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A link exists between global warming and the worldwide proliferation of harmful cyanobacterial blooms.
RNA pieces in the spliceosome, has a domain
V counterpart, containing a 2-nucleotide
bulge located 5 base pairs away from an AGC
triad (10). Formation of an analogous metal-
binding platform in this region of U6 (11) may
explain the apparent ability of spliceosomal
RNAs to retain catalytic activity in the com-
plete absence of the many protein components
that usually accompany splicing (12). A
domain V-like element could have played a
major role during the RNA world era of evolu-
tion, serving as the catalytic center for RNA
cleavage, transesterification, and polymeriza-
tion reactions.
The new structure provides a powerful
starting point for future investigations of
group II introns and the spliceosome. The
lack of electron density for domain VI,
which is important for the first step of splic-
ing in many group II introns, and the
absence of exons from the structure preclude
us from seeing how these elements dock
onto the surface created by domains I to V.
Thus, the structural details of substrate
recognition and catalysis remain undefined.
The nature of the conformational change
known to separate the two steps of splicing
(13) also remains unclear. Finally, it will be
important for our understanding of group II
intron self-splicing to capture the structures
of the other intermediates along the splicing
pathway and to pursue experiments that link
features of these structures with functionally
defined interactions.
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10.1126/science.1156721 SCIENCE VOL 320 4 APRIL 2008
utrient overenrichment of waters by
urban, agricultural, and industrial
development has promoted the
growth of cyanobacteria as harmful algal
blooms (see the figure) (1, 2). These blooms
increase the turbidity of aquatic ecosystems,
smothering aquatic plants and thereby sup-
pressing important invertebrate and fish habi-
tats. Die-off of blooms may deplete oxygen,
killing fish. Some cyanobacteria produce tox-
ins, which can cause serious and occasionally
fatal human liver, digestive, neurological, and
skin diseases (14). Cyanobacterial blooms
thus threaten many aquatic ecosystems,
including Lake Victoria in Africa, Lake Erie in
North America, Lake Taihu in China, and the
Baltic Sea in Europe (36). Climate change is
a potent catalyst for the further expansion of
these blooms.
Rising temperatures favor cyanobacteria
in several ways. Cyanobacteria generally
grow better at higher temperatures (often
above 25°C) than do other phytoplankton
species such as diatoms and green algae (7, 8).
This gives cyanobacteria a competitive advan-
tage at elevated temperatures (8, 9). Warming
of surface waters also strengthens the vertical
stratification of lakes, reducing vertical mix-
ing. Furthermore, global warming causes
lakes to stratify earlier in spring and destratify
later in autumn, which lengthens optimal
growth periods. Many cyanobacteria exploit
these stratified conditions by forming intra-
cellular gas vesicles, which make the cells
buoyant. Buoyant cyanobacteria float upward
when mixing is weak and accumulate in dense
surface blooms (1, 2, 7) (see the figure). These
surface blooms shade underlying nonbuoyant
phytoplankton, thus suppressing their oppo-
nents through competition for light (8).
Cyanobacterial blooms may even locally
increase water temperatures through the
intense absorption of light. The temperatures
of surface blooms in the Baltic Sea and in
Lake IJsselmeer, Netherlands, can be at least
1.5°C above those of ambient waters (10, 11).
This positive feedback provides additional
competitive dominance of buoyant cyanobac-
teria over nonbuoyant phytoplankton.
Global warming also affects patterns of
precipitation and drought. These changes in
the hydrological cycle could further enhance
cyanobacterial dominance. For example,
more intense precipitation will increase sur-
face and groundwater nutrient discharge into
water bodies. In the short term, freshwater dis-
charge may prevent blooms by flushing.
However, as the discharge subsides and water
residence time increases as a result of drought,
nutrient loads will be captured, eventually pro-
moting blooms. This scenario takes place
when elevated winter-spring rainfall and
flushing events are followed by protracted
periods of summer drought. This sequence of
A link exists between global warming and
the worldwide proliferation of harmful
cyanobacterial blooms.
