Occurrence Of Cyanobacteria Blooms Research Articles

More Light Please: Daphnia Benefit From Light Pollution by Increased Tolerance Toward Cyanobacterial Chymotrypsin Inhibitors

Cryptochromes are evolutionary ancient blue-light photoreceptors that are part of the circadian clock in the nervous system of many organisms. Cryptochromes transfer information of the predominant light regime to the clock which results in the fast adjustment to photoperiod. Therefore, the clock is sensitive to light changes and can be affected by anthropogenic Artificial Light At Night (ALAN). This in turn has consequences for clock associated behavioral processes, e.g., diel vertical migration (DVM) of zooplankton. In freshwater ecosystems, the zooplankton genus Daphnia performs DVM in order to escape optically hunting predators and to avoid UV light. Concomitantly, Daphnia experience circadian changes in food-supply during DVM. Daphnia play the keystone role in the carbon-transfer to the next trophic level. Therefore, the whole ecosystem is affected during the occurrence of cyanobacteria blooms as cyanobacteria reduce food quality due to their production of digestive inhibitors (e.g., protease inhibitors). In other organisms, digestion is linked to the circadian clock. If this is also the case for Daphnia, the expression of protease genes should show a rhythmic expression following circadian expression of clock genes (e.g., cryptochrome 2). We tested this hypothesis and demonstrated that gene expression of the clock and of proteases was affected by ALAN. Contrary to our expectations, the activity of one type of proteases (chymotrypsins) was increased by ALAN. This indicates that higher protease activity might improve the diet utilization. Therefore, we treated D. magna with a chymotrypsin-inhibitor producing cyanobacterium and found that ALAN actually led to an increase in Daphnia’s growth rate in comparison to growth on the same cyanobacterium in control light conditions. We conclude that this increased tolerance to protease inhibitors putatively enables Daphnia populations to better control cyanobacterial blooms that produce chymotrypsin inhibitors in the Anthropocene, which is defined by light pollution and by an increase of cyanobacterial blooms due to eutrophication.

Effects of class imbalance on resampling and ensemble learning for improved prediction of cyanobacteria blooms

This study aimed to explicitly explore the effects of the degree of class imbalance on predicting infrequently occurring events, i.e., cyanobacteria blooms. Although class imbalance poses a major issue in binary classification schemes, few efforts have been made to relate model performance with real-life applications. The data utilized herein were collected from 2013 to 2019 at 13 sites within three major rivers in South Korea; a variety of physicochemical and hydrometeorological factors were obtained as input variables, and the occurrence of cyanobacteria blooms (indicated by a cell count ≥ 1000 cells/mL) was included as a response variable. The imbalance ratio (IR) for cyanobacteria blooms differed significantly by site, ranging widely from 0.93 to 9.32. The study results suggested that class imbalance negatively affected model performance, with an increase in the IR significantly increasing the false negative (FN) rate. The application of resampling decreased the FN rate while simultaneously increasing the true positive (TP) rate, which yielded improvements that tended to increase with increasing IRs. Ensemble classifiers, which combine multiple single classifiers into an integrated classifier, alone could not successfully address the class imbalance problem; however, in combination with resampling, they consistently outperformed single classifiers. Among the ensemble classifiers, AdaBoost yielded the most stable performance across a range of IRs, irrespective of the resampling application. A variable importance analysis indicated that temperature was usually the primary influencing factor of cyanobacteria blooms. These findings highlight the effectiveness of resampling applications for addressing class imbalance, while providing useful guidelines for learning from imbalance data, including the selection of classification algorithms and model evaluation metrics.

Future Projections of Water Temperature and Thermal Stratification in Connecticut Reservoirs and Possible Implications for Cyanobacteria

AbstractFuture climate warming may increase water temperature, stratification, and the occurrence of cyanobacteria blooms in drinking water reservoirs. Herein, past relationships between air temperature, water temperature, thermal stratification, and cyanobacteria prevalence are quantified in six Connecticut, U.S.A., reservoirs. Lake‐specific empirical models were developed and used to project historical (1971–2000) and future (mid‐century, 2041–2070) water temperature and thermal stratification in the study lakes. Projections are driven with downscaled air temperature projections from three general circulation models (i.e., HadGEM2‐CC365, CCSM4, and GFDL‐ESM 2M) under Representative Concentration Pathway 8.5. Results suggest that reservoirs in Connecticut are warming relatively quickly over time and that surface, average, and bottom water temperatures may continue to increase by 0.44°C, 0.30°C, and 0.16°C per decade, respectively. Future projections of thermal stratification indicate that significant increases may occur in July–September and that stratification is likely to begin 2–4 weeks earlier and last 2–4 weeks longer by mid‐century. High‐risk cyanobacteria blooms, defined as those exceeding 70,000 cells ml−1, historically occurred in three of the study reservoirs and are correlated with the occurrence of high surface water temperatures, cool bottom water temperatures, and high total Relative Thermal Resistance to Mixing (RTRM). Days per year with extreme high water temperatures and total RTRM are projected to increase significantly in the future. This shift may favor increased dominance of certain cyanobacteria species that tend to grow best in these extreme conditions, especially in reservoirs where cyanobacteria blooms are already a concern.

