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Sodium concentration and the soil solution Ca/Mg ratio may influence soil dispersion and water movement. This study investigated the impact of electrical conductivity (EC), Na adsorption ratio (SAR), and Ca/Mg ratios on dispersion thresholds of pure clay minerals (montmorillonite, illite, and kaolinite). Replicated laboratory studies were conducted where the impact of SAR (1, 5, 12, or 24), EC (0–16 dS m−1), and specific Ca/Mg ratios on clay dispersion was determined. The results showed that Ca/Mg ratios did not influence clay dispersion of montmorillonite and kaolinite. For illite at a SAR of 12, however, dispersion was reduced by reducing the Ca/Mg ratio from 1/0, 2/1, and 1/2 to 0/1. Dispersion thresholds were <6 dS m−1 across all clays. At a SAR of 12, dispersion occurred for EC < 2 dS m−1. Kaolinite exhibited little, if any, dispersion. These results indicate that in soils having little or no organic C (i.e., subsoils), Mg does not influence dispersion thresholds and that dispersion risks can be reduced by adopting practices that maintain the EC > 2 dS m−1.

Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples (loam or clay) with predominantly smectitic, illitic, or kaolinitic clay mineralogy were studied. We measured aggregate sensitivity to slaking in soils that were untreated or treated with an anionic high-molecular-weight PAM using the high energy moisture characteristic (HEMC) method and deionized water. The index for aggregate susceptibility to slaking, termed stability ratio (SR), was obtained from quantifying differences in the water retention curves at a matric potential range of 0 to -5.0 J kg-1 for the treatments studied. For the untreated soils, the SR ranged widely from 0.24 to 0.80 and generally SR of kaolinitic > illitic > smectitic soils. The SR of PAM-treated aggregates exhibited a narrow range from 0.70 to 0.94. The efficiency of PAM in improving aggregate and structural stability relative to untreated soils ranged from 1.01 to 3.90 and the relative SR of kaolinitic < illitic < smectitic samples. These results suggest that the less stable the aggregates the greater the effectiveness of PAM in increasing aggregates stability (i.e., smectitic vs. kaolinitic samples). The effectiveness of PAM in improving structure and aggregate stability was directly related to clay activity and to soil conditions affecting PAM adsorption (e.g., electrolyte resources, pH, and exchangeable cations) to the soil particles and inversely to the inherent aggregate stability.

Mechanisms of aggregate disruption and the measurement techniques used to quantify them for different aggregate sizes affect the relation of aggregate stability to soil erodibility and to basic soil properties. We evaluated two different techniques of aggregate stability analysis that gave either a settling velocity or stability of aggregates parameter for different sized aggregates which we compared with interrill erodibility for 10 clay soils. We compared the differences in these parameters from slow wetting to reduce slaking to air‐dried aggregates and compared these differences to soil properties. Aggregate settling velocity and stability and soil interrill erodibility were strongly affected by clay mineralogy and physical–chemical properties. The mechanism of aggregate disruption was dependent on clay type. Slaking during fast wetting was important in kaolinitic/oxidic soils, whereas highly smectitic clay increased particle dispersion and slaking on swelling, with a consequent reduction in size and speed of settling aggregates. Swelling of clays may have overridden any reduction in slaking by slow capillary prewetting of illite or smectite (with no kaolinite) soils, causing aggregate instability with both slow and fast wetting procedures. Correlation analysis showed that 4.76‐ to 8‐mm aggregates with a high slaking index also demonstrated more slaking under wet sieving and slower fall velocity. Interrill erodibility had greater correlation with the mean weight diameter (MWD) of stable aggregates in the 1‐ to 2‐mm size class, than for the whole soil (aggregates < 8 mm), and no correlation was observed with any of the slaking indexes involving wet sieving or settling in water. Multiple regression analysis indicated that 89% of the variability in erodibility for prewetted soil was explained by MWD of prewetted 1‐ to 2‐mm stable aggregates (MWDW), available water content, and fall velocity of 1‐ to 2‐mm dry aggregates, while 96% of the variability in erodibility for dry soil was explained by MWDW for 1‐ to 2‐mm prewetted aggregates, water dispersible clay, and fall velocity for 1‐ to 2‐mm dry aggregates. The interrill erodibility, for dry and wet soil, was greatest for the highly smectitic and least for the high‐clay kaolinitic/oxidic, both under annual crops. The higher erodibility and lack of slaking reduction effect on our prewetted soil under simulated rainfall is explained by a confounding effect of high water table, high steady‐state runoff and slaking.

