Mitigating cyanobacterial blooms: how effective are
‘effective microorganisms’?
Miquel Lurling,1* Yora Tolman1,2 and Marieke Euwe1,3
1Aquatic Ecology & Water Quality Management Group, Department of Environmental Sciences, Wageningen University,
Wageningen, The Netherlands, 2Waterboard Delfland, Delft, The Netherlands, and 3Wetterskip Fryslaˆn, Leeuwarden,
The Netherlands
Abstract
This study examined the effects of ‘Effective Microorganisms (EM)’ on the growth of cyanobacteria, and their ability to
terminate cyanobacterial blooms. The EM was tested in the form of ‘mudballs’ or ‘Bokashi-balls’, and as a suspension
(EM-A) in laboratory experiments. No growth inhibition was observed for a laboratory strain of Microcystis aeruginosa
and for M. aeruginosa from the field at the recommended dosage of 1 EM-mudball per square-metre (0.1–0.3 g L)1).
Cyanobacteria were inhibited only at very high concentrations (5–10 g L)1 cyanobacteria), and a bloom was reduced,
being attributed to the high amount of clay and high water turbidity. For these high dosage treatments, the dissolved
oxygen concentration dropped initially to very low levels, with longer incubation indicating that nutrients were released
from the material. The EM-A suspension appeared ineffective in hampering cyanobacterial growths at recommended
usage concentrations. EM-mudballs released phosphate (160 lg P g)1) and metals (aluminium, copper, traces of lead and
lanthanum). The results of this study did not support the hypothesis that EM are effective in preventing cyanobacterial
proliferation or in terminating blooms, thereby suggesting lake restoration by ‘Effective Microorganisms’ is not a convinc-
ing eutrophication control option.
Key words
blooms, cyanobacteria, EM, eutrophication, lake restoration, Microcystis aeruginosa.
INTRODUCTION
Eutrophication has stimulated cyanobacterial prolifera-
tions or blooms in many estuaries and inland freshwater
systems (Paerl & Huisman 2008). Such blooms indicate
water quality deterioration and might pose a serious
threat to animal and human health because several
cyanobacteria can produce a variety of very potent tox-
ins (e.g. Codd et al. 2005; Dittmann & Wiegand 2006).
Dense cyanobacterial blooms might cause fish kills due
to oxygen depletion during the night (Paerl & Huisman
2009). Moreover, mass developments of surface-dwelling
and scum-forming cyanobacteria are an aesthetical
nuisance that can hamper recreation because they can
cause low water transparency and the production of
distinct odours.
Climate change is expected to aggravate cyanobacte-
ria blooms in lakes, in which increasing nutrient concen-
trations, warmer temperatures, more stable water
columns, higher salinities, increased water residence
times and elevated carbon dioxide (CO2) concentrations
are already considered key stimulative factors (Schip-
pers et al. 2004; Paerl & Huisman 2008). The summers
of 2003 and 2006, for example, which might be consid-
ered natural climate change experiments (they were the
hottest summers in Europe and the Netherlands since
recording began; Luterbacher et al. 2004; Obrego´n et al.
2007) have revealed what might become more common
in the near future in the Netherlands; namely, massive
cyanobacterial blooms.
As a consequence of the increased occurrence of
cyanobacteria-related nuisances, media attention and
public awareness, water quality authorities in the
Netherlands are confronted with a steady-increasing
number of (commercial) groups that claim to have solu-
tions for the cyanobacteria-related problems. However,
virtually all such claims on effectiveness and safety of
these methods ⁄products being promoted are based on
*Corresponding author. Email: miquel.lurling@wur.nl
Accepted for publication 3 August 2009.
 2009 The Authors
Doi: 10.1111/j.1440-1770.2009.00416.x Journal compilation  2009 Blackwell Publishing Asia Pty Ltd
Lakes & Reservoirs: Research and Management 2009 14: 353–363

anecdotal evidence rather than on scientifically defensi-
ble evidence.
To this end, one of the most heavily promoted prod-
ucts in the Netherlands following the 2006 heat waves is
the use of ‘Effective Microorganisms (EM)’, which are
embedded in the so-called ‘mudballs’ or ‘Bokashi-balls’.
The ‘EM-mudballs’ are based on a concept first developed
by Higa (1998), who suggested that the addition of EM
shifts the microbial community towards dominance by
beneficial species, while suppressing harmful bacteria.
More specifically, it is claimed that EM will ‘eat away’
phosphate, creating an environment that is not conducive
to cyanobacteria (http://www.emvereniging.nl/index2.
php/weblog/C11/P34, in Dutch), whereas the cyanobac-
teria themselves will be the ‘food for the microbes’
(http://www.youtube.com/Watch?v=R6YYON5dxok&NR=1).
