大型浅水富营养化湖泊中蓝藻水华形成机理的思考

湖泊富营养化依然是我国目前以及今后相当长一段时期内的重大水环境问题。研究蓝藻水华的形成机制 ,对于科学预测湖泊中蓝藻水华的产生 ,并采取相应措施减少其带来的影响具有重要的生态和环境意义。为探索富营养化湖泊中蓝藻水华形成机理 ,综述了目前对我国大型浅水湖泊蓝藻水华成因研究现状和对水华形成机理的一般认识。分析了导致蓝藻水华形成的化学、物理和生物等主要环境因素 ,论述了蓝藻 ,尤其是微囊藻成为水华优势种的可能原因。认为对水华的形成需要全面认识 ,营养盐浓度的升高可能仅是蓝藻水华形成、且人们可以加以控制的因素之一 ;在探索水华成因时 ,不能仅仅局限于夏季蓝藻水华发生时环境特征的研究与观察 ,而应该提前关注蓝藻的越冬生理生态特征、春季复苏的生态诱导因子及其阈值以及在复苏后 ,蓝藻如何在生长过程中形成群体 ,并逐步成为湖泊水生生态系统中的优势种乃至形成水华的过程。并需要对蓝藻越冬的生存对策、蓝藻群体的形成的条件、蓝藻在春季复苏的触发条件及其生态阈值、以及蓝藻在与其它藻类种群竞争中取胜的生理生化特征有足够的认识。蓝藻水华的“暴发”是表观现象 ,其前提还是藻类一定的生物量 ,且是一个逐渐形成的过程。根据生态学的基本理论和野外对水华形成过程的原位观测     

书讯

《水华蓝藻生物学》一书由藻类学家胡鸿钧研究员编著,已于2011年4月下旬由科学出版社出版。这是国内第一部有关水华蓝藻的综合性参考书。该书共分为9章,较系统地论述了水华蓝藻的形态、细胞结构、分类、生态、毒素种类、毒性、毒理、分子生物学的研究概况以及蓝藻水华发生机理。共收录整理了国内外已报道的水华蓝藻26     

书讯

《水华蓝藻生物学》一书由藻类学家胡鸿钧研究员编著,已于2011年4月下旬由科学出版社出版。这是国内第一部有关水华蓝藻的综合性参考书。该书共分为9章,较系统地论述了水华蓝藻的形态、细胞结构、分类、生态、毒素种类、毒性、毒理、分子生物学的研究概况以及蓝藻水华发生机理。共收录整理了国内外已报道的水华蓝藻26     

蓝藻毒素的类型及其产毒基因

水体富营养化及蓝藻水华的频繁发生,严重破坏水域生态系统,有毒水华蓝藻产生的藻毒素,污染水体且危害水生动物和人类健康。本文综述了水华蓝藻的次级代谢产物藻毒素及藻毒素合成基因的国内外研究进展,介绍了蓝藻毒素的类型、不同毒素毒性机理、产毒基因以及利用产毒基因进行产毒蓝藻的分子生物学检测等,并对研究中存在的问题和未来的研究方向进行了展望,目的是为建立有毒水华蓝藻的预警机制、科学评价产毒蓝藻及其藻毒素的生态、环境危害及生态环境治理提供理论和技术支撑。     

水华蓝藻对鱼类的营养毒理学效应

水体富营养化导致蓝藻水华的发生已成为全球关注的水环境问题,很多鱼类处于水生态系统食物链的最高级,蓝藻水华的主要次级代谢产物-微囊藻毒素可通过鱼类的摄食活动或生物富集作用在鱼体组织中累积,并通过食物链危及人类健康。近年来,微囊藻毒素对鱼类的毒性效应引起众多科学家的关注。在天然水体中不少鱼类可以主动摄食蓝藻,所以,水华蓝藻对鱼类来说既具有营养物作用、也具有潜在的毒性作用。鉴于目前机械收获的水华蓝藻生物量资源化利用问题以及水产饲料业亟需大力开发鱼粉替代蛋白源的需要,从营养学和毒理学这两个角度来研究水华蓝藻对鱼类的营养作用和毒性效应具有较高的理论和现实意义。主要概述了蓝藻粉、蓝藻细胞对鱼类的营养学和毒理学效应,以期拓展水华蓝藻对鱼类毒性效应的研究视野,同时也为水华蓝藻的资源化利用提供新的思路。     

