Soil Spatial Heterogeneity Research Articles

Stochastic hazard assessment framework of landslide blocking river by depth-integrated continuum method and random field theory

AbstractLandslide-induced barrier dams pose a threat to the safety of humans, livestock and nearby infrastructures. The efficient assessment of landslide blocking river is crucial for disaster prevention and mitigation solutions. This study proposes a novel stochastic assessment framework to evaluate the landslide blocking river through the prediction of their deposition depths and considering the heterogeneity of shear strength parameters on the potential sliding surface. The depth-integrated continuum method (DICM) is used to simulate the landslide runout process. Using an enhanced Karhunen-Loève expansion (KLE) method, the spatial variations in soil's shear strength parameters are modeled by random fields to incorporate the effects of soil's spatial heterogeneity on the landslide deposition pattern. Subsequently, the multi-response surrogate model is constructed to relate the random field variables to the deposition depths based on extreme gradient boosting (XGBoost). To improve the performance of the surrogate model, principal component analysis (PCA) and sliced inverse regression (SIR) methods are employed for the dimension reduction of output and input variables, respectively. Furthermore, the algorithm for river blockage identification is developed to search for the deposition ridges. To demonstrate the capability of the stochastic assessment framework, an example of the first Baige landslide in Tibet, China is simulated, and the affected region and deposition depths of the landslide are predicted to calculate the probability of river damming. The presented methodology provides a practical means for improving the landslide blocking river prediction and new insights for early warning and risk mitigation.

Microbiological mechanism of hydrogen fertilizer effect in soil.

For a long time, intercropping and rotation of leguminous with non-leguminous crops is widely used to reduce the application of nitrogen fertilizer and increase yield in agroecosystems. At present, most researchers considered that this management measure is helpful for reducing fertilizer consumption and increasing its efficiency, as it can improve nutrient supply of legumestonon-legumes, the spatial nutrient utilization efficiency by enhancing soil spatial heterogeneity, and improve soil structure and disease resistance. However, current theories cannot fully explain the positive effect of crop rotation and inter-cropping systems involving legumes. A large amount of hydrogen (H2) can be produced as an obligatory by-product of nitrogenase responsible for nitrogen (N2) fixation in the root nodules of leguminous plants. Despite of substantial amounts of H2 enriched in the rhizosphere of legumes, only a minor proportion of H2 is found to leak to soil surface. Increasing evidence showed that most H2 released in soil is immediately depleted in the surrounding of N2-fixing nodules by H2-oxidizing bacteria (HOB) thriving in soil. HOB can use H2 as an electron donor to assimilate and fix CO2 through redox reactions to synthesize cellular substances and consequently promote plant growth. To date, however, little is known about the biological mechanism and ecological process behind the "hydrogen fertilizer effect". Therefore, we review the H2-induced plant growth-promoting effects and its microbiological mechanisms. Our aims were to explore a new way for enhancing agroecosystem production, and to provide scientific basis for future utilization of H2 in agricultural production practices.

WITHDRAWN: Characterization of soil response in mining with grouting into overburden bed-separation based on similar material simulation

Revealing the response laws of soils under various mining conditions is of significance for the scientific protection of farmland in mining areas. To avoid the interference from the spatial heterogeneity of natural soil on the research results, similar simulation experiments were employed. Two models for soil responses under mining with and without grouting into overburden bed-separation were designed, and monitoring was conducted for soil quality factors (moisture content, silt and clay content, and bulk density) and surface deformation factors (subsidence, inclined, and horizontal deformation). The results indicate that it can significantly control surface subsidence in mining with grouting into overburden bed-separation, the maximum subsidence value was reduced by 66.67%, the average subsidence value of each measuring point in the main section was reduced by 78.92%, and the subsidence area was reduced by 34.68%. The coefficient of variation of soil quality factors in the mining-affected area was obviously higher than that in the control area and the initial value before mining. Compared with mining without grouting, the variation coefficient of soil quality factor under mining with grouting was reduced by 2.71-6.79%. Soil quality factors and surface deformation factors show a significant quadratic function relationship, among which horizontal deformation has the greatest influence on soil quality factors, followed by subsidence and inclination. Therefore, it can effectively control surface subsidence and protect cultivated land when mining with grouting into overburden bed-separation.

