Mechanism study on the frequent variations of cell-bound microcystins in cyanobacterial blooms in Lake Taihu: Implications for water quality monitoring and assessments

Although Microcystis-based toxins have been intensively studied, previous studies using laboratory cultures of Microcystis strains are difficult to explain the phenomenon that microcystin concentrations and toxin variants in natural blooms differ widely and frequently within a short-term period. The present study was designed to unravel the mechanisms for the frequent variations of intracellular toxins related to the differences in cyanobacterial colonies during bloom seasons in Lake Taihu, China. Monitoring of Microcystis colonies during warm seasons indicated that the variations in microcystins in both concentrations and toxin species were associated with the frequent alteration of Microcystis colonies in Lake Taihu. High concentration of microcystins in the blooms was always associated with two Microcystis colonies, Microcystis flos-aquae and Microcystis aeruginosa, whereas when Microcystis wesenbergii was the dominant colonial type, the toxin production of the blooms was low. Additionally, environmental factors such as temperature and nutrition were also shown to have an effect on the toxin production of the blooms, and may also potentially influence the Microcystis species present. The results of the present study provides insight into a new consideration for quick water quality monitoring, assessment and risk alert in cyanobacterium- and toxin-contaminated freshwaters, which will be beneficial not only for water agencies but also for public health. (C) 2009 Elsevier Ltd. All rights reserved.

Seasonal variations in stable isotope ratios of two biomanipulation fishes and seston in a large pen culture in hypereutrophic Meiliang Bay, Lake Taihu

This paper reports on seasonal changes in stable carbon and nitrogen isotope ratios of seston and muscle tissue of silver carp and bighead carp during 2004 and 2005, focusing primarily on the carbon sources and trophic relationships among phytoplankton, zooplankton and silver carp and bighead carp in a large fish pen of Meiliang Bay (Lake Taihu, China). delta C-13 showed a minimal value in March 2005 and a maximal value in August 2005 in seston both inside and outside the pen, whereas delta N-15 of seston showed the minimum in winter and the maximum during algal blooms. A positive correlation between delta C-13 of silver carp and that of seston suggested that temporal variation Of delta C-13 in seston was preserved in fish via the food chain. The differences of delta C-13 among seston, zooplankton and muscle tissue of silver carp and bighead carp ranged only 0.2-1.7%, indicating that plankton production was the primary food source of filter-feeding fishes. According to a mass balance model, we estimated that the contributions of zooplankton to the diets of silver carp and bighead carp were 45.7% and 54.3%, respectively, based on the delta N-15 values of zooplankton and planktivorous fishes. (C) 2007 Elsevier B.V. All rights reserved

Seasonal Variations in Chlorophyll a Concentrations in Relation to Potentials of Sediment Phosphate Release by Different Mechanisms in a Large Chinese Shallow Eutrophic Lake (Lake Taihu)

The relationship between chlorophyll a and fractionation of sediment phosphorus, inorganic phosphate-solubilizing bacteria (IPB), and organic phosphate-mineralizing bacteria (OPB) was evaluated in a large Chinese shallow eutrophic lake (Lake Taihu) and its embayment (Wuli Bay). At the three study sites, the increase of chlorophyll a concentrations in April paralleled those of the iron bound phosphate accounting for major portion of sediment inorganic phosphate, and in June significantly higher OPB and IPB numbers (especially OPB) in sediment were main contributors to the peaks of chlorophyll a concentration. Even though IPB peaked from February to June, it should serve as an unimportant P source due to the irrelevancy with chlorophyll a and soluble reactive phosphorus (SRP). By contrast, at the other site in the embayment, the calcium-bound phosphate was predominant and solid, which was difficult to be released, and neither IPB nor OPB were detectable in the sediment, indicating weak potential for phosphorus release from the sediment, which was reflected in the small seasonal variation in SRP concentration in water column. Hence, the extents to which the three general mechanisms behind phosphate release from sediment (desorption of iron bound phosphate, solubilization by IPB and enzymatic hydrolysis by OPB) operated were different depending on seasons and sites in Lake Taihu, they may jointly drive phosphate release and accelerate the eutrophication processes.