Blooms Like It Hot
Hans W. Paerl
and Jef Huisman
Institute of Marine Sciences, University of North Carolina
at Chapel Hill, Morehead City, NC 28557, USA. E-mail:
Institute for Biodiversity and
Ecosystem Dynamics, University of Amsterdam, 1018 WS
Amsterdam, Netherlands. E-mail: jef.huisman@science.
Undesired blooms. Examples of large water bodies
covered by cyanobacterial blooms include the Neuse
River Estuary, North Carolina, USA (top) and Lake
Victoria, Africa (bottom).
Published by AAAS
on April 4, 2008 www.sciencemag.orgDownloaded from
events has triggered massive algal blooms in
aquatic ecosystems serving critical drinking
water, fishery, and recreational needs. At-
tempts to control fluctuations in the discharge
of rivers and lakes by means of dams and
sluices may increase residence time, further
aggravating cyanobacteria-related ecological
and human health problems.
In addition, summer droughts, rising sea
levels, increased withdrawal of freshwater for
agricultural use, and application of road salt as
a deicing agent have led to rising lake
salinities in many regions. Several common
cyanobacteria are more salt-tolerant than
freshwater phytoplankton species (12, 13).
This high salt tolerance is reflected by increas-
ing reports of toxic cyanobacterial blooms in
brackish waters (2, 6).
Some cyanobacteria have substantially
expanded their geographical ranges. For
example, Cylindrospermopsis raciborskii
the species responsible for “Palm Island mys-
tery disease,” an outbreak of a severe hepati-
tis-like illness on Palm Island, Australia (4)—
was originally described as a tropical/subtrop-
ical genus. The species appeared in southern
Europe in the 1930s and colonized higher lat-
itudes in the late 20th century. It is now wide-
spread in lakes in northern Germany (14).
Similarly, the species was noted in Florida
almost 35 years ago and is now commonly
found in reservoirs and lakes experiencing
eutrophication in the U.S. southeast and mid-
west (2). It is adapted to the low-light condi-
tions that typify eutrophic waters, prefers
water temperatures above 20°C, and survives
adverse conditions through the use of special-
ized resting cells (14). These bloom character-
istics suggest a link to eutrophication and
global warming.
More detailed studies of the population
dynamics in cyanobacterial blooms are needed.
For example, competition between toxic and
nontoxic strains affects the toxicity of
cyanobacterial blooms (15). Furthermore,
viruses may attack cyanobacteria and mediate
bloom development and succession (16). It is
unclear how these processes are affected by
global warming. What is clear, however, is that
high nutrient loading, rising temperatures,
enhanced stratification, increased residence
time, and salination all favor cyanobacterial
dominance in many aquatic ecosystems. Water
managers will have to accommodate the effects
of climatic change in their strategies to combat
the expansion of cyanobacterial blooms.
1. J. Huisman, H. C. P. Matthijs, P. M. Visser, Harmful
Cyanobacteria (Springer, Dordrecht, Netherlands, 2005).
2. H. W. Paerl, R. S. Fulton III, in Ecology of Harmful Marine
Algae, E. Graneli, J. Turner, Eds. (Springer, Berlin, 2006),
pp. 95–107.
3. I. Chorus, J. Bartram, Toxic Cyanobacteria in Water
(Spon, London, 1999).
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Shelf Sci. 71, 580 (2007).
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Univ. Press, Cambridge, 2006).
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559, 401 (2006).
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Ser. 101, 1 (1993).
11. B. W. Ibelings, M. Vonk, H. F. J. Los, D. T. van der Molen,
W. M. Mooij, Ecol. Appl. 13, 1456 (2003).
12. L. Tonk, K. Bosch, P. M. Visser, J. Huisman, Aquat. Microb.
Ecol. 46, 117 (2007).
