Seasonal snow cover plays a fundamental role in sustaining human activities in mountain communities. Runoff originating from the European Alps is a primary water source for millions of people. However, Alpine snow resources are increasingly threatened by rising temperatures and changes in precipitation patterns due to climate change. These factors underscore the need for accurate and widespread monitoring of the Alpine snow resources.From a hydrological perspective, snow water equivalent (SWE) is crucial to assess the water amount stocked in the snowpack and, therefore, the water availability after snowmelt. The most historically widespread SWE measurement practices consist in the direct assessment of the snow bulk density through field campaigns involving vertical coring or snow pits. Although these methods are highly accurate, they provide limited temporal and spatial coverage due to the significant manpower required and the inaccessibility of many sites during the snow season.In the last decades, the development of sensors based on cosmic ray neutron sensing (CRNS) allowed the measurement of continuous SWE data in already monitored sites, filling the gaps associated with manual measurements. However, applying CRNS to monitor snowpacks in inaccessible sites remains largely unexplored as the standard procedure to retrieve SWE from neutron counts relies on site-specific parameters derived from reference measurements.This work presents a network of 26 CRNS sensors located across the Italian Alps. The network is among the most extensive of its kind both in terms of both the number of probes and elevation range (1422 – 2901 m a.s.l.). Its broad coverage provides unprecedented insights into the possibility of retrieving SWE data independently of most of the site-specific features usually required. Notably, the parameterisation used to convert neutron counts into SWE is common to all probes in the network.Manual SWE data from 13 sites within the network, collected during the 2023–2024 and 2024–2025 snow seasons, were used to calibrate and validate the network-wide parameterisation. The calibration process involved 35 direct SWE measurements performed at 6 sites during the first half of the 2023 – 2024 season. A total of 111 manual SWE data were used as the validation dataset.The analysis shows that the application of a shared set of parameters results in a good representation of the snowpack characteristics. Moreover, the data from unmonitored sites of the network show high correlations with monitored sites at similar elevations. These results suggest that deploying CRNS probes can be used to overcome common limitations of snow monitoring, such as site accessibility issues, lack of manpower to perform manual measurements, and safety hazards linked to the harsh mountain environment.This abstract is part of the NODES project which has received funding from the MUR–M4C2 1.5 of PNRR funded by the European Union - NextGenerationEU (Grant agreement no. ECS00000036).

Understanding and predicting soil erodibility in mountain environments is challenging due to complex interactions among environmental, pedological, and biological processes, which contribute to high spatial variability. This is particularly evident in the Aosta Valley Region (NW Italian Alps), where previous studies reported pronounced soil heterogeneity. Building on these findings, we estimated the topsoil erodibility factor (K factor of the USLE), assuming that, given the uniform texture, soil organic matter (SOM) would be the main driver of K variation. K was calculated using two equations-USLE and EPIC. We also tested, in a demonstrative way, SOM values beyond the conventional threshold of the USLE nomograph to explore its influence on K in highly organic alpine soils. A digital soil mapping (DSM) approach with machine learning was used to model the spatial distribution of K. Pedological field data were analyzed to evaluate their relationship with K, and USLE-based erosion values were calculated for observed profiles to assess K estimate reliability. Results show that: (i) the USLE K equation better captures mountain complexity; (ii) SOM significantly reduces K, with stone cover exerting additional influence; (iii) the model identified key regional drivers of K (carbon stock, elevation, pH), producing consistent spatial maps at 40 m resolution; and (iv) K values vary across soil horizons, humus systems, land uses, and soil types. Complementary analysis of erosional denudation supports the central role of SOM in enhancing alpine soil resistance. These findings provide insights for future soil monitoring, conservation, and restoration strategies in mountain ecosystems.

