Shallow Soil Samples Research Articles

Natural Hydrogen in the Northern Perth Basin, WA Australia: Geospatial Analysis and Detection in Soil Gas for Early Exploration

The scope of this work is to empirically check and prove the practical applicability of the Primordially Hydridic Earth (PHE) concept for early exploration of the resources of naturally occurring hydrogen. With the PHE concept postulates interpreted within the local geological, tectonic, petrological and geophysical context, the reconnaissance plan, as well as the field exploration and data acquisition programs, were put together and implemented in the field. The results obtained from the surface (<1m deep) soil gas survey performed in Western Australia (WA) resulted in values of hundreds of ppm H<sub>2</sub>, including three samples with a concentration of hydrogen exceeding the gas sensor detection limit of 2,000 parts per million (ppm) (the all-Australia record). Similarly, several of the shallow soil samples used for obtaining headspace gas extracts yielded dozens % H<sub>2</sub>, which was established utilizing Gas Chromatography (GC) technology. The latter tests established the all-Australia record of 58.3% (norm.) H<sub>2</sub> concentration from 15 m depth, being the highest reading from the area of research. At one location, a concentration of He exceeding 8,000ppm was detected in a 1m surface soil gas sample analyzed by the independent lab. The most important outcome was finding natural hydrogen where it was expected and predicted. On the other hand, H<sub>2</sub> concentrations exceeding the natural background of 1-3ppm were not detected in the soil gas readings outside of the areas identified using the PHE concept as a theoretical foundation. It may be stated that overall, the practical application of the PHE concept along with the thoroughly planned utilization of carefully selected exploration techniques brings satisfactory results.

Evaluation of the hillslope fine-scale morphology under forest cover with pit-mound topography - Integration of geomorphometry, geophysical methods, and soil features

Forested hillslopes are zones of specific surface hydrology and geomorphic activity regimes. Their distinct properties, namely terrain microrelief (<10 m in diameter and height), are often a result of past disturbances that control forest stand conditions, soil formation processes, and superficial processes. A clear bioindicator of the past forest disturbance is pit-mound topography, which, however, is challenging to study because of its complexity and relatively small sizes of individual forms (usually <5 m in diameter). The present study analyzed the spatial representation, geomorphometric, and geophysical evaluation of the rare pit-mound topography in the Karkonosze Mountains National Park, SW Poland, Central Europe. For this task, two digital terrain models (DTMs) have been considered and were based on different quality point clouds collected during airborne and terrestrial laser scanning (ALS and TLS, respectively). The first data allowed the production of the DTM in 1 × 1 m spatial resolution, while the second data offered the DTM in 0.025 × 0.025 m resolution. Various geomorphometric derivatives (Terrain Ruggedness Index, Geomorphons, Topographic Wetness Index, Valley Depth, and Negative Openness) were applied and compared based on these models. In the further part of the study, we applied electrical resistivity tomography (ERT) and electromagnetic induction (EMI), assisted by shallow soil sampling and analyses to support the interpretation of geophysical models.Our TLS-based DTM offered higher-quality models and a better representation of pit-mound topography. The high-quality TLS-based DTM elevation model can support close-to-reality hydrological and geomorphic modeling. The geophysical investigation allowed us to isolate a critical difference between treethrow pits and mounds better represented by ERT models than shallow EMI models. The differences were partly supported by soil properties, namely lower electrical resistivity in treethrow pits were related to higher moisture conditions, organic matter, organic carbon, and silt content in pits. As a general property, pit-mound topography resulting from tree uprooting adds to the complexity of forested hillslope hydrology and geomorphic activity. The surficial heterogeneity in hillslope topography was also evident in soil properties with sharp changes in short distances between treethrow mounds and pits.

