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Spatial Variability of Arsenic in Soils in Arsenic Contaminated Shallow Tube Well Command Areas Used for Irrigated Wetland Rice Cultivation

Manotosh Howlader, MSc. (Stat.)
Senior Scientific Officer
Agricultural Statistics Division, BRRI-Gazipur.

Md. Shahjahan Kabir
SSO
Agricultural Statistics Division, BRRI-Gazipur.

Md. Rokonuzzaman, MSc. (Stat.)
Scientific Office
Agricultural Statistics Division, BRRI-Gazipur.

Abstract/ Executive Summary:

The experiments were carried out during the Boro season 2007 and 2008 in four Shallow Tube Well (STW) command areas: B. Baria and Faridpur Sadar upazila, the smallest administrative unit in Bangladesh. Each command area was grided by 20m distance and the sampling points were georeferenced by a global positioning system (GPS). Composite soil samples (0-15 cm), Plants and water samples were collected from the grids. The spatial dependency of soil arsenic gives an indication that longer irrigation channels prior to inlets into rice fields and discouraging standing water for long periods in rice plots could be positive measures in reducing arsenic loading in irrigated rice soils. Majority of the rainfed T.Aman area falls under favorable or moderately suitable growing environment located almost allover the country.

Keywords: Spatial variability, STW, Command area, Arsenic (As)

Location: BRRI HQ, Gazipur

Start Date: 00-00-2007

End Date: 00-00-2008

Program Area: Resource Development and Management

Commodity: Contamination of soil

Objectives:

This paper assesses the distribution of arsenic concentration in the soil surrounding of a single arsenic contaminated STW in two different locations in Bangladesh; identify the means to reduce As contamination in rice soils as well as food chain.

Methodology:

Soil samples were collected from grid points geo-referenced by GPS for As analysis. Composite soil samples (0-15 cm) were collected from the grids. Semivariograms were calculated to evaluate the spatial variability of soil As for each individual site by GS+ 5.3.2. Maximum lag distance and lag interval for the semivariance were determined iteratively to best fit the model having highest R² and the lowest residual sum of squares (RSS) values. Kriging interpolation was performed to spatially describe the distribution of As concentration in topsoil. Analysis of data on arsenic concentration in water flowing through the irrigation channel were analyzed and the result (not shown) showed that As concentration reduces with the distance from the tube well indicating that a considerable amount of arsenic in water is absorbed in soils, probably more near the source.

Source of Information: BRRI Annual Report 2007-08

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

This is observed that the spatial distribution of arsenic concentration in the command areas STW in four locations are presented in Map 1. Soil arsenic concentration was spatially related with the distance from the tube well along the irrigation channel. The effective distance of this spatial dependency varied with the topsoil texture, the distance being longer for the soils with higher clay content and shorter with higher sand and or silt. Within a command area, the spatial variability in soil arsenic was not consistent throughout resulting from the micro differences in plot elevation. The concentration was higher in relatively depressed areas where the irrigation water could stay longer than the area with higher elevation.

Knowledge Management: Report/Proceedings