Modelling glacier variation and its impact on water resource in the Urumqi Glacier No. 1 in Central Asia

Antibiotic resistance genes in integrated surface ice, cryoconite, and glacier-fed stream in a mountain glacier in Central Asia

Glacier ice, cryoconite, and glacier-fed streams are interconnected features that have important implications for the dynamics and distribution of abiotic and biotic materials. However, the presence and behavior of antibiotic resistance genes (ARGs) within these glacial environments remained largely unexplored. Addressing this gap, we hypothesized that ARGs are widely distributed and exhibit distinct yet interconnected patterns of diversity and dynamics in these glacial environments. Here, we investigated ARGs in a mountain glacier in Central Asia. A total of 944 ARGs, spanning 22 antibiotic classes, were identified, with 633 ARGs shared across all three environments. Cryoconite exhibited the highest ARG richness, followed by ice, while stream biofilm displayed the lowest value. Exploring ARG profiles, we observed a consistent pattern in terms of antibiotic class and resistance mechanism across all three environments. Beta-lactam resistance genes exhibited the highest diversity, followed by multidrug, glycopeptide, and MLS. The predominant mechanisms were antibiotic inactivation, antibiotic efflux, and target alteration. The most prevalent ARG is cls, followed by mdfA, ropB, fabI, and macB. The similarity in ARG profiles between surface ice and cryoconite samples was more pronounced than their resemblance to stream biofilm samples. The variations of ARG profiles between any pair of environments were largely contributed by turnover component. Further insights into microbial interactions revealed 2328 significant associations between 80 OTUs and 356 ARGs, indicating complex relationships. Certain OTUs, including those from the genera Polaromonas, Ferruginibacter, Hymenobacter, Phormidesmis, Novosphingobium, and Polymorphobacter, were speculated as potential hosts for a variety of ARGs. Our findings underscore the intricate dynamics of antibiotic resistance in glacial ecosystems, emphasizing the need for a holistic understanding of ARG distribution, diversity, and associations across diverse environmental compartments. This research contributes valuable insights into the potential ecological implications of antibiotic resistance dissemination in cold environments, particularly as influenced by increasing climate change.

The role of subsurface ice in sustaining bacteria in continental and maritime glaciers

In supraglacial environments, surface and subsurface ices are two distinct and connected microhabitats in terms of physicochemical and biological aspects. At the frontline of climate change, glaciers lose tremendous ice masses to downstream ecosystems, serving as crucial sources of both biotic and abiotic materials. In this study, we studied the disparities and relationships of microbial communities between surface and subsurface ices collected from a maritime and a continental glacier during summer. The results showed that surface ices had significantly higher nutrients and were more physiochemically different than subsurface ices. Despite lower nutrients, subsurface ices had higher alpha-diversity with more unique and enriched operational taxonomic units (OTUs) than surface ices, indicating the potential role of subsurface as a bacterial refuge. Sorensen dissimilarity between bacterial communities in surface ices and subsurface ices was mainly contributed by the turnover component, suggesting strong species replacement from surface to subsurface ices due to large environmental gradients. For different glaciers, the maritime glacier had significantly higher alpha-diversity than the continental glacier. The difference between surface and subsurface communities was more pronounced in the maritime glacier than in the continental glacier. The network analysis revealed that surface-enriched and subsurface-enriched OTUs formed independent modules, with surface-enriched OTUs having closer interconnections and greater importance in the network of the maritime glacier. This study highlights the important role of subsurface ice as a bacterial refuge and enriches our knowledge of microbial properties in glaciers.

Impact of Climate Change on the Glacier and Runoff of a Glacierized Basin in Harlik Mountain, Eastern Tianshan Mountains

The impact of climate change on glaciers and the hydrological processes in the easternmost end of the eastern Tianshan Mountains has yet to be understood. This study investigated the glacier change (area, surface elevation and volume change) and analyzed the variation of the observed runoff series over the past four decades in the Yushugou Basin, Eastern Tianshan Mountains. The hydrological processes were also simulated through the HBV-light model to quantify the impact of climate change on the glacier and runoff. The results showed that the glacier area has decreased by 13% and the total volume has decreased by 0.018 km3 over the past four decades. A significant increasing trend (p < 0.01) was detected for the annual runoff and monthly runoff (May to September; p < 0.01). The simulation results revealed that the Yushugou River was highly recharged by glacial runoff and a negative tendency was found for the glacier mass balance on the basin scale over the past 38 years. As a region with an extremely dry climate and the lowest precipitation in the Tianshan Mountains, the observation and simulation of glaciers is critical to the security assessment of local water resources.

