Phytoplankton community of the drinking water supply reservoir Borovitsa (South Bulgaria) with an emphasis on cyanotoxins and water quality

The phytoplankton diversity, algal biomass, and selected physicochemical parameters were investigated in the drinking water reservoir (Borovitsa) located in the Kardzhali region, Bulgaria. Particular attention was given to Cyanoprokaryota and presence of cyanotoxins in the water samples. Twenty-nine species belonging to six divisions (Cyanoprokaryota, Chlorophyta, Zygnemophyta, Dinophyta, Euglenophyta and Bacillariophyta) were identified. The microscopic examination of the phytoplankton samples showed the dominance of Ankyra judayi, Oocystis lacustris (Chlorophyta) and Aphanizomenon flos-aquae (Cyanoprokaryota) in July 2006, and Microcystis pulverea, Synechococcus elongatus (Cyanoprokaryota), Radiococcus planktonicus (Chlorophyta) and Melosira varians (Bacillariophyta) in September 2006. A blooming event due to Aphanizomenon flos-aquae was observed in July 2006. The reservoir exhibits a tendency to shift from an oligotrophic environment to a state of mesotrophy. Presence of cyanotoxins such as anatoxin-a, microcystins and saxitoxins were analyzed by HPLC and ELISA methods. Our results demonstrated the presence of anatoxin-a and microcystins (0.09 μg/L) in the raw water samples from July 2006, and saxitoxins (2.5 μg/L) and microcystins (0.18 μg/L) in the raw water samples from September 2006. The study underlines that permanent monitoring programs of Cyanoprokaryota in the reservoirs used as sources of drinking water and toxicity assessments should be implemented. Indirect exposure and transfer of cyanotoxins through food chains must also be considered.     

Seasonal dynamics of picophytoplankton in Lake Kinneret, Israel

1. Picophytoplankton (picocyanobacteria and picoeukaryotes) communities in Lake Kinneret were studied from 1988 to 1992. No prochlorophytes were observed in the lake. 2. Picocyanobacteria were a prominent and ubiquitous component of the phytoplankton, being present at all depths throughout the year, with concentrations ranging from 2 ± 10–8 ± 10⁵ cells ml^?1. Low cell numbers in winter and spring were followed at the end of the annual dinoflagellate bloom by maximal abundances in summer-autumn in the epilimnion. High cell numbers (> 10⁴ cells ml^?1) were sometimes also found in the anaerobic hypolimnion. Net growth rates for picocyanobacteria ranged from 0.29 to 0.60 divisions day^?1. 3. Picoeukaryotes were a very minor constituent of the picoplankton, mostly present in winter and spring, and sometimes at the end of autumn, with concentrations ranging from 44 to 5700 cells ml^?1. Higher cell numbers tended to occur in the near surface water layers. In August-September, picoeukaryotes were found only in the hypolimnion. In December, the occurrence of picoeukaryotes in the deep water layers probably resulted from advection with cold water currents from the Jordan river. Net growth rates for picoeukaryotes ranged from 0.26 to 0.43 divisions day^?1. 4. Overall, the contribution of picophytoplankton to the phytoplankton standing crop in Lake Kinneret was limited; picocyanobacteria and picoeukaryotes accounted for no more than 7.0 and 0.1% of total algal biomass (semiannual average), respectively. 5. Picophytoplankton cell numbers in pelagic waters were usually similar to those in shallower lake stations. 6. Picocyanobacteria appear to be an autochthonous population, whereas picoeukaryotes are probably brought annually by the Jordan River and do not maintain themselves in the lake.     

The role of environmental parameters in the structure of phytoplankton assemblages and cyanobacteria toxins in two hypereutrophic lakes