13. P. H. Moisander, E. McClinton III, H. W. Paerl, Microb.
Ecol. 43, 432 (2002).
14. C. Wiedner, J. Rücker, R. Brüggemann, B. Nixdorf,
Oecologia 152, 473 (2007).
15. W. E. A. Kardinaal et al., Aquat. Microb. Ecol. 48, 1 (2007).
16. M. Honjo et al., J. Plankton Res. 28, 407 (2006).
n 2006, Yamanaka and colleagues (1) dis-
covered that mouse fibroblasts could be
reprogrammed to a pluripotent, embry-
onic stem (ES) cell–like state by the simple
introduction of four transcription factors,
Oct4, Sox2, Klf4, and c-Myc. This finding has
since been reproduced (26) and extended to
human fibroblasts using the same cocktail of
genes (7, 8) or one composed of Oct4, Sox2,
Nanog, and Lin28 (9). These so-called “in-
duced pluripotent stem cells” (iPS cells)
appear similar to ES cells in that they can give
rise to all the cells of the body and display fun-
damental genetic and morphologic ES cell
characteristics (see the figure). The concept of
an iPS cell brings together decades of work in
the fields of ES cell biology and nuclear
reprogramming that predicted it might be pos-
sible to impose pluripotency upon a somatic
cell (10). iPS cells not only have the potential
to produce patient-specific stem cells, but
they also provide a platform to study the biol-
ogy of pluripotency and cell reprogramming.
In Science Express, Aoi et al. (11) broaden the
application of iPS cell methodology to murine
epithelial cell types, highlighting differences
when compared with reprogramming of
fibroblasts. And on page 97 of this issue,
Viswanathan et al. (12) address the role of one
of the reprogramming factors, Lin28, in regu-
lating microRNAs (miRNAs) in ES cells. The
findings of Viswanathan et al., and recent
work by Benetti et al. (13) and Sinkkonen et al.
(14), advance our knowledge of the little-
understood roles of miRNAs in ES cells.
Collectively, these studies take us closer to
understanding how ES cells maintain an
undifferentiated, self-renewing, and pluripo-
tent state, and to defining how pluripotency
can be imposed on other cell types.
To date, fibroblasts and mesenchymal
stem cells have been used to generate iPS cells
(19). A next step is to determine whether
other cell types are susceptible to reprogram-
ming. Toward this end, Aoi et al. produced iPS
cells from two epithelial cell populations,
adult mouse hepatocytes and gastric epithelial
cells, by expressing Oct4, Sox2, Klf4, and
c-Myc. Like iPS cells generated from fibro-
blasts (iPS-fibroblast), those from primary
hepatocytes (iPS-Hep) and gastric epithelial
cells (iPS-Stm) were pluripotent and gave rise
to adult and germline chimeras. However,
iPS-Hep and iPS-Stm differ from iPS-fibro-
blast cells in several important respects, indi-
cating that the dynamics of reprogramming
may not be equivalent in these cell types. For
instance, although c-Myc was used, iPS-Hep
and iPS-Stm cell–derived chimeric mice did
not display the c-Myc–dependent tumori-
genicity observed in iPS-fibroblast–derived
chimeric mice. In addition, iPS-Hep and iPS-
Stm cells could be generated using less strin-
gent selection conditions. Thus, epithelial cell
types may be more prone to reprogramming
than fibroblasts.
How do these differences inform us about
the mechanism of reprogramming? Given that
ES cells are an epithelial population, charac-
terized by cell adhesion (mediated by the
membrane protein E-cadherin), one possibil-
ity is that epithelialization is an event required
The requirements for reprogramming different
somatic cell types to a pluripotent state may
not be equivalent.
