Divergent responses of diverse microalgae commonly found in drinking water source water to UV-C treatment

Microalgae pose major problems for drinking water treatment processes either through membrane fouling or through blooming events in source water during the summer months. Disinfection treatments such as chlorination and UV-C treatment of drinking water are designed to remove microorganisms including microalgae and bacteria. In order to treat water efficiently it is critical to understand the effect of UV-C treatment on the viability and vitality of phytoplankton. Moreover, this information can be used to assess the utility of UV-C treatment as a potential pre-treatment option for water clean-up. In this study we tested the population growth of 6 phytoplankton species representing three major taxonomic groups (green algae, diatoms and cyanobacteria), commonly found in freshwater lakes in North America and relevant for water treatment facilities. We exposed these species to UV-C treatment and monitored their post-exposure population growth over a 52–55-day period using a plate-based MPN (most probable number) method. We found the green alga Scenedesmus quadricauda and the cyanobacterium Anabaena flos-aquae to be most tolerant to the treatment, while the cyanobacterium Microcystis aeruginosa and the diatom Asterionella formosa were found to be most sensitive with viability being reduced at comparatively lower doses. No significant delays in growth post treatment (i.e. time lags) were reported within species. Asterionella formosa and Aulacoseira granulata showed the longest time lags of all species, which might be in part correlated with DNA repair mechanisms and other physiological adaptations. This work provides the basis for the assessment of UV-C treatment efficacy on freshwater phytoplankton.

     

The effect of environmental parameters and cyanobacterial blooms on phytoplankton dynamics of a Portuguese temperate Lake

The increasing occurrence of cyanobacterial blooms in freshwaters is of great concern due to the ability of many cyanobacteria to produce cyanotoxins. In the present work, the eutrophied Vela Lake (Central Portugal), used for recreational purposes and as a water source for agriculture, was monitored every fortnight between 2000 and 2001. Phytoplankton diversity and densities were measured and correlated to environmental parameters. A seasonal phytoplanktonic succession was observed and it was mainly correlated with conductivity, temperature, total suspended solids and nutrients availability (particularly phosphorus). Diatoms were dominant during winter months (inferior temperatures and higher nutrients availability) followed by green algae in early spring and then cyanobacteria from late spring until early autumn (less nutrient availability and higher temperatures). A massive cyanobacterial bloom of Aphanizomenon flos-aquae occurred early in May 2001 and was preceded by the lowest nitrogen levels measured in the water during all the study period. At the time of this bloom senescence, dissolved oxygen was severely depleted and a massive death of ichthyofauna was recorded. A Microcystis aeruginosa bloom was also detected in July 2001 and it occurred following a rapid decrease in abundance of green algae and diatoms. By considering not only the environmental parameters but also the occurrence of cyanobacterial blooms as explanatory variables in a canonical correspondence analysis, the variance explained for the phytoplanktonic assemblage during the study period was increased in about 7% achieving a total of 61.0%, indicating a correlation that may be due to the known competitive advantage and/or allelopathy of the bloom-forming cyanobacteria towards microalgae.     

Winter phytoplankton communities in different depths of three mesotrophic lakes (Łęczna-Włodawa Lakeland, Eastern Poland)

Phytoplankton samples were collected from three mesotrophic lakes: Piaseczno, Rogóźno and Krasne during winter seasons (from January to March). The samples were analyzed for species analysis and abundance of planktonic algae in relation to different depths of water column (0–7 m). Selected water physical-chemical parameters were also measured. Abundance of phytoplankton depended strongly on the thickness of snow and ice cover or mixing conditions. The maximal phytoplankton total number reached about 5 × 10⁶ ind. L⁻¹ beneath the clear ice in the Krasne Lake, minimal numbers were recorded under the thick snow and ice layers in the Piaseczno Lake (2 × 10³ ind. L⁻¹). The winter phytoplankton communities were dominated by flagellates principally cryptomonads (Cryptomonas spp. Rhodomonas minuta), euglenophytes (Trachelomonas volvocina, T. volvocinopsis), dinoflagellates (Peridinium bipes, Gymnodinium helveticum) and chrysophytes (Mallomonas elongata, M. akrokomos, Dinobryon sociale) or non-motile small species of blue-green algae (e.g. Rhabdoderma lineare, Limnothrix redekei), diatoms (Stephanodiscus spp., Asterionella formosa), and green algae (e.g. Scenedesmus spp., Monoraphidium spp.). Phytoplankton abundance and structure showed differentiation during the winter season and along the water column as well.     

