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The spatio-temporal morphodynamics in relation to the fortnightly tidal variations and seasonal river discharge variations in a meandering estuarine channel were investigated. Intensive topographic surveys (longitudinal and transverse) every 3–4 months using a digital sonar system equipped with a differential global positioning system and continuous monitoring of salinity and turbidity with moored instruments were carried out during 2009–2012 in the upstream section of the highly turbid macrotidal Chikugo River estuary, Japan. The results revealed that the tidal flow dominated in the estuary for most of the year except for the rainy season in which river flow dominates. During the low flow season, tidally induced net upward sediment transport dominates and deposition takes place in the upstream section especially in the inner part of the meander. It contributes towards the strengthening of the existing estuarine turbidity maximum (ETM) in the upstream section of the estuary, and the channel capacity reduced gradually during this period. However, large flood events led to the breakdown of this ETM zone in the upstream during the rainy season and exported the sediments to the downstream tidal flat which resulted in the rapid increase of channel capacity. This further exhibited that the ETM zone was migrated to the downstream part of the estuary during the rainy season. There were significant differences in the seasonal trends of morphological evolution in the estuary which further greatly influenced the channel capacity. The drastic changes in channel morphology due to the sediment export by the high river flow during the flood season was approximately recovered through the sediment import by the fortnightly tidal cycle during the dry season over a seasonal basis. The study concludes that the morphological changes in the tide dominated estuaries are strongly influenced by the fortnightly tidal variations as well as the seasonal river discharge variations. Unlabelled Image • Morphological evolution in an estuary is influenced by the river and tidal forcing • There was significant difference in the seasonal trends of morphological evolution • Erosion and downward sediment export are dominant during the flood season • Net upward sediment transport and deposition are dominant during the dry season • Morphology of the meander maintained a dynamic equilibrium on a seasonal scale [ABSTRACT FROM AUTHOR]

The transport processes and fate of 137Cs in eastern Chinese seas (ECSs) that consists of the Bohai, Yellow, and East China Seas, have not been well established. In this study, we measured the concentrations of 137Cs in the ECSs water and surface sediments during 2013–2014. Combined with a number of published 137Cs inventory data from drainage basins and sediment accumulation rates in the ECSs, the distribution, sources and budgets of 137Cs in the ECSs were investigated. The 137Cs activity in the water column and surface sediments ranged from 0.03 to 1.92 Bq/m3 and from 0.30 to 5.22 Bq/kg, respectively. No 134Cs signal was observed, suggesting that the Fukushima accident had limited impact on the ECSs during the investigation period. Mass balance of 137Cs suggests that at least 7.4 × 1012 Bq/y of 137Cs imported into the ECSs from the Northwestern Pacific that accounts for 0.7% of the 137Cs transported by the Kuroshio Current, and this value is 5.2 times higher than the sum of atmospheric fallout and total riverine input. The apparent half-lives of 137Cs are estimated to be 15.1 y for the ECS and 7.7 y for the YS. The vertical profiles in the continental shelf edge and the Yangtze River Estuary reveal that the upwelling of the Kuroshio Subsurface Water is the main mechanism of 137Cs import into the ECSs. The high level of 137Cs in oceanic water masses and the low level of 137Cs in riverine and coastal waters make 137Cs a good indicator for tracing water mass movement and interaction. In addition, good correlation between 137Cs activity and mean grain size (φ) indicates that 137Cs can serve as an effective tracer to track dispersal pathways of fine sediments in river-dominated marginal seas. Unlabelled Image • The spatial distribution of 137Cs in surface sediments and seawater was investigated. • Oceanic inputs dominate the source of 137Cs in eastern Chinese seas. • The apparent half-lives of 137Cs are 7.7–15.1 y in eastern Chinese seas. • 137Cs is useful to track fine sediment transport in river-dominated marginal seas. • 137Cs is useful to trace water mass movement and exchange in marginal seas. [ABSTRACT FROM AUTHOR]

Abstract This study was aimed at untangling the relative impacts of successive phases of human modifications on changes in bedload transport along a 430 km-long river reach: the Rhône River from Motz dam to the sea. We used a 1D hydraulic model to solve for water lines across a range of discharges and all along the reach. Next, using grain sizes measured in the channel, we estimate flow competence and mean annual bedload transport capacities using the Recking (2013) bedload transport equation. In addition, we used the Generalized Threshold Model to estimate the relative fine and coarse fractions of the load. Bedload transport estimates were carried out under present-day hydraulic conditions and compared to estimates based on model runs simulating an unimpeded flow regime and using grain sizes measured in bars as a proxy for conditions prior to armouring. Our results show that present-day bedload transport along the Rhône is significantly fragmented by multiple closely spaced dams. Mean annual bedload capacity varies between 2500 and 16,300 m3/year over all the reaches, with an average of 4700 m3/year. Results of the GTM analysis suggest that this load is composed of 89% fines. We find bed sediment mobility to be very low in most reaches, and that potentially mobile sediments are finer than the median grain size in the riverbed even at high flows. Our results suggest that bedload capacities were 25–35 times higher prior to bed armouring and flow modifications; dams had an impact 2–3 times more important on transport capacities than channel embankments, and bed armouring was foremost a response to channel embankments. Based on an analysis of the ratio of sediment yields to transport capacities, we propose a conceptual scheme illustrating how bedload supply, channel morphology, and surface texture coevolved in the Rhône over the past century and half. Graphical abstract Unlabelled Image Highlights • Mean annual bedload capacity is 4700 m3/year with strong intra-reach variability. • Bed mobility is very low and the majority of transported sediments are fines. • Bedload transport rates were up to 35 times higher prior to embankments and dams. • Dams had an impact 2–3 greater than changes in grain-size on BL transport capacities. • The effects of successive dams show strong overlap. [ABSTRACT FROM AUTHOR]

Abstract Integrated models addressing microplastic (MP) generation, terrestrial distribution, and freshwater transport are useful tools characterizing the export of MP to marine waters. In Part I of this study, a baseline watershed-scale MP mass balance model was developed for tire and road wear particles (TRWP) in the Seine watershed. In Part II, uncertainty and sensitivity analysis (SA) methods were used to identify the parameters that determine the transport of these particles to the estuary. Local differential, local range and global first-order variance-based SA identified similar key parameters. The global SA (1000 Monte Carlo simulations) indicated that most of the variance in TRWP exported to the estuary can be apportioned to TRWP diameter (76%), TRWP density (5.6%), the fraction of TRWP directed to combined sewers with treatment (3.9%), and the fraction of TRWP distributed to runoff (versus roadside soil; 2.2%). The export fraction was relatively insensitive to heteroaggregation processes and the rainfall intensity threshold for road surface washoff. The fraction of TRWP exported to estuary in the probabilistic assessment was centered on the baseline estimate of 2%. This fraction ranged from 1.4 to 4.9% (central tendency defined as 25th to 75th percentile) and 0.97% to 13% (plausible upper bound defined as 10th to 90th percentiles). This study emphasizes the importance of in situ characterization of TRWP diameter and density, and confirms the baseline mass balance presented in Part I, which indicated an appreciable potential for capture of TRWP in freshwater sediment. Graphical abstract Unlabelled Image Highlights • Tire and road wear particles (TRWP) are a recognized microplastic (MP) material. • TRWP fate was assessed using integrated MP model described in Part I. • Local and global (probabilistic) sensitivity and uncertainty analyses were performed. • TRWP diameter and density are important determinants of estuarial export. • Central tendency of fraction of TRWP exported to estuary was between 1.4 and 4.9%. [ABSTRACT FROM AUTHOR]

