Spheres of influence

Back to Moss Dub for this post because Chris Carter has sent me some stunning images of the filamentous desmid Desmidium grevillei that I talked about in my earlier post.   I mentioned that it is surrounded by a mucilaginous sheath, which was just apparent in my brightfield image.   Chris has added Indian ink to the wet mount.  The ink forms a dense suspension in the water but is repelled by the mucilage around the desmid cells, resulting in a much better impression of the extent of the sheath around the cell than is otherwise possible.

Desmidium-grevillei_CCarter_#1_Sept19

Desmidium grevillei from Moss Dub, photographed by Chris Carter using Indian ink to highlight the mucilage sheath around the cells. 

Indian ink is a negative stain, which means that it is the background, rather than the specimen itself, which takes up the colour.   This, in turn, alters the passage of light through the sample and appears to improve the contrast of the final image.   Chris’ images of the apical view show this well, and also illustrates the complicated three-dimensional arrangement of the chloroplasts within each semi-cell.   His photographs also show the pores through which the mucilage is secreted.

The curious thing about this negative stain is that, whilst it appears to emphasis a halo of nothingness around the Desmidium filament, it is actually drawing our attention to something important.   In his presidential address to the British Phycological Society in 1981 A.D. Boney referred to mucilage as “the ubiquitous algal attribute” and goes on to list the many functions that the slimes produced by a wide range of algal groups may perform.  Not all will apply to our Desmidium but Boney does use desmids as examples of some of the roles slime may play: it can be, for example, a buoyancy aid, keeping the desmids in the well-lit regions of a lake or pond and it can protect cells against desiccation if a pond or lake dries out.  It may also play a role in helping desmids adhere to their substrates and there is also evidence that mucilage layers may help to protect algae from toxins.

Desmidium-grevillei_apical_view_CCarter_Sept19

Apical view (at four different focal planes) of Desmidium grevillei from Moss Dub, photographed by Chris Carter, September 2019.

But that’s only part of the story.   There is two-way traffic across the membranes of algal cells, with essential nutrients moving into the cell but, in some cases, enzymes moving in the opposite direction.  If nutrients are in short supply then these enzymes can help the cell by breaking down organic molecules in order to release nutrients that can then be absorbed. Those enzymes take energy to manufacture, and the sheath of gunk around the filament means that there is a lower chance of them diffusing away before doing their job (see “Life in the colonies …”).   The same principle applies to sexual reproduction too, with mucilage serving, in some cases, as “sperm traps” or simply as the phycological equivalent of KY Jelly.

It is not just the algae that benefit from this mucilage: the outer layers, especially, can be colonised by bacteria which will also be hoovering up any spare organic molecules for their own benefit with, no doubt, some collateral benefits for the organisms around them.  The connection is probably too tenuous to count as a symbiosis with the desmids but we could think in terms of mutual benefits.

So that “nothing” really is a “something”, and that is before we consider the role of these extracellular compounds in the wider ecosystem.  I mentioned the role of similar compounds in consolidating the fine sediments on coastal mudflats in “In the shadow of the Venerable Bede” to give a flavour of this.   The least prepossessing aspect of the least prepossessing plants can, given time, change landscapes.  That should give us all pause for thought.

Desmidium-grev_apical_pore_CCarater

Close-up of Desmidium grevillei filament with focus on the left-hand cell adjusted to show the apical pores.   Photographed by Chris Carter from material from Moss Dub collected in September 2019.

Reference

Boney, A.D. (1981). Mucilage: the ubiquitous algal attribute.  British Phycological Journal 16: 115-132.

Domozych, D. S., & Domozych, C. R. (2008). Desmids and biofilms of freshwater wetlands: Development and microarchitecture. Microbial Ecology https://doi.org/10.1007/s00248-007-9253-y

Sorentino, C. (1985). Copper resistance in Hormidium fluitans (Gay) Heering (Ulotrichaceae, Chlorophyceae). Phycologia 24: 366-388. https://doi.org/10.2216/i0031-8884-24-3-366.1

 

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The little tarn of horrors …

In addition to desmids, we found several other algae in the samples collected from Cogra Moss.  One of these consisted of colonies of cells in mucilaginous masses attached to floating mats of vegetation (which looked like terrestrial grasses).  We decided that these were probably Chrysocapsa epiphytica, the second representative of the Chrysophyta I’ve described in this blog this year (see also “Fade to grey …”).  As is the case for Chromulina, much of what we know about Chrysocapsa epiphytica is down to the patient work of John Lund who first described this species back in 1949.

