Having investigated the microscopic world at Wolsingham (see “The River Wear in January” and “The curious life of biofilms), I decided that it would be interesting to head further upstream and see how much difference there was between the algae at the two locations. I drove up to Wearhead on a cold Saturday morning to take a look but was immediately faced with a conundrum: the River Wear is formed from the confluence of two very different streams, both with extensive catchments on the moors of the northern Pennines. One of these is Burnhope Burn, which is fed by Burnhope Reservoir, about a kilometre above Wearhead, and the other is Killhope Burn, which drains a large area of blanket bog, forestry and, importantly, abandoned metal mines. Burnhope Burn is on the left of the photograph above whilst Killhope Burn comes in from the right. I thought it might be rather interesting to take a sample from each and see how they compared.
The two streams look quite different to one another. Burnhope Burn, its flow regulated by the reservoir, is the Cain of the pair whilst Killhope Burn is the unruly turbulent Abel. This was apparent, too, when I was collecting the samples and, again, when I peered at them through my microscope. Burnhope Burn’s biofilm was thicker and the most conspicuous algae that I could see were green filaments of Klebsormidium. Killhope Burn’s was thinner and dominated by diatoms. Many of the same diatoms were found in the two samples, but Burnhope Burn had more of the motile Nitzschia species that benefit from the tangled matrix of green algal filaments that thrived there.
Views of the biofilm from Burnhope Burn (a.) and Killhope Burn (b.) just above their confluence to form the River Wear, February 2018.
I’ve tried to capture the essence of the biofilm from Burnhope Burn in the schematic diagram below. Compare this with the diagram of the biofilm from the Wear that I showed in my earlier post. In both cases, we have a mix of organic and inorganic elements, with the organic matter further divided into living organisms and agglomerations of particulate matter. A few of the species are common to both but there are also some notable differences. The biofilm in the Wear, for example, had almost no green algae (though that may change over the coming months) whilst that from Burnhope Burn has many filaments of Klebsormidium. There were motile diatoms at both locations but the species are different: Navicula lanceolata and N. gregaria at Wolsingham and Nitzschia dissipata at Burnhope Burn. People usually describe differences in the ecology of diatoms in terms of their chemical environment but I sometimes wonder if, in the case of motile diatoms, the nature of the matrix within which they live also plays a role in determining which thrive.
The difference between Burnhope and Killhope Burns is a variation of the theme that I discussed in “Small details in the big picture …”. Again, regulation of a river or stream plays a role in determining which species of algae can thrive. However, whereas I found a lot of Platessa oblongella in the unregulated streams of the Ennerdale catchment, the more base-rich environment of the Pennines means that I am much less likely to find P. oblongella in these streams. In fact, I don’t think I have ever seen it in north-east England (see distribution maps in “Why do you look for the living amongst the dead”).
That reminds me: I was going to write more about the ecology of Platessa oblongella before I was diverted by desmids and Wearhead. Soon …
A schematic view of the vertical structure of a submerged biofilm from Burnhope Burn, Wearhead, February 2018. a. Klebsormidium fluitans; b. Phormidium; c. Nitzschia dissipata (valve view); d. N. dissipata (girdle view); e. Gomphonema cf. calcifugum (valve and girdle views); f. inorganic particles; g. fine particulate organic matter. Scale bar: 20 micrometres (= 1/40th of a millimetre).