We evaluated the variability of cyanotoxins, water chemistry, and cyanobacteria communities in two hypereutrophic drowned river mouth lakes (Spring Lake and Mona Lake; summer 2006) in west Michigan, USA. Even with considerable geographical and watershed similarity, local variations in nutrient concentrations and environmental factors were found to influence the differences observed in cyanobacteria assemblages and cyanotoxins levels between the two lakes. Limnothrix sp. dominated the phytoplankton community in Spring Lake (82% of biovolume) and was negatively correlated with total phosphorus (TP) concentrations. Although Spring Lake was treated with alum during the previous year, Limnothrix sp. was able to bloom in the lower P environment. In contrast, the N₂-fixing cyanobacterium, Anabaena flos-aquae, dominated the phytoplankton in Mona Lake (64% of biovolume). N₂-fixing cyanobacteria dominance in Mona Lake was correlated with higher TP lower dissolved nitrogen levels. Cylindrospermopsis raciborskii was found in both systems; however, the toxin-producing polyketide synthetase gene was not present in either population. The higher TP in Mona Lake appeared to account for the 3-fold increase in cyanobacteria biovolume. Restoration plans for both lakes should include assessments of internal loading and continued phytoplankton monitoring to track the temporal distribution of cyanobacteria species and cyanotoxin concentrations.     

Harmful cyanobacteria and their cyanotoxins in Egyptian fresh waters – state of knowledge and research needs

Cyanobacterial blooms have increased in freshwater ecosystems worldwide in the last century, mostly resulting from eutrophication and climate change. These blooms represent serious threats to environmental and human health because of the production of harmful metabolites, called cyanotoxins. Like many countries, Egypt has been plagued with cyanobacterial blooms in most water sources, including the Nile River, irrigation canals, lakes and fishponds. However, the data about cyanotoxins produced in these blooms are limited. Only two types of cyanotoxins, microcystins and cylindrospermopsin, have been identified and characterised, mainly from Microcystis and Cylindrospermopsis blooms. The data revealed the presence of microcystins in raw and treated drinking waters at concentrations (0.05–3.8 µg l^?1), exceeding the WHO limit (1 µg l^?1) in some drinking water treatment plants. In addition, Nile tilapia Oreochromis niloticus caught from ponds containing heavy cyanobacterial blooms have accumulated considerable amounts of cyanotoxins in their edible tissues. The data presented here could be the catalyst for the establishment of a monitoring and management programme for harmful cyanobacteria and their cyanotoxins in Egyptian fresh waters. This review also elucidates the important research gaps and possible avenues for future research on cyanobacterial blooms and cyanotoxins in Egypt.     

Water quality improvement and phytoplankton response in the drinking water source in Meiliang Bay of Lake Taihu, China

Water quality experienced changes throughout the 3-year ecological engineering experiment in the drinking water source in Meiliang Bay of Lake Taihu. Average concentrations of TN, TP, NH₄⁺, BOD₅ and transparency in the drinking water source during the period of July–December 2005 were 1.85, 0.13, 0.23, 3.03 mg L⁻¹ and 27.5 cm, respectively, decreasing by 47.9%, 21.2%, 83.3%, 54.4% and 24.2%, compared to concentrations from the same period in 2003. Concentrations of chlorophyll a and COD were 89.9 μg L⁻¹ and 6.45 mg L⁻¹, increasing by 27.9% and 17.7%, compared to the values in 2003. Cyanobacteria (mainly Microcystis) dominated the phytoplankton community in the ecological engineering area during July–December 2005. Densities of cyanobacteria and Microcystis were higher in 2005 than in 2004 and higher inside the engineering area than outside. Density percentages of cyanobacteria and Microcystis to total algae were above 90% and 60% during the bloom period. Average density of flagellate algae was higher during July–December 2005 than in 2004. Changes in water quality in the engineering area resulted mainly from the weakening of waves, decrease in concentrations of suspended solids, and assimilation of mass algae and periphytons. In spite of initial improvement of water quality, cyanobacterial bloom still determined the phytoplankton dynamics and variations. Additionally, nutrient concentration still remained at a high level without control of external loading. Therefore, a more holistic approach and long-term management should be adopted in Lake Taihu.     

First results on the water chemistry, algae and trophic status of an Andean acidic lake system of volcanic origin in Patagonia (Lake Caviahue)

