Well,

Cyanobacteria have been commonly referred to as ‘blue-green algae’. However, cyanobacterial blooms are not always blue-green. In fact, they can be blue, bright green, brown,white or red. Bloom appearance can be best described as “pea soup” or “spilled paint” on the water’s surface.

There are other floating organisms which may be misidentified as cyanobacteria, such as: diatoms, green algae, duckweed and pollen.

Also, Cyanobacteria Like plants, they use sunlight to make food(nutrients) and energy, lack in sunlight and/or nutrients may be growth affect like what occurs to plant, yellow colour.

Sincerely

Hello Maria,

Did you check the samples thoroughly? Apart from the cyanobacteria Woronichinia , you would have definitely discerned the presence of any diatoms due their completely different morphology. BGA tend to turn yellowish only in case of intense sunlight, masking their photosynthetic apparatus with carotenoids and this especially happens when their is a condition where the water body is exposed to intermittent intense sunlight between overcast conditions. Dissolved phosphates would have to be high enough also to cause a bloom of such a magnitude. The yellowish appearance may also be due to the nature of pigments and the spectrum of the reflected light as this happens with Arthrospira, appearing yellowish green apparently but upon closer inspection they greenish with blue hue.

Apart from this, try to ascertain whether any Chyrophycean algae are present there or not because the superficial water colour is uncannily akin to golden brown algal blooms.

I hope you get to the bottom of it.

With regards,

Dr. Abhishek Mukherjee

I agree with Dr. Abhishek Mukherjee

@ Waqas Al-Joboory

Thank you

The sun light was very intense and with the storms of this year we have a lot of Pt

The list of taxons i found are:

Specie .............% relative in biovolume

Woronichinia naegeliana 87,87%..................139650cels/ml.... 8.5mm3/L

Aphanocapsa delicatissima 0,15%

Pseudanabaena limnetica 0,42%

Aphanizomenon cf flos-aquae 1,61%

Dolichospermum sigmoideum 0,01%

Cylindrospermopsis raciborskii 0,01%

Aphanizomenon "morphotipe" gracile 0,05%

Aphanizomenon flexuosum 0,01%

Fragilaria crotonensis 5,83 % .......... 1353 cels/ml..... 0.568mm3/L

Aulacoseira granulata 0,38%

Ulnaria acus 0,22 %

Botryococcus braunii 0,0001%

Eutetramorus sp 0,08%

Plagioselmis lacustris 0,16 %

Plagioselmis nannoplanctica 0,39%

Cryptomonas pyrenoidifera 1,09 %

Cryptomonas reflexa 0,67 %

Gymnodinium cf cnecoides 0,09%

Gymnodinium sp 0,11%

Ceratium hirundinella 0,11%

Trachelomonas volvocinopsis 0,02%

Lepocinclis cf ovum 0,0001%

Chrysochromulina parva 0,10%

Haptophyta 0,05%

Mallomonas sp 0,14 %

Ochromonas 0,36%

Nephrodiella semilunaris 0,03%

Staurastrum pingue 0,02%

Thanks for your interest and comments

Maria

Dear Maria, Could you send us a picture of what you see in your microscope?

Maria Van Herk photos m1, m2 (first and second) and m13(last one) are alive samples, the others are lugol fixed

Thank you for the pictures. I cannot tell the color of W. naegeliana from the lugol samples, however, I am used to working with lugol samples and they do not look different to me. Sorry, I cannot help you any further.

The pictures indeed suggest a bloom of Woronichinia naegeliana. The blooms of this species I've seen so far in Belgium were more greenish, however with the current heatwave maybe this might change. I agree with Dr. Abhishek Mukherjee that some photo-protection might be involved here...

