Buried Horizons Research Articles

Activity concentration and distribution of 40K in the soil profile of the Rostov agglomeration.

The activity concentration of 40K in soils of Rostov agglomeration was studied. Natural and anthropogenically modified soils of Rostov agglomeration were studied: Haplic Chernozems, Haplic Chernozems (Technic), Urbic Technosols. Activity concentration 40K in soils was measured by gamma-spectrometric method of radionuclide analysis. The total mass fraction of K2O was determined by X-ray fluorescence method on a Spectroscan MAKS-GV instrument. Knowing the total mass fraction of K2O, we calculated its potential radioactivity based on the fact that one gram of natural potassium has an activity concentration of 28.5 Bq. Comparison of the two methods allows estimating the involvement of 40K in biogenic cycles. No significant differences between the actual and calculated activity concentration of 40K in the soil-forming rock were revealed, while in horizons A and B the calculated activity is significantly higher. At the same time, there are no reliable differences between native and their buried analogs. The direct influence of the granulometric composition on the activity concentration of 40K was not established, but in the urban horizons with lightened granulometric composition the average activity of 40K is the lowest by reliably significant values when comparing this index with native, buried horizons and the group of heavy urban horizons. This implies that 40K is more actively involved in biogenic cycles than its stable isotopes. The burial under urban deposits is accompanied by a weak change in the activity concentration of 40K in the profile, while the difference between genetic horizons is leveled out.

A method to estimate surface mass-balance in glacier accumulation areas based on digital elevation models and submergence velocities

AbstractMeasuring surface mass-balance in the accumulation areas of glaciers is challenging because of the high spatial variability of snow accumulation and the difficulty of conducting annual field glaciological measurements. Here, we propose a method that can solve both these problems for many locations. Ground-penetrating radar measurements and firn cores extracted from a site in the French Alps were first used to reconstruct the topography of a buried end-of-summer snow horizon from a past year. Using these data and surface elevation observations from LiDAR and Global Navigation Satellite System instruments, we calculated the submergence velocities over the period between the buried horizon and more recent surface elevation observations. The differences between the changes in surface elevation and the submergence velocities were then used to calculate the annual surface mass-balances with an accuracy of ±0.34 m w.e. Assuming that the submergence velocities remain stable over several years, the surface mass-balance can be reconstructed for subsequent years from the differences in surface elevation alone. As opposed to the glaciological method that requires substantial fieldwork year after year to provide only point observations, this method, once submergence velocities have been calculated, requires only remote-sensing data to provide spatially distributed annual mass-balances in accumulation areas.

The microbiome of buried soils demonstrates significant shifts in taxonomic structure and a general trend towards mineral horizons

Burial mounds represent a challenge for microbiologists. Could ancient buried soils preserve microbiomes as they do archaeological artifacts? To investigate this question, we studied the soil microbiome under a burial mound dating from 2500 years ago in Western Kazakhstan. Two soil profile cuts were established: one under the burial mound and another adjacent to the mound surface steppe soil. Both soils represented the same dark chestnut soil type and had the same horizontal stratification (A, B, C horizons) with slight alterations. DNA samples isolated from all horizons were studied with molecular techniques including qPCR and high throughput sequencing of amplicon libraries of the 16S rRNA gene fragment. The taxonomic structure of the microbiome of the buried horizons demonstrated a deep divergence from ones of the surface, comparable to the variation between different soil types (representatives of the soil types were included in the survey). The cause of this divergence could be attributed to diagenetic processes characterized by the reduction of organic matter content and changes in its structure. Corresponding trends in the microbiome structure are obvious from the beta-diversity pattern: the A and B horizons of the buried soils form one cluster with the C horizons of both buried and surface soil. This trend could generally be designated as ‘mineralization’. Statistically significant changes between the buried and surface soils microbiomes were detected in the number of phylogenetic clusters, the biology of which is in the line of diagenesis. The trend of ‘mineralization’ was also supported by PICRUSt2 functional prediction, demonstrating a higher occurrence of the processes of degradation in the buried microbiome. Our results show a profound shift in the buried microbiome relatively the “surface” microbiome, indicating the deep difference between the original and buried microbiomes.