Geostatistical modelling of soil properties towards long-term ecological sustainability of agroecosystems

A profound grasp of the quantitative spatial heterogeneity and distribution of the soil physicochemical attributes is crucial in understanding agricultural landscapes for ensuring the provisioning of soil ecosystem services. However, the analysis of data from remote sensing, like NDVI, can be of help in analysing the capacity of the landscape to provide supporting ecosystem services such as primary productivity. The research investigated and addressed the dispersion of important soil physico-chemical attributes in agricultural lands of the temperate Himalayan region of India using a geostatistical method and combining normalized difference vegetation index (NDVI) time-series data and the regression Kriging method. A 206 soil samples were gathered and assessed for soil parameters like pH, EC, OC, and available N, P, K, Ca, and Mg from Kishtwar district of Jammu. The coefficient of variation (CV) for pH and electrical conductivity (EC) ranged notably from 8.75 % to 118.98 %, highlighting diverse soil characteristics critical for local management practices. Mean elevation averaged 2743.32 m (m), with a moderate NDVI of 0.15, indicating dynamics in vegetation cover. Soil pH ranged from intensely acidic to marginally alkaline, with varying EC levels. Seemingly high organic carbon (OC), nitrogen (N), and potassium (K) levels, accompanied by medium phosphorus (P), calcium (Ca), and magnesium (Mg) levels were found in the region. The study employed ordinary kriging (OK) to map the spatial distribution of soil parameters, utilizing mean square error (MSE), root mean square error (RMSE), and the Moran’s I index. Exponential models were the best fit models for OC, while spherical models were fit for pH, EC, N, P, and Ca. Mathematical models were best fit for K and Mg. Spatial analysis using spherical and exponential models revealed distinct distribution patterns for pH, N, P, Ca, and Mg. The results of the degree of spatial dependence from the semi-variogram analyses indicated a strong (0.06 %) to moderate (0.51 %) to weak (2.81 %) dependence. The interpolated maps showed a distinct gradient in elevation (1053–4413 m), OC (0.13–2.80 %), NDVI (−0.16–0.54), pH (4.80–8.00), EC (0.03–9.80 dS m−1), N (201.15–993.19 kg ha−1), P (3.00–96.00 kg ha−1), K (124.88–1110.71 kg ha−1), Ca (7.00–46.00 meq 100 g soil−1), and Mg (2.30–21.50 meq 100 g soil−1) at the regional scale, indicating a wide range of spatial soil heterogeneity. The heterogeneity maps of soil parameters generated by this research can be effectively used by land planners and farm managers at a regional scale for crop nutrient management to reduce soil contamination risk. These maps serve as baseline materials and effective tools for suitable land management strategies such as conservation-effective tillage, integrated nutrient management, and organic farming based on the spatial distribution of soil properties and they can significantly enhance the long-term ecological sustainability of agro-ecosystems’ management.

Soil spatial heterogeneity created by river–sea interaction influences Tamarix chinensis root features in the Yellow River Delta

AbstractSalt‐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.

Microtopography effects on pedogenesis in the mudstone-derived soils of the hilly mountainous regions

Topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are referred to microtopographies. In hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physicochemical, and geochemical attributes of profiles were analyzed. The results showed that from the summit to the toeslope, soil thickness increased significantly and profile configuration changed from A–C to A–B–C. The total contents of Ca and Na decreased at the summit, backslope, and footslope, while the total contents of Al, Fe and Mg showed an opposite trend. On the summit and shoulder of the hillslope, weathered materials were transported away by gravity and surface erosion, exposing new rocks. As a result, soil development in these areas was relatively weak. In flat areas such as the footslope and toeslope with sufficient water conditions, the addition of weathered components and the prolonged contact between water, soil, and sediment led to further chemical weathering, resulting in highly developed characteristics. Microtopography may influence physicochemical properties, chemical weathering, and redistribution of water and materials, causing variations in pedogenic characteristics at different slope positions.

