For want of a nail …

How much mercury does it take to kill a fish?   A quick search on Google reveals  just over 270000 hits for the search terms “mercury”, “toxicity” and “fish”, with one reputable-looking source close to the top of the list suggesting just under one part per million is all it takes to kill a rainbow trout within 24 hours.   Exposure to a lower concentration might also have the same effect, albeit over a longer period, and even very low concentrations might be enough to disrupt metabolism and impair breeding potential, or to kill delicate life stages such as fry.    Much more could be written about the effects of mercury but this is not, actually, my subject for this post.

We often find the term “parts per million” in discussions about harmful chemicals in the environment but what exactly does this mean?  How can we visualise what one part per million actually looks like?   Here are two examples:  one gram of rice consists of about 30 grains.  Now imagine being asked to look for three grains of rice in one bag of sugar.   A bag of sugar weighs a kilogramme, so this is equivalent to searching for one part in 10,000.   One part of rice per million would be searching for three grains of rice in 100 bags of sugar.   Alternatively, you could think of one part per million as the equivalent of emptying a “tall” Starbucks coffee into an Olympic-sized swimming pool (50 metres x 25 metres x 2 metres).

Metaphors and analogies such as these are useful means of conveying information about toxicity and risk but they introduce a further problem of making the quantities seem so infinitesimally small that they trivialise serious issues.   So let’s try two further analogies: first, a single screw may cost a few pennies and, therefore, be just one or two “parts per million” of the total cost of a car.  Yet, the absence of that screw might have serious implications for the performance of the car as a whole.   And a chilli con carné needs only a tiny amount of chilli powder to impart the spicy heat that characterises the dish.   However much meat and rice you serve, it is the tiny quantities of spices that define dishes such as this.

Many of the nutrients and minerals that sustain our ecosystems exist at concentrations well below one part per million in the natural world, sometimes as low as a few parts per billion (a thousand times smaller than “parts per million” – imagine a pinch of salt in ten tonnes of potato crisps).   Yet these, in turn, provide vital nuts and bolts in the machinery of life.   Toxic metals such as mercury interfere with these nuts and bolts without which the performance of whole organisms can shudder to a halt.

For want of a nail, the shoe was lost; for want of a shoe, the horse was lost, and so on ….

La Grand Assiette de Lac Léman


Lake Geneva / Lac Léman from the marina at Thonon-les-Bains in the early morning.

From Lyon, I travelled about 200 km along the course of the Rhône to Thonon-les-Bains, a resort beside Lake Geneva (“Lac Léman” in French) to join a meeting of diatom specialists.  There are few more appropriate places for me to give a talk on the need for intercalibration as we were just 500 metres or so from a large water body shared by two countries.   And this is not just a theoretical exercise as the many restaurants bordering were proudly serving lake fish.   Management of the lake, therefore, has direct consequences for local livelihoods.

Remember, too, that this lake is bordered by some large communities, most notably Geneva itself (just under 200,000 people), so there have been substantial inputs of pollution over the years.   As far back as 1880 Switzerland and France shared a common fisheries management policy but this broke down in 1911, after which a combination of overexploitation and pollution hit the fisheries hard.  Indeed, the most highly-prized fish in the restaurants in Thonon-les-Bains was “fera”, a member of the genus Corygonus, a member of the salmon family that is found in only a few lakes in the UK.  Corygonus fera, which was indigenous to Lake Geneva is, in fact, thought to be extinct.  It had a very distinct habitat in the deeper waters of the lake but as pollution increased, so the oxygen levels in these regions decreased.

Pollution levels have now decreased again and, since 1980,  Switzerland and France again have an agreement on management of the fishery.  The fera we were eating last week was a testament to the success of this policy.   It was not C. fera, but a close relative that had been introduced. The sheer quantity that was available around the lake suggests a highly productive fishery although it did lead me to wonder whether this would be sustained if the lake quality continued to improve.


La Grand Assiette de Lac Léman from Le Beau Rivage restaurant in Thonon-les-Bains, featuring a salmon tartare, smoked fera and a mousse also made from fera.  Plate of frites just visible on the right hand side of the picture and a glass of Chimay behind.

Think of the pollution in the lake as being equivalent to the manure you put on your garden.   In the lake this “feeds” the algae which, in turn, are eaten by the zooplankton, the main food of Corygonus.   If there is too much pollution/manure, the lake/garden suffers as the bacteria suck the oxygen out of the water/soil.   However, if lake / garden had just the “natural” nutrients, there would be a much lower quantity of produce available for the fishermen / gardener to remove.   Somewhere in between, there is a state with just enough nutrients to support a productive fishery / garden.  It may not be “natural”, but it does represent a balance, of sorts, between nature and economy.  I can’t, in other words, extol the beauty of the environment, and the virtues of conservation and, simultaneously, praise the local delicacies without at least a minor twinge of conscience.