IntroductionAlpine tundra vegetation, also shaped by snow persistence, is expected to undergo shifts in plant community composition under climate change as snow cover duration declines, with potential consequences for soil biogeochemistry and microbial communities. However, the relationships among snow-driven vegetation types, soil carbon (C) and nitrogen (N) forms, and prokaryotic community functional organization remain poorly understood.MethodsIn this study, we investigated soil C and N forms and the functional organization of prokaryotic communities across three vegetation types shaped by different snow cover duration: snowbed communities dominated by Salix herbacea (SB, with long snow cover duration), alpine sedge swards dominated by Carex curvula (CC, with short snow cover duration), and intermediate transitional plant assemblages.ResultsC-related forms were mainly associated with vegetation type, with higher C content in CC than in SB. Conversely, mineral N forms varied primarily with timing within the snow free season, with higher concentrations in the early snow free season, indicating different spatial and temporal controls on soil C and N dynamics. Microbial community composition differed among vegetation types, whereas alpha diversity varied little. Despite this, prokaryotic functional groups differed markedly. CC were associated with higher relative abundance of cellulolytic prokaryotes, whereas SB were enriched in N-related functional groups inferred from FAPROTAX assignments, suggesting potential differences in N cycling-related microbial functions among vegetation types.DiscussionThese results show that soil biogeochemistry and microbial functional organization in alpine tundra soils are shaped by both snow-driven vegetation types and timing across the snow free period. Under climate change, reduced snow cover duration and SB contraction may cause the loss of a microhabitat with specific functional biodiversity, with potential consequences for soil C and N cycling.

Cosmic-Ray Neutron Sensing (CRNS) has emerged among proximal sensors as a reliable technique for non-invasive Soil Moisture (SM) estimation at a scale much larger than the usual point-scale sensors and at sub-daily resolution (Bogena 2015). The CRNS method is now widely used by research institutions and agencies around the world and nation-wide CRNS soil moisture networks have been established (Andreasen 2017, Bogena 2022). A procedure for proper use and calibration has been published by the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture (IAEA 2017). CRNS is also mentioned as a method for the measurement of Soil Water Content (SOHYD_168 variable) in prime eLTER sites (Zacharias 2024). Another flourishing application of the same technology is the measurement of Snow Water Equivalent (SWE - equivalent amount of liquid water stored in the snowpack), with Électricité de France being the first to deploy a full network on the French Alps and the Pyrenees (Paquet and Laval 2007). A smaller but more dense network has been recently deployed on the mountains of Veneto, Italy, by the Regional Agency for Environmental Protection of Veneto (Valt et al. 2024). CRNS is based on detecting ambient neutrons close to the land surface, generated as a consequence of the flow of high-energy particles from space and strongly absorbed by water molecules. The rate of neutron count rate by a detector placed above ground is correlated to the SM within a volume spanning up to a dozen hectares extension and up to 50 cm depth. In the case of SWE, the neutron count rate by a detector placed at the ground and buried by the snow is correlated to the SWE in the snowpack. Finapp developed a light and safe detector based on a lithium-doped plastic scintillator material, suitable for CRNS applications on field (Gianessi 2024). We report ongoing measurements by Finapp CRNS probes integrated in eLTER monitoring sites in Austria (Landslide Observatory at Hofermühle), Spain (Doñana Biological Reserve - DBR) and Italy (Istituto Angelo Mosso). Between Nov. 2022 and the end of 2023, Finapp probes were installed in the DBR, inside Doñana National Park (SE Spain), an LTSER Platform (eLTER), for a comparative monitoring of different habitats. Fig. 1 shows the measured SM dynamics in 3 different sites within the DBR during the period of co-existence of the 3 probes: Juniper (woodlands on top of stabilized sand dunes), Monte Negro (heathlands in the lowland mantle) and Monte Blanco (xeric shrubland on top of stabilized sand dunes). They show a coherent dynamical response to rain events, characteristic of very sandy soils where water quickly infiltrates towards inferior horizons and feeds the aquifer. The effect of the 2024 dry summer is clearly visible. The region of Lower Austria is highly prone to landslides, therefore a long-term monitoring project on slow-moving landslides was established in 2014 at three different sites (Landslide Observatories) to investigate surface and subsurface dynamics (Marr et al. 2023). This monitoring network is embedded in the Austrian LTSER Platform Eisenwurzen as LTER NoeSLIDE. A CRNS probe was installed in May 2023 at the Landslide Observatory at Hofermühle to investigate the role of SM as a triggering factor for landslides. On Feb. 20th 2024, a field sampling campaign of the SM within the sensor footprint was performed and used as a calibration point. Activities in this site included rover mapping campaigns, in which the probe was unmounted and moved to different points to the purpose of obtaining a mapping of the relative variation of SM across the site. Within the Histalp project precipitation time series, we identify the meteorological station of Waidhofen/Ybby as the most relevant to describe patterns at Hofermühle, which is about 7 km away*2. It shows a mean annual precipitation rate of 1197 mm/a (1896-2021) with the wettest months being June, July and August. Between Sept. 12th and 16th 2024, an exceptional atmospheric pattern led to long-lasting heavy rainfalls in many parts of Austria (BML 2024), which is also reflected in the data provided in Fig. 2. The probe at the Istituto Mosso LTER site (NW Italian Alps, 2901 m a.s.l.) was installed in Dec. 2023 to continuously measure SWE during the snow-covered season 2023/2024. To assess the performance of the probe, the measured data were compared with SWE values collected during targeted field campaigns. Fig. 3 shows the variability of the continuous SWE during the analysed period and the SWE values measured in the field, highlighting the good accuracy of the probe. The probe is currently installed to measure the SWE during the snow-covered season 2024/2025, while more probes are planned to be installed at the site with the goal to measure both SWE and SM (during the snow-free season). The same technology has been applied to notably different scenarios, highlighting the versatility and reliability of CRNS for monitoring the dynamics of water in different forms and under a variety of conditions. We suggest that the spreading use of CRNS probes in monitoring networks will improve the comparability across scales and environments.

