544
areas not directly exposed to wave action, belts of
Typha and Aponogeton become separated by large
beds of water lily, namely, Nymphaea sp., which
may fi nd anchorage in depths as great as 4 m. The
bottom deposits are generally relatively constant
throughout the lake. The mud is usually soft and
black with an admixture of decomposing plant
matter. In general, the artifi cial lakes of this region
are of warm monomictic type. Maximum water
temperatures of epilimnion and hypolimnion are
22 and 24 °C, respectively. Storms and squalls prevent the formation of stable epi- and hypolimnion
during the rainy season. The thermocline is usually
at a depth of 10 m. The water pH ranges from 6.8
to 9.0. Hypolimnion had low DO. The water
showed fairly high level of nitrates and nitrites
mainly because of release of sewage effl uents into
the lake. Samples of mud from the profundal region
were always devoid of macroscopic animal life.
The phytoplankton predominantly consisted of
Anabaena , Volvox , Pediastrum , Staurastrum , diatoms, etc. The zooplankton comprised of
Brachionus calycifl orus , Keratella tropica ,
Trichocerca sp., Filinia sp., Daphnia sp.,
Ceriodaphnia sp., Moina sp., Bosmina longirostris , etc. Preliminary analysis of fi sh food consumed indicated that the littoral invertebrates
played a remarkably restricted role in the feeding
habits of adult fi shes. The mean standing crop of
benthic invertebrates had been estimated as 230 kg/
ha. Study, further, indicated that the invertebrates
are usually randomly distributed throughout the
upper layers of the mud. Twenty-one species of
fi shes were known to occur in the lake. There
occurred also a rich diversity of aquatic birds in the
lake. The general features of Lake McIlwaine are
considered as typical of certain other lakes in
Africa, notably Lake Fundudzi (Soutpansberg in
South Africa), Lake Shirwa (in Malawi), etc. The
standing crop of the lake is considered as of average richness.
24.6.2 A Limnological Study of the
Afram Arm of Volta Lake
The Afram arm of the Volta Lake is shallow. It
receives frequent winds, which, together with
the fl oods of the June to September, create
near- isothermal conditions. The upper 10 m is
well oxygenated, 2 mg/l (approx.), reaching
the bottom for most part of the year. It is poor
in nutrients. TDS values lied between 40 and
60 mg/l. Frequent algal blooms of Oscillatoria
curviceps , Microcystis aeruginosa , etc.,
occurred. The NPP in some areas had ranged
between 8.4 and 142.5 mg C/m
3 /h. It has been
suggested that the high tropical temperatures
encourage quick recycling leading to relatively
high organic production, thus making this arm
non-oligotrophic (Obeng 1977 ).
Summary
1. In Tanzania , Lake Natron is a salt lake located
in northern Tanzania, close to the Kenyan border. It is an important habitat for fl amingos
and is home to endemic algae, invertebrates
and even fi sh that can survive in salt water.
2. In Kenya , the Yala Swamp is a wetland in
western Kenya. The wetland is said to act as a
fi lter for waters that fl ow into Lake Victoria
from two major rivers. It is sometimes considered as the source of the River Nile. The
swamps harbour endangered fi sh species like
Oreochromis esculentus and Oreochromis
variabilis which have disappeared from Lake
Victoria itself. The critically endangered
Sitatunga Antelope( Tragelaphus spekii ) still
lives in the swamps’ papyrus. In addition,
Lake Bogoria is a shallow (depth about 10 m)
saline, alkaline, meromictic lake, situated in a
volcanic region in Kenya. The lake is a Ramsar
site and has been a protected National Reserve.
3. In Nigeria , the Hadejia-Nguru wetlands are
situated in Yobe State in northern Nigeria. The
wetlands are important ecologically and economically. They are threatened due to reasons
like reduced rainfall in recent years, a growing
population and upstream dam construction.
Further, Lake Chad is one of the biggest lakes
in Africa bordering countries like Chad,
Cameroon, Niger and Nigeria on the edge of
the Sahara Desert. Lake Chad is economically
very important.
