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INTRODUCTION
Water characteristics and quality are defined by
specific physical, chemical and biological properties, and
how these properties impact the survival, reproduction,
growth and management of aquatic life (Aduwo and
Adeniyi, 2019). Indeed, the sustainability and
development potential of any country may not be possible
without water (Salla and Ghosh, 2014). Lakes may be
monitored for recreational, domestic and/or used as a
component of hydro-power generating systems. In
developing countries, lakes are primarily used by the local
inhabitants for transportation, fishing, washing, cooking
and irrigation practices (Okoro et al., 2014). However,
most records these days indicates that water quality is
increasingly deteriorating, and this is cause of a global
concern (Mahananda et al., 2005). A previous study (Salla
and Ghosh, 2014) emphasized that about 75% of surface
water may be contaminated by different kinds of
pollutants. Pollutants may include heavy metals
(Awoyemi et al., 2014) or nutrients (e.g. phosphate and
nitrate) from industrial discharges (Mahananda et al.,
2005) or agricultural activities. Higher concentrations of
nutrients, e.g. phosphorus and nitrogen, may cause
hypoxia and algal bloom (Anitha, 2002; Garg et al.,
2009), which may cause low light penetration, obstruction
of oxygen levels and loss of aquatic life and biodiversity
(e.g. fish mortality) (Parashar et al., 2006). For these
reasons, the constant monitoring of water quality in lakes
is essential and can be conducted by quantifying the level
of physical and chemical parameters. The physical
properties of a lake include water temperature, colour,
odour and taste, solids and turbidity (Aduwo and Adeniyi,
2019), while the chemical assessment involves the
measurements of cations, anions, nutrient compounds,
toxic and non-toxic compounds, and oxygen demands by
inorganic and organic substances (Ademoroti, 1996).
A typical lake and a major source of water for the local
population of South-Eastern and Niger-Delta region in
Nigeria is Lake Oguta. The lake serves as a source of
income to the community (fishing and also dredging the
lake for sand, which is used in the construction industries)
(Nfor and Akaegbobi, 2012). However, the lake has been
exposed to threats due to excessive oil exploration
(Isinkaye and Emelue, 2015) and sewage disposal (Nfor
and Akaegbobi, 2012). Currently, records on the physical
and chemical status of the lake are needed, but very few are
existing or have been explored (Nfor and Akaegbobi,
2012). The investigation of water quality levels (physical
and chemical properties) of Lake Oguta by a comparison
with a set of standards (Dirican, 2015) may provide
information for Government management policies (Patil et
al., 2012). The objective of this paper is to evaluate water
quality and potential human exploitation (including
drinking purposes) of Lake Oguta using a suitable subset
of variables measured at weekly intervals. The parameters
ARTICLE
Assessment of the physical and chemical properties of Lake Oguta (Nigeria)
in relation to the water quality standard established by the Nigerian Federal
Ministry of Water Resources
Felix Atawal Andong1,2*, Ngozi Evelyn Ezenwaji1, Temitope Dadewura Melefa1, Funmilayo Faith Hinmikaiye1,
Obiechina Vitus Nnadi1, Olasoji Oluwafemi1
1Departmentof Zoology and Environmental Biology, University of Nigeria, Nsukka, Enugu State; 2 A.P. Leventis Ornithological
Research Institute, Department of Zoology, University of Jos, Plateau State, Nigeria
ABSTRACT
Constant assessment of physical and chemical parameters in freshwater ecosystems is largely recommended. This is even more
important when water resources, e.g. lakes in most countries, serve as a source of water for domestic and commercial purposes, and
/or when freshwater ecosystems represent a refuge for most aquatic organisms. In this paper, we investigated the physical and chemical
properties of water resources at three sampling stations of Lake Oguta, comparing the weekly values (June-July 2018) with the water
quality standard established by the Nigerian Federal Ministry of Water Resources (FMWR). The parameters analyzed included water
temperature, pH, dissolved oxygen (DO), chemical and biological oxygen demand (COD, BOD), potassium, magnesium, sodium,
calcium, phosphate, nitrate, chloride and sulphate. Most of the cations (calcium, magnesium and sodium), anions (phosphate, nitrate,
chloride and sulphate), as well as water temperature, BOD and DO were below the quality standard limits. The basic chemistry and
temporal variations may have been caused mostly by natural factors such as geology, topography, meteorology, hydrology, water
levels and biological activity. Being in line with the recommended standard levels, the nutrient concentrations, pH and hardness in the
current study may indicate favourable conditions for the life of aquatic organisms and contemporary co-existence with the human
exploitation for drinking purposes. Nevertheless, to assure a safely and conscious exploitation of this water resource, we recommend
continuity in the monitoring studies. To assure an accurate evaluation of the physical and chemical parameters, future studies should
include a larger sample size and extended study periods (including other seasons).
