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Effect of Climate Change on Groundwater Quality for Irrigation Purpose in a Limestone Enriched Area

Sourav Hasan
Agricultural Engineer
Department of Agricultural Extension, Khamarbari, Comilla, Bangladesh

A. K. M Adham
Professor and Head
Dept. of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Md. Touhidul Islam
Agricultural Engineer
M.Sc. in Irrigation and Water Management, Dept. of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Deen Islam
Associate Professor
Dept. of Irrigation and Water Management, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.

Abstract/ Executive Summary:

A study was carried out at Panchbibiupazila in Joypurhat district, Bangladesh, where underground geology is limestone enriched, to investigate the effect of climate change on groundwater quality for irrigation purpose using numerical simulation model. The numerical simulation model included dispersion/diffusion, advection, ion exchange, formation of complexes in the aqueous phase, and the dissociation of water. Fifteen groundwater samples were collected from the study area to evaluate the quality parameters used for the purpose are pH, electrical conductivity (EC), total dissolved solid (TDS), sodium adsorption ratio (SAR), soluble sodium percentage (SSP), residual sodium carbonate (RSC), magnesium adsorption ratio (MAR) and total hardness (TH). Only two samples were in the dangerous category in terms of magnesium adsorption ratio. Rest of the parameters showed that groundwater is suitable for irrigation purpose. In the numerical simulation model the mass action, transport, and site action equations are expressed in a differential/algebraic form and solved by finite element method (FEM). Results revealed that the dissolution of limestone was directly proportional to the acidification of rainwater i.e. inversely proportional to the pH of rainwater.

Dissolution of limestone was also proportional to the increase of intensity of rain that leads to the increase of velocity of water and vice versa. Dissolution of limestone was directly proportional to the increase of temperature as well. Among the factors that were included in the study, pH of water in contact had the maximum effect on the dissolution of limestone. The enhanced dissolution of calcium ions may be expected to block the filter of the pumping well and deteriorate the quality of groundwater as well. Water also becomes hard for increasing the dissolution of calcium ions will limit the suitability of the water for irrigation.

Keywords: Climate Change, Groundwater, Irrigation, Dissolution, Limestone, pH, Rainfall, Temperature and Chemical Reaction

Location: In Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Climate change, Groundwater, Water quality

Objectives:

This study is related to sustainable groundwater development from limestone-enriched aquifers. The purpose of the study is to synthesize all the parameters used in assessing the suitability of water for irrigation in the limestone-enriched area. The result of the study will help the people of the study area to know the quality of water with regard to agriculture and can plan crop cultivation accordingly.

Methodology:

Fifteen groundwater samples were collected from Panchbibiupazila in Joypurhat district using acid-washed bottles to avoid unpredictable changes in characteristic as per standard procedures. At the time of sampling, bottles were thoroughly rinsed two to three times with groundwater to be sampled. The quality parameters of the groundwater samples – pH, electrical conductivity (EC), total dissolved solid (TDS), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), magnesium adsorption ratio (MAR), total hardness (TH) and Kelly’s ratio (KR) - were measured to determine the suitability of water for irrigation purposes. The pH values of groundwater samples were measured by taking 50 ml of water in a beaker and then the electrode of the pH meter was placed into the water samples as mentioned.

Electrical conductivity of water was determined by taking 100 ml of collected water in a beaker and then the electrode of conductivity meter was immersed into the water sample according to the technique expressed. Total dissolved solid was measured by evaporating 100 ml water sample to dryness and then the remaining was weighed following the method as suggested.

II.1 Model Study A developed model was used for numerical simulation. Dispersion/diffusion, advection, ion exchange, formation of complexes in the aqueous phase, and the dissociation of water were involved in the developed model. Dissolved inorganic carbon remains in one of four major forms (CO2aq, H2CO3, HCO3 - and CO3 2- ) in CO2-H2O system. Firstly, carbon dioxide is converted into hydrogen and bicarbonate; secondly, bicarbonate is dissociated into hydrogen and carbonate ions, and finally, the limestone is dissolved. Almost all of these reactions depend on pH and temperature.

II.2 Model Fitting At first, 10 days averaged rainfall and temperature data (450 days) were analyzed. Then the analyzed data were used as input in the model. Rainfall and temperature trend were observed. The effects of pH, rainfall, and temperature were observed for Ca2+ ion dissolution in the study area from the model. All data were compared with reference case.

Source of Information: International Review of Civil Engineering (I.RE.C.E.), Vol. 7, N. 1 January 2016 ISSN 2036 - 9913

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The pH value revealed that the groundwater was acidic in nature. The electrical conductivity (EC) of all samples was good for irrigation. The total dissolved solid (TDS) of 80% of the samples were excellent and 20% samples were in good category. The groundwater of the study area had low soluble sodium percentage from 13.76 to 29.67, which indicated that it was suitable for irrigation. SAR values were <10, classifying groundwater of the area as excellent for irrigation.

The residual sodium carbonate (RSC) of 80% of all sample were safe and 13% of the samples were marginal. Only two samples (D5 and H4) contained extreme magnesium adsorption ratio (>50%), which were dangerous for irrigation. Total hardness of all sample were soft (0 to 75 mg/L). Kelly’s ratio revealed that the groundwater of the study area was suitable for irrigation.

Dissolution of limestone increased more with acidification of rain water. Increasing amount of rainfall increased the dissolution of limestone. Dissolution decreased slightly from reference case with increasing temperature. Among all effects of global warming, pH effect was the highest on dissolution of limestone followed by rainfall effect. So, it is concluded that the acidification of water is the major concern for limestone dissolution.

Knowledge Management: Journal