Secondary Soil Minerals Research Articles

Mechanisms controlling the dissolved load, chemical weathering and CO2 consumption rates of Cauvery River, South India: role of secondary soil minerals

Hydrochemical assessment of the Cauvery River Basin (CRB), an east flowing Western Ghats (WG) river, is carried out to understand the dissolved load sources and controlling mechanisms with quantification of source-wise input to the dissolved load. Silicate weathering rates (SWR) and associated CO2 consumption rates (CCR) are evaluated on account of silicate basement of CRB comprising of granulites and supracrustal rocks. The source-wise solute load contributions estimated using the chemical mass balance model signify that 68% of total load is from chemical weathering followed by anthropogenic (18.5%) and atmospheric (13.5%) inputs respectively, indicating that chemical weathering is the major solute load controlling mechanism for CRB. The intensity of silicate chemical weathering occurring in the CRB is measured by degree of weathering index (Re). It is found to be higher (> 3), suggesting an incomplete weathering of drainage rocks (primary minerals) resulting in formation of soils comprising of secondary minerals including oxides, alumino-silicates and clay minerals (kaolinite, montmorillonite and smectite). Detailed understanding of the mechanism of chemical weathering is carried out using Ca/Na and Mg/Na elemental ratios of different end-members including primary minerals from rocks and secondary minerals from soils. The Na-normalized mixing diagram reveals that chemical weathering of secondary minerals is dominating and the solute load contribution to the total dissolved load is significantly higher (35.5%) from secondary minerals than primary minerals (23.5%). The SWR and associated CCR are estimated to be 13 t km−2 year−1 and 3.3 × 105 mol km−2 year−1, respectively, at outlet (Musiri) of the CRB. Results additionally signify that SWR of the east flowing WG river, Cauvery, are several times (~ 4) lower than the average SWR of west flowing WG rivers even though the associated CCR are comparable for both river systems.

Impact of abiotic and biogeochemical processes on halogen concentrations (Cl, Br, F, I) in mineral soil along a climatic gradient.

In contrast to earlier ideas that halogens behave inertly in soil, extensive biogeochemical cycling of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) has been shown for temperate forests. To further advance our understanding of halogen behaviour in soil beyond humid temperate forests, we sampled soil profiles in protected areas along the Chilean Coastal Cordillera, representing a pronounced climatic gradient spanning from arid to humid. Halogen concentrations in soil were analysed by combustion ion chromatography. Highest average total halogen concentrations occurred at the arid site (Cl, F: 4270 and 897 mg kg-1) as well as the humid end of the climatic gradient (Br, I: 42.6 and 9.8 mg kg-1). Vertical distribution patterns of halogens were most pronounced at the humid end of the gradient and became less distinct under drier climate. The climatic gradient demonstrates the important role of biotic processes (e.g. the halogenation of organic matter) on the retention of halogens in the soil. However, this climate-specific role may be overridden by mainly abiotic processes within a given climate zone (e.g. weathering, leaching, sorption to secondary soil minerals, evaporative enrichment), resulting in vertical relocation of halogens in the soil. Since some of these processes oppose each other, complex interactions and depth distributions of F, Cl, Br and I occur in the soil. In summary, our findings provide new insights into the fate of halogens in mineral soil of different climatic zones, which is important, for example, when radiohalogens are deposited on a large scale after nuclear accidents.

Earthworm mucus contributes to the formation of organo-mineral associations in soil

