The Atacama Plateau in the Central Andes (28-22 degrees S) is characterised by a dry and cold periglacial tundra due to the high altitude, low precipitation, and high evaporation. Endogenous freshwater sources - e.g.: seasonal streams and lakes, subsurface reservoirs, surface snow/ice patches - are available, though they are highly sensitive to climatic changes. The near surface hydrological network is highly modified by the distribution and seasonal evolution of perennial frozen ground, i.e. permafrost, which is also expected to change in the future. The interplay between permafrost and hydrology, especially in relation to future climate change, is poorly explored. To address this issue, we carry out long-term ground temperature measurement and modelling, snow coverage survey, tritium- and stable isotope analysis of surface waters on the Ojos del Salado Massif, which is representative of high altitude mountains on the Atacama Plateau. According to our results, a highly transient surface hydrological network - lakes, springs and streams - forms during each summer where permafrost is widespread and ground thawing (i.e. active layer) is present (similar to 4900-6500 m a.s.l.). In this system, the water is of meteoric origin and relatively young (<10 years). The development of the network is strongly influenced by the active layer, which plays a crucial role in storing, seeping, and discharging groundwater. However, future permafrost degradation is expected to reduce the seasonal presence of shallow water, and hence, modify groundwater recharge patterns.

The discharge of fertilizers and untreated sewage from the Indian subcontinent was attributed to damage the coastal ecosystem and threat to the fishery resources. Based on the recent data collected along the Indian coasts, the issues were reanalyzed to identify potential mechanisms responsible. Carbon, nitrogen and oxygen isotopes revealed that the fertilizers used in the agricultural soil contaminate groundwaters, then fluxed to the coastal ocean. Similarly, the impact of municipal sewage is restricted close to the coast rather than spreading to the international waters. This reanalysis suggests that the occurrence of coastal eutrophication, hypoxia or shift in the ecosystem was mainly caused by natural processes such as coastal upwelling, stratification and reversing of coastal currents than hitherto hypothesized as the discharge of fertilizers and municipal sewage.

The extraradical mycelium of mycorrhizal fungi is among the major carbon pools in soil that is hard to quantitatively assess in-situ. Established method of in-growth mesh bags in temperate ecosystems is difficult to apply in the tropics, where mesh bags are often damaged by termites. Here we introduce a modification of the ingrowth mesh bag technique, in which mesh bags are enforced by stainless steel mesh. Its performance was tested in the Dong Nai (Cat Tien) National Park in Vietnam across two monsoon tropical forests, dominated by tree species associated with either ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi. Armored ingrowth mesh bags remained intact, while about 60 % of non-armored mesh bags were damaged by termites after 180 days of exposure. The biomass of extraradical mycelium of ectomycorrhizal fungi estimated by PLFA analysis was similar in the armored and non-armored mesh bags and did not differ between studied forests. However, fungal community composition slightly differed between armored and non-armored mesh bags in the ECM-but not in the AM-dominated forest. Fungal mycelium gathered in the AM-dominated forest was depleted in N-15 compared to that collected in the ECM-dominated forest. Overall, our results argue for using armored mesh bags as a robust tool for harvesting the biomass of extraradical mycelium of mycorrhizal fungi in tropical ecosystems.

PurposeOver the past three decades, open-pit mining has been expanding in arid and semi-arid areas of China.Open-pit mining profoundly changes the soil environment and has a profound impact on the circulation of soil water in the aeration zone.Therefore, this research explores the impacts of open-pit coal mining on soil moisture processes in the semi-arid grasslands of Eastern Inner Mongolia Autonomous Region, China.Materials and methodsSoil samples were collected from depths of 0-500 cm at Shengli No. 1 open-pit mine's inner dump and a nearby natural grassland. These soil samples were analyzed for stable isotope characteristics (delta 2H,delta 18O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\delta 2 H, \delta {18} O}$$\end{document}) and moisture content. Collection of underground water samples inside and outside the mining area for conductivity analysis.Results and discussionSoil evaporation loss in the mine's inner dump was significantly higher than in the grassland, with rates of 22.26% for delta 18O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\delta {18} O}$$\end{document} and 6.61% for delta 2H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\delta 2 H}$$\end{document}. The limiting depth of soil evaporation at the mine was found to be 260 cm, compared to 200 cm in the grassland. The increased underground water conductivity in the mine area was linked to heightened soil evaporation loss. Isotopic profiling of the soil indicated that the open-pit mining led to deeper preferential flow infiltration during heavy precipitation, reaching 280 cm in the mine area versus 220 cm in the grassland.ConclusionsThe surface soil moisture content (SMC) increased due to mining activities intensified water-heat exchanges with the atmosphere, leading to more frequent and severe wet-dry cycles. This study provides a comprehensive understanding of open-pit mining's impact on SMC, evaporation, and infiltration in semi-arid areas, offering critical insights for ecological reclamation and sustainable mine construction.

