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From April 2012 to January 2013 (over four seasons), in situ microcosm experiments were conducted in Lake Taihu, perturbed over a range of pC[O.sub.2] scenarios (270, 380, and 750 µatm; 1 atm = 101.325 kPa). The influence of C[O.sub.2] level on microcosms was greatest during the spring because of the high growth rate of phytoplankton. In this season, rising C[O.sub.2] levels caused a pH reduction, and the maximum reduction was 0.6 units when C[O.sub.2] level was enhanced from the present level to 750 µatm. The doubling of C[O.sub.2] level could increase the net primary production (NPP) by 65% during spring when the concentrations of other nutrients were maintained. The rise of NPP could cause a decline of dissolved inorganic carbon (DIC) concentration, and C[O.sub.2] enrichment might mitigate the extent of this decline. Meanwhile, higher C[O.sub.2] may slow or prevent a loss of diversity of phytoplankton in microcosms in this season. During the other three seasons, Microcystis predominated, and the percentage of cyanobacteria did not alter with the change of C[O.sub.2]. We did not observe a significant increase in the abundance of any taxa with the rise of C[O.sub.2] during the in situ microcosm experiments. D'avril 2012 a janvier 2013 (quatre saisons), des experiences en microcosmes in situ ont ete menees dans le lac Taihu, les microcosmes etant perturbes de maniere a couvrir une fourchette de scenarios de pC[O.sub.2] (270, 380 et 750 µatm; 1 atm = 101.325 kPa). L'influence des niveaux de C[O.sub.2] sur les microcosmes etait la plus grande au printemps en raison du taux de croissance eleve du phytoplancton. Durant cette saison, l'augmentation des concentrations de C[O.sub.2] causait une reduction du pH, la reduction maximum etant de 0,6 unite quand la concentration de C[O.sub.2] etait rehaussee a 750 µatm. Le fait de doubler la concentration de C[O.sub.2] pouvait se traduire par une augmentation de 65 % de la production primaire nette (PPN) au printemps, quand les concentrations d'autres nutriments etaient maintenues constantes. L'augmentation de la PPN pouvait causer une diminution de la concentration de carbone inorganique dissous (CID) dans l'eau et l'augmentation du C[O.sub.2] pouvait attenuer l'ampleur de cette diminution. Par ailleurs, des teneurs en C[O.sub.2] plus elevees pouvaient ralentir ou empecher une baisse de diversite du phytoplancton dans les microcosmes durant cette saison. Durant les trois autres saisons, Microcystis predominait, et le pourcentage de cyanobacteries ne variait pas en fonction de la concentration de C[O.sub.2]. Aucune augmentation significative de l'abondance d'un taxon associee a l'augmentation du C[O.sub.2] durant les experiences en microcosmes in situ n'a ete observee. [Traduit par la Redaction], Introduction Atmospheric C[O.sub.2] levels have increased from their preindustrial level of 270 µatm (1 atm = 101.325 kPa) to the current level of 400 µatm. Furthermore, the Intergovernmental Panel on [...]

We describe the pattern and the principal factors affecting the phytoplankton biomass-nutrient relationship in the pelagic zone of large lakes. The results showed that the phytoplankton abundance and biomass of Cyanophyta, Cryptophyta, and Pyrrophyta were significantly correlated with trophic states. The total phosphorus (TP)-biomass relationship curves showed that the increment of biomass with TP is weak at high TP levels. The decrease in biomass at the high end of the curves might be a synthesis of the pattern of responses of the major taxonomic groups (except cyanobacteria) to environmental variables. Light limitation might be one of the important factors causing the decrease in the TP-biomass curve at high TP concentrations. If the mean underwater available light is lower than ~250 µmol photons-[m.sup.-2] x [2.sup.-1], clear-water species decline and cyanobacteria become dominant. The responses to available light of these key species play a central role in modulating the biomass-nutrient relationship. Our results contribute to the understanding of this relationship in the pelagic zone of large eutrophic lakes and have important practical implications for lake management. Resume : Nous decrivons la relation entre la biomasse de phytoplancton et les nutriments dans la zone pelagique de grands lacs et les facteurs qui influent sur cette relation. Les resultats montrent que l'abondance du phytoplancton et la biomasse de cyanophytes, de cryptophytes et de pyrrophytes sont fortement correlees a l'etat trophique. Les courbes de phosphore total (TP)-biomasse indiquent que, a TP eleve, l'augmentation de la biomasse co'incidant avec une augmentation du TP est faible. La diminution de la biomasse a l'extremite superieure des courbes pourrait refleter un effet synthetique des reactions des principaux groupes taxinomiques (a l'exclusion de cyanobacteries) a des variables du milieu. La restriction de la lumiere pourrait etre un des facteurs importants a l'origine de la diminution observee de la courbe TPbiomasse a des concentrations de TP elevees. Si la lumiere moyenne disponible sous l'eau est inferieure a environ 250 (xmol photons-m-2-s-1, l'abondance des especes d'eau claire diminue et les cyanobacteries deviennent dominantes. Les reactions de ces especes cles a la lumiere disponible jouent un role central dans la modulation de la relation entre biomasse et nutriments. Nos resultats contribuent a une meilleure comprehension de cette relation dans la zone pelagique de grands lacs eutrophes et ont d'importantes consequences pratiques en ce qui concerne la gestion des lacs. [Traduit par la Redaction], Introduction Phytoplankton distributions and composition are important for both aquatic ecosystems and the global environment because phytoplankton are the major primary producers in most aquatic ecosystems and are responsible for [...]

