(In)Competent Authority?


Back in June last year, when everyone was still reeling from the outcome of the vote to leave the EU, I wrote a post entitled “Who will watch the watchmen now?”   In it I suggested that not only did the UK get strong environmental legislation from the EU, it also benefited from collective oversight that ensured that Member States actually enforce this legislation.  This is exercised, ultimately, by the Court of Justice of the European Union, a body whose jurisdiction will cease once we leave the EU.   That was what prompted the title of my post: good environmental legislation needs independent scrutiny.  Where will that come from once we leave the EU?

I was pleased to see this point being made forcefully in reports from the House of Commons Environmental Audit Committee and the House of Lords European Union Committee recently, as well as in a very useful report by Green Party MP Caroline Lucas.   One recommendation of the Environmental Audit Committee is that the Government should introduce a new Environmental Protection Act to maintain and enforce environmental standards after we leave.  One of the witnesses to the Committee made it clear that the terms of reference of the UK’s Supreme Court meant that we could not assume that it would fill the legal void left once the European Court of Justice no longer had authority.   Even assuming that the Supreme Court could play a role, however, there would still need to be an organisation that scrutinised the activities of government agencies responsible for the environment and initiated the legal actions.  I suggested in my earlier post that this body must be wholly independent of government.

The Government’s aim, as stated in their white paper on Brexit, is that all EU legislation will be transposed into UK law in the first instance via the Great Repeal Bill, after which Parliament (and, where appropriate, the devolved assemblies) will be able to decide which elements of that law to keep, amend or repeal (clauses 1.1 – 1.3 in the Brexit white paper).  However, Caroline Lucas points out that much of the new legislation is likely to be in the form of Statutory Instruments rather than Acts of Parliament, which will mean that there will be less scope for intense scrutiny by Parliament.  If she is correct then this is an important – and worrying – loophole that those of could be exploited to water down future legislation.

One point that Caroline Lucas makes (and which I touched upon in my earlier post) is that the European Commission grants a degree of flexibility in the implementation of legislation in the form of “derogations”.   Does this mean that the UK governments will transpose into UK law the right to give themselves lower targets or extended deadlines?   Again, who will hold the governments to account?  DEFRA and their counterparts in the devolved administrations will continue to talk the talk, but the devil will lie in the detail and only the eagle-eyed are likely to notice when the sharp edges of current legislation are quietly eroded away.

Another possible fate of transposed legislation, highlighted in the Environmental Audit Committee report, is that it will simply be ignored, again without the oversight of the European Commission and the European Court of Justice.  The result will be “zombie legislation”, either not enforced or not updated to the latest scientific understanding.   An unspoken question hovering behind much of this report is “is DEFRA up to the task?”   The overall tone of the report suggests that the Committee is not yet convinced that it is.   The question remains: who will watch the watchmen?

I have worked with the UK’s environment agencies for 25 years now, and my travels around Europe convinced me that they were amongst the most effective at translating the fine words of EU environmental legislation into positive outcomes.  Results in many cases are impressive (see “The state of things, part 1”).  However, I have felt for a number of years that their effectiveness has been slipping.  This started roughly when the coalition government introduced austerity measures after the 2010 general election, leading to substantially less money being available for the public sector.  As the Environment Agency tightened its belt, it was noticeable that activities that were driven by EU legislation were less affected than most.  The fear of the European Commission bringing infraction proceedings trumped almost all other factors when determining budgets (with the exception, perhaps, of flood protection).   Chris Smith, Chairman of the Environment Agency adds in a recent blog that is well worth reading that this period also saw the Agency’s ability to speak publicly in defence of the environment being limited by the coalition government.

The answer to this worrying situation is a body that can engage the government at the highest level in informed debate.   This will almost certainly not be performed by yet another DEFRA-funded agency.  But if not this, then what?   I believe that the charity sector, professional bodies and environmental and wildlife charities may have to step in to fulfil this brief.  Anglers already do this via the organisation Fish Legal (formerly the Anglers Co-operative Association); the time may have come for the rest of the environment and conservation sectors to learn from this well-organised lobby group.  Perversely, if the “people” now have control of their own destiny (as the Brexiteers claim), then the government must be ready for those same people to ask the hard questions about their performance that we had previously delegated to Brussels.

