Discharge is one of the most important quantitative characteristics of springs. Not only does it specify the yield of groundwater, but it also reflects the water retention conditions of the aquifers. An analysis of the long-term spring discharge allows to link them to the hydrogeological and meteorological conditions of the area as well as to calculate the seasonal and multiannual variability parameters. The data from 84 springs in the south of Poland from the PIG-PIB databases were used in the paper. The time series differ in length and come from the period 1973–2016. The spring discharge variability index varies widely: from 2 to over 2 thousand, wherein the contribution of slightly variable, variable and highly variable springs is around 33%. The discharge of individual springs featured significant seasonal variations. Not only does the volume of outflowing water depend on the atmospheric conditions, but primarily on the properties of aquifer which feeds the spring’s groundwater catchment and on its location. The discharge of fissure springs as well as low-flow outflows is generally more variable than that of porous or karst springs. The seasonality of discharge depends less on the discharge of the spring and more on its elevation – springs which are at higher altitudes are characterized by a bigger seasonality index of discharge and a later date of its yearly peak discharge.

The aim of the study is to identify the flow seasonality of the Vistula river in 14 water-gauge cross-sections located along the river course (from Skoczów to Tczew). For this purpose, the following characteristics were used: seasonality index (IS), period of seasonal concentration (PK) half-flow date (TPO), and concentration index (GMO).  Hydrometric data from the 1951–2016 period were shared by IMGW-PIB. The average time of seasonal concentrations and half-flow dates in the analysed cross-sections occurred in April or May. Along the Vistula river the mean PK and TPO regress towards winter (are earlier and earlier). The average seasonality index is comprised in the range 22–32%, while  the values of the concentration index fall into the range 10.0–14.5. The highest IS values characterize the upper part of the river down to the Goczałkowice water-gauge (here it reaches the maximum). Next the IS rapidly decreases, due to the summing of the flows from the Vistula river tributaries varying conditions of flow formation (from Carpathian Mountains and Uplands). A significant increase in the IS is visible below the mouths of the Dunajec and then the San rivers. A local maximum of the seasonality index occurs in the Zawichost cross-section. Next, the IS slowly decreases along the river down to the Vistula river mouth. One exception is the Włocławek water-gauge where a small increase of the IS can be noticed. It is due to the functioning of a dam and a big reservoir in the town. The changes of the concentration index along the Vistula river are similar to the seasonality index changes but the differences between the values of extremes are less visible. In the five analysed flood years, both the seasonality indexes and the concentration indexes were quite high in the upper part of the Vistula river and average in the central and lower parts of the river. The half-flow dates and the periods of seasonal concentration were stable along the whole river’s course but very diversified in particular years. The changes of the examined seasonality characteristics in dry years were very similar to analogical changes in normal years. Only in 1959 was the situation different when the IS was very low and the PK and TPO occured later and later down the river’s course.

Runoff from a karstic catchment (southern part of the Krakow–Częstochowa Upland) was analyzed. The Prądnik-Ojców river gauge station, which closes the upper and the most interesting from the hydrological point of view part of the catchment (67.5 km2), was selected for detailed analyses. The 1961–2014 timespan was studied. Characteristic  water discharges and runoff structure were analyzed. Based on the results, water resources were evaluated as large. The specific discharge reached 6.5 dm3∙s–1∙km–2, being slightly higher than the average for Poland (5.62 dm3∙s–1∙km–2), but comparable to other karstic catchments located in the Upland Belt of Poland. The discharge is stable both in the annual hydrological cycle as well as in the multiannual course. The 53-year long series did not reveal any statistically important tendencies in runoff and the multiannual changes of runoff were predominantly related to changes in precipitation. The structure of runoff is dominated by groundwater runoff, which reached 90% on average, and the unit groundwater runoff reached 5.8 dm3∙s–1∙km–2. This value is a little higher (up to 1.5 dm3∙s–1∙km–2) in comparison with the neighboring karstic catchments.

The aim of this study is to investigate the distribution of soil temperature in a forest clearing in the Wielkopolska National Park. The results of measurements of ground temperature at depths of 0, 5, 10, 20, 50 and 100 cm at the UAM Ecological Station in Jeziory were analyzed. Characterization of the annual and diurnal course and the thermal stratification of the soil in the period 2002–2015 was made. The variability of soil temperature gradients between levels at different depths was investigated. During the warm period there is a lapse, and in the cold period an increase in the temperature with depth. In March and September a reversal of the thermal profile takes place in the ground. The greatest amplitude between the surface and the depth of 100 cm occurs in December and is 5,2°C. The amplitude is also high in June, i.e. 4,8°C. Temperature gradients decrease with depth. In the soil layer of 0–5 cm there are greater changes in temperature (on average 0,04°C/1 cm), and with depth the rate of change is lower (0,0001°C/1cm in the layer of 50–100 cm). A high thermal activity of soil in layers up to 20 cm is indicated by the smallest difference in temperature between the layers at the surface. The deepest layers store most heat. The layer of 20–50 cm is characterized by high heat accumulation in the warm half of the year – then the greatest differences between the 20 and 50 cm levels occur. The average diurnal ground temperature in Jeziory in the years 2002–2015 is 9,8°C and does not change with depth. The diurnal amplitude of temperature changes – it decreases with the depth. The highest amplitude of temperature is characterized by the lowest layers of soil and is 8,4°C on average throughout the day. The amplitude values decrease with depth to 0,0°C at a depth of 100 cm. It is clearly shown that the maximum temperature of soil is shifted in time with depth. The greatest diurnal changes of soil temperature in the warm half of the year are in the layer up to 50 cm, and in the cold half of the year – to a depth of 20 cm. The obtained results show that the thermal conditions of the ground in a forest clearing are different from those characterizing the ground  in open areas.