Environmental geochemical baseline determination and pollution assessment of heavy metals in farmland soil of typical coal-based cities: A case study of Suzhou City in Anhui Province, China

Soil is the foundation of agricultural green development and human survival; the study of local environmental geochemical baselines can guide soil management and ensure the safe use of soil. In this study, a total of 100 shallow farmland soil samples were collected in each township of Yongqiao District, Suzhou City, Anhui Province, China. Herein, the contents of 10 heavy metal elements including As, Hg, Cd, Pb, Cr, Cu, Mn, Ni, Zn and Fe were determined. In addition, the geochemical baseline of heavy metals was calculated based on the relative cumulative frequency curve method, and the soil pollution status was evaluated. The results show that the average contents of As, Hg, Cd, Cu, Mn and Zn exceeded the soil background values of Anhui Province by 3.82%–64.74% (1.04–1.65 times), meanwhile, the average contents of Pb and Cr were lower than the soil background values of Anhui Province. The average contents of Cd, Cr, Cu, Mn and Ni exceeded the Chinese soil background values by 1.61%–64.74% (0.98–1.65 times). The geochemical baseline values of As, Hg, Cd, Pb, Cr, Cu, Mn, Ni, Zn and Fe were 9.585 mg/kg, 0.028 mg/kg, 0.112 mg/kg, 21.59 mg/kg, 53.66 mg/kg, 19.31 mg/kg, 543.8 mg/kg, 24.93 mg/kg, 50.57 mg/kg and 2.654%, respectively. The pollution assessment results also showed that most of the farmland soil samples in the study area were non-polluting or slightly polluted based on geochemical baselines. Hg and Cu in a few samples were moderately polluted, and Cd in only one sample was moderately intensely polluted. Combined with the distribution of pollution and field investigation, it is considered that Hg comes from atmospheric deposition and agricultural non-point source pollution of industrial pollution. Cu comes from animal husbandry and agricultural pollution. Meanwhile, Cd is related to natural sources, wood processing and agricultural fertiliser application. The study demonstrated that the calculation of soil geochemical background value should take full account of the differences between the various regions, combined with the current state, particularly the pre-consideration of the distribution of elements or pollutants. Then, reasonably select the evaluation standard value so that the evaluation results can truly reflect the state of soil pollution.

Field assessment of metal and base cation accumulation in green stormwater infrastructure soils

Green stormwater infrastructure (GSI) is adopted to reduce the impact of stormwater on urban flooding and water quality issues. This study assessed the performance of GSI, like bioretention basins, in accumulating metals. Twenty one GSI basins were considered for this study, which were located in New York and Pennsylvania, USA. Shallow (0–5 cm) soil samples were collected from each site at inlet, pool, and adjacent reference locations. The study analyzed 3 base cations (Ca, Mg, Na) and 6 metals (Cd, Cr, Cu, Ni, Pb, and Zn), some of which are toxic to ecosystem and human health. The accumulation of cations/metals at the inlet and pool differed between the selected basins. However, accumulation was consistently higher at the inlet or the pool of the basin as compared to the reference location. Contrary to prior research, this study did not find significant accumulation with age, suggesting that other factors such as site characteristics (e.g., loading rate) might be confounding. GSI basins that receive water only from parking lots or parking lots and building roofs combined showed higher metals and Na accumulation as compared to the basins that received stormwater only from building roofs. Cu, Mg and Zn accumulation showed a positive relationship with the organic matter content in soil, indicating likely sorption of metals on organic matter. Ca and Cu accumulation was greater in GSI basins with larger drainage areas. A negative relationship between Cu and Na implies that Na loading from de-icers may reduce Cu retention. Overall, the study found that the GSI basins are successfully accumulating metals and some base cations, with highest accumulation at the inlet. Additionally, this study provided evidence of GSI effectiveness in accumulating metals using a more cost efficient and time averaged approach compared to traditional means of stormwater inflow and outflow monitoring.

Microplastics and mesoplastics as emerging contaminants in Tehran landfill soils: The distribution and induced-ecological risk

Environmental pollution with microplastics (MPs) and mesoplastics (MEPs) and their potential risks to human health and ecosystem quality have aroused the concern of communities. Therefore, the pioneering study was conducted on Tehran landfill soil contamination with MPs and MEPs. 56 shallow and deep soil samples were collected from different landfill areas in the wet and dry seasons. The physical and chemical characteristics of MPs and MEPs were measured using a stereomicroscope and FTIR-ATR spectroscopy, respectively. The results showed that the average MP abundance in shallow and deep soil was 863 ± 681 and 225 ± 138 particles/kg soil, and for MEPs, it was 29.8 ± 6.4 and 18.1 ± 8.3 particles/kgsoil. The low-density plastic particles were separated completely by flotation with H2O, NaCl, and ZnCl2 solutions, but PVC was only separated by 90%. Over 90% of MPs and MEPs were LDPE, PP, and PS polymers, explained by their widespread applications in single-use products and their consumption in Iran. Films, white and black, and 0.1–0.5 mm were the dominant shapes, colors, and sizes of MPs, respectively. The prevailing MEPs were film-shaped and in white and yellow colors, with a size of 0.5–1.0 cm. Canonical correlation analysis indicated that total organic matter and moisture were highly correlated with MP shapes. The calculated polymer hazard index values have a wide range at different sampling points, and this index yielded hazard levels III-IV and II-IV for MPs and MEPs, respectively, while according to the pollution load index category, the hazard level of MPs and MEPs was I-II and I. The potential ecological risk index from combined polymers has been estimated to be of minor to extreme danger for MPs and of minor risk for MEPs. Our findings provided baseline data on MPs contamination in Tehran landfill soil and its associated ecological risk, which aids policymakers in implementing risk-reduction measures.

