Soil Mineral Weathering Research Articles

Long-term temporal response of Eastern Canadian lakes chemistry along a large spatial gradient of atmospheric sulfate deposition.

A major consequence of the Industrial Revolution was the acidification of continental water bodies by sulfates (SO42-) and nitrates deposited over long-range distance from atmospheric emissions. Regulation policies were implemented in the 1980s leading to the general decrease of SO42- concentrations in freshwaters and progressive recovery from acidification, a complex process that is still ongoing. The surface water SO42- decrease has been linked to declining calcium (Ca2+) and increasing dissolved organic carbon (DOC) concentration. Here, up to 40 years (1983-2023) of chemical data in 46 lakes of Eastern Canada are analyzed for long-term trends and spatial patterns along a large gradient of SO42- deposition, including the relation with catchment geomorphology. The average lake SO42- concentration decreased along the distance from sulfur dioxide sources. SO42- concentration decreased significantly in every lake and faster close to the emission sources. In 70% of the lakes, the SO42- decline drove concurrent but slower Ca2+ and magnesium declines, leading to an overall increase in the Ca2+/SO42- ratio, in pH and in alkalinity for 72% of the lakes. The Ca2+ concentration is now below the crucial threshold for large zooplankton species in most lakes. Increasing trends in lake sodium concentration suggest an intensification of mineral weathering in catchment soils, potentially linked to rising temperatures, which could be involved in the observed recovery. DOC increased in 67% of lakes which drove a concurrent increase in aluminum in some lakes. The numerous environmental changes in progress across temperate and boreal lakes will deeply modify the structure and functioning of these systems, especially in the context of climatic changes.

Weathering of Buried Standard Pieces of Serpentine under Varied Soil Treatments and Relevant Analysis of Microbial Community Structure

Carbon sink processes related to the weathering of silicate minerals are often accompanied by physical, chemical, and biological effects. In particular, plant-microbe synergistic effects are important for soil mineral weathering, but relevant correlation analyses and quantitative studies remain sparse. In this research, a standard serpentine test specimens (STSs) with specific specifications were used to study serpentine weathering under different environmental conditions (abiotic or biotic) and correlated it with the microbial community structure under the growth of Setaria viridis. The results showed that the environment with growing S. viridis had the strongest weathering capacity for STSs, which was 35 times higher than that of the abiotic environment group, and a significant increase in soil inorganic and organic carbon contents compared with the abiotic environment and the environment without plant growth. The bacteria with strong weathering ability were enriched in the soil of around STSs, such as Pseudomonas spp. and Sphingomonas spp. In addition, the fungal community of Ascomycetes is also heavily enriched, accelerating STSs weathering. The addition of bacterial agent (Bacillus subtilis) further promoted the STSs weathering under the growth conditions of S. viridis. The soil surrounding the buried STSs was also enriched with heavy metal tolerant Massilia spp. and disease suppressing Lysobacter spp., while the abundance of fungi functionally associated with pathotypes was reduced, thereby benefiting plant growth. This study provides basic information for the serpentine bio-weathering coupled with carbon sequestration by using plant-microbe synergistic effects.

Spodosol development and soil organic carbon distribution along a lithosequence in perhumid coastal temperate rainforest