Determination of microcystin-LR and its metabolites in snail (Bellamya aeruginosa), shrimp (Macrobrachium nipponensis) and silver carp (Hypophthalmichthys molitrix) from Lake Taihu, China

This paper describes seasonal changes of microcystin-LR (MC-LR) and its glutathione (MC-LR-GSH) and cysteine conjugates (MC-LR-Cys) in three aquatic animals - snail (Bellamya aeruginosa), shrimp (fMacrobrachium nipponensis) and silver carp (Hypophthalmichthys molitrix) collected from Lake Taihu, China. MC-LR, MC-LR-GSH, and MC-LR-Cys were determined by liquid chromatography electrospray ionization mass spectrum (LC-ESI-MS). The mean MC-LR concentrations in the hepatopancreas of snail and shrimp and liver of silver carp were 6.61, 0.24, and 0.027 mu g g(-1) dry weight (DW), respectively: while the average MC-LR-Cys concentrations were 0.50, 0.97, and 5.72 mu g g(-1) DW, respectively. MC-LR-GSH was usually not detectable in these samples. The above results suggest that: (1) in aquatic animals, especially fish, the main excretion form of MC-LR could be MC-LR-Cys, but not MC-LR-GSH, whereas MC-LR-Cys might play an important role in detoxication of MC-LR and (2) that efficiency of MC-LR-Cys formation differs among species. The main detoxication pathway of MC-LR in aquatic animals is suggested as follows: when MC-LR enters into liver/hepatopancreas, it firstly conjugates with polypeptide or protein (including GSH, PP-1 and 2A) containing Cys residues, perhaps also some free cysteine; subsequently, MC-LR-Cys is degraded from these polypeptide or protein; and finally is excreted from animals by the compound of MC-LR-Cys. (C) 2009 Elsevier Ltd. All rights reserved.

Simultaneous determination of microcystin contaminations in various vertebrates (fish, turtle, duck and water bird) from a large eutrophic Chinese lake, Lake Taihu, with toxic Microcystis blooms

This is the first to conduct Simultaneous determination of microcystin (MC) contaminations in multi-groups of vertebrates (fish, turtle, duck and water bird) from Lake Taihu with Microcystis blooms. MCs (-RR, -YR, -LR) in Microcystis scum was 328 mu g g(-1) DW. MCs reached 235 mu g g(-1) DW in intestinal contents of phytoplanktivorous silver carp, but never exceeded 0.1 mu g g(-1) DW in intestinal contents of other animals. The highest MC content in liver of fish was in Carassius auratus (150 ng g(-1) DW), followed by silver carp and Culter ilishaeformis, whereas the lowest was in common carp (3 ng g(-1) DW). In livers of turtle, duck and water bird, MC content ranged from 18 to 30 ng g(-1) DW. High MC level was found in the gonad, egg yolk and egg white of Nycticorax nycticorax and Anas platyrhynchos, suggesting the potential effect of MCs on water bird and duck embryos. High MC contents were identified for the first time in the spleens of N. nycticorax and A. platyrhynchos (6.850 and 9.462 ng g(-1) DW, respectively), indicating a different organotropism of MCs in birds. Lakes with deaths of turtles or water birds in the literatures had a considerably higher MC content in both cyanobacteria and wildlife than Lake Taihu, indicating that toxicity of cyanobacteria may determine accumulation level of MCs and consequently fates of aquatic wildlife. (C) 2009 Elsevier B.V. All rights reserved.

Transfer, distribution and bioaccumulation of microcystins in the aquatic food web in Lake Taihu, China, with potential risks to human health

In this paper, accumulation and distribution of microcystins (MCs) was examined monthly in six species of fish with different trophic levels in Meiliang Bay, Lake Taihu, China, from June to November 2005, Microcystins were analyzed by liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS). Average recoveries of spiked fish samples were 67.7% for MC-RR, 85.3% for MC-YR, and 88.6% for MC-LR. The MCs (MC-RR+MC-YR+MC-LR) concentration in liver and gut content was highest in phytoplanktivorous fish, followed by omnivorous fish, and was lowest in carnivorous fish; while MCs concentration in muscle was highest in omnivorous fish, followed by phytoplanktivorous fish, and was lowest in carnivorous fish. This is the first study reporting MCs accumulation in the gonad of fish in field. The main uptake of MC-YR in fish seems to be through the gills from the dissolved MCs. The WHO limit for tolerable daily intake was exceeded only in common carp muscle. (C) 2008 Elsevier B.V. All rights reserved.

Food Consumption by In Situ Pen-Cultured Planktivorous Fishes and Effects on an Algal Bloom in Lake Taihu, China

Silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) were used as a new pen-cultureed biomanipulation technique to control algal blooms in Meiliang Bay of Lake Taihu. In order to evaluate the capacity of these two fishes to decrease algal blooms, diel feeding samplings were carried out in May (without algal blooms) and September (with algal blooms) in 2005. Based on estimated food consumption by the Elliott-Persson model, silver carp increased daily food consumption from 2.07 g dry weight per 100 g wet body weight in May before the outbreak of algal blooms to 4.98 g dry weight per 100 g wet body weight in September during algal blooms outbreak. However, no obvious variation of food consumption was observed in bighead carp during the study period. This species 1.88 and 1.54 g dry weight of plankton per 100 g wet body weight in May and September, respectively. Silver carp had a higher feeding capacity for plankton than bighead carp. Biotic factors (i.e., fish size and conspecific competition with natural species in the lake) may affect the feeding behaviors of both carps as well as seasonal variation of plankton communities in the pen.

