Chemical quality status of groundwater for irrigation in some selected aquifers of Bangladesh

摘要

The chemical quality of groundwater for irrigation has a considerable impact on soil-plant system because its quality is based upon type and quantity of dissolved ionic constituents. Considering this fact, an attempt was made to collect 20 groundwater samples from the selected aquifers of three districts viz., Pabna, Rangpur and Netrakona of Bangladesh in order to classify them on the basis of their suitability for irrigation usage. The chemical analyses included pH, EC, TDS, cations (Ca, Mg, K, Na, Fe and Mn) and anions (CO3, HCO3, Cl, BO3, PO4 and SO4). Groundwater samples were acidic to alkaline (pH=6.20-8.40) in nature and were not problematic for crop production except two samples. TDS values of all the water samples were rated as fresh water (TDS<1,000 mg L-1) in quality. EC and SAR indicated low salinity (C1) to medium salinity (C2) and low alkalinity (S1) hazards combinedly expressed as C1S1 and C2S1. As per EC values, all the collected samples could be safely applied for crops growing on soils with moderate level of permeability and leaching. SAR values were excellent in quality for irrigating soils and crops. On the basis of SSP, 14 samples were excellent, 5 samples were good and the rest 1 sample was permissible classes. Groundwaters were free from RSC and belonged to suitable in category. Out of 20 samples, only 1 sample was moderately hard, 17 samples were hard and the rest 2 samples were very hard in quality. In the study areas, Mn ion in 9 samples and HCO3 ion in 7 water samples were treated as contaminants for continuous long-term irrigation system. The detected levels of Fe, Cl, BO3, PO4 and SO4 in groundwater samples were below the permissible limit as irrigation water and might not pose threat to soil environment. The relationship between chemical quality parameters like pH, EC, TDS, SAR, SSP, RSC and HT was established and combinations such as pH vs TDS, EC vs TDS, SAR vs SSP, RSC vs HT and pH vs HT exhibited significant positive correlation. Conclusively, groundwater samples could be safely applied for irrigating soils and crops grown in the study areas but some groundwater samples should be treated to remove Mn and HCO3 ions as contaminants for better utilization of continuous long-term irrigation system.