Integrated Long-Term Spatio-Temporal Assessment of Hydrochemical Attributes of Cauvery River, Southern India

Current study assesses multidecal hydrochemical data of the Cauvery river basin (CRB) to understand spatio-temporal variations, hydrogeochemical facies, irrigation water quality, solute sources, and controlling mechanisms along with statistical analysis and pCO2 estmations. The data used for this study are surface water quality data of CRB for years 1990–2016 on monthly basis. Spatial varations indiacte solutes in downstreams are several times higher than upstreams suggests influence of climatic conditions like sub-humid upstream to semi-arid downstream and anthropogenic activities. Temporal analysis reveals solute concentrations follow the order; pre-monsoon > post-monsoon > monsoon throughout basin suggests control of monsoonal climate in the basin like high precipitation in monsoon season (June–November) resulting in dilution while high temperatures during pre-monsoon season (March–May) leading to evaporation. Gibbs diagram suggests principal solute load regulating mechanism of CRB is water–rock/soil interaction i.e., chemical alteration (weathering) of minerals. The HCO3 normalized Na + K versus Ca + Mg diagram reveals the role of anthropogenic activities and are asserted by scatter plot of Na versus Cl. Further, the correlations and principal component analyses of multidecadal data evince that, chemical weathering follows anthropogenic and atmospheric inputs as the primary mechanism for acquiring solutes in CRB. The irrigation water quality index for year 2016 indicate most of the samples have low and no restriction to irrigational usage. Estimated aqueous pressure of CO2 (pCO2) of CRB waters are higher than the atmospheric pCO2 irrespective of season throughout the basin and an observed decreasing trend of pCO2 with respect to pH signify the extreme chemical weathering nature of the basin.