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Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
Volta Lake: Physical and Biological Aspects
LETITIA E. OBENG
Institute of Aquatic Biology, Council for Scientific and Industrial Research
A chimota, Ghana
The Volta River project from this aspect is
perhaps exemplary in that its planning received
much study prior to its launching. The
preparatory commission (1946) believed the
scheme to be soundly conceived,' but its
magnitude was such that the commission thought
that it should not be embarked upon without
every assurance that it could be carried through
to a successful conclusion.'
The project was successfully launched. The
Volta River was dammed. Volta Lake was
formed. This lake is the largest man-made lake
in Africa, having an area of 8300 km', a length of
402 km, a maximum depth of 905 meters, and a
shoreline of >6400 km and enclosing several
million cubic meters of water.
Ghana's inland water system is extensive and
forms a close-knit network over the whole country. Volta Lake, being the focal point of this extensive water system, is literally in touch with
almost all parts of the country.
Worthington [1966] gives a good resume of
what one might expect with the creation of a major impoundment of this kind. Certainly, the
Volta experience has established most of these
possibilities as hard facts. Much land has been
lost, possibly land with minerals. The ecological
revolution that accompanied the inundation, the
effect of the change and the new environment on
the people, and the obvious economic potentialities of Volta Lake earned it a place as a
project deserving national attention.
In 1924 the idea of a Volta River project was
born. Before 1952, Ghana's Volta River project
was a dream. In 1962 the project became a reality
with the beginning of the construction of the
dam. By 1964, Volta Lake was forming. In 1965,
after a number of earlier desultory and halting
starts, Volta Lake research made a significant
breakthrough to gain recognition as an essential
part of Volta Lake management: an institute for
hydrobiological studies on a long-term basis, the
Institute of Aquatic Biology, was established by
the Council for Scientific arid Industrial Research
of Ghana, and scientists, mostly Ghanaian
nationals from various government-sponsored
organizations, embarked on various aspects of
Volta Lake research.
Three years later in January 1968 the national
research effort was reinforced by the launching of
the Volta Lake Research Project jointly by the
government of Ghana and the United Nations
Development Program (UNDP). Primarily designed for the production of hydroelectric power
for the electrification of the countryside of
Ghana and the establishment of industrialization
schemes, the Volta River project was also conceived as a multipurpose project to provide,
among other things, facilities for lake transportation, a fishery industry, agriculture, and recreation.
Associated with the creation of the lake were
expected as well as unpredicted far-reaching
effects. Apart from the physical removal of people from their traditional homes and their
resettlement in unfamiliar environments, there
have been other aspects of the project indicating
that certain factors should receive intensive attention and study well in advance of the actual construction of dams and that engineers, designers,
biologists, and other appropriate persons should
work in close cooperation even at the planning
stage.
VOLTA LAKE IN THE GHANA SETTING
Ghana has an area of 238,699 km2, a northsouth length of 675 km, and a coastline with a
maximum width of 553 km. The physiography of
Ghana has interesting characteristics that undoubtedly contributed to the feasibility of the
creation of Volta Lake. The landscape, on the
whole, shows wide plains, a number of gentle
87
Copyright American Geophysical Union
Vol. 17
Geophysical Monograph Series
88
Man-made Lakes: Their Problems and Environmental Effects
VOLTA LAKE RESEARCH: A CASE STUDY
slopes, and a limited series of hilly ranges with
isolated peaks. The Afadjato in the Volta region,
which is the highest point in Ghana, is only 910
meters above sea level.
The most easily noticeable feature in the relief
is the Kwahu scarp (the Voltaian escarpment),
which originates somewhere around Wenchi in
the midwestern part of the country, crosses the
country toward the southeast, and passes
through the Ashanti-Mampong area and
Mpraeso to the south where, with the Akwapim
range, it forms the southernmost boundary of
the Volta River basin. From the eastern side the
highland area of the Volta region joins the
Voltaian escarpment to form a link and to constitute a raised boundary around a well-protected
basin of low-lying plains into which the lake
water collected when the dam was built across the
lower part of the Volta River.
On the western side the raised edge has its steep
side facing away from the lake, so there is
generally a stretch of low-lying shore. On the
eastern side the steep side of the Volta region
highlands, including the Buem range, faces the
lake. Thus the shoreline on the eastern side has a
different character from that on the western side.
Source of lake water. The Voltaian escarpment provides in the southwestern region of the
country a clear demarcation of the catchment
area of the Volta River and its tributaries. The
Voltaian drainage system covered well over twothirds of the country before the formation of the
lake [Wills, 1962]. All minor rivers and streams
north of the Voltaian escarpment and east of the
Volta region highlands now drain into Volta
Lake. South of the scarp a few large rivers (the
Ankobra, Tano, Pra, Kakum, Amissah, Nokwa,
Ayensu, and Densu) discharge directly into the
Atlantic Ocean.