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Water quality of Lake Oguta, Nigeria 75
that have been measured, i.e. water temperature, pH,
dissolved oxygen, chemical and biological oxygen demand,
potassium, magnesium, sodium, calcium, phosphate,
nitrate, chloride and sulphate were compared with the
standards assessed by the Nigerian Federal Ministry of
Water Resources FMWR (NIS, 2015).
METHODS
Study area
Imo State is located in South-Eastern Nigeria;
currently, the State is famous for its largest natural lake
or fresh water lake, Lake Oguta (Nfor and Akaegbobi,
2012) (Fig. 1). The lake is located in a low-lying platform,
at 50 m above sea level, between latitudes 5°4’’and 5°44’
N, and longitudes 6°45’and 6°50’ E. Four rivers (Njaba,
Awbuna, Utu and Orashi) are connected to the lake
(Ahiarakwem and Onyekuru, 2011). However, all year
round, rivers Njaba and Awbuna discharges into the lake,
while Utu Stream flows in during the rainy season
(Ahiarakwem et al., 2012). The river Orashi flows past
the lake in its South-Western portion. It is recorded that,
the total annual inflow from the rivers and streams is
about 25,801 m3 (Ahiarakwem, 2006), while the annual
return and overland flow into the lake is estimated to be
about 69,000 and 138,000 m3 (Okoro et al., 2014). Also,
the annual recharge of the lake from precipitation is about
693,000 m3, while the annual groundwater inflow into the
lake has been estimated (2,750,400 m3) (Ahiarakwem et
al., 2012). Indeed, the total annual water inflow, heavily
outweighs the total annual outflow, thus, the lake is
adequately recharged all the year round (Ahiarakwem,
2006). The surface area of the lake ranges between 1.8
km2 and 2.5 km2. The shoreline length is around 10 km;
maximum and mean depths are 8.0 m and 5.5 m,
Fig. 1. Map of Lake Oguta. Sampling stations are indicated with red triangles.
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F.A. Andong et al.76
respectively (Nfor and Akaegbobi, 2012). May be, owing
to the low cation concentration and alkalinity of the water,
conductivity may range between 8.6-30 µS cm–1 (Odigi
and Nwadiaro, 1988; Okorondu and Anyadoh-Nwadike,
2015); also, the surface water temperature (24-31°C),
Secchi-disc-transparency (0.61-4.50 m) (Odigi and
Nwadiaro,1988; Nwadiaro, 2018) may vary seasonally
with rainfall. The lake experiences a weak, unstable
thermal stratification, which may develop towards the
middays of the warmer months (i.e. April-August)
(Nwadiaro, 2018).
Selection of sampling site, data collection
and processing
After a pre-sampling survey aimed at assessing the
general characteristics of the lake and activities in the
catchment, we identified three peculiar zones, i.e. station
1, or lake bank (human activities active, e.g. washing);
station 2, lake flows into each other; and station 3, area
with active farming. We traversed the lake using a boat
and collected water samples every week, from June to
July, 2018. The distance between sampling stations was
2.5 km; and before sample collection, we ensured that the
containers were thoroughly rinsed with the lake water.
