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Abstract This study provides a description of the water quality status in the tributaries of the upper Tagus River and a preliminary risk assessment for freshwater organisms. A wide range of physico-chemical parameters, nutrients, metals and organic contaminants (20 pesticides, and 32 point source chemicals, mainly pharmaceuticals) were monitored during spring, summer and autumn of 2016. Monitoring of organic contaminants was performed using conventional grab sampling and passive samples (POCIS). The variation of the different groups of parameters as regards to land use and sampling season was investigated. The prioritization of organic and inorganic contaminants was based on the toxic unit (TU) approach, using toxicity data for algae, invertebrates and fish. Finally, the compliance with the Environmental Quality Standards (EQS) set as part of the Water Framework Directive (WFD) was evaluated for the listed substances. This study shows that the land use characteristics had a large influence on the spatial distribution of the contaminants and other water quality parameters, while temporal trends were only significant for physico-chemical parameters, and marginally significant for insecticides. Acute toxicity is likely to occur for some metals (copper and zinc) in the most impacted sites (TU values close to or above 1). Low acute toxicity was determined for organic contaminants (individual compounds and mixtures) on the basis of grab samples. However, the assessment performed with POCIS samples identified diuron, chlorpyrifos and imidacloprid as potentially hazardous compounds. Several contaminant mixtures that may cause chronic toxicity and that should be considered in future regional chemical monitoring plans were identified. Our study also shows that some metals and pesticides exceeded the WFD regulatory thresholds and that only 30% of the sampled sites had a good chemical status. Further research is needed to identify chemical emission sources and to design proper abatement options in the Tagus river basin. Graphical abstract Unlabelled Image Highlights • Chemical status evaluated in 16 sites of the Tagus river basin over three seasons. • Land use had a stronger influence than season on contamination patterns. • Copper and zinc may exert acute toxicity to primary producers and invertebrates. • Diuron, chlorpyrifos and imidacloprid identified as priority hazardous compounds. • Only 30% of the sampled sites showed good chemical status as per the WFD. [ABSTRACT FROM AUTHOR]

Abstract The main objective of the present study is to prioritize those pharmaceuticals that have higher chances to be detected in water due to incomplete removal in Wastewater Treatment Plants (WWTPs). To do so, the total consumption of pharmaceuticals in Catalonia (NE Spain) were compiled to calculate the predicted environmental concentrations (PECs) in wastewater effluents and in river water. PECs were estimated using publicly available consumption data in the period of 2013–2016 for a suite of 165 compounds. The selected compounds were based on generic pharmaceuticals with emphasis on drugs consumed by people aged 65 or over as they represent the age group with the highest consumption of pharmaceuticals. The mean total consumption of pharmaceuticals in the period studied was of 623 ± 3 t per year. Paracetamol, metformin and ibuprofen were the most administered drugs although the highest PEC values corresponded to metformin, amoxicillin and metamizole. Finally, predicted environmental levels together with acute and chronic toxicological data allowed estimating the risks of these compounds. Amoxicillin is expected to pose adverse effects for cyanobacteria, whereas metformin and ibuprofen pose a small potential for adverse effects to invertebrates and fish, respectively. Graphical abstract Unlabelled Image Highlights • Consumptions of 165 pharmaceuticals used by elderly people have been reported. • The mean total consumption of pharmaceuticals studied between 2013 and 2016 was 623 ± 3 t year−1. • Amoxicillin is expected to pose adverse effects for cyanobacteria. • Metformin pose a small potential for adverse effects to invertebrates and fish. • Moreover, ibuprofen also poses a small potential for adverse effects to fish. [ABSTRACT FROM AUTHOR]

Abstract Losses of phosphorus (P) from arable land lead to P enrichment in surface waters and thus to eutrophication. To gain deeper insights into riverine P processing and transport, the temporal and spatial changes of P compounds along the lowland river Warnow and its tributaries were investigated. Surface water samples were taken monthly between August 2016 and August 2017 and analyzed for the four P fractions: dissolved reactive (DRP), dissolved nonreactive (DNP), particulate reactive (PRP) and particulate nonreactive (PNP) phosphorus. P-composition differed between the courses of the upper Warnow and the impounded middle Warnow due to differences in their hydrological conditions. In the catchment of the upper course, riverine lakes were the sources of PNP and DRP during the summer and autumn. From the catchment of the middle course, mainly PRP and DRP had been introduced into the river. The negative relationship between PRP and the chlorophyll (Chla) concentration (rho = −0.43, p < 0.001) indicated that this P fraction is potentially bioavailable. During the rainy summer of 2017, substantially higher amounts of DRP occurred in the whole Warnow river. The potentially bioavailable P fractions (DRP, PRP, DNP) supported phytoplankton growth in the middle course, and the PNP loads increased with increasing biomass. Total phosphorus (TP) loads increased along the Warnow flow path, due to increasing discharge volume. The annual TP load of 40 t to the estuary was dominated by DRP (32%) and PNP (31%), with smaller contributions by PRP and DNP (19% and 18%, respectively). Our results demonstrate that detailed information on P fractions are helpful to understand P-cycling in rivers and its influence on eutrophication processes. This knowledge should be included in the development of effective management strategies for the improvement of water quality. Graphical abstract Unlabelled Image Highlights • Not only TP and DRP, but all P fractions should be monitored regularly to estimate the eutrophication risk. • Particulate P (PRP, PNP) plays a crucial role in P transport and cycling. • Potentially Bioavailable P fractions (DRP, PRP, DNP) made up a great amount of total P load to the estuary. • Riverine lakes are sources of particulate and dissolved P during autumn and summer. [ABSTRACT FROM AUTHOR]