AbstractA dense concentration of old‐growth forest and a wet, cold climate promote mineral weathering and leaching in coastal temperate rainforest soils. Our objective was to assess soil development and soil organic carbon (SOC) distribution across 18 soil profiles in remote, upland terrain of southeast Alaska where pedon data are sparse. We made soil morphological observations, collected samples, and completed laboratory analyses to measure SOC content, pH, and particle size distribution. The survey of upland backslope soils included north‐ and south‐facing hillslopes derived from three lithologies (slate, metavolcanic, and phyllite). The soils across all sites were very gravelly (51.8 ± 20.4% coarse fragments), acidic (mineral soil pH 4.85 ± 0.45), and moderately deep (96.56 ± 37.80 cm); thin, broken E horizons were underlain by thick, carbon‐rich spodic horizons. Soil development was relatively consistent as demonstrated by the Profile Development Index with values from 15 to 26 and Podzolization Index values spanning 8 to 14. A mean pedon SOC stock of 198.02 ± 81.42 Mg C ha−1 (n = 18) was calculated using data collected for all upland organic and mineral soils from our work. The accumulation of SOC was similar among soils formed from contrasting lithologies with averages of 182 ± 15.70 Mg C ha−1 for slate, 188 ± 53.80 Mg C ha−1 for metavolcanic, and 218 ± 124 Mg C ha−1 for phyllite. Our work contributes to soil morphological observations, laboratory data, and SOC stock estimates required to better constrain and model pedogenic processes and SOC stock in remote forests where data sets are limited.

Climate forcing controls on carbon terrestrial fluxes during shale weathering

Climate influences near-surface biogeochemical processes and thereby determines the partitioning of carbon dioxide (CO2) in shale, and yet the controls on carbon (C) weathering fluxes remain poorly constrained. Using a dataset that characterizes biogeochemical responses to climate forcing in shale regolith, we implement a numerical model that describes the effects of water infiltration events, gas exchange, and temperature fluctuations on soil respiration and mineral weathering at a seasonal timescale. Our modeling approach allows us to quantitatively disentangle the controls of transient climate forcing and biogeochemical mechanisms on C partitioning. We find that ~3% of soil CO2 (1.02 mol C/m2/y) is exported to the subsurface during large infiltration events. Here, net atmospheric CO2 drawdown primarily occurs during spring snowmelt, governs the aqueous C exports (61%), and exceeds the CO2 flux generated by pyrite and petrogenic organic matter oxidation (~0.2 mol C/m2/y). We show that shale CO2 consumption results from the temporal coupling between soil microbial respiration and carbonate weathering. This coupling is driven by the impacts of hydrologic fluctuations on fresh organic matter availability and CO2 transport to the weathering front. Diffusion-limited transport of gases under transient hydrological conditions exerts an important control on CO2(g) egress patterns and thus must be considered when inferring soil CO2 drawdown from the gas phase composition. Our findings emphasize the importance of seasonal climate forcing in shaping the net contribution of shale weathering to terrestrial C fluxes and suggest that warmer conditions could reduce the potential for shale weathering to act as a CO2 sink.

Impact of earthworms on soil Si availability and wheat Si concentration in low- and high-Si soils

Silicon (Si) is a beneficial element known to increase growth and the stress resistance of plants, including resistance against drought. However, as with many other elements, only a small fraction of Si in soils is available for plant uptake. Plant-available Si originates either from the weathering of soil minerals or from the dissolution of phytoliths in plant litter. It is known that soil fauna plays a role in both processes that contribute to the availability of Si in the soil. However, very little is known about the interactions between the weathering of soil minerals and the dissolution of Si by earthworms from phytoliths and subsequent Si uptake by plants. In greenhouse pot experiments, this study investigated the effect of an epigeic earthworm species (Dendrobaena veneta) on Si availability and uptake by wheat (Triticum aestivum) grown in soils with high or low Si availability. In addition, Si-rich plant litter (wheat straw) was added to the topsoil in some treatments. The addition of plant litter significantly increased the available Si in the soil. Plant litter addition was positively correlated with the Si concentration in wheat in low-Si soil, but not in high-Si soil. Earthworms increased Si availability in soil and casts of the low-Si soil and partly of the high-Si soil, but not Si uptake by wheat. These results suggest that earthworms play an important role in regulating the Si status of soils and may influence Si uptake by plants, especially in soils with initially low Si content and when earthworm population densities are high.

