Analysis of temporal hydrochemical and isotopic variations in spring waters of Eastern Peloponnesus (Greece)

Abstract

The temporal variation of groundwater hydrochemistry has been used to support observations on the nature of groundwater circulation inside geological terrains of various lithological formations in Eastern Peloponnesus. In the present study, variations in groundwater physical-chemical properties such as electric conductivity, CO2 partial pressure, and calcite saturation index were used to give indications with regard to the nature of the geological formation, the groundwater residence time, and the mode of water circulation inside the hydrogeological systems. Additional isotopic values (δ18Ο) were defined in order to support the aforementioned objectives. The seasonal variations of these properties during three years of monitoring were determined for individual springs appearing in the geological setting of Argolis peninsula, which is mostly composed of carbonate (karstificated in places), ophiolitic and flysch formations. The variation of the parameters was also approached by calculating the coefficient of variation used to detect whether the groundwater flow is of diffuse or/and conduit type. Coefficient of variation values of less than 5% were considered as indicative of the diffuse flow type and therefore a long contact residence time, while higher values were associated with fast-flowing water. However, the isotopic measurements and the overall hydrochemical analysis combined with in situ observations, related to the flow characteristics of the springs, revealed that a spring can be fed by a common diffuse type system although it shows a rather high coefficient of variation.