Abstract As the "Water Tower of Asia", rivers originating from the Tibetan Plateau provide water resources for more than one billion residents in both its local and surrounding areas. With respect to the essential role that this region plays in terms of water resources in Asia, we provide an overview of the mechanisms governing the water quality, including the major ions and trace elements release, in eleven rivers of the Tibetan Plateau. Overall, the rivers running on the Tibetan Plateau reflect an alkaline aquatic environment, with an average pH of 8.5; and the total dissolved solids (TDS, ~339 mg L−1) are much higher than the global average value. Over 80% of the water ionic budget in the rivers of the plateau is comprised of Ca2+, Mg2+, HCO 3 – and SO 4 2−. The main mechanisms that control the river water chemistry on the Tibetan Plateau are natural processes and present a visible spatial heterogeneity. For instance, in rivers of the southern Tibetan Plateau, the water quality is mainly controlled by the rock-weathering, while rivers of the central and northern Tibetan Plateau are also largely affected by evaporation-crystallization processes. In general, most of the rivers on the Tibetan Plateau are uncontaminated and still in a pristine condition. However, it should be noted that due to the natural process such as rock-weathering and groundwater leaching, and anthropogenic activities such as urbanization and mining operations, the concentrations of several toxic elements (e.g., As, Cd, Pb, Mn, Hg and Tl) in some of the basins are higher than the China national standard (GB) and the World Health Organization (WHO) guidelines for drinking water. With increasing anthropogenic activities on the plateau and changes in the river basins, it is necessary to conduct the long-term monitoring of the river water chemistry of this climate-sensitive and eco-fragile region. Graphical abstract Unlabelled Image Highlights • Natural processes dominate the water chemistry in rivers of the Tibetan Plateau. • Human activities have certain impacts on the water quality in the Tibetan rivers. • Waters in parts of the rivers of the Tibetan Plateau are not safe for drinking. [ABSTRACT FROM AUTHOR]

Abstract Coupled nitrogen and oxygen isotopes of nitrate have proven useful in identifying nitrate sources and transformation in rivers. However, isotopic fractionation and low-resolution monitoring limit the accurate estimation of nitrate dynamics. In the present study, the spatio-temporal variations of nitrate isotopes (15N and 18O) and hydrochemical compositions (NO 3 − and Cl−) of river water were examined to understand nitrate sources in the Xijiang River, China. High-frequency sampling campaigns and isotopic analysis were performed at the mouth of the Xijiang River to capture temporal nitrate variabilities. The overall values of δ15N-NO 3 − and δ18O-NO 3 − ranged from +4.4‰ to +14.1‰ and from −0.3‰ to +6.8‰, respectively. The results of nitrate isotopes indicated that NO 3 − mainly originated from soil organic nitrogen (SON), chemical fertilizer (CF), and manure and sewage wastes (M&S). The negative correlation of nitrate isotopic values with NO 3 −/Cl− ratios suggested the importance of denitrification in NO 3 − loss. The results of Bayesian model with incorporation of isotopic fractionation during the denitrification showed that SON and CF contributed to the most (72–73%) nitrate in the wet season; whereas approximately 58% of nitrate was derived from anthropogenic inputs (M&S and CF) in the dry season. The nitrate flux was 2.08 × 105 tons N yr−1 during one hydrologic year between 2013 and 2014, with 86% occurring in the wet season. Long-term fluctuations in nitrate flux indicated that nitrate export increased significantly over the past 35 years, and was significantly correlated with nitrate concentrations. The seasonal pattern of nitrate dynamics indicated the mixing of nitrified NO 3 − and denitrified NO 3 − between surface flow and groundwater flow under different hydrological conditions. Overall, the present study quantitatively evaluates the spatio-temporal variations in nitrate sources in a subtropical watershed, and the high-frequency monitoring gives a better estimate of nitrate exports and proportional contributions of nitrate sources. Graphical abstract Unlabelled Image Highlights • Evaluate spatio-temporal contributions of nitrate sources by Bayesian mixing model. • Identify temporal nitrogen dynamics by high-frequency analysis of nitrate isotopes. • Nitrate concentrations determine the long-term pattern of nitrate flux. [ABSTRACT FROM AUTHOR]

Abstract Although microplastics are a recognised pollutant in marine environments, less attention has been directed towards freshwater ecosystems despite their greater proximity to possible plastic sources. Here, we quantify the presence of microplastic particles (MPs) in river organisms upstream and downstream of five UK Wastewater Treatment Works (WwTWs). MPs were identified in approximately 50% of macroinvertebrate samples collected (Baetidae, Heptageniidae and Hydropsychidae) at concentrations up to 0.14 MP mg tissue−1 and they occurred at all sites. MP abundance was associated with macroinvertebrate biomass and taxonomic family, but MPs occurred independently of feeding guild and biological traits such as habitat affinity and ecological niche. There was no increase in plastic ingestion downstream of WwTW discharges averaged across sites, but MP abundance in macroinvertebrates marginally increased where effluent discharges contributed more to total runoff and declined with increasing river discharge. The ubiquity of microplastics within macroinvertebrates in this case study reveals a potential risk from MPs entering riverine food webs through at least two pathways, involving detritivory and filter-feeding, and we recommend closer attention to freshwater ecosystems in future research. Graphical abstract Unlabelled Image Highlights • Microplastic ingestion by riverine macroinvertebrates was assessed over South Wales. • Microplastics were identified in approximately 50% of macroinvertebrate samples. • Ingestion of microplastics was observed in all taxa, across all sites. • No difference in microplastic burden was observed downstream of sewage treatment works. [ABSTRACT FROM AUTHOR]

