Silt Fractions Research Articles

ИК-спектры поглощения фракций гранулометрических элементов чернозема типичного целинного Курской области

The fractions of granulometric elements isolated by the method of roiling from the humusaccumulative horizon A of the deep typical virgin chernozem of the Kursk Region were studied using infrared spectroscopy. According to the data obtained, the fractions of granulometric elements differ significantly in their material composition. The coarse dust fractions mainly consist of quartz, feldspar, polysaccharides and a small amount of specific humus substances. The fine dust fractions, and in particular the silt fraction, differ significantly in material composition from the coarse dust fractions. They are mainly composed not only of polysaccharides, but also of clay minerals, including alternating layer formations of the mica-montmorillonite type, a much higher amount of specific humus substances, and less quartz and feldspar. The medium dust fractions occupy an intermediate position in terms of material composition and are closer to the fine fractions than to the coarse dust fractions. The method of infrared spectroscopy makes it possible to reveal fundamental differences in the material composition between individual granulometric fractions. However, a number of specific features inherent to individual components of the soil solid phase are not apparent in the infrared spectra of granulometric fractions. This is due to the active interaction between the organic and mineral components of the soil. As a result of such interactions many active centers and functional groups are blocked and do not appear in the infrared spectra.

Гравитационное движение грунтов на склонах и их влияние на состояние водных объектов

The purpose of the research is to study the features of the movement of particles, aggregates and geological bodies (landslides) downhill under the influence of a number of natural and man-made factors, to study the most common natural and man-made objects that reduce the activity of the development of slope processes. Two of the most common slope exogenous geological processes are considered – surface flushing and landslide. These processes contribute to the entry of silt fraction into the sediments of water bodies. The study of pollution of water bodies with heavy metals still remains relevant when assessing the geo ecological state of the environment. On the Volga River basin the principles are proposed and the zoning is presented. According to natural and technogenic objects, four categories of sites were allocated hierarchically for monitoring the pollution of the territory with heavy metals. The zoning of the bed of water bodies for the distribution of silty sediments – sorbents of pollutants was carried out. The elements of the energy approach are presented, giving an understanding of the most likely locations of pollutants – energy traps and potential barriers. Practical examples of the spread of pollutants in the natural and man-made environment and the interaction of natural and man-made processes in the landslide system are given. For the landslide process, the most typical interactions between a geological body and man-made objects are presented. On the example of the most typical landslides for the European part of Russia, the measures aimed at their stabilization, as well as the impacts contributing to their activation, are presented. Natural and man-made potential barriers to the landslide process are considered.

Морфолого-генетична та агрономічна характеристики контрастних за засоленням ґрунтів солонцевого комплексу Приорілля

The article presents the results of field and laboratory studies on the determination of the morphological, genetic and agronomic characteristics of the soils of the Solon complex of Prioril, contrasting in terms of salinity - the establishment of the peculiarities of the morphological structure of the profiles, the granulometric composition, and the parameters of the main agrochemical, salt and physicochemical parameters of the salt marsh of the meadow-black earth shallow salt marsh and black earth-meadow soil - as typical components of the salt complex of the Oril river valley. Standardized field survey and laboratory-analytical methods were used. It has been established that manifestations of halogenation increase with depth in the Luchno-chernozem salt marsh. Alkalinity in the humus-iluvial horizon increases to a strong degree, in deeper horizons - to a very strong one; the degree of salinity increases to medium, strong, and finally to very strong in the bedrock. According to the depth of the upper horizon of salt accumulation, this soil is classified as saline. The content of absorbed sodium in the humus-iluvial and illuvial horizons corresponds to the "saline" gradation. The chernozem-meadow soil is non-saline according to the content of toxic salts in the entire profile, there are no signs of physical and physico-chemical salinity. The content of the silt fraction in the salt marsh profile increases with depth and reaches its maximum value in the illuvial horizon, which is typical for salt marshes and is explained by the redistribution of soil colloids in the profile, the granulometric composition of the salt marsh in the humus-eluvial and illuvial horizons is light clay, in the humus-illuvial - medium clay. The profile of the chernozem-meadow soil is also heterogeneous in granulometric composition, which is heavier from medium loam in the humus horizon to heavy loam in the transitional horizons. The reason for this may be ancient alluvial processes that formed the soil-forming rock of the single-forest terrace. The content of humus in the salt pan in humus-eluvial and humus-iluvial horizons is average, the content of mineral (nitrate and ammonia) nitrogen is very low. The content of mobile potassium turned out to be elevated, and the content of mobile phosphorus was very high. In the chernozem-meadow soil, the content of humus in the humus arable horizon is high, in the first transitional one, it is average. The content of mineral nitrogen is low. The content of mobile phosphorus exceeds the upper limit of the high level by 3.5 times, and mobile potassium by 3.1 times, which is typical for the soils of closed depressions and is a consequence of long-term accumulation of surface runoff waters. Conclusions. The salt marsh complex of Priorillya with the number of salt marshes in the soil cover of about 50% is typical for the southern part of the Middle Forest Steppe in terms of the structure of soil profiles and soil halogenation. A characteristic feature of the studied salt marsh complex is the significant contrast of its components in terms of halogenation manifestations: at a short distance there are salt marsh highly saline salt marsh and leached chernozem-meadow soil without physical and physico-chemical signs of salinity.