The acidic caldera lake Caviahue (Patagonia, Argentina) and its main tributaries were studied on two dates during September 1998. The main results are: The acidity of the Lake Caviahue (pH: 2.56, acidity: >5 mmol H⁺ l^–1) is controlled by the extremely acidic Upper Rio Agrio (pH: 1.78, acidity: >20 mmol H⁺ l^–1). The high sulphate contents of both the river and the lake can be attributed to sulphuric acid generated by the uptake of sulphurous gases in the crater lake of Copahue Volcano at approximately 2800 m a.s.l. The high concentrations of both Fe and trace metals (e.g. Cr, Ni, Zn) in Lake Caviahue originate from sulphur–acid interactions with the predominantly volcanic geology of the catchment area. The P-rich andesitic geology influences both the Upper and Lower Rio Agrio and Lake Caviahue. Both were found to have high phosphorus concentrations (300–500 g P l^–1) indicative of a high potential for eutrophication. The plankton community consisted of bacterioplankton, phytoplankton and rotifers. The phytoplankton was dominated by one green alga, Keratococcus raphidioides (>90% of total abundance) followed by a green sphaerical and Chlamydomonas sp. The total phytoplankton density was about 15000 cells ml^–1 in the upper 10 m of the water column. Rotifers were represented by one bdelloid species and their abundance was highly variable (360–4040 ind l^–1) in the water columm. In the Upper and Lower Rio Agrio, the epilithic community was dominated by one chloroccocal species and two species of Ulothricales. According to trophic categories based on phytoplankton density and TP concentration, Lake Caviahue can be classified as mesotrophic/eutrophic. However, chlorophyll a concentrations observed were not in agreement with this state.     

Phytoplankton dynamics in the stratified water column of Lake Bonney,Antarctica

Phytoplankton populations in perennially ice-covered Lake Bonney, Antarctica grow in a unique non-turbulent environment. The absence of turbulence generated by winds or major streams, combined with strong vertical gradients in temperature and nutrients, create vertically stratified environmental conditions that support three discrete phytoplankton populations in the east lobe of this lake. Phytoplankton biomass and photosynthesis were measured in the east lobe of Lake Bonney during the winter-spring transicion (September) to mid-summer (January). During this period, irradiance beneath the ice increased from 0.03 to 1.9 mol quanta m⁻² d⁻¹. Chlorophylla concentrations ranged from 0.03 to 3.8 μl⁻¹ within the trophogenic zone (just beneath the permanent ice cover to 20 m) and photosynthesis ranged from below detection to 3.2 μg Cl⁻¹ d⁻¹. Our results indicate: (1) phytoplankton photosynthesis began in late winter (before 9 September, our earliest sampling date); (2) maxima for phytoplankton biomass and production developed sequentially in time from the top to the bottom of the trophogenic zone, following the seasoral increase in irradiance; and (3) the highest photosynthetic efficiencies occurred in early spring, then decreased over the remainder of the phytoplankton growth season. The spring decrease in photosynthetic rates for shallower phytoplankton appeared to be related to nutrient availability, while photosynthesis in the deeper populations was solely lightdependent.     

Endocrinological investigation into the reproductive cycles of two sympatric skate species, Malacoraja senta and Amblyraja radiata, in the western Gulf of Maine

The smooth skate, Malacoraja senta, and thorny skate, Amblyraja radiata, are two commercially exploited batoids found within the Gulf of Maine. During the past five years, we conducted a large study to accurately describe important biological life history parameters previously lacking for these species. As part of that project, the current study reports our findings on the hormonal profiles associated with the reproductive cycles of M. senta and A. radiata. Blood samples were obtained from mature M. senta and A. radiata of both sexes from all months of the year, and plasma testosterone (T), estradiol (E₂) and progesterone (P₄) concentrations were determined using radioimmunoassay (RIA). In female M. senta and A. radiata, monthly T concentrations ranged from 4,522 pg ml⁻¹ to 1,373 pg ml⁻¹ and 31,940 pg ml⁻¹ to 14,428 pg ml⁻¹, E₂ concentrations from 831 pg ml⁻¹ to 60 pg ml⁻¹ and 8,515 pg ml⁻¹ to 2,902 pg ml⁻¹, and P₄ concentrations from 3,027 pg ml⁻¹ to 20 pg ml⁻¹ and 3,264 pg ml⁻¹ to 331 pg ml⁻¹, respectively. No statistical differences were detected between any months for any hormone. Estradiol concentrations were not correlated with ovary weight, shell gland weight, or diameter of the largest follicles in either species. Monthly T concentrations in male M. senta and A. radiata ranged from 23,146 to 12,660 pg ml⁻¹ and from 57,500pg ml⁻¹ to 24,737 pg ml⁻¹, while E₂ concentrations ranged from 7.5 pg ml⁻¹ to undetectable and 103 to 30 pg ml⁻¹, respectively. No statistical differences were observed between months for either steroid. Testosterone concentrations were weakly correlated with testes weight and percent of stage VI spermatocysts in A. radiata, however, no correlation was detected between T and stage VI spermatocysts in M. senta. Collectively, these data support the previous conclusion that M. senta and A. radiata of both sexes are capable of reproducing year round in the western Gulf of Maine.     

