Search

Benggangs are a special type of soil erosion in the hilly granite regions of the tropical and subtropical areas of Southern China. They cause severe soil and water loss, which can severely deteriorate soil quality and threat to the local ecological environment. Soils (red soil, sandy soil and detritus soil) were collected from collapsing wall of a typical Benggang in Changting County of Fujian Province, and their physicochemical and mineralogical properties were analyzed. Five different monovalent cations were used to saturate the soil samples to examine the specific ion effects on the shear strength and clay surface properties. Red soil had a higher clay content, plastic limit, liquid limit and shear strength than sandy soil and detritus soil. The studied soils mainly consisted of kaolinite, hydroxy-interlayer vermiculite, illite and gibbsite clay minerals. The soils saturated with K + , NH 4 + and Cs + had greater cohesion than the Li + - and Na + , the cohesion of the red soil saturated with Li e.g. , the cohesion of the red soil saturated with Li + , K + , NH 4 + -saturated soil, respectively. While the internal friction angle was slightly different, which indicated that different monovalent cations affected the shear strength differently. K + cations were 1.05, 1.23, 1.45 and 1.20 times larger than that of the Na + -saturated soil, respectively. While the internal friction angle was slightly different, which indicated that different monovalent cations affected the shear strength differently. K + -, NH 4 + -saturated clay particles and showed strong specific ion effects on the clay surface properties. The changes in clay surface properties strongly affected the soil mechanical properties. Soils saturated with K + -saturated clay particles had higher zeta potentials and thinner shear plane thicknesses than Li + - and Na + -saturated clay particles and showed strong specific ion effects on the clay surface properties. The changes in clay surface properties strongly affected the soil mechanical properties. Soils saturated with K + , NH 4 + and Cs + could increase the shear strength, and then increase the stability of the collapsing wall, thus might decrease the erosion intensity of Benggang. The results provide a scientific basis for the interpretation of and practical treatment of Benggang., Competing Interests: The authors declare there are no competing interests., (©2024 Huang et al.)

Benggang is one of the most serious soil erosion problems in tropical and subtropical areas in southern China. Little work has been reported on the surface properties of soil colloidal particle and its influence on soil swelling of different soil layers in collapsing wall of Benggang. In this present work, the effects of sodium concentration on soil swelling, and the correlations between soil swelling rates and soil colloidal surface properties were comprehensively evaluated by carefully examining soil physicochemical properties and soil colloidal surface properties of red, sandy and detritus soil layers from a collapsing wall. Our results showed that the soil swelling rates of red, sandy and detritus soil layers all exponentially decreased with increasing initial water contents. The relationship between soil swelling rate and the thickness of shear plane showed an extremely significant negative correlation for red soil layer and no correlation for sandy and detritus soil layers. Moreover, the elevating sodium concentrations reduced the thickness of shear plane from 39.69 to 0.76 nm for red soil layer, followed from 22.56 to 0.79 nm for sandy soil layer and from 18.61 to 0.64 nm for detritus soil layer. These findings indicated that the soil particle interactions played a crucial role in the development and occurrence of Benggang. This work will be helpful in understanding the mechanisms of soil mass loss on the gully head and collapsing wall of Benggang., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Zhang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

This study aimed to determine the microbial diversity at different soil depths (0-5 and 5-20 cm) in a subtropical orchard during different seasons (i.e., spring, summer and autumn) to advance knowledge of the roles of microbes in orchard ecosystem balance. In tracking experiments conducted in an orchard (established in 1996), the phospholipid fatty acid (PLFA) biomarker method was employed to determine the soil microbial system. The total PLFA concentration did not vary significantly between soil depths but changed between seasons. It peaked in the summer at 258.97 ± 23.48 μg g soil-1 from 0-5 cm and at 270.99 ± 58.94 μg g soil-1 from 5-20 cm. A total of 33 microbial fatty acid biomarkers were observed and identified in the sampled soil. The quantities of PLFAs for 29 microbial groups varied significantly between seasons, except for 15:0 iso 3OH, 15:1 iso G, 16:0 2OH, and 17:0 iso 3OH. The bacterial PLFAs and fungal and actinomycetic PLFAs in the orchard soil collected in summer were significantly more abundant than those collected in the spring or autumn (P < 0.01). The number of soil microorganism species (richness) and the Simpson and Shannon-Wiener indexes were all highest in summer. The total PLFAs, bacterial PLFAs, fungal PLFAs, actinomycetic PLFAs, richness, and Simpson and Shannon-Wiener indexes were all significantly negatively correlated with soil pH, total organic carbon (TOC), total nitrogen (TN) and the cation exchange capacity (CEC) (P < 0.05)., Competing Interests: The authors have declared that no competing interests exist.