Spatial and temporal variations of microcystins in hepatopancreas of a freshwater snail from Lake Taihu

In this paper, spatial and temporal variations of three common microcystins (MC-RR, MC-YR, and MC-LR) in the hepatopancreas of a freshwater snail (Bellamya aeruginosa) were studied monthly in two bays of Lake Taihu. Microcystins (MCs) concentration in hepatopancreas was quantified by liquid chromatography-mass spectrometry (LC-MS). The MCs concentrations in hepatopancreas were higher at Site 1 than those at other sites, which was in agreement with the changes of intracellular MCs concentrations in the water column. There was a significant correlation between MCs concentrations in the hepatopancreas and that in the seston, suggesting that spatial variances of MCs; concentrations in hepatopancreas among the five sites were due to spatial changes of toxic Microcystis cells in the water column. PCCA indicates that in addition to Microcystis, other factors (e.g., water temperature) also substantially affected the accumulation of MCs in hepatopancreas of the snail. (C) 2008 Published by Elsevier Inc.

Controlling factors of spring-summer phytoplankton succession in Lake Taihu (Meiliang Bay, China)

The spring-summer successions of phytoplankton and crustacean zooplankton were examined weekly in Meiliang Bay of the subtropical Lake Taihu in 2004 and 2005. During the study period, the ecosystem of Meiliang Bay was characterized by (i) clearly declined nitrogen compounds (nitrate, TN, and ammonium) and slowly increased phosphorus compounds (TP and SRP), (ii) increased total phytoplankton density and rapid replacement of chlorophyta (mainly Ulothrix) by cyanobacteria (mainly Microcystis), and (iii) rapid replacement of large-sized crustaceans (Daphnia and Moina) by small-sized ones (Bosmina, Limnoithona, and Ceriodaphnia). Results from the CCA and correlation analysis indicate that the spring-summer phytoplankton succession was primarily controlled by abiotic factors. Cyanobacteria were mainly promoted by increased temperature and decreased concentrations of nitrogen compounds. The pure contribution of crustacean was low for the variation of phytoplankton suggesting a weak top-down control by crustacean zooplankton in the subtropical Lake Taihu.

In situ study on effect of food competition on diet shifts and growth of silver and bighead carps in large biomanipulation fish pens in Meiliang Bay, Lake Taihu

Silver and bighead carps were cultured in large fish pens to reduce the risks of cyanobacterial bloom outbreaks in Meiliang Bay, Lake Tauhu in 2004 and 2005. Diet compositions and growth rates of the carps were studied from April to November each year. Both carp species fed mainly on zooplankton (> 50% in diet) in 2004 when competition was low, but selected more phytoplankton in 2005 when competition was high. Silver carp had a broader diet breadth than did bighead carp. Higher densities and fewer food resources increased diet breadths but decreased the diet overlap in both types of carps. It can be predicted that silver and bighead carps would be released from diet competition and shift to feed mainly on zooplankton at low densities, decreasing the efficiency of controlling cyanobacterial blooms. Conclusively, when silver and bighead carps are used to control cyanobacterial blooms, a sufficiently high stocking density is very important for a successful practice.

Phosphorus fractions and alkaline phosphatase activity in sediments of a large eutrophic Chinese lake (Lake Taihu)

Spatial, vertical, and seasonal variations in phosphorus fractions and in alkaline phosphatase activity (APA) were investigated in sediments in a large-shallow eutrophic Chinese lake (Lake Taihu) in 2003-2004. The phosphorus content was highest in the most seriously polluted lake area. Iron-bound phosphorus (Fe(OOH)-P) dominated (47% on average) among the phosphorus fractions determined according to Golterman (Hydrobiologia 335:87-95, 1996). Notably, organically-bound P comprised a further significant additional portion (acid-soluble + hot NaOH-extractable organic P = 25%), which was highest at the most polluted sites. The Fe(OOH)-P content was the lowest in spring (April, 2004), suggesting that degradation of organic matter led to the release of iron-bound phosphates. Sediment APA showed a significant positive relationship with both organically-bound P and Fe(OOH)-P. Consequently, organically-bound P is an important portion of the sediment phosphorus in Lake Taihu. It is mainly derived from freshly-settled autochthonous particles and from external discharges. Organically-bound P induces APA and may lead to the release of bioavailable phosphates from the organic sediments, thereby accelerating lake eutrophication.