Characterizing a weathering profile over quartz-mica schists in undulating terrain in Peninsular Malaysia

The weathering profile can be differentiated into an upper, 4.8 m thick, pedological soil (zone I) and a lower, >16.2 m thick, saprock (zone II). Zone I comprises thin IA and IB soil horizons of firm, clayey sand with lateritic concretions, and a IC soil horizon of stiff, clayey silt with quartz clasts and lateritized core-stones. Zone II comprises steeply dipping to vertical, bands of pinkish to grey, stiff silt with distinct relict foliation (highly weathered schist) inter-fingering with bands of reddish yellow, firm clayey silt with indistinct foliation (completely weathered schist) towards its top, and bands of white to light grey, hard silt with distinct foliation (moderately weathered schist) towards its bottom. Lateral variations in abundance of differently weathered schist and preservation of fracture planes allow zone II to be separated into IIA, IIB and IIC sub-zones. The pedological soil (zone I) can be correlated with Class VI of standard rock mass weathering classifications, whilst the saprock sub-zones IIA, IIB and IIC are correlated with Classes V, IV and III, respectively. Silt fractions in the profile consist predominantly of sericite flakes, whilst the sand fractions are mostly of quartz grains and the clay fractions of mainly illite and kaolinite. Decreasing densities, unit weights and silt contents up the profile, but increasing porosities and clay contents, indicate increasing in situ alteration of the schist bedrock. Lowering of an unconfined groundwater table as a result of down-cutting by rivers in adjacent valleys is considered responsible for development of the weathering profile.

Sorption capacity of organic matter to heavy metals and its use for polluted soils recover soils recover

The article considers the results of leached chernozems and yellow soil research in Central Russia and in the South of Central China. The research has demonstrated that organic matter has an increased sorption capacity for heavy metals (HM), including lead (Pb) and cadmium (Cd), which are hazardous environmental pollutants. Studies conducted on chernozems demonstrate features of HM migration along a soil profile. Thus, the total content of elements accumulates in the upper humus horizon, further down the profile it gradually decreases, following a decrease in an amount of organic matter. In a soil-forming rock an accumulation of metals is again noted due to the alkaline reaction of soil solution and silt fraction, which is enriched in soil-forming rocks. A significant increase in elements content in soils of arable land (farmland soils) was revealed in comparison with a fallow territory and a forest belt. This phenomenon explains by an additional supply of HMs as an admixture of mineral fertilizers applied on plowed chernozems. In addition, HMs are also appear as a result of agricultural machinery operations during flammable fuel combustion. The ability of organic matter to increased sorption of HMs can be used to restore heavily polluted areas. Farmland soils of Sichuan province were studied as a model experiment. Keywords: CHERNOZEMS, YELLOW SOIL, HEAVY METALS, LEAD, CADMIUM, TOTAL CONTENT, EXCHANGE COMPOUNDS, VORONEZH OBLAST, SICHUAN PROVINCE

Сорбционная способность органического вещества к тяжелым металлам и ее применение при восстановлении загрязненных почв

