The long wait is over …

I have not been to my regular haunts in the western Lake District for two months now.   We usual collect samples at two month intervals but our August trip was compromised by the wet weather we had during the latter part of the summer.  You can see the evidence for this in the graph below, showing how river levels fluctuated.   I should point out that, for personal safety reasons, we can only go out when the river is low so even the values during the latter part of August would have made wading problematic.  Samplers, it was once pointed out to me, are part of the benthos, not part of the plankton.  Also, values on the river level graph are recorded at the gauging station, and will not be the same at the point where we sample.  We have learned, over the years, to make a mental adjustment to get a sense of what conditions will be like when we arrive.

By early September, however, levels were low once again but, annoyingly, I had other commitments, including the course I wrote about in “Cyanobacteria inside their comfort zones …”.   Anticipating river conditions based on weather forecasts and juggling with other diary commitments is all part of the job.  This particular trip has been harder to organise than most.   I have had to make and cancel hotel reservations on three separate occasions, and on a fourth, I drove across and stayed overnight, only to find the rivers were higher than I had hoped when I checked the hydrograph first thing in the morning.  

River levels in the River Cocker (Scale Hill) from 1 August to the time of writing.   Data from www.riverlevels.uk.   Values are averages for each day and the dashed line is the level on the day of my visit.  The photograph at the top of the post shows Oedogonium growing on submerged stones in the River Cocker at Low Lorton.

When I finally got to the River Cocker, I was greeted by the sight of lush growths of green algae across the riverbed.  This turned out to be a near-monoculture of Oedogonium, which we last encountered in the River Derwent earlier in the summer (see “Borrowdale landscapes …”).  It is a very common genus, albeit one that is very hard to identify to species and also one for which generalisations about ecology are difficult.  

What I can say, with some confidence, is that the quantity of algae present in these streams waxes and wanes in a predictable manner, with highest values recorded in winter, but it is not so easy to say which species will proliferate on any particular occasion.  That also gives us a clue about the possible reason for the patterns that we see: because the biomass fluxes happens at a number of sites across several catchments, irrespective of which species are present, it must be driven by external factors that are common to all of these sites.   And because the fluxes are most extreme in rivers that are downstream of lakes (as is the case for the Cocker), we suspect that temperature plays a role.  Because water has a high specific heat capacity, Crummock Water acts as a huge “heat pump”, making the water in the Cocker ever so slightly warmer during autumn and early winter than is the case in nearby rivers that do not drain out of lakes. 

Filamentous algae are well placed to take advantage of this growth as they are simple and straightforward photosynthesis machines.  Sunlight is trapped by their chloroplasts and converted into the building blocks of cells which divide mitotically, allowing biomass to accrue without the complications faced by more sophisticated organisms.  There is a certain amount of phenological control in some filamentous algae, but this is mostly concerned with the onset of sexual reproduction (see “The intricate ecology of green slime …”).  Most of the time, filamentous algae don’t see the need for sexual reproduction (see “Tales from the splash zone …”) so the Oedogonium in the River Cocker is free to take advantage of the slightly warmer water compared to nearby streams, and convert as much of the late autumn sunlight as possible.  Meanwhile, the bugs that normally graze away any algae that cover submerged stones are dancing to the tunes played by their own internal clocks and lack the capacity to increase as quickly as their food supply.  The result is the green riverbed that I saw in the River Cocker when I visited. 

Oedogonium filaments from the River Cocker, October 2023.   The lower image shows a cell with a number of cap cells.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).

My comment about Oedogonium being able to accrue biomass without the complications faced by larger organisms needs a little qualification, because not every cell is able to divide.  The photograph above shows a cell with a fine collection of “caps”, demonstrating that it has divided numerous times.  There is, in other words, a first tentative step towards specialisation of cell function and, from this, we may also infer some redistribution of photosynthesis products along the filaments.  

Some of these “cap cells” were conspicuously brown compared to the cells on either side.  This is quite a common sight but I have found nothing in the literature that may explain what is going on.  The colour is suggestive of ochre and my working hypothesis is that these cap cells are particularly metabolically active, requiring the chloroplasts in the cell to work harder than the cells on either side. This will mean that these cells evolve more oxygen and this, in turn, will mean that iron and manganese in the water are more likely to precipitate out.  The lower photograph shows one of these brown cap cells colonised by diatoms (Gomphonema) and filamentous bacteria.   Oedogonium often has a substantial payload of epiphytes but not usually concentrated in a few locations.  Once again, what is it about the cap cells in particular that makes this a good location for other algae?   The literature is silent. 

More Oedogonium filaments from the River Cocker, October 2023, this time showing iron/manganese preciptitation around cap cells and associated epiphytes.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).

I always leave my regular sampling locations curious about what I will see next time I visit.  This time, however, this curiosity is leavened with a sense of trepidation as the long-term weather forecasts seem to suggest we are in for a wet autumn (driven by the El Niño in the western Pacific).  As a result, I am also anticipating spending more time over the next few weeks poring over the hydrographs and weather forecasts trying to predict when river levels will be low enough to pull on my waders and get back into the river.  Uncertainty will be the only certainty in my life over the next few weeks …

Some other highlights from this week:

Wrote this whilst listening to:  Frankie Archer, who blends traditional folk music with electronica.  I saw her on Later … with Jools Holland a couple of weeks ago and then found that she was playing at Darlington Library a few days later.   Her haunting melodies have stayed with me …

Currently reading: Qian Zhonghsu’s Fortress Beseiged.  Classic Chinese novel set on the eve of the Sino-Japanese war.

