JOURNAL OF INTERNATIONAL ACADEMIC RESEARCH FOR ...The fluorescence activated cell sorting (FACS)...
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PHYTOPLANKTON COMMUNITY STUDY FROM EUTROPHIC WETLAND EMPLOYING FLUORESCENCE ACTIVATED CELL SORTING METHOD
ANINDITA SINGHA ROY1
DEBAJIT BHOWMICK2 RUMA PAL1
1Phycology laboratory, Department of Botany, University of Calcutta, Kolkata, West Bengal, India
2Centre for Research in Nanoscience and Nanotechnology, Acharya Prafulla Chandra Roy Sikhsha Prangan, University of Calcutta, Kolkata, West Bengal, India
Abstract
The fluorescence activated cell sorting (FACS) method was used for a rapid
screening, sorting and counting of phytoplankton populations from a eutrophic wetland. The
abundance of phytoplankton population was estimated to be 8.34 ×10^4 cells/µL. Around 25
different phytoplankton genera belonging to different groups like chlorophytes,
cyanobacteria, bacillariophytes and euglenophytes were sorted and identified. Identified
genera included Cosmarium sp., Chlorococcum sp., Tetraedron spp., Tetrastrum sp.,
Scenedesmus spp., Chlorella sp., Kirchneriella spp., Crucigenia spp., Chlamydomonas sp.,
Ankistrodesmus spp., Centritactus sp., Selenastrum sp., Pediastrum spp., Lepocinclis spp.,
Trachelomonas spp., Phacus spp., Spirulina spp., Synechococcus sp., Synechocystis sp.,
Anabaenopsis spp. Rhabdoderma sp., Chroococcus sp., Planktolyngbya spp., Merismopedia
spp., Pseudoanabaena sp., Cyanarcus sp. Some planktonic groups were also sorted and
designated as unknown species (US). Also Shannon diversity index (H’) was calculated
which helped inferring the diversity of the selected wetland to be moderately high. Overall
the FACS process was found to be an alternative, fast, accurate and efficient method for
phytoplankton counting and diversity determination.
Keywords: Autofluorescence, Fluorescence Activated Cell Sorting (FACS), Flow Cytometry
(FCM), Wetland, Photopigments, Phytoplankton.
Introduction
Phytoplankton community is a dynamic functioning component of an aquatic
ecosystem having an important role to play. Their abundance and diversity pattern are
essential in water quality assessment, including the influence of environmental variables
(Palmer 1956; Sladacek 1973; Bahura 2001; Naselli-Flores et al. 2013). The species
composition of phytoplankton also provides information about nutrient status like
eutrophication or pollution level of that particular aquatic ecosystem (Willen 1976; Naselli-
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Flores et al. 2013). In order to obtain a reliable information on the phytoplankton abundance,
different methods like light microscopic cell counting method (Willen 1976), chlorophyll-a
estimation (Arnon 1949; Strickland and Parsons 1972), sedimentation technique (Utermohl
1925, 1931, 1958), etc can be applied. Chlorophyll-a estimation describes the total biomass
of the phytoplankton community, but cannot decipher the species diversity which is a big
demerit for statistical analysis of biotic and abiotic variables of aquatic ecosystem. Light
microscopic field study is superlative regarding total count, species diversity index
determination and identification also. Nevertheless, there may always be a chance for
misinterpretation of the water quality assessment due to erroneous manual counting,
especially in ecosystem with very high plankton count.
With the development of Florescence Activated Cell Sorting (FACS), an
alternative and attractive plankton counting method has emerged recently as compared to
other methods cited above. FACS grabs a greater advantage over light microscopy due to
rapid cell counting along with the physical separation of the cells from a mixed assemblage
(Trask et al. 1982; Phinney and Cucci 1989; Veldhuis and Kraay 1990; Partensky et al.