The article considers the results of leached chernozems and yellow soil research in Central Russia and in the South of Central China. The research has demonstrated that organic matter has an increased sorption capacity for heavy metals (HM), including lead (Pb) and cadmium (Cd), which are hazardous environmental pollutants. Studies conducted on chernozems demonstrate features of HM migration along a soil profile. Thus, the total content of elements accumulates in the upper humus horizon, further down the profile it gradually decreases, following a decrease in an amount of organic matter. In a soil-forming rock an accumulation of metals is again noted due to the alkaline reaction of soil solution and silt fraction, which is enriched in soil-forming rocks. A significant increase in elements content in soils of arable land (farmland soils) was revealed in comparison with a fallow territory and a forest belt. This phenomenon explains by an additional supply of HMs as an admixture of mineral fertilizers applied on plowed chernozems. In addition, HMs are also appear as a result of agricultural machinery operations during flammable fuel combustion. The ability of organic matter to increased sorption of HMs can be used to restore heavily polluted areas. Farmland soils of Sichuan province were studied as a model experiment. Keywords: CHERNOZEMS, YELLOW SOIL, HEAVY METALS, LEAD, CADMIUM, TOTAL CONTENT, EXCHANGE COMPOUNDS, VORONEZH OBLAST, SICHUAN PROVINCE

A Combination of Shade Trees and Soil Characteristics May Determine Robusta Coffee (Coffea canephora) Yield in a Tropical Monsoon Environment

Shade trees may have contrastive effects on Robusta coffee (Coffea canephora Pierre ex A. Froehner) yield, which may be additionally influenced by soil properties and reproductive stages of the plant. The current study is aimed at examining the interaction effects of shade trees, soils with different properties, and reproductive stages on coffee yield and identifying key factors influencing the yield. The current study was conducted in Dakha, Kontum of Vietnam on 133 farms, randomly selected from two soils, and two reproductive stages of coffee plants planted with and without shade trees. The coffee yield was measured, and surface soil samples were taken from these farms to be analyzed for 16 variables. The results showed that shade trees enhanced coffee yield significantly (by 28%) in the young reproductive stage but exhibited an insignificant effect in the old stage. The silt fraction, total nitrogen, cation exchange capacity, and shade trees were key factors determining 52% of the coffee yield in the sandy clay loam soil, while silt content and shade trees determined 23% of the yield in the clay soil. These findings suggest that shade trees, together with some soil properties, should be considered to improve coffee production under a tropical monsoon climate region.

Repeated Palaeofloods of 8.2–6.4 ka and Coeval Rise of Neonatal Culture in the Upper Yangtze River, China

Flood events have long been very frequent along the Yangtze River in Chongqing, China. A complete sedimentary sequence of alluvia, found in the Yuxi profile (YXP) was applied to explore features of the palaeoflood layers that maintained records related to the contexts of flooding hydroclimate. The AMS14C dating results dependent on animal bones from the YXP validate that the chronology of the palaeoflood layers was dated, between ca. 8200 and 6400 a BP, and multiple cultural layers were intercut among these palaeoflood layers. By means of particle size and end-member analyses for the palaeoflood sediments, the fractions of fine silt and clay in deposits account for a high proportion of the flood sediments, suggesting that the overbank flood was the main power in building the palaeoflood layers. Due to the climatic episodes defined by pollen assemblages, the thickness of the flood layers is positively correlated with soil erosion because of different hydrothermal conditions. The wavelet spectra of the mean particle-size series also suggest that there may be two major palaeoflooding cycles of ~700 and ~30 years. Despite the sustained palaeoflooding, the Yuxi Culture grew from small to big, and was never broken off, in terms of the findings of artificial remains in the YXP.

Influence of Robinia pseudoacacia L. and Quercus robur L. artificial forest plantations on the particle-size distribution of calcic chernozem

The particle-size distribution is one of the most important characteristics of soils, which determines most of their properties and features of the main regimes. Artificial forest plantations in the steppe act as a powerful environment-transforming factor, which over time is capable of changing even quite conservative properties of soils, including their particle-size distribution. The study of the influence of forest plantations on the particle-size distribution was carried out using soil samples taken from calcic chernozem, chernozem under the plantation of R. pseudoacacia L. and under the plantation of Q. robur L. The determination of the particle-size distribution was carried out by the pipette method, with the preparation of the sample by trituration with a solution of sodium pyrophosphate. The classification of granulometric fractions is given according to N. A. Kaczynskii. The analysis of the characteristics of the ratio of particle-size distribution of the studied chernozems revealed that the zonal chernozem is characterized by an increased content of the sand fraction and a reduced content of the silt fraction in the H1 and H2 horizons compared to the lower horizons. The calcic chernozem under the plantation of R. pseudoacacia L. is characterized by a relatively uniform distribution of the content of sand, dust and silt fractions along the soil profile. In calcic chernozem under the plantation of Q. robur L., the maximum content of the sand fraction was found in the surface horizon, with a gradual decrease in the content of this fraction with depth, while the content of dust and silt fractions increased with depth. The growth of R. pseudoacacia L. and Q. robur L. plantations on calcic chernozems leads to an increase in the content of sand fractions and a decrease in dust and physical clay fractions. There is also a certain change in the profile distribution of fractions, especially sand, under the influence of the growth of forest plantations. Each of the investigated calcic chernozems is characterized by a specific ratio of «sand : dust : silt» fractions, which indicates a different genesis of granulometric fractions.

