Pedogenic Minerals Research Articles

Soil development trajectories, chemical weathering and pedogenic mineral (trans)formation on glauconitic calcarenites in a Mediterranean area

Glauconite forms in shallow marine basins under oxic to suboxic conditions. It is an Fe-rich sheet silicate often found in calcareous sandstones. How soils evolve on glauconitic sandstones (calcarenite) is poorly addressed: therefore, we investigated the evolutional trajectories. These soils should be enriched in Fe, depleted in K and contain kaolinite and smectite resulting from weathering. We investigated 11 soil profiles on glauconitic calcarenite in a Mediterranean area. The elemental contents, fractions of Fe and Al, soil mineralogy, magnetic susceptibility and stable isotopic composition (C, O) of the bulk soil and carbonates were analysed to explore pedogenesis.The carbonates reflect a former marine basin having onshore organic matter resulting from freshwater input. With soil formation, the primary carbonates were replaced by pedogenic carbonates having a lower δ13C and δ18O signal. Several sites were influenced by human activity since ancient times, reflected by the magnetic susceptibility. The shallow soils had a low weathering degree (CIA of 55 to 70). The better developed Vertisols exhibited a CIA value of up to 85. All soils contained smectite and quartz and, depending on the weathering degree, calcite. Kaolinite formation was connected to high Ca, K, Mg and Na losses. The high oxalate- and dithionite-extractable Fe contents are explained by glauconite weathering. Kaolinite is inherited from the parent material but also actively forms in the soils probably through precipitation from soil water. Due to the presence of smectite and oxyhydroxides the soils sequester a high amount of soil organic carbon (up to 30 kg/m2). Topography exerts a distinct influence on weathering and soil formation. Deepest soils and an advanced weathering stage were measured on footslope sites and shallow soils having a low weathering degree on crest/shoulder sites. Soils on glauconitic calcarenite represent a unique weathering environment that should be investigated even more at the micro-scale.

Exploring the Deuterium Excess of Cretaceous Arctic Paleoprecipitation Using Stable Isotope Composition of Clay Minerals from the Prince Creek Formation (Maastrichtian) in Northern Alaska

We report estimated stable isotope compositions of Artic paleoprecipitation using phyllosilicates sampled from three paleosols and two bentonites in the Prince Creek Formation (Maastrichtian) in northern Alaska. Previous studies reported a deuterium excess in estimates of Arctic paleoprecipitation from the Late Cretaceous by combining hydrogen and oxygen proxy sources, including pedogenic minerals, dinosaurian tooth enamel phosphates, pedogenic siderites, and n-alkane biomarkers. The new dataset produced in this study removes uncertainty on possible explanations (photosynthetic and transpiration) of the deuterium excess by producing stable hydrogen and oxygen isotopic signatures from the same source material. The δD of the phyllosilicates range from −171‰ to −72‰ VSMOW and δ18O ranges from 5.0 to 11.8‰ VSMOW. By assuming a MAT of 6.3 °C and calculating uniquely derived fractionation equations for each phyllosilicate, we report estimated isotopic composition of Late Cretaceous paleoprecipitation with an average δD value of −133‰ VSMOW, corresponding to an average δ18O value of −20.3‰ VSMOW. The estimates of Late Cretaceous paleoprecipitation do not intersect the Global Meteoric Water Line and reveal a reported deuterium excess ranging from 7 to 46 per mil. These results confirm the presence of a deuterium excess in Late Cretaceous Arctic paleoprecipitation and provide new insight to assessing possible explanations for this phenomenon.

Sulphur Contents in Arable Soils from Four Agro-Ecological Zones of Ghana

There is limited data on Sulphur (S) contents in arable soils for appropriate fertilizer recommendations in Ghana. Five study areas in a reconnaissance survey (RS), followed by an in-depth study of two areas comprising farms of different durations of cultivation, were investigated for the current total S and sulphate contents. Basic soil properties were measured using standard laboratory procedures. Total S and sulphate contents were determined using LECO instrument dry combustion and HPLC, respectively. The results showed wide variations in total S contents from 31 to 603 mg kg−1 in the Guinea Savannah (GS) zone. The mean trend was Forest > Forest-Transition (F-S) > north Guinea Savannah (nGS) > Deciduous Forest (DF) > south Guinea Savannah (sGS) in the RS sites, with a similar trend in the main study sites. Sulphate contents ranged from 5 to 25 mg kg−1, constituting 0.8 to 37% of the total S. The mean percent trend was sGS = DF > Forest > nGS > F-S. Soil organic carbon (SOC) was the major predictor of total S along with pedogenic minerals. Total S and crystalline pedogenic minerals predicted the sulphate contents. The results highlight the need for ecologically-based S fertilizer programmes to boost crop yields.

