Besotted by beavers …


The beaver dam at Dubh Loch, Knapdale, Argyll, photographed in April 2013.

Beavers are back in the news. An article in today’s Independent reports that Natural England have granted a licence to Devon Wildlife Trust to manage a population of beavers that had escaped from a wildlife park.   This overturned a decision by the Department for Environment, Food and Rural Affairs which argued that beavers are an invasive non-native species and that the Devon population should, therefore, be trapped and returned to a zoo. As I wrote in 2013 (see “In pursuit of beavers …”), beavers do challenge our preconceptions of what is “natural” and I can also report two other recent studies that show how beavers can change both the structure and function of freshwater ecosystems.

The first is a study co-authored by my sometime colleague Nigel Willby on the Scottish Beaver Trial at Knapdale in Argyll (the locations I wrote about last year) which showed changes in the aquatic vegetation due to direct grazing by the beavers, as well as by the water level changes brought about by dam-building. A few species (Schoenoplectus lacustris and Cladium mariscus in particular) decreased due to grazing but the site where the water level rose due to dam building saw an increase in both the diversity and heterogeneity of aquatic vegetation. This, in turn, had beneficial effects on invertebrate diversity in the area.   Or, more accurately, the long-term decline and eventual extinction of beavers due to human pressures altered the balance of plants and animals and the Knapdale trials are giving us an insight into the natural state of the area 200-300 years ago. Paradoxically, our ideas of “natural” are largely shaped by our own expectations, as I commented in a post about Himalayan Balsam last year (see “The future is pink …”)

The second study looks at the wider consequences of beaver activities.   Beaver dams create large areas of standing waters in places that once would have been terrestrial or semi-terrestrial habitats with a stream running through them.   The sediments of these standing waters do not have as much access to oxygen compared to their pre-beaver condition and, consequently, organisms capable of anaerobic respiration can thrive. Respiration in the presence of oxygen produces carbon dioxide as an end-product; however, anaerobic respiration can produce methane which is a far more potent greenhouse gas than carbon dioxide.   A team from the University of Saskatoon in Canada have done some calculations and shown that the resurgence of beavers worldwide is now contributing 200 times more methane to the atmosphere than was the case in 1900.

Like all broad-scale modelling studies, the calculations are based on several assumptions and extrapolations, meaning that we need to treat the figures with caution. However, it is useful because it broadens our understanding of how beavers change landscapes from the visually obvious (less club rush, for example) to the more subtle.   And, once again, it challenges our current understandings. The reality is that beaver-mediated methane production underwent a “blip” between the 17th and 20th centuries and is now returning, slowly, to values that our medieval ancestors (those with gas chromatographs, at least) would have recognised.   Even today, greenhouse gas budgets are dominated by natural sources; though this is no cause for complacency: the absence of beavers in effect created a little extra “headroom” into which we pumped the by-products of our addiction to fossil fuels.


Whitfield, C.J., Baulch, H.M., Chun, K.P. & Westbrook, C.J. (2014). Beaver-mediated methane emission: the effect of population growth in Eurasia and the Americas. Ambio 44: 7-15.

Willby, N.W., Perfect, C. & Law, A. (2014). The Scottish Beaver Trial: Monitoring of aquatic vegetation and associated features of the Knapdale lochs 2008-2013, final report.   Scottish Natural Heritage Commissioned Report No. 688.

Ecclesiastes 3 rewritten …

For everything there is a season, and a time for every matter under heaven ..

A time to rise, a time to shower,
A time to gulp coffee and
A time to run, to catch the train
In time for work, where there is
A time for email, a time to file,
A time to scan reports before it is
Time for a meeting, whose agenda allows
A time for matters arising and
A time for PowerPoint presentations, but
The time to summarise drags on
And there is barely enough
Time for a sandwich before you are
Back at your desk where
The telephone is ringing and
The time for completing a report,
Already two weeks late, is squeezed
As emails demand more of your time.
The time for going home slips past and
Time passes reading reports on the train.
A time for pasta sauce from a jar and
A time to crash on the sofa,
Zapping through channels, lacking the
Energy to find a good book instead.
A time for a final cup of tea,
A time for bed and, in the dark,
A time to wonder where
The time for wondering has gone.