Toxic Blue-green Algae Water Blooms Found in some Lakes in the German Democratic Republic

From 1977 to 1979 plankton samples were taken from 6 lakes in the German Democratic Republic (GDR) during water blooms and examined for their toxicity to homothermal animals. Microcystis aeruginosa, Aphanizomenon flos-aquae, Anabaena spiroides, and Oscillatoria redekei were dominant in the samples. With the exception of Oscillatoria redekei the algae tested had toxic effects on mice after intraperitoneal injection. The rate of survival of the test animals was particularly low when the algae were disintegrated by ultrasound or freeze-drying prior to injection, this indicating the endogenic character of the toxins. Water blooms of Microcystis aeruginosa taken from Lake Pehlitzsee (Eberswalde District) showed the highest toxicity with an LD₃₀ as high as 45 and 43.7 mg/kg, respectively. Injection of the lyophilized cells of Aphanizomenon flos-aquae brought about the same symptoms in the test animals as in the case of Microcystis, but the LD₃₀ was 200 mg/kg.     

Multiple asexual reproduction of Asterionella formosa Hass. from Lake Baikal and Angara reservoirs

The living plankton diatom Asterionella formosa from Lake Baikal and the Irkutsk Water Reservoir was studied using light microscopy. New facts were obtained which provide evidence of the occurrence of multiple asexual reproduction of Asterionella formosa.     

The influence of daylength,light intensity and temperature on the growth rates of planktonic blue-green algae

The in vitro growth rates under continuous light of the four dominant blue-green algae in Lough Neagh, Anabaena flos-aquae Bréb., Aphanizomenon flos-aquae Ralfs fa. gracile Lemm., Oscillatoria agardhii Gom. and Oscillatoria redekei van Goor were slower than in situ rates from Lough Neagh that had been corrected for hours of light received by the algae. However, by culturing on a 6: 18 light-dark cycle in vitro growth rates were obtained that were similar to the in situ rates. Under continuous light small species showed the fastest growth with Oscillatoria redekei the dominant species. However, this pattern was almost completely reversed under the light-dark cycle with Oscillatoria redekei only exhibiting the fastest growth rate under low light conditions. This observation showed agreement with Lough Neagh field data which showed that Oscillatoria redekei reached its maximum crop in April while the other three species were dominant during the summer months. Compared to the generally assumed high thermal tendency of blue-green algae the temperature maxima of the four species were low. No growth was observed at 35°C for any species while Anabaena flos-aquae was severely inhibited at 25°C.     

Contribution of benthic blue-green algal recruitment to lake populations and phosphorus translocation

1. A two-season investigation was undertaken to determine the contribution of benthic recruitment to the population development of several species of blue-green algae. 2. Gloevtrichia echinulata populations were shown to be heavily subsidized by benthic recruitment, deriving on average 40% of their planktonic colonies from the benthos. 3. Benthic recruitment of Aphanizomenon flos-aquae, Anabaena flos-aquae and a second Anabaena species contributed less than 2% to planktonic increases, while Microcystis aeruginosa recruitment was negligible. 4. Phosphorus translocation via migrating G. echinulata accounted for most of the phosphorus (P) in the planktonic colonies, and constituted a significant portion of the internal loading of the lake. 5. Estimated P translocation via Aph. flos-aquae was relatively minor, although there was evidence of luxury uptake in the benthos.     