南亚热带贫营养水库春季浮游植物群落结构与动态

2005年1~6月,通过每两周一次的高频率采样,对南亚热带贫营养水库——梅溪水库的水文、营养盐和浮游植物进行了调查,并计算水体浮游植物生物量。主要结果如下:梅溪水库浮游植物具有物种少,生物量低,以飞燕角甲藻(Ceratium hirundinella)和多甲藻(Peridinium sp.)为优势藻的特征。12次采样24个样品共检测到浮游植物42种。浮游植物在早春(1~3月)和晚春(4~6月)有显著的差别,其中每次采样浮游植物早春平均13种,晚春平均21种。浮游植物总的细胞丰度为31~273 cells·ml^-1,总生物量为0.176~2.024 mg·L^-1之间。晚春浮游植物平均生物量明显高于早春。低营养盐和弱酸性水体有利于能够垂直迁移获得营养的鞭毛藻类和其它藻类之间竞争,而使其成为整个春季优势类群。在晚春,随着水温显著增加,浮游植物丰度和生物量也明显增加,但是降雨的增加降低了水体的透明度,大大减缓了由水温上升导致生物量增长的趋势。水温是梅溪水库浮游植物变化的主要限制因子,但是降雨有明显的干扰作用。     

Evaluation of water corrosion,scaling extent and heterotrophic plate count bacteria in asbestos and polyethylene pipes in drinking water distribution system

Corrosion and scaling is one of the most important factors influencing drinking water quality that cause health disorders and economic problems. The aim of this study was to evaluate these phenomena in two sources of surface (Makou city) and ground water (Khoy city) in water networks. Corrosion and scaling potential was surveyed by Langelier, Ryzener, aggressiveness, Larson and Puckorius Indices and with measuring water physical, chemical, and microbial parameters. Statistical paired samples t-test displayed significant difference in means value of Langelier, Ryzener, Puckorius indices between cold and warm seasons of the year in Khoy samples and significant difference in means value of Ryzener, Puckorius and aggressiveness indices between cold and warm seasons of the year in Makou samples (p-value <0.001). Heterotrophic plate count water samples investigated in two cold and hot seasons in Khoy were respectively 14 ± 16 cfu ml^?1 and 41 ± 26 cfu ml^?1 and in the town of Makou were 11 ± 7 cfu ml^?1 and 61 ± 29 cfu ml^?1, respectively. In terms of health impacts, corrosion in different mains is important, then providing proper measures for balancing water quality before entering to the network and substituting of mains to prevent economic and health problems are necessary.     

Assessing water quality and classifying trophic status for scientifically based managing the water resources of the Lake Timsah,the lake with salinity stratification along the Suez Canal

Lake Timsah is considered as the biggest water body at Ismailia City with a surface area of 14?km². It is a saline shallow water basin lies approximately mid-way between the south city of Suez and the north city of Port Said at 30^o35′46.55“N and 32^o19′30.54″E. Because it receives water with high and low salinities, salinity stratification is producing in the Lake Timsah, with values of 14–40‰ for the surface water and over 40‰ for the bottom water. The temperature of the lake water decreased to below 19 °C in the winter and rose to above 29?°C in the summer; the concentration of dissolved oxygen ranged between 6.5 and 12.2?l^?1 and the pH fluctuated between 7.9 in its lower value and 8.2 in its higher value. Water transparency was very low as indicated by Secchi disc readings recorded during this study and varied between 0.3 and 2.7?m. The main chemical nutrient (phosphorus) reached its highest levels of 96?µg?l^?1 in winter and their lowest values of 24?µg?l^?1 during summer. This nutrient concentration is high especially by comparing with those of unpolluted marine waters, but is typical of the more eutrophic coastal waters worldwide. The composition and abundance of phytoplankton with dominancy of diatoms and increased population density (20,986 cell l^?1) reflect the eutrophic condition of the lake. The intensive growth of phytoplankton was enriched by high concentration of chlorophyll a with annual values ranged between 6.5 and 56?µg?l^?1. The objective of the present work was quantitative assessment of the quality of the water of the Lake Timsah using different approaches. During the present study, three different approaches were applied for the quantitative assessment of Lake Timsah water quality: the trophic state index (TST); trophic level index (TLI) and water quality index (WQI). Application of the trophic state and trophic level indices (TSI & TLI) revealed that the Lake Timsah has trophic indices of 60 and 5.2 for TSI and TLI, respectively. Both indices reflected the eutrophic condition of the lake waters and confirmed that the eutrophication is a major threat in the Lake Timsah. On the other hand, the WQI calculated for the Lake Timsah during the present study with an average of 49 demonstrated that the water of the Lake Timsah is bad and unsuitable for main and/or several uses. Moreover, WQI allows accounting for several water resource uses and can serve a more robust than TSI and/or TLI and can be used effectively as a comprehensive tool for water quality quantification. In conclusion, the three subjective indices used for the assessment process for the lake water are more suitable and effective for needs of the sustainable water resources protection and management of the Lake Timsah.     

