Badland Landscapes Research Articles

Timing of gully development in a structurally controlled badland landscape, western Turkey

The development of badlands at a global scale has become an increasingly relevant research topic in various earth science disciplines with respect to climate change and extensive erosion over the past few decades. Not only understanding badland forming processes but also investigating the potential causes and timing of badlands at a spatio-temporal scale is of great importance to unravel the genesis of badlands. To address these key aspects, this work focuses on a multi-method study in a Mediterranean badland landscape, Kula Badlands, western Turkey, exposed in two tributary catchments of the Gediz river. The Kula Badlands is recognised with its dense gully network deeply incised into fine grain and weakly consolidated Miocene and Quaternary sediments. These badlands are known to have developed within the extensional tectonic regime of a mini-graben system. However, the genesis, timing and incision history of the gully and badland development of the Kula Badlands require further investigation. In this work, timing and behaviour of gully erosion and sedimentation are studied with age control using appropriate luminescence and radiocarbon dating methods combined with geological and geomorphological observations. Sedimentation pattern and age results demonstrate a staircase-like form resembling river terraces in badland gullies. Sediment burial ages of badland deposits show an estimated age range of 140 ka to 0.5 ka. An accelerated incision is observed during the mid-Holocene with alternating erosion and sedimentation waves in response to upstream erosion. This period coincides with increased human activity in the area. Although, an apparent link between the timing of the preserved deposition and climate change could not be observed. A volcanic damming and subsequent breaching, and an interplay between tectonics and climate are likely to have triggered and accelerated the badland erosion and sedimentation activity within the spatial gully network pattern along the fault lines.

Chronicle of a death foretold: The vanishing of an emblematic cultural landscape results in the loss of its unique plant communities

Badlands are peculiar geomorphological formations shaping landscapes of high ecological and cultural value. In the last decades, land reclamation for agricultural purposes and the cessation of traditional land use, such as sheep grazing, led to their decline in extent in many areas. To quantify the changes in badland-related plant communities, we resurveyed badland vegetation in a site of the Crete Senesi (Siena, central Italy) after 16 years (2006–2022), using 48 quasi-permanent vegetation plots and by means of uni- and multivariate analysis of variance. We found an increase in the total vegetation cover of plant communities growing in former bare soil and sparsely vegetated areas, in line with an overall decrease in the extent of bare soil surfaces in the study area, which we highlighted through the analysis of multitemporal satellite images. Pioneer vegetation characterized by the endemic plant Artemisia caerulescens subsp. cretacea changed into ruderal annual grasslands, while former bare soils were colonized by such pioneer vegetation. In contrast, perennial grasslands remained stable. Grasslands with shrubs became more similar to perennial grasslands in species composition. Species richness increased in former bare soils, and using the total vegetation cover as a proxy for successional stages, we found that Shannon diversity and evenness peaked at about 90% of total cover. In all the stages of colonization, short distance dispersal species prevailed, both therophytes (Avena sterilis, Parapholis strigosa) and perennials (Artemisia caerulescens subsp. cretacea, Bromopsis erecta). Long distance dispersal species (Galatella linosyris) started colonizing at about 60% of total vegetation cover, and at high vegetation cover all the functional groups coexisted. Our results confirm that the badland landscapes of southern Tuscany and specialist plant diversity adapted to badlands are vanishing after a diminishing of active land management, suggesting the current ineffectiveness of the Natura 2000 network in their conservation.

Surrogate-assisted distributed swarm optimisation for computationally expensive geoscientific models

Evolutionary algorithms provide gradient-free optimisation which is beneficial for models that have difficulty in obtaining gradients; for instance, geoscientific landscape evolution models. However, such models are at times computationally expensive and even distributed swarm-based optimisation with parallel computing struggle. We can incorporate efficient strategies such as surrogate-assisted optimisation to address the challenges; however, implementing inter-process communication for surrogate-based model training is difficult. In this paper, we implement surrogate-based estimation of fitness evaluation in distributed swarm optimisation over a parallel computing architecture. We first test the framework on a set of benchmark optimisation problems and then apply to a geoscientifc model that features landscape evolution model. Our results demonstrate very promising results for benchmark functions and the Badlands landscape evolution model. We obtain a reduction in computationally time while retaining optimisation solution accuracy through the use of surrogates in a parallel computing environment. The major contribution of the paper is in the application of surrogate-based optimisation for geoscientific models which can in the future help in better understanding of paleoclimate and geomorphology.

