Study on the influence of hydro-chemical parameters on ... - Core

Egyptian Journal of Aquatic Research (2012) 38, 157–170

National Institute of Oceanography and Fisheries

Egyptian Journal of Aquatic Research http://ees.elsevier.com/ejar www.sciencedirect.com

FULL LENGTH ARTICLE

Study on the influence of hydro-chemical parameters on phytoplankton distribution along Tapi estuarine area of Gulf of Khambhat, India Basil George a, J.I. Nirmal Kumar

a,*

, Rita N. Kumar

b

a P.G. Department of Environmental Science and Technology, Institute of Science and Technology for Advanced Studies and Research (ISTAR), Vallabh Vidya Nagar, Gujarat 388120, India b Department of Biological Science and Environmental Science, N.V. Patel College of Pure and Applied Science, Vallabh Vidya Nagar, Gujarat 388 120, India

Available online 17 February 2013

KEYWORDS Estuary; Tapi; CCA; Phytoplankton; Hydrochemistry

Abstract Physicochemical properties play a major role in determining the density, diversity and occurrence of phytoplankton in an estuarine ecosystem. The present study is conducted to assess the relationship between physicochemical parameters and phytoplankton assemblages which in turn can serve as a suitable method to assess the quality of estuarine ecosystem. Results showed an increased concentration in physicochemical parameters and phytoplankton density during postmonsoon season followed by pre-monsoon and monsoon season. Canonical correspondence Analysis (CCA) between environmental variables and dominant taxa of phytoplankton indicated the influence of freshwater on phytoplankton distribution in the estuarine precinct. ª 2013 National Institute of Oceanography and Fisheries. Production and hosting by Elsevier B.V. All rights reserved.

Introduction Estuaries are important coastal ecosystems which occur where there is a confluence of fresh and marine environments and create a salinity gradient from the inner to outer estuary (Prandle, 2009). Estuaries have been called the ‘‘nurseries of the sea’’ because the protected environment and abundant food provide an ideal location for organisms to inhabit and reproduce. Cer* Corresponding author. E-mail address: [email protected] (J.I. Nirmal Kumar). Peer review under responsibility of National Institute of Oceanography and Fisheries.

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tain aspects of estuaries such as their high productivity and availability of natural interconnectors between maritime and inland waterways make them desirable locations for human settlements. Residential, recreational and industrial developments (such as marinas, harbors or ports) are usually located right at the waterfront with supporting structures such as embankment impacting on the upper shore communities. Estuaries are often challenged by land development and land reclamation is particularly detrimental in this respect as it results in a permanent loss of estuarine habitat. Phytoplankton is an assemblage of heterogeneous microscopic algal forms of aquatic systems whose movement is more or less dependent upon water currents (Kudela and Peterson, 2009). Phytoplankton is the main representative of primary production in estuarine ecosystems. A number of factors define the role of phytoplankton in estuarine production such as

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salinity, temperature, light (influenced by turbidity), nutrients, water dynamics and the configuration of the water basin. Also, phytoplankton composition influences various processes such as nutrient recycling, grazing, particle sinking and food webs (Cetinic et al., 2006). The quality and quantity of phytoplankton and their seasonal patterns have been successfully utilized to assess the quality of water and its capacity to sustain heterotrophic communities (Hulyal and Kaliwal, 2009). Dynamic changes in pH, trace metal speciation, and concentrations of dissolved gases like oxygen, carbon dioxide, methane, inorganic nutrients (nitrate, phosphate, silicate) and organic compounds such as amino acids, organo-sulfur compounds are all closely associated with fluctuations in phytoplankton composition. Trophic linkages also exist, between the phytoplankton as primary producers and populations of consumer organisms including bacteria, zooplankton, benthic invertebrates, and fish. Phytoplankton community also acts as useful indicators of water quality (Abuzer and Okan, 2007). Socio-economic development in Gujarat State and rapid industrialization along southern part have led to the emergence of many industries near this river utilizing freshwater according to their needs and conveniently disposing off the wastewater either into the river or in the estuary depending upon their location. As a result, many new townships have come up and some of the older cities which are several kilometers inland have flourished at the cost of quality of river water. Industrial as well as anthropogenic interventions into the estuarine area result in discharge of partially-treated and untreated wastewater into the fragile ecosystem. This study extends for one year and aims to determine the present nutrient status and phytoplankton composition of Tapi estuarine ecosystem (Gulf of Khambhat, India) which is prone to industrial as well as anthropogenic pressure.

(PO4-P), nitrate (NO3-N), ammonia and silicate (SiO4-Si) were estimated by ascorbic acid method, cadmium reduction method, nitroprusside method and silicomolybdic method respectively (APHA, 1998). The data quality was ensured through careful standardization, procedural blank measurements, spike and duplicate samples. Measurements of in situ temperature (C), pH and salinity (ppt) was made using probes, while DO was measured using Winkler’s method (Strickland and Parsons,1979).The chlorophyll-a estimation was done spectrophotometricaly by filtering the samples using glass fiber filter papers and extracted in 90% acetone. Plankton samples were collected using planktonic net of 20 micrometer (lm) mesh size and were preserved in 4% formalin for future use. The plankton identification was carried out with help of literatures and books including Cyanophyta (Desikachary, 1959), Marine planktons (Newell and Newell, 1977) and Identification of Marine Phytoplankton (Thomas, 1997). The enumerations of phytoplankton were carried out with the aid of light microscope by Lackey’s drop method (Lackey, 1938). Relationships between phytoplankton species composition and environmental factors were calculated by Canonical Correlation Analysis (Ter Braak and Verdonschot, 1995) using Statistica 9 software (Statsoft). CCA is a direct ordination that selects the combination of environmental variables that maximize the dispersion of the scores of species (Nabout et al., 2006). The results of environmental variables are shown by arrows radiating from the center of the graph along with the points for samples. The arrow representing the environmental variable indicates the direction of maximum change of that variable across the diagram. The position of the species point represents the environmental preference of the species.