Remnant wetlands under palm swamps in the Araripe Plateau, Brazilian semiarid

Palm swamps are typical of the plateaus in the Brazilian savanna, but they are present in remnant in the Brazilian semiarid region, exceptionally in selective concave sectors of the edge and steep slopes at the Araripe Plateau. This study aimed to investigate the genesis and evolution of remnant wet soils under buriti palms/palm swamps in the Brazilian semiarid. Three pedons were selected, described, and classified according to the World Reference Base for soil resources. Soil samples were collected from the surface down to the lithic contact at each pedon. Morphology, chemical, and physical attributes were analyzed. Optically stimulated luminescence (OSL) dating was applied to buried horizons at soil profile soil profile number 1. Our results show that remnant wetlands are associated with dynamics of the hydrogeological conditions and the regional relief, strongly influenced by the morphostructure and the current morphogenesis of the Araripe Plateau. In clear contrast with typical semiarid soils, the hydrolysis and ferrolysis have produced acid, hyperdystrophic, and C-rich horizons. Evidence of colluvium and alluvium show that the soils are polycyclic. The ages between <200 to 850 yr reveal evidence of a parent material of colluvium/alluvial origin from a current sedimentation phase, attributed to erosion scarp, mass movements, and fluvial flow with low capacity.

Digital morphometrics and genesis of soils with buried horizons and lithological discontinuities in southeastern Brazil

Soil morphometrics aims to measure attributes observed in soil profiles. The use of digital technologies in the morphological study of soil profiles has yet to be further explored by the scientific community. Particularly, soils with buried horizons, which are common in lowlands and floodplains throughout the world, have never been examined using digital morphometrics. This study aimed to examine the morphology and genesis of three soil profiles with buried horizons in Brazil using digital soil morphometrics combined with wet-chemistry and mineralogical analyses (including X-ray diffraction – XRD). Digital analyses used three proximal sensors – portable X-ray fluorescence spectrometry (pXRF), visible near-infrared (Vis-NIR) and mid-infrared (MIR) diffuse reflectance spectrometry. The soils had buried horizons and were classified as Typic Udifolists (TU), Typic Dystrustepts (TD) and Typic Endoaquents (TE). Each soil profile was sampled in a 15 × 15 cm grid, with 40 samples per profile. All sensors identified the buried soil horizons. Vis-NIR and MIR identified the presence of several key minerals and variations in soil organic matter (SOM) that were not observed in the whole soil pits. PXRF captured discontinuities in the parent material, not only between deposited and buried horizons, but also within horizons. The deposited material above TU and TE was derived from neighboring Fe-rich Oxisols and Ultisols, as shown by high Fe content and absorption features of Fe oxides. Sensor analyses were quick and environmentally friendly. Proximal sensor data enhanced morphological assessment of soil profiles, and provided insights otherwise very difficult or even impossible with only traditional and visual methods.

The Hidden History of the South‐Central Cascadia Subduction Zone Recorded on the Juan de Fuca Plate Offshore Southwest Oregon

