Wet Sieving Research Articles

Studies on the weight of the gastrointestinal tract, digesta composition and occurrence of gastro- and enteroliths in adult domesticated ostriches fed different diets

Comminuting the ingested material in the stomach and fermentation in the large intestine of ostriches, allows an efficient utilization of fiber-rich feedstuffs. The entire gastrointestinal tract (GIT) of 61 adult ostriches (both sexes; av. age of 15 mo), which had previously been fed a ration consisting of either haylage and pelleted compound feed (HP) or haylage, corn silage and pelleted compound feed (HCP), was the subject of the present investigations. The weight of the different compartments of the GIT was measured. The digesta was differentiated into inorganic and organic substances. Wet sieving was used to separate the collected stones (>19 mm), small stones (1 mm), and sand (<1 mm). Ostriches fed the HCP diet had a significantly higher empty gizzard weight (3,435 g) compared to those fed the HP diet (3,064 g). Additionally, the weight of the empty cecum (left and right parts) was increased (P < 0.05) for ostriches fed the HCP diet (107 and 122 g, respectively) in comparison to those fed the HP diet (93.4 and 108 g, respectively). The weight of pure digesta in the gizzard and left or right cecum for ostriches fed the HP diet was higher (1,640, 448, and 471 g, respectively) compared to those fed the HCP diet (P < 0.05). The contents of crude ash and HCl-insoluble ash in the digesta of all the GIT compartments were higher for ostriches fed the HP diet in comparison to those fed the HCP diet (P < 0.05). Independent of the type of the offered diet, the large stones occurred only in the proventriculus and gizzard (2.71 and 4.76%, respectively), while sand dominated in the distal colon (30.3%). The high proportion of stones in the gizzard form the “mechanical equipment” which enables the animals to grind basic feed such as corn silage or haylage, and these are almost completely excreted as sand. Continuous stone replacement for ostriches is necessary but the amount mostly depends on the type of feed.

Disentangling nematode and arbuscular mycorrhizal fungal community effect on the growth of range-expanding Centaurea stoebe in original and new range soil

AimsNumerous organisms show range expansions in response to current climate change. Differences in expansion rates, such as between plants and soil biota, may lead to altered interactions in the new compared to the original range. While plant-soil interactions influence plant performance and stress tolerance, the roles of specific soil organisms driving these responses remain unknown.MethodsWe manipulated the abundances of nematodes and arbuscular mycorrhizal fungi (AMF), collected from original and new range soils, and examined their effects on the biomass of range-expanding Centaurea stoebe and native Centaurea jacea. In the first approach, nematode and AMF communities were extracted from field soils, and inoculated to sterilized soil. In the second approach, the abundance of soil organisms in soil inocula was reduced by wet sieving; at first, plants were grown to condition the soil, and then plant-soil feedback was determined under ambient and drought conditions.ResultsThe origin of soil communities did not influence the biomass production of range-expanding or native plant species, neither by addition nor by (partial) removal. However, after conditioning and under drought, range expanding C. stoebe produced more biomass with soil communities from the original range while C. jacea, native to both ranges, produced more biomass with new range soil communities.ConclusionsWe show that nematode and AMF communities from original and new range have similar effect on the growth of range expanding C. stoebe. Our results highlight that the effect of soil communities on plant growth increases after soil conditioning and under drought stress.

Effect of nitrogen and phosphorus addition on soil aggregation and its associated organic carbon

ABSTRACT Although the response of plant productivity and soil biogeochemical processes to nutrient addition has been widely investigated, little is known about the effects of N and P addition on soil aggregate fractions, an important indicator of soil organic C stability. We investigated the effects of exogenous N and P inputs on soil aggregates and their associated organic C in a 6-year fertilisation experiment in a subtropical Chinese fir (Cunninghamia lanceolata) plantation. A wet sieving method was used to determine the aggregate size distribution. Our results showed that the most abundant aggregate was the macroaggregate, ranging between 59% and 74%. The least abundant fraction was the smallest (silt and clay), ranging between 10% and 15%. Neither the soil aggregate fractions nor their associated organic C differed significantly after 6 years of N and P addition at the 0.05 level. In contrast, the oxalate-extractable iron Fe and pyrophosphate-extractable Fe of 0–10 cm soil were significantly decreased by P addition; this may alter aggregate formation over longer periods. Thus, future studies should examine the effects of nutrient addition on aggregates over a longer period. In particular, more attention should be paid to the effects of P addition in subtropical forests.