The rates of temporal and spatial species turnover have been compared in different organisms and scales, revealing that both are not independent but, rather, associated. However, the knowledge is limited for the association between spatial turnover and temporal turnover. Here, we performed two investigations of the phytoplankton composition in the lakes of the Yangtze River catchment in China in the spring and summer of 2012, which covered regional spatial scale and two‐season temporal scale. We analysed the association between temporal and spatial species turnover in phytoplankton. The results showed that 1) the two‐season temporal turnover of phytoplankton varied based on the mean values and the coefficient of variance of environmental variables, and pH was the most important variable negatively affecting the temporal turnover; 2) the spatial beta diversity of phytoplankton in summer was higher than that in spring, and the distance decay pattern was significant in summer, but not in spring; 3) the variation in spatial turnover in spring and summer was attributed to the primary environmental variables (nitrogen, phosphorus and underwater available light) and broader‐scale spatial variables; 4) the proportion of jointly explained variation of spatial Bray–Curtis dissimilarity by the environment and space increased from ~38% (spring) to ~55% (summer), which was mainly due to the variation in spatially structured environmental variables during the two‐season temporal turnover, such as pH and ion concentrations; 5) the community compositions in summer were more similar between the lakes with similar two‐season temporal turnover. These results indicate that the spatial turnover of phytoplankton composition in summer was partially predetermined by the variation in environmental variables and phytoplankton composition during the process of two‐season temporal turnover, and highlight the understanding of temporal variations in spatial beta diversity as well as the underlying assembly mechanisms in phytoplankton. [ABSTRACT FROM AUTHOR]

The diversity and composition of photosynthetic picoeukaryotes (PPEs) in two large shallow lakes in China (Lake Taihu and Lake Chaohu) were investigated from flow cytometry sorted samples using Miseq high-throughput sequencing. We collected 65 samples covering different regions of the two lakes over four seasons to unveil spatial and temporal patterns of PPEs community composition. The use of flow cytometry sorting largely improved the efficiency of detecting PPEs sequences and over 70% of the retrieved reads belonged to PPEs. Chlorophyta and Bacillariophyta dominated PPEs in most of the samples. A distinct but complex seasonality of PPEs composition emerged at the OTUs level. NGS-based Miseq sequencing facilitates an in-depth view of numerous rare OTUs. Nearly 80% of the PPEs OTUs were rare and lots of them were detected only in one season, whereas most of the abundant OTUs were frequently detected in all seasons but only changed in relative abundances. Besides, a close relative of the marine PPEs species Ostreococcus sp. (OTU_1144, 99% identity) was discovered in freshwater systems for the first time and was abundant especially in winter. The diversity and community composition of PPEs were more dependent on season rather than sampling sites. Temperature, phycocyanin and NO3AN concentrations in Lake Taihu explained the PPE composition variations, whereas in Lake Chaohu TN/TP ratios, temperature, pH and nephelometric turbidity units (NTU) seemed to be the most important factors. In addition, a great number of OTUs belong to nonpigmented picoeukaryotes, especially Chytridiomycota, Perkinsozoa, Ciliophora and Cercozoa, which are known to include algae parasites as well as predators. The results of mantel test also showed that the community of photosynthetic and nonpigmented picoeukaryotes were significantly correlated in both lakes. [ABSTRACT FROM AUTHOR]