Phytoplankton population dynamics of a small reservoir: use of sedimentation traps to quantify the loss of diatoms and recruitment of summer bloom-forming blue-green algae

A vertical series of sedimentation traps was placed in a smallreservoir (Guelph Lake, Southern Ontario, Canada) in the springthrough summer of 1981 to intercept floating and sinking phytoplanktoncells. Information from the sedimentation traps was used todetermine the sinking loss rates of diatoms and to estimatethe relative contribution of sedimentation to the loss of thesespecies. Sinking loss rates varied with time and with depth.Sinking loss rates for Stephenodiscus astrea, Melosira granulata,and Asterionella formosa increased with the onset of thermalstratification. The abundance of Cyclotella meneghiniana declinedas the surface pH increased. The results showed good agreementbetween the proposed sedimentary fluxes of diatoms and the correspondingmaximum standing crop. Information from the trap catches wasalso used to examine the possibility of recruitment of summerblue-green species from the sediments. Specific migration ratesof floating colonies of Microcystis aeruginosa, Gompliosphaerialacustris and of Lyngbya Birgei filsments at 10 m were high(>1) for periods of time in August. For these blue-greenalgae, estimates of the population gain due to recruitment fromthe sediments ranged from 2 to 4% of the maximum standing crop.The high rates of accumulation of total phosphorus (TP) in thedownward facing trap at 10 m provided further evidence thatresuspension of material from the sediments occurred at thistime. The appearance of these blue-green algae cointided withhigh surface temperatures and the development of anoxic conditionsat 10 m. The growth or recruitment of Aphanizomenon flos-aquaewas initiated under different environmental conditions thanthose for Mierocystis, Gomphosphaeria and Lyngbya. Evidencesuggests that the Aphanizomenon filaments present at Station1 originated from the Station 3 end of the lake and were advectedtowards Station 1. ¹Present address: Zoology Department, University of Alberta,Edmonton, Alberta T6G 2E1, Canada. ²Present address: CSIRO Division of Fisheries Research, GPOBox 1538, Hobart, Tasmania, Australia 7001.     

Limnology of Heart Lake,Ontario

Heart Lake, a small dimictic lake in Southern Ontario shows classical characteristics of eutrophy: high phytoplankton populations, blooms of blue-greens, predominently Aphanizomenon flos-aquae, in summer, a shallow photic zone decreasing seasonally in response to dense phytoplankton crops and a hypolomnion which is deoxygenated from early summer to fall turnover. Large decreases occur in TDP and SRS in particular, but also in TDN from spring to summer.The distribution of individual species of algae with depth in the epilimnion was seldom uniform but, more commonly conformed to a definite pattern. The simultaneous existence of different patterns in different species provides evidence of spatial heterogeneity (niche diversification) in the epilimnion, which could lessen any interspecific competition.Diatom stratigraphy in a 70 cm core revealed that the lake has been eutrophic throughout but may have gone through 3 periods; of these, the most recent one was the most eutrophic and was preceeded by a period of unusually low water levels.     

Lysis of Aphanizomenon flos-aquae (Cyanobacterium) by a bacterium Bacillus cereus

A phytoplankton-lytic (PL) bacterium, Bacillus cereus, capable of lysing the bloom-forming cyanobacterium Aphanizomenon flos-aquae was isolated from Lake Dianchi of Yunnan province, China. This bacterium showed lytic activities against a wide range of cyanobacteria/algae, including A. flos-aquae, Microcystis viridis, Microcystis wesenbergi, Microcystis aeruginosa, Chlorella ellipsoidea, Oscillatoria tenuis, Nostoc punctiforme, Anabaena flos-aquae, Spirulina maxima, and Selenastrum capricornutum. Chlorophyll a contents, phycocyanin contents, and photosynthetic activities of the A. flos-aquae decreased evidently in an infected culture for a period. Bacterium B. cereus attacked rapidly A. flos-aquae cells by cell-to-cell contact mechanism. It was shown that the lysis of A. flos-aquae began with the breach of the cyanobacterial cell wall, and the cyanobacterial cell appeared abnormal in the presence of the PL bacterium. Moreover, transmission electron microscope examinations revealed that a close contact between the bacterium and the cyanobacterium was necessary for lysis. Some slime extrusions produced from B. cereus assisted the bacterial cells to be in close association with and lyse the cyanobacterial cells. These findings suggested that this bacterium could play an important role in controlling the Aphanizomenon blooms in freshwaters.     