Cultural highlight:  A Ken Loach double-bill: first, a stage adaptation of his film I, Daniel Blake at the Gala Durham, then his latest film The Old Oak at the Tyneside Cinema.  The latter uses several locations in Co. Durham including Blackhall Rocks (see “County Durham’s tropical seashore”)

Culinary highlight:  vegetarian tasting menu at Rebel in Heaton.

Cyanobacteria inside their comfort zones …

Last week saw the second presentation of the FBA’s algae identification course for 2023, with another dozen keen participants being introduced to the intriguing world of freshwater algae.  The week starts with sampling in the vicinity of the FBA’s laboratory, first at Windermere itself (see “A hitchhiker’s guide to phytoplankton …”) and then, the following morning, at other sites in south Cumbria.  I usually join the group heading to Cunsey Beck, which flows from Esthwaite Water to Windermere but heavy overnight rain meant that river levels were too high for safe wading.   Instead, we joined Allan Pentecost on a trip to White Scar Quarry, right at the south-eastern tip of the Lake District.   It is an area that Allan knows very well and I always enjoy visiting with him because I learn a lot (see, for example, “Love and sex in a tufa-forming stream …”).

Just at the edge of the quarry, a small seepage flows across a wide bedding plane and, Allan pointed out to us, an impressive range of Cyanobacteria, green algae and moss co-existed side-by-side.   If you look at the photograph at the top of the post, you can see the seepage emptying onto the bedding plane just above the “d.”.   At low flow conditions, there is just a gentle trickle of water running in a narrow band approximately at the centre of the picture.   However, when there is more water coming down the quarry, then the water spreads out further and is also augmented by rainfall landing directly on the bedding plane.  The result is a zonation, roughly akin to what would be seen on a rocky shore, albeit not for seaweeds.  

Following this from the left we have:

1. The driest area, dominated by Nostoc commune whose ecosystem-building capabilities in otherwise adverse environments I’ve described in earlier posts (see “Landscape architects …” for the most recent of these);
   
2. An only occasionally wetted area dominated by dark brown mats of Scytonema.  The colonies described in “Poking around amongst sheep’s droppings …” came from very close to here and will give you some idea of what to expect;
   
3. A slightly wetter area has reddish mats of filamentous cyanobacteria. Schizothrix, Phormidium and Homoeothrix all feature here.  An example of a Phormidium growing at the air-water interface (and, therefore, presumably tolerant of desiccation) is described in “Fieldwork notes, August 2021”)
   
4. The central zone is almost permanently wet and here there is a distinct growth of the green alga;
   Mougeotia, a very common alga in this part of the world.  Recent posts which mention this genus include “Something, somewhere, just for a moment …” and “The man who stares at algae …” (both, incidentally, describe the interplay between green algae and Cyanobacteria in Lake District streams).

From here, the sequence is reversed except, at the right-hand side of the picture frame (e.) we did not see more Nostoc commune but, instead, patches of Rivularia haematites and bright patches of the moss Philonotis fontana.  I last wrote about Rivularia in “Building landscapes …”, based on another excursion that Allan led, this time in the Malham area of Yorkshire rather than in the Lake District.   I wonder, in retrospect, if the moss is, itself, a result of the ecosystem-building properties of Nostoc that I mentioned above and also wrote about in “How to make an ecosystem (2)”.   If I had teased apart those Philonotis clumps, would I have seen colonies of Nostoc lurking at the bottom, perhaps?   We hear a lot about all the problems Cyanobacteria cause in the Lake District at the moment so it is useful, once in a while, to remind ourselves that Cyanobacteria helped to build this wonderful landscape in the first place.

Microscopic views of the zonation at White Scar Quarry, Cumbria, September 2023.  a. Nostoc commune; b. Rivularia haematites; c. Phormidium sp.; d. Mougeotia sp.   No scale bars, I’m afraid, as the images were grabbed ad hoc while I was teaching, but other posts referenced should all have indications of size.

Some other highlights from this week:

Wrote this whilst listening to:  Africa Express Presents … The Orchestra of Syrian Musicians and Guests.  

Currently reading: Maggie O’Farrell’s The Wedding Portrait, set in Renaissance Italy.

Cultural highlight:  Exquisite Korean-American film Past Lives directed by Celine Song.  A love story mostly set against the Manhattan skyline.

Culinary highlight:  It may seem like a minor achievement, but I made the best shortbread of my life this week, following the Ayrshire Shortbread recipe in Cerys Matthew’s cookbook, Where the Wild Cooks Go ….  The vegan haggis that I made from her recipe also went down well a couple of weeks ago.

Patches of Philonotis fontana on the bedding plane at White Scar Quarry, September 2023.

Negative capability …

At the start of the month I wrote about J.M.W Turner’s visit to Borrowdale in the English Lake District and reflected not just on what he saw but on what he might have seen (see “Borrowdale landscapes …”).  I started with a view very similar to the one he painted (my camera was pointed upstream whilst his easel was positioned so that he could see the view downstream).  I then focussed on successively finer and finer detail, finishing with views photographed and drawn using a microscope.  

I’ve now taken this a step further and reassembled the parts that I viewed through the microscope into a “landscape”, of sorts, a highly magnified view of the stream bed.  The photograph I included in the post showed a patchwork of green and brown, the former being filamentous algae (Oedogonium) and the latter mostly diatoms.  I’ve depicted the Oedogonium mostly on the left of the picture (including one cell releasing a motile zoospore) with a mixture of the diatoms Tabellaria flocculosa and Fragilaria pectinalis on the right hand side.  To give a sense of scale, the Tabellaria cells are about a 50^th of a millimetre long. 

