Alpine headwaters emerging from glaciers and rock glaciers host different bacterial communities: Ecological implications for the future

Ecological "Windows of opportunity" influence biofilm prokaryotic diversity differently in glacial and non-glacial Alpine streams

In glacier-fed streams, the Windows of Opportunity (WOs) are periods of mild environmental conditions supporting the seasonal development of benthic microorganisms. WOs have been defined based on changes in biofilm biomass, but the responses of microbial diversity to WOs in Alpine streams have been overlooked. A two year (2017-2018) metabarcoding of epilithic and epipsammic biofilm prokaryotes was conducted in Alpine streams fed by glaciers (kryal), rock glaciers (rock glacial), or groundwater/precipitation (krenal) in two catchments of the Central-Eastern European Alps (Italy), aiming at testing the hypothesis that: 1) environmental WOs enhance not only the biomass but also the α-diversity of the prokaryotic biofilm in all stream types, 2) diversity and phenology of prokaryotic biofilm are mainly influenced by the physical habitat in glacial streams, and by water chemistry in the other two stream types. The study confirmed kryal and krenal streams as endmembers of epilithic and sediment prokaryotic α- and β-diversity, with rock glacial streams sharing a large proportion of taxa with the two other stream types. Alpha-diversity appeared to respond to ecological WOs, but, contrary to expectations, seasonality was less pronounced in the turbid kryal than in the clear streams. This was attributed to the small size of the glaciers feeding the studied kryal streams, whose discharge dynamics were those typical of the late phase of deglaciation. Prokaryotic α-diversity of non-glacial streams tended to be higher in early summer than in early autumn. Our findings, while confirming that high altitude streams are heavily threatened by climate change, underscore the still neglected role of rock glacier runoffs as climate refugia for the most stenothermic benthic aquatic microorganism. This advocates the need to define and test strategies for protecting these ecosystems for preserving, restoring, and connecting cold Alpine aquatic biodiversity in the context of the progressing global warming.

Assessment of Human Health Risk Indices Due to Metal Contamination in the Surface Water of the Negro River Sub-Basin, Áncash

The accelerated loss of glacial cover in the Cordillera Blanca in Áncash, Peru, exposes the underlying rocks with high concentrations of sulfides from the Chicama Formation to oxidation and leaching processes, generating acid rock drainage (ARD) in glacial and periglacial areas. These are transported by surface runoff, contaminating the surface water with high concentrations of metals and sulfates, as well as increasing the acidity, which poses a risk to human health and the ecosystem. Therefore, the risk indices for human health due to metal contamination were evaluated at 19 surface water sampling points distributed in the Río Negro sub-basin. Hydrochemical analyses revealed average metal concentrations in the following order: Fe (28.597 mg/L), Al (3.832 mg/L), Mn (1.085 mg/L), Zn (0.234 mg/L), Ni (0.085 mg/L), Co (0.053 mg/L), Li (0.036 mg/L), Cu (0.005 mg/L), and Pb (0.002 mg/L). The risk was determined by calculating the Heavy Metal Pollution Index (HPI) and the Hazard Index (HI). The average HPI value was 360.959, indicating a high level of contamination (HPI ≥ 150). The human health risk assessment indicated that adverse effects caused by iron, lithium, and cobalt in children and adults should be considered. Through the use of Pearson correlation analysis, principal component analysis, and cluster analysis, it was identified that SO42-, Fe, S, Al, Co, Mn, Ni, Zn, and Li originate from natural sources, associated with the generation of ARD in glacial and periglacial areas.

