Effect of climate warming on a change in thermal and ice conditions in the largest lake in Poland – Lake Śniardwy

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.

Detecting Patterns of Changes in River Water Temperature in Poland

The study determined water temperature trends of rivers in Poland in the period 1971–2015, and also their spatial and temporal patterns. The analysis covered daily water temperature of 53 rivers recorded at 94 water gauge stations and air temperature at 43 meteorological stations. Average monthly, annual, seasonal and maximum annual tendencies of temperature change were calculated using the Mann–Kendall (M–K) test. Regional patterns of water temperature change were determined on the basis of Ward’s hierarchical grouping for 16 correlation coefficients of average annual water temperature in successive 30-year sub-periods of the multi-annual period of 1971–2015. Moreover, regularities in monthly temperature trends in the annual cycle were identified using 12 monthly values obtained from the M–K Z test. The majority of average annual air and water temperature series demonstrate statistically significant positive trends. In three seasons: spring, summer and autumn, upward tendencies of temperature were detected at 70%–90% of the investigated water gauges. In 82% of the analysed rivers, similarity to the tendencies of change of monthly air temperature was concluded, with the climatic factor being recognised as of decisive importance for the changes in water thermal characteristics of the majority of rivers in Poland. In the winter months, positive trends of temperature were considerably weaker and in general statistically insignificant. On a regional scale, rivers with a quasi-natural thermal regime experienced temperature increases from April to November. In the other cases, different directions of change in river water temperature (RWT) were attributed to various forms of human impact. It was also found that for the majority of rivers the average annual water temperature in the analysed 30-year sub-periods displayed upward trends, statistically significant or close to the significance threshold. Stronger trends were observed in the periods after 1980, while a different nature of water temperature change was detected only in a couple of mountainous rivers or rivers transformed by human impact. In the beginning of the analysed period (1971–2015), the average annual water temperature of these rivers displayed positive and statistically significant trends, while after 1980 the trends were negative. The detected regularities and spatial patterns of water temperature change in rivers with a quasi-natural regime revealed a strong influence of climate on the modification of their thermal regime features. Rivers characterised by a clearly different nature of temperature change, both in terms of the direction of the tendencies observed and their statistical significance, were distinguished by alterations of water thermal characteristics caused by human activity. The results obtained may be useful in optimising the management of aquatic ecosystems, for which water temperature is a significant indicator of the ongoing environmental changes.

Patterns of Changes in Average Annual Water Temperatures of the Rivers of the Arctic Zone of Russia Associated with Climate Changes

The paper considers changes in temperature regime of rivers flowing northerner than 60th latitude. The investigation bases on data about average monthly water temperatures from 90 hydrological gages for the period 1960-2012. Annual water temperatures for this period were calculated according to the generally accepted method as average monthly temperature from May to September and according to the proposed in this paper calculation method for the entire period with positive water temperatures. It is shown that the calculation of annual water temperatures only from the average monthly temperatures from May to October, underestimates annual water temperature. The paper estimates changes in the average annual water temperatures calculated by both methods over the period 1991–2012 compared to 1961-1990 These periods cover intensive climate change, as well as the time after the construction of the largest hydroelectric power stations. Statistical analyzes of the obtained series for trends (according to the Spearman rank correlation test) and series uniformity disturbances (Mann-Whitney U-test) were carried out. A significant increase in the average annual water temperatures in rivers on most rivers of the Russian Arctic is shown. The greatest changes are observed in the territories of Yakutia. Significant changes are also noted on the Kola Peninsula. At the same time, the magnitude of the changes depends on various hydrological characteristics of the basin. Significant changes to date have occurred in less than 50% of the investigated rivers.

Walleye recruitment success is less resilient to warming water temperatures in lakes with abundant largemouth bass populations

Lakes respond heterogeneously to climate, with implications for fisheries management. We analyzed walleye (Sander vitreus) recruitment to age-0 in 359 lakes in Wisconsin, USA, to (i) quantify the relationship between annual water temperature degree days (DD) and walleye recruitment success and (ii) identify the influence of lake characteristics — area, conductivity, largemouth bass (Micropterus salmoides) catch rates, and mean DD — on this relationship. The relationship between walleye recruitment and annual DD varied among lakes and was not distinguishable from zero overall (posterior mean = −0.11, 90% CI = −0.34, 0.15). DD effects on recruitment were negative in 198 lakes (55%) and positive in 161 (45%). The effect of annual DD was most negative in lakes with high largemouth bass densities, and, on average, the probability of recruitment was highest in large lakes with low largemouth bass densities. Conductivity and mean DD influenced neither recruitment nor the effect of annual DD. Walleye recruitment was most resilient to warming in lakes with few largemouth bass, suggesting that the effects of climate change depend on lake-specific food-web and habitat contexts.

