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This paper reports a study of oxygen and redox conditions, trophic status, and phytoplankton community in the meromictic Lake Idro (Italy) from 2010 to 2014. The sequence of causes and effects of meromixis are also evaluated by comparing recent research with studies conducted from the late 1960s to the mid-1990s. In the last half century, Lake Idro was steadily meromictic due to solutes which accumulated in its deep waters, along with both dissolved nutrients and chemically reduced substances produced by the anaerobic microbial metabolism. These substances were retained in bottom waters and made unavailable to upper layers until stratification broke. Mixing episodes occurred in 2005-2006 altering stratification, and oxygen and nutrient distribution within the lake. The potential full overturn effects were also evaluated as potential oxygen consumption due to the oxidation of reduced substances to forecast possible oxygen exhaustion and collapse of biological communities. Finally, meromixis is discussed as a potential threat for deep perialpine lakes using Lake Idro as a reference to comparatively evaluate the present status and possible future trends. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lake Maggiore has reached a stable oligotrophic status after a recovery process from mesotrophy that began in the early 1980s. However, the most recent phytoplankton and water chemistry data seem to indicate that various changes are taking place, including a slight increase in TP values, and almost regular blooms have occurred since 2005. Meteoclimatic data collected over the last few decades in the Lake Maggiore watershed highlight an increase in the frequency of extreme rainfall events. Here, for the period 2000-2013, we analyse the relationships between the phytoplankton dynamics and selected extreme precipitation events, in order to evaluate the possible role of rainfall in affecting the nutrient availability and phytoplankton dynamics. Among the algal groups, cyanobacteria showed the strongest relationship with the precipitation pattern, particularly on a short-term temporal scale. Our results support the hypothesis that rainfall may lead to a short-term increase in nutrients that stimulate the growth of phytoplankton and the development of blooms in summer, when epilimnetic waters are usually nutrient depleted. The almost regular cyanobacterial blooms recorded in Lake Maggiore since 2005 can be interpreted as a response to changing precipitation patterns and therefore as a sign of climate-induced eutrophication. [ABSTRACT FROM AUTHOR]

The official involvement of Italy in Antarctic research dates back to 1985, when Mario Zucchelli Station (the former Terra Nova Bay Station) was established in Terra Nova Bay. Italy joined the Antarctic Treaty in 1987. This article is an overview of the wide-ranging research in marine biology performed in the last three decades by the author's team in the Ross Sea. Fundamental questions have been addressed, related to cold adaptations-with special attention to the molecular bases-evolved by marine organisms along with progressive cooling in this geographic area, also analysed in comparison with other important areas, such as the Peninsula, the Weddell Sea, the sub-Antarctic and the Arctic. The basic stepping stone of this research was the integration of ecophysiology with molecular aspects, in the general framework of biodiversity, adaptation and evolution. Investigations have addressed a number of Ross Sea taxa, comprising fish, birds, urchins, whales, seals and bacteria. Its significance has special meaning in view of the control that Antarctica exerts on the world climate and ocean circulation, which has awakened great interest in the evolutionary biology of the organisms that live there. [ABSTRACT FROM AUTHOR]

Diatoms have been often used to track trophic changes from sedimentary records: recent studies demonstrated that these organisms can even be valuable indicators of climatic variability, although it is often difficult to discriminate the role of trophic and climatic drivers. Moving from the hypothesis that oligotrophication and climate affected the composition of the diatom assemblages by changing the resource ratio, we analysed the vernal diatoms succession in Lake Maggiore, between 1984 and 2007, using multivariate techniques (cluster analysis, canonical correspondence analysis, multivariate regression trees), in order to single out the oligotrophication effects from those attributable to climatic variability. Our results point out that Si, TP, temperature and wind emerged as key explanatory variables in species selection, with a stronger link between trophic and climatic drivers after the lake reached a stable oligotrophic status. Peculiar climate-driven events (deep mixing and floods) affected the in-lake Si:P ratio, giving an advantage to diatoms that are excellent P, but poor Si competitors. The classical role of Fragilaria and Tabellaria as early-warning indicators of eutrophication should be reconsidered, taking into account that both can be useful indicators of climate change, when links between their physiological resource needs and environmental data coming from robust limnological investigations can be established. [ABSTRACT FROM AUTHOR]

The hypothesis that climate changes may strongly interfere with the peculiar hydrological patterns in the Mediterranean basin and alter the structure of the aquatic biota was tested in a shallow Sicilian lake. A phytoplankton survey, carried out monthly in the brackish and shallow Biviere di Gela, in 2005–2007, revealed a transformation in the structure of its phytoplankton assemblage as compared with similar data collected in 1987–1988. An analysis of the trends followed by precipitation and temperature over the last 40 years, showed reduced water inflows, due to increased air temperature and evapotranspiration rather than to a decrease in the amount of precipitation. A consequent reduction in water level occurred, which almost caused the disappearing of the lake at the beginning of the century. This reduction in water level disrupted the littoral zone of the lake and transformed it from a clear, macrophyte-dominated environment to a turbid one characterized by huge summer blooms of the cyanobacteria Aphanizomenon ovalisporum, Cylindrospermopsis raciborskii, and Pseudanabaena limnetica. The addition of freshwater from a nearby dam reservoir, to restore water levels, likely opened the way to another alga, Prymnesium parvum, whose allelopathic and toxic glycosides further contributed to the transformation of the lake biota. On the whole, the Biviere di Gela is an example of how climate changes, coupled with inadequate management procedures, may negatively impact Mediterranean aquatic ecosystems. [ABSTRACT FROM AUTHOR]

‘Venice is sinking while the sea level is rising’ is a common statement in issues concerning the future of the Venice lagoon. The search for a reliable interpretative tool for measured sea-level changes has taken on more urgency since the sea-level rise was indexed as the consequence of global warming—with catastrophic scenarios for both the ecotone and the city, linked to increasing lagoon erosion, sudden modifications of biological equilibriums, loss of wetlands, salt aggression and an increasing frequency of exceptional high tide events. However, the peculiar hydrodynamics of the northern Adriatic Sea, made more complex by the freshwater inflow from the Po River, and the conceptual limits of existing long-term predictive systems, would suggest a more cautious approach to the scenarios yet proposed for the next century. [ABSTRACT FROM AUTHOR]