Earthworms are considered as “ecosystem engineers” impacting soil properties as well as nutrient and element cycles. As they move through soil, earthworms secrete cutaneous mucus which is metabolized by soil microorganisms and a source of plant-available nutrients. Earthworm-processed soil contains carbon enriched, earthworm-specific soil aggregates (e.g. casts and middens) in comparison to earthworm unaffected soil. The reason could be that organic polymeric substances in earthworm mucus bind to soil minerals. The objective of this study was to investigate the small-scale interactions between earthworm mucus and secondary soil minerals, e.g. goethite and illite, leading to the formation of organo-mineral associations. We characterized the chemical composition of earthworm mucus by FTIR and 13C-NMR spectroscopy and compared spectra of mucus to microbial extracellular polymeric substances (EPS), an abundant and well-known type of organic matter that binds with soil minerals. Mucus from anecic (Lumbricus terrestris L.) and endogeic (Aporrectodea caliginosa Sav.) earthworm species was dominated by proteins and carbohydrates. Between 21 and 36% of the total organic carbon in the mucus containing treatments adsorbed to illite and goethite, and most of the binding with goethite was associated with phosphorus containing mucus compounds. The surface charge of newly-formed organo-mineral associations was determined by measuring the isoelectric point (IEP). The IEP of mucus-goethite associations was 6.8, which was lower than the bare goethite IEP of 8.4. The zeta potential of mucus-illite associations was greater than bare illite. We conclude that the specific adsorption of earthworm mucus constituents to soil minerals leads to the formation of mucus-mineral associations. These associations contribute to retention of organic substances from earthworm mucus in soil (micro-)aggregates and explain the altered physicochemical properties of earthworm-formed aggregates in comparison to the earthworm unaffected “bulk” soil material.

Germanium in the soil-plant system-a review.

Germanium (Ge) is widespread in the Earth's crust. As a cognate element to silicon (Si), Ge shows very similar chemical characteristics. Recent use of Ge/Si to trace Si cycles and changes in weathering over time, growing demand for Ge as raw material, and consequently an increasing interest in Ge phytomining have contributed to a growing interest in this previously rather scarcely considered element in geochemical studies. This review deals with the distribution of Ge in primary minerals and surface soils as well as the factors influencing the mobility of Ge in soils including the sequestration of Ge in secondary mineral phases and soil organic matter. Furthermore, the uptake and accumulation of Ge in plants and effects of plant-soil relationships on the availability of Ge in soils and the biogeochemical cycling of Ge are discussed. The formation of secondary soil minerals and soil organic matter are of particular importance for the concentration of Ge in plant-available forms. The transfer from soil to plant is usually low and shows clear differences between species belonging to the functional groups of grasses and forbs. Possible uptake mechanisms in the rhizosphere are discussed. However, the processes that are involved in the formation of plant-available Ge pools in soils and consequently its biogeochemical cycling are not yet well understood. There is, therefore, a need for future studies on the uptake mechanisms and stoichiometry of Ge uptake under field conditions and plant-soil-microbe interactions in the rhizosphere as well as the chemical speciation in different plant parts.

Origin of silica in rice plants and contribution of diatom Earth fertilization: insights from isotopic Si mass balance in a paddy field

Background and aims: The benefits of Si for crops is well evidenced but the biogeochemical cycle of Si in agriculture remains poorly documented. This study aims at identifying and quantifying the Si sources (primary and secondary soil minerals, amorphous silica, irrigation, Si-fertilizer) to rice plants. Method: Field experiments were carried out with and without application of diatomaceous earth (DE) under rice and bare conditions to determine the water and dissolved mass balance in paddy fields (Karnataka, Southern India). The fate of the Si brought by irrigation (DSi) (uptake by rice, uptake by diatoms, adsorption) was assessed through a solute mass balance combined with silicon isotopic signatures. Results: Above the ground-surface, about one third of the DSi flux brought by borewell irrigation (545 mmol Si.m−2) to bare plots and half of DSi in rice plots were removed from solution within minutes or hours following irrigation. Such rate is consistent with the rate of DSi adsorption onto Fe-oxyhydroxides but not with diatom blooms. In rice and rice + DE experiments, the isotopic fractionation factor (30e) between bore well and stagnant water compositions is close to −1 ‰, i.e. the isotopic fractionation factor known for rice, indicating that above-ground DSi removal would be dominated by plant uptake upon adsorption. Within the soil layer, pore water DSi decreases much faster in rice experiments than in bare ones, demonstrating the efficiency of DSi rice uptake upon adsorption. Total irrigation-DSi to plant-Si would then represent 24 to 36% in rice experiments (over 1460 ± 270 mmol Si m−2 in biomass) and 15 to 23% in rice + DE ones (over 2250 ± 180 mmol Si m−2). The δ30Si signature of whole plants was significantly different in the rice + DE plot analyzed, 0.99 ± 0.07 ‰, than in the rice one, 1.29 ± 0.07 ‰. According to these δ30Si signatures, the main Si source from the soil would be the amorphous silica pool (ASi). A slight contribution of DE to the rice plant could be detected from the Si isotopic signature of rice. Conclusions: The δ30Si signatures of the various soil-plant compartments, when associated to Si mass balance at soil-plant scale, constitute a reliable proxy of the Si sources in paddy fields. The solute Si balance is controlled by rice uptake in rice plots and by adsorption in bare ones. The main Si sources for the rice plants were soil ASi, irrigation Si and to a lesser extent Si fertilizer when it was applied.