Materials and methods

Estuarine environment are subjected to varied change in physicochemical properties due to continuous mixing of fresh water with marine water. Estimating the water quality is very important in determining the quality of ecosystem (Chang, 2008).Water temperature is an important parameter which influences the chemical process such as dissolution-precipitation, adsorption–desorption, oxidation–reduction and physiology of biotic community in an aquatic habitat (Aken, 2008). Stenseth et al. (2004) suggested that variability in temperature may induce variations in marine and estuarine ecosystems at all levels of the food chain, from primary productivity to the top predators including fisheries. Annual changes of temperature as observed in this study shows a gradual fall from the rainy season to winters and a steady raise in summer till the onset of rains in both the estuaries. Temperature variation in Tapi estuary was recorded in the range of 22–33.2 C. Umra reported the highest temperature of 33.6 C in May, 2009 and lowest of 23.7 C was noted at Causeway in January, 2009. The highest temperature was noticed during post-monsoon season in all the sites of Tapi estuary (Fig. 5a). The surface-water temperature at the all stations during a particular season throughout the period of study, showed a maximum fluctuation of 1–2 C only. The results found to be well agreed with investigations carried out by Martin et al. (2008) for Cochin Estuary of south India where they reported a temperature variation of 28–32 C during pre-monsoon period. Bharadwaj

Gulf of Khambhat, is an extensive area of estuarine habitats located between 20350 -22200 N latitude and 72050 -72550 E longitude in Gujarat State. The Gulf is characterized by several inlets of sea and creeks formed by about 16 large, medium and small rivers such as Narmada, Tapi, Mahi and Sabarmati. Tapi is one of the major perennial rivers flowing towards west coast of India and is an important source of freshwater to this region. The 720 km long river originates near Multai in the Betoul District of Madhya Pradesh and commands a catchment area of 65,145 km2. River passes through hilly terrain of the Western Ghats before entering the coastal alluvial plains of Gujarat to meet Gulf of Khambhat near the Dumas (Latitude 21400 N and Longitude 72400 E). Three study sites were selected along the northern and southern estuarine region of Tapi River along a stretch up to 25 km upstream. The selected study sites in Tapi estuary are: (1) Hazira which is on the lower reaches, (2) Umra in the middle reaches, and (3) Causeway in the upper reaches. All three sites are separated approximately by a distance of 7 km (Fig. 1). The surface water samples were drawn in monthly intervals during the period from July 2009 to June 2010 during high tide. The surface water samples were collected in polyethylene bottles and stored in ice boxes at 4 C and brought to the laboratory. The hydro-chemical parameters such as phosphate

Results and discussion

Study on the influence of hydro-chemical parameters on phytoplankton distribution along Tapi estuarine area

Figure 1

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Selected study sites along Tapi estuarine region.

et al. (2010) also recorded a wide variation in temperature ranging from 29.7 to 38.7 C while estimating the water quality of the Chhoti Gandak river of Ganga Plain. pH is known as the master variable in water since many properties, processes and reaction are pH dependent. Due to the buffering capacity of the sea water, generally the pH ranges from 7.8 to 8.3 in estuaries (Millero, 1986). Abel (1996) reported that even though the pH of 5–9 is not directly harmful to aquatic life, such changes can make many common pollutants more toxic. Significant changes in pH occur due to disposal of industrial wastes, acid mine drainage etc. Slightly alkaline range in pH was reported at all studied sites and it varied from 6.9 to 8.6 in the study period. The highest pH of 8.6 was observed in June, 2010 at Hazira (Fig. 5b). Satpathy et al. (2009) also observed a pH range of 7.7–8.3 along the coastal waters of Kalpakkam, South east coast of India .The pH of water also depends upon relative contents of free CO2, carbonates, bicarbonates and calcium. The water tends to be more alkaline when it possesses carbonates, but lesser alkaline when it supports more bicarbonates, free CO2 and calcium. Omstedt

et al. (2010) reported that the marginal change in pH from one month to the other may be due to the excessive buffering activity of sea water. The decrease in pH value in upper reaches can be attributed to the freshwater influence on these areas (Islam, 2007) which was mostly observed in monsoon season. Dissolved oxygen is an important constituent of water and its concentration in water is an indicator of prevailing water quality and ability of water body to support a well-balanced aquatic life. Dissolved oxygen concentration showed remarkable seasonal variations with the range of 0.1 mg L1 in May at Hazira to 12.3 mg L1 in December at Causeway. Dissolved oxygen concentration was registered high during the postmonsoon period followed by monsoon and pre-monsoon period (Fig. 5C). Upper reaches reported more DO than middle and lower reaches. Similarly, Jack et al. (2009) while working on coastal waters of Benghazi reported dissolved oxygen level of 9.2–10.1 mg L1 during post-monsoon period. Higher dissolved oxygen present in the upper reaches Tapi estuaries might be due to the freshwater influence in these areas. The positive correlation of DO with chlorophyll-a value indicates the

