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Organic micropollutants enter rivers mainly with discharges of wastewater treatment plants (WWTP) and pose a risk to aquatic ecosystems and water quality. A considerable knowledge gap exists for disentangling overlapping processes and driving conditions that control the fate of these pollutants. Thus, the aim of this study was to identify the driving parameters for attenuation of selected pharmaceuticals (carbamazepine, diclofenac, tramadol and venlafaxine) under field conditions. The presented study was performed at a small river (Ammer River, mean discharge 0.87 m 3  s -1 ) which is hydrologically complex due to karstification, numerous artificial discharges, and engineered modifications of the channel. We applied a Lagrangian sampling scheme at two sequential river reaches. In general, for the investigated compounds and over the length of the tested reaches, the absolute net attenuation representative for 24 h was low (≤ 23% net attenuation), yet calculated half-lives were comparable to literature. Photodegradation is specifically relevant for the first river reach characterized by a higher net attenuation of the photosensitive compound diclofenac (14.5% ±11.3%) compared to the second section (9.8% ±13.7%). This is likely due to a spatial difference in canopy shading, which is supported by significant correlations (R 2  ≥ 0.8) of the temporally changing 'temperature' and 'solar radiation' with time-specific degradation rate constants of photosensitive compounds for consecutive hourly water parcels. In general, the presented spatially and temporally resolved approach is a suitable tool to determine the attenuation of organic micropollutants and to narrow down the interpretation of net attenuation to a few reasonable processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

Polycyclic Aromatic Hydrocarbons (PAH) ubiquitously occur in rivers and threaten the aquatic ecosystem. Understanding their fate and behaviour in rivers can help in improving management strategies. We develop a particle-facilitated transport model considering suspended sediments with sorbed PAH from different origins to investigate the turnover and legacy of sediment-bound PAH in the baseflow-dominated Ammer River in southwest Germany. Our model identifies the contributions of dissolved and particle-bound PAH during wet and dry periods to the annual load. The analysis of in-stream processes enables investigating the average turnover times of sediments and attached PAH for the main stem of the river. The legacy of sediment-bound PAH is studied by running the model assuming a 50% reduction in PAH emissions after the introduction of environmental regulation in the 1970s. Our results show that sediment-bound and dissolved PAH account for 75% and 25% of the annual PAH load, respectively. PAH are mainly emitted from urban areas that contribute over 74% to the total load. In steep reaches, the turnover times of sediments and attached PAH are similar, whereas they differ by 1-2 orders of magnitude in reaches with very mild slopes. Flow rates significantly affect PAH fluxes between the mobile water and the riverbed over the entire river. Total PAH fluxes from the river bed to the mobile water are simulated to occur when the discharge is larger than 5 m 3 s  -1 . River segments with large sediment storage show a potential of PAH legacy, which may have caused a PAH release over 10-20 years after the implementation of environmental regulation. This study is useful for assessing environmental impacts of PAH in rivers (e.g., their contribution to the river-water toxicity) and exemplifies that the longitudinal distribution, turnover, and legacy potential of PAH in a river system require a mechanistic understanding of river hydraulics and sediment transport., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Regular sediment inputs are required for deltas to maintain their surface elevation relative to sea level, which is important for avoiding salinization, erosion, and flooding. However, fluvial sediment inputs to deltas are being threatened by changes in upstream catchments due to climate and land use change and, particularly, reservoir construction. In this research, the global hydrogeomorphic model WBMsed is used to project and contrast 'pristine' (no anthropogenic impacts) and 'recent' historical fluvial sediment delivery to the Ganges-Brahmaputra-Meghna, Mahanadi, and Volta deltas. Additionally, 12 potential future scenarios of environmental change comprising combinations of four climate and three socioeconomic pathways, combined with a single construction timeline for future reservoirs, were simulated and analysed. The simulations of the Ganges-Brahmaputra-Meghna delta showed a large decrease in sediment flux over time, regardless of future scenario, from 669 Mt/a in a 'pristine' world, through 566 Mt/a in the 'recent' past, to 79-92 Mt/a by the end of the 21st century across the scenarios (total average decline of 88%). In contrast, for the Mahanadi delta the simulated sediment delivery increased between the 'pristine' and 'recent' past from 23 Mt/a to 40 Mt/a (+77%), and then decreased to 7-25 Mt/a by the end of the 21st century. The Volta delta shows a large decrease in sediment delivery historically, from 8 to 0.3 Mt/a (96%) between the 'pristine' and 'recent' past, however over the 21st century the sediment flux changes little and is predicted to vary between 0.2 and 0.4 Mt/a dependent on scenario. For the Volta delta, catchment management short of removing or re-engineering the Volta dam would have little effect, however without careful management of the upstream catchments these deltas may be unable to maintain their current elevation relative to sea level, suggesting increasing salinization, erosion, flood hazards, and adaptation demands., (Copyright © 2018 Elsevier B.V. All rights reserved.)