Contribution to the Volta Lake water from the
north comes through the Red Volta, which has its
source outside Ghana in the Upper Volta; the
White Volta, which also rises from outside
Ghana and receives large rivers including the
Kulpwan and the Nassia within Ghana; and the
Black Volta, the most important of the three
Voltas, which has tributaries in Upper Volta but
travels a long distance between Ghana and Ivory
Coast and forms the boundary between the two
countries in the west before turning sharply into
Ghana and crossing it north of Wenchi to join
the other two Voltas. In addition to the Voltas,
from the western side of the country, the Pru,
Sene, Obosum, Dwija, Afram, and Pawmpawm
together with their numerous tributaries drain
into the lake. From the eastern side the Oti,
Daka, Asukawkaw, and Dayi rising from the
Volta region highlands also take water to the
lake. The country is very well watered with rivers
and streams that are either intermittent or permanent in their flow. Although the Voltas originate
outside Ghana, the bulk of the water collected in
the lake comes from water sources entirely within
Ghana.
Geologic background. From limnological considerations, the geologic character of the basin
is relevantly interesting. Bates [1962] considers the Volta River system to be ancient and to
have been in existence at the beginning of the
Paleozoic age. The Ghana Geological Survey
defines the term Voltaian as applicable to rocks
consisting of 'a series of shales, mudstones,
sandstones, arkoses, conglomerate, tillite and
limestone.'
The Sene plain has arkoses, the Obosom has
sandstone, and the Oti Valley has rpudstone.
Bates [1962] records also that, to understand
the geologic nature, the value of data on stratigraphic classification is reduced because there
are lithographic variations in the various parts
of the Voltaian basin that make generalization and composite description of the areas inaccurate. However, from vertical sections and
borehole samples, analyses give some basic information on the chemical composition of shale,
sandstone, and limestone material from the
Voltaian area.
Climate. A peculiar feature about the
Ghanaian climate is the harmattan. The air
masses that cause this state traverse the Sahara
Desert before reaching Ghana. They are dry,
have a relatively low humidity, and therefore give
a general feeling of low temperature from
November to February when they blow over
most of Ghana. On the other hand, another set of
air masses that comes from the sea during other
parts of the year is, in general, cool and moist.
Prior to the formation of the lake, temperatures taken in the shade about 4 meters above
ground varied only slightly from year to year
(on the order of about 2°-3°F) [Walker, 1962].
The average maximum temperature reaches the
highest level from February to April generally
in the south and from April to May in the
north. The annual mean temperature as recorded
by Walker [1962] prior to the formation of
Copyright American Geophysical Union
Vol. 17
Geophysical Monograph Series
LETITIA E. OBENG
Man-made Lakes: Their Problems and Environmental Effects
the lake showed a low variation for the whole
country when the temperatures were adjusted for
altitude.
Rainfall has an effect on the character of water
content in the basin. Walker [1962] considered
the pattern to be significantly important not only
because of its seasonality but also because of its
variability from year to year. He distinguished
four patterns of rainfall that varied from north to
south but graded into each other so well that they
were not clearly demarcated on the basis of their
areas and periods of occurrence. He has recorded
that, in general, January is a dry month but that
there is much variation in the period of onset, extent, and duration of the rainy season. He
believes Ghana to receive, on the average, the
same amount of rain expected in a typical
tropical area. The highest rainfalls were 218 cm in
the Ahanta-Nzima region in the west and 71 cm
around Accra.
Volta Lake appears to have received a
favorable endowment in its choice of location
and supply of water and an interesting basis for
its chemical character. All these factors are relevant to the design of the studies required to
support its full use and exploitation.
VOLTA LAKE RESEARCH
Organization. In a case study of Volta
Lake research, it is not out of place to comment
on its organization, since it is the infrastructure
on which the success or failure of the research
depends.
Ghana, fortunately, awoke to the importance
of full-time scientific research in the use of
natural resources for national development very
early in her postindependence history. Statutory
recognition was given to research in the late fifties
when the National Research Council was established. This body has metamorphosed
through the Ghana Academy of Sciences into the
Council for Scientific and Industrial Research,
which has nine full-time research institutes studying the country's soils, cocoa, crops, forests, inland water system, food, buildings and roads, industries, and animals. It is an extensive organization that has been given by an act of Parliament
the responsibility for conducting research of
national importance.
The institute for the inland water system has
concentrated much effort on Volta Lake not only
because it is the physical focal point of the inland
water system but also because of its challenging
Vol. 17
89
nature and the national expectations from its
creation. The research staff of the institute and
their supporting technical and field staff are temporarily assigned to the Volta Lake Research
Project, which was initiated in 1968 to augment
existing lake research. This project is jointly
sponsored by the government of Ghana and the
UNDP. Some staff from the University of Ghana,
the Volta River Authority, the Ministry of
Agriculture, and the Ministry of Health are also
assigned to the project. This national staff of
more than 30 people is joined by a United
Nations staff of up to 10 people, and they are
supported by a turnover of more than 70 junior
local staff.
Administratively, the Food and Agriculture
Organization is the executing agency on behalf of
UNDP, and the project manager is its representative. The Volta River Authority is the
cooperating agency on behalf of the government
of Ghana, and there is also a Ghanaian comanager.
The United Nations Special Fund contributed
US$1,336,000 for a period of 3 years toward the
project, and this amount was matched by an
equivalent contribution in cash and kind by the
government of Ghana. The purpose of the project was to assist Ghana in strengthening research
on fisheries and hydrobiology, public health, and
the resettlement of the peoples displaced by
Volta Lake.
The project has laboratories at Akosombo, the
damsite of the lake, which has adequate facilities
but is unfortunately not the most convenient
place for a research headquarters because of its
location at the southernmost end of the 402-kmlong lake. Because of the transportation and
communication problems of this isolation, it was
decided at the beginning that the project should
also use outside facilities at the universities and
the Council for Scientific and Industrial
Research.