Chrysocapsa_epiphytica

Colonies of Chrysocapsa epiphytica growing on submerged vegetation at Cogra Moss, Cumbria, September 2019.  Cells are 7.5 – 15 micrometres long and 7.5 – 12 micrometres wide. 

He described the various mucilaginous lobes as “reminiscent of the …. human brain”.  The spherical, oval or ovoid cells form a layer, two to four cells deep, at the surface of the colony.   The cells have the typical yellow-brown colour of chrysophytes and, though it is hard to see the chloroplasts in this photograph, John Lund says that there are usually two, sometimes four, in mature cells.

Its presence in a soft-water lake probably means that it is a species that relies on dissolved carbon dioxide rather than bicarbonate as its raw material for phytosynthesis (see “Concentrating on carbon …” for some background on this).   We know, from laboratory studies, that most chrysophytes rely exclusively on carbon dioxide, and lack the capacity to use bicarbonate.  This confines them to water where the pH is low enough to ensure a supply of carbon dioxide (the chemistry behind this is explained in “Buffers for duffers”. It may also explain why Chromulina lives in surface films rather than submerged in the pond (the locations where we’ve it found are unlikely to have sufficiently low pH).

One extra twist to the story is that many chrysophytes are “mixotrophic”, meaning that they can switch between using photosynthesis as a means of getting the carbon they need to grow from inorganic sources, and “feeding” on other organisms.  Our Chrysocapsa epiphytica, in other words,  has parked itself beside a convenient supermarket of pre-packaged carbon in the form of decaying vegetation and associated bacteria which it then ingests by a process known as “phagotrophy”.

Phagotrophy is, in fact, a very ancient characteristic, insofar as the very first eukaryotic cells were the result of Cyanobacteria-type cells being ingested by larger heterotrophic cells and being retained as on-board “energy farms” rather than digested and treated as one-off vegetarian dinners.   However, the shift to a permanent role for chloroplasts within a eukaryotic cell involved a lot of rewiring of intercellular machinery, and effectively “switching off” the intercellular mechanisms involved in phagotrophy.   Retaining the ability to “feed” on bacteria alongside a capacity for photosynthesis is the cellular equivalent of a hybrid car: there is a lot more to cram under the bonnet.  Flexibility, in other words, comes at a cost.

On the other hand, phagotrophy does not just result in extra carbon for the Chrysocapsa cells in Cogra Moss.   In an oligotrophic tarn such as this, the extra nutrients that are obtained when the bacteria are absorbed will also be a useful boost.   Once again, though, you can see that, in environments where nutrients are more plentiful, the cost to the cell of maintaining the equipment required for phagotrophy outweighs the benefits.

I’m sure that a close inspection of the land around Cogra Moss would have revealed insectivorous plants such as Drosera(sundew) and we also recorded Utricularia minor, an aquatic insectivorous plant, in another tarn we visited whilst desmid-hunting (see “Lessons from School Knott Tarn”).  Chrysocapsa is, in many senses, a microscopic equivalent of these carnivorous plants.   OK, so it has a taste for bacteria rather than flesh but, somewhere out there, there must be a sub-editor in search of a headline …

References

Lund, J.W.G. (1949). New or rare British Chrysophyceae. 1.  New Phytologist48: 453-460.

Maberly, S. C., Ball, L. A., Raven, J. A., & Sültemeyer, D. (2009). Inorganic carbon acquisition by chrysophytes. Journal of Phycology 45: 1052-1061. https://doi.org/10.1111/j.1529-8817.2009.00734.x

Raven, J. A. (1997). Phagotrophy in phototrophs. Limnology and Oceanography 42: 198-205. https://doi.org/10.4319/lo.1997.42.1.0198

Saxby-Rouen, K. J., Leadbeater, B. S. C., & Reynolds, C. S. (1997). The growth response of Synura petersenii(Synurophyceae) to photon flux density, temperature, and pH. Phycologia 26: 233-243. https://doi.org/10.2216/i0031-8884-36-3-233.1

Saxby-Rouen, K. J., Leadbeater, B. S. C., & Reynolds, C. S. (1998). The relationship between the growth of Synura petersenii (Synurophyceae) and components of the dissolved inorganic carbon system. Phycologia 37: 467-477.  https://doi.org/10.2216/i0031-8884-37-6-467.1

Terrado, R., Pasulka, A. L., Lie, A. A. Y., Orphan, V. J., Heidelberg, K. B., & Caron, D. A. (2017). Autotrophic and heterotrophic acquisition of carbon and nitrogen by a mixotrophic chrysophyte established through stable isotope analysis. ISME Journal. https://doi.org/10.1038/ismej.2017.68

 

The desmid dilemma …

Cogra_Moss_Sep19_JJohn

The second location we investigated during the Quekett Microscopy Club / British Phycological Society weekend was Cogra Moss, a small reservoir about four kilometres north of Ennerdale Water.  It is also  about a kilometre or so west of Lampleugh Green where I was staring mournfully at my flat tire whilst the advance party, unaware of my predicament, was out collecting samples.  They must have missed me by a matter of minutes.

