Soils are a dominant source of nitrous oxide (N2O), a potent greenhouse gas. The complexity of drivers of N2O production and emissions has hindered our ability to predict the magnitude and spatial dynamics of N2O fluxes. Soil moisture can be considered a key driver because it influences oxygen supply, which feeds back on N2O sources (nitrification versus denitrification) and sinks (reduction to dinitrogen). Soil volumetric water content is directly linked to dissolved oxygen and to redox potential, which regulate microbial metabolism and chemical transformations in the environment. The relationship between soil moisture and N2O is usually based on incubations of soil at different soil moisture levels. Few studies have focused on the interaction between soil moisture and nitrogen dynamics in the vadose zone. In this thesis soil column and chamber experiments were performed in order to investigate the relationship of soil moisture dynamics to redox sensitive nitrogen dynamics in the organic matter layer of a pasture peatland in Sacramento, Bay Delta area, California. Field data has been analyzed and statistics has been used to evaluate the influence of irrigation practices on spatial pattern of measurements. Data indicate that organic peatland might be an important source of nitrous oxide emissions. The comparison of rainfall, saturation and deposition shown that trace gases emissions, dissolved nitrate and ammonium changed considerably along the soil column profile as a response of the microbial community to the high variability in redox, soil moisture, oxygen experienced by the soil at different depth. Water movement favored the formation of zones at different redox condition, redistributed the nutrient along the soil profile, and considerably changed mineralization,nitrification and dissimilatory reduction to nitrate (DNRA) rates. It was observed an asymmetrical behavior between nitrogen and ammonium profiles. Experiments shown that this assimetry is a function of the degree of saturation (as well as its duration). Also the fraction of the total N2O that is actually emitted to the atmosphere depends heavily on the structure and wetness of the soil. The nitrous oxide dynamic is therefore a function of the antecedent wetness condition, the nutrient content of the peat-land, the physical characteristics of the peat-land and the vertical stratification of layers at different redox and oxygen condition, which may affect the annual N budget. In addition, the combined use of soil column and chamber experiments suggest a negative correlation between soil moisture and N2O in dynamic condition and a functional dependence of N2O emissions from the oxygen concentration. We found that the time scale of water dynamic was faster than the biological scale of trace gas emissions. Finally, the relationship of nitrous oxide versus water content was reproduced by using a lumped model which include oxygen dynamic. Preliminary results suggest that by accounting for oxygen dynamic, it is possible to reproduce the functional behavior observed in the experiment and that the latter is depending on the physical and biological properties of the soil. Keywords: water dynamics, nitrous oxide emissions, nitrate ammonification,feammox, denitrification, soil heterogeneity, oxygen, redox.

Forest management involves dealing with conflicts between the protection of nature and the use of natural resources. Bad management practices have led to significant forest degradation worldwide. It is estimated that globally about 13 million hectares of forest are lost every year, leading to a massive loss of biodiversity and other forest-related ecosystem services, such as soil stabilisation and watershed protection. This is particularly dangerous in poor regions, where livelihoods are strongly based on locally available natural resources. In 2000, IUCN and WWF have introduced a new restoration approach called Forest Landscape Restoration (FLR) that aims to regain ecological integrity and enhance human well-being in deforested or degraded forest landscapes. FLR goes well beyond planting trees: it is about re-designing the landscape mosaic in a way that both nature and people are benefited. To this purpose, different actions should be taken at different locations across the landscape. From a planning perspective, this calls for proper methods and tools that help identifying where to act and what to do. The present research aimed to contribute to this problem by developing and testing spatial decision tools to support the design of landscape mosaics. More specifically, the study