During our sample collection we were guided by a
standard procedure (APHA, 1998; Awoyemi et al., 2014).
Water samples were collected by gently lowering the
container into the lake (Ozoko, 2015). In the field, each
water sample was first analysed to quantify dissolved
oxygen (DO) using the Winkler’s method (Aduwo and
Adeniyi, 2019). We measured also, the surrounding
temperature (28.0-33.0°C) and water temperature (25.5-
27.8°C) for each station using a mercury-in-bulb
thermometer (graduation 0-360°C). The probe was
lowered into the water for at least five minutes, and
readings were recorded immediately while the
thermometer was still in the water, necessarily to avoid
interference with ambient temperature. Hydrogen activity
(pH) was measured using a portable Hanna Field pH
meter (Model PHS 25), inserted into the water and
allowed to attain a steady value. Further, water samples
for chemical analyses were preserved using 10 ml 6N
HNO3 (Awoyemi et al., 2014), and transported to the
National Center for Energy Research and Development
Laboratory, University of Nigeria, Nsukka, Enugu State
(6º 51’21” N 7º23’45” E). In the laboratory, biochemical
oxygen demand (BOD) was quantified using iodiometric
titration (Aduwo and Adeniyi, 2019). While chemical
oxygen demand (COD) was quantified in the laboratory
using the chromic acid wet digestion titrimetric method
(Awoyemi et al., 2014). An ultraviolet atomic absorption
spectrophotometer (Ozoko, 2015), was used for
quantification of cations, i.e. sodium (Na+), potassium
(K+), magnesium (Mg2+) and calcium (Ca2+). While the
major anions, i.e. phosphate (PO43-), nitrate (NO3-),
sulphate (SO42-), were assessed through ion
chromatography (Dionex) (APHA, 1998; Dirican, 2015).
Statistical analysis
Data were analysed using SPSS (Statistical Package
for Social Science) version 20.0; the physical and
chemical parameters were first checked for normality and
homogeneity of variance. Analysis of variance (ANOVA)
was used to test the level of significance (set at P<0.05);
Duncan’s New Multiple Range Test (DNMRT) was used
to separate monthly station means.
RESULTS
The results of the physical and chemical parameters
quantified from the analysis of Lake Oguta, compared to
water quality standard established by the Nigerian Federal
Ministry of Water Resources (FMWR), are presented in
Tab. 1. Water temperature was significantly different
between months in two stations, i.e. stations 2 and 3
(P=0.01 and P=0.03, respectively). The range of values in
the three stations (25.6-27.8°C), was below the Federal
standard limit (<35ºC). Values of pH were significantly
different between months in station 3 (P=0.03); the pH
range in the current study (6.5-7.1) was within the standard
limit (6.5-8.5). Also, DO range was below (3.4- 5.7 mg L–
1) the standard limit (7.5 mg L–1), and was not statistically
significant between months in the three stations (P>0.05).
COD values ranged between 24.4 and 26.7 mg L–1;
differences between months were statistically significant
only in station 3 (P=0.01). BOD was significant between
months in stations 1 and 3 (P=0.01 for both); further, the
range of BOD values recorded in the three stations (3.9-5.9
mg L–1) was below the standard limit (8.3 mg L–1).
Potassium (2.6-4.3 mg L–1) showed significant differences
between months in stations 1 and 2 (P=0.01). Sodium (1.3-
2.5 mg L–1) showed significant differences in station 3
(P=0.03); below the standard limit (200 mg L–1). Among
algal macronutrients, i.e. phosphate and nitrate; phosphate
concentrations (0.9-1.3 mg L–1) showed no differences
between months, and having lower values compared to the
standard limit (<13.5). While nitrates ranged between 2.4
and 5.8 mg L–1 below the standard limit (50 mg L–1) with
significant differences between months in station 3
(P=0.01). Other parameters ranged between 10.5 and 14.0
mg L–1 (chloride) and 3.5 and 5.6 mg L–1 (sulphate). At the
stations 1 and 2, differences in chloride concentrations were
statistically significant (P<0.05), while sulphate was
significant only in station 1 (P=0.04); these two parameters
were below the standard limit. The water parameters
measured, e.g. magnesium and calcium especially in its
complex form, i.e. mgCaCO3 (150 mg L–1), is used as an
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Water quality of Lake Oguta, Nigeria 77
indicator of water hardness in Nigeria (NIS, 2007).