As I was painting this, however, I was reminded of Kenneth Clark’s statement that “… love of creation cannot really extend to the microbe” (see: “Is this the first microscopic landscape painting?”).  I disagreed when I first read it, and I disagree now, quoting David Attenborough in reply: “no-one will care about what they have never experienced”.  Turner did not experience the microscopic world; we are, therefore, in no position to comment on how he would have responded as an artist.  He sought out visual experiences and his art is a response to this – first via field sketches and then via oil paintings worked up sometimes years later in a studio. But his art strives to do more than describe what he saw, as a scientist of his era would have wanted to do.   He was much influenced by ideas of the sublime, that nature could and should provoke strong emotions, and that it was his duty, as an artist to capture both nature and those emotions on canvas.  

We could argue that our response to a landscape can be divided into a component that we can understand and explain, and a component that is mysterious.  Enlightenment scientists wanted to swing the balance towards the former – to understand and explain the types of rocks, the identities of the trees and plants and so on.  By the end of the eighteenth century, however, artists were moving in a different direction, encapsulated by Keat’s articulation of “negative capability” – that a thinker should be “capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason”.   Turner would have looked through a microscope not with a scientist’s urge to explain and understand but with an artist’s capacity to accept that there is much that is still unknown.  It was not, for him, about a compulsion to understand, as an Enlightenment scientist would have felt; rather it was about accepting that there was a limit to the extent that a landscape – large or small – could be broken down into explainable units.  Modern ecologists share these emotions, even if their language is very different.  They might prefer to say “uncertain” rather than “mysterious” but the essence is the same: we can often generalise about a situation (a Lake District stream, for example) but still not predict exactly what species we will find, or in what quantities they will occur.  Negative capability seems to be something that an ecologist should cultivate – recognising the point where the benefits of greater detail diminish and we are at risk of losing the big picture.

Some other highlights from this week:

Wrote this whilst listening to:  Beth Orton and Self-Esteem – in readiness for our trip to Green Man later this month.  And Sean-Nós Nua, a rather wonderful album of traditional Irish folk songs by Sinéad O’Connor who died this week.

Currently reading: Black-eyed Blonde, a Philip Marlowe novel written in the style of Raymond Chandler by Benjamin Black.

Cultural highlight:  Miss Saigon at the Crucible Theatre, Sheffield.

Culinary highlight:   Bibimbap, at Ginseng, a Korean restaurant in Sheffield following our theatre visit. 

Borrowdale landscapes …

In 1797 J.M.W. Turner visited Borrowdale in the Lake District and sat down close to this spot to sketch the view.   He completed a painting (now in a private collection) based on these sketches a few years later which, when compared with my photograph, clearly takes some liberties with topography but which otherwise catches the drama of the scenery in this narrow valley.  Turner’s painting also suggests that there are considerably more bankside trees now than when he visited.

Having finished my last post with a comment about how art moves in step with technology, and knowing that Turner was in close correspondence with scientists during his lifetime, I thought I would revisit the location and reveal some aspects of the river that Turner would not have had a chance to see.  I visited on a hot day in June following a long period of low flows which was nostalgic for me as my very first visit to Borrowdale was in 1976, during a drought when the riverbed was dry in many places.   On that occasion, we stayed at the Royal Oak in Rossthwaite which still looks much as I remember it (see photograph at the end of the post) 

Much as was the case in the River Ehen (see “Scattered patches of plenty …”) the warm dry conditions had allowed filamentous algae to flourish and dipping my camera below the surface in the marginal areas where the water was ponded captured this particularly well.  There is a distinct biofilm and, above this, flocs which, when I was able to examine these under the microscope, revealed themselves to be Oedogonium.   The bubbles are oxygen, the exhaust gas from photosynthesis.

An underwater landscape in the River Derwent just downstream from Longthwaite Bridge.  The field of view captures approximately 10 centimetres of stream bed.

The biofilm from the main channel was dominated by diatoms rather than Oedogonium (although this was also present) and also by many cells of Monoraphidium arcuatum.   The two most abundant diatoms were both chain-forming taxa: Tabellaria flocculosa and a Fragilaria that could not be identified with precision from live material, but which is likely to be F. pectinalis or a close relative.   The fluffy appearance of the brown biofilm visible in the picture above is likely to be the result of the entangled chains of these two species.   

A microscopic view of the biofilm from the River Derwent at Longthwaite Bridge, June 2023.   See photos below for indication of scale.

While I was scanning the slide, I noticed a chain of Oedogonium cells that were liberating zoospores.   I was sufficiently entranced by the amoeboid movement of the zoospore towards the break in the filament that I forgot to start taking photographs until it was almost free but the photograph below shows the final stages as the zoospore squeezes out of the filament, rounds off and the ring of flagellae at one end start beating in unison to take it away from the mothership.   These zoospores are generally associated with actively-dividing cells in the filament – evidenced by the presence of “caps” just below the point where the cell has split open (see “More about Oedogonium”).   

Algae from the from the River Derwent at Longthwaite Bridge, June 2023.  Top: Monoraphidium arcuatum; middle: Tabellaria flocculosa; bottom: Fragilaria cf. pectinalis. Scale bar: 20 micrometres (= 1/50^th of a millimetre).  

Having collaborated with David de la Haye on Flow.State at SEFS I’m now wondering why I limited myself to just visual arts.   It would have been intriguing to listen, as well as see, those oxygen bubbles on the algal films.  Turner would have been intrigued by both the microscopy and the sounds but, in many ways, he was the progenitor of both of us, dragging landscape painting from imagined views of idealised nature to approaches that were firmly based in reality.   Not only can his paintings be located in space and time but also, especially later in his career, he tackled the vagaries of the British weather more honestly than any of his forbears.  He, more than anyone, demonstrated that landscape should be based on what is in front of you rather than what you think ought to be there.  We are the inheritors of that tradition. 