Recent Changes in Glaciers in the Northern Tien Shan, Central Asia

The Tien Shan is regarded as the “Water tower of Central Asia,” being a solid reservoir of freshwater resources and also a natural and early warning indicator of climate change. Research on glaciers is important for the sustainable development and management of water resources in Central Asia. This study investigated the spatiotemporal dynamics of glaciers in the northern Tien Shan from 1990 to 2015 using multi-source remote sensing and meteorological data. The results showed that the total area and volume of glaciers in the northern Tien Shan exhibited negative trends, decreasing by 456.43 km2 (16.08%) and 26.14 km3 (16.38%), respectively. The reduction in the total glacier area exhibited an accelerating trend, decreasing by 0.60%/a before 2000, but by 0.71%/a after 2000. Glaciers in the outer northern Tien Shan region, with areas < 2 km2 showed the greatest shrinkage, especially those in the northeastern and southwestern regions. All aspects in the northern Tien Shan exhibited negative trends in the glacier area, especially in the east–west aspects (shrinkage of 24.74–38.37%). Regarding altitude, the termini of glaciers rose continuously from 1990 to 2015, particularly for glaciers below 3700 m, with a total area decrease of 30.37%, and the lower altitude of the glaciers showed a higher area decrease.

Landscape and vegetation traits of urban green space can predict local surface temperature

Societal and technological advances have triggered demands to improve urban environmental quality. Urban green space (UGS) can provide effective cooling service and thermal comfort to alleviate warming impacts. We investigated the relative influence of a comprehensive spectrum of UGS landscape and vegetation factors on surface temperature in arid Urumqi city in northwest China. Built-up area range was extracted from Luojia 1-01 (LJ1-01) satellite data, and within this range, the landscape metric information and vegetation index information of UGS were obtained based on PlanetScope data, and a total of 439 sampling grids (1 km × 1 km) were generated. The urban surface temperature of built-up areas was extracted from Landsat8-TIRS images. The 12 landscape metrics and 14 vegetation indexes were assigned as independent variables, and surface temperature the dependent variable. Support Vector Machine (SVM), Gradient Boost Regression Tree (GBRT) and Random Forest (RF) were enlisted to establish numerical models to predict surface temperature. The results showed that: (1) It was feasible to predict local surface temperature using a combination of landscape metrics and vegetation indexes. Among the three models, RF demonstrated the best accuracy. (2) Collectively, all the factors play a role in the surface-temperature prediction. The most influential factor was Difference Vegetation Index (DVI), followed by Green Normalized Difference Vegetation Index (GNDVI), Class Area (CA) and AREA. This study developed remote sensing techniques to extract a basket of UGS factors to predict the surface temperature at local urban sites. The methods could be applied to other cities to evaluate the cooling impacts of green infrastructures. The findings could provide a scientific basis for ecological spatial planning of UGS to optimize cooling benefits in the arid region.

Bacterial communities in surface and basal ice of a glacier terminus in the headwaters of Yangtze River on the Qinghai-Tibet Plateau

BACKGROUND

On the front lines of climate change, glacier termini play crucial roles in linking glaciers and downstream ecosystems during glacier retreat. However, we lack a clear understanding of biological processes that occur in surface and basal ice at glacier termini.

METHODS

Here, we studied the bacterial communities in surface ice and basal ice (the bottom layer) of a glacier terminus in the Yangtze River Source, Qinghai-Tibet Plateau.