had three main objectives. The first objective was the identification of criteria and indicators (C&I) for the prioritisation of forest restoration interventions. Knowing which areas are ecologically more suitable to host a restoration intervention is a prerequisite of any FLR-based plan. There can be areas where restoration is more urgent, areas where it is more likely to succeed and areas where it is expected to bring the highest ecological benefits. Unfortunately, a widely accepted framework for the prioritisation of forest restoration areas is lacking. This problem was addressed by conducting an expert survey to define a set of readily applicable C&I. This was based on a two round Delphi involving 37 people, aimed at defining the key criteria and a broad set of indicators, and a final face-to-face meeting with a smaller group of experts, aimed at refining the list of indicators and making them operational. Finally, 8 criteria and 22 indicators were obtained, whose main advantage is their spatial character, which makes them suitable for spatial analysis and mapping. The second objective was the development of a GIS-based multicriteria methodology to identify reforestation priorities, to design a number of landscape-scale reforestation options and to assess them according to their socio-ecological performance. The prioritisation was based on two main non-compensatory factors: the need for biodiversity conservation and the ecological feasibility of reforestation. Suitability maps were generated for both factors through spatial multicriteria analysis and threshold pairs used to extract priority areas. The minimum suitability levels and the total area to be reforested were used as input parameters to generate a finite number of resulting reforestation options. These were assessed for their ability to conserve biodiversity and improve living conditions of local communities by introducing additional ecological and socioeconomic indicators. The methodology was tested in an area of Chiapas (Mexico), where forest degradation is significant and poverty widespread. The tool proved to be effective in shaping compact reforestation areas and easy to use. Nevertheless, it does not allow the user to a priori define targets on both conservation and livelihood standards. Also, the forest-poverty link was little explored and the issue of access to forest resources totally neglected. This leads to the third objective of the thesis: the definition of a spatial optimization model to re-design the landscape mosaic through reforestation in a way that nature protection is enhanced, the provision of ecosystem services is ensured and livelihoods are sustained. Either one of two possible uses was assigned to forest: protection, if forest is primarily devoted to biodiversity conservation, and harvest, if forest is available for the collection of timber. The model, which is an Integer Programming-based one, identifies land to be reforested and assigns this to the two uses such that all environmental classes over the landscape are adequately covered by protected forest, each village has a sufficient amount of harvestable forest at short distance and a given amount of erosion-prone land is reforested. The model also accounts for opportunity costs, by limiting the amount of economically strategic lands (e.g. agriculture) to be converted to forest. The model is the first of its kind to account for local peopleâ€TMs livelihoods by ensuring the accessibility to natural resources. The application to a case study in central Chiapas (Mexico) showed that increasing the demand for the provision of an ecosystem service does not significantly affect the ecological benefits up to a given threshold. Although some assumptions had to be made, the model provided a demonstration that the principles of the FLR can be put in practice and ad hoc planning tools can be designed to support decision-makers in their activity. Most of all, the model provided a solution to the problem of conserving biodiversity in poor regions where maintaining the access to local natural resources is vital to people. Redesigning forest landscapes for nature conservation and livelihood improvement is a difficult task. But one of dramatic importance as well. This study provided tools that can be of practical help to decision-makers and planners willing to undertake the challenge. Nevertheless, the problem is complex and intrinsically affected by uncertainty: further research effort is needed to test indicators, include the time dimension into the model and involve stakeholders in the decision process.