Effects of Grassland Patches on the Composition and Stability of Soil Aggregates in the Qinghai-Tibet Plateau

Grassland patchiness was an important process in the succession of grassland degradation. The changings of soil aggregates were affected by grassland patches, which in turn affect soil organic carbon mineralization. In this study, the soil aggregates were divided into three particle sizes: macroaggregates (2-0.25mm), microaggregates (0.25-0.053mm) and clay-silt aggregates (<0.053mm) through the wet sieve method. The indoor culture method measured the cumulative mineralization of soil organic carbon. The study analyzed the changes of soil aggregates in the grassland patches of the Qinghai-Tibet Plateau, and the influences of soil aggregates on the soil organic carbon mineralization. The results of the study showed that grassland patches caused significant differences in soil aggregates. Compared with native vegetation, single plant patches and bare area formed by degradation would reduce the stabilities of aggregates and increased the amount of organic carbon mineralization. Soil aggregates of grassland patches have a significant effect on the cumulative mineralization of organic carbon. Therefore, study of changes in soil aggregates and the impacts of aggregates on organic carbon mineralization would help to accurately understand the future carbon cycle of terrestrial ecosystems and climate changes.

Aggregate fractions shaped molecular composition change of soil organic matter in a rice paddy under elevated CO2 and air warming

To understand how climate change impacts soil fertility and ecosystem functioning, it is necessary to explore how different pools of soil organic matter (SOM) at aggregate scale are functionally affected in their molecular composition. Here, we collected rhizospheric soil at rice harvest from a paddy field in which a simulated climate change experiment was conducted for 6 years, including CO2 enrichment up to 500 μmol mol−1 (CE), air warming by 2 °C (WA), combination of CO2 enrichment and air warming (CW), and the ambient environment as control. The soil samples were separated in three aggregate fractions (macroaggregates, 2000-250 μm; microaggregates, 250-53 μm; clay & silt, <53 μm) by wet sieving procedure, their molecular composition was detected by off-line pyrolysis gas chromatography mass spectrometry (GC/MS), and the analysis of microbial communities was conducted by phospholipid fatty acids (PLFAs). The mass proportion of macroaggregates increased by 32%, 55%, and 109%, while that of microaggregates decreased by 30%, 14% and 54%, compared to control under CE, WA, and CW treatments, respectively. The mass proportion of macroaggregates was significantly positively correlated with root biomass, while it was significantly negatively correlated in microaggregates, which suggested that the formation of macroaggregates was derived from microaggregates due to root entanglement, and/or mucilage. The molecular composition of SOM depleted in phenolic compounds (phenols and phenolic compounds) while accumulated in lipids (alcohols, alkanes/alkenes/alkynes and fatty acids) with decreasing aggregate size. The increased yields of lipids and phenolic compounds in macro-and microaggregates under CE treatment were likely related to the enhanced root litter, whereas they were reduced under WA treatment due to increase of fungal dominance. A lesser increment of those compounds was noticed under CW treatment and it was attributed to the antagonistic effect, in which the increment effect of CO2 elevation can be counteracted by warming. The molecular composition hardly changed in clay & silt fraction under all climatic treatments, thus suggesting that the effect of elevated CO2 and/or warming on SOM molecular composition faded with decreasing aggregate size. Shared by control and a climatic treatment, changes of common molecules in the whole soils depended on their distribution among aggregates. Moreover, the differences in common molecules distribution induced by climatic treatments were significantly correlated to those in mass proportion of aggregates. Considering that common molecules dominated the molecular abundance across all aggregate fractions, our findings indicate that the alteration of SOM molecular composition in the whole soils under climatic treatments appears to be modified by the variation in mass proportion of aggregates.