Climate and sea level forcing of terrigenous sediments input to the eastern Arabian Sea since the last glacial period

Analyses of mass accumulation rate (MAR), laser grain-size, clay mineralogy, and SrNd isotopic compositions of <2 μm and < 63 μm grain-size fractions have been applied to sediments from the International Ocean Discovery Program (IODP) Site U1456, which span the last 31 ka, in order to constrain (i) past changes in the relative proportions of the fine-grained detrital sediments derived from the Indus River and the Deccan Traps and the dynamics of sediment transport to the Laxmi Basin and (ii) past changes in Indian monsoon rainfall and latitudinal migration of Intertropical Convergence Zone since the last glacial period. Sr and Nd isotopes results combined with clay mineral assemblages suggest that clay-sized sediments at IODP Site U1456 derive mainly from the Indus River (70–90%), followed by a minor contribution from rivers draining the volcanic province of the Deccan Traps (10–30%). During the Last Glacial Maximum, clay mineralogy was dominated by illite and chlorite primarily derived from the highlands of the Indus River basin. The combination of lower temperatures and lower monsoonal rainfall during glacial times led to a reduction of smectite formation rates in the floodplains, while glacial erosion accelerated in the Himalayan and Tibetan highlands leading to the release of large quantities of illite and chlorite minerals into the Arabian Sea. In addition, glacial low sea-level stands allowed a connection between river mouths and the heads of deep-sea channels favoring the southward transfer of sediments to IODP Site U1456 by turbidity currents. Each maximum of the summer insolation curve, associated with a northward shift of the ITCZ and an intensification of summer monsoon rainfall (from 31 to 25 ka BP and from 12 to 8 cal ka BP), was associated with enhanced rainfall in the Indus floodplain which in turn led to an increase in the physical erosion and weathering of plain soils, which were rich in pedogenic minerals (such as smectite), and/or a higher production rate of smectite in the soils of the Indus floodplain. A compilation of three Nd isotopic composition records obtained at sites located on a N-S latitudinal transect in the eastern Arabian Sea have allowed us to establish the impact of sea level variations and latitudinal migration of the ITCZ over time on the sedimentation of the eastern Arabian Sea.

Stable Isotope Tracers of Cretaceous Arctic Paleoprecipitation

We report estimated stable isotope compositions of depositional waters and paleoprecipitation from the Cretaceous Arctic to further elucidate the role of the global hydrologic cycle in sustaining polar warmth during that period. Estimates are based on new hydrogen isotopic analyses of n-alkane biomarkers extracted from Late Cretaceous and mid-Cretaceous terrestrial deposits in northern Alaska and the Canadian High Arctic. We integrate these new results with earlier published work on oxygen isotopic analyses of pedogenic siderites, dinosaurian tooth enamel phosphates, and pedogenic clay minerals from the same field areas. Average Late Cretaceous δD values of −143‰ VSMOW corresponded with average δ18O values of −24.1‰ VSMOW, and average mid-Cretaceous δD values of −106‰ VSMOW corresponded with average δ18O values of −22.1‰ VSMOW. The distributions of water isotope δD and δ18O values from Cretaceous Arctic deposits do not intersect with the Global Meteoric Water Line, suggesting an apparent deuterium excess ranging from about 40 to 60 per mil. We considered several possible explanations for these Cretaceous results including (1) mass-balance changes in zonal patterns of evaporation and precipitation at lower latitudes, (2) concentration of 2H in leaf tissue waters from continuous transpiration by coniferous paleofloras during the Arctic growing season, and (3) concentration of 2H in the groundwaters of methane-emitting Arctic soils.