This work presents a post-event survey study, addressing the geomorphic response and large wood budget of two torrents, Grimmbach and Orlacher Bach, in southwestern Germany that were affected by a flash flood on May 29, 2016. During the event, large amounts of wood clogged and damaged a bridge of a cycling path at the outlet of the Grimmbach, while the town of Braunsbach was devastated by discharge and material transported along the Orlacher Bach. The severity of the event in these two small catchments (30.0 km 2 and 5.95 km 2 , respectively) is remarkable in basins with a relatively low average slope (10.7 and 12.0%, respectively). In order to gain a better understanding of the driving forces during this flood event an integrated approach was applied including (i) an estimate of peak discharges, (ii) an analysis of changes in channel width by comparing available aerial photographs before the flood with a post-flood aerial surveys with an Unmanned Aerial Vehicle and validation with field observations, (iii) a detailed mapping of landslides and analysis of their connectivity with the channel network and finally (iv) an analysis of the amounts of large wood recruited and deposited in the channel. The morphological changes in the channels can be explained by hydraulic parameters, such as stream power and unit stream power, and by morphological parameters such as the valley confinement. This is similar for LW recruitment amounts and volume of exported LW since most of it comes from the erosion of the valley floor. The morphological changes and large wood recruitment and deposit are in the range of studied mountain rivers. Both factors thus need to be considered for mapping and mitigating flash flood hazards also in this kind of low range mountains., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Metals are concerning pollutants in estuaries, where contamination can undergo significant remobilisation driven by physico-chemical forcing. Environmental concentrations of metals in estuarine sediments are often higher than natural backgrounds, but show no contiguity to potential sources. Thus, better understanding the metal mobility in estuaries is essential to improve identification of pollution sources and their accountability for environmental effects. This study aims to identify the key biogeochemical drivers of metal mobilisation on contaminated estuarine sediments through (1) evaluation of the potential mobilisation under controlled conditions, and (2) investigation of the relevance of metal mobilisation for in situ pollution levels in an area with multiple contaminant sources. Sediments from a saltmarsh adjacent to a coastal landfill, a marina, and a shipyard on the Thames Estuary (Essex, UK) were exposed in the laboratory (24h, N=96, 20°C) to water under various salinity, pH, and redox potential. Major cations, Fe(II), and trace metal concentrations were analysed in the leachate and sediment. Salinity, pH and redox had a significant effect on metal mobilisation (p<0.001), e.g. under certain conditions Fe(II) leaching was increased ~1000-fold. Measurements in situ of surface and subsurface sediment cores revealed that landfill proximity poorly explained metal spatial distribution. However, physicochemical parameters explained up to 97% of geochemically normalized metal concentrations in sediments. Organic matter and pH were dominant factors for most of the metal concentrations at the sediment surface. At subsurface, major cations (Ca, Na, Mg and K) were determinant predictors of metal concentrations. Applying the empirical model obtained in the laboratory to geochemical conditions of the studied saltmarsh it was possible to demonstrate that Fe mobilisation regulates the fate of this (and other) metal in that area. Thus, present results highlight the importance of metal mobility to control sediment pollution and estuarine fate of metals., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Metal pollution is a global problem in estuaries due to the legacy of historic contamination and currently increasing metal emissions. However, the establishment of water and sediment standards or management actions in brackish systems has been difficult because of the inherent transdisciplinary nature of estuarine processes. According to the European Commission, integrative comprehension of fate and effects of contaminants in different compartments of these transitional environments (estuarine sediment, water, biota) is still required to better establish, assess and monitor the good ecological status targeted by the Water Framework Directive. Thus, the present study proposes a holistic overview and conceptual model for the environmental fate of metals and their toxicity effects on aquatic organisms in estuaries. This includes the analysis and integration of biogeochemical processes and parameters, metal chemistry and organism physiology. Sources of particulate and dissolved metal, hydrodynamics, water chemistry, and mechanisms of toxicity are discussed jointly in a multidisciplinary manner. It is also hypothesized how these different drivers of metal behaviour might interact and affect metal concentrations in diverse media, and the knowledge gaps and remaining research challenges are pointed. Ultimately,estuarine physicochemical gradients, biogeochemical processes, and organism physiology are jointly coordinating the fate and potential effects of metals in estuaries, and both realistic model approaches and attempts.

Plastic litter accounts for 50-80% of waste items stranded on beaches, floating on the ocean surface and lodged in the seabed. Organic pollutants can be absorbed onto plastic particles from sea water, attached to their surfaces or included in the plastic matrix as additives. Such chemicals may be transported to remote regions by buoyant plastics and ocean currents. We have estimated mass fluxes of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and perfluorooctanoic acid (PFOA) to the Arctic via the main ocean currents and compared them to those in the dissolved state and in air. Substance fluxes with atmospheric or sea water currents account for several tons per year, whereas those mediated by plastics are four to six orders of magnitude smaller. However, the significance of various pollutant transport routes does not depend only on absolute mass fluxes but also on bioaccumulation in marine food chains., (Copyright © 2010 Elsevier Ltd. All rights reserved.)