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Climate change will impact mountain watershed streamflow both directly—with changing precipitation amounts and variability—and indirectly—through temperature shifts altering snowpack, melt, and evapotranspiration. To understand how these complex processes will affect ecosystem functioning and water resources, we need tools to distinguish connections between water sources (rain/snowmelt), groundwater storage, and exit fluxes (streamflow/evapotranspiration), and to determine how these connections change seasonally and as climate shifts. Here, we develop novel watershed‐scale approaches to understand water source, storage, and exit flux connections using a dynamic‐flux particle tracking model (EcoSLIM) applied in California's Cosumnes Watershed, which connects the Sierra Nevada and Central Valley. This work develops new visualizations and applications to provide mechanistic understanding that underpins the interpretation of isotopic field data at watershed scales to distinguish sources, flow paths, residence times, and storage selection. In our simulations, streamflow comes primarily from snow‐derived water while evapotranspiration generally comes from rain. Most streamflow starts above 1,000 m while evapotranspiration is sourced relatively evenly across the watershed and is generally younger than streamflow. Modeled streamflow consists primarily of water sourced from precipitation in the previous 5 years but before the current water year, while ET consists primarily of water from precipitation in the current water year. ET, and to a lesser extent streamflow, are both younger than water in groundwater storage. However, snowmelt‐derived streamflow preferentially discharges older water from snow‐derived storage. Dynamic‐flux particle tracking and new approaches presented here enable novel model‐tracer comparisons in large‐scale watersheds to better understand watershed behavior in a changing climate. Plain Language Summary: Climate change will alter the hydrologic cycle: storms will be more intense and higher temperatures will result in less snow, earlier melt, and more early‐season water use by plants. To understand the combined effect of these changes, we need models to simulate water flows and precisely study the effects of rain, snowmelt, subsurface storage, streamflow, and plant water uptake. These models can show us how water flows between different components of the landscape, and how this flow changes seasonally and in response to climate change. This study develops new modeling tools that simulate the Cosumnes River in the Sierra Nevada (California, USA) and will help interpret field data at watershed scales. The majority of simulated streamflow originates from snow while plants rely on rainfall for evapotranspiration (ET). Most streamflow starts as precipitation above 1,000 m while ET comes from water that falls evenly across the watershed. Water used for ET is generally younger than streamflow: most streamflow is 1–5 years old, while most ET is less than 1 year old. Both ET and streamflow are younger than water stored in the subsurface. These new modeling tools, called dynamic‐flux particle tracking, will help us predict how watersheds will behave as climate changes. Key Points: Dynamic‐flux particle tracking (DFPT) is a novel technique to investigate watershed function and connectionWater source wedge plots illustrate connectivity between source water elevation, precipitation phase, and water exit pathways and locationDFPT shows how source phase and watershed conditions influence age‐ranked storage selection behavior [ABSTRACT FROM AUTHOR]

Floodplains constitute a vital and integrated component of the riverine network ensuring the connectivity and continuity of the river with the upland watershed areas. However, the sediment trapping efficiency of floodplains has not been well investigated. The purpose of this experimental study was to evaluate the functionality of floodplains to act as either sources or sinks for fine sediments and sediment‐bound nutrients (e.g., total phosphorus) during floods of various return periods. Thus, we hypothesized that (i) soil texture, in terms of topsoil erodibility and (ii) the magnitude of the incoming flood, in terms of the applied shear stress, are the two key parameters govern river floodplains' ability to store or release fine sediments and total phosphorus, during major flood conditions. Topsoil erodibility experiments were coupled with site‐specific flood inundation maps to estimate the eroded fine sediment mass and the total phosphorus release rates per unit area per unit time of each flood condition considered. Results suggested that the floodplain soils of the upstream reaches act as net sources, the floodplains of the midstream reaches have a dual functionality; during low magnitude flood events (up to 10‐year return periods), they act as net sinks, while during higher flood events, they act as sources; and the floodplains of the downstream reaches largely act as sinks. This study results are applicable for watershed managers to identify floodplain areas vulnerable to erosion and sources of nutrient pollution. [ABSTRACT FROM AUTHOR]

Mountain System Recharge processes are significant natural recharge pathways in many arid and semi‐arid mountainous regions. However, Mountain System Recharge processes are often poorly understood and characterized in hydrologic models. Mountains are the primary water supply source to valley aquifers via lateral groundwater flow from the mountain block (Mountain Block Recharge) and focused recharge from mountain streams contributing to focused Mountain Front Recharge at the piedmont zone. Here, we present a multi‐tool isogeochemical approach to characterize mountain flow paths and Mountain System Recharge in the northern Tulare Basin, California. We used groundwater chemistry data to delineate hydrochemical facies and explain the chemical evolution of groundwater from the Sierra Nevada to the Central Valley aquifer. Stable isotopes and radiogenic groundwater tracers validated Mountain System Recharge processes by differentiating focused from diffuse recharge, and estimating apparent groundwater age, respectively. Novel application of End‐Member Mixing Analysis using conservative chemical components revealed three Mountain System Recharge end‐members: (a) evaporated Ca‐HCO3 water type associated with focused Mountain Front Recharge, (b) non‐evaporated Ca‐HCO3 and Na‐HCO3 water types with short residence times associated with shallow Mountain Block Recharge, and (c) Na‐HCO3 groundwater type with long residence time associated with deep Mountain Block Recharge. We quantified the contribution of each Mountain System Recharge process to the valley aquifer by calculating mixing ratios. Our results show that deep Mountain Block Recharge is a significant recharge component, representing 31%–53% of the valley groundwater. Greater hydraulic connectivity between the Sierra Nevada and Central Valley has significant implications for parameterizing groundwater flow models. Our framework is useful for understanding Mountain System Recharge processes in other snow‐dominated mountain watersheds. Key Points: A multi‐tool isogeochemical approach differentiates among mountain recharge pathwaysIncorporating chemical reactions in the End‐Member Mixing Analysis strongly improves mixing ratio calculationMountain block recharge originating from the Sierra Nevada accounts for 31%–53% of recharge in the southern Central Valley [ABSTRACT FROM AUTHOR]

After peak snowmelt, baseflow is the primary contributor to streamflow in snow-dominated watersheds. These low flows provide important water for municipal, agricultural, and recreational purposes once peak flows have been allocated. This study examines the correlation between peak snow water equivalent (SWE), post-peak SWE precipitation, and baseflow characteristics, including any yearly lag in baseflow. To reflect the hydrologic processes that are occurring in snow-dominated watersheds, we propose using a melt year (MY) beginning with the onset of snowmelt contributions (the first deviation from baseflow) and ending with the onset of the following year's snowmelt contributions. We identified the beginning of an MY and extracted the subsequent baseflow values using flow duration curves (FDCs) for 12 watersheds of varying sizes across Colorado, USA. Based on the findings, peak SWE and summer rain both dictate baseflow, especially for the larger watersheds evaluated, as identified by higher correlations with the MY-derived baseflow. Lags in the correlation between baseflow and peak SWE are best identified when low-snow years are investigated separately from high-snow years. The MY is a different and more effective approach to calculating baseflow using FDCs in snow-dominated watersheds in Colorado. [ABSTRACT FROM AUTHOR]

The hydrochemical characteristics of river water are influenced by a multitude of factors, reflecting the surrounding geographical environment. The Shaliu River, located in the northeastern Tibetan Plateau (TP), serves as a typical inland alpine permafrost watershed. In this study, we compiled data on dissolved strontium (Sr) concentration, 87Sr/86Sr isotopic, and hydrochemical profiles from the Shaliu River during the ablation period (May–October). Additionally, we gathered information on the Sr concentration and 87Sr/86Sr in the sediment of the river. The pattern of spatial heterogeneity in observed strontium (Sr) compositions can largely be attributed to lithological characteristics encountered at different locations along the river. The chemical components of Sr in the waters are derived from a combination of carbonate and silicate materials, with carbonates contributing between 69% and 81% and silicates contributing 19%–31%. The annual dissolved Sr flux is estimated to be 132 t/a. In addition to the influence of lithology and weathering processes, we propose that freeze‐thaw cycles within the permafrost layer may significantly affect the chemical mass flux in alpine permafrost watersheds because they generate substantial amounts of loose and easily erodible materials. Climate warming may further intensify the weathering processes in these watersheds, potentially leading to an increase in the Sr flux. This study is crucial for developing a comprehensive understanding of the geochemical composition of dissolved solutes in alpine permafrost regions, as well as for identifying the factors that regulate river water chemistry. Plain Language Summary: Understanding the sources and processes of radiogenic Sr has been a longstanding focus of research. The Shaliu River is a typical inland alpine permafrost watershed on the northeastern Tibetan Plateau. This study presents data on dissolved strontium (Sr) concentration, 87Sr/86Sr, isotopic ratios, and hydrochemical profiles from the Shaliu River during the ablation period (May–October). The main findings of the study are as follows: (a) The chemical components of Sr in the waters are derived from a combination of carbonate and silicate materials, with carbonates contributing between 69% and 81% and silicates contributing 19%–31%; (b) Secondly, the annual dissolved Sr flux is estimated to be 132 t/a; (c) In addition to the influence of lithology and weathering processes, we propose that freeze‐thaw cycles within the permafrost layer may significantly affect the chemical mass flux in alpine permafrost watersheds due to the generation of substantial amounts of loose and easily erodible materials. Key Points: Strontium (Sr) in the Shaliu River waters comes from a mix of carbonates (69%–81%) and silicates (19%–31%)The annual dissolved Sr flux is estimated to be 132 t/aThe freeze‐thaw processes of the permafrost layer have a profound influence on alpine permafrost watersheds under a warming climate [ABSTRACT FROM AUTHOR]