The late stages of zoospore release by Oedogonium from the River Derwent, Longthwaite Bridge, June 2023.   The ring of flagellae are not visible in these photographs but could just be seen by careful focussing.   Scale bar: 20 micrometres (= 1/50^th of a millimetre).  

Reference

Hill, D. (1996).  Turner in the North.  Yale University Press, New Haven and London.

The Royal Oak Hotel at Rossthwaite in Borrowdale.   

Some other highlights from this week:

Wrote this whilst listening to: Glastonbury 2023.   Stand out sets by Hozier, Blondie and Sudan Archives 

Currently reading: Still reading Lessons in Chemistry by Bonny Garmus.  

Cultural highlight:  Glastonbury

Culinary highlight:   SEFS13 conference banquet at St James’ Park was in a dark unprepossessing room but they served a restaurant-quality three course vegan meal to about 400 people, which is quite an achievement.

Scattered patches of plenty …

I was back in the Lake District this week, looking at how my regular sampling locations had fared through a prolonged period of low flow (no substantial rain since March) and, for the last week or so, very warm weather.  The most noticeable impact of this was prolific filamentous algae growths in several of the rivers.  This is the time of year when we normally expect to find few visible algal growths, not because conditions are unfavourable to their growth but because the invertebrates that live on and around stream bottoms graze the algae as fast as it grows.   

The streams I visit are, for the most part, very remote with no or very few artificial sources of enrichment.  This means that the usual default on seeing obvious algal growths of assuming that there must be excessive nutrients does not work here.   Even a low concentration of nutrients, if constantly replenished, can be enough to sustain healthy algal growth.   Warm water just makes the environment that little more conducive.  In this case, the lack of any storms has also contributed to this metaphorical “perfect storm”.

At some of the sites we visited these algal growths were distributed widely across the stream bed, growing on any stone of pebble size or larger.  At a few, however, the algae were most obvious on and in the near vicinity of mussels (Margaritifera margaritifera).  There were too many of these mussel-hogging algal clumps for it to be a coincidence which made me wonder what was going on.

Filamentous algae (mostly Oedogonium) growing on freshwater mussels (Margaritifera margaritifera) in the River Ehen, June 2023.  The photograph at the top of the post shows another clump of Oedogonium, also in the River Ehen.

Others have noticed this too, albeit on the zebra mussel (Dreissena polymorpha) and in the Great Lakes rather than the English Lake District.  Their explanation goes something like this: mussels are filter-feeders, drawing sustenance from particulate matter in the water.  They use enzymes to break down this particulate matter and expel anything that they cannot utilise.  The particulate matter will contain some phosphorus which is released by these enzymes, thus creating a nutrient-rich zone, no more than a few centimetres in extent, around the mussel which fuels algal growth.  “Nutrient-rich”, that is, by comparison with the naturally low concentrations of nutrients found in west Cumbrian streams.

We can think of mussels, then, as miniature “sewage treatment works”, because the fine particulate organic matter on which mussels feed is really a natural analogue of the human sewage that sewage works process.  Sewage treatment works tend to be good at removing carbon from our sewage (converting it to manures, sludge and biogas) but less good at removing nutrients, hence the reason that we often see extensive beds of filamentous algae downstream of sewage works.   I once described a natural river as “A very dilute compost heap …” and we could also think of a sewage works as a very concentrated river ecosystem, as all the processes that take place in a sewage works are intensified versions of what happens naturally even in the most pristine Lake District stream.  

Oedogonium (along with a couple of filaments of Mougeotia and some diatoms) from the River Ehen, June 2023.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).  

Reference

Francoeur, S. N., Winslow, K. A. P., Miller, D., & Peacor, S. D. (2017). Mussel-derived stimulation of benthic filamentous algae: The importance of nutrients and spatial scale. Journal of Great Lakes Research 43: 69-79.

Some other highlights from this week:

Wrote this whilst listening to: ÁTTA, new album by Sigur Rós

Currently reading: Lessons in Chemistry by Bonny Garmus.  Only just started it but it comes highly recommended by my wife and daughter.

Cultural highlight:  My first visit to the Spanish Art Gallery in Bishop Auckland, a 25-mile round trip by bicycle on a sunny Saturday and an extensive, and well-laid out, collection of Spanish art, mostly with a religious theme.

Culinary highlight:   Vegan versions of a Scotch Pie and a Forfar Bridie from the relatively new Honeyman’s Bakery in our village.   

The fieldwork experience …

“Experiment” and “experience” have the same root in the Latin word experiri, meaning “try”, which makes sense up to a point.  One lunchtime on my recent trip to China, I experienced fried chicken’s feet.  I say “experience” but, in truth, I was the unwitting subject of my son, Ed’s experiment.  The difference between an experiment and an experience lies in the active and passive partners.  The experiment, as traditionally understood, involves someone actively imposing their will on something else.  An experience is a more equal process.  Ed bought the fried chicken’s feet, but I was under no obligation to partake.

Fried chicken’s feet on sale at a Wuhan street food market.   The photograph at the top of the post shows Mellbreak reflected in Crummock Water.

This post is actually about fieldwork rather than chicken’s feet, but the same principles apply.  Just before I headed off to China, I spent a day in the field in the Lake District, blessed by some wonderful views to distant fells.  These days are all about experience.  We have an itinerary but, beyond that, we do not have an agenda and we certainly do not intervene beyond collecting some measurements and samples.  For this particular set of sites, we have a strong idea of what to expect but that just makes the exceptions that much more intriguing.   I wrote about one of these in “Golden-brown”; another occurred in the River Cocker just downstream from Crummock Water where a dense growth of a red alga smothered Fontinalis antipyretica.  I see this same alga growing on rocks in late autumn and winter in the River Ehen but here I found it in spring growing on other plants.  Checking back through my field notes, I see that this is not a totally unique record, but it is an outlier from my general experience and deserves further investigation.  The previous post (“Acid trip …”) is the result of the happy conjunction of two people comparing their observations of the same site at different times.   

