Glacier-fed streams (GFSs) export large amounts of suspended sediment (SS) and associated mercury, with important implications for downstream water quality, yet the controls on Hg export remain poorly constrained. This issue is particularly acute on the Tibetan Plateau, where glacier meltwater sustains major Asian rivers. Here, we quantify seasonal and diurnal variability (n = 350) in SS and Hg across six Tibetan Plateau GFSs and synthesize observations from 36 GFSs worldwide. Tibetan Plateau GFSs exhibit total Hg (THg) concentrations and yields comparable to Alaska, but higher than most GFSs with similar glacier coverage. In GFSs without proglacial lakes, THg export scales with SS and increases with glacier coverage and velocity, indicating mobilization of erosion-derived, particle-associated Hg. THg-SS hysteresis differs among glacier thermal regimes in response to particle sorting and subglacial drainage evolution. Our results suggest that intensifying melt and rainfall on the Tibetan Plateau may increase Hg yields and delay the timing of peak Hg export, whereas expanding proglacial lakes may temporarily buffer further downstream Hg export. This study identifies controls on SS and THg export in Tibetan Plateau GFSs and highlights implications for downstream water quality and ecosystem exposure under glacier retreat.

Coastal wetlands regulate the transport and transformation of dissolved organic matter (DOM) between land and the ocean. It is known that DOM exported from tidal wetlands is chemically distinct from DOM in adjacent estuaries, yet its sources and compositional dynamics remain poorly resolved. Here, we investigated tidal variability in the optical and molecular composition of surface water DOM through absorbance and fluorescence spectroscopy and high-resolution mass spectrometry. Surface water samples were collected over multiple tidal cycles at three tidal marshes along a surface water salinity gradient in the Chesapeake Bay. At all sites, ebb tides consistently exported marsh-derived DOM enriched in terrestrial signatures with larger, more degraded, aromatic (e.g., tannin-like and condensed hydrocarbon-like) molecules. As water levels decreased during ebb tides, DOM composition gradually shifted from more protein-like and lipid-like to more condensed hydrocarbon-like substances, suggesting a sequential release of compositionally distinct DOM pools that may be distributed along the lateral gradient in the landscape. Tidal variability was minor at the low-salinity marsh due to limited hydrologic connectivity and greater riverine inputs. Our findings highlight the finer-scale tidal dynamics of surface water DOM, providing insights into how increasing hydrological alterations may affect coastal carbon cycling and downstream ecosystem functioning.

Mining has the potential to negatively impact receiving aquatic ecosystems by releasing trace elements such as selenium, mercury, arsenic and cadmium, but dietary patterns in invertebrates and fishes can mask effects of mine releases on their exposure. We compared trace element concentrations in water, benthic invertebrates and salmonid fishes at two coal-mine impacted streams with those from three reference streams in the upper Smoky River basin, Rocky Mountain foothills, Canada. The region has a high natural background concentration of selenium, evidenced by concentrations that exceed guideline values (>1 µg/L in water, > 4 mg/kg in invertebrates, > 11 mg/kg in fish egg/ovary) even at reference streams, but streams affected by upstream coal mining had significantly elevated concentrations in fish muscle (P < 0.05). Stable isotope analysis revealed that fish that were more strongly connected to the terrestrial detrital pathway had lower selenium (P < 0.001) and mercury (P < 0.01) concentrations, suggesting greater uptake from the algae-grazer pathway that is exposed to mine runoff. Selenium and mercury both showed evidence of biomagnification in food webs while arsenic and cadmium strongly biodiluted, further explaining differences in fish concentrations among sites. The high concentrations of selenium in fish muscle meant that it was the most important of the four elements in elevating risk to human consumers, and mine-impacted streams had the highest hazard quotients. Our findings highlight the importance of characterizing the diets of fishes with ecological tracers such as stable isotopes when investigating contaminant accumulation and point to the need to carefully consider future coal mine development because of consequences for downstream ecosystems and human health.

