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The relative influence of seasonal patterns in hydrological flow and seasonal differences in biological and geochemical activity on stream chemistry patterns is difficult to discern because they covary; temperate systems are characterized by lower mean flow in the summer (i.e. corresponding to deeper flow paths, elevated temperature, and biological activity), and higher mean flow in the winter (i.e. corresponding to shallower flow paths, depressed temperature, and biological dormancy). Using 2018 data, when seasonal stream flow conditions reversed, and two prior conventional water years, the relationship between monthly acid-relevant analyte concentrations and streamflow were compared within and between winter and summer to provide insight into controls on characteristic seasonal chemistry patterns at two mid-Appalachian sites with distinct geology (weatherable mafic and weather resistant siliciclastic). Acid neutralizing capacity (ANC) increased (1) with lower flow, in both seasons and (2) in summer, for all flow conditions. The compounding impacts resulted in a doubling of concentration from typical winter with high flow to summer with low flow at both sites. Base cation patterns tracked ANC at the mafic site, resulting in an ~ 60% increase of from winter with high flow to summer with low flow; distinctions between summer and winter contributed more to the seasonal pattern (72%) than changes in flow. Sulfate increased at the mafic site (1) with higher flow, in both seasons and (2) in winter, for all flow conditions, resulting in an ~ 50% increase from summer with low flow to winter with high flow; distinctions between winter and summer conditions and flow contributed similarly (40–60%) to the typical seasonal chemical pattern. The biogeochemical mechanism driving differences in stream chemistry between summer and winter for the same flow conditions is likely increased rates of natural acidification from elevated soil respiration in summer, resulting in greater bedrock weathering and sulfate adsorption. Findings highlight the significance and consistency of growing vs dormant season variations in temperature and biological activity in driving intra-annual patterns of stream solutes. This data set informs parameterization of hydro-biogeochemical models of stream chemistry in a changing climate at a biologically relevant, seasonal, timescale. [ABSTRACT FROM AUTHOR]

Rivers are pivotal in the global carbon cycle, transporting terrestrial carbon to the ocean while emitting significant amount of CO2 ${\mathrm{C}\mathrm{O}}_{2}$ to the atmosphere. However, the partitioning of fluvial inorganic carbon (IC) between downstream transport and atmospheric evasion remains uncertain due to intricate hydrodynamic and biogeochemical processes. Inspired by Budyko's hydrological work, this study introduces a dimensionless framework to identify critical factors in fluvial IC partitioning: the IC fraction in equilibrium with the atmosphere and the ratio of advection to evasion timescales. River catchment analyses and modeling reveal that the equilibrium ratio determines the fraction of IC stably transported downstream. The hydrodynamic‐driven timescale ratio determines the fate of out‐of‐equilibrium IC, with low‐order streams favoring atmospheric evasion and higher‐order streams promoting downstream transport. This framework provides a simple yet robust approach to predicting river carbon dynamics, with implications for land‐to‐ocean transport, fluvial emissions, and climate mitigation strategies such as enhanced weathering. Plain Language Summary: Rivers contain large amounts of dissolved inorganic carbon originating from the decomposition of organic matter and soil water fluxes. This carbon is partly transported downstream across the river network to the ocean and partly emitted as CO2 ${\mathrm{C}\mathrm{O}}_{2}$ to the atmosphere. Quantifying the partitioning between these fluxes is crucial for accurate carbon budgets from the local to the global scale, but the complex interplay of biogeophysical processes makes it challenging. Inspired by Budyko's seminal work in hydrology, we present a framework that determines the main chemical and physical processes governing the fluvial inorganic carbon partitioning. We identify two dimensionless numbers (or indexes) that can be defined with only a few parameters and provide quantitative and robust predictions on fluvial carbon fate. These numbers are linked to water turbulence and chemistry, and their values change across the river network. Key Points: Rivers partition inorganic carbon between downstream transport and CO2 ${\mathrm{C}\mathrm{O}}_{2}$ emissions to the atmosphereIncorporating key hydrodynamic and biogeochemical processes, we identify the dimensionless numbers that govern the inorganic carbon partitioningWater hydrodynamics plays a critical role in the fate of the carbon that is out of equilibrium with the atmosphere [ABSTRACT FROM AUTHOR]

Rivers in karst areas face increased risks from persistent growth in human activity that leads to changes in water chemistry and threatens the water environment. In this study, principal component analysis (PCA), ion ratio measurements, and other methods were used to study the water chemistry of the Qingshuijiang River Basin over the past 10 years. The results showed that the main ions in the river were Ca2+ and HCO3–, with a cation order of Ca2+ (mean: 0.93 mmol/L) > Mg2+ (mean: 0.51 mmol/L) > Na+ (mean: 0.30 mmol/L) > K+ (mean: 0.06 mmol/L) and HCO3– (mean: 2.00 mmol/L) > SO42– (mean: 0.49 mmol/L) > Cl– (mean: 0.15 mmol/L) > NO3– (mean: 0.096 mmol/L) > F– (mean : 0.012 mmol/L). In the past 10 years, the concentration of major ions in the river water in the basin has increased significantly. The weathering input of rock (mainly upstream carbonate) was the main source of Mg2+, Ca2+, and HCO3−, though sulfuric acid was also involved in this process. While K+ and Na+ were affected by the combination of human activity and the weathering input of silicate rock in the middle and lower reaches of the river, human activity was the main source of SO42−, NO3−, and F− ions. Irrigation water quality and health risks were evaluated by calculating the sodium adsorption ratio (SAR), soluble sodium percentage (Na%), residual sodium carbonate (RSC), and hazard quotient (HQ). The findings indicated that the river water was generally safe for irrigation and drinking, and the health risks were gradually reduced over time. However, long-term monitoring of the river basin is still essential, especially for the risk of excessive F− in a few tributaries in the basin. [ABSTRACT FROM AUTHOR]

Forests are critical source regions of high-quality drinking water but forest disturbances such as harvesting can alter stream dissolved organic carbon (DOC) concentrations and influence source water treatability. Most stream DOC-centric forest harvesting impact studies report on effects <10 years post-harvest; less is known about the legacy effects of forest harvesting on stream DOC. Here, inter- and intra-catchment variability in stream DOC concentration and export were evaluated in two northern hardwood-dominated headwater catchments (unharvested reference and 24 years post-clearcut). The relationship between stream DOC and the concentration, spatial distribution, and hydrologic connectivity of hillslope solute pool DOC was investigated. Stream DOC concentrations in the legacy clearcut catchment exceeded those in the reference catchment for all flow conditions. Inter-catchment differences in DOC export were inconsistent. Hillslope solute pool DOC concentrations decreased with soil depth but were not significantly different between catchments. Concentration–discharge regression analysis indicated that DOC was primarily transport-limited (flushing) in both catchments. Aqueous potassium silica molar ratio data indicate the influence of groundwater on stream chemistry and streamflow was similar in both catchments. Results suggest that while clearcut harvesting can have detectable decadal-scale effects on stream DOC concentrations in northern hardwood-dominated headwater catchments, the effects are limited and likely do not pose a reasonable threat to downstream drinking water treatment operations. [ABSTRACT FROM AUTHOR]

Soil and water characteristics in micro basins with different land uses/land cover (LULC) can influence riparian vegetation diversity, stream water quality, and benthic diatom diversity. We analyzed 18 streams in the upper part of the La Antigua River basin, México, surrounded by cloud forests, livestock pastures, and coffee plantations. Concentrations of P, C, and N were elevated in the humus of forested streams compared to other land uses. In contrast, cations, ammonium, and total suspended solids (TSS) of water streams were higher in pastures and coffee plantations. These results indicate that LULC affects stream chemistry differently across land uses. Vegetation richness was highest (86–133 spp.) in forest streams and lowest in pastures (46–102), whereas pasture streams had the greatest richness of diatoms (9–24), likely due to higher light and temperatures. Some soil and water characteristics correlated with both true diversity and taxonomic diversity; soil carbon exchange capacity (CEC) correlated with vegetation diversity (r = 0.60), while water temperature correlated negatively (r = − 0.68). Diatom diversity was related to soil aluminum (r = − 0.59), magnesium (r = 0.57), water phosphorus (r = 0.88), and chlorophyll (r = 0.75). These findings suggest that land use affects riparian vegetation, while physical and chemical changes influence diatom diversity in stream water and soil. The lack of correlation between vegetation and diatom diversity indicates that one cannot predict the other. This research is an essential first step in understanding how land use changes impact vegetation and diatom diversity in mountain landscapes, providing valuable insights for environmental monitoring and conservation efforts in tropical cloud forests. [ABSTRACT FROM AUTHOR]

In this investigation, the spatiotemporal distribution of cyanobacteria and their relationships with variations in water chemistry (physico-chemical parameters and heavy metal) of Sutlej River, Punjab (India) has been analyzed by employing multivariate statistical methods. Sutlej River exhibits a rich array of cyanobacterial diversity, comprising 28 species across 15 genera, distributed among 11 families and spanning 5 orders within the class Cyanophyceae. In terms of relative abundance, Microcystis aeruginosa (17.47%) was documented as the most abundant taxa followed by Microcystis robusta (16.55%), Merismopedia punctata (11.03%), Arthrospira fusiformis (6.67%) and Pseudanabaena galeata (3.68%). Significant variations were observed among sampling sites in most of the physico-chemical parameters. Principal Component Analysis delineated sampling sites into two discernible groups according to variations in water chemistry. River Pollution Index (RPI) showed that river water is under the unpolluted (RPI 1.5) to negligibly polluted category in the upstream sites, while moderately polluted (RPI 5.5) in the downstream sites. Heavy metal Pollution Index (HPI) revealed consistent heavy metal contamination at sites RWS7 and RWS8 across all seasons. Conversely, site RWS1 consistently exhibited lower HPI values throughout the three studied seasons. Further, Canonical Correspondence Analysis identified that pH, TDS, TA, NO3, Na, and NH4 are the key physicochemical parameters which affect the spatiotemporal distribution of cyanobacteria in the studied river system. Overall, this study will offer significant information for hydrologists, ecologists, and taxonomists to develop future holistic strategies for further monitoring of the Sutlej River and other similar habitats. [ABSTRACT FROM AUTHOR]

