Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains.
In this work, the authors examined the presence of cyanobacteria and cyanotoxins in 21 samples collected from fresh water bodies located in 5 provinces in Poland: Lublin (2), Podlasie (1), Pomerania (6), Warmia-Masuria (1) and Wielkopolska (11). In addition, to determine the general pattern of geographical distribution, frequency of cyanobacteria occurrence, and cyanotoxins production, the published data from 238 fresh water bodies in Poland were reviewed. On the basis of these collected results, we concluded that Planktothrix, Aphanizomenon, Microcystis and Dolichospermum were dominant. The general pattern in geographical distribution of the identified cyanobacterial genera was typical of other eutrophic waters in Europe. The production of cyanotoxins was revealed in 18 (86%) of the 21 samples analyzed in the present work and in 74 (75%) of the 98 total water bodies for which the presence of toxins had been examined. Among the 24 detected microcystin variants, [Asp 3 ]MC-RR was most common. These results can be verified when more data from the less explored water bodies in the southern and eastern parts of Poland are available.
A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north-east Poland), is characterized by: (i) carbonate sediments with a CaCO 3 content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO 3 À and forming thick CaCO 3 encrustations. Thus, this study was aimed at evaluating the CaCO 3 production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO 3 per 1 m 2 were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0Á0625 m 2 ) per transect. The composition and structure of phytoplankton and the physico-chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m À2 and CaCO 3 encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685Á5 and 438 g m À2 , respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m À2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO 3 sedimentation.
Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includes in-situ lake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment.
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