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

ASHFAQUE AHMED
Ecology and Environment Laboratory, Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

MIKAEL OHLSON
Department of Ecology and Natural Resource Management,Norwegian University of Life Sciences, Ås-1432, Norway

SIRAJUL HOQUE
Department of Soil, Water and Environment, University of Dhaka, Bangladesh

MD. GOLAM MOULA
Plantation Trial Unit Division, Bangladesh Forest Research Institute, Rupatali, Barisal, Bangladesh

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, ANOVA 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: The southern coastal zone of Bangladesh

Start Date: 27-02-2006

End Date: 00-00-2006

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

1. This study examines the affect of different hydrological conditions on the edaphic features of different islands (chars) in the coastal zone of Bangladesh with an assumption that soils of different islands will show variability in its physico-chemical parameters due to fluctuation of tidal inundation.

Methodology:

Geomorphology of the study area: 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. Climate: 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% (Data were collected from the Climate division, Bangladesh Meteorological Department, Government of the People's Republic of Bangladesh for 1985 to 2005. Dynamics of the study area: 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 (images of 1989 and 2006 are shown only). It is clear from the image of 1989 that one of the islands, namely Char Taposhi, was in the early stage of land accretion. Plantation started in that char in 1987. In 1992, the char was distinctly visible and about 70% of the char of current size was formed. Land is still accreted there towards the south i.e. seawards direction. Numerous new chars are being raised and it is becoming a continuous strip. New land is accreted to the eastern boundary of the Char Motherbunia making the channel narrower and flow of the river in this channel seems to be blocked in near future as numerous chars are rising at the mouth of the channel, at the northern part of the Rangabali police station. Sample collection: 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" N and 90°27'0" - 90°30'30" E). Soil samples were collected on 27th February, 2006 from three different islands (chars) with different hydrological regime. Analytical methods: 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 (Jenkin,UK). Calcium and Mg as ions were determined by atomic absorption spectrophotometer. Water soluble S as SO₄2- was measured by the turbidimetric method of Hunt. One gram air dried soil sample was digested with nitric acid-perchloric acid mixture (2 : 1). Phosphorus content of the digest was determined by vanadomolybdophosphoric yellow colour method in nitric acid system as described by Jackson. Total K was determined by flame photometer. Total S content of the digest was determined by turbidimetric method. Total N of the soil was determined by the modified Kjeldahl method as described by Jackson. Water soluble chloride was determined titrimetrically with standard 0.05 N silver nitrate solution. Organic C (%) was determined by Walkley and Black's wet oxidation method. Organic matter content was calculated from the organic carbon value by multiplying with a factor 1.724. Soil samples were analysed at Soil Chemistry Laboratory of Soil, Water and Environment Department, University of Dhaka, Bangladesh. Statistical analysis: Different variables of each soil samples were subjected to analysis of variance (ANOVA). 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. Biol. Sci. 19(1): 27-40, 2010 (January)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The result presented here showed that the soils of the islands were fairly homogeneous as regards to soil chemistry. Soil analysis did not show general patterns of spatial variations among the islands and within the islands. The results thus indicate that broad-scale hydrology did not appear to be responsible for differences found in the edaphic variables.

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