Diatoms from a holy river …


Having written about the diatoms I found in the Ganges headwaters a week or so ago (see “Diatoms from the Valley of Flowers”) I now travel about 250 kilometres downstream, descending 3000 metres in the process, to the holy city of Rishikesh on the Ganges itself.   As in the Valley of Flowers, I had time and space for a single sample, and scrambled down to one of the many ghats, toothbrush in hand, to get a sample (and amuse the locals).  You can see a photograph of me collecting the sample at the end of “A cautionary tale”.  The ghat I chose was just under water at the time of collection, but the water level was fluctuating throughout our visit, so it might have been deeper at times, and probably fully exposed for periods too.  As we were in Rishikesh towards the end of the monsoon period, the chances are that it spent more time submerged than exposed in the weeks before our arrival, but I cannot be sure.

My sample comes from the flat surface of a concrete ghat, roughly at water level at the time I visited (the river was running across my feet as I sampled) but the biofilm on the surface of the ghat was so thin that I wondered if I had any algae at all in my bottle at the end of some ferocious brushing with my toothbrush.   The plate below gives an indication of the diversity of diatoms that, despite my forebodings, I found on the slide that I prepared.  Of these, Adlafia minuscula var. muralis was the most abundant organism and this, along with Nitzschia palea, which was also frequent, suggested that the water at Rishikesh was quite enriched.   Halamphora montana, which was also frequent, is a species that can thrive in intermittently wet conditions, consistent with its presence on a ghat that was not fully submerged.  In contrast to these, Gomphonema pumilum (which was also frequent) and Achnanthidium minutissimum (rare) are more often associated with cleaner water.


Diatoms from the River Ganges at Rishikesh, September 2016.  a.  c.: Gomphonema pumilum; d.: Navicula sp.; e. Adlafia minuscula var. muralis; f. Achnanthidium minutissimum; g. Cymbella sp.; h., i.: Halamphora montana; j. Cocconeis euglypta; k. Nitzschia cf inconspicua; l. Nitzschia palea.  Scale bar: 10 micrometres (= 100th of a millimetre).

As you can see from the photograph at the top of the post, and from images in earlier posts, Rishikesh sits just at the foot of the Himalayas, just at the point where the Ganges enters the Deccan Plateau.  Were I to turn around and photograph the view in the opposite direction, the landscape would be flat for as far as the eye can see.   There is, nonetheless, a substantial population in the Ganges valley upstream of Rishikesh, with several substantial towns, the largest being Srinagar, a city of 150,000 on the Alaknanda tributary.   Sewage treatment in these areas is rudimentary so a high organic loading would not be surprising.

The low numbers of algae is no great surprise.  I recall sampling streams in Nigeria during the wet season and finding very little: the high, scouring flows and turbid water both make conditions difficult for algae at times such as these.   The predominance of indicators of poor water quality may also be a consequence of the monsoon, as the heavy rains not just overload the limited sewerage systems, but also wash organic matter into the rivers from terrestrial sources.   There is some evidence that water quality is worse during this period than it is during either the pre- or post-monsoon period.

There is, however, a belief that the Ganges has peculiar powers of self-purification. I recall Eric Newby writing about this in his classic book Slowly Down The Ganges, and there does seem to be limited evidence that Ganges water has some novel anti-microbial capabilities.   I do, nonetheless, wonder at the health consequences of performing an immersive “puja” in such a polluted river.   The irony is that the term “pollution” actually has its origins in religion, relating the defilement of holy places by man, so the state of the holy Ganges may have the dubious honour of being truly polluted in both the original and modern senses of the word.


Nautiyal, C.S. (2009). Self-Purificatory Ganga Water Facilitates Death of Pathogenic Escherichia coli O157:H7.  Current Microbiology 58: 25-29.

