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Planktonic diversity of a polluted creek system

The demand for power-generating plants has been increasing regardless of several   appeals in energy  conservation. Factors such as urbanisation and industrialisation propel the need for energy production (Singh,  2015).  Consequently, it increases the need for cooling water at various steps during energy generation procedures. In general, water bodies, such as rivers and ocean were often used as key sources to meet the in-satiated demand for cooling water.

Water  drawn  into  power  plants  usually  contains organisms such as phytoplankton, algal propagules, zooplankton, invertebrate larvae and fish  larvae which are often  considered  as  a  representative  of  local  ecological communities (York  and  Foster,  2005).  These  traversing communities can be used as a mirror-reflection to determine the adverse  impacts  such as  decreased biomass  and  productivity of phytoplankton and  hetero- trophic bacteria (Choi et al., 2002;  Shiah  et  al.,  2006) and   reduction in survival  and diversity of zooplankton communities (Taylor,  2006 in the  aquatic environment.

The damage in the transiting plankton cells often associates with factors such  as  the  type  of  organisms, conditions  of  operational systems,  temperature, and chlorine residues  (Bamber  and Seaby, 2004;  Capuzzo,  1980; Poornima et al., 2005).  Among these factors, thermal stress was reported as a causative factor for transiting plankton mortality (Taylor, 2006).  In general, seasonal variation of Indian coastal water temperature widely varies (maximum of 10 °C), thereby forcing the organisms to live in upper lethal temperature limits (Krishnakumar et al., 1991). Further, mortality of planktonic communities was also strongly related to the discharge of heated waste materials in tropical coastal water (Poornima et al., 2006).

It is apparent that  power  plant  intake  systems pump  seawater along with   existing   biota   into   a  series   of  mechanical  devices (strainers, screens,  tubes,  etc.) for filtration. The strainers and screens perform the function  of impingement, thus restricting the entry  of large marine organisms and  debris  as well as supplying water  with  microorganisms (planktonic and nektonic species) to the condenser for heating cause entrainment  (Greenwood, 2008;   Mayhew   et  al.,  2000;   Bamber  and Seaby,  2004).  This micro-marine biota often releases effluents in the same environment.  However, the variety   of physical   and chemical stresses faced by this micro marine biota may reflect on the survival of such organisms varying in biodiversity in the released environment.

Studies  have  been  conducted worldwide to  address  the  impact  of power plant effluent on plankton community (Shiah  et al.,  2006;  Lo et al., 2016).  In India, few reports on the thermal impact on planktonic organisms are available from various  vicinities (Selvin- Pitchaikani et  al.,  2010).  For instance, reduction in benthic fauna   (Kailasam   and Sivakami,   2004) and zooplankton species (Easterson et al., 2000) was recorded.

Notably,  no  attempts were  made  to  address  the  impact  of a coal- based  thermal power  plant  along  the  coastline of Tamil  Nadu. Eccentrically, Ennore  creek  is the  most  exploited and  polluted water body that is located  along this coastline and receives effluent discharges from   major   industries  including  fertilizers,  rubber  factories,  steel rolling,  motor  vehicles and oil refineries surrounded by thermal power plants.  Particularly, studies  on understanding the change  in planktonic biodiversity of the  Ennore  creek  system  after  the  discharge of heated effluents from the power  plant  into  the polluted aquatic ecosystem are not available.

North  Chennai  Thermal  Power  Station  (NCTPS), a coal-based thermal power   plant    operated  by   Tamil   Nadu   Generation  and   Distribution Corporation Limited (TANGEDCO), is located  at the confluence point of the Ennore  creek  with  the  Bay of Bengal,  South  India  (Fig.  1). The NCTPS Power Plant Unit shares its southern boundary with the Ennore creek (13°13′54.48″ N, 80°19′26.60″ E), northern boundary with  Ennore  port, eastern boundary with the Bay of Bengal coast, and western boundary with Buckingham canal.

By 1995,  NCTPS was commissioned with  a total  power  production capacity  of 630 MW (with  three  units  of 210 MW each) discharge point;  EHE4 for an area  1 km away from the discharge point; and EHE5 for the Ennore  creek  mouth 500 m away  from the discharge point.  The study  participants were  well informed about  the  study  sites because  sampling  was done  monthly by the  same  crew.

Surface  water  samples  were  collected  using  a clean  plastic  bucket and  planktons were collected  using  plankton nets with a mechanical flow  meter  (64-micron net  by vertical  haul).  Parameters such as temperature, salinity, dissolved oxygen (DO) and conductivity was measured using the YSI-85 DO meter.  The concentrated phytoplankton was preserved by the addition of formaldehyde (2 per cent) and Lugol’s iodine (1 per cent) solution. Phytoplankton number was counted by following the Utermohl sedimentation method (Utermohl, 1931;  Utermöhl, 1958) under  an inverted compound microscope (Carl Zeiss); the total  number of organisms per liter  of seawater was calculated.

A sampling of zooplankton was carried out using vertical hauls of a 300-μm net with a flow meter (Hydro-Bios) at all designated points.  The samples collected were preserved in formaldehyde (4 per cent buffered) and zooplankton number was counted under   a stereo zoom microscope.

Approximately 11  species  of fish  and  larvae  were  reported at  this  vicinity  (WAPCOS, 2014) and the  input  parameters required for the  FH model  availability were  restricted to two  dominant and  commercially important species (Mugil cephalus and Sardinella longiceps). According to our survey, it was assumed that 90% of eggs belong to M. cephalus, 9% of S. longiceps and the  remaining 1 per cent of eggs belong  to other  species.

The present study observes predominant changes in the phytoplankton community at various sites. Here, the order of dominance of phytoplankton at the  site EHE1 was Bacillariophyceae > Dinophyceae > Cyanophyceae, whereas at the   sites EHE2 to EHE5, the   order was Bacillariophyceae > Cyanophyceae > Dinophyceae. The observation of phytoplankton community structural changes such as the dominance of Cyanophyceae group and reduction in Dinophyceae as well as Bacillariophyceae seems to have ecological significance.

Although  the Ennore  coast was fed with polluted waters  containing high nutrient sources  from Ennore,  Cooum, and Adyar estuaries (Shanthi and Ramanibai, 2011),  augmented supply of microscopic cell clusters  from repositories of the Ennore creek system may  proliferate algal  cells, thereby leading  to bloom  shortly. Notably, Pravakar Mishra  et al. (2015) recorded Trichodesmium sp. bloom  along the Ennore coast and this was also reported in the present investigation performed in the  Ennore  creek  system. The change in phytoplankton community also reflected the reduction in population diversity.

Reference

This paper had been originally published in Marine Pollution bulletin. To cite the original work
use
Jebarathnam. P.P. J., G .Nandhagopal, R. B. Bose, S. Ragumaran and V. Ravichandran, 2018.
Impact of coastal power plant cooling system on planktonic diversity of a polluted creek
system, Marine Pollution Bulletin, 133: 378–
391.https://doi.org/10.1016/j.marpolbul.2018.05.053
For any correspondence please contact prince@niot.res.in.

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