Rewriting history at Talkin Tarn …

One of the joys of modern technology is the ability to right obvious wrongs.   So, having watched my wife’s crew struggle in a regatta at Talkin Tarn, near Brampton, last weekend, having been entered in the wrong class and the wrong age category and then racing in a men’s rather than a woman’s boat, I had no option but to turn to Photoshop for justice.   Here, in a rewritten version of the Talkin Tarn regatta, you can see the DARC novice women’s coxed four half a length head of their opposition with about 400 metres to go.   The backdrop is the Pennine fells, looking north towards Hadrian’s Wall.


Talkin Tarn regatta 2014: DARC novice women’s coxed four half a length ahead of the opposition.  

I have to confess that the entertainment value of watching one crew busting a gut to go slightly faster than another crew pales after the first hour, so I wandered off to poke around the lake’s margins.   The water here contained some just discernable green specks, all between about half a millimetre and a millimetre across.   Under the microscope, these resolve into spherical colonies each composed of filaments which gradually taper from the base.   These colonies belong to a cyanobacterium (blue-green alga) called Gloeotrichia echinulata. I’ve written about relatives of Gloeotrichia in previous posts (“Blue skies and blue flowers in Upper Teesdale”, “”Looking” is not the same as “seeing” …”, “More about Rivularia”) and have commented that the large light coloured cells, called “heterocysts” are responsible for nitrogen fixation, which enables the alga to grow even when nitrogen is relatively scarce. In the case of Talkin Tarn, the scarcity is probably not absolute but relative to other nutrients such as phosphorus. It means that the Gloeotrichia can grow even when the supply of this important nutrient has run out.


Colonies of Gloeotrichia echinulata in a drop of water from Talkin Tarn, July 2014.   The drop is 12 millimetres across.

One other difference between the filaments of Gloeotrichia and those of Rivularia is the dark specks inside the cells.   These are gas vacuoles which make the cells and colonies of Gloeotrichia more buoyant than other algae. Leave a sample from Talkin Tarn to stand for a while and the colonies of Gloeotrichia will rise to the surface. This gives cyanobacteria a competitive advantage over other algae in lakes as they now have an adaptation that keeps them closer to the sunlight which powers their photosynthesis as well as one that helps them to overcome nitrogen limitation and an adaptation.   It is no surprise that cyanobacteria are so prolific in lakes around the world.


Microscopic views of a Gloeotrichia echinulata colony from Talkin Tarn.   The left hand image shows an entire colony, about half a millimetre across.   The right hand image shows the same colony at higher magnification.   Note the large, round light-coloured heterocysts at the base of each filament. Scale bar: 10 micrometres (= 1/100th of a millimetre).

Gloeotrichia also has the ability to produce compounds called “microcystins” which are powerful toxins.   There are many records of livestock, dogs and humans suffering liver damage through ingesting contaminated water.   Although the rowers at Talkin Tarn were warned to wash their hands after racing, the risk is only high if a large amount of Gloeotrichia-containing water is swallowed. That is unlikely in a sport such as rowing, where the idea is to stay in the boat, but swimming in Talkin Tarn would not be a good idea. Rowing, though, is not without such dangers: the Durham women’s novice crew’s previous opponents suffered an “ejector crab” at the start which dumped one of them into the River Wear. On that occasion, cyanobacteria in the River Wear were the least of their worries and the Durham crew were able to cruise serenely down the river to a glorious victory.   Photoshop not required.



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