As at Moss Dub they found some promising locations around the margins and, in the small tarn at the north-east corner, some patches of Sphagnum from which desmids could be squeezed, plus some floating vegetation.   Once again, I’ve illustrated some of those that we encountered, with a warning that this is a limited selection of the more photogenic ones and we’ve sent samples off to David Williamson for a more comprehensive analysis.   And, once again, the sheer diversity of desmids in the sample is a source of wonderment.   How can one small lake support so many variations on a one type of alga?  I’ve speculated on such issues in the past, drawing on G.E. Hutchinson’s “Paradox of the Plankton” (see “Baffled by the benthos (1)”).   In that post I suggested that it is partly a matter of scale and perception and, in this case, I suspect that the desmids we see in a Sphagnum squeezing are adapted to a wide range of microhabitats.  That means that the desmids would have had a three-dimensional arrangement within the Sphagnum whilst it is in situ but this is lost when we drag a handful of moss from the lake margin and squeeze it into a pot.

Cogra_Moss_desmids_#1

Desmids from Cogra Moss: a. Eurastrum crassum (length: 140 – 180 micrometres; width: 75 – 92 micrometres); Netrium digitus (length: 130 – 390 micrometres; width: 40 – 82 micrometres); Closterium kuetzingii (length: 300 – 550 micrometres) and Pleurotaenium trabecula (length: 277 – 600 micrometres; 22 -46 micrometres).  The photograph of Cogra Moss at the top of the post is by Judy Johns.

Cogra_Moss_desmids_#2

More desmids (and other algae) from Cogra Moss: e. Micrasterias thomasiana (length: 200 – 288 micrometres; breadth: 170 – 269 micrometres); Tetmemonus laevis(length: 67. 5 – 123 micrometres; breadth: 20 – 31.5 micrometres);
g. Schroederia setigera (85 – 200 micrometres long); h. Gonatozygon monotaenium (length: 90-327 micrometres; width: 6.2-12.5 micrometres); i. Staurodesmus extensus (width: 42-50 micrometres, including spines); j. Cylindrocystis gracile (length: 20 – 80 micrometres; width: 11 – 15 micrometres).

But, coming at this issue of desmid diversity from another direction, the term “desmid” is about as particular as the term “mammal”, insofar all belong to the same Class.   In “The big pictures …” I described how desmids were related to other green algae (acknowledging, in the process, that the term “green algae” is, itself, outdated).   This listed five separate families of desmids: four in the order Desmidales and one in the Zygnemetales (I’ve listed the examples from this and the previous post in the table below).   Think laterally and translate this level of organisation to the landscape around Cogra Moss and Ennerdale: the forests contain red squirrels (Rodentia), foxes (Carnivora) and deer (Artiodactlya) and there are otters in the River Ehen (another Carnivora but in the family Mustelidae rather than Canidae).   If we can appreciate how different mammals can interact within a landscape, then we should be able to apply the same principles on a much finer scale to organisms that are five orders of magnitude smaller.   It’s the principle behind fractals, but applied to biological  diversity rather than to geometry.

Earlier in the year, I published a paper with two colleagues that tried to explain how the way we study the microbial world can shape and, in many cases, impede our understanding (it’s open-access, so click on the link below if you want to read it).  We illustrated this with pictures that tried to demonstrate how microscopic algae interact with other organisms.  These included host plants, in the case of epiphytic algae, but also the protozoans that feed on them.  Most of our examples were diatoms, and there was a reasonable literature on which we could draw.  Curiously, I’ve never come across papers that provide this contextual information for desmids. Perhaps I just don’t look in the right places.   If it is out there and I’ve missed it, please do let me know.

Reference

Kelly, M. G., King, L., & Yallop, M. L. (2019). As trees walking: the pros and cons of partial sight in the analysis of stream biofilms. Plant Ecology and Evolution152: 120-130.

Organisation of the class Conjugatophyceae with examples encountered in Moss Dub and Cogra Moss.

