An Endorheic Lake in a Changing Climate: Geochemical Investigations at Lake Trasimeno (Italy)

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. In the long term, a progressive warming of lake water and a strong
increase of total dissolved inorganic solids have been observed, indicating Lake Trasimeno as a
paradigmatic example of how climate change can cause large variations of water quality and
quantity. Furthermore, the rate of variation of lake water temperature is very close to the rate of
variation of land-surface air temperature, LSAT, suggesting that shallow endorheic lakes can be
used as a proxy for global warming measurements.