1999). Applications of standard techniques of FACS in the field of maritime research are
numerous and expanding (Trask et al. 1982; Phinney and Cucci 1989; Lange et al. 1996),
mainly focusing on oceanographic work (Olson et al. 1985; Veldhuis and Kraay 1990;
Campbell et al. 1997; Marie et al. 1997; Chisholm et al. 1988; Partensky et al.1999; Sciandra
et al. 2000; Veldhuis and Kraay 2000; Jacquet et al. 2001; Shalapyonok et al. 2001;
Dandonneau et al. 2006). Generally, two inherent properties of the aquatic cells like the size
and photosynthetic pigment fluorescence are taken into consideration for addressing the
ecological questions. Allometric (size versus pigment fluorescence) and ataxonomic (two-
colour pigment fluorescence) analyses provide an estimate of particle concentration which is
helpful in terms of characterizing aquatic plankton assemblages (Trask et al. 1982; Phinney
and Cucci 1989). FACS requires small sample volumes, but allows more samples and less
sub-sampling to obtain good statistical significance (Dubelaar and Jonker 2000). Thus, along
with rapid analysis of large number of cells from small sample volumes, FACS permits more
significant statistical data analysis very easily, thereby minimizing errors associated with
manual calculation and increasing higher chances of accuracy in data accumulation
(Gisselson et al. 1999; Dubelaar and Jonker 2000).
From previous reports it is evident that FACS is a powerful tool for studying
phytoplankton ecology. Establishment of monocultures of eight algal species monitoring the
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optical properties of the samples such as Forward Light Scatter (FLS), Perpendicular Light
Scatter (PLS), chlorophyll fluorescence, etc. by Trask et al. (1982) brought into light a new
application of FACS. Combination of parameters made it evident that all the eight species
could be resolved separately. Phinney and Cucci (1989) also succeeded in studying
phytoplankton diversity by considering two inherent properties which is size and
phytoplankton pigment fluorescence. The discovery of one of the smallest known
phytoplankton Prochlorococcus marinus to be abundant in all major subtropical oceans in
terms of both biomass and productivity by Veldhius and Kraay (2000) was another milestone
of FACS application. The observations were based on the combination of parameters like
size, autofluorescence, DNA-specific fluorescent staining, etc. Li and Dickie (2001) also
observed the predominance of phytoplankton including Synechococcus and Cryptophytes in
Bedford Basin surface. The results were based on chlorophyll auto fluorescence and cell size.
Recently, Cellamare et al. (2009) was successful to screen the phytoplankton community
from four different freshwater aquatic ecosystems where forty-five phytoplankton taxa were
isolated, including green algae (29), cyanobacteria (8), diatoms (7), and cryptomonad (1) with
the help of FACS. However, FACS study of phytoplankton community especially in
freshwater environment is limited (Crosbie et al. 2003; Tijdens et al. 2008; Toepel et al.
2004, 2005; Cellamare et al. 2009).
In the present investigation, suitability of live-cell sorting flow cytometry was
assessed for quantitative analysis and diversity determination of phytoplankton community
from a freshwater eutrophic wetland of Ramsar site, India. The natural samples were directly
analyzed without any prior culture maintenance. Being eutrophic, this wetland harbors a
diverse and abundant phytoplankton assemblage. Thus, light microscopic counting becomes
time consuming and with high chance for manual error. The alternative method of FACS was
used for swift and accurate counting of the huge phytoplankton population along with
physical separation or sorting of cells using proper gating parameters based on the
fluorescence pattern and cell size. The number of events occurring and the duration of
analysis were recorded for estimating the cell concentration.
Materials and methods:
Study site:
The investigation was carried out in freshwater eutrophic wetland, commonly known
as ‘East Kolkata wetland’ (EKW), declared as the “Wetland of International Importance” by
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Government of India and “Ramsar Site no. 1203” in Ramsar Convention in 19th August 2002
(Ramsar Secretariate 2013). It harbors one of the oldest traditions of resource recovery from
the Kolkata Municipal waste. The geographic location of the studied site was 88° 24.641′ east
latitude and 22° 33.115’ north latitude, as obtained from GARMIN GPS map 76 CSx device.
Flow cytometric determination:
The sample water was collected in an amber bottle after filtering through
approximately 100 µm pore sized phytoplankton net. The filtered samples were brought to
the laboratory in cold condition. The light scattering and the fluorescent properties of the
unicellular organisms were determined in Fluorescence Activated Cell Sorter (FACS), BD
FACS Aria Tm III which could measure up to 70,000 particles/sec. The machine was equipped
with a 100µ nozzle, and the flow rate of the sample was maintained at 6µL/ min (lowest
possible). Sheath pressure was adjusted to 20 Psi. Available laser emissions of 488nm,
642nm and 375nm were set as light sources. Forward scatter (FSC) indicates the cell size and
shape while the side scatter (SSC) is indicative of cell granularity, size and refractive index.
