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Showing papers in "Earth Surface Processes and Landforms in 2021"



Journal ArticleDOI
TL;DR: In this paper, the authors present a review of the impact of vegetation establishment in gully channels and catchments, especially regarding their effect on headcut retreat and network development, the trapping of sediment by check dams and reduction of catchment sediment yield.
Abstract: Gully erosion is a major environmental problem, posing significant threats to sustainable development. However, insights on techniques to prevent and control gullying are scattered and incomplete, especially regarding failure rates and effectiveness. This review aims to address these issues and contribute to more successful gully prevention and control strategies by synthesizing the data from earlier studies. Preventing gully formation can be done through land use change, applying soil and water conservation techniques or by targeted measures in concentrated flow zones. The latter include measures that increase topsoil resistance and vegetation barriers. Vegetation barriers made of plant residues have the advantage of being immediately effective in protecting against erosion, but have a short life expectancy as compared to barriers made of living vegetation. Once deeply incised, the development of gullies may be controlled by diverting runoff away from the channel, but this comes at the risk of relocating the problem. Additional measures such as headcut filling, channel reshaping and headcut armouring can also be applied. To control gully channels, multiple studies report on the use of check dams and/or vegetation. Reasons for failures of these techniques depend on runoff and sediment characteristics and cross-sectional stability and micro-environment of the gully. In turn, these are controlled by external forcing factors that can be grouped into (i) geomorphology and topography, (ii) climate and (iii) the bio-physical environment. The impact of gully prevention and control techniques is addressed, especially regarding their effect on headcut retreat and network development, the trapping of sediment by check dams and reduction of catchment sediment yield. Overall, vegetation establishment in gully channels and catchments plays a key role in gully prevention and control. Once stabilized, gullies may turn into rehabilitated sites of lush vegetation or cropland, making the return on investment to prevent and control gullies high. (c) 2020 John Wiley & Sons, Ltd.

33 citations


Journal ArticleDOI
TL;DR: A wide range of factors have prompted these research efforts, including basic understanding of stream systems, protection and restoration of aquatic ecosystems, and environmental hazards in mountain environments as discussed by the authors, and a growing community of researchers and river managers is extending understanding of large wood in rivers to climatic, forest, landform and social contexts not previously investigated.
Abstract: Dynamics and functions of large wood have become integral considerations in the science and management of river systems. Study of large wood in rivers took place as monitoring of fish response to wooden structures placed in rivers in the central United States in the early 20th century, but did not begin in earnest until the 1970s. Research has increased in intensity and thematic scope ever since. Awide range of factors has prompted these research efforts, including basic understanding of stream systems, protection and restoration of aquatic ecosystems, and environmental hazards in mountain environments. Research and management have adopted perspectives from ecology, geomorphology, and engineering, using observational, experimental, and modelling approaches. Important advances have been made where practical information needs converge with institutional and science leadership capacities to undertake multi-pronged research programmes. Case studies include ecosystem research to inform regulations for forest management; storage and transport of large wood as a component in global carbon dynamics; and the role of wood transport in environmental hazards in mountain regions, including areas affected by severe landscape disturbances, such as volcanic eruptions. As the field of research has advanced, influences of large wood on river structures and processes have been merged with understanding of streamflow and sediment regimes, so river form and function are now viewed as involving the tripartite system of water, sediment, and wood. A growing community of researchers and river managers is extending understanding of large wood in rivers to climatic, forest, landform, and social contexts not previously investigated. © 2020 John Wiley & Sons, Ltd.

31 citations


Journal ArticleDOI
TL;DR: In this paper, an extended and critical literature review of insects as zoogeomorphic agents, with reference to various taxonomic orders and families of insects having a burrowing behaviour, is presented.
Abstract: Insects are the largest and most diverse group of living organisms on Earth, playing a critical but underestimated role as agents of geomorphic change. Burrowing insects create micro-scale landforms such as subterranean tunnels and surface mounds and, by this way, exert an influence on hydrology, soil erosion and sediment transfer at a wider landscape scale. However, social insects represented by ants and termites were the main taxa studied as geomorphic agents and ecosystem engineers. This article proposes an extended and critical literature review of insects as zoogeomorphic agents, with reference to various taxonomic orders and families of insects having a burrowing behaviour. It provides a large overview of their primary and secondary impacts on Earth surface systems, both supported by naturalistic evidence and available quantitative data. Some evolutionary insights are discussed based on fossil evidence of geomorphic work by insects and, at finer temporal scale, on recent advances in radiometric and luminescence dating of insect mounds. Finally, this article explores the fruitful links between geomorphology and entomology, and suggests several research perspectives in order to develop an integrated understanding of the importance of insects in Earth surface processes and landforms. © 2020 John Wiley & Sons, Ltd.