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Figure 2 CCA bi-plot showing relationship between the environmental parameters and phytoplankton composition at Causeway (OS: Oscillatoria subbrevis, OP: Oscillatoria perornata, SS: Spirulina subtilissima, SM: Spirulina meneghiniana, MA: Microcystis aeruginosa, AA: Anaebena anomala, AC: Anaebena circularis, MP: Merismopedia punctata, No: Nostoc sp., AH: Ankistrodesmus hantzschii, CV: Chlorella vulgaris, CP: Chlorella pyrenoidosa, SI: Spirogyra indica, PS: Pediastrum simplex, PD: Pediastrum duplex, CM: Coscinodiscus marginatus, GA: Gyrosigma acuminatum, NA: Navicula amphirhynclius, PE: Pinnularia elongetum, NP: Nitzschia palea, PN: Pleurosigma normanni, SN: Surirella nervosa, SG: Staurastrum gracile).

role of phytoplankton in contributing DO in water. Moreover, highest DO concentration was observed during post-monsoon period because of maximum occurrence of the phytoplankton density (Morgan et al., 2006). With the progression of winter, DO raised to its peak value, and it might be due to high rate of photosynthesis by phytoplankton population that forms the major source of DO (Sharma and Rathore, 2000).The lowest DO concentration observed at the lower reaches might be because of the influence of salinity, temperature, conductivity, currents and upwelling tides (Davis, 1975). High biological activity during pre-monsoon can also lead to low dissolved oxygen concentration in estuaries as observed in Chesapeake Bay (Levinton, 2001). The lower dissolved oxygen concentration reported at middle reaches of Tapi River during pre-monsoon might be due to the domestic as well as industrial effluents released into the region as these are the main source of oxidisable organic matter (Abdullai et al. 2008). Salinity is the indicator of freshwater incursion in the near shore coastal water as well as extrusion of tidal water in inland water bodies. Salinity was recorded in the range of 1.2–31.5& (Hazira, June, 10). Salinity was found highest in pre-monsoon period and lowest in monsoon season (Fig. 5d). The freshwater inflow from Tapi River influenced significantly on the lowering of salinity during the monsoon season while the influx of seawater has the overall control on high salinity values in the summer months. In Kalpakkam Coast of South east India, a similar observation was made by Satpathy et al. (2009). They

recorded salinity ranging from 23.4 to 35.9 ppt and the highest being recorded during pre-monsoon season. Also similar results have been registered by Martin et al. (2008) from Cochin Estuaries in which the salinity was in the range of 0 ppt during monsoon to 30 ppt in pre-monsoon which found to be corroborated with present results. During summer the evaporation exceeds precipitation which ultimately results in increased salinity (Joseph and Ouseph, 2010). Ammonium (NH4+) represented 80% of Dissolved Inorganic Nitrogen (DIN) and its highest values were always associated with fresh water inflow (Martin et al., 2008). Peak surface water ammonia concentration showed positive correlation with chlorophyll-a which indicates the contribution of ammonia due to phytoplankton proliferation. Ammoniacal nitrogen was found in the range of 0.001 at Hazira in July, 10 to 0.744 mg L1 in December, 09 at Causeway during the study period (Fig. 5e). Satpathy et al. (2009) also observed ammonia concentration ranging from 0.009 to 0.2 mg L1 along Kalpakam coastal water which supports the lower ammonia concentration observed at lower reaches in the present study. The negative correlation of salinity with ammonia indicates the freshwater source of this nutrient into the estuarine environment. Castane et al. (2006) had also reported similar ammonia concentration in the range from 0.7 to 11.2 mg L1 from river waters of Reconquista River of Argentina. Sankaranarayanan and Qasim (1969) suggested that the spatial and temporal variation in ammonia concentration


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Figure 3 CCA bi-plot showing relationship between the environmental parameters and phytoplankton composition at Umra (OP: Oscillatoria perornata, MA: Microcystis aeruginosa, AA: Anaebena anomala, AC: Anaebena circularis, MG: Merismopedia glauca, AH: Ankistrodesmus hantzschii, CV: Chlorella vulgaris, CG: Closterium gracile, AA: Amphiprora alata, BM: Biddulphia mobiliensis, CA: Chaetoceros affinis, CM: Coscinodiscus marginatus, CT: Cymbella tumida, FO: Fragilaria oceanic, GA: Gyrosigma acuminatum, NV: Navicula viridis, NA: Nitzschia amphibian, SU: Synedra ulna, Gy: Gymnodium).

might also be due to its oxidation to other forms or reduction of nitrates to lower forms in coastal waters. Phosphate concentration in coastal waters depend upon its concentration in the freshwater that mixed with the seawater within the sea-land interaction zone, phytoplankton-uptake addition through localized upwelling, and replenishment as a result of microbial decomposition of organic matters (Paytan and Mclaughlin, 2007). Phosphate concentration in surface waters of Tapi estuary was noticed in the range of 0.001 mg L1 in October at Hazira to 0.822 mg L1 in January at Umra (Fig. 5f). Domestic as well as industrial effluents released from in and around Surat city may be the major contributors of phosphate into estuarine environment of Tapi estuary. Silveira and Ojeda (2009) emphasized the role of urban release on phosphate concentration on their study on Yutacan Coast and their results found to be corroborated with the present studies. Liu et al. (2009) reported that sea water serves as the main source of phosphate in estuarine and coastal waters except those receives freshwater contaminated with domestic wastes containing detergents as well as wastes from agro field rich with phosphate-phosphorous fertilizers and pesticides. Gabche and Smith (2002) while working on two estuaries of Cameron concluded that the increased concentration of phosphate after monsoon was the result of agricultural run-off along with city drainage which in-turn will serve as important phosphate contributors to the coastal environment. Vidal (1994) suggested that re-suspension of phosphate from

