Evaluation of geogenic and anthropogenic impacts on spatio-temporal variation in quality of surface water and groundwater along Cauvery River, India

Abstract

Assessment of groundwater and surface water quality along a river is important as it directly affects the agricultural, industrial activities and population. The objective of the study is to assess the quality of the Cauvery river water and adjacent groundwater for drinking and irrigational purposes and to identify the infuence of geogenic and anthropogenic sources. Groundwater and surface water samples were collected along the course of the river at approximate intervals of 25 km. The samples were analysed for electrical conductivity, pH, sodium, calcium, magnesium, potassium, bicarbonate, chloride and sulphate. Sodium was identified as the dominant cation and bicarbonate was the dominant anion for both river water and groundwater. These values were compared with limits recommended by the Bureau of Indian Standards for drinking purposes. The total dissolved solids were found to exceed the permissible limits for drinking water in most of the groundwater samples, and it was below the permissible limits in river water samples. Most of the river water samples were found to be suitable as per the drinking water quality standards, but most of the groundwater samples were unsuitable based on the concentration of major ions. Irrigation water quality was also assessed based on magnesium hazard, residual sodium carbonate, sodium percentage, sodium adsorption ratio, permeability index and salinity hazard. Most of the river water samples collected were suitable for irrigation, whereas most of the groundwater samples collected were doubtful for irrigation based on residual sodium carbonate and sodium percentage. Drinking water and irrigation water quality indices were also computed to assess the characteristics of water. Groundwater quality in locations nearer to the confluence of tributaries and industrial areas was of poor quality, while both river water and groundwater near the coast were poor, both for drinking and irrigation purposes. Comparison of the dissolved load with other rivers of the world was also made, which reveals that the Cauvery River yields comparatively higher dissolved load per area than most of the rivers. The chemical load in the river is due to natural and anthropogenic sources. Therefore, it is necessary to enforce the existing norms for the discharge of treated effluents by industries and townships along the river so as to reduce the chemicals contributed by anthropogenic sources.