Assessment of Coastal.pmd

J Environ. Science & Engg. Vol. 54, No. Singh 2, p. 217-226, et al / J. April Env. Sci. 2012Eng., 54(2), 2012

Assessment of Coastal Water Quality at Bakkhali, West Bengal (India) SHIV SINGH1*, BHASKAR BHADURI2, PRASANTA KUMAR BANERJEE3 AND SIDDHARTHA DATTA4 Spatial variations of some physico-chemical water quality of the coastal water of a segment of Bakkhali (Bay of Bengal) were studied between the months of November 2009 and February 2010 before 12:00 a.m. The studies were carried out at three coastal sites of Bakkhali Beach (south extreme point, middle point and far north point, about 1.2 km along the shore) which is influenced by anthropogenic input from land-based sources. The site receives domestic, agricultural and industrial wastes. The water is being used for fishing, transportation of goods and by people for several purposes. The banks of the estuarine channels have traditionally been preferred locations for human settlement. Considering the various uses of this coastal segment, between Bakkhali to Haldia, the studies related to water quality monitoring were carried out. The pH, temperature, turbidity, salinity, TDS and conductivity vary in range of 8.24 – 8.65, 27.50C-31.50C, 480 NTU - 808 NTU, 21.6 PSU-30.0 PSU,676 mg/L -934 mg/L and 1.72 mS/cm -1.97 mS/ cm respectively . Dissolved oxygen, biochemical oxygen demand (BOD) concentrations at different sites vary within a narrow range 6.05 mg/L–8.1mg/L and 1.05 mg/L – 3.0 mg/L respectively .Chemical oxygen demand concentrations vary in a wide range of 170 mg/L – 812 mg/L. The bacterial count at the sampling site varied from 76-150 CFU. Key words: Dissolved Oxygen, Biochemical Oxygen Demand, salinity, turbidity, azide modification, Colony Forming Unit Introduction

The activities in coastal areas, combined with pollutants flowing from streams far inland and others carried through the air great distances from their source are the primary causes of nutrient enrichment, hypoxia, harmful algal blooms, toxic contamination, sedimentation, and other problems that plague coastal waters1.

Bakkhali is one among the many popular beaches of India. It is situated in the state of West Bengal and is located 80 km away from Diamond Harbour. Bakkhali is located on one of the many deltaic islands spread across Southern Bengal. Coastal length of Bakkhali beach is about 1.2 km. Bakkhali (latitude 210 35’ N, longitude 880 15’ E) is situated in the lower reaches of South 24- Parganas along the coastal tract of west as shown in Fig 1 1. These are twin towns now forming one continuous locality. Coastal waters of Bakkhali are one of the nation’s greatest assets, yet they are being bombarded with pollution from tourism.

Changes in chemical, physical, biological, and radiological (e.g. Th, U, K which are discharged from industries) quality of water, can be harmful to its existing, thus discharge of toxic chemicals from an industry waste pipe or the release of livestock waste into a nearby water body is considered as pollution.

1

Ph D Scholar, Chemical Engineering Department, IIT Kanpur, Kanpur - 208 016, India. e-mail: [email protected] Chemical Engineering Department, IIT Kanpur, Kanpur - 208 016, India. 3 Chemical Engineering Department, Jadavpur University, Kolkata (India). 4 Chemical Engineering Department, Jadavpur University, Kolkata (India). + Corresponding author 2

217

Assessment of coastal water quality at Bakkhali, West Bengal (India)

Fig. 1: Location of Bakkhali Beach On the other hand nutrients generated from natural processes, are not considered as pollutants. Coastal waters are subjected to cumulative impacts from a variety of pollutants—from near and far and from point, nonpoint, and airborne sources. According to National Research Council the concerns over water quality relate not just to the water itself, but also to the danger of diffusion of toxic substances into other ecosystems. The aquatic environment for living organisms can be affected and bioaccumulation of harmful substances in the water-dependent food chain can occur. A variation of inland surface water quality is noticed due to seasonal variation of river flow, operation of industrial units and use of agrochemicals. Overall, the inland surface water quality in the monsoon season is within tolerable limit with respect to the standard set

by the Department of Environment (DoE). However, quality degrades in the dry season. The salinity intrusion in the Southwest region and pollution problems in industrial areas are significant. In particular, the water quality around Dhaka is so poor that water from the surrounding rivers can no longer be considered as a source of water supply for human consumption. The largest use of water is made for irrigation. Besides agriculture, some other uses are for domestic and municipal water supply, industry, fishery, forestry and navigation. In order to address the non point source pollution of coastal waters, many agencies have come up with various proposals and some programs are been effectively organized targeting various programs, funds, training, technical assistance, incentives, disincentives, and other management tools2. 218