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。     

蓝藻毒素对底栖动物的毒理学研究进展

近年,由于人类活动加剧,大量氮磷等营养物质流入湖泊等缓流水体,导致水体富营养化。而由此引起有害蓝藻水华的频繁爆发,使生态环境和人类健康受到严重威胁。相关研究表明,蓝藻水华的爆发不仅能够使水体水质恶化,其中一些产毒藻类还会产生大量蓝藻毒素,对水生生物产生重要影响。底栖动物作为水体生态系统的重要组成部分,在食物网中有重要作用,同时其中的许多种类又与人类息息相关,因此关于水华蓝藻毒素对淡水底栖动物的毒理学研究具有重要意义。在介绍蓝藻毒素概况的基础上,综述了蓝藻毒素的致毒机理和对底栖动物的影响,展望了研究方向。     

微囊藻毒素生态学研究

通过对微囊藻毒素的生态学进行综述,认为藻毒素的产生和含量的变化受水环境生物多样性、环境因子和微囊藻自身生物量等的影响。保障蓝藻在种群竞争、生态演替中获得竞争优势的各因素中,藻毒素发挥了重要调节作用。研究蓝藻的产毒机制,对于理解水体富营养化机制,实施蓝藻水华的生物控制,最终对富营养化水体进行生态修复具有重要的理论意义和现实作用;     

三峡水库香溪河库湾夏季藻类水华的时空动态及其影响因素

2008年6-8月,三峡水库香溪河库湾相继暴发蓝藻和绿藻水华.依据香溪河库湾夏季的每周监测,对研究区2次水华分别进行聚类和判别分析,研究了2次水华的时空动态及其影响因素.结果表明：研究区2次水华过程均可划分为无水华组、过渡组和水华组;2次水华的暴发对可溶性硅(DSi)、硝态氮与亚硝态氮(NO₃--N+NO₂^--N)和磷酸盐(PO₄^3--P)3种营养盐的吸收程度不同;蓝藻水华暴发期间的DSi、总氮/总磷(TN/TP)、DSi/TN和DSi/TP值均低于绿藻水华;判别蓝藻水华暴发的参数为叶绿素a(Chl a)、TN和PO₄^3--P,而Chl a和DSi则是绿藻水华暴发的判别因子,将2次水华过程划分为水华组和无水华组的判别效果更好;判断蓝藻和绿藻水华暴发的叶绿素a临界浓度分别为40和20 μg·L^-1.     

高温强太阳光照条件下蓝藻水华形成的实验研究

富营养化和藻类水华尤其是蓝藻水华在全世界范围内的湖泊中都有发生,但富营养化和水面藻类水华出现之间没有等同关系.目前人们对水华形成机制还不是很了解,对水华的具体形成过程也不是很清楚,因此若能通过一定的途径使没有形成水面水华的富营养水体出现水面水华就对水华形成机制的研究很有意义.实验选用高温季节里,于2007年8月28日将室外塑料蓝桶中培育的浮游植物丰富的天然水体-其中含有类颤藻鱼腥藻但其并不占据优势,引入到无色透明玻璃瓶中.实验初始水体的chl-a、TN和TP依次为 615.20mg·^-3、9.144mg·L^-1和0.453mg·L^-1.2007年8月29日对各处理进行营养盐的梯度添加,添加的营养盐为KNO₃和KH₂PO₄.共有4个营养盐添加梯度,添加的N/P(质量比)为7:1,其中添加的N的梯度为(mg·L-1):0,0.5,1.0和2.0.实验过程中测定了水温、光合有效辐射、氮磷营养盐、叶绿素a和浮游植物种类的数量变化.结果表明实验过程中各处理的营养盐和chl-a含量均比开始时有下降,同时各处理中水面出现了类颤藻鱼腥藻水华,且类颤藻鱼腥藻的数量随处理中营养盐添加量的增多而升高.这说明了含有少量鱼腥藻的高chl-a含量的天然水体在高温季节引入到透明玻璃容器中后能形成水表面鱼腥藻水华,玻璃容器中的高温强光照条件和营养盐的添加能促进鱼腥藻在竞争中取得优势.本实验利用小玻璃容器,排除了鱼类、风浪、底泥等多个因素的影响,集中关注营养盐添加和高温强光照因子,成功重现了蓝藻表面水华的发生.营养盐添加水平与浮游植物种间竞争并导致水体表面水华发生之间的关系在此实验中得到很好的体现.虽然本实验不能揭示蓝藻水华形成的具体机制,但为蓝藻水华形成机制研究提供了便捷的途径而很有意义.     

