Green processes for the management and the valorisation of freshwater ecosystems

Freshwater ecosystems, including streams, rivers, lakes, reservoirs and wetlands, cover less than 1% of the Earth’s surface but support approximately 6% of all described species and provide essential provisioning, regulating, supporting and cultural ecosystem services. Despite their ecological and socio-economic importance, they are among the most threatened environments worldwide due to global change and human pressures such as hydromorphological alterations, habitat degradation, pollution, invasive species and water overexploitation. According to the European Environment Agency, around 63% of EU surface waters had not achieved “good” ecological status in 2021, with little improvement since 2015 despite the objectives of the Water Framework Directive. Freshwater ecosystems remain underrepresented in biodiversity research and conservation planning compared with terrestrial and marine environments. Addressing current knowledge gaps is therefore crucial to support effective environmental policies and management strategies. Within this context, the Circular Economy framework offers innovative opportunities for the protection, restoration and valorisation of freshwater resources. This thesis investigates green processes for the management and valorisation of freshwater ecosystems, in line with the objectives of NODES (“Digital and Sustainable North-Western Italy”), funded by the Italian Ministry of University and Research through the National Recovery and Resilience Plan. Specifically, it contributes to Spoke 2 – Green Technologies and Sustainable Industries, coordinated by the University of Turin. The research is structured around three main topics. The first section addresses knowledge gaps concerning bioindicators used for ecological status assessment. Diatoms are widely recognised as reliable indicators of river quality because of their broad distribution, year-round occurrence and ecological relevance. However, the autecology of many taxa remains poorly understood. This study describes the ecological preferences of more than 400 diatom taxa in the Po River Basin, with particular emphasis on nutrient-related responses. These data were used to define ecological thresholds corresponding to “good” status by analysing relationships between the Italian diatom index (ICMi) and nutrient concentrations. The section also investigates abiotic factors influencing the occurrence of the invasive diatom Achnanthidium delmontii. The second section focuses on pollution from anthropogenic sources and explores bioremediation as a sustainable mitigation strategy. Selected diatom species were tested for their ability to remove nitrate, phosphate and arsenic from water under both controlled conditions, assessing their potential application in water treatment and ecosystem restoration. The third section examines invasive alien species, a major driver of biodiversity loss and habitat degradation. The research focuses on Elodea nuttallii, one of the most widespread aquatic invasive plants of concern in the European Union. The study investigates the biotic and abiotic factors affecting its distribution in an urban river system and evaluates innovative approaches for biomass valorisation as sustainable alternatives to disposal and incineration. Overall, this thesis integrates ecological knowledge with biotechnological and bio-based solutions to support the sustainable management of freshwater ecosystems. By improving understanding of diatom ecology, evaluating nature-based approaches for pollution control and developing circular strategies for invasive plant management, it contributes to enhancing ecosystem resilience and promoting evidence-based environmental management.