Singh et al / J. Env. Sci. Eng., 54(2), 2012

time, and differences in the local channel form5. Coastal environments are economically important and are significantly involved in transporting terrestrial organic matter and associated nutrient elements to the sea where these further contribute to biogeochemical cycling. The balance in the concentrations of biogenic elements in coastal water reflects the healthy state of this water. The complex dynamism in physicochemical characteristics of coastal waters is related to reverie flow, upwelling, atmospheric deposition, vertical mixing and other anthropogenic sources6-7.

Many of the largest cities of the world have evolved along the water bodies or the ocean’s rim. The exponential growth of metropolises and the concentration of people in small urban areas have tremendously increased the burden of governance of waste and wastewater. The discharge of wastewater into the oceans, affects the economy and tourism potential, dwindles the aesthetics of the beaches and estuaries, and creates magnitude of hygiene problems. The assimilation of wastewater treatment mechanisms is essential to have a sustainable environment. Enabling the bacterial and chemical oxidation of organic matter derived from any source can reduce the deterioration of water quality. In doing this, the major elements from the waste, namely carbon, nitrogen and phosphorus can be oxidized thus reducing the biological and chemical oxygen demand of the aquatic systems. This facilitates the survival of flora and fauna in the natural environment. The levels of suspended and dissolved organic, inorganic matter and gases reflect the chemical characteristics of wastewater 2. DO (dissolved oxygen), BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand), pH, salinity and turbidity are most extensively measured parameters to quantify the water quality index of the water body. It is considered as the major characteristic used in stream pollution control while COD is an important and quickly measured parameter for stream, sewage and industrial waste samples to determine their pollution levels and is a measure of the oxygen equivalent to that portion of organic matter, present in the wastewater sample that is susceptible to oxidation. Salinity is identity of a saline water body and accounts for the total amount of salts. Salinity may be affected by human interference in case any industrial waste water is released at sites of low dispersal. Temperature, pH, Turbidity, Conductivity, Total Suspended Solids (TSS), Nitrate, Nitrite, Total Nitrogen and Total Phosphate are other most important physicochemical properties of seawater3.

The main objectives of this study were to assess the coastal water quality in a segment of Bay of Bengal at Bakkhali, which is frequently visited by tourists. Comparing this to other pristine water sources one would be able to measure the impact of tourist activities on these coastal waters. The physicochemical properties measured here are DO, BOD, COD, TDS, Temperature, Turbidity, Microbial properties and Salinity, disincentives, and other management tools to address nonpoint source pollution of coastal waters1. The BOD test is very valuable in the analysis of sewage, industrial effluents and grossly polluted waters4 .It is considered as the major characteristic used in stream pollution control. Material and methods The study was carried out at three coastal sites of Bakkhali Beach (south extreme point, middle point and far north point, about 1.2 km along the shore) which are influenced by anthropogenic input from landbased sources. Latitude and longitude of the studyFig 1 sites are 210 35’ N and 880 15’ E respectively (Fig 1). Surface water samples were collected in different months at all the sites during high tide and low tide (before 12:00 PM) in month of November 2009 to February 2010 and were taken immediately to the laboratory for experimental studies. During southwest and northeast monsoon seasons (June–September and November–January/February), the coastal currents are quite high (50–60 cm s_1) during high tide time (Nov) and low (18-28cm s -1 ) during low tide time (December, January and February).Samples were collected after heavy rain and post monsoon season. Water temperature and pH were measured in situ by digital pH meter and also cross checked in the laboratory.

