Awal, Mohd Abdul
Founder & Chief Advisor, Health & Pollution Research Farm, 23-09-37 Avenue, Apt, No: 1, Long Island City, New York, USA
Causal Factors, Heavy Metals, Top-Dying Disease, People Health Problems, Environmental Factors
Sundarbans, Bangladesh
Risk Management in Agriculture
Evaluation
Nine plots were selected for sampling, choosing areas to reflect different intensities of top-dying. Sixty-three(63) sediment samples were tested for the various parameters, including x elemental concentrations being determined by ICP-MS. The relationships between top-dying and chemical or growth parameters were tested using correlation coefficients, the variations between plots were tested using analyses of variance and differences in seedling and sapling numbers using chi-square statistics. Results of seedling and sapling regeneration showed a marked reduction in numbers in areas with greater concentrations of several chemical parameters. However, adult tree growth was generally not correlated with the chemical parameters. Also, most of the individual elements and parameters studied had no significant correlation with the average intensity of top-dying of Heritiera fomes. However, exchangeable K, sediment moisture content and sediment pH were significantly related and Sn, Pb, Zn and Ni were also close to significance. These results show that the chemical composition of the soil appeared to be an important factor related to tree regeneration, though not to adult tree size, and in some cases to be related to the top-dying of Heritiera fomes in Sundarbans. It is suggested that the latter effect is due to a weakening of the vigour of the trees, allowing other factors such as pathogenic agents to damaged the plants. 2.1. Field Sampling Methods Fieldwork was performed between October 2003 and March 2004. Sampling was from the area of the Sundarbans near Chandpai, which is the area most accessible to people and also potentially the one that is most polluted. Three areas (termed ‘compartments’) from this region were selected (numbers 26, 28 and 31) because they were believed to represent a range of severity of top-dying disease as well as of human activities, as outlined in Awal et al. (2009). Within each of the three compartments, sampling of vegetation, mangrove sediment and water took place within three 20m x 20m plots, chosen to reflect a range of top-dying intensities (high, medium and low for that area). The sampling was conducted in a randomised block design, in that a plot was sited within a particular top-dying intensity block, but the precise location of that plot was randomised so as not to bias the detailed data collection. Therefore a total of nine plots was sampled. It should be noted that the material making up the mangrove sediments will include marine, coastal and freshwater deltaic sediments as well as biological material such as tree litter-fall. The relative importance of these sources will depend to a great extent on the patterns of river discharge (Dyer, 1986) and the extent of tidal inundation, and will also therefore vary spatially throughout the Sundarbans. 3.2. Laboratory Analyses Initial chemical and physical properties of the mangrove sediment samples and the water were determined in Dhaka University. These were the electro-conductivity for the determination of sediment and water cation exchange capacity; the pH of both sediment and water; the percentage moisture content of the sediments; soil particle analysis determined by a Plunger Hydrometer; the concentrations of S (name of method?), soluble N (digestion method), and total N (Kjeldahl method. All remaining elemental concentrations were determined using Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) at Bradford University. 2.2.1. Electro-Conductivity Fifty ml of distilled water was added to (how much of?) the sediment, and the mixture shaken mechanically and then stirred 5-7 times to ensure thorough mixing. The sediment suspension was left overnight for it to reach its stable suspension position phase. Finally water EC was recorded by using an EC meter. 2.2.2. pH The pH of the sediment samples was measured by adding 50 ml of distilled water; 20 g of sediment was weighed using an analytical balance and placed into a graduated glass beaker, and then 50 ml of distilled water was added to the soil to the sediment, then shaken and stirred 5-7 times to ensure thorough mixing. The mixture was left overnight for it to reach its stable suspension position phase before recording the pH using a pH meter. For the pH of the water samples, 50ml each of water sample and distilled water were taken, stirring was done in the same way as for the sediment pH measurement, and the sample solution left overnight before filtering using a Whatman No. 42 filter paper and then recording the pH as above. 2.3. Particle Size Analysis Each sediment sample was air dried, ground to a powder, sieved, then reacted with hydrogen peroxide solution (H2O2), according to the procedure described in Black et al. (1965). In the hydrometer, the blank reading was taken after 40 seconds, and the second reading after two hours, maintaining the temperature at 29oC; and these values were used to calculate the particle size (Black et al., 1965). 2.3.1. Percentage Moisture Content of the Sediment Approximately 50g of sediment was passed through a 2 ml sieve. The sieved material was then weighed and heated to 105ºC for 24 hours to dry it completely. The dry sediment was then reweighed and the difference in weights gave the weight of moisture. This amount of moisture was expressed as a percentage of the original wet sediment weight.
Science Innovation. Vol. 2, No. 2, 2014, pp. 11-21.
Journal