Development of a lateral topographic weathering gradient in temperate forested podzols

Mineral weathering is an important soil-forming process driven by the interplay of water, organisms, solution chemistry, and mineralogy. The influence of hillslope-scale patterns of water flux on mineral weathering in soils is still not well understood, particularly in humid postglacial soils, which commonly harbor abundant weatherable primary minerals. Previous work in these settings showed the importance of lateral hydrologic patterns to hillslope-scale pedogenesis. In this study, we hypothesized that there is a corresponding relationship between hydrologically driven pedogenesis and chemical weathering in podzols in the White Mountains of New Hampshire, USA. We tested this hypothesis by quantifying the depletion of plagioclase in the fine fraction (≤2 mm) of closely spaced, similar-age podzols along a gradient in topography and depth to bedrock that controls lateral water flow. Along this gradient, laterally developed podzols formed through frequent, episodic flushing by upslope groundwater, and vertically developed podzols formed through characteristic vertical infiltration. We estimated the depletion of plagioclase-bound elements within the upper mineral horizons of podzols using mass transfer coefficients (τ) and quantified plagioclase losses directly through electron microscopy and microprobe analysis. Elemental depletion was significantly more pronounced in the upslope lateral eluvial (E horizon-dominant) podzols relative to lateral illuvial (B horizon-dominant) and vertical (containing both E and B horizons) podzols downslope, with median Na losses of ∼74 %, ∼56 %, and ∼40 %, respectively. When comparing genetic E horizons, Na and Al were significantly more depleted in laterally developed podzols relative to vertically developed podzols. Microprobe analysis revealed that ∼74 % of the plagioclase was weathered from the mineral pool of lateral eluvial podzols, compared to ∼39 % and ∼23 % for lateral illuvial podzols and vertically developed podzols, respectively. Despite this intense weathering, plagioclase remains the second most abundant mineral in soil thin sections. These findings confirm that the concept of soil development as occurring vertically does not accurately characterize soils in topographically complex regions. Our work improves the current understanding of pedogenesis by identifying distinct, short-scale gradients in mineral weathering shaped by local patterns of hydrology and topography.

Normative Mineralogy of 1170 Soil Profiles across Canada

Weathering of soil minerals provides base cations that buffer against acidity, and nutrients that support plant growth. In general, direct observations of soil minerals are rare; however, their abundance can be determined indirectly through soil geochemistry using normative-calculation procedures. This study compiled a data set of major oxide content from published and archived soil geochemical observations for 1170 sites across Canada (averaged over the soil profile [A, B, and C horizons], weighted by depth and bulk density to a maximum depth of 50 cm). Quantitative soil mineralogy (wt%) was systematically determined at each site using the normative method, ‘Analysis to Mineralogy’ (A2M); the efficacy of the approach was evaluated by comparison to X-ray Diffraction (XRD) mineralogy available for a subset of the study sites. At these sites, predicted A2M mineralogy was significantly related to estimated XRD, showing a strong linear relationship for plagioclase, quartz, and K-feldspar, and a moderate linear relationship for chlorite and muscovite. Further, the predicted A2M plagioclase content was almost identical to the estimated XRD soil mineralogy, showing no statistical difference. The Canada-wide predicted quantitative soil mineralogy was consistent with the underlying bedrock geology, such as in north-western Saskatchewan and north-eastern Alberta, which had high amounts of quartz due to the Western Canadian Sedimentary Basin. Other soil minerals (plagioclase, potassium feldspar, chlorite, and muscovite) varied greatly in response to changing bedrock geology across Canada. Normative approaches, such as A2M, provide a reliable approach for national-scale determination of quantitative soil mineralogy, which is essential for the assessment of soil weathering rates.

Recent progress in understanding the ecology and molecular genetics of soil mineral weathering bacteria.

Mineral weathering bacteria play essential roles in nutrient cycling and plant nutrition. However, we are far from having a comprehensive view of the factors regulating their distribution and the molecular mechanisms involved. In this review, we highlight the extrinsic factors (i.e., nutrient availability, carbon source) and the intrinsic properties of minerals explaining the distribution and functioning of these functional communities. We also present and discuss the progress made in understanding the molecular mechanisms and genes that are used by bacteria during the mineral weathering process, or regulated during their interaction with minerals, that have been recently unraveled by omics approaches.

