Earth Surface Processes and Landforms最新文献

Dolines are a widespread karst landform, and understanding their genesis can provide critical information about the evolution of subsurface karstification and groundwater flow zones. Swarms of collapse dolines characterise the karst in the southern portion of the Irecê Basin, northeastern Brazil. The basin comprises Neoproterozoic carbonate rocks approximately 100 m thick, bounded by less soluble older quartzites. The distribution of dolines is not uniform, as they cluster along NW-SE axes and are aligned with cave systems and permeability (fracture) corridors mostly associated with the Almas and Água de Rega ephemeral rivers. Detailed analysis of sectors with a higher density of dolines was performed using LiDAR and unmanned aerial vehicle (UAV) imagery at two different scales to obtain morphometric and orientation patterns. As expected, scale dependency is observed, with an increase in density and circularity index at a higher resolution scale, but a decrease in mean area and perimeter. However, Voronoi polygon indices are similar at both scales (6.86 ± 1); the departure from the more stable number of six due to the clustering of dolines associated with NW-SE oriented structural trends. Doline density trends closely follow the orientation of caves, but they are not always spatially connected, since doline evolution may either occlude the caves or be related to a non-identified void. The Irecê Basin karst system displays a continuum of landforms evolving initially from high-density fracture zones (fracture corridors), which work as favourable dissolution zones, grading into more integrated flow routes, cave systems and eventually clusters of collapse dolines. Collapse dolines are widespread karst landforms worldwide, and their genesis requires the presence of dissolution voids at depth, which may pass undetected from the surface. In some sectors of Irecê Basin, the existence of doline alignments but the absence of known caves indicates the potential of collapse dolines to be used as proxies for subsurface karstification. Such an approach may allow the prediction of the location and orientation of subsurface zones of enhanced dissolution that can potentially represent productive aquifers or favourable zones for geofluids.

Salt-tolerant Tamarix chinensis roots are crucial in preserving wetland soil and carbon sequestration, which is essential for wetland ecology. Soil-water-salt conditions influence the growth of these roots in coastal saline areas, but the specific factors and their effects remain unclear. Using principal component and partial least square–structural equation modelling (SEM) methods, we studied T. chinensis root features in six Yellow River delta communities. Results showed varied root features across locations, with larger roots further inland. Root growth negatively correlated with soil texture and salinity and positively with groundwater levels. Soil texture and salinity decreased with distance from the coast, while groundwater increased with distance from the Yellow River. This suggests that geographical location influences soil-water-salt conditions, impacting root characteristics. The principal component analysis–derived root feature index captured 56.7% of root feature variation. SEM revealed geographical locations indirectly influence root features, with the Yellow River's proximity primarily affecting them through groundwater and coastal distance influencing via soil sand content and salinity. The study underscores the importance of these findings for wetland conservation and ecology.

As glaciers retreat worldwide, local basal depressions are exposed where new pro-glacial lakes are forming. Although the formation of such new lakes has been mapped widely, the impact of their interaction with the glacier on sediment dynamics and the thermal state is rarely studied. At the example of Witenwasserengletscher, Switzerland, we use historic aerial imagery and a bathymetric survey to investigate in detail the interaction of glacier retreat, lake formation and sedimentation. Three lakes have emerged since the mid-1990s with mean depths between 1.25 and 6 m. The deepest lake lost contact to the ice in 2009 with a delta forming from mobilized sub-glacial sediment. Phases of direct contact of the glacier with the lakes are found to increase terminus retreat and affect the thermal state and sedimentation. In summer, lake water temperatures in these small ice-contact lakes stay close to 0°C, whereas the disconnected eastern lake shows temperatures consistently over 6°C. Temperature profiles from 2021 show that after losing ice contact, warm sediment-rich glacial water forms an underflow that is breaking through the summertime stratification with warm water over cold water. In this case, density stratification is dominated by suspended sediment rather than temperature. Sedimentation shows a high multiannual variability and is dependent on a multitude of factors, ultimately on the routing of glacial streams. These tend to migrate towards the centre of the valley as the glacier retreats. Our study shows that during deglaciation lake evolution, sediment redistribution and the thermal state are highly dynamic and pro-glacial lakes strongly affect the sediment evolution and may thereby impact on the ecosystem in pro-glacial streams.

In response to the revision of our article on the nontectonic origins of unusually steep and overturned strata in the Mesozoic of the Holy Cross Mountains (HCM), we refute arguments that the authors of discussion make our theory implausible. The authors focused on proving the presence of strike-slip faults in the HCM, but at the same time, they believe that fold deformations precede the faults that cut them. The explanations provided by the critics still do not explain the extraordinary convergence of the morphology, surface of the fault and deformations occurring in its vicinity over a distance of 27 km. This problem was solved in our previous study, in which we have suggested that the steep and overturned orientation of the Oxfordian strata may be the result of non-tectonic processes. We consider the arguments used by the critics to be incorrect.