Order / Family Examples
Desmidales  
     Closteriaceae Closterium
     Desmidaceae Desmidium, Euastrum, Pleurotaenium, Staurodesmus, Tememorus
     Gonzatozygaceae Gonatozygon
     Peniaceae No examples in these posts, but see “Desmid Diversity” for illustrations of representatives in Kelly Hall and Long Moss tarns.
Zygnemetales  
     Mesotaeniaceae Cylindrocystis
     Zygnemetaceae Not desmids: Filamentous algae including Mougeotia, Spirogyra and Zygnema – examples from Ennerdale area are described in several other posts,

Desmids from Moss Dub

Moss_Dub_Sep19_ZHenderson

I’d like to say that this post is about an excursion I made beyond Ennerdale Water and along the valley of the River Liza in order to find some different habitats from those that I usually write about in this blog.  I’d like to but, in truth, I was sitting by a road about ten miles away waiting for roadside assistance whilst my compatriots on the Quekett Microscopy Club / British Phycological Society algae weekend went up the valley on a glorious mid-September afternoon without me.  Whilst I was sitting waiting for a tyre to be replaced in a garage in Egremont they were casting plankton nets and squeezing handfuls of Sphagnum beside Moss Dub, a small tarn set amidst woodland close by the River Liza.

Moss Dub is set within one of Britain’s oldest and most ambitious rewilding schemes, Wild Ennerdale, where nature is allowed to shape the landscape as far as possible free from human interference.  However, Moss Dub, as we found out, is far from a natural water body.  A path forks and the two arms act as bunds encompassing a shallow pond, now partly overgrown with aquatic vegetation.   There is evidence of past mining activity – for iron and copper – in the area and my guess is that Moss Dub was, in the far past, a reservoir associated with the Lingmell mine located on the hillside above the River Liza and active in the late 19thcentury.     Whatever its history, it proved to be a rich location for desmids, and we spent a happy Saturday dipping Pasteur pipettes into the vials of peaty water that they collected and peering through our microscopes (If you want to know more about how to collect desmids, look at the post I wrote after our last excursion to the Lake District: “Desmid masterclass”).

There were some conspicuous green growths suspended in the water at the margin of the pond.  Even without a microscope, their filamentous nature was obvious.  When magnified, we saw chains of green cells set within a distinct mucilaginous sheath.  Each filament was composed of short cells with a distinct notch on either side.   This is a representative of Desmidium, one of a relatively small number of filamentous desmids.  We met D. schwartziion our previous excursion (see “Lessons from School Knott Tarn”); that species was present here along with D. grevillei, which is similar in many respects but the cross-section is lemon-shaped rather than triangular.

Desmidium_grevillei_MossDub

Desmidium grevillei from Moss Dub, Ennerdale Valley, September 2019.  a. shows a macroscopic view of filaments in a Petri dish; b. shows a filament of cells, along with a distinct mucilaginous sheath whilst c. shows a cell in cross-section.  I forgot to bring my graticule so cannot add scale bars to any of the images in this post.   Instead, I will quote dimensions from the Freshwater Algal Flora of Britain and Ireland to give an indication of size.   Cells of D. grevillei are 30 – 56 micrometres wide (50 micrometres is 1/20thof a millimetre).   The photo at the top of this post is a view of Moss Dub, taken by Zeneb Henderson

There were numerous other desmids in the sample.  A couple are illustrated below, and we’ve sent the sample off to David Williamson for a more thorough examination, and some definitive names.  On the right-hand side of the plate there is a different green alga, Coelastrum pulchrum, a member of the Chlorophyceae that forms spherical colonies with a fixed number of cells (“coenobia”).  We met Coelastrum microporum in the River Wear last summer (see “More green algae from the River Wear”): cells of C. pulchrum, by contrast, have a blunt projection.

Moss_Dub_algae

More algae from Moss Dub: d. Micrasterias radiosa (142 – 191 micrometres across); e. Euastrum pinnatum (65-75 micrometres across; 125 – 170 long); f. Coelastrum pulchrum (about 100 micrometres in diameter). 

The final desmid I’ve illustrated is Closterium lunula, large by desmid standards as it can reach half a millimetre or more in length.  Members of this genus have prominent vacuoles at each end of the cell within which small crystals can be seen.  Because C. lunula is so large it is easy to see both vacuole and watch Brownian motion move the crystals within.   Studies have shown that these are crystals of barium sulphate and also that the crystals are scattered throughout the cells, just happening to be easier to see I the vacuoles.  Quite what role they play remains speculation: barium is not required for plant nutrition and is, indeed, toxic in high concentrations.   It is also scarce in the soft waters where Closteriumis most often encountered, both in absolute terms and relative to other trace metals, which only adds further to the mystery.

