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The Tibetan Plateau (TP) is suffering from a substantial decline in terrestrial water storage (TWS) in exorheic basins, threatening water resources that are critical for ∼2 billion people downstream. TWS changes are commonly estimated using gravity satellites through observations of the total terrestrial mass storage (TMS) change, with an implicit assumption of a negligible contribution from sediment transport. Through long‐term (2002–2017) sediment flux observations in seven headwater basins on the TP, we reveal that the gravity satellite‐derived TMS has decreased at a rate of 3.85 ± 0.23 Gt yr−1 in the seven basins, of which 0.35 ± 0.04 Gt yr−1 is contributed by sediment transport. Neglecting this contribution leads to an overestimation of the TWS loss by 10.1 ± 1.3%, equivalent to the annual water demand of an additional 0.62 million people in the surrounding nations. Regionally, the overestimation is surprisingly high in the Indus River and Yarkant River basins, reaching up to 50.8%–77.6%. Plain Language Summary: Accurate quantification of the change in the terrestrial water storage (TWS) on the Tibetan Plateau (TP) is imperative to improve the assessment of water availability that are critical for ∼2 billion people downstream. Through long‐term sediment flux observations, here we find that sediment transport makes a substantial contribution to gravity satellite‐derived TWS change in regions with a high erosion rate such as the TP, which has never been taken into consideration in previous studies. Neglecting this contribution leads to an overestimation of the TWS loss by about 10% on average for the seven headwater basins on the TP. The contribution is especially high in the Indus River and Yarkant River basins. Our findings improve the regional estimation of water availability and thus support climate adaptation and sustainable water resource management. Key Points: For the first time, we quantify the contribution of sediment transport to gravity satellite‐based estimation of TWS change on the TPNeglecting the contribution of sediment transport leads to an overestimation of the TWS loss by 10.1% on averageThe overestimated TWS loss is equivalent to the annual water demand of an additional 0.62 million people in surrounding nations [ABSTRACT FROM AUTHOR]

The battering of bedrock by bedload collisions is the primary mechanism by which bedrock rivers erode and landscapes evolve. The energy imparted via impacts acts to detach bedrock via the growth and intersection of surface fractures. We present impact experiments designed to test the influence of particle impact energy on bedrock erosion rates. We found that erosional efficiency increased with increasing impact energy. Notably, these increases in efficiency are not captured by a widely‐used mechanistic bedrock erosion model. Observed increases in erosional efficiency were linked with enhanced elastic energy dissipation captured by differences in the coefficient of restitution. We suggest that this increase in energy dissipation is indicative of enhanced crack extension for high velocity impacts. Our experiments indicate a clear energy‐dependence for bedrock detachment processes that is not yet captured by bedrock incision models but may be integrated into long‐term erosion rates and landscape evolution. Plain Language Summary: Bouncing sediment grains batter the bedrock beds of rivers during floods. As these impacts collide with the bed, they slowly chip away at the riverbed bedrock. It's perhaps intuitive that a grain with more energy when it collides with the riverbed is able to chip away more bedrock. But, how much more destructive are these high energy impacts? We designed an experiment where we hit a bedrock sample with a steel ball at a range of impact energies, over and over again, up to 30,000 times, and measured how much material was chipped away. High energy impacts eroded more material, but this increased efficiency of erosion is not fully captured by impact‐based erosion models. We hypothesize that for higher energy impacts, a larger fraction of the incoming energy is used to crack the bedrock, more easily eroding material. We liken the relative influence of these high energy impacts to a battering ram, where only a few strikes can easily break down a door, whereas lower energy impacts, similar to a simple knock, are unlikely to achieve the same result. We suggest that this effect may be important in determining the influence of extreme events on bedrock erosion over long timescales. Key Points: Impact experiments demonstrate that bedrock erosional efficiency is enhanced with increasing impact energyExperimentally‐derived coefficients of restitution and rock resistance coefficients indicate enhanced elastic energy dissipation with increasing impact energyResults suggest that more energetic impacts enhance crack extension, increasing erosional efficiency [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that vegetation‐generated turbulence can enhance erosion rate and reduce the velocity threshold for erosion of non‐cohesive sediment. This study considered whether vegetation‐generated turbulence had a similar influence on natural cohesive sediment. Cores were collected from a black mangrove forest with aboveground biomass and exposed to stepwise increases in velocity. Erosion was recorded through suspended sediment concentration. For the same velocity, cores with pneumatophores had elevated turbulent kinetic energy compared to bare cores without pneumatophores. However, the vegetation‐generated turbulence did not increase bed stress or the rate of resuspension, relative to bare cores. It was hypothesized that the short time‐scale fluctuations associated with vegetation‐generated turbulence were not of sufficient duration to break cohesion between grains, explaining why elevated levels of turbulence associated with the pneumatophores had no impact on the erosion threshold or rate. Plain Language Summary: Mangrove habitat grows by retaining sediment. To restore these systems, it is necessary to understand how vegetation influences the transport and retention of sediment. This study used sediment cores collected from the interior of a mangrove forest to study how the aboveground roots, called pneumatophores, influence hydrodynamic conditions and sediment transport, and in particular the onset and rate of sediment erosion. Individual pneumatophores generate eddies that enhance turbulence, compared to conditions without pneumatophores. In sandy soil, vegetation‐generated turbulence can enhance erosion. However, in this study, vegetation‐generated turbulence did not increase the rate of erosion for natural cohesive (muddy) sediment, suggesting that the mangrove forest interior has naturally greater resistance to erosion and sediment loss. Key Points: For the same velocity, cores with pneumatophores had higher turbulent kinetic energy (TKE) compared to cores without pneumatophoresUnlike sands, the inception of erosion and erosion rates for cohesive sediment were better predicted by bed shear stress than by TKEModelers should parameterize erosion within vegetation differently for cohesive and non‐cohesive sediment [ABSTRACT FROM AUTHOR]

