁻. Most of the ions (Na⁺, Ca²⁺, Mg²⁺, Cl⁻, and SO₄⁻) showed decreasing trends in concentrations after deforestation, indicating a dilution effect in stream water due to the reduction of the supply of solutes with precipitation in the open deforested area. The fluxes of these ions decreased by 5–7% in the first year after deforestation, although the stream runoff increased by 5%. In the second year, the decrease in ion fluxes was greater, from 6% to 24%. This finding confirms that only limited soil erosion occurred after the deforestation because the soil was well protected during logging works by covering harvester lanes with branches. Only K⁺ and NO₃⁻ ions showed increasing trends in both concentrations and fluxes in the partially deforested catchment in the first two to three years after deforestation. Spruce die-offs, common in Europe, may decrease the concentration and fluxes of base cations in surface water in a nutrient-limited environment. However, the simultaneous planting of young broad-leaved trees with post-harvesting regrowth could create a nutrient sink that protects the catchment area from nutrient depletion.

Flysch-type aquifers in the Eastern Carpathians usually feed periodic and low-discharge springs. However, in some areas, such as in the upper part of the Połonina Wetlińska Massif, perennial springs with a relatively high discharge were identified. Therefore, the aim of this study was to identify recharge and groundwater flow patterns of three high-discharge springs based on the response of spring discharge to rainfall and on the relationship between specific electrical conductivity of water and spring discharge. The relation between spring discharge and rainfall was investigated by cross-correlation analyses. Generally, cumulative rainfall over a period from 10 days to 3 months is most strongly correlated with discharge; however, the response time of spring discharge varies throughout the year. Faster response to rainfall occurs in the spring after snowmelt, while in the summer and autumn months the response time increases. Two flow systems were identified: 1) a relatively deep, fissure-pore flow system with a long response time to precipitation and 2) a shallow, fissure-dominated system with a short response time, which is superimposed on the longer response. A small range of specific electrical conductivity combined with the varying discharge of two springs suggests that dilution of groundwater by rainwater does not play a significant role. The differences in the studied springs’ response to rainfall can be attributed to the recharge area, regolith features and local bedrock structures, i.e. occurrence of joints and faults, monoclinal dip of rock layers and gravitational slope deformations including ridge-top trenches, which, thus far, have been underestimated in determining groundwater storage capacity in the flysch part of the Carpathians.