Buttiker, B. (2005). Evolution of fish and crayfish, and of fishery in Lake Geneva.   Archives des Sciences 58: 183-191.

Laurent, P.J. (1972). Lac Léman: effect of exploitation, eutrophication, and introductions on the salmonid community.   Journal of the Fisheries Research Board of Canada 29: 867-875.

Lake Geneva / Lac Léman also feature in William Boyd’s recent novel Waiting for Sunrise.

Remembering Jean-Gabriel




La Mere Jean, a traditional Lyonnaise bouchon, in Rue des Marroniers, near Place Bellecour.

I had visited Lyon once before, for a meeting during the Water Framework Directive’s intercalibration exercise. This is part of the no-man’s land where science and the EU collide. We spoke the language of scientists but our antennae also became finely tuned to subtexts that reflected the diversity of approaches to environmental management around the EU. Looking back, I can see the extent to which attitudes to public sector management in general shape the way that countries approach EU legislation. I also see, however, a reluctance amongst scientific colleagues to acknowledge this, even though it is widely recognised in the academic literature on environmental policy.

A principle called “subsidiarity” underpins the EU. This means that responsibility for implementing policy is always devolved to the lowest possible level. In the case of environmental policy, this is usually the Member State. This means that there could be 27 separate approaches to any piece of legislation. The intercalibration exercise tried to make sure that all these approaches led to roughly the same end-points. This, in turn, ensures the mythical “level playing field” that the EU is supposed to create.

The principle of the WFD is that we measure the condition of our water bodies in terms of their deviation from their natural or unimpacted state. Several thousand years of human activity complicates our understanding of that ideal condition, leaving plenty of scope for countries to interpret this as they see fit. I also got the impression that the approach to assessing ecological condition also reflected, to some extent, public sector budgets, with those countries with traditions of high taxation and generous provision of public services opting for more labour-intensive methods.   

We came to the exercise with strong ideas about how things ought to be done, and strong reasons why we should not change our methods. Mostly, of course, these discussions were conducted via email but this made the few face-to-face meetings that we did hold that much more important. Sharing meals took on greater significance, as it is here that the friendships were formed that, in turn, reduced the friction when we disagreed. I had particularly warm memories of the meeting we held in Lyon, largely because it was the last meeting at which Jean-Gabriel Wasson, our French colleague, participated fully. Jean-Gabriel was, himself, a tough negotiator but he pointed us towards bouchons such as La Mere Jean where we could enjoy Lyonnaise food at its best, our discussions continuing with a lubrication of local wine. Gradually, we found solutions, often involving compromises that make sense only when you stand back and take a continent-wide perspective. A few months later, Jean-Gabriel was diagnosed with cancer and a year after that he was dead. His legacy is the joined-up view of ecological status that we hammered out at meetings such as this one in Lyon.




Artistic diversions in Lyon




I spent this morning in the Musee des Beaux Arts in Lyon (apologies, but I can’t find out how to insert an acute accent with this software) and was particularly struck by this picture by Pascal-Adolphe-Jean Dagnan-Bouveret, Une Noce Chez Le Photographer (1879).   Look at it closely: it is a naturalistic painting of a photographer and his subjects, from an age when photography involved long exposures to produce stilted, black and white images.  My first impression was that this was simply a scene of 19th century life, but as I continued to look, a more radical interpretation occurred to me.  Dagnan-Bouveret (who I had not previously encountered) seems to be saying: “look at how much more real I can make my painting, compared to your photographs.”  Look at the man and boy in the right hand corner: the latter squirming to escape the tobacco fumes that are being blown into his face.  Look at the expressions and actions of the observers on the left hand side.   The bride and groom may have the serious expressions and formal poses that we expect of photographic portraits from this age, but here they are rendered in vivid colours.  This painting is, in short, everything that nineteenth-century photography was not.   “It may take longer to produce”, he says, “and it may cost you more money, but look how much more you get for your investment.”   This is, in effect, the last stand of naturalism before it is overtaken by modernism on the one hand and developments in photography on the other.  Although, it is worth remembering, that widespread use of colour photography is still more than 70 years in the future.  My parent’s wedding photographs, from 1960, for example, were all black and white.

