ALPINE LAKES, INDICATORS OF GLOBAL CHANGE: ECOLOGICAL CHARACTERIZATION AND ENVIRONMENTAL PRESSURES IN TWO LAKES FROM ITALIAN ALPS

Alpine lakes are among the most remote aquatic environments in Europe. Although remote, their small size and the high turnover of surface waters render alpine catchments extremely receptive and vulnerable to anthropogenic impact on a local (i.e., water abstraction, tourism, introduction of alien species) and a global scale (long-range transport of pollutants, acid rain, global warming). Alpine lakes are indicators of global environmental change and “early warning systems” for the mountain environment. Many studies have considered single lakes or groups of lakes; however, because of the wide extent of the Italian Alpine area together with the difficulty of sampling, there have been few studies of the Alpine lakes as a whole. Since it was not possible to extend the research to all Italian Alpine lakes, two lakes (Balma Lake, Cottian Alps, 2100 m a.s.l. and Dimon Lake, Carnic Alps, 1872 m a.s.l.) were selected for this study according to the following criteria: a) the geographic location of the research groups involved in the project, Department of Life Sciences, University of Trieste and Istituto Zooprofilattico Sperimentale del Piemonte, Liguria e Valle d’Aosta; b) site geomorphology and accessibility; 3) presence of fish after introduction for recreational fishing. The main aims of this PhD project were: a) conduct ecological characterization based on biotic components (macrobenthic invertebrates, benthic diatoms, ostracods and fish); b) study the pressures and changes via analysis of biotic components; c) obtain background data for future research. The overarching objectives were: 1) obtain topographic and bathymetric maps of lakes using new technologies (drones); 2) characterize the hydrochemistry; 3) characterize macrobenthic invertebrates, benthic diatoms and ostracods since typical biological components of Alpine lakes and widely used to assess ecological status of surface freshwater; 4) investigate changes in chironomids, ostracods and benthic diatoms composition over time based on paleolimnological analysis. These biological components can yield information to different perturbations and, given a good time-control, it is possible to estimate phases and amplitudes of disturbance; 5) investigate environmental contamination through trace elements detection in macrobenthic invertebrates; 6) characterize fish communities, obtaining information about their biological and sanitary condition. Sampling was performed during the ice-free season (summer and autumn of 2017 and 2018) at both lakes. The physicochemical features of the lakes were in line with published literature but differed from each other due to the geo-lithological context of the two areas. The biodiversity of the littoral macrobenthic communities was comparable with other high-altitude environments, where Diptera Chironomidae and Oligochaeta generally predominate. Paleolimnological analysis of Balma Lake highlighted significant differences in subfossil chironomid communities before and after the introduction of fish and between modern and subfossil communities, with a significant reduction in diversity. Macrobenthic invertebrates from the two lakes were found to differ in trace element concentration, which was higher in Dimon Lake. Individuals of bullhead (Cottus gobio) and minnow (Phoxinus phoxinus) were captured from Dimon Lake, whereas only brook trout (Salvelinus fontinalis) were captured from Balma Lake, with individuals belonging to age classes 0+ to 4+. Health monitoring revealed hepatic steatosis in C. gobio from Dimon Lake, probably linked to an adaptation of the fish to the winter season. Finally, the analysis of benthic diatoms and ostracods is preliminary, and the results need to be further elaborated and developed in the future. This PhD thesis has produced new data about the ecology and conservation status of two Alpine lakes, which may guide local administrations in their decisions to implement conservation and monitoring plans.