Abstract The pollution of natural waters and sediments with metals derived from acid mine drainage (AMD) is a global environmental problem. However, the processes governing the transportation and transformation of AMD metals such as Cd in mountainous areas are poorly understood. In this study, the Cd isotopic composition and Cd concentration of river water and sediments (16 sampling sites) from an AMD-affected river in southern China were determined. Cd concentration in river water declined from its source at a tailings dam (304 μg L−1) to a point 14 km downstream (0.32 μg L−1). Sediment Cd concentration ranged from 0.18 to 39.9 μg g−1, suggesting that anthropogenic Cd is derived primarily from the tailing dam and easily enters the solid phase of the river. Isotopic data showed that the dissolved Cd in rivers was characterized by δ114/110Cd values ranging from 0.21‰ to 1.03‰, with a mean of 0.48‰. The greatest Cd isotope difference was observed between the water and sediments in the LW dam (Δ114/110Cd river-sediment = 1.61‰, site 1), likely due to a rapid weathering dissolution of the ore tailings. In the river's upper reach (sites 2–3), isotope difference between river and sediment (Δ114/110Cd river-sediment) ranged from 1.0‰ to 0.91‰. This suggests that a host of secondary processes might have impacted Cd isotope fractionation, including adsorption, ternary complexation and/or (co)precipitation of Cd on secondary oxides and hydroxides. In the middle and lower reaches, an abruptly elevated δ114/110Cd value near farmland (site 10) suggests the existence of a second Cd source. Based on the chemical properties of water samples we can attribute this heavy isotope signature to agricultural fertilizer and drainage from agricultural fields. Our results suggest that Cd isotope is a tracer for identifying and tracking Cd sources and attenuation mechanisms (adsorption/(co)precipitation) in a complex mountain watershed. Graphical abstract Unlabelled Image Highlights • Mineral, tailings, sediments and AMD-contaminated river water were analyzed for Cd isotope ratios. • Distinctive Cd isotope signatures associated with transport and fate of riverine Cd. • Agricultural activities contributed a heavy isotope signature input of Cd. • Cadmium stable isotope is a promising tracer of attenuation processes in acid mine drainage. [ABSTRACT FROM AUTHOR]

Abstract Rivers are important sites of both nitrogen removal and emission of nitrous oxide (N 2 O), a powerful greenhouse gas. Previous measurements have focused on nitrogen-rich temperate rivers, with cold, low-nitrogen river systems at high-altitude receiving less attention. Here, nitrogen removal rates were estimated by directly measuring dissolved N 2 and N 2 O of the Yellow River in its source region of the Tibetan Plateau, a frigid high-altitude environment. We measured the dissolved N 2 and N 2 O using N 2 :Ar ratio method and headspace equilibrium technique, respectively. Dissolved N 2 in the river water ranged from 337 to 513 μmol N 2 L−1, and dissolved N 2 O ranged from 10.4 to 15.4 nmol N 2 O L−1. Excess dissolved N 2 (△N 2) ranged from −8.6 to 10.5 μmol N 2 L−1, while excess dissolved N 2 O (△N 2 O) ranged from 2.1 to 8.3 nmol N 2 O L−1; they were relatively low compared with most other rivers in the world. However, N 2 removal fraction (△N 2 /DIN, average 21.6%) and EF 5r values (N 2 O − N/NO 3 − N, range 1.6 × 10−4–5.0 × 10−2) were comparable with many other rivers despite the high altitude for the Yellow River source region. Furthermore, the EF 5r values increased with altitude. Estimated fluxes of N 2 and N 2 O to the atmosphere from the river surface ranged from −67.5 to 93.5 mmol N m−2 d−1 and from 4.8 to 93.8 μmol N m−2 d−1, respectively, and the nitrogen removal from rivers was estimated to be 1.87 × 107 kg N yr−1 for the Yellow River source region. This is the first report of nitrogen removal for a frigid high-altitude river; the results suggest that N removal and N 2 O emission from cold high-altitude rivers should be considered in the global nitrogen budget. Graphical abstract Unlabelled Image Highlights • Excess dissolved N 2 and N 2 O in the Yellow River source region were lower than other rivers. • N 2 O emission factor increased with the elevation of the Yellow River in its source region. • N 2 removal fraction and N 2 O emission factor in this study were comparable with other rivers. • The nitrogen removal from the Yellow River source region was about 1.87 × 107 kg N yr−1. [ABSTRACT FROM AUTHOR]

