I know that the focus of this blog can meander, depending on what takes my fancy week-to-week. My core business is, however, writing about the hidden world of algae so, having written about Sam Mendes’ use of the River Tees Upper in his film 1917 in my previous post, I thought that I ought to take a trip up Teesdale to take a closer look at what is growing in the river at this time of year. With Storm Ciara looming ominously on the forecast, I knew that if I did not sacrifice my Saturday morning it might be a while before I had another opportunity (there’s a graph at the end of this post which confirms this hunch). And so I found myself buffeted by the wind with clouds scudding across the sky and the peaty water of the Tees thundering across the sequence of cascades that make up Low Force.
The main river was, even after a period without much rain, too deep and fast-flowing for me to venture far in so my activities were confined to the margins. The rapid current, however, means that there were few of the small and medium-sized stones that I would normally remove and inspect. Most had been picked up and transported further downstream leaving wide expanses of the Whin Sill bedrock. In the shallow areas towards the edges that were not exposed to the full force of the current, there were dark green patches that I picked at with a pair of forceps. When I was able to look at these under my microscope, I saw that they were Ulothrix zonata, a common inhabitant of northern British streams during the winter, and an alga that I have written about previously (see “The intricate ecology of green slime …” and “Bollihope Bhavacakra” amongst others).
Ulothrix zonata growing on Whin Sill in the River Tees at Low Force, Teesdale in February 2020. The upper and central pictures on the left hand side show vegetative filaments and the lower picture shows empty cell walls after zoospores had been released, to which a germling is attached. Scale bar: 20 micrometres (= 1/50thof a millimetre).
The rocks were very slippery, even when not covered by green patches of Ulothrix zonata. My usual approach to collecting specimens is to remove the whole stone and scrub the top surface with a toothbrush. That, however, was impossible here so I had to resort to brushing the surface of the Whin Sill and hoping that enough of the slippery film remained attached to my toothbrush, which I then agitated in a bottle containing some stream water to shake the gunk off before repeating the process. The small amount of material that I did manage to transfer from the rocks imparted a chocolate-brown hue to the water that signifies that diatoms were present.
Sure enough, when I did get a drop of the suspension under my microscope, there were diatoms aplenty, mostly wedge-shaped cells of Gomphonema growing at the end of long, branched mucilaginous stalks. These, like Ulothrix zonata, are very common in northern British streams at this time of year. I described similar assemblages from the River Wear at Wolsingham although, in that case, the Gomphonema shared their habitat with motile Navicula species as well (see “The River Wear in January”). The Gomphonema in the River Tees is most likely G. olivaceum or a relative but I will need a closer look to be sure. If I used an old Flora such as Hustedt’s 1930 Süsswasser-flora Mitteleuropas, I would have been able to be more assertive in naming this “Gomphonema olivaceum” but we now know that diatom systematics are more complicated than was thought to be the case in Hustedt’s days.
Gomphonema olivaceum-type colonies growing on Whin Sill in the River Tees at Low Force, Teesdale, February 2020. Scale bar: 20 micrometres (= 1/50th of a millimetre).
The sequences of 2017 were filmed in June not January so George Mackay would not have found the bedrock of the Tees to be quite as slippery as it was on my visit. As the water warms up, grazers become more active and, as a result, the biofilms in the summer are much thinner than those in January. That means that fewer slippery, slimy polysaccharides are produced, making it easier to keep your balance when walking at the edges of the river.
As I mentioned in my previous post, the sequence in 1917 involves George Mackay falling into a river in Picardy but crawling out of a river in Upper Teesdale. I know less about the rivers of Picardy than I do about those in northern England, but a combination of low relief, extensive canalisation and the presence of heavy industry and coal mining in the area will mean that the algae found there will be very different to those in the Tees. However, if 1917 can get 10 Oscar nominations (including for best sound editing) despite having the call of a Great Northern Diver echoing over No-man’s Land, then we can be fairly sure that the Wrong Sort of Algae is a level of detail that Sam Mendes and Roger Deakins thought they could safely ignore.
You can find some information about the diatoms of Picardy rivers in this paper:
Prygiel, J. & Coste, M. (1993). The assessment of water quality in the Artois-Picardie water basin (France) by the use of diatom indices. Hydrobiologia 269: 343-349.
This week’s other highlights:
Wrote this whilst listening to: Michael Kiwanuka and other acts who will be playing at the Green Man festival in August. I’ll be there too, talking about slimy algae, at Einstein’s Garden, the on-site science festival, along with (I hope) a gang of volunteers from the British Phycological Society.
Cultural highlight: Two picks this week. The first was Monteverdi’s Vespers performed at Durham Cathedral. The cavernous interior of the cathedral joins the choir and orchestra as part of the experience, providing resonances that raise the experience beyond anything that a CD can offer. The second is Bong Joon-ho’s film Parasite, a strong contender, along with 1917, at this evening’s Oscar Awards Ceremony.
Currently reading: John le Carré’s Mission Song
Culinary highlight: a Napoli pizza cooked with locally-grown flour (www.gilchesters.com), part of a push this year to source more of our ingredients locally. There’s obviously more to a Napoli pizza than can be grown in the UK but it is a start.
River levels at the Tees at Middleton-in-Teesdale (x km downstream from Low Force) in the week from 3 to 9 February 2020. The arrow shows the time of my visit; note the steep rise in level a few hours later, coinciding with Storm Ciara moving through the region. Graph from the excellent https://riverlevels.uk website.