30 citations





Journal ArticleDOI
TL;DR: In this article, the evolution of glacial lakes that formed in the deglaciated area since the end of the Little Ice Age (LIA; 1850) was traced.
Abstract: Funding information Swiss Federal Office for the Environment; GCOS Switzerland; European Space Agency Abstract Retreating glaciers give way to new landscapes with lakes as an important element. In this study, we combined available data on lake outlines with historical orthoimagery and glacier outlines for six time periods since the end of the Little Ice Age (LIA; 1850). We generated a glacial lake inventory for modern times (2016) and traced the evolution of glacial lakes that formed in the deglaciated area since the LIA. In this deglaciated area, a total of 1192 lakes formed over the period of almost 170 years, 987 of them still in existence in 2016. Their total water surface in 2016 was 6.22 0.25 km. The largest lakes are > 0.4 km (40 ha) in size, while the majority (> 90%) are smaller than 0.01 km. Annual increase rates in area and number peaked in 1946–1973, decreased towards the end of the 20th century, and reached a new high in the latest period 2006–2016. For a period of 43 years (1973–2016), we compared modelled overdeepenings from previous studies to actual lake genesis. For a better prioritization of formation probability, we included glacier-morphological criteria such as glacier width and visible crevassing. About 40% of the modelled overdeepened area actually got covered by lakes. The inclusion of morphological aspects clearly aided in defining a lake formation probability to be linked to each modelled overdeepening. Additional morphological variables, namely dam material and type, surface runoff, and freeboard, were compiled for a subset of larger and ice-contact lakes in 2016, constituting a basis for future hazard assessment.

24 citations


Journal ArticleDOI
TL;DR: The results show that eco‐engineering species determine the mud content of the estuary, which suggests large effects on the morphology of estuaries with aggravating habitat degradation.
Abstract: Sediment-stabilizing and -destabilizing organisms, ie microphytobenthos (biofilms) and macrozoobenthos (bioturbators), affect the erodibility of muddy sediments, potentially altering large-scale estuarine morphology Using a novel eco-morphodynamic model of an idealized estuary, we investigate eco-engineering effects of microphytobenthos and two macrozoobenthic bioturbators Local mud erodibility is based on species pattern predicted through hydrodynamics, soil mud content, competition and grazing Mud resuspension and export is enhanced under bioturbation and prevented under biostabilization through respective exposure and protection of the supra- and intertidal Bioturbation decreases mud thickness and bed elevations, which increases net mud fluxes Microphytobenthos reduces erosion, leading to a local mud increase of intertidal sediments In multi-species scenarios, an effective mud-prone bioturbator strongly alters morphology, exceeding that of a more abundant sand-prone moderate species, showing that morphological change depends on species traits as opposed to abundance Altering their habitat, the effective mud-prone bioturbator facilitates expansion of the sand-prone moderate bioturbator Grazing and species competition favor species distributions of dominant bioturbators Consequently, eco-engineering affects habitat conditions while species interactions determine species dominance Our results show that eco-engineering species determine the mud content of the estuary, which suggests large effects on the morphology of estuaries with aggravating habitat degradation

23 citations


Journal ArticleDOI
TL;DR: In this paper, a multimethod approach including climate, meteorological, and ground temperature data analysis, aerial image correlation, as well as geotechnical testing and modeling, led to the reconstruction of the two events.
Abstract: The fronts of two rock glaciers located in South Tyrol (Italian Alps) failed on 13 August 2014, initiating debris flows in their downslope channels. A multimethod approach including climate, meteorological, and ground temperature data analysis, aerial image correlation, as well as geotechnical testing and modeling, led to the reconstruction of the two events. An integrated investigation of static predisposing factors, slowly changing preparatory factors, and potential triggering events shed light on the most likely reasons for such failures. Our results suggest that the occurrence of front destabilization at the two rock glaciers can only partly be explained by the occurrence of heavy rainfall events. Indeed, antecedent hydrological and thermal ground conditions were characterized by a saturated active layer favored by a snow-rich winter and extensive precipitation in late spring and summer. Also, the rising trend of air temperature during spring and summer months since 1950s might explain the concurrent marked displacement of the two rock glaciers. Indeed, geotechnical investigations have provided strong indications that one of the investigated rock glacier fronts was at a marginally stable state prior to 2014. As rainfall events more intense than the one that occurred in August 2014 were previously recorded in the same area without resulting failures at the studied rock glaciers, we propose that both predisposing and preparatory destabilizing factors have played a key role in the 2014 rock glacier front failures.