In 2020, Colorado experienced the most severe wildfire season in recorded history, with wildfires burning 625 357 acres across the state. Two of the largest fires burned parts of Rocky Mountain National Park (RMNP), and a study was initiated to address concerns about potential effects on drinking water quality from mobilization of ash and sediment. The study took advantage of a wealth of pre‐fire data from adjacent burned and unburned basins in western RMNP. Pre‐ and post‐fire data collection included discrete sample collection and high‐frequency water‐quality measurements using in‐stream sensors. Kruskal–Wallis tests on discrete data indicated that specific conductance, base cations, sulphate, chloride, nitrate, and total dissolved nitrogen concentrations increased post‐fire, whereas silica and dissolved organic carbon (DOC) did not (p ≤ 0.05). In‐stream sensors captured large spikes in concentrations of nutrients, turbidity, and DOC in the burned basin that were missed by discrete sampling. Sensor data indicated nitrate and turbidity increased by up to one and two orders of magnitude, respectively, from pre‐event concentrations during storms, and DOC increased up to 3.5×. Empirical regression equations were developed using pre‐fire data and applied to the post‐fire period to estimate expected stream chemistry in the absence of fire (a 'no‐fire' scenario). Overlays of actual post‐fire chemistry showed the timing and magnitude of differences between observed and 'estimated' chemistry. For most solutes, observed post‐fire concentrations were notably greater than expected under the 'no‐fire' scenario, and differences were greatest during storm events. Comparison of data from the burned and unburned basins indicated DOC concentrations were affected by climate as well as fire. Results from this study demonstrate the importance of both pre‐fire data and high‐frequency data for characterizing dynamic hydrochemical responses in wildfire‐affected areas. [ABSTRACT FROM AUTHOR]

Antecedent hydrological conditions are recorded through the evolution of dissolved lithium isotope signatures (δ7 ${\delta }^{7}$Li) by juxtaposing two storm events in an upland watershed subject to a Mediterranean climate. Discharge and δ7 ${\delta }^{7}$Li are negatively correlated in both events, but mean δ7 ${\delta }^{7}$Li ratios and associated ranges of variation are distinct between them. We apply a previously developed reactive transport model (RTM) for the site to these event‐scale flow perturbations, but observed shifts in stream δ7 ${\delta }^{7}$Li are not reproduced. To reconcile the stability of the subsurface solute weathering profile with our observations of dynamic stream δ7 ${\delta }^{7}$Li signatures, we couple the RTM to a distribution of fluid transit times that evolve based on storm hydrographs. The approach guides appropriate flux‐weighting of fluid from the RTM over a range of flow path lengths, or equivalently fluid residence times. This flux‐weighted RTM approach accurately reproduces dynamic storm δ7 ${\delta }^{7}$Li‐discharge patterns distinguished by the antecedent conditions of the watershed. Plain Language Summary: Storm events often cause characteristic shifts in stream solute chemistry. Interpreting these signals offers insight into the water‐rock interactions occurring within watersheds. Here, we use lithium stable isotopes and reactive transport modeling to relate how long water spends in a catchment, or how deep water infiltrates through a catchment, to the extent of chemical weathering. We show that the first significant storm after a dry season exports more chemically evolved water, while a wet season storm releases less evolved, shallower, and younger water. Our results indicate that stream flow δ7 ${\delta }^{7}$Li in small watersheds offers a sensitive record of hydrological conditions prior to the storm, reflecting subtle shifts in the efficiency of the Critical Zone to generate, transport, and ultimately export solutes. Key Points: Stream lithium stable isotope ratios (δ7Li) recorded at high frequency over storm events are sensitive to antecedent conditionsA reactive transport model cannot produce observed shifts in stream chemistry through variations in flow rate aloneFlux‐weighting of model fluid outputs based on time‐varying fluid transit time distributions describes stream δ7Li over storm hydrographs [ABSTRACT FROM AUTHOR]

Stream water chemistry at catchment outlets is commonly used to infer flow paths of water through catchments and to quantify the relative contributions of various flow paths and/or end-members, especially during storm events. For this purpose, the number and nature of these flow paths or end-members are commonly determined with principal component analysis based on all available conservative solute data in inverse end-member mixing analyses (EMMAs). However, apart from the selection of conservative solutes, little attention is paid to the number and choice of the solutes that are included in the analysis, despite the impact this choice can have on the interpretation of the results from an inverse EMMA. Here, we propose a methodology that tries to fill this gap. For a given pair of measured solutes, the proposed methodology determines the minimum number of required end-members, based on the synchronous variation of the solutes during storm events. This allows identification of solute pairs for which a simple two-end-member mixing model is sufficient to explain their variation during storm events and of solute pairs, which show a more complex pattern requiring a higher-order end-member mixing model. We analyse the concentration–concentration relationships of several major ion pairs on the storm-event scale, using multi-year, high-frequency (< 60 min) monitoring data from the outlet of two small (0.8 to 5 km 2) French catchments with contrasting land use, climate, and geology. A large number of storm events (56 % to 79 %) could be interpreted as being the result of a mixture of only two end-members, depending on the catchment and the ion pairs used. Even though some of these results could have been expected (e.g. a two-end-member model for the Na +/Cl- pair in a catchment close to the Atlantic coast), others were more surprising and in contrast to previous studies. These findings might help to revise or improve perceptual catchment understanding of flow path or end-member contributions and of biogeochemical processes. In addition, this methodology can identify which solute pairs are governed by identical hydro-biogeochemical processes and which solutes are modified by more complex and diverse processes. [ABSTRACT FROM AUTHOR]

The planning and management of water in the river basins require the identification of places where the quality of groundwater is being threatened. The risk of launching the accumulated pollutants present in the solid phase of the soil may be caused by both the changes in the pressure gradients in the aquifers and the changes in the hydrogeochemical balances. In the example of the Ner river valley, into which wastewater from the Łódź agglomeration has been discharged, the factors threatening the chemical status of groundwater were determined. This assessment was carried out based on the results of the determination of the hydrodynamic balance disturbances in the Upper Cretaceous formations, model studies of groundwater flow and hydrogeochemical studies conducted on the sorption complex of the Ner alluvium as well as the chemistry of the river water, alluvial water and groundwater. The results showed that the river water is heavily anthropogenically transformed. Model studies have shown that when the Ignacew -intake wells are pumped collectively, the inflow takes place through the Ner valley, where the hydrogeological window between the Quaternary and the Upper Cretaceous aquifers is found. The withdrawal by the Ignacew intakes may result in the reversal of piezometric pressures in the valley, which creates the possibility of the infiltration of polluted surface water into groundwater. Observations indicate the need to take into account the zones where surface water and water from the river alluvium are a real threat to the chemical status of the aquifers. These aspects are important when determining the protection zones and in renewable and disposal resource assessments of the Main Groundwater Reservoirs. [ABSTRACT FROM AUTHOR]

The lichen biota of eastern North America is fairly well-documented with most taxa reported from terrestrial ecosystems. While some taxa are described as living near water bodies potentially subjected to inundation, no amphibious lichen communities have been described. To address this gap in our understanding of the region's lichen ecology, thirteen rocky river sites in two river basins of central North Carolina, U.S.A. were explored for amphibious and riparian lichen biotas during periods of low water level, restricted to saxicolous species subjected to inundation, however infrequent. Specimens of encountered taxa were collected and their heights above water level were measured during field visits. Three communities were discerned from field observations in increasing height from low water level, here termed: Mesic Fluvial, Xeric Fluvial and Riparian. These communities are described in terms of species number and composition, height above water, functional traits and taxonomic class composition, as well as characteristic species both in open riverscour and shaded rocky riverbank habitats. From measured heights, two trimlines are described separating the three communities: Fluvial Trimline, often co-occurring with a band of deposited silt, and Riparian Trimline. With the use of nearby stream gage height data, percent inundation for the 2023 water year was estimated for the three communities as 3–10 months for Mesic Fluvial, 0.5–4 months per year for Xeric Fluvial, and < 1–3 months for Riparian lichens. Environmental variables were explored for relationships with the three communities, finding the most significant positive relationships between Mesic Fluvial species richness and several stream physical and water chemistry variables. Recommendations for future stream lichen surveys are offered. [ABSTRACT FROM AUTHOR]

The study was conducted at the upper coastal region of Qua Iboe River, Nigeria, between November 2018 and August 2019 (ten months), to access the concentrations of potentially toxic elements (PTEs) and human health risks associated with water from the river via ingestion. Eight PTEs were assessed from the four stations, using atomic absorption spectrophotometer. The findings were compared with Nigerian drinking water quality standards. The spatial mean concentrations of some PTEs (Mn, Cr, Ni, Cd, Fe and Pb) were exceeding the permissible limits due to anthropogenic activities and seasonal influences. The values for heavy metal pollution index (HPI) were exceeded the threshold (100), while comprehensive pollution index (CPI) indicating moderate to heavily pollution. The hazard quotient (HQ) values for Fe and Cr in children and adults, and hazard index (HI) values were exceeded the threshold value of 1. Daily chronic intake (CDI) values for Fe and Cr mostly were above the oral reference dose of contaminant (mg/kg/day). The findings showed that Fe and Cr were the dangerous PTEs contributed to higher HQs and HI values, indicated that the river is not suitable for domestic use via ingestion. [ABSTRACT FROM AUTHOR]

