Arnside and beyond

By gladders


Bogbean, Menyanthes trifoliata, Sunbiggin Tarn, Cumbria. Bogbean is a common plant of the edges of upland tarns and lakes, or in boggy places where it can keep its feet wet. It was growing here at the edge of the tarn, in dark water sparkling in the bright sunlight. It's not always easy to get close enough for a good look at its flowers, but with its frilly petals, yellow stigma and red stamens, it is surely one of our prettiest wild plants.

While all too many days are spent in meetings or in front of a computer at work, I do occasionally get out to remind myself of what it is ultimately all about. Today I joined Mags and Alan P, an expert on algae. Alan has been contracted to identify the algae growing in Sunbiggin Tarn, and as well as collecting algal material he was also taking water samples for analysis. So we bobbed about in our little inflatable boat, trying to stay in one place, while he took samples.

Sunbiggin is unusual in being a marl lake, enriched with calcium carbonate. It is set in an upland limestone landscape, surrounded by one of the most botanically rich areas in the English uplands. Most of our tarns in Cumbria are in the catchments of very acidic rocks, and consequently have a very different aquatic plant flora. Sunbiggin is the more unusual for having been the site of a breeding colony of thousands of black-headed gulls until about 15 years or so ago. One might have expected that the gull guano would have had a disastrous effect on the nutrient status of the tarn, and that it would be like pea soup as a result. But it isn't, and the bed is covered in stoneworts, which are usually indicative of high water quality. The lime in the water may have helped to bind the phosphorus, and render it unavailable to algae. Alan's work should help us piece together what is going on.

So, a very relaxing and stimulating day, to make up for the long journey to London and back yesterday.

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