Environmental Engineering Reference
In-Depth Information
Table 2
Concentration of nutrients in the sediments of Lagos Lagoon System
Sampling
location
Total PO
4
3-
-P (Mean ± SD)
(mg kg
-1
)
Bioavailable PO
3
-P
(Mean ± SD) mg kg
-1
NO
2-
/NO
3
(Mean ± SD)
(mg kg
-1
)
Percent
bioavailable (%)
P:N
Ratio
Akoka
326.6 ± 15.2
4.65 ± 0.76
1.42
11.24 ± 0.38
0.41
Okobaba
619.3 ± 33.4
7.45 ± 0.26
1.2
0.92 ± 0.06
8.1
Iddo
1,203.9 ± 171.6
20.94 ± 0.62
1.74
0.71 ± 0.08
29.49
Ijora
253.5 ± 100.8
4.52 ± 0.52
1.78
6.56 ± 0.12
0.69
Leventis
65.9 ± 31.8
9.48 ± 0.84
14.38
4.43 ± 0.12
2.14
Cowry Creek
174.5 ± 96.0
8.90 ± 0.78
5.1
9.85 ± 0.32
0.9
Falomo
637.2 ± 4.2
17.03 ± 0.28
2.67
0.56 ± 0.08
30.36
Mean
468 ± 387
10.4 ± 6.2
4.0 ± 4.8
4.90 ± 4.47
10.3
collected from the Lagos Lagoon between January 2004 and
March 2005 were analysed, and all physicochemical
parameters were determined. Table
1
gives the results for
physicochemical properties of the water samples collected
from different parts of the Lagos lagoon. Points Q, R and S
are Iddo, Oko-Baba and Oworonshoki, respectively, by
(Fig.
1
) and are close to human activities, while Cow (Five
Cowrie Creek) and PAL (Palavar Island) are points on the
Lagos Lagoon that are far from industrial or domestic
activities.
The dissolved oxygen (DO) at points Q, R and S
appeared to be independent of tide or seasons and is suitable
for aquatic life to survive. This is because in spite of pol-
lution of the water by sewage and other domestic wastes,
the impact of the pollution is not felt because of the rela-
tively large volume of water in the Lagos Lagoon which
facilitates dilution of the pollutants. The highest DO values
were observed at COW and PAL which are far from human
and industrial activities.
The biochemical oxygen demand (BOD) values for
points Q and S were the highest. This was probably because
of the untreated sewage discharged into the Lagos Lagoon
at point Q, and industrial effluents and domestic wastes at
point S which may contain high level of organics.
The chloride content of the water is expectedly high.
This is due to the presence of chloride salts in the sea water
which flows into the Lagos lagoon when the tide is high.
The pH range at all the points fall within the WHO limit for
unpolluted water (6.5-8.5).
Generally, points Q, R and S were more polluted than
COW and PAL in terms of the DO, BOD and pH values of
the samples collected. This may be because domestic wastes
are discharged into the Lagos lagoon at these points.
Nutrients Status in the Sediments of Lagos
Lagoon System
Abayomi et al. (
2011
) reported on the potential of the Lagos
lagoon sediment to act as a sink for anionic nutrient from
highway run-off and roadside soils contiguous to the lagoon
system. Concentrations of total phosphorus ranged from
73 ± 20 to 622 ± 514 mg kg
-1
in the wet season and
170 ± 10 to 1,320 ± 480 mg kg
-1
in the dry season. The
bioavailable concentration had a range of 2.57 ± 0.64 to
9.4 ± 5.1 mg kg
-1
and 4.8 ± 0.7 to 22.0 ± 0.9 mg kg
-1
for the wet and dry season, respectively. The concentrations
of bioavailable NO
2-
/NO
3-
in the roadside samples ranged
from 0.53 ± 0.64 to 12.35 ± 32.88 mg kg
-1
for the wet
season and 0.39 ± 0.08 to 21.35 ± 0.50 mg kg
-1
for the
dry season. In the Lagoon sediment, phosphorus had a mean
concentration range of 468 ± 387 mg kg
-1
total phospho-
rus and 10.4 ± 6.2 mg kg
-1
bioavailable phosphorus for
the sampled locations (Table
2
). Watersheds of the high-
ways on the lagoon had higher concentrations of these
nutrients relative to other locations on the Lagoon which
confirm roadside as soils as sources of nutrient input into
the Lagos Lagoon.
Average Phosphate Concentration in the Lagos
Lagoon
Results from the study showed a mean bioavailable phos-
phate concentration range of 0.046-0.91, 0.046-0.453 and
0.048-0.492 mg L
-1
, respectively, for the top, middle and
bottom strata of the lagoon. Mean total phosphate concen-
trations were in the range of 0.054-0.513, 0.041-0.961 and
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