Program. The design of the Volta Lake
research program makes it possible to consider
almost all aspects of hydrobiological research in
terms of their practical application to development. The major sections are limnology, fish
biology, fish technology, aquatic weeds, public
health, agriculture, and game and wildlife. These
sections take into account, on an immediate as
well as a long-term basis, madating the lake with
a view toward developing fisheries, guarding
against pollution in various forms to ensure a
Copyright American Geophysical Union
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
VOLTA LAKE RESEARCH: A CASE STUDY
the use of the potentialities of Volta Lake. The
safe level of health, and eventually providing
research program incorporates a reasonable
facilities for recreation. Although these items
amount of basic investigation and therefore
may appear unrelated, the conduct of the studies
provides a refreshing opportunity for practicing
is so organized as to encourage maximum coor- the operational interdependence of basic and
dination of the various activities undertaken by
nonbasic research and for applying this research
the project. to the various faunal relationships and levels of
In detail the Volta research program covers
productivity in the lake to economic advantage.
limnological studies involving the physical and
The program covers almost all the problems
chemical characteristics of the medium, plank- being tackled by the other man-made lakes in
ton, periphyton, bacteria, algae, and invertebrate
Africa. It combines research into fisheries being
fauna and their relationship to fish production. conducted at Kariba, Kainji, and Jinja with
Studies on fisheries take into account the diversity
research on the use of lake water for domestic
of fish species; their population and distribution;
and agricultural problems. Volta Lake shares
and their feeding, growth, health, breeding, public health problems with Kainji Lake and
spawning, and migration habits. There are also
Lake Nasser, has the nuisance of aquatic
sections on determining, as far as possible, the turnover both in fish productivity and in weeds in common with Lake Kariba, has passed
catch. Studies on gear technology and fish through a phase similar to Kariba's 'Operation
processing, preservation, and marketing have Noah,' and like Lake Nasser and Kainji Lake
entertains the hope of using lake water for irrigabeen included as an essential part of the program. tion. In addition to these similarities, in the
These sections of the program bring the field
Ghana setting, Volta Lake promises great hopes
staff into direct contact with the fisherfolk on
for transportation and recreational activities.
whom the eventual establishment of a viable fishing industry will depend. Since the vigor and
In another sense, Volta presents an interesting
zeal with which the fishermen carry out their
feature for study by the fact that it traverses a
countryside that varies from conditions of savanwork are closely linked with their state of health, the presence of any disease-causing organisms nah land to forest. Unlike Nasser, Kariba, and
Kainji, Volta has an emphatic dendritic form that
and parasite-supporting agents likely to threaten
links it with hilly regions as well as plains and
the health and virility of the fishermen becomes
of vital concern. Public health implications that spreads its associated riverine connections
associated with such an artificial impoundment well over two-thirds of the whole of Ghana. In
therefore are a major factor in the research comparison with the other lakes, Volta stands
program. Invertebrates of medical importance shoulder high in its proportionate size to the
(especially the schistosome-supporting mollusks, country that owns her. The position of Volta
mosquitoes, tsetse flies, and others) receive atten- Lake in the country makes inland fisheries for
tion. The mollusks are associated with aquatic Ghana very important. Above all it is so conweeds that invariably become established when veniently located in west Africa that it is able to
impoundments are made, and the study of these share its benefits with neighboring countries.
weeds also becomes an unavoidable part of the From an economic point of view it is a veritable
research even though the weeds themselves do gold mine whose treasures are being worked according to a comprehensive, multidisciplinary,
not constitute serious physical obstructions, as mission-oriented, and well-coordinated research
they do in some other lakes. Other aspects of the research program include
program.
shoreline soil studies for future afforestation and
These salient features of Volta research,
agriculture and the establishment of game and
together with the close cooperation between nonwildlife parks for recreational and educational
Ghanaian staff from four continents of the world
purposes. Attention has also been given to working on a complex research program with a
rehabilitation of the resettled people, in- group of Ghanaian scientists from the fifth contivestigations of their social problems, and appor- nent to achieve the aspirations of a developing
tionment of land to them for agriculture. country in the management and use of the
Volta Lake research is scientific in approach, benefits from one of the largest man-made lakes
in the world, give Volta Lake research a
but first and foremost it is mission oriented to aid
90
Copyright American Geophysical Union
Vol. 17
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
91
LETITIA E. OBENG
uniqueness that makes it almost a blueprint for
the approach to research on man-made lakes in
developing countries.
VOLTA LAKE RESEARCH
Vol. 17
1964-1970: METHODS,
OBSERVATIONS, AND COMMENTS
Limnology
In the early stages of work on Volta Lake,
more as a result of necessity than as a result of
desire, unsophisticated but effective methods
were employed in studies of the rapidly altering
medium; however, as the water increased and the
lake extended its width, the need for adequate
sampling methods became real. Stations were
selected in parts of the lake for regular sampling.
In the account presented it must be constantly
borne in mind that, for a lake of the size of Volta,
normal sampling methods can hardly be expected
to give results that yield easily to generalization.
