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Journal of Applied Sciences and Environmental Management
World Bank assisted National Agricultural Research Project (NARP) - University of Port Harcourt
ISSN: 1119-8362
Vol. 8, Num. 1, 2004, pp. 5-9
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Journal of Applied Sciences & Environmental Management, Vol. 8, No.
1,
June, 2004, pp. 5-9
Distribution
and Statistical Analysis of Bacteria in Lake Alau in
the Arid Northern Nigeria
1IDAKWO,
P Y; * 2ABU, G O
1Department of Food Science, Ramat Polytechnic,
P.M.B. 1070, Maiduguri, Borno State, Nigeria
2Environmental and Industrial
Microbiology Unit, Department of Microbiology, University of Port Harcourt,
P.M.B. 5323, Port
Harcourt
*Corresponding author: E-mail:
Code Number: ja04001
ABSTRACT:
The
direct microscopic count using bright field illumination was subjected to
a statistical comparison with four different microbial cell viability procedures
viz., pour plate, spread plate, most probable number (MPN) and membrane filtration
(MF) for the analysis of the distribution of bacteria in water samples from
Lake Alau Dam in the arid Northern Nigeria. A total of 27 samples were collected
from three locations of the dam site and analysed. The total coliform represented
32% of the 22 isolates and of this 10% represented the
fecal coliform bacteria. The fecal coliform level of 6.0 x 102 to
8.8 x 102/100ml placed lake Alau Dam water samples in the EEC Grade
A2 and thus, the water is recommended for further treatments before it can
be distributed to
municipalities for domestic use. Statistical analysis using one-way analysis
of variance (ANOVA) showed significant differences in counts between three locations,
based on the direct microscopic counts. There were no significant differences
in counts between locations using the four cultural methods. There was an honestly
significant difference (hsd, 5% level, Tukeys test) between the direct microscopic
counts and the four cultural methods, but there was not honestly significant
difference (hsd, 5% level) between the four cultural methods. It is concluded
that in the absence of more sophisticated procedures, the four cultural methods
together with the direct bright field microscopic count procedure served to establish
a good measure of the microbiological
quality of the Lake Alau water, this is strengthened by the statistical correlations.
@JASEM
The drinking water of most
countries, communities and municipalities is obtained from surface sources
such as rivers, streams and lakes (Diamant, 1980). Such
natural water supplies particularly streams and rivers are likely to be polluted
with domestic, industrial and agricultural wastes (Diamant, 1980; Wong, 1979).
In Maiduguri, the Borno State Capital in the arid Northern Nigeria, drinking
water is obtained from boreholes. The annual rainfall ranges from 500mm to
1000mm and relative humidity is about 49%, with evaporation of 2934mm per year
and temperature range of 38 to 40oC during the hottest months of
March and April, under shade (NYSC, 1990/91
report). These factors together with persistent draught, very short rainfall
period and desertification had made the water table very difficult to reach. In
addition, the cost of drilling new boreholes and maintenance of the old ones
had been on the increase. The Borno State Government in an effort to solve the
water problem in Maiduguri had sought the assistance of the World Bank and this
led to the initiation of a water project in 1986 to channel water
from Lake Alau to treatment
plants located in Maiduguri for purification and subsequent distribution to the
metropolis. The assessment of potability generally is based on knowledge of the
sanitary condition of the supply as determined by bacteriological monitoring.