Rivers are the main inland water sources for domestic, industrial and irrigation purposes and often carry large municipal sewage, industrial wastewater discharges and seasonal run-off from agricultural land to the coastal region4. The spatial heterogeneity within the river, however, is due to existing local environmental conditions such as light, temperature, water discharge and flow velocity that change with 219


Results and discussion

pH: pH was measured at 300C in the laboratory. Samples were collected in small dark bottles along with few drop of chloroform to prevent photosynthesis of algae present in sample water. pH was measured by electrometric method using a pH meter.

pH: The pH values for coastal surface water of all the sites vary between 8.24 to 8.65 during month of November 2009 to February 2010 as shown in Fig. 2 and given in Table 1 1. The maximum pH value at the Site A was 8.65 in the month of February and the minimum value at Site B (8.24) in the month of November. The pH values of all the water samples increase from month of November to February because all the sampling sites receive maximum rain-water till the month of November after which winter sets in. The effect of acid rain due to large amount of acid gas emissions from the nearby Haldia industrial area starts subsiding after the month of November. This leads to a gradual increase in pH. The mild alkalinity may probably be due to some alkaline discharge from the Haldia industrial area or due to rainwater-runoff from embankments rich in soluble alkaline matters. Site B has minimum value of pH as this place is situated close to a water canal through which wastewater arising out of anthropogenic activities, comes in substantial

Temperature: Temperature was measured at the sampling site with a thermometer. Turbidity: Apparatus used to measure turbidity was Turb430 IR Portable Turbidity Meter. Salinity: The measurements were conducted with a Guildline Autosal Laboratory Salinometer (Model 8400B).Practical Salinity, S, is calculated using the following equation8. Total Dissolved Solid: TDS was measured by Optics Technology Manufactures Digital Total Dissolved Solid TDS Meter Dissolved Oxygen: DO was measured by azide modification method. It has been observed that Dissolved Oxygen (DO) levels in natural and wastewaters depend on the physical, chemical and biochemical activities in the water body. The analysis for DO is a key test in water pollution and waste treatment process control. The azide modification is used for most wastewater, effluent, and stream samples, especially if samples contain more than 50 mg NO2–-N/L and not more than 1 mg ferrous iron/ L9. Other reducing or oxidizing materials should be absent. If 1mL KF solution is added before the sample is acidified and there is no delay in titration, the method is applicable in the presence of 100 to 200 mg ferriciron/L10-11.

Fig. 2: pH variation w.r.t. site and time (month) quantity. Statistical analysis of pH at different sites are shown in Table 2 2. Temperature: Temperature ranges of coastal surface water at the sites A, B and C from November 2009 to February 2010 are given in Table1 Table1. The temperatures of surface water at these sites vary from 27.50C to 31.5 0 C during sampling time. The maximum temperature was found at site A and site B (31.50C) during month of November and minimum temperature was at site A and site B (27.50C) during December. With the cessation of rainfall and the setting in of winter, there is a drop in the ambient air temperature. This, coupled with a sharp drop in the atmospheric moisture content which accelerates the evaporation

Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand: Both the properties were calculated by using traditional methods11-12. Conductivity: Conductivity was measured by Hanna Bench Top Conductivity Meter (EC215). Bacterial analysis of samples: It was done by plate count method in nutrient agar media13-14. 220


Table 1: The analytical results A pH Temp DO BOD COD TDS Salinity Turbidity Bact Cond.

B

C

Nov

Dec

Jan

Feb

Nov

Dec

Jan

Feb

Nov

Dec

Jan

Feb

8.26 31.5 6.8 5.3 560 994 21.5 929 150 1.72

8.36 27.5 7.5 4.2 540 934 22.5 601 114 1.78

8.5 28.9 8.1 4.1 420 700 28.5 549 96 1.88

8.65 30 8.5 3.9 520 740 29.6 550 80 1.91

8.24 31.5 7.2 5 496 910 21.6 808 100 1.75

8.49 27.5 7.7 5.3 556 897 22.9 757 120 1.79

8.4 28 7.9 4.8 468 680 28 550 106 1.81

8.64 29.8 8.7 4.4 560 787 29.5 600 92 1.95

8.36 31 7.6 3.3 400 887 22.2 628 96 1.77

8.45 28.5 7.8 5.8 676 676 23 602 86 1.81

8.5 28 8.5 3.9 464 720 28.6 580 80 1.87

8.52 30 8.9 4.1 490 780 30 480 76 1.97

*All the values are average of 4

Table 2: Statistical analysis

Mean Std. Error Median Mode Std. Dev Variance Kurtosis Skewness Range Minimum Maximum Sum