Differences of bacterioplankton communities between the source and upstream regions of the Yangtze River: microbial structure, co-occurrence pattern, and environmental influencing factors

The source area of the Yangtze River is located in the hinterland of the Qinghai-Tibet Plateau, which is known as the "Earth's third pole." It is the water conservation area and the natural barrier of the ecosystem of the Yangtze River basin. It is also the most sensitive area of the natural ecosystem, and the ecological environment is very fragile. Microorganisms play key roles in the biogeochemical processes of water. In this paper, the bacterioplankton communities in the source and upstream regions of the Yangtze River were studied based on 16S rRNA high-throughput sequencing, and their environmental influencing factors were further analyzed. Results showed that the upstream region had higher richness and diversity than the source region. The predominant bacterial phyla in the source and upstream regions were Proteobacteria, Firmicutes, and Actinobacteriota. The bacterial phyla associated with municipal pollution and opportunistic pathogen, such as Firmicutes and Actinobacteriota, were more abundant in the upstream. By contrast, distinct planktonic bacterial genera associated with mining pollution, such as Acidiphilium and Acidithiobacillus, were more abundant in the source region. The co-occurrence network showed that the interaction of bacterioplankton community is more frequent in the upstream. The bacterioplankton community compositions, richness, and functional profiles were affected by the spatial heterogeneity. Moreover, variation partitioning analysis further confirmed that the amount of variation in the source region independently explained by variables of altitude was the largest, followed by water nutrient. This paper revealed the spatial distribution of planktonic bacterial communities in the source and upstream regions of the Yangtze River and its correlation with environmental factors, providing information support for ensuring the health and safety of aquatic ecosystems in the Yangtze River Basin.

Niche-mediated bacterial community composition in continental glacier alluvial valleys under cold and arid environments

Introduction

Bacteria are an essential component of glacier-fed ecosystems and play a dominant role in driving elemental cycling in the hydrosphere and pedosphere. However, studies of bacterial community composition mechanisms and their potential ecological functions from the alluvial valley of mountain glaciers are extremely scarce under cold and arid environments.

Methods

Here, we analyzed the effects of major physicochemical parameters related to soil on the bacterial community compositions in an alluvial valley of the Laohugou Glacier No. 12 from the perspective of core, other, and unique taxa and explored their functional composition characteristics.

Results and discussion

The different characteristics of core, other, and unique taxa highlighted the conservation and difference in bacterial community composition. The bacterial community structure of the glacial alluvial valley was mainly affected by the above sea level, soil organic carbon, and water holding capacity. In addition, the most common and active carbon metabolic pathways and their spatial distribution patterns along the glacial alluvial valley were revealed by FAPTOTAX. Collectively, this study provides new insights into the comprehensive assessment of glacier-fed ecosystems in glacial meltwater ceasing or glacier disappearance.

The microbiome of the ice-capped Cayambe Volcanic Complex in Ecuador

A major challenge in microbial ecology is to understand the principles and processes by which microbes associate and interact in community assemblages. Microbial communities in mountain glaciers are unique as first colonizers and nutrient enrichment drivers for downstream ecosystems. However, mountain glaciers have been distinctively sensitive to climate perturbations and have suffered a severe retreat over the past 40  years, compelling us to understand glacier ecosystems before their disappearance. This is the first study in an Andean glacier in Ecuador offering insights into the relationship of physicochemical variables and altitude on the diversity and structure of bacterial communities. Our study covered extreme Andean altitudes at the Cayambe Volcanic Complex, from 4,783 to 5,583 masl. Glacier soil and ice samples were used as the source for 16S rRNA gene amplicon libraries. We found (1) effects of altitude on diversity and community structure, (2) the presence of few significantly correlated nutrients to community structure, (3) sharp differences between glacier soil and glacier ice in diversity and community structure, where, as quantified by the Shannon γ-diversity distribution, the meta-community in glacier soil showed more diversity than in glacier ice; this pattern was related to the higher variability of the physicochemical distribution of variables in the former substrate, and (4) significantly abundant genera associated with either high or low altitudes that could serve as biomarkers for studies on climate change. Our results provide the first assessment of these unexplored communities, before their potential disappearance due to glacier retreat and climate change.