A 3D model integrating mineralogical, petrological, and geostatistical resource estimation was developed for Zone C of the Kofi Birimian gold deposit in Western Mali. Petrographic analysis identified two forms of gold mineralization: (i) native gold or electrum inclusions within pyrite, and (ii) disseminated native gold along pyrite fractures. Four types of hydrothermal alteration–epidotization, chloritization, carbonatization, and albitization were observed microscopically. Statistical analysis of geochemical data classified five lithologies: mafic dyke, felsic dyke, diabase, faulted breccia, and intermediate quartz diorite. Minerals identified petrographically were corroborated by multivariate correlations among elements (Cr, Fe, Ni, Al, Ti, Na, and Ca), as revealed by Principal Component Analysis (PCA). A 3D borehole-based model revealed spatial correlations between hydrothermal alteration zones and associated geochemical anomalies, notably tourmalinization (B) and albitization (Na), with the latter serving as a key indicator for new exploration targets. The spatial associations of anomalous Ag, B, Hg, As, and Na commonly linked to tourmalinization suggest favorable zones for gold and silver mineralization. Geostatistical analysis identified isotropic continuous mineralized structures for most elements, including gold. Spherical isotropic variograms with ranges from 35 to 75 m were fitted for in situ resource estimation (e.g., silver ≈ 40 m; gold ≈ 60 m). The resulting estimated resources (indicated + inferred), based on a 1.0 g/t Au cut-off, are 2.476 Mt at 3.5 g/t Au indicated (0.278 Moz or 8.67 t), and 1.254 Mt at 2.78 g/t Au inferred (0.112 Moz or 3.49 t). This study provides a framework for identifying new mineralized zones, and the multidisciplinary approach demonstrates the connections between mineralogy and the information embedded in geochemical datasets, which are revealed through appropriate tools and an understanding of the underlying processes.

Karst landscapes develop in soluble rocks, such as carbonates and evaporates, but also in various types of rocks that develop pseudokarst features. The main aim of this work is to introduce a new karst map of Georgia (scale: 1:1,500,000) presenting karst and pseudokarst features, which occupy about 17.9% (12,454 km 2 ) of the entire territory of the country and include over 1500 known caves. We distinguish two types of karst features—karst (developed in carbonate rocks) and pseudokarst, and also five subtypes, mainly based on their lithology. About 10.2% (7120 km 2 ) of the country is occupied by karst (carbonate rocks), and about 7.7% (5334 km 2 ) of the country is occupied by pseudokarst features. This karst map of Georgia will provide important assistance to local and foreign researchers interested in studying Georgian karst features.

Selenite adsorption behavior was investigated on amorphous Al and Fe oxides, clay minerals: kaolinite, montmorillonite, and illite, and 45 surface and subsurface soil samples from the southwestern and midwestern regions of the United States as a function of solution pH. Selenite adsorption decreased with increasing solution pH. The triple layer model, a chemical surface complexation model, was able to describe selenite adsorption as a function of solution pH by simultaneously optimizing both inner‐sphere and outer‐sphere selenite surface complexation constants. The fit of the triple layer model to selenite adsorption by soils was much improved over that obtained previously by optimizing solely an inner‐sphere selenite surface complexation constant and the protonation constant in the constant capacitance model. In this previous application, the deprotonation constant had been neglected; thereby, preventing the reactive surface hydroxyl group from deprotonating; a chemically unrealistic situation. The selenite surface speciation predicted using the triple layer model was in agreement with that obtained for other strongly adsorbing anions such as molybdate. Direct spectroscopic investigations of selenite surface configuration are needed to corroborate the species predicted by the modeling approach.