Use of Radioisotope Ratios of Lead for the Identification of Historical Sources of Soil Lead Contamination in Santa Ana, California.

Lead (Pb) is an environmental neurotoxicant that has been associated with a wide range of adverse health conditions, and which originates from both anthropogenic and natural sources. In California, the city of Santa Ana represents an urban environment where elevated soil lead levels have been recently reported across many disadvantaged communities. In this study, we pursued a community-engaged research approach through which trained “citizen scientists” from the surrounding Santa Ana community volunteered to collect soil samples for heavy metal testing, a subset of which (n = 129) were subjected to Pb isotopic analysis in order to help determine whether contamination could be traced to specific and/or anthropogenic sources. Results showed the average 206Pb/204Pb ratio in shallow soil samples to be lower on average than deep samples, consistent with shallow samples being more likely to have experienced historical anthropogenic contamination. An analysis of soil Pb enrichment factors (EFs) demonstrated a strong positive correlation with lead concentrations, reinforcing the likelihood of elevated lead levels being due to anthropogenic activity, while EF values plotted against 206Pb/204Pb pointed to traffic-related emissions as a likely source. 206Pb/204Pb ratios for samples collected near historical urban areas were lower than the averages for samples collected elsewhere, and plots of 206Pb/204Pb against 206Pb/207 showed historical areas to exhibit very similar patterns to those of shallow samples, again suggesting lead contamination to be anthropogenic in origin, and likely from vehicle emissions. This study lends added weight to the need for health officials and elected representatives to respond to community concerns and the need for soil remediation to equitably protect the public.

Annual and perennial crop composition impacts on soil carbon and nitrogen dynamics at two different depths

AbstractThe sustainability of an agricultural field is largely influenced by crop growth habit and management practices such as tillage. Both strongly interact to shape ecosystem properties such as the fluxes and stocks of carbon and nitrogen. Recently, researchers have worked to develop perennial grain crops in order to enhance key ecosystem processes, such as carbon cycling and nitrogen fixation, with the use of perennial crops rather than traditionally used annual crops. In this study, we aimed to understand how soil disturbance combined with vegetation type [annual monoculture crops vs. perennial monocultures (intermediate wheatgrass (IWG)) vs restored native vegetation (RNV)] influenced the soil carbon and nitrogen dynamics. We collected soil samples at two depths (0–15 cm and 15–30 cm) from each vegetation treatment and incubated the soils in the laboratory for 120 days to determine the efflux of carbon and also analyzed the mineralization of both carbon and nitrogen. The results demonstrated the soils from the IWG had the greatest carbon flux, as well as carbon and nitrogen storage (annual monoculture &lt; RNV &lt; IWG). The differences in carbon flux, carbon and nitrogen storage from the IWG to the annual monoculture were 27, 40, 20%, respectively, while the IWG to the RNV was 11, 20, 10%. Shallow soil samples exhibited greater differences in all C and N comparisons between treatments compared to deeper soil samples. Taken together, our findings indicate that crop vegetation type and soil depth strongly influence carbon and nitrogen dynamics.

Comparative Study of Soil Index Properties of Gudu Sokoto State And Oworoshoki Area Lagos State, Nigeria.