Abstract In dual wave farms, i.e., arrays of wave energy converters (WECs) with a dual function – generation of renewable power and mitigation of coastal erosion – the spacing between the WECs is a fundamental design parameter. The present research has the objective of establishing how this parameter affects the shoreline evolution behind the array and, on this basis, to propose and apply a method to determine the optimum spacing for coastal protection. The method is demonstrated on a beach subjected to severe erosion. Five case studies are considered: four with different inter-WEC spacings, and one without the wave farm (baseline). A spectral wave propagation model is applied to analyse the variations in significant wave height behind the WEC array. Longshore sediment transport rates are calculated, and a shoreline model is applied. We find that in all the case studies the dry beach area is greater than in the baseline (no farm) case study, which proves the capacity of the dual WEC array to mitigate the erosive trends of the system. Importantly, we obtain that the inter-WEC spacing plays a fundamental role in the evolution of the shoreline and, consequently, in the effectiveness of the WEC array for coastal protection. The case studies with intermediate spacings yield the best performance in terms of dry beach area. More generally, the benefits of dual wave farms in terms of protection of coastal properties and infrastructure, and the ensuing savings in conventional coastal defence measures (coastal structures, beach nourishment, etc.) contribute to the development of wave energy by enhancing its economic viability. The methodology presented in this paper can be used to optimize the design of dual wave farms elsewhere. Graphical Abstract Highlights • Dual wave farms are proposed for carbon-free energy production and coastal defence. • Their coastal defence efficiency is investigated based on the shoreline evolution. • The spacing between wave energy converters plays a fundamental role. • We propose and apply a method to determine the optimum spacing for coastal defence. • Dual wave farms are shown to have potential as a tool for coastal erosion control. [ABSTRACT FROM AUTHOR]

Abstract For many years, scientists have tried to understand, describe and quantify water and sediment fluxes, with associated substances like pollutants, at multiple scales. In the past two decades, a new concept called connectivity has been used by Earth Scientists as a means to describe and quantify the influences on the fluxes of water and sediment on different scales: aggregate, pedon, location on the slope, slope, watershed, and basin. A better understanding of connectivity can enhance our comprehension of landscape processes and provide a basis for the development of better measurement and modelling approaches, further leading to a better potential for implementing this concept as a management tool. This paper provides a short review of the State-of-the-Art of the connectivity concept, from which we conclude that scientists have been struggling to find a way to quantify connectivity so far. We adapt the knowledge of connectivity to better understand and quantify water and sediment transfers in catchment systems. First, we introduce a new approach to the concept of connectivity to study water and sediment transfers and the associated substances. In this approach water and sediment dynamics are divided in two parts: the system consists of phases and fluxes, each being separately measurable. This approach enables us to: i) better conceptualize our understanding of system dynamics at different timescales, including long timescales; ii) identify the main parameters driving system dynamics, and devise monitoring strategies which capture them; and, iii) build models with a holistic approach to simulate system dynamics without excessive complexity. Secondly, we discuss the role of system boundaries in designing measurement schemes and models. Natural systems have boundaries within which sediment connectivity varies between phases; in (semi-)arid regions these boundaries can be far apart in time due to extreme events. External disturbances (eg. climate change, changed land management) can change these boundaries. It is therefore important to consider the system state as a whole, including its boundaries and internal dynamics, when designing and implementing comprehensive monitoring and modelling approaches. Connectivity is a useful tool concept for scientists that must be expanded to stakeholder and policymakers. Graphical abstract Unlabelled Image Highlights • We introduce a conceptual framework for modelling and measuring water and sediment fluxes. • System phases and fluxes are differentiated to enable quantification of connectivity. • The mutual benefits of combining modelling and measuring to understand connectivity is shown. • Necessary data for measuring and/or modelling water and sediment transfer is identified. [ABSTRACT FROM AUTHOR]

Abstract The physical sustainability of deltaic environments is very much dependent on the volume of water and sediment coming from upstream and the way these fluxes recirculate within the delta system. Based on several past studies, the combined mean annual sediment load of the Ganges-Brahmaputra-Meghna (GBM) systems has previously been estimated to vary from 1.0 to 2.4 BT/year which can be separated into components flowing from the Ganges (260 to 680 MT/year) and Brahmaputra (390 to 1160 MT/year). Due to very limited data and small contribution of the Meghna system (6–12 MT/year) to the total sediment flux of the GBM system, the data of the Meghna is not considered in the analysis assuming the sediment flux from GB system as the sediment flux of GBM. However, in this paper our analysis of sediment concentration data (1960–2008) collected by Bangladesh Water Development Board shows that the sediment flux is much lower: 150 to 590 MT/year for the Ganges versus 135 to 615 MT/year for the Brahmaputra, with an average total flux around 500 MT/year. Moreover, the new analysis provides a clear indication that the combined sediment flux delivered through these two major river systems is following a declining trend. In most of the planning documents in Bangladesh, the total sediment flux is assumed as a constant value of around 1 billion tons, while the present study indicates that the true value may be around 50% lower than this (with an average decreasing trend of around 10 MT/year). Graphical abstract Unlabelled Image Highlights • The temporal natural of the sediment flux in GBM delta has been explored. • Sediment flux to the GBM delta is not constant which is being considered in planning documents. • Sediment flux from the Ganges and Brahmaputra is decreasing due to multiple reasons. • The combined decrease in sediment from the Ganges and Brahmaputra is 10 MT/year. • Considering the sediment trend is vital for sustainable management of the GBM Delta. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Within the Oil-Sands industry in Alberta, Canada, tailings ponds are used as water recycling and tailings storage facilities (TSF) for mining activities. However, there could be possible circumstances under which a sudden breach of an embankment confining one of the TSFs may occur. Such a tailings pond breach would result in a sudden release of a huge volume of Oil Sands process-affected water (OSPW) and sediment slurry containing substantial amount of chemical constituents that would follow the downstream drainage paths and subsequently enter into the Lower Athabasca River (LAR). This study investigates the implications of OS tailings release on the water and sediment quality of the LAR by simulating the fate of sediment and associated chemicals corresponding to a hypothetical breach and release scenarios from a select set of tailings ponds using a two-dimensional hydrodynamic and constituent transport model. After predicting the total volume, time evolution and concentration of sediment and associated chemicals (metals, polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs)) reaching the LAR, the transport and deposition of these materials within the study reach is simulated. The results show that, depending on tailings release locations, between 40 and 70% of the sediment and associated chemicals get deposited onto the river bed of the 160 km study reach while the rest leaves the study domain during the first three days following the release event. These sediment/chemicals deposited during the initial spill may also have long-term effects on the water quality and aquatic ecosystem of the river and the downstream delta. However, care has to be taken in interpreting the results as further analysis has shown that the outcomes of such model simulations are very sensitive to the various underlying assumptions as well as the values assigned to some model parameters representing the physical properties of the tailings material. [ABSTRACT FROM AUTHOR]

