Francesco Frondini (1), Walter Dragoni (1), Giovanni Chiodini (2), Stefano Caliro (3), Carlo Cardellini (1),Marco Donnini (4), Nicola Morgantini (5), 2016, Short and long term chemical and isotopic variations of Lake Trasimeno (Italy), EGU General Assembly 2016, 17-22/04/2016,
URL: http://www.cnr.it/prodotto/i/405046

Lake Trasimeno, located in Umbria (central Italy), is a shallow lake of a remarkable naturalistic interest and a sig-nificant resource for the economy of the region (Ludovisi and Gaino, 2010; ragoni, 2004). The Lake Trasimenohas an average area of about 124 km2 with a maximum depth of approximately 5.5 m, has no natural outlet andthe volume of water stored is strictly linked to rainfall. In order to limit water level variations in 1898 an efficientoutlet was built. At present the water exits from the Lake only when the level reaches a fixed threshold above theoutlet channel, so during periods with low precipitation the evaporation becomes the most relevant output fromthe lake. For instance, between 1989 and 2013 the outlet did not work, and the maximum depth of the lake wasreduced to little more than three meters. In the framework of climate change, it is important to understand thechanges that could affect Lake Trasimeno in the near future. To this aim it is necessary to individuate the long termtrends of the hydrologic, chemical and physical characteristics of the Trasimeno water and distinguish them fromthe short term variations. At the present it is available a long record of hydrologic data allowing reliable studieson quantitative variations at Lake Trasimeno (Dragoni et al., 2015; Dragoni et al., 2012; udovisi and Gaino,2010), but the definition of the chemical and isotopic trends of lake water it is still a problematic task. On the basisof new chemical and isotopic data, collected from 2006 to 2015, it is possible to observe (i) short term and/orvery short (seasonal) variations in temperature, salinity and saturation state with respect to carbonate mineralsand a long term trends in isotopic composition of water and total load of mobile species (Cl, Na). The short termvariations readily respond to the precipitation regime and are strongly related to lake level; the long term trendis probably related to the progressive increase of near-surface atmospheric temperature observed in the last decades.

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