The high Arctic resistome: stress-response genes, virulence determinants, and microbial populations in human-impacted environments of Spitsbergen.

Abstract The Tibetan Plateau, often called the “Asian Water Tower,” is highly sensitive to extreme droughts and intense precipitation because of its complex topography and strong monsoonal influences, which pose significant risks to regional and downstream water and ecosystem security. This study uses CMFD daily precipitation data for 1979 to 2015 and bias corrected and downscaled CMIP6 daily precipitation data for 2016 to 2100 to identify and project two types of sequential compound events: drought followed by extreme precipitation (CDEP) and extreme precipitation followed by drought (CWDE). A dynamic identification framework was applied, defining drought with a 30 day precipitation threshold, defining extreme precipitation with a 3 day threshold, and pairing events within intervals from one to three months. Our results show that the frequency of both CDEP and CWDE increases markedly with longer lag times. During the historical period, event hot spots were concentrated in the southern and central Plateau. Under future SSP scenarios, CDEP risk expands northward into interior arid regions such as Northern Tibet and the Qaidam Basin, while CWDE remains centered in the south and central Plateau but extends toward inland areas. Importantly, the increase in event frequency is not monotonic with warming; the strongest enhancement occurs under moderate emissions, specifically SSP245 and SSP370. Overall, warming and a moister atmosphere intensify the alternation between dry and wet extremes, driven by enhanced monsoonal moisture transport, orographic lifting, and stronger land-atmosphere coupling. These findings provide a scientific basis for improving drought and flood risk management and climate adaptation strategies in high mountain watersheds of the Tibetan Plateau.

Glacial retreat releases a vast reservoir of microbes into downstream ecosystems, yet the functional consequences of this transfer are unknown. Here we used genome-resolved metagenomics across a Svalbard glacier-foreland-fjord continuum and reconstructed 309 metagenome-assembled genomes (MAGs) to track microbial fate. Glacial taxa dominated foreland soils (75% of MAGs) but were rare in fjord sediments (14%), which hosted endemic marine lineages (83%). Although heterotrophy was ubiquitous, carbon fixation pathways were primarily encoded by glacial MAGs. The foreland was a denitrification hotspot, whereas sulfur oxidation dominated in the fjord. Genomic traits for cryoprotection and complex carbon degradation further distinguished glacial from marine taxa. We conclude that glaciers host functionally distinct microbiota, but strong environmental filtering at the land-sea interface limits functional propagation to marine ecosystems, implying glacier loss may disrupt terrestrial microbial biodiversity and biogeochemistry more profoundly than coastal systems. Metabolically unique glacial microbes dominate foreland communities but rarely persist in fjords, showing limited functional transfer across the land-sea interface, based on genome-resolved metagenomics along a glacier-to-fjord gradient

ABSTRACT Reservoirs are vital tools for managing riverine water resources but also influence water quality through in‐lake nutrient (i.e., nitrogen [N] and phosphorus [P]) dynamics that affect downstream ecosystems. This study presents a multiscale spatiotemporal characterization of water quality in Carlyle Lake, an agriculturally impacted reservoir in Illinois, United States. We combined manual spatial surveys (2016–2017) with high frequency buoy data (2016–2019) to reveal the distinct biogeochemical processes within the reservoir. The upper subbasin had large subdaily fluctuations and high levels of turbidity and nitrate (NO 3 − ‐N) relative to the lower subbasin, reflecting longitudinal sedimentation and denitrification. In contrast, the lower subbasin exhibited high phosphate (PO 4 3− ‐P) that often exceeded the 0.05 mg/L guideline, consistent with sediment‐driven P release under low dissolved oxygen (DO) and warm conditions. Vertical sampling profiles demonstrated occasional hypoxia near the sediment–water interface in the lower subbasin that coincided with elevated PO 4 3− ‐P levels, while homogeneous temperature and NO 3 − ‐N profiles with depth indicated limited stratification. Nutrient flux estimates showed that Carlyle Lake acted as a N sink (i.e., 43%–77% NO 3 − ‐N reduction) and P source (i.e., 40%–50% PO 4 3− ‐P release). Our high frequency monitoring data identified a 27–32‐day NO 3 − ‐N transit time across the reservoir, highlighting the value of continuous data for capturing nutrient dynamics to inform water management strategies for systems that are under increasing pressure from agricultural practices and climate variability.