Background Climate change (CC) is regarded as the main factor behind changes in alpine vascular plant assemblages (Gottfried et al. 2012, Pauli et al. 2012). In the alpine life zone, a shift in the floristic composition is often a consequence of upward species migration and local loss (Pauli et al. 2012). Moreover, local changes in abundance have led to species’ distribution ranges expanding or retracting (Staude et al. 2022), resulting in a shift towards more nutrient- and warm-demanding plant assemblages as well as drought-adapted vegetation types (Liberati et al. 2019, Gottfried et al. 2012). Here, we investigated the vascular plant assemblages and soil properties in a GLORIA (GLobal Observation and Research Initiative in Alpine environments) target region in the N-Apennines (Italy). The site was established in 2001 and has been monitored at seven year intervals. The study area is included in a LTER site and is part of the SENTINEL (The reSponsEs of italian mouNTaIN Ecosystems to cLimate change) project, initiated in 2023 with funding from the Italian Ministry of University and Scientific Research (MUR). The aims of this study consist of assessing temporal shifts in the ecology of plant assemblage requirements as well as to unravel possible environmental drivers such as warming temperature and soil inorganic N availability. Methods Across four summits in the study site (1722-1978 m a.s.l., https://www.lteritalia.it/wordpress/?page_id=264), we investigated directional changes of plant assemblages to assess eutrophication, thermophilization and xerophilization processes as well as to assess ecological requirements of “winner” (increasing in abundance) and “loser” (decreasing in abundance) plant species. Environmental conditions were indirectly assessed based on Pignatti’s ecologic indicators for the Italian flora (Pignatti 2005). Moreover, we assessed changes in species richness to assess the expected biodiversity loss. Soil properties were evaluated through 10 cm deep soil temperature trend since 2001 and by measuring inorganic N soil concentration in the summer of 2023. Results and discussion We found a net increase in species richness in the lowest summits at the treeline ecotone (+12) and lower alpine (+4) belts. The two highest summits, up to the alpine belt, had a net species loss (-2 each). Noteworthy losses were the low stature (sub)alpine perennial species Myosotis alpestris , Soldanella alpina and Aster alpinus , while the most successful colonizers were the graminoids Festuca paniculata and Poa pratensis , and the Fabaceae Anthyllis vulneraria and Trifolium repens . A shift towards more nutrient-demanding species was the most pronounced pattern we observed (Fig. 1), being more intense in the treeline ecotone and the lower alpine belt (Fig. 1). This finding is in line with a previous European study, highlighting signs of increased nutrient demands in 52 GLORIA summits up until 2015, although the trend not significant (Staude et al. 2022). We also detected low level of local thermophilization and adaption to drought, but both supported by a few obvious thermophilous and drought-adapted winners and losers. Changes in species abundance of winning (3-9% of the species) and losing (2-8% of the species) species supported significant shifts in the ecologic indicators, especially related to increased nutrient requirements (Fig. 2). Eutrophication appeared to lead to both the expansion of more acquisitive species such as Genista tinctoria, F. paniculata and Brachypodium genuense , and the retraction of species growing on more oligotrophic substrates like Agrostis rupestris and Viola calcarata subsp. cavillieri . In our study area, the soil N-NH4+ concentration at the end of the growing season was comparable to the values recorded in the alpine tundra at the LTER site Istituto Mosso (NW Italian Alps, 2525-2840 m asl) (Magnani et al. 2017), ranging between 3 - 8 mgkg-1. The N-NO3- concentration was high, especially at one site (Mommio), ranging between 0.5 - 2.7 mgkg-1. This high soil inorganic N content could be related not only to the increase in temperature but also to the high N wet deposition. At the LTER site Istituto Mosso, the N critical threshold was greatly exceeded, revealing that the area is exposed to excessive N input through atmospheric deposition (Balestrini et al. 2024). In the N-Apennines, an increased level of N deposition, affecting beech growth, has been already estimated for the period 1850-2014 (Gentilesca et al. 2018). Moreover, recent studies found the increase in plant nitrogen availability and use significantly controlled by increasing mean annual temperature (Hu et al. 2024, Salazar et al. 2020). The M. Cimone Meteorological Observatory, located in the study area, has recorded a large increase in the mean, minimum and maximum annual air temperature between 1951-2018 (Costanzini et al. 2024). The increase of in situ soil mean temperature (+0.46°C per decades) as well as increased in duration of the vegetative period in the Eastern slope of the GLORIA site ‘Pian Cavallaro’ (M. Cimone) reflects trends in air temperature during the last two decades. Thus, plant species’ productivity may also have been stimulated by the well-established trends of higher temperatures and longer growing seasons, promoting the growth of nitrophilous species compared to others. Conclusions This initial investigation has revealed a complex and multifaceted picture of the ongoing dynamics in alpine vascular plant assemblages, highlighting an alarming biodiversity loss. The stronger influence of eutrophication over thermophilization highlights multiple, complex responses to warming, likely acting beyond the simple increase of species demands for higher temperatures. The SENTINEL project will continue to investigate the relationships between vegetation, atmosphere, soil, and plant-insect multi-trophic interactions to disentangle CC impacts on plant species and ecosystem functioning.