Factors controlling spatiotemporal variability of soil carbon accumulation and stock estimates in a tidal salt marsh

Abstract. Tidal salt marshes are important contributors to soil carbon (C) stocks despite their relatively small land surface area. Although it is well understood that salt marshes have soil C burial rates orders of magnitude greater than those of terrestrial ecosystems, there is a wide range in accrual rates among spatially distributed marshes. In addition, wide ranges in C accrual rates also exist within a single marsh ecosystem. Tidal marshes often contain multiple species of cordgrass due to variations in hydrology and soil biogeochemistry caused by microtopography and distance from tidal creeks, creating distinct subsites. Our overarching objective was to observe how soil C concentration and dissolved organic carbon (DOC) vary across four plant phenophases and across three subsites categorized by unique vegetation and hydrology. We also investigated the dominant biogeochemical controls on the spatiotemporal variability of soil C and DOC concentrations. We hypothesized that subsite biogeochemistry drives spatial heterogeneity in soil C concentration, and this causes variability in total soil C and DOC concentrations at the marsh scale. In addition, we hypothesized that soil C concentration and porewater biogeochemistry vary temporally across the four plant phenophases (i.e., senescence, dormancy, green-up, maturity). To test these interrelated hypotheses, we quantified soil C and DOC concentrations in 12 cm sections of soil cores (0–48 cm depth) across time (i.e., phenophase) and space (i.e., subsite), alongside several other porewater biogeochemical variables. Soil C concentration varied significantly (p < 0.05) among the three subsites and was significantly greater during plant dormancy. Soil S, porewater sulfide, redox potential, and depth predicted 44 % of the variability in soil C concentration. There were also significant spatial differences in the optical characterization properties of DOC across subsites. Our results show that soil C varied spatially across a marsh ecosystem by up to 63 % and across plant phenophase by 26 %, causing variability in soil C accrual rates and stocks depending on where and when samples are taken. This shows that hydrology, biogeochemistry, and plant phenology are major controls on salt marsh C content. It is critical to consider spatiotemporal heterogeneity in soil C concentration and porewater biogeochemistry to account for these sources of uncertainty in C stock estimates. We recommend that multiple locations and sampling time points are sampled when conducting blue C assessments to account for ecosystem-scale variability.

Forests high on CO2: A glimpse into how scientists study the biochemical machinery of forest ecosystems

Are forests across the planet storing more carbon as a result of rising atmospheric carbon dioxide (CO2) concentration? In this text, I propose to reflect on the work of researchers who are asking that very question. The focus is on a particular approach called free-air CO2 enrichment (FACE) experiments, in which forests in their local environment are subjected to a CO2 concentration higher than in the ambient air, to test the CO2 fertilization hypothesis. This hypothesis predicts that forests store more carbon in those conditions. FACE studies held the promise of establishing cause–effect relations and transcending the here and now. They emerged in the United States in the late 1980s, at a time when ecology scaled up to make itself relevant to the then nascent Earth System science. FACE experiments in forests are now conducted in Australia, the United Kingdom, and Brazil, and their results are closely scrutinized by a small research community. The text, first, presents the engineering feat that underpins FACE experiments in forests and discuss two problems highlighted by scientists because they impede hasty generalization from the data: the timescale needed to witness forests change and the spatial heterogeneity of forest soils. It then shows how scientists contend with their incomplete understanding of forest ecosystems as they bring together computer models and empirical data to build consensus around the sources of epistemic uncertainty. To conclude, I propose to rework the idea of “the macroscope” to conceptualize what scientists do when they seek to study forests as complex, layered, multi-scale systems. I wish to capture how researchers, who willingly endorse a planetary gaze, problematize their own predicament. This, as I suggest, has to do with the immanence of forests in the world.