Sulfur accumulation in soil in a forested watershed historically exposed to air pollution in central Japan

Forest soils that have accumulated anthropogenic sulfur (S) as a result of historical air pollution may gradually or suddenly release inorganic sulfate either by desorption of inorganic sulfate or by mineralization of organic S, even after mitigation of previous air pollution. The release of inorganic sulfate from soil to surface water leads directly to watershed acidification. Thus, whether the organic S compounds that have accumulated in soils are resistant to microbial activity, due to formation of organo-mineral complexes, is essential information for management of forest soil ecosystem services. A nationwide air pollution monitoring survey by the Japanese Ministry of the Environment identified acidification of both surface water and soil in the Lake Ijira watershed of central Japan, presumably sourced from the Chukyo Industrial Area which lies upwind of the watershed. We compared the amount of S accumulated in the Ijira soils (Dystrudepts) with that in comparable soils in other watersheds in central Japan that were less affected by industrial air pollution. To determine how much mineral-associated organic S had accumulated in the Ijira soils, we measured pyrophosphate- extractable S. We used high-resolution x-ray fluorescence (HRXRF) spectroscopy with a double-crystal type high energy resolution spectrometer to estimate the oxidation states of both mineral-associated and free organic S. We also measured S isotope compositions to explore S dynamics in the soils. We found that more S had accumulated in the Ijira soils than in the comparable soils from other watersheds in central Japan. Concentrations of total S in the Ijira soils varied among soil horizons, reaching more than 1000 mg S kg−1 in some horizons. Mineral-associated organic S accounted for more than half of the total accumulated S. High-resolution x-ray fluorescence spectrum analyses showed that mineral-associated organic S was retained at both high and low oxidation states. The δ34S values of total S in the deeper horizons tended to be higher than those of the uppermost horizons of the Ijira soils and correlated positively with concentrations of extractable Al and Fe oxides (which characterize pedogenic minerals). Our results suggest that about half of total accumulated S in Ijira soils is stabilized in pedogenic minerals and the remainder comprises free organic S and adsorbed inorganic sulfates. There might have been repetitive mobilization and immobilization of S and the degraded organic S might have greater affinity with pedogenic minerals. Further, the ratio of total C to mineral-associated organic S correlated negatively with concentrations of extractable Al and Fe oxides, suggesting that organic S is more resistant to mineralization than organic C because S is preferentially associated with the pedogenic minerals. Monitoring of the chemical states of S compounds in soils historically exposed to air pollution is recommended to assist in prediction of the fate of the S compounds that have accumulated in them.

The fate of calcium in temperate forest soils: a Ca K-edge XANES study

Calcium (Ca) plays a crucial role for plant nutrition, soil aggregation, and soil organic matter (SOM) stabilization. Turnover and ecological functions of Ca in soils depend on soil Ca speciation. For the first time, we used synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the Ca K-edge (4038 eV) to investigate Ca speciation in soils. We present Ca K-edge XANES spectra of standard compounds with relevance in soils (e.g. calcite, dolomite, hydroxyapatite, anorthite, clay mineral-adsorbed Ca; Ca oxalate, formate, acetate, citrate, pectate, phytate). Calcium XANES spectra with good signal-to-noise ratios were acquired in fluorescence mode for Ca concentrations between 1 and 10 mg g−1. Most standard spectra differed markedly among each other, allowing the identification of different Ca species in soils and other environmental samples as well as Ca speciation by linear combination fitting. Calcium XANES spectra obtained for samples from different horizons of twelve temperate forest soils revealed a change from dominating lithogenic Ca to clay mineral-bound and/or organically bound Ca with advancing pedogenesis. O layer Ca was almost exclusively organically bound. With increasing SOM decomposition, shares of oxalate-bound Ca decreased. Oxalate-bound Ca was absent in calcareous, but not in silicate subsoil horizons, which can be explained by microbial decomposition in the former vs. stabilization by association to pedogenic minerals in the latter soils. Synchrotron-based Ca XANES spectroscopy is a promising novel tool to investigate the fate of Ca during pedogenesis and—when performed with high spatial resolution (µ-XANES), to study aggregation and SOM stabilization mechanisms produced by Ca.

Petromagnetic Properties of Fallow Soils as an Indicator of the Organic-Matter Content

The magnetic properties of chernozem soils, dark and light gray forest soils, and sod-podzolic soils present in the Republic of Tatarstan have been researched and described using the petromagnetism method, coercive spectrometry, and X-ray phase analysis with the purpose of improving the soil monitoring system in relation to fallow and virgin soils. In the course of soil genesis, iron compounds undergo transformations and the magnetic parameters of the soil profile change in comparison with the parent rocks. It can be said that the magnetic profile reflects the pedogenesis processes. A statistically significant relationship between the humus content on the one hand and the susceptibility and intensity of remanent saturation magnetization (Jrs) on the other hand has been identified. A technique making it possible to separate the contributions of lithogenic and pedogenic magnetic minerals to the saturation remanence (Jrs) intensity has been developed on the basis of coercive spectrometry. In the studied soils, the pedogenic component primarily consists of the organogenic extracellular constituent of the magnetite–maghemite association, which is the best candidate to proxy in assessments of the humus concentration in soils at various depths with magnetic methods.