Seasonal changes in the concentration of estrogens and testosterone in the plasma of the stallion

A blood sample was taken from each of 15 stallions at monthly intervals for 14 consecutive months. Plasma concentrations of estrogens and testosterone were measured by radioimmunoassay methods. Estrogens in peripheral blood were present in much higher amounts than testosterone and were principally in a water-soluble, solvolyzable form (> 98%). The major component in the solvolyzed extracts behaved chromatographically as estrone. The mean plasma level (± S.E.) of estrogens averaged across months was 52.9 ± 4.5 ng ml^?1. Individual stallions showed considerable month-to-month variation; for example, single monthly samples ranged from 29.5 to 160.6 ng ml^?1 for the stallion with the highest single value.The highest mean monthly concentration was 69 ± ng ml^?1 in May, and plasma levels were < 40 ng ml^?1 during November and December. For the 11 Thoroughbred stallions in the study, the mean concentrations of estrogens were 73 ± 5.8 ng ml^?1 for May to July and 45 ± 4.1 ng ml^?1 for November to January (P > 0.001).The mean monthly concentrations (± S.E.) of testosterone ranged from 0.22 ± 0.05 to 0.90 ± 0.14 ng ml^?1, and individual samples ranged from < 0.02 to 2.8 ng ml^?1 of plasma. While the highest mean level of testosterone was seen in September, there was a significant difference (P < 0.01) between the values in the breeding season (May–July, 0.73 ± 0.07 ng ml^?1) and the non-breeding season (November–January, 0.38 ± 0.08 ng ml^?1). No marked seasonal changes were observed, however, in testosterone levels in several stallions. It was concluded that plasma estrogen levels may provide a more sensitive index of endocrine function of the testes in the stallion.     

太湖西北湖区2003-2012年间氮磷浓度及浮游植物主要类群变化趋势分析

基于2003-2012年太湖竺山湖和西部沿岸区水体理化指标与浮游植物丰度的逐月监测数据,分析了两个湖区氮磷营养盐状态和浮游植物丰度以及浮游植物主要类群的年际变化趋势及季节变化特征,探讨了浮游植物群落变化与水温及营养盐指标间的关系。结果表明：10年间两个湖区氮磷营养盐浓度总体呈下降趋势,以竺山湖TN、NH₃-N浓度和西部沿岸区NO₃-N浓度下降最为显著;浮游植物丰度总体呈上升趋势,蓝藻在群落结构中日益占据绝对优势;季节变化上,氮营养盐浓度表现为春冬季节高于夏秋季节,TP浓度和浮游植物丰度呈相反的变化趋势。Pearson相关分析显示,水温、NH₃-N浓度和TN/TP是影响蓝藻丰度及其在浮游植物群落中所占比例的主要因素。在温度和营养盐结构的共同作用下,10年间两个湖区蓝藻水华暴发时间逐渐提前,而消退时间逐渐滞后,水华持续时间逐年上升。在全球变暖背景下,太湖水华治理需执行更加严格的氮磷限制阈值,且在重污染的西北湖区控磷依然是关键。     

Phytoplankton assemblage structure and dynamics as indicator [-2pt] of the recent trophic and biological evolution of the western basin of Lake Como (N. Italy)