Mobile evaporite enhances the cycle of physical–chemical erosion in badlands

Abstract. Chemical weathering driven by physical erosion is a natural process that strongly affects chemical and solid matter budgets at the Earth's surface. However, the influence of extreme climatic erosion on chemical weathering dynamics is poorly understood. Badland landscapes formed in highly erodible substrates have the potential to respond to individual events on scales that are rapid enough for direct observation. Here, we assess the geochemical and grain-size composition of suspended sediment and riverine chemistry measurements collected from two catchments during the 2017 Nesat and Haitang typhoons in southwestern (SW) Taiwan. During the typhoons, the Na+ concentration covaried with suspended sediment concentration (SSC), which we attributed to sodium-induced deflocculation. Evaporite weathering at peak rainfall is succeeded by peak silicate weathering at maximum discharge. Overall, our observations suggest that initial weathering of near-surface evaporite enhances the physical erosion of silicate rock during extreme rainfall events.

Accumulation of radiocarbon in ancient landscapes: A small but significant input of unknown origin

The persistence of organic carbon (C) in soil is most often considered at timescales ranging from tens to thousands of years, but the study of organic C in paleosols (i.e., ancient, buried soils) suggests that paleosols may have the capacity to preserve organic compounds for tens of millions of years. However, a quantitative assessment of C sources and sinks from these ancient terrestrial landscapes is complicated by additions of geologically modern (~ 10 Ka) C, primarily due to the infiltration of dissolved organic carbon. In this study, we quantified total organic C and radiocarbon activity in samples collected from 28- to 33-million-year-old paleosols that are naturally exposed as unvegetated badlands near eastern Oregon’s “Painted Hills”. We also used thermal and evolved gas analysis to examine the thermodynamic stability of different pools of C in bulk samples. The study site is part of a ~ 400-m-thick sequence of Eocene–Oligocene (45–28 Ma) paleosols, and thus we expected to find radiocarbon-free samples preserved in deep layers of the lithified, brick-like exposed outcrops. Total organic C, measured in three individual profiles spanning depth transects from the outcrop surface to a 1-m depth, ranged from 0.01 to 0.2 wt% with no clear C-concentration or age-depth profile. Ten radiocarbon dates from the same profiles reveal radiocarbon ages of ~ 11,000–30,000 years BP that unexpectedly indicate additions of potentially modern organic C. A two-endmember mixing model for radiocarbon activity suggests that modern C may compose ~ 0.5–2.4% of the total organic C pool. Thermal and evolved gas analysis showed the presence of two distinct pools of organic C, but there was no direct evidence that C compounds were associated with clay minerals. These results challenge the assumption that ancient badland landscapes are inert and “frozen in time” and instead suggest they readily interact with the modern C cycle.

Geological features of the Special Nature Reserve of Montalbano Jonico Badlands (Basilicata, Southern Italy)

ABSTRACT A geological, geomorphological and geo-touristic map, at 1:5000 scale, has been produced for the most representative area of the regional ‘Special Nature Reserve of Montalbano Jonico Badlands’, with the aim to represent the scientific and landscape features which allowed the establishment of the Reserve. The area is located in the Province of Matera (Basilicata), on the southwestern sector of the Apennines Quaternary foredeep, in Southern Italy. The map highlights stratigraphic signatures of international interest and badland landscapes, imprinted on a clayey marine succession straddling the Early-Middle Pleistocene boundary. This stratigraphic interval can be considered as an international reference section for global paleoclimatic signatures during Marine Oxygen Isotopic Stages 20–18 and for the base of the Middle Pleistocene Subseries/Subepoch. With the goal to disseminate these knowledges, to improve future research and to promote sustainable geo-tourism, the map allows visitors to enjoy the scientific features and scenery of the Reserve.