Weathering of tephra and the formation of pedogenic minerals in young Andosols, South East Iceland

Frequent tephra deposition and a steady influx of aeolian material of multiple origins, dominate soil formation in Iceland. Little is known about the weathering behaviour, mineral formation and alteration of tephra and Icelandic Andosols after tephra deposition.Two sampling sites in the volcanically active area south of Vatnajökull in South East Iceland were selected according to the presence of two distinctive tephra layers; a light coloured, rhyolitic, tephra from the Öræfajökull eruption in 1362 CE and a black, basaltic, Veiðivötn tephra from 1477 CE. Through a combination of physical, chemical and mineralogical analyses, the present research improves the understanding of changes in properties, weathering processes and mineralogy in Andosols after the deposition of tephra and aeolian material. It adds significant knowledge about the impact of explosive volcanic eruptions and consequences of heavy tephra fall and erosion on soil development in Iceland in particular, but may have wide-ranging influence on the management of volcanic soils worldwide.Both pedons can be classified as Andosols, showing silandic and vitric soil properties. The soils were acidic and dominated by sand. Feo/Fed ratios above 0.75 in all soils indicated a low degree of soil development. The major portion of the clay size particles mainly derived from poorly crystalline and amorphous constituents (e.g. allophane and ferrihydrite). In spite of the low soil age (less than 650 years) and the prevailing cool climatic conditions, we observed signs of pedogenesis and the presence of secondary clay minerals in both, soils and tephra. It was mainly secondary chlorite, which could be verified. Usually it takes more time under given environmental conditions for clay minerals to form and alter. The phyllosilicates we found are supposedly attributed to aeolian influx of material from older, more weathered, more developed eroded surfaces of unknown origin and chemical composition, maybe from sources outside Iceland. This and the particular local site conditions (e.g. moisture, soil temperature, SOM), rather than the primary composition of the parent material, are the driving factors in the development of the investigated Andosols and the alteration of minerals. Additionally, the high volcanic activity in Iceland constantly provides new tephra to the soils.

Paleosols in an outcrop of red beds from the Upper Cretaceous Yaojia Formation, southern Songliao Basin, Jilin Province, NE China

Paleosols in an outcrop of fluvial–lacustrine red beds have been recognized in the Upper Cretaceous Yaojia Formation in southern Songliao Basin, Songyuan City, Jilin Province, NE China. They are recognized in the field by pedogenic features, including root traces and burrows, soil horizons and soil structures. Root traces are remnants of small herbaceous plants, elongating and branching downwards in the red paleosols. They are filled by calcite, analcime, and clay minerals in spaces created by the decay of the plant roots. Burrows are found near the root traces with backfilled cells made by soil-dwelling insects. Soil horizons include calcic horizons (Bk horizon) with continuous calcareous layers, argillic horizons (Bt horizon) with clay films and dark brown to black iron-manganese cutans, vertic horizons (Bw horizon) with slickensided claystone, and deformed soil structure and gleyed horizons (Bg horizon) with mottles and reticulate mottles. Soil structures of the paleosols include pseudo-anticlinal structures, subangular blocky structures, and angular blocky structures. The micro-pedogenesis characteristics are also observed, including micrite pedogenic minerals and clay skins. Based on the pedogenic features above, paleosols types including Aridisol, Alfisol, and Vertisol are interpreted in the red beds of the Yaojia Formation. Forming in the Late Cretaceous, the paleosols can provide more details about the seasonal climate conditions and terrestrial sedimentary system in lacustrine basin.

Loess magnetic susceptibility flux: A new proxy of East Asian monsoon precipitation

Abstract Magnetic susceptibility (χ) of loess-paleosol sequences on the Chinese Loess Plateau (CLP) has been widely used as a proxy for East Asian summer monsoon (EASM) precipitation variability. Such records typically show strong climate forcing in the ~100 ka orbital eccentricity band, but exhibit weak precessional (~23 ka) forcing relative to that seen in oxygen isotopes from marine sediments. This is puzzling as monsoons should be highly sensitive to precession variations. We assert that this lack of precessional signal is because χ is a concentration, which is strongly affected by the dilution effect of dust sedimentation rate superimposed on rainfall rate. χ-flux on the other hand corrects for dust accumulation rate and bulk density effects to better reveal pedogenic mineral ingrowth rates associated with rainfall. In this study, we compare three 600 ka records of loess pedogenic χ-flux from the CLP with Chinese speleothem δ18O records and a 550 ka loess-paleosol 10Be flux record from Baoji which has also been used as a monsoon precipitation proxy record. Pedogenic χ-flux exhibits clear signals of orbital precession, whereas χ (-concentration) does not.