Abstract Hydrological droughts have a diverse range of effects on water resources. Whilst the impacts of drought on water quantity are well studied, the impacts on water quality have received far less attention. Similarly, quantifications of water scarcity have typically lacked water quality dimensions, whilst sectoral water uses are associated with both water quantity and quality requirements. Here we aim to combine these two elements, focussing on impacts of droughts on river salinity levels and including a salinity dimension in quantifications of water scarcity during drought and extreme drought conditions. The impact of historical droughts on river salinity (electrical conductivity (EC) was studied at 66 monitoring stations located across the Southern USA for 2000–2017. Salinity was found to increase strongly (median increase of 21%) and statistically significantly (p ≤ 0.05) during drought conditions for 59/66 stations compared to non-drought conditions. In a next step, a salinity dimension was added to water scarcity quantifications for 15 river basins in Texas. Water scarcity was quantified using data of sector water uses, water availability, river salinity levels and salinity thresholds for sector water uses. Results showed that the dominant factor driving water scarcity highly differed per basin. Increases in water scarcity were further compounded by drought-induced decreases in water availability, increases in sectoral water demands and increases in river water salinity. This study demonstrates that droughts are associated with important increases in river salinity, in addition to reduced water availability, and that both of these aspects should be considered when quantifying water scarcity. Alleviating water scarcity should therefore not only focus on increasing water availability and reducing water demands (quantity aspects), but also on improving water quality. Graphical abstract Unlabelled Image Highlights • Impacts of droughts on river salinity were statistically analysed for southern US. • Median increase in river salinity of 21% during droughts • Impacts of salinity dimension on water scarcity levels were quantified for Texas • Increasing water scarcity during droughts due to a combination of reduced water availability and increased river salinity • Alleviating water scarcity should not only focus on water quantity aspects, but also on improving water quality. [ABSTRACT FROM AUTHOR]

Abstract The European Union (EU) has recommended the monitoring of specific priority substances (PSs, Directive 2013/39) and some contaminants of emerging concern (CECs, Decision 2015/495) in surface waterbodies. The present study provides spatial distributions and temporal variations of a wide range of multi-class PSs and CECs in four stressed rivers in Portugal (Ave, Leça, Antuã, and Cértima). Thirteen micropollutants were found in all four rivers, including the priority pesticide isoproturon (up to 92 ng L−1), various pharmaceuticals (up to 396 ng L−1), and the UV-filter 2-ethyl-hexyl-4-methoxycinnamate (EHMC, up to 562 ng L−1) identified in Decision 2015/495. The industrial priority compound perfluorooctanesulfonic acid (PFOS) was found in three rivers (Antuã, Cértima, and Leça) below the method quantification limit, together with four pharmaceuticals not included in these EU guidelines. The already banned priority pesticide atrazine was detected in Ave, Antuã, and Leça (up to 41 ng L−1) and simazine in Cértima and Leça (up to 26 ng L−1). Acetamiprid and imidacloprid (included in Decision 2015/495) were only detected during the dry season in the Ave. Leça river was selected as a waterbody case study for assessment of fluorescence excitation-emission matrices (EEMs). These results matched the spatial distribution trend of micropollutants along the river, with stronger fluorescence response and higher concentrations being found downstream of industrial areas and urban wastewater treatment plants (WWTPs). Moreover, the fluorescence signature of surface water collected downstream of an urban WWTP aligned very well with that obtained for the respective WWTP effluent. Thus, actions are needed to preserve a good environmental status of these stressed European waterbodies. Graphical abstract Unlabelled Image Highlights • Spatial and seasonal variations of multi-class micropollutants were studied. • Four stressed rivers in Portugal were monitored in dry and wet seasons. • Ketoprofen, tramadol, enrofloxacin and thiacloprid were measured at highest levels. • The fluorescence EEMs of surface water matched the distribution of micropollutants. • Correlation of fluorescence signatures found for azithromycin, carbamazepine, EHMC. [ABSTRACT FROM AUTHOR]

Abstract Quantitative chemical analyses of 428 organic contaminants (OCs) indicated the presence of 313 OCs in the sediment extracts from Sava River, Croatia. Pharmaceuticals were present in higher concentrations than pesticides thus confirming their increasing threat to freshwater ecosystems. Toxicity evaluation of the sediment extracts from four locations (Jesenice, Rugvica, Galdovo and Lukavec) using zebrafish embryotoxicity test (ZET) accompanied with semi-quantitative histopathological analyses exhibited correlation with cumulative number and concentrations of OCs at the investigated sites (10.05, 15.22, 1.25, and 9.13 μg/g respectively). Toxicity of sediment extracts and sediment was predicted using toxic unit (TU) approach and persistence, bioaccumulation and toxicity (PBT) ranking. Additionally, influential OCs and genes were identified by graph mining of the prior knowledge informed, site-specific chemical-gene interaction models. Predicted toxicity of sediment extracts (TU ext ) was similar to the results obtained by ZET and associated histopathology with Rugvica sediment being the most toxic, followed by Jesenice, Lukavec and Galdovo. Sediment TU (TU sed ) favoured OCs with low octanol-water partition coefficients like herbicide glyphosate and antibiotics ciprofloxacin and sulfamethazine thus indicating locations containing higher concentrations of these OCs (Galdovo and Rugvica) as the most toxic. Results suggest that comprehensive in silico sediment toxicity predictions advocate providing equal attention to organic contaminants with either very low or very high log K ow. Graphical abstract Unlabelled Image Highlights • Pharmaceuticals are a major component of river sediment pollution. • ZET and histopathological analysis are good indicators of sediment toxic potential. • In silico sediment toxicity predictions should include OCs with low or high log K ow. [ABSTRACT FROM AUTHOR]

