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
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