The Ecological Differentiation of Particle-Attached and Free-Living Bacterial Communities in a Seasonal Flooding Lake-the Poyang Lake

Particle-attached (PA) and free-living (FL) bacterial communities play essential roles in the biogeochemical cycling of essential nutrients in aquatic environments. However, little is known about the factors that drive the differentiation of bacterial lifestyles, especially in flooding lake systems. Here we assessed the compositional and functional similarities between the FL and PA bacterial fractions in a typical flooding lake-the Poyang Lake (PYL) of China. The results revealed that PA communities had significantly different compositions and functions from FL communities in every hydrological period, and the diversity of both PA and FL communities was affected mainly by the water regime rather than bacterial lifestyles. PA communities were more diverse and enriched with Proteobacteria and Bacteroidetes, while FL communities had more Actinobacteria. There was a higher abundance of photosynthetic and nitrogen-cycling bacterial groups in PA communities, but a higher abundance of members involved in hydrocarbon degradation, aromatic hydrocarbon degradation, and methylotrophy in FL communities. Water properties (e.g., temperature, pH, total phosphorus) significantly regulated the lifestyle variations of PA and FL bacteria in PYL. Collectively, our results have demonstrated a clear ecological differentiation of PA and FL bacterial communities in flooding lakes, suggesting that the connectivity between FL and PA bacterial fractions is water property-related rather than water regime-related.

Benthic Biofilms in Glacier-Fed Streams from Scandinavia to the Himalayas Host Distinct Bacterial Communities Compared with the Streamwater

Microbial life in glacier-fed streams (GFSs) is dominated by benthic biofilms which fulfill critical ecosystem processes. However, it remains unclear how the bacterial communities of these biofilms assemble in stream ecosystems characterized by rapid turnover of benthic habitats and high suspended sediment loads. Using16S rRNA gene amplicon sequence data collected from 54 GFSs across the Himalayas, European Alps, and Scandinavian Mountains, we found that benthic biofilms harbor bacterial communities that are distinct from the bacterial assemblages suspended in the streamwater. Our data showed a decrease in species richness in the benthic biofilms compared to the bacterial cells putatively free-living in the water. The benthic biofilms also differed from the suspended water fractions in terms of community composition. Differential abundance analyses highlighted bacterial families that were specific to the benthic biofilms and the suspended assemblages. Notably, source-sink models suggested that the benthic biofilm communities are not simply a subset of the suspended assemblages. Rather, we found evidence that deterministic processes (e.g., species sorting) shape the benthic biofilm communities. This is unexpected given the high vertical mixing of water and contained bacterial cells in GFSs and further highlights the benthic biofilm mode of life as one that is determined through niche-related processes. Our findings therefore reveal a "native" benthic biofilm community in an ecosystem that is currently threatened by climate-induced glacier shrinkage. IMPORTANCE Benthic biofilms represent the dominant form of life in glacier-fed streams. However, it remains unclear how bacterial communities within these biofilms assemble. Our findings from glacier-fed streams from three major mountain ranges across the Himalayas, the European Alps and the Scandinavian Mountains reveal a bacterial community associated with benthic biofilms that is distinct from the assemblage in the overlying streamwater. Our analyses suggest that selection is the underlying process to this differentiation. This is unexpected given that bacterial cells that are freely living or attached to the abundant sediment particles suspended in the water continuously mix with the benthic biofilms. The latter colonize loose sediments that are subject to high turnover owing to the forces of the water flow. Our research unravels the existence of a microbiome specific to benthic biofilms in glacier-fed streams, now under major threats due to global warming.

Role of rock glaciers and other high-altitude depositional units in the hydrology of the mountain watersheds of the Northern Patagonian Andes

Mountain depositional landforms are important units for freshwater supply in regions with water deficits and significant droughts during the summer season. In the Northern Patagonian Andes, the cold climatic events during the Pleistocene period left a large number of glacial and periglacial depositional landforms, among which a glacial cirque called La Hoya stands out. An analysis of geomorphological landforms, climatic data, soil temperature, flows in springs and streams, electrical conductivity measurements, and stable isotope determination of water, were made to study the hydrological role of these depositional mountain landforms. In this region, precipitations are concentrate during the winter season when an important snow cover accumulates and persists until spring. During winter and spring seasons, part of the snowmelt infiltrates, being kept in solid states inside the depositional landforms, and part of it contributes to the runoff between winter and summer. At the ends of spring and early summer, the snowmelt is the main water contribution to the La Hoya watershed. During late summer and autumn, the most important water contribution is from groundwater discharge. Where glacial ice is absent and the presence of permafrost is limited or non-existent, morphosedimentary units are important landforms for water storage and streams sustenance. This is the case of the city of Esquel, which depends exclusively on the "Los Bandidos" stream for water supply, which is sustained throughout the year by these landforms. The increase in temperature and the decrease in precipitation in this region highlights the importance of the high-altitude depositional landforms for the capture, storage, and distribution of water resources in the Northern Patagonian Andes.

