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Lake Śniardwy is the largest among more than 7000 Polish lakes. So far, it has not been a subject of detailed investigations concerning long-term changes in water temperature or ice regime. A considerable change in thermal and ice conditions has been observed in the period 1972–2019. Mean annual water temperature increased by 0.44°C dec−1 on average, and was higher than an increase in air temperature (0.33°C dec−1). In the monthly cycle, the most dynamic changes occurred in April (0.77°C dec−1). In the case of ice cover, it appeared increasingly later (5.3 days dec−1), and disappeared earlier (3.0 days dec−1). The thickness of ice cover also decreased (2.4 cm dec−1). Statistical analysis by means of a Pettitt test showed that the critical moment for the transformations of the thermal and ice regime was the end of the 1980’s. In addition to the obvious relations with air temperature for both characteristics, it was evidenced that the occurrence of ice cover depended on wind speed and snow cover. The recorded changes in the case of Lake Śniardwy are considered unfavourable, and their consequences will affect the course of physical, chemical, and biological processes in the largest lake in Poland.

The paper presents the applicability of LiDAR data in limnological research with respect to the identification of the shoreline of lakes, and consequently the scale of overgrowing of lakes. Data obtained from the Head Office of Geodesy and Cartography from the period 2011 2016 provided the basis for the identification of shorelines for 14 lakes of the Pomeranian Lakeland. The paper employs the orthophotomap for the determination of the range of lake vegetation. Using the line determined based on the orthophotomap and that determined based on LiDAR points, the zone of overgrowing of the analysed lakes was delineated. In all the analysed cases combined, the water surface area was found to be reduced in comparison to the shoreline identified through LiDAR scanning by 161.5 ha, suggesting a 21.2% share of vegetation in the surface area of lakes.

There are a total of several million lakes in the world, which includes only approximately 30 crater lakes. Due to this extreme global rarity, they are the subject of research in many scientific disciplines. In spite of the widespread interest in them, however, many issues still require detailed investigation. In the case of the Morasko crater lake (Poland), hydrological research has been weakly developed so far. The undertaken analysis, which employed a complex research procedure involving the use of georadar, geological corings and bathymetric measurements, aimed to determine the primary bottom of the lake, and further to determine the scale and rate of its evolution. The modern water level suggests that the lake basin is currently approximately 55% filled in with organic matter, and the rate of its sedimentation in the deepest place can be estimated at approximately 0.8 mm·y−1.

The paper presents the dynamics of daily water temperature fluctuations in Lake Kierskie (West Poland) and determines the effect of air temperatures and wind speed on the variability of the parameter (water temperature). The analysis was based on hourly water temperature values from the period from May 2012 to January 2018. The data analysis permitted the description of the thermal regime of waters in the lake in the hourly cycle in reference to each month, and designation of months characterised by the highest and lowest stability of water temperatures. More than half of the analysed days was characterised by a change in water temperature not exceeding 1°C. The course of water temperature showed strongly positive correlations with air temperature, and weak correlations with wind speed. Water temperatures in the lake were correlated the strongest with air temperatures with a 24 h time step.

Ice conditions in lakes are one of the basic factors considerably affecting the functioning of lake ecosystems, and the term of ice end modifies the course of further processes (thermal stratification, biological conditions, etc.) occurring outside the winter season. The paper presents the analysis of the effect of teleconnection patterns (NAO, SCAND, EA, EAWR) on ice conditions in lakes in North Poland, determining the relations between the teleconnection conditions in the cold half-year and selected features of the ice regime, i.e. dates of ice start and ice end, ice duration, and maximum ice thickness. Deviations of values of the aforementioned parameters in positive and negative phases of the considered teleconnection patterns were calculated in reference to mean values from the years 1956–2014. Two of them were determined to have considerable effect on the parameters of the ice regime, namely NAO, modifying ice start and ice end, ice duration, and maximum ice thickness in the season, and SCAND, considerably changing ice end, ice duration, and maximum ice thickness. The EA teleconnection pattern only affects ice end, and EAWR shows no correlations with the analysed ice parameters in lakes.

