Changes In Microtopography Research Articles

Microstructural and micromechanical evolution features of asphalt with aging: An atomic force microscopy study

This study explores the aging effects on matrix asphalt (MA) and styrene-butadiene-styrene modified asphalt (SBSMA) using atomic force microscopy (AFM). Aging was simulated with the rolling thin-film oven test (RTFOT) and the pressure aging vessel (PAV) test. Key changes in microtopography, surface roughness, adhesive forces, Young's modulus, and energy dissipation were analyzed. The findings reveal significant microstructural changes with aging, including an increase in the size and a decrease in the number of beelike structures, increased surface roughness, and Young's modulus, which indicate material hardening. The analysis shows a reduction in adhesive force and energy dissipation, suggesting increased brittleness and viscosity. Notably, SBSMA exhibits better aging resistance than MA, as demonstrated by its lower roughness, stronger adhesive forces, and less reduction in energy dissipation, highlighting the effectiveness of the SBS modifier in mitigating aging impacts. These results underscore the critical role of material composition in the aging behavior of asphalt binders.

Spatial Distribution and Relationship between Slope Micro-Topography Changes and Soil Aggregate Stability under Rainfall Conditions

Natural rainfall affects the stability of soil aggregates by the kinetic energy of the rain changing the morphological characteristics of slope micro-topographic factors. Although the relationship between the stability of soil aggregates and micro-topography is not very significant at the slope scale, there are also rules to be found. This study aims to explore the relationship between slope micro-topography and aggregate stability, and to observe the spatial distribution of aggregate stability after water erosion. In this study, a digital elevation model of slope micro-topography was established by using a three-dimensional laser scanner to observe the slope erosion changes after rainfall events and clarify the spatial changes of soil aggregate stability and its relationship with slope micro-topography by combining geostatistics and generalized additive model (GAM). The results showed that the area of serious water erosion in the lower part of the slope accounted for 38.67% of the slope, and the micro-topography index of the slope changed obviously after rainfall, with the slope increasing by 3.1%, the surface roughness increasing by 5.34%, the surface cutting degree increasing by 26.67%, and the plane curvature decreasing by 61.7%. In addition, the GAM model was used to fit the multivariate variables. The results revealed that the slope and surface roughness were the key factors affecting the stability of water-stable aggregate. The slope and surface roughness were negatively correlated with the stability of water-stable aggregates.

Determine the Optimal Vegetation Type for Soil Wind Erosion Prevention and Control in the Alpine Sandy Land of the Gonghe Basin on the Qinghai Tibet Plateau

There is a dearth of research regarding the windbreak and sand stabilization functions of Caragana liouana shelter forests in the Gonghe Basin of the Qinghai-Tibet Plateau. Therefore, the aim is to elucidate the patterns of near-surface wind–sand activity in artificial Caragana liouana forests of varying ages and mixed forests of different configurations in alpine sandy areas. Additionally, this research seeks to clarify the windbreak and sand fixation effects of these forests. To this end, we have selected artificial forests of Caragana liouana of varying ages (10-year-old pure Caragana liouana forest (10aZJ-C), 17-year-old pure Caragana liouana forest (17aZJ-C), 37-year-old pure Caragana liouana forest (3aZJ-C)) and shrub mixed forests of different mixing modes (10-year-old Caragana liouana and Caragana korshinskii mixed forest (10aNZ-HJ), 10-year-old Caragana liouana and Artemisia desertorum mixed forest (10aSZ-HJ), an 10-year-old Caragana liouana and Salix cheilophila mixed forest (10aWZ-HJ)) within the Sand Control Station of Shazhuyu Village in the Gonghe Basin of the Qinghai-Tibet Plateau as the research subjects. Naked sand dunes were used as the control plot (CK), and through field observations of the wind speed profile, sand transport rate, and micro-topographic changes of each stand plot, we analyzed the wind–sand flow structure characteristics and sand transport process of Caragana liouana of different ages and their mixed forests, eventually proposing suitable afforestation configuration modes for the alpine sand area of the Gonghe Basin in Qinghai. The findings indicate that the wind speed profile within each stand plot follows a linear distribution pattern. Compared to naked dune land, the windbreak effect of each plot decreases as the height from the ground increases. Among them, the 10aWZ-HJ plot significantly alters the wind speed profile and has a substantial windbreak effect; at a height of 200 cm, the windbreak effect can still reach 41.27%. The sand transport rate of each plot fits into an exponential function relationship, with the correlation coefficients (R2) of the fitting equations for each plot all exceeding 0.95 and significantly lower than the control plot, suggesting vegetation can effectively reduce near-surface sand transport. The sand-fixing effects at the height of 0–45 cm from the ground in each plot are as follows: 37aZJ-C > 17aZJ-C > 10aWZ-HJ > 10aNZ-HJ > 10aZJ-C > 10aSZ-HJ. Overall, all plots indicate a state of accumulation. The 10aWZ-HJ plot has the largest relative accumulation area at 88.00%, and the highest average intensity of wind erosion and accumulation at 1.11. Taking into account the stability of the stand and the total protection time, this study suggests that it is suitable to mainly use mixed forests of Salix cheilophila and Caragana liouana in the alpine sand area of the Qinghai-Tibet Plateau. The results of this study can provide a theoretical basis for the construction of windbreak and sand-fixing forests in alpine sand areas.

