Freshwaters in a changing climate: effects of water scarcity on the (photo)chemistry of Alpine streams

The term “alpine” has two quite different meanings. When the word is capitalized, Alpine streams refer to running waters of the Alps, at any elevation. When not capitalized, alpine streams refer to running waters of the alpine zone above the tree line, anywhere in the world. In this PhD thesis, the first context was adopted. The work described in the following sections sought to examine, at least in part, the effects of climate change-related drought conditions on the chemistry of streams born from and flowing through the Italian Alps. A sampling campaign was carried out on three streams of the Piemonte region, Italy, through the whole year 2022, which has been defined as one of the worst ever experienced by Alpine water courses. The analysis of nutrient concentrations downstream of the wastewater treatment plants operating on the rivers allowed to get insights into the impacts of their effluents on the final receiving basins under drought conditions. The streams displayed some shared features, e.g. higher nutrient concentrations downstream, most marked in the lowest flows months. For the Stura di Lanzo, the Principal Component Analysis (PCA) showed some interesting negative correlations between the chemical variables and the flow regimes. Moreover, correlations with the ecological and microbiological variables in the same conditions were looked for. The hydrological and chemical parameters measured on one of the streams were used to model the photochemistry transformation of three common pollutants (acetaminophen, diclofenac and naproxen) under the same water scarcity conditions. The modelling highlighted how the chemical and hydrological conditions determined by the drought in 2022 actually shaped the photochemical transformation of the pollutants (e.g. the increased nitrate, nitrite and organic carbon concentrations during low flows enhanced the photodegradation by •OH and 3CDOM* downstream of the WWTP, whereas shallower and slower waters led to an increased direct photolysis). An enhanced photochemical transformation rate under drought conditions, however, does not necessarily lead to a sufficient removal of the compounds before they reach the sea. Besides this, the photochemistry of a pool of pharmaceuticals (chlorpromazine, lamotrigine and tiapride) traced by UHPLC-HRMS-QTOF in the sampled river waters was studied. Direct photolysis and indirect photochemistry were described, transformation products formed by photolysis identified and the second order reaction rate constants measured through nanosecond Laser Flash Photolysis. The effects of both 2022 drought and varying DOC, NO3− and water depth on the behavior of the three molecules were then investigated by photochemical modelling. In the last part of the work, the focus was shifted towards sustainable methods for the removal of contaminants from wastewaters, to prevent them from reaching the natural environment. The efficiency of ZVI-Fenton process at pH 4 in eliminating a selection 2 of contaminants of emerging concern (CECs) and bacteria from secondary municipal wastewater was assessed and compared to the results obtained with the same method at different pH values. The tested treatment was proven to be rather effective in the degradation of both the contaminants (ibuprofen, cefazolin and sulfamethoxazole) and the microorganisms, but at the same time the results call for further studies to overcome the main issues related to the pH limitations.