Audouinella hermainii growing on Fontinalis antipyretica in the River Cocker, just downstream from Crummock Water, April 2023.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).

I read recently that the word “experiment” was first used in the 17th century in a religious context.   Most prayer, at the time, followed fixed formulae but a movement towards less formalised prayer, where the worshipper saw the encounter with the Divine in a more open-ended way.  The experience of God, in other words, is too easily drowned out by the words of the supplicant.  Prayer, in this 17th century manifestation, became about listening.  And, before I meander too far off topic, fieldwork, too, can be about listening to the stories nature has to tell us rather than imposing our own interpretations on what we see before us.  Or, to come from another angle, seeing the exceptions to a general rule we have been taught introduces seeds of doubt around which alternative explanations may crystallise.  “There’s a crack in everything”, as Leonard Cohen wrote.  “That’s where the light gets in”.

I touched on this subject in “Form without function?”.  Geoffrey Fryer, the subject of that post, was a proponent of what a modern social scientist would refer to as “qualitative research”.  He wrote about this at length in his valedictory essay in the journal Freshwater Biology: Quantitative and qualitative: numbers and reality in the study of living organisms.  He was not arguing that qualitative and quantitative approaches were alternatives but was concerned that modern scientists rush too quickly into measurements without first spending time observing the organism or system they were studying.  It is about experiencing rather than dominating nature. 

Great Gable dominating the skyline behind Wastwater, April 2023.  

Of course, experiments are an essential part of the scientific method.  The problem with observation is that you can establish patterns, but it is much harder to determine causes.  For this, the ecologist has to bring unruly nature under strict control, evoking Yahweh’s mandate to Adam in Genesis 1:28: “…Rule over the fish of the sea and the birds of the air and over every living creature that moves on the ground”.  We can gain much from experiments but, at the same time, stripping out much of the complexity that is an inevitable part of most ecosystems can, on occasion, give misleading results.  Experiments need to work in tandem with experience if robust inferences and profound insights are to be achieved.  

And what of chicken’s feet?  I’m still not a convert without actively disliking them.  There is a lot of skin, cartilage and bone on a chicken’s foot.  But that raises a whole other set of issues.  My experience was conditioned by a lifetime in the West where we prioritise the taste of soft tender meat over the diverse textures that other parts of the bird may offer.  Our experiences are partly the result of our conditioning (more on this in “On fieldwork …”).   Having started the post by praising “experience”, I end worrying whether I can trust my experiences.  But going into nature equipped with this awareness does, at least, mean that I’m forever conscious of “falsifiability” which, if nothing else, lends a sense of anticipation to even the most mundane sampling trip.  

Reference

Fryer, G. (1987). Quantitative and qualitative: numbers and reality in the study of living organisms. Freshwater Biology 17: 177-189.

A street food market in Wuhan with, bottom, a wok containing “long bao” (soup dumplings).

Some other highlights from this week:

Wrote this whilst listening to: John Haycock.  Intriguing mixture of West African kora and electronica.

Currently reading:  Cuddy by Benjamin Myers.  Excellent novel about the influence of St Cuthbert in the north of England.

Cultural highlight:  Choral evensong at Durham Cathedral. 

Culinary highlight:  A Rachel Roddy recipe that involved cutting fresh asparagus stalks into very fine strips, then sautéing these slowly in butter, onions and wild garlic and serving with home-made tagilatelli.

Entrances and exits …

Having shown in two recent posts how the presence of one alga influences the quantity of many others in the River Irt, I thought I should see if this relationship holds in other streams in the region.   As Gomphonema exilissimum was the “ecosystem engineer” in the River Irt, I started with Croasdale Beck because I knew that this, too, had abundant populations of Gomphonema at certain times of the year.   Whereas the River Irt flows out of Wastwater, Croasdale Beck tumbles straight off the west Cumbrian fells.  It is, as a result, a much flashier stream than the Irt, and this has a big effect on the stream’s algae.

Gomphonema in Croasdale Beck shows the same general annual pattern as it does in the River Irt but without the coupling to diatom biomass that I showed in “High-rise habitats” (there are weak relationships, but these are not statistically-significant).  The most abundant Gomphonema is different at the two sites I visit on Croasdale Beck: G. parvulum at the upper site and G. calcifugum at the lower one.  Neither grows on long stalks in Croasdale Beck although I have certainly seen relatives of G. calcifugum form long stalks elsewhere in northern England (see: “And the Oscar for the best alga in a supporting role goes to …”).  I suspect that the harsher conditions compared to the River Irt would mean that “high-rise” growth forms would get scoured away too frequently and that, in turn, means that there is less opportunity for other algae to exploit the habitat that a cushion of stalk-forming Gomphonema creates.   

Gomphonema parvulum (top row) and Gomphonema calcifugum (bottom row), the two most common species of Gomphonema in Croasdale Beck (seen in the photograph at the top of the post)

Both Gomphonema species in Croasdale are at their most abundant about now (just as in the River Irt).   As March passes to April so a different diatom, Odontidium mesodon will become abundant and then, during the summer, it will be Fragilaria that dominates (at least two species – F. gracilis and F. novadensis) before, towards the end of the year, Meridion constrictum will become abundant.   Platessa (P. saxonica and P. oblongella) show a weaker trend, with dropping to minima in mid-summer before rising again, whilst Achnanthidium shows no annual trend at all.  