The influence of weathering processes on microtopographic changes of sandstone under simulated upper intertidal conditions from hourly to weekly scales

Micro-scale surface changes of bedrock on shore platform have been monitored with micro-erosion meters (MEMs) and show significant downwearing over several (≥2) years. At short-term temporal scale of hours to days, rock surface behaviors are reversible and do not generate net surface lowering. Therefore, there is a temporal gap between the two temporal scales of surface behaviors over which grain detachment must occur. In this study, an upper intertidal zone (2-h immersion with subsequent 2-week exposure) was simulated in the laboratory to investigate the fast erosion rate at high elevation identified from the Otway coast in south-eastern Australia using MEMs.During the experiments, the microtopography of rock surface was monitored 2-hourly during the daytime period (0−12 h) on Day 1 (beginning), 8 (middle) and 14 (end) of the 14-day simulation to understand the cumulative effect of short-term surface changes on rock weathering and erosion at longer timescales in order to provide insights into the role of rock surface dynamics in shore platform evolution. Through manipulation of the salt content of water as well as temperature and humidity in the controlled measures, the experiment was also designed to test the primary weathering process in driving short-term surface changes at this particular tide level. Results show the primary role of temperature-induced salt crystal volume change in generating the short-term rock surface movements on high tidal to supratidal rock. Although the cumulative effect of short-term surface behaviors on rock microtopography appeared to be observed over longer timescales, it still remains uncertain if this drives rock decay at the weekly scale. Future studies are required to monitor the rock surface over a sufficiently long period (up to months) to determine the temporal threshold of erosion and understand the linkage between short-term surface changes and rock decay.

Long-term vs short-term subsite erosion rates on microtidal shore platforms (Southern Mallorca, Balearic Islands, Western Mediterranean)

We address changes in microtopography of a supratidal rocky surface on calcareous rocks in the shore platform of s'Alavern (S de Mallorca) by means of a TMEM monitoring device. TMEM site was installed in 2004 and subsequent microtopographies were obtained in 2005, 2008 and 2021; as well as a bi-hourly monitoring in 2005. When comparing subsite short-term erosion rates against long-term erosion rates, the results indicate that the erosion rates obtained during time intervals of less than 5 years show higher erosion rates (0.45 vs. 0.22 mm year−1) and with greater variance than those obtained for monitoring intervals greater than a decade. When comparing the variability of the value of the microtopographical altitude in hourly intervals with the behaviour of those same points on a long-time scale, it is evident that, in the short term, those points that experience negative displacements show higher long-term erosion rates than those that experience positive shifts on an hourly scale. However, this pattern is not statistically significant, which suggests that the magnitude and trend of the microtopography change is reflecting the role of different processes and agents that are operating at different temporal scales.

