A Study on Diversity and Abundance of Micro-Phytoplankton in River Cauvery and its four Upstream Tributaries in South Karnataka, India

The phytoplanktons are the common primary producers contribute substantial amount of dissolved oxygen. Dynamics of all aquatic ecosystems center on the primary productivity. Over all investigation revealed that the presence of phytoplankton species like, Gomphonema, Navicula, Cyclotella, Melosira, Nitzschia, Synedra, Scenedesmus, Chlorella, Ankistrodesmus, Oocystis, Closterium, Gloeocystis, Crucigenia, Chlorococcum, Spirogyra, and Ulothrix etc., were recognized as pollution indicators. One liter of mid stream surface water samples were collected and preserved in 10% Lugols–Iodine. Phytoplanktons were counted by Lackey’s drop method using Epifluorescence microscope. SNK test revealed that river Lakshmanatheertha exhibit significant difference. Calculations of Pearson’s correlation coefficients (p<0.01) showed positive correlation of mean abundance of micro phytoplanktons with micro zooplankton. Further, utilization of organic matter in aquatic environments by the bacteria is through the phytoplankton. Several physico-chemical factors and varying influx conditions cause changes in phytoplankton abundance and diversity. Chlorophyll-a is considered as the most reliable index of phytoplankton abundance and biomass. Temperature, pH and conductivity were important in the distribution and abundance of phytoplanktonic species. Increased algal growth was recorded in the presence of micro nutrients such as chloride, TASA and calcium. The initial hypothesis that the four upstream tributaries are similar to each other in mean abundance of micro phytoplankton, but are markedly different from that of main river Cauvery was rejected. In this investigation more abundance of phytoplankton was noticed in the river Lakshmanatheertha, this was due to more contamination of industrial and sewage pollution, suggests that this river was more favorable to abundance of micro phytoplankton.


INTRODUCTION
Phytoplanktons are the primary producers of any aquatic habitat, they floats passively in water surface and sometimes, they may extend down to various depths where light is available for photosynthesis. Phytoplanktons, include green algae, blue green algae, diatoms, desmids, euglenoids etc., are important among the aquatic flora. They are ecologically significant as they form the basic link in the food chain of all aquatic animals, and when in large numbers they make the water greenish (Misra et al., 2001;Harsha & Malammanavar, 2004), Several, physico-chemical factors (Homyra and Sabrina Naz, 2006) and varying influx conditions (Hunszar & Reynolds, 1997) can markedly influence the aquatic system, and cause changes in the phytoplankton abundance, diversity and succession Sharma et.al 2007. In case of blooms or scum, Cyanobacteria pose a series of problems for water quality, fisheries resources, agriculture and human health (Codd, 1995). The planktonic algae contribute substantial amount of dissolved oxygen in the aquatic systems (Harilal, 2005). Micro algae are indeed the biological starting point for energy flow in the food chain in most aquatic ecosystems (Rahaman & Sosamma E., 2003), and also gives information relating to the amount of energy available to support bioactivity of the system (Saha et al., 2001). The dynamics of all aquatic ecosystems center around primary productivity for supports different food chain and food webs (Mishra and Tripathi, 2002). The magnitude and dynamics of primary production has become an essential parameter to assess the state of pollution in aquatic ecosystems. In polluted environment majority of plants and animals find it difficult to survive but those which could tolerate the stress of pollution alone may survive. These individuals can act as indicator of pollution, more specifically bioindicators of the trophic state of the ecosystem (Danielkutty & Sobha, 2006, Malik & Umesh Bharti, 2012. Algae are simplest plants inhabiting all kinds of habitats and are sensitive to pollution, hence are called biological indicators of water quality (Hegde and Sujata, 1997). Algae are significantly involved in water pollution and they bring about an enrichment of algal nutrients in water and this may selectively stimulate the growth of a few types producing massive surface growths or "blooms" that inturn reduce the water quality. Certain algae are able to flourish in water polluted with organic wastes and play an important part in "Bio -purification" of the water body (Palmer, 1980). Generally, in aquatic environment more information is available on abundance of phytoplankton with respect to marine and lentic waters only. Very few studies are available on Indian lotic fresh waters, viz. on physico-chemical (water quality) parameters of river Mahanadi (Mithra, 1995), on pollution status of river Sabarmati at Kheda (Jamson & Rana, 1996), impact of sewage on Diatom community in river Alakananda (Nautiyal et al., 1996), on toxic metals of river Ramaganga at Moradabad (Sharma and Pande, 1999), on river Parvathyputhanar (Prasanthan & Nayar, 2000), on Quality of water in Parvathyputhanar in Thiruvananthapuram (Jayashree, 2002), on Vamanapurum river of Thiruvanathapurum, Kerala (Mini et al., 2003) and on lotic ecosystems in and around Courtallam, Tamil Nadu (Drusilla et al., 2005). Earlier studies carried out on river Cauvery includes, rotifers as biological indicators of water quality (Sampath et al., 1979), phytoplankton as indicators of water quality (Somashekar, 1985;Somashekar, 1997a and1997b). However, not much more information is available on the abundance of microphytoplankton in river Cauvery and its important tributaries in Karnataka state, India.