Use of Sr isotopes as a tool to decipher the soil weathering processes in a tropical river catchment, southwestern India

River water composition (major ion and 87Sr/86Sr ratio) was monitored on a monthly basis over a period of three years from a mountainous river (Nethravati River) of southwestern India. The total dissolved solid (TDS) concentration is relatively low (46mgL−1) with silica being the dominant contributor. The basin is characterised by lower dissolved Sr concentration (avg. 150nmolL−1), with radiogenic 87Sr/86Sr isotopic ratios (avg. 0.72041 at outlet). The composition of Sr and 87Sr/86Sr and their correlation with silicate derived cations in the river basin reveal that their dominant source is from the radiogenic silicate rock minerals. Their composition in the stream is controlled by a combination of physical and chemical weathering occurring in the basin. The molar ratio of SiO2/Ca and 87Sr/86Sr isotopic ratio show strong seasonal variation in the river water, i.e., low SiO2/Ca ratio with radiogenic isotopes during non-monsoon and higher SiO2/Ca with less radiogenic isotopes during monsoon season. Whereas, the seasonal variation of Rb/Sr ratio in the stream water is not significant suggesting that change in the mineral phase being involved in the weathering reaction could be unlikely for the observed molar SiO2/Ca and 87Sr/86Sr isotope variation in river water. Therefore, the shift in the stream water chemical composition could be attributed to contribution of ground water which is in contact with the bedrock (weathering front) during non-monsoon and weathering of secondary soil minerals in the regolith layer during monsoon. The secondary soil mineral weathering leads to limited silicate cation and enhanced silica fluxes in the Nethravati river basin.

Uranium isotopes in soils as a proxy for past infiltration and precipitation across the western United States

The intermittent presence of large Pleistocene lakes in the southwestern interior of North America, a region that is now a semi-arid desert, suggests repeated oscillations between profoundly different climatic conditions. The origin of these shifts is still unresolved due to inconsistencies in existing climate proxy data (for example, pollen, lake levels, and oxygen isotopes in speleothems). To resolve the inconsistencies in the water balance over the last 10 to 60 kyr, we use uranium isotopic variations in secondary soil minerals to quantify net infiltration and precipitation along a north-south transect in western North America. We show that winter infiltration increased by 30 to 100 percent, and precipitation by a lesser amount, in the valleys of the Great Basin and Mojave deserts between 60 and ∼26 ka. This increase in infiltration and precipitation preceded the Last Glacial Maximum (LGM) and the timing of most lake highstands in the region by 5 to 10 kyr, respectively, suggesting a possible Last Precipitation Maximum (LPM) that coincided with a minimum in winter insolation. Subsequent decreases in infiltration and precipitation after the LGM can be reconciled with the timing of lake highstands if colder summer temperatures due to a minimum in summer insolation reduced lake evaporation. The soil records, combined with a range of proxy data, suggest that seasonal insolation is the long-term driver for large shifts in both precipitation and surface water variability in the region.