Mineralogy of Particulate Suspended Matter of the Severnaya Dvina River (White Sea, Russia)

This paper seeks to generalize the data obtained over 4 years of investigation of the suspended sediment mineral composition in Severnaya Dvina River. The sampling of the river water to isolate suspended particulate matter (SPM) using the method of sedimentation from large water volumes (200–800 L) was carried out at two points of the delta with different hydrological regimes every month for four years. SPM samples weighing 1 g and more allowed us to obtain and preserve for different analytical procedures the grain size fractions from 1.0–0.5 to <0.001 mm (from sands to pelit). The analyses of fractions revealed a sharp prevalence of pelitic fractions (<0.01 mm) (near 90% on average), while the share of silt was 4%–5%. Coarse fractions were found in the SPM of the main stream of the river but were absent in the samples taken at the point near the river–sea boundary. The determinations of clastic, clay, and some other minerals using the method of X-ray diffraction analysis have shown that in the group of clastic minerals, quartz and plagioclase prevail. Among the clay minerals, smectite and illite were present in high quantities, and chlorite and kaolinite were in lower quantitative. The distribution of minerals in the grain size fractions showed that the sum of clastic minerals reached its highest content of up to 84% in silt fractions (0.05–0.01 mm), while the sum of clay minerals in this fraction was minimal (about 15%). Investigations of seasonal variations of clastic and clay minerals during the whole period showed that the contents of minerals in the SPM of the Severnaya Dvina did not change much over the year. As a result of this work, the following trend was established on the behavior of all kinds of minerals: during the periods of high water in spring and autumn, a slightly increased quantity of clastic minerals was detected in comparison to winter and summer, while the variations in the quantities of clay minerals were insignificant.

Impact of topsoil mining for unfired mudbricks on soil quality in eastern KwaZulu‐Natal, South Africa

AbstractTopsoil mining associated with informal mud brick making is common in rural villages of South Africa. The impact of topsoil mining on soil quality, however has not been investigated. This study therefore assessed the impact of topsoil mining associated with unfired mud bricks on selected soil quality indicators in two villages of KwaZulu‐Natal, South Africa. First, local miners were interviewed to ascertain information related to topsoil mining, brickfield site identification and soil suitability for mud bricks. Two brickfields per village mined for ≤5 and > 20 years, respectively were used in this study. Experiment consisted of three treatments, that is, unmined, mined and recovering lands replicated three times. Nine soil samples were collected (0–10 cm) from each site (three composite samples per treatment) with corresponding bulk density samples taken at 0–5 cm using core rings. The average topsoil mining depth was 30 cm. Interviews revealed that isidaka (poorly drained sandy clay) and isibomvu (red soil) are preferred over ubumba (clayey) soils. Topsoil mining increased silt fraction across all studied brickfields with an average of 45.2% in mined compared with 30.6% in unmined treatments. The response of clay fractions was variable across villages and mining time. Mining significantly decreased mean weight diameter, exchangeable bases, organic carbon, and nitrogen content and stocks and porosity while it increased bulk density. Results show that topsoil mining for mud brick making results in poor soil physical quality, nutrient availability and carbon storage with implications for land degradation in mud brickfields.