That’s enough about Moss Dub for now.  A few words about Ennerdale Bridge, where we were based before I sign off from this post.  I usually stay at the Shepherd’s Arms when I am in the area and Keith and his staff hosted most of us and fed all of us.  It is a comfortable, unprententious inn, living mostly off walkers doing the Coast-to-Coast walk and with a menu that managed to put a smile on the faces of vegetarians and non-vegetarians alike.  Our daytime events took place in the community room of The Gather, a community-owned and run café and shop,  That gave us the satisfaction of knowing that the money we paid for the room was going to good use.   Their coffee keeps me going during long days of fieldwork in the area so I’m keen to make sure that they thrive!

Closterium_lunum

Closterium lunula (400 – 663 micrometres long) from Moss Dub, showing the terminal vacuole (ringed) and (below) a close up showing rectangular crystals of barium sulphate inside the vacuole.

Reference

Brook, A. J., Fotheringham, A., Bradly, J., & Jenkins, A. (1980). Barium accumulation by desmids of the genus Closterium (Zygnemaphyceae). British Phycological Journal 15: 261-264. https://doi.org/10.1080/00071618000650251

Microscopy_at_the_Gather

Quekett Microscopy Club and British Phycological Society members getting stuck into analysis of samples from Moss Dub and the Ennerdale valley at The Gather, Ennerdale Bridge, September 2019.

Hard cheese …

A day or so after my return from my trip to Orleans, The Guardian published an article on deadly algae on Brittany’s beaches.   The alga in question is Ulva, which I have written about a few times in the past.  It is a genus that is often associated with elevated concentrations of nutrients (see “Venice’s green fringe” and “News from Qingdao …”).  In Qingdao, the accumulations of algae caused problems during the 2008 Olympic sailing events but, in Brittany, there have actually been deaths associated with these growths.   Although green algae do not produce toxins themselves, the mats are so thick that the algae at the bottom cannot get the light and oxygen they need and so die and rot.   However, the thickness of the mats also means that the bacteria involved in breaking down dead plant matter are also starved of oxygen and, under such conditions, they can use sulphate as an energy source.  This, however, produces the toxic gas hydrogen sulphide which accumulates until released by, in this case, people stepping on the mats.

The problem in Brittany is concentrated on the north coast, close to where the Seine empties into the English Channel, rather than the south coast, where the Loire joins the Bay of Biscay.  Seine or Loire, the problem is similar: France has a large and vociferous farming lobby and inorganic nutrients, much deriving from agriculture, spill out of the rivers into the sea where they encourage the growth of algae.  It is not just green algae: there are also toxin-producing dinoflagellate blooms which can render shellfish dangerous for human consumption.  The combination of seashores piled high with rotting algae and restaurants unable to source local produce for their “fruits de la mer” is a major worry in a region where tourism makes a significant contribution to the economy.   It is also the classic environmental challenge, as economically-rational activities have malign consequences 100 km or more away, creating major headaches for policy-makers.

There is, however, good evidence from modelling studies that a reduction in the nitrogen in rivers that empty into the coast around Brittany will have positive effects.  One of these went so far as to envisage the adoption of organic farming in all agricultural areas of the Seine basin, leading to a halving of nitrogen load and a likely very significant reduction in the frequency of dinoflagellate blooms.   Another study indicated a likelihood of much less Ulva if river nitrate concentrations were much reduced.

That’s the theory. Putting such reductions into practice is a different matter because it means taking on the farming lobby.  There is a simple logic, in a farmer’s eyes, to raising output by adding more of the nutrient that limits growth.  The flaw in the argument is that nitrate is highly soluble and a proportion of the nutrient that a farmer spreads on his fields will be washed into nearby water courses when it rains.   No farmer wants to pay for fertilizer that is not nourishing his plants so there ought to be a solution that is agreeable to both them and the environment.   In reality, implementing policies that protect one sector (seafood harvesting, in this case), whilst not undermining another (agriculture), all within a framework in which market forces drive much of the decision-making is a fiendish challenge.

I think that this is one of the reasons why right-leaning politicians are rarely enthusiastic about the environment: simply leaving market forces to decide outcomes means that “externalities” – consequences of a commercial activity that are not reflected in the price – will be ignored.   Environmental regulation implies a need for interventions to control activities in order to protect wider interests, but that is an anathema to free market purists.  Regulation should, in theory, limit the “externalities” and create an environment in which sectors such as agriculture, seafood harvesting and tourism can co-exist.  Again that’s the theory but regulating the environment invariably results in labyrinthine bureaucracies that soak up money from taxes which free market purists would prefer not to have levied in the first place.