AbstractNew seismic reflection data collected and processed as part of early career scientist training at sea and in classroom projects fill gaps in seismic coverage of the Cascadia subduction zone and provide new insights into anomalous subduction behavior and mass wasting along the south‐central Cascadia Subduction Zone (CSZ) between 42°20’N and 44°15’N. The data reveal at least six distinct buried horizons of folded and faulted sediments similar to strata recently interpreted to result from in situ deformation induced by the load imposed by a large blocky mass transport deposit known as the 44°N slide. Although our results support prior studies indicating that the south‐central CSZ has experienced large slope instabilities, they indicate that the slides were more frequent but volumetrically smaller than previously thought. Similar strata have not been observed elsewhere beneath the abyssal plain adjacent to the Cascadia subduction zone. The structure of the deformation front along this segment is also indistinct, in contrast to the clear frontal faults outboard of folded trench strata observed immediately to the north and south (and generally throughout the rest of Cascadia). We attribute the anomalous nature of this segment of the margin to past subduction of shallow and rough seafloor, which resulted in greater uplift of the forearc than elsewhere along the margin. A consequence of this postulated history would be the shedding of older, more consolidated blocks onto the Juan de Fuca plate, resulting in the observed distinctive stratigraphy offshore southern Oregon.

Millennium timescale carbon stability in an Andisol: How persistent are organo-metal complexes?

Significant linear correlation between organic carbon (OC) and reactive aluminum and iron (metal) are often observed across a wide range of acidic soils including Andisols, and often explained by the formation of stable organo-metal complexes. However, the chemical variation and the long-term stability of the complexes remain unclear. We thus compared two buried A horizons (the burial period of 0.5 and 4.6 kyr, based on tephra chronology) to examine the changes in OC chemistry as well as its association with the metal phases extractable by sodium pyrophosphate (PP) and acid oxalate (OX). Both horizons were subdivided into six layers, and then the layer with the highest OC in each horizon was subjected to particle-size fractionation after maximum dispersion. 14C ages of the bulk and the size fractions were consistent with the tephra-based burial ages. Younger 14C age was shown for the organo-mineral fractions of finer sizes in both horizons, in accord with our previous study using a surface Andisol. PP-extractable metal concentration (metalPP) showed a highly significant linear correlation with OC across all the layers and the fractions from both horizons, whereas OX-extractable metal showed the correlation only within the younger buried horizon. Solid-state 13C NMR spectroscopy showed a stronger metalPP correlation with alkyl C than with aromatic C especially among the older horizon layers and the 14C age variation among the size fractions in this horizon was not related to aromaticity. Significant decline in the proportion of O-alkyl C and concurrent increase in that of aromatic C from the younger to older horizon may suggest preferential degradation of O-alkyl C under the buried condition. Over the burial time, however, the correlation between metalPP and aromatic C weakened whereas metalPP-alkyl C correlation increased. These results imply a shift in the dominant organic ligand in the organo-metal complexes. Furthermore, the shift in the distribution of total OC and metalPP from 0.2–2 μm fraction to <0.2 μm fraction suggested a physical weakening of microaggregates where organo-metal complexes likely acted as glue. The observed changes imply reduced OC stability, which may lead to the eventual disappearance of buried A horizons. The current study demonstrated that, while organo-metal complexes appeared persistent based on the OC-metalPP correlation, the changes in the nature of OC-metal association including the partial breakdown of microaggregates took place, in the millennium timescale.

Soil organic carbon stabilization mechanisms and temperature sensitivity in old terraced soils

Abstract. Being the most common human-created landforms, terrace construction has resulted in an extensive perturbation of the land surface. However, our mechanistic understanding of soil organic carbon (SOC) (de-)stabilization mechanisms and the persistence of SOC stored in terraced soils is far from complete. Here we explored the factors controlling SOC stability and the temperature sensitivity (Q10) of abandoned prehistoric agricultural terrace soils in NE England using soil fractionation and temperature-sensitive incubation combined with terrace soil burial-age measurements. Results showed that although buried terrace soils contained 1.7 times more unprotected SOC (i.e., coarse particulate organic carbon) than non-terraced soils at comparable soil depths, a significantly lower potential soil respiration was observed relative to a control (non-terraced) profile. This suggests that the burial of former topsoil due to terracing provided a mechanism for stabilizing SOC. Furthermore, we observed a shift in SOC fraction composition from particulate organic C towards mineral-protected C with increasing burial age. This clear shift to more processed recalcitrant SOC with soil burial age also contributes to SOC stability in terraced soils. Temperature sensitivity incubations revealed that the dominant controls on Q10 depend on the terrace soil burial age. At relatively younger ages of soil burial, the reduction in substrate availability due to SOC mineral protection with aging attenuates the intrinsic Q10 of SOC decomposition. However, as terrace soil becomes older, SOC stocks in deep buried horizons are characterized by a higher temperature sensitivity, potentially resulting from the poor SOC quality (i.e., soil C:N ratio). In conclusion, terracing in our study site has stabilized SOC as a result of soil burial during terrace construction. The depth–age patterns of Q10 and SOC fraction composition of terraced soils observed in our study site differ from those seen in non-terraced soils, and this has implications when assessing the effects of climate warming and terrace abandonment on the terrestrial C cycle.