Structurally Controlled Landscape Evolution in Kula Badlands, Western Turkey

Badlands are extensively eroded landscapes consisting of weakly consolidated deposits within highly dense drainage systems. Their controlling and shaping factors can differ in relation to various internal and external conditions and processes that are not always well understood. This study focuses on the development of a badland landscape affecting Miocene and Quaternary sand-clay sediments in the extensional tectonic regime of Western Turkey with a multidisciplinary approach. The area between Kula and Selendi towns exhibits a badland topography with extensively eroded surface features, deepened gullies within poorly consolidated, sand clay-sized sediments. The results of structural field mapping and morphometric analyses using a 5 m resolution DEM to study the role of structural control in the development of badlands are presented in this study. Field data analysis supported by the quantitative assessment of longitudinal gully profiles illustrates the role of pre-existing structures as faults, their orientation and geometry in net erosion-sedimentation and the development of deepened gully networks. Representative illustrations, field photographs and block diagrams are presented to show the relationship between the rock structure and badland landscape. The connection between the extensional tectonics, erosional dynamics and geomorphology point to a structurally-controlled landscape in the Kula badlands in Western Turkey.

Regional distribution and characteristics of major badland landscapes in Turkey

Badlands are extremely rugged, outstanding landscapes that can be seen in all ice-free climate regions over erosion-susceptible unconsolidated materials, and they have drawn attention with their spectacular and iconic forms. Unlike nearly all badlands researches conducted at the experimental site and watershed scale, so far, the broader-scale evaluation has been neglected in the analysis of badland distribution, characteristics, and dynamics. Our study provides an integrative new insight into badland landscapes by investigating the distribution, characteristics and controlling factors of Turkish badlands on a broad, regional scale. We inventoried Turkish badlands using aerial imagery and studied their distribution using K-means clustering, an unsupervised machine learning algorithm, based on a set of major conditional geo-environmental factors that control the regional distribution and characteristics of badlands, including tectonics, lithology, topography, climate, and vegetation. Here, we identified, a total of 4494 km2 of badland areas which are non-uniformly distributed across Turkey, substantially clustered in the Central Anatolian Plateau (CAP). According to our regional analyses, we have determined a total of five badland regions comprising three major types classified as Semi-arid, Mediterranean, and Montane (humid), together with two transitional types in-between the Semi-arid and Montane badland regions. Our results indicate that temperature seasonality (0.83), mean annual precipitation (0.83), and precipitation seasonality (0.76) are predominantly assigned to the badlands clusters. The clastic rocks are revealed as the most crucial and inevitable factor for the development of Turkish badlands, which are represented in a wide geologic time-scale (Cretaceous to Quaternary) and diverse lithological units (i.e., lacustrine, volcaniclastics, and terrestrial). Neogene and Paleogene terrestrial clastics (77 %) constitute the majority of the lithologic settings of these badland landscapes. The active and complex tectonic history of Turkey has portrayed the fundamental frame of the identified badland regions, by providing a susceptible environment (i.e., development of sedimentary basins) and promoting badland development through successive base-level changes. Furthermore, tectonically-modulated (i.e., formation of orogenic belts, and uplifting of CAP) climate dynamics outline the distribution pattern and differentiation of the regional characteristics of badlands in Turkey. Overall, our regional-scale approach to badland mapping and regional synthesis may decipher not only the tectonic and climatic conditions of the identified badlands regions, but it may also contribute to the implementation of future effective strategies for the detection and mapping of erosion susceptible and high sediment flux areas in very broad spatial contexts of similar unexplored territories.