The comparative study of the soils sample collected from Gudu and Oworoshoki area, Sokoto state and Lagos State was carried out to compare the index properties of soil at shallow soil deposit. The Global Positioning System (GPS) was used to locate the coordinates of the site. Shallow soil samples (disturbed and undisturbed) at different depths (1m, 2m and 3m) were collected from both study areas (Gudu and Oworoshoki). The disturbed samples were collected using hand trowel, digger, hoe and polythene bags while the undisturbed samples were collected using short pipes (samplers) by stroking each pipe into the ground completely with a hammer at each depth. Disturbed and undisturbed soils collected at different shallow depths (1m, 2m and 3m) were taken to the laboratory for natural moisture content, specific gravity, sieve analysis, Atterberg limits and unit weight test. Empirical equations were used for analyzing the soil samples and AASTHO System of classification was used for classifying the soil samples. The results of the test on Gudu soil samples has shown that the soil sample collected at depth 1.0m and 2.0m are nonplastic materials and were classified according to AASHTO standard as A-3 and sample at depth 3.0m as A-4 which is silty soil while Oworoshoki soil samples has shown that Soils from depth 1.0m, 2.0m and 3.0m are nonplastic (NP) because the Plastic Index (PI = 0) is zero and the soil samples are classified as A – 3 according to AASHTO standard.

The use of fractal theory to study the sources of soil Cd and Pb pollution in Youjiang River Basin

Fractal theory can be applied to study the complexity of spatial structures in nature, and operates by extracting the deterministic parameters driving complex processes. However, to date there has been little reported application of fractal theory to the analysis of the sources of soil heavy metal pollution. This study aimed to determine the sources of heavy metal accumulation in the shallow soil of the Youjiang River Basin. A total of 71 shallow soil samples were collected across an area of 1,000 km2 for the analysis of Cd and Pb to determine the spatial distribution of heavy metal pollution in the basin. The fractal characteristics of Cd and Pb for the eastern, central and western parts of the study area were analyzed using a content-frequency fractal model. The results showed that the content-frequency fractal distributions of Cd and Pb in the area were similar and multifractal. Linear models described the three different groupings of the sample points well with a scattering of several high points, indicating a chaotic distribution of high-content Cd and Pb areas. Two linear models similarly could describe the fractal distributions of these two elements in the eastern part of the study area, with a scattering of several high-value points, whereas although the fractal distributions of the central and western parts of the study area also showed linear distributions, the linear fit for the western part of the study area was slightly worse. The fractal distributions indicated that the spatial distributions of soil Cd and Pb show several trends, which indicates the influence of multiple geochemical processes. When combined with regional industrial and mining enterprises and high density population, the fractal Cd and Pb distributions infer that soil Cd and Pb in the area originate from the same sources, and four major geochemical process are responsible for the distribution of Pb and Cd: 1) the soil formation process; 2) modern agricultural production; 3) industrial sources and dense population; 4) aluminum resources development and utilization. Among these, exploitation and utilization of aluminum resources is the most complex, resulting in a chaotic distribution of Cd and Pb.

PXRF Measurements on Soil Samples for the Exploration of an Antimony Deposit: Example from the Vendean Antimony District (France)

Mineral exploration is increasingly challenging in inhabited areas. To evaluate the potential of soil analysis by pXRF (portable X-ray fluorescence) as a low-footprint exploration technique, we revisited a historic Sb district in an agricultural area and performed shallow-soil sampling (Ah and B horizons) along profiles across known veins to capture the endogenic geochemical anomaly signals. Despite an expected bias between pXRF measurements and laboratory analyses, the former effectively located the Sb veins, especially when using their multi-element capabilities. Composition data processing (CoDa) and horizon-selective sampling significantly improved the method’s efficiency. On-site measurements allow dynamic sampling and mapping, helping with faster, cost-effective sample selection for further laboratory investigations. Based on this case study, where similar geochemical patterns were obtained for both horizons, application of an on-site approach to a humic horizon can increase survey efficiency and decrease impacts.