The historical effects of land development on water management currently require a new approach, in many cases involving attempts at the restoration of the quasi-natural state. This is evident in reference to many regions in Poland, where the hydrographic network has been diminishing over the centuries, among others in favour of obtaining new agricultural land. Such activities overlap with natural processes causing transformations of the hydrosphere. The most serious problems currently include water deficits resulting from climate change and human activity. This paper employed archival bathymetric maps from the beginning of the 20th century for the determination of the scale of changes in the morphometric parameters of six lakes in western Poland. It was determined that over a period of more than a hundred years, the surface area (12.2%) and original volume of water bodies (13.9%) were largely reduced. This situation was caused by both natural (overgrowing and shallowing) and anthropogenic (change in water level) factors. The obtained information points to the need of an inventory of historical bathymetric maps of lakes. In combination with modern research, this will allow for the determination of changes in the water resources of lakes and, in a longer-term perspective, potential possibilities of their renaturisation. This knowledge is important in the context of the reconstruction of water resources in the territory of Poland, where their deficits are recorded increasingly frequently. It should also be emphasised that the restoration of the natural capacity of water retention in lakes is a more economical solution and, most importantly, it is not invasive for the environment.

The objective of this study was to analyse spatial variability of the trace elements (TEs) and rare earth elements (REEs) concentration in lake bottom sediments in Bory Tucholskie National Park (BTNP); Poland. The following research questions were posed: which factors have a fundamental impact on the concentration and spatial variability of elements in bottom sediments, which of the elements can be considered as indicators of natural processes and which are related to anthropogenic sources. The research material was sediments samples collected from 19 lakes. The concentrations of 24 TEs and 14 REEs were determined. The analyses were carried out using the inductively coupled plasma mass spectrometry (ICP-QQQ). Cluster analysis and principal component analysis were used to determine the spatial variability of the TEs and REEs concentrations, indicate the elements that are the indicators of natural processes and identify potential anthropogenic sources of pollution. The geochemical background value (GBV) calculations were made using 13 different statistical methods. However, the contamination of bottom sediments was evaluated by means of the index of geo-accumulation, the enrichment factor, the pollution load index, and the metal pollution index. The BTNP area is unique because of its isolation from the inflow of pollutants from anthropogenic sources and a very stable land use structure over the last 200 years. This study shows high variability of TE and REE concentrations in lake sediments. The values of geochemical indices suggest low pollution of lakes bottom sediments. It was found that TEs originated mainly from geogenic sources. However, the concentrations of Li, Ni, Sc, Se, Be, Se, Ag, Re, Tl, Cd, Sb and U may be related to the impact of point sources found mainly in the Ostrowite Lake. Almost all REEs concentrations were strongly correlated and their presence was linked to with geochemical processes. The elements allowing to identify natural processes and anthropogenic pollution sources were Cr, Co, Cu, Ag, Cd, Zn, Bi, Re, Ba, Al and Rb in TEs group and Nd, Gd, Yb, Lu, Eu, Dy and Ce in REEs group. The analysis shows high spatial variability of TE and REE concentrations in lake sediments. The values of geochemical indices point to low pollution of lakes sediments. The anthropogenic sources only for two lakes had an impact on concentrations of selected TEs and REEs. The analyses allowed to identify elements among TEs and REEs documenting geochemical processes and those indicating anthropogenic sources of pollution.

Lake water-level fluctuation is a complex and dynamic process, characterized by high stochasticity and nonlinearity, and difficult to model and forecast. In recent years, applications of machine learning (ML) models have yielded substantial progress in forecasting lake water-level fluctuations. This paper presents a comprehensive review of the applications of ML models for modeling water-level dynamics in lakes. Among the many existing ML models, seven popular ML model types are reviewed: (1) artificial neural network (ANN); (2) support vector machine (SVM); (3) artificial neuro-fuzzy inference system (ANFIS); (4) hybrid models, such as hybrid wavelet-artificial neural network (WA-ANN) model, hybrid wavelet-artificial neuro-fuzzy inference system (WA-ANFIS) model, and hybrid wavelet-support vector machine (WA-SVM) model; (5) evolutionary models, such as gene expression programming (GEP) and genetic programming (GP); (6) extreme learning machine (ELM); and (7) deep learning (DL). Model inputs, data split, model performance criteria, and model inter-comparison as well as the associated issues are discussed. The advantages and limitations of the established ML models are also discussed. Some specific directions for future research are also offered. This review provides a new vision for hydrologists and water resources planners for sustainable management of lakes.

