Abu Zabaal Lakes (three) were formed during the last century. The 1st
and the 2nd lakes were formed during the fifth and eighth decades, respectively.
The 3rd lake was formed in the ninth decade and there is a small depression
still in the filling phase now (Fig. 1). These lakes were
formed probably due to fracture and extraction of basalt rocks and they became
gradually filled up by ground water and seepage (Abd Ellah, 2003). The seepage
source may be from Imailliya Canal, Bahr El-Baqar drain and the cultivated areas
close to the lakes. Abu Za'baal Lakes are located in north of El-Qalubiya Governorate.
They occupy the area between latitude 30° 16.62` and 30o 17.58`
N and longitude 31° 20.90` and 31° 21.69` E. The 1st lake lies between
latitudes 30° 16.84` and 30° 17.58` N and longitudes 31° 20.94`
and 31° 21.53` E (375.846x103 m2). The 2nd lake extends
between latitudes 30° 16.78` and 30° 17.15` N and longitudes 31°
20.90` and 31° 21.22` E (151.848x103 m2). The 3rd
lake lies between latitudes 30° 16.62` and 30° 16.82` N and longitudes
31° 21.09` and 31° 21.29` E (80.386x103 m2). The
filling phase depression extends between latitudes 30° 6.71` and 30°
16.82` N and longitudes 31° 21.59` and 31o 21.69` E. The lakes
waters cover an area of 608.050x103 m2. The water depth
in the 1st lake was sharply increased northward (0.6 to 20.0 m with average
of 10.219 m). The water depth of the 2nd lake varied from 2.9 to 7.6 m with
average 6.12 m and the 3rd lake depth varied from 0.8 to 7.l m with average
of 5.791 m. The highest water storage was 3840.464x103 m3 in
the 1st lake while the lowest water storage was 465.516x103 m3
in the 3rd lake. The water storage in the 2nd lake was 928.095x103
m3. The total water storage was 5234.075x103 m3.
The 1st lake is the widest (61.81% of total water surface area), deepest and
largest (73.38% of the total water storage) basin. The 3rd lake is narrower
(13.22% of total water surface area), shallower and smaller (8.89 of the total
water storage) (Abd Ellah, 2003).
Formation of Abu Zabaal Lakes has led to a number of changes in the existing microhabitats that a large number of different species of fauna and flora became re-established in such new ecological setting. The area thus opened several possibilities for various forms of development in tourism and recreational activities, fisheries and limited agricultural or soil reclamatory activities. Water can be rendered unsatisfactory from technical or aesthetic points of view by the microorganisms it contains. Thus, the bacteriological examination of water is necessary to disclose the presence of microorganisms that might constitute a health hazard.
Phytoplankton composition, chemical and morphometrical characteristics of Abu Zabaal Lakes waters were studied by Abd Ellah (2003) and Hussian (2005). The heavy metals pollution and its effect on some fish species and pathological conditions of Tilapia zillii caught from these lakes were also investigated (Gaber and Fadel, 2005; Mohamed and Gad, 2005; El-Mansy, 2005).
The present investigation is concerned with studying of the total bacterial counts at 22 and 37°C and bacterial indicators of sewage pollution (total and faecal coliforms, in addition to faecal streptococci). These parameters are usually used for evaluating the sanitary quality of water. Rate of bacterial reproduction, cell volumes, biomass, daily production and activity of bacteria as indications of trophic status in the studied lakes were also investigated. As far as we know, this work represents the first bacteriological study on Abu Za'baal Lakes.
Materials and Methods
Sampling and Sampling Stations
Water samples were collected seasonally during the period of Autumn 2003-Summer
2004 from the three lakes of Abu Zabaal. The largest first lake was represented
by 5 stations, while the other two lakes were represented by 2 stations (one
for each) (Fig. 1).
The temperatures of surface and near-bottom waters (SW and N-BW) were measured
using a digital thermometer and the pH values were recorded using a pH meter.
Water transparency was measured by black/white standard 25 φ Sechi disc.
Total bacterial Counts
The total counts of bacteria at 22 and 37°C on plate count agar, was
carried out, using the standard spread method (Clark, 1971).