The sediment composition of the seabed governs its mobility, hence determining sediment transport and morphological evolution of estuaries and tidal basins. Bed sediments often consist of mixtures of sand and mud, with spatial gradients in the sand/mud content. This study aims at increasing the understanding of processes driving the sediment composition in tidal basins, focusing on depositional processes. We show that bed sediments in the Wadden Sea tend to be either mud‐dominated or sand‐dominated, resulting in a bimodal distribution of the mud content where the two modes represent equilibrium conditions. The equilibria depend primarily on the sediment deposition fluxes, with bimodality originating from the dependence of suspended sand/mud concentrations on the local bed composition. Our analysis shows that bimodality is a phenomenon that is not only specific for the Wadden Sea; it can be expected for a wide range of suspended sediment concentrations and thus also in other systems worldwide. Plain Language Summary: The bottom of coastal seas is often composed of two sediment types, namely sand and mud. The evolution of the seabed, and thus of our coasts, depends on how these sediment types move. A correct representation of the spatial sand‐mud patterns in the bed is therefore essential if we want to understand and predict coastal evolution. Studying a large data set we found that sediment beds tend to be either sandy or muddy, with lower chances of finding something in between (i.e., bimodality). Although segregation of sand and mud has often been attributed to erosion processes, we found that this is mainly the result of depositional processes, and especially of the suspended sediment concentrations. Sand concentrations largely depend on local conditions, while local mud concentrations are much more affected by conditions elsewhere and/or earlier. The difference in the suspended sand and mud concentrations leads to multiple equilibria in the bed composition—resulting in the previously mentioned bimodality—for a very wide range of conditions. Therefore, we also expect bimodality and sharp sand‐mud transitions in other systems worldwide. Key Points: Mud contents in the sediment bed can be bimodally distributed, resembling preferential sand‐mud segregationBimodality represents the existence of two stable equilibrium conditions, which are a result of the deposition fluxes of sand and mudBimodality is expected for a large range of suspended sediment concentrations in sand‐mud systems [ABSTRACT FROM AUTHOR]

Glaciers are commonly conceptualized as bodies composed of snow and ice. Yet, many glaciers contain a substantial amount of rock, especially those abutting steep mountains. Mountain slopes erode, depositing rocks on glaciers below. This loose rock (or debris) is buried in glaciers and melts out lower down creating a debris cover. Debris cover reduces ice melt, which changes the shape and movement of glaciers. Glacier movement, specifically basal sliding, efficiently sculpts landscapes. To date, we know little about the impacts of surface debris on conditions below glaciers. To help remedy this, we run numerical model simulations which show that debris‐covered glaciers erode slower than glaciers unaffected by debris. Reduced melt under surface debris lowers sliding speeds and causes sediment to accumulate at the bed, potentially establishing conditions for surging. The influence of surface debris cover on the subglacial environment may hold substantial implications for alpine sediment storage and landscape evolution. Plain Language Summary: Glaciers are imagined as bodies composed entirely of snow and ice. But many glaciers, especially those in steep mountains contain a substantial amount of rock as well. Rocks are deposited on glaciers from steep mountain slopes above them. This loose rock (or debris), buried by snow, can completely cover glaciers' lower reaches as it melts out of the ice. Debris reduces melt, which changes the glacier shape and in turn how glaciers move down valley. To test how debris‐covered glaciers erode and sculpt landscapes we use numerical models. Our simulations show that debris‐covered glaciers erode landscapes at lower rates than glaciers unaffected by debris. The reduced amount of melt from debris cover causes glaciers to slide slower and causes sediment to accumulate under debris‐covered ice, shielding bedrock from erosion. The tendency for debris‐covered glaciers to build sediment layers at their bed may lead to the rapid speed up and advancement of glaciers, also known as surges. The influence of surface debris cover on the subglacial environment may hold substantial implications for alpine sediment storage and landscape evolution. Key Points: Erosion is reduced under debris‐covered ice because of compounding effects between reduced surface melt and the subglacial environmentTill accumulates under debris‐covered ice because surface melt is suppressed by surface debris coverDebris cover on glaciers promotes subglacial fluvial conditions that can store sediment in alpine environments, altering erosional patterns [ABSTRACT FROM AUTHOR]