MATERIALS AND METHODS
One liter of mid stream surface water samples from rivers Lakshmanatheertha, Harangi, Hemavathy, Lokapavani and Cauvery were collected in polythene cans for the study of micro phytoplankton fortnightly during the study periods. The water samples were preserved in 10% Lugols-Iodine solution, since, absorption of Iodine from Lugols solution by plankton cells promotes settling of the cells. Further, it stains the cells and also preserves flagella intactly. Micro phytoplankton, from one liter preserved samples was concentrated by sedimentation method for 24 hours. The sedimentation was concentrated to only 20ml, by siphoning off the remaining 980ml of the supernatant. Their abundance was counted by Lackey"s (1938) drop method. The total number of Phytoplanktons was counted separately by examining one drop of water on a slide under 40X magnification using Epifluorescence microscope (BX40, Olympus, Japan). Identification was done by following Fritsch (1975), Desikachary (1959) and Anand (1998). The number of micro phytoplankton was calculated by using the formula of (Nomita Sen et al., 1992). The mean abundance of log 10 transformed values of micro-Phytoplanktons data were used for one-sample Kolmogorov-Smirnov test, the Student-Neuman-Keuls test, one-way ANOVA, calculation of Pearson"s correlation coefficients and stepwise multiple regression analysis.

RESULTS
A summary of abundance of micro phytoplankton, measured for all the rivers studied revealed that, the mean abundance of micro-phytoplankton was similar in the rivers Harangi (11 Org. ml -1 ) and Hemavathy (10 Org. ml -1 ), but was significantly more in river Lakshmanatheertha (19 Org. ml -1 ) followed by river Cauvery (14 Org. ml -1 ) and river Lokapavani (13 Org. ml -1 ). The SNK test showed that, the mean abundance of microphytoplankton in the river Lakshmanatheertha was more and also significantly different from all the rivers studied. Whereas, in the river Cauvery and Lokapavani it was similar and also significantly different than other three water courses. It is noteworthy that the lowest number (5 Org. ml -1 ) of micro-phytoplankton was recorded in the rivers, Lakshmanatheertha, Harangi, Hemavathy and Lokapavani, and highest number (69 Org. ml -1 ) in the river Lakshmanatheertha were the lowest and highest numbers among the five rivers (Table 1).
The abundance of micro phytoplankton, showed few correlations with the other microbial and physico-chemical (water quality) variables (Tables 2 and 3). In the river Lakshmanatheertha the mean abundance of micro phytoplankton showed positive correlations with Abundance of micro zooplankton and total micro plankton among other microbial variables, and with Temperature, Conductivity, BOD, Carbon di-Oxide, Chloride, TASA, Calcium and Chlorophyll-a, and negatively correlated only with the SWV among water quality variables. In the river Harangi, it showed positive correlation with the abundance of particle bound bacteria, abundance of total bacteria, micro zooplankton and total micro plankton and with pH (F), Conductivity, Chloride, TASA, Nitrate and Chlorophyll-a and negatively correlated with Rainfall and COD. In the river Hemavathy, the micro phytoplankton was positively correlated with the abundance of free living bacteria, total bacteria and total plankton and negatively correlated only with pH (L). In the river Lokapavani, it was positively correlated only with the total plankton and negatively with the CFU"s and only with Chlorophyll-a among the water quality variables. In the river Cauvery, the abundance of micro phytoplankton was positively correlated with the micro zooplankton and total plankton; and only negatively correlated with pH (L).
The density of micro phytoplankton under different classes is given in the Generally, Euglenophyceae members represented less in number compared to other three groups. Species composition and frequency distribution of four different classes revealed that, total 57 types of micro phytoplankton were identified up to generic level. The largest and most diverse group was Chlorophyceae comprising 30 genera followed by Bacillariophyceae 14 genera, Cyanophyceae 10 genera and Euglenophyceae 3 genera However, frequency of occurrence of Bacillariophyceaean genera were more compared to Chlorophyceaean genera (Tab. 5).

