The Ecology of Cowside Beck, a Tributary of the River Skirfare in the Malham Area of Yorkshire
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The ecology of Cowside Beck, a tributary of the River Skirfare in the Malham area of Yorkshire Oliver Gilbert, Helen Goldie, David Hodgson, Margaret Marker, Allan Pentecost, Michael Proctor and Douglas Richardson Dedicated to the memory of Oliver Lathe Gilbert 7th September 1936 - 15th May 2005 Published by Field Studies Council, Malham Tarn Field Centre, Settle, North Yorkshire BD24 9PU. Tel: 01729-830331 E-mail: [email protected] www.field-studies-council.org Copies of this report may be purchased from the Field Centre. This report can also be consulted on the website above. Contributors The late Oliver L. Gilbert (formerly Department of Landscape, University of Sheffield) Helen Goldie (Department of Geography, University of Durham) 2 Springwell Road, Durham DH1 4LR David Hodgson (The Craven Pothole Club) 9 Craven Terrace, Settle, North Yorkshire BD24 9DF Margaret Marker (formerly School of Geography and Environmental Science, Oxford University) 5 Wytham Close, Eynsham, Oxon OX29 4NS Adrian Norris (formerly The Leeds Museum Resource Centre) 17 West Park Drive, Leeds LSl6 5BL Allan Pentecost School of Health and Life Sciences, Kings College, University of London, 150 Stamford Street, London SE1 9NH Michael C. F. Proctor School of Biosciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter EX4 4PS Douglas T. Richardson (formerly Department of Earth Sciences, University of Leeds) 5 Calton Terrace, Skipton, North Yorkshire BD23 2AY If you would like to be involved in this work please contact: Cowside Beck Research Project at Malham Tarn Field Centre ii Contents Foreword (Adrian Pickles) 1 Introduction (Oliver Gilbert) 2 Physical background: Geomorphology (Helen Goldie, Margaret Marker) 4 Physical background: Water chemistry (Michael Proctor, Douglas Richardson) 9 Lower Plants Aquatic bryophytes (Michael Proctor) 12 Lichens (Oliver Gilbert) 15 Freshwater algae (Allan Pentecost) 20 Freshwater invertebrates (Douglas Richardson) 23 Mollusca (Adrian Norris) 25 Cave studies (David Hodgson) 27 Discussion (Oliver Gilbert) 29 Further Research (Michael Proctor, Adrian Pickles) 35 Acknowledgements 36 References 36 Appendices Appendix 1. Water chemistry (M.C.F. Proctor; D.T. Richardson) 38 Appendix 2. Bryophytes (M.C.F. Proctor) 42 Appendix 3. Algae: diatoms (D.T. Richardson) 43 Appendix 4. Freshwater invertebrates (D.T. Richardson) 45 Colour Plates iii Foreword In 2001 Oliver Gilbert dropped the pebble of an idea into the Research Seminar pool - the idea of a group working collaboratively on Cowside Beck. This is the second report arising from the ripples of Oliver’s pebble. Oliver compiled the first draft of this report; the final version was completed by Michael Proctor and collated by Elizabeth Judson. Oliver saw almost all of this report before he died. He was delighted that so much work had been done and in his last letter to me, written just 6 days before the end, was thinking about the next stage of the work. There can be very few research groups focused on one relatively small geographical area that cut across traditional subject boundaries, across the professional-amateur divide and which engage conservation professionals, land owners and managers with active researchers. The Cowside Beck research project is a rare thing; it should be nurtured, not only for the memory of Oliver Gilbert but for the understanding it can help us develop about a special place, that will serve as an exemplar for others. I hope that the ripples from Oliver’s unassuming inspiration continue to spread in the future. Adrian Pickles Malham Tarn Field Centre November 2005 1 Introduction This project was an outcome of the second Malham Tarn Research Seminar (16-18 November 2001) at which a number of participants from different disciplines decided to collaborate in an interdisciplinary study of the Cowside Beck, the next valley just to the north of the Field Centre. In A Nature Conservation Review, (Ratcliffe 1977), the Malham–Arncliffe group of open water sites including Cowside Beck is listed as Grade 1* and the beck is described as ‘A good example of a torrential upland limestone stream’, in spate, ‘the water level rising by at least 1.5 m.’ It is a part of the Malham/Arncliffe SSSI, and falls within the Craven Limestone Complex Special Area of Conservation. English Nature (1994 a,b) classified Britain’s rivers into six major types based on their geology and vegetation. Twenty-five examples were proposed as a national series of river SSSIs. They included in the section ‘Mountains and Moors’ the Malham /Arncliffe streams which include Cowside Beck and its tributaries; these were the object of our study. Inevitably the coverage of this report is uneven. A good deal was already known about the freshwater algae (Lund 1961, Pentecost 1981, 1991, 1999), the geology was known in some detail (Shaw 1982; Arthurton, Johnson & Mundy, 1988)), and some information was on record for the lichens (Gilbert 1996, Seaward & Pentecost 2001) and bryophytes (Proctor 1960, Pentecost 1991). For other groups and aspects it was often a matter of starting from scratch. The main fieldwork for the project took place over two field seasons, 2002 and 2003. Some of the participants were already familiar with the site; to others it was new. For those living near Malham, fieldwork could be spread around the year. The contribution of those from farther afield were necessarily limited to shorter intensive visits. Different groups of organisms vary greatly in the ease with which they can be found, identified and recorded. Bryophytes and lichens are conspicuous, and most can be identified in the field, so these surveys can be relatively complete. Algae and cyanobacteria require microscopic examination, but thirty years of recording make the tufa-depositing becks, in particular, among the best-studied streams in the country. Freshwater invertebrates, often present in their larval form, can only be sampled by methods which willy-nilly disturb the limited areas of stream-bed that can be studied; this provides a broad picture but leaves much to be discovered regarding their true diversity and ecology. The cave studies have probably picked up the main points of interest. Perhaps inevitably, the limits of the stream course have been interpreted disparately for different groups of organisms. Thus, most freshwater invertebrates are obligate aquatic species but the mollusc survey covered three true aquatics and 24 others in associated damp habitats. Most of the Cowside catchment supports semi-natural vegetation ranging from calcareous grassland on limestone, through neutral and acid grasslands on drift, to heather-bilberry-cotton-grass communities on peat. The farms in the catchment include some improved grassland but there is little run-off of agricultural chemicals into the streams. Darnbrook Farm lies within the Craven Limestone Grassland Wildlife Enhancement Scheme implemented by English Nature. Most of the watercourses are in a very natural condition; there has been no canalisation, damming, work to improve the trout fishing or significant water abstraction. In places where cattle congregate they disturb the riverbed. A feature of the catchment is that on the south side two tributary streams are among the best examples of tufa depositing watercourses in the country, while on the north side, at the upper levels, the streams are highly acidic and their headwaters include a shallow tarn at 640m surrounded by eroding blanket bog. Other features adding to the diversity are extensive intermittently flowing sections, springs and flushes, gorges, waterfalls, caves, and a gravel fan where Cowside Beck meets the River Skirfare (Fig. 1). The valley contains a major population of Mountain Avens (Dryas octopetala), the most southerly in England. 2 3 Physical Background: Geomorphology Cowside Beck is a tributary of the River Skirfare (Littondale), which flows into the River Wharfe. It has a catchment of c. 20 sq km with contrasting conditions ranging from peat-covered glacial drift areas on Millstone Grit and Wensleydale Series (formerly termed Yoredales) on Fountains Fell (662 m) and Darnbrook Fell (624 m), to seasonally dry valleys and a few surface streams on limestones in the west and south, rising on the Malham high country plateau (538 m). The karstic nature of much of the total catchment makes it difficult to define its boundaries precisely (as Waltham et al, 1997). The geology of the area has recently been revised, Fig. 3 correlates the new and the old terminologies, and the somewhat different division of the Carboniferous strata in the two Geological Survey sheets covering the area. The Cowside Beck system and its segments The Upper Cowside valley heads at 400 m in a seasonally dry sector about 875 m in length, it is then fed by intermittent springs. The general alignment here is northeast. The permanent risings appear at 350-375 m altitude downstream of which Upper Cowside stretches for 1.5 km as a small meandering stream with a bed of moss covered limestone boulders and earth banks. Between Thoragill Beck and the confluence with Darnbrook Beck, Upper Cowside swings to align west-east. We have called the part below this confluence Lower Cowside Beck. A little below the confluence the stream enters an 800 m long limestone gorge section, downstream of which Lower Cowside Beck, now a small permanent river with larger boulders in its bed, again trends north-east, for 3 km to the confluence with the Skirfare. In this sector there is a clear valley-in- valley cross section. The overall long-profile (see fig. 2) is well adjusted to the Skirfare at Arncliffe where it is incised into a large depositional gravel fan. A stream ordering exercise identified the importance of the Darnbrook catchment, showing Darnbrook Beck to be a fourth order stream. Lower Cowside Beck remains fourth order after its confluence with Darnbrook Beck since Upper Cowside Beck is third order, thus not affecting order at the confluence.