During the last decades, most glaciers have been retreating and losing mass in all high-mountain regions, where permafrost has also undergone warming, degradation, and ice loss. In this context, rock glaciers, a visual indication of the presence of mountain permafrost, have gained attention because they host shallow groundwater resources. Hence, rock glaciers could represent a contributor for future water supply, especially in arid and semi-arid mountain areas and/or during dry periods. However, a growing body of literature, mostly composed of local scale studies, has reported high concentrations of solutes, including trace elements, in rock glacier-fed waters, with negative implications on water quality. Therefore, the potential for rock glaciers to function as safe sources for drinking water supply may be questioned, although the main drivers of solute export from rock glaciers are still little understood. Here, we investigated how geographical and geological settings, together with cryospheric conditions, influence the water chemistry of intact (containing internal ice) and relict (without internal ice) rock glaciers, and assessed the potential implications for water quality. To do this, we assembled an unprecedented dataset on 201 rock glacier springs from mountain ranges across Europe, North and South America, and we applied a combination of machine learning, multivariate and univariate analyses, as well as geochemical modelling. Several intact rock glacier springs had higher concentrations of sulphate and trace elements (e.g., Ni, Al, U) than relict ones. Accordingly, one third of springs issuing from intact rock glaciers had a water quality that did not meet the requirements of drinking water standards, with respect to only 5 % of relict rock glacier springs. The ice presence combined with specific lithologies (e.g., paragneisses) enhanced solute concentrations in rock glacier springs, due to intense oxidation of sulphide minerals that was also responsible for the elevated trace element concentrations. Since rock glaciers are emerging as key mountain water resources as well as potential threats to water quality, we call for an international effort to investigate the hydrochemistry of rock glacier springs across the globe, especially in understudied mountain ranges (e.g., Himalayas, Caucasus) and where these springs are used for drinking purposes.Brighenti, S., Colombo, N., et al. Factors controlling the water quality of rock glacier springs in European and American mountain ranges. Science of the Total Environment 953, 175706 (2024). https://doi.org/10.1016/j.scitotenv.2024.175706NC and SB equally contributed to this work. NC and MF were supported by the project NODES, which has received funding from the MUR – M4C2 1.5 of PNRR funded by the European Union – NextGenerationEU (Grant agreement no. ECS00000036).