Soil and dust magnetism in semi-urban area Truskavets, Ukraine

The objective of this paper was to study pollution in the semi-urban area of Truskavets (Ukraine) using low-cost and energy-efficient magnetic measurements. Soil magnetic properties were measured near a railway station (transect) and near a road (transect and grid). To compare the magnetic properties of the soils from the urban areas, we sampled in a forest area located 2–3 km from Truskavets. Additionally, ten dust samples were taken 150 cm above the ground from the smooth surface of the tree bark. Near the Stebnyk Ring (the end of the second transect), we established a grid (20 × 20 m) and measured the soil magnetic susceptibility MS (mass-specific χ, and volume κ). There were taken 55 soil samples within the upper 0–5 cm of the topsoil. The results showed that low-frequency MS of the natural soil was within the range of 8–10 × 10–8 m3/kg, a low value for the Ukraine soils. The urban soils collected near the roadway and the railway had high MS values. Soil pollution was confirmed by the frequency dependence of magnetic susceptibility: χfd = 2–3%. Our results, based on the thermomagnetic, hysteresis, isothermal (IRM), and anhysteretic remanent magnetization (ARM) measurements, suggested that magnetite is responsible for the increase in the magnetic signal of the urban soils. Natural soils normally contain a single domain (SD) grains. It has also been found that the high coercivity haematite and goethite are stable pedogenic minerals in the Truskavets natural soil. Overall, the magnetic measurements have proven to be a rapid, low cost, non-destructive and efficient technique for soil monitoring and air quality assessment.

Diversity and peculiarities of soil formation in eolian landscapes – Insights from the mineral magnetic records

Magnetic properties of loess-paleosol sequences are widely utilized as sensitive, easily-obtained and reliable proxy archives of past climate change in continental settings. However, soil formation in aeolian landscapes may occur under different and changing conditions of dust sedimentation, which will affect the growth and development of the pedogenic magnetic component. This phenomenon is explored in our study by analyzing depth variations of the following magnetic characteristics: frequency dependent magnetic susceptibility, anhysteretic magnetic susceptibility and the ratio between anhysteretic susceptibility and isothermal remanent magnetization acquired in a 100 mT back field (χarm/IRM-100 mT), along three loess-paleosol profiles from NE Bulgaria. A conceptual model for the time evolution of the grain size of the pedogenic magnetic fraction with soil depth is proposed, which is build upon the mechanism of soil formation – accretional or in stable land surfaces, or a combination of the two. Another magnetic ratio – isothermal remanence acquired in a 300 mT back field divided by low field magnetic susceptibility (IRM-300 mT/χ) is utilized as a proxy for the changes in the ratio of silt to clay fractions, indicative of changes in dust sedimentation regimes during glacial-interglacial transitions. According to the proposed conceptual model, verified by the magnetic signature of three Holocene soils from NE Bulgaria, discrimination between accretional soils and soils developed without dust additions during soil forming period can be done. Accretional soils are characterized by parallel changes in grain size sensitive magnetic proxies. Soils, developed at stable landscape conditions show gradation of the depths at which maximum enhancement of various proxies occurs with deepest occurrence of the maximum in χfd, followed by depth of maximum χarm and χarm/IRM-100 mT. Another implication of the new conceptual model is that the mean coercivity of the pedogenic component of accretional soils will be higher than that of soils developed without eolian input at equal temperature conditions because of the soils' thermal gradient and different depths, at which pedogenic minerals form in the two settings. The results revealed that the Holocene soils (So) has developed under different soil-forming conditions than paleosols from the same sites.