. MORPHOLOGICAL CHARACTERISTICS SOILS OF THE BELIGATIVE STRUCTURES OF THE KAMIANETS-PODILSKYI KAMIANETS-PODILSKYI STATE HISTORICAL RESERVE MUSEUM

The article presents micromorphological descriptions of soil profiles of key areas of the research territory. The results of micromorphological analysis and synthesis of selected soil samples are illustrated. For the first time the process-and-genetic features of urborendzins of beligerative structures were studied through the evaluation of their micromorphological structure.&#x0D; Urborendzins of the beligerative landscape complex of the Kamianets-Podilskyi State Historical Preserve Museum are intrazonal biolithogenic polygenetic soils with complex phylogeny exposed to a long-term anthropogenic influence. It is important to establish their genesis, which is accompanied by a number of obstacles caused by the significant amplitude of the soil profile, morphological features, physical-and-chemical features and the presence of buried horizons in such soils. To solve the problem of age and ontogenesis staging of urborendzins, along with comparative-and-geographical, we use a complex paleopedological method with active application of micromorphological analysis, which allows to establish process-and-genetic features of soils by diagnosing elementary soil processes according to sustainable features at the micro level of solid phase formation.&#x0D; Micromorphological structure evaluation makes it possible to consider soil as a system at the microscopic level and observe the natural flow of soil-forming processes in their interaction and ratio at all morphological levels - from microscopically small volumes of soil mass to soil profile in general. Consequently, micromorphological analysis is a unique one and possesses significant advantages over other methods of physical geography.&#x0D; Urborendzins of the object under study have a complex problematic genesis and the use of micromorphological analysis and micromorphological synthesis is acceptable to solve these problems. The evaluation of the micromorphological structure of these soils was carried out for the first time, their micromorphological features were not previously determined as well as the genesis in general. Our micromorphological analysis allowed us to establish the process-and-diagnostic features of the studied soils and shows that in comparison with the background soil, the deposits of the «Day Tower» are more carbonated. Under the conditions of the washing regime, fragments of limestone deposits provide constant involvement of new weathered carbonated material in soil formation processes, which promotes saturation of soil solutions with calcium cations and, accordingly, formation of more stable microaggregation of soil mass and reduction of mobility of silty particles downwards the profile, fixed through by micromorphological researches in the form of the presence of high-order microaggregates. Comparing the background soil with the sediments of the «Day Tower», it can be stated that the agrorendzin typical, in contrast to urborendzin, leached from carbonates, is characterized by the practical absence of microorshteins, humic substances are mainly in a dispersed state and signs of movement of organo-clay substances downwards the profile can be traced much more clearly. This indicates that the background agrorendzin is formed under conditions of active biogenic and accumulative processes, carbonate leaching and illimerization.&#x0D; Key words: micromorphological analysis, synthesis, soil, beligerative complex.

