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Nigerian Journal of Agriculture, Food and Environment. 10(4):64-74
Etim and Obot, 2014
Published December, 2014
SPATIAL AND TEMPORAL VARIATIONS IN THE PHYSICOCHEMICAL CHARACTERISTICS OF STUBBS CREEK, NIGER
DELTA, NIGERIA
Etim, L. and Obot*, O. I.
ABSTRACT
Department of Fisheries and Aquatic Environmental Management, University of Uyo, Nigeria
*Corresponding author: ofonobot@gmail.com; 07081554411
The quality of water in Stubbs creek, Niger-delta, Nigeria was assessed using standard methods from September 2011 to
August 2013. The results of the analysis showed parameter ranges of temperature (24-29 oC), turbidity (3.6-115.7 NTU),
electrical conductivity (1045-9380 µS/cm), salinity (1-13.6 ‰), alkalinity (18.5-88.4 mg l -1), total suspended solids (1.4148.21 mg l-1), dissolved oxygen (3.2-7.60 mg l-1 ), biochemical oxygen demand (1.1-3.4 mg l-1), nitrate (1.28-20.6 mg l -1),
phosphate (0.08-2.08 mg l-1), calcium (102-625 mg l-1), magnesium (245-916 mg l-1), pH (4.5-7.73), and transparency (0.31.75 m). Of the fourteen parameters measured, four (turbidity, salinity, alkalinity and total suspended solids,) showed
significant (p<0.05) spatial variations. Temperature, turbidity, alkalinity, biochemical oxygen demand, phosphate, magnesium
and pH showed significant (p<0.05) seasonal variations. The levels of turbidity, electrical conductivity, calcium and
magnesium exceeded the permissible limits indicating environmental pollution.
Key words: Water quality, Pollution, Stubbs creek
INTRODUCTION
Increasing population, urbanization and industrialization have increased pressures on water leading to declining
benefits (Clarke, 1994). In recent years, environmental concerns related to the health and vitality of aquatic
ecosystem has become emerging issues in Nigeria. Water houses living organisms which are necessary for the
functioning of aquatic systems but can be disturbed by pollution. Indeed, the biological status of aquatic
environment such as the abundance, biomass and distribution of various indigenous populations which largely
depend on their respective physiological condition, dynamics of various life stages, productivity and growth
pattern are a reflection of the prevailing water quality variables (APHA, 1985). The physical, biological and
chemical characteristics of water are important parameters as they may directly or indirectly affect its quality and
consequently its suitability for the distribution and production of fish and other aquatic animals (Moses, 1983).
Important physical and chemical parameters influencing the aquatic environment are temperature, rainfall, pH,
salinity, dissolved oxygen and carbon dioxide. Others are total suspended and dissolved solids, total alkalinity and
acidity and heavy metals contaminants (Lawson, 2011). Water temperature is probably the most important
environmental variable. It affects metabolic activities, growth, feeding, reproduction, distribution and migratory
behaviours of aquatic organisms (Largler et al., 1977, Crillet & Quetin 2006 and Suski et al., 2006). pH is one of
the vital environmental characteristics that decides the survival, metabolism, physiology and growth of aquatic
organisms (Lawson, 2011). pH higher than 7 but lower than 8.5 according to Abowei (2010) is ideal for biological
productivity, but pH at <4 is detrimental to aquatic life. Salinity is an important ecological parameter in its own
right; and it is important in some chemical processes. Dissolved oxygen affects the solubility of and availability of
nutrients. Dissolved carbon dioxide is important in primary production and phytoplankton biomass (Lawson,
2011). Alkalinity between 30 and 500 mg l-1 is generally acceptable to fish and shrimp production (McNeely et
al., 1979 and Abowei & George 2009), between 20 and 500 mg l-1 according to Boyd (1982) will permit plankton
production for fish culture. High alkalinity results in physiological stress on aquatic organism and may lead to loss
of biodiversity. The physico-chemical parameters of water bodies vary in concentration on a seasonal, diurnal or
even hourly basis. These variations may be related to pattern of water use and rainfall (Abel, 1996; Akin-Oriola,
2003). This work was carried out to investigate the physical and chemical parameters of Stubbs creek and to make
deductions on the state of the ecosystem in terms of pollution and productivity.
