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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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of Chemistry, Cambridge, UK, ed. 2, 2008).
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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
... Further gradients exist within each region, both in air temperature and other drivers, such as urbanization, agriculturalization, and industrialization, that could be the source of this residual signal. Nonetheless, warming air temperature leads to warmer water temperature, which in turn is known to influence water quality (e.g., O'Reilly et al., 2015;Paerl and Huisman, 2008;Shuvo et al., 2021). ...
... The degree of warming varies across the Great Lakes, but Lake Superior is warming the fastest, with an increase of +2.5 • C in summer surface water temperatures between 1979 and 2006 (Austin and Colman, 2007) and was identified as the second fastest warming lake in a global study (O'Reilly et al., 2015). Warming leads to a suite of ecosystem effects (Woolway et al., 2022, including increases in primary production (Shuvo et al., 2021), alterations in fish habitat (Kraemer et al., 2021;Mandrak, 1989;Sharma et al., 2007;Smith et al., 2012), and increased intensity and frequency of algal blooms (Ho et al., 2019;Paerl and Huisman, 2008), even in oligotrophic and 'cold' lakes (Reinl et al., 2023(Reinl et al., , 2021. Additionally, climate change will bring an increased frequency and intensity of heatwaves and storms (Rahmstorf and Coumou, 2011;Seneviratne et al., 2012), both of which are associated with increased primary production (Blagrave et al., 2022;Hampton et al., 2022;Stockwell et al., 2020) and reduced water clarity in the nearshore (Blagrave et al., 2022). ...
We provide the first comprehensive analysis of spatial heterogeneity in water quality across the Canadian nearshore regions of the Laurentian Great Lakes (LGL) with periodic sampling in the ice-free seasons from 2000 to 2019 for 24 water quality variables from 52 nearshore sites. We asked: (1) What is the extent, range, and magnitude of spatial heterogeneity in water quality conditions across the nearshore of the Canadian Great Lakes? and (2) How do features of anthropogenic development, sub-basin characteristics, anticipated coastal circulation, and weather influence water quality conditions in the nearshore of the Canadian Great Lakes? Principal Components Analysis explained 42% of the variation in water quality across the Canadian Great Lakes, with high spatial heterogeneity both within and among lakes, ranging from oligotrophic conditions in Lake Superior to eutrophic conditions in Lake Erie. Lakes Erie and Ontario generally had higher concentrations of chloride, chlorophyll a, and nutrients while higher silicate concentrations were observed in Lake Superior. Consistent patterns of degraded water quality were observed in Areas of Concern, such as Hamilton Harbour, Bay of Quinte, Nipigon Bay, and near Thunder Bay. Across the nearshore of the Canadian Great Lakes, regions with warmer air temperatures, in addition to urbanized and agricultural landscapes, were associated with deteriorated water quality. Our study highlights the importance of improving management practices across urban and agricultural landscapes, particularly in consideration of climatic change cumulatively degrading water quality conditions in the highly biologically, culturally, and socioeconomically important nearshore regions of the LGL.
... Rising temperatures and thermal stratification can favor cyanobacteria growth allowing them to outcompete other phytoplankton groups (Fadel et al., 2015;Wagner and Adrian, 2009). They often bloom and dominate aquatic ecosystems during dry season when water temperature rises as they outcompete other groups such as diatoms and green algae at higher temperatures (Paerl and Huisman, 2008). Some species use gas vesicles to float upward during stratified conditions and accumulate in dense surface blooms shading nonbuoyant diatoms and green algae and suppressing them through competition for light (Jöhnk et al., 2008). ...
... Over the last decades, many studies have demonstrated that cyanobacterial blooms are promoted by higher temperatures and nutrient loadings (Burford et al., 2020;Davis et al., 2009;Fadel et al., 2019;Jöhnk et al., 2008;Paerl and Huisman, 2008;Slim et al., 2014). Changing climatic conditions are predicted to increase the frequency and toxicity of cyanobacterial blooms (O'Neil et al., 2012). ...
