Temperature Effects Explain Continental Scale Distribution of Cyanobacterial Toxins

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.Peer reviewe

Treatment of Hypolimnion Water on Mineral Aggregates as the Second Step of the Hypolimnetic Withdrawal Method Used for Lake Restoration

The study aimed to assess the usefulness of mineral aggregates in orthophosphate (OP) removal from hypolimnetic water withdrawn from eutrophic lakes. Two low-cost and easily available reactive materials were tested: lightweight expanded clay aggregate (LECA) and crushed limestone (LS). Their performance regarding OP removal and the effect on the pH, Ca2+, Mg2+, N-NO3 and N-NH4 concentrations of treated water were investigated in a column experiment with four-filter beds made of LECA and amended with LS (additions of 0, 25, 50 and 75% of the bed volume). The highest OP removal (>50%) was achieved in LECA beds with high (75% by volume) amendments of LS. Neither LECA nor LS distinctly affected the pH (maximum pH increase, from 7.1 or 7.2 to 7.6, occurred in the case of the LECA bed). In real-life conditions, it is not feasible to install a full-scale bed made of these mineral aggregates on the outflow from a lake due to the large required size of such a bed. At the operation time set for 30 d, the size of a bed would need to reach between 6113.2 and 12,226.4 m3. The proposed bed should be just one of the elements of an integrated treatment system. Constructions consisting of sorption beds ought to be coupled with adequately designed zones of aquatic vegetation. Three conceptional solutions were proposed for in situ treatment of the withdrawn water, differing in arrangement and construction of the potential sorption bed. Application of such solutions should be regarded as a substantial improvement of Olszewski’s method, as it can mitigate the pollution of downstream ecosystems

Treatment of Hypolimnion Water on Mineral Aggregates as the Second Step of the Hypolimnetic Withdrawal Method Used for Lake Restoration

The study aimed to assess the usefulness of mineral aggregates in orthophosphate (OP) removal from hypolimnetic water withdrawn from eutrophic lakes. Two low-cost and easily available reactive materials were tested: lightweight expanded clay aggregate (LECA) and crushed limestone (LS). Their performance regarding OP removal and the effect on the pH, Ca2+, Mg2+, N-NO3 and N-NH4 concentrations of treated water were investigated in a column experiment with four-filter beds made of LECA and amended with LS (additions of 0, 25, 50 and 75% of the bed volume). The highest OP removal (>50%) was achieved in LECA beds with high (75% by volume) amendments of LS. Neither LECA nor LS distinctly affected the pH (maximum pH increase, from 7.1 or 7.2 to 7.6, occurred in the case of the LECA bed). In real-life conditions, it is not feasible to install a full-scale bed made of these mineral aggregates on the outflow from a lake due to the large required size of such a bed. At the operation time set for 30 d, the size of a bed would need to reach between 6113.2 and 12,226.4 m3. The proposed bed should be just one of the elements of an integrated treatment system. Constructions consisting of sorption beds ought to be coupled with adequately designed zones of aquatic vegetation. Three conceptional solutions were proposed for in situ treatment of the withdrawn water, differing in arrangement and construction of the potential sorption bed. Application of such solutions should be regarded as a substantial improvement of Olszewski’s method, as it can mitigate the pollution of downstream ecosystems

Harmful blooms across a longitudinal gradient in central Europe during heatwave: Cyanobacteria biomass, cyanotoxins, and nutrients

Climate change has increased the frequency, duration and intensity of heatwaves in Europe. These extreme events result in alterations of physical, chemical, and biological properties of lakes that may synergistically promote cyanobacterial dominance. In our study we focused on cyanobacterial blooms in lakes distributed over a longitudinal gradient in Central Europe during one of the “top ten European heat waves” in summer 2015. 92 lakes were included in the study, located across three climatic subregions: cool northern lakes, situated in Lithuania, temperate northern lakes in Poland, and warm northern lakes in Croatia. The objective of the study was to determine if cyanobacterial biomass, predominant species, and cyanotoxin concentration differed, across the south-north gradient, as a function of water temperature, total phosphorus, and total nitrogen. Statistical significance of observed patterns was tested using the Kruskal-Wallis rank sum test and the generalized linear model. We found the lowest average epilimnion temperature, but the highest average cyanobacterial biomass in the northern, ‘cool’ lakes while the highest average temperature with the lowest average cyanobacterial biomass in the southern, ‘warm’ lakes. The concentration of cyanotoxins was also the highest in the ‘cool’ lakes. Total phosphorus and total nitrogen correlated significantly with cyanobacterial biomass, cyanotoxins concentration and biomass of some cyanobacterial species (mainly Planktothrix agardhii), regardless of the latitude. Only in the ‘cool’ lakes concentration of cyanotoxins (microcystins and anatoxin-a) correlated significantly with cyanobacterial biomass and the biomass of some dominant cyanobacterial species (P. agardhii). Our results emphasized the differences of heat weaves impact on lakes of various latitudes, with the strongest increase in toxic cyanobacterial blooms in northern ‘cool’ lakes, situated in high latitudes. On the other hand, nutrients directly enhanced blooms across all the studied latitudes of Central Europe. The cyanobacteria species dominating in blooms might be recognized as ecological indicators of climate change, especially in the north-eastern part of Europe

Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer

To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature.Peer reviewe

Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer

To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L−1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4°C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature