Water management is facing a growing number of challenges in many river basins worldwide, as the equal distribution of the available water resources is increasingly influenced by several, uncertain climatic and anthropic pressures. Within the current and projected water scarcity and drought scenario, such issue represents even a greater challenge in those basins that have been massively regulated in the XX century, as water managers are asked to find balanced policies to stay ahead with multiple, interdependent and ever-increasing water-related requirements. In this context, water conflict has become a recurring problem, with the freshwater ecosystems becoming the sole providers of unbearable human water needs and experiencing a severe alteration of their natural renewability and ecological integrity. In fact, the concern of sustaining the freshwater ecosystems has evolved throughout the years, coming to the fore since the 1990s under the concept of "ecosystem services", defined as the multiple benefits that people obtain from ecosystems. With a high number of challenges still ahead for implementing such paradigm in real-world water management practices, few investigations inspect the long-term evolution of highly regulated basins, being vulnerable freshwater systems characterized by a profusion of ecosystem services in a context of complex management policies and changing anthropic and climatic pressures. We focus our attention on the highly interconnected Garda-Mincio system (Northern Italy), further broadening the results to the regulated basins of the European perialpine region. First, to examine the modification of the freshwater systems from their pristine to their regulated conditions, we carried out an extensive collection of daily hydro-meteorological data by consulting public online sources as well as digitizing historical data contained in hand-written documents. The resulting database, which represents a valuable source of long-term daily hydro-meteorological data for the Garda-Mincio system, additionally underscored the complexity of constructing and maintaining a consistent and up-to-date database within an inter-regional context. The collected data were then adopted to investigate the climatic and anthropogenic drivers that have progressively influenced water availability, the provision of the changing water demands and the trade-offs with the existing water ecosystem services over the last two centuries. Statistical analyses were performed to outline the evolution of the annual and seasonal trends of Lake Garda water levels and outflows over the period 1888-2020, discussing the role of the Salionze Dam operational rules (completed in 1951) as well as the influence of the main water needs of the downstream Mincio River basin (i.e. hydropower production, irrigation and fluvial ecosystem sustenance). The role of hydro-meteorological factors was assessed by implementing a water balance model for Lake Garda, the largest lake in Italy, over the period 1928-2020, performing uncertainty and sensitivity analyses on specific water balance components (i.e. over-lake evaporation and basin evapotranspiration). We then focus our analyses on the management of the hydraulic infrastructures that regulate the first and highly water-stressed stretch of the Mincio River downstream Lake Garda, i.e. the Salionze Dam and the Pozzolo-Marenghello infrastructures, where both high and low flow conditions reveal the inability of the current operational rules to support the new variety of water abstractions while maintaining appropriate environmental flow conditions and flood protection. These analyses were carried out through in-situ measurements and numerical simulations, updating the aging rating curves of the existing hydraulic infrastructures. Drawing on the Garda-Mincio system, we inspected the evolution of the freshwater regimes within the European perialpine lakes framework, discussing the outcomes to describe which common factors drove management policies in the area. Eventually, we discuss our outcomes recommending future sustainable and adaptive water management policies in the area.

Sediment records of two Italian subalpine lakes (Lake Garda and Lake Ledro) were analyzed in order to reconstruct their ecological evolution over the past several hundred years. A multi-proxy and multi-site approach was applied in order to disentangle the effects of local anthropogenic forcings, such as nutrients, and climate impacts on the two lakes and their catchments. Biological indicators (sub-fossil pigments, diatoms and Cladocera) were used to reconstruct changes in the aquatic food web and to define the lake reference conditions, while geochemical methods, i.e. wavelength-dispersive X-ray fluorescence spectroscopy (WD-XRF), were used to provide quantitative information on the different physical or chemical processes affecting both lake and catchment systems. Sub-fossil pigments and diatoms, together with their respective inferred TP values, suggested very stable oligotrophic conditions in both lakes until the 1960s. The period following was affected by nutrient enrichment, which led to a drastic shift in the phytoplanktonic community. The response of sub-fossil pigments and diatoms to major climatic anomalies such as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA) were not pronounced, and the taxonomic composition remained relatively stable. On the contrary, these proxies showed an indirect response to climate variability since the beginning of the nutrient enrichment phase in the 1960s. In Lake Garda, the winter temperature regulates the water column mixing, which in its turn controls the degree of nutrient fertilization of the entire water column, and the related phytoplankton growth. In Lake Ledro a rapid reorganization of planktonic diatoms was observed only during the temperature recovery after the LIA, while recent temperature effects are masked by the prevailing nutrient effects. In Lake Garda, Cladocera remains responded in quantitative and qualitative terms to climatic changes, whereas in Lake Ledro they appeared to be mainly affected by variations in hydrological regimes, i.e. flood events. Cladocera remains corroborated the nutrient enrichment after the 1960s in both lakes as inferred by diatoms and pigments. In Lake Garda, the geochemical data showed a pronounced shift in elemental composition since the mid-1900s, when major elements and lithogenic tracers started to decrease, while some elements related to redox conditions and other (contaminant) trace elements increased. The general trends since the mid-1900s agree with the biological records. However, some differences recorded in the two different basins of Lake Garda reflected the effects of local conditions, both related to hydrology and sedimentation patterns. Lake Ledro showed higher short-term variability for most elements, even though some features were comparable to Lake Garda. The geochemical record of Lake Ledro revealed a major influence of human-induced lake-level fluctuations and catchment properties. This paleolimnological study allows us to place temporally restricted limnological surveys into a longer-term secular perspective, which is highly valuable for the definition of lake reference conditions. Because the restoration targets are usually based on the lake reference conditions, this study highlighted also the necessity to pay particular attention to the lake-specific sensitivity patterns. The multi-proxy and multi-site approach showed that the lake conditions of large and deep lakes in northern Italy, such as Lake Garda, are mainly driven by nutrient enrichment and/or climate change. In contrast, smaller lakes with larger catchment areas, such as Lake Ledro, are seemingly more impacted by conditions and processes occurring in the drainage basin.