Hydropeaking, resulting from flexible hydropower operations, causes rapid hydraulic fluctuations and disrupts downstream ecosystems, posing significant ecological challenges. This study develops an enhanced ecohydraulic modeling framework to assess the responses of fish habitats to different hydropeaking scenarios for the European grayling ( Thymallus thymallus ) and brown trout ( Salmo trutta ). A two-dimensional hydrodynamic model was coupled with a novel habitat module that introduces a machine learning-based habitat suitability computation method. This method effectively captures the nonlinear and coupled effects between flow velocity and water depth, outperforms traditional habitat suitability approaches (e.g., geometric mean and fuzzy logic), and yields stable, ecologically consistent habitat suitability results. To complement local habitat assessment, a habitat connectivity index (HCI) was also developed to quantify longitudinal connectivity and migration pathways across life stages under dynamic flow conditions. Results demonstrated that hydropeaking frequency was the primary driver of habitat variability, while spill gate closing time played a secondary role. Lower frequencies increased temporal variability but expanded opportunities for accessing high-quality patches; higher frequencies stabilized conditions but reduced ecological flexibility. Longer closing times enhanced short-term stability, but their effect was relatively minor compared with that of frequencies. The HCI approach enabled the prediction of migration pathways and the identification of critical corridors under extreme flow regulation. The proposed framework offers a valuable tool for evaluating habitat quality and connectivity dynamics under hydropower regulation, providing practical insights for adaptive ecological flow management in regulated rivers. • An improved ecohydraulic model is developed to assess the impacts of hydropeaking events on fish habitats. • Species- and life-stage-specific modeling reveals differential habitat requirements and sensitivities. • Hydropeaking frequency is identified as the primary driver affecting habitat stability of both suitability and connectivity compared to spill gate closing time. • An explicit spatial method is proposed to predict potential migration pathways under extreme flow regulation.

Abstract Glacier retreat is projected to drive major shifts in the hydrology of many high‐elevation and high‐latitude watersheds. In particular, future decreases in glacier runoff are hypothesized to reduce the stability of hydro‐biogeochemical export. We test this hypothesis using a decade of discharge, dissolved organic carbon, total dissolved nitrogen and soluble reactive phosphorus data from four Alaskan watersheds spanning a gradient in glacier cover. We demonstrate that glacier decline leads to lower and more variable runoff across years, with 2.6–4.3 times greater interannual variability in lightly‐glacierized compared to glacier‐dominated watersheds. Biogeochemical export also became more stochastic with retreat, with up to a five‐fold increase in interannual variability. However, the responses of riverine concentrations and yields to changes in glacier cover varied widely between constituents. Such shifts in the magnitude and stochasticity of hydro‐biogeochemical yields have important implications for the ecological stability of downstream ecosystems.