(The photograph at the top of this page shows Cracken Edge in the Peak District, in November 2016)


How to make an ecologist #12

Jos, our home for the two years that we spent in Nigeria, was located on a plateau in central Nigeria, at an altitude of about 1200 metres, 700 metres above the surrounding countryside, which spared the city from the worst of the summer heat.  During colonial times, Jos’ mild climate had led to it being the hill station for expatriates although, unlike in India, the administration did not decamp here en masse. The agreeable climate also made this area an attractive base for Christian missionary organisations and there was also a school for expatriate missionary children.  There was, we discovered, a large community of expatriates – from the US, Canada and UK in particular – and infrastructure to support these.  Major First World dilemmas such as procuring a steady supply of Extra Virgin Olive Oil began to appear less daunting.

The university driver dropped us at the Plateau Hotel, which was to be our home for the first six weeks while the university sorted out a house for us.  It was early Friday evening when we arrived, and we had the weekend to orientate ourselves.   On Monday morning Sam Agina, one of our new colleagues, collected us in his car and drove us through the town to the campus, weaving his way through the noisy mêlée of taxis, motorcycles, brightly-decorated lorries and pedestrians that thronged the streets.  The University of Jos was part of the second wave of Nigerian universities, having been founded in 1975, originally as an outpost of the University of Ibadan (itself, an offshoot of the University of London, my own alma mater).   The Botany Department occupied a brand new building at one edge, well designed with wide corridors that were open on one side so that cool breezes could circulate.  The laboratories were as modern as those that we had left behind in the UK, at least until you opened the cupboards under the benches, which were largely empty.  The department was, actually, well equipped with teaching microscopes but had very little other equipment and reagents, too, were always in short supply.    Running practical classes was always a test of our ingenuity and research was almost out of the question.


The Botany and Zoology building at University of Jos’ Bauchi Road Campus, 1990.

Even if we had had better facilities, there was little time for research as we both had very heavy teaching loads.   All science students, along with medics and pharmacologists and some education students, did a common first year, which meant that classes were very large – up to 500 students crammed into a lecture hall (some outside, leaning in through the windows), trying to listen to a lecturer at one end talk without a microphone and draw onto a blackboard.  To add to the challenge, there was often another lecture scheduled at the other end of the long room, and no dividers between the two classes.  After this introductory year, classes became smaller as we just had the botanists, zoologists and education students to teach, and final year classes often only had 20 or 30 single honours students.  That teaching was much more rewarding and close, in intellectual level, to teaching in UK universities.  The biggest difference was that the curriculum was much more traditional and less informed by recent developments.  The course was heavy on taxonomy and systematics, but weak on biochemistry where the lack of opportunities to turn theory into practice was a real drawback.


With University of Jos botany undergraduates at Assop Falls, Plateau State, Nigeria during a field trip in December 1989,

The titles of the modules I taught show the nature of the course: Cryptogamic Botany I (2nd year), Cryptogamic Botany II, Phycology I and Statistics (3rd year) and Phycology II and Palaeobotany (4th year).   I found myself teaching all of the parts of a traditional botany degree that have been slowly excised in order to make “plant science” courses more appealing to British undergraduates.  Our students, in other words, had the firm foundations in classification and systematics that their British counterparts lack but, unfortunately, this was at the expense of those parts of a modern plant science degree that really might contribute to the development of a country such as Nigeria.   The allocation of the Palaeobotany was, I presume, because of my experience working on Holocene vegetation history (see “How to make an ecologist #10”).  This left approximately 99.9997% of the history of plants on earth for me to vamp my way through.  I think I managed to keep one step ahead of the students who were, in any case, far too polite to tell me if I was not.

