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

Abstract

Karst aquifer recharge areas are usually difficult to identify because of the complexity of these aquifers’ characteristics. On the other hand, their identification is very important in the aim of protecting the groundwater resources that these aquifers host. Regarding this topic, this paper presents an approach aimed at identifying karst aquifer recharge areas by the application of oxygen-18 and deuterium isotopes composition of groundwater coupled with hydrological features. Oxygen-18 and deuterium isotope composition of Capodacqua di Spigno Spring, in the South of the Latium Region, has been applied with rainfall and discharge values related to the feeding aquifer of this spring. As δ18O and δ2H values of groundwater samples are natural tracers of the recharge area’s elevation, we propose a model, based on the distribution of the basin surfaces involved as recharge areas, in relation to elevations. The model estimates, for any discharge value, the percentage of the topographic area involved in the aquifer recharge. The setting up of this simulated distribution is supported by a Weibull cumulative probability function. The results show that the measured discharges increase as larger areas with lower elevations are involved in the recharge process.

Responses of Spring Discharge to Different Rainfall Events for Single-Conduit Karst Aquifers in Western Hunan Province, China

“…Many methods are applied to identify karst groundwater systems, such as hydrogeochemical analysis [ 10 ], environmental isotope method [ 11 , 12 , 13 ], time-series analysis [ 14 , 15 ] and artificial tracer tests [ 16 , 17 ]. Tracer tests provide the most effective means for identifying the point-to-point connections between flow inputs (sinkholes or sinking streams) and outputs (springs).Tracer test can not only identify the flow path of karst groundwater, but also can calculate the geometric parameters (transport velocities and dispersion) of groundwater flow, which is helpful to analyze the internal structure of karst aquifers [ 18 ].…”

Karst Recharge Areas Identified by Combined Application of Isotopes and Hydrogeological Budget

“…The latter is performed using the empirical method for estimating potential evapotranspiration (PET) proposed by Thornthwaite (1948) [22], applied to the inverse hydrogeological budget method (IHBM) [23][24][25]. Specifically, in the present study, the previously mentioned isotope-driven model [21] has been improved. The model extension consists of a preliminary check procedure to estimate the influence degree of seasonality combined with amount effect of rainfall (input) on spring water (output).…”

“…In fact, the elevation identified by the isotope is always an average recharge elevation. Based on this consideration, an isotope-driven model has been set up [21], which estimates, for any discharge value of a spring, the percentage of the topographic area involved in the aquifer recharge and its spatial distribution. Specifically, the model identifies the main recharge areas according to the oxygen and hydrogen isotopes' (δ 18 O and δ 2 H) rates of variation, which are detected in groundwater samples taken at the spring.…”

Magnesium as Environmental Tracer for Karst Spring Baseflow/Overflow Assessment—A Case Study of the Pertuso Karst Spring (Latium Region, Italy)

“…The difficulty in having karst spring discharge data and defining a single fixed crosssection, related both to the activation of different circulation mechanism of groundwater within the aquifer both to lack of in-depth monitoring, implied the increasing of artificial and environmental tracer application to assess karst spring discharges, different water sources and pathways, groundwater residence times and other hydrogeological processes [27,[31][32][33][34][35][36].…”

“…Other environmental tracers, as major ions and isotopes, which differently from the artificial ones do not require injection points, can be naturally detected sampling spring water at different times during the hydrological year and carrying out subsequent laboratory analyses [27,31,32,[40][41][42][43][44][45][46]. For example, in karst setting with predominance of limestone reservoirs, the Mg 2+ /Ca 2+ ratio is usually used to assess groundwater residence time, whereas in dolomitic geological settings the lower hydraulic conductivity of rocks, compared with that of limestone, favours the Mg 2+ concentration increasing, as the waterrock interaction is longer.…”