LIMNOLOGICALLY IMPORTANT PHYSICOCHEMICAL PARAMETERS OBSERVED IN MARINE WATER SAMPLES AROUND DIGHA COAST IN BA Y OF BENGAL

Sea water, in addition to containing substantial amount of salt (sodium chloride) contains a variety of important chemical constituents like nitrate, phosphate, sulphate, silicate, chloride of Sodium, Potassium, Magnesium, Iron, Zinc, Nickel, Cobalt, Copper, Lead etc. It is well-established fact that the survival and nonnal well being/viability of the entire Faunal Diversity in an ecosysteln depends on composition of such parameters. Any significant alteration in such Chemical and Physical parameters (collectively called as Limnological parameters) as the component of Marine Environment may significantly affect the entire chain and even be catastrophic to a few susceptible living organisms up to the extent of extinction. It is with this view point that we had monitored/ analyzed the associated water samples in respect of important Physical and Chemical parameters as components of limnogical constituent. Such important Physical parameters arc namely : Temperature, Density, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), pH, Conductance, Turbidity etc. The Chemical parameters include: Chlorinity, Salinity, Alkalinity, Free Carbon Dioxide, Total Hardness, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Sulphate, Nitrate, Oxylate, Phosphate etc.


INTRODUCTION
Sea water, in addition to containing substantial amount of salt (sodium chloride) contains a variety of important chemical constituents like nitrate, phosphate, sulphate, silicate, chloride of Sodium, Potassium, Magnesium, Iron, Zinc, Nickel, Cobalt, Copper, Lead etc. It is well-established fact that the survival and nonnal well being/viability of the entire Faunal Diversity in an ecosysteln depends on composition of such parameters. Any significant alteration in such Chemical and Physical parameters (collectively called as Limnological parameters) as the component of Marine Environment may significantly affect the entire chain and even be catastrophic to a few susceptible living organisms up to the extent of extinction. It is with this view point that we had monitored/ analyzed the associated water samples in respect of important Physical and Chemical parameters as components of limnogical constituent. Such important Physical parameters arc namely : Temperature, Density, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), pH, Conductance, Turbidity etc. The Chemical parameters include: Chlorinity, Salinity, Alkalinity, Free Carbon Dioxide, Total Hardness, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Sulphate, Nitrate, Oxylate, Phosphate etc.
Although similar studies on such aspects at different places of Indian Ocean as well as Bay of Bengal has been widely carried out by variety of researchers, but very little work at the coastal area surrounding this important tourist place has been carried out. Hence, we are regularly monitoring such water quality parameters as a baseline data for the past fifteen years (ever since the establishment of this centre). As experimental strategy, the water samples collected fortnightly and periodically throughout the year for the consecutive five years (March 1998to February 2004 have been studied and reported through data vide Table nos. 1-6 respectively.    All  All   All  All The seasonal occurrence of commercial sea fish species in this coastal zone is given through

MATERIALS AND METHODS
The physical and chemical parameters like temperature, pH and Dissolved Oxygen were measured immediately after the sampling in the field only. The samples were. generally collected regularly once or twice a week throughout the study period for carrying out measurements in the laboratory for both the Physical and Chemical parameters. Surface water temperature, density, total dissolved solids and total suspended solids were measured through conventional means. However, pH and conductance were measured by the Elico pH meter (model No. LI-120) and Elico conductivity meter ( Martin (1970), Wilson (1975), Atson (1978), NEERI (1988)

RESULTS
The mean values for such Limnologically important physicochemical parameters for every two months of interval distinct to pre and post periods of a particular season for all the three climatic conditions are expressed here through the Tables namely no. 1-6, respectively for the period (March 1998-February 2004. The occurrence of free carbon dioxide was distinctly reported only during the monsoon period that too in the traces, The significance of mean values of different parameters reported was analyzed using one way analysis of variance technique: Snecedar and Cochran (1967) for each parameter separately.
From the results observed here, it appears that except the temperature, chlorinity/salinity, conductance as well as dissolved solids, all other parameters remain almost constant to the seasonal/diagonal variations, which depict the normalcy in the general water quality parameters of our study samples taken from around Digha sea beach. The significance of the variation of chlorinity/salinity data with regard to monsoonal change is such that such values increase moderately to significant to higher range from monsoon to post monsoon and further to pre monsoon respecti vel y .

