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Earth's terrestrial topography evolves in response to the interaction of tectonics, climate, and lithology. Recent discoveries suggest that the grain size of sediments produced on hillslopes and transported through river networks is key to understanding these interactions. Hillslope grain size varies systematically with erosion rate and residence time, the degree of chemical and physical weathering, and the fracture density and susceptibility to weathering of rock. Variations in initial grain size strongly influence the spatial evolution of grain size distributions as particles mix and wear during downstream transport through channel networks. In rivers, the size and flux of the coarse fraction of the sediment load control the rate of incision into bedrock and thus govern channel slope and ultimately the relief of actively eroding landscapes. These relationships suggest that a primary way that tectonics, climate, and lithology influence landscape evolution is through their controls on sediment grain size. Recent research reveals the central role of sediment grain size in controlling bedrock river morphodynamics, linking grain size to channel slope and topographic relief. Tectonics, climate, and lithology govern the size of sediments produced on hillslopes; hence, grain size mediates their influence on landscape evolution. Feedbacks linking sediment grain size, topography, weathering, erosion, and sediment transport provide new opportunities for advances in Earth surface science. [ABSTRACT FROM AUTHOR]

CONCLUSIONS Despite the breadth and intensity of human impacts to lowland rivers it is essential that river managers have knowledge of fluvial dynamics in the context of historic and planned human impacts to rivers. Lowland rivers often have broad valleys and deltas characterized by multiple raised channel belts and distributaries separated by expansive flood basins. Lowland rivers are unique geomorphic and hydrologic settings that support distinctive environmental processes and a range of human activities. Study results raise important issues as regards management options for coastal draining lowland rivers along passive margins with broad lowland rivers undergoing high rates of sea level rise. [Extracted from the article]

Changes in 137Cs export over time following clearcutting were investigated in a Japanese forested catchment affected by the Fukushima nuclear accident. A total of 13% of the catchment area was clear-cut 2 years after the accident. Annual suspended solids (SS) export at the catchment outlet increased 1.4 to 2.0 times after clearcutting; however, 137Cs export increased slightly (up to 1.1 times), corresponding to 0.21% to 0.30% of the 137Cs inventory in the catchment. The smaller change in 137Cs export than in SS export was due to a rapid decrease in the activity concentration following clearcutting. This decrease was likely caused by both natural attenuation and SS derived from sources with a low activity concentration in the clear-cut area. Monitoring of the sediment transport from hillslopes in small-scale experimental plots showed that the 137Cs yield in the skid trail was 3.6 to 21 times greater than those in clear-cut and unlogged forest floors. This significant 137Cs transport was due to greater soil erosion (by up to two orders of magnitude) along the skid trail, despite the lower activity concentration than those in the other plots. This indicates that while skid trails were involved in the rapid decrease of the activity concentration of SS, they were a potential source of the increased export of 137Cs and SS. Net 137Cs export increased by clearcutting (the export excluding the decrease accompanied by natural attenuation) was estimated to account for only 0.092% of the inventory in the catchment for 2.5 years. These results imply that the impact of clearcutting on 137Cs export was temporary in this catchment. [ABSTRACT FROM AUTHOR]

Understanding Earth surface responses in terms of sediment dynamics to climatic variability and tectonics forcing is hindered by limited ability of current models to simulate long-term evolution of sediment transfer and associated morphological changes. This paper presents pyBadlands, an open-source python-based framework which computes over geological time (1) sediment transport from landmasses to coasts, (2) reworking of marine sediments by longshore currents and (3) development of coral reef systems. pyBadlands is cross-platform, distributed under the GPLv3 license and available on GitHub (). Here, we describe the underlying physical assumptions behind the simulated processes and the main options already available in the numerical framework. Along with the source code, a list of hands-on examples is provided that illustrates the model capabilities. In addition, pre and post-processing classes have been built and are accessible as a companion toolbox which comprises a series of workflows to efficiently build, quantify and explore simulation input and output files. While the framework has been primarily designed for research, its simplicity of use and portability makes it a great tool for teaching purposes. [ABSTRACT FROM AUTHOR]

