Environmental tracer approach to discharge evaluation of Pertuso Spring (Italy)

Discharge evaluation of karst springs used for drinking water supply is a key aspect for sustainable management and protection of the environment status of these water resources. Karst spring discharge is influenced by spatial and temporal variability involved in the transfer of water in hydrological cycle. Thus, quantification of karst spring water budget is essential to determine the groundwater available resources and for better understanding its seasonal changes in the hydrological year. This paper deals with the results of the first year of the Environmental Monitoring Plan, related to the catchment project of Pertuso Spring, which is going to be exploited to supply an important water network in the South part of Roma district. The aquifer feeding Pertuso Spring is the most important water resource in the southeast part of Latium Region, Central Italy, used for drinking, agriculture and hydroelectric supplies. This complex hydrogeological system is characterized by a strong local hydraulic connectivity between Aniene River and karst aquifer, witch influence the aquifer water budget. Thus, the application of water budget to evaluate Pertuso Spring discharge can be highly uncertain. The aim of this study is to combine stream discharge measurements and water geochemical properties in order to set up a reliable technique to evaluate karst spring discharge. As a matter of fact, in this paper, it is presented the application of Magnesium as a reliable tracer of discharge evaluation of Pertuso Spring. The concentration values of Magnesium ion have been recorded in some cross sections of the Aniene River, and they have been correlated with discharge values obtained by the traditional current meter, to provide information about groundwater and surface water interactions. The application of Magnesium as an environmental tracer provides a means to evaluate discharge of Pertuso Spring, as it came up to be a marker of the mixing of surface water and groundwater. On the other hand the Magnesium ion concentration provides information on changes in water quantity and quality.