The paper is an attempt to analyse whether there is or is not a relation between the thickness of ice covers that form on flow-through lakes under constant hydrometric supervision and on endorheic lakes not under constant hydrometric supervision. In order to do so, two benchmark lakes were selected – Raduńskie Górne and Ostrzyckie and six endorheic lakes: Kamionko, Kniewo, Stare Czaple, Zamkowisko, and Żuromino, including one seasonal outflow lake – Boruckie. Additionally, data on air temperature was also taken into consideration so as to determine the thermal characteristics of the analysed period. The data was obtained from the Limnological Station of Gdansk University, collected during patrol research carried out in the winter seasons of 2003–2008. In order to evaluate the formulas, additional measurements were made in 2016. The analysed lakes are located within the water catchment area of the upper Radunia in the central part of the Kashubian Lakeland. The benchmark lakes are located in the Radunia-Ostrzyce tunnel valley while the endorheic ones are located on the postglacial upland. The data analysis has revealed a strong relationship between the ice cover thickness on the benchmark lakes and the endorheic ones. Based on the analysis, models were developed for calculating ice thickness on the small endorheic lakes.

This article is an attempt to analyse and compare several selected parameters regarding ice phenomena using the correlation analysis of two lakes, which are benchmark lakes located in the central part of the Kashubian Lakeland. These lakes are: Raduńskie Górne, a larger one (387.2 hm2) and Ostrzyckie, a smaller one covering an area of 308.0 hm2. The analysis covered measurement sequences for the period 1971–2010. The material for analysis regarding data on ice phenomena on Lake Raduńskie Górne was obtained from the University of Gdańsk Limnological Station in Borucino while the data for Lake Ostrzyckie was obtained from the Institute of Meteorology and Water Management (IMGW). Relations between the following parameters of the ice regime were analysed: duration of the ice phenomena, duration of the ice cover, average and maximum thickness of the ice cover. The analysis and data comparisons have revealed that there are strong and very strong relations between the analysed parameters, which made it possible to develop proper statistical models. Hence, should there be a lack of data on the ice-cover pattern for one of these lakes it is possible to recreate them using the elaborated empirical models and data for the other.

The lakes selected for the analysis are situated in the Kashubian Lakeland which is a proper research area as there is a benchmark lake with a long data series within the region. This lake is located in the central part of the lakeland, in the upper Radunia water catchment area, while the lakes not being hydrometrically supervised constitute part of the upper Łeba water catchment area. The main objective of this study is to determine the relationship between ice cover thickness on the flow-through lake undergoing constant hydrometric supervision and some selected flow-through lakes not being monitored. The following lakes were selected for the study: Lake Raduńskie Górne (the benchmark lake) and four hydrometrically unmonitored lakes: Długie, Wielkie, Reskowskie and Łapalickie. The fieldwork research was done in the period of 2003–2008. Moreover, in order to evaluate the data calculated with the use of empirical formulas, additional fieldwork research was carried out in 2016. The analysis made it possible to develop formulas that allowed the thickness of the ice covering the selected flow-through lakes of the upper Łeba water catchment area to be assessed with decent accuracy.

Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes ... Limnological Review (2011) 11, 4: 135-142 DOI 10.2478 IntroductionLake oxygen content is one of the basic factors affecting lake ecology. A variety of aqueous organisms considered to be aerobes limit their reproductive activity and may even suffer physical elimination in the face of oxygen deficits or a complete lack of oxygen in water. At the same time, lake water oxygen levels determine the number and vertical distribution of many species. Furthermore, oxygen content in water is a control factor of the redox state of other important elements in a lake ecosystem, such as carbon, nitrogen, phosphorus, iron, and manganese. Consequently, oxygen levels determine conditions of their circulation in a water body.Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes in northern Poland Abstract:The oxygen content in a lake is a fundamental factor in lake ecology. In stratified lakes, deep waters are isolated from the atmosphere for several months during the summer; therefore, oxygen (substantially consumed by biological and chemical processes at this time) cannot be replaced before the autumnal mixing period. Hypolimnetic oxygen depletion has been considered an indicator of lake productivity since the early twentieth century. Many recent studies have been in opposition to this view by showing that the areal hypolimnetic oxygen depletion rate (AHOD) is poorly correlated with seston biomass and/or phosphorus concentration. The objective of this study is to show relationships between the mean values of total phosphorus (TP), total nitrogen (TN), chlorophyll a, and water transparency (Secchi disk depth, SDD) during the thermal stratification formation period and the AHOD rate. Hypolimnetic oxygen conditions in five dimictic lakes in northern Poland were examined in 2009 and 2010. Two of them were studied in the previous year. Monthly oxygen profiles taken from April to August, midsummer temperature profiles, and morphological data of the lakes were used to determine the AHOD rate. Standard water quality parameters such as concentrations of chlorophyll a, TP, and TN, as well as water transparency measured at the same time were used to calculate the trophic state indices (TSI) according to the Carlson-type formulas.On the basis of the collected data it is shown that AHOD is highly correlated with the TSI value for chlorophyll a, and poorly correlated with the TSI values for water transparency and phosphorus content. The best correlation between AHOD and TSI has been found for chlorophyll a (r 2 =0.702; p<0.001), as well as for overall TSI, determined by averaging separate component indices (r 2 =0.826; p<0.000). No correlation was found between AHOD and total nitrogen concentration. The research also confirmed previous observations, which pointed to a significant role of the hypolimnion depth in increasing oxygen deficits.

Abstract:The paper presents assessment results of the ice dynamics on Lake Raduńskie Górne (Upper Radunia Lake) based on long-term observations of the course of ice phenomena. Interannual changes in lake ice phenology parameters (freeze-onset, ice-on, freeze duration, melt-onset, permanent ice cover duration, ice-off, melt duration) in the years 1961-2010 are discussed. In addition, the ice cover thickness was taken into consideration. The analysed parameters of ice phenology were compared to each other as well as to the mean air and water temperatures of the winter half-year (November-April). The main periods of the ice regime of the lake have been determined and described. The permanent ice cover constitutes on average 79%, freeze-up period 13%, and break-up period 8% of the whole time of ice phenomena. It was shown that the weather parameters crucial for ice formation are the mean air and surface water temperatures. On Lake Raduńskie Górne the ice phenomena can only occur when mean air temperature in the winter half-year, at Borucino wheather station, is lower than 4.9°C, and water temperature (at a depth of 0.4 m) is lower than 5.7°C. In turn permanent ice cover is created when the mean air temperature of the winter half-year is lower than 3.9°C. The maximum and mean ice cover thickness on Lake Raduńskie Górne ranged, respectively, from 0.5 to 50 cm, and from 0.5 to 38.3 cm. These parameters were strongly positively correlated (r = 0.87-0.88, p <0.05) with the duration of the ice cover period.