One area where our new Department did have a genuine strength was microbiology and there was a strong slant towards this in the degree course.  There were a number of undergraduate and MSc projects that set this knowledge into a local context, exploring the interactions between microbes and the local community.  One, I recall, looked at how bacteria impregnated the calabashes (hollowed out gourds) that the Fulani women used to make a popular yoghurt-like drink so that they never needed a starter culture.  Others looked at the efficacy of indigenous medicines, with the students showing that several local herbal remedies had genuine anti-microbial activities.  This was all done without the containment facilities of a western research laboratory: I recall peering at a row of Petri dishes lined up on the bench at the back of a research laboratory and being told that they all contained cultures of Gonorrhoea. I promptly took a quick step backwards.


Our home in Nigeria: House 5 Road 5 on the University of Jos Senior Staff Quarters, 1990.

The local focus of the Department showed me, ultimately, where my own skills might be best spent.  Rather than struggle with research that would have been difficult to publish in an International journal, I set out to write a textbook with a colleague that could be published at a price students could afford.   I have no formal statistical training but I knew enough to write a basic textbook.  I hoped, too, that my own struggles with everything mathematical would mean that I could write with a measure of empathy for the student, and also that an affordable book would equip them to go out and design experiments themselves.   Science, I was beginning to understand, was less about what you knew, and more about knowing how to find out what you didn’t know.


The cover of the statistics textbook I co-wrote for local students in Nigeria.  It was published by ABIC books, Enugu (ISBN: 978-022-038-0)

A new diatom record from West Sussex

Some part-time sleuthing on a sample that I was sent a couple of weeks ago have resulted in a new addition to the UK freshwater diatom flora.   The slide came to me from an Environment Agency laboratory with a question mark over a small diatom that was quite abundant but which did not match any of the species with which they were familiar.  It was a small diatom, only about 10 micrometres (1/100th of a millimetre) long, with very fine features, but there were enough features visible for me to realise that it was not something that I had seen before either.   I sent images off to a couple of colleagues and we decided that it was a species of Nupela, probably N. neglecta.

Nupela was only established in 1991. Before that, species that we now place in this genus were spread between Achnanthes and Navicula, as people struggled to understand its characteristics.   If you look at diatom keys written before Nupela was established (and several written subsequently – including my own), the presence of a raphe on either or both valves is seen as an important distinguishing characteristic, and the small number of genera that have a raphe on just one valve were generally assumed to be related.   Nupela, however, has some representatives that have a raphe on one valve (formerly placed in Achnanthes) and representatives that have a raphe on both valves (formerly placed in Navicula).  Nupela neglecta has a raphe on both valves, but one of the valves has raphe slits that only extend for about half the total length.   Stir in the small size and morphological details that are barely visible with the light microscope and there is ample scope for confusion.


Valves of Nupela cf neglecta with a full raphe.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  The double lines indicate a single valve at different focal points.  Photographs: Chris Carter.


Valves of Nupela cf neglecta with a short raphe.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  The double lines indicate a single valve at different focal points.  Photographs: Chris Carter.

The sample was collected from the River Stor, a tributary of the River Arun, in West Sussex, downstream of Storrington sewage works (NGR: TQ 0681 1641).  This is a small hard water stream (average pH: 7.9; average alkalinity: 170 mg L-1 CaCO3) with very high concentrations of nutrients (average dissolved reactive phosphorus: 0.99 mg L-1; average total oxidised nitrogen: 5.0 mg L-1).   These observations are similar to those made by Marina Potapova and her colleagues for habitatas where they found N. neglecta in the USA.  And this raises an interesting paradox: normally, the presence of a rare and exotic organism is considered to be a reason for conserving a habitat.  In this case, however, the rare species seems to be associated with a polluted habitat and, as a result, the Environment Agency will be doing their best to drive any organism that thrives here (however rare) to extinction.   Discuss.


Krammer, K. & Lange-Bertalot, H. (1991). Süswasserflora von Mitteleuropa2: Bacillariophyceae; 4. Teil: Achnanthaceae, Kritische Ergänzungen zu. Achnanthes s.l., Navicula s. str., Gomphonema, Gesamtliteraturverzeichnis Teil 1-4.  Spektrum Akademischer Verlag, Heidelberg.  (see p. 440 for account of Nupela)

Potapova, M.G., Ponader, K.C., Lowe, R.L., Clason, T.A. & Bahls, L.L. (2003).  Small-celled Nupela species from North America.   Diatom Research 18: 293-306.