The riverine system is usually considered as a natural reservoir of antibiotic resistance genes (ARGs) and more susceptible to anthropogenic activities. In this study, the occurrence and distribution of 14 antibiotics belonging to 7 categories together with 23 corresponding ARGs in Ba River of Xi'an China were investigated in March and July 2017. Sulfonamides, quinolones, macrolides and tetracyclines were detected in high frequencies ranged from 85.7% to 100%. Tetracyclines were detected with high concentrations in water samples (up to 8.54 × 10 2  ng L −1 ) and sediment samples (up to 2.08 × 10 3  μg kg −1 ), respectively. The total concentrations of antibiotics were much higher in July in comparison with March. The sul 1, tet A, tet C, tet Z, gyr A, erm F, cml A and bla TEM were the predominant ARGs in terms of absolute abundance. For both water and sediment samples in March compared with July, the relative abundance of ARGs had no significant difference except for sul 3. The tetracyclines had positive correlation with tet genes, whereas the remaining antibiotics had no significant correlations with their corresponding ARGs, suggesting that environmental factors and cross-selection may significantly influenced the distribution of ARGs. Redundancy analysis was performed to further predict the influences of environmental factors on antibiotics and ARG abundance. The findings suggest that anthropogenic activities contribute significantly to the persistence of antibiotics pollution. [ABSTRACT FROM AUTHOR]

We aim to answer a question: how does the geological setting affect flood dynamics in lowland alluvial rivers? The study area covers three river reaches: not trained, relatively large on the European scale, flowing in broad valleys cut in the landscape of old glacial plains. We focus on the locations where levees [both: a) natural or b) artificial] were breached during flood. In these locations we identify (1) the erosional traces of flood (crevasse channels) on the floodplain displayed on DEM derived from ALS LIDAR. In the main river channel, we perform drillings in order to measure the depth of the suballuvial surface and to locate (2) the protrusions of bedrock resistant to erosion. We juxtapose on one map: (1) the floodplain geomorphology with (2) the geological data from the river channel. The results from each of the three study reaches are presented on maps prepared in the same manner in order to enable a comparison of the regularities of fluvial processes written in (1) the landscape and driven by (2) the geological setting. These processes act in different river reaches: (a) not embanked and dominated by ice jam floods, (b) embanked and dominated by rainfall and ice jam floods. We also analyse hydrological data to present hydrodynamic descriptions of the flood. Our principal results indicate similarity of (1) distinctive erosional patterns and (2) specific geological features in all three study reaches. We draw the conclusion: protrusions of suballuvial bedrock control the flood dynamics in alluvial rivers. It happens in both types of rivers. In areas where the floodplain remains natural, the river inundates freely during every flood. In other areas the floodplain has been reclaimed by humans who constructed an artificial levee system, which protects the flood-prone area from inundation, until levee breach occurs. [ABSTRACT FROM AUTHOR]

Sediments delivered to freshwater and marine environments can make important contributions to the aquatic bioavailable nutrient pool. In the Great Barrier Reef (GBR) catchments, particulate nutrients comprise an important fraction of the end of catchment loads; however, their contribution to the bioavailable nutrient pool is not well understood. This research determined which particulate nutrient parameters are the best indicators of the potential effect of fine sediment (<10 μm) on phytoplankton growth. Surface and subsurface sediments were lab-generated to cover a wide spectrum of particulate nutrient bioavailability from key soil types, land uses and erosion processes (hillslope and gully) in a wet and a dry tropics catchment of the GBR. Phytoplankton bioassays were used to assess freshwater and marine phytoplankton responses to sediments. The best indicators were selected by regressing measurements of phytoplankton growth against nutrient bioavailability parameters measured on the sediments. The selected indicator equations included organic carbon (C) pools for both fresh and marine water, highlighting the role of bacteria in mediating nutrient availability for phytoplankton. The equations also included various fractions of particulate nitrogen (N) (differentiating the adsorbed ammonium-N from the particulate organic N), and the ratios of C to N, which indicate the lability of the organic matter present in the sediment. Dissolved reactive phosphorus was also an important indicator in freshwater. The indicators performed better in assessing bioavailability potential than traditional methods to monitor particulate nutrients, e.g., particulate N and particulate phosphorus. Phytoplankton bioassays indicated that nutrients in sediment can promote phytoplankton growth, with nutrient bioavailability depending not only on sediment load, but also sediment characteristics associated with its parent soil. These characteristics vary with soil type, land use and erosion process. Findings will help prioritize erosion control to catchment areas which are most likely to contribute large amounts of bioavailable particulate nutrients to the GBR. [ABSTRACT FROM AUTHOR]

The Baixo Sabor hydroelectric scheme was recently constructed (began operating in 2015), blocking fish migration immediately at the river mouth. As a compensation measure for spawning habitat loss the Vilariça River which confluences with Sabor River, immediately downstream from the Baixo Sabor scheme, was chosen for rehabilitation site as an attempt to replace the spawning grounds lost in Sabor River for the potamodromous cyprinid Iberian barbel ( Luciobarbus bocagei ). Restoration activities included: placement of submerged weirs with fish ramps to increase the lotic/lentic sequence, bank reinforcement, boulder placement and river water profile increase. Water from the nearest reservoir was channeled underground to the lower Vilariça River in order to increase the water flow. The most appropriate volume of water was determined by means of a 1D model coupled with the CASiMiR to determine the weighted usable area for barbel spawners. Nine spawning grounds were identified. Fish migrations began in mid-April when water temperature increased (c. 16 °C) and water flow decreased. Barbel tend to spawn in coarse substrate with shallow water and moderate current. Ontogenetic differences in habitat use were reported, with barbel juveniles preferring weaker currents and deeper zones when compared to spawners. Females also display different preferences, which are more apparent after spawning. Both life-stages exhibit the maximum habitat suitability at c. 1.5 m 3 /s. The habitat model used in this study was able to accurately predict the occurrence of spawning grounds, representing, therefore, a valuable decision-making support tool for river managers. [ABSTRACT FROM AUTHOR]

