Non-Nitrogen-Fixers or Nitrogen-Fixers? Factors Distinguishing the Dominance of Chroococcal and Diazotrophic Cyanobacterial Species.

Global warming and eutrophication are the main factors driving the development of cyanobacterial dominance in aquatic ecosystems. We used a model linking water temperature, oxygen saturation, concentrations of PO43-, NO3-, NH4+, total dissolved iron (TDFe), and SO42- to cyanobacteria to test the turnover patterns of cyanobacterial dominance of non-nitrogen-fixing (chroococcal species) and nitrogen-fixing (filamentous diazotrophic) species. Statistical analysis was performed using decision trees. The dominance patterns of the two morphologically and ecologically distinct cyanobacterial species were associated with different environmental factors. However, SO42- was the most important factor that explained whether non-nitrogen-fixing or nitrogen-fixing species would dominate. Other important factors were water temperature, phosphate concentration, and oxygen saturation. The model for dominance of non-nitrogen-fixing species used SO42-, PO43-, and water temperature (upper layers), and SO42-, the ratio of PO43-/NH4+, and oxygen saturation (bottom layers). In contrast, water temperature, SO42-, and NH4+ in the upper layers and SO42-, NH4+, and water temperature in the bottom layers were used for the dominance of nitrogen-fixing species. The dominance of Aphanizomenon flos-aquae was explained by different sets of variables, indicating the presence of different strains of this species. The other cyanobacteria species showed dominance patterns that could be explained by one set of variables. As cyanobacterial blooms proliferate due to climate change, it is important to know which factors, in addition to phosphorus and nitrogen, are crucial for the mass development of the various cyanobacterial species.

Interactions between Ciliate Species and Aphanizomenon flos-aquae Vary Depending on the Morphological Form and Biomass of the Diazotrophic Cyanobacterium.

Aphanizomenon flos-aquae can form extensive blooms from freshwater to the brackish environment and, being a diazotrophic species, contribute significantly to the nitrogen and carbon cycle. It occurs as single filaments or aggregates and could be used as an alternative nutrients source for bacteria and ciliates. Ciliates are a group of organisms playing a crucial role in the transfer of nitrogen from primary producers to higher trophic levels in aquatic food webs. The aim of the experiment was to study the effects of the cyanobacterium A. flos-aquae on the community of five ciliate species (Spirostomum minus, Euplotes aediculatus, Strobilidium sp., Vorticella sp. and Paramecium tetraurelia). The response of each species to the presence of a low/high cyanobacterial biomass and to the different morphological forms of A. flos-aquae (single filaments or aggregates) was demonstrated. The results of the experiment showed the variability of interactions between the cyanobacterium A. flos-aquae and ciliates and pointed out the possible benefits that A. flos-aquae provides to the ciliates (e.g., a substrate for the development of bacteria as food for ciliates or as a source of nitrogen and carbon).

Possible consequences of climate change on global water resources stored in dam reservoirs.

Construction of dams and transformation of rivers, not only affects river-related and adjacent habitats, but also establishes new threats to surface freshwater resources globally. Predicted climate changes and increase of mean annual temperature will affect thermal regimes of dam reservoir ecosystems, severely altering their functioning. Analyzing three projections of representative concentration pathway (RCP 4.5, 6.0 and 8.5) for period of 2061-2080, we found that mean annual temperature at dam reservoir locations will increase by 3.06 °C to 4.74 °C from present. The highest projected increase of temperature was identified for dam reservoirs located in high latitudes of Northern Hemisphere, and therefore dam reservoirs located there will be most significantly affected. Numerous consequences of temperature increase are already recorded. Further increase will amplify unfavorable effects on numerous ecosystems, including dam reservoirs which are built on the purpose of the human population development. Our study indicates a threat for artificially stored water globally, with special attention to high latitudes in northern hemisphere and latitudes close to 200S meridian in southern hemisphere.

Synergistic impact of socio-economic and climatic changes on the ecosystem of a deep dam reservoir: Case study of the Dobczyce dam reservoir based on a 30-year monitoring study.

Climate change, increasing inequality in freshwater supply and consumption, as well as human land use activities are remarkable drivers of the alteration of the water cycle on the Earth. The aim of our research was to determine if socio-economic and climatic changes affected the ecosystem of a deep dam reservoir which is used for drinking water. A 30-years data series showed that suburbanization did not negatively affect the quality of the water. Moreover, 30 years of socio-economic and political changes resulted in land use changes (increase of forest from 45 to 50% and decrease of agricultural land from 53 to 43%) and better management of the catchment, as well as the modernization and introduction of new technologies. Furthermore, simultaneous climatic changes affected various physical and chemical features of the studied reservoir, and the most important finding is that the thermal stratification period is extended as an effect of global warming (begins earlier and lasts longer). The complexity of the processes contributing to the functioning of the ecosystem is large, so some processes might be a result of synergistic effects of global warming and socio-economic changes. Our 30-year monitoring study explicitly shows how the ecosystem of a deep dam reservoir reflected these changes.

Variations in zooplankton functional groups density in freshwater ecosystems exposed to cyanobacterial blooms.

The recently observed decline of biodiversity has become a major problem on Earth. Anthropogenically-driven climate change and eutrophication of natural habitats represent great threats to both terrestrial and aquatic ecosystems. Particularly vulnerable are freshwater ecosystems, where the mentioned changes promote development of cyanobacteria. Extension of the cyanobacterial bloom period, increase of cyanobacterial biomass production and toxicity may involve numerous changes in freshwater ecosystem functioning. We conducted a study in water bodies exposed to cyanobacterial blooms of different duration: short-lasting and long-lasting cyanobacterial blooms. We tested the impact of cyanobacterial biomass on densities of zooplankton species grouped into functional groups (functional groups densities) under conditions of different bloom length periods. The functional groups of zooplankton were identified on the basis of three functional traits of each species: mean body length (BL), potential food source (FS) and feeding type (FT). The results of the study showed that assembling species into functional groups may be helpful in understanding the interactions between biotic components of ecosystem. The results showed that the response of each functional group density for cyanobacterial biomass development depends on the functional traits of the animals (i.e. how the species interact with the whole food web) and may be different depending on the bloom intensity, which acts like a factor selecting adapted species.

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.

Microcystins affect zooplankton biodiversity in oxbow lakes.

The authors tested the hypothesis that zooplankton diversity and density are affected by the presence of cyanotoxins in the water. The authors focused on 4 oxbow lakes of the Vistula River in southern Poland, which are subjected to mass cyanobacterial development. In 2 of the oxbows (Piekary and Tyniec), microcystins released into the water were found. The highest concentration of microcystins (0.246 µg/L) was observed for microcystins LR. Zooplankton diversity showed a weak response to the presence of microcystins released into the water. The Shannon index (H') of total zooplankton diversity decreased in the Piekary and Tyniec oxbows during periods when the microcystin concentrations were highest. The same trend was noted for diversity of rotifers in both oxbows and for diversity of copepods in Piekary, but not for copepods in Tyniec. No such trends were found for the diversity of cladocerans in any of the oxbows, nor was a relationship found between density of zooplankton and microcystins. Statistical analyses showed that the number of species in individual samples was negatively correlated with the levels of sulfates, phosphates, and ammonia, but the microcystin concentration was positively related to those levels. This points to the complexity of the interactions and synergies among toxins, abiotic factors, and zooplankton biodiversity. In focusing on the problem of cyanotoxins, conservation studies should pay attention to this complexity. Environ Toxicol Chem 2017;36:165-174. © 2016 SETAC.