Deconstructing Pluripotency
Anne G. Bang and Melissa K. Carpenter
Novocell Inc., 3550 General Atomics Court, San Diego, CA
92121, USA. E-mail:
Published by AAAS
on April 4, 2008 www.sciencemag.orgDownloaded from
... Increasing temperature favours growth of cyanobacteria (Jöhnk et al., 2008) and therefore the frequency of harmful cyanobacterial blooms is increasing with global warming (Paerl & Huisman, 2008). ...
... However, this difference became smaller with increasing proportion of the cyanobacterium in the food and vanished completely at poor food quality. This may suggest constraints in adaptation to high temperatures with increasing food quality limitation imposed by cyanobacteria, a phenomenon increasingly expected in future scenarios (Jöhnk et al., 2008;Paerl & Huisman, 2008). ...
Full-text available
Surface waters are warming due to climate change, potentially pushing aquatic organisms closer to their thermal tolerance limits. However, cyanobacterial blooms are expected to occur more often with rising temperature, increasing the likelihood of poor‐quality food available for herbivorous zooplankton. Zooplankton can adapt locally by genetic differentiation or via adaptive phenotypic plasticity to increasing temperatures, but there is limited knowledge on how these processes may be affected by food quality limitation imposed by cyanobacteria. To test the effects of cyanobacteria‐mediated food quality on local temperature adaptation, we measured juvenile somatic growth and reproduction of five Daphnia magna clones from different latitudinal origin grown on three food qualities at 20, 24, and 28°C. Additionally we estimated short‐term heat tolerance, measured as knockout time (time to immobility) at lethally high temperature, of two clones acclimated to the three temperatures and two food quality levels to test for the effects of food quality on adaptive plastic responses. As expected, clones from lower latitudes showed on average better somatic growth and reproduction than clones from higher latitudes at higher temperatures. However, the difference in somatic growth diminished with increasing cyanobacteria abundance in the diet, suggesting constraints on local genetic adaptation under predicted decreases in food quality. As expected, short‐term heat tolerance of the clones generally increased with increasing acclimation temperature. However, heat tolerance of animals acclimated to the highest temperature was larger when grown at medium than at good food quality, whereas the opposite response was observed for animals acclimated to the lowest temperature. This suggests a better adaptive phenotypic response of animals to elevated temperatures under higher cyanobacteria abundance, and thus shows an opposite pattern to the results for somatic growth. Overall, we demonstrate that food quality limitation can mediate responses of D. magna life history traits and heat tolerance to increasing temperatures, and that the effects differ depending on the time scale studied, that is, mid‐term (somatic growth) versus short‐term (tolerance to acute heat stress). These aspects will need further attention to accurately predict of how organisms will cope with future global warming by local adaptation and adaptive phenotypic plasticity.
... Besides eutrophication, other environmental pressures influence phytoplankton assemblage structure. For example, warming and extreme weather events, including storms and drought, may also favor the global expansion of cyanobacterial blooms (Giani et al., 2020;Havens et al., 2019;Kasprzak et al., 2017;Moss, 2011;Paerl & Huisman, 2008;Paerl et al., 2020;Stockwell et al., 2020). ...
Full-text available
In the tropics, seasons are delimitated by the extent of rainfall resulting in seasonal differences in water parameters shaping phytoplankton community dynamics. Dry periods can intensify eutrophication and often result in seasonal or even perennial cyanobacterial dominance. This study was developed to evaluate phytoplankton response to trophic state and seasonal differences of environmental filters (dry and rainy periods) using the morphology-based functional groups (MBFG) approach. We also aimed at identifying environmental thresholds of each MBFG dominance in six man-made lakes located in the tropical semiarid region of Brazil. Our results showed clear MBFG association with lakes’ trophic states. The dominant groups in mesotrophic conditions were members of MBFGs V (unicellular flagellates) and VI (non-flagellated with a siliceous exoskeleton), and in meso-eutrophic MBFG IV (medium size without specialized traits) dominated. Conversely, MBFG VII (with mucilage and aerotopes) and VIII (nitrogen-fixing cyanobacteria) dominated mostly under eutrophic conditions, though linked to shallower euphotic zones. Light and phosphorous were the most important environmental thresholds associated with MBFG’s dominance. Overall, most of the lakes displayed seasonal differences in environmental filters. In contrast to what was expected, the rainy season was associated with higher nutrients, suspended solids, and reduced euphotic depth compared to the dry season. Our results, overall, show that the effects of seasonality varied across lakes and highlight eutrophication as the main environmental factor for MBFG selection suggesting reduced seasonality effects during dry years in the tropics.