Genomic and metabolic adaptations of biofilms to ecological windows of opportunity in glacier-fed streams

In glacier-fed streams, ecological windows of opportunity allow complex microbial biofilms to develop and transiently form the basis of the food web, thereby controlling key ecosystem processes. Using metagenome-assembled genomes, we unravel strategies that allow biofilms to seize this opportunity in an ecosystem otherwise characterized by harsh environmental conditions. We observe a diverse microbiome spanning the entire tree of life including a rich virome. Various co-existing energy acquisition pathways point to diverse niches and the exploitation of available resources, likely fostering the establishment of complex biofilms during windows of opportunity. The wide occurrence of rhodopsins, besides chlorophyll, highlights the role of solar energy capture in these biofilms while internal carbon and nutrient cycling between photoautotrophs and heterotrophs may help overcome constraints imposed by oligotrophy in these habitats. Mechanisms potentially protecting bacteria against low temperatures and high UV-radiation are also revealed and the selective pressure of this environment is further highlighted by a phylogenomic analysis differentiating important components of the glacier-fed stream microbiome from other ecosystems. Our findings reveal key genomic underpinnings of adaptive traits contributing to the success of complex biofilms to exploit environmental opportunities in glacier-fed streams, which are now rapidly changing owing to global warming.

Rock glaciers and related cold rocky landforms: Overlooked climate refugia for mountain biodiversity

Mountains are global biodiversity hotspots where cold environments and their associated ecological communities are threatened by climate warming. Considerable research attention has been devoted to understanding the ecological effects of alpine glacier and snowfield recession. However, much less attention has been given to identifying climate refugia in mountain ecosystems where present-day environmental conditions will be maintained, at least in the near-term, as other habitats change. Around the world, montane communities of microbes, animals, and plants live on, adjacent to, and downstream of rock glaciers and related cold rocky landforms (CRL). These geomorphological features have been overlooked in the ecological literature despite being extremely common in mountain ranges worldwide with a propensity to support cold and stable habitats for aquatic and terrestrial biodiversity. CRLs are less responsive to atmospheric warming than alpine glaciers and snowfields due to the insulating nature and thermal inertia of their debris cover paired with their internal ventilation patterns. Thus, CRLs are likely to remain on the landscape after adjacent glaciers and snowfields have melted, thereby providing longer-term cold habitat for biodiversity living on and downstream of them. Here, we show that CRLs will likely act as key climate refugia for terrestrial and aquatic biodiversity in mountain ecosystems, offer guidelines for incorporating CRLs into conservation practices, and identify areas for future research.

Distinct Microbial Communities in Adjacent Rock and Soil Substrates on a High Arctic Polar Desert