Tracing elevational changes in microbial life and organic carbon sources in soils of the Atacama Desert

Abstract The Atacama Desert frequently serves as model system for tracing life under extremely dry conditions. We hypothesized that traces of life in the Atacama Desert follow distinct micro- and macro-scale gradients such as soil depth and elevation, respectively. Different depth intervals of surface soils (0–1, 1–5, and 5–10 cm) were sampled at five sites along an elevational transect near the Quebrada Aroma, spanning from the hyperarid core of the desert towards the arid Western Andean Precordillera (1300 to 2700 m a.s.l.), and from one additional site in the hyperarid core near Yungay. We determined the contents of major elements, pedogenic minerals and oxides, organic carbon (OC), and its δ13C and δ15N isotopic composition. The presence of living microorganisms was assessed by cultivation, and bacterial community composition was analyzed based on 16S rRNA gene sequencing. Additional information about past and present plant and microbial life was obtained from lipid biomarker analysis. We did not detect consistent micro-scale distributions for most of these proxies within the soils. However, concentrations of OC and of long-chain, plant wax-derived n-alkanes increased in soils along the aridity gradient towards the wetter sites, indicating the presence of past life at places presently not covered by vegetation. Likewise, bacterial abundance and diversity decreased as hyperaridity increased and the microbial community composition changed along the transect, becoming enriched in Actinobacteria. The distributional patterns of phospholipid fatty acids (PLFAs) confirmed the larger bacterial diversity at the higher, more humid sites compared to the drier ones. Archaeal isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) and bacterial branched (br)GDGTs, which can also indicate past life, did not follow a clear elevational trend and were absent at the driest site. Taken together, plant-derived and microbiological markers follow primarily the macro-scaled elevation and aridity gradient. Viable bacteria are present even at the driest sites, while detected biomolecules also indicate past life. The detection of past plant life in nowadays apparently lifeless regions suggests that conditions for life were less hostile in former times.

Characterizing nutrient pathways in Quebec (Canada) vineyards: Insight from stable and radiogenic strontium isotopes

Soils are a crucial interface of Earth's Critical Zone, responsible for the biogeochemical cycling of mineral nutrients. While the sources of essential nutrients such as Ca (and Sr) in plants have been widely studied, the processes by which these nutrients are transferred from the soil to the plants is less clear. We present new evidence for systematic nutrient fractionation between soils, grapes and wines from five vineyards from the Quebec terroir (Canada) using the novel stable Sr (δ88/86Sr) isotope system. We coupled this approach with traditional radiogenic 87Sr/86Sr measurements on the same samples (bulk soils, labile fraction of these soils, whole grapes, and wines) from five vineyards from the Quebec terroir (Canada) to ensure that variations in δ88/86Sr values were provoked by processes involved in Sr transfer instead of mixing between different sources. The δ88/86Sr values generally decrease from the bulk to the labile fractions of the soils to the grapes. A decrease in the difference between the soil fractions (Δ88/86Srbulk-labile) with increasing δ88/86Sr values in the labile fraction is interpreted to reflect increasing pedogenic mineral precipitation and higher soil fertility. The depleted δ88/86Sr values of the grapes are consistent with a preferential uptake of lighter isotopes by plants. This effect is magnified in soils showing higher secondary mineral precipitation. An increase in the δ88/86Sr values from the grapes to the wines reflects the separation of the skin/seeds and the juice (pulp enriched in 88Sr) in the winemaking process. This mixing relationship is supported by a correlation between the Sr concentrations and the δ88/86Sr values of the wines and grapes. These findings suggest promising new applications of stable Sr isotopes values for studying soil fertility and the impact of nutrient availability for plant growth in agricultural ecosystems as well as the impact of the maceration processes in the production of wine.The overall similarity of 87Sr/86Sr ratios of the labile soil fractions, grapes and wines from the same vineyard support the hypothesis of a same Sr source, from the soil solution to its transfer to the grape and wine and confirm the potential of the 87Sr/86Sr ratios as a proxy for geographic provenance of wine.However, slightly lower 87Sr/86Sr ratios in the grape pulps (by 0.00040 on average compared to the skins and seeds) suggest that the sources of nutrients available for plant uptake vary during the vegetative cycle. The grape seeds and skins formed in the early growth cycle are characterized by rapid growth due to enhanced rhizosphere activity (enhanced mineral dissolution) providing higher nutrient levels. The enhanced mineral solubility results in higher 87Sr/86Sr ratios in the skin and seeds derived from enhanced dissolution of 87Sr-enriched silicate minerals. In contrast, the pulp develops later in the growth cycle when rhizosphere activity and mineral solubility is reduced, resulting in a lesser contribution from silicate minerals and thus reflect a higher proportion of dissolved carbonate contributing to the lower 87Sr/86Sr ratios of the pulps.