As anthropogenic eutrophication and the associated increase of cyanobacteria continue to plague inland waterbodies, local officials are seeking novel methods to proactively manage water resources. Cyanobacteria are of particular concern to health officials due to their ability to produce dangerous hepatotoxins and neurotoxins, which can threaten waterbodies for recreational and drinking-water purposes. Presently, however, there is no cyanobacteria outlook that can provide advance warning of a potential threat at the seasonal time scale. In this study, a statistical model is developed utilizing local and global scale season-ahead hydroclimatic predictors to evaluate the potential for informative cyanobacteria biomass and associated beach closure forecasts across the June–August season for a eutrophic lake in Wisconsin (United States). This model is developed as part of a subseasonal to seasonal cyanobacteria forecasting system to optimize lake management across the peak cyanobacteria season. Model skill is significant in comparison to June–August cyanobacteria observations (Pearson correlation coefficient = 0.62, Heidke skill score = 0.38). The modeling framework proposed here demonstrates encouraging prediction skill and offers the possibility of advanced beach management applications.
Full-text available
How fast does lake surface water temperature (LSWT) react to climate warming or cooling? The thermal response of lakes varies with the season and, typically, day‐to‐day fluctuations are larger in summer. The reason is that lakes are stratified systems where the thermally reactive volume is smaller in summer and, hence, its heat capacity (thermal inertia) is reduced. We define the dimensionless parameter δ as the ratio between the surface volume reacting to the net heat flux through the air‐water interface and the volume of the whole lake. By referring to a fully controlled case study obtained by means of a one‐dimensional physically based model (Simstrat), we investigate the variability of δ throughout the year and its dependence on LSWT. Then, we compare the results with the parameterization adopted in the hybrid data‐driven model air2water. Our analysis confirms that δ follows an exponential decay with increasing LSWT (i.e., a thinner surface layer in summer), and shows that this functional dependence varies between the warming and the cooling periods. These findings contribute to the understanding of the effect of a warming climate on water bodies and ecosystems by providing a simple tool to estimate the rate of change in lakes' water temperature.
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Microcystin (MC) is a toxic secondary metabolite produced by select cyanobacteria that threatens aquatic and terrestrial organisms over a diverse range of freshwater systems. To assess the relationship between environmental parameters and MC, researchers frequently utilize correlational analyses. This statistical methodology has proved useful when summarizing complex water quality monitoring datasets, but the correlations between select parameters and MC have been documented to vary widely across studies and systems. Such variation within the peer-reviewed literature leaves uncertainty for resource managers when developing a MC monitoring program. The objective of this research is to determine if correlational analyses between environmental parameters and MC are helpful to resource managers desiring to understand the drivers of MC. Environmental (i.e., physical, chemical, and biological) and MC correlation data were retrieved from an estimated 2,643 waterbodies (largely from the north temperate region) and synthesized using a Fisher’s z meta-analysis. Common water quality parameters, such as chlorophyll, temperature, and pH, were positively correlated with MC, while transparency was negatively correlated. Interestingly, 12 of the 15 studied nitrogen parameters, including total nitrogen, were not significantly correlated with MC. In contrast, three of the four studied phosphorus parameters, including total phosphorus, were positively related to MC. Results from this synthesis quantitatively reinforces the usefulness of commonly measured environmental parameters to monitor for conditions related to MC occurrence; however, correlational analyses by themselves are often ineffective and considering what role a parameter plays in the ecology of cyanobacterial blooms in addition to MC production is vital.