Uncertainty Analysis of Post-Failure Behavior in Landslides Based on SPH Method and Generalized Geotechnical Random Field Theory

In slope stability analysis, the inherent heterogeneity and spatial variability of soil significantly influence the aftermath of landslides, including critical aspects like runout distance, influence distance, and volume. This research integrates Smoothed Particle Hydrodynamics (SPH) with random field theory to precisely model the large deformation events in slopes with anisotropic shear parameters, while leveraging Graphics Processing Unit (GPU) parallel computing to expedite the generation of random field samples and SPH simulations. This approach meticulously examines how spatial heterogeneity of soil affects slope instability, simulating soil parameters across varied geological settings. It considers the fluctuation scale of anisotropy, the cross-correlation of cohesion and the angle of internal friction, along with their coefficient of variation (CV), to elucidate their impact on landslide magnitude and severity. This study furnishes a robust tool for a holistic assessment of slope impacts and landslide volumes. Additionally, by delineating the computational efficiency disparities between GPUs and Central processing units (CPUs), it underscores the pronounced efficiency benefits of GPU computing. The insights garnered offer fresh perspectives and methodologies in slope stability analysis and disaster risk evaluation, contributing to the finer prediction and management of this prevalent and grave geological hazard.

Formation of reactive intermediates in paddy water from different temperature zones for the promotion of abiotic ammonification

The paddy field is a hot area of biogeochemical process. The paddy water has a large capacity in photo-generation of reactive intermediates (RIs) due to abundant photosensitive dissolved organic matter (DOM), which is influenced by the spatial heterogeneity of paddy soils but rarely been explored. Our work presents the first investigation of the role of soil properties on photochemistry in paddy water. Soil organic matter (SOM), determined by the temperature, was the dominant factor for the photo-generation of RIs in paddy water of main rice producing areas. The RI concentrations generated with abundant SOM from cool regions are 0.05–8.71 times higher than those for the warm regions in China. The humic-like substance and aromatic-like compounds of DOM plays an essential role in RIs generation, which is abundant in paddy soils rich in SOM from Chinese cool regions. In addition, RIs can efficiently accelerate the photo-ammonification of urea and free amino acids by 15.2 %–164 %, leading to 0.13–0.17 mmol/L/d photo-produced ammonium after fertilization, which is preferentially absorbed by rice. The findings of this study will extend our knowledge of the geochemistry of global paddy field ecosystem. The potential role of RIs in nitrogen cycle should be highlighted in the agroecosystem.

Dominant herbaceous plants contribute to the spatial heterogeneity of beech and riparian forest soils by influencing fungal and bacterial diversity

Understanding of factors that shape diversity patterns in forest ecosystems is a main challenge in forest ecology and management practices. Although herbaceous plants are known to contribute to the maintenance of the structure and function of temperate forests, their impact on fungal and bacterial communities in soils is largely unknown. Therefore, we conducted a comparative study of soil fungal and bacterial diversity in two Central European deciduous forests, focusing on plots with dominant herbaceous species of contrasting morphology, phenology, reproduction, and ecology, including Allium ursinum and Dentaria enneaphyllos in a beech forest, as well as Aegopodium podagraria and Ficaria verna in a riparian forest. Plots with a mixture of herbaceous species and without plant cover were also studied. In both forests, fungal communities showed the strongest association with spatial location, part of which was explained by between-site variability in soil chemistry and was also influenced by herbaceous vegetation. The community composition of saprotrophic fungi depended on the presence and type of herbaceous vegetation in both forests. In addition, herbaceous plants affected the composition of arbuscular mycorrhizal fungi community in the beech forest, while in the riparian forest they affected endophytes and plant pathogens. For bacteria, soil chemistry played the most important role. Our results showed that dominant herbaceous vegetation is one of the drivers shaping microbial community composition, contributing to spatial heterogeneity of forest sites. Given that herbaceous species, especially those forming monospecific patches, affect the soil biotic properties in temperate forests, they should be included in forest management practices.

