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Edaphic Conditions of Different Islands Under Different Hydrological Regimes in the Coastal Zone of Bangladesh

Ashefaque Ahmed
Ecology and Environment Laboratory, Department of Botany, University of Dhaka, Dhaka-lOOO, Bangladesh.

Md. Golam Moula
Plantation Trial Unit Division, Bangladesh Forest Research Institute, Rupatali, Barisal, Bangladesh.

Sirajul Hoque
Department of Soil, Water and Environment, University of Dhaka, Bangladesh.

Mikael Ohlson
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, As-1432, Norwa.

Abstract/ Executive Summary:

Physical and chemical properties of soils from the southern coastal zone of Bangladesh were studied to understand the effect of inundation on different soil variables. Soil samples were collected from three different islands representing different hydrological regimes, viz. Char Motherbunia (Island I) is inundated twice daily, Char Taposhi (Island II) is inundated by high tide and Char Kashem (Island III) is totally raised, inundated only during storm surges. Three transects in each island perpendicular to the river Buragauranga were established. Five soil samples, each with a composite of five sub-samples, were collected from each transect, 15 variables were tested from total 15 samples of each island. To test the variations among the islands and within the island, ANOV A was used. Soils of the three islands were found to be rather similar in chemical properties, although there were some significant differences in pH and potassium concentration. The results indicated that broad-scale hydrology did not effect the variation found in the edaphic condition rather duration and amplitude may be responsible for some observed variation. A correlation matrix of the soil variables showed a strong correlation among chemical elements and that the majority of elements were significantly correlated with pH

Keywords: Edaphic conditions, Coastal zone, Hydrological regimes, Tidal amplitude

Location: coastal areas of Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land management

Objectives:

To identify the edaphic conditions of different islands under different hydrological regimes in the Coastal Zone of Bangladesh

Methodology:

The coastal areas of Bangladesh are divided into three distinct regions: the western, central and eastern coastal zones. The western part is characterized by numerous criss-crossed channels and creeks, the central zone, where the present study was conducted, is featured by the discharges of the three mighty rivers (Ganges, Brahmaputra and Meghna) and is an area of continuous process of accretion and erosion that made the area most active among the three zones. Tropical maritime climate prevails in the coastal zones. The mean temperature in the coastal areas varies between 19°C in winter and 29°C in summer. The amount of rainfall varies from about 3,000 mm in the west, down to 2,300 mm in the centre and as high as 4,000 mm in the east. Average monthly humidity values ranged between 71 and 92%. The coastal zone and islands included in the present study. Thematic mapper (TM) images from Landsat, prepared by Bangladesh Space Research and Remote Sensing Organization (SPARRSO), showed the dynamics of the river bed and vegetation pattern of the study area. Images were collected from Bangladesh Space Research and Remote Sensing Organization of different years from 1989 to 2006. Soil samples were collected from a segment of the coast at the Rangabali Police Station (administrative unit) of Galachipa upazila (sub district) of Patuakhali district (21°53'10" - 22°0'0" Nand 90°27'0" - 90°30'30" E). Soil samples were collected on 27th February, 2006 from three different islands (chars) with different hydrological regime. Three chars (islands), namely Char Motherbunia (hereinafter referred to as Island I) (latitude 21°56'48" - 21°58'24"N and longitude 90°28'48" - 90029'E), Char Taposi (hereinafter referred to as Island II) (latitude 21°52' - 21°54'18" Nand longitude 90°29' - 90030'48"E) and Char Kashem (hereinafter referred to as Island III) (latitude 21°52' - 21°54'18"N and longitude 90°25' - 90027'48"E), were selected from the central coastal zone, amongst numerous Islands raised along the coastal area of Bangladesh. Sampling areas : Soil pH was determined by using fresh soil to water (distilled water) ratio of 1 : 2.5 with the help of a pH meter (Jenway). Twenty gram fresh soil was leached with 100 ml deionized distilled water maintaining 1 : 5 ratios and the conductivity of the leachate was measured by electrical conductivity meter. Water soluble Na' and K' were determined by flame photometer. Calcium and Mg as ions were determined by atomic absorption spectrophotometer. Different variables of each soil samples were subjected to analysis of variance (ANOV A). Island and location were used as factors. To compare soil samples among the islands and locations, ANOVA was performed using general linear model procedures in SAS 9.1 program. Interactions between islands and locations were also tested for soil samples. Pearson correlations were calculated for soil sample variables.

Source of Information: Dhaka Univ. J. BioI. Sci. 19(1): 27-40, 2010 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Soils of mangroves had been considered as homogeneous entities where different physical factors such as tidal amplitude, period of inundation, microtopography had been explained as the responsible reasons for variation. But different studies in the last few years had indicated that the presence of different mangrove species were the other responsible factors for the variability of different soil parameters. For examples, variations in sulphide content, acidity total organic matter content and trace metals were found in soils that were dominated by different mangrove species. Capacity of different mangrove species to change the conditions of the adjacent soil of their root systems had also been found responsible. Mangrove litters with different organic composition might also have caused the variation in the soil conditions. The variations found in the soil variables of the present study might be explained due to the physical factors such as amplitude and duration of tidal inundation and further study is needed to comment on the capacity of Sonneratia apetala , planted and growing extensively in the coastal islands, including the islands studied, to change the soil conditions adjacent to their root systems.

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