Tree-ring stable isotopes indicate mass wasting processes at Radicofani in the upper Orcia Valley (Tuscany, Italy)

Tree-ring carbon (C) and oxygen (O) stable isotope (SI) chronologies spanning the period 1983–2012 were analysed at three Pinus nigra Arn. sites located in the upper Orcia Valley (Tuscany, Italy) in a badlands landscape. The goal of the study was to determine the extent to which tree-ring stable isotopes (SI) can serve as a proxy for mass wasting processes. To this end, we applied an established dual-isotope model to detect physiological changes between trees growing at three sites, one along the upper border of a well-studied shallow landslide, one on the landslide, and one in a stable area, as control. We further analysed whether trees at the three sites showed different δ18O responses to climate and to precipitation δ18O. Tree-ring δ13C and δ18O variations and trends revealed impairments of the photosynthetic process at the landslide site. We found that trees growing on the landslide show signs of reduced photosynthetic capacity since the onset of the landslide in 1993, whereas since 2000, while producing compression wood during periods of landslide activity, the trees show trends of higher average maximum net photosynthesis. The correlation analysis performed between the SI chronologies and the climatic variables revealed that the climatic signals at the site located on the landslide are masked by growth stress induced by the mass wasting processes. The most distinct differences in climate responses between sites were found in tree-ring δ13C in response to mean temperature and to mean temperature range, and in tree-ring δ18O in response to precipitation δ18O. Our research confirms that it is possible to reconstruct mass-wasting processes on forested slopes and to date geomorphological events by considering the trees' physiological conditions as recorded by stable C and O isotopes in tree rings, and by comparing affected with unaffected sites.

Tectonic geomorphology of an active slow-moving, intrabasinal fault: The Galera Fault (Guadix-Baza Basin, central Betic Cordillera, southern Spain)

In this work, we prove the usefulness of morphometric analyses, typically applied to basin-border faults, to define the tectonic geomorphology of a slow-moving, intrabasinal structure: the Galera Fault (Guadix-Baza Basin, southern Spain). The Galera Fault is a 30 km-long, oblique-slip fault with major left-lateral and minor vertical slip components. Through geological and structural analyses, we define for the first time the detailed surface geometry of the fault, which is characterized by features typical of left-lateral strike-slip faults. The morphometric analysis indicates that a combination of slow slip rates and the high erodibility of the juxtaposed basin infill deposits favours a rapid landscape response to fault activity that erases many landscape effects related to active tectonics. This masking is more effective on features generated by strike-slip displacement, leaving only subtle evidence, such as local stream deflections and upstream widening of catchments. In contrast, geomorphic effects related to vertical displacement are better preserved, including the control of the geometry of the main rivers and morphological differences in the drainage network between the two fault blocks. On the upthrown fault block, streams are generally shorter and steeper and have greater valley incision, leading to the development of a badland landscape. Moreover, the vertical deformation of a Middle Pleistocene glacis surface (ca. 90 m) demonstrates the important role of this slow-moving intrabasinal fault in the generation of relief in the Betic Cordillera during recent Quaternary time. Although the impact of this fault on relief building is very low in comparison with oblique-slip, basin-border faults in the mountain range, it has a key control on the Quaternary landscape evolution.

Badland landscape response to individual geomorphic events

Landscapes form by the erosion and deposition of sediment, driven by tectonic and climatic forcing. The principal geomorphic processes of badland – landsliding, debris flow and runoff erosion – are similar to those in full scale mountain topography, but operate faster. Here, we show that in the badlands of SW Taiwan, individual rainfall events cause quantifiable landscape change, distinct for the type of rainfall. Typhoon rain reduced hillslope gradients, while lower-intensity precipitation either steepened or flattened the landscape, depending on its initial topography. The steep topography observed in our first survey is inconsistent with the effects of any of the rainfall events. We suggest that it is due to the 2016 Mw 6.4 Meinong earthquake. The observed pattern in the badlands was mirrored in the response of the Taiwan mountain topography to typhoon Morakot in 2009, confirming that badlands offer special opportunities to quantify natural landscape dynamics on observational time scales.