pH

Temp

DO

BOD

COD

Salini

Turbi

Bact

TDS

Cond

8.46 0.036 8.49 8.36 0.12 0.014 -0.034 -0.12 0.41 8.24 8.65 93.11

29.1 0.41 28.9 27.5 1.39 1.9 -1.15 0.38 4 27.5 31.5 320.7

8.03 0.16 7.9 8.5 0.55 0.29 -1.14 0.19 1.7 7.2 8.9 88.4

4.4 0.22 4.2 4.1 0.73 0.52 -0.11 0.51 2.5 3.3 5.8 48.8

508.1 22.9 496 N/A 76 5781 1.38 0.81 276 400 676 5590

26.0 1.13 28 N/A 3.51 12.35 -2.23 -0.17 8.4 21.6 30 286.4

609.5 28.62 600 550 94.92 9010 1.139 1.172 328 480 808 6705

95.09 4.30 96 96 14.2 203.5 -0.75 0.37 44 76 120 1046

791.91 29.64 780.00 N/A 98.32 9665.89 -1.72 0.29 258.00 676.00 994.00 8711.00

1.81 0.02 1.81 1.81 0.07 0.00 2.03 1.17 0.25 1.72 1.97 19.94

period are shown in Fig. 3 3. Statistical analysis of temperature variation is shown in Table 2 2. Dissolved Oxygen: DO is a very important water quality parameter required to assess the waste assimilative capacity of the coastal waters. DO is affected largely by waste influx, especially the organic particulate matter, which causes depletion of DO in the process of organic degradation15. Dissolved oxygen level (7.2 to 8.9 mg /L) was generally high at all the sites indicating that these systems were well oxygenated. This value is high because of all the samplings were done in between 10:00 a.m. to 11:00 a.m. At that time photosynthetic rates of sea algae are maximum. The maximum value of dissolved oxygen is at site C (8.9 mg/L) during month of February and minimum value is at Site B (7.2 mg/L) in month of November during

Fig. 3: Temperature variation w.r.t. site and time(month) of surface water, brings down the temperature of surface water. As the ambient temperature starts rising after the month of December, the temperature of the surface water also starts rising. The temperature variations along with site and time during the study 221


the sampling time. Dissolved oxygen variability with respect to site and time (month) is given in Table 1 and shown in Fig. 4 4. There is a slight difference in dissolved oxygen value of coastal water. The DO value was high at site C in February due to the fact that it was a clean site away from tourist and local people activity. The DO value was lower at site B in month of November due to influx of flood water from river and tourist activities (fishing boating, swimming etc). There are many shops, restaurants and hotels at Bakkhali beach and this site is affected by the wastewater coming from the locality situated near the beach. Statistical analysis is carried out of these samples and the results are given in Table 2 2.

Fig. 4: Dissolved oxygen variation w.r.t. site and time

Biological Oxygen Demand: Normally Biochemical Oxygen Demand (BOD) of seawater varies in between 0.4 mg/L – 4.5 mg/L16. BOD is a gross measure of the oxygen demanding potential of the effluent. Assimilative capacity varies in accordance with the variations in hydrodynamic conditions and other ecological processes16. Based on the measured data, the average values of BOD varied between 3.3 mg/L – 5.8 mg/L. The values are given in Table 1 and Fig. 5 with respect to time and site. In most of the cases BOD value decreases from the month of November to February. BOD tests were performed in absence of photosynthesis, hence all bottles were kept in dark. BOD5-20 values are higher (5.8 mg/L) at site C in December and lower (3.3 mg/L) at site C in month of November. The maximum level of BOD for sea water type 2 (SW2) designated for bathing and commercial fisheries is 3.0 mg/L 17. BOD value at site C in December is high due to digging of earth near the sampling point. BOD value at site C in month of November is lower since this point is the cleanest point at beach. Site C was not affected by tourist activity. Statistical analysis of BOD samples is given in Table 2 2.