Vyverman, W. & Compère, P. (1991).  Nupela giluwensis gen. & spec. nov.  A new genus of naviculoid diatoms.  Diatom Research 6: 175-179.

How to make an ecologist #11


The last time I had time to reflect on my professional life, I wrote about my time as a postdoctoral researcher studying the history of Mediterranean landscapes (see “How to make an ecologist #10”).  That was just an 18 month contract and as the months ticked down towards the conclusion, I had to think about what I wanted to do next.  Heather and I shared a desire to see more of the world but, rather than just follow the standard backpacker’s routes around the more exotic parts of the world, we wanted to settle somewhere (preferably warm) and live and work for a couple of years. But where, and what would we do?

The sad truth is that, having spent several years learning more and more about less and less, I had relatively few transferable skills that would make me employable outside my narrow specialism of freshwater ecology and, outside of the developed world, this pretty much limited me to work in universities or research institutes.   Ten years earlier, there were ample opportunities for British academics to work in Commonwealth universities, but there were few opportunities by the late 1980s.  I scanned the job vacancies in New Scientist and the Times Higher Education Supplement, but there were few that were worth pursuing.   As the time to the end of my contract started to be counted in weeks rather than months, I heard from someone that Nigeria was still recruiting lecturers.  I wrote a letter more in hope than serious anticipation and, to my surprise, both Heather and I were invited to interviews at the Nigerian education attaché’s office amidst the computer, hi-fi and photography shops on Tottenham Court Road in central London.   A letter arrived a couple of weeks later offering us both jobs at the University of Jos in Plateau State, central Nigeria.  I was to be a “Senior Lecturer” and Heather was “Lecturer #2”.   The prospect of two jobs made this doubly attractive even if the salaries on offer were miniscule.   Friends who had worked in Nigeria in the early 1970s had earned good salaries by UK standards, with plenty of benefits.  The Nigerian economy had, however, crashed in the early 1980s and local salaries were about a tenth of their UK equivalents.  However, we were young and idealistic, and living on local salaries would be no great hardship for a couple of years.  The point of our endeavours was to immerse ourselves into the local culture rather than just observe from the outside.  Living on the same – or similar – terms to those around us was a part of the deal.


The dusty backstreets of Kano, in northern Nigeria, photographed in 1990.  The top photograph shows calabashes on display in Kurmi market.

And so we landed at Kano airport in northern Nigeria in late November 1989, just days after the fall of the Berlin Wall.   The university had given us an extra baggage allowance so we travelled with two trunks and a couple of suitcases each, along with an uneasy sense of problems ahead as we got this all through customs.   Serendipitously, we had met, via a friend, a Nigerian Anglican minister called Henry who was doing an MA in Theology in Durham just as we were preparing to leave.   He had told us that he had a sister who was a customs officer at Kano Airport and took our names and flight details.  We thought nothing more of this at the time but, as we were queuing at passport control, a Nigerian official pulled us from the line and we were introduced to Henry’s sister and then fast-tracked through immigration.   It was our first experience of the myriad byzantine pathways by which one navigated Nigerian bureaucracies.  In two years we never had first-hand experience of the corruption that is rife in Nigeria’s public sector but this was the first of many instances where being a friend of a friend eased our way through the complexities of Nigerian official life.

And so we emerged into the noise and heat of the arrivals hall, wrestling to keep control of our baggage trollies from the many taxi drivers and touts, and looking for representatives of the University of Jos who we assumed would be waiting for us.   There was nothing.  Crowds milled around us, offers of taxis and hotels were shouted at us, but no-one came for us.  The mass of people slowly thinned out as our fellow passengers were met or found themselves taxis, but still we waited in the arrivals hall with all our luggage.  Eventually, after consultation with an airport official, all our luggage was piled into two taxis and we were ferried to the Central Hotel, the biggest and (at the time) most superficially luxurious of Kano’s hotels (the assumption being, I presume, that we were rich bature [white people] who would settle for nothing less).  We unloaded our luggage, paid the taxi driver in dollars, not having any local currency at this stage, and checked into the hotel.