Abstract: Cohesive sediment is an important component of aquatic environments, which must be monitored and managed for environmental, engineering, and human health reasons. While the hydrodynamic aspects of sediment erosion and transport are well understood, the erodibility of cohesive sediment has proved more difficult to address and predict. Erodibility is the propensity for the sediment to be eroded, and is represented typically as an erosion threshold or erosion rate. It is an attribute of the sediment itself, and is dependent on the sediment properties that dictate the resistive forces in the sediment, such as gravity, friction, cohesion, and adhesion. This paper reviews recent findings from a range of disciplines to create a comprehensive picture of the physical, geochemical and biological properties that influence the erodibility of cohesive sediment. By identifying these key sediment properties, we provide the background for a discussion on how changes in and interactions between the properties generate significant spatial and temporal variations in erodibility. We discuss the development of a predictive model of erodibility, and emphasize the need for more comparable field and laboratory data. [Copyright &y& Elsevier]

Summary: A stochastic model of sediment transport by rainfall-runoff was tested with a simple laboratory experiment. Although the conceptual basis of the model has been previously published [Lisle, I.G., Rose, C.W., Hogarth, W.L., Hairsine, P.B., Sander, G.C., Parlange, J.-Y., 1998. Stochastic sediment transport in soil erosion. Journal of Hydrology 204, 217–230] and its mechanistic underpinnings were convincingly theorized, it had not been corroborated with measurements. Small-scale flume experiments, ∼0.8m long, with simulated rainfall were used to imitate “wash-off” of sediment (0.225mm silica sand) from an impervious surface. Fitting two parameters (ejection and deposition rates) to minimize least squares error resulted in good agreement between stochastic model and measurements, R 2 ∼0.9. However, the fitted parameter values differed from values that would be expected following Lisle et al.’s (1998) physical explanation of the ejection and deposition rates. While some of the discrepancy may be attributable to particle interactions, the conceptualization of deposition as a quiescent settling process in mechanistic erosion models may need to be reevaluated. [Copyright &y& Elsevier]

Sediment flux on transport-limited hillslopes is well known to vary nonlinearly with slope, diverging as the angle of stability is approached. To date, however, no study has validated the precise form of the nonlinear slope-dependent transport model over geologic time scales in a non-steady-state landform. In this paper, we show how cinder cones can be used to validate the nonlinear transport model using Lathrop Wells cinder cone in Nye County, Nevada, as a type example. Cinder cones are well suited for this purpose because they can be radiometrically dated and their angles of stability can be constrained by measurement of subsurface contacts between primary fallout and overlying colluvial deposits reworked from upslope. Forward model results with a generalized, nonlinear transport model characterized by diffusivity, κ, and nonlinear exponent, n, show that the evolution of the cone rim and base are most sensitive to κ, while the cone midpoint is most sensitive to n. Analyses of the full cone shape, therefore, permit the two model parameters to be independently inferred if the cone age and angle of stability are independently known. Results for Lathrop Wells imply that n = 2 in the generalized, nonlinear transport model, which is consistent with Roering et al.'s (1999) widely used form of that model. [ABSTRACT FROM AUTHOR]

The article reports on the use of the physics-based model known as the Integrated Hydrology Model in simulating continuous hydrologic response and event-based sediment transport for the R-5 catchment. The sediment-transport simulations were conducted in one-year periods for a total of six years. The sediment-transport simulations were conducted for six selected events. The multi-year water-balance results from the hydrologic-response simulations match the observed aggregate behavior of the catchment. Event hydrographs were generally simulated best for the larger events.