The effectiveness of four different washing extractants--HCl, FeCl3, citric acid, and EDTA--in removing Cd, Pb, and Zn from polluted soil was studied. The removal of these metals, their redistribution between fractions, and the potential risks posed by them, in soils washed with the tested extractants, were examined. Although all the rounds of washing removed Cd, Pb, and Zn from soil, the first round removed more metals than subsequent rounds. Each of the four extractants had different effects on the removal of the metals. At the end of the first round of washing, HCl, EDTA, and FeCl3 were the most effective in removing Zn, Pb, and Cd, respectively. Both the single round and five successive rounds of washing with various extractants resulted in significant increases in Pb in the exchangeable/acid extractable fraction. Washing with HCl, EDTA, and FeCl3 significantly reduced potential risks (calculated as the Potential Risk Index, PRI) posed by Cd in washed soil. The first round of washing, using all extractants, increased the risks posed by Pb and Zn. However, five successive rounds of washing with FeCl3 and EDTA reduced the risk posed by Pb, and washing with citric acid and FeCl3 increased the risks posed by Zn. EDTA and HCl were better for reducing Zn risks, and successive washing with EDTA and FeCl3 were more effective in reducing Pb risks than the other extractants. Finally, five successive rounds of washing, with all the extractants, effectively reduced the potential risks posed by Cd. Among the four reagents, EDTA was advised to be the alternative of the washing reagent by significantly reducing the PRI values of Cd, Pb, and Zn.

This study investigates biogeochemical reductive release of arsenate from beudantite into solution in a crater area in northern Taiwan, using a combination of X-ray absorption near-edge structure (XANES) and atomic absorption spectrometry. Total arsenic (As) concentrations in the soil were more than 200 mg/kg. Over four months of laboratory experiments, less than 0.8% As was released into solution after reduction experiments. The 71% to 83% As was chemically reduced into arsenite (As(III)) and partially weathering into the soluble phase. The kinetic dissolution and re-precipitation of As, Fe, Pb and sulfate in this area of paddy soils merits further study.