That’s why I really would encourage you to read Kate Raworth’s Doughnut Economics (see “The limits of science …”).  Every environmental scientist needs to reflect on how the changes they want to see need structural alterations that permeate throughout society, and not just technological fixes.  And, yes, those changes might affect our own lifestyle too. If French farmers use less fertiliser then they will produce less milk per hectare.  That, in turn, will result in less of the wonderful French cheeses that we all love and, probably, higher prices.  So, in the final analysis, it is not just the use of nitrate fertiliser that will have to change, it is our own aspiration.  Before we can make a difference we will have to live differently ourselves.  That’s the tough challenge we all have to face.

References

Passy, P., Le Gendre, R., Garnier, J., Cugier, P., Callens, J., Paris, F., … Romero, E. (2016). Eutrophication modelling chain for improved management strategies to prevent algal blooms in the Bay of Seine. Marine Ecology Progress Series 543: 107-125.  https://doi.org/10.3354/meps11533

Perrot, T., Rossi, N., Ménesguen, A., & Dumas, F. (2014). Modelling green macroalgal blooms on the coasts of Brittany, France to enhance water quality management. Journal of Marine Systems 132: 38-53. https://doi.org/10.1016/j.jmarsys.2013.12.010

 

A river runs through it …

Loire_at_Orleans_Sept19

I made an journey via Paris to Orleans last weekend to wave off my wife and daughter as they walk part of the Camino de Santiago.   The part of this austere Medieval pilgrimage route that they chose to follow happens to be one that meanders along the Loire Valley, passing chateaux and wineries en route.   Apparently, blisters are providing an element of self-mortification to keep the spirit of pious ascetism alive.

Orleans has a beautiful Medieval old town, dominated by a cathedral, along with plenty of reminders that it was here that Joan of Arc whupped the English.   More importantly, for a freshwater ecologist, a river runs through it.   The mighty Loire – the longest river in France – rises in the Masif Central and then flows north until it reaches Orleans, then it swings round to flow west to join the Atlantic Ocean at Nantes, a total length of just over 1000 km.  The river at Orleans is broad and shallow, divided into two channels by a wooded island; the left-hand chnnel is braided, with many small gravel islands, some with grass and herbaceous vegetation, and the water is generally shallow.  However, the bed of the river itself was a dark green in colour.  The Loire Valley is known as the “Garden of France” and this gives a clue to the scale of nutrient enrichment that we might expect in the river.  In the backwaters, this green backdrop was enlivened by patches of red due to the aquatic fern Azolla (see “Escape to Southwold”).

Azolla_Loire_Sept19

Patches of Azolla floating over algae-smothered substrata in a backwater of the River Loire at Orleans.  The picture at the top of the post shows a view looking downstream from the left side of the Pont George V. 

I brought a sample of the algae from some stones that were just within reach of the shore home on the Eurostar in a Perrier Water bottle for a closer inspection and was surprised by the diversity. In particular, I noticed several clumps of a narrow cyanobacterium that proved hard to photograph (possibly Homoeothrix janthina: see “Algae from the Alto Duoro”) along with many green algae.  I also saw Cladophoraglomerata, which is one of the classic indicators of nutrient rich conditions, along with Stigeoclonium, two forms of Spirogyra, two forms of Oedogonium and myriad green unicells and coenobia.  Stigeocloniumis another good indicator of nutrient enrichment,as  the filaments narrow to long colourless “hairs” when key nutrients are scarce – these cells are physiological adaptions to scavenge phosphorus and their absence at Orleans shows that this nutrient is not in short supply (see “A day out in Weardale”).

Stigeoclonium_Loire_Orleans_Sept19

Stigeoclonium cf. tenue (based on properties of erect filaments) from the River Loire at Orleans, September 2019.  Scale bar: 10 micrometres (1/100thof a millimetre). 

As well as green algae and cyanobacteria, there were also a lot of diatoms.  A few of these are illustrated below, and I’ll describe the diatoms in more detail in a future post.   As well as those I have photographed, I also saw long chains of a species of Fragilaria and another small araphid (possibly Staurosira) as well as Ulnaria ulna and some cells of Gomphonema and Navicula.   Note, in particular, the tube of Encyonema (possibly E. prostratum).   I’ve talked about tube-forming diatoms before (see “An excuse for a crab sandwich, really …”) but still can’t really explain what advantage this structure confers on a diatom.   What we can, perhaps, say, is that tube-dwelling is one of a several habits represented in the diatoms from Orleans – chains, erect, free-living motile, epiphytes  and more – and the mass of other algae create a rich diversity of microhabitats that the diatoms can exploit.

diatoms_Loire_Orleans

Some diatoms from the River Loire at Orleans: a. – d. Diatoma vulgare; e. Cocconeis pediculus; f. Encyonemasp.   Scale bar: 10 micrometres (= 1/100thof a millimetre).  The identity of the tube-dwelling form will have to wait until a cleaned sample is available. 