Lithological and bioclimatic impacts on soil phosphatase activities in California temperate forests

Organic phosphorus (Po) biogeochemical cycling is known to be impacted by soil-forming factors, yet little is known about interactions among soil-forming factors on the drivers of Po cycling, soil phosphatases. A comprehensive assessment of lithological and bioclimatic impacts on soil phosphatase activities was conducted using lithological and vegetation-constrained climatic (i.e., bioclimatic) gradients in temperate California forests. Soils (0–5, 5–15 cm depth) from twelve combinations of three lithologies (andesite, basalt, granite) and four bioclimatic zones (blue oak, ponderosa pine, red fir, white fir) encompassing a wide range of MAP (330–1400 mm) and MAT (5.0–17.0 °C) were analyzed for resin P (Presin), Po, microbial biomass P and total P (Pt), activities of three phosphatases, and soil properties (e.g., organic carbon [OC], pedogenic minerals). Across soil depths, lithology influenced phosphomonoesterase (ACP, ALP) activities more than bioclimate, whereas the opposite occurred for phosphodiesterase (PDE). Correlations of phosphatases with edaphic (e.g., pedogenic minerals, clay content) and climatic variables (MAP, MAT) varied by lithology (e.g., ACP and OC, Rbasalt = 0.61, p < 0.01 and Rgranite = 0.20, p = 0.28), indicating lithological dependence of bioclimatic impacts. Within bioclimates, phosphomonoesterase but not PDE activities were correlated with OC much more strongly than with pedogenic minerals, suggesting limited lithological impacts in vegetation- and climate-constrained ecosystems. This study demonstrates that the enzymes that catalyze the two distinct steps of Po mineralization, phosphomonoesterase versus phosphodiesterase, can express differential and even opposite relationships with edaphic variables depending on the combination of lithology and bioclimate. Additionally, OC, Presin, and Po may not necessarily be the best predictors of phosphatase activities as commonly proposed. Lithology type and/or pedogenic minerals that integrate lithology and bioclimate context may enable a more comprehensive assessment of phosphatases in soil P cycling sensitive to bioclimatic variability.

The weathering of volcanic tephra and how they impact histosol development. An example from South East Iceland

Little is known about the impact of tephra deposits from explosive volcanic eruptions on soil formation and weathering processes in organic soils. The weathering of tephra of basaltic and rhyolitic origin and their impact on Icelandic histosols were studied through a combination of physical, chemical and mineralogical analyses. Two sampling sites were selected according to the presence of the light coloured rhyolitic tephra from the Öræfajökull eruption in 1362 CE and a dark-coloured basaltic Veiðivötn tephra from 1477 CE in the volcanically active area south of Vatnajökull in South East Iceland.The determining factor of pedogenesis in the investigated histosols is the OM, but the influence of tephra and aeolian material from external sources must be taken into consideration. The soils are the result of altered plant residues and volcanic material (tephra and aeolian material). Plant remnants, as well as the soil itself, are protected from decomposition by the prevailing anaerobic conditions, a low soil pH and the repeated addition of inorganic matter. Clay formation is low, while metal-humus complexes are predominant. Feo/Fed ratios indicated a generally low degree of weathering, being higher close to the basaltic tephra.The mineralogy was dominated by plagioclase and pyroxene, with quartz and zeolite as minor components. In contrast to previous research on Icelandic soils, our investigations revealed layer silicates at both sites. While we found evidence of smectite in the soils at Kálfafell, hydroxy interlayered minerals were found at Reynivellir. In the basaltic tephra, traces of layer silicates could be verified. In contrast, the rhyolitic tephra did not show any pedogenic minerals, suggesting that it had hardly altered since its deposition in 1362 CE. It is not the chemical composition of the inorganic parent material, but the location that may be an influencing factor on the formation of clay minerals in the investigated histosols.

Evolution of porosity and clay mineralogy associated with chemical weathering of black shale: A case study of Lower Cambrian black shale in Chongqing, China