Understanding microbial niche variability in polar regions can provide insights into the adaptive diversification of microbial lineages in extreme environments. Compositions of microbial communities in Arctic soils are well documented but a comprehensive multidomain diversity assessment of rocks remains insufficiently studied. In this study, we obtained two types of rocks (sandstone and limestone) and soils around the rocks in a high Arctic polar desert (Svalbard), and examined the compositions of archaeal, bacterial, fungal, and protistan communities in the rocks and soils. The microbial community structure differed significantly between rocks and soils across all microbial groups at higher taxonomic levels, indicating that Acidobacteria, Gemmatimonadetes, Latescibacteria, Rokubacteria, Leotiomycetes, Pezizomycetes, Mortierellomycetes, Sarcomonadea, and Spirotrichea were more abundant in soils, whereas Cyanobacteria, Deinococcus-Thermus, FBP, Lecanoromycetes, Eurotiomycetes, Trebouxiophyceae, and Ulvophyceae were more abundant in rocks. Interestingly, fungal communities differed markedly between two different rock types, which is likely to be ascribed to the predominance of distinct lichen-forming fungal taxa (Verrucariales in limestone, and Lecanorales in sandstone). This suggests that the physical or chemical properties of rocks could be a major determinant in the successful establishment of lichens in lithic environments. Furthermore, the biotic interactions among microorganisms based on co-occurrence network analysis revealed that Polyblastia and Verrucaria in limestone, and Atla, Porpidia, and Candelariella in sandstone play an important role as keystone taxa in the lithic communities. Our study shows that even in niches with the same climate regime and proximity to each other, heterogeneity of edaphic and lithic niches can affect microbial community assembly, which could be helpful in comprehensively understanding the effects of niche on microbial assembly in Arctic terrestrial ecosystems.

Testing Different Membrane Filters for 16S rRNA Gene-Based Metabarcoding in Karstic Springs

Introduction: Karstic springs are used worldwide by rural communities as sources of fresh water for humans and livestock. In Romania, one-third of the population has no direct access to a public water supply. The present study is part of a country-wide project to develop simple, quick and cheap methods for seasonal environmental and microbiological monitoring of karstic springs used as drinking water by rural populations. Critical steps for monitoring workflow consist of evaluating water quality and selecting suitable membrane filters to efficiently capture environmental DNA for further microbial diversity estimation using 16S rRNA gene-based metabarcoding. Methods: Several commercial membrane filters of different compositions and pore sizes were tested on the water sampled from three karstic springs in Romania, followed by water chemistry and whole community 16S rRNA gene-based metabarcoding analysis. Results: We found that different types of applied membrane filters provide varying recovery in diversity and abundance of both overall and pathogenic bacteria. Conclusions: The result of the experiment with different filters shows that mixed cellulose ester, cellulose acetate, and nitrate membranes of 0.20 and 0.22 µm are the best for amplicon-based metabarcoding monitoring of karst springs.

Glacier Ice Thickness Estimation and Future Lake Formation in Swiss Southwestern Alps—The Upper Rhône Catchment: A VOLTA Application

Glacial lake formations are currently being observed in the majority of glacierized mountains in the world. Given the ongoing climate change and population increase, studying glacier ice thickness and bed topography is a necessity for understanding the erosive power of glacier activity in the past and lake formation in the future. This study uses the available information to predict potential sites for future lake formation in the Upper Rhône catchment located in the Southwestern Swiss Alps. The study integrates the latest available glacier outlines and high-quality digital elevation models (DEMs) into the Volume and Topography Automation (VOLTA) model to estimate ice thickness within the extent of the glaciers. Unlike the previous ice thickness models, VOLTA calculates ice thickness distribution based on automatically-derived centerlines, while optimizing the model by including the valley side drag parameter in the force equation. In this study, a total ice volume of 37.17 ± 12.26 km3 (1σ) was estimated for the Upper Rhône catchment. The comparison of VOLTA performance indicates a stronger relationship between measured and predicted bedrock, confirming the less variability in VOLTA’s results (r2 ≈ 0.92) than Glacier Bed Topography (GlabTop) (r2 ≈ 0.82). Overall, the mean percentage of ice thickness error for all measured profiles in the Upper Rhône catchment is around ±22%, of which 28 out of 42 glaciers are underestimated. By incorporating the vertical accuracy of free-ice DEM, we could identify 171 overdeepenings. Among them, 100 sites have a high potential for future lake formation based on four morphological criteria. The visual evaluation of deglaciated areas also supports the robustness of the presented methodology, as 11 water bodies were already formed within the predicted overdeepenings. In the wake of changing global climate, such results highlight the importance of combined datasets and parameters for projecting the future glacial landscapes. The timely information on future glacial lake formation can equip planners with essential knowledge, not only for managing water resources and hazards, but also for understanding glacier dynamics, catchment ecology, and landscape evolution of high-mountain regions.