DISCUSSION
The result described here showed that, the mean abundance of micro-phytoplankton in the river Lakshmanatheertha was more and also significantly different than the other water courses studied. The initial hypothesis that the four upstream tributaries are similar to each other in mean abundance of micro phytoplankton, but are markedly different from that of main river Cauvery was rejected. The low level of water, maximum anthropogenic activities, discharge of sewage, agricultural wastes and other untreated effluents contamination, all of which enriches the nutrient level in the water, might be the reason for increased abundance of micro phytoplankton in the river Lakshmanatheertha. Similarly, Gadhia, et al., 2000, was reported that higher concentration of nutrient discharge causes increased abundance of micro phytoplankton. Somashekar (1988) reported the high algal growth in river Cauvery due to discharge of effluent. Calculations of Pearson"s correlation coefficients (p<0.01) between mean abundance of microphytoplankton, and other microbial or environmental variables (Tables 2 and 3) did not show uniform pattern. In the rivers Lakshmanatheertha, Harangi and Cauvery, the micro phytoplankton showed significant positive correlation with micro zooplankton. This implies, the micro zooplankton represented the most important consumers of phytoplankton production (Froneman, 2000). Similarly, the maximum phytoplankton abundance often associated with high ciliate abundance (Alder et al., 2000). Further, the mean abundance of micro phytoplankton showed positive correlations with the abundance of particle bound bacteria and total bacteria in the river Harangi, and with freeliving bacteria and total bacteria in the river Hemavathy. Bacterial utilization of organic matter is significant in aquatic environments and its supply through the phytoplankton (Bertilsson & Jones, 2003;Cesar Daniel et al., 2005). Whereas, the negative correlation of micro phytoplankton with CFU"s in the river Lokapavani suggest that both are considered to be competitors for dissolved mineral nutrients (Chrzanowski & Grover, 2001).The positive correlation between micro phytoplankton with Chlorophyll-a in the rivers Lakshmanatheertha, Harangi and Lokapavani, implies that Chlorophyll-a is considered as the most reliable index of phytoplankton abundance and biomass (Tripathy et al., 2005). Significant positive correlations with pH in river Harangi and with temperature in the river Lakshmanatheertha, revealed temperature and pH were important in the distribution and abundance of phytoplanktonic species (Bouvy et al., 2000). Similarly, the positive correlation of conductivity with phytoplankton abundance in Lakshmanatheertha and Harangi rivers, suggests, high electric conductivity in water influence the biological productivity (Sarojini, 1994), and also positively correlated with the BOD in the river Lakshmanatheertha only, this in agreement with the similar findings of Pandey et al., 2000. A significant positive correlation also noticed with the Nitrate in the river Harangi. The high concentration of Nitrate favored the phytoplankton abundance in fresh waters (Philiphose, 1959;Munawar, 1970). In the river Lakshmanatheertha, the mean abundance of micro phytoplankton was positively correlated with the Carbon di-Oxide. The important substances involved in this growth are nitrogenous compounds together with Carbon di-Oxide (Palmer, 1980). Similar positive correlation also noticed with the chloride and TASA in the rivers Lakshmanatheertha and Harangi, and with calcium in river Lakshmanatheertha, suggesting, Chloride, TASA and Calcium were the micro nutrients; their increased concentration in water might have favored the increased growth of algae (Sengar et al., 1985). Whereas, the surface water velocity in the rivers Lakshmanatheertha and Harangi, and rainfall in the river Harangi, showed significant negative correlations, because high flow due to rain influences the increased concentration of turbidity in the water, which inturn reduces the phytoplankton production and abundance (Yakovlev, 2001). Microphytoplankton plays a key role in maintaining proper equilibrium between abiotic and biotic components of ecosystem. Being an index of trophic status, phytoplankton reflects the overall environmental condition of the system and its potentiality (Agarwal et al., 1993). In the present investigation the group Bacillariophyceae showed dominance in terms of density in all the five watercourses studied. The finding is in conformity with the reports of Imevbore (1970) in the river Niger, and Tiwari et al., (2000) in the river Ganga. The group Bacillariophyceae particularly Gomphonema and Navicula species have also been selected as indicators of certain industrial wastes and sewage (Palmer, 1980). In this study Gomphonema sp. was abundant in rivers Lakshmanatheertha and Cauvery (Table. 4) which suggested that, these ecosystems were contaminated with industrial and sewage pollution. This condition was noticed in the river Lakshmanatheertha only. But, the sewage water carried by the river Lakshmanatheertha may enter the main river Cauvery, might be the reason for increased abundance of Gomphonema sp in the river Cauvery also. Along with this, other indicator species like, Cyclotella, Nitzschia, Fragellaria, Gyrosigma, Amphora, Cocconeis and Synedra in the rivers Lakshmanatheertha and Lokapavani, were also found abundant, which were mainly used to calculate the pollution index of water (Palmer, 1980). Further, the high abundance of species like Oocystis, Scenedesmus, Spirogyra, Chlorella, Tetrahedron, Ulothrix, Tetrastrum, Schroederia and Closterium in the river Lakshmanatheertha indicates the enrichment of water with nutrients, sewage and other effluent contaminations, which leads to eutrophication. Euglenoids was least in number compared to other groups all of which were used as indicator of pollution (Palmer, 1980).