sediments also add significant portion of these nutrients to the estuarine water. The noticeable seasonal variation in phosphate concentration as observed in this study might be due to various processes like adsorption and desorption of phosphate and buffering action of sediments under varying environmental conditions (Pomeroy et al., 1965). Nitrogen cycle involves elementary dissolved nitrogen oxides; NO3, NO2 and reduced forms: NH4, NH3 play a significant role in sustaining the aquatic life in marine environment. Nitrate is one of the most important indicators of pollution of water which represents the highest oxidized form of nitrogen. In the present study nitrate concentration was observed greater at upper reaches when compared to middle and lower reaches (Fig. 5g). Nitrate content was varied from 0.16 mg L1 in June at Hazira to 1.43 mg L1 in December at Causeway was noticed in the study year. Similar results were obtained by Prasannakumar et al. (2002) on their study on eastern Arabian Sea in which they have reported 1– 2 mg L1 of nitrates during pre-monsoon period. Satpathy et al. (2009) also reported the range of nitrate from 0 to 4.28 mg L1in the coastal waters of Kalpakkam. The most important source of the nitrogen is biological oxidation of organic nitrogenous substances, which derived from sewage and industrial waste or produced indigenously in the water (Sharma et al. 2008). Zepp (1997) observed that variation in nitrate and its reduced inorganic compounds are predominantly the result of biologically activated reactions. Quick assimilation

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Figure 4 CCA bi-plot showing relationship between the environmental parameters and phytoplankton composition at Hazira. (OP: Oscillatoria perornata, MA: Microcystis aeruginosa, AA: Anaebena anomala, CG: Closterium gracile-, PA: Pleurosigma aestuarii, AA: Amphiprora alata-, CA: Chaetoceros affinis, FI: Fragilaria intermedia, FO: Fragilaria oceanic, MM: Melosira monoliformis, NA: Navicula amphirhynclius, NC: Navicula cuspidate, NV: Navicula viridis, NA: Nitzschia amphibia, SU: Synedra ulna).

by phytoplankton and enhancement by surface run-off results in large scale spatio-temporal variation of nitrate in the coastal regions. Edokpayi et al. (2010) had observed negative correlation of nitrate with salinity also concluded that freshwater influx is the main source of nitrate in coastal waters which corroborated with results of our study. Silicate is one of the important nutrients which regulate the phytoplankton distribution in estuaries. The variation of silicate in coastal water is influenced by physical mixing of seawater with freshwater, adsorption into sedimentary particles, chemical interaction with clay minerals, co-precipitation with humic components, and biological removal by phytoplankton, especially by diatoms and silicoflagellates (Satpathy et al., 2009). The lowest silicate concentration was reported at Hazira (0.32 mg L1) during June, 10 and highest (7.9 mg L1) at Causeway during December, 09 (Fig. 5h). In the present study, freshwater discharge from the backwaters rich in silicate into the coastal water could be the reason for higher value during post-monsoon period. The higher post-monsoon values of silicate could also be due to heavy influx of freshwater derived from land drainage carrying silicate leached out from rocks and also from bottom sediments exchanging with overlying water because of turbulent nature of water in the estuaries (Saravanakumar, 2008) which is supported by positive correlation between freshwater fractions and silicate. Silicate showed strong negative correlation with salinity and strong positive correlation with DO. This showed that freshwater, which is rich in DO could be the main source of silicate in these coastal water regions as entry of silicate mainly takes place through land drainage rich with weathered silicate material (Lal,

1978). The results obtained in the present study were found to correlate the results obtained by Martin et al. (2008) in Cochin Estuary, west coast of India in which they reported silicate range from 2 to 9.5 mg L1.Satpathy et al. (2009) suggested that the low concentration of silicate observed during pre-monsoon might be because of adsorption of reactive silicate into suspended sedimentary particles, chemical interaction with clay minerals, co-precipitation of soluble silicon with humic compounds and iron, and biological removal by phytoplankton, especially by diatoms and silicoflagellates. Primary productivity potential of the marine environments depends upon the phytoplankton, which alone contributes 90% of the total marine primary production. Thus chlorophyll-a which constitutes the chief photosynthetic pigment of phytoplankton, is an index that would provide the primary production potential upon which the biodiversity, biomass and carrying capacity of that system depends upon (Sarma et al., 2006). The highest chlorophyll-a concentration was reported during post-monsoon period at Causeway (13.5 mg m3) and the lowest concentration was observed at Hazira during pre-monsoon season (0.32 mg m3). The higher concentration of chlorophyll is reported during post-monsoon period (Fig. 5i) and it might be due to the higher phytoplankton abundance during this period. Sridhar et al. (2006) reported similar chlorophyll-a concentration in lower reaches (0.28–1.48 mg m3) in the Palk Bay of south coast of India. Prasannakumar et al. (2002) from their studies on plankton productivity of Bay of Bengal, suggested that high phytoplankton production during post-monsoon period could be attributed to the upwelling that brings the nutrient rich deeper


Figure 5

(a–i) Hydro-chemical properties of three sites of Tapi estuary (July 2009–June 2010).