The Nanling Mountains, an important mountain range and watershed in south China, harbor a wealth of relictual plant species, and are considered a 'museum' of subtropical biodiversity. With respect to birds, however, the roles of the Nanling Mountains in impeding the dispersal of the subtropical birds and, as a result, shaping their population and community structures have received little consideration. To examine these roles, we compiled and analyzed two datasets. 1) To test the mountains' influence on gene flow, we undertook a comparative phylogeographic study comparing mitochondrial COI and Cytb DNA sequences of five sylvioid resident bird species of the mountains (Huet's fulvetta Alcippe hueti, red‐billed leiothrix Leiothrix lutea, greater necklaced laughingthrush Pterorhinus pectoralis, Indochinese yuhina Staphida torqueola and mountain bulbul Ixos mcclellandii). 2) To examine differential community development over the history of modern birds, we examined distributional data of all species of the Nanling region using public species occurrence records. For part 1), we sampled 327 individuals from 36 sites and conducted correlation analysis of genetic and geographic distances, taking into account the landscape of the mountains. We found that the mountains do not seriously impede gene flow among populations but influenced species differently. For part 2), comparative analysis of 446 species in 81 families indicated that family membership influenced the community composition of birds in Nanling region. Variation in family distributions is attributable to both environmental and evolutionary factors. Overall, we found that the Nanling Mountains are not currently a substantial barrier to gene flow among the species we studied but act as a corridor and refuge for these birds. However, analyses on higher ranked community data suggest the mountains acted as a barrier in older times, corresponding to the known diversification events in southeast Asian avifauna. [ABSTRACT FROM AUTHOR]

Streamflow generation in mountain watersheds is strongly influenced by snow accumulation and melt as well as groundwater connectivity. In mountainous regions with limestone and dolomite geology, bedrock formations can host karst aquifers, which play a significant role in snowmelt–discharge dynamics. However, mapping complex karst features and the resulting surface‐groundwater exchanges at large scales remains infeasible. In this study, timeseries analysis of continuous discharge and specific conductance measurements were combined with gridded snowmelt predictions to characterize seasonal streamflow response and evaluate dominant watershed controls across 12 monitoring sites in a karstified 554 km2 watershed in northern Utah, USA. Immense surface water hydrologic variability across subcatchments, years and seasons was linked to geologic controls on groundwater dynamics. Unlike many mountain watersheds, the variability between subcatchments could not be well described by typical watershed properties, including elevation or surficial geology. To fill this gap, a conceptual framework was proposed to characterize subsurface controls on snowmelt–discharge dynamics in karst mountain watersheds in terms of conduit flow direction, aquifer storage capacity and connectivity. This framework requires only readily measured surface water and climatic data from nested monitoring sites and was applied to the study watershed to demonstrate its applicability for evaluating dominant controls and climate sensitivity. [ABSTRACT FROM AUTHOR]

Water temperatures in mountain streams are likely to rise under future climate change, with negative impacts on ecosystems and water quality. However, it is difficult to predict which streams are most vulnerable due to sparse historical records of mountain stream temperatures as well as complex interactions between snowpack, groundwater, streamflow and water temperature. Minimum flow volumes are a potentially useful proxy for stream temperature, since daily streamflow records are much more common. We confirmed that there is a strong inverse relationship between annual low flows and peak water temperature using observed data from unimpaired streams throughout the montane regions of the United States' west coast. We then used linear models to explore the relationships between snowpack, potential evapotranspiration and other climate‐related variables with annual low flow volumes and peak water temperatures. We also incorporated previous years' flow volumes into these models to account for groundwater carryover from year to year. We found that annual peak snowpack water storage is a strong predictor of summer low flows in the more arid watersheds studied. This relationship is mediated by atmospheric water demand and carryover subsurface water storage from previous years, such that multi‐year droughts with high evapotranspiration lead to especially low flow volumes. We conclude that watershed management to help retain snow and increase baseflows may help counteract some of the streamflow temperature rises expected from a warming climate, especially in arid watersheds. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the effect of forest damage caused by forest fires or shallow landslides on the rainfall thresholds needed to initiate bedload transport in mountain watersheds. Two bedload monitoring systems were used: a slot sampler and a hydrophone. These were installed in a forest fire-damaged site, a shallow landslide-damaged site, and a control site. A total of 199 effective rainfall-bedload data were collected from 2014 to 2016. Total rainfall amount (TR) and peak rainfall intensity (PRI) were found to be the most effective rainfall indices to predict bedload transport initiation. We also used linear functions to estimate percent threshold lines of the rainfall indices and used performance evaluations to select a representative threshold line for each site. As a result, the forest fire-damaged and shallow landslide-damaged sites had lower TR and PRI reference values than the control site, indicating that lower TR and PRI values can initiate bedload transport in damaged mountain forest areas. Although our study results may be limited by different characteristics between the study sites and insufficient data collection, it still indicates that forest damage caused by forest fires and shallow landslides affects bedload transport. Future studies are needed to further confirm these findings. [ABSTRACT FROM AUTHOR]

Increasing stream metal concentrations apparently caused by climate warming have been reported for a small number of mountain watersheds containing hydrothermally altered bedrock with abundant sulfide minerals (mineralized watersheds). Such increases are concerning and could negatively impact downstream ecosystem health, water resources, and mine‐site remediation efforts. However, the pervasiveness and typical magnitude of these trends remain uncertain. We aggregated available streamwater chemistry data collected from late summer and fall over the past 40 years for 22 mineralized watersheds throughout the Colorado Rocky Mountains. Temporal trend analysis performed using the Regional Kendall Test indicates significant regional upward trends of ∼2% of the site median per year for sulfate, zinc, and copper concentrations in the 17 streams affected by acid rock drainage (ARD; median pH ≤ 5.5), equivalent to concentrations roughly doubling over the past 30 years. An examination of potential load trends utilizing streamflow data from eight "index gages" located near the sample sites provides strong support for regionally increasing sulfate and metal loads in ARD‐affected streams, particularly at higher elevations. Declining streamflows are likely contributing to regionally increasing concentrations, but increasing loads appear to be on average an equal or greater contributor. Comparison of selected site characteristics with site concentration trend magnitudes shows the highest correlation for mean annual air temperature and mean elevation (R2 of 0.42 and 0.35, respectively, with all others being ≤0.14). Future research on climate‐driven controlling mechanisms should therefore focus on processes such as melting of frozen ground directly linked to site mean temperature and elevation. Plain Language Summary: "Mineralized" watersheds contain bedrock with abundant sulfide minerals that, when weathered, often produce naturally acidic and metal‐rich streamwater, known as acid rock drainage (ARD). Increasing metal concentrations have been recently identified in a small number of ARD streams, apparently due to climate change. These trends are concerning because, even at low concentrations, dissolved metals can negatively affect downstream ecosystem health and the quality of water resources. However, we currently do not know how widespread these upward metal trends are regionally, and thus the scope of potential environmental impacts. To address this issue, we aggregated available streamwater chemistry data collected over the past 40 years for mineralized watersheds throughout Colorado. In the 17 sampled ARD streams, we found significant regional upward trends in concentration of ∼2% of the site median per year for two metals of primary environmental concern, zinc and copper. This rate of increase equates to concentrations roughly doubling over the past 30 years. We examined possible driving mechanisms for these marked concentration trends and conclude they are mainly due to increasing sulfide weathering rates (rising metal mass export) rather than simply declining streamflows (less dilution), with melting of frozen ground being a likely major driver of accelerated weathering. Key Points: Sulfate, zinc, and copper concentrations are increasing regionally in streams affected by acid rock drainage throughout ColoradoDeclining streamflows are contributing to increasing concentrations, but increasing loads are likely an equal or greater contributorTrend slopes are positively correlated with mean annual temperature and elevation, suggesting melting of frozen ground is a major driver [ABSTRACT FROM AUTHOR]

Reanalysis datasets provide a reliable reanalysis of climate input data for hydrological models in regions characterized by limited weather station coverage. In this paper, the accuracy of precipitation, the maximum and minimum temperatures of four reanalysis datasets, the China Meteorological Assimilation Driving Datasets for the SWAT model (CMADS), time-expanded climate forecast system reanalysis (CFSR+), the European Centre for Medium-Range Weather Forecast Reanalysis (ERA). and the China Meteorological Forcing Dataset (CMFD), were evaluated by using data from 28 ground-based observations (OBs) in the Source of the Yangtze and Yellow Rivers (SYYR) region and were used as input data for the SWAT model for runoff simulation and performance evaluation, respectively. And, finally, the CMADS was optimized using Integrated Calibrated Multi-Satellite Retrievals for Global Precipitation Measurement (AIMERG) data. The results show that CMFD is the most representative reanalysis data for precipitation characteristics in the SYYR region among the four reanalysis datasets evaluated in this paper, followed by ERA5 and CFSR, while CMADS performs satisfactorily for temperature simulations in this region, but underestimates precipitation. And we contend that the accuracy of runoff simulations is notably contingent upon the precision of daily precipitation within the reanalysis dataset. The runoff simulations in this region do not effectively capture the extreme runoff characteristics of the Yellow River and Yangtze River sources. The refinement of CMADS through the integration of AIMERG satellite precipitation data emerges as a potent strategy for enhancing the precision of runoff simulations. This research can provide a reference for selecting meteorological data products and optimization methods for hydrological process simulation in areas with few meteorological stations. [ABSTRACT FROM AUTHOR]