Surrogate-assisted Bayesian inversion for landscape and basin evolution models

Abstract. The complex and computationally expensive nature of landscape evolution models poses significant challenges to the inference and optimization of unknown model parameters. Bayesian inference provides a methodology for estimation and uncertainty quantification of unknown model parameters. In our previous work, we developed parallel tempering Bayeslands as a framework for parameter estimation and uncertainty quantification for the Badlands landscape evolution model. Parallel tempering Bayeslands features high-performance computing that can feature dozens of processing cores running in parallel to enhance computational efficiency. Nevertheless, the procedure remains computationally challenging since thousands of samples need to be drawn and evaluated. In large-scale landscape evolution problems, a single model evaluation can take from several minutes to hours and in some instances, even days or weeks. Surrogate-assisted optimization has been used for several computationally expensive engineering problems which motivate its use in optimization and inference of complex geoscientific models. The use of surrogate models can speed up parallel tempering Bayeslands by developing computationally inexpensive models to mimic expensive ones. In this paper, we apply surrogate-assisted parallel tempering where the surrogate mimics a landscape evolution model by estimating the likelihood function from the model. We employ a neural-network-based surrogate model that learns from the history of samples generated. The entire framework is developed in a parallel computing infrastructure to take advantage of parallelism. The results show that the proposed methodology is effective in lowering the computational cost significantly while retaining the quality of model predictions.

Badland Erosion and Its Morphometric Features in the Tropical Monsoon Area

Climatically driven processes are important controls on the Earth’s surface and on interactions between the hydrological cycle and erosion in drainage basins. As a result, landscape forms such as hillslope topography can be used as an archive to reconstruct historical climatic conditions. Recent progress in the Structure-from-Motion (SfM) photogrammetric technique allows for the construction of high-resolution, low-cost topography data using remote-controlled unmanned aerial vehicle (UAV) surveys. Here, we present the climatic effects on the hillslope erosion rate that can be obtained from the drainage frequency of hillslopes. We quantify the centimeter-scale accuracy of surveys across 72 badland hillslopes in SE Taiwan, which is a tropical monsoon area with an annual precipitation of over 2 m. Our observations indicate that climatic erosion results in a higher drainage frequency and the number of furrows, instead of drainage density. Additionally, the morphometric slope index (MSI) has a strong positive correlation with erosion and its rate but shows a negative correlation with drainage length and a positive correlation with inclination. This suggests that the erosion pattern is due to gravitational mass wasting instead of hydrological erosion. MSI should always be calculated relying on the normalized slope length and is less applicable to landslide-dominated erosion. We, therefore, suggest that UAV-driven digital elevation models (DEMs) are integrated into erosion mapping to aid in identifying erosion patterns. We highlight the unique opportunity for cross-climate zone comparative studies offered by badland landscapes and differential rainfall patterns, with remote sensing techniques and the morphometric slope index.

Los paisajes áridos abarrancados como recurso turístico

Los paisajes abarrancados, presentes en todo el mundo, en algunos lugares por sus particulares características, constituyen recursos turísticos y algunos de ellos han sido declarados Patrimonio de la Humanidad por la UNESCO. Los objetivos principales de este trabajo han sido: analizar la importancia de las áreas abarrancadas en la Región de Murcia; hacer una selección de los principales paisajes de badland en la Región, mostrar en estas áreas sus valores y proponerlos como recursos turísticos, considerando sus potencialidades y amenazas que sufren o pueden sufrir. En las áreas seleccionadas se han comparado los valores geológicos, geomorfológicos, paisajísticos, educativos y culturales, diferenciando entre las intensamente intervenidas por la actividad agrícola y las que han mantenido una evolución seminatural. Se ha realizado un análisis DAFO de dichas áreas. Y se ha llevado a cabo una evaluación aplicando los criterios específicos de: i) valor científico y educativo; ii) accesibilidad; y iii) valor turístico. Cada criterio se evaluó según una escala de tres puntos y diferente grado. Los resultados muestran que las cinco áreas estudiadas poseen suficientes valores como para convertirse en áreas de gran interés geoturístico. No obstante, es necesario implementar medias de divulgación y concienciación de dichos valores, entre la población regional y las distintas administraciones, que permitan minimizar las amenazas y potencien las fortalezas.

