• Energy Research

Two small high mountain lakes in the Alps were monitored in 1984-2003 to follow their response to changes in human impact, such as deposition of atmospheric pollutants, fish stocking and climate change. The results were compared to occasional samplings performed in the 1940s, and to the remains found in sediment cores. When monitoring started, the most acid-sensitive of them, Lake Paione Superiore, was acidified, with evident effects in its flora and fauna: benthic diatoms assemblage was shifted towards acidophilous species, and zooplankton lost the dominant species, Arctodiaptomus alpinus. Palaeolimnological studies outlined that lake acidification paralleled the increasing input of long-range transported industrial pollutants, traced by spherical carbonaceous particles. On the contrary, the biota of Lake Paione Inferiore appeared to be mainly affected by fish stocking. In the last twenty years, decrease in acid load from the atmosphere led to an improvement in lake water quality, with an increase in both pH and alkalinity. First signs of biological recovery were identified, such as change in diatom flora and appearance of sensitive species among benthic insects. However, climate change and episodic deposition of Saharan dust were important driving factors controlling lake water chemistry. Further monitoring to assess the effects of climate change and of the increasing load of nitrogen and other pollutants is recommended.

Two small high mountain lakes in the Alps were monitored in 1984-2003 to follow their response to changes in human impact, such as deposition of atmospheric pollutants, fish stocking and climate change. The results were compared to occasional samplings performed in the 1940s, and to the remains found in sediment cores. When monitoring started, the most acid-sensitive of them, Lake Paione Superiore, was acidified, with evident effects in its flora and fauna: benthic diatoms assemblage was shifted towards acidophilous species, and zooplankton lost the dominant species, Arctodiaptomus alpinus. Palaeolimnological studies outlined that lake acidification paralleled the increasing input of long-range transported industrial pollutants, traced by spherical carbonaceous particles. On the contrary, the biota of Lake Paione Inferiore appeared to be mainly affected by fish stocking. In the last twenty years, decrease in acid load from the atmosphere led to an improvement in lake water quality, with an increase in both pH and alkalinity. First signs of biological recovery were identified, such as change in diatom flora and appearance of sensitive species among benthic insects. However, climate change and episodic deposition of Saharan dust were important driving factors controlling lake water chemistry. Further monitoring to assess the effects of climate change and of the increasing load of nitrogen and other pollutants is recommended.

Deep lakes south of the Alps (DSL: Maggiore, Lugano, Como, Iseo and Garda) are characterised by varying trophic states and dissolved oxygen (DO) concentrations. Some of these lakes experience anoxic conditions in deep waters. We hypothesised that the increase in temperature and water-column stability observed in these lakes during recent decades influenced the deep-water DO concentration. In particular, we tested whether the thermal regime of the lakes and the depth of mixing affect oxygen replenishment during winter-spring turnover. To this aim, we analysed long-term trends and seasonal variability of oxygen levels in the DSL during 1992-2016. We included in our analysis the effects of environmental variables, such as winter air temperature and atmospheric modes of variability. Our results showed a recent decrease in the deep-water oxygen content in lakes Maggiore, Como and Garda and an increase of the extent of anoxic conditions in lakes Lugano and Iseo. Our results suggest that, beside cultural eutrophication, rising environmental pressures, such as global warming, can influence the future trends of the oxygen levels and ecological states of deep lakes.

Deep lakes south of the Alps (DSL: Maggiore, Lugano, Como, Iseo and Garda) are characterised by varying trophic states and dissolved oxygen (DO) concentrations. Some of these lakes experience anoxic conditions in deep waters. We hypothesised that the increase in temperature and water-column stability observed in these lakes during recent decades influenced the deep-water DO concentration. In particular, we tested whether the thermal regime of the lakes and the depth of mixing affect oxygen replenishment during winter-spring turnover. To this aim, we analysed long-term trends and seasonal variability of oxygen levels in the DSL during 1992-2016. We included in our analysis the effects of environmental variables, such as winter air temperature and atmospheric modes of variability. Our results showed a recent decrease in the deep-water oxygen content in lakes Maggiore, Como and Garda and an increase of the extent of anoxic conditions in lakes Lugano and Iseo. Our results suggest that, beside cultural eutrophication, rising environmental pressures, such as global warming, can influence the future trends of the oxygen levels and ecological states of deep lakes.

Lake Maggiore is the second largest lake in Italy, with a surface area, maximum depth and volume respectively of 212 km2, 370 m, and 37.5 km3. Politically, the catchment belongs in equal parts to Italy and Switzerland. Lake water is used for tourism, recreational-environmental activities, public and private navigation, professional and sport fishery, hydroelectric production, irrigation and drinking. Long-term studies provide a history of industrial pollution and eutrophication followed by successful re-oligotrophication. Thermal studies show an increase in the water temperature in the 0-30 m layer of about 1.4 °C during the last 45 years. The new physical conditions of the water column, coupled with an increase of recreational uses and the trade in exotic aquarium species, resulted in an increase of cyanobacteria blooms and alien species introduction (Dreissena polymorpha, Corbicula fluminea, Sinanodonta woodiana, Procambarus clarkii and Orconectes limosus). The water European Directive (2000/60/EC) classifies as "lowest quality" typology those lakes which have exotic species.

Lake Maggiore is the second largest lake in Italy, with a surface area, maximum depth and volume respectively of 212 km2, 370 m, and 37.5 km3. Politically, the catchment belongs in equal parts to Italy and Switzerland. Lake water is used for tourism, recreational-environmental activities, public and private navigation, professional and sport fishery, hydroelectric production, irrigation and drinking. Long-term studies provide a history of industrial pollution and eutrophication followed by successful re-oligotrophication. Thermal studies show an increase in the water temperature in the 0-30 m layer of about 1.4 °C during the last 45 years. The new physical conditions of the water column, coupled with an increase of recreational uses and the trade in exotic aquarium species, resulted in an increase of cyanobacteria blooms and alien species introduction (Dreissena polymorpha, Corbicula fluminea, Sinanodonta woodiana, Procambarus clarkii and Orconectes limosus). The water European Directive (2000/60/EC) classifies as "lowest quality" typology those lakes which have exotic species.

Eleven stations located at different altitudes in the Italian part of the Lake Maggiore watershed (North-Western Italy) were selected to highlight trends in temperature and precipitation. The data available cover a period of about 30 years for six of the stations and 60-70 years for five sites. Data (maximum and minimum temperatures, precipitation amount, snow cover) were collected on a daily basis, and monthly, annual and seasonal values calculated. The results clearly showed increasing trends of temperature at most sites, with different significance for minimum and maximum temperatures and for the different seasons. Examination of the longest data series suggests that it is mainly in the last 30 years that this tendency towards warming has emerged. No significant trend emerged for precipitation amount, apart from a decrease recorded at one site. The analysis of data on a daily basis at four stations showed that precipitation volume has been quite constant in the last 70 years, while the number of rainy days per year has been decreasing, a particularly striking trend over the last 25-30 years. These results lead to the hypothesis that there has been an increasing occurrence of stormy precipitation events in the last decades.