Increasing energy demand driven by rapid population and economic growth, the need for climate change mitigation, and the depletion of fossil fuels is stimulating the search for renewable, climate neutral energy sources. Hydropower provides an efficient, low maintenance and flexible form of energy, which can provide ancillary benefits such as flood control, water storage and job creation. Yet, the construction of dams for hydropower production has been recognised by scientists as one of the major threats to the ecological integrity of river systems. For instance, the fragmentation of river systems alters the flow, thermal, and sediment regimes of rivers, and restricts the free movement of aquatic organisms. Disruption to the natural flow regime results in the degradation of physical habitat features which generate acoustic stimuli that are relevant to organisms. In addition, initial flooding of terrestrial habitats results in the rapid decay of organic matter, which releases greenhouse gases (GHG) into the atmosphere. Conservation and management of river systems therefore requires a greater understanding of the processes and mechanisms which underpin the ecohydrological impacts of hydropower. In this context, this doctoral thesis aims to investigate: (i), the ramifications of a global boom in hydropower construction, (ii) the prediction of GHG emissions from hydropower reservoirs, and (iii) the temporal and spatial changes in underwater river soundscapes affected by hydropower. Researchers have investigated the social, economic and ecological consequences of reservoir construction for decades. However, the lack of coordinated, georeferenced databases has hindered catchment decision making, and limited the development of regional and global research in particular. In Chapter 1, the primary objectives were to create a high resolution, georeferenced database of hydropower dams under construction or planned to assess the dimension and spatial distribution of hydropower developments, their density relative to available catchment water resources and the future impact on river fragmentation. Data were collected on hydropower schemes under construction or planned with a capacity of 1 MW or above, from government and non-government databases, grey literature and news reports. Spatial analyses were conducted in a geographical information system (GIS) on the extent of global development, impact per water availability and potential consequences for existing status of river fragmentation. The relative contribution of hydropower reservoirs to the global GHG budget, particularly in sub-tropical and tropical regions, remains the subject of intense critical debate. The initial objective of the second study was therefore, to identify principal parameters and underlying processes that drive GHG emissions from reservoirs. The second step was to review global reservoir emission measurements and their source pathways in hydropower systems. Meteorological and landscape derived parameters were then correlated with the GHG measurements in order to assess if and which selected parameters might explain variations in GHG emission data. Similarly, existing empirical models were applied to the measured data to assess their suitability in predictive modelling. Finally, a newly developed process based model (FAQ-DNDC v1.0) was used to simulate ‘net’ CO2 emissions from a newly flooded tropical reservoir and compared to the measured results. The final study (Chapter 3) examined the influence of hydropower systems on the underwater acoustic properties of river habitats. Using recently developed acoustic sensors in addition to traditional hydrophones, the study characterised the temporal and spatial changes in river soundscapes affected by hydropeaking, compared their frequency composition to unaffected river soundscapes, and critically appraised the ecological implications. The results of Chapter 1 indicate that we are now experiencing an unprecedented growth in global hydropower construction. Over 3,700 dams are planned or under construction, primarily in Africa, South America and East Asia. The expansion in dam building will reduce the number of free flowing rivers on a global scale by approximately 21%. The results of Chapter 2 show that variation in measured emissions due to the inherent heterogeneity of the underlying processes, in addition to methodological limitations, impede the prediction of GHG emissions. Source pathways of CO2 are similar for the majority of systems, however, pathways of CH4 emissions are highly variable and dependent on local operating conditions and the configuration of the given hydropower system. A newly developed process based model (FAQ-DNDC v1.0) shows that a mechanistic approach may provide the basis for the ‘net’ assessment of future hydropower reservoirs. Chapter 3 reveals that distinct river soundscapes undergo changes which are highly correlated to hydropower operations, and thus rapid sub-daily changes occur at timescales not often found in natural systems. These changes occur mostly in low frequency bands, which are within the range of highest acoustic sensitivity for fish. In pool habitats affected by hydropeaking, sound pressure levels in the lower frequencies (~0.0315 kHz) may increase by up to 30 decibels. Similarly, sound pressure levels of riffles increase by up to 16 decibels in the low to mid frequencies (~0.250 kHz). Overall, the findings of this thesis have a number of implications for river catchment management. Hydropower construction is taking place in some of the most ecologically sensitive areas of the globe, thus, this research provides a timely contribution to: (i) Provide a foundation for future research at catchment, regional and global scales. For instance, systematic conservation based planning is required to designate ‘no go’ areas to promote the long-term survival of biodiversity. Strategic positioning of future dams or reconfiguration of existing hydropower systems may reduce the combined impacts on biodiversity and GHG emissions without losing power capacity. (ii) Assess driving parameters of GHG emissions, critically appraise current predictive GHG emission models and use a process based approach to simulate ‘net’ emissions from a sub-tropical reservoir. Future reservoirs will sequester, mineralise and emit an increasing quantity of carbon to the atmosphere, and subsequently, will take a greater role in the global GHG budget. This research concludes that, in some cases empirical models may not be suitable for making robust estimations of future GHG’s from hydropower reservoirs. Combining the underlying carbon cycling processes within a process-based model allows the estimation of ‘net’ CO2 emissions from hydropower reservoirs. This approach may be integrated by catchment planners into the future lifecycle assessment of hydropower reservoirs. (iii) Characterise acoustic changes in underwater sound in rivers affected by hydropeaking. The findings emphasise that flow regulation by hydropower results in rapid changes to the amplitude and frequency spectrum of the riverine acoustic environment. These changes persist for longer periods than other forms of anthropogenic sound and may have implications for the whole biota. Thus, future studies should focus on measuring the behavioural and physiological impact on riverine organisms in order to develop guidelines for hydropower licensing.