Climate change undermines forests' health, vitality, and, as a consequence, tree functionality, productivity, and resilience to biotic disturbances. Mountain and sub-alpine forests are particularly susceptible to climate extremes and are showing signs of degradation in Europe. Warmer temperatures, drought, higher frequency and intensity of natural disturbances increasingly alter species distribution and survival, their growing capacity, reproduction, establishment, as well as their potential adaptation to climate change. Real-time monitoring of trees' and stands' responses to such events provides an effective way to better understand and even foresee the adverse side effects of climate change. The use of advanced and innovative monitoring tools and devices is required for ensuring long-term, large-scale, and real-time monitoring of forest dynamics. Here, we present the TreeTalker Italia Network (TTIN), i.e., the first largescale network of tree-proximal sensors (TreeTalkers (c)) at a national scale in Italy. We describe the recent advances, innovations, and potential of such devices for continuous monitoring and research. As a primer, we argue that TTIN will provide effective support to ongoing science and policy efforts for monitoring natural resources' dynamics on a large scale (e.g., forest inventory, climate impacts), including their effects on human well-being.

Blockstreams and blockfields are periglacial features induced by strong frost-action processes. As their formation can be associated with specific environmental conditions such as permafrost (in absence of an impermeable layer below), these landforms have been recognized worldwide as key factors in paleoclimate reconstructions. However, their internal morphology and origin, especially in alpine environments, were poorly investigated. In particular, the fine material at their base has almost never been characterized from the pedogenic point of view. We opened and described a 12 m-wide, 3 m-deep soil transect inside and between two blockstreams in the Ligurian Alps (NW Italy); we took samples from each pedogenic horizons and analysed them to obtain chemical, physical, mineralogical, and micromorphological data. The soil transect was characterized by deep involutions likely caused by ancient, deep cryoturbation associated to former ice-rich permafrost and its collapse during thawing (load casting). Many other macro- (i.e. large platy structure, fragic properties, vesicular porosity, wedge cast-like structures, Fe-Mn nodules above a permeable layer) and micro-morphological features (i.e. Fe-Mn concentrations, fractured clay coatings, silt caps) evidence ice-rich permafrost, while the intensity of pedogenesis points to a particularly long soil forming processes and preservation of soil materials during different Pleistocene glacial and interglacial periods.

Climate change is reducing the extent of cold aquatic habitats and their unique biodiversity in mountain areas. However, a variety of cold rocky landforms (CRLs) are thermally buffered and feed cold springs (<2 °C) that may represent climate refugia for cold-adapted organisms. These landforms, hitherto overlooked by freshwater research, include rock glaciers, debris-covered glaciers, talus slopes, protalus ramparts, and young moraines. Here, we investigated the warm-season water temperature of 228 springs from clean (ice) glaciers, CRLs, and reference slopes (not sourced by any of these features) in 13 mountain ranges of Europe, South America, and North America. Only springs from glaciers (90%) and CRLs (45%) had average stream temperatures below the thermal optimum for coldwater organisms of 2 °C. Springs fed by CRLs were 3 °C–5 °C (up to 9 °C) colder than those from nearby reference slopes. In general, cold springs were rarer in Mediterranean/semi-arid climates than in temperate and sub-polar climates. Landforms comprising barren and coarse rocky surfaces or ice/rock mix, having a simple or absent soil/vegetation structure, and higher likelihood of permafrost more often supported cold springs. When water temperatures were compared to air temperature, most CRL springs were thermally buffered against warm periods, cumulative heat, and daily temperature fluctuations. With cold conditions maintained in a variety of climates and mountain landscapes, CRL springs in mountains likely have high conservation value. We call for integrated ecological and hydrological research for these ecosystems, aimed at understanding their potential as climate refugia.

Alpine tundra ecosystems are highly sensitive to climate change,particularly due to their dependence on the duration and timing of snow cover.This study investigated the effects of the climate extreme years 2022 and 2023 on carbon(C)and nitrogen(N)forms in two alpine tundra communities:snowbed(SB)and Carex curvula(CC),located at high elevation in the North-West(NW)Italian Alps.During these years,both sites experienced exceptionally low snow cover duration and elevated mean soil temperature during the snow-free season.Dissolved organic carbon(DOC)concentrations significantly increased by+65%in SB and+42%in CC compared to 2016-2021,likely reflecting enhanced microbial decomposition of organic matter.In contrast,soil ammonium and nitrate levels showed no significant changes,indicating differential responses between C and N processes.These findings suggest that DOC is a sensitive(early)indicator of climate-induced shifts in soil functioning.Given the critical role of alpine tundra in global C cycling,understanding DOC dynamics under climate extreme events is crucial to predict future ecosystem feedback to global change.

