Research
The River Chess has been used as a site of scientific study by a range of students (from school children to PhD students) and academics.
Professor Roger Wotton of University College London describes his work on the ecosystem engineers of the River Chess:
We are all familiar with the common animals and plants of chalk streams – trout, banded demoiselle damselflies, water crowfoot – but less familiar with many of the organic materials that are carried by the current and which become deposited over the stream bed. Lift a water crowfoot plant and you will find an accumulation of fine mineral and organic particles deposited around its base. Some of these particles are clearly aggregates and, after examination under a microscope, are seen to be faecal pellets produced by invertebrates.
Since 1975 I have been working in northern Sweden on large rivers fed by snow melt. Here, huge numbers of faecal pellets produced by suspension-feeding blackfly larvae are transported downstream. My work on these rivers, with Professor Björn Malmqvist of the University of Umeå, has been published in a number of research papers (view a list of example papers) and we were lucky enough to receive a Royal Society grant to allow comparison with a lowland river. As I live in Berkhamsted, we chose the River Chess and used fine-meshed nets to collect organic matter being carried downstream. It came as no surprise to find that the faecal pellets of blackfly larvae were abundant and close examination of water crowfoot plants show thousands of these tiny animals to be anchored to the divided leaves, sometimes in such numbers that they convey a grey-brown colour to the edges of the plant.
In the last decade, the Natural Environment Research Council and the Environment Agency joined to promote studies on lowland streams – the LOCAR project, described at http://www.nerc.ac.uk/research/programmes/locar/. The chalk streams chosen were the Pang/Lambourn and the Frome/Piddle. These had been studied intensively for a number of years and were monitored to provide detailed hydrological records. Together with Dr Geraldene Wharton from Queen Mary University of London and Mr Jon Bass from the Centre for Ecology and Hydrology, I was awarded a grant to investigate the role played by water crowfoot plants in retaining organic matter (the basis of the nutrients supplying the ecosystem) and the effect of blackfly larvae in this retention (faecal pellets being very much larger than their constituent particles and thus much more likely to become deposited). Both water crowfoot and blackfly larvae are very significant players in this process (for a summary see: http://www.nerc.ac.uk/publications/planetearth/2005/winter/win05-farmersfishers.pdf). We could not have completed our work without the support of Dr Jacqui Cotton and Dr Luke Warren who were, respectively, Post-Doctoral Research Assistant and PhD student on our LOCAR project.
Having investigated the role of blackfly larvae in chalk streams, I then turned to another very common animal, the water shrimp Gammarus. Hold a net against the bed of a chalk stream, kick the stones in front of it and you will see just how abundant these animals are. Your net will likely contain hundreds of shrimps. Their method of feeding is quite different to that of blackfly larvae. Instead of using fans to filter out particles, Gammarus chews fallen leaves and other large detritus but it, too, then produces large numbers of faecal pellets. Dr Paul Joyce (a PhD student working with me on this project) found that these are deposited within the stony substratum and provide a store of organic matter which, again, is important in the chalk stream ecosystem, providing nutrients for plants and also providing food for invertebrates, just as do blackfly larval faecal pellets. All the work on Gammarus was based on the River Chess.
In summary, water crowfoot, blackfly larvae and Gammarus can all be described as ecosystem engineers. The crowfoot plants create fast-flowing channels that keep their leaves clean (and provide spawning grounds for fish) and yet promote the retention of organic matter adjacent to their roots. Blackfly larvae engineer faecal pellets that are many times larger than the tiny particles that they collect from the water column and Gammarus chews up larger particles of detritus to make many smaller faecal pellets which are retained in the substratum. Chalk streams are, indeed, interesting and important ecosystems.
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