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Lake Mcilwaine: The Eutrophication and Recovery of a Tropical African Man-Made Lake PDF

257 Pages·1982·10.21 MB·English
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LAKE McILW AINE MONOGRAPHIAE BIOLOGICAE VOLUME 49 Editor J.ILLIES Schlitz, F.R.G. Dr W. Junk Publishers The Hague-Baston-London 1982 LAKE McIL WA INE The Eutrophication and Recovery of a Tropical African Man-Made Lake Edited by J. A. THORNTON With the assistance of W.K.NDUKU Dr W. Junk Publishers The Hague-Baston-London 1982 Distributors: 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 CIP Main entry under title: Lake McIlwaine : th e eutroPhication and recovery of a tropical African man-made lake, (Monographiae hiologicae ; v. 49) Bibliography / by Margaret J. Thornton & J.A. Thornton Includes indexes. l. Eutrophication--Zimbabwe--McIlwaine, Lake . 2. Limnology--Zimbabwe --McIlwaine, Lake. 3. Water quality management--Zimbabwe--McIlwaine, Lake. 4. McIlwaine, Lake (Zimbabwe) I. Thornton, J. A. (Jeffrey A.) II. Series. QPl.P57 vol. 49 [QHl95.Z55] 574s 82 -l5238 [363 .7'394'09689 l] AACR2 ISBN-13: 978-94-009-7985-7 e-ISBN-13: 978-94-009-7983-3 DOl: 10.1007/978-94-009-7983-3 Cover design: Max Velthuijs Copyright © 1982 by Dr W. Junk Publishers, The Hague. Soflcover reprint oft he hardcover Js t edition J 982 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form by any means, mechanical, photocopying, recording, or otherwise, without the prior written permission oft he publishers, Dr W. Junk Publishers, P.O. Box 13713, 2501 ES The Hague , The Netherlands. Preface 'And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. ' Genesis 1:6 Lake McIlwaine is a man-made lake. It was formed in 1952 by the Hunyani- poort Dam and is situated on the Hunyani River some 37 km southwest of Salisbury* in the Republic of Zimbabwe**. It is a lake of many aspects: being a popular recreational site, the City's primary water supply reservoir (and the fourth largest impoundment in Zimbabwe), a source of irrigation water to downstream farms, an important fishery, and, until the 1970s, the receptacle of Salisbury's sewage effluent. It is, in short, typical of so many 'urban' lakes in Africa and throughout the world. Lake McIlwaine is also unique, to my knowledge: being amongst the first of the major man-made lakes on the continent to suffer from what is known as cultural eutrophication, and the first to be r:ehabilitated to a mesotrophic state through a rational programme of lake management. This volume synthesizes this process of eutrophication and recovery in terms of the geology and geography (Chapter 2), physics (Chapter 3), chemistry (Chapter 4) and biology (Chapter 5) of the lake, and, whilst discussion of the trophic relationships between these components is beyond the scope of this monograph, discusses its utilisation, conservation and management (Chapter 6). * Subsequent to writing, the name of the Zimbabwean capital was changed to Harare on 18 April 1982. - Ed. ** The Colony of Southern Rhodesia was granted independence by H. M. Government on 18 April 1980 and became the Republic of Zimbabwe. All names used in this monograph are those currently in use at the time of writing. VII The recovery of Lake McIlwaine was effected through the efforts and foresight of a large numer of individuals: in Government, in the University, in commerce and industry, and in the general pUblic. Their efforts formulated the principles, policies and legislation and, more importantly, implemented these same which resulted in the recovery of the lake. Some of these people have now recorded the roles played by their colleagues and themselves in this endeavour, and my sincere thanks, as editor, go out to them, collectively and individually, for without their expertise this monograph would not have been possible. Acknowledgement must also be made to the Government of Zimbabwe, particularly to the Ministry of Natural Resources and Water Development; to the City of Salisbury; and to the University of Zimbabwe, who generously funded large portions of the research programmes; and to Lever Brothers (Pvt.) Ltd. and Mobil Oil Zimbabwe (Pvt.) Ltd. and others who equally generously provided monies for various necessary items of equipment. I am grateful for the co-operation and assistance of my colleagues and friends at the University of Zimbabwe, in the Department of National Parks and Wild Life Management, in the Division of Water Development, and latterly in the Hartbeespoort Dam Ecosystem