The Red River originates in the U.S., drains into Lake Winnipeg, and is a significant pathway for nutrients. We investigate its role as a source for pesticides, pharmaceuticals, per - and polyfluoroalkyl substances (PFASs), and microbes bearing antibiotic resistance genes (ARGs). We delineate agricultural, urban, and rural land-use for organic contaminants to determine the extent of chemical transboundary riverine fluxes, and characterize levels and trends of organic contaminants and ARGs between spring and fall 2014 and 2015. The herbicide atrazine peaked at over 500 ng/L (14-day time-weighted average) near the border, indicating that the U.S. represents the major source into Canada from the Red River. Neonicotinoid insecticides had relatively constant concentrations, suggesting more widespread agricultural use in both countries. Pesticide concentrations were greatest post-application in June and July. Mass loadings of pesticides over the sampling periods, from the river to Lake Winnipeg, ranged from approximately 800 kg of atrazine, to 120 kg of thiamethoxam and clothianidin, to 40 kg of imidacloprid. Exposure distributions for atrazine exceeded benchmark water quality guidelines for protection of aquatic life (0.2% probability of exceeding chronic benchmark) with no exceedances for neonicotinoids. Seven pharmaceuticals were detected, mostly at low ng/L levels downstream of the City of Winnipeg wastewater treatment plant. Carbamazepine, the only pharmaceutical detected consistently at all sites, contributed on average 20 kg each year into Lake Winnipeg. While minor inputs were observed all along the river, city inputs represented the greatest source of pharmaceuticals to the river. Both PFASs and ARGs were observed consistently and ubiquitously, indicative of an anthropogenically-influenced system with no indications of any single point-source signature. While transboundary flux from the U.S. was an important source of pesticides to the Red River, especially for atrazine, observed concentrations of all measured contaminants suggest that known aquatic toxicological risk is minimal. [ABSTRACT FROM AUTHOR]

Besides gas-water-exchange in surface waters, respiratory consumption of dissolved oxygen (DO) in adjacent riparian groundwater may trigger the addition of so far hardly explored sources from the unsaturated zone. These processes also systematically influence stable isotope ratios of DO and were investigated together with Cl − as a conservative tracer for water mixing in a near-river riparian groundwater system. The study focused on a losing stream section of the Selke River at the foot of the Harz Mountains (Germany). The study area exposed steep DO gradients between the stream water and riparian groundwater between April 2016 and May 2017. Our results indicated dominant influences of microbial community respiration with observed DO concentration gradients. These observations can be explained by DO from the river that is subject to fractionation by microbial respiration with a typical fractionation factor (α r ) of 0.982. However, with such respiration dominance, we expected a simultaneous enrichment of δ 18 O DO towards values that are more positive than the well-known atmospheric O 2 signal of +23.9‰ versus the Vienna Standard Mean Ocean Water standard (VSMOW). Surprisingly, our measurements revealed much lower δ 18 O DO values between +22‰ and +18‰ in the near-river groundwater. Mass balance calculations revealed that the DO pool in the shallow and unconfined aquifer receives contributions of up to about 80% by diffusion of oxygen from the vadose zone with a distinctly lower isotope value than the one of the atmosphere. This finding about additional oxygen sources from the unsaturated zone has numerous ramifications for oxygen related processes in near-river environments including the oxidation of pollutants, nutrients and ecosystem health. [ABSTRACT FROM AUTHOR]

We investigated the concentrations of perfluoroalkyl substances (PFASs) and organophosphate flame retardants (OPFRs) in 44 tap water samples, collected from eight major cities in South Korea served by four representative watersheds, to evaluate the water contamination status. The total concentrations of PFASs and OPFRs ranged from 1.44 to 224 ng/L (median = 11.9 ng/L), and 74.0 to 342 ng/L (median = 151 ng/L), respectively. The predominant compounds in tap water were perfluorohexane sulfonate (PFHxS), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), tris(2-chloroethyl) phosphate (TCEP), tris(chloroisopropyl) phosphate (TCIPP), and tris(2-butoxyethyl) phosphate (TBOEP). Tap water originating from the Nakdong River within an industrial complex showed a notably higher PFHxS proportion to total PFASs. In addition, significantly higher PFAS levels were found in river-originating tap water than in lake/reservoir-originating tap water (Mann-Whitney U test, p < 0.05). Meanwhile, major OPFRs showed no clear difference in distribution by region, and no significant difference in major OPFR levels was observed according to tap water origin. Finally, the average human exposure via tap water consumption was estimated for PFASs (46.8 ng/person/day) and OPFRs (254 ng/person/day). [ABSTRACT FROM AUTHOR]