Cause-and-effect in Mediterranean erosion: The role of humans and climate upon Holocene sediment flux into a central Anatolian lake catchment

The debate in historical geomorphological studies about the causes of erosion in regions such as the Mediterranean has been long-standing. The relative roles of climate change and human impacts can be difficult to disentangle in the absence of highly resolved chronologies. Here we reconstruct the erosion history of a small lake catchment in central Anatolia, located on the edge of one of the Mediterranean's most iconic badland landscapes in Cappadocia. Because these lake sediments are annually laminated, precisely dating clastic inwash layers and calculating recurrence intervals and flux rates is possible. Lake cores have been analysed for μXRF elemental geochemistry and via thin sections, along with proxies for hydroclimate (oxygen isotopes) and land cover (pollen). Peaks in titanium, along with other detrital elements, and changes in clastic layers indicate increased sediment influx into Nar Lake between 9300 and 8000 cal BP (ceramic Neolithic, when obsidian mining took place nearby) and again, more importantly, during the last 2500 years (Iron Age to modern), the latter exhibiting three phases of enhanced catchment erosion. Multiproxy comparisons show that these phases were related primarily to periods of increased human impact on vegetation and soils around the lake. Most sediment influx has been in the form of turbidites, linked to the presence of a fan delta at the lake edge, although this store does not appear to have significantly delayed sediment delivery from eroding hillslopes to the lake bed. The marked increase in detrital influx during the late Holocene implies that badland development in the lake catchment is recent and largely anthropogenic, rather than ancient and of climatic causation, and probably involving stream capture. The record also shows that sediment influx diminished markedly at times when human land use disintensified, which in turn indicates that hillslope degradation is reversible with appropriate land management.

The use of the slope–area function to analyse process domains in complex badland landscapes

AbstractThis paper explores the effectiveness of the widely‐used functional relationship between drainage area (A in m2) and slope (S in m/m) to identify local process domains and aid interpretation of process interactions in a complex badland landscape. In order to perform this investigation, a series of sub‐basins tributary to the Formone River in the Orcia catchment (central Italy) were selected as a suitable study area within which to explore our questions, given these basins' general representativeness of local terrain, the availability of a high resolution digital terrain model and previous extensive geomorphological research. Eroding basins containing both calanchi and landslides are common in the sub‐humid badland landscape of central Italy, where field observation identifies a complex pattern of erosive processes associated with a history of uplift, despite which parts of the local landscape appear disconnected. Results reveal that the shape of all S–A curves (plotted using S data binned on log A) is comparable with that described in the literature, although sub‐basins containing calanchi generally plot with higher S values than non‐calanchi ones, except in the ‘fluvial’ section of the plots. Second, when viewed on total data (non‐binned) S–A plots, landslide source area domains and calanchi domains are entirely coincident in all basins, supporting a cause–effect relationship. Additional plotting of the frequency characteristics of the raw data in a new way supports the interpretation that calanchi frequently initiate in landslide scars.In general though, although the S–A plots can contribute to the disentanglement of geomorphological behaviour in some complex erosional landscapes, it became apparent that in this landscape, process domains do not separate out with clarity along the A axis as suggested by theory. Despite this, an alternative, broader‐scale morphoevolutive model can be proposed for the development of within‐landslide calanchi, driven by changes to basin connectivity to the base channel. © 2018 John Wiley & Sons, Ltd.

The Potential of Permanent Gullies in Europe as Geomorphosites

Geotourism is a useful way to educate societies in the field of geomorphology and related natural hazards. Geosites, including geomorphosites, represent the basis for the development of this type of tourism. This study describes 12 representative gully regions within nine European countries. The characteristics of 42 permanent gullies, gully systems, and badland landscapes are presented. Based on scientific values of the sites, educational lessons to be learned were identified that are mainly related to (i) gullies as a geological window, (ii) present-day geomorphological processes and (iii) stages of historical gully erosion reflecting past human–environment interactions. To evaluate possible education activities, a geotouristic assessment of the studied gullies and badlands was made, based on scientific, educational, functional and touristic indicators. This assessment demonstrates a large difference between the selected gully and badland sites, particularly with regard to functional and tourist values. The geotouristic potential of gullies (badlands) is the highest in Italy and Spain and the lowest in Romania and Latvia. In some countries, permanent gullies are not regarded as geotouristic attractions at all, while in others, they constitute a significant element of their tourism development strategy. In our opinion, all activities must be part of a broader strategy for the development of geotourism in gully and badland regions, for example, gullies may be included as geosites within existing or planned geoparks.