We studied the phytoplankton assemblage of the western basin of Lake Como (Northern Italy) during 1997. The phytoplankton assemblage was composed of 65 taxa, belonging to six taxonomic groups. Chlorophyta were represented by the highest number of taxa (28) followed by Bacillariophyceae (17), Cyanoprokaryota (9), Dinophyceae (6), Chrysophyceae (3) and Cryptophyta (2). The total assemblage density and biomass ranged from 902 ind ml^–1 and 134.5 mm³ m^–3 in February to 58 766 ind ml^–1 and 9360 mm³ m^–3 in October. The density and biomass variation at three stations showed a common pattern, with higher values in the southern part of the basin where TP concentrations were always greater. The phytoplankton succession was analysed by cluster analysis (average linkage clustering) and non-metric multidimensional scaling (NMDS) ordination, both applied to a dissimilarity matrix obtained from a calculation of the Bray–Curtis index. In general, the seasonal succession followed a simple pattern, with a clear spring phase. These results are discussed considering the trophic evolution of the lake and its recent colonization by Dreissena polymorpha.     

Microcystin production by cyanobacteria in the Mwanza Gulf (Lake Victoria,Tanzania)

In order to investigate the potential for microcystin (MC) production by cyanobacteria in the Mwanza Gulf (Lake Victoria, Tanzania), nutrients, phytoplankton and microcystins were sampled inshore (3 m depth) and offshore (18 m depth) from May to August 2002. Significant differences in soluble reactive phosphorus (SRP) and nitrate concentrations between offshore and inshore indicated eutrophication via terrestrial run-off. Though the concentrations of SRP and nitrate ranged between 36–127 and 35–726 μg l ⁻¹ each, the phytoplankton biovolume was generally low. The phytoplankton community was dominated by diatoms (Nitzschia acicularis), a number of cyanobacterial species (Aphanocapsa sp., Anabaena sp., Planktolyngbya spp., Microcystis sp.) and cryptomonads. The water column was completely mixed and Nitzschiapeaked in abundance during July. All cyanobacteria were low in abundance during the entire study period (0.1–1.6 mm ³ l ⁻¹). Microcystins were analysed using high performance liquid chromatography coupled with diode array detection High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD) and in most samples no microcystins were detected. The highest concentration of [Asp ³]-MC-RR was found in open water at the surface on July 2nd, 2002 (1 μg l ⁻¹). MC concentrations did not pose a potential health risk in the Mwanza Gulf during the study period, however, it is possible that the period of higher cyanobacterial biovolumes has been missed during the sampling period of this study.     

Demonstrated transfer of cyanobacteria and cyanotoxins along a freshwater-marine continuum in France

The frequency of cyanobacterial proliferations in fresh waters is increasing worldwide and the presence of associated cyanotoxins represent a threat for ecosystems and human health. While the occurrence of microcystin (MC), the most widespread cyanotoxin, is well documented in freshwaters, only few studies have examined its occurrence in estuarine waters. In this study we evaluated the transfer of cyanobacteria and cyanotoxins along a river continuum from a freshwater reservoir through an interconnecting estuary to the coastal area in Brittany, France. We sampled regularly over 2 years at 5 stations along the river continuum and analysed for phytoplankton and cyanotoxins, together with physico-chemical parameters. Results show that cyanobacteria dominated the phytoplanktonic community with high densities (up to 2 × 10⁶ cells mL⁻¹) at the freshwater sites during the summer and autumn periods of both years, with a cell transfer to estuarine (up to 10⁵ cells mL⁻¹) and marine (2 × 10³ cells mL⁻¹) sites. While the temporal variation in cyanobacterial densities was mainly associated with temperature, spatial variation was due to salinity while nutrients were non-limiting for cyanobacterial growth. Cyanobacterial biomass was dominated by several species of Microcystis that survived intermediate salinities. Intracellular MCs were detected in all the freshwater samples with concentrations up to 60 μg L⁻¹, and more intermittently with concentrations up to 1.15 μg L⁻¹, at the most upstream estuarine site. Intracellular MC was only sporadically detected and in low concentration at the most downstream estuarine site and at the marine outlet (respectively <0.14 μg L^-1 and <0.03 μg L⁻¹). Different MC variants were detected with dominance of MC-LR, RR and YR and that dominance was conserved along the salinity gradient. Extracellular MC contribution to total MC was higher at the downstream sites in accordance with the lysing of the cells at elevated salinities. No nodularin (NOD) was detected in the particulate samples or in the filtrates.     