Seasonal variations of rare earths and yttrium distribution in the lowland Havel River, Germany, by agricultural fertilization and effluents of sewage treatment plants

REE and Y (REY) distribution in the lowland Havel River passing the Federal State of Berlin, Germany, depends on contributions of point sources such pharmaceutical and high-tech industries, acid water from the open pit lignite mining, and medical application of very stable organic Gd chelates. Another omnipresent dispersed source of REY are water-soluble Ca-phosphates containing micro-amounts of Eu(II)-bearing barite as components of common agricultural fertilizers. After distribution in the field during the cold season (October through March) these Ca-phosphates dissolve and secondary phosphates and calcite precipitate both being enriched in light REE. Heavy REE are preferably exported by runoff together with part of the micro-contaminant barite leading to high Yb/Nd ratios in the Havel water and REY distribution patterns with only small Eu deficits. During the warm season (April through September) light REE together with phosphate are leached from secondary soil minerals by runoff. The micro-component barite is retained in vegetation-covered soil. Thus, REY patterns of Havel water show significant Eu deficits. The high Gd anomalies result from medical applications of Gd-chelates which after urination pass the sewage treatment plants. The seasonal variations of total Gd in the Havel River are artifacts based on seasonal locally varied discharge of effluents from sewage treatment plants. The natural Gd concentration of 8pmol/l in the northern Havel is enhanced to 3300pmol/l, when the Havel River leaves Berlin territory. The elimination of phosphate from Lake Tegel water affects the fractionation of REE but not the concentration of total Gd. Although enhanced in total phosphorus (TP), the REE concentrations in the water from the Spree River and the Teltow Canal are less than in the Havel water before their confluence. Only Yb and Lu do not decrease. The contributors of the Havel River are high in total organic carbon (TOC) and dissolved organic carbon (DOC) compared to the Havel water before their indicating that REY are preferentially sorbed by settling organic matter. Applying PHREEQC and assuming that only 10% of TP is present as ortho-phosphate yields that only carbonate complexes are essential.

Modelling of Soil Organic Matter and Elements of Soil Nutrition Dynamics in Mineral and Organic Forest Soils: the ROMUL Model Expansion

Abstract Soil organic matter (SOM) dynamics is an important pool in biological turnover of carbon and other elements of plants nutrition in forest ecosystems. Problems at its modelling are: quantification of SOM fractions which are decomposing with specific rates; description of humification, obtaining dependencies of SOM rates of transformation in dependence on external factors. Different methods of fractionating of SOM are now in use based on different solubility of fractions/ This approach presents difficulties at model's initialization. We expanded a model of SOM dynamics ROMUL based on successive stages of mineralization and transformation of fresh litter, which correspond to SOM pools in horizons L, F and H of forest floor. A1 et al. are horizons in mineral soil. Rates of transformation of one SOM pool into another in these horizons can be obtained from experimental data. The dynamics of N, Ca and Mg is described using main equations of SOM transformations with inserting of additional constants or functions as independent multipliers for rates of transformation. Pools of elements available for plants nutrition, and some intermediate pools such as secondary soil minerals have been added to the model. New ROMUL has been successfully applied to ICP Forest plots in Russia.