Tareq, S.M., Rahamen, S.M., Rikta, S.Y., Nazrul Islam, S.M. & Sultana, M.S. (2013).  Seasonal variation in water quality in the Ganges and Brahmaputra River, Bangladesh.  Jahangirnagar University Environmental Bulletin 2: 71-82.


Diatoms from the Valley of Flowers


My visit to the Valley of Flowers in India (see “Into the Valley of Flowers …”) is a fast fading memory but I have finally managed to get the diatom samples that I smuggled into my suitcase properly mounted and spent some time last weekend peering down my microscope and trying to match what I could see with the habitat that I remembered.

The sample I collected came from a first order stream which appeared from the mouth of a glacier a couple of hundred metres above us on the [north] side of the valley.  About 500 metres downstream it joined the Pushpanati River, a tributary of the Aleknanda, itself a tributary of the mighty Ganges.   It was just over a metre wide and a few centimetres deep and had a mixture of pebbles and gravel as its substratum.  Some of the larger stones were encrusted with what looked like growths of Chamaesiphon  (see “A bigger splash …“).  There were also a few flocs of green algae which turned out to be Zygnema, a relative of Mougeotia and Spirogyra ( see “Fifty shades of green …”) with two distinctive star-shaped chloroplasts.  They are not at their best in the photograph below because they made the journey from India to the UK soused in local vodka (a cheap and effective preservative for algae: your liver will not begrudge you this particular experience …).


Vinood, our guide, looking at the stream that I sampled in the Valley of Flowers, August 2016.


Vodka-soused Zygnema sp from a glacier-fed tributary stream of the Pushpanati River (Valley of Flowers),  August 2016.  Scale bar: 20 micrometres (= 1/50th of a millimetre).

The diatoms were a surprise as almost all belonged to a single species, Diatoma mesodon, a species familiar to me from very high quality streams in Europe.  Ninety-five percent of all the diatoms I looked at belonged to this species, an unusually high proportion compared with other samples that I have examined, especially as there are no human pressures in the area that might influence diversity.   The Diatoma cells formed zig-zag chains, though these fell apart during the preparation process and the images just show individual valves.   Other diatoms present in small numbers included Meridion circulare var. constrictum (syn: Meridion constrictum) and two species of Eunotia, all of which suggest relatively soft water.

The low diversity intrigued me.   I have seen very low diversity with headwater streams, possibly because there is low potential for organisms from upstream to “seed” the location.   As small tributaries merge, so incocula from the sparse assemblages of these headwater streams will combine to create more diverse communities downstream.  Curiously, a recent paper argues the opposite: that headwaters are, in fact, hotspots of microbial diversity, and that this declines with increasing distance downstream.   However, this study takes a much broader view than just algae.  The authors suggest that it the close connection between headwater streams and the surrounding catchment leads to soil bacteria being washed into the stream.   So this result does not really contradict my observation; rather it highlights the limited insight that one may glean through looking at a single group of organisms.

Had I had more time (and more samples containers), it would have been interesting to follow the valley as far upstream as possible, to see if the other streams flowing down from the hillside had similar assemblages of algae, or if their algae were different.   My guess is that the patchwork of habitats would mean that the total diversity for the valley (“beta diversity”) would be considerably greater than the diversity at any particular site (“alpha diversity”).   If anyone wants to test this hypothesis, then all they need to do is make a three day journey from Delhi, with an extra day set aside for acclimatisation, followed by a two day hike up to a height of 3500 m.  And don’t forget to pack that bottle of vodka …


Diatoma mesodon from a glacier-fed tributary stream of the Pushpanati River (Valley of Flowers), August 2016.   a. – e.: valve views; f. – g.: girdle views.  Scale bar: 10 micrometres (= 1/100th of a millimetre.


Other diatoms from a glacier-fed tributary stream of the Pushpanati River (Valley of Flowers),  August 2016,  a. – b.: valve and girdle views of Meridion circulare var. constrictum; c. Eunotia islandica; d. E. paratridentula; e. Cymbella cf naviculiformis.  Scale bar: 10 micrometres (= 1/100th of a millimetre).