21 citations





Journal ArticleDOI
TL;DR: In this paper, the authors investigated the variability of the drag experienced by tidal flows in a mangrove creek system and subsequent effects on tidal asymmetries and ranges, and found that the interaction between creek flow and sheet flow in an intertidal forest is a key driver of the change in the dynamics of high-water conditions.
Abstract: Aboveground root structures enhance drag on tidal currents in intertidal mangrove forests whereas the creeks dissecting such forests provide low‐resistance conduits for tidal flows. Here, observations from an established mangrove forest in the Whitianga estuary, Aotearoa New Zealand, are used to investigate the variability of the drag experienced by tidal flows in a mangrove creek system and subsequent effects on tidal asymmetries and ranges. Tidal flow speed maxima in the creek occurred at overbank water levels during the sheet flow stage on rising tides, but at water levels below the creek bank (the creek flow stage) on falling tides. Inferred bulk drag coefficients for the creek were greater during the sheet flow than the creek flow stage, and were linearly correlated with the bulk drag coefficients at stations in the adjacent forest. Although falling tides, associated with larger bulk drag coefficients, had an increasingly longer duration than rising tides towards the back of the forest, we observed ebb‐dominant flow speed asymmetry that declined inland in the creek. Conversely, flow speeds within the forest were consistently flood‐dominant, in accordance with smaller bulk drag coefficients during rising tides. Along the full length of the mangrove system, high‐water levels were lowered by up to 12 cm/km within the creek and 36 cm/km within the mangrove forest. Creek bed roughness associated with bulk drag coefficients observed in deeper parts of the creek was much greater than the hydraulic roughness of the sediment. For accurate simulations of landscape‐scale feedbacks between the creek and mangrove forest, incorporating both direct and indirect contributions of the vegetated forest platform to creek bed roughness is essential. These findings show that the interaction between creek flow and sheet flow in a mangrove creek system is a key driver of tidal asymmetries as well as the attenuation of high‐water conditions.


Journal ArticleDOI
TL;DR: Biogeomorphology has been expanding as a discipline, due to increased recognition of the role that biology can play in geomorphic processes, as well as due to our increasing capacity to measure and quantify feedbacks between biological and geomorphological systems as discussed by the authors.
Abstract: Biogeomorphology has been expanding as a discipline, due to increased recognition of the role that biology can play in geomorphic processes, as well as due to our increasing capacity to measure and quantify feedbacks between biological and geomorphological systems. Here, we provide an overview of the growth and status of biogeomorphology. This overview also provides the context for introducing this special issue on biogeomorphology, and specifically examines the thematic domains of biogeomorphological research, methods used, open questions and conundrums, problems encountered, future research directions, and practical applications in management and policy (e.g. Nature based solutions). We find that whilst biogeomorphological studies have a long history, there remain many new and surprising biogeomorphic processes and feedbacks that are only now being identified and quantified. Based on the current state of knowledge, we suggest that linking ecological and geomorphic processes across different spatio‐temporal scales emerges as the main research challenge in biogeomorphology, as well as the translation of biogeomorphic knowledge into management approaches to environmental systems. We recommend that future biogeomorphic studies should help to contextualise environmental feedbacks by including the spatio‐temporal scales relevant to the organism(s) under investigation, using knowledge of their ecology and size (or metabolic rate). Furthermore, in order to sufficiently understand the ‘engineering’ capacity of organisms, we recommend studying at least the time period bounded by two disturbance events, and recommend to also investigate the geomorphic work done during disturbance events, in order to put estimates of engineering capacity of biota into a wider perspective. Finally, the future seems bright, as increasingly inter‐disciplinary and longer‐term monitoring are coming to fruition, and we can expect important advances in process understanding across scales and better informed modelling efforts