There is an increasing interest in dynamical food web modeling, and recent advances of computational biology provide new algorithms and tools for modern systems ecology. In this work stochastic individual-based models are used for simulating food web dynamics in two case studies: the Kelian river, in Borneo, Indonesia and a marine ecosystem in Gulf of Guinea. The two cases present effects from human perturbations. In both cases, we constructed food webs, based on real databases. We parameterized the stochastic dynamical model for the system models and performed sensitivity analysis (and community response indicators) in order to quantify the relative importance of system components. The main aims are to understand the importance of functional diversity of aquatic ecosystems and relations between the dynamics of species and the whole community in perturbed ecosystems due to human activities (pollution due to gold mining activity and human settlements in the case of the Kelian river ecosystem and the impact of Fish Aggregation Devices on skipjack tuna communities in the case of the Gulf of Guinea ecosystem). In Kelian river case, our results suggest that invertebrate shredders are indicators of human impact on the river. In downstream sites our results show that the river is more polluted and the relative importance of grazers and shredders decrease. The primary producers disappear downstream as consequence of mine activity and human waste. In the marine system case study, we analyzed the effects of association between tunas and FADs, and compared this to the behavior of free tuna individuals. The results suggest that skipjack tuna is affected by the use of FADs as fishing strategy on them. Some individual species show more sensibility to variation of population size of tuna. These two studies contribute to better understand how functional diversity is related to human impact. This kind of approach may help in shaping systems-based conservation and marine fisheries management strategies. Keywords: food web, aquatic ecosystems, stochastic model, sensitivity analysis

Firstly, I proposed a very simple SIS/SIR model for a general vector-borne disease transmission considering constant population sizes over the season, where contact between the host and the vector responsible of the transmission is assumed to occur only during the summer of each year. I discussed two different types of threshold for pathogen persistence that I explicitly computed: a "short-term threshold" and a "long-term threshold". Later, I took into account the seasonality of the populations involved in the transmission. For a single season, the model consists of system of non linear differential equations considering the various stages of the infection transmission between the vector and the host population. Assuming the overwintering in the mosquito populations, I simulated the model for several years. Finally, I studied the spatial spread of a vector-borne disease throught an impusive reaction-diffusion model and I showed some simulations.