Regulation of soil nitrogen cycling by shrubs in grasslands

Globally, grasslands are experiencing shrub expansion, but the effects of such plant community shifts on soil N cycling are seldom investigated. We explored the spatial heterogeneity of total soil N content by grid sampling down to a soil depth of 1.2 m, and analyzed net ammonification and nitrification rates in the top 0.2 m, during the growing season, in response to the patchiness of grasses and four shrub species in a grazed meadow on the Tibetan Plateau. The δ15N analyses of plant, soil, and mineral N (NH4+ and NO3−) revealed differences in N absorption strategies between shrubs and grasses. Heterogeneity in the total soil N distribution was common to at least a depth of 1.2 m. The lower δ15N values of the 1.2 m soil profile under shrubs were consistent with the lower δ15N values of leaves, aboveground litter, and roots of shrubs compared to grasses, reflecting the imprint of long-term N cycling in the soil as affected by shrubs. Increases in total soil N stock in the entire 1.2 m profile by 28%–32% under non-leguminous shrubs relative to grasses were ascribed to N accumulation in the lower 0.8 m. Consequently, deep sampling is essential for accurate estimation of soil N storage in shrubby meadows. The total N stock in soil under the leguminous shrub species was similar to that under grasses, which showed that the effect of shrubification on soil N storage depends on the shrub species. Nitrification rates in the topsoil under all shrubs were greater than under grasses, producing higher 15N-depleted NO3− contents under shrubs. Therefore, the lower δ15N signatures of shrub tissues compared to grasses reflected a preferential or adaptive uptake of NO3− by shrubs. The expansion of shrubs in grasslands creates high heterogeneity in N cycling and storage down to a considerable soil depth.

Spatial soil heterogeneity rather than the invasion of Spartina alterniflora drives soil bacterial community assembly in an Eastern Chinese intertidal zone along an estuary coastline

The invasion of Spartina alterniflora (S. alterniflora) significantly influences the stability and transformation of soil organic carbon in coastal ecosystems. However, the impact of this invasion on the assembly of soil bacterial communities along estuary coastlines and soil profiles remains unclear. This study involved collecting soil samples from different environments (areas covered with S. alterniflora vs. barren flats) along the coastline of an estuary. The samples were taken at different depths (0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm, 80–100 cm) within a 1-meter soil profile in the intertidal area of Xiaoyangkou Estuary in Jiangsu, China. The invasion of S. alterniflora had a notable impact on soil SOM (soil organic matter), DOC (dissolved organic carbon), POC (particulate organic carbon), and MAOC (mineral-associated organic carbon). Concurrently, the soil layer primarily influenced the levels of soil DOC and MAOC. The dominant bacterial communities inside the soil consisted of Proteobacteria (27.4–50.2 %), Bacteroidota (5.2–23.3 %), and Desulfobacterota (9.5–19.8 %), which participates in several elemental cycles, such as the carbon, nitrogen, sulfur, and phosphorus cycles. The changes in the patterns and functions of bacterial communities related to carbon cycling were mostly associated with the estuary shoreline, rather than being influenced by the invasion of S. alterniflora or variations in soil depths. Soil total carbon (TC) and SOM displayed a greater influence than other soil organic fractions on the distribution of the bacterial community. Furthermore, elements such as As, Cr, and Zn also exerted a significant impact on the assembly of soil bacterial communities. Our research findings suggest that the influence of S. alterniflora invasion on the composition and functioning of soil bacterial communities is contingent upon the specific features of the area. These characteristics, in turn, control the stability of soil carbon and the transformation of various types of soil carbon.