Multi-attribute parameterization modelling to assess response of microtopographic variation to rainfall-seepage coupled erosion

Slope microtopography redistribution caused by the process of surface–subsurface hydrology results in the randomness and nonlinearity of erosion behavior. However, the erosion effects of various microtopographic features under the rainfall-seepage coupled impact remain inadequately explored. In this work, a specialized parameterization framework was employed, coupling numerical attribute, shape, and structure with the spatial pattern of microtopography, specifically to quantify changes in microtopography and to clarify their response mechanisms to rainfall-seepage erosion on purple soil slopes. The continuous rainfall-seepage simulation experiments were conducted on a 15° tilled-slopes differing in microreliefs (conventional tillage, CT; artificial digging, AD; ridge tillage, RT) with constant rainfall intensity of 1.0 mm min−1 coupling three seepage rates of 2, 4 and 8 L/min, respectively. Results revealed that the elevation decay occurred in the stage of transition from sheet erosion to rill erosion for CT, AD and RT slopes, representing a “erosion > deposition” feature. The numeric roughness and multifractal pattern of microtopography showed RT > AD > CT slope during the rainfall-seepage erosion. The spatial change of microtopography was attributed to structural-oriented factors because the nugget ratio with less than 25 % accounted for 73.33 %. Synchronously, the runoff, sediment yields and concentrations increased with the increase of rainfall-seepage intensity. It was found that the response of roughness index on soil erosion was more obvious for smooth surface with relatively contribution rate of 81 %, while the change of microstructure (H) and multifractal shape (ΔD) were more sensitive to erosion process on AD and RT slopes respectively. The results reported in this study have important implications for an in-depth apprehending of microtopography erosion effects in saturation-excess dominated slope cropland.

Abrupt permafrost thaw drives spatially heterogeneous soil moisture and carbon dioxide fluxes in upland tundra.

Permafrost thaw causes the seasonally thawed active layer to deepen, causing the Arctic to shift toward carbon release as soil organic matter becomes susceptible to decomposition. Ground subsidence initiated by ice loss can cause these soils to collapse abruptly, rapidly shifting soil moisture as microtopography changes and also accelerating carbon and nutrient mobilization. The uncertainty of soil moisture trajectories during thaw makes it difficult to predict the role of abrupt thaw in suppressing or exacerbating carbon losses. In this study, we investigated the role of shifting soil moisture conditions on carbon dioxide fluxes during a 13-year permafrost warming experiment that exhibited abrupt thaw. Warming deepened the active layer differentially across treatments, leading to variable rates of subsidence and formation of thermokarst depressions. In turn, differential subsidence caused a gradient of moisture conditions, with some plots becoming consistently inundated with water within thermokarst depressions and others exhibiting generally dry, but more variable soil moisture conditions outside of thermokarst depressions. Experimentally induced permafrost thaw initially drove increasing rates of growing season gross primary productivity (GPP), ecosystem respiration (Reco ), and net ecosystem exchange (NEE) (higher carbon uptake), but the formation of thermokarst depressions began to reverse this trend with a high level of spatial heterogeneity. Plots that subsided at the slowest rate stayed relatively dry and supported higher CO2 fluxes throughout the 13-year experiment, while plots that subsided very rapidly into the center of a thermokarst feature became consistently wet and experienced a rapid decline in growing season GPP, Reco , and NEE (lower carbon uptake or carbon release). These findings indicate that Earth system models, which do not simulate subsidence and often predict drier active layer conditions, likely overestimate net growing season carbon uptake in abruptly thawing landscapes.

Soil‐water response in a volcanic ash hillslope affected by fissures and microtopographic changes caused by the Kumamoto earthquake, in Japan

AbstractWe examined soil‐water response in a hillslope with multi‐layered volcanic soils affected by fissures formed by intense shaking during the 2016 Kumamoto earthquake in Japan. Pressure head and volumetric water content responses in a 6 × 20 m hillslope ridgeline plot were monitored by tensiometers and capacitance‐based soil moisture sensors, respectively. The plot contained seven seismic fissures (0.3–0.8 m deep and 0.4–2.2 m wide) formed parallel to the ridgeline that exposed underlying soil layers, while areas with topsoil occurred between the fissures. Among the alternating layers, the andisol (ca. 1.0 m deep) consistently experienced high pressure heads (>−150 cm H2O) and volumetric water contents (>0.58 cm3 cm−3), indicating high water‐holding capacity. This andisol was a key layer for storing soil water and causing slow drainage into the deeper matrix, resulting in abrupt increases in volumetric water content during storms. Rainwater directly reaching the bottom of fissures without percolating through the topsoil caused rapid soil‐water response compared to the soil layer where water percolated via topsoil. Analysis of in‐situ soil water retention curves, recession rates and water storage changes revealed that the second andisol had unique characteristics for retaining water in the hillslope. The findings of this study show that spatial and temporal variability of soil water responses varied associated with earthquake‐induced fissure formation and soil water characteristics of multi‐layered volcanic soils.