The paper presents a mineralogical analysis of sediments of the biggest lake in the Morasko Meteorite Reserve (Poland). The lake is filled by phytogenic sediments at the top, while at the bottom there are Neogene clays. The main components are: clay minerals in fine fraction and quartz and feldspars in coarse sandy fractions. The presence of disturbed ferrous zones suggests the existence of a dynamic factor that caused deformations in the sediments. Cavities, crevices, cracks, and traces of parching or fragmentation of mineral material can be interpreted as deformations related to the impact of meteorite fragments in non-consolidated soft sediments in the Morasko meteorite nature reserve. Meteorite fragments that left numerous deformed structures were most probably consituted meteorite debris that originated from the fragmentation of the meteorite before its impact.

The paper presents an attempt to assess the effect of damming of lakes on water resources, based on the example of Lake Powidzkie (Central Poland) and its catchment. The region in which the analysed object is located has the greatest water deficits in Poland. The co-occurrence of unfavourable natural and anthropogenic factors contributed to a considerable reduction in the water resources retained in the lake. Particularly low water levels were recorded in the 1990s and in the first decade of the 21st century. The situation was not improved by a water dam constructed on the out-flow from the lake in the 1960s, due, among other things, to neglect in its exploitation. With regard to the modernisation of the dam in 2010 and the favourable hydrological situation in the winter of 2011, it was possible to retain the excess water and substantially reduce its outflow. The restoration of the lost water resources, and the hydrological benefits of this were still observable several years later. Problems related to water deficits are becoming increasingly common in many regions of the world. One solution to mitigate such a situation may be, among others, to dam natural lakes. This is simpler, cheaper, and less invasive for the environment than the construction of new water reservoirs.

The paper presents an analysis of water temperature fluctuations in four rivers: Nysa Łużycka, Bóbr, Bystrzyca, and Nysa Kłodzka, in south-west Poland (Fore-Sudetic region) in the period 1971–2014. The obtained results show an evident increase in water temperature ranging from 0.15 °C·dec/1to 0.33 °C·dec/1. Such changes were particularly determined by changes in air temperature. Water temperature increased in two analyzed stations: Zielona Góra and Wrocław by 0.37 and 0.35 °C·dec/1, respectively. While the variability of the rate of warming of particular rivers in the analyzed region should be associated with local factors occurring in the catchments, the contribution of forest cover is of key importance. A change in water temperature constituting its primary parameter will cause further transformation of the discussed river ecosystems. Combined with poor water quality, rising water temperatures can become a factor inhibiting further economic development of the Fore-Sudetic region in Poland.

The paper discusses changes in the hydrological regime of high mountain Lake Morskie Oko located in the Tatra Mountains, in the Tatra Mountains National Park, a UNESCO biosphere reserve (MaB). According to the research conducted in the years 1971–2015, its water stages decreased by 3.5 cm·dec−1, mean annual water temperature increased by 0.3°C·dec−1 and the duration of ice phenomena and ice cover was reduced by 10 day·dec−1. No considerable changes in maximum values of ice cover thickness were recorded. Such tendencies are primarily caused by long-term changes in climatic conditions – air temperature and atmospheric precipitation. The hydrological regime of the lake was also determined by changes in land use in the lake’s catchment and its location in high mountains.

Lake surface water temperature (LSWT) is a key indicator which drives ecosystem structure and function. Quantifying the impact of climate change on LSWT variations is thus of great significance. In this study, observed data of LSWT during the period 1969-2018 in a high mountain lake (Morskie Oko Lake, Central Europe) were analyzed. The results showed that the prominent warming of the LSWT and air temperature began around 1997. A logistic non-linear S-curve function was used to model monthly average LSWT. The non-linear model performed well to capture monthly average LSWT and air temperature relationships (Nash-Sutcliffe efficiency coefficient 0.86 and the root mean squared error 1.63 °C). Using the 2009-2018 period as base scenario, a sensitivity analysis was conducted. The results showed that the annual mean LSWT will likely increase about + 1.29 °C and + 2.64 °C with air temperature increases of + 2 °C and + 4 °C respectively at the end of the twenty-first century. If realized, such a scenario will cause serious consequences on lake ecosystem.