MATERIALS AND METHOD
Stubbs creek is located within latitude 4.57o and Longitude 7.98o. It is a tidal creek. The mangrove of this creek
has been overtaken by nipa palm (Nypa fruticans), a very fast growing and competitive exotic species, naturalized
in Nigeria and considered adapted to the mangrove biome. It is considered native to Asia and Oceania. Human
activities going on within and around this creek include farming, fishing, and washing, disposal of excreta,
bathing, swimming and timber transportation. Three sampling stations were chosen (Fig.1). Stations 1 and 2 were
areas of increased human activities, while station 3 was a relatively calm spot.
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Nigerian Journal of Agriculture, Food and Environment. 10(4):64-74
Etim and Obot, 2014
Published December, 2014
Station 1 is located at the point where Stubbs creek empties into Qua-Iboe River with coordinates 4o 33’ 42.00” N
and 7o 59’ 11.64” E. The vegetation along the creek is mainly nipa palm.
Station 2 is located along Stubbs creek with coordinates 4o 34’ 25.00” N and 7o 59’ 17.00” E. From this point,
farming on the adjourning lands with human settlements could be observed.
Station 3 is located along Stubbs creek with coordinates 4o 34’ 36.04” N and 8o 0’ 10.91” E. Although close to a
bridge, the station was observed to have less human activities.
Fig.1: A map of Stubbs creek showing the sampling stations
Monthly sampling at the three stations for 24 months (September 2011 – August 2013) was carried-out. The
following physico-chemical parameters were determined: temperature, pH, dissolved oxygen (DO), Biological
oxygen demand(BOD)5, turbidity, Electronic conductivity (EC), salinity, alkalinity, total suspended solid (TSS),
nitrate, phosphate, calcium, magnesium, and transparency. Temperature, pH, dissolved-oxygen, transparency,
EC, and salinity were measured in situ. Temperature was measured with a thermometer, transparency with a
secchi-disc; DO, BOD, pH, and EC with Hanna H1 98186 meter and salinity with a refractometer. Water samples
for other physicochemical parameters (turbidity, alkalinity, BOD, nitrate, phosphate, calcium and magnesium)
were collected and analysed according to Stirling (1999). Rainfall data was collected from the Meteorological
unit, Department of Geography, University of Uyo, Nigeria.
SPSS (version 19) package was used to determine the means, range, standard deviation, one way Analysis of
Variance (ANOVA) and Duncan Multiple Range Tests was used to separate means. All statistical test was carried
out at 5 % probability test.
RESULTS AND DISCUSSION
Data showing the means and standard error values of physico-chemical parameters measured along the three
chosen stations in Stubbs creek from September 2011 to August 2013 is presented in Table 1. Of the fourteen
parameters measured, four (turbidity, salinity, alkalinity, and TSS) showed significant (p<0.05) spatial variations.
Temperature, salinity, alkalinity and transparency increased downstream while turbidity, TSS, BOD and
magnesium decreased downstream. Temperature, turbidity, alkalinity, BOD, phosphate, magnesium and pH
showed significant (p<0.05) seasonal variations. Rainfall data collected from the Meteorological unit, Department
of Geography, University of Uyo, Nigeria is presented in Figure 2. The rainfall data showed a seven month wet
season period, which stretched from April to October, and a dry season extending from November to March.
Similar data from the Niger–delta by International Institute for Tropical Agriculture (IITA), Onne, Rivers State,
Nigeria has been reported by Abowei and George (2009) and Deekae et al., (2010).