Water quality monitoring is based on the detection of coliform bacteria and the
specific indicator of human faecal contamination, Escherichia
coli (Atlas, 1991; Bonde, 1977). The traditional methods for
detecting coliform bacteria rely on culturing on a medium that selectively permits
the growth of Gram negative bacteria and differentially detects lactose utilizing
bacteria e.g., using M-Endo, E.M.B. or BGLB media (Mahbubani et al., 1990). There
are several problems with the viable culture methods used for routine monitoring
of the bacteriological quality of water supplies. These include maintaining the
viability of bacteria between the time of collection and enumeration, lack of
growth of viable but non-culturable bacteria (Spence et
al., 1974), due to stress, induced by chemicals in the water, time required
for detection and confirmation of enteric bacteria (which can be days) and lack
of specificity for detection of true fecal coliforms. Rapid and sensitive, non-culture,
genetically based procedures for the environmental detection of coliforms i.e.,
using the polymerase chain reaction (PCR) and detection of the amplified DNA
with gene probes had been developed (Atlas, 1991; Mahbubani et
al., 1990). Tests based on detection of B-D glucuronidase, such as the colilert
test (Access Analytical system, Brandord Conn. USA), have been suggested as alternate
approaches for detecting coliforms (Edberg and Kontnick, 1986), but detection
of such enzymatic activities still requires culturing the
bacteria. It has been reported (Chang et al., 1989) that use of β-D-
glucuronidase activity may fail to detect a significant proportion (circa 30%)
of faecal coliform bacteria in some cases because of occurrences of high incidence
of β-D- glucuronidase negative E. coli. Alternatively, standard
cultural methods can be used if subjected to proper statistical
analysis.
The objective of this study therefore was to analyse, statistically, the data
obtained using one direct microscopic method with data from four cultural methods
in the enumeration of heterotrophic bacteria in a lake situated in an arid zone
of Northern Nigeria. The goal was to establish the bacteriological quality of
the water with a high degree of confidence that is protective of this community,
like many others in developing countries.
MATERIALS AND METHODS
Sampling
Sites
Lake Alau is located on latitude
11o41N and
longitude 13o, 16 E on the South Eastern (SE) part of Maiduguri, the
Borno State Capital Nigeria. There are no permanent human settlements around
the lake except the tents of migrant
fishermen around the bank of the lake. For the purpose of this study, the lake
was divided into three sampling points based on the physical relief of the lake
and the density of human activities around it.
Collection and Processing
of Samples
A total of 27 water samples
were
collected from the sampling points. At each point, samples were collected from
the surface (0-0.25m), middle (2.5m) and bottom water (5m). A total of 9 samples
were collected from each point. Adequate precautions were taken to avoid contamination
of samples. The samples from the middle and bottom were collected using a device
similar to the Niskin sampler (Niskin, 1962). In each case pre-sterilized, 200ml
plastic bottles were used and a space of about 1.5cm was left in each bottle
to facilitate mixing. Sample collection spanned from
March to August. In the arid Northern Nigeria, this period spans over one
third of the dry season (i.e. October to June) and two thirds of the rainy
season (i.e.
June to
September).
For the direct
microscopic counts the samples were first diluted and the cells fixed using
formaldehyde. The cells were counted under brightfield illumination using the
improved Neubauer Hemocytometer. Total viable counts (TVC) were determined
by pour plate, spread plate, membrane filtration (MF) and the 5 tube most probable
number (MPN)
procedures (Greenberg, 1985). The MF method was extended to include determination
of the total coliform and fecal coliform counts. Positive tubes from the lauryl
tryptose broth of the MPN procedure were examined for the
presence of Escherichia coli by testing the culture for the ability to
grow in Brilliant green lactose bile broth medium at 44.5oC (Greenberg,
1985). The biochemical oxygen demand (BOD) which is indicative of the level of
biodegradable organic matter (Brower and Zar, 1979) was performed
on the lake Alau water samples.
Statistical Analysis
In order to determine statistical
relationships among the bacterial populations recovered at the three locations,
a one way analysis
of variance (ANOVA) test was used (Spence et al., 1974). A similar analysis
was applied to test the relationships of the five methods used for the
enumeration. Where significant differences were observed, the data were further
subjected to Tukeys test (Spence et al., 1974) which determines how honestly
significant (hs) the observed differences are. Thus, this test is usually performed
only if the F value obtained in an analysis of variance indicates a significant
difference. The Tukeys test is described by the
equation:
where MSwg is the within group
mean square calculated in the analysis of variance; Ng is the number of cases
in each group; the value
qα also called studentised range statistics is obtained from
qα tables (Spence et al., 1974).
Correlations to be established
The following correlations were
sought viz., statistical conclusions relating the bacterial populations at
the three sampling locations, both inter-location and intra-location on the
one hand and statistical conclusions relating the five methods used on the
other. Correlations arrived at would strengthen or weaken the choice and application
of any of the methods for monitoring of the water quality of Lake Alau.