The sediment load on the Chinese Loess Plateau has sharply decreased in recent years. However, the contribution of terrace construction and vegetation restoration projects to sediment discharge reduction remains uncertain. In this paper, eight catchments located in the Loess Plateau were chosen to explore the effects of different driving factors on sediment discharge changes during the period from the 1960s to 2012. Attribution approaches were applied to evaluate the effects of climate, terrace, and vegetation coverage changes on sediment discharge. The results showed that the annual sediment discharge decreased significantly in all catchments ranging from −0.007 to −0.039 Gt·yr −1 . Sediment discharge in most tributaries has shown abrupt changes since 1996, and the total sediment discharge was reduced by 60.1% during 1997–2012. We determined that increasing vegetation coverage was the primary factor driving the reductions in sediment loads since 1996 and accounted for 47.7% of the total reduction. Climate variability and terrace construction accounted for 9.1% and 18.6% of sediment discharge reductions, respectively. [ABSTRACT FROM AUTHOR]

Surface runoff has been recognized as an important medium of pesticides transport to surface water and groundwater causing critical risk to the aquatic ecosystem. Although total pesticide transport in surface runoff in most cases reported being below 1% of applied mass, much larger losses may occur in extreme cases. In this study, surface runoff potential of Imidacloprid and Clothianidin was investigated in an upland field with 5% slope under two simulated rainfall experiments of 70 mm/h intensity. Additionally, the downward movement of the pesticides was determined in soil ( n  = 87) taken at several depths on different time scales. The result showed that the second rainfall experiment caused more surface runoff than first rainfall experiment, and accounted 30.0 mm and 21.2 mm of applied rainfall, respectively. The cumulative surface runoff developed during first and second rainfall experiments was equal to 30% and 44% of the applied rainfall, respectively. The sediment transport in runoff was relatively higher in second rainfall than first rainfall, and was mostly stable after 30 min of rainfall. The chemical masses of Imidacloprid and Clothianidin were primarily transported in runoff sediments than runoff water and accounted for 10.8% and 7.93% of the applied mass, respectively. The transport of Imidacloprid both in runoff water and sediment was 1–2 times greater than that of Clothianidin. The concentrations of both pesticides were measured highest in the second fraction of runoff (10 min) collected during the first experiment. In soil, the transport of both pesticides prior to rainfall experiment was 1–2 times greater than post-rainfall experiments. The concentration of these pesticides decreased continuously with the time in the upper layer of soil; while a gradual increase of the pesticides mass was observed in the second soil layer. The cumulative mass transport of both pesticides was directly proportional to the cumulative runoff depth. [ABSTRACT FROM AUTHOR]

For wave energy to become a fully-fledged renewable and thus contribute to the much-needed decarbonisation of the energy mix, the effects of wave farms (arrays of wave energy converters) on coastal systems must be addressed. The objective of this work is to investigate the effects of wave farms on the longshore sediment transport and shoreline evolution of a gravel-dominated beach and, in particular, its sensitivity to the longshore position of the farm based on eight scenarios. Nearshore wave propagation patterns are computed by means of a spectral wave propagation model (SWAN), variations in sediment transport rates induced by the farm are calculated, and a one-line model is applied to determine the shoreline position and dry beach area. The significant wave height at breaking is reduced in the lee of the wave farm, dampening sediment transport. We find that changes in the dry beach area induced by the wave farm are highly sensitive to its alongshore position, and may result in: (i) erosion relative to the baseline scenario (without wave farm) in three of the eight scenarios, (ii) accretion in three other scenarios, and (iii) negligible effects in the remaining two. These results prove that the alongshore position of the wave farm controls the response of the beach to the extent that it may shift from accretionary to erosionary, and provide evidence of its effectiveness in countering erosion if appropriately positioned. This effectiveness opens up the possibility of using wave farms not only to generate carbon-free energy but also to manage coastal erosion, thus strengthening the case for the development of wave energy. [ABSTRACT FROM AUTHOR]

Tidal marshes are both important sites of in situ methylmercury production and can be landscape sources of methylmercury to adjacent estuarine systems. As part of a regional investigation of the Hg-contaminated Penobscot River and Bay system, the tidal fluxes of total suspended solids, total mercury and methylmercury into and out of a regionally important mesohaline fluvial marsh complex, Mendall Marsh, were intensively measured over several tidal cycles and at two spatial scales to assess the source-sink function of the marsh with respect to the Penobscot River. Over four tidal cycles on the South Marsh River, the main channel through which water enters and exits Mendall Marsh, the marsh was a consistent sink over typical 12-h tidal cycles for total suspended solids (8.2 to 41 g m −2 ), total Hg (9.2 to 47 μg m −2 ), total filter-passing Hg (0.4 to 1.1 μg m −2 ), and total methylmercury (0.2 to 1.4 μg m −2 ). The marsh's source-sink function was variable for filter-passing methylmercury, acting as a net source during a large spring tide that inundated much of the marsh area and that is likely to occur during approximately 17% of tidal cycles. Additional measurements on a small tidal channel draining approximately 1% of the larger marsh area supported findings at the larger scale, but differences in the flux magnitude of filter-passing fractions suggest a highly non-conservative transport of these fractions through the tidal channels. Overall the results of this investigation demonstrate that Mendall Marsh is not a significant source of mercury or methylmercury to the receiving aquatic systems (Penobscot River and Bay). While there is evidence of a small net export of filter-passing (<0.4 μm pore size) methylmercury under some tidal conditions, the mass involved represents <3% of the mass of filter-passing methylmercury carried by the Penobscot River. [ABSTRACT FROM AUTHOR]

The mercury contaminated upper Penobscot Estuary in Maine provided a unique opportunity to rigorously examine the effect of sediment type and particle size on mercury concentrations in sediments, and to explain why sediments at different locations in the estuary had different mercury concentrations. This is because the Penobscot Estuary contains a large, well-mixed pool of mobile sediments of many different types (muds, sand, gravel, wood chips), which are the source of material for the permanently deposited surface sediments. Despite this mixing, average surface sediment mercury concentrations were very different in different locations, ranging from 238 ng/gdw to 1032 ng/gdw in the 11 subareas studied. Average total mercury concentrations were highly related to the type of sediment (wood chips > muds > sands) regardless of location in the estuary. The characteristics in both mobile and surface sediments that were positively related to total mercury concentrations were % organic matter (measured as loss on ignition) and %fines (measured usually as <62.5 μ). Also, in a subset of samples it was shown that mercury was positively associated only with the very finest (<44 μ) particles. Thus, side embayments of the estuary such as the Orland River and Mendall Marsh, which experience lower velocity currents and so accumulate more fine particles, tended to be much higher in mercury concentrations. This knowledge will be important in managing remediation of this system, as fine particles can be the most difficult to trap or to retain if dredging is employed. Methyl mercury was well correlated with total mercury and so its distribution would also be affected by transport characteristics. This was the case even in the mobile sediments, which were more oxic and not expected to provide a good habitat for methylation. [ABSTRACT FROM AUTHOR]