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Nigerian Journal of Agriculture, Food and Environment. 10(4):64-74
Etim and Obot, 2014
Published December, 2014
Table 1: Physico-chemical parameters of Stubbs creek for the period of study
Parameters
Temperature (o C)
Turbidity (NTU)
EC (µS/cm)
Salinity (‰)
Alkalinity (mg/l)
TSS (mg/l)
DO (mg/l)
BOD (mg/l)
Nitrate (mg/l)
Phosphate (mg/l)
Calcium (mg/l)
Magnesium (mg/l)
pH
Transparency (m)
Station 1
(Mean± S.E)
26.65±0.31
31.73±3.29a
3812.59±199.17
6.37±0.64b
37.49±2.62b
12.02±1.56a
5.77±0.13
2.20±0.15
4.76±0.81
1.43±0.13
226.38±24.13
588.42±33.47
6.55±0.14
0.94±0.08
Station 2
(Mean± S.E)
26.60±0.28
41.99±4.29ab
3035.35±336.64
3.30±0.53a
29.83±3.25a
16.62±1.98ab
5.61±0.18
2.21±0.17
5.35±0.59
1.39±0.11
197.83±18.63
621.08±36.78
6.60±0.12
0.80±0.06
Station 3
(Mean± S.E)
25.90±0.25
52.19±6.11b
3038.44±356.33
2.88±0.62a
26.60±1.18a
20.96±2.73b
5.77±0.11
2.24±0.12
4.84±0.63
1.42±0.04
212.08±16.30
625.21±33.16
6.55±0.16
0.76±0.04
Means on the same row with different superscripts are significantly different (p<0.05)
Fig. 2: Graph showing rainfall data during the period of study obtained from Meteorological unit, Department of
Geography, University of Uyo, Nigeria.
Figure 3 shows the spatio-temporal variation in temperature. Temperature range of 24 to 29 oC was recorded
during the study. These values were within the acceptable levels for survival, metabolism and physiology of
aquatic organisms (Lawson, 2011). Similar result has been reported by Olomukoro et al., (2009) at Ekpan creek.
Temperature increased downstream. Spatial variation was not significant (p>0.05). A low between-station
temperature range was observed during the study. This may be due to the fact that Stubbs creek is a lotic water
body with fast moving currents causing easy dilution. Negligible spatial variations in temperature have also been
observed by Edokpayi and Nkwoji (2007). Temperature is an important characteristic that can vary widely and is
influenced by a number of variables including geographic location, shading, water body size and depth. Seasonal
variation was significant (p<0.05) with higher dry season mean than wet season . Higher temperature values
recorded in the dry season were expected since heat from sunlight increases temperature of surface water.
Similarly, the drop in water temperature in the wet season is attributed to heavy rainfall experienced during the
period.
Spatio-temporal variation of turbidity is presented in Figure 4. It ranged from 3.6 – 115.7 NTU. Spatial variation
was significant (p<0.05). Turbidity reduced downstream with a mean of 41.97 NTU. This was in contrast to the
observed mean of 2.85 NTU by Davies, (2009) at Woji-Okpoka creek. The high turbidity obtained may be due to
the influx of particulate materials into the creek (Olomukoro et al., 2009). Seasonal variation was significant
(p<0.05) with higher wet season mean than dry season. Lawson, (2011), Ideriah et al., (2010) and Akintola et al.,
(2011) reported turbidity variation pattern not governed by season.
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Etim and Obot, 2014
Published December, 2014
Fig. 3: Spatio-temporal variations in temperature along Stubbs creek
Fig. 4: Spatio-temporal variations in turbidity along Stubbs creek
The EC ranged from 1045 to 9380 µS/cm. The EC exceeded the 1,000 µS/cm maximum for fresh waters but were
below 40,000 µS/cm minimum for marine waters, hence an indication of the brackish nature of the creek. The
high EC indicates the presence of high concentrations of total dissolved solids from non-point sources such as
municipal and industrial effluents (McNeely et al., 1979). Spatial variation was not significant (p>0.05). Although
there was no significant seasonal variation (p<0.05), higher dry season mean than wet season mean was recorded.
Fig. 5: Spatio-temporal variations in EC along Stubbs creek
Salinity range of 1 to 13.60 ‰ was observed in this study, indicating the creek’s brackish nature. Similar results
have been reported by Lawson, (2011). Salinity of 6.30 ‰ at station 1 was twice the value at station 2 (3.30 ‰)
and station 3 (2.88 ‰). This may be due to high brackish water dilution from Qua-Iboe River into the creek. At
this point, the Atlantic Ocean is just about 700 m away. Salinity increased downstream. Spatial variation was
significant (p<0.05). Although there was no significant seasonal variation (p<0.05), higher wet season mean than
dry season mean was recorded.
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Etim and Obot, 2014
Published December, 2014
Fig. 6: Spatio-temporal variations in Salinity along Stubbs creek
Alkalinity ranged from 18.5 to 88.4 mg l-1 with a mean of 31.31 mg l-1. These values did not exceed the
recommended 200 mg l-1 by FEPA (1991). Spatial variation was significant (p<0.05) as alkalinity increased
downstream. Seasonal variation was significant (p<0.05) with higher dry season mean than wet season mean.
