Identifying Karst Aquifer Recharge Areas using Environmental Isotopes: A Case Study in Central Italy

Abstract

Water resources management is one of the most important challenges worldwide because water represents a vital resource for sustaining life and the environment. With the aim of sustainable groundwater management, the identification of aquifer recharge areas is a useful tool for water resources protection. In a well-developed karst aquifer, environmental isotopes provide support for identifying aquifer recharge areas, residence time and interconnections between aquifer systems. This study deals with the use of environmental isotopes to identify the main recharge area of a karst aquifer in the Upper Valley of Aniene River (Central Italy). The analysis of 18O/16O and 2H/H values and their spatial distribution make it possible to trace back groundwater recharge areas based on average isotope elevations. The Inverse Hydrogeological Balance Method was used to validate spring recharge elevations obtained by the use of stable isotopes. Areas impacted by direct and rapid rainfall recharge into the study area were delineated, showing groundwater flowpaths from the boundaries to the core of the aquifer. The results of this study demonstrate the contribution that spatial and temporal isotope changes can provide to the identification of groundwater flowpaths in a karst basin, taking into account the hydrogeological setting.

Karst Spring Recharge Areas and Discharge Relationship by Oxygen-18 and Deuterium Isotopes Analyses: A Case Study in Southern Latium Region, Italy

“…where R = 2 H/ 1 H for hydrogen and 18 O/ 16 O for oxygen, the ratio of the heavy to light isotope and RSMOW is the isotopic ratio of the standard (Standard Mean Ocean Water) [1].…”

“…where R = 2 H/ 1 H for hydrogen and 18 O/ 16 O for oxygen, the ratio of the heavy to light isotope and R SMOW is the isotopic ratio of the standard (Standard Mean Ocean Water) [1]. Results, shown in Table 1, are expressed as per million deviations from the internationally accepted standard VSMOW according to Equation (1).…”

“…where R = 2 H/ 1 H for hydrogen and 18 O/ 16 O for oxygen, the ratio of the heavy to light isotope and R SMOW is the isotopic ratio of the standard (Standard Mean Ocean Water) [1]. Results, shown in Table 1, are expressed as per million deviations from the internationally accepted standard VSMOW according to Equation (1). The analytical error is ±0.2% for δ 18 O and ±1% for δ 2 H. During the same days, that groundwater samples were taken, and discharge measurements were carried out along the river near Capodacqua di Spigno Spring, by the current-meter.…”

“…Therefore, identifying recharge areas coupled with karst aquifer hydrogeological characteristics, which are related to the main kind of groundwater drainage, is important information for sustainable management of these groundwater resources. This is important as groundwater coming from karst aquifers is a key source of fresh water for human supply [1].…”

“…In particular, oxygen-18 and deuterium isotopes have been applied, as environmental tracers of karst spring discharge, to determine the quantitative characteristics of Capodacqua di Spigno Spring. These stable isotopes, which have been already used in several studies to determine the mean altitude of the recharge area of aquifers [1,10,14], have also been involved in this study to define how the recharge area of Capodacqua di Spigno Spring varies according to the discharge, supplied by the same spring, in different periods of the year.…”