The series of events that eventually gave birth to this blog started with a visit to the River Wear at Wolsingham on the first day of 2009. I had visited on a whim, intending to blow away the cobwebs after lunch on New Year’s Day, but with no real plan. But I thought it would be interesting to pull on my waders and have a look at the river bed and, while I was there, I may as well collect a sample too. Those observations and that sample must have triggered something in my mind, because I returned every month after that and, on each occasion, the samples and observations generated sketches which, in turn, made me curious about the factors that drove the algal communities in our rivers.
I thought it would be interesting to repeat that exercise during 2018 as my thinking has moved on over the past nine years. I’m essentially visiting the same site and making the same observations but, this time, filtering them through deeper beds of experience. The River Wear at this point is about 30 metres wide, a broad, shallow, riffled stretch, skirting the small town of Wolsingham roughly at the point where Weardale broadens out from a narrow Pennine valley to the gentler landscape of the Durham coalfield. There are a couple of small towns upstream but the ecological condition of the river is still good. Although there are still concerns about concentrations of heavy metals arising from the mines that are scattered around the upper parts of the valleys, I can see no serious effects of toxic pollution when I look at the plants and animals that live at Wolsingham.
If you follow this blog you will not be surprised to hear that, even in the depths of winter, algal communities in the River Wear are thriving Most of the larger stone surfaces are covered with a discernible brown film, up to a couple of millimetres thick. The very top layer is dark brown in colour, with a lighter brown layer beneath this. When I put a sample of this under my microscope, I saw that it was dominated by gliding cells of Navicula lanceolata, though other diatoms were also present (described in more detail in “The ecology of cold days”) and there were also a few thin filaments of a blue-green alga.
A submerged cobble photographed in situ in the River Wear at Wolsingham, January 2018, covered with a thick diatom-dominated biofilm.
I’ve included a picture of the view down my microscope because one of the questions that I’ve been trying to answer over the past few years is how we construct an understanding of the microscopic world using microscopy (see “The central dilemma of microscopy” and “Do we see through a microscope?”). Of course, a single view field of view does not convey all the information I require, so my understanding is actually built up from observations of a large number of separate fields. The boat-shaped cells of Navicula lanceolata were almost ubiquitous in these, as were patches of amorphous organic matter (“fine particulate organic matter” – see “A very dilute compost heap …”). In total, I found 15 different species of algae in my preliminary analysis, of which Navicula lanceolata comprised about half of the total, with thin filaments of the cyanobacterium Phormidium and the diatom Achnanthidium minutissimum each constituting about 15 per cent.
A view of the biofilm from the River Wear, Wolsingham in January 2018.
However, my earlier comment about the biofilms having distinct layers means that simply observing what organisms are present will not tell us the whole story about how those organisms are organised within the biofilm (see “The multiple dimensions of submerged biofilms …”) so the next step is to hypothesise how these organisms might be arranged in the biofilm before I disrupted their microhabitat with my sampling. The schematic diagram below attempts to capture this, but with a few provisos. First, I said that the biofilm was a couple of millimetres thick but my portrayal only shows about a tenth of a millimetre; second, there is considerable spatial and temporal variation in biofilms and my depiction amalgamates my direct observations in January 2018 with information gleaned from a number of other visits. Gomphonema olivaceum (probably a complex of two or three species in this particular case), for example, is often more prominent than it was last week, and I have also omitted Achnanthidium minutissimum altogether. I suspect that this is less abundant in the mature biofilms but that the cobble surface is a patchwork of different thicknesses, reflecting different types of disturbance. That raises another issue: the scale at which we generally collect samples is greater than the scales at which the forces which shape biofilms operate. The whole image below, for context, occupies about the same width as a single bristle on the toothbrush that I used to collect the sample.
It is difficult to convert what we “see” back to the original condition when working under such constraints and, inevitably, decisions are guided by what others before us have written. That brings a different set of problems: Isaac Newton may have seen further by “standing on the shoulders of giants” but Leonardo da Vinci’s usually rigorous objectivity lapsed on at least one occasion when his eye was led by assumptions he had inherited from earlier generations (see “I am only trying to teach you to see …”). What my picture is actually showing, in other words, is a mixture of what I saw and what I think I should have seen. This two-way process in art extends from the very earliest drawings we make through to the most sophisticated Old Masters so I am in good company. In truth, I am not trying to depict a particular point in space or time so much as to encapsulate the idea of a biofilm from that river that is more than a random aggregation of cells.
A schematic view of the vertical structure of a submerged biofilm from the River Wear, Wolsingham, January 2018. a., Navicula lanceolata (valve view); b., N. lanceolata (girdle view); c. Navicula gregaria (valve view); d. N. gregaria (girdle view); e. Gomphonema olivaceum (valve view); f. G. olivaceum (girdle view); g. Phormidium; h. inorganic particles; i. fine particulate organic matter. Scale bar: 20 micrometres (= 1/40th of a millimetre).
You can find out more about the condition of the River Wear (or any other river or lake) using the Environment Agency’s excellent Catchment Planning webpages
Three good books that discuss the relationship between pictorial representation and the mind are:
Cox, Maureen (1992). Children’s Drawings. Penguin, Harmondsworth.
Gombrich, E.H. (1977) Art and Illusion: a study in the psychology of pictorial representation. 5th Edition. Phaidon, London.
Hamilton, James (2017). Gainsborough: a Portrait. Weidenfield & Nicholson, London.