The sediment-transport version of the Integrated Hydrology Model (InHM) is further tested for the case of multiple-species sediment transport with both rainsplash and hydraulic erosion using data from the Johansen et al. (2001) field experiments. The ability to simulate sub-plot scale interactians between surface water hydrology and multiple-species sediment transport with InHM is clearly demonstrated. Sensitivity analysis reveals that the erodibility coefficient has a substantial impact on the simulated total sediment mass. New spatio-temporal, data-rich field experiments are needed to continue the evaluation of the sediment-transport version of InHM and, subsequently, fully exploit the concept-development capabilities of the model. [ABSTRACT FROM AUTHOR]

Abstract: Recent years have seen a rapid expansion in the acquisition and use of information on diffusive transport in phases relevant to the solid Earth (crystals, melts and fluids). Although far from complete, the data base on diffusion coefficients is now sufficiently large that broad constraints can be placed upon the length- and time scales of many natural transport phenomena in which diffusion plays a role. Conversely, observations of diffusion progress in specific natural samples can be used to extract time–temperature information for a variety of geologic and geochemical processes, ranging from sediment burial and crustal erosion to fluid-mediated reactions and biosignature retention. Despite this undeniable progress, several major challenges remain that largely define the frontiers of research in solid-Earth diffusion. Perhaps foremost among these is the need to address and understand the multi-scale, multi-path aspects of diffusion in many systems—a complication that is not limited to polyphase materials (individual mineral grains can exhibit clear indications of multi-path behavior even when visible evidence of such paths is lacking). Many other diffusion frontiers are linked in one way or another to this multi-scale issue; they include: diffusion of molecular H2O and the effect of H species on diffusion in minerals and rocks; diffusive fractionation of multiple isotopes of a single element; diffusion at the extreme conditions of the deep Earth; reconciliation of observations from natural samples and laboratory studies; and development of theoretical approaches to ‘predict’ diffusion behavior in regions inaccessible to observation. [Copyright &y& Elsevier]

Abstract: Significant portions of the global soil organic carbon (SOC) pool must reside on sloping terrains where the spatial distribution of SOC reflects the combined effects of geomorphic processes and biological C cycling. Using a newly developed soil C mass balance model that explicitly includes soil production and sediment transport, we investigated the relative roles of sediment production/transport vs. biological C cycling in creating the observed spatial patterns of SOC storage within two grass-covered hillslopes in California. The study sites differed in bedrock geology, climate, and erosion rates. Measurements of SOC, soil texture, plant C inputs, and soil thickness were combined with topographic surveys and published soil erosion and production rates in the analysis. Soil thickness was found to be the key control on SOC storage, and soil thickness is balance between soil production and curvature-dependent erosional losses. Additionally, topographically varying rates of plant C inputs, decomposition rates, and SOC erosional losses or depositional inputs were found to only partially explain the observed SOC storage patterns. We used the measured relationships between SOC storage, soil thickness, and topographic curvature to create SOC storage maps of the two watersheds. At both sites, about 70% of the hillslope SOC is stored in depositional areas that are susceptible to episodic mass wasting. At the drier site, there was a larger SOC storage despite the lower soil C % because the clay-rich bedrock resulted in the development of relatively thick soils for a given slope curvature. We conclude that the geomorphic processes driving soil thickness provide fundamental mechanisms that control the spatial SOC patterns on vegetated hillslopes. [Copyright &y& Elsevier]

In broad terms, fluvial systems can be considered as comprising two basic geomorphologic features, a channel and its floodplain (overbank), each of which may accumulate sediment or undergo erosion. The sedimentary relationships between channels and floodplains, the resultant sedimentary architecture and the form of the dependent landscape may all be considered in terms of the relative rates of channel and floodplain aggradation and/or erosion. Using this approach, the Herbert River in north Queensland can be divided into seven ‘fluvial fields’. By considering the likely migration directions of field boundaries in the lower floodplain we conclude that, contrary to many sequence- stratigraphic models, lowering sea-level would drive a general aggradation of the system on the Great Barrier Reef shelf, whereas a sea-level rise would cause further incision of the modern coastal plain. [ABSTRACT FROM AUTHOR]