This work aimed to evaluate the evolution of pore networks and clay mineral in black shale weathering systems in Chongqing, China. The pore-size distributions, relationships between fractal dimensions and minerals, and clay mineral weathering pathways were evaluated for three weathering profiles, A, B, and C, which were characterized as weak, weak to moderate, and moderate to intense based on the Chemical Index of Alteration. It was found as the shale density decreased, the porosity and specific surface area increased with decreasing depth during weathering. The largest pore diameter peak in a pore-size distribution graph shifted further right as the degree of weathering increased. Micro-transition pores (<100 nm) dominated the parent shale, while mesopores (0.1–1 μm) and macropores (>1 μm) dominated the saprock and regolith zones. The surface fractal dimension of the micro-transition pores was positively correlated with the pyrite and carbonate content, but negatively correlated with secondary clay mineral content. By contrast, the surface fractal dimension of the macropores was negatively correlated with pyrite and carbonate content and positively correlated with secondary clay mineral content. These relationships indicate that micro-transition pores at the surface became smoother and macropores became rougher during weathering. Inherited micas, including illite, predominated the clay fractions along transects as weathering proceeded. The pedogenic minerals (i.e., smectite, vermiculite, kaolinite, and mixed-layer minerals) were minor components in the saprock and regolith zones. Smectite formation was likely due to direct transformation from mica or illite under strongly acidic conditions. A second possibility is transformation proceeded through mixed-layer mineral intermediates, i.e., mica-smectite/illite-smectite and mica-vermiculite/illite-vermiculite. The weathering of clay minerals in black shale from weak to intense weathering stages was mica/illite → mica-smectite/illite-smectite or mica-vermiculite/illite-vermiculite → “chlorite” (including vermiculite, hydroxy-interlayered vermiculite?, and chlorite?) → smectite → kaolinite → gibbsite. This study revealed pore geometry evolution depends on transport-limited solutions that facilitate mineral breakdown and formation. The clay mineral weathering pathways were controlled by the weathering environment and duration.

Sulfur accumulation rates in volcanic soils of eastern Japan over the last millennium based on tephrochronology

Soils have an important role as a reservoir of essential elements for forest ecosystems. Although previous chronosequence studies have determined accumulation rates of several elements in soils, they have not focused on sulfur (S), a secondary macronutrient. We investigated S accumulation rates in five volcanic soils, dated by the use of tephras from the following volcanoes: Mt. Komagatake (tephra Ko-a, 1929 CE), Mt. Tarumae (tephra Ta-a, 1739 CE), Mt. Fuji (tephra F-Ho, 1707 CE), Towada caldera (tephra To-a, 915 CE), and Mt. Haruna (tephra Hr-FP520, 520 CE). The soils were sampled from A horizons formed above the tephra layer, and total S and pedogenic minerals (Ald, Fed, Alo, and Feo) were analyzed to determine the relationships between their estimated pools and soil age. The fractionation of S by oxidation state was determined by S K-edge XANES analysis in constituents of soils from Mt. Komagatake and Mt. Haruna. Our results showed that the S accumulation rate was almost constant over the last millennium. To extend our analysis to longer soil formation times, we extrapolated the S accumulation–age relationship to 10cal. ka and compared the resulting values with previously reported S data from horizons that likely developed during that time period in soils from Mt. Nantai dated by tephra Nt-S (14–15cal. ka). The similarity of the extrapolated values to the Nantai soil values suggests that the S accumulation rate may have been constant since 10cal. ka. In addition, the growth of the S pool with soil age was linearly proportional to the growth of pedogenic mineral pools. Sulfur isotope composition of soil total S depended not on soil age, but rather on the soil origin as indicated by location. The predominant oxidation state of the S fraction changed from reduced to oxidized with soil age during the Holocene. These results suggest that the constant S accumulation rate may reflect the variable influence of exogenous S sources as well as the association of S compounds with pedogenic minerals. Sulfur compounds may accumulate at a constant rate in Japanese volcanic soils as the result of biological transformation followed by retention of S in association with the pedogenic minerals.

Magnetic and spectral signatures of Cerrado soils in the state of Goiás, Brazil

Abstract: The objective of this work was to estimate the iron oxide contents (hematite and goethite) and to characterize the color and the spectral and magnetic signatures of Cerrado soils in the state of Goiás, Brazil. Six Oxisols and one Inceptisol were studied. Spectral and magnetic signatures were determined by diffuse reflectance spectroscopy (DRS) and magnetic susceptibility, respectively. Then, the spectral curves and the second derivative calculations were used to determine hematite and goethite contents, as well as soil color after conversion into tristimulus values. Hematite and goethite contents were also obtained by x-ray diffractometry, and soil color was also defined in the field (Munsell color chart). The values for the isomorphic substitution of iron by aluminum and the degree of redness were also determined. DRS can be used to estimate hematite and goethite contents, as well as the color of Cerrado soils in the state of Goiás. The spectral signature can point out the main soil properties related to the contents of organic matter, iron oxides, kaolinite, and gibbsite. The magnetic signature, characteristic of soils rich in iron oxides (hematite and goethite), shows the predominance of pedogenic minerals.