Natural mycorrhizal association of two tropical N-fixing monospecific plantations Southeastern Brazil

Forest association with arbuscular mycorrhizal fungi (AMF) can improve the uptake of nutrients and hence the growth of host plants and it exerts a crucial role in tropical nutrient-poor soils. Our work aimed to verify if there is natural mycorrhizal colonization in Plathymenia reticulata and Dalbergia nigra monospecific plantations. Soil sampling was collected in the vicinity of the trees and fine roots were selected. The fine roots were washed, clarified and then stained. The spore isolation and identification were assessed by the wet sieving and sucrose density centrifugation. Both P. reticulata and D. nigra roots have fungal structures (vesicles and hyphae). The species Glomus macrocarpum and Ambispora leptoticha were identified in the soil under P. reticulata and Glomus macrocarpum, Glomus agregatum, and Claroideoglomus etunicatum in the soil under D. nigra. Both species can naturally be associated with AMF and we can suggest that different fungi are colonizing the roots of each species.

Long-term manure application to improve soil macroaggregates and plant-available nitrogen in a Mollisol

Long-term incorporation of manure has shown many benefits to improve soil productivity, but its effects on nitrogen (N) partitioning in soil aggregates and availability to plants is not well understood. The aim of this study was to examine the influence of different long-term field fertilization regimes on N partitioning and availability in soil aggregates. Soils from a field after 25-yr treatments of no fertilization (CK), mineral fertilizer (NPK), NPK with stover return (NPKS), and NPK with manure application (NPKM) were examined for N partitioning after adding 15N-labelled urea and incubating for 42 days. Using a wet sieving procedure, soil was separated into macroaggregates (> 250 μm, coarse particulate organic matter or cPOM), microaggregates (53–250 μm), and silt + clay (< 53 μm, inter mineral-associated OM or inter-MOM). The OM in microaggregates was further separated into fine free POM (ffPOM), physically protected intra-aggregate POM (iPOM), and intra mineral-associated OM (intra-MOM). Total N and 15N concentrations were determined. All fractions except ffPOM (limited mass) were used to cultivate ryegrass (Lolium perenne L.) and 15N uptake was determined. Mass of macroaggregate was 10 % higher from NPKM and NPKS with significantly higher use efficiency than that from NPK while the opposite was true for intra-MOM fraction with no differences in other fractions. The 15N retained in cPOM, intra-MOM, and inter-MOM ranged from 24 to 34%, 28–37 %, and 33–38 %, respectively, and that from ffPOM and iPOM was 1–4% of all retained in aggregates. Ryegrass N uptake was in the range of 14–19 %, 14–24 %, and 3–5% for the cPOM, inter-MOM, and the intra-MOM, respectively. However, the total amount of 15N fertilizer retained in aggregates from the NPKM treatment (14 %) was the lowest due to its higher amount (86 % of 15N) as in soluble phase compared to other treatments (78–83 %). This research concludes that long-term manure application resulted in increased formation of macroaggregates, higher plant-available N in the aggregates, and larger amount of soluble N that contributed to the high yield in the field illustrating the role of manure to improve soil productivity and sustain crop production.

Study on the Potential Rare Earth Elements in Coal Combustion Product from Banjarsari Power Plant, South Sumatera

Coal combustion produt (CCP) from Banjarsari power plant, both fly ash and bottom ash are numerous and have not been utilized optimally. CCP contains rare earth elements so that the potential needs to be assessed as a resource and reserve of rare earth elements (REE) in the future. The stages of this research were sample preparation and testing of grain size distribution using the wet and dry sieving method. Grain morphology was observed under a microscope and the determination of mineralogical content with XRD, oxide content with XRF and elemental content with ICP-MS. Fly ash grain size distribution of 76.15% passed 200 mesh sieve (0.074 mm) while the bottom ash was only 0.2%. Grain morphology is sub-rounded and there are still coal that has not been completely burned. The dominant mineral content is quartz, mica mineral (muscovite), clay mineral (kaolinite), lime, siderite, magnetite and hematite. The dominant oxides are SiO2, Al2O3, Fe2O3 and CaO. Based on ICP-MS test results, 16 elements of REE were detected. The total REE contents for each sample, FA and BA were 264.97 ppm and 49.22 ppm, respectively. REE of CCP from Banjarsari power plant which has the potential to be extracted is the content of cerium 80.5 ppm, neodymium 42.9 ppm, yttrium 41.8 ppm and lanthanum 31.4 ppm from fly ash while at the bottom ash there is no potential to be extracted.