Oxygen pattern. Soon after the completion of
the dam in 1964 the oxygen distribution in the
lake was closely followed. Ewer [1966] reported
that immediately after the dam closure a 300%
surface oxygen saturation was recorded in
midstream about a mile north of the dam. This
record had dropped within 4 weeks to 16% oxygen saturation in surface layers, and an absence
of oxygen was reported at the 10-meter depth.
Entz [1969] found an obvious increase in dissolved oxygen between 1967 and 1969. Oxygen
was present down to the bed of the lake at the
A fram confluence, some 20 miles from the dam.
In mid-1969, A. E. Kpekata (personal communication, 1970) reported oxygen to be present
at 30 meters at Ajena in May, detectable on the
bed in August, and at 5% saturation on the bed in
September. A survey in the northwest along the
Black Volta and White Volta showed 27-55% oxygen saturation down to the bed, and the surface
layers in all the other riverine arms were well oxygenated. This change very much favored
productivity at various levels and affected fish
and invertebrate distribution.
Stratification. As the lake conditions
changed, tendencies toward stratification, as normally interpreted, were also watched with much
interest. Beauchamp [1969] records Lake
Tanganyika, an old natural African lake, to be
permanently stratified. It has large deposits of
organic matter and little outflow of water.
Volta Lake had comparatively few organic
deposits during its initial period of formation; it
had a good inflow system and little temperature
variation with depth, and stratification (as conventionally understood) was not expected to be
an important feature of this tropical lake.
However, Viner [1969] reported that, on
September 4-5,1965, he recognized three distinct
layers: an upper oxygenated layer at about 5
meters, a middle moderately oxygenated layer,
and a very clearly marked anaerobic layer, slight
but certain at the Afram confluence and strongly
marked at Krachi. In 1966, Entz [1969] recorded
a downward gradient of dissolved oxygen that he
interpreted as a factor of a stratification pattern
near Akosombo, but he also observed, as had
Biswas [1969] earlier, that the delineation was
destroyed by a number of factors (including wave
and wind action, the rainy season, and the harmattan) that caused a mixing and turnover of the
water.
Biswas made an early study of temperature
changes, and his account gives an interesting
pattern of the variations that took place up to
1966 between the bottom and surface layers. It
would seem that the temperature variation with
depth is now virtually negligible.
Turbidity. Observations so far describe a
definite decreasing gradient of maximum turbidity from the northern region southward
toward Kpandu. This decrease appears to be
related also to the rainy season, which brings an
influx of organic materials from the rivers into
the lake. During August and September 1970,
areas north of the Daka confluence were the most
turbid, the transparency ranging between only 9
and 10 cm. It seems likely that the variations in
turbidity also affect the spatial distribution of
fish.
Chemical studies. A good deal of chemical
analysis has been made over the period of study
to follow the pattern of distribution and concentration of certain ions. From 1966-1969, Entz
[1969] compiled much data from analyses carried
out both in the field and the laboratory.
An interesting feature that emerged from the
chemical studies is the distribution of some of the
chemical factors. In 1968, for instance, the
Pawmpawm arm had a higher chloride content
than anywhere else in the lake. Phosphate ion
concentration was also higher in the lake water
above the Oti than below it. Temperature, dissolved O, and pH decreased with depth; CO2,
Copyright American Geophysical Union
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
92
VOLTA LAKE RESEARCH: A CASE STUDY
H 2 S, NH 4 ,+ Fe++, and P0, - increased,
whereas Ca++, Na+, Cl , K+, and Si0 2
did
not seem to show any definite pattern of distribution.
Entz reports measuring quite high values of
Fe++ at the surface of a section of the lake water
at one time and explains this finding to be
probably the result of settled laterite dust on the
surface layers. Down to 10 cm the value was low,
but at greater depths where 0 2 and pH values
were low the Fe++ values could be extremely
high. In the main, chemical analyses made over
the 6-year period by various persons show
much similarity in results. Studies to interpret the
data so far collected in terms of productivity
are in progress.
-
-
---
Plankton and Algae
With limnophysical and chemical data as
background, studies of phytoplankton production
in relation to availability or unavailability of certain chemicals can be seen in a useful light. Oxygen, light penetration, and the influence of the
degree of turbidity on phytoplankton development and distribution have a direct relation to
plankton-feeding fish and their growth, abundance, and distribution. Observations made in
196C. by Rajagopal [1969] show a correlation between these factors. It is also interesting that he
recorded in 1966, as was reported from 19641965 by Proszynska [1969], that the southern
section of the lake was unsuitable for plankton
formation and that cladocerans and copepods
were absent. The Afram region near Ampem
provided a better habitat for their development.
Proszynska also recorded an interesting case
of recurrent mass death of crustacean plankton in
the early months of the formation of the lake
near Ajena and suggested that this occurrence
was probably due to the unfavorable chemical
changes in the lake environment. The areas
affected later became repopulated probably by
plankton brought in by the current from more
satisfactory areas.
Later, in January 1969, by using a bolting silk
no. 25 net, vertical hauls were made at some
places and at different depths down to 15 meters
from the damsite to Mpaha in the north [Rajagopal, 1970]. Cyclops spp., Bosmina sp., Moina
sp., Ceriodaphnia sp., Rotifera, Filinia sp.,
Trichocerca sp., and Keratela sp. appear to have
been the main organisms in the samples. Rajagopal recorded total zooplankton at the time to
range from 1620 to 15,300 organisms per cubic
meter column of water. Later in the year,
plankton was recorded from the surface down to
65 meters at the Afram confluence, but the
irregular distribution of the plankton at different
depths in the column of water during the period
of study was again a clear indication of the mixing of the waters.