... In Taihu, under the situation of an increase in internal loading, although the eutrophication of lakes has increased, there is no significant increase in nutrient input. During the cyanobacteria outbreak season, the death and decomposition of algae can easily lead to hypoxia on the sediment surface, and many benthic macroinvertebrates will suffocate [52,53]; however, in the cold season, macroinvertebrates will not be disturbed by more pollutants. For multiyear changes, these two effects are superimposed on macroinvertebrates in different seasons in one year. ...
Full-text available
In eutrophic lakes, even if external loading is controlled, internal nutrient loading delays the recovery of lake eutrophication. When the input of external pollutants is reduced, the dissolved oxygen environment at the sediment interface improves in a season without algal blooms. As an important part of lake ecosystems, macroinvertebrates are sensitive to hypoxia caused by eutrophication; however, how this change affects macroinvertebrates is still unknown. In this study, we analysed the monitoring data of northern Lake Taihu from 2007 to 2019. After 2007, the external loading of Lake Taihu was relatively stable, but eutrophication began to intensify after 2013, and the nutrients in the sediments also began to decline, which was related to the efficient use of nutrients by algal blooms. The community structure and population density of macroinvertebrates showed different responses in different stages. In particular, the density of oligochaetes and the Shannon–Wiener index showed significant differences in their response to different stages, and their sensitivity to eutrophication was significantly reduced. Under eutrophication conditions dominated by internal loading, frequent hypoxia occurs at the sediment interface only when an algal bloom erupts. When there is no bloom, the probability of sediment hypoxia is significantly reduced under the disturbance of wind. Our results indicate that the current method for evaluating lake eutrophication based on oligochaetes and the Shannon–Wiener diversity index may lose its sensitivity.
Full-text available
Lake Balaton, a shallow polymictic freshwater lake in Central Europe, became eutrophic in the 1970s. To retain the inorganic nutrients from the main tributary River Zala, a semi-artificial system called the Kis-Balaton Water Protection System (KBWPS) was constructed in the early 1980s. In 2015, the system was reconstructed and modernised, thus offering the opportunity to evaluate the effectiveness of the functional connection between the KBWPS and Lake Balaton over the past 20 years and to compare its impact before and after the reconstruction. To this end, time series data of algal biomass in Lake Balaton between 1999 and 2019 based on Landsat 7 satellite data were analysed. Over the last 20 years, the algal biomass in Lake Balaton showed an increasing trend (0.009 ± 0.011% increase per year), with territorial specificities also observed. No change was noted in the western part, while an increase was recorded in the eastern part of the lake. A significant difference in the rate of algal biomass accumulation was noticed before (annual increase of 0.008 ± 0.019%) and after (0.240 ± 0.306% per year) the KBWPS reconstruction. Given that the largest increase in algal biomass after reconstruction was observed in the outermost KBWPS basin of Lake Balaton, it appears that mesoscale environmental, water balance, or other factors affecting the lake are playing a role in this increase, rather than the KBWPS reconstruction. This research highlights the potential to study aquatic ecosystems using Earth observation techniques, and how mesoscale factors such as changes in the local climate regime or shifts in lake management can greatly impact the trophic state of a large shallow lake. Effectively identifying these factors is crucial in maintaining the proper status of aquatic ecosystems.
Understanding the dynamic interplay between physical and biological processes is a major challenge in ocean-related studies, especially to develop predictive capabilities and while addressing the climate change impacts. Biological and physical dynamics in the oceans are coupled, and primary producers being the most important element in an ecosystem, the subject is vastly explored, in terms of the chaotic interactions between various elements of the ecosystem in different spatiotemporal scales. Fluid (ocean) properties are a key factor interacting with plankton behaviour, driving the biological processes and their spatiotemporal patterns. The present chapter is on the role of density gradient in determining the vertical profile of chlorophyll-a in a warm/stratified region, the north-eastern Arabian Sea (NEAS), during the winter-spring season. The dynamics of the recurring bloom (green Noctiluca), one of the important regional ecosystem issues, is explained for initial, peak, and withdrawal stages based on in situ observations. The Bio-Argo and conductivity-temperature-depth (CTD) profiler-based analysis for 2003–2019 shows the early onset of the spring bloom and intensification in the subsurface chlorophyll maxima (SCM) in the NEAS since the recent past. The empirical orthogonal teleconnection (EOT) is effectively utilised to explain the surface-subsurface interaction in maintaining the upper layer production pattern and the adaptive strategies of the phytoplankton in respect of the buoyancy control.