RESULTS

Surface and basal ice harbored distinct bacterial communities but shared some core taxa. Surface ice communities had a higher α-diversity than those in basal ice and were dominated by Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, and Cyanobacteria while basal ice was dominated by Firmicutes and Proteobacteria. The bacterial communities were also substantially different in functional potential. Genes associated with functional categories of cellular processes and metabolism were significantly enriched in surface ice, while genes connected to environmental information processing were enriched in basal ice. In terms of biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur, bacterial communities in surface ice were enriched for genes connected to aerobic carbon fixation, aerobic respiration, denitrification, nitrogen assimilation, nitrogen mineralization, sulfur mineralization, alkaline phosphatase, and polyphosphate kinase. In contrast, bacterial communities in basal ice were enriched for genes involved in anaerobic carbon fixation, fermentation, nitrate reduction, 2-aminoethylphosphonic acid pathway, G3P transporter, glycerophosphodiester phosphodiesterase, and exopolyphosphatase. Structural equation modeling showed that total nitrogen and environmental carbon:phosphorus were positively while environmental nitrogen:phosphorus was negatively associated with taxonomic β-diversity which itself was strongly associated with functional β-diversity of bacterial communities.

CONCLUSIONS

This study furthers our understanding of biogeochemical cycling of the mountain cryosphere by revealing the genetic potential of the bacterial communities in surface and basal ice at the glacier terminus, providing new insights into glacial ecology as well as the influences of glacier retreat on downstream systems.

Assessing glacier retreat and its impact on water resources in a headwater of Yangtze River based on CMIP6 projections

Glacier retreat caused by global warming alters the hydrological regime and poses far-reaching challenges to water resources and nature conservation of the headwater of Yangtze River, and its vast downstream regions with dense population. However, there is still lack of a robust modeling framework of the "climate-glacier-streamflow" in this water tower region, to project the future changes of glacier mass balance, glacier geometry, and the consequent impacts on runoff. Moreover, it is imperative to use the state-of-the-art sixth phase Coupled Model Intercomparison Project (CMIP6) to assess glacio-hydrology variations in future. In this study, we coupled a glacio-hydrological model (FLEX^G) with a glacier retreat method (Δh-parameterization) to simulate glacio-hydrological processes in the Dongkemadi Glacier (over 5155 m.a.s.l), which has the longest continuous glacio-hydrology observation on the headwater of Yangtze River. The FLEX^G-Δh model was forced with in-situ observed meteorological data, radar ice thickness, remote sensing topography and land cover data, and validated by measured runoff. The results showed that the model was capable to simulate hydrological processes in this glacierized basin, with Kling-Gupta efficiency (I_KGE) of daily runoff simulation 0.88 in calibration and 0.70 in validation. Then, forcing by the bias-corrected meteorological forcing from the eight latest CMIP6 Earth system models under two climate scenarios (RCP2.6 and RCP8.5), we assessed the impact of future climate change on glacier response and its hydrological effects. The results showed that, to the end of simulation in 2100, the volume of the Dongkemadi Glacier would continuously retreat. For the RCP2.6 and RCP8.5 scenarios, the glacier volume will decrease by 8.7 × 10⁸ m³ (74%) and 10.8 × 10⁸ m³ (92%) respectively in 2100. The glacier runoff will increase and reach to peak water around 2060 to 2085, after this tipping point water resources will likely decrease.

Runoff change controlled by combined effects of multiple environmental factors in a headwater catchment with cold and arid climate in northwest China

The limited runoff in cold and arid regions is sensitive to environmental changes, and it is thus urgent to explore the change and controlling factors of runoff under the background of global warming and intensified human activities. However, previous studies have rarely considered the combined effects of multiple controlling factors at varying scales over time. With the headwater region of the Manas River in northwest China as the study area, we investigated the change in runoff for the period of 1954-2016 and its relationship with regional environmental factors (e.g. precipitation PCP, temperature TMP, potential evapotranspiration ET₀, snow cover extent SCE, land use, and normalized difference vegetation index NDVI) and/or global atmospheric circulation (e.g. North Atlantic Oscillation NAO, Arctic Oscillation AO, Pacific Interdecadal Oscillation PDO, and El Nino Southern Oscillation ENSO). In particular, the combined effects of multiple environmental factors were determined at different scales by the multiple wavelet coherence. The annual runoff significantly increased at a rate of 0.508 × 10⁸ m³/decade, and the climate tended to be warmer and wetter. Among the regional and global environmental factors, NDVI and ENSO were the single factor mostly correlated with runoff, while NDVI-TMP and ENSO-PDO were the combined factors with the stronger relations on runoff, respectively. The regional environmental factors had larger impacts on runoff than the global environmental factors, and the natural factors outperformed human activities in controlling runoff. The accelerated melting of snow/glacier induced by the increasing temperature dominated runoff change, and the increasing water inputs from wetter climate may play a second role in runoff. The runoff characteristics in cold and arid regions seem to be different from those regions with little snow/glacier, which should be paid more attention. The employed multiple wavelet coherence is helpful in determining the processes dominating runoff change.