Analysis of spatial heterogeneity of soil physicochemical properties in northern Malawi

Topography and fertility management practices are critical when examining distribution of spatial heterogeneity of soil properties. The study was carried out on a 52-ha land with undulating topography of a village in Northern Malawi to analyze spatial soil heterogeneity with attention to topography and soil fertility management practices in 2021. The spatial heterogeneity of 12 soil chemical properties and soil texture were examined using geostatistical analysis. At 0–20 cm depth, 115 geocoded surface soil samples were collected. Remotely sensed images were captured using an unmanned aerial vehicle, processed, and analyzed to generate and visualize topographic data. Soil fertility management practices were described using field observations and questionnaire survey. The geostatistical analysis revealed spatial heterogeneity of most soil properties at a scale of 80–650 m. The spatial structure of soil pH, available phosphorus (P), total carbon (TC), total nitrogen (TN), and clay showed strong spatial autocorrelation (Q value <0.25). Calcium (Ca2+) and potassium (K+) had moderate spatial autocorrelations (Q values >0.25–< 0.75), whereas magnesium (Mg2+), sodium (Na+), sand, and silt had weak spatial autocorrelations (Q value >0.75). The spatial heterogeneity in TC, K+, Mg2+, CEC, clay, silt, and sand was influenced by the area's topography, whereas pH, P, TN, and Ca2+ were influenced by soil fertility management practices. While change can be negative or positive, differences in topography and fertility management practices significantly changed the physicochemical soil properties, and consequently affected their distribution. TN and P increased with the application of fertilizer, and manure, respectively. Increase in elevation and slope induced positive changes in CEC, K+, Mg2+ and clay. These results could be helpful in the development and application of precision agriculture in the village.

Annual 30 m winter wheat yield mapping in the Huang-Huai-Hai plain using crop growth model and long-term satellite images

There are great challenges for the accurate prediction of wheat yield at large-scale region due to the spatial heterogeneity of soil, management and meteorological conditions. The Huang-Huai-Hai plain (HHHP) is the most important wheat producing area in China. Timely and effective prediction of wheat yield in the HHHP is of great significance for ensuring food security. However, there is still a lack of studies on long-term wheat yield prediction with high spatial resolution in the HHHP. In this study, the simulation results (including phenological information, LAI and yield) of WheatGrow model and the meteorological variables were used to train regression model, which was applied in the corresponding satellite images and gridded meteorological variables to develop wheat yield prediction model (SCYMvp). Then time-series yield maps of wheat in the HHHP (2001-2020) were obtained and the digitization footprint was estimated. We found that SCYMvp model developed by combining machine learning algorithm (ML) with two state variables (phenological information and GCVI) had the best performance (r = 0.7, NRMSE = 15 %) for wheat yield prediction in the HHHP. Compared with other yield prediction models, SCYMvp model reduced the error of yield prediction to some extent. Meanwhile, SCYMvp model showed good accuracy in wheat yield prediction at the irrigated fields and rainfed fields. In addition, extreme climate events had a weak influence on the SCYMvp model in wheat yield prediction. The yield prediction with high spatial resolution generated by SCYMvp model in the HHHP during past 20 years had good consistency and low error with the statistical yield in the spatio-temporal scale. Compared with the GlobalWheatYield4km product, the SCYMvp model had a better ability to capture spatial heterogeneity of wheat yield at site scale. In addition, required data size per hectare for predicting wheat yield showed a significant increasing trend. The results indicated that the SCYMvp model developed in this study can effectively map wheat yield with high spatial resolution in the study area, and has good potential in smallholder farming economy with large spatial heterogeneity of management conditions.

Responses of community traits and soil characteristics of Achnatherum inebrians-type degraded grassland to grazing systems in alpine meadows on the Qinghai-Tibet Plateau.