In arid regions, the stable hydrogen and oxygen isotopic composition in raindrops is often modified by sub-cloud secondary evaporation when they descend from cloud base to ground through the unsaturated air. As a result of kinetic fractionation, the slope and intercept of the delta H-2-delta O-18 correlation equation decrease. The variation of deuterium excess from cloud base to the ground is often used to quantitatively evaluate the influence of secondary evaporation effect on isotopes in precipitation. Based on the event-based precipitation samples collected at Urumqi Glacier No. 1, eastern Tianshan during four-year observation, the existence and impact of secondary evaporation effects were analyzed by the methods of isotope-evaporation model. Under high air temperature, small raindrop diameter and precipitation amount, and low relative humidity conditions, the remaining rate of raindrops is small and the change of deuterium excess is large relatively, and the slope and intercept of delta H-2-delta O-18 correlation equation are much lower than those of Global Meteoric Water Line, which mean that the influence secondary evaporation on precipitation enhanced. While on the conditions of low air temperature, high relative humidity, heavy rainfall, and large raindrop diameter, the change of deuterium excess is small relatively and the remaining rate of raindrops is large, and the slope and intercept of delta H-2-delta O-18 correlation equation increase, the secondary evaporation is weakened. The isotope-evaporation model described a good linear correlation between changes of deuterium excess and evaporation proportion with the slope of 0.90%/%, which indicated that an increase of 1% in evaporation may result in a decrease of deuterium excess about 0.90%.

Increased permafrost temperatures have been reported in the circum-Arctic, and widespread degradation of permafrost peatlands has occurred in recent decades. The timing of permafrost aggradation in these ecosystems could have implications for the soil carbon lability upon thawing, and an increased understanding of the permafrost history is therefore needed to better project future carbon feedbacks. In this study, we have conducted high-resolution plant macrofossil and geochemical analyses and accelerator mass spectrometry radiocarbon dating of active layer cores from four permafrost peatlands in northern Sweden and Norway. In the mid-Holocene, all four sites were wet fens, and at least three of them remained permafrost-free until a shift in vegetation toward bog species was recorded around 800 to 400 cal. BP, suggesting permafrost aggradation during the Little Ice Age. At one site, Karlebotn, the plant macrofossil record also indicated a period of dry bog conditions between 3300 and 2900 cal. BP, followed by a rapid shift toward species growing in waterlogged fens or open pools, suggesting that permafrost possibly was present around 3000 cal. BP but thawed and was replaced by thermokarst.

This study reports day-night and seasonal variations of aqueous brown carbon (BrCaq) and constituent humic-like substances (HULIS) (neutral and acidic HULIS: HULIS-n and HULIS-a) from the eastern Indo-Gangetic Plain (IGP) of India during 2019-2020. This is followed by the application of the receptor model positive matrix factorization (PMF) for optical source apportionment of BrCaq and the use of stable isotopic ratios (813C and 815N) to understand atmospheric processing. Nighttime BrCaq absorption and mass absorption efficiencies (MAE) were enhanced by 40-150 % and 50-190 %, respectively, compared to the daytime across seasons, possibly as a combined effect from daytime photobleaching, dark-phase secondary formation, and increased nighttime emissions. MAE250 nm/MAE365 nm (i.e., E2/E3) ratios and Angstrom Exponents revealed that BrCaq and HULIS-n were relatively more aromatic and conjugated during the biomass burning-dominated periods while BrCaq and HULIS-a were comprised mostly of nonconjugated aliphatic structures from secondary processes during the photochemistry-dominated summer. The relative radiative forcing of BrCaq with respect to elemental carbon (EC) was 10-12 % in the post-monsoon and winter in the 300-400 nm range. Optical source apportionment using PMF revealed that BrCaq absorption at 300, 365 and 420 nm wavelengths in the eastern IGP is mostly from biomass burning (60-75 %), followed by combined marine and fossil fuel-derived sources (24-31 %), and secondary processes (up to 10 %). Source-specific MAEs at 365 nm were estimated to be the highest for the combined marine and fossil fuel source (1.34 m2 g-1) followed by biomass burning (0.78 m2 g-1) and secondary processing (0.13 m2 g-1). Finally, 813C and 815N isotopic analysis confirmed the importance of summertime photochemistry and wintertime NO3--dominated chemistry in constraining BrC characteristics. Overall, the quantitative apportionment of BrCaq sources and processing reported here can be expected to lead to targeted source-specific measurements and a better understanding of BrC climate forcing in the future.

