ECOLOGICAL SHIFTS OF STREAM ECOSYSTEMS IN A DEGLACIATING AREA OF THE EUROPEAN ALPS

PhD ThesisThis 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

Causality and momentum conservation from relative locality

Theories with a curved momentum space, which became recently of interest in the quantum-gravity literature, can in general violate many apparently robust aspects of our current description of the laws of physics, including relativistic invariance, locality, causality and global momentum conservation. We here explore some aspects of the particularly severe pathologies arising in generic theories with curved momentum space for what concerns causality and momentum conservation. However, we also report results suggesting that when momentum space is maximally symmetric, and the theory is formulated (DSR-)relativistically, with the associated relativity of spacetime locality, momentum is globally conserved and there is no violation of causality.Comment: 20 pages, 6 figures, latex (V2: minor editing

AGN Feedback in Galaxy Groups: the two interesting cases of AWM 4 and NGC 5044

We present AGN feedback in the interesting cases of two groups: AWM 4 and NGC 5044. AWM 4 is characterized by a combination of properties which seems to defy the paradigm for AGN heating in cluster cores: a flat inner temperature profile indicative of a past, major heating episode which completely erased the cool core, as testified by the high central cooling time (> 3 Gyrs) and by the high central entropy level (~ 50 keV cm^2), and yet an active central radio galaxy with extended radio lobes out to 100 kpc, revealing recent feeding of the central massive black hole. A recent Chandra observation has revealed the presence of a compact cool corona associated with the BCG, solving the puzzle of the apparent lack of low entropy gas surrounding a bright radio source, but opening the question of its origin. NGC 5044 shows in the inner 10 kpc a pair of cavities together with a set of bright filaments. The cavities are consistent with a recent AGN outburst as also indicated by the extent of dust and H_alpha emission even though the absence of extended 1.4 GHz emission remains to be explained. The soft X-ray filaments coincident with H_alpha and dust emission are cooler than those which do not correlate with optical and infrared emission, suggesting that dust-aided cooling can contribute to the overall cooling. For the first time sloshing cold fronts at the scale of a galaxy group have been observed in this object.Comment: 4 pages, 1 figure, to appear in proceedings of the conference "The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", June 2009, Madison Wisconsi

Involvement of recreational anglers in the eradication of alien brook trout from high altitude lakes

Stocking programmes for recreational angling are primarily responsible for the spread and ecological impact of introduced sh in high-altitude, originally shless lakes. In 2013, the Gran Paradiso National Park started an eradication campaign of brook trout by intensive gill-netting. Local anglers were invited to attend two angling sessions to start the eradication before gill-netting in an experimental lake, as part of an education action devoted to these critical stakeholders. The angling sessions turned out to be a valuable help for the eradication campaign and the aim of this study is to report on the outcomes of these angling sessions. Angling techniques were highly size-selective, removing a substantial part of the adult population and of the sh biomass, but their contribution to the eradication of small sh (<15cm) was irrelevant. Therefore, angling cannot completely eradicate age-structured populations. However, there is scope to use angling sessions as a support for eradication campaigns and as an emergency measure for recent sh introduc- tions. Similar actions should be considered whenever a sh eradication programme is planned. These ndings, however, do not imply a general endorsement for angling within protected areas

A Chandra - VLA Investigation of the X-ray Cavity System and Radio Mini-Halo in the Galaxy Cluster RBS 797

We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and VLA data. RBS 797 (z = 0.35), is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate an higher metallicity along the cavity directions. This is likely due to the AGN outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than the surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow (CF), as it nicely follows the trend P_radio vs. P_CF predicted by the re-acceleration model.Comment: Accepted for publication in ApJ, 14 pages, 13 figure

Behind the impact of introduced trout in high altitude lakes: adult, not juvenile fish are responsible of the selective predation on crustacean zooplankton

Introduced fish seriously affect zooplankton communities in mountain lakes, often leading to the loss of large species. Selective predation is recognized to be the ultimate cause of such a strong impact. Here we describe the selection of zooplankton prey by analyzing the stomach contents of more than 300 brook trout (Salvelinus fontinalis) inhabiting seven alpine lakes in the Gran Paradiso National Park (western Italian Alps). Our results show that planktivory is much more common in young fish, which feed on a larger number of taxa, but also adult fish maintain the ability to feed on zooplankton. There is a direct dependence between the length of zooplankton prey and the length of their fish predators, and adult, not juvenile fish are responsible of the selective predation on large crustacean zooplankton, which drive the impact of introduced fish throughout the entire zooplankton community. In some rare cases, large zooplankton populations develop in the presence of brook trout, and planktivory can become an important temporary resource for adult fish during the ice-free season. Thus, in the early stages of the establishment of non-native trout in alpine lakes, large-bodied zooplankton may represent an important food resource

Impact of AGN feedback on galaxies and their multiphase ISM across cosmic time

We present simulations of galaxy formation, based on the GADGET-3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for AGN feedback. Our sub-resolution model describes a multiphase ISM, accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies (Mhalo, DM 43 2 . 1012 M&09, at z = 0), to investigate: (i) the effect of different ways of coupling AGN feedback energy to the multiphase ISM; (ii) the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); (iii) how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive BHs and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at z = 0 is reduced by up to an order of magnitude, and the BH is prevented from accreting below z 72 2, when the galaxy disc forms

Spectral index-flux relation for investigating the origins of steep decay in γ-ray bursts

γ-ray bursts (GRBs) are short-lived transients releasing a large amount of energy (10 − 10 erg) in the keV-MeV energy range. GRBs are thought to originate from internal dissipation of the energy carried by ultra-relativistic jets launched by the remnant of a massive star’s death or a compact binary coalescence. While thousands of GRBs have been observed over the last thirty years, we still have an incomplete understanding of where and how the radiation is generated in the jet. Here we show a relation between the spectral index and the flux found by investigating the X-ray tails of bright GRB pulses via time-resolved spectral analysis. This relation is incompatible with the long standing scenario which invokes the delayed arrival of photons from high-latitude parts of the jet. While the alternative scenarios cannot be firmly excluded, the adiabatic cooling of the emitting particles is the most plausible explanation for the discovered relation, suggesting a proton-synchrotron origin of the GRB emission.The research leading to these results has received funding from the European Union’s Horizon 2020 Programme under the AHEAD2020 project (Grant agreement n. 871158). G. Ghir. acknowledges the support from the ASI-Nustar Grant (1.05.04.95). M.B., P.D., and G.G. acknowledge support from PRIN-MIUR 2017 (Grant 20179ZF5KS). G.O. acknowledges financial contribution from the agreement ASI-INAF n.2017-14-H.0. S.A. acknowledges the PRIN-INAF “Towards the SKA and CTA era: discovery, localization, and physics of transient sources” and the ERC Consolidator Grant “MAGNESIA” (nr. 817661). M.G.B. and P.D. acknowledge ASI Grant I/004/11/3. O.S.S. acknowledges the INAF-Prin 2017 (1.05.01.88.06) and the Italian Ministry for University and Research Grant “FIGARO” (1.05.06.13) for support. G.O. and S.R. are thankful to INAF—Osservatorio Astronomico di Brera for kind hospitality during the completion of this work. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester