A Comparative Study of Ion Chemistry of Groundwater Samples of Typical Highland and Midland Sub-watersheds of the Manimala River Basin, Kerala, South India

Abstract

Results of the detailed study of the chemistry of ions present in the groundwater samples of Peruvanthanam and Valiyathodu sub-watersheds of the Manimala river basin are analysed using the AQUACHEM 4.0 software to understand general chemical characteristics and geochemical processes involved. The study reveals that cations, such as sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) and anions, such as bicarbonate (HCO₃^-), sulphate (SO₄^2-), chloride (Cl^-), nitrate (NO₃^-) are present. Recognition methods such as (a) Box and Whisker diagram (b) Piper diagram (c) Durov diagram (d) Radial plot and (e) Stiff diagram were prepared to delineate the seasonal variations in chemical constituents. The major ionic concentration of the groundwater samples of Peruvanthanam sub-watershed is Mg²⁺>Ca²⁺>HCO₃^->Cl^->SO₄^2->NO₃^->Na⁺>K⁺ and that of Valiyathodu is Mg²⁺>Ca²⁺>HCO₃^->Cl^->NO₃^->SO₄^2->Na⁺>K⁺. A critical analysis of Piper diagram reveals that in Peruvanthanam sub-watershed the pre monsoon groundwater samples belong to the zone of bicarbonates, chloride and sulphates, the monsoon season samples belong to the bicarbonate and chloride zone and the post monsoon samples belong to the zone of prevailing bicarbonates. In Valiyathodu sub-watershed, the pre monsoon and post monsoon samples have dominant bicarbonates, while the monsoon samples show predominance of both bicarbonates and chloride. Radial plots and Stiff diagrams for Peruvanthanam sub-watershed show that Mg²⁺-Ca²⁺-HCO₃^-, Mg²⁺-Ca²⁺-Cl^- and Mg²⁺-Ca²⁺-HCO₃^-- Cl^- are the dominant water types during the pre monsoon season. Mg²⁺-Ca²⁺-HCO₃^--Cl^-, Mg²⁺-Ca²⁺-Cl^-- HCO₃^- and Mg²⁺-Ca²⁺-HCO₃^--Cl^--SO₄^2- are dominant during the monsoon and Mg²⁺-Ca²⁺-HCO₃^- and Mg²⁺-Ca²⁺-HCO₃^--Cl^- are the dominant water types during the post monsoon season. In Valiyathodu sub-watershed during the pre monsoon - Mg²⁺-Ca²⁺-HCO₃^--Cl^- and Mg²⁺-Ca²⁺-HCO₃^-, during the monsoonm - Mg²⁺-Ca²⁺- HCO₃^--Cl^-, Mg²⁺-Ca²⁺-Cl^-- HCO₃^- and Ca²⁺-Mg²⁺-HCO₃^--Cl^-, and during the post monsoon - Mg²⁺-Ca²⁺-HCO₃^--Cl^- and Ca²⁺-Mg²⁺-HCO₃^--Cl^- are the dominant water types.

DOI: http://dx.doi.org/10.5755/j01.erem.66.4.4037