Round Loch of Glenhead

Round Loch of Glenhead This is a lake in a granite catchment in Galloway, south-west Scotland, which was the focus of a number of studies in the 1970s and 80s. Palaeolimnological studies showed that the loch was naturally acid (pH ~5.5), but had become more acid from approximately 1850 onwards (pH <5.0), due to acid rain.  As a result of legislation on sulphur emissions, introduced partly as a result of these studies, the pH gradually increased and there has also been a shift in the ecology although, interestingly, not back towards the assemblage associated with pre-impact conditions.

Round Loch, epiphytic algae Submerged stones and plant stems in the littoral region of the lake  were surrounded by a dark brown translucent cloud, but as soon as I scooped it out of the water, it collapsed into an amorphous slimy gunk. are now coated with an amorphous, slimy brown gunk.   There is anecdotal evidence (R. Flower, unpublished) that these brown growths were either absent or much less conspicuous in the late 1970s and early 1980s when regular visits to the loch started. 
Round Loch of Glenhead, view down microscope Staring down my microscope at a sample of this gunk, I could see a rich mixture of algae. There were long filaments of a green alga called Mougeotia – cells whose chloroplasts were flat plates, which could rotate round the central axis of the cell in order to catch as much light as possible. Tangled around this were much thinner filaments of a blue-green alga called Lyngbya –a close relative of the Phormidium which we met in the River Wear, and chains of Round Loch of Glenhead, dioramaTabellaria, albeit a different species to the one we met in Wastwater. Within this tangled web, there were other algae: Merismopeodia, an ordered array of blue-green cells within a mucilaginous matrix; elegant vase-shaped cells of Dinobryon and, creeping through this tangle, diatoms. One was a species of Navicula but there were also larger boat-shaped cells – some almost a tenth of a millimetre long – of a type known as Frustulia.  And, to complete this submerged melange, there were trapped particles of peat, washed in from the catchment, and responsible for the dark brown colour of the gunk. Attached to the plant stems, I saw several cells of small, asymmetrical diatoms belonging to a genus called Eunotia, along with needle-shaped cells of another genus, Peronia.