Quantitative evidence of sudden shifts in ecological structure and function in large shallow lakes is rare, even though they provide essential benefits to society. Such 'regime shifts' can be driven by human activities which degrade ecological stability including water level control ( WLC) and nutrient loading. Interactions between WLC and nutrient loading on the long-term dynamics of shallow lake ecosystems are, however, often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we focus on a large shallow lake (Lake Chaohu) located in one of the most densely populated areas in China, the lower Yangtze River floodplain, which has undergone both WLC and increasing nutrient loading over the last several decades. We applied a novel methodology that combines consistent evidence from both paleolimnological records and ecosystem modeling to overcome the hurdle of data insufficiency and to unravel the drivers and underlying mechanisms in ecosystem dynamics. We identified the occurrence of two regime shifts: one in 1963, characterized by the abrupt disappearance of submerged vegetation, and another around 1980, with strong algal blooms being observed thereafter. Using model scenarios, we further disentangled the roles of WLC and nutrient loading, showing that the 1963 shift was predominantly triggered by WLC, whereas the shift ca. 1980 was attributed to aggravated nutrient loading. Our analysis also shows interactions between these two stressors. Compared to the dynamics driven by nutrient loading alone, WLC reduced the critical P loading and resulted in earlier disappearance of submerged vegetation and emergence of algal blooms by approximately 26 and 10 years, respectively. Overall, our study reveals the significant role of hydrological regulation in driving shallow lake ecosystem dynamics, and it highlights the urgency of using multi-objective management criteria that includes ecological sustainability perspectives when implementing hydrological regulation for aquatic ecosystems around the globe. [ABSTRACT FROM AUTHOR]

The recruitment of overwintering benthic cyanobacteria from the sediment surface is important for the development of cyanobacterial blooms during warm spring seasons. Thus, controlling the growth of cyanobacteria at the benthic stage to inhibit their recruitment is vital to control or delay the formation of summer blooms. In this study, overwintering benthic cyanobacteria were exposed to ascending hydrogen peroxide (H 2 O 2 ) concentrations (0, 1, 5, and 20 mg/L) in a simulated overwintering environment. Photosynthetic pigments, physiochemical features, and antioxidant responses were evaluated to determine the inhibitory effects of H 2 O 2 on the growth of benthic cyanobacteria and to identify the potential mechanisms thereof. These H 2 O 2 -treated cyanobacteria were then collected through filtration and transferred to an optimum environment to evaluate their recovery capacity. The results showed that chlorophyll a and phycocyanin contents, photosynthetic yield, and esterase activity decreased significantly in H 2 O 2 treated groups compared to the control. The activities of superoxide dismutase (SOD) and catalase (CAT) in benthic cyanobacteria were inhibited after 72 h exposure to H 2 O 2 , while the malondialdehyde (MDA) contents were stimulated at the same time. These results indicate that H 2 O 2 can inhibit the growth of benthic cyanobacteria, and H 2 O 2 -induced oxidative damage might be one of the mechanisms involved. The recovery experiment showed that the impairment of benthic cyanobacteria was temporary at a low dose of 1 mg/L H 2 O 2 , but permanent damage was induced when H 2 O 2 concentrations were increased to 5 and 20 mg/L. Overall, our results highlight that H 2 O 2 is a potential cyanobacteria inhibitor and can be used to decreasing the biomass of overwintering cyanobacteria, and could further control the intensity of cyanobacteria during the growth seasons. [ABSTRACT FROM AUTHOR]

Ref: Can. J. Aquat. Sci. 69(12): 1935-1946 (2012). In the original paper, the last paragraph of the Discussion contained a typo where a less than symbol should have been a [...]