Lithium isotope ratios (δ7Li) of rivers are increasingly serving as a diagnostic of the balance between chemical and physical weathering contributions to overall landscape denudation rates. Here, we show that intermediate weathering intensities and highly enriched stream δ7Li values typically associated with lowland floodplains can also describe small upland watersheds subject to cool, wet climates. This behavior is revealed by stream δ7Li between +22.4 and +23.5‰ within a Critical Zone observatory located in the Cévennes region of southern France, where dilute stream solute concentrations and significant atmospheric deposition otherwise mask evidence of incongruence. The water‐rock reaction pathways underlying this behavior are quantified through a multicomponent, isotope‐enabled reactive transport model. Using geochemical characterization of soil profiles, bedrock, and long‐term stream samples as constraints, we evolve the simulation from an initially unweathered granite to a steady state weathering profile which reflects the balance between (a) fluid infiltration and drainage and (b) bedrock uplift and soil erosion. Enriched stream δ7Li occurs because Li is strongly incorporated into actively precipitating secondary clay phases beyond what prior laboratory experiments have suggested. Chemical weathering incongruence is maintained despite relatively slow reaction rates and moderate clay accumulation due to a combination of two factors. First, reactive primary mineral phases persist across the weathering profile and effectively "shield" the secondary clays from resolubilization due to their greater solubility. Second, the clays accumulating in the near‐surface profile are relatively mature weathering byproducts. These factors promote characteristically low total dissolved solute export from the catchment despite significant input of exogenous dust. Plain Language Summary: Chemical weathering of silicate minerals by meteoric water serves as a long‐term regulator of atmospheric CO2. The extent to which these reactions produce secondary minerals dictates the chemical composition of soils and rivers. The isotope composition of metals is a potent tracer of this chemical weathering and significant progress has been gained in application of lithium stable isotopes for this purpose. Here, we demonstrate that water draining a mountainous landscape subject to a wet, temperate climate in Southern France produces isotopically heavy lithium in stream water. These signatures suggest an environment in which chemical weathering rates keep pace with the rates of soil erosion. To reveal the underlying causes of this behavior, we develop a numerical model that simulates the flow of water and its interaction with rock in the subsurface using measured data from the field site, including soil, bedrock, and water chemistry. We show that new minerals formed in the subsurface resist dissolution and effectively retain lithium. This work leverages the sensitivity of lithium isotopes to analyze weathering conditions that typify upland watersheds subject to cool, wet climates. Key Points: Small, upland watersheds under Mediterranean climate display characteristically high lithium stable isotope ratios (δ7Li)In a watershed in southern France subject to strong atmospheric inputs, weathering incongruence leads to high stream δ7Li valuesIsotope‐enabled reactive transport modeling indicates that at this site soil clays retain lithium and are resilient to (re‐)solubilization [ABSTRACT FROM AUTHOR]

Coupled simulations of surface and variably saturated subsurface flow, termed integrated hydrologic models (IHMs), can provide powerful insights into the complex dynamics of watersheds. The system of governing equations solved by an IHM is non‐linear, making them a significant computational burden and challenging to accurately parameterize. Consequently, a large fraction of the IHM studies to date have been "numerical hypothesis testing" studies, but, as parallel computing continues to improve, IHMs are approaching the point where they might also be useful as predictive tools. For this to become reality, the predictive uncertainty of such highly parameterized simulations must be considered. However, uncertainty is seldom considered in the IHM literature, likely due to the long runtimes of the complex simulations. The questions considered herein are how much uncertainty is there in an IHM for a common watershed simulation scenario, and how likely is it that any one realization of a system will give the same relative change as any other due to a perturbation in recharge? A stochastic ensemble of 250 permeability field realizations was used to show that uncertainty in a high‐mountain headwaters systems is dominated by the subsurface. Recharge perturbation scenarios echo these results, but the uncertainty of changes in streamflow or groundwater pressure heads were significantly smaller than the uncertainty in their base‐case values. The main finding is that IHMs do provide confident, predictive estimates of relative changes in watersheds, even when uncertainty in specific simulation outputs may be high. Plain Language Summary: Watershed simulations that consider stream‐groundwater interactions require the specification of lots of parameters to define the model but there is often little data to base those parameters on. Consequently, simulation results have uncertainty and if it is not quantified then any predictions made by these models have no "plus‐or‐minus" factors, giving an illusion of high confidence. The catch is that quantifying uncertainty is computationally expensive, which is why it is seldom done, yet at some point the uncertainty must be explored if these models are to be used for predictions. The work in this paper assesses the variability of predictions for a "typical" watershed simulation under three different rainfall scenarios using an ensemble of 250 random versions of the system. The results show that groundwater has higher variability than surface flows, meaning the latter is simulated with higher confidence. However, an important finding is that the relative changes due to the changes in the rainfall were generally consistent across the ensemble. The main point is that even with limited confidence in what an output will be, the relative change of that output (e.g., a 10% increase in recharge increases streamflow by 10%) can likely be inferred with much greater confidence. Key Points: Ensemble simulations of coupled surface‐subsurface flows in a high mountain watershed were performed using the numerical model ParFlowUncertainty throughout the simulation domain was significant and was dominated by the subsurface domainRelative changes in the surface‐ and groundwater values due to a perturbation had smaller confidence intervals than the base‐case values [ABSTRACT FROM AUTHOR]

The seasonal dynamic of the suprapermafrost groundwater significantly affects the runoff generation and confluence in permafrost basins and is a leading issue that must urgently be addressed in hydrological research in cold and alpine regions. In this study, the seasonal dynamic process of the suprapermafrost groundwater level (SGL), vertical gradient changes of soil temperature (ST), moisture content in the active layer (AL), and river level changes were analyzed at four permafrost watersheds in the Qinghai–Tibet Plateau using comparative analysis and the nonlinear correlation evaluation method. The impact of freeze–thaw processes on seasonal SGL and the links between SGL and surface runoff were also investigated. The SGL process in a hydrological year can be divided into four periods: (A) a rapid falling period (October to mid-November), (B) a stable low-water period (late November to May), (C) a rapid rising period (approximately June), and (D) a stable high-water period (July to September), which synchronously respond to seasonal variations in soil moisture and temperature in the AL. The characteristics and causes of SGL changes significantly varied during these four periods. The freeze–thaw process of the AL regulated SGL and surface runoff in permafrost watersheds. During period A, with rapid AL freezing, the ST had a dominant impact on the SGL. In period B, the AL was entirely frozen due to the stably low ST, while the SGL dropped to the lowest level with small changes. During period C, ST in the deep soil layers of AL (below 50 cm depth) significantly impacted the SGL (nonlinear correlation coefficient R2 > 0.74, P<0.05), whereas the SGL change in the shallow soil layer (0–50 cm depth) showed a closer association with soil moisture content. Rainfall was the major cause for the stable high SGL during period D. In addition, the SGLs in periods C and D were closely linked to the retreat and flood processes of river runoff. The SGL contributed approximately 57.0 %–65.8 % of the river runoff changes in the period D. These findings will help to facilitate future hydrological research in the permafrost basins and the development and utilization of water resources in cold and alpine regions. [ABSTRACT FROM AUTHOR]

Coastal mountain rivers export disproportionately high quantities of terrestrial organic carbon (OC) directly to the ocean, feeding microbial communities and altering coastal ecology. To better predict and mitigate the effects of wildfires on aquatic ecosystems and resources, we must evaluate the relationships between fire, hydrology, and carbon export, particularly in the fire‐prone western United States. This study examined the spatiotemporal export of particulate and dissolved OC (POC and DOC, respectively) and particulate and dissolved black carbon (PBC and DBC, respectively) from five coastal mountain watersheds following the 2020 CZU Lightning Complex Fires (California, USA). Despite high variability in watershed burn extent (20–98%), annual POC, DOC, PBC, and DBC concentrations remained relatively stable among the different watersheds. Instead, they correlated significantly with watershed discharge. Our findings indicate that hydrology, rather than burn extent, is a primary driver of post‐fire carbon export in coastal mountain watersheds. [ABSTRACT FROM AUTHOR]

Langbein and Schumm (1958) connected precipitation to erosion in a right-skewed curve used in earth science textbooks for over six decades, where denudation increases with precipitation on the arid/semiarid limb and decreases in humid regions. Development of the catchment-averaged 10Be denudation method a quarter-century ago led geomorphologists to evaluate this hypothesis using data not influenced by the Anthropocene, with mixed findings. The Sonoran Desert in Arizona, USA, is optimal for investigating the longstanding hypothesis of increased erosion from arid to semiarid climates due to: (i) the modern orographic effect aligning elevated precipitation with altitude, mirroring Neotoma packrat midden paleoecology research for the Holocene and late Pleistocene; (ii) the region has been tectonically quiet for the residence times of analyzed 10Be ranging from ca. 8,000-110,000 years. Our significant finding echoes Langbein and Schumm's work, revealing heightened erosion along an elevation-precipitation gradient from arid to semiarid conditions. Notably, the significance of precipitation-elevation contrasts with the absence of significant correlation between 10Be denudation and attributes like slope, drainage area, relief, or landform type (e.g., alluvial fan, pediment, mountain watershed). Modern faunalturbation, increasing along this gradient, exposes more ground to rainsplash and overland flow at higher elevations, adding complexity to these results. Further insights unveil that (i) catchments in areas with substantial Quaternary base level reduction imitate tectonic effects, tripling 10Be denudation rates; (ii) basaltic boulders and cobbles yield an armoring influence; (iii) historical erosion acceleration due to urbanization and wildfires insignificantly affects 10Be denudation rates in the Sonoran Desert; and (iv) minute desert catchments yield anomalous erosion rates. [ABSTRACT FROM AUTHOR]