The work discusses the air temperature course of winter periods (December–March) in Poland in the years 1720–2015. The analysis is carried out for area mean values calculated from 5 stations: Szczecin, Wrocław, Warsaw, Wilno and Lwów. The time series of the mean area winter temperature (hereinafter PLZ) consists of combined observational (140 years) and  reconstructed (156 years) data. The PLZ reconstruction is based on independent variables, i.e. the values of the maximum area of the Baltic Sea covered with ice in a given ice season and the monthly temperatures in January and March from the Central England Temperature (CET) data set. The obtained correlations between the independent variables and the PLZ  are strong, highly significant and stable. A statistical analysis shows that the course of PLZ is strongly correlated (r = 0.80, p <0.001) with the series of mean winter temperatures in Europe reconstructed by Luterbacher et al. (2006). In the analysed period of the years 1720–2015 the course of winter temperatures is non-stationary, there were periods of cooling and warming with different amplitude and duration. The variation range of PLZ falls within the limits from –6.24 (in 1929) to +3.35°C (in 1990). Winters with temperatures below 0°C account for 72% of winters in the examined period. Relatively mild winters dominated  ver Poland during the analysed period, with an average temperature ranging from –1°C to 0°C and from 0°C to 1°C, accounting for a total of 39.5% of all winters. The trend occurring in the PLZ time series is very weak (+0.0020 (±0.0012)°C·year–1; p = 0.103) and statistically insignificant, despite the fact that the highest PLZ values in the entire analysed period occur after the year 1988. The analyses show that the variability of PLZ in the entire examined period does not go beyond the limits of natural variability and the recent increase in PLZ is not unprecedented. Similarly strong temperature increases in winter temperatures were observed several times after the year 1720. The coldest winters occurred between the decades 1751–1760 and 1841–1850. The greatest variability of PLZ is observed in the twentieth century, when the coldest (1961–1970, decade mean PLZ –2.253°C) and the warmest decades (1991–2000, PLZ +0.020°C) occurred in the entire analysed period. The breakthrough in the course of PLZ, combined with the change in the thermal structure of winters, which can be identified with the end of the Little Ice Age, occurred gradually in the years 1858–1885 along with an increase in the intensity of the zone circulation. Changes in the solar constant and the frequency of volcanic eruptions did not affect the variability of winter temperatures.

Areas located within the hot, arid zone are characterized by extremely low availability of fresh water. In the Tunisian regions of Kébili and Medenine, deep-water sources and connate groundwater constitute its main sources. Surface waters, as well as shallow groundwaters found in those areas, are affected by a high level of salinity, which significantly reduces their use for either drinking or agriculture. Due to intensifying droughts the rainwater accumulation system, neither fulfils the needs of residents nor the developing agriculture. Waters in the oases of El Faour (Kébili) and Beni Kchedeche (Medenine) were analyzed in 2017 to find out their chemical composition, as well as their suitability for irrigation. The chemical composition of the investigated waters is dominated by the Na+, Ca2+, Cl– and SO4 3– ions. The value of electrolytic conductivity (EC) was found to be within the range of 1100 to 6400 μS/cm. The highest concentration of nitrate was 44 mg/L. Salinity indicators classified this water mainly as unsuitable for irrigation on the basis of sodium adsorption ratio (SAR) and EC, sodium total percentage (%Na) and Kelly’s ratio (KR). The iron concentration in all examined wells exceeded the recommended values set for potable water and ranged from 0.6 to 2.5 mg/L.

The study area is located in the gorge section of the Upper Vistula river valley between Tyniec and Piekary near Kraków, where natural and industrial overbank alluvia with a different radionuclide activity, heavy metals content and grain size composition occur. Overbank deposits cover three levels of the floodplain where three cores of deposits were  collected. Alluvia of the lowest level along the channel are more heterogeneous and coarser than those on the middle and the highest level. Most of the overbank deposits were accumulated in the lower regime of water flow. On the basis of luminescence dating it was determined that the accumulation of overbank deposits on the first level started  200 years ago and on the highest level – 3,000 years ago.
All the three alluvium cores investigated in this study show a similar and regular vertical pattern of 137Cs and 210Pb activity. The vertical distribution of 137Cs in the profiles reflects its postdepositional migration and soil mixing due to ploughing. At the same time the vertical distribution of 210Pb seems not to be disturbed by this process. Moreover,  he peaks of 137Cs are concomitant with a decrease in heavy metal concentration in the top part of all profiles. This reflects the diminishing of industrial activity in Poland after the early 80’s of the 20th century. The vertical profile of 210Pb activity in the two cores from the upper levels of the floodplain wasused for the estimation of accumulation rates which occur to be approximately 0.4 cm/year. The vertical differentiation of heavy metals concentration in these profiles reflects both the economic changes in this region over the last century as well as the fluvial activity of the Vistula river. The higher pollution in the upper parts of the two profiles can be correlated with the industrial period which began at the end of the 19th century and lasted up to the middle of the 20th century in the upper Vistula river basin (Silesian Upland and Kraków Upland). The decrease of pollution at the top of all the profiles have results from economic recession and pro-ecological activities since the 1990’s.