The origin and the limnology
of the Ethiopian Rift Valley lakes have received less attention from scientists
than some of the larger lakes further south. Despite the fact that these lakes
are of great importance to the economy of Ethiopia, and are critical to the
survival of local communities, there were no intensive and extensive limnological
studies on these lakes until recently. It became obvious that the Ethiopian
Rift lakes can serve as a natural laboratory for comparative limnological studies
due to their unique chemical, physical and ecological features. They also proved
to be very sensitive indicators of past and recent climatic changes that took
place in this particular area of eastern Africa. Recently, several excellent
books have synthesized the available information in the areas of geomorphology,
climatology, and limnology of African Great Lakes, but very little information
has been synthesized on the Rift Valley lakes of Ethiopia. Since significant
limnological data have accumulated on the Ethiopian Rift Valley lakes, but these
data are spread out in various publications, many of which are not readily accessible
to the international scientific community, a book to synthesize most of this
literature is necessary. It is hoped that this book will stimulate the interest
and curiosity of many limnologists around the world. The various chapters will
provide a comprehensive coverage of the literature, and deal both with past
and ongoing work on Ethiopian limnology and fisheries.
PREFACE
There have long been many studies of the waters in the southern parts of the
African Rift Valley, and these are frequently referred to in several chapters
of this book; but the northern, Ethiopian, part of the valley and its adjoining
uplands was not included in that early work. Presumably that was partly because
Ethiopia was only briefly occupied as a colony by a European nation, and partly
because the enormously dissected nature of the highlands has always made travel
there very difficult.
However, biological investigators from other continents have always been attracted
to the study of African biota, and, as is well documented in this book, there
were several papers published on fish and other aquatic organisms of the country
by visiting scientists during the first two thirds of the twentieth century.
I, indeed, was one of them, because with my long-term interest in aquatic biota,
I always carried a bug net with me during my twenty months of extensive travelling
around as the junior member of The Locust Control Mission to Ethiopia during
the second world war, and that enabled me later to write a paper on the aquatic
Hemiptera. The compelling interest of the Ethiopian biota is not only that it
is upland African, but that it is part of the tenuous biogeographical link with
Eurasia. For instance, Tilapia nilotica, which at one time was called manus-christae,
occurs in both the Awash and Jordan River basins, and one can find the European
river limpet Ancylus fluviatilis in Ethiopian streams. Ethiopia, moreover, unlike
other African lands, shares roses with Europe.
It has long been clear that lakes are an important resource for the peoples
of Africa as producers of both water and food fishes, as well as sources of
disease such as Schistosoma, Dracunculus and malaria, so the need that they
be managed effectively has long been obvious. It is therefore heartening that
several agencies have supported research on Ethiopian lakes during the past
few decades, and that this has been done, not only to gather data and enhance
understanding, but also as a means of training a cadre of local people in the
sciences of limnology and fisheries on which such management has to be based.
This is very apparent in the names of the authors of chapters in this book,
many of whom are Ethiopians. To that extent, this publication marks a turning
point in the history of aquatic science in the African continent, and it is
heartening to see that the final, integrative, chapter on threats and strategies
for the conservation of the lakes is written by Dr. Zinabu Gebre-Mariam, an
Amhara who lives on the bank of Lake Awasa.
In short, I regard this book as marking two important achievements. The first
is that it summarises what is so far known about the lakes of the northern part
of the Rift Valley and it gives access to the literature to date; and the second
is that it provides a solid basis for further limnological work in the area,
which, one hopes will be largely done by local scientists to the benefit of
both scientific knowledge and their native lands. Africa will benefit enormously
from their contributions.
H.B.N. Hynes
Distinguished Emeritus Professor
University of Waterloo, Ontario
Canada
TABLE OF CONTENTS
Preface
Acknowledgements
Authors addresses
Chapter 1.
Introduction, C. Tudorancea & W.D. Taylor
Historical background
Physiography
Climate
Chapter 2.
The Main Ethiopian Rift System: an overview on volcanic,
tectonic, rifting, and sedimentation processes, G. Wolde Gabriel
Introduction
Pre-rift geology
Significance of the Main Ethiopian Rift
Geological history of the Main Ethiopian Rift
Northern sector
Central sector
Southern sector
Comparison and contrasts
Conclusions
Chapter 3.
Lake morphology and chemistry, R.M. Baxter
Introduction
Morphometric and hydrological characteristics of the lakes
Water chemistry
The Bishoftu lakes
Stratification and nutrient dynamics
Chapter 4.
Phytoplankton distribution in lakes of the Ethiopian Rift Valley, Elizabeth
Kebede
Introduction
Background
Species composition
Phytoplankton biomass
Crater lakes
Salinity, nutrients and light
Seasonality
Long term changes
Chapter 5.
Primary and secondary production in the pelagic zone of Ethiopian Rift Valley
lakes, W.D. Taylor, Elizabeth Kebede & Zinabu Gebre-Mariam
Introduction
Primary production
Zooplankton
Bacterioplankton
Synthesis and prospectus
Chapter 6.
Zoobenthic and weedbed faunas, C. Tudorancea
Introduction
Composition and abundance of benthic fauna in the rift lakes
Benthic fauna of the crater lakes
Invertebrate fauna associated with the aquatic vegetation
Spatial distribution in relation to water depth and sediments
Diversity of benthic fauna and water chemistry
Seasonal variations
Chapter 7.
Free-living aquatic nematodes of the Ethiopian Rift Valley, Eyualem Abebe
Introduction
Species composition
Species distribution
Diversity
Abundance of nematodes
Spatial and temporal distribution within lakes
Chapter 8.
A general view on the communities of the Chironomidae adults in the Ethiopian
Rift Valley lakes, A.D. Harrison
Introduction
Non-saline lakes
Bottom dwellers
Weed-bed dwellers
Saline lakes
Conclusions
Chapter 9.
Ostracoda in the Ziway-Shala-Awasa Basins, K. Martens
Introduction
The Limnocythere species flock
Speciation in Limnocythere
Chapter 10.
Fishes of the Ethiopian Rift Valley, A.S. Golubtsov, Yu. Yu. Dgebuadze &
M.V. Mina
Introduction
Sampling localities and methods
Taxonomy, life history and distribution of the Ethiopian Rift Valley fishes
Introduced exotic species
Discussion
Endemic fish species in the Ethiopian Rift Valley
Distribution of fish species within the Ethiopian Rift Valley
Ethiopian Rift Valley within a framework of the ichthyofaunal provinces
Problems of conservation of fish faunas in the Ethiopian Rift Valley
Appendix. An artificial key to fish species of the Ethiopian Rift Valley
Chapter 11.
The Ethiopian Rift Valley lakes: major threats and strategies for conservation,
Zinabu Gebre-Mariam
Introduction
Problems related to human activity
Land use and modifications
Irrigation
Urbanization and human settlement
Industrial uses of water
Examples from other Ethiopian lakes
Problems due to human inactivity
Lack of information
Absence of lake monitoring systems
Absence of water use policies
Strategies for conservation
Recognition of the problem
Limnological research and education
Consideration of environment problems with developmental planning
Integrated management
Local environmental legislation and sustainable water use policy
Participatory approach to water management
Subject index
Taxonomic index