Northern Hemisphere lakes are losing their ice cover due to climate change. Here we explored six decades of observational data (1961–2017) showing trends in air temperature, wind speed and precipitation over northern Poland, as well as changes in the ice conditions for five lakes with different morphometry. We evaluated whether and to what extent climatic effects, including atmospheric warming, changing wind speed and rainfall during fall and winter, influence ice conditions in morphometrically different lakes in Northern Poland. Our analysis demonstrated that ice cover duration and thickness decreased at rates of 5.4 days decade−1 and 2.5 cm decade−1, respectively. Ice conditions were influenced (65–75%) by the direct effects of air temperature change and to some extent by an interaction of warming with wind speed and precipitation (5–10%). While stronger autumnal winds result in longer ice cover duration, the effect of precipitation is bimodal with either an enhancement of ice formation by autumnal rain or accelerated ice loss during spring. To project future changes in ice conditions, we used a 1D hydrodynamic lake model forced with four climate model projections under low, medium and high Representative Concentration Pathway (RCP) scenarios. Our simulations demonstrate that current ice conditions will stabilize under the low emission scenario (RCP 2.6) but decrease under both the medium and high emission scenarios (RCP 6.0 and 8.5). During the 21st century, the lakes are projected to lose their ice at a rate between 4.5- and 10-days decade−1 and ice thickness will decrease by between 3.0 and 5.0 cm decade−1. The rate of change will be greater in smaller rather than larger lakes and more so for those situated further inland. The probability of ice-free winters will increase for all lakes and among all future scenarios by between 4 and 69% with the highest potential frequency of ice-free winters in smaller and deeper but relatively wind-exposed lakes.

Dissolved oxygen in water (DO) is one of the primary parameters determining its quality. It remains in close relation to water temperature. The article presents results of DO and water temperature measurements performed for five stratified lakes in Poland in the years 2007-2014. The measurements were performed with monthly frequency in the summer half-year (May-October) in the deepest place of each of the lakes. The compared data show the complex character of the course of both of the parameters. The analysis of depth profiles revealed the prevalence of a decreasing tendency, or no tendency was recorded - both in the case of DO and water temperature. Due to the incoherent character of the water in the case of stratified lakes, a more detailed comparison was performed, referring to changes occurring in zones developed during summer stratification. It was determined that the temperature of the epilimnion was directly dependent on air temperature, and in all cases it showed an increasing tendency. Simultaneously, along with an increase in temperature, in the majority of cases, DO concentration in the zone decreased. In reference to the waters of the hypolimnion, increasing, decreasing, and no tendencies were recorded. The above distribution is determined by individual factors of the lakes - morphometry, trophic status, groundwater alimentation, etc. Several years of measurements of DO and water temperature in depth profiles of several lakes in Poland constitute valuable information on the current transformations of the environment of this part of Europe. In the future, the information can provide the basis for long-term analyses over the next decades, enriching global knowledge on those parameters of key importance for water ecosystems.

The paper presents water temperature fluctuations in coastal rivers (Rega, Parsęta, Słupia, Łupawa, Łeba) located in the southern Baltic Sea area in Poland. Based on the available detailed data on daily values of the analysed characteristic in the years 1971-2015, tendencies of changes in the period were determined. It includes an analysis of temperature fluctuations in reference to mean annual and mean monthly values. In all of the five cases, the mean annual temperature showed an increasing tendency. The value of water warming in particular rivers was approximate, and ranged from 0.26 °C∙dec-1to 0.31°C∙dec-1. At the monthly scale, the highest increase was recorded in April, and amounted to 0.46°C∙dec-1on average. Water temperature fluctuations were particularly determined by climatic changes, and strongly correlated with air temperature. Local factors characteristic for coastal rivers, i.e. presence of infrastructure of small water power plants and predominance of groundwater alimentation, had a secondary effect on changes in the thermal regime of the analysed rivers.

The paper presents the effect of North Atlantic Oscillation of macroscale atmospheric circulation (NAO) on the hydrological conditions of Lake Morskie Oko located at an altitude of 1392.8 m a.s.l. in the highest range of the Carpathians. The paper applied detailed hydrometric information from the years 1971-2010 concerning water level fluctuations, water temperature, terms of the commencement and end of ice phenomena and ice cover, as well as meteorological data concerning air temperature and atmospheric precipitation, and monthly and seasonal NAO indices. The performed analysis suggests that the majority of analysed hydrological characteristics of Lake Morskie Oko was not prone to variability of NAO intensity in its various phases. The situation results from the local conditions, particularly responsible for the course of processes and phenomena in Lake Morskie Oko, simultaneously obscuring the effect of macroscale factors.