Magnesium concentrations were significantly different in
station 3 (P=0.01) and ranged between 3.1 and 4.6 mg L–1,
below the standard limit (20 mg L–1), while calcium values
were not statistically different between months in any of
the three station, and ranged between 1.9 and 2.9 mg L–1,
below the standard limit (150 mg L–1).
DISCUSSION
In the current study, the range of surface water
temperature in the three stations was not beyond the
Federal standard (<35°C) and also within the values
reported in other studies, e.g. 26.5-33°C (Oluyemi et al.,
2010); 26.4-31°C (Rim-Rukeh, 2013); 25-28°C (WHO,
2011); and 24.2-26.2°C (Nwoko et al., 2015). Usually, air
temperature can seriously influence water temperature,
hereby causing differences in the surface and / or mid-
bottom level temperature of a lake. Such changes in water
temperature can also influence other water quality indices
(Dirican, 2015). In the current study, the weather
condition was cooler due to several rain showers
experienced at the sampling station. High temperature
values increase the metabolic rate of aquatic organisms,
with important effects on O2 production and consumption.
In case of excessive primary production, this can cause a
Tab. 1. Monthly variations in the physical and chemical parameters in the three sampled stations, and comparison with the limits set by
the standards of the Nigerian Federal Ministry of Water Resources.
Variable Duration Station 1 Station 2 Station 3 FMWR
Temperature (°C) June 27.17 ± 0.18 26.60 ± 0.06 27.78 ± 0.15 <35.0 6.5-8.5
July 26.67 ± 0.13 25.57 ± 0.19 27.17 ± 0.12
t-test, P-value 2.261, 0.087 5.316, 0.006 3.182, 0.033
pH June 7.10 ± 0.15 6.70 ± 0.12 6.50 ± 0.06
July 6.97 ± 0.18 6.93 ± 0.09 6.83 ± 0.09
t-test, P-value 0.571, 0.598 1.606, 0.184 3.182, 0.034
DO (mg L–1) June 3.73 ± 0.15 5.67 ± 0.15 3.77 ± 0.09 7.5
July 3.40 ± 0.15 5.53 ± 0.15 3.93 ± 0.12
t-test, P-value 1.581,0.189 0.649, 0.552 1.118, 0.326
COD (mg L–1) June 25.17 ± 0.12 24.36 ± 0.10 26.67 ± 0.12
July 25.56 ± 0.13 24.41 ± 0.10 25.67 ± 0.04
t-test, P-value 2.226, 0.090 0.401, 0.709 7.973, 0.001
BOD (mg L–1) June 4.38 ± 0.20 3.85 ± 0.10 4.74 ± 0.14 8.3
July 5.90 ± 0.06 4.05 ± 0.10 5.67 ± 0.07
t-test, P-value 7.233, 0.002 1.411, 0.231 5.899, 0.004
Potassium (mg L–1) June 3.27 ± 0.17 2.58 ± 0.01 4.13 ± 0.05
July 4.16 ± 0.07 3.01 ± 0.06 4.30 ± 0.13
t-test, P-value 4.866, 0.008 6.697, 0.003 1.206, 0.294
Magnesium (mg L–1) June 3.68 ± 0.16 3.13 ± 0.07 3.65 ± 0.05
July 4.29 ± 0.15 3.37 ± 0.09 4.64 ± 0.04 20
t-test, P-value 2.779, 0.050 2.040, 0.111 14.569, 0.0001
Sodium (mg L–1) June 2.22 ± 0.15 2.38 ± 0.41 2.17 ± 0.07 200
July 1.71 ± 0.12 1.33 ± 0.06 2.51 ± 0.08
t-test, P-value 2.718, 0.053 2.539, 0.064 3.307, 0.030
Calcium (mg L–1) June 2.48 ± 0.09 2.17 ± 0.17 2.80 ± 0.12 150
July 2.30 ± 0.15 1.93 ± 0.09 2.90 ± 0.12
t-test, P-value 1.026, 0.363 1.265, 0.275 0.612, 0.573
Phosphate (mg L–1) June 1.01 ± 0.04 0.90 ± 0.05 1.16 ± 0.09 < 13.5
