Wiaux et al 2014 Geoderma

Earth and Planetary Science Letters, 2009

Keywords: weathering erosion soil geochemistry hillslope processes sediment transport channel incision Hillslopes have been intensively studied by both geomorphologists and soil scientists. Whereas geomorphologists have focused on the physical soil production and transport on hillslopes, soil scientists have been concerned with the topographic variation of soil geochemical properties. We combined these differing approaches and quantified soil chemical weathering rates along a grass covered hillslope in Coastal California. The hillslope is comprised of both erosional and depositional sections. In the upper eroding section, soil production is balanced by physical erosion and chemical weathering. The hillslope then transitions to a depositional slope where soil accumulates due to a historical reduction of channel incision at the hillslope's base. Measurements of hillslope morphology and soil thickness were combined with the elemental composition of the soil and saprolite, and interpreted through a process-based model that accounts for both chemical weathering and sediment transport. Chemical weathering of the minerals as they moved downslope via sediment transport imparted spatial variation in the geochemical properties of the soil. Inverse modeling of the field and laboratory data revealed that the long-term soil chemical weathering rates peak at 5 g m − 2 yr − 1 at the downslope end of the eroding section and decrease to 1.5 g m − 2 yr − 1 within the depositional section. In the eroding section, soil chemical weathering rates appear to be primarily controlled by the rate of mineral supply via colluvial input from upslope. In the depositional slope, geochemical equilibrium between soil water and minerals appeared to limit the chemical weathering rate. Soil chemical weathering was responsible for removing 6% of the soil production in the eroding section and 5% of colluvial influx in the depositional slope. These were among the lowest weathering rates reported for actively eroding watersheds, which was attributed to the parent material with low amount of weatherable minerals and intense coating of the primary minerals by secondary clay and iron oxides. We showed that both the morphologic disequilibrium of the hillslope and the spatial heterogeneity of soil properties are due to spatial variations in the physical and chemical processes that removed mass from the soil.

Geomorphology, 2008

A toposequence of Holocene soils located between 1100-2400 m asl in the Italian Alps served as the basis for the following analyses: the weathering of limestone and dolomite, the calculation of mass balances, understanding the formation of pedogenic Fe and Al, the determination of soil mineral and clay mineral reactions and transformation and the measurement of accumulation and stabilisation mechanisms of soil organic matter. Leaching of carbonates is most intense at the lower elevations, although calcite and dolomite have a higher solubility at low temperatures. The pCO 2 in the soil is higher at lower elevations and weathering is driven mainly by carbonic acids. At higher elevations, organic acids appear to determine the mineral transformations and weathering reactions to a greater extent. This suggests that two very different weathering regimes (carbonic and organic acid weathering) exist along the toposequence. The transformation of mica into vermiculite is the main process in both the clay and fine-earth fraction. Weathering of silicate minerals started even before the carbonates had been completely removed from the soils. The transformation mechanisms of silicate minerals in the A and O horizon at higher elevations was at least as intensive as that at the climatically warmer sites. The neoformation of pedogenetic clays at climatically cooler sites was slightly greater than that at the warmer sites. However, the formation rate of secondary Fe and Al phases was more pronounced at lower elevation, which means that this process seemed to be driven dominantly by carbonic acid (weathering of primary minerals). Soil organic matter (SOM) abundance in the mineral soil is nearly 15 kg/m 2 at all sites and, surprisingly, no climate-driven effect could be detected. In general, the preservation and stabilisation of SOM was due to poorly crystalline Al and Fe phases and vermiculite, regardless of some variations in the composition of the parent material (varying calcite/dolomite ratio).

Soil and Tillage Research

Ecosystem in responses to land use change create feedbacks in soils and ecological processes in Critical Zone (CZ). The identification and quantification of such changes is needed as a part of understanding the relationship between climate, CO 2 emission, humidity, biological activity, soil carbon, surface redox, and plant nutrient cycling and lithology, mineralogy, biogeochemistry of bedrocks. The CZ observation as complex investigation of three Luvic Phaezoem soils under secondary deciduous forest, grassland and cropland from Moscow region, Russia, was fulfilled with the main goal to study weathering processes in soils along global gradients of environmental change. Detailed study of mineralogy and chemistry (XRD, XRF), surface area, porosity, organic matter, carbon/microbial biomass, moisture content, monitoring of total soil respiration was performed. Ecosystem in responses to land use change the parameters of CZ (CO 2 emission, humidity, biological activity). Land use change result in climate parameter on a local scale (soil climatic gradients) and formed feedback in weathering intensity and basic soil properties-organic matter, acidity, bulk density, WHC, surface properties and porosity, mineralogy and geochemical changes. The decreasing of smectites in the upper parts of the profile and the increasing of illite and vermiculite content was observed. Montmorillonite into vermiculite transformation, which took place only under the forest, which caused the decreasing of pH, soil vermiculite may also derive from muscovite. The intensity of the given process increases as the following: forest soil < grassland < cropland. The given tendency was explained by both the mineral transformations and redistribution of mineral components within the soil profile. The redistribution of chemical elements between the different sub-fractions of silt and clay is in relationship to the land use. As a general trend, we can conclude that clay fractions in a comparison with bulk soil samples are enriched in both OC and N. Mineralogical and chemical changes influenced the surface properties and porosity. The 50-150 years of different land use resulted in these feedbacks with maximum in aboveground zone and soils as main point of surface of a given CZ.