Indigo dye-pits in Kano, northern Nigeria, 1990.

Kano is an ancient, dusty city, sitting at the south end of the trans-Saharan trade routes.   It is a fascinating place, with an old town still dominated by buildings in the traditional Hausa style, with traders lining narrow lanes selling a huge range of traditional and modern goods.   We would have our chances to explore  Kano on later visits but this first visit saw us confined to Central Hotel, trying to contact the University of Jos by telephone and, then, waiting for their driver to cover the 300 kilometres between the two cities to collect us.   It was mid-afternoon before he arrived and stared askance at the heap of luggage that he had to cram into his Peugot 504 estate along with us.   We were, however, about to get our first lesson in the ability of Nigerian drivers to wedge enormous amounts into what appears, at first glance, to be an impossibly small space.   Finally, we squeezed ourselves into the small spaces that remained once our luggage had been installed and the car pulled out of the Central Hotel’s car park and we headed into the northern Nigerian savannah for the last stage of our journey.


A reconstruction of Zaria mosque, built in the traditional Hausa style, at Museum of Traditional Nigerian Architecture (MOTNA), Jos, photographed in 1990.

Desmids on the defensive …


I made a short diversion back to the car after sampling at Ennerdale’s south-eastern end (see “Reflections from Ennerdale’s Far Side …”) crossing the boggy land behind the gravel spit and dipping into one of the pools to pull out a handful of submerged Sphagnum in the hope of finding some desmids, a group of algae that I have not looked at for some time (see “Swimming with desmids …” for my most recent post on this group).

Squeezing the water from a handful of Sphagnum from a bog pool into a vial and allowing the contents of this water to settle is usually a reliable way of collecting desmids; however, on this occasion the haul was rather meagre.  There were plenty of diatoms, but desmids were sparse and limited to a few Pleurotaenium and Euastrum species and some rather impressive cells of Xanthidium armatum.

The distinctive feature of the genus Xanthidium is the bristling armoury of spines around the margins.  The arrangement of spines varies between species and X. armatum has one of the most impressive collections, with bundles of three or four short spines at each angle.   The photograph below does not really capture the depth of the cell, and it is also not possible to see that there are two “decks” of marginal spines, but also bundles of spines on the top surfaces as well as at the margins.   This is truly a man-of-war amongst desmids.


Xanthidium armatum from a boggy pool at the south east end of Ennerdale Water, January 2017.  Scale bar: 10 micrometres (= 1/100th of a millimetre).  The photographs at the top of this post show the pool from which the sample was collected.

I’m intrigued by desmids but do not claim great competence with the group, so this is a good place to advertise a field meeting organised jointly by the British Phycological Society and the Quekett Microscopical Society.   We will be using the Freshwater Biological Association beside Windermere as our base but heading out to various desmid-rich locations in the Lake District over the course of the weekend.  There will be opportunities to look at other groups of algae too, but desmids will be the main focus of our weekend.  David John of the Natural History Museum will be helping with this group, but there will be experts on other groups available too.  If you are interested in coming, let me know and I will keep you informed as the programme evolves.

A simple twist of fate …


Amidst the dreary nothingness of the sample that prompted the previous post, I stumbled across the diatom in the photograph above.  This image gives a misleading impression as it is a relative large diatom with considerable variation in three dimensions and my first thought was that I was looking at a fragment of vaguely diatom-like structures amidst a unfocussed blur.   Careful use of the fine focus control revealed the twisted nature of the structure and I was able to create this semi-focussed image from a “stack” of images of the individual focal planes using Helicon Focus software.   The scale bar is 10 micrometres (= 1/100th of a millimetre).  As there are relatively few diatoms with a frustule with such a contorted form, it was relatively easy to identify it as Surirella spiralis Kützing 1844.

Surirella spiralis is one of a small number of diatoms whose outline is twisted.   There are diatoms that show considerable curvature within a single plane (see Stenopterobia sigmatella in “Reflections from Ennerdale’s Far Side”) but few where this curvature occurs between planes.   The only other diatom with this feature that I have written about in this blog are Entomoneis (see “A typical Geordie alga …”) and Cylindrotheca (see “Back to Druridge Bay”).   These twisted diatoms, like sigmoid diatoms such as Stenopterobia, typically have motile habits.  In my post on Stenopterobia I wondered what advantage a sigmoid outline conferred on a diatom and we really need to ask the same questions when thinking about twisted diatoms.  I have the germ of an idea, but want to think it over some more before unleashing it onto the world.