Scattered light (a sizing parameter) was measured at FSC (Filter-488/10), SSC (Filter-488/15)
channels. Emitted fluorescence was detected and distributed among the filters viz. FITC
(Filter-530/30), PE (Filter-585/42), PE-Texas Red (Filter-616/23), Per CP-Cy 5-S (Filter-
780/60) and APC (Filter- 660/20). The following emission filters represent wavelengths of
different major photo pigments’ auto-fluorescence range. For instance, chlorophyll-a on
excitation at 488nm, emits fluorescence at around 685nm (Red fluorescence) (Trask et al.
1982; Phinney and Cucci 1989). This wavelength corresponds to PE-Texas Red (Filter-
616/23) of the instrument. Again phycoerythrin on excitation at 488nm or 550 nm, emits
orange fluorescence at 560-585nm (Trask et al. 1982; Phinney and Cucci 1989) which
corresponds to PE (Filter-585/42) of the instrument. Similarly, another important
photopigment phycocyanin has blue-green fluorescent emission at around 670nm on being
excited at 640nm (Dubelaar and Jonker 2000). This emission resembles that of APC (Filter-
660/20) or PE-Texas Red (Filter-616/23) of the instrument. Orange to yellowish orange
fluorescence of carotenoid pigments have a resemblance to that of FITC (Filter-530/30) of
the instrument used (Phinney and Cucci 1989). All parameters were adjusted to logarithmic
scale. The duration of analysis and number of events occurring were recorded for estimating
the cell concentration. After analyzing, different types or sub-communities were gated based
on florescence patterns and size and then desired gates were sorted (Fig.1). Cell sorting was
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done following 4 way sorting precision and the total sub communities obtained are
represented in Fig.1. The choice of gating parameters like FSC-A versus FSC-H or APC-A
versus PE-Texas Red-A was absolutely a trial and error method to distinguish the clusters of
sub-communities. Afterwards, light microscopic observations were carried out for
identification of individual genus from the sorted sub-communities. Each community was
represented by different colour in order to distinguish them from one another. Total number
of 1,300,000 events or cells (Fig.1a or black box of Fig.1j) represented the entire community.
Of the total events, P1 community (Fig.1a) was selected as the mother community. The P1
community was plotted separately (Fig.1b,c) and was further divided downstream into
community P2 and P3 in one cytograms based on PE-Texas Red (Filter-616/23) and APC
(Filter- 660/20) (Fig.1b) and into P4, P5, P6 and P7 taking PE (Filter-585/42) and Per CP-
Cy5-S (Filter- 780/60) into consideration in another cytogram as parameters for subdivision
(Fig.1c). Numbers of cells/events in P2, P3, P4, P5, P6 and P7 have been displayed in Fig.1j.
Communities P2 and P3 were found to occur as distinct small clusters and thus were not
classified further. However, communities P4, P5, P6 and P7 were further separately plotted in
different graphs based on different parameters as shown in Fig. 1(d to g respectively and j).
For instance, P4 community was plotted (Fig.1d,j) taking PE-Texas Red and APC into
consideration and was classified into distinct colonies of P13, P14, P25, P26 and P27. The
number of cells occurring in each sub-communities of P4 is represented in Fig.1j, along with
the percentage of occurrence. Similar attempts were taken for communities P5, P6 and P7
using sets of parameter for downstream subdivision as depicted in Fig.1(e to j).The P5
community showed to be further classified into sub-communities like,P8 and P9
(Fig.1e,j),whereas P6 community showed divisions of P15, P16, P17 and P18 sub-
communities (Fig.1 f, j) and lastly P7 was subdivided into P11 and P12 sub-communities
(Fig.1g,j). It was found that communities P8 and P12 could be further subdivided for better
analysis. But P8 (Fig.1h,j) was classified downstream into P19, P20 and P21. Sub-community
P12 (Fig.1i,j) also showed divisions of P22, P23 and P24 sub-communities as separate
distinct clusters. Thus, based on the above mentioned gating parameters, the cells were gated
and sorted into 19 sub-communities. After cell sorting they were collected on a multiwell
(99-welled) microplate. The microplate with the sorted samples was checked under light
microscope (BD Pathway 855), where 3x3 montage captured images were taken for the final
19 subpopulations to study the diversity and the number of the phytoplanktons (Fig.2,
representing a sorted sub-community P9). Further, microscopic identification was done
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employing proper phytoplankton monographs (Prescott 1982; Desikachary 1959; Komarek
and Anagnostidis 1999, 2005, 2013; Anand 1998; Jaiswal and Tiwari 2003; Rath and
Adhikari 2005) and confirmed from Algaebase (Guiry and Guiry 2015). Fig. 3 illustrates the
different phytoplanktons that were gated and sorted under BD FACS Aria Tm III, viewed and
identified under low, high and oil immersion objective of Carl-Zeiss Axiostar microscope.
