Determining the probability of cyanobacterial blooms: the application of Bayesian networks in multiple lake systems

A Bayesian network model was developed to assess the combined influence of nutrient conditions and climate on the occurrence of cyanobacterial blooms within lakes of diverse hydrology and nutrient supply. Physicochemical, biological, and meteorological observations were collated from 20 lakes located at different latitudes and characterized by a range of sizes and trophic states. Using these data, we built a Bayesian network to (1) analyze the sensitivity of cyanobacterial bloom development to different environmental factors and (2) determine the probability that cyanobacterial blooms would occur. Blooms were classified in three categories of hazard (low, moderate, and high) based on cell abundances. The most important factors determining cyanobacterial bloom occurrence were water temperature, nutrient availability, and the ratio of mixing depth to euphotic depth. The probability of cyanobacterial blooms was evaluated under different combinations of total phosphorus and water temperature. The Bayesian network was then applied to quantify the probability of blooms under a future climate warming scenario. The probability of the "high hazardous" category of cyanobacterial blooms increased 5% in response to either an increase in water temperature of 0.8°C (initial water temperature above 24°C) or an increase in total phosphorus from 0.01 mg/L to 0.02 mg/L. Mesotrophic lakes were particularly vulnerable to warming. Reducing nutrient concentrations counteracts the increased cyanobacterial risk associated with higher temperatures

Combating cyanobacterial proliferation by avoiding or treating inflows with high P load—experiences from eight case studies

Increased external nutrient loads of anthropogenic origin, especially those of phosphorus (P), were one of the major causes of eutrophication during the first half of the twentieth century in Europe. They led to deterioration of lake ecosystems, particularly including noxious blooms of (potentially toxic) cyanobacteria. From the 1970–1980s, strategies to decrease the phosphorus loads from sewage were increasingly implemented, among them are the ban of phosphates in detergents, the expansion of sewer systems and improvement in wastewater treatment to remove nutrients. Case studies of eight lakes, whose response to point source reduction of phosphorus was observed over decades, show that a pronounced reduction of the phosphorus load from point sources can be achieved either by the diversion of inflows carrying high loads, by upgraded sewage treatment, or by phosphorus precipitation in the major tributary directly before its inflow into the water body. Outcomes demonstrate that in order to effectively control cyanobacterial blooms, the measures taken need to reduce in-lake concentrations of total phosphorus below 20–50 µg L−1, with this threshold varying somewhat between lakes depending in particular on hydromorphological and biological conditions. Whether and when load reduction succeeds in controlling cyanobacteria depends primarily on the load remaining after remediation and on the water residence time

Különböző országokból származó cianobaktérium populációk toxicitása

7 Microcystis és 2 Planktothrix toxintermelő cianobaktérium minta vizsgálatára került sor, melyek a Velencei tóból, Braziliából és Németországból származnak. A minták egy része a természetben gyűjtött biomassza, míg másik része törzsizolátum. A toxicitás detektálására Thamnotox kittet, patkány májsejtvonalat, egértesztet alkalmaztunk. Az eredményeket összevetettük a HPLC-s analízis eredményeivel, mely szerint a brazil mintákban microcystin LR forma, vagyis a legtoxikusabb variáns nem fordult elő. A magyar és német minták egyaránt tartalmazták mindhárom vizsgált microcystin formát (LR, RR, YR), azonban a magyar mintákban az LR forma koncentrációja egy nagyságrenddel nagyobb volt, mint a német mintákban. Toxicitásban a magyar és brazil minták mutattak hasonlóságot, bár a brazil minták nem tartalmaztak LR variánst, de az RR forma koncentrációja olyan magas volt (12,5 és 14,8 mg/g), hogy ez jelentkezett a hasonló toxicitásban. A német minták alacsonyabb toxicitása a kisebb toxintartalommal magyarázható. A korreláció a Thamnotox teszt eredmények és az egérteszt eredmények között igen szoros (r: 0,967), míg a teljes toxin koncentráció és az egérteszt között 0,473, ugyanígy a teljes toxin koncentráció és a Thamnotoxkit teszt között (r: 0,680) jóval gyengébb az összefüggés. Hasonló eredményre jutottunk a májsejtekre kifejtett toxikus hatással kapcsolatban is. A biomassza kivonatok toxikusabbnak tűnnek, mint az a microcystin tartalommal magyarázható lenne, tehát feltételezhető, hogy a már ismert toxinokon kívül más toxikus hatású vegyületekkel is kell számolnunk a cianobaktériumoknál