Scientific grazing management is of great significance for the ecological health and sustainable use of alpine meadows. To explore appropriate management methods of alpine grasslands of the Qinghai-Tibet Plateau degraded by Achnatherum inebrians (Hance) Keng ex Tzvele presence, we studied the effects of different grazing systems on the A. inebrians population, grassland vegetation community traits, soil characteristics and soil microbial community structure for cold- season grazing plus supplementary feeding pasture (CSF) and four-season open public pasture (FOP) in Tianzhu County, Gansu Province. Compared with FOP, the CSF site showed significantly inhibited reproduction of A. inebrians, especially the crown width, seed yield and number of reproductive branches per plant were as high as 50%, significantly increased the aboveground biomass of edible forage and soil water content by 57% and 43-55%, better soil nutrients, and significantly reduced soil bulk density by 10- 29%. Different grazing systems affected the composition and diversity of soil microbial communities, with a greater effect on fungi than on bacterial flora. The most abundant phyla of bacteria and fungi were Proteobacteria and Ascomycota for CSF (by 30-38% and 24-28%) and for FOP (by 67-70% and 68-73%), and the relative abundance and species of bacterial and fungal genera were greater for CSF than FOP. The α-diversity indexes of fungi were improved, and the β-diversity of fungi was significant difference between CSF and FOP. However, the grazing utilization time was prolonged in FOP, which reduced the diversity and abundance of soil bacteria and increased soil spatial heterogeneity. The use of A. inebrians-type degraded grassland in the cold season, and as a winter supplementary feeding and resting ground, could effectively inhibit expansion of A. inebrians, promote edible forage growth, enhance grassland productivity and community stability, and improve soil structure. The results guide healthy and sustainable utilization of A. inebrians-type degraded grassland in the Qinghai-Tibet Plateau.

Agricultural activities lead to sediment infilling of wetlandscapes in the Canadian Prairies: Assessment of contributions by tillage, water and wind erosion

Soil erosion and sediment delivery models have been increasingly employed in studies of catchment sediment dynamics in current years. These models are also used to represent the spatial interaction of soil erosion and sediment transport processes, thereby providing spatially-distributed predictions of soil redistribution rates for agricultural landscapes. It has been widely recognized that individual soil erosion processes and their interactions contribute towards total soil erosion; however, quantifying the rates and patterns of soil erosion processes and their interactions within topographically complex landscapes is challenging. Therefore, the objective of this research was to estimate and model the relative contributions of tillage, water and wind erosion towards total soil erosion in the Canadian Prairie provinces of Manitoba and Alberta using 137Cs, a fallout radionuclide tracer, and three well-established models: (i) Tillage Erosion Model (TillEM); (ii) Revised Universal Soil Loss Equation, version 2 (RUSLE2); and (iii) Single-event Wind Erosion Evaluation Program (SWEEP). The findings indicate that the patterns of 137Cs-estimated soil erosion were closely matched with the erosion pattern predicted by TillEM and suggests that tillage erosion dominates the pattern of total soil erosion on the knolls of hummocky landscapes. Additionally, soil particle size variation within the wetland catchments reflected the modeled patterns of water and tillage erosion. Furthermore, our findings confirmed that colour coefficients are useful in identifying spatial heterogeneity of soil within wetland catchments and reflect the patterns of soil loss and gains. These results indicate that water and tillage erosion, and also their interactions, are main erosion processes in the Canadian Prairie Pothole Region (PPR), but that soil movement by tillage practices has been the predominant redistribution process.

Spatial heterogeneity of soil dissolved organic matter characteristics in the riparian zone of the Three Gorges Reservoir