Rare earth elements in soil and plant systems - A review

The rare earth elements (REEs) form a chemically uniform group and include yttrium (Y), lanthanum (La) and the lanthanides cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Their average abundance in the Earth’s crust range from 66µg g−1 in Ce to 0.5µg g−1 in Tm and «0.1µg g−1 in Pm. Recent great improvements in more routine analytical technique, the use of REEs as fertilisers, at least in East Asian agriculture, and the importance of these elements as indicators in both pedological and physiological processes and reactions have contributed to an increased interest in these previously less considered elements in environmental sciences. This review of recent and current literature deals with REEs in primary and secondary soil minerals, concentrations in surface soils, factors influencing adsorption, solubility and transport in soils, including weathering and transformations of REE minerals, and vertical distribution in soil profiles. Reviewed and discussed are also concentrations, distribution and localisation of REEs in plants and plant organs, soil-plant relationships and interactions, effects on plant growth and crop production and their importance in plant physiology and biochemistry. The REEs are found, usually several elements together, as phosphates, carbonates and silicate minerals finely dispersed especially in magmatic and metamorphic rocks. REE concentrations in surface soils of humid climates, such as the A(E)-horizons of Podzols and Laterites, are usually lower than in the parent material, due to higher weathering and leaching rates than of the average soil constituents. Some fractionation may occur due to the formation of more element-specific secondary minerals. Transfer from soil to plant is usually low, but extreme accumulators are found, e.g., among several species of ferns. Roots have generally higher concentrations than shoots. Possible uptakemechanisms of REEs are discussed. Uptake is positively, though often weakly, correlated with soil acidity and easily soluble concentrations of the elements, but rarely well related to their total concentrations in the soil. Under certain conditions, low concentrations of at least some REEs seem to favour plant growth and productivity, but the physiological mechanisms are still not well understood. Some considerations concerning the boundary between essential and non-essential micro nutrients are discussed.

Strontium isotope constraint on the provenance of basic cations in soil water and stream water in the Kawakami volcanic watershed, central Japan

AbstractPositive correlations among the concentrations of Sr, Ca and Mg in soil water and stream water in a forested volcanic watershed at Kawakami, central Japan indicate that the Sr isotope can be used as a tool to elucidate the source and transport of the essential terrestrial ecosystem nutrients, Ca and Mg. The 87Sr/86Sr ratio in surface soil water varied widely along a 74 m slope; it was almost identical to the 87Sr/86Sr ratio of exchangeable soil and existing plants with different rooting zones (Japanese oak and bamboo grass), but differed significantly from that of soil minerals. In contrast, the 87Sr/86Sr ratios of stream water at baseflow periods were uniform regardless of location and time, and were indistinguishable from those of the weathered andesite bedrock. The Sr isotopic and elemental data indicate that Sr, Ca and possibly other cations (e.g. K, Mg) in the plant cycle efficiently with exchangeable soil through soil water and without a large supply of cations from secondary soil minerals, while cations in stream water are controlled mainly by exchange reactions with bedrock derived secondary minerals occurring in the lower soil horizon to water‐saturated zones. It is calculated that about 10% of Sr and Mg and 20% of Ca in stream water are derived from wet precipitation, while the contribution of atmospherically derived Sr and Ca in the exchangeable soil pool increases from 22 to 72% and from 42 to 87% respectively, with increasing distance from the valley. This increase of Sr and Ca in the exchangeable soil pool coincides with rock derived, low Ca materials dominating in the surface soil of the upper elevation in the slope. Copyright © 2001 John Wiley & Sons, Ltd.

Phosphorus fractions in montane forest soils of the Cordillera de Piuchué, Chile: biogeochemical implications

The Hedley fractionation procedure as modified by Tiessen and Moir (1993) was used to evaluate the amounts of P in several soil chemical pools in an old, unglaciated landscape at 600 m elevation in the Cordillera de Piuchue, Chile (42° 30′ S. 74° W). This is an area of primary forests which have escaped disturbance from forest harvesting, land clearing and the deposition of anthropogenic chemicals. Two study watersheds are conifer-dominated with moorland on wind-exposed ridgetops. In a third study watershed, vegetation is dominated by evergreen broadleaf trees. Soils are thin (ca. 40 cm) and have a high organic matter content. Across all communities, most of the soil P is in non-labile forms in organic combinations or in combination with secondary soil minerals. Little P was present in primary minerals. The remainder (ca. 20%) was in labile forms extractable with anion exchange resin or bicarbonate solution. From litterfall and allometric relationships, we estimated the annual P requirement of growing vegetation to be <1 kg ha-1 in the moorland and < 3 kg ha-1 in the conifer and mixed forests. This is substantially less than the standing pool of resin-extractable P (ca. 20 kg ha-1), which is considered to be P fraction most readily available to plants. Resin-extractable P was strongly correlated with soil carbon content ( R2 =0.72 − 0.87, p < 0.001) suggesting that soil organic matter is the likely proximate source of plant-available P. On a kg ha-1 basis, the most labile forms of P did not differ significantly across 3 of the 4 community types despite dramatic differences in species, live biomass and annual P requirement, suggesting little control of available P pools by forest vegetation type. On a more detailed level, resin-extractable P was strongly correlated with HCO3-extractable organic (and inorganic) P. This is consistent with other findings of P behavior in acid soils high in organic matter in which microbial transformations are key in regulating pools of plant-available P.