Boletín de la Sociedad Geológica Mexicana

Canadian Journal of Soil Science, 2010

Organo-mineral complexation in soils is strongly controlled by pedogenesis, but the mechanisms controlling it and its interaction with cultivation are not yet well understood. We compared the mineralogy and quality of organic carbon (C) among organo-mineral fractions from two soils with contrasting pedogenic origin. Sequential density fractionation (SDF; using 1.6, 1.8, 2.1, 2.4 and 2.6 g mL-1 sodium polytungstate solutions) followed by thermal analysis was applied to a Chernozem from Ellerslie, Alberta, and a Luvisol from Breton, Alberta, each under native and cultivated land uses. Similar clay mineralogy suggested that pedogenic controls on organic C stabilization were related to long-term vegetation cover. In addition to large differences in total organic C quantities, bulk soil and isolated fractions showed significant differences in organic C quality. Samples under native vegetation revealed greater organo-mineral complexation at Ellerslie compared with Breton, as expressed by ...

Geoderma, 2006

Significant portions of the global soil organic carbon (SOC) pool must reside on sloping terrains where the spatial distribution of SOC reflects the combined effects of geomorphic processes and biological C cycling. Using a newly developed soil C mass balance model that explicitly includes soil production and sediment transport, we investigated the relative roles of sediment production/transport vs. biological C cycling in creating the observed spatial patterns of SOC storage within two grass-covered hillslopes in California. The study sites differed in bedrock geology, climate, and erosion rates. Measurements of SOC, soil texture, plant C inputs, and soil thickness were combined with topographic surveys and published soil erosion and production rates in the analysis. Soil thickness was found to be the key control on SOC storage, and soil thickness is balance between soil production and curvature-dependent erosional losses. Additionally, topographically varying rates of plant C inputs, decomposition rates, and SOC erosional losses or depositional inputs were found to only partially explain the observed SOC storage patterns. We used the measured relationships between SOC storage, soil thickness, and topographic curvature to create SOC storage maps of the two watersheds. At both sites, about 70% of the hillslope SOC is stored in depositional areas that are susceptible to episodic mass wasting. At the drier site, there was a larger SOC storage despite the lower soil C % because the clay-rich bedrock resulted in the development of relatively thick soils for a given slope curvature. We conclude that the geomorphic processes driving soil thickness provide fundamental mechanisms that control the spatial SOC patterns on vegetated hillslopes. D

Ecosystems, 2013

Pedogenic thresholds occur where soil properties change abruptly and/or nonlinearly with a small increment in environmental forcing; soil process domains are the regions between thresholds where soils change much more gradually across a large range of environmental forcing. We evaluated thresholds and domains in basalt-derived soils on two rainfall gradients in Hawaii-one from 260 to 3,540 mm/y precipitation on 150,000-year-old substrate, the other from 600 to 3,760 mm/y on 4,100,000-year-old substrate. We identified thresholds associated with the initiation of biological uplift of nutrients at about 700 mm/y on the younger substrate, the depletion of primary minerals at about 2,100 mm/y on the younger and about 900 mm/y on the older substrate, and the initiation of anoxic conditions and associated Fe mobility at about 2,500 mm/y on the older substrate. These thresholds delineated process domains characterized by pedogenic carbonate accumulation and wind erosion (dry young substrate); by weathering and biological uplift of nutrients (intermediate rainfall young substrate and dry old substrate); by surface Fe enrichment and nutrient depletion (wet young substrate and intermediate rainfall old substrate); and by Fe mobilization and loss (wet old substrate). Soils on the older substrate were more highly weathered, lower in total and available P, and characterized by more crystalline clays than otherwise comparable soils on the younger substrate. Prior to European contact, Hawaiian cultivators developed an intensive rainfed agricultural system in the weathering/biological uplift domain on the younger substrate; we suggest that only this domain could support indigenous agricultural intensification in upland soils.