Assessment of Cd–Pb Pollution in Soils of the Youjiang River Basin, South China

To determine the distribution, migration, and accumulation characteristics of heavy metal pollution in the Youjiang River basin in South China, 71 shallow soil samples were collected from, and amounts of Cd and Pb were determined. Heavy metal pollution in the river basin was assessed using pollution index methods, potential ecological risk index, and geo-accumulation index. The spatial distribution characteristics of Cd and Pb pollution were analyzed by kriging spatial interpolation. The results show that Cd and Pb levels were elevated to some extent in the study area. Results from the single-factor pollution index calculation show that a few Cd samples reached the level of severe pollution and was distributed in the southeastern part of the study area adjacent to Pingguo large bauxite production base. Moderately polluted area accounted for approximately 20% of the total samples and was distributed along the edge of the severely polluted area, in the center (Tiandong county), midwest (near Baikuang power plant), and west (city of Baise) of the study area. The highest levels of Pb pollution only reached the level of slight contamination. The spatial distribution of Pb was similar to the severely polluted area of Cd. The calculation and spatial distribution of the single potential ecological risk index also showed the same result. Cd pollution greatly exceeded Pb pollution in the study area. The spatial distributions of pollution index and potential ecological risk index for Cd and Pb were consistent. The area of severe pollution was concentrated in the southeast, and moderate pollution was found in the northwest of the study area. This indicated that the development of mineral resources, population agglomeration, and thermal power plant were the main cause of Cd and Pb pollution; it also indicated that the spatial migration ability of heavy metals in the study area was not strong. The calculation and spatial distribution of geo-accumulation indexes both showed a similar pollution degree for Cd and Pb.

Experimental study of land subsidence in response to groundwater withdrawal and recharge in Changping District of Beijing.

Over exploitation of groundwater in Changping District of Beijing city has caused serious land subsidence in the past decades. In recent years, the operation of the South-to-North Water Transfer Project has reduced the land subsidence rate. In this paper, Experimental tests are performed using the GDS Consolidation Testing System to characterize the compression and rebound of soils at depths of less than 100 m caused by groundwater withdrawal and recharge in Changping District. The results indicate that the compressible layers are the main contributors to land subsidence. The first compressible layer experiences greater deformation and more considerable hysteresis than the other compressible layers with the same decrease in the pore water pressure. Therefore, the exploitation of the adjacent aquifer should be controlled in the future. The deformation in the second and third compressible layers is a gradual and long-term process with little rebound; therefore, the subsidence should be seriously addressed when the groundwater in the two compressible layers is exploited on a large scale. In the same compressible layer, silty clay is more compressible and hysteretic than silt. For the same soil sample, the deformation rate decreases gradually as the pore water pressure decreases, whereas the creep deformation shows an overall increasing trend. A parameter named the subsidence index Cw is proposed in this paper to describe the soil compressibility during groundwater withdrawal. All the soil samples are characterized by elastic-plastic deformation, and the shallow soil samples with less pore water pressure decrease are more likely to rebound.

Paracoccidioides brasiliensis habitat: far beyond armadillo burrows?

Paracoccidioides spp. isolation from environmental samples is rare and hardly reproducible. Molecular techniques have facilitated the fungal detection. However, it can be still difficult. Some strategies to enhance the capacity of DNA detection have been adopted, including the analysis of soil samples belonging to the habitat of animals from which Paracoccidioides spp. have already been isolated, notably armadillo burrows. To date, the detection of Paracoccidioides spp. has not yet been reported from outbreak hotspots. Clusters and outbreaks of acute paracoccidioidomycosis (PCM), usually a more severe clinical form, have currently occurred in urban areas being associated to climate changes, deforestation, and great constructions. These occurrences potentially signalise the fungus’ environmental niche, a riddle not yet solved. The authors performed an environmental investigation in a deeply disturbed area, after a highway construction in Rio de Janeiro, Brazil, where a recent outbreak of acute PCM occurred. Specific DNA sequences of Paracoccidioides brasiliensis were detected in shallow soil samples around the highway, reinforcing the association between the road construction and this PCM outbreak.

Valley reshaping and damming induce water table rise and soil salinization on the Chinese Loess Plateau

A megaproject, “Gully Land Consolidation” (GLC), was launched on the Chinese Loess Plateau in 2011 to combat land degradation and create new farmlands. However, the newly-claimed farmlands have suffered soil salinization, and the mechanism of salinization has been inadequately addressed. In this study, a creek valley that completed the GLC project in 2014 was selected and a total of 17 new farmlands along the reshaped creek valley were investigated in 2016. Moreover, the hillslope farmlands without conducting the GLC project, the loess parent material that used to fill the stream channel, and the water samples from reservoirs, irrigation wells and spring outlets in the reshaped valley were sampled and chemically analyzed. We found that the new farmlands experienced a significant rise in the water table that played a key role on soil salinization. After GLC, >80% of the sampling sites (14 out of 17) showed a shallow depth (≤3 m) from the soil surface down to the groundwater influence zone. Moreover, the closer the downstream farmlands to the newly-built dams, the shallower the water table, indicating considerable impacts of constructing dams on the water table depth in the near-dam farmlands. At the study site, more than half of the shallow soil samples (20 cm depth) underwent light soil salinization, and the most significant soil salinity occurred in the upper stream farmlands. The interplay between a near-surface water table, a high evaporation rate, landform features, and the alkaline properties of the loessial soil has led to the significant soil salinization in the upper stream of the valley. To mitigate soil salinization and ensure the sustainability of the newly-created farmlands in GLC, drainage trenches in the downstream near-dam farmlands and the drainage canals on both sides of the reshaped valley are suggested, which improve the drainage efficiency and control the water table depth.