Effect of climatic changes on the development of the thermal-ice regime based on the example of Lake Charzykowskie (Poland)

The paper discusses the course of air temperature in the years 1961-2014 in Chojnice (Central European Lowland), and its effect on water temperature and occurrence of ice cover on Lake Charzykowskie. An increase in mean annual air temperature was determined by 0.31°C per 10 years, and its even faster increase in the winter season (December-March), by 0.37°C per 10 years on average. An increase in mean annual water temperature in the lake by 0.24°C per 10 years also occurred. An increase in air and water temperature in winter months caused a reduction of the period of occurrence of ice cover. In the years 1961-2014, the persistence of ice cover was subject to a decrease by 3.7 days per 10 years on average, and the mean thickness of the ice cover decreased from 30 to 19 cm.

The transformation of rivers’ temperature regime downstream of reservoirs

The article is dedicated to the problem of the transformation of rivers’ temperature conditions influenced by artificial reservoirs. A quantitative estimation of average water temperatures over ten days, and maximum and average annual water temperatures of regulated rivers downstream of reservoirs was made on the basis of the data analysis of a complete period of instrumental observations of the Republican Hydrometeorological Centre of the Republic of Belarus. It is established that the character and the parameters of the transformation of temperature conditions of the regulated rivers along with morphometric features of the reservoirs are determined by the meteorological conditions of the year and the operating conditions of the water-engineering system. The length of the cooling period effect varies from 20 days downstream of small reservoirs to 50-70 days downstream of small and average size reservoirs. The warming effect is less significant by temperature, but lasts longer and is appreciable around 200-240 days in a year. An increase in the average annual water temperature up to 0.5°C and a decrease in maximum temperature down to 1.1°C are observed in the tail-water of average size storage pools. Small size storage pools demonstrate an annual increase in annual water temperature up to 0.3°C and a decrease in maximum temperature down to 0.3°C. Small size water pools show an increase both in annual water temperature up to 0.5°C and maximum water temperature up to 0.3°C. Typical changes in temperature conditions of rivers are observed for a distance of 130 kilometres below the dam of average size water pools, along 70 kilometres in small water pools and along 30 kilometres in tiny ones.

The influence of environmental variables on larval growth of stoneflies (Plecoptera) in natural and deforested streams

A total 14 streams located in the Tatra Mts (Slovakia) were investigated. The studied river basins have different deforestation range (0–45.5%) influenced by windstorm. Daily and annual water temperature suggested that in streams overflowing through the area deforested by windstorm the temperature was higher than in selected non-disturbed streams. Higher average nutrient concentrations in samples from these streams are connected with nutrient mobilization from disturbed forest soils after the windstorm. Most of the damaged streams have higher trophic status, including POM and biofilms. The growth of the most abundant larvae increases with deforestation. Growth of species Leuctra rauscheri, Protonemura Montana, and Perlodes intricatus correlates with the sum of daily temperatures over a given time interval. Growth of species Brachyptera seticornis, Leuctra autumnalis and Isoperla sudetica are affected by stream trophy.

Abundance of three species of Isopoda (Peracarida, Isopoda) associated with a coral reef environment in Pacific Mexico

Fragments of dead coral belonging toPocilloporaLamarck, 1816 were used during a 1-year period as artificial micro-habitats and positioned at a coral reef community at Islas Marietas, Bahía Banderas, on the west coast of Mexico, to attract and capture isopods. Three species of isopods, totaling 961 specimens were collected. The dominant species wasJoeropsis dubia(Menzies, 1951) (Joeropsididae) (83.03% of the total number of specimens), followed byCalifanthura squamosissima(Menzies, 1951) (Paranthuridae) (9.78%), andParacerceis sculpta(Holmes, 1904) (Sphaeromatidae) (7.18%). The average density of isopods was of 12.0 × 10−2ind. ⋅ cm−2. A positive relationship between water temperature and total density of individuals during the sampling period was found. Annual water temperature changes influenced the abundance of each species in a similar way, with the higher abundances associated to the lower temperatures, which is also related to an increase in primary productivity and the presence of upwellings in the area.