In which the author’s mercenary instincts are revealed …


The first two limited edition prints available from

A few people have asked how they can get copies of the pictures I talk about on this blog, prompting me to take my first tentative steps into online selling, via the arts and craft website Folksy. There are currently two prints on sale there: one of the River Ehen (see “A winter wonderland in the River Ehen”) and one from Pangong Tso (see “Subaquatic landscapes in Pangong Tso”) and you can pay via Paypal with a credit or debit card.

The pictures are available as limited edition Giclée prints.   Giclée prints are produced using professional-grade scanners and printers with archival pigment inks and high quality papers.   One of the benefits is that I can manipulate the size of the images and print them at a size that is more convenient for display.   The prints that I have produced so far are mounted to fit in a standard 40 x 50 cm frame. Selling them mounted rather than framed makes it cheaper to post them, but if you would like a framed print, get in touch and I can organise this for you.   Get in touch, too, if any of the images on display at interest you.

The etymology of “giclée” is amusing: the term was coined by an employee of Californian fine-art printers Nash Editions (that’s Graham Nash, as in Crosby, Stills and Nash, if you are interested).   They originally called their prints “digigraphs” but I guess “giclée” sounds that little bit more sophisticated.   Be aware that giclée means something rather rude in French. If I tell you that “gicler” means to squirt, you can probably work out the rest for yourself.

Sales pitch over. You’ll notice that my sharp business acumen has missed the lucrative Christmas market by a month but I’ll post a reminder next November, just in time to solve your dilemma of what to buy for anyone too polite to say “and why would I want a picture of algae on my wall?”

Abstraction and reality in Upper Teesdale

Just before Christmas I wrote about a visit to Upper Teesdale to collect desmids (see “Hunting for desmids in Upper Teesdale”) and mentioned that I was working towards a painting.   That painting is now finished and is reproduced below.   The style of this painting is quite to the other pictures I’ve been working on recently, drawing on ideas I explored during the final year of my Fine Art degree.   I was interested, during this period, in exploring the boundaries between figurative and abstract art and found algae to be an ideal resource for this investigation.   To me, they are living organisms with defined parameters yet they are beyond the boundaries of most people’s sense of reality.   “Most people” included my tutors and this led to some challenging discussions about just how far I could alter the shapes and colours I was using.   They felt that I was too rigid and unwilling to push my artistic experiments too far. In many ways they were right but there were also times when I felt that they were asking me to do the phycological equivalent of drawing a cow with five legs.


Upper Teesdale. 2015. 86 x 91 cm. Acrylic on canvas,

The picture shows five different desmids that I collected from Upper Teesdale in December.   To me, these organisms are as much a characteristic of the area as the more famous gentians (see “Blue skies and blue flowers in Upper Teesdale”) and to present them in an context that evokes abstract art emphasises the lack of familiarity that most of the visitors to this area has to these organisms.

The lower picture shows a close-up of some of the desmids in the picture, to show how the painting was built up as a series of washes of very dilute acrylic paint over a white ground, with the details of the desmid blocked out in stages using masking fluid. The result is a “negative” image of each of the desmids. The final stage of the painting was to use a syringe to add translucent trails of paint thinned with acrylic gloss medium to give a translucent effect that imparts some visual energy into the finished picture.

You can see more work on this general theme at


Upper Teesdale. Detail.


The Martial Heavens

If you follow this blog you’ll know that I am interested in the interactions between art and science and in trying to understand the benefits that art can bring to science and vice versa. Art and science (or, for that matter, art and other academic disciplines) do not always dovetail neatly: science is evidence-driven, art deals with experiences.   Academic study, generally, requires there to be a critical distance between subject and investigator and there are situations where too much “experience” may compromise this. But, at the same time, the friction at the art-science divide can generate synergies that are mutually-beneficial.

There is a good example on show in Newcastle at the moment: Matthew Flintham was the Leverhulme Artist-in-Residence in the Geography Department at Newcastle University, working with my colleague Alison Williams, and has produced a series of depictions of the restricted airspace above military training areas in the UK.   His exhibition, the Martial Heavens, is currently displayed at the Ex Libris Gallery in the University and one of the pieces is illustrated below. In the foreground you can see a large-scale map of an area of Northumberland that includes the Otterburn training area. Resting on this is a to-scale wireframe model that shows the limits of the restricted airspace above the training area.


Matthew Flintham: the Martial Heavens exhibition. Ex Libris Gallery, Newcastle University, January 2015.