When we compare the results over the 5-year
period, it appears that the plankton population
fluctuated not only in distribution but also in size
over the months of the year. The Afram wing,
once rich in zooplankton (at least around
Ampem), was reported in 1969-1970 to have a
lower number of zooplankton than the northern
parts of the lake.
Proszynska, who had the opportunity to
observe the Cladocera and Copepoda from
1964-1965 and to make qualitative studies of
them during the first 18 months after the lake
began to form, writes, `. . . there is no one common feature which can be generalized for the
whole period of investigation.'
Blooms of Microcystis were not uncommon
between 1966 and 1967. Rajagopal also reports a
large proportion of Gymnodinium near the shore
at Mpaha in 1969 and a bloom of Synedra there
and also near Kete Krachi. At the Afram confluence, Vo/vox was abundant. From the surface
to 65 meters, colonies per cubic meter ranged
from 4000 to 350,000 in number.
The plankton pattern in 1970 is still variable. A
longer period of study is needed for a clear picture to emerge, but generally it appears that, during favorable periods, zooplankton is abundant
and shows a decreasing gradient from the north
of the lake southward. The phytoplankton picture is even less clear. The zooplankton distribution also appears to follow the vertical oxygen
gradient; at the Afram confluence zooplankton
was present, on a day of continuous study, from 5
meters down to the bottom, and the water was
habitable for fish. Where there was deoxygenation and high turbidity, the adverse effect on the
distribution of the organisms was also apparent.
Algal collections made directly from the water
have been mostly Spirogyra and Oscillatoria, but
it appears that various objects in the water support more species of algae. Again, it would not be
prudent to generalize at this stage of our
knowledge and the present state of the lake on
the plankton and algal picture and the
significance of their occurrence in the overall
pattern of study.
Bacteria. Studies made in 1965 and subse-
Copyright American Geophysical Union
Vol. 17
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
LETITIA E. OBENG
Vol. 17
93
quently by Biswas [1969, also unpublished report,
1970] and Ofori [1970] have shown that bacteria
do not cause any major concern at this stage. It is
likely that bacteria may require attention as shore
areas become contaminated by settlers.
Periphyton. Limited studies on periphyton
production were undertaken by Entz [1968].
Glass slides were stuck in 2.54-cm nylon fish nets
that were hung vertically near the damsite for
different lengths of time. The periphyton
developed over these different lengths of time
after which their density was calculated.
Invertebrate fauna. Bottom fauna has been
studied over a period of time, and accounts have
been documented. Record was also made in
1965-1966, during the initial stages of formation,
of the lake invertebrate fauna associated with
aquatic weeds that had then developed [Obeng,
1969a]. Subsequent collections have shown an increase in the variety of the species of invertebrates then present. Most of these, especially
the chironomid larvae, form food for fish.
Fish Studies
Species and population studies. Unfortunately,
before the dam was closed, very little had been
recorded of the fish in the Volta River. After the
closure of the dam, between 1964 and 1966,
Denyoh [1969] recorded a number of species of
fish that had then been identified. The fish had
been caught with limited facilities near Akosombo and Kpandu. Since then, others, including
Adiase [1969], have recorded other species
belonging to other genera (also see Evans and
Vanderpuye [this volume]).
Adiase [1968] reported a pattern of distribution
that, although it was not definite, gave a rough
idea of the occurrence of certain species. It
appears that almost all the species then recorded
occurred throughout the entire length of the lake.
The tilapias were numerous in the south and near
Ampem in the Afram region where plankton had
also been found to be abundant. Near the dam
where plankton had been reported to be scanty in
the upper layers of the water, few specimens of
tilapia could be caught. Lates niloticus, one of the
most highly priced species in the lake, appeared
to be present in all areas.
The fish population pattern has also changed
over the period under observation. From catches
made from 5 months after lake formation to 1966
it was reported that some species became reduced
in numbers as the lake formed. Chrysichthys spp.
occurred in small quantities in 1964 near
Akosombo but became the predominant species
in 1966. Lates niloticus, on the other hand, had
been caught in reasonable numbers both at
Akosombo and Kpandu, but it had increased
considerably near Kpandu and decreased in the
Akosombo area by 1966. Ctenopoma spp. also
gradually became rare.
With the continued stabilization of lake conditions and increased favorable distribution of
dissolved oxygen and food, a variety of fish began
to form the basis of what could become a
prosperous fishing industry. Bottom feeders like
Labeo spp. and Synodontis spp. and the carnivorous Hydrocyon spp. and Lates niloticus have
increased in size and number.
It has not been necessary to stock the lake with
fish. There was a boom in the fish population
after the initial adverse ecological changes that
affected some fish. It has, however, been
necessary to assess the present fish stock and the
unit catch effort in the interest of successful
management, although, when one deals with a
lake the size of Volta, one has to recognize that it
is nearly impossible to be categorical about quantities.
Fish biology. The usefulness of results from
catch assessment in terms of fishing management
is incomplete without relevant information on
which to determine fish productivity. Information obtained by studying fish species and their
population structure, food and feeding habits
(and the availability of such food), distribution
pattern, growth rate, size and maturation cycle,
spawning habits, and seasonal migratory activities are essential parameters that will determine the stock turnover for a period of years.