Sewage sludge (SS) applied to sloping fields at rates that exceed annual forest nutrient requirements can be a source of phosphorus (P) in runoff. This study investigates the effects of different slopes (18, 27, 36, and 45%) on P in runoff from plots amended with SS (120 Mg ha). Lateritic soil (pH 5.2) was exposed to five simulated rainfalls (90 mm h) on outdoor plots. When sludge was broadcast and mixed with surface soils, the concentrations and loss in runoff of total P in the mixed sample (MTP), total P in the settled sample (STP), total particulate P (TPP), total suspended P (TSP), and total dissolved P (TDP) were highest at 1 or 18 d after application. Initially, pollution risks to surface waters generally increased to different degrees with steeper slopes, and then diminished gradually with dwindling differences between the slopes. The runoff losses coefficient of MTP increased in the order 36 > 45 > 27 > 18%. The initial event (1 and 18 d) accounted for 67.0 to 83.6% of total runoff P losses. Particulate fraction were dominant carriers for P losses, while with the lower slopes there was higher content of P per unit particulate fraction in runoff. Phosphorus losses were greatly affected by the interaction of sludge-soil-runoff and the modification of soil properties induced by sludge amendment. It is recommended to choose lower slopes (<27%) to reduce risk of P losses. Thus, the risk of application sludge to sloping fields in acid soils should be studied further in the field under a wider diversity of conditions., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Radio pollutant removal is one of several priority restoration strategies for the environment. This study assessed the effect of low molecular weight organic acid on the lability and mechanisms for release of (137)Cs from contaminated soils. The amount of (137)Cs radioactivity released from contaminated soils reacting with 0.02 M low molecular weight organic acids (LMWOAs) specifically acetic, succinic, oxalic, tartaric, and citric acid over 48 h were 265, 370, 760, 850, and 1002 Bq kg(-1), respectively. The kinetic results indicate that (137)Cs exhibits a two-step parabolic diffusion equation and a good linear relationship, indicating that the parabolic diffusion equation describes the data quite well, as shown by low p and high r(2) values. The fast stage, which was found to occur within a short period of time (0.083-3 h), corresponds to the interaction of LMWOAs with the surface of clay minerals; meanwhile, during the slow stage, which occurs over a much longer time period (3-24 h), desorption primarily is attributed to inter-particle or intra-particle diffusion. After a fifth renewal of the LMWOAs, the total levels of (137)Cs radioactivity released by acetic, succinic, oxalic, tartaric, and citric acid were equivalent to 390, 520, 3949, 2061, and 4422 Bq kg(-1) soil, respectively. H(+) can protonate the hydroxyl groups and oxygen atoms at the broken edges or surfaces of the minerals, thereby weakening Fe-O and Al-O bonds. After protonation of H(+), organic ligands can attack the OH and OH(2) groups in the minerals easily, to form complexes with surface structure cations, such as Al and Fe. The amounts of (137)Cs released from contaminated soil treated with LMWOAs were substantially increased, indicating that the LMWOAs excreted by the roots of plants play a critical role in (137)Cs release., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

To recognize physiological response of plants to cadmium (Cd) toxicity in rhizosphere of plants, the pot experiments were employed to investigate how low-molecular-weight organic acids (LMWOAs) were exudated from tobacco and sunflower roots of Cd-amended soils. The aims of this study were to assess the effect of LMWOAs on uptake of Cd by tobacco and sunflower under pot experiments, thus comparing the ability of tobacco and sunflower for phytoremediation. Surface soils (0-20 cm) were collected from Taichung Experiment Station (TC) (silty loam). Cadmium chloride (CdCl(2)) was amended into TC soil, giving Cd concentrations of 1, 5, 10 mg kg(-1) soil. Soils with different concentrations of Cd were put into 12 cm (i.d.) pots for incubation, and then 2-week-old tobacco and sunflower seedlings were transplanted into the pots. Tobacco and sunflower were grown in greenhouse for 50 days, respectively. The rhizosphere and bulk soils, and fresh plant tissues were collected after harvest. The Cd concentrations in the plant and transfer factor values in the sunflower were higher than that in the tobacco. No LMWOAs were detected by gas chromatograph in bulk soils, and low amounts of LMWOAs were found in uncontaminated rhizosphere soils. Acetic, lactic, glycolic, malic, maleic, and succinic acids were found in the tobacco and sunflower rhizosphere soils. Concentrations of LMWOAs increased with increasing amendment of Cd concentrations in tobacco and sunflower rhizosphere soils. Correlation coefficient (r) of concentrations of Cd amendment versus LMWOAs exudates of tobacco and sunflower were 0.85 and 0.98, respectively. These results suggest that the different levels of LMWOAs present in the rhizosphere soil play an important role in the solubilization of Cd that bound with soil particle into soil solution and then uptake by plants.

The carbon isotope analysis [delta13C values] of organic samples can be a useful research in ecological studies because delta13C values are indicative of the plant source. This study investigated the changes in plant communities along the grassland-forest boundary in the alpine forest at Ta-Ta-Chia long term ecological research (LTER) site in central Taiwan using carbon isotope data. The aim of this study was focused on the forest fire affected the change of vegetation community. Four pedons from grassland dominated by Miscanthus transmorrisonensis (pedons 1 and 2), transition zone by Tsuga and Yushania nittakeyamensis (pedon 3), and forest zone by Tsuga and nittakeyamensis (pedon 4) were examined. Soil organic matter (SOM) delta13C values in the upper soil horizon were similar to delta13C values of the overlaying vegetation types. This indicates that the boundary between these plant communities remained the same in the past decades. The delta13C values of the grassland SOM ranged from -19.4 per thousand to -24.1 per thousand, showing decrease with soil depth. This suggests that C4 plants (transmorrisonensis) have replaced C3 plants of Tsuga and nittakeyamensis. The delta13C values of the Tsuga forest area (pedon 4) range from -27.0 per thousand to -23.5 per thousand and showed only slight change with soil depth, implying that C3 plants have remained the major species in the forest.