Severe soil erosion can cause both loss of ecosystem services and riverine environmental contaminations. Thus, understanding the spatiotemporal characteristics of soil loss at the watershed scale is critical for sustainable management of land and water resources. The primary objective of this study was to estimate the spatiotemporal variation in water runoff and soil loss in the Tokoro River watershed (TRW), Hokkaido, Japan. Assuming that agricultural land, which becomes bare depending on the season, is the main source of erosion and that large soil losses occur especially during the snowmelt/freeze-thaw period, we quantified and analyzed the mechanism of soil loss using the Soil and Water Assessment Tool 2012 (SWAT2012). Simulation results based on a publicly available dataset showed that croplands were the primary source of stream sediment load, contributing to 86% of the total soil loss. Furthermore, the soil loss rate was high (241.1–270.9 Mg km−2 yr−1) in sub-basins with a higher percentage of cropland, especially sloped croplands. These sub-basins had a higher risk of productivity loss due to intense erosion and river contamination by muddy runoff. Soil loss mainly occurred in early spring (March and April) and late summer (August – October), accounting for 36% and 45% of the annual soil loss, respectively. Vegetation removal by harvest exacerbated soil loss in October. In March, soil drainage was suppressed by frozen soil, resulting in high surface runoff and soil loss. Therefore, surface runoff when the soil was frozen was considered an important driver of soil loss. The estimation error of the stream sediment loads out of the 95% prediction uncertainty accounted for 26% of the total absolute error. This error could be attributed a lack of certainty in the observation data of high stream sediment loads and the model's underestimation of water runoff during intense snowmelt and rainfall events. [ABSTRACT FROM AUTHOR]

This study assessed the hydropower potential of a mountain watershed within the Sunkoshi River basin in Sindhupalchok, Nepal, utilizing geographic information systems (GIS) and the soil and water assessment tool (SWAT) hydrological model. Topographical, soil, land use, meteorological, and discharge data were employed to assess the study area for the appropriateness of hydropower generation. SWAT was utilized to delineate the Sunkoshi basin into 23 distinct subbasins and involved the creation of a detailed river network, incorporating various hydrological attributes including stream links, stream order, stream length, and slope gradient. After that, it was employed to simulate river discharges within these subbasins. The Sequential Uncertainty Fitting Version 2 (SUFI-2) algorithm, integrated within the SWAT Calibration and Uncertainty Program (SWAT-CUP), was employed to calibrate and validate the model. This step involved the adjustment of 25 selected parameters to enhance the model's accuracy and reliability in representing the hydrological processes of the Sunkoshi basin. Model performance was assessed utilizing three well-established efficiency criteria: coefficient of determination ( R 2 = 0.79), Nash–Sutcliffe efficiency (NSE = 0.73), and percent bias (PBIAS = 17.59). The study identified 36 sites across streams of order 3, 4, and 5 as having potential for hydropower generation. The hydropower potential at each identified site was evaluated using estimated stream flow and topographical head at various probability of exceedance (PoE) levels (40%, 45%, 50%, and 60%). The aggregate hydropower potential of the basin was quantified, yielding a potential of 371.30 MW at a 40% PoE. The findings suggest that an integrated approach combining SWAT-based hydrological modeling within a GIS can accurately assess a river basin's hydropower potential and provide insights into further evaluation of the comprehensive environmental assessment of the fragile Himalayan watersheds. [ABSTRACT FROM AUTHOR]

Stream corridor erosion can majorly contribute to the overall sediment and phosphorus load in urbanizing watersheds. However, the relative contribution of stream bed and bank erosion, compared with upland watershed sources and the potential for stream restoration to mitigate total contaminant loads, is poorly understood. In this study, a new method was developed, using the percent impervious cover (PIC) indicator of urbanization to evaluate the relative contribution of the stream corridor versus upland watershed contributions to observed total sediment and phosphorus loads in the receiving watercourse. This method was used to develop a cost-optimized mitigation plan, including implementing low-impact development (LID) stormwater infrastructure for urban areas and agricultural best management practices (BMPs) for rural areas in the watershed and stream restoration for the degraded stream reaches. A new cost–benefit analysis methodology is developed and used to assess the relative benefits of the mitigation measures for the case study of the Tannery Creek sub-watershed of the East Holland River in Ontario, Canada. The novel contributions of this study include the development of three relationships to estimate sediment and associated phosphorus loading based on contributing catchment area and land use, as well as a method to optimize the costs and benefits of planned mitigation measures. The results support stream restoration as an essential and cost-effective part of a comprehensive water quality watershed management plan to help maintain healthy streams in urbanized watersheds. [ABSTRACT FROM AUTHOR]

The CO2 storage (Fs) is the cumulation or depletion in CO2 amount over a period in an ecosystem. Along with the eddy-covariance flux and wind-stream advection of CO2, it is a major term in the net ecosystem CO2 exchange (NEE) equation and even dominates in the equation under a stable atmospheric stratification while this equation is used for forest ecosystems over complex terrains. However, estimating the Fs remains challenging due to the frequent gusts and random fluctuations in boundary-layer flows that arouse tremendous difficulties in catching the true trend of CO2 changes for its storage estimation from eddy-covariance along with the atmospheric profile techniques. Using the measurements from Qingyuan Ker Towers equipped with NEE instrument systems separately covering mixed-broadleaf, oak, and larch forests towers in a mountain watershed, this study investigates the gust periods and CO2 fluctuation magnitudes while examining their impact on Fs estimation in relation to the terrain complexity index (TCI). The gusts induce CO2 fluctuations at numerous periods of 1 to 10 min over two hours. Diurnal, seasonal, and spatial differences (P < 0.01) in the maximum amplitude of CO2 fluctuations (Amax) ranges from 1.6 to 136.7 ppm and these difference in a period (Pmax) at the same significant level ranges 140 to 170 second. The Amax and Pmax are significantly correlated to the magnitude and random error of Fs with diurnal and seasonal differences. These correlations decrease as CO2 averaging time windows becomes longer. To minimize the uncertainties of Fs, a constant [CO2] averaging time window for the Fs estimates is not ideal. Dynamic averaging time windows and a decision-level fusion model can reduce the potential underestimation of Fs by 29%-33%, 37 being equivalent to 1.9%-4.3% underestimation of the NEE for temperate forests in complex terrains. The relative contribution of Fs to the 30-min NEE observations ranged from 17% to 82% depending on wind speed and TCI. The study's approach is notable as it incorporates TCI and utilizes three flux towers for replication, making the findings relevant to similar regions with a single tower. [ABSTRACT FROM AUTHOR]

Relict periglacial landforms play an important ecosystem role in mountain regions and are becoming relevant in the global context of climate change. In the eastern region of the North Patagonian Andes, many relict periglacial landforms, such as rock glaciers and solifluction lobes, are distributed in mountain watersheds, including the La Hoya mountain watershed. In this watershed, we analyzed hydrochemistry and macroinvertebrate communities across water sources, associated to different landforms (rock glaciers, solifluction lobes, debris slopes, wet meadows, and the collector stream). The results showed that the highest concentrations of nitrates and soluble reactive phosphorus were registered on springs associated with rock glaciers and solifluction lobes, coincident with low water temperature. Macroinvertebrate taxonomic richness was highest in the collector stream and wet meadows. While rock glaciers and solifluction lobes supported low diversity, their assemblages were unique (highest Local Contribution to Beta Diversity). In summary, rock glaciers and solifluction lobes are the principal nutrient contributors to the La Hoya watershed and provide refuge for unique and potentially cold-adapted macroinvertebrates. Due to ongoing climate change in cold environments, ice glaciers and mountain permafrost may disappear or be reduced. In this context, relict periglacial landforms, such as rock glaciers or solifluction lobes, could act as climate change refugia. This assumption requires support from further research at broader scales; nevertheless, our work suggests that the potential ecological and conservation value of relict periglacial landforms should not be underestimated. [ABSTRACT FROM AUTHOR]

Snow avalanches are thought to influence large wood dynamics within mountain streams, but studies that explicitly quantify their impact are minimal. In three headwater catchments of the Frying Pan River, Colorado, USA, we found that wood loads in stream reaches intersected by avalanche pathways ranged from 220 to 8,500 m3/ha and were significantly greater than in non‐avalanched reaches. Inter‐catchment differences in the number of avalanche occurrences were not reflected in control reach wood loads, suggesting that elevated loads may be restricted to the general vicinity of the avalanche pathway. However, the sizable wood volumes in avalanche reaches generated notable geomorphic impacts, indicating that avalanches can create hotspots of in‐stream geomorphic complexity and influence the overall habitat mosaic of the stream ecosystem. Loads in avalanche reaches were moreover significantly greater than literature values for similar streams and recruitment processes, emphasizing the importance of snow avalanches as a wood recruitment mechanism. Plain Language Summary: Snow avalanches are thought to contribute downed, dead wood to mountain streams, but the volume and mobility of supplied wood is unknown. Because downed wood is important for many stream processes (such as habitat creation and sediment storage), an increased understanding of the importance of avalanches for wood supply has notable implications for management of mountain watersheds and their ecosystems. Here we study several streams within the Frying Pan River Basin in Colorado, USA, where avalanche paths commonly intersect the streams that flow along steep mountain valley bottoms. We find that the volume of wood within the length of stream intersected by snow avalanches that occurred in Winter 2019 is substantially greater than the wood volumes outside those reaches. We additionally discover that in‐stream wood volumes within the avalanche areas in this study are significantly greater than values reported by other studies for similar streams and recruitment processes. Overall, our work further emphasizes that avalanches are important suppliers of wood to mountain streams and calls for future studies to continue to expand understanding of how snow avalanches impact mountain stream ecosystems. Key Points: In‐stream wood loads supplied by avalanches are on the order of 102–103 m3/ha within avalanche‐impacted reachesAvalanche‐derived wood may have low mobility but generate hotspots of geomorphic complexityLoads in avalanche reaches are significantly larger than literature values for comparable streams and recruitment mechanisms [ABSTRACT FROM AUTHOR]