Controls on soil organic carbon stocks in tidal marshes along an estuarine salinity gradient

Abstract. Tidal marshes are sedimentary environments and are among the most productive ecosystems on Earth. As a consequence they have the potential to reduce atmospheric greenhouse gas concentrations by sequestering organic carbon (OC). In the past decades, most research on soil organic carbon (SOC) storage in marsh environments has focused on salt marshes, leaving carbon dynamics in brackish and freshwater marshes largely understudied and neglecting the diversity among tidal marshes. We therefore conducted an extensive sampling campaign to quantify and characterize SOC stock in marshes along a salinity gradient in the Scheldt estuary (Belgium and the Netherlands). We find that SOC stocks vary significantly along the estuary, from 46 in freshwater marshes to 10 kg OC m−2 in salt marshes. Our data also show that most existing studies underestimate total SOC stocks due to shallow soil sampling, which also influences reported patterns in OC storage along estuaries. In all sampled tidal marsh sediments the SOC concentration is more or less constant from a certain depth downward. However, this concentration decreases with increasing salinity, indicating that the amount of stable SOC decreases from the upper estuary towards the coast. Although the net primary production of macrophytes differs along the estuary, our data suggest that the differences in OC storage are caused mainly by variations in suspended sediment concentration and stable particulate OC (POC) content in the water along the estuary. The fraction of terrestrial suspended sediments and POC that is transported downstream of the maximum turbidity zone is very limited, contributing to smaller amounts of long-term OC sequestration in brackish and salt marsh sediments. In addition, high rates of sediment deposition on freshwater tidal marshes in the maximum turbidity zone promote efficient burial of OC in these marsh sediments.

Geochemical Examination of Surficial Soil Overlying Uranium Deposit in Manyoni, Central Tanzania

Geochemical compositions of surface to shallow soil samples of Manyoni uranium deposit in Tanzania were determined by X-ray fluorescence analysis (XRF). Uranium, calcium and chlorine are abundant at the depth of 40 cm to 140 cm. Strong correlations between U, CaO and chlorine suggest uranium and carbonates deposition in a Salt Lake system. Strontium content is higher (370 to 480 ppm) than the average upper continental crust UCC (320 ppm) at the depth of 60 cm to 120 cm suggesting Sr accumulation in carbonates. TiO2 and Fe2O3 abundances appear along the profile but have normal concentrations below the average UCC content. Vanadium is positively correlated to Fe2O3 and Ni (mafic sources) concentrations and negatively correlated to U. Uranium precipitation is suggestive of abrupt evaporation during dry season at Manyoni depositional basin. Chlorine (Cl) with high concentration in the vertical profile may be yielded in the sediments after evaporation of the lake water.

Land use effects on organic carbon storage in soils of Bavaria: The importance of soil types

Numerous studies have reported substantial changes of soil organic carbon (SOC) stocks after converting forests into agricultural land and vice versa. However, some studies suggested that agricultural soils might contain similar amounts of SOC as forest soils. Losses of SOC induced by cultivation might be overestimated due to shallow soil sampling and application of inaccurate pedotransfer functions. We investigated the impact of different land uses on total SOC storage down to the subsoil on the basis of 270 soil profiles in southeast Germany under similar climatic and pedogenic conditions using an equivalent soil mass (ESM) approach. Land use effects on SOC storage were strongly affected by soil class, which comprised soil types with similar pedogenesis. Both slightly lower (<20%) and even higher SOC stocks were found under cropland compared with forest land for different soil classes. A comparison of different soil classes under grassland and forest land also showed no considerable differences of SOC stocks. Soil cultivation may not generally be associated with a strong decline of SOC, as tillage probably promotes the formation of organo-mineral associations and a relocation of SOC with depth may decrease its decomposition. This finding should be taken into consideration when estimating and managing the emission and sequestration of C in soils. We assume that many studies based on topsoils alone may have underestimated agricultural SOC stocks, particularly when an ESM approach is used. Our results highlight the need for soil type-specific evaluations in terms of interpreting the effects of land use management on SOC stocks.

