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

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

DR. D.N.R. Poul
CSO and Head
Agricultural Statistics Division, BRRI, Gazipur

Abstract/ Executive Summary:

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. It was observed that the spatial distribution of arsenic concentration in the command areas STW in four locations. 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.

Keywords: Arsenic , GPS, GIS, STW, RSS, Semivariograms, and Ground water

Location: B. Baria, Sonargaon,Faridpur and Satkhira

Start Date: 30-06-2002

End Date: 31-12-2004

Program Area: Socio-economic and Policy

Non-commodity: Arsenic, Analysis and interpretations

Objectives:

The study was undertaken to map the spatial distribution of arsenic concentration in the soils in the command area of a single arsenic contaminated STW

Methodology:

Ground water irrigated rice fields of four different locations were intensively sampled on regular grid spacing during Boro 2003. 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.

Source of Information: BRRI Annual Report 2003-04

Article Link (Online Journal):

Funding Source:

1. Government

Budget: 250000

Total Budget (Tk.) : 250000

Achievement/Findings:

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.

Knowledge Management: Report/Proceedings