Annual trends in relative proportions of six common diatom genera in Croasdale Beck.   Vertical lines divide the year into 12 months.  

The diatoms are, in other words, behaving just as the terrestrial vegetation.  Outside my window I can see crocuses where, a few weeks ago, I would have seen snowdrops.  Daffodils are also beginning to appear.   In nearby woodlands, I can see celandine, but this will soon be replaced by wood anenomes, bluebells and then wild garlic.  The processes that drive these changes in higher plants are hard-wired into the genomes.  We know much less about the reasons for changes in stream diatoms.  Maria Snell made a convincing case for seasonal changes in diatoms in a stream on the other side of Cumbria being the result of changes in nutrient supply.  However, I think it unlikely that Croasdale Beck experiences the same scale of nutrient flux.   We know that the rise and fall of Asterionella formosa (another late winter/spring diatom) in Cumbrian lakes is a much more nuanced story, with temperature playing a key role and there is no reason to assume that the same does not apply to stream diatoms too.   Nutrients will certainly be part of this tale, but there is a richer cast of characters than this simplistic interpretation allows. 

Cobbles from Croasdale Beck in February 2023, their upper surfaces glistening with a thick film of diatoms.

Why is seasonality in stream diatoms overlooked?   One possible reason is that most sampling frequencies are too low to detect patterns within individual streams.  Another, however, is that diatomists are not primed to look for this type of pattern.   The Freshwater Benthic Diatoms of Central Europe, the one-volume handbook that many of us use, describes over 800 common species, and includes ecological and habitat notes for all of these.   However, there is not a single comment on seasonality.  By contrast, preferences for chemical water quality are described in detail.   A benign explanation may be that seasonal preferences vary around Europe, but it is also possible that seasonality in diatoms is widely overlooked.   The two reasons – not being told to expect seasonal patterns and not sampling consistently at the same sites with sufficient frequency – are intertwined.

It is the inverse of Newton’s famous statement, “if I have seen further it is by standing on the shoulders of giants”.  What if those we thought of as “giants” were actually, themselves, only dwarves?   Maybe there are more patterns under our noses that earlier generations of diatomists had overlooked but which are ripe for a new generation to discover?   Wouldn’t science be boring if everything the “giants” of earlier generations told us turned out to be true and there was nothing left for us to discover? 

References

Maberly, S. C., Hurley, M. A., Butterwick, C., Corry, J. E., Heaney, S. I., Irish, A. E., … & Roscoe, J. V. (1994). The rise and fall of Asterionella formosa in the South Basin of Windermere: analysis of a 45‐year series of data. Freshwater Biology 31: 19-34.

Snell, M. A., Barker, P. A., Surridge, B. W. J., Benskin, C. M. H., Barber, N., Reaney, S. M., … & Haygarth, P. M. (2019). Strong and recurring seasonality revealed within stream diatom assemblages. Scientific Reports 9: 3313.

* All the world’s a stage,
And all the men and women merely Players,
They have their exits and their entrances ….
                        William Shakespeare, As You Like It Act 2 Scene 7

Some other highlights from this week: 

Wrote this whilst listening to: Lynyrd Skynyrd (pronounced ‘lēh-‘nērd ‘skin-‘nērd) following the death of their guitarist Gary Rossington. I’ve long been uncomfortable about a band that performed with the Confederate flag as a backdrop.  It raises similar issues for me as the film Tár, about the extent to which it is possible to separate an artist’s views from their work.  This week, however, I’ll give them the benefit of the doubt …

Currently reading: Lessons, by Ian McKewen

Cultural highlight:  Fergus McCreadie Trio at the Sage, Gateshead although, to be honest, I’m still on a high after the Vermeer exhibition at the Rijksmuseum 

Culinary highlight:   Slightly belated shout-out for Gertrude’s Restaurant and Bar in Amsterdam where we ate and drank last week.   “Small plates” and a bottle of an Alsatian Orange Gewürztraminer.  

And finally, two sketches made on my iPad after the Vermeer show.   My disappointment is that Vermeer’s “The Art of Painting” was too fragile to travel from Vienna.  Otherwise, I could have drawn someone photographing a painting of someone painting someone.  I had to make do with drawing someone photographing a painting of someone.

The man who stares at algae …

At the risk of writing a post that leads to every reader silently screaming “get a life …”, Lemanea, the subject of my previous post, was not the only alga growing on the stones on the bed of the River Irt.   Alongside the dark brown tufts of Lemanea there are also patches of green algae.   And when you look closely at these, you see that they often arise from dark brown and also that these are a different shade of dark brown from the Lemanea patches on the rock surface itself.  

Unfortunately, you cannot see this clearly in my photographs.  We visited Cinderdale Bridge at the end of a long day, the water was 6 ^oC and the screen on my camera is not very good for assessing the quality of images of small green and brown blobs moving in the current in real time.  You’ll just have to trust me when I tell you this.   

I might not be able to take perfect underwater macro photographs, but I can recognise an excellent stream phycologist from some distance.  So can you.   They have three hands: one to hold the bathyscope that lets them see the stream bed, one to manipulate a pair of forceps underwater and one to hold the sample vial into which a small portion of the algal community will be dropped.  Two-handed people cope by using their knees to support a bathyscope held by the same hand that is gripping a sample vial.  Somehow, I managed to transfer a small piece of this green/brown floc into a vial and get the lid screwed on without disaster.

Mougeotia (green) and Microcoleus autmnalis (brown) from the River Irt in a Petri Dish (approx. 9 cm diameter).   The photograph at the top of the post show filaments of Mougeotia growing out of mats of Microcoleus autumnalis in the River Irt at Cinderdale Bridge, February 2023.   Scale bar: 20 micrometres (= 1/50^th of a millimetre).