Mineral dust plays an important role in Earth's climate system, yet it is difficult to identify dust imprints in paleofluvial sediments, especially on orbital timescales. Here, we present high‐resolution authigenic carbonate Ca–Mg–Sr compositions in a fluvial sequence under the transport pathway of Asian dust. The Mg/Ca, Sr/Ca, and Mg/Sr ratios exhibit distinct transitions in both secular trends and orbital cycles at ∼8 Ma. Before ∼8 Ma, given similar Mg and Sr partitioning behaviors during carbonate formation, hydroclimate changes yielded strong orbital signals in the Sr/Ca and Mg/Ca ratios but no detectable signals in the Mg/Sr ratios. After ∼8 Ma, given the strengthened input of Mg‐rich dust during cold‒dry periods, the Mg/Sr and Mg/Ca ratios clearly exhibited orbital signals, but the Sr/Ca ratio did not. Such transitions in carbonate composition corroborate the dust‐induced changes in fluvial hydrochemistry, offering an innovative methodology for detecting orbital dust cycles in paleofluvial systems. Plain Language Summary: A set of criteria, that is, transport and sedimentation dynamics, the surface morphology of quartz grains and provenance indices, were employed to recognize eolian deposits in past fluvial sediments. However, distinguishing eolian dust at orbital scales poses a challenge, as high‐resolution records that meet these criteria are difficult to reconstruct. Here, we present high‐resolution records of authigenic carbonate compositions from Neogene fluvial sediments in the Linxia Basin, a key downwind catchment area for Asian dust. The carbonate elemental compositions, in conjunction with sedimentary Sr‒Nd isotopes, exhibit a long‐term two‐stage evolution marked by a pivotal shift at ∼8 Ma. This transition is most likely attributed to an increase in Asian dust deposition since that time. On orbital timescales, the periodic fluctuations in extrabasinal dust flux, characterized by Mg‐rich but Sr‐poor components (mostly dolomite), have led to pronounced alterations in the orbital patterns of carbonate Ca‐Mg‐Sr compositions since ∼8 Ma. Our findings indicate that carbonate Ca‐Mg‐Sr compositions can offer a straightforward and innovative approach for pinpointing eolian dust activity on orbital timescales when extrabasinal dust can be appropriately distinguished. Key Points: A close examination of carbonate compositions offers a new method for identifying orbital dust cycles within continental fluvial systemsThe authigenic carbonate composition in a fluvial sequence in NE Tibet shows a distinct orbital transition at ∼8 MaMg‐rich dust markedly altered the river chemistry during the cold/arid stages, with a less pronounced effect during the warm/humid stages [ABSTRACT FROM AUTHOR]

Long Island Sound (LIS) is a highly urbanized estuary that receives high inputs of nitrogen pollution leading to summertime hypoxia in the bottom waters of its western region. Though LIS hypoxia has been well-studied for decades, there is a paucity of information regarding eutrophication-induced acidification due to the challenges of obtaining high-precision observations of the marine carbonate system. In this work, we established a time-series of carbon dioxide (CO2) system observations in LIS through measurements of dissolved inorganic carbon (DIC) and total alkalinity (TA) during thirteen sampling events between March 2020 and August 2022. This time span captured both seasonal and interannual variation, including the contrast between two historic drought years (2020 and 2022) and one high-freshwater flow year with significant tropical storm activity (2021). Observations revealed reduced acidification in western LIS (WLIS) (minimum aragonite saturation state, Ωar > 1.5) during the high-river discharge summer of 2021, corresponding to a decrease in the DIC/TA ratio of the Housatonic River. By contrast, LIS bottom water DIC and DIC/TA were higher during the drought summers of 2020 and 2022 (bottom DIC/TA = 0.9-1.0 and 0.85-0.9 in 2020 and 2021, respectively), leading to more acidified conditions and persistent aragonite undersaturation (minimum Ωar <1.0 and 1.1 in 2020 and 2022, respectively). Increased river discharge mitigated respiration-induced acidification in WLIS, likely due to a combination of decreased estuarine residence time and reduced riverine DIC/TA. These results motivate future studies of the carbonate chemistry of LIS and its freshwater endmembers in relation to hypoxia dynamics, with consideration of climate related shifts in physical and biological dynamics of the estuary with time. [ABSTRACT FROM AUTHOR]

This study provides an in-depth analysis of the hydrochemical characteristics and their controlling factors in the lower reaches of the Yellow River. Through water quality sampling and analysis over two hydrological periods within a year, combined with hydrochemical methods and machine learning techniques, the study reveals the joint impact of natural factors and human activities on the spatiotemporal variations in hydrochemical constituents. The findings indicate that the water in the lower reaches of the Yellow River exhibits weak alkalinity (the pH is between 7 and 8), with the primary hydrochemical type being HCO3·SO4—Ca·Na·Mg. The temporal variation in the hydrochemical constituents is mainly influenced by rainfall, where nitrate levels are higher during the flood season due to the flushing effect of rainfall, whereas other hydrochemical constituents show an opposite temporal pattern due to the dilution effect of rainfall. The spatial variation in the Yellow River's hydrochemistry is primarily controlled by a combination of human activities and rainfall. Using Gibbs diagram analysis, it is identified that rock weathering is the main source of ionic constituents, while agricultural fertilization, industrial emissions, and domestic wastewater discharge have significant impacts on the hydrochemical constituents. Compared to other rivers worldwide, the concentration of hydrochemical constituents in the lower reaches of the Yellow River is relatively high, especially nitrate and sulfate, which is closely related to the geological characteristics of the Yellow River basin and intense human activities in the middle and lower reaches. Principal component analysis reveals that the main controlling factors for hydrochemical constituents during the dry season in the lower reaches of the Yellow River are rock weathering dissolution and industrial activities, followed by domestic wastewater; during the flood season, the main controlling factors are rock weathering dissolution and industrial activities, followed by agricultural activities and domestic wastewater. The research findings provide theoretical support for water resource management and water quality protection in the lower reaches of the Yellow River. [ABSTRACT FROM AUTHOR]

Large‐scale wildfires are becoming increasingly common in the wet forests of the Pacific Northwest (USA), with predicted increases in fire prevalence under future climate scenarios. Wildfires can alter streamflow response to precipitation and mobilize water quality constituents, which pose a risk to aquatic ecosystems and downstream drinking water treatment. Research often focuses on the impacts of high‐severity wildfires, with stream biogeochemical responses to low‐ and mixed‐severity fires often understudied, particularly during seasonal shifts in hydrologic connectivity between hillslopes and streams. We studied the impacts of the 2020 Holiday Farm Fire at the HJ Andrews Experimental Forest where rare pre‐fire stream discharge and chemistry data allowed us to evaluate the influence of mixed‐severity fire on stream water quantity and quality. Our research design focused on two well‐studied watersheds with low and low‐moderate burn severity where we examined long‐term data (pre‐ and post‐fire), and instantaneous grab samples collected during four rain events occurring immediately following wildfire and a prolonged dry summer. We analysed the impact of these rain events, which represent the transition from low‐to‐high hydrologic connectivity of the subsurface to the stream, on stream discharge and chemistry behaviour. Long‐term data revealed total annual flows and mean flows remained fairly consistent post‐fire, while small increases in baseflow were observed in the low‐moderately burned watershed. Stream water concentrations of nitrate, phosphate and sulfate significantly increased following fire, with variance in concentration increasing with fire severity. Our end member mixing models suggested that during rain events, the watershed with low‐moderate severity fire had greater streamflow inputs from soil water and groundwater during times of low connectivity compared to the watershed with low severity fire. Finally, differences in fire severity impacts on concentration‐discharge relationships of biogenic solutes were most expressed under low catchment connectivity conditions. Our study provides insights into post‐wildfire impacts to stream water quality, with the goal of informing future research on stream chemistry responses to low, moderate and mixed severity wildfire. [ABSTRACT FROM AUTHOR]

We investigated the characteristics of pharmaceutical concentrations and antimicrobial activities in river water from the Tone River system in Gunma Prefecture. The mean concentrations of diphenhydramine, clarithromycin, carbamazepine, and bezafibrate in the midstream of the Tone River were 8.6, 29, 3.8, and 8.1 ng/L, respectively. Their concentrations were nearly half of those in the midstream of the Ayase River, the main water source of which is wastewater. Seasonal variations in pharmaceutical concentrations were high in winter and low in late spring and autumn. This variation depended on the flow rate of the river water, which in turn depended on the rainfall in the upstream area. Except for bezafibrate, the pharmaceutical concentrations in river water did not change after 5 days of incubation at 30°C, indicating that biochemical degradation during the hot summer season was minimal. A comparison of the concentrations between the sampling locations revealed that the pharmaceutical load was proportional to basin population, and the annual fluxes of pharmaceuticals from Gunma Prefecture were estimated to be 98, 210, 28, and 53 kg/year, respectively. Disc diffusion assay of some samples of Tone River water extracts revealed inhibition zones owing to their antimicrobial activity. However, no relationship was observed between the diameter of the inhibition zone and clarithromycin concentration in the river water. These results suggest that the antimicrobial activities of the river samples were not dependent on clarithromycin. We are currently investigating the pollution and drug-resistant bacteria present in the Tone River in detail. [ABSTRACT FROM AUTHOR]

Increased occurrence, size, and intensity of fire result in significant but variable changes to hydrology and material retention in watersheds with concomitant effects on stream biogeochemistry. In arid regions, seasonal and episodic precipitation results in intermittency in flows connecting watersheds to recipient streams that can delay the effects of fire on stream chemistry. We investigated how the spatial extent of fire within watersheds interacts with variability in amount and timing of precipitation to influence stream chemistry of three forested, montane watersheds in a monsoonal climate and four coastal, chaparral watersheds in a Mediterranean climate. We applied state-space models to estimate effects of precipitation, fire, and their interaction on stream chemistry up to five years following fire using 15 + years of monthly observations. Precipitation alone diluted specific conductance and flushed nitrate and phosphate to Mediterranean streams. Fire had positive and negative effects on specific conductance in both climates, whereas ammonium and nitrate concentrations increased following fire in Mediterranean streams. Fire and precipitation had positive interactive effects on specific conductance in monsoonal streams and on ammonium in Mediterranean streams. In most cases, the effects of fire and its interaction with precipitation persisted or were lagged 2–5 years. These results suggest that precipitation influences the timing and intensity of the effects of fire on stream solute dynamics in aridland watersheds, but these responses vary by climate, solute, and watershed characteristics. Time series models were applied to data from long-term monitoring that included observations before and after fire, yielding estimated effects of fire on aridland stream chemistry. This statistical approach captured effects of local-scale temporal variation, including delayed responses to fire, and may be used to reduce uncertainty in predicted responses of water quality under changing fire and precipitation regimes of arid lands. [ABSTRACT FROM AUTHOR]