A total of 256 water samples were collected from the river, precipitation, and permafrost active layer in a typical small alpine catchment during the ablation periods in 2020 and 2021. The results indicated that every water body was alkaline, and the TDS and EC concentrations were in the following order: precipitation Ca2+ & AP; Mg2+ and Na+ + K+ > Mg2+ > Ca2+, respectively; the anion concentration showed the order of SO42 � > Cl- > NO3 . The results revealed that permafrost and river water had similar geochemical compositions. Similar & delta;2H and & delta;18O values were also observed between river and permafrost water. Additionally, the water chemistry of rivers and permafrost revealed that the chemical weathering of carbonate and silicate rocks is an important source of riverine solutes; however, silicate weathering played a more crucial role. Both hydrochemistry and stable isotopes collectively indicated that there was a close hydraulic connectivity between the water content in river and permafrost active layer in the small alpine catchment. Based on the end-member mixing analysis model, the water in permafrost active layer and precipitation accounted for 62% and 38% of the runoff, respectively, indicating that it was dominated by permafrost during the ablation period. The warming and hu-midification of climate tend to facilitate permafrost degradation. Thus, studying the transformation of different water bodies in alpine regions is imperative to provide water resource security and sustainable development in alpine regions.

Global warming has significantly impacted the hydrological processes in alpine cryosphere region. Water age is an essential descriptor of the hydrological function within a catchment. However, the mechanism of streamwater age variability remains unclear due to limited observational data and high altitudes of alpine catchment. In this study, long-term stable isotopic data on streamwater in a catchment in the central Tibetan Plateau (TP) were collected to assess the water age using the sine-wave approach and gamma distribution. Results showed that the mean streamwater age was 77 days, and that 30 % of streamwater was less than 41 days old on average. The streamwater age in this study was relatively younger than that in low-elevation natural catchments, indicating that the rapid drainage process occurs within the glacier and permafrost catchment. The fraction of young water (Fyw) of the streamwater decreased from 39 % at an upstream site to 28 % at the outlet, revealing the impact of permafrost (low Fyw: 25 %) on streamwater age. These variabilities were related to glacier and permafrost coverage, specifically in catchments with higher glacier coverage that are prone to have a lower water age. Temporally, the streamwater age was significantly influenced by precipitation, relative humidity, and glacier change and, to a lesser extent, permafrost change. Mechanically, glacier and permafrost changes influenced the water age by increasing the vertical flowpath length. This study provides new insights into the change in hy-drological processes in alpine headwater catchments under global warming.

The Arctic soil communities play a vital role in stabilizing and decomposing soil carbon, which affects the global carbon cycling. Studying the food web structure is critical for understanding biotic interactions and the functioning of these ecosystems. Here, we studied the trophic relationships of (microscopic) soil biota of two different Arctic spots in Ny-angstrom lesund, Svalbard, within a natural soil moisture gradient by combining DNA analysis with stable isotopes as trophic tracers. The results of our study suggested that the soil moisture strongly influenced the diversity of soil biota, with the wetter soil, having a higher organic matter content, hosting a more diverse community. Based on a Bayesian mixing model, the community of wet soil formed a more complex food web, in which bacterivorous and detritivorous pathways were important in supplying carbon and energy to the upper trophic levels. In contrast, the drier soil showed a less diverse community, lower trophic complexity, with the green food web (via unicellular green algae and gatherer organisms) playing a more important role in channelling energy to higher trophic levels. These findings are important to better understand the soil communities inhabiting the Arctic, and for predicting how the ecosystem will respond to the forthcoming changes in precipitation regimes. Wetter soils, with a higher organic matter content, host more diverse soil biota and support more complex food webs, in which bacterivorous and detritivorous pathways are relevant in supplying energy.