Fig. 5: BOD variation w.r.t. site and time

Fig. 6: COD variation w.r.t. site and time

Chemical Oxygen Demand: It varies between 400 mg/ L – 676 mg/L. The value is higher compared to BOD. This signifies that the sampling site is highly affected by organic matters which come from Haldia industrial region (petrochemical, leather, fertilizer industries etc.). The COD average values of different sites with respect to the sites and time (month) are given in Table 1 and shown in Fig. 6 6. The COD value is highly dependent on total dissolved solids value. The samples

Fig. 7: Salinity variation w.r.t. site and time

222


contain high TDS value. The maximum value was found at Site C (676mg/L) during December 2009. This is because of digging operation at site C during the sampling time when the current was quite high. The minimum value was found at site C (400 mg/L). This sampling was done soon after heavy rainy season. Due to constant dilution of the saline water by rain water, the COD at this place was low. The statistical analysis is given in Table 2

Fig. 8: Turbidity variation w.r.t. site and time

Salinity: The average value of salinity of surface water at the sampling site during the study time ranges from Table 1 21.6- 30.0 PSU (Table 1). The salinity corresponding to each location and time is shown in Fig. 7 7. Salinity at Site C (30.0 PSU) during month of February is higher than others because of high tide and no dilution of river water and local wastewater and Site A has lower value (21.6 PSU) in month of November because of the influx of river or fresh water. In the month of November, the coastal site A receives more rain water and flood water so it contains lesser salinity. The average salinity of sea water is 35 PSU. Indian estuaries have often been described as “monsoonal”. The salinity of estuary totally depends upon nature of tide and salinity of coastal water depends on the amount of rain water received during the monsoon time. At the end of the monsoon, the coastal water at Bakkhali beach is completely changed due to replacement of the pre monsoon water by freshwater flowing through the estuaries. This replacement is complete because the estuaries are flushed many times over. Salinity at all the sampling sites increases from the month of November to February. The statistical data of salinity variation is shown in Table 2 2.

Fig. 9: Bacterial colony variation w.r.t. site and time (month)

Fig. 10: Total dissolved solid variation w.r.t. site and time (month)

Turbidity: During the study period, turbidity of surface water at different sites varied between 480 NTU Table 1 808 NTU (Table 1) and shown in Fig. 8 8. The maximum value was found at site B (808 NTU) in November and minimum value at site C (480 NTU) during February. Maximum value was found just after the rainy season and minimum value when the sea water was clear and during low tide. In month of February sea wave is very slow. When rain falls on land it is either absorbed by vegetative areas and loose soil, or it flows over the hard surfaces into local waterways such as lakes, rivers and the sea. As rainwater runs off hard surfaces such as concrete, asphalt and evenly packed soil, it gathers speed and is able to carry a

Fig. 11: Conductivity variation w.r.t. site and time (month) 223


large suspension of particles such as soil. The swiftly moving water also can erode land and dissolve pollutants such as fertilizers and motor oil. As the water moves faster and increases in volume, more erosion occurs and more pollutants and soil particles are carried into local bodies of water. Depending on the size of the particles in the soil, the water can remain turbid (cloudy) for several days. More severe impact targets plant and animal life if the turbidity remains longer without dispersal. Water clarity is an important parameter in most bodies of water. Algae, phytoplankton and bottom dwelling plants, submerged aquatic vegetation, need sunlight to manufacture food through photosynthesis. If the turbidity of the water is so high then it will not allow sunlight to penetrate to the necessary depth and plant life will begin to die. Since plants are the basis of the food chain, other animals are soon affected. The statistical data of turbidity are shown in Table 2 2. Turbidity continuously decreases during the sampling time from November to February.