Wildfires strongly influence forest ecosystem processes, including carbon and nutrient cycling, and vegetation dynamics. As fire activity increases under changing climate conditions, the ecological and biogeochemical resilience of many forest ecosystems remains unknown.To investigate the resilience of forest ecosystems to changing climate and wildfire activity over decades to millennia, we developed a 4800‐year high‐resolution lake‐sediment record from Silver Lake, Montana, USA (47.360° N, 115.566° W). Charcoal particles, pollen grains, element concentrations and stable isotopes of C and N serve as proxies of past changes in fire, vegetation and ecosystem processes such as nitrogen cycling and soil erosion, within a small subalpine forest watershed. A published lake‐level history from Silver Lake provides a local record of palaeohydrology.A trend towards increased effective moisture over the late Holocene coincided with a distinct shift in the pollen assemblage c. 1900 yr BP, resulting from increased subalpine conifer abundance. Fire activity, inferred from peaks in macroscopic charcoal, decreased significantly after 1900 yr BP, from one fire event every 126 yr (83–184 yr, 95% CI) from 4800 to 1900 yr BP, to one event every 223 yr (175–280 yr) from 1900 yr BP to present.Across the record, individual fire events were followed by two distinct decadal‐scale biogeochemical responses, reflecting differences in ecosystem impacts of fires on watershed processes. These distinct biogeochemical responses were interpreted as reflecting fire severity, highlighting (i) erosion, likely from large or high‐severity fires, and (ii) nutrient transfers and enhanced within‐lake productivity, likely from lower severity or patchier fires. Biogeochemical and vegetation proxies returned to pre‐fire values within decades regardless of the nature of fire effects.Synthesis. Palaeorecords of fire and ecosystem responses provide a novel view revealing past variability in fire effects, analogous to spatial variability in fire severity observed within contemporary wildfires. Overall, the palaeorecord highlights ecosystem resilience to fire across long‐term variability in climate and fire activity. Higher fire frequencies in past millennia relative to the 20th and 21st century suggest that northern Rocky Mountain subalpine ecosystems could remain resilient to future increases in fire activity, provided continued ecosystem recovery within decades. [ABSTRACT FROM AUTHOR]

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We installed a purpose‐built network of co‐located Global Navigation Satellite System (GNSS) stations and meteorological instrumentation to investigate water storage in a high‐mountain watershed along the Idaho‐Montana border. Twelve GNSS stations are distributed across the Selway‐Lochsa watersheds at approximately 30–40 km spacing, filling a critical observational gap between localized point measurements and regional geodetic and satellite data sets. The unique coupling of geodetic and hydrologic observations in this network enables direct comparison between co‐located GNSS measurements of the elastic response of the solid Earth and local changes in measured water storage. This network is specifically designed to address questions of hydrologic storage and movement at the mountain watershed scale. Here, we describe technical details of the network and its deployment; introduce new hydrologic, meteorologic, and geodetic data sets recorded by the network; process and analyze the source data (e.g., time series of daily three‐dimensional GNSS site positions, removal of non‐hydrologic signals); and characterize basic empirical relationships between water storage, water movement, and GNSS‐inferred surface displacement. The network shows preliminary evidence for spatial differences in displacement resulting from a range of snow loads across elevations, but longer and more complete data records are needed to support these initial findings. We also provide examples of additional scientific applications of this network, including estimations of snow depth and snow water equivalent from GNSS multipath reflectometry. Finally, we consider the challenges, limitations, and opportunities of deploying GNSS and weather stations at high elevations with heavy snowpack and offer ideas for technical improvements. Plain Language Summary: We have installed a network of co‐located weather and high‐precision Global Navigation Satellite System (GNSS) stations in and around a mountain watershed along the border of Idaho and Montana. This network is designed specifically to address questions related to local water availability, such as where and how much water is stored in the form of snowpack, surface water, groundwater, soil moisture, etc., throughout the year. By measuring the vertical motion of GNSS stations attached to bedrock, we can use Earth's surface as a giant scale to weigh the amount of this stored water. Meteorological instrumentation provides an independent measurement of water stored in the study area, enabling comparison of GNSS‐recorded movement and changing amounts of water. We show initial time series from the meteorological and GNSS stations within the network, showing how changing water storage influences GNSS vertical movement. We also provide brief examples of additional uses of this network, including the use of ground‐reflected GNSS signals to estimate snow depth and snowpack water content. Key Points: We introduce a custom network of co‐located Global Navigation Satellite System (GNSS) and meteorological stations designed to study water storage in a high‐mountain watershedThe network fills a gap in continuous GNSS‐based solid Earth deformation monitoring in the northern Intermountain WestWe record differences in surface displacement and observed hydrologic loading across the network at high spatial resolution [ABSTRACT FROM AUTHOR]

In order to analyze the impact of rainstorm design on mountain torrent disasters in small watersheds in mountainous areas this paper uses a spatio-temporal variable source mixed runoff generation model, taking Guankou, and Hanwangchang in Sichuan Province as the research area, the response rules of descending water in high vegetation cover basins to different reproduction periods and rainstorm type conditions of different designs are analyzed, and the peak flow, peak present time and peak lag time of the river basin under different rain types and recurrence period conditions are compared and analyzed. The research findings show that the spatio-temporal variable source mixed runoff generation model is suitable for the simulation of hydrological processes with good simulation accuracy in mountainous areas with high vegetation coverage. The latter rain patterns in the Guankou and Hanwangchang basins have more flood peaks than those formed under the front and middle conditions under the same recurrent period, but the front rain patterns produce more floods than middle and rear rain patterns. Under the conditions of different rainfall patterns, with the increase in return period, the peak discharge of the Guankou and Hanwangchang drainage basins shows an increasing trend. The forest and grass vegetation coverage rate is Hangwangchang>Guankou watershed, and the peak emergence time of the Guankou is earlier than that of the Hangwangchang watershed under the design rainstorm conditions of different return periods, the vegetation coverage of forest and grass can regulate the runoff process of flood to a certain extent. The lag time between the occurrence time of the flood peak and the occurrence time of rainstorm peak in the Guankou watershed and the Hanwangchang watershed is forward type>middle type>rear type. Revealing the quantitative law of the high vegetation covered watershed in the southwest mountain area for the design of rainstorm patterns in different return periods has a guiding significance in analyzing the formation process of rainstorm and flood in the high vegetation coverage basin of the southwest mountain area, and improving the flood forecasting accuracy and flood control and disaster reduction capability of the basin. [ABSTRACT FROM AUTHOR]

Exploring the characteristics of uneven temporal and spatial distribution of precipitation in mountain watersheds can provide a reference for regional agricultural development and resource utilization, and contribute to the protection of the ecological environment. Based on the daily precipitation observation data of 40 meteorological stations in the Wujiang River Basin from 1963 to 2021, the temporal- and spatial-variation characteristics of the precipitation concentration degree (PCD) and precipitation concentration period (PCP) were analyzed using the Randall S analysis method, Mann–Kendall test method, Pettitt method, wavelet analysis and empirical orthogonal function (EOF). The results showed that the fluctuation range of PCD in Wujiang River Basin from 1963 to 2021 was 0.34–0.59, with a multi-year average of 0.47, which was obviously higher than the national average level and is showing a trend of slowly increasing. The fluctuation range of PCP was between 17.1 and 21.5 days, with a multi-year average of 19.0. The annual precipitation was mostly concentrated around the middle of July and showed a slowly decreasing trend. The abrupt change in PCD and PCP occurred around 1983 and 2001, respectively. There is an obvious Hearst phenomenon in PCP. In the future, the trend of precipitation concentration in the middle period will remain in advance, and the degree of precipitation concentration will continue to increase. The maximum precipitation in the flood season will continue to be delayed. The spatial pattern of the first mode of PCD and PCP in the Wujiang River basin was consistent and showed an opposite pattern between the upper reaches and the middle-lower reaches of the basin, which reflects the influence of the topography of the basin on the spatial distribution of precipitation. The distribution of precipitation is affected by topography. The elevation change in the basin was complex, and the leeward slope varied a lot. Therefore, it has a significant impact on precipitation. Areas with less precipitation are at higher elevations and on mountain leeward slopes, with a lack of moist air flow. The area with more precipitation was the summer monsoon mountain windward slope, and the topography blocks the increase in precipitation. The elevation of the central region is relatively uniform and the terrain is flat. Therefore, the distribution of precipitation is more uniform. [ABSTRACT FROM AUTHOR]

Urban waterlogging occurs when precipitation events cause urban runoff to exceed the capacity of stormwater systems, causing water accumulation on the land surface. Valparaiso City is one of the main metropolitan centers in Chile. Rapid urban growth forced the city to invest substantial resources to upgrade its stormwater system. The most recent is the Argentina stormwater canal. However, soon after the stormwater canal was operational, solids (sandy clay, fine sand) washed-off from upland watersheds accumulated in the lower elevation sectors of the canal, close to the conduit outfall to Valparaiso Bay. This has degraded the water conveying capacity of the canal and increased waterlogging hazards if extreme storms and high tide events combine. This research explores management scenarios for reducing the hazard of waterlogging in the canal. Hydrological and in-stream hydrodynamic modeling is used to propose watershed management scenarios aimed to reduce flows and suspended solids wash-off. The impact of those scenarios for reducing waterlogging hazard is assessed. [ABSTRACT FROM AUTHOR]

This study compares the flood regime of rivers in Ukraine and Austria over the last decades. We used data from mountain and lowland watersheds, where floods are caused by different processes. In order to identify possible shifts in the day of occurrence of annual flood maxima, we apply the kernel density method to the time series of two subperiods (1960–1987 and 1988–2015). We use the Mann Kendall test at a 5% significance level to identify significant positive or negative trends in the series of annual maximum discharges. In Austria, we observe an increasing trend in summer floods associated with increasing precipitation. In the lowland areas of Ukraine, a clear reduction in spring floods is observed, linked to shallower snow packs in a warming climate. In the Ukrainian Carpathians, on the other hand, where floods occur throughout the year, an increase in the portion of liquid precipitation during the cold period of the year leads to earlier floods and an increase in the probability of flooding in winter. [ABSTRACT FROM AUTHOR]