Unravelling causal thickets …

The workshop I mentioned in a post a few days ” (the “thirty-three percent rule”) had the somewhat cryptic title “Untangling the Causal Thickets in River Health Assessment”. Time to explain: few of the issues which we encounter in rivers can be distilled to a single, straightforward cause. The jargon term in freshwater biology is “multiple stressors” but even this is a simplification because nature, itself, introduces further layers of complexity. A river at the end of a long, dry spell during the summer changes dramatically after a natural event such as a heavy downpour causes a flood which scours away the vegetation and turns the stones. Finally, we have to stir climate change into the mix, as these natural seasonal processes are gradually tweaked by greenhouse gases.

The term “causal thickets” is no more than a synonym for “multiple stressors” except that it also recognises that not all of the complexity that we observe is due to human activity. Also, more importantly, it links ecology, via the work of Wimsatt and other philosophers, to a broader literature on decision-making in the face of complexity. Wimsatt’s argument, in a very condensed form, is that a robust understanding of a complex system requires that we do not become over-reliant on a single strand of evidence. “Things are robust”, he argues, “if they are accessible (detectable, measurable, derivable, producible, or the like) in a variety of independent ways.”

The problem we all recognised was that the current approach to assessing the health of rivers in the UK and Ireland involves putting a lot of effort into a relatively small number of methods. This is inevitable, to some extent, as we have been grappling with the requirements of a new and, in many ways, radical piece of legislation, the Water Framework Directive. The wording of the WFD is such that the focus of methods has been on describing the structure of ecosystems, rather than looking in detail at how it works. I can identify the carburettor of my car by shape, but I need to know that this is where the fuel and air are mixed together if I want to tune the engine to perfection.

This does not mean that effort over the past ten years has been wasted. The big achievement has been to develop a shared ambition for the state of Europe’s waters. We’ve got the broad brush picture; we can compare the state of a stream in the west of Ireland with one in Cyprus. But now we need to start filling in the details and this is where the problems lay. However, the armoury of techniques we’ve developed may be too limited, too focused on structure, rather than on function, to let us do this.

This brings me back to Wimsatt’s definition of robustness as being accessible in multiple ways. Could it be that too much of the limited budget for this assessment is being spent on labour-intensive techniques that focus on structure rather than function? I went into the workshop thinking that this was probably the case but, intriguingly, the message I heard back from agency staff gave only limited support. The loudest message from them was the need for rapid assessment tools, to fill in the gaps in space and time within the broad picture that the current approaches gave them. The current network of sites (constrained by resources required to survey and sample these) is such that there may be 40 or more tiny tributaries, any of which may be contributing to the total pollution detected at the monitoring site. Methods that allowed 15 or 20 of these to be surveyed in a day with limited lab work afterwards was what they needed. Not cutting edge ecology. Sorry.

Keep on running …

So the Great North Run is over for another year.  I ran it in 1 hour 40 minutes 37 seconds, if anyone is interested, a minute slower than last year, but still a respectable placing overall (enough runners to fill the Stadium of Light behind me, and a respectable home crowd at Victoria Park [Hartlepool United] in front).

But suppose the Great North Run was a relay rather than a mass start, and each runner started only when the previous runner finished?   Suppose each 13.1 miles was run in series rather than in parallel?  My back-of-the-envelope calculations are that the 55,000 or so runners ran about 720,000 miles (1152800 km) in total, which is enough to circumnavigate the earth almost 29 times.   This would, however, take about 19 years to complete.   We could also have run to the moon and back, with mileage to spare.

Of course, the Great North Run is the tip of the iceberg, as almost all of us will have covered a much greater distance in training.   Let’s say we each did 100 miles of training as well as the run itself: this means that we covered just over 6 million miles.  We could run our relay back and forth to the moon a few more times or we could look for the next target.   Six million miles – the grand total of every Great North Runner’s race and training – will get us precisely one 25th of the total distance from earth to the sun (93 million miles, 150 million kilometres).   It all makes my 13.1 miles yesterday seem rather puny.

Who do you think you are?

As well as the diatom growths, the bed of the River Browney was also covered with skeins of a green-coloured alga which, when I removed it, had a soft, felt-like texture.   This is Vaucheria, a very common constituent of enriched rivers in Britain.   Under the microscope, the filaments can be seen to be long tubes (think of sausage skins) within which there are numerous tiny green chloroplasts.   This is not the first bright green alga that I have written about in this blog but appearances, in the world of algae, can often be deceptive.


