UVIF Pond Water - What's Causing the Aqua Fluoresence?

[Andrew Dayer]

I've been doing some UVIF things lately for a project and saw this effect in my garden pond which I thought was quite cool.

 

The water looks pretty clear in daylight with plenty of microorganisms buzzing around - the larger ones are clearly visible to the naked eye. With a UV torch (Alonefire X901 UV, 365nm), the lily pads fluoresce red as expected but the water glowed a pale aqua colour. I really liked the effect of the shadows of the water boatmen (Corixidae) and snail fading into the depths.

 

The attached image was taken with an unmodified Nikon D750 with a 105mm f2.8D (macro) and no additional filtration (I would normally use the Hoya UV/IR block but forgot – it was pretty late at night). Illumination was 2x Vivitar 285HV’s with UV block filter removed and 2x ZWB1 (2mm each) over the windows. Exposure was at f8 with ISO 1600. Post-processing has not substantially altered the water colour; it is consistent with the effect seen with the UV torch (the water boatmen move around too quickly for long exposures).

 

I’ve looked at water samples under a compound microscope and although the effect could be seen in a hand sample, it wasn’t apparent on the microscope slide. I couldn’t see anything showing this fluorescence, just some volvox that glowed red and bacteria. The conditions were not great – the Nikon UVF microscope when u/s, so this exercise was by trying to illuminate from above with multiple handheld UV torches. And the microscope slides turnout to fluoresce as well.

 

Could the aqua fluorescence be due to a colloidal suspension or perhaps the bacteria but to fast and too weakly to see at x400? Any help or thoughts welcome.

 

[colinbm]

It is good that you took the adventure.
What is the bottom of the pond made of, is it fluorescing ?

[Andrew Dayer]

7 minutes ago, colinbm said:

It is good that you took the adventure.
What is the bottom of the pond made of, is it fluorescing ?

 

I had a lot of fun - it was warm(ish) and dry - but quite amazing how little darkness there is at this time of year (I'm not that far north; I'm almost exactly 52oN). Still, lots of stuff glows in the dark!

The pond is about a metre - call that 3 feet - deep and lined with butyl rubber. I looked at using an off-cut as a black backgound for UVF studio work but didn't have enough; there was no appreciable fluorescence with this lighting set up.

The effect is definity suspended in the water column.

 

[Andy Perrin]

We've seen that several times here - I don't know what causes it but it may not be the material at the bottom.

 

See my two posts here:

 

 

 

Also Otoien saw it:

 

[nfoto]

What you have observed, and photographed, is very normal. Lots of fine particulate matter that ca n cause such bright fluorescence. I have many examples from my aquatic plant cultures.

[otoien]

Nice contrast with the the water boatmen! It does not take deep water to get this blue-green fluorescence, some of the links pointed to by Andy includes very shallow pools of melt-water in the early spring.

[Lou Jost]

Diatom frustules show aqua fluorescence under deep UV, though this probably doesn't explain your observations. Tonic water (water + quinine) also fluoresces aqua.

[Andrew Dayer]

Thanks all. I'll have a think about how to identify fluorescing agents. Maybe freezing, centrifuging or chromatography... I don't recall seeing this effect earlier in the year so seasonality might be a factor.

 

I'll have to come back on my struggles with UVF and flash when I've got time...

[Andrea B.]

I'm thinking the chlorophyll from algae is what is fluorescing in your pond -- if your garden pond does have algae. Chlorophyll fluoresces blue-green around 685 nm. 

ADDED:  man, did I ever screw that up. I was wanting to mention an algae bloom. Here is one example:  LINK

[Andy Perrin]

45 minutes ago, Andrea B. said:

I'm thinking the chlorophyll from algae is what is fluorescing in your pond -- if your garden pond does have algae. Chlorophyll fluoresces blue-green around 685 nm. 

Whaat? 685nm is red. Chlorophyll fluorescence is red. 
 

https://en.m.wikipedia.org/wiki/Chlorophyll_fluorescence

[Lou Jost]

Ditto, chlorophyll fluoresces red.

[Andrew Dayer]

I suppose chlorophyll fluorescence at 685nm is the red in the lily pads?

I noticed that blanket weed - filamentous algae - growing on the pond edges or floating around is brick red with the UV torch. Looking at the snail in my image (inverted, cruising around on the surface tension), the blanket weed growing on its shell appears green not red. I wonder if blanket weed is in the shadow of the UV flash and actually illuminated by the visible aqua fluorescence?

