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.

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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.

This study aimed to characterize the effluents of 3 flow-through farms with annual production rates of 250, 750 and 2500 t yr −1 at a site with a total annual production of 4400 t yr −1 . We determined the nutrient loads from rainbow trout Oncorhynchus mykiss farms using nutritional and hydro logical mass-balance models and estimated the fluxes into a regulated stream and into the Mediterranean Sea between March 2008 and February 2009. When compared with the influent, farming activity significantly decreased dissolved oxygen (p < 0.001) and increased biochemical oxygen demand, suspended solids, and nitrogen and phosphorus fractions (p < 0.05) in the effluents. The load predictions of 44.3 kg N and 8.4 kg P t −1 of fish produced by the nutritional method were close to the measured values of 43.9 kg N and 8.8 kg P t −1 of fish produced. The load prediction for suspended solids was the same as the measured value of 278 kg t −1 of fish produced. The predictions were well correlated with measurements for suspended solids and for total nitrogen and phosphorus. The estimated annual mass fluxes of nitrogen and phosphorus from trout farms at the site into the eastern Mediterranean Sea were 125 to 127 and 24 to 25 t yr −1 , respectively. The nutritional mass-balance model may be the method of choice as a decision tool for the envi ronmental impact assessment of land-based aquaculture because of its simplicity and easy application.