Dominant role of deglaciation in Late Pleistocene–Early Holocene sediment aggradation in the Upper Chenab valley, NW Himalaya

AbstractSediment transfer from the interiors of the Himalaya is complex because the archives are influenced by both glacial and monsoonal cycles. To deconvolve the coupling of glacial and monsoonal effects on sediment transfer processes, we investigate the Late Pleistocene–Holocene sediment archive in the Upper Chenab valley. Optically stimulated luminescence (OSL) ages from the archive indicate major aggradation during ca. 20–10 ka. Isotopic fingerprinting using Sr-Nd isotopes in silt fractions together with clast counts in boulder-pebble fractions indicate a decreasing Higher Himalayan sediment flux in the archive with time. Decreasing clast size, increasing clast roundness, increasing matrix to clast ratio, and dominance of the Higher Himalayan sourcing unequivocally suggest strong glacial influence during the initial stages of the archive formation. This evidence also agrees with the existing retreat ages of glaciers in the Upper Chenab valley. Results of our study also show that the upper parts of the archive contain significant fluvial sediment contribution from the Lesser Himalaya, which suggests an active role of the stronger Indian Summer Monsoon (ISM) in the region during the Early Holocene. The apparent decrease in sediment supply from the Higher Himalayan sources could have been due to longer source-to-sink transport in the Early Holocene and/or increased hillslope flux from Lesser Himalayan sources.

Integrating GIS techniques and lab analyses to assess the effect of sediments on the physical and chemical properties of soil and water in Um Naaj marsh, southern Iraq

A study for the evaluation of some physical and chemical properties of soil and water of certain sites in southern Iraqi marsh called Umm Naaj, a part of Al-Hawizeh Marsh, has been carried out using the integration between fieldwork, lab analyses, and GIS techniques. Sixteen water and soil samples were collected, then transferred to the lab. In the lab, some chemical properties of water samples were determined, while soil samples are subjected to some chemical and physical analysis. IDW method in GIS software had been utilized for interpolation of spatial distribution of chemical and physical properties of soil and water through the study area. Results of analysis and interpolation maps showed that the clay fraction was the dominant in soil samples, followed by silt and sand. Regarding chemical properties, all soil samples are an alkaline reaction. The percent of minerals for silt fraction indicate that calcite was the dominant mineral followed by quartz and illite. The x-ray diffraction analysis results indicated the presence of regular Mica-Smectite mixed layer mineral. The interpolation maps indicated that there is an effect of sediments on some properties in different levels where some properties were highly affected and some moderately and some have no effect on soil and water quality.

The Contributions of Soil Biochemical Properties as Determinant of Pineapple (Ananas comosus [L.] Merr.) Plantation LandProductivity in Central Lampung Regency

One of the management challenges in pineapple cultivation at plantation scale is the still occurrence of disparity in land productivity across the cultivated area although the cropping practices have been implemented for many years. In the case of a pineapple plantation in Central Lampung Regency, contribution of soil biochemical properties in terms of various soil enzyme activities as a determinant factor of land productivity has never been elaborated. This research was aimed to study the relationships among biochemical and other soil properties with land productivity or pineapple yield at plantation scale. Rhizosphere soil-composite samples were taken purposively from 4 stations at the largest Indonesian pineapple plantation representing blocks with high and low yield and growth at vegetative and generative phase. Relationships amongst the studied parameters were evaluated using PCA and linear multiple regression analysis. The results showed significant contributions of the rhizosphere soil properties on the pineapple yield according to equation: Yield = 64.895 – 6.546 PCA1 +13.057 PCA2 – 7.722 PCA4 (R2= 0.612), where PCA1 consisted of soil available-P, available-K, and CEC; PCA2 was of soil base saturation, total microbe population, enzyme activities of cellulase and invertase, while PCA4 was of soil organic C, silt fraction, and phosphatase activities.

Patterns of organic carbon and nitrogen stocks in soil particle-size fractions along an aridity gradient in Northern China’s deserts

Clay and silt fractions (<53 μm in particle size) play a critical role in soil organic carbon (SOC) storage and are used to characterize SOC storage in terrestrial ecosystems. However, there is unclarity about SOC content and stock in soil particle-size fractions in deserts where the soil is immature. In this study, we investigated the composition of soil particles and the stocks of SOC and N in two particle-size fractions of 0–53 μm and 0–100 μm at the top (0–30 cm) and deeper (30–50 cm) layers along an aridity gradient. The very fine sand (53–100 μm in particle size) was the major component of bulk soil. The C and N stocks in the top 50 cm of soil decreased linearly with increasing aridity, from 63.5 MgC ha−1 to 4.1 MgC ha−1 and from 4.6 MgN ha−1 to 0.8 MgN ha−1, respectively. Organic C content in two soil particle-size fractions and their contribution to bulk SOC decreased linearly with increasing aridity. Organic C content in < 100 μm soil particle-size fraction accounted for 57.8 %-99.2 % of bulk SOC, and it was only 0.6 %-24.2 % in the < 53 μm fraction. SOC stock was estimated by < 100 μm soil particle-size fractions compared with clay and silt (<53 μm). Organic C content in two soil particle-size fractions was higher in the alpine and steppe deserts than in the Gobi and sandy deserts; it was significantly higher at 0–30 cm than at 30–50 cm for all deserts. Vegetation cover was the first predictor for the organic C content in two soil particle-size fractions and their contribution to bulk SOC, addressing the direct contribution of plant-derived C inputs to soil particle-size fraction. Our study provides strong empirical evidence that organic C and N in deserts are better estimated by soil particles < 100 μm rather than clay and silt-sized fraction (<53 μm in particle size).