This abundance and diversity of green algae reminded me of some of the lush growths I had seen in UK rivers during the 2018 heatwave (see “Talking about the weather …”).  In a healthy river in the UK, I would expect to find less conspicuous growths than this, as invertebrate grazers would keep the algal biofilm shorn to a short stubble.   If, for any reason, the invertebrates cannot keep up with the algal growth, then a feedback loop is set up: the algae suck the valuable oxygen the invertebrates need from the water, the grazing reduces in intensity yet further, leading to a situation such as that I saw in the River Loire is the result.

Warm weather exacerbates the situation because water holds less oxygen at high temperatures.  In my posts about the River Wear last summer I commented that the plants in the river suggested that the river was more enriched with nutrients than was actually the case and I suspect that this was the result of these interactions.   The more southerly, more continental climate of the Loire Valley will experience these effects more often and it is possible that what I am looking at in Orleans may become the norm for UK rivers, as global warming intensifies.  Over the past decade I’ve worked on how to estimate the threshold concentrations of nutrients that a healthy river can endure.  However, nutrients rarely exert a direct effect on the plants and animals in a river but, instead, work through their effect on other factors such as oxygen. That will mean that global warming may wipe out any benefits of expensive nutrient reduction programs based on current estimates of the relationship between nutrients and river ecosystem health.  That’s a rather depressing prospect.

So I’ll end on a more cheerful note: the reason Heather and Rosie chose to start their Camino in Orleans was that they wanted to avoid a flight if possible.  At least that is how they sold it to me.   That they also chose to start their pilgrimage in a town close to the Sancerre vineyards may be pure coincidence.   Or maybe not ….

References

Surt, M.M., Jansen, M.A.K., Harrison, S.S.C. (2011).  Invertebrate grazing and riparian shade as controllers of nuisance algae in a eutrophic river. Freshwater Biology 56: :2580-2593

Wilco, C.E., Verbrak, P., Durance, I., Vaughn, I.P. & Ormerod, S.J. (2016).  Field and laboratory studies reveal interacting effects of stream oxygenation and warming on aquatic ectotherms.  Global Change Biology 22: 1769-1778.

Orleans_cathedral_Aug19

Orleans cathedral, August 2019.

Follow the data, stupid …

A perennial problem with ecology is that it is a discipline that is far better at describing problems than it is at solving them. The Water Framework Directive (WFD) encapsulates this: after nineteen years, we have a pretty good idea of the condition of Europe’s waters but have made very little progress in restoring the half that do not yet achieve good ecological status.

The reason for this is, I suspect, because describing the problem is a task that lies squarely within the remit of a scientist whilst finding solutions requires interactions that go beyond the boundaries of science, encountering vested interests along the way.   The agricultural sector’s enthusiasm for the environment is tempered by their desire to maximise yield and earn a living from the land, politicians are wary of regulations that may deter business or raise prices for the consumer and all of us are too wedded to the luxuries that the modern world offers.

The WFD can be seen as an embodiment of the social contract, articulated by philosophers such as Thomas Hobbes whereby individuals forego some rights in order to transcend the state of nature (“… nasty, brutish and short.”) and give us access to the benefits of an ordered society.  In this case, we all consent to forego some freedoms in return for a share in the benefits that a healthy aquatic environment will bring to all of us.   “Freedom” might seem like a weighty word in this context but anyone who has watched their sewerage charges creep steadily upwards over the past twenty years should recognise this as the price we pay for the freedom to flush away life’s less desirable by-products.

The problem is defining the point at which we hand over our natural rights to a higher authority.   We understand this when driving: an urban speed limit of 30 miles per hour reflects the point at which the risk we pose to other road users are deemed societally unacceptable and our right to drive as fast as we wish has to be curtailed.  If we can translate that principle into environmental governance then we can set “speed limits” for the major pressures that impact on the aquatic environment.   How do we get from an ecologist’s understanding of a “healthy” river (“good ecological status”, in WFD parlance) to the “speed limit” for nutrients, widely recognised as one of the major pressures affecting both freshwater and marine systems?