Governments adopt strategies to follow the objective Europe 2020 and focus on the development of Renewable Energy Technologies, RET, to improve the transition of the production of energy from fossil fuels sources to renewable energy sources, RES. More than decades before, the energy transition towards renewable energies emerges as a relevant objective of the European governments. The fluctuating prices of oil and the uncertainty on the future supply of fossil fuels open new challenges for communities to actuate an energy transition towards RES. The RET can afflict deeply the landscape structure and by this point of view the energy transition is one of the most relevant drivers in the landscape change of the last three decades. In several cases energy transition may face opposition from regions and communities because of the change that RET produce in local landscapes and related economic, cultural and ecological functions. This change has been defined as a conflict between the local narrative of the right to the landscape by local communities and the global narrative that aims at a low carbon future. Exploring the relationship between Ecosystem Services (ES) and Renewable Energy (RE), the conflict among a global perspective and a local perspective has been resumed by several authors as a trade-off among provisioning and regulating ES from one side and cultural ES from the other. The overcoming of this conflict can be based on bottom-up processes that enhance the energy transition starting by local organizations of communities that want to reach a self-sufficieny in renewable energy supply. Transition management is possible if we produce innovation at local scale. An ES approach supports the transition management and the envisioning future energy landscapes by offering transparent trade-offs, exposing risks and benefits. If societies produce clean energy it may happen that RET afflict other ES. The main paradigm for the sustainability of a energy landscape is that the introduction of RET should not cause crucial trade-offs among the other ES, this is why this research wants to study this relationship, as several authors have already stressed. By the literature review it is possible to state a general gap of knowledge in integrated approaches in the evaluation of RET, considering diverse RES and ES provided by the landscape and evaluating a trade-off through a participatory process. To fulfill such gap and produce an enhancement of knowledge, this research follows the main objective of introducing a trade-off analysis into a design approach to formulate long-term visions for sustainable energy landscapes. The results we got indicate that it is possible to plan and design with the ES sustainable energy landscape.This process facilitates a sustainable energy transition of communities through a participatory landscape design that reduce the trade-off between the Renewable Energy and the ES supplies.

River/stream water temperature is one of the master water quality parameters as it controls several key iogeochemical, physical and ecological processes and river ecosystem functioning. Thermal regimes of several rivers have been substantially altered by climate change and other anthropogenic impacts resulting in deleterious impacts on river health. Given its importance, several studies have been conducted to understand the key processes defining water temperature, its controls and drivers of change. Temporal and spatial river temperature changes are a result of complex interactions between climate, hydrology and landscape/basin properties, making it difficult to identify and quantify the effect of individual controls. There is a need to further improve our understanding of the causes of spatiotemporal heterogeneity in river temperatures and the governing processes altering river temperatures. Furthermore, to assess the impacts of changing river temperatures on the river ecosystem, it is crucial to better understand the responses of freshwater biota to simultaneously acting stressors such as changing river temperatures, hydrology and river quality aspects (e.g. dissolved oxygen levels). So far, only a handful of studies have explored the impacts of multiple stressors, including changing river temperature, on river biota and, thus, are not well known. This thesis, thus, analysed the changes in river temperature behaviour at different scales and its effects on freshwater organisms. Firstly, at a regional scale, temporal changes in river temperature within long (25 years) and short time periods (10 years) were quantified and the roles of climatic, hydrological and landscape factors were identified for North German rivers. Secondly, at a reach scale, spatial temperature heterogeneity in a sixth-order lowland river (River Spree) was quantified and the role of landscape factors in inducing such heterogeneity was elucidated. Thirdly, at a site scale, short-term behavioural responses (namely drift) of three benthic invertebrate species to varying levels of water temperature, flow, and dissolved oxygen, and to combinations of those factors were experimentally investigated. Results from this thesis showed that, at a regional scale, the majority of investigated rivers in Germany have undergone significant annual and seasonal warming in the past decades. Air temperature change was found to be the major control of increasing river temperatures and of its temporal variability, with increasing influence for increasing catchment area and lower altitudes (lowland rivers). Strongest river temperature increase was observed in areas with low water availability. Other hydro-climatological variables such as