The paper presents the analysis of tendencies in water level changes in 32 lakes in Poland during 1976–2010. Series of monthly, seasonal, and annual precipitation and air temperature for 9 meteorological stations were also studied. The trend analysis for all of the studied series of water levels in lakes showed high spatial and temporal variability. Series of annual water levels in the case of 6 lakes showed statistically significant increasing tendencies, and in 7 lakes, significant decreasing trends. Series of annual amplitudes in the majority of lakes (22) showed a decreasing trend, but they were statistically significant only in three cases. The tendencies for air temperature fluctuations are more statistically significant than precipitation. The key role in determining water level changes is played by local factors, particularly including human economic activity, obscuring the effect of natural factors on water level changes. The paper describes cases of changes in water levels in lakes under anthropopressure related to among others: agricultural irrigations, hydropower infrastructure, water transfers, navigation, or mining.

Prediction of rivers and lakes water temperature plays an important role in hydrology, ecology, and water resources planning and management. Recently, machines learning approaches have been widely used for modelling water temperature, and the obtained results vary depending on the kind of models and the selections of the appropriates predictors. In the present paper, a new family of machines learning are proposed and compared to the famous air2stream model, using a large data set collected at 25 lakes in the northern part of Poland. The proposed models were: (i) the extremely randomized trees (ERT), (ii) the multivariate adaptive regression splines (MARS), (iii) the M5 Model tree (M5Tree), (iv) the random forest (RF), and (v) the multilayer perceptron neural network (MLPNN). The models were developed using the air temperature as input variables and the component of the Gregorian calendar (year, month and day) number. Results obtained were evaluated using several statistical indices: the root mean square error (RMSE), the mean absolute error (MAE), correlation coefficient (R) and Nash-Sutcliffe efficiency coefficient (NSE). Obtained results reveals that the air2stream model outperformed all other machines learning models and worked best with high accuracy at all the 25 lakes, and none of the ERT, MARS, M5Tree, RF and MLPNN models was able to provides an improvement of the water temperature prediction compared to the air2stream.

Accurate water temperature forecasting in lake systems is important for environmental impact assessment and fisheries management, among others. In this study, two models are developed and applied for water temperature forecasting in lake systems: (1) the multi-layer perceptron neural network (MLPNN) model; and (2) the wavelet transform and MLPNN integrated model (WT_MLPNN). The models are applied to forecast daily lake surface water temperature (LSWT) of eight lowland Polish lakes. Long-term daily LSWT from eight lakes and daily air temperatures from seven meteorological stations are used for daily LSWT forecasting. The results from the two models are compared with those obtained from two other widely used models: the physically-statistically based hybrid air2water model and a non-linear regression model (S-curve). The modelling results show that the air2water model performs the best, followed by the WT_MLPNN, MLPNN, and the non-linear regression model. Overall, the air2water, WT_MLPNN, and MLPNN models reproduce well the seasonal and inter-annual variations of the LSWT dynamics in the eight lakes. The non-linear regression model, although providing the lowest accuracy, can still provide good preliminary estimates of the LSWT for the eight lakes. The outcomes of the present research can provide references for forecasting lake surface water temperature and sustainable management of lake ecosystems.

Lake disappearance is one of the results of water eutrophication which leads to lake shallowing and overgrowth, and small and shallow lakes are the most threatened with degradation. We studied the effect of lake shallowing on its overgrowth, taking into account the morphometric parameters of water bodies. The study was performed in 20 lakes located in the central west part of Poland. The degree of lake shallowing was evaluated on the basis of bathymetric maps made in the 1960s and studies carried out presently. Additionally, an analysis of littoral coverage and macrophyte growth forms was investigated. Moreover, the composition, intensity of phytoplankton blooming, and physico-chemical parameters of the lake water were analyzed. Redundancy analysis shows that the lake volume, average depth, shallowing rate, and change in volume were the parameters that most strongly correlated with the share of macrophytes in the lakes. According to the regression analysis, the share of emergent macrophytes was significantly correlated with lake shallowing. No relation was found between phytoplankton blooming and lake shallowing. Conversely, the lakes with the highest rate of shallowing were characterized by the greatest share of vegetation, which suggested that vegetation growth had a significant impact on lake shallowing.