EVALUATION OF ENVIRONMENTAL FACTORS ON CYANOBACTERIAL BLOOM IN EUTROPHIC RESERVOIR USING ARTIFICIAL NEURAL NETWORKS1

Cyanobacterial blooms are a common issue in eutrophic freshwaters, and some cyanobacteria produce toxins, threatening the health of humans and livestock. Microcystin, a representative cyanobacterial hepatotoxin, is frequently detected in most Korean lakes and reservoirs. This study developed predictive models for cyanobacterial bloom using artificial neural networks (ANNs; self‐organizing map [SOM] and multilayer perceptron [MLP]), including an evaluation of related environmental factors. Fourteen environmental factors, as independent variables for predicting the cyanobacteria density, were measured weekly in the Daechung Reservoir from spring to autumn over 5 years (2001, 2003–2006). Cyanobacterial density was highly associated with environmental factors measured 3 weeks earlier. The SOM model was efficient in visualizing the relationships between cyanobacteria and environmental factors, and also for tracing temporal change patterns in the environmental condition of the reservoir. And the MLP model exhibited a good predictive power for the cyanobacterial density, based on the environmental factors of 3 weeks earlier. The water temperature and total dissolved nitrogen were the major determinants for cyanobacteria. The water temperature had a stronger influence on cyanobacterial growth than the nutrient concentrations in eutrophic waters. Contrary to general expectations, the nitrogen compounds played a more important role in bloom formation than the phosphorus compounds.     

PRODUCTION OF SECONDARY METABOLITES BY FILAMENTOUS TROPICAL MARINE CYANOBACTERIA: ECOLOGICAL FUNCTIONS OF THE COMPOUNDS

Cyanobacterial blooms are becoming more common in many reef habitats. The broadly acting feeding deterrent compound ypaoamide, produced by a mixed cyanobacterial assemblage, has been linked to bloom formation and mass fish die-offs ( Siganus argenteus and Siganus spinus ) in Guam. Specific metabolites produced by Lyngbya majuscula Gomont act as both feeding attractants to the specialist herbivore Stylocheilus longicauda , and as effective feeding deterrents to generalist fishes. Two-dimensional TLC (2D-TLC) analysis of cyanobacterial crude extracts was used to select chemically distinct populations (chemotypes) of bloom-forming filamentous cyanobacteria for chemical and ecological evaluation. Crude extracts produced by different species, chemotypes, and chemically distinct Micronesian marine cyanobacterial assemblages deter feeding activity of generalist reef herbivores. The ecological function of cyanobacterial secondary metabolites, especially as related to diversity of compound production and the relationship of metabolite production to bloom formation is discussed.     

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.     

Impact of external forces on cyanophage–host interactions in aquatic ecosystems

Cyanobacterial (algal) blooms have by convention been attributed to the excessive level of nutrients from pollution and runoff, which promotes the rapid growth and multiplication of cyanobacteria or algae. The cyanophage (virus) is the natural predator of cyanobacteria (the host). The aim of this review is to unveil certain pressures that disrupt cyanophage–host interactions and the formation of cyanobacterial blooms. This review focuses principally on the impact of greenhouse gases, ozone depletion, solar ultraviolet radiation (SUR) and the role of recently discovered virophages, which coexist with and in turn are the natural predator of phages. The key findings are that the increase in SUR, the mutation of cyanophages and cyanobacteria, along with changing nutrient levels, have combined with virophages to impede cyanophage–host interactions and the resultant viral infection and killing of the cyanobacterial cell, which is a necessary step in controlling cyanobacterial blooms. Consider this a ‘call to action’ for researchers interested in corrective action aimed at evolving aquatic ecosystems.     

Targeted deep sequencing reveals high diversity and variable dominance of bloom-forming cyanobacteria in eutrophic lakes

Cyanobacterial blooms in eutrophic lakes are severe environmental problems worldwide. To characterize the spatiotemporal heterogeneity of cyanobacterial blooms, a high-throughput method is necessary for the specific detection of cyanobacteria. In this study, the cyanobacterial composition of three eutrophic waters in China (Taihu Lake, Dongqian Lake, and Dongzhen Reservoir) was determined by pyrosequencing the cpcBA intergenic spacer (cpcBA-IGS) of cyanobacteria. A total of 2585 OTUs were obtained from the normalized cpcBA-IGS sequence dataset at a distance of 0.05. The 238 most abundant OTUs contained 92% of the total sequences and were classified into six cyanobacterial groups. The water samples of Taihu Lake were dominated by Microcystis, mixed Nostocales species, Synechococcus, and unclassified cyanobacteria. Besides, all the samples from Taihu Lake were clustered together in the dendrogram based on shared abundant OTUs. The cyanobacterial diversity in Dongqian Lake was dramatically decreased after sediment dredging and Synechococcus became exclusively dominant in this lake. The genus Synechococcus was also dominant in the surface water of Dongzhen Reservoir, while phylogenetically diverse cyanobacteria coexisted at a depth of 10 m in this reservoir. In summary, targeted deep sequencing based on cpcBA-IGS revealed a large diversity of bloom-forming cyanobacteria in eutrophic lakes and spatiotemporal changes in the composition of cyanobacterial communities. The genus Microcystis was the most abundant bloom-forming cyanobacteria in eutrophic lakes, while Synechococcus could be exclusively dominant under appropriate environmental conditions.     

