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Assessment of Irrigation Water Quality by Using Principal Component Analysis in an Arsenic Affected Area of Bangladesh

Rezwanul Mahmud
Faculty of Agriculture, Shinshu University, Minamiminowa, Nagano, Japan

Naoto Iioue
Faculty of Agriculture, Shinshu University, Minamiminowa, Nagano, Japan

Ranjit Sen
Bangladesh Agricultural Research Institute, Gazipur-1701, Bangladesh

Abstract/ Executive Summary:

The irrigation water quality was assessed around Budhol union under the district of Brahmanbaria in Bangladesh where underground water is highly arsenic (As) contaminated. Three types (surface, shallow tube well and deep tube well) of irrigation water samples were collected for physio-chemical analyses, which included pH, EC, TDS, Ca, Mg, Na, K, Fe, Zn, Cu, Mn, P, B, As, CO₃, HCO₃, Cl, SO₄ and NO₃. Comparative study and the distribution pattern of anionic and cationic constituents were performed for three types of arsenic contaminated irrigation water sources. Among the water sources, surface irrigation water was found less arsenic and manganese toxicity for irrigation. On the other hand, shallow tube wells water used for irrigation purpose contain more soluble arsenic then surface water and deep tube wells. Depth of tube well is correlated with arsenic concentration of well water. In order to understand the distribution of individual geochemical variables in the irrigation water samples collected from the sites affected by arsenic toxicity, principal component analysis was performed. The results of principal component analysis showed that geochemical variables have tendency to accumulate into three distinct groups. Well Depth, As and Mn were belongs to one group, which indicate that WD might have positive effect on As and Mn.

Keywords: Arsenic contaminated area, Irrigation water quality, Principal component analysis.

Location: Southeastern part of Bangladesh, under the district of Brahmanbaria and Agricultural Chemistry Laboratory, Bangladesh Agricultural Research Institute, Gazipur

Start Date: 01-03-2003

End Date: 25-03-2003

Program Area: Crop-Soil-Water Management

Commodity: Water quality

Objectives:

To clarify the general variation patterns of geochemical variables occurring in irrigation water collected from various sites of an As affected area of Bangladesh
To improve the environmental methodology for assessment of the degree and pattern of pollution in a certain type of soil

Methodology:

Study area: The study area is located in the Southeastern part of Bangladesh, under the district of Brahmanbaria. The soil type is non-calcareous alluvium type. The region is belongs to the aquifer of Late Pleistocene coarse sands, gravels and cobbles of the Tista and Brahmaputra megna-fans and basal fan delta gravels along the incised Brahmaputra channel. Deep tube well, shallow tube well and pond are used for irrigation in this area. Procedure for water sample collection: Water samples were collected from 5 ponds, 7 shallow tube wells, and 6 deep tube wells at Budhol union under the district of Brahmanbaria during the month of March 2003. For each sample site, three samples were taken for chemical analysis. Water samples were collected in one liter plastic bottle. The ground water samples were collected at running condition of the tube wells and surface water samples were drawn from midstream at 0-15 cm below the surface of pond water. The collected water samples were tightly sealed as early as possible to avoid exposure to air. Water sampling techniques were followed. The chemical analyses were conducted at the Agricultural Chemistry Laboratory, Bangladesh Agricultural Research Institute, Gazipur, Bangladesh. Methods used for chemical analysis: The pH and electrical conductivity (EC) values were determined electrometrically using digital pH and digital conductivity meter. Total dissolved solids (TDSs) were estimated by weighing the solid residue obtained by evaporation of a measured volume of water samples to dryness. Potassium and sodium were determined by flame emission spectrophotometer. Calcium, magnesium, iron, zinc, copper and manganese were analyzed directly by atomic absorption spectrophotometer. Bicarbonate was determined by acidimetric titration while chloride was determined by argentometric titration. Phosphorus, boron and nitrate were determined colorimetrically whereas sulphate was analyzed turbidimetrically. As was analyzed directly by atomic absorption spectrophotometer with hydride generator. Determination of irrigation water classification: The classification of irrigation water quality was carried out according to sanitary classification criteria. Statistical Analysis: Principal Component Analysis (PCA); The purpose of PCA is usually to determine a few linear combinations of the original variables, which can be used for summarizing the data with minimal loss of information. Principal components were computed by factors that are the eigenvectors of the correlation matrix of the original data. PCA as the multivariate analytical tool is used to reduce a set of original variables and to extract a small number of latent factors (principal components, PCs) for analyzing relationships among the observed variables. The number of factors extracted from the variables was determined by a scree test according to Kaiser’s rule. This criterion retains only factors with eigenvalues that exceed one. Throughout the study the software packages SPSS 12.0 and Excel Statistics 5.0 were used. Our intention was to get as many positive loadings as possible in order to achieve a more meaningful and interpretable solution. Factor Loading: The contribution of the original variables to the extracted principal component is proportional to the linear combinations of original variables. These contributions are called “Factor Loading”. When several variables have large loadings on a principal component, they may be interpreted as being strongly associated with each other and significant in that principal component. On the other hand, a small loading of variables on a principal component indicates that the variable is not associated with the principal component. Principal component analysis and factor analysis have been used for irrigation water quality, which are under the influences of many factors during the chemical analysis. Three factors were extracted from the irrigation water samples. The PCA methods contained in the statistical SPSS program was applied to the chemical concentration data in order to study the geochemistry variables capable of promoting a characterization of the hydrochemistry of the region and to identify the fundamental factors that govern the general behavior of the irrigation water sources.

Source of Information: J. Soil. Nature. 1 (2):08-17, (2007)

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

From this study, the following conclusions could be made: Degree of arsenic concentration in irrigation water Shallow Tube Well> Deep Tube Well> Pond/surface water. Depth of tube well and arsenic concentration relationship. High arsenic concentration< 100 meter> Low arsenic concentration. Depth range, where arsenic concentration remain high is 50 meter to 100 meter. As and Mn toxicity were found among STW and DTW, which might be due to the presence of certain minerals and further study needed in this regards.

Knowledge Management: Journal