In the present study some of the water quality parameters were spatially examined with water quality and pollution indices in the Büyük Menderes River (BMR). In addition, the more effective parameters on the indices were determined among the parameters measured in the study. The measured water quality parameters were detected as WT:16.5-25.9 °C, pH:7.5-9.3, DO:nd-12.2 mgL-1, EC:312-30215 µScm-1, Salt:0.17-19.6 %o, NO2-N:nd-0.31 mgL-1, NO3-N:nd-1.08 mgL-1, NH4-N:0.035-25.2 mgL-1, TP:0.011-7.45 mgL-1, MBAS:nd-7.79 mgL-1 ve COD:nd-128.9 mgL-1. In the present study, several parameters were determined as the second class and third class of water quality according to the Turkish Water Pollution Control Regulation*. WQI value range was determined as from Bad (38.82) to Excellent (92.35), and CPI as from "Sub Clean (0.39) to Highly Polluted (9.62)" in the stream. It was determined that there was no compatibility between WQI and CPI used in determining the environmental risks in the study area. The GIS was found to be effective in interpreting the spatial distribution of the results obtained and in identifying the key areas that require control. Different statistical analyses were used to determine the relationships between variables. In multiple linear regression (MLR) analysis, it was determined that the most critical parameter affecting the indices was NH4-N. The results obtained from WQI and CPI in the present study indicate that anthropogenic activities are effective in the region. [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 results of studying water chemistry in small rivers of Khabarovsk City during spring flood in 2018–2022 are presented. The concentrations of major ions and nutrients in river water are shown to vary widely due to the considerable difference between the water chemistry in snowmelt water, groundwater, and wastewater, as well as waters from worn-out systems of water supply and water disposal. In the early period of snow melting, maximal TDS and the concentrations of chloride and sodium ions in the center of the city in excess of the MAC, and chloride-sodium composition due to the application of deicing agents were found in the water of rivers draining regions with intense traffic. The heaviest pollution of river water with ammonium and nitrate nitrogen and phosphates was recorded in the beginning of spring flood because of their export from catchment surface areas. It is shown that, during spring flood, the concentrations of dissolved substances in the water of many rivers, except for those fed by municipal wastewaters, gradually decrease, and water chemistry becomes hydrocarbonate-calcium. [ABSTRACT FROM AUTHOR]

The formation history of the Irkutsk Reservoir is considered along with its effect on changes in the nearby area and water chemistry. The results of hydrochemical studies, carried out by the authors in 2022 in reservoir bays and tributaries are analyzed and compared with earlier studies. The waters of rivers flowing into the Irkutsk Reservoir were found to belong to sulfate-hydrocarbonate magnesium-calcium type. The chemistry of the waters of rivers, bays of the Irkutsk Reservoir in the key areas, where inhabited localities, cottage settlements, and garden plots are situated, was found to differ from the background chemistry and to be chloride-hydrocarbonate magnesium-calcium. The microelement composition of water in the major portion of the reservoir corresponds to the ranges of the basic concentrations of microelements at the source of the Angara River. [ABSTRACT FROM AUTHOR]

This study addresses the pressing issue of nonpoint source water pollution in Kentucky, particularly associated with large-scale agriculture. Centered on the outer bluegrass region of Central Kentucky, the research examines the water quality of headwater streams during the agricultural season. The approach involves geospatial land cover classification using aerial imagery. Water quality data were collected during the agricultural growing season from May to October 2018. Land cover classification utilized ERDAS Imagine 2016 and ESRI ArcGIS 10.6 GIS software, while conventional water quality parameters were measured with a YSI ProDSS® multiparameter water probe and a Marsh-McBirney Flo-Mate 2000 flow meter. Statistical analyses show significant differences in stream water chemistry, suggesting the impact of agricultural nonpoint source pollution. Forested streams exhibited more varied conditions, indicating a potentially better environment. As agricultural land percentage increased, water chemistry variation suggested a measurable threshold for changes. Significant differences in water quality between agricultural and forested streams highlight the potential benefits of expanding riparian zones beyond regulations. Enlarging these zones is proposed as a strategy to mitigate nonpoint source pollution in Kentucky's waterways. [ABSTRACT FROM AUTHOR]

Kentucky is one of the largest coal-producing states; surface coal mining has led to changes in natural land cover, soil loss, and water quality. This study explored relationships between actively mined and reclaimed areas, vegetation change, and water quality parameters. The study site evaluated 58 watersheds with Landsat-derived variables (reclamation age and percentage of mining, reclaimed forest, and reclaimed woods) as well as topographic variables (such as elevation, slope, drainage density, and infiltration). Water samples were collected in spring (n = 9), summer (n = 14), and fall (n = 58) 2017 to study changes in water quality variables (SO42−, alkalinity, conductivity, Ca2+, Mg2+, Mn2+, Al3+, and Fe2+, Fe3+) in response to changes in land cover. Pearson correlation analyses indicated that conductivity has strong to very strong relationships with water quality variables related to coal mining (except Al3+, Fe2+, Fe3+, Mn2+, elevation, slope, and drainage density) and land cover variables. In addition, separate regression analyses were performed, with conductivity values based on samples collected in the fall. First, conductivity responses to mining percentage, reclamation age and topographic variables were examined (adjusted R2 = 0.818, p < 0.01). Next, vegetation cover change parameters were added to the same model, which yielded slightly improved R2 (adjusted R2 = 0.826, p < 0.01). Finally, reclamation age and mining percentages were used to explain the quantity of reclaimed forested areas as a percentage of watersheds. The model was significant (p < 0.01), with an adjusted R2 value of 0.641. Results suggest that the quantity (area as a percentage) of reclaimed forests may be a predictor of the mining percentage and reclamation age. This study indicated that conductivity is a predictable water quality indicator that is highly associated with Coal-Mine-Related Stream Chemistry in areas where agriculture and urban development are limited. Water quality is not suitable for various purposes due to the presence of contaminants, especially in mined sites. These findings may help the scientific community and key state and federal agencies improve their understanding of water quality attributes in watersheds affected by coal mining, as well as refine land reclamation practices more effectively while such practices are in action. [ABSTRACT FROM AUTHOR]

Terrestrial soils in forested landscapes represent some of the largest mercury (Hg) reserves globally. Wildfire can alter the storage and distribution of terrestrial-bound Hg via reemission to the atmosphere or mobilization in watersheds where it may become available for methylation and uptake into food webs. Using data associated with the 2007 Moonlight and Antelope Fires in California, we examined the long-term direct effects of wildfire burn severity on the distribution and magnitude of Hg concentrations in riparian food webs. Additionally, we quantified the cross-ecosystem transfer of Hg from aquatic invertebrate to riparian bird communities; and assessed the influence of biogeochemical, landscape variables, and ecological factors on Hg concentrations in aquatic and terrestrial food webs. Benthic macroinvertebrate methylmercury (MeHg) and riparian bird blood total mercury (THg) concentrations varied by 710- and 760-fold, respectively, and Hg concentrations were highest in predators. We found inconsistent relationships between Hg concentrations across and within taxa and guilds in response to stream chemical parameters and burn severity. Macroinvertebrate scraper MeHg concentrations were influenced by dissolved organic carbon (DOC); however, that relationship was moderated by burn severity (as burn severity increased the effect of DOC declined). Omnivorous bird Hg concentrations declined with increasing burn severity. Overall, taxa more linked to in situ energetic pathways may be more responsive to the biogeochemical processes that influence MeHg cycling. Remarkably, 8 years post-fire, we still observed evidence of burn severity influencing Hg concentrations within riparian food webs, illustrating its overarching role in altering the storage and redistribution of Hg and influencing biogeochemical processes. [ABSTRACT FROM AUTHOR]

High latitude regions across the globe are undergoing severe modifications due to changing climate. A high latitude region of concern is the Gulf of Alaska (GoA), where these changes in hydroclimate undoubtedly affect the hydrogeochemistry of freshwater discharging to the nearshore ecosystems of the region. To fill the knowledge gap of our understanding of freshwater stream geochemistry with the GoA, we compile stream water chemistry data from 162 stream sites across the region. With an inverse model, we estimate fractional contributions to solute fluxes from weathering of silicate, carbonate, and sulfide minerals, and precipitation. We assess weathering rates across the region and compare them against global river yields. The median fractional contribution of carbonate weathering to total weathering products is 78% across all stream sites; however, there are several streams where silicate weathering is a dominant source of solutes. Weathering by sulfuric acid is elevated in glacierized watersheds. Finally, cation weathering rates are lower in GoA streams compared to the world's largest rivers; however, weathering rates are similar when compared to a global dataset of glacier fed streams. We suggest that hydrologic changes driven by glacier ice loss and increased precipitation will alter river water quality and chemical weathering regimes such that silicate weathering may become a more important source of solutes and sulfide oxidation may decrease. This contribution provides a platform to build from for future investigations into changes to stream water chemistry in the region and other high latitude watersheds. Plain Language Summary: The Gulf of Alaska (GoA) is a region in high latitudes that is experiencing significant changes due to climate change. These changes affect the chemistry of freshwater streams that flow into the nearby ecosystems. We collected data on the chemistry of stream water from 162 sites in the region. Using a model to estimate where the different solutes in the water come from, such as minerals and rain. We found that carbonate minerals are the main source of solutes in most streams, but in some streams, silicate minerals are more important. Glaciers in the region cause higher levels of sulfide weathering. Compared to the largest rivers in the world, the rates at which minerals are released in the GoA streams are lower, but similar to streams fed by glaciers worldwide. We predict that as glaciers melt and precipitation increases, the chemistry of the streams will change, with more silicate minerals being released and less weathering of sulfide minerals. This study provides a foundation for future research on the effects of climate change on stream water chemistry in the region and other high latitude areas. Key Points: Carbonate weathering dominates the solute flux of chemical weathering derived productsWeathering by sulfuric acid is elevated in glacierized basins compared with non‐glacierizedSilicate weathering is strongly controlled by glacier coverage, relief, and air temperature [ABSTRACT FROM AUTHOR]