Genesis and soil environmental implications of intact in-situ rhizoliths in dunes of the Badain Jaran Desert, northwestern China

Desert rhizoliths are generally found as weathered, broken and scattered samples on dune field surface, but rarely in-situ in their initial states buried under the soil of desert in the Badain Jaran Desert, northwest China. This study offers an assessment of the morphological, mineralogical, and chemical properties of intact and in-situ rhizoliths found in soils of swales and depressions among dune chains. The characteristics of these rare and precious objects were assessed using optical polarizing microscopy, cathodoluminescence, scanning electronic microscopy, radiocarbon dating, and stable isotopic analyses, providing the opportunity for discussion of the rhizolith formation mechanisms and associated environmental conditions. Field and laboratory investigations showed that the in-situ intact rhizoliths were formed only in the places where Artemisia shrubs are living, and the remaining root relicts within rhizoliths belong to this species. The spatial distribution of rhizoliths also suggested that low topographic positions on a landscape provided soil moisture, and redox environments favored rhizolith formation. A semi-closed redox environment in the subsoil at swales and depressions, where water is always present, along with the sandy soil texture, facilitated fast water percolation to deeper depths and condensation. Such a soil environment not only provides water for Artemisia growth, but also for the weathering of minerals such as felspars and calcite from primary carbonates, and for the decomposition of root relicts. Furthermore, harsh climatic conditions, such as strong winds and solar radiation, led to water evaporation through dead root channels and triggered the calcification along the root relicts. The entrapped lithogenic carbonates and to a lesser extent the decomposition of Artemisia roots provided the carbon sources for the rhizoliths formation, while the weathering of soil minerals, particularly feldspars and carbonates, was the main source of Ca. Rhizoliths in the Badain Jaran desert formed relatively quickly, probably over a few soil drying episodes. This led to the entrapment of a large quantity of lithogenic carbonates (more than 90% of carbon) within rhizolith cement. The re-dissolution of the entrapped lithogenic carbonates in rhizolith tubes should be taken into account in the paleoenvironmental interpretation of 14C ages, the latter suggesting that rhizoliths formed during the Holocene (~ 2053 years cal BP, based on root organic relicts).

Water balance affects foliar and soil nutrients differently.

Water balance influences soil development, and consequently plant communities, by driving weathering of soil minerals and leaching of plant nutrients from the soil. Along gradients in water balance, soils exhibit process domains where chemical properties are relatively stable punctuated by pedogenic thresholds where soil chemical properties change rapidly with little additional change in water balance. We ask if plant macronutrient concentrations in leaves also exhibit non-linear trends along water balance gradients, and if so, how these non-linearities relate to those in soils. We analyze foliar nutrient concentrations and foliar N:P ratios from eight species that span a range of growth forms along three water balance gradients (three of the species are found on multiple gradients). The gradients are located on basaltic substrate of different ages and have previously been characterized by studies on soil development. We find that maximum concentrations of foliar macronutrients occur at an intermediate water balance. As with soil nutrients, time mediates the effect of water balance on foliar nutrients, such that plants on older soils attain maximum nutrient concentrations at a lower water balance. On both a young, 20 ky and an old, 4100 ky water balance gradient, foliar nutrients reach peak concentrations at a water balance greater than the threshold for depletion of rock-derived nutrients in surface soils. Our findings suggest that plant acquisition of essential nutrients is imperfectly predicted by overall soil nutrient availability because the regulation of internal nutrient pools by plants makes nutrient pools within leaves partially independent of soil nutrient availability.

