Aggregate Particle Size Research Articles

Effect of Coarse Aggregate Size on the Performance of PE/HPP Hybrid Fiber Concrete

Three kinds of continuously graded coarse aggregates with maximum particle sizes of 10mm, 16mm and 20mm were selected from pebble and gravel respectively, then, Slump test, compressive strength test and bending toughness test were carried out to study the influence of maximum particle size of coarse aggregate on the workability, compressive strength, wear resistance and bending behaviour of PE/HPP hybrid fiber concrete. The results show that with the increase of the maximum particle size of coarse aggregate, the work performance, compressive strength and bending toughness of hybrid fiber concrete are improved.

Insight into the aggregation and phase behavior for aqueous solution of ethylene glycol monobutyl ether with self-assembly induced optical and electrical properties

Ethylene glycol monobutyl ether (EGMBE) is a polar small molecule with amphiphilic characteristics, which can form various aggregates in aqueous solution. The solubility of EGMBE decreases as the temperature increasing with a lower critical solution temperature (LCST). The influence of temperature and salinity on aggregation behavior and solubility of EGMBE were thoroughly investigated in this paper. The phase transition temperatures of EGMBE aqueous solutions with different concentrations were determined and compared with literature. The completed phase diagram of the ternary system (water + NaCl + EGMBE) was constructed. The measured liquid-liquid equilibrium (LLE) data can be well fitted to the commonly used empirical equations Othmer–Tobias, Bancroft and Setschenow. The dynamic light scattering (DLS) measurement shows that the particle size of EGMBE aggregates increases with increasing concentration, reaching its maximum at EGMBE mass fraction of about 30 %. Increasing temperature and inorganic salt concentration can both promote the increase of particle size, especially when approaching the phase separation point, the particle size increases sharply, and the corresponding viscosity of EGMBE solution abnormally increases with increasing temperature. The Tyndall effect of EGMBE solution was also observed to be most significant at mass fraction around 30 %. It is interesting to note that the conductivity of EGMBE solution increases with increasing concentration, reaching its maximum value when the EGMBE mass fraction is about 30 %, though EGMBE is not conductive. The investigation of pyrene fluorescence probes and surface/interfacial tension also demonstrated the aggregation and surface adsorption of EGMBE.

Contribution of soil aggregate particle size to organic carbon and the effect of land use on its distribution in a typical small watershed on Loess Plateau, China

Soil organic carbon (SOC) is an important pool in the global carbon cycle, playing a vital role in moderating atmospheric CO2 concentrations. Soil is the largest carbon pool in terrestrial ecosystems and, as the basic unit of soil structure, soil aggregates are key to protecting soil carbon pools. However, the influence of soil aggregate particle size, SOC distribution, and the contribution of different particle sizes to SOC is still unclear, particularly under different land use types. In this study, soil samples were collected from five land use types (slope farmland (SF), forest (FL), grassland (GL), shrubland (SL), and terraced field (TF)) in a typical small watershed in the Loess Plateau, China. We analyzed the soil aggregate particle size, composition, and stability after dry and wet sieving, SOC content of different particle sizes in aggregates, and the effects of different aggregate particle sizes and land use on the distribution of SOC. The results showed that, the surface soil (0 ∼ 20 cm) water-stable aggregates were relatively stable, particularly under FL, the mean weight diameter (MWD) value was 2.16 mm. Deep soil (40 ∼ 60 cm) non-water stable aggregates were more stable, and GL was optimal, the MWD value was 3.94 mm. SOC and total nitrogen (TN) were significantly correlated with water-stable aggregate stability indicators (p < 0.01). The SOC content in the small aggregates (0.25 ∼ 2 mm) was the highest and lowest in the microaggregates (<0.25 mm) under different land use. The carbon/nitrogen (C/N) ratio of microaggregates was significantly higher in SF (the C/N ratio was 23.17) and GL (the C/N ratio was 31.04) than in other land uses (p < 0.01) in the 20–40 cm soil layer. In surface soil, small aggregates contributed>50% to SOC in SF and TF. In deep soil, small aggregates under all five land uses made the largest contribution rate to SOC at 57%. These findings indicate that carbon sequestration in the study area can be improved by a combination of appropriate soil management with ecological construction to increase the content of small aggregates, strengthen the fixation and protection of SOC, and reduce carbon emissions in the soil.