The paper presents historical (1971-2015) and scenario-based (2006-2100) changes in surface water temperatures in 10 lakes of Poland. The analysis of historical measurement (1971-2015) showed that mean annual lake surface water temperature (LSWT) was characterised by an increasing tendency by 0.37°C∙dec-1 on average, and was higher by 0.01°C∙dec-1 than air temperature in the analogical period. The highest increase in LSWT was recorded in spring months (April, May) and in summer (July). The future changes in LSWT was based on simulations of 33 AOGCMs available in the scope of CMIP5 project for RCPs: 2.6, 4.5, 6.0, and 8.5. The developed empirical-statistical downscaling models (ESD) use the air temperature field as predictors, with consideration of autocorrelation for two preceding months. ESD models are characterised by high quality of reconstruction of water temperatures in the historical period, with correlation from 0.82 (December, February) to 0.93 (July). The future CMIP5 scenarios for the period 2006-2100 assume an increase in air temperature at the end of the 21st century from +1.8°C (RCP 2.6) to +5.1°C (RCP 8.5) in reference to the period 1971-2005. According to the downscaling models, this corresponds to an increase in water temperature in the analysed lakes ranging from +1.4°C (RCP 2.6) to +4.2°C (RCP 8.5) in the years 2081-2100, respectively, with evident variability between the adopted emission paths beginning from the period 2041-2060. At a monthly scale, water temperature will increase the slowest in February (2081-2100: RCP 2.6 = +0.5°C, RCP 8.5 = +1.8°C). The highest increase in temperature will occur from May to August (RCP 8.5 = +6°C in June).Substantial effects of transformations of the thermal regime are already observed today, e,g. in the reduction of the ice season length. According to developed scenarios, a further considerable increase in water temperature will be the primary factor determining the transformation of lake ecosystems. The obtained results provide a theoretical basis for further research conducted in the scope of many disciplines, among others hydrology, hydrobiology, ecology, water management, energy production, etc. In the case of Poland, issues related to low water resources per capita are particularly important. Contemporary studies concerning changes in water resources showed that the natural factor playing the key role in their reduction is temperature increase and therefore it should constitute for the possibly fast development of multidisciplinary concepts of mitigation policy to potential impact of climate change.

The objective of the paper was the determination of the effect of teleconnection patterns (North Atlantic Oscillation (NAO), Arctic Oscillation (AO), East Atlantic pattern (EA), East Atlantic/Western Russia (EAWR), and Scandinavian pattern (SCAND)) on changes in air and water temperature in Polish lakes. Correlations of circulation indices with air and lake water temperature were analysed in the monthly cycle. Deviations of values of such components in different phases of the analysed atmospheric circulations types from mean average from the years 1971 to 2015 were also determined. The research showed a variable effect of the atmospheric circulations types. The strongest effect on water temperature was observed in winter, when AO and NAO circulation showed particularly evident influence. Deviations of water temperature from mean values from the analysed multi-annual period generally oscillated around 1.0 °C, reaching a maximum value of 1.4 °C. The presented research shows the complexity of processes determining changes in lake water temperature, the course of which depends on many factors with both regional (e.g., ice cover on lakes) and local range (conditions of water exchange, human pressure).

This paper presents an analysis of the influence of the North Atlantic Oscillation on the pattern of lake ice phenology in Poland. The research embraced 22 lakes in Poland over the period 1961–2010. Strong relations were found to hold between NAO and individual characteristics of ice phenology. In a negative NAO phase, one can observe a later appearance of ice phenomena and ice cover compared with the average values, ice cover persisting even 30 days longer and being thicker even by more than 10 cm. In turn, in a positive NAO phase the duration of ice phenomena and ice cover is shorter, the cover being less thick and solid. The observed spatial differences in the effect of NAO on the pattern of ice phenomena in Poland show this matter to be fairly complex. The most significant factor changes in climatic conditions, which manifest themselves in the continentality of the climate growing eastwards.

This paper presents the effect of the North Atlantic Oscillation (NAO) on the thermal characteristics of lakes in Poland. In the analysis, the use was made of monthly air temperatures recorded at fifteen meteorological stations, water temperatures of twelve lakes, and Hurrell’s winter NAO indices. Over the study period (1971–2010), there was a marked increase in the temperatures of both, air and lake waters. Depending on the NAO phase, water temperatures were observed to depart from mean values, being markedly higher than average (even by 1°C) in the positive winter NAO phase. The differences in water temperatures were statistically significant in the winter-spring season. In turn, in the negative NAODJFM phase lake water temperatures in winter and spring were markedly lower than average (in March even by 1.0°C). The unique response of some lakes depends on their morphometric parameters, including their mean depth.