Evolution of sedimentary environments and geography of the Gavkhouni Playa during the Late Quaternary

Gavkhouni Playa, as lowland of the Zayandehrud River catchment area, is located in an inter-mountain basin in Central Iran. A total of 16 sedimentary cores were taken from the inner and outer parts of the basin, and surrounding areas to investigate depositional systems of the Gavkhouni Playa during the late Quaternary. Sedimentary facies were identified based on sedimentary texture, type of evaporite minerals, presence of organic materials, color changes, and other microscopic characteristics, and sampling was performed based on changes in types of sediment and sedimentary facies. A total of 80 sediment samples were selected for granulation analysis by two methods of wet sieving for coarse-grained particles and Laser Particle Sizer Analysette for smaller than sand (silt and clay) particles. Sedimentology parameters were measured by the Sedilizer software, and the results were statistically analyzed by the SPSS software. The major types of sediments in the Gavkhouni Playa sub-surface, mud and sedimentary environments included aeolian, fluvial, deltaic, lacustrine, and playa environments. According to 14C-AMS isotope dating analysis, the sedimentation rate for 40 ka period, is about 0.4 and 0.25 mm in western and eastern parts per year, respectively. Paleogeography of the Gavkhouni Playa and its extent have been reconstructed for the last 40 ka BP. The results showed that the Gavkhouni Basin extended to the western part of sand dunes during the late Pleistocene. During the early-middle Holocene, coastline regression and the Zayandehrud Delta progression toward the playa occurred in the northern part of the area. During this time, aeolian sands spread to the Gavkhouni Playa. In the Late Holocene, arid conditions caused a decrease in water level and coastline regression along with the domination of the playa environment in the Gavkhouni margin. But, there were still ephemeral lake conditions in the center of the Playa. Gavkhouni Playa experienced an increase in the level and progression of the coastline towards land about 3000 years ago. The presence of arid conditions about 1000 years ago (cal. BP) changed the Gavkhouni lands into a playa environment, and this situation was dominant in the area almost to the present day.

A Novel Index (RI) to Evaluate the Relative Stability of Soils Using Ultrasonic Agitation

As soil stability is a complex phenomenon, various methods and indexes were introduced to assess the strength of soils. Because of the limitations of different stability methods and indexes (including wet sieving-based), we aimed to presents a relative stability index (RI) that was based on the estimated components of the soil overall disruptive characteristic curve (SODC): (1) soil disruption constant (Ki, that is based upon dispersion energy of soils); (2) resulting change in mean weight diameter (ΔMWD). To evaluate the effectiveness and limitations of RI as well as to compare it with classical soil stability indexes of mean weight diameter (MWD) and geometric mean diameter (GMD). Ultrasonic agitation (UA) along with a wet sieving method (followed by dry sieving) was applied against four different soils named on the basis of sample location, Qingling soil (QL), Guanzhong soil (GZ), Ansai soil (AS), and Jingbian soil (JB). To evaluate the relative strength of soils at different applied energies (increase in sonication duration usually resulted in increased input energy and temperature of soil–water suspension), soils were subjected to six sonication durations (0, 30, 60, 120, 210, and 300 s) with a fixed (and exact) initial amplitude and temperature. Output energy was calculated based on the amplitude and temperature of the suspension, vessel, and system. The most abrupt and maximum disruption of soil aggregates was observed at a dispersion energy level of 0–200 J g−1. The MWD value of surface and subsurface ranged between 0.58 to 0.15 mm and 0.37 to 0.17 mm, respectively, while GMD was ranged from 0.14 to 0.33 mm overall. The results for MWD and GMD showed a similar trend. MWD and GMD showed more strong associations with physicochemical characteristics of soil than RI. A non-significant correlation was found between RI and MWD/GMD. Contrary to MWD and GMD, RI was significantly positively correlated with sand content; this finding indicated the influential role of sand in assessing the soil’s relative strength. The results indicated that JB soil possessed the least MWD and GMD but proved to be relatively stable because of having the highest RI value.