AbstractDissolved organic matter (DOM) is one of the active soil carbon fractions. The characteristics of DOM in the riparian zone are closely related to the occurrence of eutrophication. However, there is no scientific consensus on how flooding intensity on DOM distribution in the riparian zone of the Three Gorges Reservoir (TGR). In this study, 99 soil riparian samples were collected from three water level elevations (145–155 m asl, 155–165 m asl and 165–175 m asl) in both mainstream and tributaries of the Yangtze River within the TGR. DOM characteristics were investigated using ultraviolet–visible absorption spectra and three‐dimensional fluorescence excitation–emission matrix‐parallel factor analysis as well as principal component analysis (PCA). The result showed that dissolved organic carbon (DOC), absorption coefficient at 254 nm (a254), absorption coefficient at 350 nm, specific ultraviolet absorbance at 254 nm (SUVA254), and humification index (HIX) decreased while freshness index (β:α) and biological index (BIX) increased with the decline of the water level elevations. The trend in the DOM characteristics along the riparian zone was mainly attributed to the variation in the bioavailability of DOM and fluorescence components (C1, C3 and C4). Overall, our study highlights the newly formed DOM during the dry season, indicated by β:α and BIX, might be more accumulated at the lower elevation. Furthermore, because of the greater lability during the reservoir impoundment, the newly formed DOM can be easily utilized by algae and may raise water eutrophication under re‐flooding and longer flooding, thus enforced strategic mitigation measures could help to achieve the goal of riparian restoration in TGR.

Spatial Distribution, Migration, and Ecological Risk of Cd in Sediments and Soils Surrounding Sulfide Mines—A Case Study of the Dabaoshan Mine of Guangdong, China

Acid mine drainage (AMD) resulting from metal sulfide mining activities can lead to contamination by potentially toxic elements (PTEs) primarily concentrated around the mining area and gradually spreading outward. However, ecological risks do not correspond directly to PTE concentrations, making it challenging to effectively manage the mining environment and accurately prevent potential ecological impacts. In this paper, we analyzed Cd levels in sediments, soils, and corresponding rice grains sampled from four villages near Dabaoshan Mine of Guangdong, China, in 2017. Our results reveal that Cd is the most prominent pollutant element, exhibiting significant enrichment and spatial heterogeneity in both soil and sediments and higher accumulation levels in rice grains compared to other PTEs. Cd concentrations in soil decrease from the tailings pond to the river terrace, with a slight increase after Taiping River joins and flows into the alluvial plain. However, the concentrations in sediments show the opposite trend. The bioconcentration factor (BCF) for Cd in agricultural soil from the river terrace is lower than that from the alluvial plain and the degree of exceeding the maximum permit level (MPL) of Cd in rice grains increases along the river. Mineral transformation and topography are important factors in controlling the geochemical behavior of PTEs. Remediation efforts alter the physicochemical properties of the river, resulting in the release of PTEs during schwertmannite transformation followed by their adsorption by clay minerals. Furthermore, the random forest (RF) analysis highlights that the bioavailability and potential ecological risk of Cd in soils are governed by the occurrence form of Cd in different topographies, mainly controlled by TFe2O3, Mn, and CaO in the river terrace and CaO, Al2O3/SiO2, and Mn in the alluvial plain. Therefore, considering the impact of topography on mineral compositions, physicochemical properties, and occurrence form of PTEs in soil and sediments is essential for assessing ecological risk in mining areas.

Temporal and operation-induced instability of apparent soil electrical conductivity measurements

Measuring apparent soil electrical conductivity (ECa), using galvanic contact resistivity (GCR) and electromagnetic induction (EMI) techniques, is frequently conducted to reveal spatial soil heterogeneity. Various studies have demonstrated the possibilities for significant changes in the measured quantities over time with relatively stable spatial structure representations. The objective of this study was to quantify the effects of temporal drift and operational noise for three popular ECa mapping instruments. They were placed in stationary positions approximately 8 m apart in an area with relatively low ECa. Temporal drift was assessed using a series of 4.5-h data logs recorded under different weather conditions (from extremely hot to near freezing temperatures). The two EMI instruments were also used to quantify the effect of minor changes in the height, pitch and roll of the sensor with respect to the ground. These operational noise tests were replicated over several days. Our results reveal the GCR measurements of ECa, along with perpendicular coplanar EMI measurements, have shown relatively strong stability over time. Each operational effect introduced measurement uncertainties comparable to the impact of a change in temperature and soil water content.