Understanding the mechanisms behind land–ocean sediment transport processes is crucial, due to the resulting impacts on the sustainable management of water and soil resources. This study investigated temporal trends and historical phases of sediment flux delivered to the sea by nine major rivers in China, while also quantifying the contribution of key anthropogenic and natural driving forces. During the past six decades, sediment flux from these nine major rivers exhibited a statistically significant negative trend, decreasing from 1.92 Gt yr −1 during 1954–1968 to 1.39 Gt yr −1 , 0.861 Gt yr −1 and 0.335 Gt yr −1 during 1969–1985, 1986–1999 and 2000–2016, respectively. We used a recently developed Sediment Identity approach and found that the sharp decrease in sediment load observed across China was mainly (~95%) caused by a reduction in sediment concentration. Reservoir construction exerted the strongest influence on land–ocean sediment fluxes, while soil conservation measures represented a secondary driver. Before 1999, soil erosion was not controlled effectively in China and reservoirs, especially large ones, played a dominant role in reducing riverine sediments. After 1999, soil erosion has gradually been brought under control across China, so that conservation measures directly accounted for ~40% of the observed decrease in riverine sediments. With intensifying human activities, it is predicted that the total sediment flux delivered to the sea by the nine major rivers will continue to decrease in the coming decades, although at a slower rate, resulting in severe challenges for the sustainable management of drainage basins and river deltas. [ABSTRACT FROM AUTHOR]

Reactive nitrogen (N) and phosphorus (P) inputs to surface waters modify aquatic environments, affect public health and recreation. Source controls dominate eutrophication management, whilst biological regulation of nutrients is largely neglected, although aquatic microbial organisms have huge potential to process nutrients. The stoichiometric ratio of organic carbon (OC) to N to P atoms should modulate heterotrophic pathways of aquatic nutrient processing, as high OC availability favours aquatic microbial processing. Heterotrophic microbial processing removes N by denitrification and captures N and P as organically-complexed, less eutrophying forms. With a global data synthesis, we show that the atomic ratios of bioavailable dissolved OC to either N or P in rivers with urban and agricultural land use are often distant from a “microbial optimum”. This OC-deficiency relative to high availabilities of N and P likely overwhelms within-river heterotrophic processing. We propose that the capability of streams and rivers to retain N and P may be improved by active stoichiometric rebalancing. Although autotrophic OC production contributes to heterotrophic rates substantial control on nutrient processing from allochthonous OC is documented for N and an emerging field for P. Hence, rebalancing should be done by reconnecting appropriate OC sources such as wetlands and riparian forests that have become disconnected from rivers concurrent with agriculture and urbanisation. However, key knowledge gaps require research prior to the safe implementation of this approach in management: (i) to evaluate system responses to catchment inputs of dissolved OC forms and amounts relative to internal production of autotrophic dissolved OC and aquatic and terrestrial particulate OC and (ii) evaluate risk factors in anoxia-mediated P desorption with elevated OC scenarios. Still, we find stoichiometric rebalancing through reconnecting landscape beneficial OC sources has considerable potential for river management to alleviate eutrophication, improve water quality and aquatic ecosystem health, if augmenting nutrient source control. [ABSTRACT FROM AUTHOR]

River water quality in rapidly urbanising Asian cities threatens to damage the resource base on which human health, economic growth and poverty reduction all depend. Dhaka reflects the challenges and opportunities for balancing these dynamic and complex trade-offs which goals can be achieved through effective policy interventions. There is a serious problem of water pollution in central Dhaka, in the Turag-Tongi-Balu River system in Bangladesh with the river system being one of the most polluted in the world at the moment. A baseline survey of water chemistry and total coliforms has been undertaken and shows dissolved oxygen close to zero in the dry season, high organic loading together with extreme levels of Ammonium-N and total coliform in the water. Models have been applied to assess hydrochemical processes in the river and evaluate alternative strategies for policy and the management of the pollution issues. In particular models of flow, Nitrate-N, Ammonium-N and indicator bacteria (total coliforms) are applied to simulate water quality in the river system. Various scenarios are explored to clean up the river system, including flow augmentation and improved effluent treatment. The model results indicate that improved effluent treatment is likely to have a more significant impact on reducing Ammonium-N and total coliforms than flow augmentation, but a combined strategy would greatly reduce the pollution problems in the Turag-Tongi-Balu River System. [ABSTRACT FROM AUTHOR]

In this study, the Li River and the middle-lower reaches of the Shaying River in the Shaying River basin were selected for an investigation on the effects of floodgates on macroinvertebrate communities; additionally, the relationships among floodgates, macroinvertebrate communities and river longitudinal connectivity were explored. The Li and Shaying rivers had similar ratios of molluscs and scrapers, but their species compositions were significantly different. The water level fluctuations in the Li River were based on natural hydrological characteristics, and these were very different from the fluctuations in the reaches of the Shaying River that were divided by a serious of floodgates. The effects of floodgates resulted in a reduction in the number of taxa, Shannon-Wiener index, Margalef index, and Fisher index and an increase in the Harrison index. The upper reaches of the Li and Saying rivers had similar macroinvertebrate communities, but these were very different from the lower reaches of the Saying River. The total number of species and the number of aquatic insect species increased with the river connectivity gradient and the variations in the α-diversity and β-diversity indices along reaches confirmed the hypothesis that the longitudinal connectivity of the Shaying River was significantly affected by floodgates. The results of Pearson and PLS tests showed that some plankton variables and physical water parameters could possibly describe how the gradient of river longitudinal connectivity was related to the floodgates in the Shaying River basin. The results of partial correlations showed, even when excluding the effects of water pollution, the protozoa richness and electrical conductivity still had significant influences on the distribution patterns of macroinvertebrate communities. When considering the results of correlation analyses and regression together, these same variables could be used to describe how the gradient of river longitudinal hydrological connectivity is related to floodgates in future studies. [ABSTRACT FROM AUTHOR]

