ARI Volume 1 Number 2.pdf - Zoology and Environmental Biology ...

Physico-chemical parameters of an African aridzone man made lake
Table 1: Physico-chemical Parameters is Relation to Stations in Lake Alau
Parameters
S T A T I O N S
1 2 3 4 5
Temperature o C
25.25±0.18
Depth (m)
Current (Cm/sec)
Transparency (m)
pH
Dissolved oxygen (Do)
(mg/l)
Conductivity (homs/cm)
Free Co2 (mg/l)
Alkalinity (mg/l)
Biochemical oxygen
Demand BOD (mg/l)
Nitrate-Nitrogen (No3-N)
(mg/l)
Phosphate-phosphorus (P-
Po4) (mg/l)
Total dissolved Solids TDS
(mg/l)
b
2.85±0.18 c
26.71±0.30 b
0.36±0.01 b
6.79±0.05 b
6.15±0.05 a
31.45±0.75 b
2.55±0.05 b
30.30±0.32 b
4.34±0.32 a
4.27±0.18 a
0.34±0.00 b
63.31±0.30 b
25.05±0.14 b
3.64±0.03 b
25.46±0.27 b
0.33±0.02 b
6.97±0.03 b
6.35±0.05 a
128.8±0.52 b
2.90±0.01 ab
36.85±0.05 b
4.30±0.28 a
5.43±0.19 a
0.28±0.00 b
67.88±0.28 a
25.05±0.19 b
3.92±0.25 b
25.08±0.36 b
0.35±0.01 b
6.83±0.02 b
5.18±0.02 b
119.42±0.83 a
2.85±0.02 ab
40.67±0.18 a
4.45±0.50 a
5.4 o ±0.25 a
0.37±0.10 a
59.17±0.42 b
27.24±0.12 a
7.23±0.13 a
25.10±0.28 b
0.42±0.03 a
7.29±0.05 b
6.32±0.01 a
115.47±0.75 a
3.06±0.04 a
47.00±0.02 a
5.03±0.33 a
5.73±0.37 a
0.31±0.01 b
65.84±0.62 a
25.13±0.00 b
3.18±0.06 b
19.62±0.22 a
0.26±0.01 c
6.59±0.01 b
5.15±0.03 b
118.41±0.16 a
2.84±0.04 ab
37.25±0.24 b
5.31±0.25 a
6.30±0.50 a
0.32±0.01 b
60.73±0.33 b
The mean values with the same superscript on the same row are no t significantly different at P ≤ 0.05
The mean values recorded for depth showed
that station 4 had the highest mean depth of
7.23 ± 0.13 m. The lowest mean value of 2.85
± 0.18 m was recorded in station 1. Station 4
was significantly deeper than all other stations
(P < 0.05). There was no significant difference
in depth between stations 2, 3 and 5 (P > 0.05).
These stations were significantly different from
station 1 (P < 0.05). The depth variations of
each station may be attributed to the structure
of the Ngadda river valley and the surrounding
land prior to impoundment. The water current
varied from 19.62 ± 0.22 cm/sec in station 5, to
26.71 ± 0.30 cm/sec in station 1. Station 5 was
significantly different from all the other stations
(P>0.05). The highest mean water current
observed in station 1 may be due to regulation
from the dam site, and the release from this
station resulting in a constant flow of water. A
factor of potential limnological significance is
water movement within the lake produced by
discharge from the upstream reservoir and the
release down stream (station 1). The actual
effects of the current on the chemistry and the
biota of the lake are not known, but one may
speculate that significant water movement
through the surface of the lake may prevent
development of anoxic conditions in an
otherwise stagnant environment and thereby
preclude release of sediment bound nutrients.
The values recorded for lake Alau were low
compared with 32.80 cm/sec recorded in lake
Chad (Nwoko, 1991). The reason may be due to
large volume of water in lake Chad compared
with lake Alau.
115
The highest mean values of Secchi disc
transparency recorded was 0.42 ± 0.03 m in
station 4, while the lowest mean value was 0.26
± 0.01 m in station 5. Stations 1, 2 and 3 were
not significantly different P > 0.05). These
stations were significantly different from
stations 4 and 5 (P < 0.05). Light penetration
in a lake estimated by use of Secchi disc is an
indicator of water transparency and turbidity
(Olsen, 1975). The mean transparency values
from other stations showed signs of good
quality except for station 5, which reflect high
turbidity during the study period. The high
turbidity may be linked to the constant
disturbance and agitation of the water body by
canoe paddlers, as well as constant washing in
of sand material from the burrow pits. The
quality may not, however, have adverse effect
on the aquatic organisms in the lake. The
values of transparency recorded in lake Alau
was low compared with the findings of Nwoko
(1983) in Lake Chad (0.92m) and Adeniji (1989)
in Jebba lake (0.75 m).
The mean pH values recorded for all
stations varied between 6.59 ± 0.01 and 7.29 ±
0.05. There was no significant difference
(P>0.05) between the values recorded for all
stations. Lake Alau falls between acidic and
alkaline Lake. The pH range obtained in the
lake suggests a medium carbon dioxide supply
and medium productivity. The pH range is
comparatively narrow but falls within the
recommended range (6.5 – 9) as suitable for
aquatic life (Adeniji, 1989). A pH of 5.5 – 10
was recommended as optimum range for