Quantification of Agricultural Terrace Degradation in the Loess Plateau Using UAV-Based Digital Elevation Model and Imagery

Agricultural terraces are important artificial landforms on the Loess Plateau of China and have many ecosystem services (e.g., agricultural production, soil and water conservation). Due to the loss of rural labor, a large number of agricultural terraces have been abandoned and then the degradation of terraces, caused by rainstorm and lack of management, threatens the sustainability of ecological services on terraces. Our previous study has found its geomorphological evidence (sinkhole and collapse). However, no quantitative indicators of terrace degradation are identified from the perspective of microtopography change. A framework for quantifying terrace degradation was established in this study based on unmanned aerial vehicle photogrammetry and digital topographic analysis. The Pujiawa terraces in the Loess Plateau were selected as study areas. Firstly, the terrace ridges were extracted by a Canny edge detector based on high-resolution digital elevation model (DEM) data. The adaptive method was used to calculate the low and high thresholds automatically. This method ensures the low complexity and high-edge continuity and accuracy of the Canny edge detector, which is superior to the manual setting and maximum inter-class variance (Otsu) method. Secondly, the DEMs of the terrace slope before degradation were rebuilt through the terrain analysis method based on the extracted terrace ridges and current DEM data. Finally, the degradation of terraces was quantified by the index series in the line, surface and volume aspects, which are the damage degrees of the terrace ridges, terrace surface and whole terrace. The damage degrees of the terrace ridges were calculated according to the extracted and generalised terrace ridges. The damage degrees of the terrace surface and whole terrace were calculated based on the differences of DEMs before and after degradation. The proposed indices and quantitative methods for evaluating agricultural terrace degradation reflect the erosion status of the terraces in topography. This work provides data and references for loess terrace landscape protection and its sustainable management.

Effects of microtopography change driven by seepage and slope gradients on hillslope erosion of purple soil

Seepage is the prominent hydrological process on tilled hillslopes covered by purple soil, which can easily exacerbate slope instability and soil loss. Laboratory simulated experiments with a seepage intensity of 4 L min−1 under different slope gradients (5°, 10°, and 15°) were conducted to analyze how seepage induced the erosion impacts the microtopographic change during water erosion process. Three tillage practices, i.e., smooth slope (CK), artificial diffing (AD) and ridge tillage (RT) with different initial microrelief were designed in this study. Results showed that the variation of soil surface roughness (SSR) to seepage erosion showed CK > AD > RT, and the most severe on the midslope and downslope, fluctuating from −4.23% to 12.40%. The sharpness of soil surface microtopography (SSM) on RT and AD decreased as the slope gradient increased. Compared to CK, AD and RT effectively controlled runoff loss. Both AD and RT were unable to reduce soil loss when the seepage duration exceeded 45 min, that was, the sediment yield increased by 815.50% and 730.25%, respectively. The response of surface runoff and sediment yields to microtopography changes was characterized applying multivariate linear equation. The applicability of multifractal parameters was weakened in the terms of the response to soil erosion caused by seepage. In contrast, the contribution rate of RUp to soil erosion was 69.40% and that of RDown was 58.76% in SSR indexes under seepage condition, which were the optimal parameters assessing the changes of surface runoff and sediment yields. This study contributes to elucidating seepage erosion effects in purple soil slope and understanding hydrological processes based on SSM changes.

