Estimating the Isotopic Altitude Gradient for Hydrogeological Studies in Mountainous Areas: Are the Low-Yield Springs Suitable? Insights from the Northern Apennines of Italy

Abstract

Several prior studies investigated the use of stable isotopes of water in hydrogeological applications, most on a local scale and often involving the isotopic gradient (evaluated by exploiting the so-called altitude effect), calculated on the basis of rainwater isotopes. A few times, this gradient has been obtained using the stable isotopic contents of low-yield springs in a limited time series. Despite the fact that this method has been recognized by the hydrogeological community, marked differences have been observed with respect to the mean stable isotopes content of groundwater and rainwater. The present investigation compares the stable isotopic signatures of 23 low-yield springs discharging along two transects from the Tyrrhenian sea to the Po Plain of Italy, evaluates the different isotopic gradients and assesses their distribution in relation to some climatic and topographic conditions. Stable isotopes of water show that groundwater in the study area is recharged by precipitation and that the precipitation regime in the eastern portion of the study area is strongly controlled by a shadow effect caused by the Alps chain on the air masses from central Europe. Stable isotopes (in particular the δ18O and deuterium excess (d-excess) contents together with the obtained isotopic gradients) allow us to identify in the study area an opposite oriented orographic effect and a different provenance of the air masses. When the windward slope is located on the Tyrrhenian side, the precipitation shows a predominant oceanic origin; when the windward slope moves to the Adriatic side, the precipitation is characterized by a continental origin. The main results of this study confirm the usefulness of low-yield springs and the need for a highly detailed survey-scale hydrological investigation in the mountainous context.

Exploring mobility in Italian Neolithic and Copper Age communities

“…With this in mind, we could observe that converted values from the samples of Buca di Spaccasasso (SS), Grotta Nisco (GN) and all the sites scattered in the Roman area are consistent with modern precipitations; the lower values recorded at Celano Pratovecchio (CE) might instead be associated to the location of this site on the Apennines mountain chain, with peaks higher than 2000 mt a.s.l.. These areas are typically characterised by low mean annual temperatures and consequent low δ 18 O values in precipitations 59 , 60 , 72 , 73 . The samples from Fontenoce di Recanati (FR) are also characterised by relative low oxygen isotope values, though this site is located at a much lower altitude than Celano (CE).…”

“…Human teeth from Grotta Nisco (GN, n = 7) show similarly high δ 18 O values (26.9 ± 0.5 ‰), which converted to environmental waters give values of − 6.0 ± 0.9‰, (Table S1) consistent with modern local precipitations (− 6 to − 7‰ 72 , 73 ).…”

The Role of Faults in Groundwater Circulation before and after Seismic Events: Insights from Tracers, Water Isotopes and Geochemistry

“…To fill the gap between 974 m and 1800 m, 11 minor punctual springs in the area have been selected. The small selected springs are characterized by a low flowrate during the entire hydrologic year and accordingly to their limited extensions and elevation of recharge area (not so different form the punctual spring altitude) and their rapid flow response to the rainfall events, they can be used as natural pluviometers [54][55][56]. All the minor springs were monthly sampled during the entire hydrologic year in 2017.…”

Using Stable Isotope Analysis (δD and δ18O) and Tracing Tests to Characterize the Regional Hydrogeological Characteristics of Kazeroon County, Iran

“…Only groundwater feeds the springs during a dry season. In this way, the isotopic value measured in the dry period can be considered to be an average of the entire seasonal recharge that occurs mainly during the wet season [46].…”

“…The altitude effect is a temperature related feature and presents depletion of isotopic values with increasing elevation. It can be a useful tool in determining altitude of the recharge areas [46]. During orographic uplift, the air masses cool and heavier isotopes precipitate the former, resulting in precipitation depleted in 18 O.…”