Biological diversity in mountain ecosystems has been increasingly studied over the last decade. This is also the case for mountain soils, but no study to date has provided an overall synthesis of the current state of knowledge. Here we fill this gap with a first global analysis of published research on cryptogams, microorganisms, and fauna in mountain soils above the treeline, and a structured synthesis of current knowledge. Based on a corpus of almost 1400 publications and the expertise of 37 mountain soil scientists worldwide, we summarise what is known about the diversity and distribution patterns of each of these organismal groups, specifically along elevation, and provide an overview of available knowledge on the drivers explaining these patterns and their changes. In particular, we document an elevation-dependent decrease in faunal diversity above the treeline, while for cryptogams there is an initial increase above the treeline, followed by a decrease towards the nival belt. Thus, our data confirm the key role that elevation plays in shaping the biodiversity and distribution of these organisms in mountain soils. The response of prokaryote diversity to elevation, in turn, was more diverse, whereas fungal diversity appeared to be substantially influenced by plants. As far as available, we describe key characteristics, adaptations, and functions of mountain soil species, and despite a lack of ecological information about the uncultivated majority of prokaryotes, fungi, and protists, we illustrate the remarkable and unique diversity of life forms and life histories encountered in alpine mountain soils. By applying rule- as well as pattern-based literature-mining approaches and semi-quantitative analyses, we identified hotspots of mountain soil research in the European Alps and Central Asia and revealed significant gaps in taxonomic coverage, particularly among biocrusts, soil protists, and soil fauna. We further report thematic priorities for research on mountain soil biodiversity above the treeline and identify unanswered research questions. Building upon the outcomes of this synthesis, we conclude with a set of research opportunities for mountain soil biodiversity research worldwide. Soils in mountain ecosystems above the treeline fulfil critical functions and make essential contributions to life on land. Accordingly, seizing these opportunities and closing knowledge gaps appears crucial to enable science-based decision making in mountain regions and formulating laws and guidelines in support of mountain soil biodiversity conservation targets.

The decades-old problem of distinguishing spruce (Picea sp.) from larch (Larix sp.) wood is still debated in wood identification. Although species-specific anatomical traits have been proposed to address this issue, their variable appearance and limited diagnostic power hinder reliable differentiation, particularly for archaeological wood samples. Finding a stem disk collected over a century ago from a glacial moraine deposit brought us to face the Larix/Picea identification problem again. Here, we skimmed the literature for wood anatomical features typical for each species and examined these traits in the subfossil wood disk. Key features assessed included heartwood and sapwood colour differences, earlywood-to-latewood transitions, tracheid pitting in radial walls, ray tracheid pit borders, the number of epithelial cells per resin canal, and the position of resin canals in rays. Additionally, we measured tree-ring widths to attempt dendrochronological dating of the disk. Tree-ring measurements enabled precise dating and revealed a quasi-decadal occurrence of narrow and light rings, indicative of cyclical larch budmoth (Zeiraphera diniana Gn.) infestations. Based on the presence of these characteristic budmoth rings and successful crossdating with 31 published and unpublished larch chronologies, compared to poor correlation with spruce chronologies, we conclusively identified the disk as Larix decidua Mill. However, our wood anatomical observations did not distinguish between spruce and larch reliably, suggesting that some features may vary with tree age and stem position. This highlights the need for further investigation with targeted sampling of living trees to validate the diagnostic utility of certain anatomical features.