flow, baseflow, NAO, had significant contributions in river temperature variability. Spatial variability in river temperature trend rates was mainly governed by ecoregion, altitude and catchment area via affecting the sensitivity of river temperature to its local climate. At a reach scale as well, air temperature was the major control of the temporal variability in river temperature over a period of nine months within a 200 km lowland river reach. The spatial heterogeneity of river temperature in this reach was most apparent during warm months and was mainly a result of the local landscape settings namely, urban areas and lakes. The influence of urban areas was independent of its distance from the river edge, at least when present within 1 km. Heat advected from upstream reaches determined the base river temperature while climatological controls induced river temperature variations around that base temperature, especially below lakes. Riparian buffers were not found to be effective in substantially moderating river temperature in reaches affected by lake warming due to the dominant advected heat from the upstream lake. Experimental investigation indicated that increasing water temperature had a stronger short-term effect on behavioural responses of benthic invertebrates, than simultaneous changes in flow or dissolved oxygen. Also, increases in water temperature was shown to affect benthic invertebrates more severely if accompanied by concomitant low dissolved oxygen and flow levels, while interactive effects among variables vary much among taxa. These results support findings of other studies that river warming, similar to climate change, might be a global phenomenon. Within Germany, lowland rivers are the most vulnerable to future warming, with reaches affected by urbanization and shallow lentic structures being more vulnerable and, therefore, requiring urgent attention. Furthermore, river biota in lowland rivers is particularly susceptible to short-term increases in river temperature such as heat waves. Plantation of riparian buffers, a widely recognized practice to manage climate change effects, in the headwater reaches can be suggested to mitigate and prevent future warming of lowland rivers in general and also throughout river basins, as river temperature response in lowland catchments is a culmination of local and upstream conditions. However, further river temperature increase in lowland river reaches within or close to urban areas and shallow lentic structures will be more difficult to mitigate only via riparian shading and would require additional measures

Freshwater ecosystems are severely undergoing degradation due to the presence of multiple stressors that are undermining their biodiversity. In this sense, quantifying these effects on Alpine regions is challenging, due to the lack of tailored field measurements of hydrological, biological and chemical variables. This work aims to touch some of these aspects, with particular attention to hydrological dynamics and their effects on macroinvertebrates. Field activities have been conducted within the Adige catchment which has been selected as a case study in the FP7 project GLOBAQUA. Collected data have been analyzed by means of statistical tools and results showed a seasonal and spatial variability of biological communities related to hydrological and chemical variables. In particular, it has been observed that richness, diversity and relative composition of macroinvertebrates community are chiefly affected by hydrological alteration and urban pollution. Available literature confirmed that hydrological alteration is one of the most important factors affecting riverine ecosystems. In Alpine regions, most of the hydrological alterations observed are due to hydropower that represents the major source of energy in the Trentino-Alto Adige region. Since the introduction of the free energy market in Italy, hydropower production shows large fluctuations at the daily and larger temporal scales, as the managers aim at producing when the energy price is high. This increased the variability of streamflow downstream the restitution of the power plants. Changing climate is an additional stressor that can enhance the effects of these anthropogenic influences. Thereby, in this work hydrological alterations have been distinguished between those forced by climate change and those caused by the presence of hydropower plants and have been analysed in detail. The former have been analysed downstream of the Careser glacier, which has long-term observations of climatic variables, mass balances and streamflow. The main purpose of this study was finding a direct relationship linking biological indicators to streamflow variations related mainly to hydropower operations. Quantifying these effects is challenging due to the fact that the behaviour by which macroinvertebrates respond remains largely unexplained. However, analyses of similarities and independence, performed at the basin scale with data provided by the local Environmental Protection Agencies, showed evident differences in the biological communities between impacted and non-impacted sites. These results bring us to believe that a relationship between biological data and hydrological alteration is expected to exist, but that is not clearly explicated by simple correlations. Giving a quantitative interpretation of this correlation could help hydropower manager to improve and optimize the energy production with a more realistic scenario of the effects on the biological community, with also a perspective of the combined effects caused by the presence of multiple reservoirs within the basin.