July 1.23 ± 0.13 0.88 ± 0.04 1.30 ± 0.12
t-test, P-value 1.568, 0.192 0.313, 0.770 0.938, 0.401
Nitrate (mg L–1) June 3.90 ± 0.15 2.70 ± 0.06 4.90 ± 0.06 50
July 4.60 ± 0.21 2.43 ± 0.29 5.83 ± 0.09
t-test, P-value 2.711, 0.053 0.900, 0.419 8.854, 0.001
Chloride (mg L–1) June 12.70 ± 0.12 10.53 ± 0.26 13.77 ± 0.19 250
July 13.53 ± 0.18 11.47 ± 0.03 14.00 ± 0.10
t-test, P-value 3.953, 0.017 3.556, 0.024 1.107, 0.330
Sulphate (mg L–1) June 4.43 ± 0.23 3.50 ± 0.17 5.30 ± 0.06 100
July 5.20 ± 0.12 3.90 ± 0.10 5.57 ± 0.15
t-test, P-value 2.945, 0.042 2.000, 0.116 1.706, 0.163
FMEV, Nigerian Federal Ministry of Environment; pH, hydrogen ion concentration; DO, dissolved oxygen; COD, chemical oxygen demand; BOD, bi-
ological oxygen demand. All values expressed as mean ± standard error mean (±SEM). The level of significance between months was set at P<0.05.
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F.A. Andong et al.78
successive fall in the level of dissolved oxygen
concentrations due to mineralization of organic matter.
Such changes may retard the growth and reproduction of
some fishes and in some severe conditions result to the
death of the more vulnerable organisms.
By the current pH records, Lake Oguta can be
classified as weakly acidic to neutral, i.e. within the
Federal standard (6.5-8.5), and other records, e.g. 6-9 in
(WHO, 2011); 6.5-8.9 (Oluyemi et al.,2010) and 5.1-7.4
in (Rim-Rukeh, 2013). These results indicate a sufficient
buffering property of the lake, suggesting safe agricultural
and domestic uses (Oluyemi et al., 2010). Additionally,
the current pH recorded may be adequate for the life of
most aquatic organisms. In fact, a previous study
recommended a range of 6.5-8.5 for most fishes to thrive
(Egemen, 2011). On the other hand, studies suggest that
DO value higher than 10 mg L–1 indicate bad or sub-
optimal conditions for the growth of aquatic fauna (Clerk,
1986; Bhatnagar and Singh, 2010; Ekubo and Abowei,
2011). Further, high DO concentrations may indicate
excessive algal proliferation (Reynolds, 2006). Here, the
DO recorded at the three stations was not beyond the
Federal limit (7.5 mg L–1), although quite low, and near
the limit for most aquatic life (Franklin, 2013). However,
the DO values for this study may be considered around or
above values recommended for fish to survive (3-5 mg
L–1; Gorde and Jadhav, 2013). The mean BOD (3.9-5.9
mg L–1) was not beyond the Federal limit (8.5 mg L–1) or
WHO (2011) limits, and also not within other ranges from
the same lake, e.g., 0.2-0.3 mg L–1 (Nwoko et al., 2015).
The COD, which is the amount of oxygen needed to carry
out oxidation of organic waste by using strong oxidizing
agent (Awoyemi et al., 2014), was not beyond other
standards, e.g. 20- 60 mg L–1 (WHO, 2011). However, the
values were above other recorded values, e.g. 0.69- 6.74
mg L–1 (Oluyemi et al.,2010).