Stoichiometry of base cations and silicon during weathering of a deep soil profile derived from granite

Evaluation of the stoichiometry of base cations (BCs, including K+, Na+, Ca2+, and Mg2+) and silicon (Si) (BCs:Si) during soil mineral weathering is essential to accurately quantify soil acidification rates. The aim of this study was to explore the differences and influencing factors of BCs:Si values of different soil genetic horizons in a deep soil profile derived from granite with different extents of mineral weathering. Soil type was typic acidi-udic Argosol. Soil samples were collected from Guangzhou, China, which is located in a subtropical region. To ensure that the BCs and Si originated from the mineral weathering process, soil exchangeable BCs were washed with an elution treatment. The BCs:Si values during weathering were obtained through a simulated acid rain leaching experiment using the batch method. Results showed that soil physical, chemical, and mineralogical properties varied from the surface horizon to saprolite in the soil profile. The BCs:Si values of soil genetic horizons during weathering were 0.3–3.7. The BCs:Si value was 1.7 in the surface horizon (A), 1.1–3.7 in the argillic horizon (Bt), and 0.3–0.4 in the cambic (Bw) and transition (BC) horizons, as well as in horizon C (saprolite). The general pattern of BCs:Si values in the different horizons was as follows: Bt > A > Bw, BC, and C. Although BCs:Si values were influenced by weathering intensity, they did not correlate with the chemical index of alteration (CIA). The release amounts of Si and BCs are the joined impact of soil mineral composition and physical and chemical properties. A comprehensive analysis showed that the BCs:Si values of the soil derived from granite in this study were a combined result of the following factors: soil clay, feldspar, kaolinite, organic matter, pH, and CIA. The main controlling factors of BCs:Si in soils of different parent material types require extensive research. The wide variance of BCs:Si values in the deep soil profile indicated that H+ consumed by soil mineral weathering was very dissimilar in the soils with different weathering intensities derived from the same parent material. Therefore, the estimation of the soil acidification rate based on H+ biogeochemistry should consider the specific BCs:Si value.

Effects of Microbial-Mineral Interactions on Organic Carbon Stabilization in a Ponderosa Pine Root Zone: A Micro-Scale Approach

Soil microbial communities affect the formation of micro-scale mineral-associated organic matter (MAOM) where complex processes, including adhesion, aggregate formation, microbial mineral weathering and soil organic matter stabilization occur in a narrow zone of large biogeochemical gradients. Here we designed a field study to examine carbon stabilization mechanisms by using in-growth mesh bags containing biotite that were placed in a ponderosa pine root zone for 6 months and compared to the surrounding bulk soil. We sought to determine the composition of the microbial community in the mesh bags compared to the surrounding soils, analyze the direct interactions between microbes and biotite, and finally identify the nature of the newly formed MAOM within the mesh-bags. Our results revealed that minerals in the mesh bags were colonized by a microbial community that produced organic matter in situ. The 16S rRNA gene sequencing and ITS2 region characterization showed phylogenetic similarity between the mesh bag and bulk soil archaea/bacteria and fungi microbiomes, with significant differences in alpha- and beta-diversity and species abundances. Organic matter pools in the mesh bags, analyzed by Fourier transform ion cyclotron resonance mass spectrometry, contained protein- (peptides) and lipid-like compounds while the bulk soil OM was comprised of lignin-like and carboxyl-rich alicyclic molecules. These results support that the newly formed biotite associated organic compounds have a microbial signature in the mesh bags. High-resolution electron microscopy documented strongly adhered organic compounds to biotite surfaces, formation of microaggregates, elemental uptake at the microbe (organic matter)-mineral interface, and distortion of biotite layers. Overall, this study shows the direct and indirect involvement of soil microbial communities from the root zone of ponderosa pine in the formation of MAOM, soil organic carbon stabilization, microaggregation, and mineral weathering at micro- and nano-scales.