Adiase [1969] studied the feeding habits and food
preferences of a number of species.
Maturation of species under natural conditions
can be related to size ranges, and studies are being made to establish a relation between the
availability of food and spawning patterns. It is
likely that most of the fish, having been riverine
originally, still migrate to the many arms of the
lake to spawn. Certainly, juvenile species of
Alestes that occur in the lake have been taken in
samples from the Nassia River in northern
Ghana, which also flows into the lake. The spawning habits of the fish and the factors likely to
affect the successful replacement of fish are
receiving attention. However, investigations into
migratory activities of fish are difficult because
there are still substantial areas of the lake with
fully or partly submerged trees that make
Copyright American Geophysical Union
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
94
Vol. 17
VOLTA LAKE RESEARCH: A CASE STUDY
passage from the lake to the rivers that join it
difficult.
Fish technology. The physical changes of
Volta from a river to a lake have made the fisherman's gear almost obsolete. In place of a river he
is now faced with a deep inland sea. Part of the
research program has covered experiments to
determine suitable mesh sizes, net lengths and
widths, and net setting techniques. The monofilament type of net has been tested scientifically
against the traditional multifilament net and has
proved more effective. Plans are afoot to introduce
mesh sizes from 12.7 cm upward into the market for
use by the fishermen. But since the present fish
stock has not been established with any certainty,
care is being taken in the use of these nets to avoid
catching juvenile fish.
The old wooden canoes previously in use on
the Volta River are no longer quite safe, especially in storms, on this large inland sea. New
designs have been made, and prototypes are being tried before they are introduced to the
fishermen.
From as far back as one can trace, Volta fish
have been processed in two ways, by smoking
and by salting and drying. Studies into the causes
of spoilage and the problems of preservation
have been conducted as part of the research
program. In the laboratory, J. K. Agbley (unpublished report, 1969) has made preliminary
biochemical analyses to ascertain the relationship
between the fish fat content and deterioration under certain conditions, and J. C. Ofori (unpublished report, 1969) has been studying
through culture the bacteria forms occurring on
the fresh and smoked fish that contribute to
spoilage. Information obtained will be useful
background to the proposed scheme to establish
a pilot center for processing, preservation, and
marketing of fish at Kpandu-Tokor.
Public Health
The range of invertebrate fauna recorded from
vegetation and the bottom has increased during
the years following 1966. The appearance and establishment of mollusks as part of the fauna and
the possible threat of schistosomiasis were not unexpected, especially since Bulinus snails had been
previously recorded in some regions that were
subsequently inundated by the formation of the
lake.
Schistosomiasis. From 1964-1968, studies on
the schistosomiasis problem were concentrated
on the establishment of the presence of the snail
intermediate hosts, their distribution and
habitats, and their association with aquatic
plants. Investigations into the medical aspect of
the problem were not started until the arrival of
the epidemiologist and the medical biologist from
the World Health Organization (WHO) in
December 1969. Since that time the scientists
from WHO together with the national staff have
jointly tackled the problem from both the
medical and the biological angles.
Early reports have shown Bulinus truncatus
rohlfsi to be the only proven urinary
schistosomiasis host associated with Volta Lake.
Other snails like B. forskalii sp., Pila africana,
Lymnea sp., Anisus coretus, and Potadoma sp.,
recorded as present in 1965, continue to occur
[Obeng, 1969a]. In addition to these, Odei [1970]
has reported other mollusks, including Caelatura
sp., Mutela sp., B. ( Physopsis) globosus, Gyraulus
costulatus, and Ferrissia sp. No Biomphalaria
species have been found.
B. truncatus rohlfsi has so far proved to be the
most common schistosoma host snail on the lake,
and Odei [1970] reports that this snail has been
collected with an infection of Schistosoma
haematobium in the field. He observed also that
the population density of this snail seems to fluctuate with different habitats and areas on the
lake. He recorded densities ranging from 0 to 140
snails per man-hour from various habitats and
areas and field infection rates of 70-50% in the
Afram region.
It has been considered desirable to establish
with some degree of certainty the infective sites of
the disease. This observation makes it pretty certain that, although in some areas the snails may
breed in water bodies near villages situated on the
lakeshore, the lake itself constitutes the main site
of infection.
B. truncatus rohlfsi is the host snail for the S.
haematobium 'strain' [McCullough, 1959] from
which the Battor fishermen from the south Volta
floodplains normally suffer. M. A. Odei (personal
communication, 1971) has recorded that this
snail breeds in the lower reaches of the Obosom
River where it is found to be infected with S.
haematobium.
B. ( Physopsis) globosus is also a snail host for
S. haematobium elsewhere in the country,
although it is a poor one for the S. haematobium
strain that afflicts the Battor fishermen. Odei has
recorded a high density rate of 74 snails per man-
Copyright American Geophysical Union
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
LETITIA E. OBENG
Vol. 17
95
hour of this species in the upper reaches of the
Obosom, but it has not been collected in the
field in an infected condition. The breeding of
this species in large numbers in the Obosom is interesting and, with further studies, may prove to
be a fact of decisive importance.