Deep Soil Carbon: Quantification and Modeling in Subsurface Layers

Soil is the primary sink for C in forest ecosystems but is often overlooked in ecosystem C budgets. Efforts to quantify C pools often sample soils to a depth of 0.2 m despite observations that deep soil C is neither scarce nor entirely stable. This study examined the systematic sampling depth for ecosystem C analyses in the Pacific Northwest and compared best‐fit models of C in deep soil layers with laboratory measurements. Forest floor samples and mineral soil bulk density samples were collected at regular intervals from the soil surface to depths of 2.5 m from 22 sites across the coastal Pacific Northwest Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] zone. Soil samples were screened to 4.7 mm and analyzed for C content. We found that systematic soil sampling shallower than 1.5 m significantly underestimated total soil C. On average, sampling to 2.5 m compared with 0.5 m increased total C by 156% (85.3–132.7 Mg ha−1), and 21% of total C within the depth range sampled was below 1.0 m. A nonlinear mixed model using an inverse polynomial curve form and predicting total C to 2.5 m given only data to 1.0 m was reliable for 20 of 22 sites; the sites that could not be accurately modeled carried the greatest C at depth and contained noncrystalline minerals. Shallow soil sampling at best provides a biased estimate and at worst leads to misleading conclusions regarding soil C. Researchers seeking to quantify soil C or measure change with time should sample deep soil to create a more complete picture of soil pools and fluxes.

The hidden organic carbon in deep mineral soils

Current estimates of soil organic carbon (SOC) are based largely on surficial measurements to depths of 0.3 to 1 m. Many of the world’s soils greatly exceed 1 m depth and there are numerous reports of biological activity to depths of many metres. Although SOC storage to depths of up to 8 m has been previously reported, the extent to which SOC is stored at deeper depths in soil profiles is currently unknown. This paper aims to provide the first detailed analysis of these previously unreported stores of SOC. Soils from five sites in the deeply weathered regolith in the Yilgarn Craton of south-western Australia were sampled and analysed for total organic carbon by combustion chromatography. These soils ranged between 5 and 38 m (mean 21 m) depth to bedrock and had been either recently reforested with Pinus pinaster or were under agriculture. Sites had a mean annual rainfall of between 399 and 583 mm yr−1. The mean SOC concentration across all sites was 2.30 ± 0.26 % (s.e.), 0.41 ± 0.05 % and 0.23 ± 0.04 % in the surface 0.1, 0.1–0.5 and 0.5 to 1.0 m increments, respectively. The mean value between 1 and 5 m was 0.12 ± 0.01 %, whereas between 5 and 35 m the values decreased from 0.04 ± 0.002 % to 0.03 ± 0.003 %. Mean SOC mass densities for each of the five locations varied from 21.8–37.5 kg C m−2, and were in toto two to five times greater than would be reported with sampling to a depth of 0.5 m. This finding may have major implications for estimates of global carbon storage and modelling of the potential global impacts of climate change and land-use change on carbon cycles. The paper demonstrates the need for a reassessment of the current arbitrary shallow soil sampling depths for assessing carbon stocks, a revision of global SOC estimates and elucidation of the composition and fate of deep carbon in response to land use and climate change.

Excavation Dynamics and Control of Shallow Lunar Soil Sampling Manipulator

The lunar soil excavation dynamics and control are complicated because of the high coupling among manipulator, backhoe device and lunar soil with uncertain parameters. To solve this problem, a multi-body dynamic model, regard the lunar soil backhoe device as the terminal link of the manipulator is developed using supposed link method, and then the excavation dynamics is modeling on the combination of the multi-body dynamic and Balovnev soil-tool interaction formula. Based on this model, an excavation trajectory tracking controller is realized via fuzzy-computed torque method. To reduce the affection of the excavation resistance to control precision, online lunar soil parameters estimation is held in the early stage of the excavation process, and the excavation resistance compensation, determined by those estimation results, is added to the tracking controller using feed-forward form. Simulation results indicate that the controller effective, which has the characteristics of fast tracking and high control precision.