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164 water to the surface and as riverine run-off during monsoon period. Madhuprathap et al. (2001) also observed a sharp decline of chlorophyll-a value in Arabian Sea during pre-monsoon period. They suggested that this fall in chlorophyll-a value might be because of less freshwater inflow and precipitation which makes the habitat unsuitable for phytoplankton. Senthilkumar et al. (2008) reported that the positive correlation of chlorophyll-a with nitrate, phosphate and DO specifies the freshwater influence on phytoplankton productivity particularly at the upper reaches. Phytoplankton Estuarine phytoplankton communities usually comprise several taxonomic groups, and contribute to primary production and interaction between trophic levels (Roy et al. 2006). Jouenne et al. (2007) stated that phytoplankton composition varies with season and this can be ascribed to variation in nutrient access, light and temperature. Rey et al. (2004) suggested that besides their importance as the primary producers in food webs and ensuring ecological balances, species of phytoplankton can be useful indicators of water quality. As demonstrated in other geographical areas and variety of habitat types, freshwater influence is known to have profound effect on phytoplankton biomass, productivity and community composition (Harnstrom et al., 2009). Short term phytoplankton blooms are often triggered by differences in salinity or from the resultant water column stratification. Indeed in some areas, temporal changes of the phytoplankton community are very dynamic because of short term tidal variability; but other factors, such as zooplankton grazing and exchange between sediment and water column, also affect species diversity (Carstensen et al., 2007). The species composition, biomass, relative abundance, spatial and temporal distribution of phytoplankton are an expression of the environmental health or biological integrity of a particular water body (Khattak et al., 2005). Phytoplankton communities in marine tropical areas are known to be less dynamic than in temperate waters, from an annual perspective, with smaller seasonal variation in net phytoplankton growth (Qasim et al., 1972). In the present study, phytoplankton assemblage was observed higher at upper and middle reaches in Tapi estuarine regions where there is a dominance of freshwater. Sixty six species belonging to 37 genera were observed during the study period from Tapi estuary. The phytoplankton was represented by five dominant groups namely; Cyanophyceae, Chlorophyceae, Bacillariophyceae, Euglenophyceae and Dinophyceae. The genera present in different groups were Cyanophyceae (6 genera), Chlorophyceae (7 genera), Bacillariophyceae (19 genera), Euglenophyceae (2 genera) and Dinophyceae (3 genera). The highest diversity and density were observed during post-monsoon period. Bacillariophyceae was relatively abundant as compared to all other groups with 34 species, which accounted for 51% of phytoplankton followed by Chlorophyceae with 13 (20%) species, Cyanophyceae with 12 (18%) species, Euglenophyceae with 4 species (6%) and Dinophyceae consisted of 3 species (5%). Bacillariophyceae The most dominant group among phytoplankton group is Bacillariophyceae and it contributes more than 51% of the to-

B. George et al. tal phytoplankton population. A total of 34 species were recorded from the study sites. Higher number of Bacillariophyceae was observed at Hazira (28 species) followed by Umra (21 species). Eight species were reported from freshwater dominated Causeway. The density of Bacillariophyceae was encountered higher in post- monsoon months in lower and middle reaches. The most common members among the Bacillariophyceae were Fragellaria sp., Pinnularia sp., Navicula sp., Gyrosigma sp., Melosira., Nitzschia sp. Navicula longa, Eunotia sp. Pleurosigma sp. Amphiphora sp., and Amphora alata. At Causeway higher density was registered during January 2010 (0.39 · 105 cells L1) and lower density was present during July 2009 (0.1 · 105 cells L1) (Fig. 6A). The minimum density at site Umra was 0.01 · 105 cells L1 observed in October, 2009 while the maximum was 0.35 · 105 cells L1 during June, 2010. The lowest density recorded at Hazira was 0.11 · 105 cells L1 in May, 2010, while the highest density was 0.38 · 105 cells L1 in January, 2010. Nabout et al. (2006) also observed the predominance of Bacillariopycean members followed by Chlorophycean and Cyanophycean members during their study on phytoplankton community of Brazilian lakes which was in relevance with our present study. Redekar and Wagh (2000) from their studies on Bacillariophyceans of Zuari coast of India concluded that salinity has a direct influence on distribution of Bacillariophycean members which supports the predominance the group than other groups in our study. Seasonal variations of phytoplankton in Mahanadi Estuary, east coast of India was worked out by Naik et al. (2009) which revealed Bacillariophyceae to be the most dominant group followed by Dinophyceae and Cyanophyceae as observed in our present study. Ekeh and Sikoki (2004) also reported class Bacillariophyceae to be the most abundant group of phytoplankton among many tropical estuaries. Perumal et al. (2009) also recorded more than 50 percent of Bacillariophycean members in their studies of phytoplankton diversity of Kaduviyar Estuary. Bacillariophycean members can be used as suitable bio-indicators for water quality assessments as they have short generation time and many species have a specific sensitivity to ecological characteristics (Stevenson and Pan, 1999; Goma et al. 2005). During present study, both the estuaries showed highest density and diversity of Bacillariophycean members at middle reaches and lower reaches. This may be due to the role of salinity in their distribution (Redekar and Wagh, 2000).The Bacillariophycean members reported in Tapi estuaries are Eunotia amphioxys, Pleurosigma aeustuarri, A. alata, Amphora elliptica, Biddulphia mobilens, Chaetoceros affinis, Chroococcus gigantium, Coscinodiscus marginatus, Cymbella Cistula, Fragilaria crotonensis, Leptocylindrus minimus, Navicula amphirhynclius, Nitzschia amphibian, Synedra ulna. Salomoni et al. (2006) working on phytoplankton of Gravatai River recorded the presence of Bacillariophyceae such as Nitzschia, Eunotia, Pinnularia and described them as indicators of organic pollution. They also reported them as pollution tolerant species. Palleyi et al. (2011) observed that nutrients like phosphate, nitrate and silicate have significant role in distribution of Bacillariophycean group in estuarine environment. Thessen et al. (2005) reported diatoms to be prominent during the pre-monsoon and post-monsoon where there was a dominance of marine water in the estuarine region and the results were found to be corroborated with our studies. Tiwari and Nair (1998) and Senthilkumar et al. (2002) supported the dominance of