Modeling of Mass Balance Variability and Its Impact on Water Discharge from the Urumqi Glacier No. 1 Catchment, Tian Shan, China

Originating in the Tian Shan mountains, Urumqi River plays a key role in terms of water supply to downstream areas. In its headwaters, Urumqi Glacier No. 1 (UG1) is the largest glacier contributing to water discharge. Assessing its response to the changing climatic conditions in the area is of major importance to quantify future water availability. We here apply COSIPY, a COupled Snowpack and Ice surface energy and mass balance model in PYthon, to UG1, implementing a new albedo parameterization which integrates site-specific bare-ice albedo values on a pixel-by-pixel basis observed by remote sensing. We assess model performance threefold: quantitatively based on long-term measurement data of (1) surface mass balance (SMB) and (2) water discharge as well as qualitatively (3) comparing simulated snow line altitudes to such imated on the basis of time-lapse photography. Comparison of the modeled SMB with annually-averaged data from ablation stakes reveals that COSIPY including the new albedo parameterization accounts for 57.6% of the variance observed in the measurements. The original albedo parameterization performs only slightly inferior (57.1%). Glacier-wide comparison between modeled and glaciological SMB shows high agreement. In terms of discharge prediction, COSIPY reproduces onset and duration of the discharge season well. Estimated discharge from the whole catchment shows shortcomings in exactly matching the measured times series, but interannual variability is captured.

Recent Changes in Water Discharge in Snow and Glacier Melt-Dominated Rivers in the Tienshan Mountains, Central Asia

Global warming has generally led to changes in river runoffs fed by snow and glacier meltwater in mountain ranges. The runoff of the Aksu River, which originates in the Southern Tienshan Mountains, exhibited a positive trend during 1979–2002, but this trend reversed during 2002–2015. Through a comprehensive analysis, this study aims to estimate potential reasons for changes in the runoff of its two contrasting headwaters: the Toxkan and Kumalak Rivers, based on climatic data, the altitude of the 0 °C isotherm, glacier mass balance (GMB), snow cover area (SCA), snow depth (SD) and the sensitivity model. For the Toxkan River, the decrease in spring runoff mainly resulted from reductions in precipitation, whereas the decrease in summer runoff was mainly caused by early snowmelt in spring and a much-reduced snow meltwater supply in summer. In addition, the obvious glacier area reduction in the catchment (decreased to less than 4%) also contributed to the reduced summer runoff. For the Kumalak River, a sharp decrease rate of 10.21 × 108 m3/decade in runoff was detected due to summertime cooling of both surface and upper air temperatures. Reduced summer temperatures with a positive trend in precipitation not only inhibited glacier melting but also dropped the 0 °C layer altitude, resulting in a significant increase in summertime SCA and SD, a slowing of the glacier negative mass balance, and a lowering of the snow-line altitude.

Runoff Changes from Urumqi Glacier No. 1 over the Past 60 Years, Eastern Tianshan, Central Asia

Glaciers are vital to water resources in the arid land of central Asia. Long-term runoff records in the glacierized area are particularly valuable in terms of evaluating glacier recession and water resource change on both a regional and global scale. The runoff records of streams draining basins with 46% current glacier cover, located at the Urumqi Glacier No. 1 in the source area of the Urumqi River in eastern Tianshan, central Asia, were examined for the purpose of assessing climatic and glacial influences on temporal patterns of streamflow for the period 1959–2018. Results suggest that runoff from the catchment correlates well with temperature and associated precipitation data. During the period 1993–2018, it increased by 114.39 × 104 m3, which was 1.7 times the average runoff during the period 1959–1992. A simple water balance model is introduced to calculate the different components of the runoff, including precipitation runoff from glacier surface and from nonglacial areas, glacier mass balance and glacial runoff. Thus, the long-term change of each component and its response to climate change are revealed. We found that the period 1997–2018 is likely to be the “peak water” (tipping point) of the glacial runoff resulting from shrinkage of glacier area.