Particle density (ρ_s) and bulk density (ρ_b) are key factors in the calculation of total soil porosity. However, direct measurements of ρ_s and ρ_b are labour-intensive, time-consuming, and sometimes impractical. Pedotransfer functions (PTFs) provide alternative methods for indirect estimation of ρ_s and ρ_b. In this paper, the accuracy of typical 12 ρ_s and 9 ρ_b PTFs was evaluated using easily measurable soil properties (sand, silt, clay, and soil organic matter (SOM) content) from granitic residual soils collected from six study areas in subtropical China, and the accuracy of PTFs constructed based on multiple linear stepwise regression (MSR) and machine-learned algorithms (backpropagation neural network, k-nearest neighbour algorithms, random forests, support vector machines, and gradient boosted decision trees) was compared to determine the accuracy of PTFs. The results show that typical PTFs have poor accuracy (R²_adjusted < 0.020) and are not applicable to the indirect estimation of ρ_s and ρ_b in granitic residual soils. The PTFs constructed by machine learning algorithms all performed better than MSR, with the highest estimation accuracy of the PTFs constructed by the random forest algorithm, with R²_adjusted values of 0.923 and 0.933 for the ρ_s and ρ_b PTFs, respectively, and root-mean-square error of 0.020 g·cm⁻³ and 0.023 g·cm⁻³, respectively. Compared with MSR, the random forest algorithm has greater accuracy and eliminates the restriction of PTFs on predictors, which provides support for understanding the changing rules of ρ_s and ρ_b in granite residual soils in subtropical regions, evaluating soil quality and improving soil structure.

Measurement of river bathymetry has been revolutionized by high-resolution remote sensing that combines UAV platforms with SfM-MVS photogrammetry. Mapping inundated and exposed areas simultaneously are possible using either two-media refraction correction or some form of the Beer–Lambert Law to estimate water depths. If, as in turbid glacially-fed braided streams, the bed is not visible then traditional survey techniques (e.g. differential GPS systems) are required. As an alternative, here we test whether the spatial distribution of water depths in a shallow braided stream can be modelled from basic planimetric data and used to estimate inundated zone bathymetry. We develop heuristic rules using; (1) distance from the nearest river bank; (2) total inundated width along a line tangential to the local flow direction; (3) local curvature magnitude and direction; and distance from the nearest flow (4) divergence and (5) convergence regions. We parameterize them using a sample of measured water depths in stepwise multiple linear regressions and validate them using independent data. Resulting water depth distribution maps explain between 50% and 60% of the measured water depth spatial variability when compared to independent data. After incorporating modelled water depths into digital elevation models (DEMs) of exposed areas, we show that the developed method is suitable for volumetric change calculations in both dry and inundated areas.

Seismological observations provide a non-invasive and continuous means for indirectly measuring fluvial bedload transport. A significant challenge remains in independently characterising the seismic signature of bedload transport from other sources such as turbulence. We present a unique dataset from an alluvial Scottish river, combining seismic data and hydroacoustic measurements, to analyse bedload transport during three high-flow events occurring within the same year. By studying three successive events, we assess the consistency of bedload transport thresholds in response to changing flow conditions and explore the presence of hysteresis in seismic data versus water level as an indicator of coarse bedload transport. Through the use of hydroacoustic data to independently characterise bedload transport, our findings reveal that bedload transport occurred during all three events but that the threshold for entrainment varied. These entrainment thresholds were influenced by antecedent events, with a drop of 15%–20% of the threshold flow depth following the largest of the three events. In agreement with recent studies, we also found that hysteresis in the seismic versus water level data is not sufficient for identifying and analysing bedload transport: Distinct hysteresis was only observed during the largest of the three events despite all events experiencing bedload transport as observed through the independent hydroacoustic data. Our work shows the value in combining independent datasets for long-term monitoring of bedload transport to understand the evolution in the thresholds of bedload motion, providing crucial information for effective river and land-use management in a changing climate with potentially impacted high-flow events.