Nice read here, thank you Dr Abhishek Mukherjee and everyone

Great to hear your account. I can relate another case from Lake Rotoehu - a hypertrophic lake in New Zealand. We had intense blooms of Microcystis aeruginosa that turned mustard yellow. This was some time ago (maybe 18 years). I never worked out why. Other scientists I spoke all thought it must be another algae causing the colour shift. But live samples of microcystis appeared yellow under the microscope, and it far and away dominated the biomass. Conditions were consistent with Abhishek's description - very intense bloom. As I recall the colour persisted long after the longest day. Many say our sunlight is "harsher" in NZ.

Thank you so much to all of you, for your comments.

As Abhishek Mukherjee said " BGA tend to turn yellowish only in case of intense sunlight, masking their photosynthetic apparatus with carotenoids and this especially happens when their is a condition where the water body is exposed to intermittent intense sunlight between overcast conditions."

That could be the cause. This was my idea when i said "something about phoyosynthesis efficiency".

I send yoy two more photos "mustard colour" as Thomas Kennedy said from the reservoir.

Maria

The photoprotective carotenoids - as others have mentioned, are the source of the gross color. Attached is an image.

The ephemeral exposure to strong photosynthetically active radiations might have caused rapid rates of water splitting and had generated excessive reactive oxygen which needed to be neutralized for the protection of the PS II and I respectively and hence the carotenoid terpenes were synthesized to prevent the oxidative damage to the photosystems. This could be one of the plausible hypotheses.

Abhishek Mukherjee - intersting answer. For the bouyant blue-greens, would the formation of a scum have the same effect as intense light? All those cells concentrated at the surface presumably increases UV exposure, compared to colonies distributed through the water column.

Thomas Kennedy Wilding in my case, scums are related with wind and cloudydays-storms before. In stable conditions they prefere not being on the surface.

I add the diagrams of the distribution related with my sample.

Secchi disk: 0.97m Photic zone 2.43

the pH was highger than usually (9.3 until 6m were be found 7,9) and the oxygen decrease a lot in the metalimnion

red:temperature , darkblue:oxygen green:chlo a cyan:phycoci.

Thomas Kennedy Wilding - Sorry for the delayed response. It most certainly can have the same effect but depends on the angle of the incident sunlight which is a function of the hour in the day or the season itself as well as the ambient tropospheric conditions. Microbial mat exposed to sunlight that is not damaging to the cells due to the scattering and/or atmospheric attenuation or even persistent moderate cloud cover formed by the heat mediated aerosols and the DMSO generated from the DMS off decomposing cells of the microbes may never synthesize greater concentration of carotenoids as they won't be exposed to the free oxygen/oxide radical generating intensity of the UV radiation.

Any idea on dissolved nutrients? Nitrogen limitation can also cause drastic changes in pigment composition.

Very true Dr. Frenken, as nitrogen limitation is what triggers the nitrogen fixation more in diazotrophs in the first place and its one of the most important perquisites to the formation of a bloom.

Nitrogen limitation, light exposure and presence of different algae assemblages can affect this phenome. On your photos, density of Fragilaria is also high.

What i meant is not change in species composition, but a change in pigments within the Woronichinia cells.

Once they are dominant they might run themselves into a N-limitation.

N is needed for the N-rich pigment phycocyanin. Thus under N-limitation the cyanobacteria cannot produce these pigments anymore, ore even degrade them (i.e. they were used as storage compounds).

See e.g. https://tinyurl.com/ydyk32jh or https://tinyurl.com/ya2d3gxv

N:P ratio not only affect amount of pigment value but also affect protein and carbohydrate contents.

Each phytoplankton species prefers optima for env. varisbles which cause phyto. composition in water bodies.

thank you all for your interesting comments

@Thijs Frenken

PT: 0.05 mg/L

You may want to check the Beta-Carotene in the photosynthetic pathway of the Cyanobacteria. The carotenoids in single celled Cyanobacteria can diffuse light in the red and blue wavelengths. Filamentous has a different scattering of light.

Thanks @Tami

Though many factors affect, but mostly nitrogen deficiency leading to chlorosis must be vital in change of the color of bloom.

@Jayalaxmi Dash thanks