Tropical mountain ecosystems, driven by monsoonal hydrology and escalating land use, are highly vulnerable to nutrient enrichment, which threatens downstream water quality. This study investigates the spatiotemporal variability and quantitative source apportionment of dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silica (DSi) across surface water and groundwater in the Munnar Critical Zone Observatory (CZO), Western Ghats, India. Seasonal monitoring over three monsoon cycles revealed extremely elevated DIN/DIP ratios (up to 299:1), indicating severe phosphorus (P) limitation, reflecting rapid particulate P flushing combined with sustained anthropogenic nitrogen (N) inputs. This N enrichment contributes to a significant riverine DIN flux (3.79 × 103 tons/year), dominating catchment-scale transport. Hydrological analysis confirmed agricultural leaching, with nitrate (NO3-N) peaking in groundwater during the monsoon (6.98 ± 0.63mg/L), while silicate weathering significantly enriched groundwater DSi (15.22 ± 2.81mg/L). The Positive Matrix Factorisation (PMF) model apportioned 70.2% of NO3-N and 81.3% of phosphate (PO43-) to agricultural fertiliser inputs and 100% of NO2-N plus 99.2% of ammonium (NH4-N) to sewage waste; seasonally, fertiliser signals surged during the monsoon, while sewage contributions peaked in the post-monsoon baseflow. Distinct nitrogen cycling pathways were confirmed by the NO3-N/NH4-N ratios (16:1 in surface water vs. 10:1 in groundwater), signifying N loss via denitrification in septic-influenced anaerobic groundwater. These findings, underscoring significant N* excess (up to 107.35), quantify the high eutrophication potential being exported from this anthropogenically stressed headwater system. These results highlight urgent management needs, including optimised fertiliser application timing, restoring riparian buffers, and upgrading sanitation systems to curb nutrient pollution and safeguard downstream ecosystem services.

Impacts of the 2024 flash flood on water quality, pathogenic bacteria and organic contaminant risks in the Albufera Natural Park (Valencia, Spain).

ABSTRACT Antibiotic resistance has emerged as one of the most significant public health concerns of the twenty-first century. The excessive and inappropriate use of antibiotics has accelerated the proliferation of antibiotic-resistant bacteria (ARB) and genes (ARGs). Rapid urbanization and anthropogenic activities further facilitate the dissemination of ARB and ARGs into downstream river ecosystems through the discharge of treated effluents from wastewater treatment plants (WWTPs). The study investigates the occurrence, seasonal variations, and distribution of selected ARGs (blaNDM-1, blaSHV, blaCTX-M, ermB, qnrS, and vanA) and intI1 gene in WWTPs and downstream river environments. Samples (inlet, treated wastewater, and activated sludge) were collected during the winter and summer seasons over 1 year from three WWTPs employing different treatment technologies, as well as from the Ganges River (water and sediment) in North Indian cities: Kanpur, Prayagraj, and Varanasi. The results indicated that WWTPs significantly reduced ARB and ARG levels in treated effluents, a marked increase in their abundance was observed in the downstream Ganges River environment. These findings highlight that WWTPs may serve as potential hotspots for the dissemination of ARB and ARGs into the freshwater ecosystems, underscoring the urgent need for advanced treatment and monitoring strategies to mitigate antibiotic resistance spread.

ABSTRACT Since the 1960s, irrigated cotton production has expanded considerably in the northern Murray–Darling Basin, with substantial losses to evaporation from large on-farm storages used for floodplain water harvesting. Diversion of this water negatively impacts downstream communities and ecosystems. We quantified area and capacity of 2,786 storages and 10,173 km of irrigation channels and estimated annual evaporation (1987-88 to 2023–24) using remote sensing time series and meteorological data Annual evaporation was 1,247 GL; 39% of surface water take from cotton-producing catchments. Storages in 2024 covered 94,758 ha (capacity 3,300 GL); a two-fold increase since 1995 when a cap on irrigation diversions was introduced. Storages contained water for 89% of the time and were 38-100% full for 34% of the time; longer than needed for irrigation requirements. Including evaporation, it takes 11.8 ML to grow a hectare of cotton; twice the 6–7 ML ha−1 the cotton industry estimates is applied to the crop. Evaporation is not accounted for in water policy reforms, yet we consider it is just another form of water take. Under increasing water scarcity due to climate change and irrigation diversions, there is a clear need to reduce losses. We discuss implications for water policy and options for management of evaporation on-farm.

Assessing the impacts of land use and land cover on occurrence, spatial distribution of microplastics and heavy metals in an agricultural watershed, Tadepalligudem, Andhra Pradesh, India.