The impacts of wave farms (arrays of wave energy converters, or WECs) on the nearshore must be fully understood for wave technology to develop and thus contribute to a sustainable, carbon-free energy mix in the near future. The objective of this work is to investigate the role played by the farm layout on the wave propagation patterns leewards and the implications for longshore sediment transport (LST) and shoreline evolution on a gravel-dominated deltaic coast. Changes in wave propagation in four scenarios, corresponding to as many wave farm layouts, are computed by means of a spectral numerical model (Delft3D-WAVE) under (i) low-energy and storm conditions, and (ii) westerly and easterly waves - the two prevailing wave directions. On this basis, sediment transport rates are computed and changes in the shoreline position assessed using a one-line model. To quantify the impact of the wave farm on the nearshore wave conditions, sediment transport and shoreline, we define three ad hoc indicators: the non-dimensional wave height reduction, the non-dimensional LST rate reduction and the non-dimensional shoreline advance. Significant wave heights decrease in the lee of the wave farm, with the consequent reduction in LST rates. As a result, the dry beach area increases in every scenario under both westerly and easterly waves. We find that case studies with the WECs arranged on fewer rows but covering a greater stretch of coastline provide better coastal protection. These results confirm that wave farms can be used not only to generate carbon-free energy but also to protect gravel-dominated coasts. [ABSTRACT FROM AUTHOR]

Prescribed fire is a common management practice in Mediterranean region to reduce the amount of fuel and to decrease the wildfire risk. The objective of this study is to assess the effect of a prescribed fire on some soil properties, hydrological response and vegetation recovery in experimental plots 5 years after. The results showed that: i) with the exception of electrical conductivity, the prescribed fire did not affect the analyzed soil properties, and ii) overland flow and sediment transport were increased during the first two years, returning to levels pre-fire, 5 years post-fire. The rainfall threshold for overland flow generation was lower during the following months after the prescribed fire owing to the depletion of the vegetation cover. Immediately after the fire, the vegetation cover was of 1.9%, being the three main soil surface components that dominated the hydrological response: charcoal and decayed wood; blackish and greyish ash, and bare soil. However, these areas decreased very rapidly during the second year following the fire, principally, owing to the regrowth of herbaceous plants and shrubs. In addition, the vegetation cover in burned plots was 16.1% higher than that measured in the unburned ones. Overall, the prescribed fire only had an impact on runoff and sediment transport in the two years post-fire, as consequence of vegetation removal. [ABSTRACT FROM AUTHOR]

Marine eutrophication in the North-East Atlantic (NEA) strongly relies on nutrient enrichment at the river outlets, which is linked to human activities and land use in the watersheds. The question is whether human society can reduce its nutrient emissions by changing land use without compromising food security. A new version of Riverstrahler model (pyNuts-Riverstrahler) was designed to estimate the point and diffuse nutrient emissions (N, P, Si) to the rivers depending on land use in the watersheds across a large domain (Western Europe agro-food systems, waste water treatment). The loads from the river model have been used as inputs to three marine ecological models (PCOMS, ECO-MARS3D, MIRO&CO) covering together a large part of the NEA from the Iberian shelf to the Southern North Sea. The modelling of the land-ocean continuum allowed quantifying the impact of changes in land use on marine eutrophication. Pristine conditions were tested to scale the current eutrophication with respect to a “natural background” (sensu WFD), i.e. forested watersheds without any anthropogenic impact. Three scenarios representing potential management options were also tested to propose future perspectives in mitigating eutrophication. This study shows that a significant decrease in nitrogen fluxes from land to sea is possible by adapting human activities in the watersheds, preventing part of the eutrophication symptoms in the NEA rivers and adjacent coastal zones. It is also shown that any significant achievement in that direction would very likely require paradigmatic changes at social, economic and agricultural levels. This requires reshaping the connections between crop production and livestock farming, and between agriculture and local human food consumption. It also involves cultural changes such as less waste production and a shift towards lower-impact and healthier diets where half of the animal products consumption is replaced by vegetal proteins consumption, known as a demitarian diet ( http://www.nine-esf.org/node/281/index.html ). [ABSTRACT FROM AUTHOR]

A watershed model was developed using the Soil and Water Assessment Tool (SWAT) that simulates nitrogen, phosphorus, and sediment loadings in the Lower Mississippi River Basin (LMRB). The LMRB SWAT model was calibrated and validated using 21 years of observed flow, sediment, and water-quality data. The baseline model results indicate that agricultural lands within the Lower Mississippi River Basin (LMRB) are the dominant sources of nitrogen and phosphorus discharging into the Gulf of Mexico. The model was further used to evaluate the impact of biomass production, in the presence of riparian buffers in the LMRB, on suspended-sediment and nutrient loading discharge from the Mississippi River into the Gulf of Mexico. The interplay among land use, riparian buffers, crop type, land slope, water quality, and hydrology were anlyzed at various scales. Implementing a riparian buffer in the dominant agricultural region within the LMRB could reduce suspended sediment, nitrogen, and phosphorus loadings at the regional scale by up to 65%, 38%, and 39%, respectively. Implementation of this land management practice can reduce the suspended-sediment content and improve the water quality of the discharge from the LMRB into the Gulf of Mexico and support the potential production of bioenergy and bio-products within the Mississippi River Basin. [ABSTRACT FROM AUTHOR]

Mercury (Hg) was discharged in the late 1960s into the Penobscot River by the Holtra-Chem chlor-alkali production facility, which was in operation from 1967 to 2000. To assess the transport and distribution of total Hg, and recovery of the river and estuary system from Hg pollution, physical and radiochemical data were assembled from sediment cores collected from 58 of 72 coring stations sampled in 2009. These stations were located throughout the lower Penobscot River, and included four principal study regions, the Penobscot River (PBR), Mendall Marsh (MM), the Orland River (OR), and the Penobscot estuary (ES). To provide the geochronology required to evaluate sedimentary total Hg profiles, 58 of 72 sediment cores were dated using the atmospheric radionuclide tracers 137 Cs, 210 Pb, and 239,240 Pu. Sediment cores were assessed for depths of mixing, and for the determination of sediment accumulation rates using both geochemical (total Hg) and radiochemical data. At most stations, evidence for significant vertical mixing, derived from profiles of 7 Be (where possible) and porosity, was restricted to the upper ~1–3 cm. Thus, historic profiles of both total Hg and radionuclides were only minimally distorted, allowing a reconstruction of their depositional history. The pulse input tracers 137 Cs and 239,240 Pu used to assess sediment accumulation rates agreed well, while the steady state tracer 210 Pb exhibited weaker agreement, likely due to irregular lateral sediment inputs. [ABSTRACT FROM AUTHOR]