Recent weathering promotes C storage inside large phyllosilicate particles in forest soil

Mineral weathering in soils is expected to promote chemical and physical interactions between soil organic matter and mineral phases, which are known to enhance the protection of organic matter from decomposition. The investigation of mineral-organic associations (MOAs) formation during weathering is therefore crucial to understanding carbon storage processes in soils. Until now studies have been mainly conducted by building inferences from soil characteristics, through short-term laboratory experiments in simplified conditions, or over very long-term time scales using soil chronosequences. Weathering can significantly alter the mineral matrix at the annual timescale, but knowledge regarding MOA formation processes occurring in situ, over short time scales and during the first stage of mineral weathering is lacking.To fill this gap, we performed a mesh bag incubation containing large Na-saturated and organic carbon-free vermiculite particles (200–400 µm in size) in acidic soil of a Douglas-fir forest, in the Beaujolais area (France). The vermiculite bags were deposited at the interface between the forest floor and the mineral soil, where intense weathering occurs. After 20 years of soil incubation, the weathered vermiculite particles were collected and characterized at the macroscale (X ray diffraction and physicochemical analyses), at the microscale (scanning electron microscopy-SEM imaging and element mapping) and at the nanoscale (transmission electron microscopy-TEM imaging, element mapping and speciation by electron energy loss spectroscopy-EELS) on a focus ion beam (FIB) section exposing the inside section of vermiculite particles.Cation exchange capacity, exchangeable cations and elemental analysis of the vermiculite particles showed important changes after 20 years of incubation. The initial exchangeable Na pool was completely depleted. The cation exchange capacity strongly decreased from 178.1 cmolc kg−1 to 49.2 cmolc kg−1 due to interlayer hydroxylation of the weathered vermiculite. The weathering budget indicated a 10% vermiculite dissolution and an organic carbon (C) enrichment of 5 mg g−1.Microscope images and elemental mapping of control vermiculite particles (nonincubated) showed a flat, smooth surface morphology with no detected C. In contrast, 20-year weathered vermiculite particles showed irregular outer- and inner-surfaces marked by multiple cracks from chemical dissolution. Some nano- and microscale exfoliation spaces filled with C were observed inside the weathered particles. C in association with Ca occurred in nanoscale exfoliation spaces. C also occurred entrapped in nanocrystalline Mn oxides (hausmannite) or K-rich aluminosilicates, which precipitated in micro-sized exfoliation spaces. These observations indicated that C storage inside the altered vermiculite particles was both mediated by chemical binding and physical entrapment. The functional groups of the organic matter revealed by EELS spectroscopy strongly differed between nano- and microscale exfoliation spaces.This study using the mineral bag incubation method provides evidence of new processes driving C storage inside large phyllosilicate particles during their initial and recent weathering, which could contribute to long-term C stabilization.

Cryosols from Tundra and Taiga Zones of Yakutia: Properties, Clay Mineralogy, and Problems of Classification

—Data on major properties and clay mineralogy in the profiles of slightly differentiated Cryosols forming in cold ultracontinental climate of Yakutia are discussed. The particular objects are represented by the cryozems of tundra, forest-tundra, and northern taiga of the Anabar and Alazeya plateaus and by the palevaya (pale) soil of middle taiga in Central Yakutia. The differentiation of clay minerals in the vertical soil profiles is poorly pronounced because of the strong homogenizing impact of cryoturbation processes. The profile of pale soil displays minor differences in clay mineralogy despite the strong difference in acid–base conditions of the upper and lower horizons. However, the obtained data suggest that mineral weathering in pale soils of Central Yakutia is more advanced than it was concluded in the 1970s on the basis of data on the absence of pronounced trends in the vertical distribution of clay minerals in their profiles. This is in good agreement with the presence of a sufficiently thick upper humus horizon in these soils, which is typical of the soils of more humid regions. It is suggested that pale soils of Central Yakutia should be classified as soddy pale soils.

Monitoring Pedogenic Inorganic Carbon Accumulation Due to Weathering of Amended Silicate Minerals in Agricultural Soils.