Microphotographs of these samples were taken using a digital camera (Canon T2-T2 1,6x
SLR 426115). In the present communication only generic identification was included.
Phytoplankton community study:
Diversity index was determined for the phytoplankton community study by using
Shannon Wiener Index (H’). The basic formula is:
H' = -sΣi=1 pi log pi,
Where; the pi was estimated from ni/N as the proportion of the total population of
individuals (N) belonging to the ith species (ni), s equals the total number of species in the
sample (Shannon and Weaver 1948; Magurran 2004).
Results:
From the phytoplankton community of the studied eutrophic wetland, the algal and
cyanobacterial genera were sorted based on pigment fluorescence and size variation and
finally identified upto genus level by light microscopy (Table1). A total of 26 phytoplankton
genera have been identified. Most of them belonged to Chlorophytes (13 genera), followed
by Cyanobacteria with 9 genera and Euglenophytes (3 genera). The Bacillariophytic members
were recognised as a single group Bacillariophyta. Some unknown taxa were also recognized
as unknown species (US). Among the Chlorophytes, the dominant algal genus obtained was
Scenedesmus sp. (13.45% of the total phytoplankton population) followed by Chlorella sp.
(9.8% of the total). This entire process of sorting and identification of different phytoplankton
genera was based on the different auto-fluorescent properties of the chromophores. The
community P1 (Fig. 1a,j) was the main mother population taken into consideration for
analysis, from which 6 communities P2 to P7 were derived separately on the basis of
different parameters as mentioned above. These communities were further clustered into
distinct sub-communities P8 to P27 (Fig.1a to j). The genera sorted from each community are
listed in Table 1. For instance, in community P9, 12 different microplanktonic genera were
recorded viz. Chlorococcum sp. (9.30%), Tetrastrum spp. (4.65%), Scenedesmus spp.
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(20.93%), Chlorella sp. (9.30%), Kirchneriella sp. (6.97%), Ankistrodesmus spp. (2.33%),
Spirulina spp. (23.25%), Synechococcus sp. (2.33%), Synechocystis sp. (2.33%), US 2
(2.33%), US 3 (2.33%) and Diatom (18.6%). This community (P9) comprised a mixture of
phytoplankton belonging to phylum Chlorophyta, Cyanoprokaryota and Bacillariophyta.
However, community P13 was again purely picoplanktonic community (US4). Another
community P25 comprised of two taxa, Spirulina spp. (16.67%) and Synechococcus sp.
(83.33%), both of which belong to the same Cyanoprokaryotic phylum. The band-pass filters
for gating used were APC-A (660nm) versus PE- Texas Red-A (616nm). Both the filters
belonged within the range of fluorescence emission of the photopigment phycocyanin, one of
the major pigment constituent of Cyanobacteria. In other words, P25 comprised of
Cyanobacteria.
A total number of 200,000 cells were recorded in 24 seconds and the flow rate of the
sample used was 6µL/ min (lowest possible). The total phytoplankton concentration of 8.34
×10^4 cells/µL was obtained and the Shannon diversity index (H’) was calculated as 2.57,
indicating moderately high abundance of species assemblages.
Discussion:
The efficiency, accuracy and rapidity in counting phytoplankton communities makes
FACS an alternative method and many fold advantageous over other methods of ecological
analysis (Li 1995; Dubelaar and Gerritzen 2000). Waters with varying degree of pollution or
eutrophication contain phytoplankton communities with varied species composition in
different level of abundance. The expression of species diversity derived from Shannon's
formula (H’) typically range between 1.5 and 3.5 (Lloyd and Ghelardi 1964). An increase in
the number of species and a tendency towards a more equal distribution of individuals among
species can result in higher values of H' (Shannon and Weaver 1948; Sager and Hasler 1969).