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Figure 6 (A) Monthly variation in cell density of Cyanophyceae, Chlorophyceae, Bacillariophyceae, Euglenophyceae and Dinoflagellates at Causeway. (B) Monthly variation in cell density of Cyanophyceae, Chlorophyceae, Bacillariophyceae, Euglenophyceae and Dinoflagellates at Umra. (C) Monthly variation in cell density of Cyanophyceae, Chlorophyceae, Bacillariophyceae and Dinoflagellates at Hazira.

diatoms near coastal waters in west coast of India. This was reflected during the present study too, diatoms were found to flourish at mouth of both the estuaries due to hydro-chemical conditions. Chlorophyceae The Chlorophyceae is the second largest and important group of freshwater green algae. It includes some of the most common species, as well as many members that are important both ecologically and scientifically. These species contributed to 20% of the total phytoplankton species recorded. Maximum number of species (13) was documented at Causeway, followed by 7 species at Umra, and 4 species at Hazira. Ankistrodesmus flactus, Chlorella vulgaris, Scenedesmus quadricauda, Spirogyra indica, Pediastrum sp. and Closterium acerosum were the most abundant Chlorophytes. Chlorophycean densities varied distinctly at the three sampling sites. Highest density of Chlorophyceae was recorded at Causeway (0.34 · 105 cells L1) followed by Umra (0.28 · 105 cells L1) whereas the lowest density was recorded at Hazira (0.01 · 105 cells L1). Chlorophycean density was observed

high during post-monsoon season, followed by monsoon and pre-monsoon season (Fig. 6A). Similar results in Nigeris Estuary were reported by Ekwu and Sikoki (2006) where the dominance of Chlorophyceans was observed in middle and upper reaches of estuary. In present study the density of Chlorophycean members found higher in upper reaches of Tapi might be due to freshwater dominance and less saline water intrusion in the area. Dissolve oxygen, pH, alkalinity play a significant role in distribution of Chlorophycean members in freshwater zones (Rajagopal et al. 2010). Rao and Pragada (2010) reported that the absence of Chlorophycean forms in the lower reaches indicated the influence of salinity on the distribution of Chlorophyaceae members. The Chlorophyceans were reported to be dominant during winter season, as also reported by Tiwari and Chauhan (2006), that might be due to high DO, high nutrient status and slow water current during this period. Cyanophyceae Cyanophyceae is one of the major groups of phytoplankton which is mostly confined to the freshwater zones. The relative

166 abundance of Cyanophycean members may be a function of nutrient (N:P) ratios in water bodies (Smith, 1983). The occurrence of this group could be attributed to the high temperature, slightly alkaline conditions and nutrient rich freshwater discharge, turbidity due to suspended sediment which favors the growth (Harsha and Malammanavar, 2004). A total of 12 species of Cyanophyceae were recorded from three selected sites. Freshwater receiving site, Causeway supported the maximum number of species (12) followed by Umra (7 species) and 4 species at Hazira. The dominant species observed were Oscillatoria perornata, Oscillatoria subbrevis, Spirulina subtilissima, Anaebena circularis, Merismopedia glauca and Nostoc sp. Greater density of Cyanophyceae was observed during post-monsoon season followed by pre-monsoon season. At Causeway higher density was registered during January 2010 (0.38 · 105 cells L1) and lower density was present during July 2009 (0.05 · 105 cells L1) (Fig. 6A). The minimum density at site Umra was 0.01 · 105 cells L1 recorded in July 2009 while the maximum was 0.34 · 105 cells L1 November, 2009 (Fig. 6B). The lowest density recorded at Hazira was 0.01 · 105 cells L1 during pre-monsoon period while the highest density was 0.07 · 105 cells L1 in May 2010 (Fig. 6C). The density showed the highest during post-monsoon period in the upper reaches. Salinity plays a major role in determining the distribution of Cyanophycean members in an estuarine ecosystem (Evagelopoulos et al., 2009) which explains the dominance of Cyanophycean members in upper reaches when compared to lower reaches. Ning et al. (2000) observed high abundance of Cyanobacteria, but their contribution to the total phytoplankton community was relatively small in estuaries, which is substantiating the results of present study. Constant input of wastewater not only contains waste of organic matter but also contains silt and other pollutants which might also be attributed to higher Cyanophycean at upper reaches, this is in agreement with Saxena and Shrivastava (2001), while studying the sewage fed Shahpura Lake of Bhopal. Muhammad et al. (2005) and Tas and Gonulol (2007) have suggested spatial differences in distribution of blue green algae which may occur due to high organic pollution load leading to nutrient rich condition. The Cyanophyceae group was found to be the third dominant group among all phytoplankton and the highest density was observed during post-monsoon period. The observed results were found to be corroborated with studies conducted by Rao and Pragada (2010) in backwaters of Godavari Estuary where they reported the dominance of Cyanophyceae in post-monsoon period. The distribution of Cyanophyceae in the present study also showed similarity with results obtained by Sassi (1991) in which the dominance of Cyanophycean were observed in post-monsoon period particularly in the upper reaches. Dinophyceae Dinophyceae is a large group of flagellate protists. Most of them are marine plankton, but they are common in freshwater habitats as well. Their population is distributed depending on temperature, salinity, or depth. Dinophyceae was represented by three genera which accounts for 5% of total phytoplankton population. Hazira and Umra contained the maximum number of Dinophycean species (3) followed by Causeway (2). The common recorded species were Peridinium sp., Ceratium