Direct measurements of erosional response to past climate change are scarce, but mid‐latitude landscapes can record how shifts between cold and warm periods altered erosion outside glacial margins. To study hillslope responses to periglaciation, we measured bulk geochemistry and cosmogenic 10Be and 26Al concentrations in colluvium and weathered bedrock in an 18 m regolith core from Bear Meadows, Pennsylvania, ∼100 km south of maximum glacial extent. Using core lithology, cosmogenic nuclide concentrations, and regional 10Be‐derived erosion rates, we show the onset of 100‐Kyr glacial cycles at the Mid‐Pleistocene Transition (1.2–0.7 Ma) instigated multiple periglacial episodes in central Appalachia, increasing erosion rates compared to the relatively warmer Neogene. Our results show the higher efficiency of periglacial versus temperate erosion processes and highlight a pervasive Pleistocene periglacial erosion signal preserved in the 10Be inventory of surface sediments in central Appalachia, where erosion rates are slow enough to integrate previous cold‐climate processes. Plain Language Summary: During ice ages in the past 2.6 million years, mid‐latitude landscapes like central Pennsylvania were shaped by extreme cold and thawing permafrost, conditions that promote fast breakdown and transport of soil. However, the effect of these cold climates and subsequent warming on erosion rates is unclear since we often lack records of hillslope erosion of warm and cold periods. We drilled 18 m through hillslope material emplaced during permafrost thaw and into the underlying weathered bedrock, and measured the concentrations of 10Be and 26Al, two isotopes that serve as tracers of burial timing and erosion rate. The ratio of 26Al/10Be in the oldest permafrost thaw unit indicates the material was deposited about one million years ago, corresponding to a switch to colder glacial periods followed by more abrupt and extreme warming. The concentrations of 10Be in bedrock below the deposits also imply slower erosion rates prior to the onset of glacial‐interglacial cycles. Our results indicate that cold climate processes are more efficient at eroding rock and transporting sediment than temperate processes and help explain patterns in erosion rates across the mid‐Atlantic region measured over different time scales. Key Points: In situ 10Be and 26Al measured in 18 m regolith core from central Pennsylvania, 100 km south of Pleistocene maximum glacial extentPeriglacial activity began at onset of 100‐Kyr glacial cycles, marked by permafrost thaw during abrupt warming following sustained coldPleistocene periglacial conditions led to an increase in erosion rates compared to the more temperate Neogene climate [ABSTRACT FROM AUTHOR]

Sediment management is currently limited by uncertainties in the applicability of existing radionuclide tracers and the effects of urbanization. Here, we use plutonium isotopes (239+240Pu) from weapons‐testing fallout to trace sediment transport across five watersheds in an urbanizing landscape in Kansas, USA. Historic flooding in the region provided an opportunity to assess extreme connectivity of sediment sources. 239+240Pu activity of transported sediment decreased as catchments urbanized, indicating a greater contribution from subsurface bank sediment; Bayesian modeling predicted 50% (8%–80%) bank sourcing in the most rural watershed, which rose to 93% (73%–100%) in the most urban catchment. 239+240Pu activity provides explanatory information on the superposition of sediment sources, which is beyond that given by traditional organic and geochemical tracers that primarily infer vegetative and geologic sourcing, respectively. Our study demonstrates the utility of 239+240Pu as a sediment tracer for managing erosion under anthropogenic change. Plain Language Summary: Sediment is one of the most common contaminants in rivers around the globe. The susceptibility of soil to erosion increases as humans convert natural landscapes into rural and urban systems. Uncertainties remain regarding how urbanization alters sediment pathways and what tools are appropriate for quantifying this alteration. Radioactive isotopes, generated from nuclear weapons testing in the 1950s, have proven useful in this regard, although the most prominent tracer, for example, cesium, is losing some utility due to a short half‐life and extensive radioactive decay. We suggest that plutonium isotopes, which have longer half‐lives, are a viable option for tracing sediment in modern landscapes. Plutonium results suggest that in rural basins the source of sediment transitions from upland soil during low‐flows to bank material at high‐flows. On the other hand, urban streams always deliver bank sediment, regardless of storm intensity. Our study demonstrates the utility of plutonium as an alternate sediment tracer and highlights how urbanization changes the pathways and mechanisms of fluvial sediment transport. Key Points: 239+240Pu activity is a robust tracer for describing sediment sources and fluvial mixtures in a rapidly urbanizing landscapeFrequentist and Bayesian models were consistent in estimating increased bank erosion with increasing urban land useSediment sourcing is dependent on discharge in rural watersheds whereas it is independent of discharge in urban watersheds [ABSTRACT FROM AUTHOR]