Cyanobacterial bioactive metabolites—A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1–3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds.Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.     

Molecular detection of potentially toxic cyanobacteria and their associated bacteria in lake water column and sediment

We investigated the molecular diversity of cyanobacteria and bacteria during a water bloom in a lake with a long history of toxic cyanobacterial blooms (Lake Kastoria, Greece). We also tested the hypothesis whether bloom-forming cyanobacteria are preserved in the lake’s sediment 2 years after the bloom. The dominant cyanobacteria during the bloom included the potentially toxin-producing Microcystis aeruginosa and several other Chroococcales forms closely related to the genus Microcystis. This suggests that the use of cyanobacterial-specific primers seems to be very informative in describing the cyanobacteria during the water blooms. The bacterial community showed high diversity, consisting mostly of singleton and doubleton phylotypes. The majority of the phylotypes were typical lake bacteria including some potential pathogens and toxin metabolising bacteria, suggesting that the dominant toxic cyanobacteria did not have any significant effect on the bacterial community structure. In the sediment, 2 years after the water bloom, no bloom-forming cyanobacteria were retrieved, suggesting that they cannot be preserved in the sediment. Similar to the water column, sediment bacterial diversity was also high, consisting mostly of yet-uncultured bacteria that are related to environments where organic matter degradation takes place.     

Bloom dynamics and chemical defenses of benthic cyanobacteria in the Indian River Lagoon,Florida

Cyanobacterial blooms are predicted to become more prominent in the future as a result of increasing seawater temperatures and the continued addition of nutrients to coastal waters. Many benthic marine cyanobacteria have potent chemical defenses that protect them from top down pressures and contribute to the persistence of blooms. Blooms of benthic cyanobacteria have been observed along the coast of Florida and within the Indian River Lagoon (IRL), a biodiverse estuary system that spans 250 km along Florida’s east coast. In this study, the cyanobacterial bloom progression at three sites within the central IRL was monitored over the course of two summers. The blooms consisted of four unique cyanobacterial species, including the recently described Okeania erythroflocculosa. The cyanobacteria produced a range of known bioactive compounds including malyngolide, lyngbyoic acid, microcolins A–B, and desacetylmicrocolin B. Ecologically-relevant assays showed that malyngolide inhibited the growth of marine fungi (Dendryphiella salina and Lindra thalassiae); microcolins A–B and desacetylmicrocolin B inhibited feeding by a generalist herbivore, the sea urchin Lytechinus variegatus; and lyngbyoic acid inhibited fungal growth and herbivore feeding. These chemical defenses likely contribute to the persistence of cyanobacterial blooms in the IRL during the summer growing period.     

An overview of cyanobacterial bloom occurrences and research in Africa over the last decade

Cyanobacterial blooms are a current cause for concern globally, with vital water sources experiencing frequent and increasingly toxic blooms in the past decade. These increases are resultant of both anthropogenic and natural factors, with climate change being the central concern. Of the more affected parts of the world, Africa has been considered particularly vulnerable due to its historical predisposition and lag in social economic development. This review collectively assesses the available information on cyanobacterial blooms in Africa as well as any visible trends associated with reported occurrences over the last decade. Of the 54 countries in Africa, only 21 have notable research information in the area of cyanobacterial blooms within the last decade, although there is substantial reason to attribute these blooms as some of the major water quality threats in Africa collectively. The collected information suggests that civil wars, disease outbreaks and inadequate infrastructure are at the core of Africa’s delayed advancement. This is even more so in the area of cyanobacteria related research, with 11 out of 21 countries having recorded toxicity and physicochemical parameters related to cyanobacterial blooms. Compared to the rest of the continent, peripheral countries are at the forefront of research related to cyanobacteria, with countries such as Angola having sufficient rainfall, but poor water quality with limited information on bloom occurrences. An assessment of the reported blooms found nitrogen concentrations to be higher in the water column of more toxic blooms, validating recent global studies and indicating that phosphorous is not the only factor to be monitored in bloom mitigation. Blooms occurred at low TN: TP ratios and at temperatures above 12 °C. Nitrogen was linked to toxicity and temperature also had a positive effect on bloom occurrence and toxicity. Microcystis was the most ubiquitous of the cyanobacterial strains reported in Africa and the one most frequently toxic. Cylindrospermopsis was reported more in the dry, north and western parts of the continent countries as opposed to the rest of the continent, whilst Anabaena was more frequent on the south eastern regions. In light of the entire continent, the inadequacy in reported blooms and advances in this area of research require critical intervention and action.