Distribution and bioaccumulation of microcystins in water columns: A systematic investigation into the environmental fate and the risks associated with microcystins in Meiliang Bay, Lake Taihu

For the purpose of understanding the environmental fate of microcystins (MCs) and the potential health risks caused by toxic cyanobacterial blooms in Lake Taihu, a systematic investigation was carried out from February 2005 to January 2006. The distribution of MCs in the water column, and toxin bioaccumulations in aquatic organisms were surveyed. The results suggested that Lake Taihu is heavily polluted during summer months by toxic cyanobacterial blooms (with a maximum biovolume of 6.7 x 10(8) cells/L) and MCs. The maximum concentration of cell-bound toxins was 1.81 mg/g (DW) and the dissolved MCs reached a maximum level of 6.69 mu g/L. Dissolved MCs were always found in the entire water column at all sampling sites throughout the year. Our results emphasized the need for tracking MCs not only in the entire water column but also at the interface between water and sediment. Seasonal changes of MC concentrations in four species of hydrophytes (Eichhornic crassipes, Potamogeton maackianus, Alternanthera philoxeroides and Myriophyllum spicatum) ranged from 129 to 1317, 147 to 1534, 169 to 3945 and 124 to 956 ng/g (DW), respectively. Toxin accumulations in four aquatic species (Carassius auratus auratu, Macrobrachium nipponensis, Bellamya aeruginosa and Cristaria plicata) were also analyzed. Maximum toxin concentrations in the edible organs and non-edible visceral organs ranged from 378 to 730 and 754 to 3629 ng/g (DW), respectively. Based on field studies in Lake Taihu, risk assessments were carried out, taking into account the WHO guidelines and the tolerable daily intake (TDI) for MCs. Our findings suggest that the third largest lake in China poses serious health threats when serving as a source of drinking water and for recreational use. In addition, it is likely to be unsafe to consume aquatic species harvested in Lake Taihu due to the high-concentrations of accumulated MCs. (C) 2007 Elsevier Ltd. All rights reserved.

In situ study on the control of toxic Microcystis blooms using phytoplanktivorous fish in the subtropical Lake Taihu of China: A large fish pen experiment

Three large fish pens (0.36 km(2) of each) stocked with silver and bighead carp were set up in Meiliang Bay for controlling toxic Microcystis blooms. The responses of plankton communities and food consumption of silver and bighead carp were studied. Crustacean zooplankton were significantly suppressed in the fish pens. Total phytoplankton biomass, Microcystis biomass and microcystin concentration were lower in the fish pens than in the surrounding lake water, but the difference was not statistically significant. The present stocking density of silver plus bighead carp (about 40 g/m(3) in July) was likely too low to achieve an adequate control of Microcystis. Silver carp fed mainly on phytoplankton but bighead carp mainly on zooplankton: mean zooplankton contribution in the gut was 31.5% for silver carp and 64.7% for bighead carp. Compared with previous studies, both carp species preyed upon more zooplankton because of the abundant food resource. Daily rations of silver and bighead carp were estimated by Egger's model in the main growing season. Filtration rate was calculated from the daily ration and the density of plankton in the lake. During May-October, filtration rates of silver and bighead carp for phytoplankton were 0.22-1.53 L g(-1) h(-1) and 0.02-0.68 L g(-1) h(-1), respectively, and filtration rates for zooplankton were 0.24-0.44 L g(-1) h(-1) and 0.08-1.41 L g(-1) h(-1), respectively. Silver carp had a stronger ability of eliminating phytoplankton than bighead carp. To achieve a successful bioniampulation with a minimum effect of ichthyoeutrophication, the stocking proportion of bighead carp should be controlled in the future practice. (c) 2007 Elsevier B.V All rights reserved.

Microcystin accumulation in freshwater bivalves from Lake Taihu, China, and the potential risk to human consumption

The potential risk through ingestion of microcystins (MC) in contaminated mollusks has not been well studied. The present paper studied seasonal changes of MC content (determined by liquid chromatography-mass spectrometry) in various organs of three species of bivalves (Cristaria plicata, Hyriopsis cumingii, and Lamprotula leai) in Lake Taihu, China, where toxic cyanobacterial blooms occurred. Coinciding with peaks of seston MC (maximum, 5.7 mu g/L) and MC in cyanobacterial blooms (maximum, 0.534 mg/g), most organs showed sharp MC peaks during the summer, indicating both fast uptake and fast depuration by bivalves. Because hepatopancreas and intestine had considerably higher MC content than other organs, they are the most dangerous for human consumption. Both the present and previous studies show that the hepatopancreatic MC and total tissue MC often are correlated in various aquatic invertebrates. During the peak of the cyanobacterial blooms, C. plicata had higher hepatopancreatic MC content than the other bivalves, whereas H. cumingii had higher intestinal MC content than the other bivalves. Estimated daily intakes for humans from the consumption of whole tissues of the three bivalves were 0.48 to 0.94 mu g MC-LR equivalent/kg body weight (12- to 23.5-fold the tolerable daily intake value proposed by the World Health Organization), which indicates a high risk for humans consuming these bivalves.