The aim of the current study was to produce groundwater spring potential maps using novel ensemble weights-of-evidence (WoE) with logistic regression (LR) and functional tree (FT) models. First, a total of 66 springs were identified by field surveys, out of which 70% of the spring locations were used for training the models and 30% of the spring locations were employed for the validation process. Second, a total of 14 affecting factors including aspect, altitude, slope, plan curvature, profile curvature, stream power index (SPI), topographic wetness index (TWI), sediment transport index (STI), lithology, normalized difference vegetation index (NDVI), land use, soil, distance to roads, and distance to streams was used to analyze the spatial relationship between these affecting factors and spring occurrences. Multicollinearity analysis and feature selection of the correlation attribute evaluation (CAE) method were employed to optimize the affecting factors. Subsequently, the novel ensembles of the WoE, LR, and FT models were constructed using the training dataset. Finally, the receiver operating characteristic (ROC) curves, standard error, confidence interval ( CI ) at 95%, and significance level P were employed to validate and compare the performance of three models. Overall, all three models performed well for groundwater spring potential evaluation. The prediction capability of the FT model, with the highest AUC values, the smallest standard errors, the narrowest CI s, and the smallest P values for the training and validation datasets, is better compared to those of other models. The groundwater spring potential maps can be adopted for the management of water resources and land use by planners and engineers. [ABSTRACT FROM AUTHOR]

Fine particles or sediments have various effects on water quality and aquatic ecosystems. Thus, understanding the dynamics of these fine particles between water body and stream bed is an important issue in sediment research. Previous studies and analysis of empirical data suggest that fine particles are stored in the sediment bed in the low flow regime, where flow rate is smaller than the critical flow rate that mobilizes the sediment bed. These fine particles are re-suspended during flood events when the flow rate becomes larger than the critical flow rate that mobilizes bed material. The transition from pattern recognition to process analysis required incorporation of the dominant processes controlling fine particle dynamics within gravel-bedded streams into a model. The process analysis was performed using continuous flow and turbidity data at two locations on the Russian River in California to test process descriptions and then calibrate a quantitative model to represent those processes. The resulting process model coupled fine particle retention within the sediment bed by filtration and sedimentation with the release of accumulated fine particles in response to flood events. Model parameters, such as the critical flow rate required for initiating sediment bed fluidization, the maximum fine particle storage capacity within the sediment bed, and background particle concentration for the watershed, were estimated from the monitoring data. Model calibration optimized the filtration and the sediment bed fluidization parameters over two or three years of data. Overall, the difference between modeled and observed fine particle mass released from the sediment bed was within 20% of the measured mass. [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]

Pollutants' dynamics in rivers flowing through industrial areas is linked to the entrainment and transport of contaminants attached to solid particles. The transport of sediment is mainly associated to high discharges and flood episodes, and these events constitute one of the main factors causing fluxes of buried pollutants in rivers. We performed a field study in the lower River Cinca (Ebro basin, Northeast Spain) to quantify the mobilization and transfer of several contaminants present in the river bed sediments. We focused on contaminants previously identified (PCBs, DDXs, PBDEs, HBCDs and PFRs) to occur in the river. River bed sediment samples were collected during low flows and a subsequent sampling campaign was used to capture sediment borne contaminants during a flood event. Water samples were taken at the same locations as the static sediment samples and used to determine the suspended sediment concentrations and the contaminants content (i.e. mass of contaminant per sediment mass unit) during the event. We estimated mass fluxes for both sediment and pollutants, and determined that sediment transport followed a clockwise hysteresis. This is typically observed in high flow events after dry summer periods. With sediments there was a large mobilization of PFRs (36 kg in 48 h in one of the main tributaries) and PCBs not previously observed in the static sediment. Observed contaminant load ranges during the two-day sampling campaign were: PCB (34–152 g), DDT (12–213 g), PBDE (50–1740 g), HBCD (0–2.2 g) and PFR (2410–35,895 g). An environmental risk assessment was carried out by comparing the pollutant concentrations found in the sediments with the Canadian quality guidelines (ISQC), showing a significant noncompliance for PCBs in dynamic sediments. Our results point out to the need of a regular assessment of the downstream transfer of the sediment-borne pollutants in drainage basins historically affected by intense industrial activities and associated contamination. [ABSTRACT FROM AUTHOR]

Bitumen-bearing suspended sediment (SS) eroded from the McMurray Formation (MF) are fine grained (silts and clays) and coated with natural hydrophobic oils. This results in poor settling and long range transport of associated contaminants. There was a longitudinal increase in polycyclic aromatic compound (PAC) concentrations for rivers that erode the MF from upstream to downstream regardless of time-of-year, while loads were substantially increased during high flow periods when the erosive forces are the greatest and the overland flow contribution is high. Within the MF, variation in PAC contributions is seen by the Ells River having higher loads than the Steepbank River. Using the Ells and Steepbank as examples, double plot PACs ratios suggest that the PAC concentrations and signatures vary spatially within the MF but that the weathering processes may be the same. Plots of the various homologs of PACs generally illustrated a normal distribution which suggests petrogenic origins. However, several PAC ratios suggested that both the parent material and the SS are pyrogenic in nature. While it is likely that some level of atmospheric deposition (anthropogenic or from forest fire) is incorporated into the SS of the rivers, it is likely to be limited relative to the proportion of naturally eroded MF sediments. Additional analysis will be needed to distinguish the relative risk of both anthropogenic (e.g., industrial operations) and natural sources (bitumen deposits, forest fire) of PACs to the SS and to long-range depositional environments, as they may have potential aquatic ecological effects. [ABSTRACT FROM AUTHOR]

Two decades after the construction of the first major dam, the Mekong basin and its six riparian countries have seen rapid economic growth and development of the river system. Hydropower dams, aggregate mines, flood-control dykes, and groundwater-irrigated agriculture have all provided short-term economic benefits throughout the basin. However, it is becoming evident that anthropic changes are significantly affecting the natural functioning of the river and its floodplains. We now ask if these changes are risking major adverse impacts for the 70 million people living in the Mekong Basin. Many livelihoods in the basin depend on ecosystem services that will be strongly impacted by alterations of the sediment transport processes that drive river and delta morpho-dynamics, which underpin a sustainable future for the Mekong basin and Delta. Drawing upon ongoing and recently published research, we provide an overview of key drivers of change (hydropower development, sand mining, dyking and water infrastructures, climate change, and accelerated subsidence from pumping) for the Mekong's sediment budget, and their likely individual and cumulative impacts on the river system. Our results quantify the degree to which the Mekong delta, which receives the impacts from the entire connected river basin, is increasingly vulnerable in the face of declining sediment loads, rising seas and subsiding land. Without concerted action, it is likely that nearly half of the Delta's land surface will be below sea level by 2100, with the remaining areas impacted by salinization and frequent flooding. The threat to the Delta can be understood only in the context of processes in the entire river basin. The Mekong River case can serve to raise awareness of how the connected functions of river systems in general depend on undisturbed sediment transport, thereby informing planning for other large river basins currently embarking on rapid economic development. [ABSTRACT FROM AUTHOR]