Most probable numbers (MPN) of bacterial indicators of sewage pollution
(total and faecal coliforms and faecal streptococci) were determined using Multiple
Fermentation Tube (MFT) method as described by APHA (1992).
|| Location of the sampling stations in Abu Za'baal Lakes
Total Gram-Negative Bacteria
The total gram-negative bacteria in the studied lakes during different seasons
were determined, using MacConkey agar supplemented with 0.001 g L-1
crystal violet (Oxoid Manual, 1981). Several isolates of these gram-negative
bacteria were grouped, selected and characterized morphologically and biochemically
and confirmed by API 20E strip system (Biomerieux).
Rate of Reproduction
Rate of reproduction (generation time) of bacterioplankton was calculated
using the formula of Kuznecov and Romanenko (Niewolak and Sinica, 1981).
Volume of Bacterial Cells
To determine the bacterial cell volume in the tested water, the dimensions
of the cells were determined by transmission electron microscopy (JEOL, JEM-1230)
according to the method described by Zimmermann (1977). Cell volumes were calculated
according to the formula of Loferer-Kröβbacher et al. (1998)
and then the average volume of one cell was calculated.
Bacterioplankton biomass in mg of org. C m-3 and in a water column
of m2 in area, was calculated according to Romanenko's formula (Niewolak
and Sinica, 1981).
Daily Production of Bacterial Biomass
Daily production of bacterial biomass was estimated by using average values
of generation time and bacterial biomass according to the formula described
by Niewolak and Sinica (1981).
Bacterial activity in the studied lakes was estimated by the method described
by Fontvieille et al. (1992). The assay depends on measuring of the bacterial
hydrolytic activity using fluorescein diacetate (FDA). One hundred milliliter
of water collected from the studied lakes was filtered through 0.2 μm filter
and the filter was washed in 3 mL phosphate buffer (pH 7). 0.1 mL of FDA solution
(2 g L-1) was added and the mixture was incubated at 15°C overnight
and then frozen to stop the reaction. The active bacteria in the water samples
hydrolyzed the colorless fluorescein diacetate to fluorescein (yellowish green
in color). The concentration of this compound in one ml of water sample was
estimated from the optical density measured at 490 nm.
In this study, the temperature and pH of both SW and N-BW in addition to
water transparency of the studied lakes were recorded. The highest temperatures
of both SW and N-BW were recorded in Summer (31 and 29°C, respectively),
while the lowest ones were recorded in Winter (18 and 16°C) (Fig.
2 a and b). The highest pH values were recorded in the
SW (7.8 to 8.2 during Autumn and Spring, respectively), while the lowest were
recorded in N-BW (7.6 to 8.1). Generally, the water of the 3rd lake was more
alkaline compared to the other 2 lakes (Fig. 2c and d).
||Seasonal variations in surface and near-bottom waters of (a)
and (b) temperature (c) and (d) pH, respectively and (e) transparency
Water transparency of the studied lakes also varied seasonally from 60 and
85 cm during Summer to 110 and 120 cm during Winter in the 1st and 2nd lakes,
respectively. In the 3rd lake, transparency ranged from 90 to 120 cm during
Summer and Winter, respectively (Fig. 2e).
Total Bacterial Counts
The total bacterial counts at 22 and 37°C in the studied lakes were
determined seasonally. Compared to the other two lakes, the 1st lake maintained
the highest average of bacterial counts at 22 and 37°C, recording 21.8x106
and 17.8x06 cfu mL-1 in SW and 80.9x106 and
74.62x106 cfu mL-1 in N-BW, respectively during Summer
(Fig. 3a-d). Low bacterial counts were recorded
in the SW of the 3rd lake (0.6x106 and 1.4x106 cfu mL-1
at 22 and 37°C, respectively) and the 2nd lake (0.8x106 and 1.5x106
cfu mL-1) during Winter. On the other hand, the bacterial counts
were higher in N-BW compared to those in the SW.