DISCUSSION
The significance of the present work is highlighted here with the fact that similar studies at various riverine and marine points had been undertaken by sufficient number of workers such as in India by Zingde et al. (1980), Mathur et al. (1986), Malik et al. (1995), Srivastava et al. (1996), Elango et al. (1992) as well as by ourselves (1999). The significance of such work can be understood with the apprehension that any significant alteration in such physicochemical values may cause catastrophic situation for a large variety of associated marine fauna. Although Digha being a relatively pollution free zone where the general profile of such limnologically important physicochemical parameters remain static, which is due to very insignificant level of contaminants/ pollutants like-heavy metals, pesticides, insecticides/herbicides as well as hydrocarbons in the sea water composition. But our ongoing activity in this regard is of great significance from the pollution measuring as well as limnological observations point of view to prepare a baseline data for further studies.
In this regard, it is worth, to mention that continuous and indiscriminate use and exposure of such highly toxic substances in and around sea coast will damage the fabric of marine flora and faunal diversity at a very large scale up to the extent of the extinction of certain vulnerable species of fishes, shrimps, phytoplanktons and zooplanktons etc. It is well established fact that the sudden and excessive changes in Dissolved Oxygen, Biochemical Oxygen Demand (BOD), alkalinity, salinity and pH etc. may adversely affect a large number of marine species up to the extent of total disappearance in the chain process. A comparison of the number of fish species available during the pre monsoon, monsoon and post monsoon periods in relation to these Physico-chemical factors is expressed through Figures no. 1 (a-c). From the trend lines, the relationship between dissolved oxygen, alkalinity and the availability of species is evidenced.
It is with this logic that the regular monitoring of s\lch biologically important physicochemical parameters from the coastal marine water samples is being carried out as a broad objective of our laboratory at this center for establishing a database as well as estimating the actual potential and the associated threat of environmental impact from the ongoing hotel as well as agricultural and other miscellaneous activities around this beautiful sea beach which has to be protected at any cost both from the heritage as well as from the commercial fishing point of view as marine commercial fishing is a major source of common people livelihood and also earning potential foreign money. Therefore, ever since the establishment of this laboratory (in 1992), we are regularly monitoring such parameters as ongoing project of immense utility.

SUMMARY
Digha, the small but aesthetically very important place in Eastern Coast is of immense potential value both from tourism as well as commercial fishing point of view. The same is evident from documented reports of the hotel/tourism as well as marine fish products' commercial venture. For preparing annual profile of limnologically important physicochemical parameters, sea water samples were analyzed as an ongoing project/activity of our Laboratory for furnishing baseline data for industry as well as researchers, which had been the theme of our study for consecutive six years period (March 1998to Feb. 2004. Such data are very useful for correlating the occurrence and abundance of a particular marine sp. important from the Biological researchers or for the commercial viability point of view. It is scientifically well established fact that sea water quality affects survival and development of diversified faunal asses, It is with this reason that we had undergone such study to record important physical data like: Temperature, Density, pH, Total Dissolved Solids, Total Suspended Solids, Conductance and Chemical parameters like : Chlorinity, Salinity, Alkalinity, Total hardness, Free Carbon Dioxide, Dissolved Oxygen, Biochemical Oxygen Demand Sulphate, Nitrate, Phosphate. Although general trend of such parameters' constancy is ~aintained throughout the year except in case of chlorinity/ salinity, which varies significantly raising from monsoon to post monsoon and from post monsoon to pre monsoon period. Our 'observations reported here for these physicochemical parameters (for past six years-March 1998 to February 2004) merit from the point of view of assessing expected pollution threat from ongoing Agriculture and Hotel activities which release significant amount of harmful pollutants like pesticides/insecticides, hydrocarbons, detergents etc. A small amount of pollution in sea 1"Vater may alter these vital physicochemical parameters, which in turn may hamper ·the viability of entire marine faunal diversity affecting the commercial fish product, and livelihood of large number of associated fishermen.