Investigation of a toxic water-bloom of Microcystis aeruginosa (Cyanophyceae) in Lake Akersvatn,Norway

During the summer and fall of 1984 and 1985, the eutrophic Lake Akersvatn in south-eastern Norway, used as reserve drinking water reservoir, was found to produce heavy water-blooms of the colonial blue-green alga Microcystis aeruginosa. Samples of the water-bloom were found to be toxic using the mouse bioassay. No toxin was found free in the water as detected by HPLC and mouse bioassay. The toxic cells (minimum lethal dose 8–15 mg/kg body weight in mice) and purified toxin (minimum lethal dose 50 μg/kg body weight in mice) showed signs of poisoning in laboratory rats and mice identical to that of other hepatotoxin-producing M. aeruginosa blooms and strains reported from other parts of the world. The toxin has chemical properties similar to the cyclic heptapeptide reported for a South African M. aeruginosa toxin. The toxin from Lake Akersvatn bloom material has a molecular weight of 994. The toxic bloom of M. aeruginosa persisted from August to November in 1984 and reappeared in July of 1985. While water from Lake Akersvatn was not used for municipal water supply during this period, the presence of toxic blue-green algae in a drinking water reservoir indicates the need to develop monitoring and detection methods for toxic cells and toxin(s).     

Effects of the blue-green alga Microcystis aeruginosa on zooplankton competitive relations

Summary Field distribution patterns and laboratory feeding experiments have suggested that blooms of colonial blue-green algae strongly inhibit relatively large-bodied daphnid cladocerans. We conducted laboratory experiments to test the hypothesis that blooms of the colonial blue-green alga Microcystis aeruginosa would shift competitive dominance away from large-bodied daphnid cladocerans toward smaller-bodied cladocerans, copepods, and rotifers. In laboratory competition experiments, increasing the proportion of M. aeruginosa in the algal food supply resulted in a shift from dominance by the relatively largebodied cladoceran Daphnia ambigua to dominace by the copepod Diaptomus reighardi. The small-bodied cladoceran Bosmina longirostris was always numerically heavily dominant over D. ambigua, but its estimated population biomasses were only slightly higher than those of D. ambigua. Daphnia ambigua consistently outcompeted the rotifer Brachionus calyciflorus. Our results demonstrate that blooms of M. aeruginosa can alter zooplankton competitive relations in laboratory experiments, favoring small-bodied cladocerans and copepods at the expense of large-bodied cladocerans. However, contrary to predictions, blooms of M. aeruginosa did not improve the competitive ability of rotifers.     

The Influence of Toxic and Filamentous Blue-green Algae on Feeding and Population Growth of the Rotifer Brachionus rubens

The effect of toxic and of filamentous blue-green algae on feeding and population growth of the rotifer Brachionus rubens was investigated in laboratory experiments. A toxic strain of Microcystis aeruginosa was ingested, but rotifers cultured with Microcystis died faster than nonfed controls. The rigid filaments of Cylindrospermopsis raciborskii were not ingested, reduced the ingestion of simultaneously offered algae, and depressed population growth rates. The soft filaments of Anabaena flos-aquae were ingested at a moderate rate, did not reduce ingestion of other algae, and were used as an additional food in population growth experiments.     

Is food availability the main factor controlling the abundance of Euchlanis dilatata lucksiana Hauer in a shallow,hypertrophic lake?

