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.

Shallow lakes and ponds undergo frequent temporary thermal stratification. How this affects greenhouse gas (GHG) emissions is moot, with both increased and reduced GHG emissions hypothesised. Here, weekly estimations of GHG emissions, over the growing season from May to September, were combined with temperature and oxygen profiles of an 11 ha temperate shallow lake to investigate how thermal stratification shapes GHG emissions. There were three main stratification periods with profound anoxia occurring in the bottom waters upon isolation from the atmosphere. Average diffusive emissions of methane (CH₄) and nitrous oxide (N₂O) were larger and more variable in the stratified phase, whereas carbon dioxide (CO₂) was on average lower, though these differences were not statistically significant. In contrast, there was a significant order of magnitude increase in CH₄ ebullition in the stratified phase. Furthermore, at the end of the period of stratification, there was a large efflux of CH₄ and CO₂ as the lake mixed. Two relatively isolated turnover events were estimated to have released the majority of the CH₄ emitted between May and September. These results demonstrate how stratification patterns can shape GHG emissions and highlight the role of turnover emissions and the need for high-frequency measurements of GHG emissions, which are required to accurately characterise emissions, particularly from temporarily stratifying lakes.

Eutrophication continues to be the most important problem preventing a favorable environmental state and detrimentally impacting the ecosystem services of lakes. The current study describes the results of analyses of 20 year monitoring data from two interconnected Anatolian lakes, Lakes Mogan and Eymir, receiving sewage effluents and undergoing restoration. The first step of restoration in both lakes was sewage effluent diversion. Additionally, in hypertrophic Lake Eymir, biomanipulation was conducted, involving removal of benthi-planktivorous fish and prohibition of pike fishing. The monitoring period included high (H) and low (L) water levels (WL) enabling elucidation of the effects of hydrological changes on lake restoration. In shallower Lake Mogan, macrophyte abundance increased after the sewage effluent diversion in periods with low water levels even at turbid water. In comparatively deeper Lake Eymir, the first biomanipulation led to a clear water state with abundant macrophyte coverage. However, shortly after biomanipulation, the water clarity declined, coinciding with low water level (LWL) periods during which nutrient concentrations increased. A second biomanipulation was conducted, mostly during high water level (HWL) period, resulting in a major decrease in nutrient concentrations and clearer water, but without an expansion of macrophytes. We conclude that repetitive fish removal may induce recovery but its success may be confounded by high availability of nutrients and adverse hydrological conditions.

Ponds are key freshwater habitats supporting biodiversity and ecosystem services, yet they remain understudied in the context of land use and climate change. We examined 240 ponds across eight countries (seven in Europe and Uruguay) to assess how internal pond characteristics, surrounding land cover and livestock intensity, seasonal climatic variation, and climate influence nutrient concentrations across spatial and temporal scales. Nutrient concentrations were strongly associated with internal features: shallow ponds and short hydroperiods had higher total nitrogen (TN) and total phosphorus (TP) concentrations, while thermal stratification, typically found in deeper ponds, was associated with higher TN, indicating enhanced internal nutrient recycling. Land use also played a significant role with agricultural intensity increasing nutrient concentration (both TN and TP), whereas forest cover reduced TP. Seasonal variation modulated these patterns, with higher TP concentrations observed in summer, and with dilution effects during wetter and cooler periods, particularly for TN in semi-permanent ponds. These findings underscore the combined influence of physical characteristics, landscape context, and climate variability on nutrient concentrations in ponds and highlight the need for integrated, multi-scale approaches to anticipate the impacts of global climate change effects on these ecologically valuable ecosystems.

Climate warming threatens the structure and function of shallow lakes, not least those in the Mediterranean climate. We used a space-for-time substitution approach to assess the response of trophic and community structures as well as the richness and evenness of multiple trophic levels to temperature, hydrological, and nutrient constraints. We selected 41 lakes covering wide climatic, hydrological, and nutrient gradients within a short distance for reducing the effect of biogeographical factors in the western Anatolian plateau of Turkey. Generalized linear model analyses revealed that temperature was overall the most important driving variable, followed by total nitrogen (TN) and salinity. The chlorophyll a:total phosphorus ratio, the cyanobacteria:total phytoplankton biovolume ratio, the fish:zooplankton biomass ratio, the proportion of small fish, and fish richness increased with increasing temperature, whereas macrophyte plant volume inhabited (PVI, %), richness, and evenness decreased. Grazing pressure, macrophyte coverage, piscivore biomass, phytoplankton richness, and evenness decreased significantly with both increasing TN and temperature. Temperature and nutrients also separated the northern highland lakes from other lakes in a non-metric multidimensional scaling analysis. Additionally, salinity reduced richness and evenness of phytoplankton and zooplankton. Our results indicate major changes in lake structure and functioning with warming and eutrophication, and highlight the need for strict control of nutrients and water use.