Journal ArticleDOI
TL;DR: In this article, the authors revisited the centennial hydro-morphodynamic evolution of the North Branch based on historical maps, field data, and satellite images and provided a synthesis of the regime change from ebb to flood dominance.
Abstract: Net sediment transport is predominantly seaward in fluvial-dominated estuaries worldwide However, a distributary branch in the Changjiang Estuary, the North Branch, undergoes net landward sediment transport, which leads to severe channel aggradation Its controlling mechanism and the role of human activities remain insufficiently understood, although such knowledge is necessary for better management and restoration opportunities In this study we revisit the centennial hydro-morphodynamic evolution of the North Branch based on historical maps, field data, and satellite images and provide a synthesis of the regime change from ebb to flood dominance The North Branch was once a major river and ebb-dominant distributary channel Within which alternative meandering channels and sand bars developed Deposition of river-borne sediment leads to infilling of the branch, while tidal flat embankment reduces the bankfull width and modifies the channel configuration, resulting in a profound decline in the sub-tidal flow partition rate The North Branch then becomes tide-dominant with an occurrence of tidal bores and elongated sand ridges Once tidal dominance is established, extensive tidal flat reclamation enhances the funnel-shaped planform, amplifying the incoming tides and initiating a positive feedback process that links tidal flat loss, sediment import, and channel aggradation Overall, the shift in branch dominance is a combined result of a natural southeastward realignment of the deltaic distributary channels and extensive reclamation One management option to mitigate channel aggradation is to stop the aggressive reclamation and allow tidal flats to build up, which might reduce the sediment import and eventually lead to a morphodynamic equilibrium in the longer term Understanding the impact of tidal flat reclamation is informative for the management of similar tidal systems under strong human interference

Journal ArticleDOI
TL;DR: In this article, the authors investigate the sedimentary signature of the recent recession of Steffen Glacier in downstream fjord sediments, with a focus on identifying the trapping (decreased downstream sediment yield) and filtering (removal of coarse particles) effectiveness of a growing intermediate proglacial lake.
Abstract: Proglacial lakes are effective sediment traps but their impact on the reliability of downstream sediment records to reconstruct glacier variability remains unclear. Here, we investigate the sedimentary signature of the recent recession of Steffen Glacier (Chilean Patagonia, 47 degrees S) in downstream fjord sediments, with a focus on identifying the trapping (decreased downstream sediment yield) and filtering (removal of coarse particles) effectiveness of a growing intermediate proglacial lake. Four sediment cores were collected along a 14 km longitudinal transect in Steffen Fjord and the sediment physical and chemical properties were compared with aerial imagery at high temporal resolution. The caesium-137 (Cs-137) chronology of the most distal core and sediment trap data suggest that sediment accumulation in the fjord remained relatively stable through time, despite the accelerating glacier recession and the growth of Steffen proglacial lake. This is in contrast with many studies that indicate a decrease in sediment yield during proglacial lake expansion. It implies that the increase in sediment export due to accelerating meltwater production may be balanced by the sediment trapping effect of the growing proglacial lake. The fjord sediments show a slight fining upward accompanied by a marked decrease in flood-induced grain-size peaks, most likely due to the increasing filtering and dampening effect of the expanding proglacial lake. Our findings show that the filtering effect of the proglacial lake reached a threshold in 1985, when the lake attained an area of 2.02 km(2). The additional 5 km of glacier recession during the following 32 years did not have any significant impact on downstream sedimentation. This study confirms that proglacial lakes act as sediment traps but it indicates that (1) the trapping effect can be outpaced by accelerating glacier recession and (2) the filtering effect becomes stable once the lake attains a certain critical size. (c) 2020 John Wiley & Sons, Ltd.