The Shannon index obtained from the present study thus interprets the eutrophic freshwater
habitat to harbor a diverse and an uneven number of species compositions.
In the present investigation the natural heterogenous phytoplankton community was
exploited based on their size and autofluorescence property of the algal pigments. A diverse
array of pigments do occur among different algal groups such as chlorophyll (a, b, c and d),
carotenoids, phycobilliprotiens (phycocyanin, phycoerythrin and allophycocyanin),
xanthophylls, luciferin and many more. The algal phyla are characterized by particular
pigment composition. For example, Cyanoprokaryota comprises chlorophyll a as major
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pigment, together with carotenoids and phycobilliproteins (Rowan 1989; Lee 2008). Different
phyla of eukaryotic algae contain different pigment compositions having one or few pigments
as major. The phylum Chlorophyta is characterized by chlorophyll a and chlorophyll b along
with carotenoids, Rhodophyta - phycoerythrin and chlorophyll d, Bacillariophyta –
fucoxanthin, whereas Euglenophyta lack chlorophyll c, but contains chlorophyll a, b,
neoxanthin and diadeoxanthin (Rowan 1989; Lee 2008). Every pigment has a particular
fluorescent excitation and emission spectra. The instrument BD FACS Aria Tm III is usually
equipped with different optical filters like FITC (530/30), PE (585/42), PE-Texas Red
(616/23), Per CP-Cy 5/7 (780/60), APC (660/20), thereby detecting the fluorescent
properties. Using these various optical filters, a total of about 19 subpopulations had been
gated into distinct clusters. Some communities obtained were found to be pure up to generic
level (P13), some up to phylum level (P11, P25), while some with a mixture of members
belonging to different phyla (P3, P9, P14-P17, P19-P24 and P26). The concentration of
phytoplankton community obtained from the above observation was 8.34x 10^4 cells/µL. The
present wetland (EKW) under study showed the dominance of Chlorophytic members
followed by the members of Cyanobacteria, Bacillariophyta and Euglenophyta. The genus
found to be predominating was Scenedesmus sp. The phytoplankton diversity recorded was a
useful indicator for water quality assessment which was in conjunction to the reports of
Pradhan et al. (2008) Further; the putative role of the identified genera in bioremediation
from previous studies of Pradhan et al. (2008) helped this wetland to be worth for sewage
reclamation of the Metropolitan city.
Future application of FCM include more fine modification of gating principles and
further subdivisions which could ultimately help in sorting fully pure algal genera or species
also. This could be of immense help in grounds of pure strain isolation by FACS from
phytoplankton population of natural habitat, including further molecular studies and
molecular taxonomic classification.
Conclusions:
In the present investigation, the trial for accurate and rapid counting of phytoplankton
including their diversity index study was successful. This helped in indicating the actual
phytoplankton abundance of particular ecosystem with their diversification. Therefore, this
approach based on a combination of FACS followed by microscopy would be an alternative
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approach for phytoplankton counting and diversity study of any natural habitat very acutely
within a short time.
Acknowledgements:
We would like to thank University Grant Commission (UGC), New Delhi, India for
their financial assistance. We would also like to thank Department of Botany and Center for
Research in Nanoscience and Nanotechnology (CRNN) of University of Calcutta for
instrumental facilities.
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Figure legends:
Figure 1: Bivariate scatter plots analyzed using FACSort flow cytometry, showing splitting
of the main population (P1) into its subpopulations (P2-P24) (a-i) based on auto-fluorescence
and their cell size and their percent of occurrence of the total recorded population (j).
Figure 2: A 3x3 montage capture using light microscope (BD Pathway 855) showing the
sorted population P15 (comprising different algal genera belonging to single phylum-
Cyanoprokaryota).
Figure 3: Microphotographs of phytoplankton sorted and identified from a eutrophic wetland
(10μm scale): 1. Cosmarium sp., 2. Chlorococcum humicola, 3. Tetrastrum triangulare, 4.
Chlorella sp., 5. Kirchneriella sp., 6.Tetraedron minimum, 7. T. muticum, 8. T. trigonum var.
gracile, 9. T. trigonum, 10. T. caudatm var. longispinum, 11. Centritactus dubius , 12.