Understanding microtopography changes in agricultural landscapes through precision assessments of digital surface models by the UAV-RTK-PPK method without ground control points

Soil erosion on agricultural land causes severe environmental problems and damages crop plants. Structure-from-motion with multiview stereo (SfM-MVS) together with data obtained via unmanned aerial vehicles (UAVs) helps understand spatiotemporal changes in the ground surface if there is enough precise data. However, installing ground control points in the field is labor intensive and disturbs field conditions. Here, images georeferenced using the Real-Time Kinematic (RTK) method were further improved using Post-Processing Kinematic (PPK) analysis. This study aims to verify whether the UAV-RTK-PPK method can create precise digital surface models to evaluate topographic changes owing to erosion without ground control points. The effects of the camera's interior orientation parameters settings and the addition of oblique images to nadiral images on the precision were also examined to reduce the positional error by the doming and bowling phenomena. Field observations were conducted in a 150 m × 25 m potato field with 156 poles to consider the three-dimensional object shapes in the verification. The doming or bowling phenomena occurred using only the nadiral images. The precision of the digital surface model was approximately 0.40 and 0.20 m (in the Z-direction) using the estimated and fixed camera's interior orientation parameters, respectively. In contrast, the digital surface models produced by adding oblique images to the nadiral images had a precision of approximately 0.04 m, regardless of the camera's interior orientation parameters. Thus, a high-precision digital surface model was obtained from images acquired using the UAV-RTK-PPK and SfM-MVS methods without ground control points. The digital surface model positional precision was improved by adding oblique images to the nadiral images without having to consider the camera's interior orientation parameters. Topographic changes >0.05 m after erosion by heavy rainfall were evaluated without ground control points using the UAV-RTK-PPK method with oblique and nadiral images. Therefore, our method can monitor the erosion of agricultural fields that may cause crop damage, such as the greening of potatoes.

Comparison of Ground Point Filtering Algorithms for High-Density Point Clouds Collected by Terrestrial LiDAR

Terrestrial LiDAR (light detection and ranging) has been used to quantify micro-topographic changes using high-density 3D point clouds in which extracting the ground surface is susceptible to off-terrain (OT) points. Various filtering algorithms are available in classifying ground and OT points, but additional research is needed to choose and implement a suitable algorithm for a given surface. This paper assesses the performance of three filtering algorithms in classifying terrestrial LiDAR point clouds: a cloth simulation filter (CSF), a modified slope-based filter (MSBF), and a random forest (RF) classifier, based on a typical use-case in quantifying soil erosion and surface denudation. A hillslope plot was scanned before and after removing vegetation to generate a test dataset of ground and OT points. Each algorithm was then tested against this dataset with various parameters/settings to obtain the highest performance. CSF produced the best classification with a Kappa value of 0.86, but its performance is highly influenced by the ‘time-step’ parameter. MSBF had the highest precision of 0.94 for ground point classification but the highest Kappa value of only 0.62. RF produced balanced classifications with the highest Kappa value of 0.75. This work provides valuable information in optimizing the parameters of the filtering algorithms to improve their performance in detecting micro-topographic changes.

Rapid transformation of tundra ecosystems from ice-wedge degradation

Ice wedges are a common form of massive ground ice that typically occupy 10–30% of the volume of upper permafrost in the Arctic and are particularly vulnerable to thawing from climate warming. In assessing the patterns and rates of ice-wedge degradation in northeastern Alaska, we found degradation was widespread and rapidly transforming the microtopography, hydrology, soils, ground ice, and vegetation of tundra ecosystems through a sequence of degradation and stabilization stages. Across an extensive mapping area (30 km2), thermokarst troughs and pits with open water (degradation-advanced) covered 0.7% overall and 1.6% in the oldest terrain in 2018. Within an area (0.5 km2) of concentrated thermokarst, undegraded and degraded ice wedges together covered 29% of the area, and all degradation stages combined increased from 2% in 1950 to 19% area in 2018. Initial degradation peaked at 9% in 2000 and initial stabilization was trending upward at 12% area in 2018, indicating slowing degradation and a transition to stabilization. Integration and reorganization of the drainage network as troughs expanded and connected reduced impounded surface water and helped slow degradation. Degradation created large changes in microtopography, trough widths, water depths, depth to wedge ice, pH, soil and ground ice characteristics, and thermal regimes among stages. Community composition completely shifted from dominance of deciduous and evergreen shrubs in tussock tundra in the undegraded stage to dominance of aquatic mosses and forbs in flooded depressions in degradation-advanced stage. Soil slumping along trough margins and rapid colonization by aquatic mosses halted the degradation, and aquatic sedges became dominant in the stabilization-initial stage. In stabilization-advanced, aquatic mosses persisted and the diversity of wet-adapted forbs, sedges, and mosses increased. Recovery back to tussock tundra, however, is unlikely. This decadal-scale transformation has major implications for arctic land cover, tundra productivity, lake expansion and drainage, soil‑carbon balance, trace-gas emissions, and caribou and bird populations.

