Rajmund Skowron

Ice cover as an indicator of winter air temperature changes : case study of the Polish Lowland lakes

Abstract Observations of ice cover and winter air temperature measurements were carried out on six lakes in northern Poland during the period 1961–2000. Detailed analyses of the dates of formation and termination of the ice cover, the duration of maximum thickness and ice-free period during winter were carried out. Various tendencies were found in the time series of the earliest freeze-up dates, whereas the latest ice break-up dates were recorded to occur much earlier than in the past on all the lakes, with time advance being on average from 0.6 to 0.8 day year−1. The period with ice cover has been getting shorter at the rate of 0.8 to 0.9 day year−1, with the exception of Lake Hañcza, the deepest lake in the European Lowland, where the rate of 0.4 day year−1 was recorded. Similarly, there was a decreasing tendency in the maximum thickness of the ice cover, at the rate of 0.26 to 0.60 cm year−1. Despite similar tendencies, all those changes showed diverse dynamics in particular lakes. The proposed indicator of the ice cover stability confirms the above statements, and thus, the undergoing climatic changes.

CHANGEABILITY OF THE ICE COVER ON THE LAKES OF NORTHERN POLAND IN THE LIGHT OF CLIMATIC CHANGES

The study is based upon instrumental observations of ice covers which formed on the lakes in northern Poland in the period 1956–2005 and records of air temperature measured at 9 meteorological stations in the period 1960–2005. Relations between mean dates of ice cover freeze-up, ice cover duration, maximum ice thickness, and also other properties of ice regime indicate obvious dependency upon air temperatures in winter months (December-February). Both air temperatures and main properties of ice covers revealed definite trends, showing the increase in air temperature in winter (0.04–0.06°C year-1), earlier disappearance of ice cover (0.5–0.6 day year-1), its shorter duration (0.6–0.7 day year-1), and decreases in maximum thickness of the ice cover (0.2–0.25 cm year-1). The author shows considerable statistical relations between main properties of the course of the ice cover, air temperatures in winter and the NAO winter indexes. Therefore, changeability of the ice covers on the lakes in northern Poland in the latter half of the twentieth century may be treated as another proof and an indirect indicator of climatic changes undergoing in this part of Europe.

Effect of the North Atlantic Oscillation on the Pattern of Lake Ice Phenology in Poland

ab]AbstractThis 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.

Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes in northern Poland

Relationship between areal hypolimnetic oxygen depletion rate and the trophic state of five lakes in northern Poland 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 (r2=0.702; p<0.001), as well as for overall TSI, determined by averaging separate component indices (r2=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.

WATER TEMPERATURE AND ITS DIVERSITY IN THE DEEPEST LAKES OF THE TUCHOLA FOREST AND THE KASHUBIAN AND BRODNICKIE LAKELANDS

Abstract This study presents the results of monthly examinations of the vertical distribution of water thermal structure (2008-2011) carried out over a four-year period in the deepest lakes located in the Kashubian and Brodnickie Lakelands and the Tuchola Forest1. Three lakes were selected for examination (Raduńskie Górne, Zbiczno and Ostrowite). Their maximum depths slightly exceed 40 m, and their surface areas range from 121 to 362.5 ha. The results of the measurements show that, despite only minor differences in depth, water temperature varied significantly between the studied lakes. These differences were mainly apparent in the extent of the epilimnion, water thermal stratification, and in the water temperature in the bottom-most layers in summer and winter. The diversity in thermal stratification of the lakes is mainly determined by their morphometric properties, their location above sea level, and the dynamic influences of winds.

Spring warming period of Polish lake waters in a yearly thermal cycle

Abstract The study describes thermal regimes of thirty selected Polish lakes in the spring season. The author used 35-year series of daily measurements of surface water temperature in the years 1961-2005 and the measurements of the vertical distribution of water temperature taken in tens of selected water bodies. The diversified pace of the increase in surface water temperature (SWT) during the spring warming period makes it possible to distinguish two thermal phases: the early and late phases of spring warming. The limits of those phases are marked by the dates of the disappearance of ice cover and the dates when the SWT stays well over the threshold values, which amount to 4°C and 15°C respectively. The SWT increase in the lakes (April and May) causes changes in the water’s vertical thermal structure (the formation of epi- and metalimnion) and considerable dynamics of its descriptive parameters, such as water temperature, thermal stratification coefficient, thermal gradients, heat resources, etc.

Dynamics of the daily course of water temperature in Polish lakes

Abstract The study focuses on short-term changes in surface water temperature in Polish lakes, and is based upon the experimental measurements of water temperature conducted every 60 minutes during the years 1971–2015. 19 lakes were selected on the grounds of their morphometric properties. The examinations were carried out in the system of expeditionary measurements (up to 8 days) and stationary measurements (over 2 months), and included temperature of surface water and its vertical distribution. The analysis of the results showed that temperature differences of water (daily amplitudes) were observed in both time and spatial distribution. The biggest differences in water temperature occurred during spring warming, and often reached 4–5°C, while rarely exceed 2°C in the remaining periods of the yearly cycle. The mean day value occurs twice; in the morning between 8:00 (7:00 GMT) and 11:00 (10:00 GMT), and in the evening at 20:00 (19:00 GMT) and 22:00 (21:00 GMT). Daily changes in the vertical distribution of water temperature are clearly visible down to the depth of 2.5–3.5 m, whereas are just perceptible to the depth of 5.5–7.0 m.

Application of artificial neural networks (ANN) in Lake Drwęckie water level modelling

Abstract This paper presents an attempt to model water-level fluctuations in a lake based on artificial neural networks. The subject of research was the water level in Lake Drwęckie over the period 1980-2012. For modelling purposes, meteorological data from the weather station in Olsztyn were used. As a result of the research conducted, the model M_Meteo_Lag_3 was identified as the most accurate. This artificial neural network model has seven input neurons, four neurons in the hidden layer and one neuron in the output layer. As explanatory variables meteorological parameters (minimal, maximal and mean temperature, and humidity) and values of dependent variables from three earlier months were implemented. The paper claims that artificial neural networks performed well in terms of modelling the analysed phenomenon. In most cases (55%) the modelled value differed from the real value by an average of 7.25 cm. Only in two cases did a meaningful error occur, of 33 and 38 cm.

Water temperature in investigations of Polish lakes

Abstract Scientists became professionally interested in Polish lakes in the early 1850s. They focused predominantly upon the measurements of depth, observations of water stages, optical properties, and water temperature. The first systematic observations of surface water temperature were carried out in 1956. At present these measurements are conducted in 29 lakes. Investigations of the vertical distribution of water temperature were initiated in the interwar period and they contributed to a better recognition of the processes and factors conditioning dynamics of water masses. In general, measurements of water temperature have constituted fundamental observations with respect to the studies of yearly and daily courses of the temperature of surface water and the entire water mass, the influence of basin morphometry upon water thermal conditions, heat balance and heat resources, thermal conditions of bottom deposits and thermal classification of the lakes. The introduction of automatic gradient probes gave a new impulse to the investigations of water temperature in the lakes. The foundation of the Polish Limnological Society in 2001 and 18 national and international limnological conferences stimulated integration of the circle of limnologists. Specialist journals (Limnological Review, Studia Limnologica et Telmatologica) have presented around 40 publications with the leading theme of water temperature.

Forecasting surface water level fluctuations of lake Serwy (Northeastern Poland) by artificial neural networks and multiple linear regression

The aim of this study is to assess the possibility of forecasting water level fluctuations in a relatively small (<100 km2), post-glacial lake located in a temperate climate zone by means of artifi...