Fig. 7: Spatio-temporal variations in Alkalinity along Stubbs creek
TSS ranged from 1.41 to 48.21 mg l-1 with a mean of 16.53±1.30 mg l-1 and can be said to be low when
compared to the maximum permissible limit of 2000 mg l-1 (Okorafor et al., 2013), however, the value may be
indicative of the physical, geological and biological processes at the position and time of sampling according to
Morris (1985). The variations across the stations were significantly different (p<0.05). Highest TSS mean of
20.96±2.73 mg l-1 was observed in station 3 while the lowest mean of 12.02±1.56 mg l-1 was observed in station
1. Although the wet season mean of TSS was higher than that of the dry season, there was no significant (p<0.05)
difference. The higher wet season mean may be as a result of the influx of allochthonous materials and organic
matter debris into the system through surface run-off. Similar results have been reported by Akpan (2004), Ekpo
et al., (2012) and Essien-Ibok et al., (2010).
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Nigerian Journal of Agriculture, Food and Environment. 10(4):64-74
Etim and Obot, 2014
Published December, 2014
Fig. 8: Spatio-temporal variations in TSS along Stubbs creek
DO ranged from 3.2 to 7.60 mg l-1 with a mean of 5.72 mg l-1. These values were within the optimum range ( over
5 mg l-1), which Boyd, (1979) suggested will support growth of fish. Spatial variation was not significant
(p>0.05). Stations 1 and 3 had the same mean DO value of 5.77 mg l-1 while the DO for station 2 was lower (5.61
mg l-1). Seasonal variation was not significant (p>0.05) but higher wet season mean than dry season mean was
recorded.
Fig. 9: Spatio-temporal variations in DO along Stubbs creek
BOD ranged from 1.10 to 3.41 mg l-1 with a mean of 2.22 ±0.72 mg l-1. This is similar to 1.15 to 2.47 mg l-1
reported by Alagoa and Aleleye-Wokoma (2012) at Taylor creek. Spatial variation was not significant (p>0.05)
but BOD decreased downstream. Seasonal variation was significant (p<0.05) with higher wet season mean than
dry season mean. The wet season increase in BOD was probably due to the increase input of decomposable
organic matter into the creek through surface run-off (Essien-Ibok et al., 2010). Similar results have been
observed by Akpan and Offem, (1993), Akpan and Akpan (1994) and Essein-Ibok et al., (2010).
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Nigerian Journal of Agriculture, Food and Environment. 10(4):64-74
Etim and Obot, 2014
Published December, 2014
Fig. 10: Spatio-temporal variations in BOD along Stubbs creek
Nitrate ranged from 1.28-20.6 mg l-1 with a mean of 4.99±0.39 mg l-1. This is within the permissible limit of 50
mg l-1 by SON (2007), but exceeded the 10 mg l-1 level, which Michael (1992) indicated that above the level, the
nitrate is harmless but the water may have toxic substances and pollutants from individual or agricultural sources.
Elevated levels of nitrate have been reported to exhibit delayed reactions to light and sound stimuli (Robillard et
al., 2003) and can cause methaemogloobinemia (Fatoki, 2003). Maximum value was recorded in November, 2011
at station 1 while the minimum value was recorded in October, 2011 at station 2. Variations in the means across
the stations were not statistically different (p>0.05). Also, seasonal variation was not significant (p<0.05).
Fig. 11: Spatio-temporal variations in Nitrate along Stubbs creek
Phosphate ranged from 0.08 -2.08 mg l-1 with a mean of 1.41±0.06 mg l-1. Similar result (0.28-2.50 mg l-1) was
reported by Onyema et al., (2009) in Badagry creek while a higher phosphate (28.83-37.85 mg l-1) was reported
by Igbinosa et al., (2012) in Shanomi creek. The range of phosphate in this study was higher than the range of
0.01-0.03 mg l-1 for phosphorus normally found in uncontrolled streams as defined by United States Department
of Agricultural Soil Conservation Service (USDASCS) (1975) but was within the permissible limit of 5 mg l-1 by
FEPA (2003). Wetzel (2001) observed that the rate of phosphorus release into the water can double, when
sediments are frequently disturbed. The phosphate level in the creek during the study period may be a result of
release from disturbed sediment and anoxic conditions as a result of decaying macrophytes. Spatial variation of
phosphate was not significant (p>0.05). Seasonal variation was significant (p<0.05). This is attributed to
fluctuations in riverine input of organic matter, bacterial mineralization/assimilation and phytoplankton
assimilation (Akpan and Offem, 1993). Wet season mean was higher than the dry season mean. Similar results
have been reported by Oribhabor et al., (2013) in lower Cross-River, Akintola et al., (2011) in Badagry creek and
Izonfuo & Bariweni (2001) in Epie creek.