The seasonal sensitivity of Cyanobacteria and other phytoplankton to changes in flushing rate and water temperature

The phytoplankton lake community model PROTECH (Phytoplankton RespOnses To Environmental CHange) was applied to the eutrophic lake, Esthwaite Water (United Kingdom). It was validated against monitoring data from 2003 and simulated well the seasonal pattern of total chlorophyll, diatom chlorophyll and Cyanobacteria chlorophyll with respective R²‐values calculated between observed and simulated of 0.68, 0.72 and 0.77 (all P<0.01). This simulation was then rerun through various combinations of factorized changes covering a range of half to double the flushing rate and from ?1 to +4 °C changes in water temperature. Their effect on the phytoplankton was measured as annual, spring, summer and autumn means of the total and species chlorophyll concentrations. In addition, Cyanobacteria mean percentage abundance (%Cb) and maximum percentage abundance (Max %Cb) was recorded, as were the number of days that Cyanobacteria chlorophyll concentration exceed two World Health Organization (WHO) derived risk thresholds (10 and 50 mg m^?3). The phytoplankton community was dominated in the year by three of the eight phytoplankton simulated. The vernal bloom of the diatom Asterionella showed little annual or seasonal response to the changing drivers but this was not the case for the two Cyanobacteria that also dominated, Anabaena and Aphanizomenon . These Cyanobacteria showed enhanced abundance, community dominance and increased duration above the highest WHO risk threshold with increasing water temperature and decreasing flushing rate: this effect was greatest in the summer period. However, the response was ultimately controlled by the availability of nutrients, particularly phosphorus and nitrogen, with occasional declines in the latter's concentration helping the dominance of these nitrogen‐fixing phytoplankton.     

Picoplankton photosynthesis and diurnal variations in photosynthesis-irradiance relationship in a eutrophic and meso-oligotrophic lake

The abundance and relative importance of autotrophic picoplankton were investigated in two lakes of different trophic status. In the eutrophic lake, measurements of primary production were performed on water samples in situ and in a light incubator three times during the day whereas for the oligotrophic lake, only one measurement of primary production was performed on water samples in the incubator. Dark-carbon losses of phytoplankton from Lake Loosdrecht were investigated in time series. Cell numbers of autotrophic picoplankton in eutrophic Lake Loosdrecht (3.2 × 10⁴ cells ml^–1) were lower than in meso-oligotrophic Lake Maarsseveen (9.8 and 11.4 × 10⁴ cells ml^–1 at the surface and bottom respectively). In the phytoplankton of both lakes the ratio of picoplankton production increased with decreasing light intensity. In Lake Loosdrecht depth-integrated contribution of picoplankton to total photosynthesis was less than 4%. The P-I-relationship showed diurnal variations in light saturated photosynthesis, while light limited carbon uptake remained constant during the day. Dark carbon losses from short-term labelled phytoplankton during the first 12 hours of the night period accounted for 10–25% of material fixed during the preceeding light period.     

Analysis of long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa

The long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa was analyzed using periodic phytoplankton census data from January 1979 to December 2009. Population densities obtained from census data were transformed into biovolumes, and phytoplankton species were categorized into three size fractions: net phytoplankton (≥4,000 μm³ cell^?1, ≥ca. 20 μm in diameter), large nanophytoplankton (100–4,000 μm³ cell^?1, ca. 6–20 μm in diameter), and small nanophytoplankton (<100 μm³ cell^?1, <ca. 6 μm in diameter). Although the annual total biovolume gradually decreased over time, the total biovolumes in winter and spring were found to increase. Furthermore, a decrease in the biovolume of net phytoplankton and an increase in that of small nanophytoplankton were observed. Because of succession in the phytoplankton community, the average cell volume of the phytoplankton community decreased from 269 μm³ cell^?1 in the 1980s to 56 μm³ cell^?1 in the 2000s. Lake warming accompanied with the intensification of thermal stratification and the augmentation of wind speed were observed at Lake Biwa over the study period. Serial analysis correcting for autocorrelation revealed that oligotrophication in the epilimnion, induced by lake warming and limitation of light available for phytoplankton growth by wind-induced water mixing, was a potential factor in the succession of the phytoplankton community.     

Limnology and trophic status of glacial lakes in the tropical Andes (Cajas National Park,Ecuador)

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