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Microcystis is the dominant algal bloom genus in Lake Taihu. Thus, controlling the recruitment and growth of Microcystis is the most crucial aspect of solving the problem of algal blooms. Different concentrations (0.025, 0.05, and 0.1 g L) of tea extract were used to treat barrels of lake water at the recruitment stage of cyanobacteria. There was an inhibitory effect on algal growth in all treatment groups. The inhibitory effect on cyanobacteria was stronger than on other algae. The metabolic activity of cells in the treatment groups was significantly enhanced compared to the control, as an adaptation to the stress caused by tea polyphenols. The photosynthetic activity diminished in the treatment groups and was barely detected in the 0.05 and 0.1 g L treatments. The levels of reactive oxygen species increased substantially in treated cells with the algal cells experiencing oxidative damage. The effect of tea on zooplankton was also studied. The number of Bosmina fatalis individuals did not change significantly in the 0.025 and 0.05 g L treatments. These results suggested that the application of tea extracts, during the recruitment stage of blue-green algae, suppressed the recruitment and growth of cyanobacteria, thus offering the potential to prevent cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

Biofilms play important roles in microbial communities and are related to infectious diseases. Here, we report direct evidence that a bacterial nox gene encoding NADH oxidase is involved in biofilm formation. A dramatic reduction in biofilm formation was observed in a Streptococcus sanguinis nox mutant under anaerobic conditions without any decrease in growth. The membrane fluidity of the mutant bacterial cells was found to be decreased and the fatty acid composition altered, with increased palmitic acid and decreased stearic acid and vaccenic acid. Extracellular DNA of the mutant was reduced in abundance and bacterial competence was suppressed. Gene expression analysis in the mutant identified two genes with altered expression, gtfP and Idh, which were found to be related to biofilm formation through examination of their deletion mutants. NADH oxidase-related metabolic pathways were analyzed, further clarifying the function of this enzyme in biofilm formation. [ABSTRACT FROM AUTHOR]

The patterns of spatial and temporal shifts in bloom-forming cyanobacteria and the driving factors for these patterns were determined by analyzing the distribution of these cyanobacteria in Lake Chaohu using data from satellite images and field samples collected during 2012 and 2013. The cyanobacterial blooms primarily occupied the western region of Lake Chaohu, and the direction and speed of the prevailing wind determined the spatial distribution of these blooms. The cyanobacteria in Lake Chaohu were dominated by species of M icrocystis and A nabaena. M icrocystis reached its peak in June, and Anabaena had peaks in May and November, with an overall biomass that was higher than that of M icrocystis. M icrocystis generally occupied the western region of the lake in summer, whereas Anabaena dominated in other regions and seasons. Temperature may be responsible for these seasonal shifts. However, total phosphorus ( TP), pH, temperature, turbidity and nitrate/nitrite nitrogen determined the coexistence of the two genera in different regions in summer. TP was correlated with M icrocystis dominance, and pH and light availability were correlated with A nabaena dominance. Our results contribute to the understanding of shifts in bloom-forming cyanobacteria and are important for the control of cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

To establish the influence of phytoplankton blooms on the dynamics and sources of dissolved organic carbon (DOC) in Lake Taihu, the concentrations and stable carbon isotope values (δ 13 C) of DOC and particulate organic carbon (POC) were analyzed, along with environmental factors, including water temperature, chlorophyll a (Chl a ) concentration, phytoplankton community and total bacterial abundance, from March to August 2013 at five sites in Lake Taihu. Significant differences were observed in the DOC concentrations and δ 13 C DOC values at the sampling sites. On average, the proportion of DOC in the total organic carbon (TOC) pool ranged from 30% ± 10% to 81% ± 7%. POC was positively associated with both Chl a concentration and cyanobacteria biomass, suggesting that cyanobacteria blooms contribute to the POC pool in Lake Taihu. Depleted 13 C in DOC relative to POC was observed in August, indicating that DOC was partially derived from POC in August. However, Chl a explained only 40% of the variation in DOC in the entirety of Lake Taihu, and at two sites far from the estuary, the contribution of allochthonous carbon was less than 50% in August. These results suggested a greater influence of allochthonous sources on the DOC pool. Moreover, the biodegradability of DOC was further determined by the total dissolved carbohydrates to DOC ratio (TCHO/DOC), specific UV absorbance (SUVA 254 ), and the concentrations of bioavailable DOC (BDOC). On average, 17% of the variation in DOC was attributable to the BDOC pool, and the BDOC concentration correlated positively with Chl a , cyanobacteria biomass, and total bacterial abundance, suggesting that cyanobacteria–derived DOC is biodegradable and is preferentially utilized by bacteria. [ABSTRACT FROM AUTHOR]