Back at home, in my study (rather warmer than the River Irt in February), I emptied the vial into a Petri dish,  teased out a small portion roughly at the border between the brown and green parts and put this under my microscope.  The green growths were filaments of Mougeotia, an unbranched, typically slimy, alga that is common in lakes and streams in this part of the world whilst the brown sections were dense mats of the cyanobacterium Microcoleus autumnalis, also often common in these streams (see “Fieldwork notes, August 2021”.  In this and all earlier posts it was referred to as “Phormidium autumnale”).

Microcoleus autumnalis often lives in habitats where the water level fluctuates and, when exposed, dries into thin, papery layers (“in nuda terra autumno” in the original description – “in the bare earth in autumn”).   That would not be a situation that Mougeotia would enjoy.   However, here in the River Irt, the mats of Phormidiumwere permanently submerged and the Mougeiotia filaments seemed to be growing out from these, their basal sections tangled amongst the interwoven strands of Microcoleus.    I described something similar in the River Liza where Stigonema mamillosum was the host (see “Ever changing worlds …”) and I’ve touched on the idea of cyanobacteria as “ecosystem engineers” on several occasions (see “Landscape architects”).   However, there is nothing in the formal scientific literature about their role in supporting filamentous green algae in streams.   

In fact, the literature devotes very little time to the basic conundrum of how filamentous algae (which don’t have roots) stick to submerged rocks (that are too hard for roots to penetrate anyway).   Old taxonomic works often refer to filaments having “basal cells” or “holdfasts” or, in some genera, putting out rhizoids, but these are never described in great detail, and have not been followed-up in recent years.   We accept the presence of filamentous algae in streams without ever challenging their right to be there in the first place. 

Could it be that cyanobacteria, rather than facilitating colonisation by green algae occasionally, actually play this role quite often but their presence is usually camouflaged by the green algae above them or is simply overlooked by most field biologists?   The interwoven filaments of cynaobacterial mats hug the contours of rocks much more tightly than green algae, meaning that they live in the “boundary layer” where they are protected from the rough and tumble of the stream.   A green algal propagule, or a fragment of a filament, that becomes trapped within this mat, therefore, has a better chance of success than one outside the mat.   I offer this as a hypothesis rather than as a fact.  It might just help us understand why some rivers are greener than others.

References 

The paper explaining why Phormidium autumnale had to be transferred to Microcoleus is: 

Strunecký, O., Komárek, J., Johansen, J., Lukešová, A., & Elster, J. (2013). Molecular and morphological criteria for revision of the genus Microcoleus (Oscillatoriales, Cyanobacteria). Journal of phycology 49: 1167-1180.

Some other highlights from this week: 

Wrote this whilst listening to: The Art of the Fugue by J.S. Bach

Currently reading:   Girl With a Pearl Earring, by Tracy Chevalier.   Getting me in the mood for …

Cultural highlight: Vermeer exhibition at the Rijksmuseum, Amsterdam.   28 of the 37 paintings known to have been painted by Vermeer gathered in one place.  An experience of a lifetime.

Culinary highlight:   Iranian meal kit supplied by Modern Persian Kitchen which started out in Durham but now delivers nationwide.

Looking after their own …

Much has changed in the two months since I was last at the River Irt.  The conspicuous yellow-brown patches of diatoms that attracted my attention in Cold Comforts have gone, but other algae have appeared: clusters of dark brown filaments, each a couple of centimetres long, on the upper surface of boulders.   These tufts are the red alga Lemanea fluviatilis, which I’ve written about before (see“Lemanea in the River Ehen”).   Interestingly, I did not see Lemanea at Lund Bridge, the focus of the posts about winter diatoms, but at Cinderdale Bridge, a few kilometres further downstream.  Lemanea is also not found in the River Ehen close to the outfall of Ennerdale Water but becomes abundant a few kilometres further downstream.  There must be something about proximity to a lake that does not favour this genus.  

Young shoots of Lemanea fluviatilis along with green algae on a boulder in the River Irt at Cinderdale Bridge, February 2023.   The boulder is about 40 centimetres long.    The photograph at the top of the post shows the River Irt at Cinderdale Bridge.

These filaments (which are actually hollow tubes of cells) had some growths which looked remarkably like another red alga common in streams hereabouts, Audouinella hermainii.  But we could also turn that argument around and say that Audouinella looks remarkably like juvenile stages of several red algae (see “The complicated life of simple plants …”).  Unravelling the identities of these simple filaments has kept taxonomists busy for over a century and molecular analyses are still presenting us with surprises.   I’m going to assume that these are young gametophytes of Lemanea until someone convinces me otherwise, simply because of their proximity to so many other young shoots of Lemanea.  

A filament of Lemanea fluviatilis with young epiphytic gametophytes.  Scale bar: 100 micrometres (= 1/10^th of a millimetre).  

Close-up of young gametophytes on a filament of Lemanea fluviatilis in the River Irt, February 2023. 

These were not the only residents on Lemanea.   There were also some thin, unbranched filaments belonging to a cyanobacterial genus Chamaesiphon.   This is a genus with two very distinct habits: some species form dark brown/black crusts on rocks (see “A bigger splash …”) whilst other species live as epiphytes.    I last wrote about the epiphytic forms in “Whatever doesn’t kill you …”.  In that post, I was circumspect about naming the species because I could only see a single “exospore” at the end of filaments.   The population in the River Irt, however, has several filaments with a very characteristic stack of exospores so I can use the name C. confervicola with more confidence.  