RESULTS
The bacterial populations of Lake Alau using
the direct microscopic, and four cultural
methods are shown in Table 1. The five methods gave a geometric mean of 4.0
x
101 - 2.3 x 106/100ml. The results of the analysis of variance
(ANOVA) performed to confirm the consistency of the counts at the different locations
are shown in Table 2.
Table 1: Total heterotrophic bacterial population
of lake Alau (geometric mean of 9 replicates)
Sample
|
Direct Count
(Cells/100ml)
|
Pour Plate
(cfu/100ml)
|
Spread Plate
(cfu/100ml)
|
MPN
per 100ml
|
MF
per 100ml
|
ALDS
ALDM
ALDB
|
2.3x106
1.2x106
6.7x105
|
1.9x105
1.8x105
9.3x104
|
2.1x105
1.84x105
1.4x105
|
5.5x101
5.1x101
4.0x101
|
3.1x105
2.5x105
2.4x105
|
ALDS = Alau Dam Surface Water Sample: ALDM
= Alau Dam Middle Water Sample
ALDB = Alau Dam Bottom Water Sample.
The analysis showed significant
difference at the 5%
level of confidence. The five methods were also subjected to analysis of variance
to determine if any correlation existed between them. The results are shown
in Table 3 and indicate significant difference between the methods for all the
locations. The results obtained with the endo broth (Table 4) serve to establish
bacteriological quality of the samples. The biochemical oxygen demand (BOD) test
for the Lake Alau water gave values ranging between 0.32mg/l and 0.45mg/l, indicating
that the lake water is
greatly impoverished in biodegradable organic nutrients.
Table 2: Summary
of Statistical Analysis for the Comparison of data from the threeSampling Locations
using the five methods.
Methods
|
Sources of Variations
|
SS
|
df
|
MS
|
Tabulated *F value
|
Calculated F value
|
Statistical conclusion
|
Direct Count
|
BL
WL
Total
|
1.21x1013
9.00x1011
2.11x1013
|
2
24
26
|
6.03x1012
3.8x1011
|
3.40
|
16.1
|
S
|
Pour Plate
|
BL
WL
Total
|
5.40x1010
3.00x1011
3.00x1011
|
2
24
26
|
2.7x1010
1.04x1010
|
3.40
|
2.60
|
NS
|
Spread Plate
|
BL
WL
Total
|
4.35x1012
4.35x1012
4.53x1012
|
2
24
26
|
8.56x109
1.81x1010
|
3.40
|
0.47
|
NS
|
MPN
|
BL
WL
Total
|
1.23x103
3..20xx104
3.32x104
|
2
24
26
|
6.16x102
1.81x1010
|
3.40
|
0.46
|
NS
|
MF
|
BL
WL
Total
|
2.50x1010
9.50x1010
1.20x1011
|
2
24
26
|
1.23x1010
3.95x109
|
3.40
|
3.12
|
NS
|
*FV1V2 (0.05), S
= significant, NS = Not
Significant, SS = sum of squares, MS = mean square
df = degrees of freedom,
BL and WL are= Between and
within limits
Table 3: Summary
of Statistical Analysis for the Comparison of the enumeration
methods
Sample
|
Source of variation
|
ss
|
df
|
Ms
|
Tabulated F value*
|
Calculated F value
|
Statistical Conclusion
|
ALDS
|
Between Methods
Within Methods
Total
|
3.19x1013
3.46x1012
3.54x1013
|
4
40
44
|
7.9x1012
8.65x1010
|
2.61
|
92.14
|
s
|
ALDM
|
Between Methods
Within Methods
Total
|
7.73x1012
4.33x1012
1.21x1013
|
4
40
|
1.93x1012
1.08x1011
|
2.61
|
17.84
|
s
|
ALDB
|
Between Methods
Within Methods
Total
|
2.43x1012
2.01x1012
4.44x1012
|
4
40
44
|
6.9xx1011
5.02x1910
|
2.61
|
12.10
|
s
|
*FV1V2 (0.05), S
= significant, NS = Not
Significant, SS = sum of squares, MS = mean square
df = degrees of freedom
DISCUSSION
Generally organic carbon levels
of less than 1mg/l are considered to be on the low side for aquatic ecosystems.
