EFFECTS OF SEDIMENT INPUTS ON AQUATIC ANIMALS COMMUNITIES IN A MAN-MADE LAKE IN ILORIN, NIGERIA

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African Journal of Applied Zoology & Environmental Biology. 2006. Vol. 8,
86


89

ISSN 1119
-
023X

www.uniportjournals.com/ajazeb


EFFECTS OF SEDIMENT INPUTS ON AQUATIC ANIMALS


COMMUNITIES IN

A MAN
-
MADE LAKE IN ILORIN, NIGERIA



*
Chioma
G
.
Achionye
-
N
zeh and
I.
Bello

DEPARTMENT OF ZOOLOGY
,
UNIVERSITY OF ILORIN

ILORIN NIGERIA



ABSTRACT

The effects of sediments inputs on aquatic anim
a
l
s’

communities in a man

made lake in
Ilorin Nigeria

were studied.
Samples of the
sediments were

collected using Ekman’s
grab Sediments

were
sieved through

various mesh sizes until
fine silt were obtained.

Macroinvertebrates were collected using scoop n
ets and identified. The water
temperature
P
H
,

dissolved oxygen content and transparency were measured from June to September2005. The results indicated that
temperature
and dissolved

oxygen content were within tolerable range for the animals.

Silt was grad
ually being
deposited in the lake and some parts of the lake is silted up resulting in loss of water in such areas of
the environment

and decrease in the population of
Macroinvertebrates

such
as Biomphalaria

sp
, Lymnae

sp and
Asphatharia

sp in the
affect
ed
areas. The

lake was gradually being degraded due to loss of water in the environment because of siltation.


Key words:

Silt, Freshwater, Degradation
, Macroinvertebrates
, fishes and Environment.



INTRODUCTION


Reservoir or

man
-
made lake is an artif
icial basin
with a river source and it is constructed by
damming a river or
stream (
Strastraba et al 1993).
Events in the catchment natural or otherwise
determine environmental condition in the
lacustrine environment of the reservoir
and this

usually may h
ave consequences on the
performance of the reservoir function as well as
the animal in the reservoir (Strastraba
et al

1993
;
Waters1995
).

Catchment
disturbance

that results in fine
sediment inputs into streams has
been identified
a
s a major contributor to
the
degradation of

freshwater habitat (Kreutzweiser
et al
2005)

Factors such
as agricultural

tillage,

urbanization, mining, road and house construction
and logging activity result in sediments inp
uts and
deposition in wat
er bodies (Sommer and
Hassler1992,)
.

Wetzel (1990), Lind (2003) demonstrated that
siltation occurs when clay from catchment
watershed are washed into the
reservoir. Clay

sedimentation destalabilizes the benthos which
can result in loss of habitat which increases drift of
the benthic animals

or reduction in food
quality
.
Some biological consequences of sedimentation
include decline in benthic invertebrates abundance
and or changes in community structure (Wood and
Armitage 1997
,
Kreutzweiser
et al

2005).

Clay suspended in water has been shown
to
increase
turbidity. This

in turn affects fish by




*Correspondence

Author
:
C
.

G. A
chionye
-
nzeh


interfering with visual detection of prey and
reduction of overall food base by reduction of
photosynthesis. Clay turbidity can affect the ability
of sight feeding fishes to forage but not all
(Cuker1993,

Dre
nner 1997).

Sedimentation of clay is widely recognized as
a problem of
fish.
Walser and Bart (199
9
)
observed loss of coarse substrate using

fish

species as a result

of

clogging and

this lessened

the

fish community.
Whereas eggs

of benthic
spawners we
re susceptible to damage from
sedimentation
.

Elevated

levels of clay turbidity in
the water column can favour

fish

species

with
pelagic egg or larvae because of lower
susceptibility to visual
predators (Hay
es et al 1992,
Gliwicz 1999). Clay sedimentation i
s not harmful to
all fishes while there is decline in some taxa with
sedimentation , those cyprinids that are mound
builders and centrachid that excavate nests
in soft
sediments increased (Suth
erland et al 2002).

The objectives of this research are : To
m
easure fine sediment content of the lake and
some physico

chemical parameters of the lake;
To asses the effects of siltation on the
Macroinvertebrates

and fishes in Agba lake in
Ilorin , Kwara State.


STUDY AREA

Agba
Lake

is located in the eastern par
t of
Ilorin
Kwara

State. It lies between latitude
8º 30'N.

and
longitude 4
º

35
'
E.
It was

constructed and
commissioned in 1956.The depth is between 14
and17 meters. The dam has a storage capacity of
50million litres during rainy
season.The dam

was
construc
ted primarily to supply water
for domestic

and industrial
usage

in Ilorin.