Bacterial Indicators of Sewage Pollution
MPN of total and faecal coliforms (TC and FC) as well as faecal streptococci
(FS) recorded the highest average values in the 1st lake, giving rise to 522,
350 and 271/100 mL in SW and 194x102, 89x102 and 90.8x102/100
mL in N-BW, respectively, during Summer, while the lowest values (55.8, 26.6
and 21.4/100 mL in SW and 3.8x102, 2.8x102 and 2.28x102/100
m1 in N-BW) were recorded in Winter. Again here, the counts of bacterial indicators
of sewage pollution were higher in the 1st lake compared to those recorded in
the other 2 lakes (Table 1 and 2). Seasonally,
the highest counts of bacterial indicators were recorded during Summer and the
lowest values during Winter in all of the studied lakes.
||Seasonal variations in total bacterial counts at 22 and 37°C
in (a) and (b) surface, (c) and (d) near-bottom waters, respectively
|| Most probable number of bacterial indicators of sewage pollution
in surface water of Abu Zabaal Lakes
||Most probable number of bacterial indicators of sewage pollution
(x102) in near-bottom water of Abu Zabaal Lakes
|| Total counts of gram-negative bacteria in surface and near-bottom
waters of Abu Zabaal Lakes
Total Counts of Gram-Negative Bacteria
The total gram-negative (TG-N) bacteria in the collected water samples of
the studied lakes was counted along the period of study (Table
3). Generally, as recorded in the total bacterial counts and bacterial indicators,
the highest level of TG-N bacteria were recorded in the 1st lake during Summer
in N-BW, while the lowest were determined in the 3rd lake during Winter in SW.
The morphological, biochemical data in addition to API 20E revealed that E.
coli, Klebsiella pneumonia, Salmonella choleraesuis, Enterobacter
aerogenes Yersinia pseudotuberculosis and Citrobacter freundii were
dominant gram-negative organisms.
Rate of Bacterial Reproduction
To determine the rate of reproduction as a parameter of bacterial biomass
production, the generation time of bacterioplankton in the studied lakes was
performed. Bacterial generation time in the SW of 1st lake ranged from 3 h at
station 1 in Summer to 25 h at station 4 in Winter, while seasonal average ranged
from 3.77 h during Summer to 17.95 h during Winter. On the other hand, the values
in N-BW ranged from 4.9 h at station 1 to 33.33 h at station 4 with seasonal
average ranged from 6.79 to 27.28 h during Summer and Winter, respectively.
Regionally, there was a gradual increase in generation time from the first lake
to the third one (Fig. 4a and b).
Bacterial Cell Volume
The transmission electron micrograph indicated that almost all bacterial
cells in the water of Abu Zabaal Lakes are bacilli (Fig.
5). The volume of bacterial cells ranged from 0.156 to 0.427 μm3
and their average cell volume was 0.258 μm3.
The bacterioplakton biomass as indication of trophic level in the studied
lakes was determined. The seasonal averages of bacterioplankton biomass in the
SW of the 1st lake ranged from 34.05 mg org. C m-3 in Winter to
421.83 mg org. C rn-3 in Summer, while their averages in N-BW ranged
from 327.78 mg org. C m-3 to 1565.41 mg org. C m-3 during
Winter and Summer, respectively.
|| Seasonal variations in rate of bacterial reproduction in
(a) surface and (b) near-bottom waters
|| Transmission electron micrograph showing the rod-shaped bacteria
in Abu Zabaal Lakes
||Seasonal variations of bacterial biomass (mg org. C m-3)
in (a) surface and (b) near-bottom waters
The values of biomass in the SW of the 2nd lake varied from 15.48 mg org.
C m-3 during Winter to 311.53 mg org. C m-3 during Summer
and recorded 212.85 mg org. C m-3 during Winter and 973.3 mg org.
C m-3 during Summer in N-BW. Compared to the other lakes, the 3rd
one, maintained the lowest bacterial biomass recording 11.61 mg org. C m-3
during Winter and 307.66 mg org. C m-3 during Summer in SW
and 212.95 mg org. C m-3 during Winter and 967.5 mg org. C m-3
during Summer in N-BW. As regards site-wise variation, there was a gradual decrease
in bacterial biomass from the first to the third lake. In general, a higher
bacterial biomass was found in N-BW while a lower one was in SW (Fig.
6a and b).
|| Seasonal variations in bacterial biomass x 102
(mg C m-2) of water column
|| Seasonal variations of daily bacterial production in (a)
surface and (b) near-bottom waters
The lowest bacterial biomass in water column m-2 in area (649.92 mg org. C m-2) was found in the 3rd lake during Winter, while the highest (10153.8 mg org. C m-2) was recorded in the deepest 1st lake during Summer (Fig. 7).