Two interesting questions emerge from this
discussion. First, Does the presence of the snail in
the Obosom at this time indicate the tail end of a
declining population or is it the beginning of a
new establishment? If the latter, what ecologic
changes could have initiated this new population?
Second, Odei noticed that there appears to be a
demarcation in the distribution of the two
Bulinus species on the °bosom River. In the
lower reaches of the river where B. truncatus
rohlfsi occurs, there is infection among the Battor
fishermen. In the upper section on the same river
where B. ( Physopsis) globosus alone breeds, there
is also a low rate of infection among the people,
although there is no infection among the snails. It
is still to be established whether the infection is of
local origin or due to the migration of persons
from downstream; in either case, is it likely that
B. (Physopsis) globosus will eventually adapt
itself to become an effective host in the area?
Laboratory studies are testing the susceptibility
of the snail to infection with the S. haemotobium
strain of Battor presently found on the Obosorn.
Also, a close study is being made of possible field
infection of B. ( Physopsis) globosus with the
schistosorne.
The medical investigations on the problem
are also interesting. C. R. Jones (unpublished
report, 1970) reports that, in the Afram area
on the western side, for instance, urinary
schistosomiasis in children under 10 years of age
has risen to as high as 90% since the lake formation. On the eastern side the incidence is much
lower. The density of the snail host is also less,
and this low density is suspected to be related to
the steep nature of the shore, which does not encourage a dense growth of weeds. However, with
an increase in the spread of the creeping Alternanthera sp. and Vossia sp., as well as the
presence of sheltered coves and bays, the snail
population may increase. It would seem that snail
hosts are not limited to weeds but may be found
on other convenient substrata, including mud, or
may be collected browsing on rocks. The bilharzia problem is receiving serious attention.
Trypanosomiasis. Although trypanosomiasis
does not pose as serious a threat as schisto-
somiasis, the possible increase in incidence of
trypanosomiasis (sleeping sickness) in the lake
basin has not been overlooked, and studies have
been initiated and maintained on tsetse flies. F.
A. S. Kuzoe (unpublished report, 1970) records
the Daka Valley to be one of the most important
foci for trypanosomiasis in Ghana. It is also the
sole source of water supply in a dry savannah
area, and tsetse growth is associated with its
tributaries. Flies that have been caught on field
trips have been dissected for infections with
Trypanosoma sp. However, the flies Glossina
palpalis and G. tachinoides dissected within the
April-June quarter of 1970 showed only one infection with T. vivax out of 36 flies examined.
Guinea worm. An interesting recent development is a record by C. R. Jones (personal communication, 1971) of guinea worm infection in an
area north of Krachi. The incidence, although it
is localized, is high, and, even though the infective site is outside the lake, the situation is being
carefully watched.
Onchocerciasis. Simulium species were breeding widely in the Volta River before the formation of the lake. As had been expected, the formation of the lake eliminated the breeding sites
above the dam in the area flooded, but Simulium
species other than S. clamnosum, vector of
onchocerciasis (river blindness), were still present
around the lake in a defined area investigated in
1966 [Obeng, 1969b]. A number of rivers farther
north of the area examined have now shown large
populations of Simu/ium species including S.
damnosum, especially around Jasikan where in
September 1970 the flies were actively biting. The
incidence of a high rate of onchocercal parasite
infection in the area has been reported [Jones,
1970]. Both the direct and indirect association of
this high incidence with the lake has necessitated
an intensification of biological studies on the
Simu/ium larval life cycle, seasonal abundance in
relation to stream ecology, and infection rates
and the collection of other relevant information
to facilitate the design of an effective control
program.
Aquatic plants. An impressive list of common
aquatic plants occurring in Volta Lake has been
compiled. They include Pistia stratiotes, Salvinia
nymphellula, Azolla africana, Lemna sp., Cyperus
distans, Eclipta prostrata, Jussiaea repens,
Spirodela, polyrhiza, Utricularia inflexa, Vossia
cuspidata, Cyperus spp., and Ceratophyllum
demersum. The situation at Kariba is unlike the
Copyright American Geophysical Union
Geophysical Monograph Series
96
Man-made Lakes: Their Problems and Environmental Effects
VOLTA LAKE RESEARCH: A CASE STUDY
one at Volta: these weeds in Volta Lake have
been considered problems mainly because of
their association with public health and parasitic
infection problems and their nuisance in connection with fishing.
Submerged Ceratophyllum demersum, as well
as floating Pistia stratiotes, and some other littoral plant forms have been found to provide attachment for snails and other intermediate hosts
of parasites [Obeng, 1969b]. Other plants
(including Alternanthera sp., Polygonum sp., and
Jussiae repens) recorded earlier in the Volta basin
[Hall et al., 1969] have become serious marginal
plants. Conventional chemical control methods
tried on a small scale were unsuccessful, and
other methods, including biological control, are
being investigated.
Agriculture and Wildlife
Perhaps one of the most interesting and rewarding sections of Volta Lake studies has been in
agriculture. As has been stated elsewhere, farming
continues to be an active occupation around the
lake. Even the fisherfolk alternate periods of lean
fishing with farming. This alternation gives great
encouragement to drawdown and lake vicinity
agriculture. The project has carried out studies
and set up experimental plots in parts of the drawdown area. Three experimental stations have been
established at Asantekrom in the southern part of
the lake, Makongo in the north, and Vakpo near
the middle. (See other details by Kalitsi [this
volume], Taylor [this volume], and Butcher [this
volume].)