Plateau pika burrowing and yak grazing jointly determine ecosystem greenhouse gas emissions of alpine meadow

AbstractDomestic yak (Bos grunniens) have coexisted with plateau pika (Ochotona curzoniae) for thousands of and they play irreplaceable roles in shaping the structure and function of alpine meadow ecosystem. However, the mechanisms whereby the greenhouse gas (GHG) emissions change in response to the interactive effects between yak grazing and plateau pika burrowing remain unclear. In this study, we examined the response of ecosystem GHG emissions (CO2, CH4, and N2O flux) to yak grazing and pika burrowing in alpine meadow in Zoige County, China. The GHG emissions was measured with a static opaque chamber method. Our results revealed that CO2, CH4, N2O flux and CO2‐eq were significantly influenced by yak grazing and pika burrowing independently, and in conjunction. Crucially, the relative importance of pika burrowing was higher than yak grazing on a pastoral scale. Specifically, high pika burrowing led to an increase of 440.29%, and 110.72% for CO2‐eq relative to low pika burrowing under moderate and heavy yak grazing situations, respectively. The value of CO2‐eq with low pika burrowing was negative, especially under light yak grazing conditions. Furthermore, we found that GHG emissions were sensitive to plant species richness, soil temperature, soil moisture, soil organic carbon, and soil microbial factors. Structural equation modeling indicated that pika burrowing can affect CO2‐eq though altering soil temperature and belowground biomass under heavy yak grazing conditions and changing soil moisture and soil microbe under light yak grazing. The results of this study enrich our understanding of the role of small burrowing mammals in the carbon sequestration of alpine meadow. In the context of the carbon neutrality of alpine grassland ecosystem, small mammals' activities and their interactions with domestic livestock‐induced changes in microtopography on GHG emissions should not be neglected.

Microtopography change of agricultural lands during leaching by establishing internal field canal and drain network for soil salinity control in Sahl El-tina area, Egypt

Despite of supplying recommended leaching fraction, the soil of Sahl El-Tina region in Egypt is moderately saline due to the land systematic irregularity of surface irrigation. The current experiment investigated the effectiveness of changing the land microtopography only during leaching by establishing internal field canals and drains. The baseline measurements showed little salinity of irrigation water, moderate soil salinity and high drainage water being 73 times of irrigation water. Failures were observed in internal canals’ berms attributed to soil salinity and its consequent dispersion and low breaching resistance. Canals’ cross section was maintained weekly until stability was achieved after four weeks, then the daily leaching discharge increased accelerating the salinity removal rate. The results showed strong inverse relationships between leaching water quantity and both drainage water and soil salinities. There was also a strong direct relationship between soil and drainage water salinity in internal field drains. The drainage water salinity and soil salinity decreased to 50% and 23% of initial values, respectively after 64 days with an accumulated water height of 71.4 cm. After 76 days, the drainage salinity decreased to 15% of initial value equivalent to only 10 times of irrigation water salinity and the soil salinity decreased to 17% with an accumulated water height of 104 cm. The experiment ended after 90 days as the drainage salinity became unchanged. The citizen science approach was applied by involving the landowner and farmers in construction, maintenance, measurements, and data analysis.

Increased Arctic NO3− Availability as a Hydrogeomorphic Consequence of Permafrost Degradation and Landscape Drying