Summary: Soils are the central organizer of the terrestrial ecosystem. Their colloidal and particulate constituents, be they minerals, organic matter, and microorganisms, are not separate entities; rather, they are constantly interacting with each other. Interactions of these components control biogeochemical reactions, namely, the formation of short-range-ordered metal oxides, catalysis of humic substance formation, enzymatic stability and activity, mineral transformation, aggregate turnover, biogeochemical cycling of C, N, P, and S, and the fate and transformation of organic and inorganic pollutants. Furthermore, the impacts of mineral–organic matter–microorganism interactions and associated biogeochemical reactions and processes on biodiversity, species composition, and sustainability of the terrestrial ecosystem deserve close attention for years to come. This paper integrates the frontiers of knowledge on this subject matter, which is essential to uncovering the dynamics and mechanisms of terrestrial ecosystem processes and to developing innovative management strategies to sustain ecosystem health on the global scale. [Copyright &y& Elsevier]

Abstract: Clay minerals in soils reflect successive stages of mineralogical evolution, which depend on the environmental conditions that have prevailed during pedogenesis. The objective of this research was to document the mineralogy of the clay fractions (<2μm) of three Holocene loess–paleosol sections on the Chinese Loess Plateau (CLP) and to deduce the climatic and pedogenetic differences at the three sites. The three sections were located at Ansai, Luochuan and Wugong in a north–south transect of the CLP and dated from the late period of Late Pleistocene (0–23,860±90year B.P.). In general, the mineralogy of loess and paleosol was similar over the CLP. However, the pedogenesis and mineralogy of the profiles in the three sections showed significant temporal and spatial variations along the climate gradient. In Ansai the Holocene loess was preserved in thick eolian deposits and relatively homogeneous as far as grain size distribution and clay mineralogy. The clay composition as a function of depth did not vary significantly, which coincided with coarse grains and constant CaCO3 contents. In Wugong the mineral weathering and pedogenesis have resulted in a prominent increase of vermiculite in the paleosol with more clay and intensive decalcification. In general, a subtle decrease of kaolinite and smectite in paleosol occurred in southward direction. It can be concluded that pedogenesis and mineral weathering progressively weakened in going from south to north across the Loess Plateau, which signified a weaker influence of the humid and temperate summer monsoon in the north during the Holocene. In other words, the climatic changes during Holocene were not uniform across the CLP. The weak weathering and pedogenesis in Ansai indicate a stable and dry climate and pedogenic environment over the last 11,500years around Ansai. [Copyright &y& Elsevier]

The elemental geochemistry of major, minor and trace elements in iron–manganese cutans and the corresponding matrix soils, collected from three Alfisols in central China, are studied using their chemical compositions as well as correlation and factor analyses. Fe–Mn cutans accumulate high concentrations of MnO2 and Fe2O3. Mean values of these two elements in cutans are about 13.7 and 1.4 times higher than those in the matrix soils. pH, clay contents, extractable X-ray noncrystalline Fe (Feo) and the ratio of Feo to free Fe-oxide (Fed) in cutans are notably higher than those in the corresponding matrices. Cutans are also enriched in some bases and heavy metals. Averages of K, Na, Co and Pb concentrations are about 2.0, 1.4, 15.4 and 6.0 times higher than those in the matrices. Statistical analysis indicates that Co, Ni, Li, Cu and Zn are abundant in Mn minerals of cutans, while Pb exists mainly in iron minerals. Fe–Mn cutans constitute an active microzone of solid–solution–plant–air interaction, element movement and exchange in soils, which cause the contents of Fe- and Mn-oxides, elemental concentrations, and geochemical behavior of cutan to show marked differences in matrix soils. [Copyright &y& Elsevier]