Humus state of buried soils of different age archaeological monuments on the territory of Ufa (Russia, Republic of Bashkortostan)

The paper studies the humus state of buried soils on the territory of archaeological monuments: the New–Ufa Burial Ground (early Iron Age) and the Settlement Ufa–II (early Middle Ages), located in the urban district of Ufa (Russia, Republic of Bashkortostan). The soil cover of archaeological monuments is represented by Greyzemic Phaeozem over Grayzemic Phaeozem (gz–PH over gz–PH). The humus content in buried horizons is 2.06–5.26%, which is 2–4 times less in comparison with the native soil. There are two types of humus such as humate and humate–fulvate. Among humic acids, the fraction associated with calcium (HAs–2) predominates. The spectral curves of humic acids HAs–2 at different wavelengths for the buried humus–accumulative horizon of the New–Ufa Burial Ground have a steeper character and lower optical density values compared to the background soil. The spectral curves of the buried horizons of the Settlement Ufa–II have flatter disposition and, in terms of optical density, are close to the values of the native soil. Obtained results make it possible to estimate the transformation of organic matter in the soils after their burial in comparison with the modern native soil Greyzemic Phaeozem (gz–PH) of the city park.

10Be and 14C data provide insight on soil mass redistribution along gentle slopes and reveal ancient human impact

PurposeSpatial and temporal patterns of past erosional events are a useful and needed information to explain observed soil patterns in different landscapes. Soil thickness reflects the overall expression of pedogenesis and erosion. Forested soils of Northern Germany exhibit varying soil thicknesses with thin soils on crest positions and buried soils at the footslope. The aim of this study is to reconstruct the complex soil mass redistribution and soil patterns of this forested area due to different periods of erosion and stability.MethodsWe explored the explanatory power of both 10Be (in situ and meteoric) on a hillslope and we 14C-dated buried horizons at different depths.ResultsThe 10Be depth profiles did not show an exponential decrease with depth. They had a ‘bulge’ shape indicating clay translocation and interaction with oxyhydroxydes (meteoric 10Be), bioturbation and soil mass redistribution (in situ 10Be). The combined application of both 10Be and 14C dating revealed progressive and regressive phases of soil evolution. Although Melzower Forest is protected (same vegetation) since the past 250 years, both 10Be clearly indicated major soil mass redistribution along the investigated catena.ConclusionA strong erosion impulse must have occurred between 4.5 and 6.8 kyr BP indicating an earlier human impact on soil erosion than previously postulated (~ 3 kyr earlier). Our findings correlate in fact with the first settlements reported for this region (~ 6.8 kyr BP) and show their immediate effect on soils. The overall soil redistribution rates in this forest are surprisingly similar to those obtained from a nearby agricultural area.

A Mottled, Non-Lithified Paleosol in Brazil: Diagnosis by Morphological and Mineralogical Features

The identification of paleosols is difficult when no buried horizons or lithification occur. Here, we described the identification of a possible paleosol, its characterization, and which features supported its positive diagnosis. In a construction site, a vertical cut exposed an unusual red–yellow mottling with massive structure and channels (probably faunal), in contrast with the overlying homogeneous red Oxisol with fine granular structure. A similar but more deferrified section with white–yellow mottling also occurred nearby, and both were sampled as large clods. In thin sections, many oriented clay coatings occur along channel voids, suggesting illuviation, as well as dissolving Fe nodules and Mn coatings along planar and channel voids. X-ray diffraction showed a clay dominated by kaolinite, traces of illite, and absence of gibbsite, again contrasting with the gibsitic-kaolinitic clay of the Oxisol. We confirmed the diagnosis of a Paleoultisol due to the following incompatibilities with the overlying Oxisol: (1) massive, apedal structure, and higher bulk density; (2) clay coatings indicative of illuviation as key soil-forming process; (3) low clay contents in particle-size analysis due to cementation; (4) very low organic carbon consistent with long-term inhumation; and (5) kaolinitic–illitic clay. The unusual granular microstructure of the B horizon of the Oxisol is partly derived from disintegration and desilication of the Paleoultisol.