EURASIAN JOURNAL OF SOIL SCIENCE (EJSS), 2015

Processes of authigenic carbonates formation are component part of terrestrial biogeochemical cycle of carbon, which starts with co-accumulation of oxalic acid and Ca in Ca-oxalates. After plant decay are these biominerals slowly transformed under the influence of microbial processes into authigenic carbonates (calcites), depending on soil condition. The formation of authigenic calcites runs over in soil system where is rather high Ca and Mg concentration, presence of oxalomorphic plants and sufficient oxalotrophic stability of microorganisms. In addition to Caoxalates, Ca and Mg ions necessary for carbonate formation comes also from air (precipitation, dust), mineral weathering, subsurface water flow and decaying organic matter. The distribution pattern of authigenic calcites with depth, the size and shape of individual forms of calcites on loessic soils of SW Slovakia, as it is resulted from micromorphological study indicate that through the historical development of that soils as landscape units, soil water regime has played decisive role at vertical redistribution of forms (size, shape) of authigenic calcites. To this witness the depth of variation of needle calcite zones and horizons of micritic calcites occurrence depending on soil types (leaching). Needle shape calcite zones which approach closest to the soil surface, gradually coalescence to the horizons of micritic calcites with the depth. Micritic calcites are without, or with microsparitic domains. Our study concurrently support the ideas of their inorganic origin depending on evaporitic soil regime. This formations have its own historic dynamics on which depends also the preservation of calcaric nature of soils.

2020

Soil formation is highly associated with topographic position and parent material, both of which play roles in the morphological, mineralogical and weathering processes of soils, particularly on the local level. Landscape topography conducts soil formation through affecting biogeochemical process and regulating soil hydrological process in the surface part of the earth, while parent material has a considerable effect on the types and concentrations of elements found in soil. This study aimed to determine how pedogenic and other factors affect soil classification by identifying the geochemical characteristics of soils classified as vertisols, inceptisols and entisols located on different topographies and possessing different parent material. Following macro-morphological identification of six typical soil pedons, samples were taken from different soil layer and their geochemical, mineralogical and other characteristics were analyzed. These characteristics were also evaluated for possible use in identifying soil maturity stages and periods of late-quaternary soil formation. The pedogenic evolution of soils was also examined using genetic ratios, which combine major oxides and selective dissolution analysis (Fe o-Fe d) values into a single metric. All pedons had Si/Al ratios above 2, indicating arid, sub-arid, sub-humid or high precipitation with cold areas. In addition, Fe d (dithionite extractable iron) values were higher than Fe o (oxalate extractable iron) and lower Fe t (total Fe oxides) values, ranging between 0.007 % and 0.031 %. Therefore, the results clearly showed that local soil geochemical, mineralogical and morphological characteristics in the research area were strongly influenced by topographic conditions and parent material either directly or indirectly.

Soil Science Society of America Journal, 2018

Interactions with pedogenic oxides are a known mechanism of soil organic matter (SOM) protection, but little is known about how the protective power of pedogenic oxides varies with soil depth in highly weathered tropical soils. To address this issue, we followed the decomposition of a double-labeled plant litter (13 C/ 15 N) in microcosm experiments using samples collected at four depths (0-10, 10-20, 20-40, and 60-100 cm) from six Brazilian Oxisols. These soils were selected to include a range of taxonomic subtypes, spanning wide variations in mineralogy and texture. After a 12-mo incubation, we quantified the proportion of isotopically-labeled SOM (13 C/ 15 N) within the mineral fraction <53 µm (i.e., clay+silt). We found that litter-C retention increased with depth, while the opposite occurred for litter-N. Correlations between isotopically-labeled SOM and short-range order (SRO) Al-/Fe-(hydr)oxides were insignificant in topsoil (0-10 cm), but increased with depth, reaching peak significance in the 20-to 40-cm interval (r = 0.64 and 0.58, for litter-C and-N, respectively). A similar trend was observed for crystalline Al-/Fe-(hydr)oxides, which were more strongly correlated with the retention of 13 C than 15 N. We posit that in subsoil, both SRO and crystalline Al-/Fe-(hydr)oxides are more readily involved in the neoformation of mineral-organic associations. Overall, litter-C is less efficiently transferred into the clay+silt fraction of C-rich topsoil relative to C-depleted subsoil horizons, which may represent a significant C sink for Oxisols.