The effects of climate change on sediment yield and transport dynamics in cold climate regions are not well understood or reported. In this study, the Soil and Water Assessment Tool (SWAT) has been built-up, calibrated, and validated against streamflow and sediment load at several monitoring stations in a cold climate region watershed - the Athabasca River Basin (ARB) in Alberta, Canada. The model was then fed with bias-corrected spatial disaggregated high-resolution (~ 10 km) future climate data from three climate models for two emission scenarios (RCP 4.5 and 8.5), and two periods (mid- and end-century). Results show that channel erosion and deposition are the dominant processes over hill slope erosion in the basin. On average, a predicted warmer and wetter future climate has both synergetic and offsetting effects on sediment yield. Changes are sub-region specific and land-use type dependent, thus reflecting a marked spatial and temporal heterogeneity within the basin. Increases on sediment yield in future periods in the agricultural areas are up to 0.94 t/ha/yr, and are greater than reported soil formation rates in the region. Similarly, while substantial increases (by more than two fold) in the sediment load transport through the river reaches were obtained, the changes show both temporal and spatial variability, and are closely aligned with the trend of stream flows. We believe that availability of such models and knowledge of the effect of future climatic conditions would help water managers formulate appropriate scenarios to manage such basins in a holistic way. However, significant uncertainties in future sediment yield and transport, as a result of variations in climatic forcing of different climate models, need to be considered in any adaptation measures. [ABSTRACT FROM AUTHOR]

Derived from river monitoring data, concentration-discharge ( C-Q ) relationships are useful indicators of riverine export dynamics. A top-down synthesis of C-Q patterns was conducted for suspended sediment (SS), total phosphorus (TP), and total nitrogen (TN) for nine major tributaries (15 monitoring sites) to Chesapeake Bay, which represent diverse characteristics in terms of land use, physiography, and hydrological settings. Model coefficients from the recently-developed Weighted Regressions on Time, Discharge, and Season (WRTDS) method were used to make informative interpretation of C-Q relationships. Unlike many previous C-Q studies that focused on stormflow conditions, this approach allows simultaneous examination of various discharge conditions within an uncertainty framework. This synthesis on WRTDS coefficients ( i.e. , the sensitivity of concentration to discharge) has offered new insights on the complexity of watershed function. Results show that watershed export has been dominated by mobilization patterns for SS and TP (particulate-dominated species) and chemostasis patterns for TN (dissolved-dominated species) under many river discharge conditions. Among nine possible modalities of low-flow vs. high-flow patterns, the three most frequent modalities are mobilization vs . mobilization (17 cases), chemostasis vs . mobilization (13 cases), and chemostasis vs . chemostasis (7 cases), representing 82% of all 45 watershed-constituent pairs. The general lack of dilution patterns may suggest that none of these constituents has been supply-limited in these watersheds. For many watershed-constituent combinations, results show clear temporal non-stationarity in C-Q relationships under selected time-invariant discharges, reflecting major changes in dominant watershed sources due to anthropogenic actions. These results highlight the potential pitfalls of assuming fixed C-Q relationships in the record. Overall, this work demonstrates the utility of WRTDS model coefficients for interpretation of river water-quality data and for generation of sensible hypotheses on dominant processes in different watersheds. The approach is readily adaptable to other river systems, where long-term discretely-sampled data are available, to decipher complex interactions between hydrological and biogeochemical processes. [ABSTRACT FROM AUTHOR]

Land degradation is a problem affecting the sustainability of commercial forest plantations. The identification of critical areas prone to erosion can assist this activity to better target soil conservation efforts. Here we present the first use of the carbon-13 signatures of fatty acids (C14 to C24) in soil samples for spatial and temporal tracing of sediment transport in river bodies of upland commercial forest catchments in Chile. This compound-specific stable isotope (CSSI) technique was tested as a fingerprinting approach to determine the degree of soil erosion in pre-harvested forest catchments with surface areas ranging from 12 to 40 ha. For soil apportionment a mixing model based on a Bayesian inference framework was used (CSSIAR v.2.0). Approximately four potential sediment sources were used for the calculations of all of the selected catchments. Unpaved forestry roads were shown to be the main source of sediment deposited at the outlet of the catchments (30–75%). Furthermore, sampling along the stream channel demonstrated that sediments were mainly comprised of sediment coming from the unpaved roads in the upper part of the catchments (74–98%). From this it was possible to identify the location and type of primary land use contributing to the sediment delivered at the outlet of the catchments. The derived information will allow management to focus efforts to control or mitigate soil erosion by improving the runoff features of the forest roads. The use of this CSSI technique has a high potential to help forestry managers and decision makers to evaluate and mitigate sources of soil erosion in upland forest catchments. It is important to highlight that this technique can also be a good complement to other soil erosion assessment and geological fingerprinting techniques, especially when attempting to quantify (sediment loads) and differentiate which type of land use most contributes to sediment accumulation. [ABSTRACT FROM AUTHOR]

Many deltas across the globe are retreating, and nearby beaches are undergoing strong erosion as a result. Among soft and prompt solutions, nourishments are the most heavily used. This paper presents an integrated methodology to forecast the efficiency of nourishment strategies by means of wave climate simulations, wave propagations with downscaling techniques, computation of longshore sediment transport rates and application of the one-line model. It was applied to an eroding deltaic beach (Guadalfeo, southern Spain), where different scenarios as a function of the nourished coastline morphology, input volume and grain size were tested. For that, the evolution of six scenarios of coastline geometry over a two-year period (lifetime of nourishment projects at the study site) was modelled and the uncertainty of the predictions was also quantified through Monte Carlo techniques. For the most efficient coastline shape in terms of gained dry beach area, eight sub-scenarios with different nourished volumes were defined and modelled. The results indicate that an input volume around 460,000 m 3 is the best strategy since nourished morphologies with higher volumes are more exposed to the prevailing storm directions, inducing less efficient responses. After setting the optimum coastline morphology and input sediment volume, eleven different nourished grain sizes were modelled; the most efficient coastline responses were obtained for sediment sizes greater than 0.01 m. The availability of these sizes in the sediment accumulated upstream of a dam in the Guadalfeo River basin allows for the conclusion that this alternative would not only mitigate coastal erosion problems but also sedimentation issues in the reservoir. The methodology proposed in this work is extensible to other coastal areas across the world and can be helpful to support the decision-making process of artificial nourishment projects and other environmental management strategies. [ABSTRACT FROM AUTHOR]

Sediment transfer patterns during snowmelt were studied in a small Finnish agricultural watershed. Erosion rates were high as a consequence of high runoff volumes over saturated soil that partly lacked vegetation cover. Automatic high-frequency monitoring data of sediment and phosphorus concentrations in stream showed a clock-wise hysteresis loop as a dominant pattern. GIS-based modeling of runoff and soil erosion, using LiDAR DTM data, suggested that runoff and erosion mostly came from cropland that had the highest sediment contribution index. Also sediment fingerprinting with Cesium-137 suggested cropland and stream bank were the most important sources of suspended sediments in streams. Because a major part of annual sediment transfer takes place during snowmelt, it is a critical period for annual losses of pollutants. Management practices that minimize springtime sediment and pollutant losses from cropland would be needed to make a marked impact on annual pollution transfer to stream waters. [ABSTRACT FROM AUTHOR]