Удельная активность радионуклидов и их взаимосвязь с валовым химическим составом почв

The total heavy metal content and activity concentration of natural radionuclides were obtained in native and anthropogenically transformed soil of the Rostov agglomeration (south of the Russia). The specific activity of natural radionuclides in soils of the has been comparable with indicators typical for chernozems of the Rostov region. Increased activity of 40K, 232Th is observed in the upper horizons, which is due to the origin of the radionuclides themselves and fertilization in the agrogenic period of soils, before the specified areas were included in the urban area. The correlation between activity concentration of radionuclide and total content of heavy metals were derived by Spearman&amp;#x27;s Rank-Order Correlation. The study was revealed that the activity concentration of thorium and radium doesn’t provide significant correlation with the total content of heavy metals. The group of buried horizons have shown a positive correlation with naturally occurring 40K in contrast with humus horizon (AU). The carbonates-accumulating group of horizons (BCA, [BCA]) have random correlation sign by each of metals. The most significant correlation was observed for the B horizons group.

Fine root biomass stimulates microbial activity of glucose mineralization in buried humic horizon of volcanic ash soils

ABSTRACT Burial of the surface soil by volcanic ash deposition plays roles in organic matter accumulation. Assuming that decomposition of the buried humus is limited solely by labile substrate inputs, glucose inputs are hypothesized to stimulate microbial activity in buried humic horizons. We describe patterns of microbial mineralization of 14C-labeled glucose in volcanic soil profiles to test whether glucose inputs increase microbial activity similarly in the surface soil and buried humic horizons. We found that microbial biomass was dependent on fine root biomass rather than soil carbon concentration in the volcanic soil profiles. Both bacterial and fungal biomass correlated with fine root biomass. The microbial capacities of glucose mineralization in the buried humic horizons were lower than in the surface horizons. The microbial activity of glucose mineralization in the buried humic horizons is limited by (1) the smaller microbial biomass due to smaller fine root biomass and (2) the dominance of microbial community adapted to the low concentrations of substrates with low mineralization capacity. Stimulation of microbial activities in the buried humic horizons requires both fine root biomass and inputs of labile substrates.

Reforestation and soil recovery in a Mediterranean mountain environment: Insights into historical geomorphic and vegetation dynamics in the Sila Massif, Calabria, southern Italy

We investigated the genesis and local response of soils in mountain sites of the Sila Massif (Calabria, southern Italy), reforested ca. 60 years ago, and their relationships with geomorphic dynamics and forest stand structure. A multidisciplinary approach is proposed, focused on an often neglected soil profile scale and horizon-wise sampling strategy, and including pedological field observations, physical, chemical, mineralogical analyses, isotope geochemistry including fallout radionuclides (137Cs and 210Pbex), geomorphology, historical documentation of anthropogenic land cover changes, forestry and dendrometric measurements. Reforestation was carried out following extreme land degradation, which took place after forest clearance and field cultivation. Different tree species and soil preparation techniques were used according to site conditions. We focused on the main properties of selected soil profiles and the distribution of some radionuclides, in order to understand the effects of forest stands on hampering soil erosion and promoting novel soil formation, and to evaluate the potential hazard of natural gamma radiation. A comparison with soil profiles developed under naturally regenerated forest and field crops was achieved. The soil profiles in reforested sites showed a poor degree of development and a complex history of reworking processes alternated with soil-formation processes, in line with modern to historical radiocarbon dates increasing downprofile, the presence of buried horizons and 137Cs in the topsoils. Inventory changes obtained for 210Pbex and 137Cs highlight a process of soil stabilization occurred after reforestation, with more efficient effects under Calabrian pine than oak forest, whereas major geomorphic dynamics (erosion and accumulation) were triggered by forest coppicing, thinning and agricultural practices. Our data remark a positive response of the soil ecosystem to reforestation against erosion, trapping mobile material, stabilizing buried soils, promoting humus accumulation leading to new shallow topsoils, and the protective role of forests against anthropogenic and climatic-induced threats. Average values of the annual outdoor effective dose equivalents of gamma-emitting radionuclides calculated for all the soil horizons showed lower values than the population-weighted world’s average, with the exception of the soil profiles under forest stands developed on granite, exceeding this threshold. A deeper comprehension of soil genesis, geomorphic processes, land use and vegetation dynamics in vulnerable ecosystems such as mountain environments represents a fundamental basis for sustainable land management policies.

