DISCUSSIONIn any ecosystem, not a single speciesgrows independently and indefinitely,because all the species are interlinked andhas cyclic transformation of nutrients. Thephysicochemical changes in the environmentmay affect particular species and induce thegrowth and abundance of other species,which leads to the succession of severalspecies in a course of time. In Pond 1, lowdiversity of cyanobacteria was attributed toa massive bloom of Microcystis aeruginosa.Low amount of dissolved oxygen (0.8mg l-1) in pond - 1, which had a significanteffect in reducing the other cyanobacterialpopulation (tab. 2). The similar type ofresults has also been reported (Subha &Chandra, 2005; Pingale & Deshmukh, 2005;Rani et al., 2005). Frankelin (1972) reportedthat Microcystis is one of the dominantorganisms that is associated with almostpermanent blooms in tropical freshwatersthat are exposed to constant sunshine,warmth, and nutrients like phosphate,silicate, nitrate, CO2 and lime. Formation ofcyanobacterial blooms in freshwater bodiesis essentially due to buoyant nature of theseorganisms. Buoyancy of cyanobacteria isimported by the gas vacuoles which formsdense growth on the water surface in ponds,reservoirs and lakes and cause seriousnuisance because of visual appearance,production of toxins (Carmichael, 1994) andunpleasant odour produced by substancessuch as geosmin (Juttner, 1987). Jeyaraman(1972) and Qasim (1972) reported that the
dominance of cyanobacterial blooms in
general, Trichodesmium bloom in particular
may be due to two reasons: it may be a case
of the superiority of the organism competing
with the other organisms for the nutrient
supply from the environment or it may be
an instance where the metabolic products of
the dominating species and creating
unfavorable condition in the environment for
the growth of other organisms.
Murphy et al. (1976) and Bailey & Taub
(1980) reported that the development of
cyanobacterial blooms in any ecosystems,
the siderophore mediated iron uptake in
believed to be a contributing factor in their
ability to dominate other microalage. Where
as the other cyanobacterial forms that
apparently cannot synthesize siderophore are
able to utilize siderophore produced by other
bacteria (Ferreira & Straus, 1994). As also
reported in other publications addressing the
persistence and stability of various
organisms in fresh water ecosystems
(Duncan & Blinn, 1989; Scarsbrook, 2002;
Soininen & Eloranta, 2004), cyanobacteria
particularly forms their extreme blooms
throughout the main part of the summer.
The crucial role of the physico-chemical
parameters in the ecosystem on thedistribution of algal community has been
extensively analyzed in tropical and
temperate freshwater ecosystems (Lund,
1965; Reynolds, 1984; Köhler, 1994).
Chellappa et al. (2004) reported the
collective dominance by the species of
cyanobacteria was due to their capacity to
grow in turbid water and low light intensity
to maintain buoyancy and the capacity to
grow exponentially in wet period in which
nitrogenous nutrients were high. The daily
water level fluctuations attributed to increase
and decrease in phytoplankton species
diversity. Pingale & Deshmukh, (2005)
identified 87 algal species belonging to 43
genera from Kalsubai-Ratangal, Ahmednagar.
Subha & Chandra (2005) studied the algal flora
from temple tanks in and around the city of
Chennai and reported 17 species of algae
belonging to Cyanophyceae, Chlorophyceae,
Bacillariophyceae and Euglenophyceae. Of the
39 species of cyanobacteria recorded in the
present study, only 5 heterocystous
cyanobacteria such as Calothric brevissima,
Calothrix sp., Scytonema sp., Anabaena sp.
and Nostoc carneum were recorded. Hoyslew
& Pearson, (1979) and Oren & Shilo, (1979)
reported that the high levels of sulfide
content, and anaerobic conditions was
believed to exclude the heterocystous forms.
High levels of nitrogen source in the
environment is also eliminating
heterocystous forms, since nitrogen free
media is commonly used for the isolation and
purification of heterocystous cyanobacteria.
The significant positive correlation
between the cyanobacterial diversity and
micronutrients (zinc and nitrite) was
observed and also reported by Govindasamy
& Azaraiah (1999). In the present study the
significant positive correlation was observed
between the Total Cyanobacterial Species
(TCS) and dissolved oxygen (r=0.9803;
p<0.01), TCS and bicarbonate (r= 0.9928;
p<0.01) and TCS and carbonate (r=0.941;
p<0.05). Hence the present study concluded
inspite of the fact that the cyanobacteria are
ubiquitous, their population dynamics are
often influenced by the available nutrients
and the physico-chemical conditions of the
ecosystem
การแปล กรุณารอสักครู่..