Visual observations and experiments on food preference of Euchlanis dilatata lucksiana show that this euchlanid can feed on blue-green algae not consumed by the most planktonic animals. Nevertheless, even in lakes with blooms of blue-green algae, E. d. lucksiana occur infrequently and generally in low numbers. The paper is an attempt to explore into the causes for the rare occurrence of Euchlanis in the pelagial. A comparison of threshold food concentrations calculated from N and P excretion rates (Gulati et al., this volume) with the concentrations of seston in the Lake Loosdrecht shows that the latter were several times higher during study period in 1984. This implies that the food requirements of Euchlanis were always satisfied in this lake. The time needed for the consumption of the total food fraction in a liter of lake water by a concentration of 50 Euchlanis l^–1 was also calculated. This time varied from 70 to 200 days, so a Euchlanis population even at its maximum density will not cause major changes in blue-green algae biomass by grazing. Thus, food limitation cannot be viewed as a factor controlling the Euchlanis densities in Loosdrecht Lakes. There is some evidence that Euchlanis is heavily predated in Loosdrecht Lakes, losses in its biomass accounting for 126% of the production. Adaptation of this species to the littoral zone, as expressed by the deposition of eggs on plants, can also limit the occurrence of the lucksiana form to water bodies with blooms of blue-green algae.     

巢湖蓝藻水华形成原因探索及"优势种光合假说"

为探索蓝藻水华的形成原因,从2007以来对巢湖西区浮游藻类种类、优势种季节变化、初级生产力、水质参数及优势种的光合生理生态学特性作了观测。关于蓝藻水华形成过程中迅猛发展的原因,近80a已提出了10种假说,但对解释巢湖形成的蓝藻水华,尚显不足。本文基于我们对蓝藻水华的了解,提出了如下“优势种光合假说”：（1）蓝藻水华包含各种藻类,蓝藻水华发生不仅与藻细胞浓度有关,还与水体初级生产力直接有关。巢湖中这两者在夏季最大,在冬季最小。但无定量关系。（2）水华藻类中生长最快、细胞密度最大的是优势种,含有多个优势种时可能随季节更替。巢湖几乎整年发生蓝藻水华,已检测出4种优势种都是蓝藻,从早春起先是水华鱼腥藻,以后有绿色微囊藻、惠氏微囊藻和铜绿微囊藻。（3）各种环境因子都影响优势种生长,其中少数主导因子影响较大。在巢湖富营养条件下,光强、温度和pH值是主导因子。（4）主导因子对优势种光合活性的影响,可决定其能否处于优势。巢湖的温度和pH值变化可能促进了惠氏微囊藻取代绿色微囊藻,铜绿微囊藻取代惠氏微囊藻,而光强变化可能调节冬季时水华鱼腥藻取代了绿色微囊藻,春季时正好是相反的取代。     

Cyanophycean blooms in the reservoir of Val Joly (northern France) and their development in downstream rivers

A study was carried out in 1992 on the Val Joly reservoir and the rivers situated downstream: the River Helpe Majeure and the canalized Sambre into which it flows 40 km below the reservoir. Each year, blooms of blue-green algae occur in the reservoir. They are dominated by species such as Aphanizomenon flos-aquae (L.) Ralfs in 1991 or Pseudanabaena tenuis Koppe and Oscillatoria pseudogeminata G. Schmid in 1992. A typical fluvial composition of the phytoplankton was mostly restored above the confluence with the Sambre. Nevertheless, significant quantities of Oscillatoria and Pseudanabaena have been observed in the River Sambre, just below its confluence with the Helpe Majeure. The environmental conditions in the River Sambre do not allow Aphanizomenon to develop, but could favour Oscillatoria blooms.     

Interactions between Light Situation,Depth of Mixing and Phytoplankton Growth during the Spring Period of Full Circulation

Investigations lasting several years at the artificial Lake Saidenbach have shown that, due to the poor light situation expressed in terms of average daily radiation (Riley 1957), mean daily exposure (Reynolds 1973), extinction depth and the ratio ^zmis/^zeu, no mass development of the phytoplankton should actually occur during the spring complete circulation. In practice, however, the period of complete circulation of the water in spring is not only a prerequisite for, but often also the factor causing, the mass development (usually Asterionella formosa). The poor light situation and the fact that the vertical phytoplankton profile shows significant differences between the plankton concentrations at different depths indicate that the spring complete circulation does not represent a complete recirculation, and thus mixing, of the water down to the bottom but involves only episodic and local partial recirculations interspersed with periods of relatively slight turbulence. The actual mixing depth during this period of complete circulation is therefore obviously less than the mean depth of the water concerned, which is commonly assumed to equal. This permits the algae in the upper layers to grow. Respiratory losses of the phytoplankton at greater depths probably remain slight due to their adaptation to low light intensities in winter.     

