Return to Pangong Tso

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Pangong Tso, from the Indian shore, looking towards China, July 2015 (photograph: Heathe Kelly).

You may remember that a year ago I wrote some posts about a high altitude lake on the India-China border (see “Subaquatic landscapes in Pangong Tso” and references therein).   This year, Heather made a second trip to Pangong Tso (described here) under the auspices of Indus Experiences and brought me back another sample from the littoral zone.   There was a beautiful thick biofilm here, an unusual bright yellow-brown colour and a jelly-like consistency, but bubbling away as the algae photosynthesised busily.   Once again, local vodka was pressed into service as a preservative and, once again, peering through my microscope a few days later, I could see that the sample was dominated by the same long-stalked Gomphonema species that I recorded a year ago (see “Diatoms from Pangong Tso”). The jelly-like consistency did worry me, as this is not what I would expect of a pure growth of diatoms and I did wonder if there were cyanobacteria growing amongst the diatoms that had not survived the journey home in their marinade of cheap vodka.

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Growths of diatoms (predominately a long-stalked Gomphonema sp) on a boulder in the littoral zone of Pangong Tso, India, July 2015. The right hand image is a close up showing oxygen bubbles being produced by the the jelly-like masses. Photographs: Heather Kelly.

Intriguingly, the Gomphonema seems to occur in two forms: a fatter form, with a width around eight micrometres, and a narrower form, about six micrometres wide. I’ve written before about how diatoms tend to get shorter over time (see “Diminishing with age”). What I did not make clear in this post is that cell breadth tends to stay relatively constant during this process.   This does not happen with every species but it is interesting to see that the fat and narrow forms have overlapping sizes, so it is not a simple matter of the narrow ones being the far end of the size reduction sequence. More work is definitely needed here although, alas, I don’t think Pangong Tso is on the itinerary for next year’s visit to India.

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Gomphonema sp from the littoral zone of Pangong Tso, north India, July 2015.   a. – d. represent the “fat” form; e. – h. are the narrower form(s). Scale bar: 10 micrometres (= 1/100th of a millimetre).

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Subaquatic landscapes in Pangong Tso

My own private counterweight to inclination of fellow diatomists to base their science on the study of empty shells of dead organisms is to reconstruct images of what those diatoms might have looked like when they were still in their natural habitat.   The latest of these thought experiments is based on the samples I’ve described from Pangong Tso (see “Diatoms from the roof of the world” and “Diatoms from Pangong Tso”).   It comes with a number of caveats, not least of which is that the only preservative available (local vodka) would not have been kind to the non-diatom algae in the sample, so I may have over-estimated the contribution of diatoms to the total community.

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A visualisation of the subaquatic flora of Pangong Tso, September 2014, including the diatoms Gomphonema (on long stalks), Diatoma (zig-zag chains), Berkeleya rutilans (in mucilage tube, bottom left corner), Achnanthidium minutissimum (epiphytic on Gomphonema stalks) and motile Nitzschia inconspicua.  The Gomphonema cells are approximately 25 micrometres (1/40th of a millimetre) long.

The diatoms that I saw as I looked done the microscope is one that suggests a fairly mature community with only limited grazing. This may reflect the harsh environment endured in this high altitude desert or the brackish nature of the lake, or it may just be a temporary situation. It is impossible to say with so little data.   The organisms that I did see suggest several different ecological strategies.   The giants in my underwater landscape were the Gomphonema cells, which lived on the end of long branched polysaccharide stalks.   As the film of microscopic algae on any surface grows thicker, so the amount of light that penetrates through is reduced and there is a benefit to any organism that can reach up above the hoi polloi to gain access to the limited light.   Entangled amongst these are zig-zag chains of Diatoma cf moniliformis which, like the lianas of tropical forests, are entangled around these stalks.   I also saw cells belonging to the Achnanthidium minutissimum complex and I know, from other samples I’ve looked at, that these are capable of growing as epiphytes on the stalks of Gomphonema species.   Berkeleya rutilans is a species that I have not previously encountered in my studies of the microscopic world but I have followed descriptions in the literature and included a couple of cells in a mucilage tube towards the bottom left corner of the picture.   Finally, the most numerically abundant species in the sample was one that I do know very well: Nitzschia inconspicua. This is a motile diatom which is able to move through the tangle of Gomphonema stalks and Diatoma filaments in search for light.   I was co-author of a paper on the ecology of N. inconspicua published earlier this year and was pleased to see that the habitat of Pangong Tso matches our prescription almost exactly (based on the limited published data). The assumption that most diatoms are cosmopolitan has rightly been challenged in recent years but there are species that do appear to be very broadly distributed.   Even when the species is not familiar (as for the Gomphonema), the genus is identifiable from my experience in Europe. This is in stark contrast to many other groups of organisms encountered in the tropics and sub-tropics.   It does make life easier for the travelling phycologist though, fortunately, there are still plenty of surprises waiting for us out there.