Surirella, Stenopterobia and Entomoneis are all members of an order of diatoms, the Surirellales, that are the subject of a recent paper by Elizabeth Ruck, from the University of Arkansas, and colleagues.  They compared morphology and genetic differences amongst members of this order, along with a related order, the Rhopalodiales, two of whose members are Epithemia and Rhopalodia, both of which I have also written about in this blog.   Their conclusion is that current generic limits need an extensive shake up with long-established genera that seemed to be based on sensible criteria when viewed with the light microscope split apart and reassembled, based on ultrastructural and genetic characteristcs.

The main changes relevant to a freshwater ecologist are as follows:

  • Campylodiscus: some freshwater species retained in Campylodiscus, some moved to Iconella; marine species moved to Coronia. The Fastuosae group of Surirella are now included in Campylodiscus;
  • Cymatopleura: now included in Surirella
  • Entomoneis: no change
  • Epithemia: all species now merged into Rhopalodia;
  • Rhopalodia: now includes Epithemia;
  • Stenopterobia: now included in Iconella;
  • Surirella: now limited to the Pinnatae group of Surirella, plus former Cymatopleura species;
  • The genus Iconella has been re-established for a group of former Surirella species (section Robusta) along with some freshwater Campylodiscus species and Stenopterobia. Of particular relevance to this post, Surirella spiralis is now Iconella spiralis (Kützing) Ruck & Nakov in Ruck et al. 2016; and,
  • The order Rhopalodiales has been subsumed into Suriellales.

It will be interesting to see whether or not, and how quickly, these names diffuse through the community of scientists who study diatoms.   Taxonomy has a dual nature: on the one hand, specialists are driven by a desire to understand how evolutionary forces have shaped and differentiated a group of organisms; on the other hand, taxonomists act as biology’s janitors, sorting and organising information about species so that other biologists can use this for their own purposes.   I am the editor and co-translator of a guide to European diatoms that was being finalised just as this paper was published and which, as a result, uses the “old” names.   These books often have a ten or twenty year shelf life which will prolong the use of these names, and slow the uptake of new ones.   I also know, from many years training people to analyse diatoms, that taxonomic changes, however well justified, sow confusion among beginners.   On the other hand, we are entering a new era, when molecular barcoding will be used more widely for routine identification of diatoms and, for this, a correct understanding of the phylogenetic relationships amongst a group of organisms improves the accuracy of the bioinformatics routines that assign names to the diatoms.

For most practical purposes, in other words, Surirella spiralis will remain S. spiralis for some time (and Stenopterobia sigmataella will remain S. sigmatella too), if only because of the innate conservatism of most of the people who work with diatoms.   My use of the old name in this post means that the part of my readership who know at least a little about diatoms could place the diatom within a familiar framework, even if Iconella spiralis is the correct name.   The term “post-truth” has entered our political vocabulary over recent months; in diatom taxonomy and identification, however, we sometimes have to accommodate “pre-truth” as well.


Ruck, E.C., Nakov, T.., Alverson, A. & Theriot, E.C. (2016).  Phylogeny, ecology, morphological evolution, and reclassification of the diatom orders Surirellales and Rhopalodiales.  Molecular Phylogenetics and Evolution 103: 155-171.

Ruck, E.C., Nakov, T.., Alverson, A. & Theriot, E.C. (2016).  Nomenclatural transfers associated with the phylogenetic reclassification of the Surirellales and Rhopalodiales.  Notulae algarum 10: 1-4.


When is a sample not a sample?


If you have followed this blog over the years, you will probably have worked out that the only inevitable outcome of a close study of diatoms is that you are older at the end than you were at the start. Whether you are also wiser is, alas, not guaranteed.   The older : wiser ratio can vary quite a lot, depending on what, exactly, you are studying and a further factor to stir into the mix is that a freelance ecologist such as myself needs to be prepared to forego the pursuit of wisdom if the price is right.