Climate change and extreme weather events (such as droughts, heatwaves, rainstorms and floods) pose serious challenges for water management, in terms of both water resources availability and water quality. However, the responses and mechanisms of river water quality under more frequent and intense hydroclimatic extremes are not well understood. In this Review, we assess the impacts of hydroclimatic extremes and multidecadal climate change on a wide range of water quality constituents to identify the key responses and driving mechanisms. Comparison of 965 case studies indicates that river water quality generally deteriorates under droughts and heatwaves (68% of compiled cases), rainstorms and floods (51%) and under long-term climate change (56%). Also improvements or mixed responses are reported owing to counteracting mechanisms, for example, increased pollutant mobilization versus dilution during flood events. River water quality responses under multidecadal climate change are driven by hydrological alterations, rises in water and soil temperatures and interactions among hydroclimatic, land use and human drivers. These complex interactions synergistically influence the sources, transport and transformation of all water quality constituents. Future research must target tools, techniques and models that support the design of robust water quality management strategies, in a world that is facing more frequent and severe hydroclimatic extremes.
This article provides an introduction to freshwater cyanobacterial blooms, including a brief discussion of those formed by eukaryotic algae. In freshwater systems, cyanobacteria have ecological strategies such as buoyancy regulation, phosphorus mining, and nitrogen fixation that give them a competitive advantage over eukaryotic algae, and they cause visible blooms more frequently in freshwater ecosystems than other algal types. Many cyanobacterial species also have a competitive advantage at higher water temperatures (above 25 °C). Understanding cyanobacterial bloom dynamics includes information on water quality, with emphasis on nutrients, and physical factors such as water temperature and the amount of mixing in a waterbody. Calm conditions allow these organisms to float to the water surface where prevailing winds aid the development of thick accumulations on shorelines. Human and animal exposure to cyanobacteria at these shorelines is problematic because of the potent toxins some species produce that have the potential to be harmful. A synopsis of the key bloom‐forming organisms with photomicrographs is included in this article.
Full-text available
As the widespread distributed and critical zones connecting the land and ocean systems, coastal bays are special units with semi-enclosed landforms to accommodate and process dissolved organic matter (DOM) in the context of increasing anthropogenic effects globally. However, compared to other common systems that have been paid much attention to (e.g., large river estuaries, wetlands), the roles of the coastal bays in coastal carbon cycling are less explored. To fill this knowledge gap, here we combined optical techniques and ultra-high-resolution mass spectrometry to systematically investigate the DOM chemistry of the three typical coastal bays in different nutrient levels, Xiangshan Bay, Jiaozhou Bay, and Sishili Bay, in China. Results show that terrestrial signals and anthropogenic imprints were observed in these three bays to various extents. Besides, Xiangshan Bay with a higher nutrient level had the DOM characterized by lower humification and aromaticity degree than Jiaozhou Bay and Sishili Bay, which not likely mainly resulted from the differences in the primary production or photochemical processing. Further examination reveals that microbial processing likely contributes to the differences in DOM chemistry among the three bays, as indicated by different proportions of potentially transformed nitrogen-containing molecules and relative abundances of the island of stability molecules. Considering the nutrient levels in different bays, we speculate that the lower nutrient concentrations would promote the efficiency of the microbial carbon pump (MCP), which hypothesized that heterotrophic microorganisms might contribute to the formation of marine recalcitrant organic carbon. Additionally, the enrichment of oxygen-rich compounds in the unique carboxyl-rich alicyclic molecule pool of Jiaozhou Bay and Sishili Bay suggests that MCP might be more efficient in these two bays. This study emphasizes the importance of coordinating the land and ocean systems and controlling the nutrient discharge to coastal bays, thus, to potentially promote long-term marine carbon sequestration.
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.
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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.