We examine how the frequency of cyanobacterial harmful algal blooms (cyanoHABs) generates economic costs through the mechanism of residential property values. We assemble nearly two decades worth of nationwide data on property sales near US inland lakes along as well as satellite-derived measures of the annual frequency of cyanoHABs in over 2000 large lakes during the years 2008–2011. We combine these data sources to estimate broad scale hedonic property models to recover the marginal willingness to pay to reduce the frequency of cyanobacterial blooms in seven climate regions across the United States. We find heterogeneity in the marginal cost of cyanoHABs, with a 10-percentage point increase in annual occurrence reducing average home values for near-shore properties by 3.5% in the Upper Midwest, 3.8% in the South, 3.3% in the Southeast, and 4.3% in the Northeast. We find null or inconclusive results for other regions. We use our estimates to illustrate the household-, lake-, and regional-level impacts of counterfactual changes in the frequency of cyanoHABs.
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Aquatic pollution is considered a major threat to sustainable development across the world, and deterioration of aquatic ecosystems is caused usually by harmful algal blooms (HABs). In recent times, HABs have gained attention from scientists to better understand these phenomena given that these blooms are increasing in intensity and distribution with considerable impacts on aquatic ecosystems. Many exogenous factors such as variations in climatic patterns, eutrophication, wind blowing, dust storms, and upwelling of water currents form these blooms. Globally, the HAB formation is increasing the toxicity in the natural water sources, ultimately leading the deleterious and hazardous effects on the aquatic fauna and flora. This review summarizes the types of HABs with their potential effects, toxicity, grazing defense, human health impacts, management, and control of these harmful entities. This review offers a systematic approach towards the understanding of HABs, eliciting to rethink the increasing threat caused by HABs in aquatic ecosystems across the world. Therefore, to mitigate this increasing threat to aquatic environments, advanced scientific research in ecology and environmental sciences should be prioritized.
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Aquatic macrophytes are one of the important biotic components of shallow lake ecosystems. Understanding the long-term evolution of the macrophyte community is crucial for lake management. Huanggai Lake, a typical shallow lake in the middle reach of the Yangtze River, was selected as the research site for this study. Based on 210Pb/137Cs dating, aquatic plant macrofossils were used to reconstruct the succession of aquatic macrophytes in the past century. Our results show that the lake maintained a consistent natural state before 1940, with a relatively low abundance of aquatic plants dominated by species such as Najas minor. From 1940 to 1974, human activities gradually intensified in the lake leading to the emergence of eutrophic species such as Potamogeton maackianus, along with the increasing abundance of other emergent and floating aquatic macrophytes. Since 1974, more pollution-resistant, emergent species such as Potamogeton maackianus and Potamogeton crispus have become dominant. The abundance of aquatic macrophytes reached its maximum in the early 1990s. Combined with macrofossil succession and other multiple sedimentary proxy analyses, driving mechanisms for aquatic macrophytes are discussed. Both the nearby Liangzi Lake and Huanggai Lake share many common features of aquatic plant evolution. This study is the first of its kind to use plant macrofossils (with identifiable images) as a proxy for aquatic macrophyte succession in a shallow Yangtze lake. In absence of long-term monitoring records, this study highlights the increased application of plant macrofossils for reconstructing the vegetation dynamics and restoration of degraded lakes exposed to severe anthropogenic impacts over the past century.
Management of cyanobacteria has become an increasingly complex venture. Cyanobacteria risks have amplified as society moves forward in an era of accelerated global changes. The cyanobacteria management “pendulum” has progressively shifted from prevention to mitigation, with management considerations often put forth after bloom formation. A universal system (i.e., one-size-fits-all management) fails to provide a management path forward due to the inherent complexities of each lake. A tailored management plan is needed: the right species at the right time in the right place (i.e., the three Rs). The three Rs represent a customizable management strategy that is flexible and informed by advances in scientific understanding to lower cyanobacteria-associated risks. Identifying thresholds in risk tolerance, where thresholds are defined by community collectives, is essential to frame cyanobacteria management targets and to decide on what management interventions are warranted.