The present study aims to demonstrate a systematic procedure for monitoring inorganic carbon induced by enhanced weathering of comminuted rocks in agricultural soils. To this end, the core soil samples taken at different depth (including 0-15 cm, 15-30 cm, and 30-60 cm profiles) are collected from an agriculture field, the topsoil of which has already been enriched with an alkaline earth metal silicate containing mineral (such as wollastonite). After transporting to the laboratory, the soil samples are air-dried and sieved. Then, the inorganic carbon content of the samples is determined by a volumetric method called calcimetry. The representative results presented herein showed five folded increments of inorganic carbon content in the soils amended with the Ca-silicate compared to control soils. This compositional change was accompanied by more than 1 unit of pH increase in the amended soils, implying high dissolution of the silicate. Mineralogical and morphological analyses, as well as elemental composition, further corroborate the increase in the inorganic carbon content of silicate-amended soils. The sampling and analysis methods presented in this study can be adopted by researchers and professionals looking to trace pedogenic inorganic carbon changes in soils and subsoils, including those amended with other suitable silicate rocks such as basalt and olivine. These methods can also be exploited as tools for verifying soil inorganic carbon sequestration by private and governmental entities to certify and award carbon credits.

Monitoring Pedogenic Inorganic Carbon Accumulation Due to Weathering of Amended Silicate Minerals in Agricultural Soils.

The verification method described here is adaptable for monitoring pedogenic inorganic carbon sequestration in various agricultural soils amended with alkaline earth metal silicate-containing rocks, such as wollastonite, basalt, and olivine. This type of validation is essential for carbon credit programs, which can benefit farmers that sequester carbon in their fields.

Micromorphological Characteristic of Different-Aged Cryosols from the East Part of Lena River Delta, Siberia, Russia

Micromorphological investigation of soils is a powerful tool for studying the transformation of soils under the influence of various weathering mechanisms. In the Arctic region, under the influence of seasonal freezing/thawing processes, cryohydration is the leading type of weathering. Soils of different-aged islands of the Lena River Delta were investigated. Thin sections of soils were analyzed using a polarizing microscope Leica DM750P (Leica Camera AG, Wetzlar, Germany). X-ray fluorescence analysis was used to determine the chemical composition of the soils. As a result of the work, the rate of weathering of soil minerals was estimated, soil fabric was considered, as well as the chemical composition of the soil. The accumulation of poorly sorted circular striated sand due to active influence of the Lena River was noted on young soil from Samoylov isl. The formation of biogenic sand-silt crumb aggregates was noted at more ancient sites. Physical weathering of soil minerals under the influence of cryogenic processes has been noted.

Is the past history of acidic deposition in eastern Canada reflected in sugar maple's tree rings 87Sr/86Sr, Sr and Ca concentrations?

How calcium (Ca) uptake by trees in eastern Canadian forests has responded to decades of atmospheric acid deposition and its sharp decrease that started three decades ago is still largely unknown. Here, we tested a novel approach based on the measurements of Ca and strontium (Sr) concentrations and Sr isotope signature (87Sr/86Sr ratio) in sequential extracts of sugar maple tree rings and soils to assess changes in Ca availability and sources through time. The study was conducted at three sites showing a gradient of one order of magnitude in soil mineral weathering fluxes and exchangeable pools of Ca. We found that wood Ca and Sr concentrations increased with Ca and Sr concentrations in the exchangeable fraction (NH4Cl extracts) of the top mineral soil across sites. In addition, wood 87Sr/86Sr ratio was strongly correlated with 87Sr/86Sr ratio of this soil fraction. Both Ca and Sr concentrations in the exchangeable fraction of the wood decreased from pith to bark at all sites, whereas no trend was observed for the wood residual fraction. This was interpreted as a result of radial mobility of Ca in sapwood rather than a decline in the uptake of Ca and Sr by tree roots over time. The 87Sr/86Sr ratio of tree rings slightly increased over time only at the site with the higher soil exchangeable Ca pool, suggesting an increase in the contribution of soil mineral weathering relative to atmospheric deposition. In contrast with our hypothesis, our results show i) no evidence of pronounced changes in the relative contribution of the atmospheric vs. soil mineral weathering Ca components over time at the site with the smallest soil exchangeable Ca pools; and ii) the difficulty of assessing the temporal changes in the availability and the sources of Ca from sequential extractions of the wood due to a dynamic exchange process of Sr (and therefore Ca) between the exchangeable and residual fractions of the wood.