Assessing rivers' and hillslopes' sensitivity to external forcing is paramount to understand landscape evolution, in particular as a response to Quaternary climate changes. River networks are usually considered to be the main conveyors of environmental signals, such as changes in precipitation, temperature, or baselevel. Yet because hillslopes provide the source of sediment for river networks, their response to environmental change also modulates landscape dynamics. In order to characterize such behavior, we analyze the response times of a transport‐limited hillslope. We use simple numerical models of denudation to study hillslope responses to oscillatory forcing and understand their filtering effects on environmental signals. Modifications in the frequency of climate oscillation, such as the change that occurred at the Mid‐Pleistocene Transition, can significantly modulate hillslope sediment‐flux response. We infer a wide range of hillslope responses, ranging from negligible change over the full range of climate‐forcing frequencies, to a significant filtering of long‐period signals. Plain Language Summary: Landscapes are constituted of hillslopes and rivers where different types of erosion and sediment transport processes take place. Due to their large extent, river networks are an important driver of global landscape response to climatic or tectonic changes. Hillslopes have smaller dimensions but are also where most sediment production occurs and for that reason it is important to have a good understanding of how they respond to perturbations. We use simple numerical models of hillslope evolution to study the influence of oscillating changes of either the efficiency of sediment transport across the hillslope or the rate of channel downcutting at its base. Our results indicates that the period of oscillations for these perturbations controls the amplitude of the sediment flux response out of the hillslope, and provide a framework to understand how this landscape component reacts to climatic cycles such as the glacial/inter‐glacial oscillations of the Quaternary. For example, a major change occurred 800 ka ago with a shift in climate oscillation from 40 to 100 ka period. Our models suggest that in some landscapes this change in period alone could have induced a significant decrease in the amplitude of hillslope sediment flux response. Key Points: A complex hillslope dynamics is associated with the linear to nonlinear sediment flux transitionHillslopes filtering potential of external signals is highly contrasted depending on the type of forcingChanges in the climatic signal frequency at the Mid‐Pleistocene Transition could induce a significant shift in hillslope erosional response [ABSTRACT FROM AUTHOR]

The drastic decline in sediment discharge experienced by large rivers in recent years might trigger erosion thus increasing the vulnerability of their extensive deltas. However, scarce information is available on the erosion patterns in mega‐deltas and associated physical drivers. Here a series of bathymetries in the South Passage, Changjiang Delta, were analyzed to identify morphodynamic variations during high riverine flow and tropical cyclones (TCs). Results indicate that high river flow during flood season triggers large‐scale net erosion along the inner estuary, generating elongated erosion‐deposition patches. Erosion magnitude gradually weakens moving seaward with few localized bottom variations in the offshore area. TCs transport sediment landward and are accompanied by an overall weak erosion, with a less organized spatial pattern of erosion‐deposition. TCs can therefore significantly alleviate erosion, reducing the sediment loss induced by riverine flows by over 50%. These results highlight the role of TCs on the sediment dynamics of mega‐deltas. Plain Language Summary: In recent years, climate change and reduced riverine sediment inputs have significantly affected the morphology of large deltas. However, it is unknown whether typhoons cause erosion or deposition in the submerged part of a delta, due to challenge in capturing infrequent events. Here we study the impact of high river flow and typhoons on the South Passage, Changjiang Delta. Results show that high riverine flows can cause large‐scale erosion. Typhoons reduce fluvial erosion by transporting offshore sediments in the delta. The relative accretion caused by a typhoon is more than half the net erosion induced by riverine floods. This research sheds light on the sediment budget of large deltas and inform policy measures that can mitigate the effect of increasing anthropogenic pressure, extreme events, and sea level rise on delta morphology. Key Points: High riverine flow during the flood season triggers massive erosion in the Changjiang DeltaTropical cyclones reduce the overall fluvial erosion during the flood seasonDeposition triggered by typhoons can offset 50% of the estuarine erosion caused by high riverine flow [ABSTRACT FROM AUTHOR]