Harmful cyanobacteria are a global environmental problem, yet we lack actionable understanding of toxigenic versus nontoxigenic strain ecology and toxin production. We performed a large-scale meta-analysis including 103 papers and used it to develop a mechanistic, agent-based model of Microcystis growth and microcystin production. Simulations for Lake Erie suggest that the observed toxigenic-to-nontoxigenic strain succession during the 2014 Toledo drinking water crisis was controlled by different cellular oxidative stress mitigation strategies (protection by microcystin versus degradation by enzymes) and the different susceptibility of those mechanisms to nitrogen limitation. This model, as well as a simpler empirical one, predicts that the planned phosphorus load reduction will lower biomass but make nitrogen and light more available, which will increase toxin production, favor toxigenic cells, and increase toxin concentrations.
Full-text available
A series of AVHRR (Advanced Very High Resolution Radiometer) satellite images and simultaneous ship transects in July 1992 were used to show that surface accumulations of cyanobacteria (blue-green algae) in the southern Baltic Sea can cause local increases in the satellite-derived sea surface temperature (SST) by up to 1.5-degrees-C. The warmer SST is attributed to increased absorption of sunlight due to increased phytoplankton pigment concentration. The distribution of surface cyanobacterial accumulations detected as increased reflectance in the visible channel of the AVHRR satellite sensor was correlated with chlorophyll concentration at 5 m depth. Warm SST anomalies ('hot spots') appeared both in accumulations of surface-floating cyanobacteria and in areas of high chlorophyll concentration (detected by shipboard measurements). The 'hot spots' followed the detailed boundaries of the cyanobacterial plumes and probably represented a shallow, diurnally heated top layer that appeared by afternoon in conditions of low wind (2 m s-1) and weak mixing, disappeared during the night due to thermal convection and were hardly detectable on days with wind speed of 6 to 8 m s-1. The vertical extension of the top diurnally heated layer was probably less than 1 m and definitely less than 5 m, at which depth no temperature increase was detected. It is suggested that the day/night SST difference in low-wind conditions may be an indicator of near-surface phytoplankton pigment concentration.
Full-text available
Increasingly, harmful algal blooms (HABs) are being reported worldwide due to several factors, primarily eutrophication, climate change and more scientific monitoring. All but cyanobacteria toxin poisonings (CTPs) are mainly a marine occurrence. CTPs occur in fresh (lakes, ponds, rivers and reservoirs) and brackish (seas, estuaries, and lakes) waters throughout the world. Organisms responsible include an estimated 40 genera but the main ones are Anabaena, Aphanizomenon, Cylindrospermopsis, Lyngbya, Microcystis, Nostoc, and Oscillatoria (Planktothrix). Cyanobacteria toxins (cyanotoxins) include cytotoxins and biotoxins with biotoxins being responsible for acute lethal, acute, chronic and sub-chronic poisonings of wild/domestic animals and humans. The biotoxins include the neurotoxins; ana-toxin-a, anatoxin-a(s) and saxitoxins plus the hepatotoxins; microcystins, nodularins and cylindrospermopsins. Confirmations of human deaths from cyanotoxins are limited to exposure through renal dialysis at a haemodialysis center in Caruaru, Brazil, in 1996. A major effort to compile all available information on toxic cyanobacteria including issues of human health, safe water practices, management, prevention and remediation have been published by the World Health Organization. This paper will review our current understanding of CTP's including their risk to human health.