Impact of Climate Change on Soil Hydro-Climatic Conditions and Base Cations Weathering Rates in Forested Watersheds in Eastern Canada

Increases in mean annual air temperature (MAAT) and mean annual precipitation (MAP) are projected for north eastern North America, which will alter soil hydro-climatic conditions and hence the rate of many soil processes. Among them, chemical weathering of soil minerals is an essential source of base cations (BC) which control the acid-base status of surface waters and are crucial for forest nutrition. In this modeling study, MAAT and MAP projections from a regional and a global climate models were first used to project changes in soil temperature (MAST) and soil water content (SWC) with the ForStem and ForHym models for 21 eastern Canadian forested catchments. The models predicted an increase in MAST by 2.03-2.05°C and 2.87-3.42°C for the 2041-2070 and 2071-2100 periods, respectively, and small decreases (<5%) in SWC. In a second step, these projected changes in MAST and SWC were used to estimate changes in BC weathering rates (WR) and soil pH with the geochemical model PROFILE. The simulations indicated that BC WR would increase by 13-15% and 20-22% for the 2041-2070 and 2071-2100 periods, respectively. The increase in BC WR was accompanied by an increase not only in base cation concentrations, but also in soil pH at most sites, suggesting that future temperature increase has the potential to ameliorate the acid-base status and the fertility of soils in eastern Canada through its impact on WR.

Effect of common bean (Phaseolus vulgaris) on apatite weathering under elevated CO2

Plants accelerate chemical weathering of minerals through the production of carbonic acid during root respiration, root exudation, and uptake of ions. These plant processes are increased by elevated concentrations of atmospheric CO2 and may in turn affect mineral weathering. We seek to understand the effect of predicted atmospheric CO2 concentrations on plant-mediated soil mineral weathering. Phaseolus vulgaris (common bean) was grown in flow-through microcosms consisting of a mixture of 85% quartz and 15% apatite sands (by weight). Nutrient release from apatite was measured using plants grown under two atmospheric conditions: ambient CO2 (~400 ppm) and elevated CO2 (~1000 ppm). To sustain plant growth, a nutrient solution without calcium (Ca) or phosphorous (P) was supplied to the plants using peristaltic pumps. Unplanted microcosms receiving the same nutrient solution served as abiotic controls in both CO2 treatments. Using atomic absorption spectroscopy and colorimetry, Ca and P concentrations of the leachate and plant tissue were measured as proxies for apatite dissolution. Plants were harvested every 2 weeks during the 8-week experiment to understand how Ca and P release in the two CO2 treatments changed over time. After 8 weeks, P. vulgaris grown in elevated CO2 had a greater root to shoot ratio than plants grown in ambient CO2. Plants grown in elevated CO2 released more P than plants grown in ambient conditions, possibly due to greater demands for mineral nutrients. P was preferentially released by the plants and there were no significant differences in Ca released by plants. Both elevated and ambient planted microcosms had a lower pH than abiotic controls, likely due to root respiration, nutrient uptake and exudation of organic acids. Organic acids were not identified in the leachate likely due to their low concentrations and rapid breakdown. Plants released as much as 7 times more Ca than abiotic controls, regardless of CO2 concentrations. Biotic experiments released over 200 times more P than abiotic experiments. Our results show increased atmospheric CO2 can determine rhizosphere processes, which in turn affect weathering products. Thus, mineral nutrient fluxes and C sequestration in inorganic pools are likely to increase as CO2 concentrations rise.