Evaluation of the Role of Silt Content on the Flocculation Behavior of Clay‐Silt Mixtures

AbstractThe interactions and impacts of silt content on clay‐silt mixture flocculation processes and settling and floc properties were investigated from a series of laboratory experiments. The results demonstrate that the silt content in clay‐silt mixtures has an impact on the time‐evolution average floc size, peak floc size, and equilibrium floc size. Increasing the silt content reduces the floc strength, recovery factor, and average floc size. The silt fraction can present both cohesive and noncohesive characteristics in silt‐clay suspensions. The bulk concentration of clay‐silt mixtures was found to reasonably correlate with the average floc sizes under equilibrium conditions and with maximal floc sizes under both equilibrium and nonequilibrium conditions. The results also show that the flux‐settling velocities increase with increasing silt content. Specifically, the flux‐settling velocities are 0.66, 0.87, and 1.39 mm/s for mixing ratios of clay‐silt of 1:0.5, 1:1, and 1:2.5, respectively, under equilibrium conditions. Under growth‐breakup‐reflocculation (G‐B‐R) conditions, the percentage changes in the flux‐settling velocities of flocs during the regrowth period are 22%, 41%, and 42% less than those under equilibrium conditions. Therefore, both the silt content and hydrodynamic conditions need to be taken into consideration when determining the flux‐settling velocities under variable shear conditions. The findings from this research provide better insight into the highly complex role of silt in the flocculation process of clay‐silt mixtures in natural water environments.

Influence of Bedform Migration on Nitrate Reduction in Hyporheic Zones of Heterogeneous Sediments

AbstractThe transport of sediments induced by river flow leads to the formation and movement of bedforms like ripples, and the exchange flux caused by the interaction between stream and bedforms significantly influences nitrogen dynamics. Previous studies have studied the role of bedform migration on nitrogen cycling in homogeneous sediments, however, how bedform migration affects nitrate reduction in heterogeneous streambeds is still unknown. In this study, we established a series of two‐dimensional numerical models to investigate the role of bedform migration on nitrate removal in physically (permeability) and chemically (particulate organic carbon; POC) heterogeneous sediments. Results from mobile bedforms were compared with matching immobile bedforms and equivalently homogeneous mobile ones. Mobile bedforms create periodic exchange flux fluctuations, reduce solutes penetration depths and residence time, and result in decreased denitrification rate. Both a larger bedform celerity and a smaller silt fraction lead to a lower NO3− removal efficiency. Thus, the bedforms are typically assumed to be immobile potentially making an overestimation of NO3− removal. Moreover, sediment heterogeneity cannot enhance NO3− removal in mobile bedforms, where the penetration depth and the residence timescale of NO3− are suppressed, and the formation of anoxic microzone is inhibited. The finding is significantly different from the previous understanding about sediment heterogeneity that can obviously enhance NO3− removal. This study is useful for understanding nitrate processing in streambed sediments and benefits to the management of watershed nutrients.