Scenedesmus dimorphus, 13. S. quadricauda, 14. S. armatus var. bicaudatus, 16. S.
denticulatus, 17. S. itascaensis, 18. Crucigenia crucifera, 19. C. tetrapedia, 20. C. apiculata,
21. C. quadrata, 22. Pediastrum tetras var. apiculatum, 23. P. boryanum, 24. P. tetras, 25.
Selenastrum bibraianum, 26. Ankistrodesmus falcatus, 27. A. tumidus, 28. A. falcatus var.
stipitatus, 29. A. convolutes, 30. Lepocinclis globulus, 31. Trachelomonas volvocina, 32.
Phacus tortus, 33. P. Nordstedii, 34. Spirullina nordstedii, 35. S. subtilissima, 36.
Merismopedia minima, 37. M..glauca, 38. Planktolyngbya contorta, 39. Chroococcus
dispersus, 40. Synechocystis aquatilis, 41. Synechococcus elongatus, 42. Rhabdoderma
irregulare, 43. Pseudoanabaena catenata, 44. Microcystis sp., 45. Coelosphaerium pallidum,
46. Cyanarcus hamiformis.
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Table 1: List of phytoplankton diversity observed in different sorted populations:-
Sorted Population
Diversity observed from microscope
P3 Cosmarium (8.9%); Cyanophytic population (4.16%); US 1(87.5%) P9 Chloroccum (9.30%); Tetrastrum (4.65%); Scenedesmus (20.93%); Chlorella
(9.30%; Kirchneriella (6.97%); Ankistrodesmus (2.33%); Spirulina (23.25%); Synechococcus (2.33%); Synechocystis (2.33%); US 2 (2.33%); US 3 (2.33%); Diatom (18.6%)
P11 US 2 (16.67%); Trachelomonas (83.33%) P13 US 4 (100%) P14 Tetrastrum (2.99%); Scenedesmus (4.47%); Tetraedron (2.99%); Crucigenia
(2.99%); US 5 (15.40%); Synechococcus (61.19%); Rhabdoderma (2.99%); Chroococcus (2.99%)
P15 Kirchneriella (1.81%); Crucigenia (7.88%); Chlamydomonas (0.61%); Spirulina (1.2%); Synechococcus (3.03%); Synechocystis (8.48%); Chroococcus (12.12%); Planktolyngbya (1.81%); Merismopedia (7.27%); Pseudoanabaena (0.61%); Cyanophytic population (41.25%)
P16 Crucigenia (17.65%); Ankistrodesmus (2.94%); Selenastrum (8.82%); Spirulina (5.88%); Synechococcus (11.76%); Planktolyngbya (8.82%); Merismopedia (26.47%); US 2 (11.76%); Cyanophytic population (35.29%)
P17 Tetrastrum (3.57%); Chlorella (75%); Ankistrodesmus (3.57%); Selenestrum (10.71%); Diatom population (7.14%)
P19 Tetrastrum (1.47%); Scenedesmus (33.82%); Chlorella (36.76%); Tetraedron (5.88%); Spirulina (1.47%); Synechocystis (13.24%); Rhabdoderma (1.47%); Merismopedia (1.47%); Diatom (4.41%)
P20 Chlorococcum (21.51%); Tetrastrum (2.15%); Scenedesmus (24.73%); Chlorella (11.83%); Kirchneriella (1.08%); Ankistrodesmus (1.08%); Centritactus (1.08%); Selenastrum (3.23%); Rhabdoderma (2.15%); Lepocinclis (3.23%); Diatom population (27.96%)
P21 Cosmarium (2.45%); Chlorococcum (7.35%); Tetrastrum (1.22%); Scenedesmus (13.88%); Chlorella (4.08%); Kirchneriella (2.45%); Tetraedron (0.41%); Crucigenia (1.63%); Selenastrum (1.22%); Pediastrum (2.04%); Diatom (63.67%)
P22 Scenedesmus (33.33%); Spirulina (8.3%); Merismopedia (8.3%); Trachelomonas (16.67%); Diatom (33.33%)
P23 Scenedesmus (33.33%); Trachelomonas (11.11%); Diatom (33.33%) P24 US 1 (70%); Rhabdoderma (15%); Diatom (15%) P25 Spirulina (16.67%); Synechococcus (83.33%) P26 Ankistrodesmus (16.98%); Synechococcus (20.75%); Merismopedia (35.85%);
US 2 (13.21%); Cyanophytic population (8.49%)
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Figure 1:
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Figure 2
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Figure3