Soil Aggregates Stability of Forest Islands and Adjacent Ecosystems in West Africa

In the more mesic savanna areas of West Africa, many areas of relatively tall and dense vegetation with a species composition more characteristic of forest than savanna are often found around villages areas. These ‘forest islands’ may be the direct action of human activity. To better understand these patches with relatively luxuriant vegetation, our study focused on how they influence soil aggregation in comparison with nearby areas and natural savanna vegetation across a precipitation transect in West Africa for which mean annual precipitation at the study sites ranges from 0.80 to 1.27 m a-1. Soil samples were taken from 0 to 5 cm and 5 to 10 cm depths and aggregate groups with diameters: &gt; 500 μm, 500-250 μm and 250-53 μm (viz. “macroaggregates”, “mesoaggregates” and “microaggregates”) determined using the wet sieving method. The results showed significantly higher proportion of stable meso and macroaggregates in forest islands and natural savanna compared to agricultural soils (p &lt;0.05). On the other hand, although there was no effect of land-use type on microaggregates stability, there was a strong tendency for the microaggregate fraction across all land use types to increase with increasing precipitation. Soil organic carbon and iron oxides contents are the most important factors influencing aggregate stability in West African ecosystems. By increasing soil structural stability, forest islands contribute to soil erosion reduction and the control of land degradation.

Interaction between edaphic mesofauna and organic carbon within water-stable aggregates in forestry systems: A case study in northeastern Brazil

Soil mesofauna plays an important role in soil aggregation, which conditions the physical protection of soil organic carbon (SOC). Thus, our study associates the evaluation of mesofauna and SOC quantification to generate relevant information on the influencing level of these organisms on organic matter dynamics in aggregates. It is even more important investigating these indicators in places where decomposition processes are more intense, such as forest systems under tropical soils, where little is known about the interaction between these variables. In this context, the present study aimed to evaluate: (1) the influence of homogeneous Pterogyne nitens and Pinus caribaea plantations on the edaphic mesofauna community and on SOC stocks and carbon in soil aggregate classes using a native forest as a reference; and (2) the interaction between edaphic mesofauna, SOC and aggregate carbon. This study was performed on Oxisol soil areas located in the municipality of Vitória da Conquista, Bahia, Brazil. The edaphic mesofauna was evaluated using the modified Berlese-Tullgren funnel method. Physical soil fractionation was carried out by wet sieving. The organic carbon contents of the soil and aggregates were determined by wet oxidation. Implantation of homogeneous Pterogyne nitens and Pinus caribaea stands causes a reduction in the edaphic mesofauna (abundance and average richness) and in the amount of soil macroaggregates. The differences between the forest systems are largely explained by the abundance of fauna, SOC and carbon of the macroaggregates, microaggregates and silt + clay. The edaphic mesofauna has a direct and positive influence on the SOC, which highlights its important role in regulating the soil carbon dynamics in the soil.

Particle size reduction along the digestive tract of fat sand rats (Psammomys obesus) fed four chenopods.