B. George et al. sp. and Gymnodium sp. The lowest density recorded at Hazira was 0.02 · 105 cells L1 in monsoon period (Fig. 6C), while in Umra it was 0.02 · 105 cells L1 and 0.05 · 105 cells L1 at Causeway during pre-monsoon period. The distribution is regulated by salinity, temperature and pH as their occurrence is more in areas having significant marine water influence (Cremer et al. 2007). Studies carried out at Cross River Estuary of Nigeria by Ekwu and Sikoki (2006) observed Dinophycean to be the least dominant group and mostly reported from lower reaches which shows similarity with our results. Dinoflagellate community appeared relatively less in abundance in the estuaries throughout the year as compared to the diatoms and other groups. This might be due to the preferential oligotrophic nature of dinoflagellate and their competition with diatoms (Cushing, 1989). Euglenophyceae The Euglenophyceae is basically a group of unicellular flagellates. The abundance of Euglenophyceae members in a water body can be attributed to the entry of nutrients through the influx of domestic sewage which is an indication of organic pollution (Kumar and Hosmani, 2006; Laskar and Gupta, 2009). Three species of Euglenophyceae were reported from sites, which include Euglena gracilis, Euglena ehrenbergii and Phacus acuminatus. It accounts for 6% of total phytoplankton species reported. In Causeway the lowest density reported was 0.01 · 105 cells L1 during April 2010 and the highest density was 0.05 · 105 cells L1 during December, 2009. In Umra the lowest density was 0.01 · 105 cells L1 during July 2009 and the highest of 0.02 · 105 cells L1 was observed during June, 2010 (Fig. 6B). The highest number of Euglenophycean species were registered from Umra (4) followed by Causeway (3). However, they were not reported in Hazira during the study period. The representatives of Euglenophyceae inhabit freshwater basins as well as marine waters. It is established that macro-algae of this group develop widely in waters with high concentration of organic matter and basins subjected to anthropogenic eutrophication (Lee, 1999). Over 10% of the species are used as indicators of water saprobility (Kiriakov, 1987). In Tapi estuary Euglenophycean members were observed at upper and middle reaches where there occurs more anthropogenic pollution as compared to lower reaches. Their occurrence and distribution is mostly reported during post-monsoon and pre-monsoon period where the freshwater flow is low. Tiwari and Chauhan (2006) also observed similar temporal variation in Euglenophycean distribution at Kitham Lake, Agra. A higher number of Euglenophycean species was recorded in upper reaches of Tapi that might be due to increased water temperature and nutrient status, mainly because of increased anthropogenic discharges (Nwankwo, 1995). High carbon dioxide content and oxidisable organic matter with low oxygen content favors the abundance of Euglenophytes (Munawar, 1970). Canonical correlation analysis Canonical Correlation Analysis (CCA) was aimed to find the relationship between environmental variables and phytoplankton distribution (Ariyadej et al., 2004).In Causeway total of 23 dominant species and 09 environmental variables which may have contributed to phytoplankton distribution were selected

Study on the influence of hydro-chemical parameters on phytoplankton distribution along Tapi estuarine area Table 1

Simple linear correlation of the environmental variables with the CCA (p < 0.05). Causeway

Variables

167

Umra

Hazira

Axis 1 (k = 0.193) Axis 2 (k = 0. 130) Axis 1 (k = 0. .231) Axis 2 (k = 0. 149) Axis 1 (k = 0. .019) Axis 2 (k = 0.001)

Temperature 0.86 pH 0.65 DO 0.90 Salinity 0.57 Ammonia 0.65 Phosphate 0.24 Nitrate 0.24 Silicate 0.78 Chlorophyll 0.56