Cyanobacteria and Cyanotoxins in a Changing Environment: Concepts, Controversies, Challenges

Concern is widely being published that the occurrence of toxic cyanobacteria is increasing in consequence of climate change and eutrophication, substantially threatening human health. Here, we review evidence and pertinent publications to explore in which types of waterbodies climate change is likely to exacerbate cyanobacterial blooms; whether controlling blooms and toxin concentrations requires a balanced approach of reducing not only the concentrations of phosphorus (P) but also those of nitrogen (N); how trophic and climatic changes affect health risks caused by toxic cyanobacteria. We propose the following for further discussion: (i) Climate change is likely to promote blooms in some waterbodies—not in those with low concentrations of P or N stringently limiting biomass, and more so in shallow than in stratified waterbodies. Particularly in the latter, it can work both ways—rendering conditions for cyanobacterial proliferation more favourable or less favourable. (ii) While N emissions to the environment need to be reduced for a number of reasons, controlling blooms can definitely be successful by reducing only P, provided concentrations of P can be brought down to levels sufficiently low to stringently limit biomass. Not the N:P ratio, but the absolute concentration of the limiting nutrient determines the maximum possible biomass of phytoplankton and thus of cyanobacteria. The absolute concentrations of N or P show which of the two nutrients is currently limiting biomass. N can be the nutrient of choice to reduce if achieving sufficiently low concentrations has chances of success. (iii) Where trophic and climate change cause longer, stronger and more frequent blooms, they increase risks of exposure, and health risks depend on the amount by which concentrations exceed those of current WHO cyanotoxin guideline values for the respective exposure situation. Where trophic change reduces phytoplankton biomass in the epilimnion, thus increasing transparency, cyanobacterial species composition may shift to those that reside on benthic surfaces or in the metalimnion, changing risks of exposure. We conclude that studying how environmental changes affect the genotype composition of cyanobacterial populations is a relatively new and exciting research field, holding promises for understanding the biological function of the wide range of metabolites found in cyanobacteria, of which only a small fraction is toxic to humans. Overall, management needs case-by-case assessments focusing on the impacts of environmental change on the respective waterbody, rather than generalisations

Toledo triggered new WHO guidance for cyanotoxin risk assessment

In 2014, the Toledo do not drink advisory spotlighted the need for short-term cyanotoxin guideline values. These are particularly relevant for cyanotoxins because concentrations may fluctuate widely as blooms wax and wane, with concentrations above the values for safe lifetime daily consumption of 2 L of drinking water often being short-lived events. Allowing slightly higher concentrations for up to 2 weeks enables focusing investments on remediation (rather than on supplying bottled water). In 2016. a second independent chronic exposure study with cylindrospermopsin (conducted at US EPA) finally provided the data that the World Health Organisation needed for deriving a CYN guideline value. Thus, WHO now provides a far more comprehensive set of guideline values for short-term and lifetime exposure through drinking water as well as for recreational exposure, including all 4 major groups of cyanotoxins (MCs, CYNs, STXs, ATXs). The presentation will explain their derivation in the context of other hazardous substances in water to which people may be exposed because among these, cyanotoxins are probably the most widely occurring. It will also show how these values serve as guidance for short-term responses to blooms in the context of Alert Levels Frameworks for drinking water and for recreation