Full-text available
Potentially toxic Cyanobacteria, like Microcystis, form a serious threat in recreational waters and drinking-water reservoirs. We monitored the population dynamics of toxic and non-toxic Microcystis strains using rRNA of the internal transcribed spacer region in combination with DGGE to determine whether there is a seasonal succession of toxic and non-toxic Microcystis genotypes in freshwater lakes and, if so, whether this succession can explain seasonal dynamics of the toxin microcystin. We studied 3 lakes in The Netherlands, all dominated by Microcystis during summer. Coexistence of several genotypes was observed in all lakes. The seasonal succession in a deep, stratified lake started with a population consisting of several toxic genotypes at the onset of the bloom, which changed into a population dominated by non-toxic genotypes at the end of the bloom. In this lake, the genotype succession clearly accounted for the observed microcystin dynamics. In 2 unstratified lakes, we also observed a seasonal replacement of Microcystis genotypes; however, the relation between genotype succession and microcystin dynamics was less conspicuous, since toxic strains dominated throughout the bloom period. A seasonal succession of different Microcystis genotypes might often be a key mechanism determining microcystin concentrations in Microcystisdominated lakes. Therefore, factors driving the succession of toxic and non-toxic genotypes deserve further study.
Surface waterblooms of toxic cyanobacteria (scums) interfere with the use of lakes, for instance in the production of drinking water or for recreation. Routine monitoring data are not sufficient for early warning due to the large temporal and spatial variability in the occurrence of surface waterblooms, and the time lag between the formation of the scum and the availability of relevant information for risk management. We combined a "traditional" dynamic simulation model based upon differential equations with fuzzy logic to describe the three main conditions governing surface waterbloom formation: (1) a preexisting population of cyanobacteria, (2) buoyancy of the cells, and (3) stability of the water column. The attributes and membership functions of the fuzzy model were based on earlier field studies of diel changes in buoyancy and vertical distribution of cyanobacteria. The model was applied without further calibration to the large lake IJsselmeer (1200 km(2)) in the Netherlands, and we validated the model output using 12 years of NOAA-AVHRR (National Oceanic and Atmospheric Administration-Advanced Very High Resolution Radiometers) satellite images on which surface blooms are discernible as an enhanced vegetation index or increased surface water temperature. Existing surface blooms were predicted with high accuracy, but additional blooms were also predicted. A statistical test (Cohen's Kappa) showed that correct predictions of the absence or presence of surface blooms were highly unlikely to have occurred by chance only. The model can be used to predict the occurrence of surface waterblooms in advance on the basis of the long-term weather forecast, leaving time for appropriate management of the problem. The lake management has expressed interest in converting the present model into a fully operational-online-early warning system.
Freshwater lakes are biologically sensitive to changes in the surrounding environment and the impacts that such changes have on their water quality are of considerable ecological, recreational and economic importance. In this study the phytoplankton community model, PROTECH, was used to experiment with the effects of elevated temperatures and increased nutrient load on phytoplankton succession and productivity. The response of a phytoplankton community to combined incremental changes in these drivers was analysed, in order to elucidate the resulting ecological changes. Annual mean phytoplankton biomass increased with increases in temperature and nutrient loading, although the latter had the larger effect. The phenology of the dominant phytoplankton taxa changed with increasing water temperature; the three spring blooming species all peaked earlier in the year. The simulated summer bloom of Anabaena became earlier in the year and the Chlorella bloom later. The increased phytoplankton biomass was largely dominated by the cyanobacterium Anabaena, which was especially prevalent during the summer bloom. This resulted in a progressive loss of phytoplankton biodiversity with increasing water temperature and nutrient supply. Model experimentation showed that whilst both factors greatly affected the community, the changes to nutrient loading generally had the greater effect and that at low nutrient levels the effect of water temperature change was reduced considerably. Finally, the model predicted that cyanobacteria have the potential to dominate the phytoplankton community, with clear consequences for water quality, and that this dominance was at its greatest when high water temperatures were combined with high nutrient loads.