Daily Production of Bacterial Biomass
Daily production of the bacterial biomass in the SW of the 1st lake ranged
from 0.0074 g org. C m-3 at station 4 during Winter to 3.870 g org.
C m-3 at station 1 during Summer. On the other hand, their values
ranged in N-BW between 0.0222 g org. C m-3 at station 4 during Winter
and 9.47 at station 1 during Summer. The lowest values (0.0037 g org. C m-3
in SW and 0.034 g org. C m-3 in N-BW) were recorded in the
3rd lake. The highest averages of daily production (2.685 g org. C m-3
for SW and 5.533 g org. C m-3 for N-BW) of the 1st lake were recorded
during Summer. Again here, the daily production of bacterial biomass was gradually
decrease from the 1st lake to the 3rd one (Fig. 8a and b).
Bacterial activity as a criterion for trophic conditions of the studied
lakes was assessed. The bacterial activity in the SW of the 1st lake varied
between 0.13 U h-1 and ml at station 4 during Winter and 0.71 U h-1
and mL at station 1 during Summer, while the activity ranged in N-BW from 0.21
U h-1 and mL at station 5 to 0.94 U h-1 and mL at station
2 during Winter and Summer, respectively.
|| Seasonal variations of bacterial activity in (a) surface
and (b) near bottom waters
Compared to the other lakes, the 1st one, maintained the highest averages
of bacterial activity (0.53 and 0.59 U h-1 and mL in SW and N-BW,
respectively) and the lowest was recorded in the 3rd lake. In general, higher
values of bacterial activity were recorded in N-BW compared to those in SW (Fig.
9a and b).
Lakes are extremely complex ecosystem. The unique inter-relationships of their physical, chemical and biological properties give each lake its own characters. Abu Zabaal Lakes are newly formed lakes in north of El-Qalubiya Governorate, lying in the Nile Delta. The life process of all aquatic microorganisms is affected by water temperature which enhance their active multiplications. Thus, the highest bacterial counts in both SW and N-BW of the studied lakes were recorded during Summer while the lowest were in Winter. The recorded pH values of the studied lakes were on alkaline side. Such pH levels are optimum for most microorganisms and fish species (Bagde and Varma, 1991; Haraguchi et al., 2003). On the other hand, the highest pH values were recorded in the SW, while the lowest were recorded in N-BW. This might be due to the photosynthetic activity at the surface layer and bacterial degradation of organic matter at the bottom one (Rabeh, 2003a). In aquatic habitats, bacteria tend to adhere to the suspended matter. Therefore, a gradual increase in water transparency from the 1st lake to the third one was accompanied with a gradual decrease in the total bacterial counts in the same pattern.
The highest total bacterial counts at 22 and 37°C in SW and N-BW were found in the 1st lake compared to the other two lakes. This might be due to the relative ecological stability of the 1st one. On the other hand, the bacterial counts were higher in N-BW compared to those in the SW. This might be attributed to either of a lesser bactericidal effect of the solar UV rays than in SW, the N-BW being richer in organic and inorganic nutrients acting as a sink and being released from the sediment and/or sedimentation of bacteria with fine particles from the top layers.
First lake of Abu Zabaal maintained the highest bacterial indicators
of faecal pollution, TC, FC and FS in both SW and N-BW compared to the other
two lakes. The dominant gram-negative isolates recorded were E. coli,
Klebsiella pneumonia, Salmonella choleraesuis, Enterobacter
aerogenes Yersinia pseudotuberculosis and Citrobacter freundii. This
might reflect the high load of bacterial pollution due to the various activities
of fishermen at the 1st lake. On the other hand, these lakes are subjected to
direct discharge of raw sewage from the near-by unsewered areas. The results
of the present study revealed that the counts of the bacterial indicators were
high in N-BW compared to those of the SW. In addition to the earlier mentioned
reasons, this may be due to the higher concentration of ammoniacal nitrogen
in N-BW (35-764 μg L-1) compared to those in SW (26-466 μg
L-1) (Hussain, 2005).