Broadly speaking, I see art-science interactions working in two ways: firstly, where the art acts as a creative adjunct that allows a scholar to examine the available evidence in new ways and open new perspectives and, second, as means of visualising the outputs of scholarship in order to make them more accessible.   Martial Heavens is a very good example of the latter.   I homed in on Matthew’s depictions of Northumberland because it is an area of the country that I know well. In particular, I could trace the upper section of the River Coquet, which has featured in my work (see “A journey to the headwaters of the River Coquet…”) on Matthew’s map as it forms one of the boundaries of the Otterburn training area.   The casual visitor driving along beside the Coquet enjoying the spectacular landscape is likely to be unaware of many facets of both the human and physical worlds that knit together to create these vistas.   Martial Heavens opens up one of these by extending our awareness of the military’s presence from the fluttering red flags and “Danger Area” signs on the hillsides to a series of virtual boundaries that extend 10000 metres into the sky.

And then you have to adjust your focus again from the clouds high above to the stream that flows alongside the road.   The same principle applies in my work, which draws on art-based approaches in order to bring facets of Coquetdale’s geography alive to audiences who would otherwise just drive past.   My own explorations were at the microscopic scale, highlighting a microscopic world that lives on every submerged stone but, once again, it is the chemistry between art and science, between evidence and experience, that allows us to clothe the bare bone of “data” or “evidence” in a manner that makes it more real to the wider world.


More about my own work in this publication:

Kelly, M.G. (2012). The semiotics of slime: visual representation of phytobenthos as an aid to understanding ecological status.   Freshwater Reviews 5: 105-119.

Baffled by the benthos (2)

So what can we learn from studying the diversity of stream ecosystems? First of all, I don’t think that we gain very much from using conventional “diversity indices”.   These have been explored ad nauseum by ecologists, usually for no better reason than that they are easy to calculate. I pointed out in a post in December 2013 (see “A Christmas turkey …”) that calculating diversity of just the diatoms was, in any case, a meaningless exercise as diatoms are part of a community that includes many other algae as well (a paper demonstrating this is referenced below).

As I was thinking about this, I remembered reading an insightful book by an anthropologist, Paul Richards on traditional farming methods in Sierra Leone.   He pointed out that subsistence farmers were not impressed by the modern varieties of rice that promised high yields and, instead, preferred traditional “land races”. These had a broader genetic base and, though they may not yield as much in a good year, there was a good chance that there were enough seeds with some drought resistance, flood-resistance, pest resistance and so on to ensure that they would always get a harvest, regardless of any unexpected events that may occur during the farming year. The land race, in other words, was resilient in a way that the highly-bred varieties were not.

Much has been written about how all diatoms have a unique niche and how this makes them extremely sensitive environmental indicators. The problem is that there is not much hard evidence to support such assertions.   I do not doubt that most diatoms do have unique requirements; however, there is no particular reason why these niches have to be determined solely by human pressures. Is it not also possible that factors such as fungal resistance might not apply to diatoms just as it does to crop plants?   There are a few tantalising hints that this might be the case but what would this mean for ecological status assessment?

The graphs below come from a study I was involved with, in which samples were collected from streams with different levels of human impact. We’ve divided them into two groups: those that are as close to pristine as you can get (“reference”) and those that have a measurable human impact (“non-reference”).   The left-hand plots show the number of species belonging to two common diatom genera, Achnanthidium and Gomphonema. The right-hand plots show the percent of the total number of diatoms recorded that belong to these two genera. In both of these instances, the number of species within the two genera is significantly higher (Wicoxon test) in reference sites.   I chose these two taxa because I have noticed that they do tend to be more diverse in cleaner sites, which makes it unlikely that we can explain differences in distributions purely in terms of different preferences for chemical variables.   My suggestion is that this diversity reflects a more fundamental resilience in the reference assemblages that is lacking in the impacted sites.


Differences in the number of taxa of Achnanthidium and Gomphonema recorded at reference and non-reference sites in an unpublished study of ecological conditions in streams in an EU Member State.

I have used the game Jenga as a visual analogy of what I think is happening in these samples.  The left-hand image below shows an intact tower of bricks which is equivalent, in this parable, to an unimpacted community (“high ecological status”).   The objective in this game is to remove bricks from the tower without it collapsing.   The EU’s definition of “good ecological status” is a slight change in composition and abundance which, in my analogy, equates to having a few bricks removed (as in the middle photograph). The ecosystem continues to function in a near-natural manner because the remaining taxa can fulfil the “services” that the missing taxa once provided.   However, if too many bricks are removed (the right hand image), the tower collapses.   This is equivalent to lower classes of ecological status (moderate, poor or bad).   Other organisms will move in to occupy the space and use the available resources, but this new community will be very different to that expected under natural conditions.