Moreover, EM-mudballs are claimed to be safe and capa-
ble of eliminating out cyanobacterial blooms, thereby
making cyanobacteria-infested waters clear again (http://
www.emvereniging.nl, accessed 28 June 2008). As a result
of a lack of scientific tests supporting these claims, this
study examines the effectiveness of EM-mudballs and
an EM-solution (EM-A) in constraining cyanobacterial
growths and eradicating cyanobacterial blooms.
MATERIALS AND METHODS
Test organisms
The cyanobacterium Microcystis aeruginosa NIVA-CYA 43
originated at the Norwegian Institute for Water Research
(NIVA, Norway). Stock cultures of this strain were grown
in the laboratory in 100 mL Erlenmeyer flasks containing
50 mL of slightly modified Woods Hole Chu (WC) med-
ium (Lu¨rling & Beekman 1999), with vitamins added
(H (biotin) and B12 (cyanocobalamin) at 50 ng L
)1, and
B1 (thiamine HCl) at 100 ng L)1). The flasks were placed
in a Gallenkamp ORBI-SAFE Netwise Orbital Incubator
at 20C, at 25 rpm, and with an 18:6 h light:dark rhythm.
The light:dark cycle was programmed such that light
intensity increased gradually to a maximum of 130 lmol
quanta m)2 s)1, and subsequently decreased to darkness,
resulting in a daily average light intensity of 57 lmol
quanta m)2 s)1. The strain of M. aeruginosa used in this
study is completely uni- and bicellular under these given
growth conditions.
In addition to the laboratory cultures, cyanobacterial
scum material was harvested from Almere-Haven (the
Netherlands) on 16 August 2007. The collected material
consisted of >95% M. aeruginosa, as well as some Micro-
cystis flos-aquae, Anabaena sp. and 2.5% chlorophytes,
where Microcystis appeared in large colonies.
Effects of EM-mudball material on growth
of M. aeruginosa
Two experiments were performed to study the effects of
EM-mudball material on the growth of M. aeruginosa
NIVA-CYA 43 (Experiment 1, Exp. 1) and the growth of
phytoplankton (mainly M. aeruginosa) harvested from the
field (Experiment 2, Exp. 2).
The EM-mudballs were obtained from Agriton BV
(Noordwolde, the Netherlands), belonging to a batch of
12.000 EM-mudballs made with the intention of applying
them in Almere-Haven (the Netherlands); a harbour area
that had suffered from major Microcystis blooms in 2006.
The EM-mudballs had an average weight of ±300 g, with
the suggested dose being 1 ball m)2. This translates into
a mean maximum in situ concentration of 0.1–0.3 g L)1.
The EM-mudball was tested in the following concentra-
tion range: 0, 0.01, 0.1, 0.25, 0.5, 1.0, 5.0 and 10 g L)1.
EM-mudball material was added to 50 mL autoclaved
WC-medium in sterile 100 mL Erlenmeyer flasks, with
five replicates for each EM-mudball concentration. An
inoculum of M. aeruginosa NIVA-CYA 43 (Exp. 1) or of
M. aeruginosa from the field (Exp. 2) was added to each
flask. The initial chlorophyll-a concentrations were 16.0
(±0.1) and 3.8 (±1.9) lg L)1 in Exps 1 and 2 respectively.
The flasks were sealed with a cellulose plug, and placed
at random in a Gallenkamp ORBI-SAFE Netwise Orbital
Incubator under the same conditions as outlined above.
For Exp. 1, samples were taken initially, and after 2, 3,
6, 8, 9 12, 14 and 17 days. For Exp. 2, samples were
taken initially and after 3, 6, 9, 12, 15 and 18 days. In
both experiments, the samples were analysed for chloro-
phyll-a concentrations and the Photosystem II efficiency
(FPSII), using a PhytoPAM phytoplankton analyzer
(Heinz Walz GmbH, Effeltrich, Germany). One of fea-
tures of the PHYTO-PAM phytoplankton analyzer is that
it uses four different excitation wavelengths, allowing a
distinction between cyanobacteria, green algae and dia-
toms (Kolbowski & Schreiber 1995; Heinz Walz GmbH
1999; Lu¨rling & Verschoor 2003).
Growth rates were determined by nonlinear regres-
sion on chlorophyll-a data (exponential growth model) in
the program SigmaPlot 2000 (Systat Software Inc., Houn-
slow, London, UK). Growth rates were statistically evalu-
ated with a one-way ANOVA in the program SPSS (SPSS
Inc., Chicago, IL, USA) version 12.0.1. Significant differ-
ences were determined with a Tukey’s post hoc compari-
son test (P < 0.05). The EM-mudball concentration at
which the growth rates were reduced by 50%, compared
to those in controls (EC50), was determined with nonlin-
ear regression, by fitting a three-parameter sigmoidal
 2009 The Authors
Journal compilation  2009 Blackwell Publishing Asia Pty Ltd
354 M. Lurling et al.