Ground-Water Quality in Islamkot and Mithi Talukas of District Tharparkar, Sindh, Pakistan

Surface water supplies are gradually becoming short in arid and semi-arid regions of the world. Thus, assessment of groundwater quality for crop use appears to be very essential for management and utilization of precious natural water resources. This study reports the water quality of 52 hand pumps and one tubewell located in the most remote areas of desert region, viz. Islamkot and Mithi talukas of district Tharparkar. The water samples were collected during April 2016 (just before the start of rainy season). The water samples were analyzed for EC (Electrical Conductivity), pH, CO 3 , HCO 3 , Cl, Ca, Mg and Na concentration. The SAR (Sodium Adsorption Ratio) and RSC (Residual Sodium Carbonates) were estimated using their respective formula. The categorization of water samples based on their soluble salt content clearly revealed that the water bodies of majority (65%) of areas were hazardous, while 25% areas were marginal. Thus, only 11% water samples of the area under study had useable irrigation water. Because of SAR and RSC the majority (89 and 77%, respectively) of water samples were found to be free from the sodicity hazard. The study concluded that salinity, and not sodicity was the major threat to the area under irrigation with these water bodies. It is, therefore, suggested that the salinity tolerant crops and their genotypes may be used in this area to sustain crop production.


INTRODUCTION
rainfall further worsen the situation and dependent nature of the area. Because of this problem, wise management practices and other resource like groundwater can be used for irrigation purpose according to its quality criteria [1].
Almost all waters containment with salts; however, the quality of water depends on the composition and concentration of ions present in it [2][3]. It is very much critical to recognize the changes in strategies of water suitability for long term productivity of crops [4]. Quality of ground water has been assessed by different scientists in Tharparkar district. They reported that the water samples were saline and sodium hazardous [5][6]. It has been reported that the low quality of groundwater of Pakistan mainly due to available or more soluble salt within it [7]. According to the recent studies, the ground water contains high concentration of soluble salts and sodium ions that are used for irrigation purpose cause soil salinity or soil sodicity [8]. Whereas some water is suitable for irrigation purpose if it contains salt below the hazardous level [9]. This study assesses quality of ground water according to the usability for indigenous crops of the area.

Water Sampling
Populous villages of two taluka of district Tharparkar, i.e.
Mithi and Islamkot, were selected for this study. From the selected 53 locations (25 of Mithi Taluka and 28 of Islamkot Taluka), sampling of ground water from 52 hand pumps and 1 Tube well (Khario Nara) were collected and analyzed through the suggested methods [10]. The depth of water pumps were also noted (

Water Analysis
Collected water samples were analyzed following the suggested protocol [11], for EC iw through standardized digital EC meter (Cyber Scan CON 11, Singapore) and pH using digital pH meter (Lavibond pH110, Singapore). SAR [12] and RSC [12][13] were calculated with the formulas give below:

Statistical Analysis
The data were statistically analyzed for minimum value, maximum value, mean, mode standard deviation and coefficient variance using Microsoft Excel [15].

Chemical Composition and Properties of Groundwater
There are some specific quality parameters of groundwater related to the managing irrigation for better crop production. Parameters including EC iw , pH, different ions, SAR and RSC were used to evaluate the water quality for irrigation purposes [14,16].

Electrical Conductivity
EC is the measurement of conductance in water. The conductance increases with increasing salt concentration in water [17]. The data reported in Table 2 shows that EC iw of groundwater ranges from 0.3-13.5 dS m -1 and 38% of samples recoded (Table 3) above the mean (4.9 dS m -1 ) value. According to classification [14], groundwater containing EC iw values less than 1.5 dS m -1 have been considered as useable, whereas in the range of 1.5-3 dS m -1 as marginal and more than 3 dS m 1 considered as hazardous for irrigating the crops.

pH
The pH indicates the acidity and alkalinity of groundwater and the normal range of pH is 6.5-8.4 for irrigation water [16]. Out of collected 53 groundwater samples 54.7% fall in the normal range and others were above that normal limit. The pH value recorded of groundwater samples were varied from 7.3-9.0 ( Table 2) and mean value (8.06) was in the normal range.

Sodium Adsorption Ratio
The quality of irrigation water mainly depends upon the salinity and sodicity parameters. SAR is the measurement of potential hazardous of Na + over the Ca 2+ and Mg 2+ .
The SAR values are mostly used for predicting the accumulation of Na + in soil that causes the sodicity problem [18]. The minimum SAR (4.0) and maximum SAR (15.5) and mean (7.4) values were recorded ( Table 2) of groundwater samples.

Residual Sodium Carbonates
RSC is the excess value of Ca 2+ +Mg 2+ as of CO

Categorization of Water Samples
Groundwater water samples were categorized [14] in different classes (

Classification of Groundwater Samples
Groundwater samples were classified (

CONCLUSION
Quality of groundwater should be suggested periodically, because the properties of water changes time by time.
Our results reveal that the water samples vary from