A GIS-Based Multi-Criteria Decision Analysis Model for Determining Glacier Vulnerability

Investigating the causes of the spatial heterogeneity of glacial changes offers vital information about glacial behavior and provides forecasting ability to define where glacier retreat may occur in the future. This study was designed to determine the spatial distribution of Ağrı Mountain glacier vulnerability. The main goal of the current study was to assess the forecasting capabilities of Geographical Information System (GIS)-based Multi-Criteria Decision Analysis (MCDA) for determining the location of the mountain glacier retreat. To estimate the glacier retreat, the following criteria were selected: elevation, aspect, slope, direction, and glacier surface temperature anomaly (GSTA). The entropy method was used for weighting the criteria for the evaluation of the vulnerable areas of the glacier. The results of this method clearly indicate a strong relationship between GSTA, direction, and elevation criteria and glacier retreat. The glacier vulnerability map was created by synthesizing criteria layers with their weights. The vulnerability map provided a consistency of 77.8% in the short term and 92.1% in the long term. In the study, the priority melting zones were determined and glacial retreat locations were forecasted in 10-year periods.

A surrogate weighted mean ensemble method to reduce the uncertainty at a regional scale for the calculation of potential evapotranspiration

We propose a weighted ensemble approach using a surrogate variable. As a case study, the degree of agreement (DOA) statistics for potential evapotranspiration (PET) was determined to compare the ordinary arithmetic mean ensemble (OAME) method and the surrogate weighted mean ensemble (SWME) method for three domains. Solar radiation was used as the surrogate variable to determine the weight values for the ensemble members. Singular vector decomposition with truncation values was used to select five ensemble members for the SWME method. The SWME method tended to have greater DOA statistics for PET than the OAME method with all available models. The distribution of PET values for the SWME method also had greater DOA statistics than that for the OAME method over relatively large spatial extent by month. These results suggest that the SWME method based on the weight value derived from the surrogate variable is suitable for exploiting both diversity and elitism to minimize the uncertainty of PET ensemble data. These findings could contribute to a better design of climate change adaptation options by improving confidence of PET projection data for the assessment of climate change impact on natural and agricultural ecosystems using the SWME method.

Ecological networks reveal contrasting patterns of bacterial and fungal communities in glacier-fed streams in Central Asia

Bacterial and fungal communities in biofilms are important components in driving biogeochemical processes in stream ecosystems. Previous studies have well documented the patterns of bacterial alpha diversity in stream biofilms in glacier-fed streams, where, however, beta diversity of the microbial communities has received much less attention especially considering both bacterial and fungal communities. A focus on beta diversity can provide insights into the mechanisms driving community changes associated to large environmental fluctuations and disturbances, such as in glacier-fed streams. Moreover, modularity of co-occurrence networks can reveal more ecological and evolutionary properties of microbial communities beyond taxonomic groups. Here, integrating beta diversity and co-occurrence approach, we explored the network topology and modularity of the bacterial and fungal communities with consideration of environmental variation in glacier-fed streams in Central Asia. Combining results from hydrological modeling and normalized difference of vegetation index, this study highlighted that hydrological variables and vegetation status are major variables determining the environmental heterogeneity of glacier-fed streams. Bacterial communities formed a more complex and connected network, while the fungal communities formed a more clustered network. Moreover, the strong interrelations among the taxonomic dissimilarities of bacterial community (BC) and modules suggest they had common processes in driving diversity and taxonomic compositions across the heterogeneous environment. In contrast, fungal community (FC) and modules generally showed distinct driving processes to each other. Moreover, bacterial and fungal communities also had different driving processes. Furthermore, the variation of BC and modules were strongly correlated with hydrological properties and vegetation status but not with nutrients, while FC and modules (except one module) were not associated with environmental variation. Our results suggest that bacterial and fungal communities had distinct mechanisms in structuring microbial networks, and environmental variation had strong influences on bacterial communities but not on fungal communities. The fungal communities have unique assembly mechanisms and physiological properties which might lead to their insensitive responses to environmental variations compared to bacterial communities. Overall, beyond alpha diversity in previous studies, these results add our knowledge that bacterial and fungal communities have contrasting assembly mechanisms and respond differently to environmental variation in glacier-fed streams.