This study examines the chemical and mineralogical composition of waste materials from abandoned copper and manganese mines in the Iberian Pyrite Belt, Portugal, as a first step toward their potential recycling for critical and strategic raw materials (CRM and SRM). Using portable X-ray fluorescence (pXRF) and other analytical techniques, this research highlights the presence of valuable elements, including copper, manganese, and rare earth elements, in concentrations significantly above their crustal abundance. The findings underscore the dual potential of these wastes: as sources of secondary raw materials and for mitigating environmental hazards such as acid mine drainage (AMD). Recovered materials include chalcopyrite, pyrolusite, and rhodochrosite, with critical elements like cobalt, lithium, and tungsten identified. pXRF proved to be a reliable, cost-effective tool for rapid field and laboratory analyses, demonstrating high precision and good correlation with standard laboratory methods. The study emphasizes the importance of characterizing historical mining waste to support a circular economy, reduce reliance on foreign material imports, and address environmental challenges. This approach aligns with the European Union’s Critical Raw Materials Act, promoting sustainable resource use and the recovery of strategic resources from historical mining sites.

We studied the fluorescence properties of fulvic acids isolated from streams and rivers receiving predominantly terrestrial sources of organic material and from lakes with microbial sources of organic material. Microbially derived fulvic acids have fluorophores with a more sharply defined emission peak occurring at lower wavelengths than fluorophores in terrestrially derived fulvic acids. We show that the ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm, obtained with an excitation of 370 nm, can serve as a simple index to distinguish sources of isolated aquatic fulvic acids. In our study, this index has a value of ∼1.9 for microbially derived fulvic acids and a value of ∼1.4 for terrestrially derived fulvic acids. Fulvic acids isolated from four large rivers in the United States have fluorescence index values of 1.4-1.5, consistent with predominantly terrestrial sources. For fulvic acid samples isolated from a river, lakes, and groundwaters in a forested watershed, the fluorescence index varied in a manner suggesting different sources for the seepage and streamfed lakes. Furthermore, we identified these distinctive fluorophores in filtered whole water samples from lakes in a desert oasis in Antarctica and in filtered whole water samples collected during snowmelt from a Rocky Mountain stream. The fluorescence index measurement in filtered whole water samples in field studies may augment the interpretation of dissolved organic carbon sources for understanding carbon cycling in aquatic ecosystems.

This study was carried out to quantify the effects of higher organisms, invertebrate macrofauna, and macrophyte plants on the rates and pathways of microbial respiration coupled to organic matter oxidation in saltmarsh sediments. Sediment geochemistry, rates of microbial metabolism, and the abundance of anaerobic respiratory bacteria were determined at sites differing in the abundance of fiddler crab (Uca pugnax) burrows and vegetation (Spartina alterniflora) coverage. Solid-phase Fe(III) concentrations were 50 to 100 times higher, and solid sulfide concentrations were eight times lower in bioturbated, vegetated sediments (BVL) as compared to nonbioturbated, unvegetated (NUC) sediments. Integrated sulfate reduction rates were 10 times lower in BVL (2 mmol m-2d-2) as compared to NUC sediments (20 mmol m-2d-1). Directly measured Fe(III) reduction rates were high at the BVL site, whereas no Fe(III) reduction was detected at NUC or in killed sediment treatments. Molybdate, a specific inhibitor of sulfate reduction, inhibited 70% of carbon oxidation when added to NUC sediment but showed no effect on Fe(III) reduction or C oxidation in BVL sediments. Counts of Fe(III)-reducing bacteria (FeRB) were two orders of magnitude higher in BVL sediments (107cells g-1) in comparison to NUC sediments (105cells g-1). Fe(III) respiration comprised up to 100% of carbon oxidation in BVL sediments, whereas sulfate reduction was the dominant respiration process (≥70% of C oxidation) at NUC. We provide strong evidence to show that macroorganisms stimulate FeRB to outcompete sulfate-reducing bacteria in saltmarsh sediments by supplying an abundance of reactive Fe(III) through reoxidation processes.