We often see the evolutionary history of life on earth portrayed as a tree whose branches, representing each of the main groups of organisms, diverge again and again, culminating in “twigs” representing each species.   Following any “twig” back towards the “trunk” links to successively larger groupings of organisms.   So, for example, the species to which we belong, Homo sapiens, has no very close relatives, but is linked at the next level (family) to apes such as the chimpanzee.  Humans and chimps are, in turn, linked to the primates (order) such as gibbons and lemurs, which are part the mammals (class), including elephants and lions, which is part of the chordata (phylum) which links us to fish and reptiles.   Finally, the chordate belong to the Animalia (Kingdom) which links us to flies and slugs, and Animalia is part of the Domain Eukaryophyta, which links us to the rest of life except for bacteria.

We can use this analogy to express the relationship between any two organisms in terms of the number of steps along the tree before we find a common relative.  If we compared Vaucheria to Bulbochaete, which we met on 16 August, another bright green growth from the bed of a river, surprisingly we have to take eight steps (equivalent to comparing humans with plants!).   By contrast, the distance between Bulbochaete and Spirogyra is six steps (humans v fish) and between Vaucheria and Melosira (4 September) is a mere four steps (humans v gibbons).

The message is that the affinities amongst the algae are often not best discerned through seemingly obvious characteristics such as colour and shape but through biochemical composition, similarities in reproduction and the life cycle and in the structure of the DNA.  The other message is that the umbrella term “algae”, usually bit-players in any consideration of life on earth, embraces as much diversity as a typical zoo.   This is too easily forgotten, at least in part because they lack the televisual qualities that lend themselves to wildlife documentaries.   Unfortunately, in the process, we also often lose sight of the importance of algae in ecosystems.


There is no universally agreed system of higher classification (see post of 11 August).  For this exercise I used the tree of life project ( as the basis for the classification of animals and Algaebase ( for the algae.


Fertile speculations …

The River Browney does not give up it’s secrets gracefully.   To reach the lower stretches of this tributary of the River Wear, just a few kilometres outside Durham City I had to push through thick growths of Himalayan Balsam, stinging nettles, brambles and what looked suspiciously like Giant Hogweed.   The bankside luxuriance continued in the river itself, the bed of which is almost completely covered with either submerged water crowfoot or algae.   The river has wound its way down from the foothills of the Pennines, collecting the wastewater from small towns and, just a couple of kilometres upstream from where I stand, from a sewage works serving a large village on the outskirts of Durham itself.   The algae and plants all thrive in the steady supply of dilute manure that these works provide.


The River Browney at Low Burnhall Nature Reserve, just below the A167 Bridge.  Photographed in September 2013.

Many of the stones in the margins were coated with brownish filaments, waving gently in the current.  When I pick up one of the stones, these filaments collapsed into amorphous slimy masses but, under the microscope, they resolved themselves into a tangle of chains of algal cells.  Two types predominated, both with the yellow-brown colouration typical of diatoms.   The most abundant of these was chains of cylinder-shaped cells.  This was Melosira varians, a very common diatom in nutrient-rich rivers and which often forms these long brown streamers during periods of low flow during the summer.   The other type of cell was cigar-shaped when seen from above (as in fig. d, below) but rectangular when seen from the side (as in fig. c.).  These cells were mostly joined at the corners to form zig-zag chains.  You can also see, in fig. d., the transverse ribs of silica which are characteristic of this genus of diatoms.


Filamentous growths of diatoms on stones in the River Browney, County Durham, September 2013 and (inset) one of the growths on a stone removed from the stream bed.


Microscopic views of diatoms (and a few desmids) from the River Browney, September 2013.  a. low power view of the filaments; b. part of a chain of cells of Melosira varians photographed at high magnification.  Note the large number of small brown chloroplasts inside each cell (scale bar: 10 micrometres = 1/100th of a millimetre); c. zig-zag chain of Diatoma vulgare photographed at medium magnification; d. a single cell of D. vulgare at high magnification (scale bar as for b.)

These masses of cells are the microscopic equivalent of the bankside vegetation that I had to push through in order to reach the river in the first place.  The surprise was that I did not find a large number of insect larvae feasting on this abundance, as I have described from cleaner rivers such as the River Ehen.  The answer, suggested by some recent papers, is that the normal relationship between algae and their grazers breaks down in these enriched rivers.   The dense diatom growths can suck the oxygen out of the water at night when there is no sun to generate photosynthesis so the insects that would normally be feeding on the algae cannot survive.  This, in turn, will reduce the food supply of fish, as well as smothering the areas where they would normally lay their eggs.   We see, in other words, a “domino effect” as the consequences of artificially high nutrients clatter through the different groups of organisms leading, in some cases, to consequences for the way in which we are able to use these ecosystems.