Size‐based interactions and trophic transfer efficiency are modified by fish predation and cyanobacteria blooms in Lake Mývatn, Iceland

Abstract Trophic cascade studies have so far mostly focused on changes in the abundance, biomass, or average size of prey and predators. In contrast, individual size‐based interactions, playing a key role in the trophic structure and functioning of aquatic ecosystems, have been less explored. We conducted a 3‐month in situ experiment in Lake Mývatn, Iceland, with two fish treatments (with and without fish, Gasterosteus aculeatus). After the first month of the experiment, Anabaena blooms appeared in the lake. We studied the effects of fish predation and occurrence of cyanobacteria blooms on the individual size structure (i.e. the distribution of the number of organisms over a size range) of zooplankton and phytoplankton. We also assessed the potential consequences for trophic transfer efficiency (TTE) (measured as the predator to prey biomass ratio) in the planktonic food web. Our results showed that fish predation and cyanobacteria bloom had a negative relationship with size diversity of zooplankton, which became dominated by small‐sized individuals in both cases. The phytoplankton size diversity changed over time particularly due to the blooming of large‐sized Anabaena, and its increase was apparently mainly driven by changes in resources. Low zooplankton size diversity related to fish predation reduced TTE, particularly in the enclosures with fish. This may be because low zooplankton size diversity represents a lower partition of resources among consumers, thereby decreasing the trophic energy transfer. With the occurrence of Anabaena bloom, high phytoplankton size diversity coincided with a lower energy transfer in all enclosures likely due to reduced zooplankton grazing when large‐sized colony‐forming Anabaena dominated. In conclusion, our results indicate that both top‐down and bottom‐up forces significantly influence the size structure of planktonic communities. The changes in size structure were related to shifts in the energy transfer efficiency of the Lake Mývatn food web. Thus, our study underpins the importance of taking into account size‐based interactions in the study of trophic cascades, particularly in a warming climate where strong planktivorous fish predation and frequent cyanobacteria blooms may occur.

Analysis and Modelling of Taste and Odour Events in a Shallow Subtropical Reservoir

Understanding and predicting Taste and Odour events is as difficult as critical for drinking water treatment plants. Following a number of events in recent years, a comprehensive statistical analysis of data from Lake Tingalpa (Queensland, Australia) was conducted. Historical manual sampling data, as well as data remotely collected by a vertical profiler, were collected; regression analysis and self-organising maps were the used to determine correlations between Taste and Odour compounds and potential input variables. Results showed that the predominant Taste and Odour compound was geosmin. Although one of the main predictors was the occurrence of cyanobacteria blooms, it was noticed that the cyanobacteria species was also critical. Additionally, water temperature, reservoir volume and oxidised nitrogen availability, were key inputs determining the occurrence and magnitude of the geosmin peak events. Based on the results of the statistical analysis, a predictive regression model was developed to provide indications on the potential occurrence, and magnitude, of peaks in geosmin concentration. Additionally, it was found that the blue green algae probe of the lake’s vertical profiler has the potential to be used as one of the inputs for an automated geosmin early warning system.

Weather Variability, Sunspots, and the Blooms of Cyanobacteria

The roles of weather variability and sunspots in the occurrence of cyanobacteria blooms, were investigated using cyanobacteria cell data collected from the Fred Haigh Dam, Queensland, Australia. Time series generalized linear model and classification and regression tree (CART) model were used in the analysis. Data on notified cell numbers of cyanobacteria and weather variables over the periods 2001 and 2005 were provided by the Australian Department of Natural Resources and Water, and Australian Bureau of Meteorology, respectively. The results indicate that monthly minimum temperature (relative risk [RR]: 1.13, 95% confidence interval [CI]: 1.02-1.25) and rainfall (RR: 1.11; 95% CI: 1.03-1.20) had a positive association, but relative humidity (RR: 0.94; 95% CI: 0.91-0.98) and wind speed (RR: 0.90; 95% CI: 0.82-0.98) were negatively associated with the cyanobacterial numbers, after adjustment for seasonality and auto-correlation. The CART model showed that the cyanobacteria numbers were best described by an interaction between minimum temperature, relative humidity, and sunspot numbers. When minimum temperature exceeded 18 degrees C and relative humidity was under 66%, the number of cyanobacterial cells rose by 2.15-fold. We conclude that weather variability and sunspot activity may affect cyanobacteria blooms in dams.