An investigation of the magnetic properties of soils

The results of investigations of the magnetic properties of soils, including measurements of the magnetic susceptibility of the main types of soils, specimens of which were taken from different soil levels and in different regions of the former USSR, are presented. In addition to measurements of the magnetic susceptibility, investigations were also made of the dependence of the magnetic properties of soils on the density, moisture content, temperature, and the action of short-term gamma radiation. The role of primary and secondary soil minerals in soil magnetism is discussed.

Soil nutrient supply in natural and managed forests

Soils differ in their ability to supply the nutrients necessary to sustain forest productivity. Nutrients are added through natural processes such as weathering of primary and secondary soil minerals, mineralization of soil organic matter including the forest floor layer, fixation of nitrogen primarily through symbiotic microorganisms, and natural or induced atmospheric deposition. Nutrients become unavailable for plant uptake through immobilization by soil microorganisms and through chemical and mineralogical reactions including precipitation and adsorption reactions and ionic fixation within lattice structures of clay minerals. Losses of nutrients can take place through soil leaching and erosional processes. Nutrients can also be added or lost through human activities such as fertilization and harvesting. Nutrient supply continually shifts with the rate and direction dependent on the prevailing processes in the soil system, but subject to overriding human influence. Over relatively short periods of time, the soil nutrient supply can be subject to seasonal fluctuations. Factors affecting long-term nutrient availability are functions of soil mineralogy, the rate of mineralization of the organic matter of the soil and forest floor layer, and plant-soil relationships of the species occupying the site (deciduous vs. coniferous species, deep vs. shallow rooting, symbiotic nitrogen fixation). The long-term stability of the soil nutrient supply is of increasing concern in the face of a diminished forest land base, increased demand for forest products, and reluctance to apply nutrients to many forest areas because of environmental or economic constraints. There are questions to consider in evaluating the nutrient sustainability of forest areas if we expect to maintain the long-term nutrient stability of natural and managed forest ecosystems.

The mineralogy and chemistry of manganese in some Australian soils

The mineralogical and chemical compositions of 28 manganese nodules from Australian soils were studied. Specific manganese minerals were identified in 26 of these after extraction and concentration from the associated soil minerals; 10 were lithiophorite Li2A18 (Mn2+, Co, Ni)2, Mn4+10O35.14H2O; 10 were birnessite, (Ca, Mg, Na2, K2)x Mn4+Mn2+(O, OH)2; 3 were hollandite, Ba(Mn4+, Fe3+)8O16; 1 was todorokite (Mn2+, Mg, Ca)Mn4+6O13.3-4H2O; 1 was pyrolusite MnO2; 1 contained both lithiophorite and hollandite. With the possible exception of pyrolusite, all samples were found to contain varying amounts of Ni, Co, Mg, Ba, Al, K, Na, Fe, and Ca. Although there was overlap in the chemistry of the birnessite and lithiophorite groups, the mean concentrations of aluminium, iron, and lithium were lower and the mean concentration of calcium and magnesium higher in the former group. Pure manganese oxides and hydroxides appear to be quite rare as secondary soil minerals. Lithiophorite occurred mainly in neutral to acid subsurface soils, whereas birnessite, although found in both acid and alkaline soils, was more common in alkaline surface horizons. The average crystallite size of the manganese mineral aggregates was quite small, being of the order of 0.02 �m for birnessites and 0.1 �m for the lithiophorites.