Seasonality plays a critical role in cold mountain regions as variation in air temperature, ground thermal status, and precipitation phase alter the rate, timing and magnitude of hydrological and chemical transport. Additionally, cold mountain catchments can have highly variable topography, geology, permafrost, and landcover, which intrinsically add to this irregularity. Understanding how external and internal variability act to control mass fluxes requires sampling at a high spatial resolution over time, which rarely occurs in cold remote regions. In this work, we conduct five snapshot sampling surveys across 34 subcatchments during the ice‐free period in Wolf Creek Research Basin (a mesoscale montane subarctic catchment) and two additional winter surveys across a subset of sites to assess the drivers of variability in stream chemistry and discharge. We sampled for specific conductance (SpC), major ions, and dissolved organic carbon (DOC) and used statistical metrics and Bayesian mixing analysis to quantify patterns of flow and chemistry across space and time. Our results indicate patterns in both flow and chemistry remain largely consistent across seasons for all solutes. However, there was weaker correlation of chemistry between sites, suggesting asynchronous behaviour within the catchment. There was evidence of increasing production of ions and DOC along the stream network during high spring flows but not during low flows. Although concentrations and flows exhibit high seasonality in subarctic mountains, this seasonal variability does not alter spatial patterns that arise from highly variable catchment characteristics. [ABSTRACT FROM AUTHOR]

The western U.S. is experiencing shifts in recharge due to climate change, and it is currently unclear how hydrologic shifts will impact geochemical weathering and stream concentration–discharge (C–Q) patterns. Hydrologists often use C–Q analyses to assess feedbacks between stream discharge and geochemistry, given abundant stream discharge and chemistry data. Chemostasis is commonly observed, indicating that geochemical controls, rather than changes in discharge, are shaping stream C–Q patterns. However, few C–Q studies investigate how geochemical reactions evolve along groundwater flowpaths before groundwater contributes to streamflow, resulting in potential omission of important C–Q controls such as coupled mineral dissolution and clay precipitation and subsequent cation exchange. Here, we use field observations—including groundwater age, stream discharge, and stream and groundwater chemistry—to analyse C–Q relations in the Manitou Experimental Forest in the Colorado Front Range, USA, a site where chemostasis is observed. We combine field data with laboratory analyses of whole rock and clay x‐ray diffraction and soil cation‐extraction experiments to investigate the role that clays play in influencing stream chemistry. We use Geochemist's Workbench to identify geochemical reactions driving stream chemistry and subsequently suggest how climate change will impact stream C–Q trends. We show that as groundwater age increases, C–Q slope and stream solute response are not impacted. Instead, primary mineral dissolution and subsequent clay precipitation drive strong chemostasis for silica and aluminium and enable cation exchange that buffers calcium and magnesium concentrations, leading to weak chemostatic behaviour for divalent cations. The influence of clays on stream C–Q highlights the importance of delineating geochemical controls along flowpaths, as upgradient mineral dissolution and clay precipitation enable downgradient cation exchange. Our results suggest that geochemical reactions will not be impacted by future decreasing flows, and thus where chemostasis currently exists, it will continue to persist despite changes in recharge. [ABSTRACT FROM AUTHOR]

In the northern Gulf of Mexico shelf, the Mississippi‐Atchafalaya River System (MARS) impacts the carbonate system by delivering freshwater with a distinct seasonal pattern in both total alkalinity (Alk) and dissolved inorganic carbon (DIC), and promoting biologically driven changes in DIC through nutrient inputs. However, how and to what degree these processes modulate the interannual variability in calcium carbonate solubility have been poorly documented. Here, we use an ocean‐biogeochemical model to investigate the impact of MARS's discharge and chemistry on interannual anomalies of aragonite saturation state (ΩAr). Based on model results, we show that the enhanced mixing of riverine waters with a low buffer capacity (low Alk‐to‐DIC ratio) during high‐discharge winters promotes a significant ΩAr decline over the inner‐shelf. We also show that increased nutrient runoff and vertical stratification during high‐discharge summers promotes strong negative anomalies in bottom ΩAr, and less intense but significant positive anomalies in surface ΩAr. Therefore, increased MARS discharge promotes an increased frequency of suboptimal ΩAr levels for nearshore coastal calcifying species. Additional sensitivity experiments further show that reductions in the Alk‐to‐DIC ratio and nitrate concentration from the MARS significantly modify the simulated interannual ΩAr patterns, weakening the positive surface ΩAr anomalies during high‐discharge summers or even producing negative surface ΩAr anomalies. Our findings suggest that riverine water carbonate chemistry is a main driver of interannual variability in ΩAr over river dominated ocean margins. Plain Language Summary: The Mississippi river strongly impacts seawater chemistry and biological production over the northern Gulf of Mexico, leading to changes in ocean acidification. An increased acidity is concurrent with increased solubility in calcium carbonate (CaCO3), which has the potential to negatively impact calcifying organisms that build‐up hard structures of this mineral compound, like shellfish and corals. Near‐corrosive acidic conditions for CaCO3 have been documented in the proximity of the Mississippi delta during summer, but it is not well known how changes in the Mississippi river discharge and chemistry influence the year‐to‐year changes in CaCO3 solubility. Here we use a numerical model that realistically simulates oceanic and biogeochemical dynamics to investigate this aspect. Our model identifies seasonal distinctive mechanisms leading to increased CaCO3 solubility nearshore, mainly driven by the mixing of relatively more acidic Mississippi river waters (compared to seawater) during high‐discharge winters, and biological processes stimulated by riverine nutrients during high‐discharge summers. The increased CaCO3 solubility in high‐discharge years promotes suboptimal conditions for the growth of calcifying organisms, and the opposite is true in low‐discharge years. Our study highlights that river discharge, river acidity, and river nutrient concentrations are key variables modulating the interannual CaCO3 solubility patterns in river‐influenced coastal margins. Key Points: We simulated the Mississippi River impacts on interannual patterns of aragonite saturation (ΩAr) in the northern Gulf of MexicoHigh‐discharge conditions increase the frequency of suboptimal ΩAr levels for coastal calcifying species in all seasonsReduced ΩAr under high‐discharge is linked to low buffer capacity of riverine water in winter and enhanced bottom remineralization in summer [ABSTRACT FROM AUTHOR]

The Arctic is experiencing dramatic climate‐induced changes, which could have substantial consequences for nutrient export from land to streams and, thus, in‐stream nutrient availability and composition. Arctic freshwater ecosystems are low‐productive systems often limited by nitrogen (N) availability. Studying small streams is important due to their high abundance across the landscape, intimate connection to their catchments, high biogeochemical activity and high sensitivity to climate change. However, little information is available, especially in terms of N availability and composition (i.e., nitrate, ammonium, and dissolved organic nitrogen [DON]). We aimed to quantify N concentrations across small Arctic streams and explore the link between terrestrial vegetation and stream water N concentration. We conducted a literature study and extracted data from published articles, online databases, and unpublished field data. Out of 215 preselected articles, 20 met our criteria and contained 2,381 observations on stream water N concentrations in the Arctic. Data on DON was scarce: only 161 of the 2,381 observations contained DON data. We found that nitrate (NO3−), ammonium (NH4+) and DON ranged undetectable to 1,155, 547 and 1,587 μg N L−1, respectively. We found that sparsely vegetated areas had higher stream water N‐concentrations, while barren areas and higher vegetated areas had lower stream water N‐concentrations. This study provides fundamental knowledge on N availability in small streams across the Arctic, highlights data gaps and contributes to the basic knowledge needed for understanding and predicting future changes in N dynamics. Key Points: Few data are available for nitrogen concentrations across Arctic streams. Data for dissolved organic nitrogen are particularly scarceStream nitrogen concentrations and ratios vary across Arctic bioclimate subzones defined by different terrestrial vegetationClimate‐induced vegetation changes may impact stream nitrogen water chemistry [ABSTRACT FROM AUTHOR]

Urbanization can have substantial effects on water quality due to altered hydrology and introduction of constituents to water bodies. In arid and semi‐arid environments, streams are further stressed by dewatering as a result of diversions. We conducted a high‐resolution synoptic survey of two streams in Colorado, USA that transition abruptly from granitic/metamorphic forested mountains to sedimentary urbanized plains and are both highly managed for water supply, yet differ in degree of urbanization. A synoptic mass balance approach developed for mine drainage applications was adapted to elucidate effects of urbanization, geology, and diversions on stream chemistry during baseflow conditions. Urbanization was a more important driver of stream concentrations than geology. The urban area was a strong source of bromide, calcium, chloride, and manganese, while lanthanum and dissolved organic carbon were primarily sourced from the mountains. A majority of streamflow was removed by diversions near the mountains/plains interface. Groundwater accounted for 31% of the subsequent flow increase to the urbanized stream, and delivered at least 33% of chloride loading. Constituents that were primarily urban‐derived (bromide, calcium, chloride, and manganese) were 2–3 times higher in the urban region due to diversions; without diversions, stream water quality would have largely retained characteristics of forested streams through the urban reach. This study provides insights into processes that affect water quality in highly managed streams of the semi‐arid western USA. Plain Language Summary: Water supplies in the western U.S. are under pressure from increasing population growth, which results in both urban development and more water management to maximize irrigation and public supply use. Urbanization substantially alters hydrology and can introduce an array of contaminants and nutrients to water bodies. Water diversions decrease the amount of water available to dilute urban inputs. A mass balance approach, originally developed for mine drainage sites, was adapted to elucidate effects of nonpoint source urban pollution, geology, and water management in two streams in the Colorado Front Range. The urban environment introduced bromide, calcium, chloride, and manganese to streams, while lanthanum and dissolved organic carbon arose from forested, mountainous inputs. Urbanization was a more important driver of stream concentrations than changes in geology. Water diversions removed a majority of the water from streams, and impacted water quality by limiting the dilution of urban‐derived constituents. This work provides insights into processes that affect water quality in highly managed streams of the semi‐arid western U.S. Key Points: A synoptic mass balance approach was adapted to elucidate effects of urbanization, geology, and water management on stream chemistryA majority of bromide, calcium, chloride, and manganese loading occurred in the urban area, and was partly sourced from groundwaterDiversions removed the majority of water from streams, leading to increased downstream concentrations of urban‐derived constituents [ABSTRACT FROM AUTHOR]