The paper presents the analysis of the course of ice phenomena on four lakes (Lednica, Żnińskie Duże, Biskupińskie, Powidzkie) in central Poland in the period 1976–2015. The obtained results show changes in their ice regime that occurred over the last 40 years. An advance of the term of decline of ice cover was determined (by 2.5 day·dec-1on average for all lakes), as well as a reduction of duration of ice cover (by 4.4 day·dec-1 on average for all lakes), and a decrease in its maximum thickness (by 2 cm·dec-1 on average for all lakes). Such a situation should be associated with the observed warming, as confirmed by the course of air temperature for station Gniezno, where in the period of the winter half-year (November-April), an increase in temperature was recorded by 0.37°C·dec-1.

In the context of the observed climatic changes, unfavourable extreme situations occur increasingly frequently, manifested by, among others, the occurrence of droughts and floods. In the case of Poland, the central part of the country, in administrative terms covering the Wielkopolskie Province, is considered a region with a deficit of water resources. Such a situation was and is determined by a combination of natural and artificial factors. The former ones result from low precipitation and high air temperatures. The latter are the effect of intensive economic development, including large-scale meliorations. Measures mitigating this unfavourable phenomenon are related to the expansion of small retention. Its scale in Wielkopolska is the largest in the country – both in terms of the number of objects and volume of accumulated water. The key component of increasing retention is damming of lakes. According to the presented results, considerable reserves are still available in its scope. With the assumption of increasing water level in lakes by 0.2 m, it could cause an increase in water resources by 31 million m3, and assuming such an increase at a level of 0.5 m, by 78 million m3.

The aim of this paper is to carry out the process of applying TRIZ in the mobile biogas station by using its tools and techniques. The design system was chosen as the field in which TRIZ has been approached. The TRIZ method was introduced and its unique capability to solve problems was presented. To adopt TRIZ methodology to achieve the objective the deep understanding of the system and the identification of the problem was needed. Therefore, this paper presents the mobile biogas station and compares it with the current needs of the market. The research stage was carried out by the systematic following the steps outlined by the Oxford Creativity handbook. Some TRIZ tools were used to overcome psychological inertia and pessimistic people influence encountered especially at the beginning of the work. Finally, the undertaken techniques enabled a feasible and novel mobile station to be designed. The concepts were developed and detailed computer-aided models were completed. They were also analyzed and evaluated by finite element method in terms of undergone structural stress.

The objective of this paper was to analyse the effects of catchment area forestation on the temperature of river waters. Two rivers, Czerna Wielka and Szprotawa, were covered in this research project and both are located in south-west Poland, running through the largest compact forest complex in the country, Bory Dolnośląskie. Both of the rivers are located within the same climatic region, and are similar in terms of their hydrology. Land use in the catchment area however is very diverse with 71.6% forest cover in the case of the Czerna Wielka River and direct contact of the forest with the river occurs over 68.3% of its length. For the Szprotawa River, the indices amount to only 39.3% and 21.6%, respectively. Data on the daily water temperatures for both of the rivers were obtained from the Hydrological Yearbooks of Surface Waters for the period 1969–1983. The mean annual water temperature in the analysed period in the case of the Czerna Wielka River amounted to 8.0°C, and in the case of the Szprotawa River it equalled 9.2°C. During the cooler half of the year (November-April), the mean water temperature for the entire examined period amounted to 3.8°C for Czerna Wielka, and 3.6°C for Szprotawa. Higher variability was recorded for the warmer seasons (May-October), where mean temperatures amounted to 12.1°C and 14.7°C, respectively. The obtained results concur with other similar research conducted around the world, and in the context of climate change are of practical value. The important role of forests in the moderation of thermal conditions is evidently unquestionable. Therefore, minimising the impact of unfavourable climatic changes on river ecosystems and their surroundings requires striving for appropriate forest management in the near-bank (buffer) zone along banks of both larger rivers and their tributaries