It is generally accepted that microbial digestion contributes little to digesta particle size reduction in herbivores, and that faecal particle size reflects mainly chewing efficiency, and may vary with diet. Nevertheless, a decrease in mean particle size (MPS) along the gastrointestinal tract (GIT) has been reported, especially in hindgut fermenters. However, to what degree the very fine particle fraction (non-food origin, especially microbes) affects MPS is unclear. Fat sand rats (Psammomys obesus, diurnal herbivores, n = 23, 175 ± sd 24g) consumed one of four chenopods (natural dietary items in the wild) for 30days. Digestibility was related negatively to dietary fibre content. We determined digesta MPS in the forestomach, glandular stomach, small intestine, caecum, colon and faeces by wet sieving, including (MPSfines) or excluding (MPSnofines) particles < 0.25mm. The proportions of fines were higher and of MPSfines were correspondingly lower in GIT sections that harbour microbes (forestomach, hindgut), whereas MPSnofines did not differ between forestomach and glandular stomach. However, MPSnofines decreased along the GIT, indicating MPS reduction due to digestive (enzymatic and microbial) processes. The four different diets led to different MPS, but the magnitude of MPS reduction in the GIT was not correlated with dietary fibre fractions or dry matter digestibility. These results indicate that within a species, MPS cannot be used as a proxy for diet quality or digestibility, and raise the hypothesis that MPS reduction along the GIT may be more pronounced in smaller than in larger mammalian terrestrial herbivores, possibly due to the fine initial particles produced by chewing in small species.

Study on soil compaction and its causative factors at apple orchards in the Weibei Dry Highland of China

AbstractThe aim of this study was to investigate the extent and causes of soil compaction of the apple orchards in the Weibei Dry Highland. Nine ‘Red Fuji’ apple orchards with number of planting years in the ranges of &lt;10‐year, 10–20‐year and &gt;20‐year were included. Soil bulk density, porosity, penetration resistance, organic matter (SOM), clay, water and soil aggregate size distribution were determined. The results showed that the subsoil (20–30 cm) of apple orchards was compacted. The bulk density and packing density (PD) of subsoil increased sharply by an average of 17.9% and 18.0%, respectively, relative to topsoil (0–10 cm), and the porosity decreased by 17.0%. The depths of the soil layer with penetration resistance exceeding 1,000 kPa became shallower with increased planting years. Compared with &lt;10‐year apple orchards, the bulk density, PD and soil penetration resistance in 10–20‐year and &gt;20‐year apple orchards were increased, respectively, by 5.3%, 5.3% and 29.3%, but the porosity decreased by an average of 8.2%. Compared with topsoil, the water‐stable aggregates of &gt;0.25 mm and the mean weight diameter of wet sieve aggregates (MWDW) of compacted soil were 57.6% and 25.4% lower, respectively. Soil clay content increased with soil depth from 0 to 60 cm, but the SOM showed an opposite trend. Additionally, there was a dry soil layer at a depth of 20–40 cm. Thus, the factors affecting the soil compaction process were determined to be inferior agglomeration ability of soil, internal soil desiccation, and the downward migration of soil clay particles.

Critical review on microplastics in fecal matter: Research progress, analytical methods and future outlook.

There has been an ever-increasing attention over years for investigating microplastics in feces of lower to higher trophic organisms from diverse environments. Focusing on the standardization of methodologies for reliable generation and comparison of data is one of the important aspects in microplastic area. This first review, comprising 20 studies in total, critically summarizes and compares the methodological approaches for the determination of microplastics in feces as well outlines the levels and characteristics of microplastics detected in feces worldwide. Contaminations and QA/QC measures are also discussed. Despite variations among the approaches, most studies (n=12) described herein rely on the digestion processes involving H2O2 (n=7) and KOH (n=6) for the separation of microplastics, whereas very few included wet sieving (n=5), density separation using NaCl (n=3) and NaI (n=1) and enzymatic digestion (n=2). Microscopical sorting and spectroscopic methods such as infrared and Raman were combined for identification and characterization of microplastics. The detected microplastics varied by size, shape, color and polymer types and the differences in reporting units of microplastic abundance make comparison across studies difficult. Taking advantage of the current knowledge, our review identified analytical challenges and suggested appropriate methods on research into microplastic contamination in feces. This work will serve as a valuable information of available analytical methods for examining microplastics in feces and will stimulate further research to advance our understanding of microplastics from feces.