If you want to see Pangong Tso for yourself, Indus Experiences are organising a two-week geology and ecology excursion to Ladakh next year.   See you there.

Reference

Kelly, M.G., Trobajo, R., Rovira, L, & Mann, D.G. (2014). Characterizing the niches of two very similar Nitzschia species and implications for ecological assessment. Diatom Research DOI:10.1080/0269249X.2014.951398

 

Diatoms from the roof of the world

Whilst I was enjoying myself in Venice and the Dolomites, most of my family were hard at work earning an honest crust or studying. One, however, was looking at mountains considerably higher than anything that Europe has to offer.   As she was, technically, reconnoitring locations for a study visit to Kashmir and Ladakh next summer she will tell us that it was work rather than holiday, but we should treat this claim with a generous pinch of salt.

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Pangong Tsu, looking east towards the distant mountains of Tibet.   September 2014 (photo: H. Kelly)

One souvenir of her visit was a small sample of algae from the littoral zone of the remote Pangong Tsu at an altitude of 4266 metres on the Indian-Tibetan border.   Problem #1 for anyone working in such locations is how to preserve samples for the journey home. There is a simple solution: buy a bottle of cheap local vodka.   My limited experience of Indian spirits is that using them to preserve algae is a better option than drinking them and, in any case, the high altitude of Ladakh will give the partially-acclimated traveller a cracking headache without any need for chemical assistance. The downside is that the cell contents are not preserved very well but as diatomists are mostly interested in the silica cell wall this is not a problem.

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A view of the periphyton from the littoral zone of Pangong Tsu (approx.. 33° 45’ N, 78° 38’ E), photographed at 400x magnification.

A first look at the sample down my microscope revealed a number of diatoms that looked broadly familiar though which differ in detail from species with which I am familiar with in Europe.   There were, for example, a lot of cells of Gomphonema, each at the end of a long stalk, though these were not a species that I recognised.   Within this tangle of stalks, I could see a number of zig-zag chains of a species of Diatoma but, again, it was not a form I had seen in Europe.   There were other taxa, too, but I will wait until I have cleaned the material and prepared a permanent slide before commenting further.

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Gomphonema cells from the littoral zone of Pangong Tsu, September 2014. The four cells on the left are in valve view; the two on the right are in girdle view.   The stalk is visible on the right hand image. Scale bar: 10 micrometres (= 1/100th of a millimetre).

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Cells of Diatoma from the littoral zone of Pangong Tsu, September 2014.   The lefthand image is in valve view; the central and right hand images are in girdle view.   The central image shows a cell that has recently divided.   The cells are joined at the corners to form zig-zag colonies. Scale bar: 10 micrometres (= 1/100th of a millimetre).

There seems to be very little published on Pangong Tsu, as befits its remote location.   One early visitor was the famous limnologist G. Evelyn Hutchinson, as part of the Yale North India Expedition in the early 1930s.   The papers that I did find told me that the water of Pangong Tsu is slightly brackish, as the lake has no outlets and water is lost by evaporation. However, I usually associate Gomphonema with freshwater habitats, suggesting that the brackish influence is very weak. There is also evidence of very high concentrations of phosphorus in the lake, although nitrogen concentrations are very low. This suggests that growth of the organisms in the lake may be limited by nitrogen rather than phosphorus, as is usually the case in lakes.   I would be interested to know why a lake that is so remote contains phosphorus concentrations that are usually associated with human activity.

The next step is to make some permanent slides from the material and have another look, then see if any of the diatoms in this sample correspond to species found elsewhere in the region or beyond. There is a chance, based on the lake’s isolation and recent discoveries that the diversity of diatoms was much greater than hitherto thought, that there may be some previously undescribed species living in this unusual habitat.

References

Bhat, F.A., Yousuf, A.R., Aftab, A., Arshid, J., Mahdi, M.D. & Balkhi, M.H. (2011). Ecology and biodiversity in Pangong Tsu (lake) and its inlet stream in Ladakh, India. International Journal of Biodiversity and Conservation 3: 501-511.

Hutchinson, G.E. (1933). Limnological studies at high altitudes in Ladakh. Nature (London) ##: 132-136.

Hutchinson, G.E. (1937). Limnological studies in Indian Tibet.   Int. Hydrobiol. 35: 134-177.