The extent of the drawdown area has not been
calculated with certainty, but it is hoped that a
definition will be possible after the planned aerial
photography. Whatever its extent, a good
proportion of the lakeshore holds the promise of
potential use for agriculture.
Ghana cannot hope to compete with Kenya in
the field of attractive wildlife, but, as part of the
use of lake potentialities, a wildlife and game
reserve is being established on part of the
lakeshore. It is intended that this reserve will be
used for recreation, education, and sport.
CONCLUSION
I have attempted to present as balanced a picture as possible of the results of environmental
changes, both desirable and undesirable, that
have been produced by the creation of Volta
Lake. The study of these ecologic changes is to be
employed toward using the existing potentialities
in purposeful development and toward curtailing
and controlling the unsatisfactory possibilities
to prevent any undesired drawbacks.
In the course of collating the data, it has been
necessary to analyze and compare various manmade lake research programs. There is an almost
stereotype plan of research being followed on all
the African man-made lakes. The plan is well
designed and comprehensive. According to the
degree of seriousness of problems, each lake puts
stress on certain sections of the program.
However, taking an overall view of man-made
lakes with respect to what is expected of them by
way of development of fisheries, it would seem
that the need of a developing nation lies with investigations that will reasonably ensure the
maintenance of a desirable level of yield.
In the present plan of research, much emphasis
is being placed on stock assessment, processing,
preservation, and so on. This emphasis, presumably, is desirable. Stock assessment, for
instance, will give an estimation of stocks and
will help to devise a plan for wise exploitation of
the resource.
But we do not merely want to exploit
resources. Although the word exploitation is
quite respectable, I cannot help but feel that in
this respect it has a certain connotation of
irreparable destruction. I believe we should use
the potentialities of the resource rather than exploit them. To do this, we need the foresight to
consider solutions to problems on a long-term
basis. Whereas it is necessary to know what
stocks we have, I feel it is even more important,
at this stage, to initiate and encourage investigations into how to maintain the stocks.
In this circumstance, man-made lakes appear
to me to be in a peculiar situation. It may be
possible to restock a lake with new fish should
yields fall. But restocking would be only half the
solution. The vital problem is how to maintain a
sufficiently relevant concentration of nutrient
material at the lower levels of the food chains so
that the food cycles can work satisfactorily.
Fish ponds can have their basic nutrient matter
replenished by the addition of various materials,
chemical and otherwise, to the medium. Natural
lakes of long standing have deposits that serve as
reserves. Our man-made lakes are too new to
have such reserves, and they are generally too
large (true of Volta) to be treated as a fish pond.
By the time the initial postinundation boom in
Copyright American Geophysical Union
Vol. 17
Geophysical Monograph Series
Man-made Lakes: Their Problems and Environmental Effects
97
LETITIA E. OBENG
the fish yield declines, the lake would probably
not have enough bottom reserve to maintain a
satisfactory supply of nutrient material. Even if
new fish are introduced as a means of stepping up
the yield, the new population will need nutrient
materials.
How then do we augment and maintain a
satisfactory level of nutrient matter to sustain our
yields? We have started to investigate the quantity of matter brought in by the riverine areas. We
are also investigating possibilities of certain
physiological studies, but it is an exercise that
needs to be done on a wide basis.
For Volta Lake, fishing is not a sport. It is a
means of obtaining valuable protein. It provides
an occupation on which about 20,000 people depend. A decline in fish production is a serious
matter. Preventing a continuous decline is vital.
Replacing and maintaining a satisfactory level of
nutrient material appear difficult, but such a level
is important and should receive conscientious
and urgent attention.
To find a breakthrough, we shall have to identify the key factors on which the productivity of
the microflora and microfauna depends. We shall
have to understand physiology and energy absorption at that level. This search for knowledge
may entail a large amount of basic or what is
often called pure research, but it will not only be
pure in research, it will also be pure in its intention in that it will seek to contribute a solution to
a pressing problem, i.e., maintaining a satisfactory level of basic nutrients.
Do we have to try chemical fertilizers? On the
scale of Volta, such fertilizing will need careful
consideration and planning. Do we rear ducks?
How? Or do we use our aquatic weeds? There are
possible avenues that we might explore.
The important thing now, as I see it, is to
begin. Hopefully, by jointly studying the basic
requirements, we can find a solution for the
replacement and maintenance of the nutrient
materials in man-made lakes to help them out
during the critical periods.
Insofar as Volta is concerned, it must be said
on a comparative basis that the ecological nature
of the new environment and its impact on the
people and their various occupations have, on the
whole, not been unsatisfactory. The contribution
of the lake to national development shows high
promise. How events go in the future with the
maturation of the lake will depend on our
foresight and planning at the present time.
Vol. 17
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Universities Press, Accra, 1969.
Bates, D. A., Geology, in Agriculture and Land Use in
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Biswas, S., Thermal changes in the Volta Lake at Ajena,
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Butcher, D. A. P., Sociologic aspects of fishery development on Volta Lake, in Man-Made Lakes: Their
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Copyright American Geophysical Union
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Man-made Lakes: Their Problems and Environmental Effects
Vol. 17
VOLTA LAKE RESEARCH: A CASE STUDY
98
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Copyright American Geophysical Union
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