Blackwater rivers and streams have stained or tea‐colored water from tannins released by decaying plant matter. Natural conditions in these waters often differ from non‐blackwater systems. For example, the pH and oxygen levels in waters can be very low, but completely natural. We examined an existing USEPA data set and found that blackwaters existed across the contiguous United States but were most common in the east. Water chemistry showed differences between blackwater and non‐blackwater sites, but differences were not consistent across ecoregions making national scale generalizations difficult. Physical habitat data analysis did not show dramatic differences between blackwater and non‐blackwater sites. Blackwater typically arises from streams that drain tannin‐rich bogs/muskeg and wetlands, so as expected blackwater sites had a shorter Euclidean distance to wetlands than non‐blackwater sites and existed in watersheds with a higher percentage of wetland habitat. Blackwaters in Northern and Temperate Plains tended to have higher acid neutralizing capacity, conductivity, and lower True Color; a visual color scale used for water purity. We posit that differences were because Color and Dissolved Organic Carbon at these sites were from buried wetland deposits rather than contemporary wetland habitats. Research needs that may increase our understanding and management of blackwaters include development of an operational definition that includes a classification framework and reference conditions for different blackwater types, identification of stressors and their associated dynamics that negatively impact blackwater systems, and development of data‐driven, consistent, and repeatable assessment methods, including development of targets, protective of unique conditions in blackwater rivers and streams. Plain Language Summary: Blackwater rivers and stream systems have stained or tea‐colored water due to tannins released by decaying plant matter. Although blackwaters exist across the contiguous United States, they are most common in the eastern United States. Beyond their distinct appearance, the chemistry of blackwater systems can be very different from other stream types. For example, the pH and amount of oxygen in the water can be very low, but completely natural. As a result of these and other characteristics, the fish, plants, and animals that live in blackwaters can also be unique. Because of these considerations, management of these systems can be challenging. To address these challenges, U.S. Environmental Protection Agency scientists are studying these systems. One of their early findings is that different types of blackwaters exist across the country. The team has highlighted the need for a classification system to distinguish among these types. Once this system exists, scientists can begin to identify what is required to protect blackwater systems and the services they supply. Key Points: There are a substantial number of blackwater rivers in multiple ecoregions of the United StatesThe water chemistry of blackwater rivers and streams is often very different than that of non‐blackwater rivers and streamsWe explore these differences and identify research needs that would contribute to their management and protection [ABSTRACT FROM AUTHOR]

Wildfires are a worldwide disturbance with unclear implications for stream water quality. We examined stream water chemistry responses immediately (<1 month) following a wildfire by measuring over 40 constituents in four gauged coastal watersheds that burned at low to moderate severity. Three of the four watersheds also had pre‐fire concentration‐discharge data for 14 constituents: suspended sediment (SSfine), dissolved organic and inorganic carbon (DOC, DIC), specific UV absorbance (SUVA), major ions (Ca2+, K+, Mg2+, Na+, Cl−, SO42− ${{\text{SO}}_{4}}^{2-}$, NO3− ${{\text{NO}}_{3}}^{-}$, F−), and select trace elements (total dissolved Mn, Fe). In all watersheds, post‐fire stream water concentrations of SSfine, DOC, Ca2+, Cl−, and NO3− ${{\text{NO}}_{3}}^{-}$ changed when compared to pre‐fire data. Post‐fire changes in SO42− ${{\text{SO}}_{4}}^{2-}$, K+, Na+, Mg2+, DIC, SUVA, and total dissolved Fe were also found for at least two of the three streams. For constituents with detectable responses to wildfire, post‐fire changes in the slopes of concentration‐discharge relationships commonly resulted in stronger enrichment trends or weaker dilution trends, suggesting that new contributing sources were surficial or near the surface. However, a few geogenic solutes, Ca2+, Mg2+, and DIC, displayed stronger dilution trends at nearly all sites post‐fire. Moreover, fire‐induced constituent concentration changes were highly discharge and site‐dependent. These similarities and differences in across‐site stream water chemistry responses to wildfire emphasize the need for a deeper understanding of landscape‐scale changes to solute sources and pathways. Our findings also highlight the importance of being explicit about reference points for both stream discharge and pre‐fire stream water chemistry in post‐fire assessment of concentration changes. Plain Language Summary: Wildfires are becoming more common, yet the effects of wildfire on streams and their water quality remain unclear. Changes in stream water quality following a wildfire can have consequences for drinking water and aquatic ecosystems. We studied how stream water quality changed in four impacted watersheds following the 2020 CZU Lightning Complex Wildfire in central coastal California using measurements of stream water chemistry coupled with analysis of burned soils and ash from the same area. For sites with pre‐fire data, we found that wildfire impacts on stream water quality were greatest in the most extensively burned watershed. We also found that stream water quality changes were distinct across watersheds and dependent on stream discharge. Chemical measurements of potential sources of solutes, like ash and burned soils, indicate that the variability in stream water quality was consistent with contributions from ash or other burned landscape materials. The location, composition, and amount of these wildfire‐generated sources vary in space and time. This complexity can lead to some similarities as well as differences in water quality responses of different streams, like those found in our study. Key Points: Post‐fire stream water chemistry impacts were usually site, constituent, and discharge‐dependent, reflecting dynamic fire‐induced changesDespite this variability, slopes of concentration‐discharge relationships often became more positive post‐fire, implying altered surface or near‐surface sourcesHeterogeneity in fire‐generated sources and processes contributes to complexities in post‐fire stream water chemistry [ABSTRACT FROM AUTHOR]

Large sample datasets are transforming the catchment sciences, but there are few off-the-shelf stream water chemistry datasets with complementary atmospheric deposition, streamflow, meteorology, and catchment physiographic attributes. The existing CAMELS (Catchment Attributes and Meteorology for Large-sample Studies) dataset includes data on topography, climate, streamflow, land cover, soil, and geology across the continental US. With CAMELS-Chem, we pair these existing attribute data for 516 catchments with atmospheric deposition data from the National Atmospheric Deposition Program and water chemistry and instantaneous discharge data from the US Geological Survey over the period from 1980 through 2018 in a relational database and corresponding dataset. The data include 18 common stream water chemistry constituents: Al, Ca, Cl, dissolved organic carbon, total organic carbon, HCO 3 , K, Mg, Na, total dissolved N, total organic N, NO 3 , dissolved oxygen, pH (field and lab), Si, SO 4 , and water temperature. Annual deposition loads and concentrations include hydrogen, NH 4 , NO 3 , total inorganic N, Cl, SO 4 , Ca, K, Mg, and Na. We demonstrate that CAMELS-Chem water chemistry data are sampled effectively across climates, seasons, and discharges for trend analysis and highlight the coincident sampling of stream constituents for process-based understanding. To motivate their use by the larger scientific community across a variety of disciplines, we show examples of how these publicly available datasets can be applied to trend detection and attribution, biogeochemical process understanding, and new hypothesis generation via data-driven techniques. [ABSTRACT FROM AUTHOR]

Rivers are an important source of water in humid regions, but their availability is greatly limited by water chemistry. In order to accurately identify the changes in river water chemical composition, the compositional analysis method (CoDA) is proposed from the perspective of compositional data analysis theory, which considers the geochemical riverine system as a whole and detects the compositional changes of the entire watershed. The basic data analysis is carried out by traditional analysis methods, and the results show that the hydrochemical characteristics of different sections of the basin have significant features. The water chemistry of Dongxi River is of the HCO3− Ca type. The water of the Xixi River shows a gradual evolution from the HCO3-Ca type and high SO42− content in the upper reaches to the Cl-Ca type in the lower reaches. The hydrochemistry of river water in the watershed is mainly affected by rock weathering leaching (PC1) and agricultural and domestic pollutant discharge (PC2), with a contribution rate of 48.4% and 19.7%, respectively. Rock weathering, mining, and agricultural pollution are the main factors affecting the chemical composition of river water in different regions. The spatial composition of a single sample at different scales is monitored by the Mahalanobis distance approach in an iterative manner to minimize the influence of a single anomaly on the composition center. The results show that the main reasons for the change in river water chemical composition along the Xixi River are attributed to mine pollution, domestic pollution, and tea plantation and that along the Dongxi River is caused by domestic pollution. The hydrochemical composition changes after the confluence of the Xixi River and Dongxi River are mainly affected by human activities and seawater in urban areas. This research could provide new perspectives and methods for detecting the influences of human and natural factors on the hydrochemistry of river water in humid regions worldwide. [ABSTRACT FROM AUTHOR]

Shifts in water fluxes and chemical heterogeneity through catchments combine to dictate stream solute export from the Critical Zone. The ways in which these factors emerge in resultant concentration‐discharge (C‐Q) relationships remain obscure, particularly at the timescale of individual precipitation and discharge events. Here we take advantage of a new high‐frequency, multi‐element and multi‐event stream C‐Q data set. The stream solute concentrations of seven major ions were recorded every 40 min over five flood events spanning one hydrologic year in a French agricultural watershed (Orgeval) using a lab‐in‐the‐field deployment we refer to as a "River Lab." We focus attention on the recession periods of these events to consider how geochemical heterogeneity within the catchment translates into dynamic stream solute concentrations during shifts in water storage. We first show that for C‐Q relationships resulting from data acquisition over multiple flood events, lumping all trends together can lead to biases in characteristic C‐Q parameters. We then reframe C‐Q relationships using a simple recession curve analysis to consider how hydrological processes produce chemical mixing of distinct solute pools immediately following discharge events. We find three distinct classes of behavior among the major solutes, none of which can be interpreted based on water storage changes alone. The shape of C‐Q relationships for each solute can then be related to their vertical zonation in the subsurface of Orgeval, and to the capacity for subcomponents of these distributions to be readily mobilized during a discharge event. Key Points: We combine high‐frequency (every 40 min) stream chemistry data and stream discharge recession analysisWe propose a conceptual model for the relationship between water storage and solute export at the Orgeval Critical Zone Observatory (CZO), FranceThree classes of solute behavior are identified at the Orgeval CZO, related to the role of rock dissolution and amendments in their budget [ABSTRACT FROM AUTHOR]