This thesis provides a contribution to the knowledge on the effects of deglaciation on alpine stream ecosystems, taking into account also the hydroecological influence of thawing permafrost and paraglacial features. With a focus on the European Alps, a review is provided on the climate changes and shifts in the cryosphere (snow, glaciers, permafrost), the related changes in hydrology, geomorphic processes and the physical and chemical habitat of alpine river networks, and the consequent shifts in stream communities and food webs. A conceptual model is provided to summarize the complex interactions and the cascading effects triggered by deglaciation on hydrology, habitat and biota of alpine streams, that can be useful for educational purposes and to help the scientific community to contextualize these issues to other alpine areas. Deglaciation induces homogenisation of river networks, loss of biodiversity, and shifts in primary and secondary production, functional diversity and food webs. The scarce published studies on streams influenced by permafrost provide hints on the role of thawing rock glaciers (i.e. evident form of mountain permafrost) in shaping the ecology of freshwaters, and reveal important research gaps. To increase the knowledge on this topic, different alpine streams fed by waters of different origin were selected in two subcatchments (Zay, Solda) of a deglaciating area of the Central Italian Alps (Solda Valley), and their habitat conditions and benthic invertebrate communities were investigated over a two-year period. Rock glacier-fed streams could be distinguished from those fed by glaciers, groundwater and those of mixed origin because of their constantly clear and very cold waters, stable channels, and high concentrations of ions and trace elements that increased as summer progressed. Furthermore, the Zay rock glacier strongly influenced the glacier-fed stream through an intense export of solutes, which become progressively more relevant towards the end of summer. This influence was also due to the contribution of a proglacial lake and a moraine body, that both strongly decreased the glacial influence along the glacier-fed stream before its confluence with the rock glacier outflow. The wide range of habitat conditions revealed to strongly influence the benthic invertebrate communities in the study area. Channels with groundwater (krenal) and mixed (glacio-rhithral) exhibited a higher taxa richness and diversity. Peaks of abundance and biomass in the catchment were recorded just downstream the talus body, in the upper glacio-rhithral channel. Chironomidae from the cold-adapted genus Diamesa were dominant in the proglacial sections (upper kryal) of the glacier-fed streams. The proglacial lake, the moraine body and the rock glacial tributary at Zay contributed to the amelioration of the environmental features of the glacier-fed stream (lower kryal), boosting high invertebrate biomass and abundance and causing shifts in the community composition (e.g. increased Orthocladiinae and other Diamesinae chironomids, abundant Trichoptera). The two rock glacial communities differed considerably between each other. In fact, the community of the Zay rock glacial stream was partially influenced by the seepage of glacier waters, and resembled those of the surrounding lower kryal. On the contrary, the Solda rock glacial stream, detached from any glacier influence, hosted a rich and diverse community which resembled those of glacio-rhithral and krenal, even though with a higher abundance of Diamesa. Overall, the results of this thesis showed that in the advanced phases of glacier retreat, paraglacial landforms and permafrost can increasingly contribute to the riverscape diversity and shape the ecology of river networks. Because of their unique environmental settings, rock glacial streams should be considered a distinct alpine stream habitat, acting in deglaciating catchments as stepping stones that enhance the upstream colonisation of non-glacial communities following glacier retreat. At the same time, they might represent cold refugia for cold-stenothermal and/or typically glacial taxa when glaciers will be disappeared, because of the slower thawing rate of rock glacier ice. In this context, the presence of Diamesa kryal specialist species in rock glacial streams deserves further investigation, in order to understand the potential conservation value that these habitats may have in buffering the β-diversity reduction which is predicted in alpine areas as a consequence of glacier loss.

This thesis treats mathematical models for host-parasitoid interactions. It is composed of three parts. In the first part, a class of such models is analyzed theoretically. It focuses on the phenomena of multiple coexistence equilibria of competing parasitoid species. The second part is about a model for determining how a parasitoid release should be timed to optimally control the invasive fruit fly Drosophila suzukii. The third part analyzes an experiment for releasing parasitoids in a greenhouse which is infested by D.suzukii. The models presented are used to discuss how to improve such biological control strategies.