Climate-driven permafrost thaw alters the strongly coupled carbon and nitrogen cycles within the Arctic tundra, influencing the availability of limiting nutrients including nitrate (NO3−). Researchers have identified two primary mechanisms that increase nitrogen and NO3− availability within permafrost soils: (1) the ‘frozen feast’, where previously frozen organic material becomes available as it thaws, and (2) ‘shrubification’, where expansion of nitrogen-fixing shrubs promotes increased soil nitrogen. Through the synthesis of original and previously published observational data, and the application of multiple geospatial approaches, this study investigates and highlights a third mechanism that increases NO3− availability: the hydrogeomorphic evolution of polygonal permafrost landscapes. Permafrost thaw drives changes in microtopography, increasing the drainage of topographic highs, thus increasing oxic conditions that promote NO3− production and accumulation. We extrapolate relationships between NO3− and soil moisture in elevated topographic features within our study area and the broader Alaskan Coastal Plain and investigate potential changes in NO3− availability in response to possible hydrogeomorphic evolution scenarios of permafrost landscapes. These approximations indicate that such changes could increase Arctic tundra NO3− availability by ~250–1000%. Thus, hydrogeomorphic changes that accompany continued permafrost degradation in polygonal permafrost landscapes will substantially increase soil pore water NO3− availability and boost future fertilization and productivity in the Arctic.

Changing sub-Arctic tundra vegetation upon permafrost degradation: impact on foliar mineral element cycling

Abstract. Arctic warming and permafrost degradation are modifying northern ecosystems through changes in microtopography, soil water dynamics, nutrient availability, and vegetation succession. Upon permafrost degradation, the release of deep stores of nutrients, such as nitrogen and phosphorus, from newly thawed permafrost stimulates Arctic vegetation production. More specifically, wetter lowlands show an increase in sedges (as part of graminoids), whereas drier uplands favor shrub expansion. These shifts in the composition of vegetation may influence local mineral element cycling through litter production. In this study, we evaluate the influence of permafrost degradation on mineral element foliar stocks and potential annual fluxes upon litterfall. We measured the foliar elemental composition (Al, Ca, Fe, K, Mn, P, S, Si, and Zn) of ∼ 500 samples of typical tundra plant species from two contrasting Alaskan tundra sites, i.e., an experimental sedge-dominated site (Carbon in Permafrost Experimental Heating Research, CiPEHR) and natural shrub-dominated site (Gradient). The foliar concentration of these mineral elements was species specific, with sedge leaves having relatively high Si concentration and shrub leaves having relatively high Ca and Mn concentrations. Therefore, changes in the species biomass composition of the Arctic tundra in response to permafrost thaw are expected to be the main factors that dictate changes in elemental composition of foliar stocks and maximum potential foliar fluxes upon litterfall. We observed an increase in the mineral element foliar stocks and potential annual litterfall fluxes, with Si increasing with sedge expansion in wetter sites (CiPEHR), and Ca and Mn increasing with shrub expansion in drier sites (Gradient). Consequently, we expect that sedge and shrub expansion upon permafrost thaw will lead to changes in litter elemental composition and therefore affect nutrient cycling across the sub-Arctic tundra with potential implications for further vegetation succession.

Interactions between microtopography, root exudate analogues and temperature determine CO2 and CH4 production rates in fire-degraded tropical peat

Repeated fires can alter the microtopography, vegetation composition, peat surface temperature and can increase the risk of flooding in tropical peatlands. However, difficult site conditions limit our understanding of these critical factors regulating greenhouse gas (GHG, viz. CO2 and CH4) production and emissions from fire-degraded tropical peatlands. We aimed to relate the complex interactions between peat oxic and anoxic conditions due to changes in microtopography, labile C inputs in the form of plant root exudates (from ferns and sedges), and diurnal temperature change in affecting CO2 and CH4 production from fire-degraded tropical peat. We found that the mesic condition, which reflects the field moisture or water-saturated oxic conditions in hummocks, acted as a strong source of CO2 (230 ± 29 μgCO2 g−1 hr−1) and weak sink for CH4 (−5.6 ± 0.2 ngCH4 g−1 hr−1), while anoxic acted as a weak source of CO2 and strong source of CH4 (61.3 ± 6.2 μgCO2 g−1 hr−1; 592 ± 111 ngCH4 g−1 hr−1). Addition of labile C enhanced both the CO2 and CH4 production across treatments by five and two times for the two gases, respectively. Temperature sensitivity (Q10) for CO2 was higher for peat incubated under mesic conditions (1.21 ± 0.28) whereas for CH4 it was higher in peat under anoxic conditions (1.56 ± 0.35). Collectively, our result highlights how microscale changes in microtopography coupled with the quality and quantity of labile C and temperature variation can regulate GHGs production from fire-degraded tropical peatland areas, which are projected to increase with frequent fire episodes and future climate warming in the region. More importantly, changes in these critical factors may result in a net positive carbon emission with long-term elevated CH4 production and emissions rates from such fire-degraded tropical peatland areas.