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Published December, 2014
Fig. 12: Spatio-temporal variations in Phosphate along Stubbs creek
Calcium ranged from 102.00 to 625.00 mg l-1 with a mean of 212.28±11.44 mg l-1. The highest monthly value was
recorded in September, 2012 at station 1 while the lowest monthly value was recorded in November, 2012 at
station 1. Means variations across the stations were not statistically different (p>0.05), however, the highest value
was recorded in station 1 while the lowest value was recorded in station 2. Magnesium ranged from 245.00 to
916.00 mg l-1 with a mean of 611.57±19.74 mg l-1. The highest monthly value was recorded in August, 2012 at
station 1 while lowest value was recorded in February, 2012 at station 1. Means variations across the stations were
not statistically different (p>0.05), however, the highest mean was recorded in station 3 while the lowest mean
was recorded in station 1. The concentrations of calcium and magnesium exceeded the permissible limits of 75200 mg l-1 for calcium and 30-150 mg l-1 for magnesium by Alagoa and Aleleye-Wokoma (2012) and FEPA
(2003) respectively. This may be attributed to high content of bivalent cations of Ca2+ and Mg2+ as well as silt in
the soil as observed by Winger (1981). These ions enter a water supply by leaching from minerals within
an aquifer. Common calcium-containing minerals are calcite and gypsum. A common magnesium mineral
is dolomite (which also contains calcium). The general accepted classification for hardness of water is 75-150 mg
l-1 of CaCO3 for soft and 150 mg l-1 and above for hard water (Deat, 2000). This suggests that the creek can be
classified as hard water.
Fig. 13: Spatio-temporal variations in Calcium along Stubbs creek
The pH reduced downstream with minimum and maximum values of 4.50 and 7.73. Most natural water bodies are
known to have a pH range of 5-10 (Tepe et al., 2005). A pH higher than 7 but lower than 8.5 according to
Abowei, (2010), is ideal for biological productivity but lower than 4, is detrimental to aquatic life. Spatial
variation was not significant (p>0.05). Station 1 and 3 had the same value (6.55) while station 2 was higher (6.60).
Seasonal variation was significant (p<0.05) with higher wet season mean than dry season mean.
Transparency ranged from 0.30 to 1.75 m with a mean of 0.84±0.04 m. The highest value was recorded in
December, 2011 at station 1 while the lowest value was recorded in December, 2011 at station 3. Spatial variation
of transparency was not significant (p>0.05). Seasonal variation was not significant (p>0.05) also. A higher dry
season mean than wet season was recorded. This is primarily due to the fact that in the wet season, rivers receive
runoff from nearby terrestrial environment, thereby increasing the suspended solids load (Anyanwu, 2012). This
trend is consistent with reports from most Nigerian inland waters (Imoobe and Obeh, 2003).
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Etim and Obot, 2014
Published December, 2014
Fig. 14: Spatio-temporal variations in Magnesium along Stubbs creek
Fig. 15: Spatio-temporal variations in pH along Stubbs creek
Fig. 16: Spatio-temporal variations in Transparency along Stubbs creek
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CONCLUSION
The findings of this study reveal that the water in Stubbs creek is brackish and saline with high levels of turbidity,
EC, calcium and magnesium exceeding the permissible limits. High levels of these parameters indicate pollution
of the water, hence water may be unsuitable for human consumption. Anthropogenic activities going on along the
creek has been identified as sources of pollution of the aquatic environment. There is therefore the need to
monitor and conserve the creek in view of its importance. The water quality of Stubbs creek can be improved by
controlled dredging, prohibition of the discharge and dumping of refuge and human sewage into the creek. Also
riparian zone crop farming whose yield is boosted with application of fertilizers and manures should be stopped
with penalties/fines attached.
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