Protected areas are relatively free of human disturbance, are especially common in montane regions, and provide opportunities to study native fauna and flora. Stoneflies are model organisms to assess present and future environmental changes. While stoneflies inhabit cold lakes and a wide size range of lotic systems, diversity is greatest in streams draining mountain landscapes. This study addressed seasonal and elevation patterns of a stonefly fauna inhabiting a protected landscape draining the eastern flank of Mount Mitchell, the highest point of the Appalachian Mountains, USA. In total, 58 species were collected with estimated richness values ranging from 63 to 65. Species determinations were assisted with an integrative molecular approach using the mitochondrial barcode gene. Sampling during spring yielded the most species seasonally. Although certain species were only found at lower or higher sites, several were collected from across a broad range of elevations. Roughly 1/3 (21 = 36%) of the fauna present is known only from the southern Appalachian Highlands region, including one species described as new during this study. The assemblage reported here, however, did not closely align with other Appalachian fauna. Overall, well-structured faunal research continues to be important in light of continuing habitat modifications and climate change. [ABSTRACT FROM AUTHOR]

Estimation of hydrological processes is critical to water resource management, water supply planning, ecological protection, and climate change impact assessment. Mountains in Central Asia are the major source of water for rivers and agricultural practices. The disturbance of mountain forests in the region has altered the hydrological processes and accelerated soil erosion, mudflow, landslides, and flooding. We used the SWAT (Soil and Water Assessment Tool) model calibrated and validated with remote sensing data to quantify the mountainous hydrological processes in the Aktash River watershed (ARW) of Uzbekistan, Central Asia. Simulations showed that the daily surface runoff and streamflow closely responded to daily precipitation. Groundwater discharge reached its maximum in winter because of snowmelt. The wet months were from July to December, and the dry months were from January to June. The magnitudes of the seasonal hydrological processes were in the following order: fall > summer > winter > spring for precipitation and surface runoff; summer > spring > fall > winter for evapotranspiration (ET); winter > spring > fall > summer for snowmelt; fall > winter > summer > spring for water yield and streamflow; and winter > fall > spring > summer for groundwater discharge. The Mann–Kendall statistical test revealed a significant increasing trend for the annual precipitation (τ = 0.45, p < 0.01) and surface runoff (τ = 0.41, p < 0.02) over the past 17 years from 2003 to 2019. Compared to rangeland, forested land decreased monthly and annual average surface runoff by 20%, and increased monthly and annual average groundwater recharge by about 5%. Agricultural land had much higher unit-area values (mm/km2/y) of ET, groundwater recharge, and water yield than those of urban, forest, and range lands. Our research findings provide useful information to farmers, foresters, and decision makers for better water resource management in the ARW, Central Asia, and other mountain watersheds with similar conditions. [ABSTRACT FROM AUTHOR]

In the humid tropics, forest conversion and climate change threaten the hydrological function and stationarity of watersheds, particularly in steep terrain. As climate change intensifies, shifting precipitation patterns and expanding agricultural and pastoral land use may effectively reduce the resilience of headwater catchments. Compounding this problem is the limited long-term monitoring in developing countries for planning in an uncertain future. In this study, we asked which change, climate or land use, more greatly affects stream discharge in humid tropical mountain watersheds? To answer this question, we used the process-based, spatially distributed Soil Moisture Routing model. After first evaluating model performance (Ns = 0.73), we conducted a global sensitivity analysis to identify the model parameters that most strongly influence simulated watershed discharge. In particular, peak flows are most influenced by input model parameters that represent shallow subsurface soil pathways and saturation-excess runoff while low flows are most sensitive to macropore hydraulic conductivity, soil depth and porosity parameters. We then simulated a range of land use and climate scenarios in three mountain watersheds of central Costa Rica. Our results show that deforestation influences streamflow more than altered precipitation and temperature patterns through changes in first-order hydrologic hillslope processes. However, forest conversion coupled with intensifying precipitation events amplifies hydrological extremes, reducing the hydrological resilience to predicted climate shifts in mountain watersheds of the humid tropics. This finding suggests that reforestation can help mitigate the effects of climate change on streamflow dynamics in the tropics including impacts to water availability, flood pulses, channel geomorphology and aquatic habitat associated with altered flow regimes. [ABSTRACT FROM AUTHOR]

The way Alpine rivers mobilize, convey and store coarse material during high‐magnitude events is poorly understood, notably because it is difficult to obtain measurements of bedload transport at the watershed scale. Seismic sensor data, evaluated with appropriate seismic physical models, can provide that missing link by yielding time‐varying estimates of bedload transport albeit with non‐negligible uncertainty. Low cost and ease of installation allow for networks of sensors to be deployed, providing continuous, watershed‐scale insights into bedload transport dynamics. Here, we deploy a network of 24 seismic sensors to estimate coarse material fluxes in a 13.4 km2 Alpine watershed during a high‐magnitude transport event. First, we benchmark the seismic inversion routine with an independent time‐series of bedload transport obtained with a calibrated acoustic system. Then, we apply the procedure to the other seismic sensors across the watershed. Propagation velocities derived from cross‐correlation analysis between spatially consecutive bedload transport time‐series were too high with respect to typical bedload transport velocity suggesting that a faster‐moving water wave (re‐)mobilizes local coarse material. Spatially distributed estimates of bedload transport reveal a relative inefficiency of Alpine watersheds in evacuating coarse material, even during a relatively infrequent high‐magnitude bedload transport event. Significant inputs estimated for some tributaries were rapidly attenuated as the main river crossed less hydraulically efficient reaches. Only a small proportion of the total amount of material mobilized in the watershed was exported at the outlet. Multiple periods of competent flows are likely necessary to evacuate coarse material mobilized throughout the watershed during individual bedload transport events. Plain Language Summary: By driving erosion and deposition, bedload transport is a serious challenge for Alpine watershed management. Yet, the way Alpine rivers mobilize, convey, and store coarse material during high‐magnitude events is poorly known, notably due to the difficulty of measuring bedload transport in different locations at the watershed scale. In this contribution, we use a network of 24 seismic sensors to capture the motion of coarse material in a 13.4 km2 Alpine watershed during a high‐magnitude bedload transport event. Collected bedload transport estimates revealed a relative inefficiency of Alpine watersheds in evacuating coarse material, even during a relatively high‐magnitude bedload transport event. Large inputs estimated in some tributaries rapidly deposited as the flow crossed less transport‐efficient reaches, and only a comparatively negligible proportion of the total amount of material mobilized in the watershed was exported at the outlet. Multiple periods of high streamflow are likely necessary to evacuate the coarse material mobilized throughout the watershed during individual bedload transport events. This data set increases knowledge of coarse material motion within Alpine watersheds during high‐magnitude bedload transport events, and may help to improve predictions of bedload transport in the future through a better constraint on changing sediment availability in time and space. Key Points: For the first time, a high‐magnitude bedload transport event was tracked at the watershed scale by a network of 24 seismic sensorsA comparatively low proportion of the material mobilized in the watershed during the event was exported at the outlet (2.5%)Multiple periods of competent flows are likely necessary to evacuate coarse material mobilized during individual bedload transport events [ABSTRACT FROM AUTHOR]

Meighan watershed habitats, located in central Iran (Markazi Province), have undergone considerable changes in recent years. Landsat satellite images of the year 2020 were used to produce digital land use maps for the present study. Ecological quality, rarity and risk assessment analyses were performed using the Sub-Watershed-scale Ecosystem Service Modeler according to the InVEST (SWESMI) toolkit, HQR and HRA models. The images were classified into three classes including Agriculture, Rangeland, and Human-made (industrial-residential regions) impacts. The results indicated that there are three important habitats in the Meighan watershed: mountains, plains, and wetlands. Human-made changes, agriculture, and road developments were among the biggest threats and most devastating stressors in the Meighan watershed. There was an increased cumulative risk in the plain habitat of the Kharahrod (31.44%), Amanabad (27.75%) and Sarogh (26.87%) sub-watersheds. A decreased cumulative risk was identified in the mountain habitat of the Kheirabad (7.62%) sub-watershed in the Haftad-Gholleh National Park, and wetland habitat of the Meighan (4.30%) sub-watersheds. The plain habitat (with high cumulative consequence) and the wetland habitat (with high accumulative exposure) are at the highest risk from Human-made activities. Stressors related to roads and agriculture-livestock were the main stressors in the mountain habitat and wetland habitat, respectively, whereas both stressors were considerably high in the plain habitat. Due to being located in a protected area, the Kheirabad sub-watershed was found to have suitable quality and rarity compared to other sub-watersheds in central Iran. The results highlight the significance of land conservation and protected areas in maintaining the habitat quality and reducing the risks associated with habitat degradation and biodiversity. [ABSTRACT FROM AUTHOR]

The seasonal dynamic of suprapermafrost groundwater significantly affects runoff generation and concentration in permafrost basins and is a leading issue that must urgently be addressed in hydrological research in cold and alpine regions. In this study, the seasonal dynamic process of the suprapermafrost groundwater level (SGL), vertical gradient changes of soil temperature (ST) and moisture content in the active layer (AL), and river level changes were systematically analyzed at four permafrost watersheds in the Qinghai–Tibet Plateau using comparative analysis and the nonlinear correlation evaluation method. How freeze–thaw processes impact seasonal SGL, and the links between SGL and surface runoff, were also discussed. The SGL process in a hydrological year can be divided into four periods: (A) a rapid falling period (October–middle November), (B) a stable low-water period (late November–May), (C) a rapid rising period (approximately June), and (D) a stable high-water period (July–September), which synchronously respond to seasonal variations in soil moisture and temperature in the AL. The characteristics and causes of SGL changes varied significantly during the four different periods. The freeze-thaw process of the AL has crucial regulatory effects on SGL and surface runoff in permafrost watersheds. During Period A, with rapid AL freezing, the ST had a dominant impact on the SGL. In Period B, the AL was entirely frozen because of the stably low ST, and the SGL dropped to the lowest level with small changes. During Period C, ST in the deep soil layers of the active layer (below 50 cm depth) significantly impacted the SGL (nonlinear correlation coefficient R2>0.74, P<0.05), whereas the SGL change in the shallow soil layer (0–50 cm depth) had a closer relationship with soil moisture content. Rainfall was the major cause for the stable high SGL during Period D. In addition, the SGLs in Periods C and D were closely linked to the retreat and flood processes of river runoff. The SWL contributed approximately 57.0–65.8 % of the river runoff changes in Period D. These findings can provide references for hydrological research in permafrost basins and guide the rational development and utilization of water resources in cold and alpine regions. [ABSTRACT FROM AUTHOR]