High-resolution temporal measurements in remote, high-elevation surface waters are required to better understand the dynamics of nitrate (NO3-) in response to changes in meteoclimatic conditions. This study reports on the first use of a UV-Vis submersible spectrophotometric probe (UV-Vis probe) to measure the hourly concentration of nitrate nitrogen (NO3--N) in a pond located at 2722 m a.s.l. in an alpine tundra area (NW Italian Alps), during two snow-free seasons (July-October) in 2014 and 2015. Weekly analyses of NO3--N and stable isotopes of water (delta O-18 and delta H-2), together with continuous meteorological, water temperature, and turbidity measurements, were performed over the same period. The integration of in-situ UV-Vis spectrophotometric measurements with weekly samples allowed depicting the role of summer precipitation, snow melt, and temperature (air and water) in influencing NO3- dynamics. Short-duration meteorological events (e.g., summer storms and rain-on-snow events) produced rapid variations of in-pond NO3- concentration, i.e., fivefold increase in 18 h, that would not be detectable using the traditional manual collection of discrete samples. The observed seasonal variability of NO3- concentration, negatively correlated with water temperature, highlighted the important role of in-pond biological processes leading to an enhanced N uptake and to the lowest NO3- concentration in the warmer periods. The occurrence of heavy rainfall events critically altered the expected seasonal NO3- trends, increasing the N supply to the pond. The comparison of N dynamics in two years characterised by extremely different meteoclimatic conditions allowed us to obtain insights on the potential effects of climate changes (e.g., high air temperature, heavy rainfalls, and rain-on-snow events) on sensitive aquatic ecosystems as high-elevation ponds.

Rock glaciers (RGs) provide significant water resources in mountain areas under climate change. Recent research has highlighted high concentrations of solutes including trace elements in RG-fed waters, with negative implications on water quality. Yet, sparse studies from a few locations hinder conclusions about the main drivers of solute export from RGs. Here, in an unprecedented effort, we collected published and unpublished data on rock glacier hydrochemistry around the globe. We considered 201 RG springs from mountain ranges across Europe, North and South America, using a combination of machine learning, multivariate and univariate analyses, and geochemical modeling. We found that 35 % of springs issuing from intact RGs (containing internal ice) have water quality below drinking water standards, compared to 5 % of springs connected to relict RGs (without internal ice). The interaction of ice and bedrock lithology is responsible for solute concentrations in RG springs. Indeed, we found higher concentrations of sulfate and trace elements in springs sourcing from intact RGs compared to water originating from relict RGs, mostly in specific lithological settings. Enhanced sulfide oxidation in intact RGs is responsible for the elevated trace element concentrations. Challenges for water management may arise in mountain catchments rich in intact RGs, and where the predisposing geology would make these areas geochemical RG hotspots. Our work represents a first comprehensive attempt to identify the main drivers of solute concentrations in RG waters.

Long-range transport of atmospheric pollutants threatens the pristine high-elevation environments, highly sensitive to environmental changes such as the global increase of nitrogen (N) emissions. Atmospheric depositions is an important component of N cycle transferring reactive nitrogen species from the atmosphere to terrestrial and aquatic compartments. Despite this, monitoring of atmospheric deposition in Alpine tundra regions is lacking. To reduce this gap, we present the chemical and isotopic composition (delta 15N, delta 18O in nitrate) of rain and snow deposition collected over a 3-year period (2018-2020) in a LTER site (A. Mosso Scientific Institute) in NW Italian Alps at 2901 m a.s.l. The highest annual volume-weighted mean (VWM) concentrations of oxidized and reduced N species (18 and 22 mu eq L-1, respectively) occurred in summer, while the lowest (5.8 and 3.6 mu eq L-1, respectively) occurred during the snow season. The N wet deposition load (3.9 kg ha- 1 y- 1.) greatly exceeded the N critical threshold, revealing that the area is exposed to excessive N input through atmospheric deposition with potentially detrimental consequences for aquatic ecosystems. The contribution of rain to inorganic N varied between 39 , 68 %, highlighting the importance of monitoring the composition of the rain component, in addition to the snowpack, even at high-altitude sites. The nitrate isotopic composition of wet deposition showed seasonal variation with lower delta 15N-NO3 15 N-NO 3 values (-10.6 %o to-2.2 %o ) in the summer months, reflecting the influence of vehicle emissions likely combined with an increase in emissions from agricultural sources, when the air masses originate from the Po Valley. Surface meteorological data coupled to the analysis of stable isotopes and air mass back trajectories showed that local mountain-valley breeze and the elevation of the continuous aerosol layer altitude in the warm season expose the study site to N-air pollutants originating from lowland and more distant anthropized areas (e.g., Po Valley). The reported data suite represents, to date, the first docu- mentation for ecosystems above the tree line in the European scenario.