Sediment residence time in alluvial storage of black marl badlands

The aim of this study is to estimate the sediment residence time in the stream network of two small headwater catchments (Laval and Moulin) characterized by a badlands landscape entrenched into Jurassic black marls of the Southern French Prealps. The method is based on an intensive field survey of the alluvial storage along the main stream reaches from which a scaling law between the average thickness of alluvial deposits and their width was established in order to predict the volume of alluvial deposits in the entire stream network. To complete this approach, bedload sediment yield monitored over the last 30years with topographic surveying of sediment retention basins are used. The assessment of sediment residence time is performed according to a steady-state assumption, validated by the long-term dynamic equilibrium of bedload sediment yields. The results highlighted very close values of residence time between the catchments, around 3years, despite a one order of magnitude difference in drainage area. It is shown that the rate of increase of alluvial storage with drainage area is the same as for sediment yield. This is likely attributed to the high degree of confinement of the stream network, which prevent the formation of a floodplain or large internal alluvial fans. Implications of these results for the prediction of the effects of bioengineering works in controlling erosion are discussed.

Gully evolution and geomorphic adjustments of badlands to reforestation

Badlands and gullied areas are among those geomorphic environments with the highest erosion rates worldwide. Nevertheless, records of their evolution and their relations with anthropogenic land transformation are scarcer. Here we combine historical data with aerial photographs and tree-ring records to reconstruct the evolution of a badland in a Mediterranean environment of Central Spain. Historical sources suggest an anthropogenic origin of this badland landscape, caused by intense quarrying activities during the 18th century. Aerial photographs allowed detection of dramatic geomorphic changes and the evolution of an emerging vegetation cover since the 1960s, due to widespread reforestation. Finally, tree-ring analyses of exposed roots allowed quantification of recent channel incision of the main gully, and sheet erosion processes. Our results suggest that reforestation practices have influenced the initiation of an episode of incision in the main channel in the 1980s, through the hypothesized creation of disequilibrium in water-sediment balance following decoupling of hillslopes from channel processes. These findings imply an asymmetry in the geomorphic response of badlands to erosion such that in the early evolution stages, vegetation removal results in gullying, but that reforestation alone does not necessarily stabilize the landforms and may even promote renewed incision.

Bedload monitoring under conditions of ultra-high suspended sediment concentrations

The bedload response of the Moulin Ravine, a small alluvial system draining a very active Mediterranean badlands landscape entrenched into Jurassic black marls of the Southern French Prealps, has been investigated using an automatic Reid bedload slot sampler. This site is known for its exceptional sediment transport conditions thanks to a long-term monitoring program that started in the late 1980s, revealing a mean annual bedload yield of 2810tkm−2yr−1, and suspended sediment concentrations (SSCs) during flow events commonly reaching 100gL−1. With the deployment of the slot sampler, it has been possible to record instantaneous bedload fluxes during 10 s time increments and to investigate bedload response under flow conditions with ultra-high SSCs. Bedload records cover 4 flashy summer flow events induced by heavy convective storms including a 20-yr return period event. Due to the very high SSC conditions these events challenge bedload monitoring. Even if slot sampling has been recognized as insensitive to fine sediments (silts and clays), it has never been tested in such exceptional muddy flow conditions. The bedload slot sampler performed well in such conditions. A flow-invariant proportion of fines (∼15–20%) was captured in the slot sampler during flows. This proportion is equivalent to its content in the active bedload layer during summer flows, suggesting that fines enter the slot embedded with coarse particles. Instantaneous bedload fluxes recorded in the Moulin are amongst the highest hitherto reported values worldwide, providing evidence of the exceptional sediment transport conditions of marly alpine badlands. The dimensionless entrainment threshold is one order of magnitude higher than commonly reported for gravel-bed rivers, likely reflecting the cohesion effect of fines intruded in the channel surface and subsurface.