Watershed prioritization is essential in sub-watershed (SW) natural resource management. The Swat River watershed in the Hindukush mountains of Pakistan's Khyber Pakhtunkhwa province covers an area of 5337 km2. Using an Advanced Spaceborne Thermal Emission and Reflection Radiometer digital elevation model with a resolution of 30 m obtained from the United States Geological Survey (USGS), the present study identified 17 SWs (SW1–17) with drainage patterns ranging from dendritic to sub-dendritic. The SWs were assessed for their susceptibility to erosion via GIS-based assessment using a morphometry-based compound factor (CF) approach. A total of 15 linear, aerial, and relief morphometric characteristics were identified and analyzed. The SWs were ranked for each morphometric parameter based on their contribution to the erodibility of the SW. A ranking of 1 indicated that the SW had the greatest susceptibility to erosion for that parameter and a ranking of 17 indicates that it had the lowest. These rankings were summed to calculate the CF, which thus indicated the combined influence of these characteristics on the erosion susceptibility of the SW (a lower CF indicated a higher susceptibility to erosion). The SWs were consequently divided into four groups based on their susceptibility to erosion using the calculated CF: very high, high, moderate, and low susceptibility. SW8, SW12, and SW15 had the lowest CFs (8.0, 8.9, and 8.9, respectively) and were thus extremely vulnerable to erosion. In contrast, SW1, SW2, and SW4 had the highest CFs (13.4, 13.8, and 11.8, respectively) and were the least vulnerable to erosion. The very high-priority SWs were characterized by the presence of fifth-order streams, a length of the overland flow of 1.20–1.61, a very high basin relief of 1720–2937, the highest relief ratio of 102.10–205.24, a low shape factor of 1.51–2.67, and a farm factor of 0.37–0.66. The present study demonstrates that the key morphometric characteristics that impact soil erosion are basin form and relief parameters, such as the basin relief and relief ratio. This study illustrates that the CF approach to determining the susceptibility of SWs to soil erosion is extremely valuable for planners and decision-makers for soil conservation efforts at the SW level. [ABSTRACT FROM AUTHOR]

Acid rock drainage (ARD) impacts species composition in mountain streams. The potential impact for riparian birds experiencing elevated metal uptake by consumption of benthic invertebrates is concerning but not well studied. We investigated the influence of metal and rare earth element (REE) content in benthic invertebrates on the presence of breeding birds in an ARD-impacted watershed in Colorado, USA, where tree swallows in nest boxes had previously been found to have elevated metal concentrations at some sites. The concentrations of particular REEs in invertebrates were higher than those for cadmium or lead. Avian point counts indicated that most bird species detected were present at most sites, and that tree swallows were rarely found. Occupancy models showed that the availability of shrub or forest habitat was a good predictor for a few habitat-specialists, but metal and REE concentrations in water and invertebrates were not good predictors of avian presence. For other species, neither habitat type nor water quality were important predictors. Overall, this study indicates that the climate-change-driven increases in metals and REEs may not influence the presence of riparian birds in ARD-impacted streams. [ABSTRACT FROM AUTHOR]

While connectivity studies are becoming common in the Earth sciences, disconnectivity has received much less attention. Sediment storage is the direct result of sediment disconnectivity and can provide concrete evidence of the spatial patterns of disconnectivity at the catchment‐scale. In this study, we explore the catchment‐scale sediment dynamics of the Tahoma Creek watershed, a high‐gradient glacio‐volcanic landscape, within a sediment budget framework and identify and map sources of disconnectivity to determine whether they explain the spatial patterns and estimated efficiencies of sediment transfers. We found that up to 80% of the total eroded sediment is sourced from the proglacial zone. The proglacial zone is characterized by high connectivity resulting from frequent debris flows and floods, and rapidly responds to changing conditions. Down valley, however, sources of disconnectivity become increasingly more prevalent, the hillslopes become decoupled from the channel, and a majority of the eroded sediment is redeposited with as little as ∼15% reaching the outlet. The spatial distribution of sources of disconnectivity and their upslope affected areas explains, to a large degree, catchment‐scale sediment dynamics and sediment transfer efficiencies and is in close agreement with quantitative connectivity estimates. We find that steep, glaciated watersheds are predominantly disconnected over human timescales and suggest that disconnectivity is the dominant state of landscapes over most timescales of interest. Mapping sources of disconnectivity provides a straightforward and concrete approach to estimating system disconnectivity and can increase confidence when paired with quantitative indices. Plain Language Summary: Mountain watersheds supply freshwater and sediment to downstream river systems affecting flooding, fish habitat, and water quality. We argue that understanding the spatial and temporal patterns of sediment movement within a landscape requires knowing where and for how long sediment is stored and the overall efficiency of sediment transfer between different parts of the landscape. We illustrate the importance and utility of mapping landforms and landscape characteristics that delay or disrupt sediment movement using the Tahoma Creek watershed as an example. This watershed drains a portion of Mount Rainier, a volcano shaped by glaciers in Washington, USA, and is incredibly dynamic. We find that landforms and landscape characteristics that limit sediment movement are common and that mapping them gives an accurate picture of sediment movement patterns. Glaciers dramatically reshape the landscape, which controls sediment supply and movement patterns, and their legacy remains for thousands of years after they retreat. We also make use of high‐resolution elevation data representing the land surface in 2002, 2008, and 2012 to quantify how much erosion, transport, and deposition occurred and how efficiently sediment was transported. We find that sediment is transported more efficiently during extreme events, such as the 2006 floods. Key Points: Disconnectivity is the dominant but inefficient state of a system in transferring matter and energy within and between system componentsSources of disconnectivity were found to accurately explain catchment‐scale sediment dynamicsDuring extreme events, the efficiency of sediment transfer increases, resulting in rapid adjustment [ABSTRACT FROM AUTHOR]

Despite widespread observations of climate‐change induced treeline migration and shrubification, there remains few direct measurements of transpiration and dynamics of evaporative partitioning in northern climates. Here, we present eddy covariance and sap flow data at a low elevation boreal white spruce forest and a mid‐elevation shrub taiga comprised of tall willow (Salix spp.) and birch (Betula spp.) in a subarctic, alpine catchment in Yukon Territory, Canada over two hydrologically distinct years. Specific research questions addressed were: (1) How do contributions of T to ET vary between sites and years? and (2) What are the primary meteorological, phenological, and soil moisture controls and limits on ET and T across vegetation covers? In the mid‐growing season, mean T rates were greater at the dense shrub site (2.0 ± 0.75 mm d−1) than the forest (1.47 ± 0.52 mm d−1). During this time, T:ET was lower at the forest (0.48) than at the tall, dense shrub site (0.80). Of the 2 years, 2020 was considerably wetter and cooler than 2019 during the growing season. At the shrub site, during the mid‐growing season (July 1‐Aug 15), T dropped considerably in 2020 (−26%), as T was suppressed during the short, wet growing season. In contrast, T at the forest was only moderately suppressed (−3%) between years in this same period. Evapotranspiration was more strongly controlled by air temperature during the early and late season at the forest, while ET at the shrub site was more sensitive to warmer temperatures in the mid‐growing season. Distinct differences in sap flux densities, sensitivities to environmental drivers, and stomatal resistances existed between shrub species. Results suggest that warming temperatures, increases in growing season length, and increased rainfall will cause differences in evaporative response and partitioning over complex, heterogenous alpine watersheds. [ABSTRACT FROM AUTHOR]

Climate change has rapidly degraded the cryosphere in alpine headwaters, altering the runoff regime of alpine watersheds and threatening water security worldwide. To precisely simulate runoff response to climate change in alpine catchments, we took the source region of the Yellow River as a case to develop a physics‐informed deep learning (DL) model that tightly hybridizes DL with the physics of dominant hydrological processes, including the neural network‐based coupling of soil freeze‐thaw physics inspired by the Stefan equation. A physics‐informed DL model without soil freeze‐thaw representation was also established as a benchmark. Results demonstrated the former model's superiority in capturing streamflow's inter‐annual dynamics and reproducing baseflow recession properties caused by soil freeze‐thaw when average temperature rises by 1°C. This emphasizes the importance of the physics of dominant hydrological processes for DL to make credible runoff projections under rapid climate change. Furthermore, we comprehensively compared the physics‐informed DL model with a lumped model, physically‐based distributed model, and standard DL model, showing that the physics‐informed DL model performs best in simulating streamflow at multi‐timescales and the impacts of soil freeze‐thaw on runoff, and is more capable of simulating runoff relative change and trend in response to climate change. In summary, our findings demonstrate physics‐informed DL's credibility in runoff projections under drastic climate change when infused with the physics of dominant hydrological processes, and illustrate its superior ability to learn complex hydrological processes, providing a new approach for runoff simulation in permafrost‐affected alpine catchments under climate change. Plain Language Summary: The changing climate greatly affects permafrost regions in mountain headwaters, leading to the shift of the runoff regime. Projecting future runoff under climate change in such catchments is crucial for global water security. However, traditional distributed hydrological modeling falls short due to the complex and unclear underlying mechanisms, while deep learning (DL) models' unreliability in out‐of‐sample predictions might be amplified by significant climate change. To address this gap, we focused on an alpine permafrost catchment, the source region of the Yellow River, and developed a model that combines DL techniques with the fundamental physics of hydrological processes. By introducing a neural network‐based coupling of soil freeze‐thaw, inspired by a well‐known physical equation, our model outperforms the benchmark model without soil freeze‐thaw representation in simulating annual runoff variations in response to a 1°C/year temperature increase. Furthermore, our model excels in simulating runoff changes and trends caused by climate change, surpassing the lumped model, distributed hydrological model, and standard DL model. These indicate that the infused physics can help DL better capture the soil freeze‐thaw process and make more credible projections under climate change. Our study offers a valuable approach for assessing climate change impacts on runoff in permafrost‐affected mountain headwaters. Key Points: A model hybridizing deep learning and physics of dominant hydrological processes was developed for runoff simulation in alpine catchmentsPhysics‐informed deep learning model can well simulate runoff change under warming of 1°C, while the standard deep learning model can notPhysics‐informed deep learning outperforms physically‐based models in simulating runoff response to climate change in alpine catchments [ABSTRACT FROM AUTHOR]