That’s been the focus of some work I’ve been doing under the auspices of the European Commission’s Joint Research Centre, one strand of which has just been published in Science of the Total Environment.  This paper looked at the threshold concentrations for nutrients (phosphorus and nitrogen) used by EU countries, noting the very wide range of values chosen as the national “speed limit”.   The situation is complicated because, just as is the case for roads, different types of rivers require different limits and we had to look for variation between countries amidst an array of variation within countries.   What emerged, however, was a clear relationship between the threshold values and the method used to set the standard.  Those that had applied statistical or modelling techniques to national data generally had tighter thresholds than those that relied upon “expert judgement”.  I’ve included the two figures from this paper that make this point.

Poikane_et_al_2019_Fig7

Range of good/moderate lake phosphorus (a) and nitrogen (b) threshold values grouped by method used to determine the value. Different letters indicate groups that are statistically different (p ≤ 0.05).   Fig. 7 from Poikane et al. (2019).

“Expert judgement” is one of those slippery terms that often creeps into official reports.   There needs to be space within a decision-making process for an experienced professional to see through the limitations of available evidence and present a reasoned alternative.  However, “expert judgement” too often becomes a shorthand for cutting corners and, in this case, grabbing numbers from the published literature that seem vaguely plausible.  There is also a darker side because, having unhitched decision-making from the evidence, “expert judgement” can become a euphemism for the “art of the possible”.  I have seen this occur during discussions around setting and revising river phosphorus standards in the UK: the regulators themselves are under pressure to balance environmental protection with economic development and tight standards can potentially limit what can be done in a catchment.

Another of our recent papers (this one’s not open-access, I’m afraid) shows that setting standards using empirical models is far from straightforward and we also recognise that standard setting is just one part of a longer process of nutrient management.   However, setting inappropriate standards simply as an expedience seems completely barmy, as you are never going to attain your desired ecological benefits.   The cynical view might be that, as the process of environmental change is invariably greater than the electoral cycle, there is limited accountability associated with such decisions, compared with more immediate political capital kudos from bringing investment and jobs to a region.

Poikane_et_al_2019_Fig8

Range of good/moderate river phosphorus (a) and nitrogen (b) threshold values grouped method used to determine the value. Different letters indicate groups that are statistically different (p ≤ 0.05).   Fig. 8 from Poikane et al. (2019).

All of our work has shown that, in most cases, the relationship between biology and nutrients is weak and, for this reason, large datasets are needed if robust inferences are to be drawn.  This leads to one further consequence of our work: setting environmental standards may only be possible if countries pool their data in order to produce big enough datasets with which to work.  This is particularly the case for smaller countries within the EU, but also applies to water body types that may be relatively infrequent in one country but are more widespread elsewhere.   I had recent experience of this when working on the Romanian stretches of the Danube: they simply did not have a wide enough gradient of conditions in their own territory, and we had to incorporate their data into a larger dataset in order to see the big picture (see “Beyond the Tower of Babel …”).    Writing about the benefits of international collaboration as the Brexit deadline looms obviously has a certain irony, but it needs to be said.  Far from being the distant and unaccountable law maker of Brexiteer mythology, in this field the European Commission has been quietly encouraging Member States to share experience and promote best practice.  One can only speculate about the future of the UK environment once free of Brussels oversight.

References

Philips, G., Teixeira, H., Poikane, S., Salas, F. & Kelly, M.G. (2019).   Establishing nutrient thresholds in the face of uncertainty and multiple stressors: a comparison of approaches using simulated data sets.   Science of the Total Environment684: 425-433.

Poikane, S., Kelly, M.G., Salas Herrero, F., Pitt, J.-A., Jarvie, H.P., Claussen, U., Leujak, W., Solheim, A.L., Teixera, H. & Phillips, G. (2019).  Nutrient criteria for surface waters under the European Water Framework Directive: Current state-of-the-art, challenges and future outlook.  Science of the Total Environment 695.  

Note on figures:

The methods used by Member States to derive nutrient thresholds are described in more detail in Poikane et al. (2019).   In brief, the approaches are:

1 – regression between nutrient and biological response;

2 – modelling;

3 – distribution of nutrient concentrations in water bodies classified (using ecological criteria) as high, good or moderate status;

4 – distribution of nutrient concentrations in all water bodies using an arbitrary percentile;

5 – expert judgement.  This includes values taken from the literature or from older European Directives. For example, for nitrate, the common use of the value 5.65 mg-N L−1 in freshwaters is likely to be derived from the guideline value of 25 mg L−1 of nitrate in the Nitrates Directive (91/676/EEC) or now repealed Drinking Water Directive (80/778/EC).

6 – The so-called OSPAR Comprehensive Procedure is used widely in coastal and transitional waters. In this, a water body is considered to be an ‘Eutrophication Problem Area’ if actual status deviates 50% or more from reference conditions.

7 – insufficient information.