The mean counts of microbial indicators are greatly varied from method to method and from one standard to another. Thus, the ratios of 22/37°C, FC/TC and FC/FS represent a hard base of judgment, interpretation a decision making. The ratio of bacteria recovered at 22 and 37°C helps to explain any sudden fluctuation in the bacterial count. In non-polluted waters, the ratio was usually 10 or more to 1, while in polluted waters it was less than 10 (APHA, 1980). In the present study, 22/37 ratios ranged from 1.05 to 1.39 in SW and from 1.05 to 1.13 in N-BW of the 1st lake. On the other hand, the ratios ranged from 0.53 to 1.23 in SW and 1.06 to1.14 in N-BW of the 2nd lake and between 0.42 to 1.33 in SW and 1.08 to 1.16 in N-BW in the 3rd lake. Accordingly, these lakes are heavily polluted with sewage. On the other hand, the FC/TC ratio confirms the faecal origin of the coliform bacteria. The ratios ranged from 0.47 to 0.72 and from 0.42 to 0.63 in SW and N-BW of the 1st lake, respectively. In the 2nd lake, these ratios ranged from 0.52 to 0.79 and from 0.71 to 0.8 in SW and N-BW, respectively. The ratios ranged from 0.42 to 0.85 in SW and from 0.52 to 0.91 in N-BW of the 3rd lake. These results indicate that the high levels of total coliform at the three lakes were faecal coliforms. The ratio FC/FS points to the source of faeces whether it is human (>4) or animal (<0.7) (Geldreich, 1974). Accordingly, the FC/FS ratios in SW and N-BW of the 1st lake (0.98 to 1.72 and 0.82 to 1.39), the 2nd lake (1 to 2.12 in SW and 0.17 to 1.31 in N-BW) and the 3rd lake (0.8 to 1.14 and 0.8 to 1.9 in SW and N-BW, respectively) may indicate the mixed origin of faecal pollution.
High rates of bacterial reproduction (short generation time) were recorded in the 1st lake compared to the other lakes. This might be due to high amount of organic matter in the form of phytoplankton, developing and dying in the 1st lake where the highest total phytoplankton crop (1390x105 U L-1) was recorded (Hussian, 2005). In this connection, Niewolak and Sinica (1981) found that generation time ranged from 2.7 to 58.7 h, 2.6 to 59.5 h, 1.5 to 157.1 h and 2.8 to 163.4 h in dystrophic, weakly eutrophic and in 2 strongly eutrophic lakes, respectively. The intense development of bacterioplankton (short generation time) during Summer and Spring might be connected with high temperature which helps the active proliferation of bacteria and the intensive development of phytoplankton during these seasons.
The cell volume of aquatic bacteria varied between less than 0.005 to more than 5 μm3. The bacteria in a water sample, therefore, might differ in their volume in the ratio of 1:10000 (Zimmermann, 1977). In aquatic food chain, bacteria constitute a large biomass which is a continuous source of food for specialized predators (bacteriovors) (Wikner et al., 1990). Moreover, they are considered a major secondary producers as they use dissolved organic matter (DOM) derived from primary producers, producing abundant biomass (Chin-Leo and Benner, 1990). Therefore, the quantification of bacterial biomass in Abu Zabaal Lakes becomes particularly important in case of growth and production rate determinations. The seasonal and regional variations of bacterioplankton biomass in the studied lakes were connected with fluctuations of the bacterial abundance and rate of multiplication. This finding was in accordance with those of Niewolak and Sinica (1981) and Rabeh (2003b) for some fertilized polish lakes and Lake Qarun (Egypt), respectively.
Daily production of bacterial biomass in the studied lakes was the highest in Summer as the high temperature enhance active proliferation of bacteria compared to other seasons. On the other hand, the gradual decrease in the production of bacterial biomass from the 1st to the 3rd lake was accompanied with the development of phytoplankton (Hussian, 2005).
Total microbial activity is a good measure of organic matter turnover in natural
habitats, since generally more than 90% of the energy flow pass through microbia1
decomposers (Heal and Maclean, 1975). Thus, the heterotrophic activity might
be a good indicator for eutrophic condition. The determination of FDA hydrolysis
has the advantage of being simple, rapid and sensitive technique and it should
be useful, especially for comparative studies of microbial activity in the natural
habitats (Schnurer and Rosswall, 1982). In Abu Zabaal Lakes, the highest bacterial
activities were recorded during Summer and Spring, where the high temperature
may enhance the bacterial activities. Regionally, 1st lake maintained the highest
bacterial activities compared to the other studied lakes. This might be attributed
to the high organic and inorganic nutrients present in the 1st lake (Hussian,