Channel sandbars are extremely sensitive to basin-wide natural processes and human activities, and their modifications considerably affect channel stability and river ecosystem health. However, quantitatively detecting the three-dimensional dynamics of channel sandbars at a high spatial resolution over a large area remains challenging. In this study, we propose a semi-automated process to address this challenge by extracting sandbar contours from Sentinel-2 images in the Google Earth Engine (GEE) platform. We then generate contour datasets for each sandbar based on the spatial relationship between contours and water levels at nearby hydrological stations. Subsequently, digital elevation models (DEMs) are created for each sandbar using the contour dataset, and non-linear relations between sandbar areas and water levels are fitted through polynomial curves of degrees 3–6 to calculate changes in sandbar volumes. Finally, we comprehensively analysed the driving mechanisms of sandbar changes in different sub-reaches. Our findings reveal the area and volume of sandbars in three of the four sub-reaches increased significantly between 2018 and 2019; however, these values decreased significantly and continuously between 2019 and 2022. Sandbars located downstream near the dam experienced more severe erosion compared to those farther downstream. Although the morphodynamic processes of each sub-reach were different, extremely low rainfall in 2019–2020 and the operation of the Xayaburi Dam are significant global factors leading to the shrinkage of the sandbars. Furthermore, abnormal erosion with a change rate of −9.62% in area and −8.95% in volume was observed in the sub-reach between Vientiane and Khong Chiam hydrological stations between 2018 and 2019, with the susceptibility of the channel to flow scour and anthropogenic sand mining being significant factors. Although the sediment replenishment from tributaries diminishes the impact of upstream dams and droughts on the reach farther downstream, the threat to channel stability due to excessive sand mining should be given high priority. Our study highlights how satellite remote sensing, specifically utilizing time series images with fine spatio-temporal resolutions, effectively detects three-dimensional variations in sandbars and river geomorphic changes. Additionally, it demonstrates the significant post-dam alteration of erosion patterns and deposition dynamics within the sandbar region of the lower Mekong River.

Changing the soil and underlying surface conditions is a key practice for realizing irrigation on-site storage and infiltration. However, biochar addition and grass planting effects on soil infiltration and water retention capacity remain unclear. The effects of 0% biochar (C1), 1% biochar (C3), 2% biochar (C4), 3% biochar (C5) under ryegrass and 0% biochar (C2), 1% biochar (C6), 2% biochar (C7) and 3% biochar (C8) under Festuca arundinacea on infiltration behaviours were modelled by using sandy loessial soil columns with ‘bare soil + 0% biochar’ as the control (CK). (i) There is a linear relationship between cumulative infiltration and CK–C8 treatment wetting fronts (R² ≥ 0.982), which showed an initial rising trend and then tended to gradual, and the influence of different treatments was primarily reflected in the middle and late infiltration stages. (ii) Both biochar and grass planting decreased the soil infiltration capacity compared with that of the CK treatment. A high biochar addition rate was beneficial for inhibiting soil water infiltration and improving water retention ability in sandy loessial soil, however, ryegrass soil infiltrabilities under 1%, 2% and 3% biochar were all stronger than that of F. arundinacea. (iii) The cumulative infiltration fitting effects in different treatments with the Kostiakov, Kostiakov–Lewis, Philip, USDA–NRCS, Horton and Green–Ampt equations were all good, although there were some differences in the infiltration rate curves under the six different fitting equations. This study is helpful in understanding effective sandy loessial soil storage ability for irrigation and efficient water resource usage.

In carbonate coastlines, karst studies have traditionally focused on reconstructing Quaternary coastal uplift and sea level oscillations. However, their potential for investigating coastal subsidence remains unexplored in regions with limited sedimentary records and scientific monitoring. In line with this, our study delved into the utility of karst research for deciphering the Quaternary evolution of the Granada coast in southern Spain—a shoreline marked by a conspicuous scarcity of records and information regarding recent tectonic movements. The current labelling data and the absence of evidence for uplift led to the hypothesis that the Granada coast may be susceptible to subsidence, though this conjecture remained unconfirmed. While submerged marine terraces were clearly identified, they were previously interpreted as consequences of sea-level oscillations. Our multidisciplinary approach integrated karst vadose features, biostratigraphy, and the dating of 22 speleothems to address the potential uplifting or subsiding dynamics of the Granada coast. The findings indicated that the Granada coast experienced emersion between 3.5/2.4 Ma and 650 ka ago. Notably, this uplift predated similar occurrences in neighbouring coastal regions to the W and E, which occurred within the last 200–180 ka. These disparities in timing cannot be solely attributed to sea-level fluctuations, suggesting the involvement of the tectonic activity during the Quaternary. The tectonic likely led to the emergence of the Granada coast and its karstification, followed by subsidence. Furthermore, we identified the extensional faults that caused the coastal subsidence, previously documented in studies conducted in nearby regions. However, until now, their specific impact on the Granada coast had not been comprehensively stated. In summary, our research introduces a novel application of classical karst investigations in the understanding coastal subsidence and the extensional active tectonic. By comparing vadose cave ages with established chronologies in adjacent coastal areas, this approach sheds light on the complex tectonic evolution of coastal regions.