Seasonal Isotopic Variability and Major Ion Chemistry of the Cauvery River Basin Peninsular India

Abstract

Surface water and groundwater interactions are inherently complex because they occur across a range of spatial and temporal scales. This thesis envisages to improve our understanding of surface water and groundwater in the partially natural and human influenced environment of the Cauvery River Basin (CRB), which will contribute towards a better and efficient managing of water resources in a sustainable way. The primary objective of the thesis is to solve some open ended questions pertaining to the seasonality of stable isotope (and#948;D, and#948;18O) variation within the Cauvery River Basin (CRB) with the aim to characterize the relative contribution of surface water and groundwater to the streamflow by using a two-component mixing model. Secondary objective is to evaluate the sources of dissolved inorganic carbon isotope (and#948;13CDIC) ratios of the Cauvery River and its tributaries within the CRB where the lithology is dominated by a silicate basement in the upper and middle reaches and a carbonate basement in the lower reaches. The study also investigates the major-ion chemistry of river water to quantify the silicate weathering rates (SWR) within the Cauvery River Basin (CRB) over spatial and temporal scales. Sampling was done from 2014 to 2016 which resulted in six seasonal datasets of river water along with measurement of groundwater (GW) composition, comprising of three seasonal datasets. The stable isotope (and#948;D, and#948;18O) measurement recorded a negative seasonal shift in the river water isotopic composition of 8 for and#948;D and 0.95 for and#948;18O between Pre-Monsoon (PM) and South-West Monsoon (SWM) seasons which can be ascribed due to different moisture iii sources during the SWM season and enhanced evaporation from the KRS reservoir during the PM season. The results from the two-component mixing model suggest that groundwater contribution to the stream flow during the PM season was ~57 ± 4% whereas surface runoff serves as the primary component with ~53 ± 7% contribution during the SWM season...