The Bugs in our Brooks
Two years ago the NRN initiated a project to analyse chemically the quality of the water in streams in and around Eynsham. This has revealed the ubiquitous and persistent presence of high levels of eutrophic pollutants like phosphate and nitrate, along with a reduction in dissolved oxygen due to organic matter. We wanted to see how this water quality impacts the creatures that live in water because pollution changes the species that are present and reduces the diversity of species. We are fortunate that we have a local expert: Dr. Maarten van Hardenbroek van Ammerstol, from the University of Newcastle, who gave one of our popular 'Tiny Talks' during lockdown. As part of Green Week 2022 he led the Workshop, 'Bugs in Brooks', whose success has initiated a significant new component of our NRN water survey program.
Dr. Maarten van Hardenbroek van Ammerstol (‘Doc Maarten’) arrived in gum boots, riding a bicycle (evidently compulsory for Dutch citizens), laden with an embarrassment of riches – pans, petri dishes, fine instruments (various), buckets, a portable library, computer, water samples, etc., most of which he dexterously decanted onto trestle tables – and that was just the starter for 10. Additional equipment like kicknets and pipettes had been acquired by the NRN, thanks to a grant from the Oxfordshire County Council (OCC).
After introducing himself and briefing us on our Mission - get water - giving strict instructions not to frighten any horses, sheep, cattle or small mammals (e.g. children) that we might encounter en passant, Doc Maarten led the group off to try to acquire samples of the mysterious aquatic fauna that live in the Limb Brook and Wharf Stream. This was no easy matter and the group quickly noted that a doctoral education had not been wasted on Doc Maarten: he fearlessly blazed a trail through dense vegetation down a precipitous bank at several locations to get to the duck-weed-covered water.
The samples he managed to retrieve from the Limb Brook were more vegetation than water, however, so after demonstrating the Art of Kick-Netting under the bridge over the Wharf Stream, he poured the samples he had previously acquired from the Wharf stream and Chil Brook into what appeared to be photographic developing trays.
The shallow water settling in the white developing trays were instantly revealing of life, even to those us who were neophytes. Strange creatures of all shapes and sizes flitted, crawled, wriggled, danced, scrambled, snaked, swam, coiled, dived, rolled, paddled, or waved to attract our attention.
Doc Maarten gave a simple instruction: sort into petri dishes (flat transparent dishes) all creatures that look similar - and no need to know their Latin names - yet. Snails, worms, beetles, and various six or eight footed creatures (with or without segmented legs were gingerly removed from the photographic trays with tweezers or plastic pipettes. The Doc showed no such inhibitions, however, and dived in with his fingers to extract a snail, beetle, worm, or other multi-segmented, multi-legged, multi-jointed, multi-gilled denizen of the deep.
Soon the group had sorted what seemed to us naïve observers an astonishing array of aquatic animals – were these really our swimming companions? Particularly dramatic were the leeches (not a few!), but fortunately not the medicinal kind, which are the only ones that can penetrate skin. Still, under the magnifying lens a leech did look quite alien with its sucker waving around, seeking a snail, or fish on which to feed. Doc pointed to a small snaking red worm, which, he explained, was red because it contained haemoglobin, indicating that it lived in water with low oxygen and so its presence was not a good sign of healthy water. Non-biting midge larvae also were also present and are indicative of water polluted with sewage.
The easiest to spot, and one of the most frequent, were alderfly larvae – the six legs augmented by seven pairs of gills: a true ‘creepy-crawly’. Apparently the alderfly larvae, which also tolerate low oxygen, remain in the water for up to two years before pupating and emerging as adult alderflies, whose life is much more shorter-lived. The larvae feed on caddis flies and Doc soon found us a caddis fly home – a tube made of plant and silk. Again the caddis larvae lives much longer than the adult. Is there an evolutionary message there?