Studies of biogeographic patterns of fungi have long been behind those of plants and animals. The presence of worldwide species, the lack of systematic sampling design and adequate sampling effort, and the lack of research units are responsible for this status. This study investigates the biogeographical patterns of Arthrobotrys oligospora, the most widespread globally distributed nematodetrapping fungi (NTF), by stratified collecting and analyzing 2,250 samples from 228 sites in Yunnan Province, China. The A. oligospora was isolated, and 149 strains were subjected to ITS, TUB, TEF and RPB2 gene sequencing and multigene association phylogeographic analysis. The results show that at population level A. oligospora is randomly distributed throughout Yunnan Province and has no biogeographical distribution pattern. At the genetic level, the phylogenetic tree of A. oligospora diverges into five major evolutionary clades, with a low degree of gene flow between the five clades. However, the correlation between the phylogenetic diversity of A. oligospora and geographical factors was low. There was no clear pattern in the phylogenetic clades distribution of A. oligospora either without dividing the study unit or when the grid was used as the study unit. When watersheds were used as the study unit, 67.4%, 63.3%, 65.9%, 83.3%, and 66.7% of clade 1-5 strains were distributed in the Jinsha river, Red river, Peal river, Lancang river, and Nujiang-Irawaddy river watersheds, respectively. The clades distribution of A. oligospora was highly consistent with the watersheds distribution. Training predictions of the clades distributions using randomly generated polygons were also less accurate than watersheds. These results suggest that watersheds are key to discovering the biogeographic distribution patterns of A. oligospora. The A. oligospora populations are blocked by mountains in the watershed, and gene flow barriers have occurred, which may have resulted in the formation of multiple cryptic species. Watersheds are also ideal for understanding such speciation processes, explaining factors affecting biodiversity distribution and coupling studies of plant and animal and microbial diversity. [ABSTRACT FROM AUTHOR]

Groundwater discharge sustains the baseflow of alpine headwater streams, which is critical for water supply and aquatic environments in mountainous regions. Periglacial landforms typical of alpine headwaters (e.g., talus, moraine, rock glacier, alpine meadows) are important aquifers in alpine watersheds. This study examines the hydrological function of an alpine aquifer complex in a small headwater basin in the Canadian Rockies. The aquifer complex consisting of talus, alpine meadow underlain by a bedrock depression, and recessional moraine provided essentially all baseflow of a 6.5 km2 watershed, even though the upper sub‐watershed containing the aquifer complex occupies only 14% of the watershed. Chemical and isotopic signatures indicated that the recessional moraine serves as a gatekeeper of the upper sub‐watershed, whereby it integrates groundwater components from multiple aquifers and controls the discharge from the outlet springs. Field observation of discharge and the water table in the moraine aquifer showed a nonlinear groundwater storage‐discharge relationship. Numerical groundwater flow models of the upper sub‐watershed showed that the transmissivity feedback resulting from a decrease in hydraulic conductivity with depth was essential for determining the nonlinear storage‐discharge relationship. A simple exponential function was proposed to represent the observed groundwater storage‐discharge relationship, which can be implemented within large‐scale hydrological models to simulate baseflow coming out of alpine headwater regions. [ABSTRACT FROM AUTHOR]

In the Eastern Himalayas syntaxes (Tibet Plateau, China), increasing periglacial debris flows have been documented in recent decades, but minimal research has focused on the material properties and the topography of initiation areas. In this work, we applied a series of satellite images from 2000 to 2021 to examine the hanging glacier status and debris-flow initiation conditions in Sanggu watershed. Five large-scale debris flow events in 2003, 2015, 2018, 2020, and 2021 were interpreted. Visual interpretation, together with pixel dichotomy model and the COSI-Corr method, demonstrated that debris flows mainly initiated from the periglacial environment of catchments I and II. Since 2000, the glacier has exhibited general shrinkage, punctuated by occasional advance. The failure potential, expressed as the product of changed glacier area and topographic slope, positively relates to the inundation area of debris flows. This result implies that either abrupt glacier advancement or retreat may result in large debris flows, and glacier terminus position may serve as the main driving factor for debris flow initiation. Importantly, a lower limited area-slope initiation condition was developed in this work, which may provide a reference point for identifying possible failure areas of periglacial debris. The results of this work contribute to knowledge about the material properties and magnitude prediction of periglacial debris flows in alpine watersheds. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Current streamflow timing metrics, such as the center of volume, or COV, use flow days, which are days at which a specific total streamflow volume, such as 50% for COV, has passed a given point. These metrics have been used as indicators for changes in the timings of snowmelt contributions to streamflow, but they may not be indicating changes to snowmelt timings as they have a fixed volume. Using manually extracted start and end days for high-elevation, mountainous watersheds, which are regarded as true values, we developed a new method to estimate when snowmelt is entering streams. Based on RMSE and NSE values, this new method is a better model for snowmelt-driven streamflow than using flow days or the COV. In general, the trend analysis results from the different timing metrics indicate an earlier timing in the year. This method was suitable for 40 different-sized watersheds in Colorado, USA; these are all snow-dominated watersheds in a semi-arid climate. This method could be used to assess watersheds in different climates, including those that are not as snow-dominated. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of Soil & Water Conservation is the property of Bulletin of Soil & Water Conservation Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Reactive nitrogen (Nr) concentrations are higher than expected for mountain lakes in Rocky Mountain National Park, and for many years, high Nr concentrations have been attributed to atmospheric Nr deposition from regional and more distant emission sources, including combustion of fossil fuels and agricultural activities. Here, we estimated the contribution from a very local source, that of human urine, related to intensive use by visitors in Loch Vale Watershed (LVWS). Not only does urine convey hormones, pharmaceuticals, antibiotic‐resistant bacteria, and antibiotic‐resistant genes to the environment, but it also contributes Nr, which contributes to loss of biodiversity and eutrophication. Using caffeine as a specific marker for human urine, we compared the calculated maximum potential input of urine with that from wet atmospheric Nr deposition. The maximum potential input is a worst‐case scenario. Nearly 30,000 and 45,000 people hiked the 4.0 km to the Loch, the lowest lake in LVWS, in June–September 2019 and 2020, respectively. Informal trails and informal latrine sites were mapped, and the contribution of human urine was calculated based on several assumptions, including that each visitor voided their bladder on the ground once per visit somewhere in Loch Vale. The resulting Nr input from urine in Loch Vale for the summer months of June through September was 0.02 kg Nr ha−1, and prorated to a full year, the 2019 potential contribution of human waste was 0.06 kg ha−1 year−1. These values are compared with June–September 1.2 kg Nr ha−1 from wet atmospheric deposition or annual measured 2019 deposition of 2.5 kg Nr ha−1 year−1, to indicate a contribution of 2% Nr to the waters of Loch Vale from local human urine. Most Nr in this alpine and subalpine watershed is still attributable to emissions and subsequent wet atmospheric deposition, but a 2% contribution from human waste is not insignificant. In the very broadest sense, our results document an ecological disturbance from an unprecedented level of human activity in a protected and designated wilderness area. Local solutions to this local problem could include greater outreach to visitors of public lands about the consequences of their activities and installation of latrines. [ABSTRACT FROM AUTHOR]

Dissolved copper (Cu) can contribute to toxicity in aquatic systems impacted by acid mine drainage (AMD), and its bioavailability is influenced by aqueous complexation with organic ligands that predominantly include fulvic acids (FAs). Because the geochemical fractionation of FAs that accompanies sorption to hydrous aluminum oxides (HAOs) and hydrous iron oxides (HFOs) can alter Cu complexation with FA, we investigated FAs isolated from three categories of water (pristine, AMD, and in situ‐fractionated mixtures of pristine and AMD collected at stream confluences) in three mining‐impacted alpine watersheds in central Colorado, USA. We also conducted geochemical fractionation of field‐collected FAs and Suwannee River FAs by precipitating HAOs and HFOs in the laboratory. Spectral properties of the FAs (e.g., UV‐VIS absorbance) were altered by geochemical fractionation, and in acute toxicity tests with an aquatic invertebrate (Daphnia magna) Cu was more toxic in the presence of in situ‐ and laboratory‐fractionated FAs (median effect concentration [EC50] 19–50 µg Cu L−1) than in the presence of nonfractionated FAs (EC50 48–146 µg Cu L−1). After adjusting for the strain‐specific sensitivity of our D. magna, we improved the accuracy of Biotic Ligand Model predictions of Cu EC50 values for AMD‐related FAs by using an "effective dissolved organic carbon" based on spectral properties that account for among‐FA differences in protectiveness against Cu toxicity. However, some differences remained between predicted and measured EC50 values, especially for FAs from AMD‐related waters that might contain important metal‐binding moieties not accounted for by our measured spectral indices. Environ Toxicol Chem 2023;42:449–462. © 2022 SETAC [ABSTRACT FROM AUTHOR]