The present study was scheduled to be conducted in the Bagerhat district of the south-west coastal region of Bangladesh. Three coastal sub-districts (Rampal, Morrelgonj and Bagerhat) where shrimp culture is dominant were selected. Considering the limitations of time and resources, three unions from each sub-district and two villages from each union were selected following the stratified random sampling technique. Thus a total of 18 villages having shrimp culture practices were finally selected for this study. The three coastal sub-districts of Rampal, Morrelgonj and Bagerhat were selected as they were well connected with the Bay of Bengal by the rivers of Mongla, Daudkhali, Passur, Panguchi, Katakhali, Baleshwar, Bhola and Dartana .They also have the top ranking with respect to shrimp area coverage.
Collection of Surface Water: Local people used surface water from the ponds as portable water in the shrimp culture area. Therefore, surface water samples were collected from different ponds located in three coastal sub-districts of Bagherhat Sadar, Rampal and Morrelganj of Bangladesh. Samplings were performed in the month of October (2003 and 2004) for the rainy season and in April (2004 and 2005) for the summer season. Each time a total of 18 samples from each ponds were collected from 18 villages of the three coastal sub-districts of Bagherhat Sadar, Rampal and Morrelganj. Surface water from the ponds was collected from 30 cm below the water surface in a clean and well-dried 500 ml plastic bottle with airtight screw cork. Before collection of water the bottles were rinsed with pond water from the specific sources. Immediately after sampling the water was transferred to laboratory for chemical analysis.
Collection of Ground Water: For assessment of ground water quality of shrimp culture areas of Bangladesh, two tube-wells were randomly selected from each village of the study area under the three coastal sub-districts of Bagherhat Sadar, Rampal and Morrelganj. A total of 33 tube-well water samples (instead of 36) were collected from 18 villages because of 3 tube-wells in two villages were inactive. To observe the seasonal variation, ground water sampling was done both in the summer (April 2004 and 2005) and in the rainy season (October 2003 and 2004). During ground water sample collection, the tube-well was first pumped for 30 minutes to pump out the stagnant water present in the pipes. Next, fresh ground water was collected in a 500 ml clean plastic bottle with airtight screw cork from each of the selected tube-wells. Before collection of water the bottle was rinsed with tube-well water several times. The collected samples were preserved in a cool place in the lab before analysis.
Preparation of Water Samples: The collected water samples were first filtered through a Whatman No.1 filter paper for phosphorous, sulfur, boron, iron and zinc. The filtrate was collected in a clean well dried plastic bottle with airtight screw cap. In the case of non-clear filtrate, filtration was repeated on the same filter paper. The clean filtered water was used for necessary chemical analysis.
Water Analysis: Water pH was measured directly in sampled water immediately after sampling in the field using the HACH pH meter. Electrical conductivity was measured directly in water by the Metrohm EC Meter at 25oC. Potassium (K+), calcium (Ca2+), iron (Fe3+) and zinc (Zn2+) contents of water were separately measured by Atomic Absorption Spectrophotometer (AAS). Phosphorous (PO43-) content of water was determined colorimetrically by measuring the absorbance on a spectrophotometer at 890 nm using molybdate blue-ascorbic acid solution. Sulfur (SO42-) content of water was determined turbidimetrically using BaCl2 and polyvinylpyrrolidone by measuring the absorbance at 535 nm on spectrophotometer. Boron (B) content of water was determined by mixing acetate buffer solution and Azomethine-H reagent with the water and the absorbance was measured at 420 nm on a spectrophotometer. Nitrate - content (NO3) of the water was determined by using brucin reagent and conc. H2SO4 acid and the absorbance was measured at 410 nm on a spectrophotometer
People’s Perception Study on Water Quality: The scarcity of good quality water is a common phenomenon in the shrimp culture area of Bangladesh. Chemical analysis of surface and ground water is not enough to describe the impact of shrimp culture on the drinking water sources in the study area. Therefore, people’s perception of the impact of shrimp culture on the surface and ground water quality was assessed through household questionnaire survey. Categories of respondents were selected from the adjoining villages surrounding the shrimp culture areas. To get the clear and correct answer, older people over 40 years of age with different professions have been selected as respondents. This helped in getting information from various walks of life with diversified views, which increased the reliability of information and decreased the chance of data missing and error. Considering the available logistic support, resource constraints and time, a total of 325 diversified respondents were selected from the study area (shrimp pond owners – 36, household farmers – 72, shrimp culture labor – 36, professional fishermen – 90, teacher/imam/NGO professionals – 72 and government officials – 21)