0.15 0.68 0.16 0.68 0.21 0.69 0.69 0.22 0.55

0.06 0.52 0.06 0.48 0.12 0.64 0.21 0.20 0.37

for CCA analysis. Eigenvalue of axis 1 (k = 0.193), 2 (k = 0.130), 3 (k = 0.086) and 4 (k = 0.065) explained 80.93% of the relation between species and environmental data (Table 1). Species having significant correlation (0.5 to 0.5) with axis were marked in bold. In Causeway, Chlorella pyrenoidosa, O. subbrevis, Anaebena anomala, C. acerosum, Calveriosoma gracile and Cladophora glomerata showed a positive correlation with axis 1 which indicates the effect of phosphate, DO, ammonia and silicate on its distribution. The close association of salinity and pH indicated the effect of tidal influence in the estuarine area (Fig. 2). Chlorophyll-a found to influence the distribution of Ankistrodesmus hantzschii, A. circularis, P. acuminatus and S. quadricauda. Temperature, salinity, showed positive correlation with Spirulina meneghiniana, Nitzschia palea, Pleurosigma normanni, Oscillatoria curviceps, Merismopedia punctata and M. glauca. In Umra a total of 19 dominant species reported analyzed with 9 hydro-chemical parameters for CCA analysis. Eigenvalue of axis 1 (k = 0.231), 2 (k = 0.149), 3 (k = 0.112) and 4 (k = 0.075) explained 83.26% of the relation between species and environmental data (Table 1). Chlorophyll-a, chloride, alkalinity, sodium and phosphate concentration shows negative correlation with axis-1. DO, ammonia, silicate and nitrate show positive correlation with axis 2 indicating the influence of freshwater on contributing the nutrients. Silicate, ammonia, chlorophyll-a and DO found to have a positive influence on distribution of A. elliptica, Navicula cuspidate, Navicula viridis, Ceratium, E. amphioxys, A. hantzschii and S. meneghiniana (Fig. 3). M. glauca, A. anomala, C. pyrenoidosa and A. flactus showed close relationship with nitrate. Phosphate found to have positive influence on distribution of E. gracilis, O. perornata, S. quadricauda and Phacus curvicauda. Melosira sulcata, C. affinis, Fragilaria oceanic, F. crotonensis and C. marginatus found to be correlated with salinity in the estuary. In Hazira a total of 16 species of phytoplankton dominated by Bacillariophycean members were correlated with 9 hydrochemical parameters. Eigenvalue of axis 1 (k = 0.0019), 2 (k = 0.0010), 3 (k = 0.0007) and 4 (k = 0.0006) explained 89.73% of the relation between species and environmental data (Table 1). Ammonia, phosphate, nitrate, silicate and DO found to be positively correlated with axis 3. Microcystis aeruginosa, Navicula radiosa, N. cuspidate, C. vulgaris, Navicula sphaerophora, Ceratium, F. crotonensis and F. oceanica show positive correlation with axis 1 and thus signifies the role of salinity in its occurrence and distribution (Fig. 4). Ammo-

0.85 0.70 0.70 0.73 0.73 0.14 0.70 0.70 0.58

0.21 0.52 0.12 0.45 0.30 0.26 0.71 0.22 0.16

0.69 0.15 0.65 0.29 0.71 0.67 0.15 0.69 0.35

nia, phosphate, nitrate, silicate and DO found to regulate the distribution of E. amphioxys, Pleurosigma aestuarii, N. amphirhynclius, Cymbella tumida, C. marginatus and N. viridis. In the present study phytoplankton have shown a positive correlation with salinity value at all sampling stations because estuarine regions are subjected to considerable fluctuations and these micro flora were well adapted to such dynamic environment (Lionard et al., 2005). Phytoplankton needs a wide variety of chemical elements but the two critical ones are nitrogen and phosphorous (Dawes, 1981). In the present study it was registered that phytoplankton showed positive correlation with phosphate and inorganic nitrogenous nutrients but the relationship was insignificant. This may be due to lower concentration or may be rapid recycling of these nutrients. Similar observations were made by Steinhart et al. (2002) on southern Chilean lakes and Hergenrader (1980) in salt valley reservoirs, California where they have reported the positive correlation between phytoplankton and nitrogenous organic nutrients. Dawes (1981) had reported a negative relationship of phytoplankton with temperature and turbidity which supports our present observed results. Studies carried out by Ye and Cai (2011) suggested that the occurrence of Cyanophycean and Chlorophycean members were directly proportional to the concentration of dissolved inorganic nitrogen and phosphate which corroborated with our studies. Most of the species found to be correlated with the environmental variables, and this might be due to cosmopolitan characteristic of the species which indicates the species tolerance to large range in water quality (Bonilla et al., 2005). A negative correlation was observed for Cyanophycean members like O. perornata and M. glauca with environmental variables like chlorophyll-a and silicate. Most of the species belonging to Bacillariophyceae showed a positive correlation with environmental parameters like chlorophyll-a, silicate and phosphate. Chlorophycean members like A. flactus, C. acerosum and S. indica showed a positive correlation with nitrate, DO and ammonia. Similar results were also obtained by Ye and Cai (2011) for their assessment on spring phytoplankton bloom of Xiangi Bay. N. amphirhynclius and N. radiosa showed a positive correlation with pH and salinity which may have prominent effect on their distribution. The close association of salinity and pH revealed the effect of tidal influence in the estuarine area. Temperature was found to have a positive relation with C. vulgaris and M. punctata. However, the negative correlation

168 of temperature with ammonia and silicate showed the freshwater influence on these nutrients during post-monsoon season. N. cuspidate, Surirella nervosa, Thalassionema nitzschioides, A. alata, Amphora ovalis, C. marginatus and A. elliptica showed a positive correlation with chloroplyll-a, silicate and phosphate which indicates the significant role of these parameters in phytoplankton distribution (Harnstrom et al., 2009). A. anomala, N. amphibian and Gymnodium sp. showed a negative correlation with inorganic nutrients, which showed their adaptability to a wide range of variations in physicochemical properties (Varis, 1991). Conclusion The present study summarizes the seasonal fluctuations of various physico-chemical parameters and plankton diversity in the coastal waters of the Tapi estuary as exploratory statistical data output. Freshwater discharges through the river and rivulets include additions of nitrate, phosphate and silicate to the coastal water mainly during the monsoon season. The addition of nitrogenous compounds and phosphorus compounds from anthropogenic sources such as fertilizer output, as an effect of industrialization and from agricultural runoff in the northern region of the Tapi estuary, has been observed during the monsoon in the water near the upper and middle reaches. The high load of nutrients like phosphate, nitrate and silicate during the monsoon contributes to the growth of phytoplankton community which is evident from the canonical correlation analysis. Freshwater inflow and tidal influence found to be the main determining factors of phytoplankton distribution among the estuary. In the canonical correlation analysis the maximum correlation of phytoplankton with inorganic nutrients is linked to the abundance of these nutrients mostly entering during the monsoon season. The overall study provides a good outline on the prevailing condition of the estuarine ecosystem.

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