Chioma G. Achionye
-
N
zeh and I. Bello


Afr. J. of Appl. Zool. & Environ. Biol. 200
6
. Vol. 8


87

MATERIALS AND METHODS


Sediment
Collection:

Fine sediments were
collected from the lake bed with Ekman’s grab.
Five loads of sediment bed were collected from
each point. The sedime
nt
s

were
sieved using

series of mesh sieves until very fine sediments
were
collected. The

fine
sediments were

air dried
and weighed .The percentage fine sediment
s

were
calculated. Sampling

was carried out in a stratified
random manner from various sections

of the
lake
between

June to September

2005.

A qualitative sampling of invertebrates that
were exposed to dry section of the lake were
collected using scoop nets. The content of the
scoop net were preserved in 10% formaldehyde.
In the laboratory the
organi
sm were

sorted out and
identified to genus or species.

The fishes were sampled during the study
period using cast and gill
nets and

they were
identified to species.

The dissolved oxygen content of the water
was measured using
titrimetric method
. The
trans
parency of the water was measured using the
sechi disc the diameter was 20.20cm. The surface
water temperature and pH were determined using
the mercury in the mercury in glass
thermometer
and

a pH meter respectively.


RESULTS


The surface water temperatur
e in Agba lake
varied from
23º
C

to
27º
C.The water transparency
fluctuated between 88.75cm in June ,135cm in
July , 113cm in August and 91.37cm in
September.
The pH

of the water varied from 6.9 in
June 7.17

in July 7.4 in August and 7.38 in
September. Ther
e

were little fluctuation in these
physical
parameters (
Table1)

The dissolved oxygen content of the lake was
3.6mg/Lin July and in August it was 4.4mg/L in
September. The

dissolved oxygen content
fluctuated minimally.

The silt content was 11.27 to31.62%in

June,

15% in
July,

14.2 to 16 5 in August and 21.9 to
24.6% in September
. (
Table2).

The invertebrates collected were mollusk. The
two classes represented were Gastropoda and
Bivalvia. The gastropods
were
Biomphalaria

and

Lymnae

species with
Lymnae

consti
tuting about
80
% and

Biomphalaria

constituting about 15%.
Bivalves mostly
Asphatheria

species formed about
5% of the invertebrates collected.

The fishery composition of the lakeshowed
that the family ciclidae represented by
Hemichromis fasciatus
,
Tilapi
a zillii Sarotherodon
galilaeus and Oreochromis niloticus
were the most
abundant fish

species constituting about
8
5
%of
the
catch. Other

families represented were
bagridae;

Chrysithyes nigrodigitatus and
Auchenoglanis occidentalis

which formed 10%of
the
cat
ch while

family
Anabantidae represented

by
Ctenopoma

kinsleye

formed about 5% of the
catch.

Table 1

Dissolved Oxygen
,

Transparency, Temperature
a
nd
P
h Content
o
f Agba Lake

MONTH

TRANSPARENCY

TEMPERATURE
(
O
C)

DO
2

p
H

(Mg/L)

JUNE



79
-
108.30

26
-
27

3.8
-
4.6

6
.75
-
7.2


MEAN

88.75


26.50

4. 25

6.91

JULY


126
-
135.50

26.5
-
27

3.4
-
3.8

7.16
-
7.18


MEAN

145


26.63

3.6

7.17

AUGUST


106
-
120

22.5
-
26


3.6
-
4.0

7.35
-
7.5


MEAN

113.81

24

3.8

7.4

SEPTEMBER


102
-
131.5

23.5
-
23.8

4.0
-
4.6

7.36
-
7.5


MEAN

118.75

23

4.4

7.38


Chioma G. Achionye
-
N
zeh and I. Bello


Afr. J. of Appl. Zool. & Environ. Biol. 200
6
. Vol. 8


88

Table
2; Monthly

Variation
in

Silt Content
o
f Agba Lake

Month

Daily sil
t weight

(g)

Daily silt weight after
drying

(
g)