And so it is that I have spent a fair part of my time since Christmas staring down my microscope at a batch of samples that I have been sent whilst, at the same time, cursing my pecuniary instincts.   These samples are one part of a large survey and, I know, are not collected by people with any experience of freshwater algae.  Judging by the muddy sludge that I get in some of the sample tubes, I am not wholly sure that all can be trusted to distinguish a stream from a field, let alone find stones likely to yield a representative crop of diatoms.   But when, I wondered, after an hour hunting around a slide for fragments of diatoms to identify, do I throw up my hands and say “enough”?

The two photographs in this post are from one of these irksome slides.  In both cases, there is a single diatom but, also, quite a lot of mineral matter.   I would expect maybe five to ten diatoms in a field of view on a well-prepared slide from a good sample,.  In this one, there were more fields of view without diatoms than there were with (typically, I had to scroll past two empty fields between each identifiable diatom, but there could be as many as four or five empty fields between diatoms).   In theory, my first action when confronted with a slide such as this is to make another, more concentrated slide but this will also concentrate all that mineral matter.


A field of view with a single valve of Achnanthidium minutissimum (top right) from a sample from an unnamed stream.   The image at the top of the post shows a different field view, this time with a single valve of Cocconeis euglypta.  Note the large quantity of inorganic matter in the sample.

Here then, are a few questions to ask when you encounter a very sparse slide.

  • Who collected the sample? Do you trust them or not?   A lot of samples these days are collected by people who have little understanding of the ecology of benthic algae and who will not know when a sample is unlikely to yield enough diatoms for analysis;
  • Is there a lot of particulate matter that has resisted oxidation during the preparation stages? These might be telling you something about the habitat itself: mineral particles suggest a depositional, rather than an erosional, habitat.  Some organic materials, particularly from peaty habitats, are also resistant, and can obscure diatoms, unless a dilute preparation is made;
  • What is the state of the diatoms that are present on the slide? If a large proportion are broken, this may suggest that there was not a viable community of algae at the time the sample was collected and you are, in fact, counting diatoms that have been washed in from elsewhere in the catchment;
  • Do the diatoms that you do find in a sample tell a consistent story? Sometimes the diatoms I find in a sparse sample have ecological profiles which, when combined, suggests a particular interpretation but, on other occasions, I see samples that are both very sparse and very diverse, with species representative of several different environments.  When the ecological profiles are not broadly consistent then, again, it is a warning that you may be dealing with washed-in diatoms and fragments, and not an assemblage that is telling you much about the site in question.

I believe that you should be able to count at least 100 valves and have answered the second, third and fourth questions after no more than an hour’s analysis.  This is a good point at which to decide whether it is worth pushing on to complete the analysis or abandon the count.   I try to make this clear in my terms and conditions, emphasising that it takes about as long to decide that a sample cannot be analysed as it does to perform an analysis on a “normal” sample.   I should also emphasise that these suggestions apply to samples from rivers and lake littoral zones and different criteria may need to be applied when dealing with other types of samples (e.g. for palaeoecological or forensic work).

The judgements that you need to make are easier if you have direct knowledge of the site from which the sample was collected; however, this is often not possible.   As “streamcraft” is undervalued by managers (see “Primed for the unexpected” for my most recent moan on this topic), the natural habitat of the diatom analyst is the laboratory not the field and sample collection is often delegated to less-highly trained individuals.   The determination of my fellow analysts to wring every last mote of knowledge from empty silica frustules has also contributed to a greater focus on the laboratory, rather than the field.   Most of the time, to be fair, sample quality is not a factor.  We produced some PowerPoint presentations a few years ago to help people collect diatom samples (see “A cautionary tale…” for the whole story) and, let’s be honest, collecting a decent diatom sample should not be rocket science.   The question underlying all of these is whether or not the diatoms you have on a slide are an accurate representation of the assemblage of living diatoms present at a particular point in space and time.   If you cannot say “yes” with confidence, then you will certainly be older, but no-one will be any wiser.