Besemer, K., Singer, G., Quince, C., Bertuzzo, E., Sloan, W. & Battin, T.J. (2016).  Headwaters are critical reservoirs of microbial diversity for fluvial networks.  Proceedings of the Royal Society of London Series B 280: DOI: 10.1098/rspb.2013.1760

Reflections from the River Ganges


From Shimla we made our way across the Himalayan foothills to Deera Dun and, from there, to the Hindu holy town of Rishiketh, where our hotel room which overlooked the River Ganges, swollen and turbid following the monsoon rains. Rishiketh is, along with Varanasi, Allalahabad and Hardiwar, a place where Hindus believe that the veil between the earthly and celestial realms is at its thinnest, making prayers and puja performed here particularly auspicious. This may seem, at first sight, to be a long way from the science that I usually write about in this blog but a lot of my posts relate to how humans use rivers, and this includes spirituality (see also “Dipping a toe in the River Jordan

Hindus performing puja in the River Ganges at Rishiketh. The upper picture shows sunrise over the Ganges, August 2016.

Travelling along the upper stretches of the Ganges emphasises that such uses should not be dismissed lightly: the river and its tributaries run through steep-sided unglaciated valleys, with little flat land for agriculture or development. The flux of Hindu pilgrims upstream from Rishiketh to shrines at Kedarnath and Badrinath provides a major source of income for the local economy. I’m writing this post in a village called Ghangharia which has one of the highest Sikh Gurudwara in the world (3048 m) and we shared the 11 km journey from the closest road with a constant stream of friendly Sikh pilgrims. This village is largely dependent upon these pilgrims, who use this as a base to trek to a high altitude lake associated with Guru Govind Singh.

But it is not enough simply to consider the benefits of spiritually purely in economic terms. Hindus venerate the river as a god. I have a private theory that one of the origins of religion is trying to explain “low frequency, high impact” events and the Ganges has plenty of these. When the monsoons fail, the crop lands that the Ganges irrigates cannot feed the people. When the monsoons are especially intense, there is widespread flooding and loss of life. In 2013 there were severe floods in the Bhyunder Valley, in which Ghangharia is situated, with a huge loss of life locally. One small village that we saw was half buried by river sediments – including huge boulders – moved by the flood waters. The inhabitants will have seen many monsoons pass over without any harm falling on their village. Yet, in 2013, catastrophe struck. The natural inclination at times like these is to wonder “why here? why now? why me?”

Part of the village of Pulna, in Uttarakhand Province, India, submerged by river sediments following catastrophic floods in 2013.

It is easy for a westerner, watching the outward manifestation of faith, to be condescending about the veneration of a river as a god. Should not science and reason, we wonder, not now replace these old superstitions? Up to a point, yes. However, the floods in the UK last winter are evidence of the limitations of our empirical approach, particularly when dealing with low probabilities but there is a deeper reason too. A consequence of the western scientific approach has been an inclination to dominate the natural world, to use our knowledge to overrule natural forces. Man dictates how a river should behave using cement and concrete: we have lost the awe and reverence for nature that arises from a sense of its enormous potential power.

A binary split in attitudes to nature is too simplistic. My experience is that ecologists generally do have a reverence for the natural world, and some understanding of the complex interactions that interfere with straightforward cause-effect relationships. But we often work within organisations and structures created by engineers and bureaucrats, who have more simplistic notions about how the natural world should be governed. And, whatever I write about Hindus revering the Ganges as a god, in principle, the river is horribly polluted and, in the upper portions, impounded for hydroelectricity. There is a disconnect between theory and practice, particularly ironic as the central Hindu notion of karma is all about linking actions to consequences in the future. Or, as one Hindu philosopher put it, “… the cause holds the effect … in its womb”. There is, it would seem, scope for a healthy symbiosis between modern ecological thinking and a belief system that reveres, rather than tries to dominate, nature.