Multi-temporal geomorphometric analysis to assess soil erosion under different tillage practices: A methodological case study

Soil erosion is one of the main environmental threats to sustainability and crop productivity in the agricultural sector. In agricultural fields, no-till management is considered a key approach for mitigating soil erosion. The measurement of soil erosion is particularly challenging, especially when surficial morphological changes are relatively small. Conventional experiments are commonly time-consuming and labour-intensive in terms of both field surveys and laboratory methods. On the other hand, the structure from motion (SfM) photogrammetry technique has enhanced the experimental activities by enabling the temporal evolution of soil erosion to be assessed through detailed micro-topography. This work presents a multitemporal quantification of soil erosion, using SfM through uncrewed aerial vehicles (UAV) survey for understanding the evolution of no-till (NT) and conventional tillage (CT) in experimental plots. Considering that morphological changes at the plot scale had millimetre orders of magnitude, it was necessary to minimise SfM errors (e.g., co-registration and interpolation) in volumetric estimates to reduce noise as much as possible. Therefore, a methodological workflow was developed to analyse and identify the effectiveness of multi-temporal SfMderived products, e.g., the conventional difference of digital terrain models (DoDs) and the less used differences of meshes (DoMs), for soil volume computations. We validated the erosion volumetric changes calculated from the SfM outputs with the amount of soil directly collected through conventional runoff and sediment measurements in the field. In this way, we recognised the most suitable estimation method. This study presents a novel approach for using DoMs instead of DoDs to describe the microtopography changes and sediment dynamics accurately. Another key and innovative aspect of this work often overlooked in soil erosion studies, was identifying the contributing sediment surface by delineating the channels potentially routing runoff directly to water collectors. The sediment paths and connected areas inside the plots were identified using a multi-temporal analysis of the sediment connectivity index for achieving the volumetric estimates, using DoMs (e.g., 2213 cm3 for no-till management system - NT and 38155 cm3 for conventional tillage regime - CT during September 2018-June 2020) that showed mild overestimation respect to field measurements results (e.g., 2359 cm3 for NT and 4525 cm3 for CT in the same period). This difference was attributable to other factors (e.g., the soil compaction processes) or variables rather than to photogrammetric or geometric ones. The developed workflow enabled low cos quantification of soil erosion dynamics for assessing the mitigation effects of no-till management that can also be extended in the future to different scales, based on SfM and UAV technologies.

Experimental study on the effect of four single shrubs on aeolian erosion in a wind tunnel

Local plants are the most effective elements to control aeolian erosion but their effectiveness requires evaluation. A series of wind tunnel experiments were conducted to monitor the effectiveness of four single shrubs, Nitraria tangutorum, Haloxylon ammodendron, Calligonum mongolicum, and Hedysarum mongolicum, in reducing wind speed and sediment transport. Sediment flux was measured at x/h = 1 (h is the height of plant) and wind speeds were monitored at x/h = -2, −1, 1, 2, 3, and 5 in wind speeds of 6, 8, and 10 m s−1. An area of 1 m2 was scanned with and without plants to obtain bed microtopography change before and after wind application. The results showed that a sheltered zone of 5 h was observed downwind of the plants. N. tangutorum, H. ammodendron, C. mongolicum, and H. mongolicum decreased wind speed by 40%, 25%, 30%, and 40%, and blown sediment about 60%, 40%, 35%, and 30% respectively. The greatest sediment erosion (–33 mm) and lowest sediment deposition (11 mm) occurred with H. mongolicum. The lowest sediment erosion (-11 mm) and greatest sediment deposition (36 mm) were observed with N. tangutorum. The plants presented similar effectiveness in reducing wind speed in low wind speed (6 m s−1) but the difference between the plants became apparent in moderate (8 m s−1) and high (10 m s−1) wind speeds which were attributable to their different morphology. N. tangutorum had the greatest effectiveness in reducing wind speed and sediment transport especially close to the ground surface, associated with its optimum porosity (20%) and morphology.