International Journal of Aquaculture, 2013, Vol.3, No.15, 79
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84
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finally moderately soft. Hydrogen ion concentration (pH)
is the standard measure of how acidic or alkaline a
solution is. It is measured on a scale from 0-14. pH of 7
is neutral; pH less than 7 is acidic while pH greater than
7
is basic. The closer pH gets to 1, the more acidic while
the closer pH gets to 14, the more basic (Kelly-Addy et
al., 2004). The pH scale is logarithmic, which means that
a unit decrease in pH equals a tenfold increase in acidity.
Hydrogen ion concentration ranged between 7.7±0.15
(
March, 2012) and 9.1±0.13 (December, 2011). This
value exceeded the maximum permissible limit of the
standards. Nitrates are a form of nitrogen, which is found
in several different forms in terrestrial and aquatic
ecosystems. These forms of nitrogen include ammonia
(
NH
3
),
nitrates (NO
3
),
and nitrites (NO
2
) (
USEPA, 2012).
Nitrate is less toxic than the other forms of nitrogen in
the aquatic environment, such as nitrite and ammonia.
The nitrate concentration in surface water is normally
low, but can reach high levels from agricultural runoff,
or from contamination by human or animal wastes
(
CCME, 2009). Nitrates ranged between 0.6±0.14
(
December, 2011) and 113.4+8.88 (June, 2012). This
value exceeded the maximum permissible limit of the
standards. Phosphate (PO
4
3-
)
can be found as a free ion in
water systems and as a salt in terrestrial environments used
in detergents as water softeners (Turner Designs, 2012).
Phosphates can be in organic form (organically-bound
phosphates) or inorganic form (including orthophosphates
and polyphosphates). Phosphates ranged between
0.0
±0.01 (February, 2012) and 0.7±0.09 (March, 2012).
Air temperature is a measure of how hot or cold the air is.
It is the most commonly measured weather parameter.
More specifically, temperature describes the kinetic
energy, or energy of motion, of the gases that make up air.
As gas molecules move more quickly, air temperature
increases. Air temperature ranged between 26.3±1.31
(
December, 2011) and 35.3±0.48 (January, 2012). Results
of the Duncan’s Multiple Range Test showed that there
was significant difference in all the parameters excluding
nitrates throughout the study period.
Table 1 Mean values of physico-chemical parameters of River Ogun, Abeokuta, Ogun state, Nigeria
Month
December, 2011 January, 2012 February, 2012 March, 2012 April, 2012
May, 2012
June, 2012
WT
27.0
±0.41
a
30.0
±0.58
ab
30.3
±0.04
b
30.0
±0.10
ab
32.1
±0.50
b
31.7
±2.54
b
26.9
±1.1
a
DO
2.9
±0.40
a
2.8
±1.95
a
3.3
±0.77
a
4.2
±0.64
a
6.6
±0.36
b
7.7
±0.50
b
6.6
±1.21
b
COND
180.5
±6.64
c
131.3
±14.42
ab
99.0
±7.84
a
99.0
±8.44
a
119.5
±8.74
a
131.8
±8.19
ab
177.8
±33.25
bc
TDS
90.8
±3.35
c
64.8
±7.47
a
48.8
±3.68
a
49.8
±3.42
a
59.5
±4.29
a
66.5
±4.91
ab
88.8
±16.67
bc
TRANS
0.7
±0.07
c
0.7
±0.09
bc
0.7
±0.08
bc
0.6
±0.15
bc
0.4
±0.08
bc
0.2
±0.08
ab
0.6
±0.02
a
ALK
5.0
±1.35
a
4.4
±0.38
a
4.8
±0.75
a
5.0
±0.58
a
17.8
±0.25
b
5.3
±1.03
a
5.5
±0.29
a
HARD
55.0
±1.91
a
45.5
±4.79
a
47.5
±7.80
a
82.0
±37.62
a
105.0
±46.74
a
56.0
±4.76
a
67.0
±13.13
a
pH
9.1
±0.13
c
7.8
±0.30
a
8.0
±0.33
a
7.7
±0.15
a
8.2
±0.28
ab
8.1
±0.11
ab
8.7
±0.08
bc
NITR
0.6
±0.14
a
2.2
±0.92
a
2.6
±0.85
a
58.0
±4.89
a
26.1
±5.91
a
43.4
±7.95
a
113.4
±8.88
a
PHO
0.1
±0.02
ab
0.1
±0.03
ab
0.0
±0.01
a
0.7
±0.09
d
0.2
±0.05
b
0.1
±0.02
ab
0.4
±0.02
c
AIRTEMP 26.3±1.31
a
35.3
±0.48
c
31.8
±0.85
a
31.0
±0.41
a
33.3
±0.85
bc
31.0
±0.41
b
28.0
±0.58
b
Note: Variables with the same superscript across the column are not statistically significant (P ≤ 0.05). Where: WT – Water
Temperature, DO – Dissolved Oxygen, COND – Conductivity, TDS – Total Dissolved Solids, TRANS – Transparency, ALK –
Alkalinity, HARD – Hardness, pH – Hydrogen ion concentration, NITR – Nitrates, PHO – Phosphates, AIRTEMP – Air Temperature
Table 2 Selected national and international water quality standard guidelines
S/N Parameter
Maximum permissible limits in water
NAFDAC SON
FEPA
NSDW
WHO
EU
USEPA
1
Conductivity
1000
1000
70
1000
-
-
-
2
Total dissolved solids
500
500
500
500
1000
-
500
3
Hydrogen ion concentration 6.5–8.5
6.5–8.5
6.0–9.0
6.5–8.5
6.8
6.5–9.5
6.5–8.5
4
Total hardness
100
100
-
150
100
-
-
5
Total alkalinity
100
100
-
-
100
-
-
6
Nitrate
10
10
20
50
50
50
10
7
Water temperature
-
-
26
-
40
-
-
8
Dissolved oxygen
-
-
> 4
-
> 6
-
-
Note:
Source: Oketola et al., 2006; Chinedu et al., 2011; Muhibbu-din et al., 2011; Adejuwon and Adelakun, 2012. Where:
NAFDAC-National Administration for Food, Drugs and Control, SON-Standard Organization of Nigeria, FEPA-Federal
Environmental Protection Agency, NSDW-Nigerian Standard for Drinking water, USEPA-United States Environmental Protection
Agency, EU-European Union and WHO-World Health Organization