Environmental Engineering Reference
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of rotifers. In the present study, it was observed
that the pH values ranged between 7.51 and 9.01,
showing that the pH was alkaline. This observa-
tion is in agreement with the observations of
Subramanian et al. (
1987
) who suggested that
irrespective of the geology, climate, etc., the pH
of Indian River waters is predominantly alkaline.
Similar observations have also been made by
Somashekar (
1988
), Venkateswarlu (
1986
),
Bhargava (
1985
), and Mitra (
1982
). The pH val-
ues were the lowest during the post-monsoon
season and ranged between 7.52 and 7.76 at all
the stations. This was also the season when the
rotifer diversity was at its maximum. During
summer, the pH ranged between 7.74 and 8.80,
while the rotifer diversity was moderate. Least
diversity was seen in the winter months when the
pH ranged between 7.70 and 8.35. When pH and
rotifer diversity were correlated, a signifi cant
negative correlation (Table
6.17
) was observed.
Moreover, as evidenced from the elevated slope
value (Table
6.17
), even a slight alteration in the
pH may lead to perceivable changes in the rotifer
community. Contradictorily, Berzins and Pejler
(
1987
) could not determine any correlation
between peak rotifer abundance and pH and
stated that rotifers as a group exhibit a very wide
range of pH tolerance. They have been found in
waters with pH values spanning at least 2.0 units,
and many are found in waters, which defer by as
much as 5.0 units (Berzins and Pejler
1987
).
Haque et al. (
1988
) from their study observed
rotifers to be insensitive to pH. However, Green
(
1960
) stated that there could be an optimum pH
for the growth and development of a particular
species. Supporting this statement, Yin and Nui
(
2008
) demonstrated through their laboratory
experiments that pH exerted a major infl uence
on egg viability and growth rate of fi ve closely
related rotifer species of the genus
Brachious.
According to Berzins and Pejler (
1987
), several
species have peak abundances in the acidic range
(pH < 6) and thus may be adapted to these condi-
tions. According to Brett (
1989
), rotifer genera
found below pH 3 can also be found in less acidic
soft waters. Deneke (
2000
) found species richness
to be generally low in highly acidic environments
of pH values 3. His studies also suggested that
small littoral or benthic rotifers predominate over
crustaceans under highly acidic environments.
Wiszniewski (
1936
) suggested that the most
important factor infl uencing psammic rotifer
communities is pH of the lake water. Bielanska-
Grajner (
2001
) observed larger number of rotifer
species and their higher abundance in slightly
acidic to neutral waters, and the lowest quantity
and the number of rotifers were observed in waters
with the lowest pH waters among psammic rotifers.
On the contrary, Prabhavathy and Sreenivasan
(
1977
), Sampath et al. (
1979
), and Mishra and
Saksena (
1998
) have shown rotifers dominating
in alkaline waters. Finally, it may be stated from
the present study that even a slight alteration
in pH value will signifi cantly affect the rotifer
diversity.
Dhanapathi (
2000
) stated that dissolved oxy-
gen (DO) plays an important role in determining
the occurrence and abundance of rotifer commu-
nities. Arora (
1966
) has shown that dissolved
oxygen can infl uence the survival of rotifers.
Nayar (
1964
) suggested that dissolved oxygen
could be an important factor infl uencing the growth
and reproduction of
Brachionus calycifl orus
.
In the present study, it was observed that the
rotifer population was at its lowest during the
winter season when DO levels were at its maxi-
mum. Similarly, Mishra and Saksena (
1998
)
from their studies also found that rotifer numbers
were inversely proportional to the dissolved
oxygen. Prabhavathy and Sreenivasan (
1977
)
suggested that rotifers are tolerant to low dissolved
oxygen values. In the current study, when the
dissolved oxygen levels were the lowest in the
summer season, the rotifer population was not at
its highest, in fact moderate rotifers counts were
recorded in this season. Nevertheless, it was
observed that River Vishwamitri supports the
highest rotifer number during the post-monsoon
season when the dissolved oxygen levels were
moderate. The fi ndings of the current work are in
agreement with that of Zhou et al. (
2007
), who
reported no relationship of dissolved oxygen
with the vertical distribution of rotifers in Xiangxi
Bay of China. This suggests that there is no direct
correlation between the dissolved oxygen levels
and rotifer population. However, Green (
1956
) has
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