4. In Botswana , the wetlands in Botswana have a
signifi cant impact on the livelihood of the
people. The Okavango Delta (or Okavango
Swamp ) is a large inland delta, formed where
24 Wetlands of Africa
areas not directly exposed to wave action, belts of
Typha and Aponogeton become separated by large
beds of water lily, namely, Nymphaea sp., which
may fi nd anchorage in depths as great as 4 m. The
bottom deposits are generally relatively constant
throughout the lake. The mud is usually soft and
black with an admixture of decomposing plant
matter. In general, the artifi cial lakes of this region
are of warm monomictic type. Maximum water
temperatures of epilimnion and hypolimnion are
22 and 24 °C, respectively. Storms and squalls prevent the formation of stable epi- and hypolimnion
during the rainy season. The thermocline is usually
at a depth of 10 m. The water pH ranges from 6.8
to 9.0. Hypolimnion had low DO. The water
showed fairly high level of nitrates and nitrites
mainly because of release of sewage effl uents into
the lake. Samples of mud from the profundal region
were always devoid of macroscopic animal life.
The phytoplankton predominantly consisted of
Anabaena , Volvox , Pediastrum , Staurastrum , diatoms, etc. The zooplankton comprised of
Brachionus calycifl orus , Keratella tropica ,
Trichocerca sp., Filinia sp., Daphnia sp.,
Ceriodaphnia sp., Moina sp., Bosmina longirostris , etc. Preliminary analysis of fi sh food consumed indicated that the littoral invertebrates
played a remarkably restricted role in the feeding
habits of adult fi shes. The mean standing crop of
benthic invertebrates had been estimated as 230 kg/
ha. Study, further, indicated that the invertebrates
are usually randomly distributed throughout the
upper layers of the mud. Twenty-one species of
fi shes were known to occur in the lake. There
occurred also a rich diversity of aquatic birds in the
lake. The general features of Lake McIlwaine are
considered as typical of certain other lakes in
Africa, notably Lake Fundudzi (Soutpansberg in
South Africa), Lake Shirwa (in Malawi), etc. The
standing crop of the lake is considered as of average richness.
24.6.2 A Limnological Study of the
Afram Arm of Volta Lake
The Afram arm of the Volta Lake is shallow. It
receives frequent winds, which, together with
the fl oods of the June to September, create
near- isothermal conditions. The upper 10 m is
well oxygenated, 2 mg/l (approx.), reaching
the bottom for most part of the year. It is poor
in nutrients. TDS values lied between 40 and
60 mg/l. Frequent algal blooms of Oscillatoria
curviceps , Microcystis aeruginosa , etc.,
occurred. The NPP in some areas had ranged
between 8.4 and 142.5 mg C/m
3 /h. It has been
suggested that the high tropical temperatures
encourage quick recycling leading to relatively
high organic production, thus making this arm
non-oligotrophic (Obeng 1977 ).
Summary
1. In Tanzania , Lake Natron is a salt lake located
in northern Tanzania, close to the Kenyan border. It is an important habitat for fl amingos
and is home to endemic algae, invertebrates
and even fi sh that can survive in salt water.
2. In Kenya , the Yala Swamp is a wetland in
western Kenya. The wetland is said to act as a
fi lter for waters that fl ow into Lake Victoria
from two major rivers. It is sometimes considered as the source of the River Nile. The
swamps harbour endangered fi sh species like
Oreochromis esculentus and Oreochromis
variabilis which have disappeared from Lake
Victoria itself. The critically endangered
Sitatunga Antelope( Tragelaphus spekii ) still
lives in the swamps’ papyrus. In addition,
Lake Bogoria is a shallow (depth about 10 m)
saline, alkaline, meromictic lake, situated in a
volcanic region in Kenya. The lake is a Ramsar
site and has been a protected National Reserve.
3. In Nigeria , the Hadejia-Nguru wetlands are
situated in Yobe State in northern Nigeria. The
wetlands are important ecologically and economically. They are threatened due to reasons
like reduced rainfall in recent years, a growing
population and upstream dam construction.
Further, Lake Chad is one of the biggest lakes
in Africa bordering countries like Chad,
Cameroon, Niger and Nigeria on the edge of
the Sahara Desert. Lake Chad is economically
very important.
4. In Botswana , the wetlands in Botswana have a
signifi cant impact on the livelihood of the
people. The Okavango Delta (or Okavango
Swamp ) is a large inland delta, formed where
24 Wetlands of Africa