In this study, Microcystis aeruginosa was cultivated in a P-limited and P-replete culture medium and exposed to artificial UV-B radiation to investigate the interactive effect of UV-B exposure and phosphorus limitation on this harmful alga. After 15 days, both UV-B exposure and phosphorus limitation led to a significant decline in pigment content (phycocyanin and carotene) and photosynthetic activity ( F/ F and ETR), and the impact was most pronounced when the two conditions were combined. Due to the interactive effect, P-limited M. aeruginosa under UV-B exposure exhibited the lowest cell density compared to the other treatments. These results suggest that phosphorus limitation increases the stress of UV-B radiation in Microcystis. In other words, high-level UV-B radiation has higher growth inhibitory on Microcystis in P-limited lakes than in P-replete lakes. [ABSTRACT FROM AUTHOR]

SUMMARY Phytoplankton is sensitive to rapidly increasing temperature in spring. However, studies on the effect of temperature on phytoplankton have mainly focused on constant temperatures. It is necessary to clarify the determining parameters of phytoplankton shifts during temperature increases, as temperatures are predicted to fluctuate more intensively and frequently in the future. In the study, we analyzed the responses of photosynthetic properties and growth in a cyanobacterium ( Microcystis aeruginosa) and a green alga ( Chlorella pyrenoidosa), the dominant species in Taihu, to rapid increasing-temperature process in the laboratory and in the field. The results show that gradually increasing temperature inhibited photosynthesis and the growth of C. pyrenoidosa and had almost no effect on M. aeruginosa. Elevated increasing temperature range also had more significant effects on the photosynthetic properties and growth rates of C. pyrenoidosa than those of M. aeruginosa in the laboratory and in the field. All of these results suggest that the photosynthetic performance of M. aeruginosa is more suitable to gradually increasing temperature and relatively strong temperature variations than that of C. pyrenoidosa, which might partially contribute to Microcystis excluding Chlorella competitively in aquatic ecosystem. Our findings point out the possible importance of the rapid and dramatic increasing-temperature process to the formation of cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

To determine how Chlorella pyrenoidosa responds to short-term grazing and grazing-associated infochemicals from Daphnia carinata, we measured the growth, esterase activity, chlorophyll fluorescence, and cell size of the alga. Cell densities of C. pyrenoidosa exposed to D. carinata water and short-term D. carinata grazing were significantly higher than those in the control; theoretic maximum cell densities of C. pyrenoidosa in the two treatments were also higher than those in the control, which indicated that grazing-associated infochemicals by D. carinata may enhance the alga's growth. Esterase activities in the two treatments were significantly higher than those in the control, which may contribute to the rapid growth of C. pyrenoidosa exposed to D. carinata infochemicals. Chlorophyll fluorescence and cell size were not significantly influenced by D. carinata infochemicals and grazing. [ABSTRACT FROM AUTHOR]

Abstract: To establish the influence of the cyanobacterial bloom collapse on the characteristics of dissolved organic carbon (DOC) in Lake Taihu, high-molecular-weight dissolved organic matter (HMW-DOM), with sizes between 1kDa and 0.5μm, were collected using cross-flow ultrafiltration, from three different eutrophic regions. Isolated HMW-DOM was further characterized by atomic carbon to nitrogen ratio and neutral sugars composition by gas chromatography and mass spectrometry. The results indicated that the cyanobacterial cell lysis induced by nitrate depletion is the likely mechanism for DOC release. The relatively high DOC level was associated with the high chlorophyll a concentration in Meiliang Bay, one of the most eutrophic bays in the northern part of the lake. However, no significant correlations were observed between chlorophyll a concentration and HMW-DOC concentration during the demise of the cyanobacterial bloom in Lake Taihu. No significant differences were found in the HMW-DOC concentration among the three sampling sites, which were selected to represent different eutrophic status. However, a significant difference in the HMW-DOC concentration was found between October 2009 and January 2010 in all three sampling sites (p =0.02). The HMW-DOC release may be attributed to the cyanobacterial cell lysis after the peak of summer bloom. The similarity in neutral sugar composition between the HMW-DOM and cyanobacterial exopolysaccharides suggests that the cyanobacterial bloom is the source of HMW-DOM. However, the significant correlation between the carbon to nitrogen ratio in HMW-DOM and chlorophyll a concentration was only observed in Meiliang Bay, which implies that apart from the cyanobacteria-derived DOC, a fraction of DOC was from riverine input. The decline of the cyanobacterial bloom also changed the overall DOM pool, leading to a shift in the component of HMW-DOM from a C-enriched material to an N-enriched material, as revealed by the variation in the carbon to nitrogen ratios. Overall, these results demonstrate that the quantitative and qualitative DOM is affected by the post-cyanobacterial bloom in Lake Taihu. [Copyright &y& Elsevier]