Programme team of the National Institute for Water Research, CSIR, whose advice and encouragement resulted in the completion of this volume. As editor, I have had to co-ordinate the various sections of this monograph which were written by a number of independent authors and co-authors, and in some instances considerable adjustment was necessary to bring these contributions into line with the general plan ofthe volume. Should any errors or omissions have occurred during this process, I tender my sincere apo- logies. This volume forms contribution No.4 to the National Water Quality Survey of Zimbabwe. Pretoria, December 1981 JEFFREY A. THORNTON VIII Contents Preface VII Addresses of authors XI 1. Introduction The creation of Lake McIlwaine: history and design, by N. A. Burke and J. A. Thornton 2. Geology and geography Land use survey of the Upper Hunyani catchment, by K. Munzwa 11 3. Physics Physical limnology , by P. R. B. Ward 23 The hydrology of the Lake McIlwaine catchment, by B. R. Ballinger and J. A. Thornton 34 4. Chemistry Water chemistry and nutrient budgets, by J. A. Thornton and W. K. Nduku 43 The sediments, by R. Chikwanha, W. K. Nduku and J. A. Thornton 59 - Sediment chemistry, by J. A. Thornton and W. K. Nduku 59 - Sediment transport, by R. Chikwanha 66 The effects of urban run-off, by R. S. Hatherly, W. K. Nduku, J. A. Thornton and K. A. Viewing 71 - The aqueous phase: nutrients in run-off from small catchments, by J. A. Thornton and W. K. Nduku 71 - The solid phase: a study of pollution benchmarks on a granitic terrain, by R. S. Hatherly and K. A. Viewing 77 Insecticides in Lake McIlwaine, Zimbabwe, by Yvonne A. Greichus 94 IX 5. Biology An SEM study of bacteria and zooplankton food sources in Lake McIlwaine, by Monika Boye-Chisholm and R. D. Robarts 101 Phytoplankton, primary production and nutrient limitation. by R. D. Robarts, J. A. Thornton and Colleen J. Watts 106 - The algal community, by J. A. Thornton 106 - Primary production of Lake McIlwaine, by R. D. Robarts 110 - An examination of phytoplankton nutrient limitation in Lake McIlwaine and the Hunyani River system, by Colleen J. Watts 117 Zooplankton and secondary production, by J. A. Thornton and Helen J. Taussig 133 Aquatic macrophytes and Eichhornia crassipes, by M. J. F. Jarvis, D. S. Mitchell and J. A. Thornton 137 The benthic fauna of Lake McIlwaine, by B. E. Marshall 144 The fish of Lake McIlwaine, by B. E. Marshall 156 Avifauna of Lake McIlwaine, by M. J. F. Jarvis 188 6. Utilisation, management and conservation Water pollution: perspectives and control, by D. B. Rowe 195 Water supply and sewage treatment in relation to water quality in Lake McIlwaine, by J. McKendrick 202 Fisheries, by K. L. Cochrane 217 Recreation, by G. F. T. Child and J. A. Thornton 221 Research: perspectives, by J. A. Thornton 227 7. Bibliography by Margaret J. Thornton and J. A. Thornton 233 Taxonomic index 241 General index 245 x Addresses of authors B. R. Ballinger, Hydrological Branch, Division of Water Development, Ministry of Natural Resources and Water Development, Private Bag 7712, Causeway, Salisbury, Zimbabwe. Monika Boye-Chisholm, 13 Glebe End, nr. Bishops Stortford, Herts., UK (previously: Hydrobiology Research Unit, University of Zimbabwe. N. A. Burke, Designs Branch, Division of Water Development, Ministry of Natural Resources and Water Development, Private Bag 7712, Causeway, Salisbury, Zimbabwe. R. Chikwanha, Hydrological Branch, Division of Water Development, Ministry of Natural Resources and Water Development, Private Bag 7712, Causeway, Salisbury, Zimbabwe. G. F. T. Child, Director, Department of National Parks and Wild Life Management, P. O. Box 8365, Causeway, Salisbury, Zimbabwe. K. L. Cochrane, Limnology Division, National Institute for Water Research, CSIR, P.O. Box 395, Pretoria 0001, Republic of South Africa (previously: . Lake Kariba Fisheries Research Institute, Department of National Parks and Wild Life Management, Zimbabwe). Yvonne A. Greichus, Enviro Control Inc., 11300 Rockville Pike, Rockville, MD 20852, USA. R. S. Hatheriy, c/o Institute of Mining Research, University of Zimbabwe, P.O. Box MP.167, Mount Pleasant, Salisbury, Zimbabwe. M. J. F. Jarvis, Branch of Terrestrial Ecology, Department of National Parks and Wild Life Management, P.O. Box 8365, Causeway, Salisbury, Zimbabwe. B. E. Marshall, Lake Kariba Fisheries Research Institute, Department of National Parks and Wild Life Management, P.O. Box 75, Kariba, Zimbabwe. XI

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