The previous post focussed mostly on the higher plants that I found in the short stream that connects White’s Level with Middlehope Burn. I mentioned the mass growths of algae that I found growing immediately below the entrance to the adit, but I did not talk about them in any detail, instead spinning off on a tangent while I mused on why the water cress had a purplish tinge.
When I did find time to examine the algal floc, I found it to consist of a mix of three different algae, the most abundant of which was Tribonema viride, but there were also populations of a thin Microspora (not illustrated) and Klebsormidium subtile. I talked about Tribonema in the drainage from the Hadjipavlou chromite mine in Cyprus last year (see “Survival of the fittest (1)”) and both Microspora and Klebsormidium are also genera that are known to frequent these habitats. Indeed, there is evidence that the populations that grow in these extreme habitats have physiological adaptations that help them to cope with the conditions. Brian Whitton, my PhD mentor, led several studies on these adaptations in the streams of the northern Pennines in the 1970s, and Patricia Foster did similar studies in Cornwall at about the same time. There is probably a mixture of physiological strategies involved, including the production of low-molecular weight proteins, which bind the toxic metals, and the production of extracellular mucilage. Most of the populations I find in such habitats have a distinctly slimy feel due to the production of extracellular polysaccharides, and it is possible that these play a role in trapping the metal ions before they can get into the cell and cause damage.
Filamentous algae from the drainage channel below White’s Level, upper Weardale, April 2020. a., b. & c.: Tribonema cf. viride, showing the characteristic H-shaped cell ends. d. Klebsormidium cf. subtile. Scale bar: 10 micrometres (= 100th of a millimetre). The picture at the top of the post shows an artist’s impression of Chamaesiphon cf. confervicolus on the upper surface of a Potamogeton polygonifolius leaf.
I also had a look at the algae growing on the submerged leaves of Potamogeton pergonifolius in the channel between the adit and Middlehope Burn. One easy way of examining them is to add a small amount of stream water then shake the leaves vigorously in a plastic bag. The result is a brownish suspension of algae that can be sucked up with a Pasteur pipette and placed on a microscope slide. When I did this, I found a community that was dominated by a short cyanobacterium, closest in form to Chamaesiphon cf. confervicolus. The other abundant alga in the sample was Achnanthidium minutissimum, which is often common in minewaters, along with smaller numbers of a few other species. The total number of species in the sample was just 12, which is low by the standards of streams without metal pollution, but such suppression of all but the hardiest species is another characteristic effect of heavy metal pollution.
I’ve added a “cf” (from the Latin conferre, meaning “compare to”) to my identification of Chamaesiphon confervicolus because this is the closest name, based on a comparison with images in the Freshwater Algal Flora of Britain and Ireland. However, it is not an exact match. Whether this is because the metals have strange effects on Chamaesiphon (as we saw for diatoms in “A twist in the tale …”) or whether our knowledge of the species within this genus is imperfect is not clear. But discretion is the better part of valour in this instance. Chamaesiphon species fall into two groups: those that live on stone surfaces (see “Survival of the fittest (2)”) and those that live on algae and plants, such as the one we see today (another is illustrated in “More from the River Ehen”). They consist of a single, elongate but gently tapering cell, attached at one end to the plant and enclosed in a sheath. The upper end of the filament forms small spherical buds (technically “exospores”). One reason that I am wary of calling this population C. confervicolus is that most illustrations of this species show a stack of exospores in the sheath, whereas the White’s Level population all had just a single exospore.
Chamaesiphon confervicolus, growing on Potamogeton polygonifolius in White’s Level outflow, April 2020. Note the exospores at the end of the cell. f. and g. show the sheath very clearly. Scale bar: 10 micrometres (= 100th of a millimetre).
The picture at the top of this post shows an artist’s impression of the Chamaesiphon cf confervicolus on the upper surface of the Potamogeton leaf. I wanted to get some idea of the size, shape and arrangement of the epidermal and stomatal cells on the Potamogeton leaves and resorted to the tried and tested technique of painting a layer of clear nail varnish onto the leaf surface, then peeling this off when it had dried. This had the added (and unexpected) benefit of also pulling of the epiphytes, giving some idea of their arrangement on the leaf surface at the same time. One extra observation that this yielded was that upper surface was dominated by Chamaesiphon, growing in clusters, whilst the lower surface had greater representation of diatoms. I’ve also tried to portray the chloroplasts in the stomata guard cells. Plant epidermal cells generally do not contain chloroplasts, as their purpose is to protect the mesophyll cells that are the main centres of photosynthesis. Guard cells of stomata, however, need energy to open and close the stomata so these are the exception to this rule. I had not even been sure that I would see stomata on the upper surface of the cell, as these are mostly found on the underside of leaves; however, Potamogeton appears to have stomata on both surfaces. As ever, there is a certain amount of evidence along with a dose of extrapolation. Imagined, but not imaginary …
You can find a description of the terrestrial plant life of Slitt Mine and its environs in this post on Heather’s blog.
Foster, P.L. (1982). Metal resistances of Chlorophyta from rivers polluted by heavy metals. Freshwater Biology 12: 41-61.
Harding, J.P.C. & Whitton, B.A. (1976). Resistance to zinc of Stigeoclonium tenue in the field and the laboratory. British Phycological Journal 11: 417-426.
Robinson, N.J. (1989). Algal metallothioneins: secondary metabolites and proteins. Journal of Applied Phycology 1: 5-18.
Say, P.J., Diaz, B.M. & Whiton, B.A. (1977). Influence of zinc on lotic plants. I. tolerance of Hormidium species to zinc. Freshwater Biology 7: 357-376.
Sorentino, C. (1985). Copper resistance in Hormidium fluitans (Gay) Heering (Ulotrichaceae, Chlorophyceae). Phycologia 24: 366-368.
(Note that Hormidium is the old name for the genus Klebsormidium. There is an orchid genus called Hormdium and, as this was described first, it takes priority.)
Some other highlights from this week:
Wrote this whilst listening to: Bob Dylan’s New Morning and Pat Garrett and Billy the Kid. Also, Samuel Barber’s Prayers of Kirkegaard.
Cultural highlights: The Netflix series Unorthodox, about a young woman fleeing a Hassidic community in New York.
Currently reading: Agatha Christie’s A.B.C. Murders.
Culinary highlight: Arroz con leche (Spanish rice pudding) served with peaches poached in madeira.