Short-term dynamics of cladocerans in a eutrophic shallow lake during a shift in the phytoplankton dominance

The changes in the dynamics of cladocerans in Lake Vela (Portugal), as well as the morphologic and life history traits of the small-bodied cladoceran Ceriodaphnia pulchella, were studied intensively during one month characterized by deep and fast changes in the phytoplankton community: the beginning of the cyanobacteria dominance. Lake Vela, located in the Mediterranean region, is a polymictic shallow lake exhibiting characteristics typical of an advanced trophic status, namely the permanently turbid water, the reduction in biodiversity and the occurrence of cyanobacteria blooms. The density and composition of the cladocerans populations varied considerably during the short-term period analyzed. Coincident with the increase of cyanobacteria, the density of Daphnia longispina decreased drastically, associated with an increase of Bosmina longirostris and Chydorus sp. The constant density of C. pulchella, even during the cyanobacteria dominance, and the strong relationship found between weight and size, suggests that the low quality of phyto- planktonic food in Lake Vela did not play an important role in its fitness. Besides the small size of C. pulchella, this fact could be also related to its diversified diet. Nevertheless, a closer examination of the life history parameters of C. pulchella revealed a reduction in the fecundity, size at first reproduction, mean size of ovigerous females and maximum size of the population, which suggest an increase of the fish pressure after the decline of Daphnia. C. pulchella showed also a short-life cycle and a fast turnover of individuals, which constitutes also an advantage, allowing a fast adaptive response of the population.

Aplicação de Phoslock® para Remoção de Fósforo e Controle de Cianobactérias Tóxicas

This article describes the potential of Phoslock® to adsorb phosphorous in water bodies and, consequently, to reduce the occurrence of cyanobacteria blooms in eutrophic systems. This product was developed recently in Australia, to restore both freshwater and marine ecosystems, and it is environmentally harmless and functional within a wide gradient of pH (4-11). Experimental tests were performed in the laboratory in order to test product efficiency in removing filterable reactive phosphorous (FRP) in solutions with concentrations of 0.5 and 1.0 mg L-1. Moreover, we tested the potential effect of Phoslock in reducing the growth of a toxic strain of cyanobacteria, Microcystis aeruginosa (NPLJ4). The treatments with Phoslock, have shown significant immobilization (p 94%, p<0,001). The results have corroborated Phoslock’s ability to remove sources of phosphorous from aquatic systems and to limit cyanobacteria growth due to the lack of this nutrient. Among the existing alternatives to control eutrophication, Phoslock is certainly innovative and immobilizes phosphates within the ecosystem without promoting side effects on aquatic organisms and human beings

Eutrophication, toxic cyanobacteria and cyanotoxins: when ecosystems cry for help

Eutrophication of freshwater resources has been studied worldwide and its consequences are of concern especially in waters used for recreation or drinking. The occurrence of cyanobacteria blooms is nowadays much better documented and among the major impacts we may point out the decrease in water transparency and oxygen levels, the production of off-flavours and the production of toxins. Among the most common toxins, microcystins, anatoxin-a and saxitoxins are the most common in Portugal. A diversity of microcystins has been identified so far but microcystin-LR is the most common. Many aquatic organisms are capable to resist certain levels of cyanotoxins making them vectors for toxins. We analysed this possibility using a diversity of cyanotoxins and organisms and found that microcystins and bivalves seem to be the combination that maximizes toxin transfer. New challenges are presented today in this research area, by using new and more sensitive chemical, biochemical and molecular techniques. This allows us to better understand these organisms that can produce both potent toxins and innovative drugs.

農業用調整池のクロロフィルａ，ＣＯＤＭｎ及び栄養塩類濃度の季節変動特性

Seasonal changes in the vertical profile of chlorophyll-a, CODMn and nutrient concentrations in an agricultural irrigation reservoir were investigated for two years. The reservoir had a maximum depth of 9 m, a surface area of 1.2 × 105 m2 and a maximum storage volume of 5.6 × 105 m3. The hydraulic retention time was about 3 days from April to August, and was 7 days from September to March. In July, Volvox sp. were dominant when the retention time was less and nutrient supply rates were high. On the other hand, Microcystis sp. were dominant when the retention time was more and nutrient supply rates were low in September. These results coincided partly with the occurrence of cyanobacteria blooms in nutrient-rich and slow-flowing waters.

An analysis of water column distributions in Florida Bay

Florida Bay is a shallow, semi-enclosed lagoon that has recently experienced significant changes to its ecosystem. These include increased turbidity and the occurrence of cyanobacteria blooms in the central region of the bay. To accurately understand these changes we need to understand the spatial and temporal patterns in observed water quality parameters. To this end, we have used empirical orthogonal functions (EOFs) to analyze both the spatial and temporal variability in an 8-yr record of water quality variables. We have used the EOFs in two ways, one highlighting local changes occurring in the bay, the other emphasizing changes occurring on a bay-wide scale. The local analysis shows that the central region of the bay has the greatest variability in water quality parameters, especially with respect to chlorophyll and nutrient concentrations. The bay-wide analysis shows a different picture. The chlorophyll blooms in the central bay are not apparent bay-wide indicating that they are a local manifestation of processes occurring on a bay-wide scale. The spatial and temporal patterns for nitrate are dissimilar from the other nutrients raising the possibility that the mechanisms controlling nitrate differ from those controlling other nutrients. On a bay-wide scale, spatial patterns are similar to distributions of sediment type and show the significance of interactions between the water column and benthos. Time-series analysis of the EOFs shows that the dominant variation of many water quality parameters is seasonal, even though a system-wide shift occurred between 1994-1995 corresponding to an increase in rainfall and runoff from the Everglades.