The study determines the major ion chemistry of the Teesta River catchment in the Eastern Himalayan region and evaluates hydrochemical processes controlling water composition of the catchment area. Water of the Teesta River basin was in neutral to alkaline condition. HCO3−, Ca2+, Na+, Mg2+ and SO42- were identified as the dominant ionic species in the Teesta catchment water composition and Ca-Mg-HCO3 as the dominant hydrochemical facies. Higher contribution of (Ca2++Mg2+) and HCO3− towards the TZ+ and TZ−, high ionic ratios of (Ca2++Mg2+)/(Na++K+), HCO3−/(Cl−+SO42-) and low (Na++K+)/TZ+ ratio suggest carbonate weathering as a major contributor of dissolved ions in the Teesta basin water. Under-saturation with respect to both carbonate and sulphate phase minerals suggests that water can dissolve these minerals during water-rock interaction. Concentration of the analysed water quality parameters were well below the specified drinking and irrigation water limits. [ABSTRACT FROM AUTHOR]

Carbonate weathering plays a significant role in regulating global carbon budget at short time scales, and thus needs to be better constrained in the context of global warming. Riverine magnesium isotopes (δ26Mg) have the potential to trace carbonate weathering intensity (CWI) but require further testing under various climatic and geological settings. Cation exchange is an important mechanism buffering river water chemistry, especially in catchments characterized by high erosion. However, field evidence on the influence of cation exchange on riverine δ26Mg is rare. In this study, spatial riverine δ26Mg variation within the Three Rivers (i.e., the Jinsha Jiang, the Lancang Jiang, and the Nu Jiang), three extremely-high-erosion catchments in the southeastern Tibetan Plateau, was investigated to address this issue. The results showed that riverine δ26Mg values present a wide range from –1.11 ‰ to –0.59 ‰ in the Jinsha Jiang, from –1.39 ‰ to –0.65 ‰ in the Lancang Jiang, and from –1.19 ‰ to –0.50 ‰ in the Nu Jiang. An inversion model was used to partition riverine Mg2+ sources and confirmed that the riverine Mg2+ budget was dominated by carbonate weathering, followed by evaporite dissolution. However, conservative mixing could not explain riverine δ26Mg variation within the Three Rivers catchments, because measured δ26Mg values (δ26Mg measured) systematically deviated from the modeled ones (δ26Mg modeled), with Δ26Mg measured–modeled (δ26Mg measured – δ26Mg modeled) up to 0.79 ‰. The positive correlations between Δ26Mg measured–modeled and suspended particulate matter (SPM) concentrations indicate Mg isotopic fractionation was related to high suspended loads owing to extremely-high erosion rates. Given the significant cation exchange capacity of SPM, Mg2+-Na+ exchange is proposed for the first time as an explanation for the observed δ26Mg variations in the rivers draining the Tibetan Plateau, although the role of carbonate precipitation could not be excluded. The strong positive correlations between riverine δ26Mg and exchangeable Mg/Na ratios in the Three Rivers further support that light Mg isotopes may be preferentially retained in the riverine exchange pool during Mg2+-Na+ exchange, driving riverine δ26Mg towards higher values. Expanding our finding to global rivers, the negative correlation between riverine δ26Mg and CWI can be interpreted by a competition between the fast dissolution of carbonates leading to the enrichment of 24Mg in waters and Mg isotope fractionation induced by cation exchange leading to the depletion of 24Mg in the residual waters. This study provides new insight into cation exchange as a regulator of riverine δ26Mg and Mg cycling, highlighting the robustness of riverine δ26Mg in tracing CWI and constraining the carbon cycle. [ABSTRACT FROM AUTHOR]

The Arctic is warming and significant changes to the landscape, including increased vegetative cover ("greening"), are expected in the near future. These landscape changes may alter nitrogen (N) availability in terrestrial, stream, and coastal ecosystems, where production is often N limited, but the exact changes in nutrient cycling are uncertain. Here, we analyzed the relationship between vegetation greenness (i.e., NDVI) and dissolved inorganic (DIN) and organic (DON) concentrations in streams draining 14 headwater catchments (mean 3.6 km2, range 0.4–11 km2) across three samplings in the Zackenberg area, Northeast Greenland. We found large variation in DIN and DON concentrations across the sampled streams. We further show that this variation is correlated to water temperature and catchment NDVI, such that increased vegetation greenness and temperature correlated with lower DIN, and increased greenness also correlated with higher DON concentrations in streams. The results suggest that increased terrestrial vegetation due to rising air temperature could substantially alter dissolved N concentrations and form in streams, with potentially cascading impacts on coastal areas. Plain Language Summary: This study links terrestrial vegetation cover to stream water chemistry in High Arctic headwater catchments. We found significant spatial and seasonal variation in dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON) availability in streams. Nitrate (NO3− ${{\text{NO}}_{3}}^{-}$) concentration in stream water decreases and DON increases with increasing spectral median normalized difference vegetation index (NDVI) in the stream catchment (i.e., proxy for terrestrial vegetation). This shift in the form of available nitrogen (N) has significant implications as terrestrial vegetation is changing quickly in High Arctic areas, which may then alter the amount and the dominant form of N exported from catchments to coastal areas. Key Points: High terrestrial vegetation greenness (NDVI) correlates negatively with dissolved inorganic nitrogen concentrations in High Arctic catchmentsDissolved inorganic nitrogen decreases and organic nitrogen increases with increased terrestrial vegetation greennessFuture climate changes in High Arctic areas may alter the amount and form of nitrogen exported from land to sea [ABSTRACT FROM AUTHOR]

Stream water chemistry at catchment outlets is commonly used to infer the flow paths of water through the catchment and to quantify the relative contributions of various flow paths and/or end-members, especially during storm events. For this purpose, the number and nature of these flow paths or end-members are commonly determined with principal component analysis based on all available conservative solute data. Here, for a given pair of measured solutes, we propose a methodology to determine the minimum number of required end-members, based on the ion's synchronous variation during storm events. This allows identifying solute pairs, for which a simple two end-member mixing model is sufficient to explain their variation during storm events and solute pairs, which show a more complex pattern, requiring a higher-order end-member mixing model. We analysed the concentration-concentration relationships of several major ion pairs on the storm-event scale, using multi-year, high-frequency (< 60 minutes) monitoring data from the outlet of two small (0.8 to 5 km²) French catchments with contrasting land-use, climate and geology. A large number of storm-events (56 to 92 %) could be interpreted as the result of the mixture of only two end-members, depending on the catchment and the ion pairs used. Even though some of these results could have been expected (e.g. a two-end-member model for the Na+/Cl- pair in a catchment close to the Atlantic coast), others were more surprising and in contrast to previous studies. These findings might help to revise or improve the perceptual catchment understanding of flow path or end-member contributions and of biogeochemical processes. In addition, this methodology can identify, which solute pairs are governed by identical hydro-biogeochemical processes and which solutes are modified by more complex and diverse processes. [ABSTRACT FROM AUTHOR]

Simple Summary: Biodiversity is measured differently depending on the spatial scale of the study. Beta (β)-diversity, for example, is a calculated measurement that addresses changes in diversity across different assemblages in a specific region. Studies of β-diversity often address changes in diversity across gradients of environmental conditions and distance among sites. However, β-diversity of stream insects can be difficult to measure due to their hyper-diversity and challenging taxonomy. Our study investigated the association of β-diversity with habitat conditions and distance among these habitats for insects found in the coastal streams of Alabama, USA. Additionally, we looked for potential influences caused by seasonality (fall and summer) and the level of taxonomic identification (genus, species). Regardless of season, stream conditions were highly correlated with β-diversity. More specifically, stream size and water chemistry showed the highest associations with β-diversity. Changes in β-diversity were largely driven by species replacement (turnover) rather than species loss (nestedness). The taxonomic resolution had minimal effects on the calculations of β-diversity across environmental conditions. Distance among stream sites was never correlated with β-diversity. As we continue to face global insect declines, our study provides valuable insight into the patterns that drive changes in diversity across environmental gradients. β-diversity is often measured over both spatial and temporal gradients of elevation, latitude, and environmental conditions. It is of particular interest to ecologists, as it provides opportunities to test and infer potential causal mechanisms determining local species assemblages. However, studies of invertebrate β-diversity, especially aquatic insects, have lagged far behind other biota. Using partial Mantel tests, we explored the associations between β-diversity of insects found in the coastal streams of Alabama, USA, and stream conditions and distances among sites. β-diversity was expressed using the Sørensen index, βSor, stream conditions were expressed as principal components (PCs), and distances as Euclidean distances (km) among sites. We also investigated the impact of seasonality (fall, summer) and taxonomic resolution (genus, species) on βSor. Regardless of season, βSor was significantly correlated (p < 0.01; r > 0.44) with stream conditions (stream size and water chemistry), while taxonomic resolution had minimal effect on associations between βSor and stream conditions. Distance was never correlated with changes in βSor (p > 0.05). We extended the use of the Sørensen pair-wise index to a multiple-site dissimilarity, βMult, which was partitioned into patterns of spatial turnover (βTurn) and nestedness (βNest). Changes in βMult were driven mostly by turnover rather than nestedness. [ABSTRACT FROM AUTHOR]

Permafrost regions are under particular pressure from climate change resulting in widespread landscape changes, which impact also freshwater chemistry. We investigated a snapshot of hydrochemistry in various freshwater environments in the lower Kolyma river basin (North‐East Siberia, continuous permafrost zone) to explore the mobility of metals, metalloids and non‐metals resulting from permafrost thaw. Particular attention was focused on heavy metals as contaminants potentially released from the secondary source in the permafrozen Yedoma complex. Permafrost creeks represented the Mg‐Ca‐Na‐HCO3‐Cl‐SO4 ionic water type (with mineralisation in the range 600–800 mg L−1), while permafrost ice and thermokarst lake waters were the HCO3‐Ca‐Mg type. Multiple heavy metals (As, Cu, Co, Mn and Ni) showed much higher dissolved phase concentrations in permafrost creeks and ice than in Kolyma and its tributaries, and only in the permafrost samples and one Kolyma tributary we have detected dissolved Ti. In thermokarst lakes, several metal and metalloid dissolved concentrations increased with water depth (Fe, Mn, Ni and Zn – in both lakes; Al, Cu, K, Sb, Sr and Pb in either lake), reaching 1370 μg L−1 Cu, 4610 μg L−1 Mn, and 687 μg L−1 Zn in the bottom water layers. Permafrost‐related waters were also enriched in dissolved phosphorus (up to 512 μg L−1 in Yedoma‐fed creeks). The impact of permafrost thaw on river and lake water chemistry is a complex problem which needs to be considered both in the context of legacy permafrost shrinkage and the interference of the deepening active layer with newly deposited anthropogenic contaminants. [ABSTRACT FROM AUTHOR]