Journal ArticleDOI
TL;DR: The use of portable optically stimulated luminescence (OSL) readers has been extensively studied in geomorphological applications as mentioned in this paper, where the authors present case studies in which the instrument has been used to elucidate cryptostratigraphic variations in sedimentary sequences.
Abstract: The development of functional portable optically stimulated luminescence (OSL) readers over the last decade has provided practitioners with the capability to acquire luminescence signals from geological materials relatively rapidly, which allows for expedient preliminary chronostratigraphic insight when working with complex depositional systems of late Quaternary age. Typically, when using the portable OSL reader, infrared (IR) or blue post-IR OSL signals are acquired from bulk unprocessed materials, in contrast to regular luminescence dating, which is usually based on measurements on pure quartz or feldspar mineral separates, or on select silt-sized polymineralic portions. To demonstrate the utility of portable OSL measurements, this paper outlines the basic features of portable OSL readers and their constraints. Subsequently, case studies in which the instrument has been used to elucidate cryptostratigraphic variations in sedimentary sequences for geomorphological applications are reviewed. The studies can generally be grouped into three main categories. The first includes studies where the variation of portable OSL reader luminescence signal intensities with depth are plotted to generate profiles that contextualize sediment stratigraphy. In the second group, portable OSL reader luminescence signal intensities are used to interpret sediment processes that shed light on depositional histories. In the last category, luminescence signals from the portable OSL reader are calibrated to approximate numerical burial ages of depositional units. The paper concludes with a discussion of possible future directions.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the turbulence characteristics of the different surface boundary layers in the hinterland of the Gurbantunggut Desert and found that stable atmospheric conditions in the desert occur exclusively during the early morning and at night, and the onset and duration of this stable state varies seasonally.
Abstract: As the largest fixed and semi-fixed desert in China, the Gurbantunggut Desert undergoes a long period of snow cover in the winter and the rapid growth of ephemeral plants in the spring, presenting obvious seasonal changes in the underlying desert surface type, which can lead to variation in the turbulence of the near-surface boundary layer turbulence over the desert. In this study, gradient tower data and eddy covariance data from 2017 were analyzed to investigate the turbulence characteristics of the different surface boundary layers in the hinterland of the Gurbantunggut Desert. The results indicate that stable atmospheric conditions in the desert occur exclusively during the early morning and at night in the desert, and the onset and duration of this stable state varies seasonally. Two regimes of intermittent turbulence occur during the night; a weak turbulent regime that occurs when the wind speed is less than the threshold and a strong turbulent regime when the wind speed exceeds the threshold. The sensible heat flux and turbulent kinetic energy of the desert vary on a diurnal basis, with a single peak appearing at approximately 12:00 local standard time (LST). These parameters follow a seasonal pattern of summer > spring > autumn > winter in terms of the magnitude. The mean turbulence intensities of the along-wind, crosswind and vertical wind are 0.5, 0.47, and 0.14, respectively, with I u > I v > I w . The turbulence intensity is nearly constant when the wind velocity exceeds 6 m·s -1 . The normalized standard deviation of the wind velocity components (σ u , σ v and σ w ) generally satisfies a 1/3 power-law relation.

Journal ArticleDOI
TL;DR: In this article, a field monitoring study on two UK rivers invaded by signal crayfish (Pacifastacus leniusculus) assessed the impact of burrowing on bank erosion processes.
Abstract: Burrowing into riverbanks by animals transfers sediment directly into river channels and has been hypothesised to accelerate bank erosion and promote mass failure. A field monitoring study on two UK rivers invaded by signal crayfish (Pacifastacus leniusculus) assessed the impact of burrowing on bank erosion processes. Erosion pins were installed in 17 riverbanks across a gradient of crayfish burrow densities and monitored for 22 months. Bank retreat increased significantly with crayfish burrow density. At the bank scale (<6 m river length), high crayfish burrow densities were associated with accelerated bank retreat of up to 253% and more than a doubling of the area of bank collapse compared with banks without burrows. Direct sediment supply by burrowing activity contributed 0.2% and 0.6% of total sediment at the reach (1.1 km) and local bank (<6 m) scales. However, accelerated bank retreat caused by burrows contributed 12.2% and 29.8% of the total sediment supply at the reach and bank scales. Together, burrowing and the associated acceleration of retreat and collapse supplied an additional 25.4 t km−1 a−1 of floodplain sediments at one site, demonstrating the substantial impact that signal crayfish can have on fine sediment supply. For the first time, an empirical relation linking animal burrow characteristics to riverbank retreat is presented. The study adds to a small number of sediment budget studies that compare sediment fluxes driven by biotic and abiotic energy but is unique in isolating and measuring the substantial interactive effect of the acceleration of abiotic bank erosion facilitated by biotic activity. Biotic energy expended through burrowing represents an energy surcharge to the river system that can augment sediment erosion by geophysical mechanisms.