The paper presents the results of time-related changes in maximum temperatures in lakes. The analysis was carried out on the basis of 9 lakes located in the northern part of Poland. The analysis was based on daily water and air temperatures in the period 1971–2015. Mann–Kendall's and Sen's tests were applied to determine the directions and rates of change of maximum air and water temperatures. The average increase of maximum water temperature in analysed lakes was found to be 0.39 °C dec–1, while the warming trend of the maximum air temperature was 0.48 °C dec–1. Cluster analysis (CA) was used to group lakes characterised by similar changes of maximum water temperature. The first group included five lakes in which the values of the maximum temperature trends were 0.41 °C dec–1. In the second cluster the average value of maximum water temperature increase was smaller than in the first cluster (0.36 °C dec–1). Comparing the results of cluster analysis with morphometric data show that in the first cluster lakes are having a greater average depth, maximum depth and water transparency in comparison to the lakes of the second cluster.

The study evaluated the effect of environmental conditions and morphometric parameters on lake water temperature changes. The analysis was carried out on the basis of 14 lakes located in northern Poland. The assessment was based on the daily water and air temperatures from 1972 to 2016. It took into account the location of lakes (latitude, longitude, altitude) morphometric parameters (surface area, maximum and mean depth, volume), hydrological processes (rate of water exchange, course of ice phenomena), and trophic status (water transparency) as factors that can modify lake water temperature changes. Direction and rate of air and water temperature changes were analysed by means of Mann–Kendall’s and Sen’s tests. Cluster analysis (CA) was applied to group lakes characterised by similar water temperature changes. The effect of climatic and non-climatic parameters on a lake’s water temperature was assessed on the basis of principal component analysis (PCA). Water temperatures in the lakes in the years 1972–2016 were characterised by a higher rate of increase of 0.43 °C·dec−1 than the air temperature decrease of 0.34 °C·dec−1. The analysis showed a faster rate of heating of waters in western Poland. This can be explained by shorter duration of ice cover. Moreover, the changes of water temperature were affected by other factors, including the location of the lakes, their morphometric parameters, wind speed, water transparency and water exchange time.

The North Atlantic Oscillation is a macroscale type of circulation determining climate and hydrological conditions in Europe. The paper presents water level fluctuations in 19 Polish lakes in various phases of NAO of the winter season in the years 1976-2010. Correlations of the winter NAO index with monthly, seasonal, maximum, and minimum water stages, and annual water level amplitudes in lakes were calculated. Approximately 20% of the performed tests showed statistical significance. Lakes were recorded where the correlations were significant in a major part of the year, as well as lakes showing no significant correlations in any month. Deviations of mean water stages in the positive and negative phase of NAO from mean water stages were calculated for each of the lakes. This permitted classifying the lakes into two groups by Ward’s method based on deviations of water stages in the positive and negative phase of NAODJFMfrom average values. This resulted in the designation of 4 and 5 typological classes of lakes, respectively. Deviations of water stages in lakes in various phases of NAODJFMfrom mean values were determined to even exceed 20 cm. The study results can find practical applications in reference to water retention. In view of the observed environmental changes, it is possible that the hydrotechnical infrastructure on lakes will have to be developed in the future. Such a situation will permit the precise control of water level fluctuations for the purpose of the optimal adaptation of lakes for economic purposes.

Study region The study region comprises 25 lowland Polish lakes in the northern part of the country. The studied lakes provide domestic, industrial and agricultural water supply, and are major attractions for tourism, thus playing a significant role in the Polish economy. Study focus The expected impact of future climate change on lake surface water temperature (LSWT) was predicted using the air2water model, which relies solely on daily air temperature (AT) as model input. LSWT and AT observations for the period 1987–2016 were used for model calibration and validation. Then, historical (1987–2005) and future (2006–2100) AT time series from nine EURO-CORDEX climate models were used to project future LSWT under emission scenarios RCP4.5 and RCP8.5. New hydrological insights for the region The results showed that air2water can well reproduce daily LWST with root mean square errors lower than 1 °C on average. The warming trends of both AT and LSWT are expected to be lower than those observed in the past decades (after the 1980s), and ice cover and weak stratification conditions are expected to partially buffer the LSWT response to the high AT warming expected in future winters. However, the overall enduring warming will substantially alter future thermal dynamics, leading to a shortening of ice cover and inverse stratification periods, possibly leading to serious consequences for lake water quality and ecosystem health.