Lithologic discontinuity in Andisols on tea plantation area in West Java, Indonesia

Tea plantation areas are normally found on Andisols developed from volcanic eruptions. Volcanic eruptions can occur within several periods, resulting in a sequence of soil layers that can differ in every period and produce lithologic discontinuity in the soil profile. Lithologic discontinuities were investigated in Andisols on Ciater Tea Plantation in Ciater, West Java, Indonesia. Andisols in this area developed from the eruption of Mt. Tangkuban Parahu, Mt. Dano and Mt. Tampomas derived from two geological formation, the Qyd (Middle Holocene) and Qyt (Early Holocene). The objective of this research was to investigate the lithologic discontinuity of Andisols in Ciater Tea Plantation through macromorphological observations from four profiles in this location. The results showed that there were lithologic discontinuities in all profiles, indicated by unusual changing color detected by Munsell Soil Color Chart and increasing organic carbon content in certain depth. Some A buried horizons (Ab) were found, indicated that the underlying soils had developed from the parent material of the earlier eruption period than the overlying horizons. Detailed analyses of mineralogical and element in sand and silt fraction were needed to have the more accurate information of lithology discontinuities. Instruments like X-Ray Fluorescence Spectrometry and Visible Near-Infrared Diffuse Reflectance Spectroscopy can be explored to investigate the lithologic discontinuity.

Digital mapping of buried soil horizons using 2D and pseudo‐3D geoelectrical measurements in a ground moraine landscape

AbstractThe identification of buried soil horizons in agricultural landscapes helps to quantify sediment budgets and erosion‐related carbon dynamics. High‐resolution mapping of buried horizons using conventional soil surveys is destructive and time consuming. Geoelectrical sensors can offer a fast and non‐destructive alternative for determining horizon positions and properties. In this paper, we compare the suitability of several geoelectrical methods for measuring the depth to buried horizons (Apb, Ahb and Hab) in the hummocky ground moraine landscape of northeastern Germany. Soil profile descriptions were developed for 269 locations within a 6‐ha experimental field “CarboZALF‐D”. A stepwise linear discriminant analysis (LDA) estimated the lateral position of the buried horizons using electromagnetic induction data and terrain attributes. To predict the depth of a buried horizon, multiple linear regression (MLR) was used for both a 120‐m transect and a 0.2‐ha pseudo‐three‐dimensional (3D) area. At these scales, apparent electrical conductivity (ECa), electrical resistivity (ER) and terrain attributes were used as independent variables. The LDA accurately predicted Apb‐ and Ahb‐horizons (a correct classification of 93%). The LDA of the Hab‐horizon had a misclassification of 24%, which was probably related to the smaller test set and the higher depth of this horizon. The MLR predicted the depth of the Apb‐, Ahb‐ and Hab‐horizons with relative root mean square errors (RMSEs) of 7, 3 and 13%, respectively, in the pseudo‐3D area. MLR had a lower accuracy for the 2D transect compared to the pseudo‐3D area. Overall, the use of LDA and MLR has been an efficient methodological approach for predicting buried horizon positions.Highlights The suitability of geoelectrical measurements for digital modelling of diagnostic buried soil horizons was determined. LDA and MLR were used to detect multiple horizons with geoelectrical devices and terrain attributes. Geoelectrical variables were significant predictors of the position of the target soil horizons. The use of these tested digital technologies gives an opportunity to develop high‐resolution soil mapping procedures.

