Recent trends in chloride and sodium concentrations in the deep subalpine lakes (Northern Italy)

Rogora, Michela and Mosello, Rosario and Kamburska, Lyudmilla and Salmaso, Nico and Cerasino, Leonardo and Leoni, Barbara and Garibaldi, Letizia and Soler, Valentina and Lepori, Fabio and Colombo, Luca and Buzzi, Fabio (2015) Recent trends in chloride and sodium concentrations in the deep subalpine lakes (Northern Italy). Environmental Science and Pollution Research. ISSN 0944-1344

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A growing concern exists about the effects of chlo- ride (Cl) on freshwater systems. Increasing Cl concentrations have been observed in the last few decades in several rivers and lakes, mainly in northern countries. In Italy, present levels and temporal changes of sodium (Na) and Cl in water bodies have rarely been assessed. Based on long-term data for the lakes of the subalpine district in Italy (Maggiore, Lugano, Como, Iseo, Garda), we analyzed trends affecting Cl and Na concentrations during the last 25 years, with the aim of iden- tifying temporal changes and assessing possible causes. An in- depth analysis is presented for Lake Maggiore. Positive tem- poral Na and Cl trends were evident in all studied lakes, with the trends increasing since early 2000s. Data for Lake Maggiore tributaries showed a clear seasonality (higher values in winter and early spring). The NaCl used as road de-icing agent, together with Cl discharge from wastewater treatment plants, were identified as the main causes for the observed trends. Chloride concentrations in the lakes are below the threshold limit for reduced water quality and below concen- trations known to harm aquatic biota. However, considering the relevance of deep subalpine lakes, representing almost 80 % of the total freshwater volume in Italy, these trends indicate an important chemical change, which warrants further analysis.

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