Wednesday, 30 April 2014

A short excursion to the pools of Avalon

High on the Northumberland coast, as the long shores of Druridge, Embleton and Beadnall turn into towards the Scottish border, lies Holy Island. Always an extraordinary place, whether the idling in a glittering June seascape or hunkered down against winter which reaches across from Scandinavia. Holy island may be an inspiration for Authurian Avalon. The Borders have a long claim on many elements of the Arthurian legend. Our trip was less romantic, though only slightly so as the sea fret plumes rolled in over the salt marsh and swallows strafed low for sluggish insects. Right by where the causeway road to the island dips from the mainland down to the tidal stretches there are a scatter of perfect salt marsh pans, usually in clusters just in front of the second world war anti-tank blocks. The pools are ideal for students to try out the ups and downs of sampling in the field: why do oxygen probes never seem to work coherently? Yes... you need to take the plastic cover of the pH probe before it will take a reading. We were testing for spatial patterns: for example are neighbouring pools more similar in their animal life than pools further and  were there salinity gradients as you go from the salt flats up into the pools amongst toppled tank traps.
The students pulled together some revealing data. Here they are piloting where exactly to take pH measures and whether the position of the samples in and around the pools alters the outcome. All of the pools showed marked brackish conditions, though declining slightly higher up the marsh amongst  the tank block pools. The fauna of adjacent pools was markedly more similar than further apart sites. Pond area seemed to bear no relation to overall numbers of taxa. Shrimps, mosquitoes, isopods slaters and gammarid shrimps were abundant, with beetles, copepods and fly larvae as bit part players. Towards midday the sun burnt away the thicker fret, although Holy island itself came and went as if anchored on the tide. High tide itself chased a few excited walkers back along the road to the safety of the mainland, just in time for an ice cream van to materialise through the last of the mist. A perfect day out on the marshes, between the incoming tide and an arc of skylarks singing over our heads throughout

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