Most of studies on sediment dynamics in stable shallow lakes focused on the resuspension process as it is the dominant process. However, understanding of sediment dynamics in a shallow lake influenced by flood pulse is unclear. We tested a hypothesis that floodplain vegetation plays as a significant role in lessening the intensity of resuspension process in a shallow lake characterized by the flood pulse system. Therefore, this study aimed to investigate sediment dynamics in this type of shallow lake. The target was Tonle Sap Lake (TSL), which is a large shallow lake influenced by a flood pulse system of Mekong River located in Southeast Asia. An extensive and seasonal sampling survey was conducted to measure total suspended solid (TSS) concentrations, sedimentation and resuspension rates in TSL and its 4 floodplain areas. The study revealed that sedimentation process was dominant (TSS ranged: 3–126 mg L −1 ) in the high water period (September–December) while resuspension process was dominant (TSS ranged: 4–652 mg L −1 ) only in the low water period (March–June). In addition, floodplain vegetation reduced the resuspension of sediment (up to 26.3%) in water. The implication of the study showed that resuspension is a seasonally dominant process in shallow lake influenced by the flood pulse system at least for the case of TSL. [ABSTRACT FROM AUTHOR]

We investigated the occurrence of metal-based nanoparticles in a natural system, the river Dommel in the Netherlands. The river itself is well-studied as far as hydrology and water quality is concerned, easily accessible and contains one major wastewater treatment plant discharging onto this river. We sampled water from various locations along the river and collected samples of influent, effluent and sewage sludge from the wastewater treatment plant. The sampling campaign was carried out in June 2015 and these samples were analysed for seven elements using high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS), ultrafiltration with a sequence of mesh sizes and scanning electron microscopy (SEM). From the results we conclude that there are indeed nanoparticles present in the treatment plant we studied, as we found titanium and gold particles in the influent and effluent. In the river water only 10 to 20% of the mass concentration of titanium, cerium and other elements we examined is made up of free, i.e. unattached, particles with a size smaller than 20 nm or of dissolved material. The rest is attached to natural colloids or is present as individual particles or clusters of smaller particles, as it could be filtered out with 450 nm ultrafilters. We found evidence that there is no appreciable anthropogenic emission of cerium into the river, based on the geochemical relationship between cerium and lanthanum. Besides, the effluent of the treatment plant has lower concentrations of some examined elements than the surface water upstream. The treatment plant discharges much less of these elements than estimated using previous publications. However, a potential diffuse source of titanium dioxide in the form of nanoparticles or of larger particles is their use in paints and coatings, as the concentration of titanium increased considerably in the urbanised area of the river Dommel. [ABSTRACT FROM AUTHOR]

Our study aimed to explore the effects of agriculture on the phosphorus buffer capacity of 11 headwater streams in Austria. We used phosphorus adsorption curves and re-suspension experiments to determine both, the potential of the sediments to act as phosphorus source or sink and the actual phosphorus exchange between water and sediments. Additionally, we determined the alkaline phosphatase activity (APA) in epilithic and epipsammic biofilms as indicator for the phosphorus demand of the benthic and hyporheic community. We hypothesized that highly polluted streams will show decreased phosphorus buffer capacities, which were either due to saturation or restricted water-sediment interactions. Our results support the second hypothesis. Fine sediment accumulations, organic matter content, and phosphorus concentrations in water and sediments increased with percent cropland in the catchment. Below SRP concentrations of 120 μg L −1 in the stream water, sediments showed a high potential for phosphorus release, with zero equilibrium phosphorus concentrations (EPC 0 ) being more than twice as high as SRP concentrations. Above 150 μg L −1 , EPC 0 reached only 20–50% of SRP concentrations, indicating a high potential of the sediments to act as phosphorus sinks. These findings were confirmed by phosphorus uptake of these sediments during re-suspension. While APA in epilithic biofilms decreased with increasing SRP concentrations, APA in epipsammic biofilms showed the reverse pattern, indicating a restricted phosphorus supply of the hyporheic community despite phosphorus surplus in the water column. Our study shows that inputs of fine sediments from agricultural sources may reduce the phosphorus buffering mechanism of stream sediments through restrictions of water-sediment interactions. Consequently, water column and sediment processes are increasingly decoupled and phosphorus-rich stream water will not effectively reach the reactive sites in the sediments responsible for uptake. Therefore, phosphorus mitigation measures in stream ecosystems must comprise sediment management in the catchment as well as in-stream measures for the rehabilitation of the hyporheic zone. [ABSTRACT FROM AUTHOR]

Large rivers cover and function over large spatial extents. Accordingly, the detailed assessment of their morphology is complex. Here, a methodology is presented to assess large rivers' morphology (LaRiMo) based on free datasets of geographic information systems. This approach could help to achieve a comparable, transboundary assessment of large river morphology to support the implementation of the European Water Framework Directive. The analyses are based on seven parameters describing processes and characteristics related to large river morphology. These parameters are evaluated for and compared between the rivers Danube, Elbe and Loire. A significantly higher amount of gravel and sand bars within the river bed strongly supported the overall higher morphological status of the Loire. A PCA highlighted that the parameters Wetlands, Active Riparian Zones and Free Flowing Sections similarly described a good morphological situation. In contrast, Canal, Dams and Impervious Surface indicated bad morphological conditions. Finally, the approach was successfully validated with data from a detailed, field-based morphological assessment for the Danube. LaRiMo represents an efficient and cost-effective approach to assess large river morphology across large extents. This method provides comparable results across countries and regions. [ABSTRACT FROM AUTHOR]