With BOD5 values of between 0.32 to 0.45mg/l the Lake Alau water
can be considered as being low in biodegradable organic nutrients. The arid
nature of the environment may partly account for this. Bacterial numbers in
water bodies, especially the neuston or epilimnion where there is usually an
enrichment of nutrients, can be in excess of 105 cells/ml. The bacterial
load for Lake Alau shown in Table 1 is on the low to moderate side with the
highest count of 2.3 x 104/ml obtained with the direct count procedure.
This may be explained partly on the basis of the low biodegradable organic
carbon level. There is an apparent decrease in the bacterial count from the
surface to the bottom water samples, suggesting that the surface layers may
be more enriched in nutrients thus supporting more bacterial populations. Analysis
of variance showed a significant difference for the counts at the three locations
using the microscopic direct count procedure. The observed difference on subjection
to
Tukeys test showed the difference to be honestly significant. There was no
significant difference between the locations when the four cultural methods were
used. The four cultural methods were not subjected to the Tukeys test, as there
were no significant differences observed in the first instance. Thus, from this
study, the probability of finding a significant difference using the
direct microscopic
Table 4: Total and fecal
coliform counts of Lake Alau Dam Site
Samples
|
Total Coliforms at 37oC
Per 100ml
|
Faecal Coliforms
at 44.5oC Per 100ml.
|
ALDS
ALDM
ALDB
|
7.3 X 103
6.9 X 103
8.0 X 103
|
8.8 X 101
6.0 X 101
7.9 X 101
|
procedure for the counts at the
locations by chance at any given level of significance increased with different
locations in the order ALDB < ALDM < ALDS i.e.,
(7.7X105) < (8.6X105) < (1.63X106)
cells/100ml). It is often difficult to distinguish bacteria from non living
particulate material in
natural water samples (Bowden, 1977). Other authors (Wiebe and Pomeroy, 1972)
have discussed this problem with reference to phase contrast microscopy. The
use of immunological methods, such as fluorescent antibodies is a good alternative
but the detection limit of the microscope will still be the restricting factor
(Notermans and Warnars, 1991). In this study, shape and texture were used as
two important criteria to identify bacteria as did other workers (Wiebe and Pomeroy,
1972). The particles that were obviously bacteria had round shapes and smooth
surface texture. Non living particles comprised small fragments of plant and
animal material, suspended sediment and other
irregularly shaped particles. Bacteria were seldom seen attached to particles.
The low count obtained with the membrane filtration procedure also supports this
observation, and is noteworthy. Subjectivity is a noted factor in the direct
microscopic count procedure (Bowden, 1977), yet, this method could be used when
a rapid estimate of microbial population is required considering the variations
within a population of aquatic bacteria, and is sufficient to make meaningful
comparisons between techniques and populations. The five methods were subjected
to analysis of variance and results indicated significant differences in the
methods at the three locations as seen in Table 3. These were further subjected
to Tukeys test and it was observed that only a difference between a pair of
means involving the Direct Microscopic count exceeded the critical value of 3.02
x 105 cells/100ml and thus
showed honestly significant difference. Differences in means between the four
cultural methods were less than the critical value thus, suggesting the four
cultural methods were not honestly significantly different from one another in
their bacterial counts. The total and fecal coliform counts of 6.9 x 105 to
8.0 x 105/100ml and 6.0 x 102 to 8.8 x 102 respectively
confirmed Lake Alau water as being contaminated with fecal matter, placing the
Lake water in the contamination grade A2 of the EEC guidelines (Anon, 1975) and
thus, requires such treatment as pre-chlorination, coagulation, flocculation,
rapid filtration and final chlorination before it can be distributed for domestic
use. Statistical analyses are useful in establishing confidence in a given procedure
and methodology. This is because often times a sizeable amount of data is involved.
This helps in eliminating chance occurrences. The statistical conclusions arrived
at in this study can serve as a good reference for water quality issues for a
less developed
society.
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