A young filament of Lemanea fluviatilis with epiphytic Chamaesiphon confervicola. A stack of exospores is visible on the filament to the left of centre.  Scale bar: 20 micrometres (= 1/50^th of a millimetre).  

The last image in this post is a graph showing the changes in the cover of Lemanea fluviatilis in rivers in West Cumbria over the course of a year.   This shows very clearly that Lemanea is most prolific in winter and spring, becoming very sparse in summer through to autumn.  It is a similar pattern to that shown by Gomphonema.   There are algae that have pronounced summer peaks but we tend not to see these in the very nutrient-poor streams of the Lake Disrict.   My theory is that these small streams tend to be shaded and to have healthy populations of (hungry) invertebrates which are most active in the warm waters of summer.   Consequently, winter offers the best opportunity for an alga to grow relatively unmolested.   And, just as I showed how Gomphonema created a “housing estate” for other diatoms to inhabit, so Lemanea might well be determining the fluxes of the tiny Chamaesiphon confervicola filaments too.  

Seasonal changes in the cover of Lemanea fluviatilis in rivers in West Cumbria, 2019 – 2023.   Cover is expressed on the 9-point scale used for macrophyte surveys in the UK.   Vertical lines separate the twelve months.

Some other highlights from this week: 

Wrote this whilst listening to: In a Silent Way, by Miles Davies.   My favourite of his many records. 

Currently reading:   Animal, Vegetable, Miracle: Our Year of Seasonal Eating by Barbara Kingsolver.  

Cultural highlight: finally got around to seeing BAFTA-winning and Oscar nominated film Aftersun, starring Paul Mescal.  

Culinary highlight:   homemade prawn, crab and fennel cannelloni.   

High-rise habitats …

In the previous post I said that I had looked at one patch of algae in the River Irt from four different perspectives.  I’ve actually looked at this patch from five perspectives, because I forgot to count the graphs that I included in Cold Comforts.   Graphs are visual representations of the algae but they are not figurative in the sense that the photographs I’ve used are.   They are abstract in the sense that they convey an essence of the subject matter whilst being independent of visual references.   In the case of these graphs, I was able to convey a sense of changes over time that would have been impossible without sophisticated time-lapse photography.

The genus Gomphonema has featured prominently in the two earlier posts, so we’ll start with a closer look at how this changes over the course of the year.   This is mostly G. exilissimum but, as we saw in the previous post, other species are also present.   This graph shows a similar trend to the one showing chlorophyll concentrations on the riverbed over the course of a year, with the lowest values in the summer and higher values at the beginning and end of the year.   

The percent of total diatom valves belonging to the genus Gomphonema in the River Irt downstream of Wastwater (2019 – 2022).  The y axis is presented on a square-root transformed axis.   The photograph at the top of the post shows Cinderdale Bridge on the River Irt.

The question that arises is whether the Gomphonema is following a general trend in diatom biomass or whether it could actually be responsible for the annual fluctuations that we can see in biomass.   Over the course of the year, it rarely accounts for more than ten percent of all diatoms although, as we saw in the previous post, this equates to a larger proportion of total biovolume.   When we add in the stalks, then Gomphonema is by far the most abundant diatom.   The stalks do not contribute to the amount of chlorophyll that we measure, but they do create surfaces on and around which other algae can grow.   

The next step, therefore, was to look for relationships between the amount of Gomphonema and the amount of chlorophyll.   As you’ll see below, there is a positive relationship – more Gomphonema is associated with more chlorophyll.   If this was just a correlation with the annual trend in chlorophyll then we might expect to see this type of pattern in other common alga.  In fact, as the other three graphs below show, these do not show any relationship with biomass.   This is not conclusive, but it does hint to a role for Gomphonema in this particular stream as a creator of ephemeral habitats that other taxa can then exploit.   

Relationships between diatom biomass and Gomphonema (a.), Brachysira (b.), Achnanthidium (c.) and Fragilaria (d.) in the River Irt downstream of Wastwater (2019-2022).  Only the regression for Gomphonema is significant (adjusted r² = 0.44).

My interpretation is that many of the diatoms that I find in the River Irt are not particularly fussy about the substratum on which they grow, so I find them throughout the year, regardless of the biomass.   However, when Gomphonema exilissimum proliferates, the surface area available for other diatoms to colonise increases, leading to an increase in diatom biomass.   G. exilissimum has created opportunities for “high-density housing” – algal equivalents of tower blocks (“housing projects”, for North American readers).  

I suspect, too, that these Gomphonema-dominated communities make perfect meals for grazers once they get active in the spring.  The combination of crunchy protein-rich diatoms and lots of carbohydrates in the stalks creates a nutritious salad which, in turn, means that they do not last for very long.  These habitats are ephemeral, shifting in space and time.  That is probably one reason why diatoms are rarely considered to be “foundation species” in the generally adopted sense.  But in the brief window of opportunity when Gomphonema can thrive, they are every much as essential for the health of the overall community as the oak trees in an ancient woodland.

Some other highlights from this week: 

Wrote this whilst listening to: Hothouse Flowers and My Bloody Valentine: two very different bands sharing a common origin in Dublin in the early 1980s.  

Currently reading:   The Origins of Virtue by Matt Ridley.  

Cultural highlight: Transatlantic Sessions at the Sage, Gateshead, a coming together of Celtic and North American (mainly Appalachian) musicians exploring their common heritage.  Musicians included Liam Ó Maonlaí, leading me to explore Hothouse Flowers.

Culinary highlight:   Dinner at Khai Khai in Newcastle before heading to the Sage for Transatlantic Sessions.  Khai Khai is fast becoming our Indian restaurant of choice in Newcastle.