Accumulation and secondary release of legacy Pb in high Arctic glaciers of Svalbard: Insights from Pb isotopes.

Wastewater treatment plant (WWTP) discharges are a primary anthropogenic source of particulate and dissolved phosphorus that can contribute to nutrient spiralling and eutrophication, threatening downstream aquatic ecosystem health and drinking water treatability. Because fine solids are the primary vector for phosphorus transport in aquatic systems, this study departs from typical analyses of total phosphorus in WWTP discharges by providing new insights regarding the relative bioavailability of particulate phosphorus (PP) forms within them. A continuous-flow centrifuge (CFC)-based method was adapted for suspended solids collection from secondary (2°) and tertiary (3°) effluents at two WWTPs. These solids were then analyzed using chemical sequential extraction to quantify key PP forms to inform bioavailability. Non-apatite inorganic phosphorus (NAIP)-the most readily bioavailable phosphorus form-was the predominant PP fraction (typically >90 %) composing the wastewater effluent solids. It was predominantly bound to metal oxides. Benchmarking indicated that wastewater effluent solids can contain 10 to 100 times more NAIP than other commonly reported sources of PP, such as aquatic sediments from landscapes with varying levels of disturbance. Their impacts on receiving water quality are case-specific, depending on the relative magnitude and timing of NAIP loading from these and other sources. Although the relative composition of PP did not substantially differ between effluents from 2° and 3° treatment, NAIP concentrations in effluents from 3° treatment by cloth filtration were approximately 50 % lower than those in effluents from 2° treatment. These first-of-their-kind (1) application of a CFC to collect WW solids and (2) characterization PP forms and their bioavailability in WWTP effluents provide essential insight for understanding and modeling effluent-streamwater P dynamics and support targeted watershed management during sensitive environmental conditions (e.g., low flows) when receiving waters are most vulnerable.

Abstract Lakes and reservoirs play a key role in the global carbon cycle, representing important carbon sinks and sources within the terrestrial landscape under different environmental conditions. Changes in climate and land use have led to increased air and surface water temperatures; increased occurrence and duration of hypolimnetic anoxia; and altered hydrology and nutrient loading, which have the potential to affect how these freshwater ecosystems receive and process carbon. To assess how interacting environmental drivers influence carbon cycling in lakes and reservoirs, we used a 5-year whole-ecosystem experiment to investigate the effects of variable catchment, meteorology, and in-lake drivers on epilimnetic and hypolimnetic dissolved organic carbon in a small reservoir. Using a combination of whole-ecosystem models and time-series analyses, we found that primary production and other internal sources contributed a mean of 29% (range: 7–49%) of the dissolved organic carbon in the reservoir’s epilimnion over the 5-year period. We also found that sinking epilimnetic primary production, dissolved organic carbon from the sediments, and other factors were likely important sources of hypolimnetic dissolved organic carbon, especially during periods of anoxia. Both the epilimnion and hypolimnion were found to be intermittent sinks, yet net sources, of dissolved organic carbon. Overall, water temperature was identified as the most important environmental predictor for water-column dissolved organic carbon, with higher concentrations observed under seasonally elevated temperatures during the late summer and early fall. Our results suggest that lakes and reservoirs may become larger sources of dissolved organic carbon to downstream ecosystems in a warmer, more anoxic future.

The development of civilisations is part of human evolution, but it comes at the cost of nature's destruction. Unsustainable human development results in long-term human destruction itself. This paradox underscores the need to implement a sustainable approach that balances human progress with environmental preservation. Due to climate change, many activities in nature become extreme, which directly and indirectly impacts human lives. Cloudbursts and landslides are two calamities that attract researchers' attention. Cloudburst and landslide are interrelated with precipitation. Most of these incidents remain undocumented. The downstream ecosystems of the affected area witness loss of life and property. The Eastern Himalayas are prone to heavy rains, especially cloudbursts, which can cause rapid slope failures and landslides in steep hilly terrain. Recently, that region has faced many calamities that cost human lives and property. This study uses remote sensing and GIS tools to analyse the incidence, spatial distribution, and risk assessment of landslides triggered by cloudbursts in East Siang District, Arunachal Pradesh. Our study area comes in the lower Siwalik range of the Himalayas. The study uses satellite images, Digital Elevation Model (DEM) data and rainfall data. It was found that some parts of the study area are at risk of landslides and cloudbursts. The findings promote improved planning for catastrophe risk reduction in remote areas of the country.

