THE ECOLOGY OF THE WYE

MONOGRAPHIAE BIOLOGICAE

VOLUME 50

Editor

J.ILLIESi Schlitz, F. R. G.

Dr W. Junk Publishers The Hague-Boston-London 1982

The ecology of the Wye

R. w. EDWARDS AND M. P. BROOKER

Dr W. Junk Publishers The Hague-Boston-London 1982

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for the United States and Canada

Kluwer Boston. Inc. 190 Old Derby Street Hingham. MA 02043 USA

for all other countries

Kluwer Academic Publishers Group Distribution Center P.O. Box 322 3300 AH Dordrecht The Netherlands

Library of Congress Cataloging in Publication Data

Edwards, R. W. 1l1e ecology of the Wye.

(Monographiae biologicae ; v. 50) Includes index. 1. Stream ecology--Wye, River (Wales and England)

2, Wye, River (Wales and England) I. Brooker, M. P. II. Title. III. Series. QPl.P37 vol. 50 [QH1441 574s 82-6580

[574.5'26323'0942951 AACR2

ISBN-13:978-94-009-7988-8 e-ISBN-13:978-94-009-7986-4 001: 10.1007/978-94-009-7986-4

Cover design: Max Velthuijs

Copyright © 1982 Dr W. Junk Puhlishers. The Hague.

Softcover reprint of the hardcover 1st edition 1982

All rights reserved. No pari o/this puhlication may he reproduced. stored in a retrieval system. or transmilled in any/()rm or hr anr means. mechanical. photocopying. recording. or otherwise. without the prior wrillen permission o/the puhlishers Dr W. Junk Puhlishers. P.D. Box 13713. 2501 1:"5 The Hague. The Netherlands.

To our parents, whose personal sacrifice made possible our careers in science

Craig Goch Reservoir in the Elan Valley.

Preface

The valley of the River Wye has long been famed for its natural beauty and the salmon stocks which the river supports. As one of the largest substantially unpol­luted rivers in Southern Britain, the Wye, which rises in Wales and flows into England, is now of considerable significance in the strategy for conservation of freshwater habitats in the United Kingdom and is designated as a Site of Special Scientific 1 nterest by the Nature Conservancy Council (N. C. C.). However, des pi te this scientific importance, published studies of the aquatic ecology of the river during the earlier decades of this century were principally restricted to the excellent series of articles and books on the salmon written by J. A. Hutton during the period 1912-47 and scattered records of the plants of the river banks. During this period the Fishery Board and successive organisations responsible for fisheries, also published reports describing general water quality and salmon catch statistics. In 1970 a survey was undertaken by the N.C.C. which provided the basis for the decision to give it special protected status.

The Wye has been exploited as a major water source for Birmingham, through the development of reservoirs in the Elan Valley, since 1904. Further development of the capacity of the Elan catchment occurred in 1952 with the completion of the Claerwen Reservoir. Proposals to enlarge one of the already existing direct supply reservoirs, Craig Goch, to provide storage to regulate the natural flow of the River Wye drew further attention to the need to know much more about the river's general ecology and water quality. In 1974 the Welsh Water Authority, on behalf of the Craig Goch Joint Committee and Central Water Planning Unit, contracted the University of Wales Institute of Science and Technology (U.W.I.S.T.) to undertake studies of the fish popUlations, general ecology and water quality of the R. Wye with a view to providing a firm scientific baseline upon which the effects of future proposed changes in flow could be assessed. Other work was also commissi­oned at this time by the N .c.c., the Water Authority and others, and studies of the aquatic and riparian vegetation (LJ. W.I.S.T.), algae (U niversity College, Cardiff), birds (Royal Society for the Protection of Birds) and otters (Society for Promotion of Nature Conscrvation) of the R. Wye have recently been completed. Such wide ranging and yet detailed and contemporaneous investigations of a large river system, like the Wye, have not been previously undertaken in the United Kingdom, and this opportunity has been taken to draw together the results ofthese investiga-

VII

tions in this book in an effort to provide as complete a record as possible of the general ecology of the river and to speculate on the consequences of further changes of land-use and water resources of the catchment.

Much of the work described above is already published in specialist journals and reports, and this book seeks to provide a summary for the general scientific reader: those requiring more detailed description are referred to the oi-iginal publications which are listed in the bibliography.

Where groups of species all have common names, such as the birds and fish, these are used in the text. but in other cases, such as the flowering-plants, only some have such widely accepted common names and here, for the sake of consistency within the Chapter or Section, the alternative Latin name is adopted.

Apart from the scientists who took part in the studies described in this book, most of whom are cited in references, the authors wish to record their thanks to those many people who were no less important in 'putting and keeping the wagon on the road', particularly the Llysdinam Trustees, General Sir Thomas Pearson and the many land and fishery owners who provided access to the river, Dr. M. A. Learner, Dr. F. M. Slater. Dr. R. Williams and secretarial and technical staff of the Applied Biology Department, UWIST, M r. M. Owens and Mr. E. M. Staite of the Welsh Water Authority. Dr. J. Hellawell of the Severn-Trent Water Authority, Dr. R. Abel of the Central Water Planning Unit, Mr. J. Beaver of Sir William Halcrow and Partners and Mr. R. Lovegrove of the Royal Society for the Protection of Birds.

VIII

Contents

Preface

List of plates

I. Geology, land-usc and hydrology - Geology

Relief and drainage pattern Precipitation and river flo\\

- Population and land-use

2. Water quality - Introduction

General water quality of the River Wye Water quality of the Elan Valley reservoirs

3. Plants - Plant distributions within the river

Plant distributions in the Elan Valley reservoirs - Vegetation of Llangorse Lake

4. Macroinvertebrates Maeroinvertebrate distribution within the river: Platyhelminthes,

Oligochaeta. Hirudinea. Crustacea. Pleeoptera. Ephemeroptera, Tri-

VII

XI

3 6 8

II 12 24

27 46 48

choptera. Coleoptera. Hemiptera. Diptera and Mollusca 53 - Macroinvertehrate, in the Elan Valley reservoirs 76

5. Fish - Introduction 79

Distribution 79 General biology: shad. chuh. dace. roach. pike, grayling, bullhead,

brown trout and salmon 82

IX

6. Birds and mammals Birds: river breeders, river users, waders. species of marginal scrub

and woodland 103 Mammals: otter and mink llO

7. The future Land-use changes 113 Water resource developments 114 Effects of flow changes 1 15 Effects of storage I 19 General conclusions 121

Appendices I. List of pteridophyte and angiosperm species found on the Wye and four

of its major tributaries 125 2. List oflichen and bryophyte species found in the Wye and four of its major

tributaries 137 3. The occurrence of macroinvertebrates in the Wye catchment 141 4. Flight periods of adult insects collected at Newbridge-on-Wye 148 5. Species seen on the Wye Survey 151

Bibliography 155

Index 161

x

List of plates

Frontispiece. Craig Goch Reservoir in the Elan Valley VI

Plate 1. Making net collections in the Wye Gorge near Erwood (W29) 26

Plate 2. Dense growth of Ranullcu/us penici/latus in the River Wye at Ross-on-Wye (W54) 52

Plate 3. Collecting invertebrates with a cylinder sampler in the headwaters at Llangurig (near W8) 112

Plate 4. Checking the catch of a drift sampler In the flver at Newbridge-on-Wye (WI8) 122

XI