Influence of Deicer on Water Stability of Asphalt Mixture under Freeze–Thaw Cycle

In seasonal frozen soil areas, the repeated freeze–thaw cycle of internal moisture in asphalt mixture in winter and spring will accelerate the peeling of asphalt film and aggravate the water damage of asphalt pavement. It is of great significance to carry out the attenuation law of mechanical properties of asphalt mixture under freeze–thaw cycles to prevent and reduce the economic losses caused by water damage to asphalt pavement. This study will investigate the impact of deicer application on the water stability of asphalt mixtures within the climatic conditions prevalent in Northwest China. Specifically, freeze–thaw cycle tests were administered to two types of dense-graded asphalt mixtures under three distinct deicer solutions and three disparate low-temperature environments. The Marshall water immersion test and freeze–thaw splitting test were employed to evaluate the water stability of asphalt mixtures subject to multiple factors, and the relative importance of each factor was statistically analyzed using the acquired data. Results demonstrated that AC-13 and AC-16 asphalt mixtures (AC is asphalt-concrete, which is asphalt concrete, and 13 or 16 represents the maximum particle size of aggregate (13 mm or 16 mm)), saturated in 15% CH4N2O, 20% NaCl, and 20% CH2CH3OH solutions, underwent a varying number of freezing–thawing cycles (0, 5, 10, 15, 20, 25, and 30) at temperatures of −5 °C, −15 °C, and −25 °C, respectively, displayed a discernible decline in their residual stability MS0 and freeze–thaw splitting tensile strength ratio TSR. This decline was particularly marked when temperatures dropped below the solution’s freezing point. Disregarding the fixed factors of weather variation (different low-temperature environments) and road service duration (number of freezing–thawing cycles), the aggregate grading imposed a more pronounced influence on asphalt mixture water stability than the presence of deicers.

High-performance artificial aggregate prepared with recycled concrete powder and its impact on concrete properties

Given the pollution of waste concrete powder, low utilization rate, sand and stone resources shortage, and poor performance of artificial aggregate, the high-performance artificial aggregate was prepared by high dosage recycled concrete powder (RCP). The effects of curing methods, RCP grinding time, RCP:slag ratio, Na2O dosage, and Na2SiO3 modulus on the properties of the aggregate were studied. The results show that natural curing is the most effective, and the best-performing aggregate was obtained with an RCP grinding time of 40 min. The particle size coefficient of the aggregate was around 1.3, and increasing the proportion of slag increased the content of large particles. The amounts of slag and Na2O had a significant impact on the aggregate. As the amounts of slag and Na2O increased, the amount of C-(A)-S-H gel increased, the microstructure improved, and the macroscopic manifestations increased apparent density and strength and reduced water absorption. The maximum strength of the aggregate reached 8.59 MPa, and water absorption was 12.67% at this point. Concrete was prepared using the aggregate above, and the effects of aggregate curing time, aggregate pre-wetting time, and aggregate material ratios on the properties of the concrete were studied. The results show that the density of RCP artificial aggregate concrete is low, between 2030 kg/m3-2220 kg/m3. The compressive strength and splitting tensile strength of concrete increase with the increase of aggregate curing time, prewetting time, and the dosage of aggregate Slag and Na2O, which reach 59 MPa and 4.5 MPa, respectively. The aggregate strength increased, leading to interfacial failure inside the concrete, while larger aggregate particle size tended to cause aggregate failure inside the concrete.