The natural recovery of estuaries from contamination is largely determined by the timescale over which contaminated sediment is exported or buried and replaced by cleaner sediment that enters from the watershed or the ocean. That timescale depends on the size of the “pool” of contaminated sediment that resides in the estuary. The larger the pool, the longer the recovery timescale for a given rate of sediment input. A field study was undertaken as part of a study of mercury contamination in the Penobscot estuary to assess the mechanisms affecting the transport and fate of contaminated sediment. Based on measurements of water properties, currents and sediment transport and seabed samples analyzed for sediment properties and contaminant concentrations, a “mobile pool” of contaminated sediment with relatively uniform geochemical characteristics along a 20-km reach of the estuary was identified. This pool of sediment is mobilized seasonally by resuspension and trapping processes associated with salinity fronts that vary in location with discharge conditions. Sediment is transported down-estuary during high discharge and up-estuary during low discharge, with seasonal, bi-directional transport of sediment in the estuary significantly exceeding the annual input of new sediment from the watershed. This continual, bi-directional transport leads to homogenization of the chemical properties of the mobile sediment, including contaminant concentrations. The large mass of mobile sediment relative to the input of sediment from the watershed helps explain the long recovery timescale of contaminants in the Penobscot estuary. [ABSTRACT FROM AUTHOR]

Extreme floods are regarded as one of the most catastrophic natural hazards and can result in significant morphological changes induced by pronounced sediment erosion and deposition processes over the landscape. However, the effects of extreme floods of different return intervals on the floodplain and river channel morphological evolution with the associated sediment transport processes are not well explored. Furthermore, different basin management action plans, such as engineering structure modifications, may also greatly affect the flood inundation, sediment transport, solute transport and morphological processes within extreme flood events. In this study, a coupled two-dimensional hydrodynamic, sediment transport and morphological model is applied to evaluate the impact of different river and basin management strategies on the flood inundation, sediment transport dynamics and morphological changes within extreme flood events of different magnitudes. The 10-year, 50-year, 100-year and 200-year floods are evaluated for the Lower Cache Creek system in California under existing condition and a potential future modification scenario. Modeling results showed that select locations of flood inundation within the study area tend to experience larger inundation depth and more sediment is likely to be trapped in the study area under potential modification scenario. The proposed two dimensional flow and sediment transport modeling approach implemented with a variety of inflow conditions can provide guidance to decision-makers when considering implementation of potential modification plans, especially as they relate to competing management strategies of large water bodies, such as the modeling area in this study. [ABSTRACT FROM AUTHOR]

Aggregate breakdown influences the availability of soil particles for size-selective sediment transport with surface runoff during erosive rainfall events. Organic matter management is known to affect aggregate stability against breakdown, but little is known about how this translates into rainfall-induced aggregate fragmentation and sediment transport under field conditions. In this study, we performed field experiments in which artificial rainfall was applied after pre-wetting on three pairs of arable soil plots (1.5 × 0.75 m) six weeks after incorporating a mixture of grass and wheat straw into the topsoil of one plot in each pair (OI treatment) but not on the other plot (NI treatment). Artificial rainfall was applied for approximately 2 h on each pair at an intensity of 49.1 mm h − 1 . In both treatments, discharge and sediment concentration in the discharge were correlated and followed a similar temporal pattern after the onset of surface runoff: After a sharp increase at the beginning both approached a steady state. But the onset of runoff was more delayed on the OI plots, and the discharge and sediment concentration were in average only roughly half as high on the OI as on the NI plots. With increasing discharge the fraction of coarse sediment increased. This relationship did not differ between the two treatments. Thus, due to the lower discharge, the fraction of fine particles in the exported sediment was larger in the runoff from the OI plots than from the NI plots. The later runoff onset and lower discharge rate was related to a higher initial aggregate stability on the OI plots. Terrestrial laser scanning proved to be a very valuable method to map changes in the micro-topography of the soil surfaces. It revealed a much less profound decrease in surface roughness on the OI than on the NI plots. [ABSTRACT FROM AUTHOR]

Landscape Evolution Modelling (LEM) technologies provide a means by which it is possible to simulate the long-term geomorphic stability of a conceptual rehabilitated landform. However, simulations rarely consider the potential effects of anthropogenic climate change and consequently risk not accounting for the range of rainfall variability that might be expected in both the near and far future. One issue is that high resolution (both spatial and temporal) rainfall projections incorporating the potential effects of greenhouse forcing are required as input. However, projections of rainfall change are still highly uncertain for many regions, particularly at sub annual/seasonal scales. This is the case for northern Australia, where a decrease or an increase in rainfall post 2030 is considered equally likely based on climate model simulations. The aim of this study is therefore to investigate a spatial analogue approach to develop point scale hourly rainfall scenarios to be used as input to the CAESAR - Lisflood LEM to test the sensitivity of the geomorphic stability of a conceptual rehabilitated landform to potential changes in climate. Importantly, the scenarios incorporate the range of projected potential increase/decrease in rainfall for northern Australia and capture the expected envelope of erosion rates and erosion patterns (i.e. where erosion and deposition occurs) over a 100 year modelled period. We show that all rainfall scenarios produce sediment output and gullying greater than that of the surrounding natural system, however a ‘wetter’ future climate produces the highest output. Importantly, incorporating analogue rainfall scenarios into LEM has the capacity to both improve landform design and enhance the modelling software. Further, the method can be easily transferred to other sites (both nationally and internationally) where rainfall variability is significant and climate change impacts are uncertain. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) are being used in many products as they have unique antimicrobial-biocidal properties. After disposal of these products AgNPs can reach the soil environment possibly affecting soil organisms and disrupting plants. This work aimed to study the transport of AgNPs by water and sediment during overland flow and soil erosion. This was done in a laboratory setting, using a flume and rainfall simulator. A low concentration of AgNPs (50 μg·kg − 1 ) was applied to two soil-flumes with slope percentages of 20% and 10%. The rainfall was applied in four events of 15 min each with a total amount of rainfall of 15 mm during each event. After applying the rainfall, samples of the non-transported background soil (BS) and the transported sediment (Sf) were collected from the flume surface. Runoff sediment (RS) and water (RW) were collected from the outlet. AgNPs were detected in all samples collected. However, concentration varied according to sample type (soil or water), time of collection (for runoff water and sediment) and the slope of the soil flume. Higher concentrations of AgNPs in soil were detected in the BS than in the Sf likely due to the BS having more fine particles (silt and clay). The AgNPs concentration in the runoff sediments increased with subsequent applied rain events. In addition, increasing the slope of the flume from 10% to 20% increased the total AgNPs transported with the runoff sediment by a factor 1.5. The study confirms that AgNPs can be transported by both overland flow and sediment due to erosion. [ABSTRACT FROM AUTHOR]

