The skies are finally clear and we actually felt the sun on our faces for the first time this year on Monday, even if the biting wind made a fleece essential and views south down Loch Fynne were dominated by the snow-covered fells of Arran.
I had travelled about ten kilometres north from Knapdale to Kilmartin Glen, an area rich in Neolithic, bronze and iron age remains. It is a wide, flat-bottomed former valley with scattered basalt outcrops, leading down towards the Sound of Jura at Crinan. The valley bottom is grazing land, with the steeper slopes either moorland or plantation forestry or left as open moorland. Kilmartin Burn, which flows down the middle of the valley, looks far too small for the catchment it drains, as is often the case in these recently glaciated environments.
Kilmartin Glen, near Carnassarie Castle, Argyll and Bute, Scotland, April 2013.
The stream bed was surprisingly rich in vegetation, perhaps reflecting the relatively shallow slope here. Alongside the usual bryophytes that we expect in streams such as this there were some extensive growths of the water milfoil, Myriophyllum alterniflorum. I pulled up three shoots, popped them into a small glass vial with a few millilitres of stream water and shook them. The photograph below shows the water in the tube after I had removed the stems, brown with the epiphytes – the algae that live attached to and associated with the plant (the aquatic equivalent of ivy).
The left hand picture shows Myriophyllum alterniflorum in Kilmartin Burn, Argyll and Bute, Scotland in April 2013; the right hand picture shows three stems after they had been shaken in a few millilitres of water to remove epiphytes.
Myriophyllum has whorls of very finely-divided leaves – as if each had been reduced to just the veins. This means that it has a much higher surface area : volume ratio than a conventional leaf, making it easier to absorb nutrients and dissolved gases that it needs to grow. However, this also creates sheltered areas where diatoms and other algae (mostly diatoms in this example) can live a piggy-back existence protected from the stream current.
Diatoms growing on Myriophyllum alterniflorum in Kilmartin Burn. a. Ulnaria (Synedra) ulna; b. Meridion circulare; c. Cocconeis placentula. Scale bar: 10 micrometres (1/100th of a millimetre).
Under the microscope, I can see long, needle-like cells of Ulnaria ulna, fan-like colonies of wedge-shaped cells of Meridion circulare and elliptical cells of Cocconeis placentula. We encountered C. placentula in a very different habitat in Cassop Pond and it is a very common species in freshwaters throughout the UK and beyond. Ulnaria is a relative of the Fragilaria rumpens which we met at Cassop, albeit much larger. This population was composed mostly of cells that were about a tenth of a millimetre long, but they can grow to a quarter of a millimetre or more: veritable giants in the microscopic worlds where I spend so much of my time.