Stability of Aggregates Made by Earthworms in Soils with Organic Additives

Earthworm activity is a key factor in creating soil aggregates, but introduced organic matter and abiotic factors are also equally important. The purpose of this study was to investigate the stability of aggregates made by earthworms in soils with organic additives. Additionally, the two aggregate stability measurement methods were compared: (i) the wet-sieve method and (ii) the laser diffraction method. A six-month container experiment containing sixteen treatments and controls were made. Each treatment included one of four types of soil texture: sand, loam, silty loam and clay, and one of four additives: straw, peat, compost and compost with added microorganisms. To each treatment, six earthworms were added, two each of species commonly occurring in Polish soils: Dendrodrilus rubidus, Aporrectodea caliginosa and A. rosea. This study confirmed that earthworm activity was the factor favoring aggregate formation. In terms of the investigated organic additives, the efficiency of aggregate creation was as follows: compost with active bacteria, compost, peat and straw. Nevertheless, earthworms alone, without the addition of an organic additive, did not form permanent aggregates. The wet sieving and laser diffractometry methods of measuring aggregate stability were comparable for silty, clayey and loamy soils.

Effect of soil internal forces on fragment size distributions after aggregate breakdown and their relations to splash erosion

AbstractSoil aggregate breakdown is the key step of splash erosion. Recent studies have shown that it is the soil internal forces that induce aggregate breakdown and subsequent splash erosion. However, little is known about the size characteristics of soil aggregate breakdown and corresponding effects on splash erosion. In this study, Cinnamon soil and Heilu soil were adopted to investigate the effects of soil internal forces on the characteristics of aggregate fragments and splash erosion through wet sieving and rainfall simulation. The results showed the following. (1) With a decrease in electrolyte concentration in soil solution, soil net repulsive force increased; meanwhile, aggregate stability decreased and splash erosion rate increased. Additionally, when the electrolyte concentration was less than 10−2 mol L−1, soil net repulsive force hardly changed, and aggregate stability and splash erosion rate accordingly varied very little. (2) With the increase in the soil net repulsive force, the content of fragments &lt;0.053 mm released from aggregates increased, whereas the content of fragments &gt;0.25 mm decreased, thus suggesting that the aggregates tended to break into fine fractions as soil net repulsive forces increased. (3) Regression analyses showed that soil splash erosion rate decreased linearly with increases in the aggregate stability; moreover, correlation analyses showed that splash erosion rate was significantly and positively correlated with the fragments with a diameter of &lt;0.053 mm, and negatively correlated with the fragments with a diameter of &gt;0.25 mm. This study suggests that soil internal forces induce the aggregate crush and determine the size distribution of fragments available for mobilization by the raindrop impact force. Also, the raindrop impact force is the driving mechanism leading to the movement of fragments. This study provides new insights into the mechanism responsible for splash erosion and could be valuable for controlling soil erosion.Highlights Soil aggregates breakdown dynamics and splash erosion were quantitatively investigated. Soil internal forces determined the size distribution of fragments after aggregates breakdown. The movement of soil fragments largely depended on raindrop impact force. Splash erosion was driven by the soil internal forces and raindrop impact force.

Preparation of a reference material for microplastics in water\u2014evaluation of homogeneity