This study investigated the readability level of second-grade secondary school scientific stream Chemistry and Physics textbooks in Jordan, determining the effect of gender on the degree of readability, in addition to knowing the order of the textbooks according to the degree of their readability in both books. The current study was conducted to determine the readability level of chemistry and physics textbooks by involving 300 second-grade secondary school students of the public schools affiliated with the Directorate of Education, Jordan. Four Cloze tests were prepared from different topics of both textbooks to measure their readability. The test included four texts with 20 words omitted from each text, and the texts were presented in the same format as in the textbooks, with clear instructions provided for the students. A pilot sample outside the study sample was administered with the test-retest method to confirm the reliability of the four tests for both textbooks. The findings revealed that physics textbooks had a higher level of readability than chemistry textbooks. A significant difference (p≤0.05) was observed based on the type of textbook in the readability of chemistry and physics textbooks. The scientific texts in the chemistry textbook were ordered in light of their readability level. In contrast, the scientific texts in the physics textbook were not ordered in light of their readability level. The study concluded that the readability level of Jordanian Chemistry and Physics textbooks of the second grade of the scientific stream differed significantly (p≤0.05). The study recommends that the Jordan Ministry of Education should appoint a panel of experts to review the textbooks and make the necessary changes to improve their readability level. [ABSTRACT FROM AUTHOR]

Northern regions are undergoing rapid change with wildfires increasing in frequency and severity alongside thawing permafrost and altered water balance. These disturbances could cause significant change in the export of carbon, nutrients, and metals to aquatic systems, with implications for food webs and ecosystem processes. Here, we examine chemical data from a series of 52 streams and rivers that were sampled across a 250,000 km2 expanse of the Taiga Plains and Taiga Shield ecozones of the Northwest Territories, Canada. Samples were collected immediately after and for 3 years following a "megafire" that occurred in this region in 2014, and included wildfire‐affected and non‐affected catchments. While wildfire has been observed to cause significant impacts on water quality in other regions, we here report weak relationships with percent watershed burn with minor to moderate effect sizes, the greatest being a reduction in dissolved organic carbon (−32% concentration). Watershed‐specific properties were a strong driver of large spatial variability in stream water chemistry, which may overwhelm or obscure lesser wildfire effects. The watershed chemical yield‐specific response to wildfire was weaker than the response for concentrations, due to substantial variation and uncertainty in runoff among sites and years. This suggests that watershed chemical yields in this region are more sensitive to changes in water balance due to climate than to altered wildfire regimes. Plain Language Summary: Our study examines how wildfires affect the chemistry of water in northern regions. We collected data from 52 streams and rivers in the Taiga Plains and Taiga Shield ecozones of Canada. The results show that the effects of wildfires on water quality are relatively small. Other factors, such as climate and the presence of wetlands, have a much stronger influence on water chemistry in each ecozone. Understanding these changes in water chemistry is crucial for managing aquatic ecosystems. However, we found that the impact of wildfires on water quality in this region differs from that in other locations. The variability in runoff among different sites and years also adds uncertainty to our findings. Looking ahead, climate change and altered hydrology may have more substantial impacts on fluvial networks compared to wildfires in this rapidly changing region. Our research provides valuable insights into the relative importance of various landscape factors in regulating water quality, including the effects of wildfires. By examining the chemical changes occurring due to wildfires and considering the broader environmental context, we contribute to a better understanding of how these factors influence water quality in northern regions. Key Points: Wildfires in the Taiga regions of Canada had modest effects on water chemistry, with the largest impact being a reduction in DOC (−32%)Variability in stream water chemistry was driven by watershed‐specific properties overshadowing the influence of wildfiresFuture impacts on streams are likely more substantially driven by climate and altered hydrology than increasing wildfire frequency [ABSTRACT FROM AUTHOR]

Understanding the spatiotemporal dynamics of river water chemistry from its source to sinks is critical for constraining the origin, transformation, and "hotspots" of contaminants in a river basin. To provide new spatiotemporal constraints on river chemistry, dissolved trace element concentrations were measured at 17 targeted locations across the Ramganga River catchment. River water samples were collected across three seasons: pre-monsoon, monsoon, and post-monsoon between 2019 and 2021. To remove the dependency of trace element concentrations on discharge, we used molar ratios, as discharge data on Indian transboundary rivers are not publicly available. The dataset reveals significant spatiotemporal variability in dissolved trace element concentrations of the Ramganga River. Samples collected upstream of Moradabad, a major industrial city in western Uttar Pradesh, are characterized by ~ 1.2–2.5 times higher average concentrations of most of the trace elements except Sc, V, Cr, Rb, and Pb, likely due to intense water–rock interactions in the headwaters. Such kind of enrichment in trace metal concentrations was also observed at sites downstream of large cities and industrial centers. However, such enrichment was not enough to bring a major change in the River Ganga chemistry, as the signals got diluted downstream of the Ramganga-Ganga confluence. The average river water composition of the Ramganga River was comparable to worldwide river water composition, albeit a few sites were characterized by very high concentrations of dissolved trace elements. Finally, we provide an outlook that calls for an assessment of stable non-traditional isotopes that are ideally suited to track the origin and transformation of elements such as Li, Mg, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Sr, Ag, Cd, Sn, Pt, and Hg in Indian rivers. [ABSTRACT FROM AUTHOR]

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The major ion chemistry in the Taihu watershed has dramatically changed due to human disturbances; however, little is known about the similarities and differences in the responses of the inflow rivers and Taihu lake to the disturbances. Using historical (1950s–1970s) and recent (2018–2021) water chemistry data of inflow rivers and the lake, as well as socioeconomic and land use data, we explored the drivers for the major ion chemistry change and different responses of the inflow rivers and the receiving lake. The results indicated that, compared with 1950s–1970s, all the major ions and TDS in rivers and Taihu lake significantly increased (by 91% for Mg2+ and by 395% for Cl− in rivers; by 68% for HCO3− and 134% for Na+ in the lake); however, their increases in major ion composition presented a clear difference, i.e., although current dominant cation remained Ca in inflow rivers, the second dominant cation has shifted from Mg2+ (1950s–1970s) to Na+ (2018–2021) for rivers, while for the lake, the second dominant cation has become frequently Na+ (2018–2021), followed by Ca2+, indicating a clear salinization tendency. Furthermore, the change of some indicative ratio indices of inflow rivers and the lake in the past decades presented an apparent difference, i.e., the river systems had a higher increase rate in Ca2+/Mg2+ and SO42−/Cl− than the lake, while the lake had a higher increase in (Ca2+ + Mg2+)/HCO3−, TH/TA, and Cl−/Na+ than the river systems. Analyses indicated that increased human disturbances were the major driver for the similar increase in the TDS and major ions for both river systems and the lake, while the different algal biomass in the rivers and lake, the land use change, and declined hydrological connectivity in this watershed played important roles in the different alterations of the water chemistry indices. Comparison of major ion correlation change between the running and stagnant waters indicated a clear "lacunification" trend of inflow rivers in terms of water chemistry characteristics in this dense river-network region. Our work revealed the cause and effect of the fundamental water chemistry change in a rapid development region and will provide scientific basis for the integrated management and recovery in the watershed. [ABSTRACT FROM AUTHOR]

Currently, 50% of Irish rivers do not meet water quality standards, with many declining due to numerous pressures, including peatland degradation. This study examines stream water quality in the Irish midlands, a region where raised bogs have been all historically disturbed to various extent and the majority drained for industrial or domestic peat extraction. For the first time, we provide in-depth analysis of stream water chemistry within a heavily modified bog landscape. Small streams from degraded bogs exhibited greater levels of pollutants, in particular: total dissolved nitrogen (0.48 mg/l) and sulphate (18.49 mg/l) as well as higher electrical conductivity (mean: 334 μS/cm) compared to similar bog streams in near-natural bogs. Except for site-specific nitrogen pollution in certain streams surrounding degraded peatlands, the chemical composition of the receiving streams did not significantly differ between near-natural and degraded sites, reflecting the spatio-temporal scales of disturbance in this complex peat-scape. Dissolved organic carbon concentrations in all the receiving streams were high (27.2 mg/l) compared to other Irish streams, even within other peatland catchments. The region is experiencing overall a widespread loss of fluvial nitrogen and carbon calling for (a) the development of management instruments at site-level (water treatment) and landscape-level (rewetting) to assist with meeting water quality standards in the region, and (b) the routine monitoring of water chemistry as part of current and future peatland management activities. [ABSTRACT FROM AUTHOR]

The adsorbent is a solid substance that can absorb certain components from the liquid phase. Most of the adsorbents are porous materials and the adsorption process takes place, especially in the porous wall or certain location inside that particle. The main objective of this research is to study the influence of the adsorbent's surface area based on shape variation from corn stalk with adsorption ability to reduce the water river's turbidity, the influence of time with adsorption capacity in reducing river water's turbidity, the influence of adsorbent with water river and adsorption capacity, and defining adsorption kinetics from corn stalks. The shape of corn stalks that have been used such as spherical, half of spherical shape, and quarter of spherical shape. The volume of the sample is 250 mL. The measurement time is 300 minutes. The mass variations that have been used are 10 g, 15 g, and 20 g. The variation of sample takeover in the morning, afternoon, and evening. The measurement of adsorbent adsorption capacity in term of decreasing the turbidity of Babura River's water is done by inputting the adsorbent into the sample, then the measurement of the water's turbidity proceed by using a turbidity meter. The analysis result for the influence of the adsorbent's surface area in decreasing Babura River's water in the shape's variation from spherical, half of spherical shape, and quarter of spherical shape is obtained in quarter of spherical shape. The highest amount of adsorbent in decreasing the turbidity of Babura River's water is 20 g. Adsorption kinetics that has been used in the measurement of decreasing Babura River's water turbidity is second order kinetics. [ABSTRACT FROM AUTHOR]