Average silt

%

June


Week 1

400

600


25
-

38.23

31.61


Week 2

200
-
220

19.03
-

19.14


19.09


Week 3

130
-
150

10.71
-
11.82

11.27


Week 4

120
-
146

10.21
-
11.23

10. 64

July





Week 1

150
-
16
0

15.5
-
16.25

1
5.85


Week 2

14.3
-
17
0

14.16
-
17.00

15.63


Week 3

150
-
16
0

15.00
-
16.25


15.90

August





Week 1

160
-
17
0

16.24
-
17.00

16.63


Week 2

150
-
16
0

14.29
-
14.4
0

14.32


Week 3

175
-
18
0

16.70
-
18.3
6

17.68


Week 4

125
-
12
8

10.87
-
11.6
4

11.26

September





Week 1

250
-
280

21.54
-
22.73

22.14


Week 2

300
-
35
0

20.00
-
23.9
7

14.32


Week 3

300
-
40
0

21.54
-
22.7
3

22.14





DISCUSSION


The water temperature and pH values obtained in
the lake were within tolerable limits for aquatic
organisms .The temperature range obtained f
rom
June to September was within the range obtained
by Kemdirim (1990) for Shandam reservoir in
Plateau state from May to October
1990.



Transparency obtained in the present work
was between (88.75 and 135cm) .These values
attributed to the presence of suspended matter in
the lake .
S
cattering
of solar

radiation in water
increased as a result of infl
ux of suspended matter
.Kemdirim (1990) obtained high transparency
ranging from 77.50 and 293.0cm in Pankshin
reservoir and a low sechi disc transparency value
of 11.0 and 108.50cm was obta
ined in S
hendam
reservoir.
The silt content of the reservoir was

ob
served

to be high near the month of June .Silt
has gradually over the years accumulated in Agba
lake with a portion of the lake d
rying

up during the
dry season .The result is loss of aquatic
environment and the animals in the environment
during the months
of June and July .Many mollusk
especially Biomphalaria ,
Limnea

and
Asphateria
were exposed to dry condition because of loss of
water in the section in the section of the lake
habitat and the animals were
desiccated
However
when heavy rainfall comes, the
dry region regains
water again
.

There are ecological consequences if this
condition continues in this water body .
Firstly;

the
accumulation of silt in the lake has effect on the
aquatic animal
biomass.
In Agba
lake, there

is
gradual reduction of the abunda
nce of
Biomphalaria and Lymnae (Gastropod) and
Bivalves
Aspatharia
species
.

This is due to the death of these organisms in
the lake. Similar observations of decline was in
invertebrate fauna was made by Krutzweiser
et al

2005.

Furthermore, the accumulation

of silt in this
lake has effect on the animal diversity of the
lake.
There is decline in richness of animal
invertebtrates in the lake .Since there is no
precautionary measure being taken to check this
situation more silt will be washed into the lake over

a period of time resulting in decline of population
of
Biomphalaria, Lymnae

and Aspatharia in the
lake.

The factors identified as being responsible for
the deposition of silt in Agba
Lake

are:
Construction

of houses around the
lake,

the dam
was constructe
d in 1956 and there were not much
activities around the lake .The excavated soil are
washed into the lake.

Agricultural practices
around the lake led to removal of grasses that
protect the topsoil and during the rainy season the
soil is washed into the
la
ke. If

these practices
continue unabated it implies that during every
rainy season more silt will be deposited in the lake
and with time the lake will be lost as silt will have
occupied the basin instead of the water.

The fishes in this water body will be
affected
because during breeding the nest of Cichlids are
built in the shallow section of the lake and if this
habitat has been lost to silt, the eggs cannot be
deposited in dry zone and many eggs of these
Chioma G. Achionye
-
N
zeh and I. Bello


Afr. J. of Appl. Zool. & Environ. Biol. 200
6
. Vol. 8


89

fishes will be
wasted.

This research has shown
tha
t there is gradual degradation of this freshwater
habitat due to human activities around the
catchments

zone and if this development is not
checked immediately, Agba
Lake

will gradually dry
up and the animal community in it will be lost due
to devastation
of the environment.


REFERENCES


Wezel, R.G.
(1983) Limnology Saunders
cell.
coll.
P
hiladelphis 858pp
.



Hart, R. 1987: population dynamics and of five
crustacean zooplankters in a subtropical
reservoir during years of contrasting
turbidity.
Freshwa
ter Boil
.
18
:287
-
318.


Cuker, B. 1987: Field experiment on the influences
of suspended clay and p on the plankton
of a small lake.
limmol Oceanogr

.
32
: 840
-
847



Gliwicz, M. Z. 1999 suspended clay concentration
by filter


feeding z
ooplankton in a tropical
reservoir
Nature

323
: 330
-
332


Kreutzweiser, D. P. Scott S. C and GOOD, K.P.
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communities
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strea
m
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Lund, O.

L and Davalos
-
Lund, L. (1999)
suspended clay: its role in Res
rvoir
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Ecology and its Applications
83
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97 Ed.
J.G. Tundisi and M.S T
raskraba
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Academy

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ublishers.


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C. (1990) Periodicity and Succession
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