Submarine flows carve canyons into continental shelves, yet the conditions and events responsible for canyon incision are incompletely understood. Coarse sediment flux has been shown to promote terrestrial bedrock incision via abrasion in rivers, but similar processes in submarine canyons have yet to be systematically documented. We use repeat bathymetry, provenance analysis, wave modeling, and channel network analysis to show that longshore sheltering and wave focusing by the Delgada submarine canyon induce sediment accumulation and elevated wave shear stresses in its headwall region that frequently mobilize coarse bed material. These mobilizations scour bedrock in the headwall and generate abrasive turbidity currents that work to carve the canyon's active channel into bedrock. These findings highlight an important positive feedback between submarine canyons, waves, and sediment supply and suggest that submarine canyons adjacent to wave‐dominated, coarse sediment‐rich coastlines seek the shoreline through headward incision. Plain Language Summary: The carving of submarine canyons into the continental shelf is poorly understood relative to river valleys on land. We studied a submarine canyon in Northern California that is connected through littoral transport to river sediment using a combination of seafloor mapping, tracking sediments using their chemical elements, and simulating waves and currents to better understand which processes are responsible for canyon erosion. Our findings suggest that canyon focusing of wave energy and an abundant supply of coarse sediment cause erosion at the canyon's head. This finding helps explain why submarine canyon channel networks erode toward shore and predicts that canyons near mountain ranges will preferentially remain connected the shoreline. Key Points: Repeat sonar surveys and sedimentary provenance document sediment transport and erosion in Delgada submarine canyon, Northern CaliforniaHydrodynamic modeling and littoral budgets suggest that coarse sediment is mobilized by waves in the canyon head, triggering turbidity currentsSediment supply and wave focusing promote erosion of submarine canyons along tectonic coasts, encouraging littoral to deep sea connectivity [ABSTRACT FROM AUTHOR]

Previous studies have shown that sediment transport models based on bed shear stress (τ) are not accurate for regions with vegetation. The present study demonstrated that the inaccuracy arises from the influence of vegetation‐generated turbulence. Bed‐load transport rate, Qs, and near‐bed velocity were measured in a sediment‐recirculating flume with model vegetation of different vegetation volume fractions (ϕ) and with bare sand beds. At the same τ, the measured Qs increased with increasing ϕ, suggesting that vegetation‐generated turbulence, which also increased with increasing ϕ, was augmenting the bed‐load transport. At the same near‐bed turbulent kinetic energy, kt, the Qs measured in both bare and vegetated channels agreed within uncertainty, suggesting that kt may be a more universal predictor of bed‐load transport than bed shear stress. A τ‐based bed‐load transport model was reinterpreted as a kt‐based model. The new kt‐based model predicted the Qs measurements for both bare and vegetated channels. Plain Language Summary: Aquatic vegetated habitats, including wetlands and mangroves, are disappearing at an annual rate of 1% to 7%. These ecosystems provide habitat important to fisheries, enhance water quality by filtering nutrients from runoff, and also protect coastal regions from storm surge and waves. To mitigate the loss of these habitats, restoration projects import sediment to eroded areas. The success of the restoration depends on its ability to retain sediment, so that restoration design requires a good understanding of sediment transport within vegetated landscapes. However, this understanding is currently lacking, and many restoration projects fail due to unanticipated sediment loss from the restored regions. The goal of our study was to develop a predictive model for sediment transport in regions with vegetation. Using laboratory experiments with a model vegetation, we first showed that existing sediment transport models, based on studies without vegetation, underestimate by orders of magnitude the sediment transport in vegetated regions. Second, we demonstrated that the enhanced sediment transport was caused by vegetation‐generated turbulence. Finally, we proposed and verified a new model for sediment transport that incorporates the role of vegetation‐generated turbulence, which we believe will be an important guide for future coastal and riverine restoration projects. Key Points: For the same channel velocity, sediment transport rate increases with increasing vegetation volume fractionBed shear stress models, which neglect vegetation‐generated turbulence, do not apply in vegetated regionsA turbulence‐based model predicted bed‐load transport in both bare and vegetated channels [ABSTRACT FROM AUTHOR]