sulfates, phosphates, nitrates, calcium, magnesium, sodium, potassium, iron, manganese, and a few others. They do not include gases, colloids, or sediment. The TDS can be estimated by measuring the specific conductance of the water. Average value of TDS of surface water at the sampling sites during the study Table 1 time ranges from 800-994 mg/L (Table 1). The TDS corresponding to each location and time (month) is shown in Fig. 10 10. The maximum value of TDS is 994 mg/L at site A in the month of November. It is due to flood water collected at this point. This water also contains huge quantity of organic and inorganic matters which come from the Haldia industrial area. The samplings were done at high tide time and the wave currents were high at that time. The minimum value of TDS is 800 mg/L at site A in the month of January. Low tide season and lesser sea wave current are responsible for this value. There is no dilution of rain or flood water in the month of January. The statistical data of TDS variations is given in Table 2 2. Conductivity: Conductivity or specific conductance is a measure of a material’s ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. Average value of conductivity of surface water at the sampling sites during the study time ranges from 1.72-1.97 mS/cm Table 1 (Table 1). The conductivity corresponding to each location and time (month) is shown in Fig. 11 11. The minimum value of conductivity is at site A (1.72 mS/ cm) in the month of November. The value of conductivity depends on salinity and TDS value. Salinity value is minimum in the month of November. So conductivity is also less. Maximum values of conductivity are found at site C (1.97 mS/cm) during February 2010. It is due to higher salinity and TDS value. Salinity high means higher NaCl, MgCl2 and other inorganic compounds. Although a minor fraction of the total dissolved solids, nutrients (ammoniumnitrogen, nitrate-nitrogen and phosphate from fertilizers) and pesticides (insecticides and herbicides mostly) have significant negative impacts on streams and lakes receiving agricultural drainage water. If soils are also washed into receiving waters, the organic matter in the soil is decomposed by natural aquatic bacteria, which can severely deplete dissolved oxygen concentrations. All the above processes increase the conductivity. The statistical data of conductivity is

Bacterial colony: Sea water in shallow regions where the water can mix from top to bottom, due to tidal or wave motions, had a consistently higher bacterial content, ranging from 20 to 200 cells per cubic centimetre. Some microbes living and transported in ocean water, however, threaten human health. In the open ocean, far from the influences of coastal human habitation, sea water still contains huge numbers of microbes. Coastal areas can contain even greater concentrations. Vast numbers of bacteria occur both at the surface and in deep ocean waters18. Average values of bacterial colony during sampling time vary between 76-150 and are shown in Table 1 and in Fig. 9. The maximum value of bacterial colony is found at site A (150) during November due to more polluted water at that point. This pollution is due to flood water and other local waste water and also due to discharges from Haldia industrial area. Minimum value is found at site C (76) during February 2010. This point is very clean part of the beach and away from local human activity. The bacterial colony is continuously decreasing during studying time from November 2009 to February 2010.The statistical data of bacterial colony are shown in Table 2 2. Total Dissolved Solid: Total Dissolved Solids (TDS) consist mainly of carbonates, bicarbonates, chlorides, 224


shown in Table 2 2. Conductivity continuously increases during the sampling time from November to February.

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Conclusion Bakkhali is situated at the mouth of river Hugli. The nearest industrial city, Haldia is around 40 km upstream. The acid gas emissions from the industries result in a reduction in pH value of the water due to acid rain. This is countered by the addition of soluble alkaline matters from the embankments due to rainwater run-off. The surface of the sea near the coast, is constantly disturbed by the formation of waves with the resultant formation of surf. This is a natural aeration phenomenon which leads to appreciably high levels of D.O. and substantial turbidity. The concentration of pollutants carried by the river water gets drastically reduced on dilution with sea-water at the confluence of the river with the sea; hence BOD values normally get reduced. Sea water contains dissolved salts in proportions much higher than river water. So, the C.O.D., salinity and conductivity values bound to be higher. These values get reduced during rainy season due to the dilution effect of rain-water. By and large, it can be concluded that Bakhhali beach at site C is quite clean. Only the coastal sites A and B have been affected to some extent and exhibit elevated levels of pollution measuring parameters. An important aspect to be considered while discharging organic waste into the coastal sea is possible eutrophication of the coastal waters due to this, as the sewage contains significantly high amount of nutrients. Recently there have been several events of red tide and fish mortality at different locations along the east coast of India. These can be minimized through proper pre-treatment of effluents and other waste waters before releasing them into the sea. Constant monitoring of coastal waters is very essential as the frequency of new developments is fast increasing. Also a necessary balance is to be attained between the level of industrialization/urbanization and the exploitation of coastal zone environment so that the coastal ecosystem can be preserved intact. References 1.

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