Effects of Hydraulic Erosion on the Spatial Redistribution Characteristics of Soil Aggregates and SOC on Pisha Sandstone Slope

Under the long-term effects of hydraulic erosion, soil particles and nutrients are continuously lost and enriched in the process of runoff and sediment movement, leading to a change in soil organic carbon (SOC) in different spatial positions on the slope, which is closely related to the carbon balance of the ecosystem. Therefore, the changes in slope erosion intensity and the spatial redistribution characteristics of soil aggregates and SOC under water erosion conditions were quantitatively analyzed by combining field runoff plots with three-dimensional (3D) laser scanning technology. The results showed that: (1) After rainfall, the slope erosion intensity successively declined from the upper to the lower parts of the slope, and the content of soil aggregates in each soil layer changed obviously. The loss of 1–2 mm soil aggregates was the largest in the sedimentary area of the 2–4 cm soil layer, at 0.38 g/kg. The concentration of 0.5–1 mm soil aggregates was the largest in the micro-erosion area of the 2–4 cm soil layer, at 0.36 g/kg. (2) After rainfall, the overall SOC on the slope showed a loss state in the 0–2 cm soil layer and an enrichment state in the 2–4 cm soil layer. Among them, the loss of SOC in the medium erosion area of the 0–1 cm soil layer was the largest, and its content decreased by 57.58%. The enrichment in the 2–4 cm soil layer was the maximum in the micro-eroded area, with a content increase of 79.23%. (3) Before and after rainfall, the SOC of each soil layer was positively correlated with small aggregates, and the correlation gradually tended to be negative with the increase in the particle size of soil aggregates, and the SOC showed a negative correlation with large aggregates (&gt;2 mm).

Experimental Study on the Mechanical Properties and Influencing Factors of Glass Fiber-Reinforced Permeable Concrete.

In order to improve the mechanical properties and deformation characteristics of permeable concrete, glass fiber was added to this type of concrete. Based on an unconfined compressive strength test, non-contact full-field strain measurement system, and scanning electron microscopy test, the effects of aggregate particle composition, shaking time, fly ash content, fiber length, and fiber content on the strength and permeability of permeable concrete were studied. The results show that the strength and water permeability of permeable concrete are negatively correlated with an increase in shaking time. When the aggregate particle size is 5-10 mm, the permeable concrete has both good strength and permeability. Proper incorporation of fly ash improves the compactness inside the structure. The influence of different lengths of glass fiber on the strength of permeable concrete first increases and then decreases, and the permeable property decreases. With the same fiber length, the strength increases first and then decreases with an increase in the content, while the porosity and water permeability coefficient decrease. Under the test conditions, when the length of glass fiber is 6 mm, and the dosage is 2 kg/m3, the strength performance of permeable concrete is the best, and the permeability effect is good at the same time.

Influence of gradation on extrusion-based 3D printing concrete with coarse aggregate

Coarse aggregate is an indispensable component of concrete, the gradation of which plays an important role in the properties of concrete due to its effect on particle distribution. The extrusion-based 3D concrete printing (3DCP) has become a promising technology while the influence of coarse aggregate gradation on the material design and performance of 3D printed concrete still lack understanding. This study experimentally investigates the fresh and hardened properties of 3D printed concrete with 4.75–20 mm continuous and discontinuous grading coarse aggregates, including flowability, buildability, axial compression, and drying shrinkage. The results reveal that 3D printed concrete with continuous grading performs better on flowability retaining and multilayer structure stacking than that with discontinuous grading. The evaluation coefficient of aggregate particle size is proposed to characterize the average particle size of coarse aggregates with different gradations, which shows linear relationship with coarse aggregate 3D spacing in 3D printed concrete. The current axial compressive stress–strain model for the conventional concrete prediction curve is modified to predict the effect of coarse aggregate gradation on constitutive relationship of 3D printed concrete. The increasing proportion of large-sized coarse aggregates can lead to a reduction in long-term drying shrinkage of 3D printed concrete.

Study on Correlations between Tailings Particle Size Distribution and Rheological Properties of Filling Slurries