Colombian soil texture: building a spatial ensemble model

Abstract. Texture is a fundamental soil property for multiple applications in environmental and earth sciences. Knowing its spatial distribution allows a better understanding of the response of soil conditions to changes in the environment, such as land use. This paper describes the technical development of Colombia's first texture maps, obtained via a spatial ensemble of national and global digital soil mapping products. This work compiles a new database with 4203 soil profiles, which were harmonized at five standard depths (0–5, 5–15, 15–30, 30–60, and 60–100 cm) and standardized with additive log ratio (ALR) transformation. A compilation of 83 covariates was developed and harmonized at 1 km2 of spatial resolution. Ensemble machine learning (EML) algorithms (MACHISPLIN and landmap) were trained to predict the distribution of soil particle size fractions (PSFs) (clay, sand, and silt), and a comparison with SoilGrids (SG) products was performed. Finally, a spatial ensemble function was created to identify the smallest prediction errors between EML and SG. Our results are the first effort to build a national texture map (clay, sand, and silt fractions) based on digital soil mapping in Colombia. The results of EML algorithms showed that their accuracies were very similar at each standard depth, and were more accurate than SG. The largest improvement with the spatial ensemble was found at the first layer (0–5 cm). EML predictions were frequently selected for each PSF and depth in the total area; however, SG predictions were better when increasing soil depth in some specific regions. The final error distribution in the study area showed that sand presented higher absolute error values than clay and silt fractions, specifically in eastern Colombia. The spatial distribution of soil texture in Colombia is a potential tool to provide information for water-related applications, ecosystem services, and agricultural and crop modeling. However, future efforts need to improve aspects such as treating abrupt changes in the texture between depths and unbalanced data. Our results and the compiled database (https://doi.org/10.6073/pasta/3f91778c2f6ad46c3cc70b61f02532db, Varón-Ramírez and Araujo-Carrillo, 2022, https://doi.org/10.6073/pasta/d6c0bf5847aa40836b42dcc3e0ea874e, Varón-Ramírez et al., 2022) provide new insights to solve some of the aforementioned issues.

Sediment transport and morphological responses of a silty coast to a cold front event in the southwest Bohai Bay of China

Silty coast, as a transitional state between muddy coast and sandy coast, possesses a considerable percentage of the overall coast in China. Huanghua-Binzhou coast in the southwest Bohai Bay in the northeastern China is a typical silty coast which is vulnerable to cold fronts when its seabed is prone to suffer suddenly drastic erosion and deposition due to the sediment there with relatively low incipient velocity and high settling velocity. In this study, a multi-sediment fraction model was established and two-way coupled with the wave-tide-surge model to investigate the responses of the sediment transport and morphodynamics of Huanghua-Binzhou coast to a cold front event during 10–13th Oct. 2003. The model results demonstrate that three sediment fractions, i.e. mud, silt and sand, showed different responses to the storm due to their different spatial percentages and distinct physical properties. The silt fraction, as the primary fraction, played a leading role in the suspension and transport of the total sediment, and showed a pattern of “deposition-erosion-deposition” in the cross-shore direction like the total morphological change. The fine sediment was transported westward and offshore during the storm, which indicated the sediment coarsening in the study area. The depth-induced wave modulation considerably enhanced the resuspension ability of the nearshore waves for sediment and thus played a critical role in intensifying the erosion. The Huanghua waterway siltation mainly resulted from the resuspension of the offshore sediment by the strong wind waves and its westward transport by the wind-induced currents during the storm. The construction of two long jetties in 2006 can significantly reduce the deposition in the waterway by 75%, and the additional large-scale construction in 2016 can further lessen the waterway siltation by intercepting the westward sediment transport and reduce the suspended sediment concentration by 30% by the land reclamation in the study area.

A comparison of soil characteristics from four land covers around a coal mining concession area in South Kalimantan

Understanding soil characteristics is important to determine the alternative strategies of land management, particularly those related to the scheme of soil and water conservation. This study investigated soil characteristics from four land covers around the coal mining concession area located in South Kalimantan. A soil survey was conducted using a purposive sampling method with three replicates in each land cover. Soil samples that were taken at depths of 0-10 cm, 11-20 cm, and 21-30 cm, were composited before being brought to the laboratory to quantify their characteristics, such as texture and organic carbon content. Data analysis was processed using a non-parametric test with a significant level of 5%. Comparison average of soil characteristics between land covers was evaluated using the Kruskal-Wallis test and followed by Nemenyi-test. Results found that soil characteristics from four land covers significantly differed in texture and organic carbon content. The highest sand fraction was noted in shrubs (67.23±0.86%), while the greatest silt fraction was recorded in plantation forests (29.71±2.84%). Compared to other land covers, the clay content in plantation forests and reclamation area was relatively equal by around 53-54%. On another side, The highest soil organic carbon was found in plantation forests with ranging of (4.44±0.14%) followed by natural forests (4.24±0.62%), shrubs (3.38±0.09%), and reclamation area (1.14±0.09%). These findings indicated there were high variations of soil characteristics from different land covers around the coal mining concession area. Therefore, it is recommended for managers to apply adaptive strategies in supporting soil conservation efforts based on the soil characteristics in each site.