Inhibition of phytoplankton species by co-culture with a fungus

Harmful algal blooms are a serious worldwide environmental problem. Algicidal microorganisms, especially bacteria, have attracted extensive attention as possible agents for inhibiting water blooms. Such capabilities, however, are rarely reported for fungi. In this work, a fungal strain, Trichaptum abietinum 1302BG, is studied for its capability to inhibit four phytoplankton species: Microcystis aeruginosa FACH-918, Microcystis flos-aquae FACH-1028, Oocystis borgei FACH-1108, and Microcystis aeruginosa PCC 7806. The results show that the chlorophyll-a from these phytoplankton species co-cultured with Trichaptum abietinum 1302BG decreases rapidly 24 h after inoculation, and phytoplankton cells almost completely disappear 48 h after incubation. These results suggest that the fungus strain has great potential for the degradation of phytoplankton species. To the best of our knowledge, this is the first report of a white-rot fungus that can inhibit harmful algae blooms species.     

Seasonal succession of phytoplankton in Lake Yogo over 2 years: effect of artificial manipulation

We studied the seasonal variation in concentrations of nutrients and phytoplankton in Lake Yogo for 2 years, from May 2000 to May 2002, in order to clarify the seasonal succession of phytoplankton and the effect of various manipulations on it. It was revealed that in spite of the installation of aeration systems and the pumping of mesotrophic water from Lake Biwa during the summer season, the trophic state of Lake Yogo overall has not improved during the past few decades. However, the pumping of water from Lake Biwa did affect the concentrations of nutrients and the periods of cyanobacterial bloom during the summer. The pumping period was different in each year, and the cyanobacterial bloom occurred during the period without pumping in both years. The aeration destratification was not strong enough to prevent cyanobacterial blooms. Cyanobacteria and Bacillariophyceae contributed most to the phytoplankton biomass in both years. Aphanizomenon, Anabaena, and Microcystis were the main genera among cyanobacteria. The bloom of Aphanizomenon or Anabaena occurred early in the summer, and was then replaced by Microcystis. Aphanizomenon was almost always present, and often formed bloom even in winter. The seasonal succession of Bacillariophyceae was almost the same in both years and was well categorized: winter-growing species such as Aulacoseira pusilla (F. Meister) Tuji et Houki and species of Thalassiosiraceae, spring-growing species such as Asterionella formosa Hassall, Fragilaria crotonensis Kitton, and Synedra cf. acus, and fall-growing species such as Aulacoseira ambigua (Grunow) Simonsen, and Aulacoseira granulata (Ehrenb.) Simonsen.     

Responses of the planktonic diatom Asterionella formosa Hassall to abiotic environmental factors in a reservoir complex (south-eastern France)

The River Durance and its main tributary, the Verdon, are both highly regulated rivers flowing in south-eastern France. The course of both rivers is interrupted by a series of reservoirs with quite different geographical, morphometric, climatic, hydrodynamic and chemical characteristics. The planktonic diatom Asterionella formosa Hassall, which has undesirable cyclic effects from the water management point of view, was studied in this complex of reservoirs located in the Mediterranean region. The results indicate that only the monomictic calcareous reservoirs show a bimodal pattern of Asterionella formosa abundance. The population dynamics of this algal species was found to depend on both the morphometric features and the hydraulic mode of management (retention time) used at each reservoir, as well as on the physical (temperature, suspended matter) and chemical (nitrogen, silica, calcium) characteristics of the water.