Phosphate level was below the Federal standard
(<13.5 mg L–1) and even below ranges reported in other
studies (Aduwo and Adeniyi 2019). Values above the
Federal standard may indicate pollution, because it is
considered high (OECD, 1982). Usually, sewage
phosphate-based fertilizers used for agricultural activities
are the cause of higher phosphate content in water. The
nitrate content recorded here, are far below the Federal
(10 mg L–1) and the WHO (2011) standards (50.0 mg
L–1), and below concentrations reported in a previous
studies (37.2-43.9 mg L–1; Igbinosa et al., 2012). Higher
phosphate and nitrate level promote eutrophication
(Ryding and Rast, 1989).
Potassium concentrations (2.6-4.3 mg L–1) in the
current study were slightly above other records (e.g. 2.1-
2.6 mg L–1; Aduwo and Adeniyi, 2019), while sodium was
far below the Federal standard (200 mg L–1). Sulphate and
chloride values were below the FMWR standard. Chloride
can form many compounds (NaCl, CaCl2 and MgCl2), at
varying concentrations in most natural waters (Awoyemi
et al., 2014). Cloride is largely transported into the lake
water by the dissolution of salts present in the soil and /
or from polluting sources such as sewage and trade wastes
(Shaikh and Mandre, 2009). Higher values of chloride
may affect water taste; however, these values are
generally lower during the rainy than dry season (Shaikh
and Mandre, 2009; Awoyemi et al., 2014). Other
measured parameters like magnesium and calcium
contribute to water hardness. Total hardness of any water
may be defined as the sum of calcium and magnesium
concentrations and is normally expressed as milligrams
of calcium carbonate equivalent per litre (Karim and
Panda, 2014). In the present study, the hardness levels
were very low compared to the Federal standard and other
studies (e.g. 229-1494 mg L–1; Awoyemi et al., 2014).
This is probably because there are less deposits of
limestone materials around the lake, which is why the lake
experienced low values of hardness (Vermani and Narula,
1995).
CONCLUSIONS
The results presented in this paper indicates that some
of the physical and chemical parameters in Lake Oguta
were below Nigerian Federal Ministry of Water Resources
standard. For example, the physical parameters
(temperature), the cations (calcium, magnesium and
sodium), anions (phosphate, nitrate, chloride and
sulphate) as well as BOD and DO were all below the
FMWR standard. Usually, the variations observed may be
due to natural causes (geological, topographical,
meteorological, hydrological and biological) and water
level, as well as anthropogenic impacts. At present, no
attempts were made to disentangle the contribution of
natural and anthropogenic factors to the chemical
conditions of the lake. Further, considering the short
period analysed, and to assure an accurate evaluation of
the physical and chemical parameters, it is stressed that
future studies should include a larger sample size and
extended study periods (including all the seasons).
ACKNOWLEDGMENTS
The study was supported with facilities from the
Department of Zoology and Environmental Biology and
the Laboratory of the National Center for Energy
Research and Development, University of Nigeria,
Nsukka, Enugu State. We also thank the following people
for their help with various aspects of this project: Joseph
Effiong Eyo, Ike Nelson Ossai, Okoye Charles
Obinwanne and Chinedu Ifeanyi Atama.
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Water quality of Lake Oguta, Nigeria 79
Corresponding author: andongfelix@gmail.com
Key words: Physical chemical variables; lake; nutrients; aquatic
life; water quality assessment.
Conflict of interest: The authors declare no conflict of interest.
Received: 29 August 2019.
Accepted: 3 December 2019.
This work is licensed under a Creative Commons Attribution Non-
Commercial 4.0 License (CC BY-NC 4.0).
©Copyright: the Author(s), 2019
Licensee PAGEPress, Italy
Advances in Oceanography and Limnology, 2019; 10:8522
DOI: 10.4081/aiol.2019.8522
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