Being now a partly paid-up weird person, I've spent more time wondering around at night with a UV torch. Many plant leaves seem to fluoresce blue rather than red - especially on their top surfaces. Is this a different chlorophyll molecule or some sort of UV sunscreen effect? Is it possible that the aqua fluorescence in the pond is the same effect??

[Lou Jost]

58 minutes ago, Andrew Dayer said:

I suppose chlorophyll fluorescence at 685nm is the red in the lily pads?

I noticed that blanket weed - filamentous algae - growing on the pond edges or floating around is brick red with the UV torch. Looking at the snail in my image (inverted, cruising around on the surface tension), the blanket weed growing on its shell appears green not red. I wonder if blanket weed is in the shadow of the UV flash and actually illuminated by the visible aqua fluorescence?

Being now a partly paid-up weird person, I've spent more time wondering around at night with a UV torch. Many plant leaves seem to fluoresce blue rather than red - especially on their top surfaces. Is this a different chlorophyll molecule or some sort of UV sunscreen effect? Is it possible that the aqua fluorescence in the pond is the same effect??

The blues are lignins usually. They may indeed have some protective function; they are most prominent in plats with tough leaves exposed to much sun. They are an important structural component of plants. Often the top of a leaf will have lots of blue and the underside of the leaf will be more red.

 

Some plants have other colors mixed in, including yellow. 

 

I made a video about this:

 

Bryophytes (mosses and liverworts) and algae have more varied colors of fluorescence.

 

 

 

 

 

[Andrew Dayer]

15 hours ago, Lou Jost said:

The blues are lignins usually. They may indeed have some protective function; they are most prominent in plats with tough leaves exposed to much sun. They are an important structural component of plants. Often the top of a leaf will have lots of blue and the underside of the leaf will be more red.

 

Some plants have other colors mixed in, including yellow. 

 

 

Bryophytes (mosses and liverworts) and algae have more varied colors of fluorescence.

 

 

Thanks Lou. Makes sense about the lignins. I've only recently been 'forced' into UVIVF stuff and I guess had just assumed blue fluorescence was just visible light leakage from my torch (Alonefire X901UV). But that's just lazy assumtion and I should know better!

Like the video very much - definitely going hunting for some bryophytes when our current 'summer' weather eases up a bit. Did you ever make more?

[Lou Jost]

On 7/14/2023 at 4:45 AM, Andrew Dayer said:

 

Thanks Lou. Makes sense about the lignins. I've only recently been 'forced' into UVIVF stuff and I guess had just assumed blue fluorescence was just visible light leakage from my torch (Alonefire X901UV). But that's just lazy assumtion and I should know better!

Like the video very much - definitely going hunting for some bryophytes when our current 'summer' weather eases up a bit. Did you ever make more?

 No, not yet. Some day....

[Andrea B.]

This is (one example of) what I was wanting to refer to:  an algae bloom which looks cyanish/bluish. 

 https://www.environment.sa.gov.au/goodliving/posts/2018/04/sea-sparkle#:~:text=We humans can witness this,calm and warm sea conditions.

 

I had the "picture" in my head which was cyanish, but I screwed up and attributed it to chlorophyll. Duh!! 

 

Google this:  fluorescent algae bloom

A lot of cyanish examples pop up.

[Andrew Dayer]

Thanks @Andrea B.

 

The more I dig into it, the more interesting the "why..." becomes (to me at least; don't ask my wife....).

The effect is now strong enough that the pond looks slightly milky in sunlight (or at least the shadows next to sunlit bits). In dull daytime conditions ie British summer , its clearly visible with a UV torch. Not a great image but the best I will offer... the good news is my phone still works after total immersion. Twice .

I suspect, as Andrea suggests, this is more likely cyanobacteria than some colloidal suspension as the effect is increasing signifcantly (the pond recieves only rainwater). No evidence of luminescence when disturbing the water, however.

 

[Andrea B.]

oh dear, you dropped your phone in the pond ! Glad to hear it survived. 

I once knocked a converted D200 into a vernal frog pond covered with duckweed. Surprisingly the camera recovered after a while. I still have it, but of course don't use it any more. 

 

Do you have a microscope? Might be interesting to see what shows up in the water.