Ketidaksinambungan Litologi dan Karakteristik Pedogenetik pada Beberapa Andisols di Jawa Barat

Andisols developed from parent materials of volcanic eruptions. Volcanic eruptions can occur within several periods, resulting in a sequence of soil layers that can differ from each period and produced lithologic discontinuity in the soil profile. Lithologicac discontinuity was investigated in Andisols developed from the eruptions of Mt. Tangkuban Parahu (Holocene, andesitic) and Mt. Tilu (Pleistocene, basaltic) in West Java through morphological observations of three profiles at each location. The results showed that there was lithologic discontinuity in all profiles indicated by changed in color by Munsell Soil Colour Chart, organic carbon, texture and structure as the specific A buried horizon that developed from the parent material of the earlier eruption period than the horizons above. It is recommended to carry out the mineralogical and micromorphological analyses to determine the differences in minerals and micromorphology of the discontinue horizons and carbon-dating analysis in the buried layer to determine the age of the soil and the period of eruption that developed the soil. Keywords: A buried horizon, Munsell Soil Colour Chart, organic carbon, soil mineralogy, soil morphology

Floodplain soil and its bacterial composition are strongly affected by depth.

We studied bacterial abundance and community structure of five soil cores using high-throughput sequencing of the 16S rRNA gene. Shifts in the soil bacterial composition were more pronounced within a vertical profile than across the landscape. Soil organic carbon (SOC) and nitrogen (N) concentrations decreased exponentially with soil depth and revealed a buried carbon-rich horizon between 0.8 and 1.3 m across all soil cores. This buried horizon was phylogenetically similar to its surrounding subsoils supporting the idea that the type of carbon, not necessarily the amount of carbon was driving the apparent similarities. In contrast to other studies, Nitrospirae was one of our major phyla with relatively high abundances throughout the soil profile except for the surface soil. Although depth is the major driver shaping soil bacterial community structure, positive correlations with SOC and N concentrations, however, were revealed with the bacterial abundance of Acidobacteria, one of the major, and Gemmatimonadetes, one of the minor phyla in our study. Our study showed that bacterial diversity in soils below 2.0 m can be still as high if not higher than in the above laying subsurface soil suggesting that various bacteria throughout the soil profile influence major biogeochemical processes in floodplain soils.

Human-induced and natural carbon storage in floodplains of the Central Valley of California

Active floodplains can putatively store large amounts of organic carbon (SOC) in subsoils originating from catchment erosion processes with subsequent floodplain deposition. Our study focussed on the assessment of SOC pools associated with alluvial floodplain soils that are affected by human-induced changes in floodplain deposition and in situ SOC mineralisation due to land use change and drainage. We evaluated depth-dependent SOC contents based on 23 soil cores down to 3 m and 10 drillings down to 7 m in a floodplain area of the lower Cosumnes River. An estimate of 266 Mg C ha−1 or about 59% of the entire SOC stored within the 7 m profiles was found in the upper 2 m. Most profiles (n = 25) contained discrete buried A horizons at depths of approximately 0.8 m. These profiles had up to 130% higher SOC stocks. The mean δ13C of all deep soil profiles clearly indicated that arable land use has already altered the stable isotopic signature in the first meter of the profile. Radiocarbon dating showed that the 14C age in the buried horizon was younger than in overlaying soils indicating a substantial sedimentation phase for the overlaying soils. An additional analysis of total mercury contents in the soil profiles indicated that this sedimentation was associated with upstream hydraulic gold mining after the 1850s. In summary, deep alluvial soils in floodplains store large amounts of SOC not yet accounted for in global carbon models. Historic data give evidence that large amounts of sediment were transported into the floodplains of most rivers of the Central Valley and deposited over organically rich topsoil, which promoted the stabilization of SOC, and needs to be considered to improve our understanding of the human-induced interference with C cycling.