Validation of analytical methods for measurements of microplastics (MP) is severely hampered because of a general lack of reference materials, RM. There is a great need to develop such reference materials. This study presents a concept of three-component kit with immobilised MP in solid NaCl, a surfactant and clean water that can be applied for the production of many types of MP RMs. As proof of concept, an RM for polyethylene terephthalate (PET) particles in water was prepared and evaluated for its homogeneity. The particles ranged from 30 μm (Feretmin) to about 200 μm adapted by wet sieving. A specific number of PET particles were immobilized in about 0.29 g of solid NaCl by freeze-drying 1 mL of a NaCl suspension. By using manual and automated counting, twenty reconstituted 1-L water samples were evaluated for homogeneity with respect to number of PET particles from 30 μm to > 200 μm/L of water. The number of particles was 730 ± 120 (mean ± one standard deviation (SD); n = 10) and 865 ± 155 particles (n = 10) obtained by optical microscopy in two independent laboratories. This corresponded to relative SDs of 16.4 and 17.9% and a mean of 797 ± 151 particles (18.9% RSD, for n = 20). Homogeneity studies of the NaCl carrier without reconstitution resulted in 794 ± 60 particles (7.5% RSD). The homogeneity of PET in the salt carrier was also evaluated directly with respect to mass of PET per vial using an ultra-micro balance. An average mass of 293 ± 41 μg of PET was obtained (14, % RSD for n = 14). Micrographs were recorded to demonstrate the absence of major sources of contamination of the RM components. Information about the particle size distribution and particle shapes was obtained by laser diffraction (LD) and dynamic image analysis (DIA). In addition, the identity of the PET polymer was confirmed by Raman and FT-IR spectroscopy. The RM was developed for a large-scale inter-laboratory comparison of PET particles in water (ILC). Based on the homogeneity results, the material was found to be sufficiently homogeneous to be of meaningful use in the ILC. In a 3-day process, more than 500 samples of PET particles in the NaCl carrier were prepared with good potential for further upscaling with respect to the number of vials or with other kinds of polymers. The stability of PET was not evaluated but it was deemed to be stable for the duration of the ILC.

Fundamental physico-chemical and mechanical analysis of different clay types

Clay plays an important role in the most of industries that related with water treatment and food stowage industries. The adequate physic-chemical properties are the most recognized factor for the wide range of applications. The investigation of the fundamental physic-chemical and some mechanical properties of such clay is an insistent task before the selection of some material for some specific role. The analysis of the fundamental physic-chemical and grain size analysis of grain sizes of three different types of selected clays were the aims and objectives of the existing research. Clay samples were collected from three different locations in Sri Lanka and they were stored well. The clay samples were named as anthill clay, brick clay and roof tile clay. Some potion from each clay sample was separated and such separated clay samples were oven dried for 24 hours under the temperature 110°C. Each of dried clay sample was separated again and the separated portions were prepared for the test of moisture content, dry sieve analysis and wet sieve analysis. As the major results of the experiment, especially there were obtained 14.49%, 21.45% and 25.97% moisture contents with respect to anthill, brick and roof tile clays, well-graded particle arrangement in roof tile clay, gap graded particle arrangement in anthill clay and uniformly graded particle arrangement in brick clays. In addition, according to the obtained results there were seen the finer particle weight percentages as 59.90%, 37.36% and 72.38% with respect to anthill clay, brick clay and roof tile clay.

Stability of artificial soil aggregates for cut slope restoration: A case study from the subalpine zone of southwest China

The stability of soil aggregates is regarded as the key factor for soil erosion resistance on cut slopes of engineering works in serious debris flow disaster areas. Information on the stability of soil aggregates and related physicochemical properties on cut slopes is helpful to maintain the soil quality and slope stability. Therefore, in order to evaluate the stability of artificial soil aggregates for cut slope restoration, soil samples from three positions of a cut slope restored with artificial soil (upper slope, URS; middle slope, MRS; lower slope, LRS) and a nearby natural slope (NS) were analyzed. The results showed that the stability of soil aggregates (MWD, mean weight diameter; GMD, geometric mean diameter) of artificial soil on the cut slope (URS, MRS, LRS) was significantly lower than that of NS based upon fast wetting (FW) test and wet sieving. The values of MWD and GMD for slow wetting (SW) and mechanical breakdown (WS) tests in the four slopes had no significant difference. Among the three positions of cut slope, URS had the highest MWD and GMD, whereas MRS had the lowest corresponding value. Furthermore, >2 mm soil aggregates accounted for a major percentage of the total weight determined in all the tests for each slope. MWD for fast wetting increased with the increase in content of soil organic matter (SOM). Slaking was the main disruptive force leading to the breakdown of artificial soil aggregates, and FW was the best method to measure the stability of soil aggregates in these conditions. These results demonstrate that the SOM and the stability of soil aggregates on cut slope should be given more attention while conducting engineering works in serious debris flow disaster areas.