Jenga as a metaphor for ecological status: a. an intact tower of bricks, equivalent to pristine conditons, “high ecological status”; b. a few bricks are missing but the tower is still intact: “good ecological status”; c. several bricks have been removed and the tower has collapsed: “moderate ecological status” or worse.

The previous post described diversity in terms of a huge variety of microhabitats that are difficult for us to comprehend due to the differences in scale.   This post has taken a broader view of that hypothesis, suggesting that microhabitats will vary not just in space but also in time and, therefore, that the ecosystem can “bounce back” from short-term shocks rapidly, because other organisms can occupy the spaces left by those that cannot thrive and, as a result, higher trophic levels are still able to feed. In the same way that being able to recover from a cold or other bug is a characteristic of the healthy human, so having “resilience” to a short-term perturbation, whether natural or human-induced, is one property of a healthy ecosystem.


DeNicola, D.M. & Kelly, M.G. (2014). Role of periphyton in ecological assessment of lakes. Freshwater Science 33: 619-638.

Richards, P. (1985). Indigenous Agricultural Revolution. Ecology and Food Crops in West Africa. Hutchinson, London.

Baffled by the benthos (1)

We encountered G. Evelyn Hutchinson in two posts last year (see “Diatoms from the roof of the world” and “The Clear Mirror”). In the second of these, I made a passing comment to the “paradox of the plankton” which he both proposed and partially resolved.  He asked “how it is possible for a number of species to coexist in a relatively isotropic or unstructured environment all competing for the same sorts of materials” when, “according to the principle of competitive exclusion … we should expect that one species alone would outcompete all the others …”   The answer, he suggested, was that the world that plankton inhabit is far less uniform than may first appear to be the case, providing opportunities for a range of organisms, each with their own ecological specialism, to thrive.

Exactly the same question could also be asked of the benthic algae which seem to show an extraordinary diversity. It is not uncommon for me to find fifty or more algal species in a sample from one habitat on one day within a river. They are all bathed in water with the same chemical composition, so why is it that one competitive species does not overgrow all the others to produce a monoculture?

Whilst I was pondering this question, I recalled a paper written by Dicky Clymo, who supervised my undergraduate dissertation. He was a specialist on Sphagnum and peat bogs and, in 1973, wrote a paper showing how variations in the values of two physical factors (water table depth and light) and two chemical factors (hydrogen and calcium ions) across a peat bog could create a mosaic of habitats that allowed twelve different species of Sphagnum to thrive.   If we assume that a typical diatom sample covers at least 10 cm2 of the surface of a submerged rock, then this would be equivalent to surveying at least a square kilometre of peat bog, providing plenty of opportunity for this level of habitat variation.

Sampling microscopic algae is limited by our own senses: a rock surface that may look smooth to our eyes may actually have a microtopography that creates a range of habitats within which different species can survive. The image below shows small cells of the diatoms Amphora pediculus and Achnanthidium minutissimum nestling in crevices on a rock surface that, presumably, offers some protection to them from marauding grazers.

Why am I making this point?   I frequently encounter comments such as the following in papers about diatoms: “poor species discrimination can lead to the combination of morphologically similar, but ecologically disparate taxa” and the suggestion that this can “compromise ecological status assessment”.   There may be situations where this is the case, but also situations where these taxa can happily co-exist in within a very small area because the ecological factors that separate them operate at a much more localised scale than the pressures we are trying to assess. Diatomists, I am afraid, are often naïve ecologists who rarely go beyond correlating species distribution patterns with a few chemical and environmental variables that are relatively easy to measure. There is still a lot that we don’t know about how the diverse assemblages of diatoms that we encounter in rivers and streams interact with the other organisms around them, let alone with aspects of their physical environment that are invisible to the naked eye.

More about this in the next post.


A scanning electron micrograph showing the surface of a rock showing Amphora pediculus (a) and Achnanthidium minutissimum (b) living in crevices. Scale bar: five micrometres (1/200th of a millimetre). Photograph: Marian Yallop.


Clymo, R.S. (1973). Growth of Sphagnum: some effects of environment. Journal of Ecology 61: 849-869.

Hutchinson, G.E. (1961). The paradox of the plankton. American Naturalist 95: 137-145.