Large dams have become a dominant water management strategy over the last century, but they are typically managed with limited understanding of how human responses to their construction and operation influence the achievement of water management objectives. In recent years, several behavioural response patterns to large dams in human-water systems have been identified, and quantitative models developed to capture these emergent phenomena. However, there is a gap between the understanding of these phenomena in a generalised sense and communicating their relevance to water managers in local contexts. In this study we applied a generalised human-water systems model of reservoir operations during droughts and floods to two case studies in Australia; one in the water-scarce, largely agricultural Lachlan River catchment, and the other in the coastal, highly-urbanised Hawkesbury–Nepean catchment. Modelling results coupled with a qualitative review of historical socioeconomic, hydroclimatic, and water management characteristics of each case study were compared to identify potential emergent phenomena and the characteristics contributing to their development. We found reservoir effects (where increases in water storage capacity increase vulnerability to water scarcity) and lock-in behaviours are inherent risks for large reservoirs. The levee effect, whereby infrastructure reducing the probability of flooding paradoxically increases vulnerability to floods, is a risk, particularly where urbanisation is high. Sequence effects, where measures to deal with one hydrological extreme exacerbate the effects of the other extreme, are likely when operational rules constrain the adaptation of operations to hydroclimatic conditions, or when water management interactions during drought and flood are poorly understood. Where there is economic incentive to increase water usage, supply–demand cycles and rebound effects are a risk. Sensitive downstream ecosystems and high competition for limited resources make shifts in values that redirect water management priorities (pendulum swings) more likely. Identifying these emergent phenomena and their driving characteristics can help water managers identify and focus on context-specific risks to enable a proactive management approach to current and future challenges.

Abstract Assessing the risks associated with dam failure is crucial for protecting downstream populations, infrastructure, and ecosystems, particularly in regions with growing rural settlements and limited emergency preparedness. This study presents a simulation-based evaluation of potential dam break scenarios at the Kerinci Merangin Hydropower Dam, located in Jambi Province, Indonesia, a facility vital for regional energy and irrigation. Two critical failure mechanisms, overtopping and piping, were simulated using the HEC-RAS 2D hydraulic model to estimate peak discharge, inundation extent, flow velocities, and flood arrival times. The modeling incorporated key inputs such as dam geometry, digital elevation models (DEMs), breach parameters, and hydrological conditions. Results from the overtopping scenario showed that a total breach could produce a peak flow of approximately 681.5 m 3 /s, inundating critical downstream areas within 15 to 20 minutes of breach initiation. The flood extent was estimated to cover 3.42 km 2 , with maximum depths exceeding 3.7 meters in low-lying zones. Using Geographic Information Systems (GIS), spatial flood hazard mapping was conducted to categorize risk zones and identify population exposure and infrastructure vulnerability. The analysis revealed that 27% of the inundated area fell within the high-hazard zone. Based on these findings, a site-specific Emergency Action Plan (EAP) was developed, which includes hazard zoning maps, optimized evacuation routes, and early warning system components. This study demonstrates the value of integrating hydrodynamic modeling with spatial analysis to improve dam safety management, support early warning system design, and strengthen disaster preparedness. In addition, the outcomes contribute to the achievement of SDG 11 (Sustainable Cities and Communities) and SDG 13 (Climate Action) by enhancing resilience against water-related disasters and supporting sustainable risk reduction strategies.