water Article An Endorheic Lake in a Changing Climate: Geochemical Investigations at Lake Trasimeno (Italy) Francesco Frondini 1,* , Walter Dragoni 1 , Nicola Morgantini 2, Marco Donnini 3, Carlo Cardellini 1, Stefano Caliro 4 , Massimo Melillo 3 and Giovanni Chiodini 5 1 Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via Pascoli snc, 06100 Perugia, Italy 2 Arpa Umbria, Agenzia regionale per la protezione ambientale, Via Pievaiola 207/B-3 San Sisto, 06132 Perugia, Italy 3 Consiglio Nazionale delle Ricerche, Istituto di Ricerca per la Protezione Idrogeologica, Via della Madonna Alta 126, 06128 Perugia, Italy 4 Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli Osservatorio Vesuviano, Via Diocleziano 328, 80124 Napoli, Italy 5 Istituto Nazionale di Geofisica e Vulcanologia, sezione di Bologna, Via Creti 12, 40128 Bologna, Italy * Correspondence:
[email protected] Received: 18 May 2019; Accepted: 24 June 2019; Published: 26 June 2019 Abstract: Lake Trasimeno is a shallow, endorheic lake located in central Italy. It is the fourth Italian largest lake and is one of the largest endorheic basins in western Europe. Because of its shallow depth and the absence of natural outflows, the lake, in historical times, alternated from periods of floods to strong decreases of the water level during periods of prolonged drought. Lake water is characterised by a NaCl composition and relatively high salinity. The geochemical and isotopic monitoring of lake water from 2006 to 2018 shows the presence of well-defined seasonal trends, strictly correlated to precipitation regime and evaporation. These trends are clearly highlighted by the isotopic composition of lake water (δ18O and δD) and by the variations of dissolved mobile species.