The phytoplankton lysis rates in the different eutrophic regions of Lake Taihu were determined based on the activities of particle and dissolved esterase, as well as the decay rate of the latter, from August 2009 to March 2010. Two peaks were observed for the chlorophyll a concentration, one in September 2009 and another in January 2010. The highest phytoplankton lysis rates observed in October were associated with the decay of the summer bloom, whereas the minimum lysis rates observed in January were associated with the winter bloom. The highest cell lysis rates in Meiliang Bay, Lake centre, and Gonghu Bay were 0.67, 0.77, and 0.68 d-1, respectively, whereas the lowest lysis rates in these regions were 0.03, 0.01, and 0.05 d-1, respectively. Water temperature showed an apparent indirect effect on lysis rate. In addition, a significant inverse relationship was observed between lysis rates and nitrate concentration in the three lake regions, which suggests that phytoplankton cell lysis is associated with changes in nitrate concentration. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The structure and composition of the bacterial community associated with buoyant Microcystis colonies were monitored during the decline of a cyanobacterial bloom (from October 13, 2009 to January 27, 2010). When temperature decreased, the ratio between the colony-associated bacteria and the Microcystis gradually decreased as estimated by a quantitative real-time polymerase chain reaction (qRT-PCR)-based approach. Diversity of bacterial communities was determined through denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. Cluster analysis of the DGGE profiles showed that most of the bacterial communities associated with Microcystis colonies collected on the nearby dates were clustered together. The bacterial clones from four clone libraries in different months were classified into 5, 12, 6 and 12 operational taxonomic units, most of which were affiliated with Gammaproteobacteria, Alphaproteobacteria and Bacteroidetes. Shift in dominance from pathogenic Aeromonas sp. to Shewanella sp. capable of remineralization of many organic materials was observed, and both species seemed to be associated with Microcystis colonies along with the bloom decline. These results indicated that the potential harmful effects of the Microcystis bloom on the safety of lake water during the decline period should be taken into account. [ABSTRACT FROM PUBLISHER]

Microcystis aeruginosa (Kütz.) Kütz. commonly occurs as single cells at early recruitment but forms large colonies in summer. Colony formation will induce many acclimative changes. In this study, we demonstrated the photochemical changes before and after colony formation. In the laboratory, light curves showed that colonies were more responsive to high light than single cells. The values of the maximal slope of electron transport rate (ETR)-light curve (α), relative maximal electron transport rate (rETR), and onset of light saturation ( I) of colonies were significantly higher than those of single cells ( P < 0.05), indicating that colonies have higher photosynthetic capability than single cells, especially in high light, where values of rETR and I of colonies were 2.32 and 2.41 times those of single cells. Moreover, the dark-light experiments showed that colonial cells can more effectively resist darkness damage. In addition, pigments of colonial cells were higher than those of single cells ( P < 0.05). The higher pigment contents probably contribute to higher photosynthetic capability. In the field, the inhibition rate of F/ F in single cells increased significantly faster than that of colonies as light increased ( P < 0.05), but nonphotochemical quenching (NPQ) value of colonies was higher (32.4%) than that of single cells at noon, which indicated colonial cells can more effectively resist high-light inhibition than single cells ( P < 0.05). Polysaccharides of colonies were significantly higher compared to those in unicellular cells ( P < 0.05) based on their contents and ultrastructural characteristics. This finding implies that colonies could not effectively decrease photoinhibition by negative buoyancy regulation. In fact, NPQ may be an important mechanism for avoiding photodamage. All of these phenomena can help explain the ecological success of colonial M. aeruginosa in eutrophic water. [ABSTRACT FROM AUTHOR]