The study of sediment production, transport, storage and discharge in alpine drainage basins is an essential prerequisite for a better understanding of the postglacial evolution of the alpine landscape. To get an overview on sediment production and alpine landscape evolution in Romania, the current study presents the first alpine sediment storage quantification in the Romanian Carpathians. Postglacial denudation was quantified within the small alpine catchment of the Doamnei Valley (3.62 km 2 ), located in the central part of the Făgăraș Mountains. The quantification of sediment volumes was performed through a combined approach consisting of: (i) detailed geomorphological mapping of sediment storage landforms, by means of high accuracy field and remote mapping of sediment storage landforms, (ii) shallow geophysical investigations and (iii) geographic information systems modeling techniques. A total of 64 ground penetrating radar profiles were conducted through the valley for sediment thickness determination of individual landforms. Through parallel profiling, 5 electrical resistivity tomography profiles were also performed for the comparison of bedrock depths in order to determine the overall degree of accuracy of the geophysical investigations applied. In total, 79 sediment storage landforms were identified. Talus sheets were found to be the most dominant landforms within the investigated area, followed by talus cones, moraines and fluvio–torrential deposits. Sediment volume for the Doamnei Valley was calculated to be 7.08 ± 1.42 10 6 m 3 , corresponding to a mean sediment thickness of 4.20 m, with the hanging cirques and valleys subsystem storing 48.58% of the total sediment volume, despite covering just 22% of the investigated area. Sediment volume was used in the determination of mean annual denudation rates for the entire catchment (0.20 mm/y ± 0.04 mm/y) as well as for mean annual mass transfer (406.2 ± 31.6 t/km 2 /y), based on a time span of 13 ka. [ABSTRACT FROM AUTHOR]

Climate-driven increase in the frequency of extreme hydrological events is expected to impose greater strain on the built environment and major transport infrastructure, such as roads and railways. This study develops a data-driven spatial-statistical approach to quantifying and mapping the probability of flooding at critical road-stream intersection locations, where water flow and sediment transport may accumulate and cause serious road damage. The approach is based on novel integration of key watershed and road characteristics, including also measures of sediment connectivity. The approach is concretely applied to and quantified for two specific study case examples in southwest Sweden, with documented road flooding effects of recorded extreme rainfall. The novel contributions of this study in combining a sediment connectivity account with that of soil type, land use, spatial precipitation-runoff variability and road drainage in catchments, and in extending the connectivity measure use for different types of catchments, improve the accuracy of model results for road flood probability. [ABSTRACT FROM AUTHOR]

High resolution water quality data has recently become widely available from numerous catchment based monitoring schemes. However, the models that can reproduce time series of concentrations or fluxes have not kept pace with the advances in monitoring data. Model performance at predicting phosphorus (P) and sediment concentrations has frequently been poor with models not fit for purpose except for predicting annual losses. Here, the data from the Eden Demonstration Test Catchments (DTC) project have been used to calibrate the Catchment Runoff Attenuation Flux Tool (CRAFT), a new, parsimonious model developed with the aim of modelling both the generation and attenuation of nutrients and sediments in small to medium sized catchments. The CRAFT has the ability to run on an hourly timestep and can calculate the mass of sediments and nutrients transported by three flow pathways representing rapid surface runoff, fast subsurface drainage and slow groundwater flow (baseflow). The attenuation feature of the model is introduced here; this enables surface runoff and contaminants transported via this pathway to be delayed in reaching the catchment outlet. It was used to investigate some hypotheses of nutrient and sediment transport in the Newby Beck Catchment (NBC) Model performance was assessed using a suite of metrics including visual best fit and the Nash-Sutcliffe efficiency. It was found that this approach for water quality models may be the best assessment method as opposed to using a single metric. Furthermore, it was found that, when the aim of the simulations was to reproduce the time series of total P (TP) or total reactive P (TRP) to get the best visual fit, that attenuation was required. The model will be used in the future to explore the impacts on water quality of different mitigation options in the catchment; these will include attenuation of surface runoff. [ABSTRACT FROM AUTHOR]

Drought-breaking floods pose a risk to coastal water quality as sediments, nutrients, and pollutants stored within catchments during periods of low flow are mobilized and delivered to coastal waters within a short period of time. Here we use subtidal surface sediment surveys and sediment cores to explore the effects of the 2011 Brisbane River flood on trace metals zinc (Zn), lead (Pb), copper (Cu), nickel (Ni), chromium (Cr), manganese (Mn), and phosphorus (P) deposition in Moreton Bay, a shallow subtropical bay in eastern Australia. Concentrations of Zn, Cu, and Pb in sediments in central Moreton Bay derived from the 2011 flood were the highest yet observed in the Bay. We suggest flushing of metal rich sediments which had accumulated on the Brisbane River floodplain and in its estuary during the preceding 10 to 40 years of low flows to be the primary source of this increase. This highlights the importance of intermittent high magnitude floods in tidally influenced rivers in controlling metal transport to coastal waters in subtropical regions. [ABSTRACT FROM AUTHOR]

Understanding of the distribution patterns of sediment erosion, concentration and transport in river basins is critically important as sediment plays a major role in river basin hydrophysical and ecological processes. In this study, we proposed an integrated framework for the assessment of sediment dynamics, including soil erosion (SE), suspended sediment load (SSL) and suspended sediment concentration (SSC), and applied this framework to the Mekong River Basin. The Revised Universal Soil Loss Equation (RUSLE) model was adopted with a geographic information system to assess SE and was coupled with a sediment accumulation and a routing scheme to simulate SSL. This framework also analyzed Landsat imagery captured between 1987 and 2000 together with ground observations to interpolate spatio-temporal patterns of SSC. The simulated SSL results from 1987 to 2000 showed the relative root mean square error of 41% and coefficient of determination ( R 2 ) of 0.89. The polynomial relationship of the near infrared exoatmospheric reflectance and the band 4 wavelength (760–900 nm) to the observed SSC at 9 sites demonstrated the good agreement (overall relative RMSE = 5.2%, R 2 = 0.87). The result found that the severe SE occurs in the upper (China and Lao PDR) and lower (western part of Vietnam) regions. The SSC in the rainy season (June–November) showed increasing and decreasing trends longitudinally in the upper (China and Lao PDR) and lower regions (Cambodia), respectively, while the longitudinal profile of SSL showed a fluctuating trend along the river in the early rainy season. Overall, the results described the unique spatio-temporal patterns of SE, SSL and SSC in the Mekong River Basin. Thus, the proposed integrated framework is useful for elucidating complex process of sediment generation and transport in the land and river systems of large river basins. [ABSTRACT FROM AUTHOR]

This paper presents an integrated empirical methodology for assessing the amount of sediment transported from slopes to the main river in absence of a sediment transport monitoring system. The amount of transported sediment is calculated through the characterization of the sediment source areas including the identification of the slope phenomena responsible for the sediment propagation to the main river: shallow landslides, channelized debris flows and deep-seated rotational slides. On this basis, several scenarios related to the climatic conditions are defined: they indicate the number of possible slope phenomena and potential volumes of mobilized unconsolidated material from sediment source areas to the main river. This methodology was finalized and tested in the Maira River basin (south-western Italian Alps) with quite good results. [ABSTRACT FROM AUTHOR]