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.

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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SUMMARYIn this study, we have analyzed superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities, biomass accumulation and chlorophyll-a content in the Arthrospira platensis-M2 strain grown at different concentrations of zinc (Zn), tin (Sn) and mercury (Hg). We found that there is a close relationship between chlorophyll-a content and biomass accumulation in A. platensis-M2 strain as a result of Zn, Sn and Hg exposures. Sn was found to be the most toxic heavy metal among others because of the continious inhibition of both biomass and chlorophyll-a accumulation at 500 and 1000 μg mL −1 concentrations after the third day of the study, while they represented continuous increases at each Zn and Hg concentration over 7 days. Lower concentrations of Zn and Sn stimulate SOD and GR activities remarkably, probably due to oxidative stress caused by heavy metal toxicity. APX activity was significantly lowered by higher concentrations of the three metals used in this study. Our results suggest that higher heavy metal concentrations inhibited SOD, APX and GR activities but biomass and chlorophylla accumulation endured in a time-dependent manner, possibly due to some different defence mechanisms, which remain to be investigated.

IntroductionShallow lakes in Mediterranean climates, which are generally situated in lowland areas, due to their high evaporation/precipitation ratios, low geographic relief, and dense human population have long water residence times and are becoming more eutrophic (Allan et al., 1980;Borics et al., 2013). Moreover, elevated release of phosphorus from sediments or greater loads from the catchment area and destruction of submerged vegetation may trigger an increase of phytoplankton density and a related decrease in water clarity (Moss et al., 2009;Dokulil and Teubner, 2011). The increased biomass of phytoplankton and frequently occurring toxic algal blooms triggered the reassessment of lake management strategies (Borics et al., 2013). The Water Framework Directive was deigned to assess the ecological quality of surface waters through the analysis of various characteristics of aquatic flora and fauna, and to declare management plans in European countries (EC, 2009). Investigation of the functional traits of phytoplankton of shallow lakes was found to be important to estimate ecological quality and to understand the operation of these systems (Borics et al., 2012).Many attempts have been made to categorize traits and functions of phytoplankton (Reynolds et al., 2002;Borics et al., 2007;Padisák et al., 2009). At present, 40 phytoplankton functional groups (FGs) have been described, identified by numeric character codes (codons) (Padisák et al., 2009). Padisák et al. ( 2006) developed an index (Q index) using FGs to estimate the ecological status of lakes. The index combines the relative weight of FGs in the total biomass and considers a factor number for each assemblage for each type of water body. It was tested on water bodies significantly differentiated by origin, altitude, salinity, mixing, and stratification in the world (e.g., Crossetti and Bicudo, 2008;Pasztaleniec and Poniewozik, 2010) and in Turkey (e.g., Demir et al., 2014;Çelik and Sevindik, 2015).Lake morphometry and hydrology are criteria for the composition of lake biota (Murray and Pullar, 1910), and may favor distinct life strategies. Nevertheless, even taking into account the hydromorphology, substantial differences are recognizable when considering the effects of latitude and climate on phytoplankton composition and abundance (Pollingher, 1990). Moreover, lakes that are located in the same geographic region and have similar hydromorphologies could be composed of diverse phytoplankton assemblages as a result of different nutrient content and light availability (Scheffer, 1998;Naselli-Flores, 2000). In addition, Borics et al. (2014) found

The aim of this study was to determine the spatial and temporal variation of phytoplankton and water quality in response to the hydrological regime in an isolated floodplain lake (North Mollaköy Lake) of the Sakarya River. Variations in the composition, biomass and functional groups of phytoplankton and environmental parameters were monthly analyzed in subsurface samples collected from the pelagic zone at four stations from July 2012 to June 2013. A total of 109 taxa were identified, and the species which contributed the most to the phytoplankton biomass were grouped into 14 functional groups (FGs). The distribution of FGs was linked to the transition (T1 and T2), high (HW) and low (LW) water periods in North Mollaköy Lake. FGs J, MP, N, G, X1, X2, Y, W1, W2, S1, H1, B and C were the contributors to the phytoplankton biomass during the low-water period (LW) and the transition periods (T1 and T2), while Lo contributed the most during the high-water period (HW). RDA revealed that the most important factor affecting the temporal distribution of FGs was the water discharge and that there are

Azadirachtin (Aza) used as insecticide due to inhibiting growth of insects and preventing them from feeding on plants. To understand the effects of contamination of this insecticide on phototrophs, and to determine the responses of these organisms against these insecticides are extremely important in understanding how the ecosystem is affected. In this study, chlorophyll-a amount, OD 560 and antioxidant parameters (total SOD, APX, GR, Proline, MDA and H2O2) were determined in order to understand the effect of Aza on Arthrospira platensis Gomont. Aza was applied between 0–20 μg mL−1 concentrations for 7 days in the study. Enzyme analysis was conducted at the end of the 7th day. There was a statistically significant decrease in the absorbance of OD560 and the chlorophyll-a content in A. platensis cultures exposed to the Aza (0–20 μg mL−1) during 7 days due to the increase in pesticide levels. SOD activity decreased at 8, 16 and 20 μg mL−1 concentrations; GR enzyme activity showed a significant decrease compared to the control at a concentration of 20 μg mL−1. APX activity did not change significantly compared to control. The MDA content increased significantly at 16 and 20 μg mL−1 concentrations. The H2O2 content significantly increased at 12, 16 and 20 μg mL−1 concentrations (p < 0.05) while the free proline content decreased at 4 μg mL−1 concentration (p < 0.05). As a result, regarding the Aza concentrations used in this study may be a step to prevent pesticide pollution in the environment.

It is important to determine the water quality of the creeks in the Lake Sapanca basin since it is used for drinking water supply. For this purpose, environmental parameters and diatom assemblages as biological quality components were investigated to determine the ecological status of eight creeks with monthly intervals between March 2015 and February 2016. During the studied period, 19 taxa increased their relative abundance higher than 30% in at least one sample and showed a different seasonal pattern. Main nutrients [(nitrate-nitrogen, orthophosphate, total phosphorus (TP)] and some other parameters (specific conductance, temperature, pH, and dissolved oxygen) had strong impacts on the distribution of diatom assemblages. The ecological status of the creeks was characterized by using four different diatom indices, however, only Trophic Index Turkey (TIT) represented significant positive correlations with log (TP) gradient and separated the creeks as good and moderate ecological status. According to TIT, the 4th and 6th stations had a good ecological condition and were characterized by pollution-sensitive species such as Cymbella affinis, Reimeria sinuata, and Nitzschia dissipata. On the other hand, TIT resulted in the other stations having moderate ecological conditions, which had high nutrient levels and EC. Moreover, the occurrence of pollution-tolerant taxa such as Gomphonema angustatum, Ulnaria ulna, and Achnanthidium affine endorsed the moderate ecological conditions in these creeks. Based on the results, the TIT as a biological metric could be a useful tool for the assessment of running waters in the Sakarya river basin.