The dynamics of nutrients, such as phosphorus, nitrogen, and carbohydrates, during cyanobacteria cell lysis was investigated under darkness incubation in the laboratory. The cell lysis rate of cyanobacteria sampled from Lake Taihu was measured using an esterase assay. Based on particulate esterase activity, the calculated cyanobacteria lysis rate was 0.094 d–1. During 30 days of darkness incubation, Chlorophyll aconcentration decreased from 56 μg L–1to 2.0 μg L–1. Parallel to this, total particulate carbohydrate concentration decreased rapidly. The fluctuation of dissolved organic carbon concentration was a function of the production of noncarbohydrate by cyanobacteria and the decomposition of carbohydrate by bacteria. Total dissolved carbohydrates and dissolved polysaccharides concentrations showed a similar pattern, declining at the beginning of the experiment and keeping relatively stable, thereafter. In contrast, the concentration of dissolved monosaccharides remained constant during the entire process. The concentrations of NH4and PO43–increased at the early stage, and then decreased afterwards. A gradual decrease in NO3–concentration after day 8 indicated that anaerobic conditions might be produced during the cell lysis process. The present results demonstrated cyanobacteria cell lysis has a big influence on the nutrient status of the surrounding water. © 2010 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim [ABSTRACT FROM AUTHOR]

Abstract: The horizontal distribution of bloom-forming Microcystis in a specific lake area and the transport of Microcystis by wind-driven lake currents between Meiliang Bay and the open water of Taihu Lake were measured during continuous field observations from August 21 to 25, 2006. During the observations, the horizontal distributions of Microcystis, represented by Chlorophyll a, showed a clear concentration toward downwind lake areas. According to the lake currents and the Chl a concentrations on the boundary line between the Meiliang Bay and the open water, the transported Chl a was less than 2% of the total weight of Chl a in Meiliang Bay on August 22, 24 and 25. The results suggest that the horizontal distribution of the bloom-forming Microcystis was strongly affected by the wind conditions, and the wind-driven Microcystis accumulation was mainly determined by surface drift; the transport of Microcystis by lake currents was much less important in this large, shallow lake. [Copyright &y& Elsevier]

Abstract: Pentachlorophenol (PCP), which was reported to be a typical persistent organic pollutant and environmental endocrine disruptor, may cause threat to aquatic species. In this study, serum testosterone concentration, activity of liver microsome ethoxyresorufin O-deethylase (EROD) and glutathione S-tranferases (GST) of crucian carp (Carassius carassius) exposed to PCP for 7 and 15d, respectively, were examined. The results showed that testosterone concentration was induced remarkably after 7d (P<0.05), and the testosterone concentrations in 15d treatment crucian carp were higher than those in 7d treatment. It was found that there were significant effects on activities of EROD and GST after crucian carp were exposed to PCP for 7 and 15d (P<0.05), compared to the controls. EROD and GST activities increased with increase in PCP concentration and also with increase in time on exposure. The results indicated that serum testosterone, EROD and GST were sensitive endpoints to PCP. PCP may have endocrine disrupting activities and may affect the reproductive success of this species. It is possible that the changes of hepatic microsome enzyme activities may result in alterations of serum testosterone levels in crucian carp. [Copyright &y& Elsevier]

Abstract: This study was conducted to determine the role of algal–algal interactions in a multispecies microalgal population on their sensitivities to copper based on an enzyme inhibition assay using flow cytometric measures. Autofluorescence (chlorophyll a and phycocyanin) was used to identify species and count algal signals. The effect of multispecies population on copper toxicity of Microcystis aeruginousa was detected (1) at the same initial cell density, (2) at the same surface area, and (3) in the presence and absence of Chlorella pyrenoidosa and Scenedesmus obliquus. As copper concentrations increased, esterase activity of M. aeruginosa changed in a concentration-dependent manner. The 24h EC50 value of M. aeruginosa in the multispecies population was significantly (P<0.05) higher than those in the single-species population. Compared with S. obliquus, the effect of C. pyrenoidosa on M. aeruginosa was more marked (the 24h EC50 value of copper on fluorescin diacetate fluorescence of M. aeruginosa was 11μg/L). At 48h copper exposure (6μg/L) analysis of intracellular reactive oxygen species levels also showed similar algal–algal interactions in multispecies microalgal populations. The pigment assay suggested that these algal–algal interactions occurred only at low concentrations (<13μg/L, 24 and 48h copper exposure). This study demonstrates the importance of using multispecies populations to estimate metal toxicity in natural waters. [Copyright &y& Elsevier]