The influence of the mass concentration and particle size distribution on rheological parameters and slump was investigated by analyzing the mixture of overflow tailings (OT) and classified tailings (CT). The correlation between the rheological parameters, slump and characteristic value of the tailings particle diameter was discussed. Finally, the ratio parameters of a mixed tailings filling slurry were optimized using a lead–zinc mine in Guangdong, China as the engineering background. The results showed a quadratic decrease in the slump of the tailings slurry as the mass concentration increased, while the slump decreased with a decreasing particle size. With the increase in the mass concentration, the yield stress of the tailings slurry follows a quadratic function, while the plastic viscosity exhibits linear growth. The influence of tailings fine particles on the sensitivity of the yield stress and plastic viscosity to the mass concentration is reduced as their content increases. The yield stress and plastic viscosity of the tailings slurry exhibit a quadratic function decrease and linear growth as the slump increases. The slump of the tailings slurry is related to the particle size characteristic value and the mass concentration of the slurry. The correlation coefficient between the yield stress and the aggregate characteristic particle size increases most obviously at d10~d50, and the increase in the characteristic particle size will enhance the correlation between the yield stress and particle gradation. The correlation coefficient between the plastic viscosity and aggregate particle gradation parameters exhibits an initial increase followed by stabilization with an increasing characteristic particle size, with the most significant increase observed at d10~d50.

Mix design optimization of high-performance concrete using local materials

In this paper, twelve different concrete mixes made from local materials were studied with a view to determining which of the mix designs will produce high-performance concrete. Varied water-cement ratios (w/c) of 0.3, 0.35, and 0.4 were studied with different combinations of particle sizes of coarse aggregates. Twelve concrete mixes were then produced, cast, and cured for 7, 14, 21, 28, 45, and 90 days. Superplasticizer was used to facilitate the workability of the concrete mixes. A slump test was first conducted on the fresh concrete to determine its workability, while compressive, flexural, and tensile strength were determined at the end of each curing age in accordance with relevant standards. The results shows that slump value increased with an increase in w/c ratio, while the concrete with 100% 10 mm particle size coarse aggregate had a minimum slump of 24, 37, and 50 mm at w/c of 0.3, 0.35 and 0.4 respectively, but higher slump values of 70, 76 and 83 mm were obtained with concrete containing larger particle sizes combination i.e. 25% of each of 10, 12, 15 and 19 mm sizes. But strengths reduced with an increase in w/c and aggregate particle sizes. Concrete produced with w/c of 0.3 and 10 mm coarse aggregates had a strength of 52.22N/mm2 at 28 days, which was about 126% of other strengths obtained from other mixes. Statistical models were then proposed to predict the strength of the best-performed concrete mix. The study concluded that it was possible to produce high-performance concrete using local materials, if the mix is properly optimized.

Comparative analysis of fracture characteristics between rock and rock-like materials

In order to investigate the characteristics of rock and rock-like materials during the fracture process, notched semi-circular bending (SCB) experiments of 3 rocks and 2 rock-like materials were conducted in this paper. The process of the crack mouth opening was measured with a clip gauge. Acoustic emission was used to analyze the damage and failure mode of the specimens. Meanwhile, the fracture process zone (FPZ) was analyzed with the digital image correlation (DIC). Finally, the differences in the fracture process between rocks and rock-like materials were observed with a polarized microscope, and the formation mechanism of FPZ was discussed. The results indicate that the sequence from brittleness to plasticity is gypsum, marble, granite, concrete and fine sandstone. The crack opening velocity of gypsum, marble, and granite reaches 0.02–0.025 mm/s, far exceeding that of sandstone and concrete at 0.003 mm/s and 0.005 mm/s. The stronger the brittleness of geomaterials, the less significant their acoustic emission effect. Only a few acoustic emissions occur during the fracture process of gypsum with 8 hits. Its fracture occurs instantaneously rather than through a process of damage to fracture and the failure mode is tensile failure. Sandstone has the strongest plasticity, with a large count of acoustic emissions before and after fracture, with a hit number of 5062, which is 630 times of pure gypsum. The fracture is a process of damage accumulation with 94% of sandstone, 89% of concrete, 80% of granite, and 60% of marble showing a tensile and shear failure mode except gypsum. In addition, the stronger the brittleness of geomaterials, the smaller their FPZ size. The FPZ of gypsum is only about 3 mm, which can be considered as lacking, while other materials are about 6–11 mm. The formation of FPZ depends on whether an interlocking structure can be formed inside the material, which is related to the base material and crystalline or aggregate particle size.

Effect of mix design parameters on the behavior of compression cast concrete

Compression casting is a novel method for producing high-performance concrete. However, the optimal mix design parameters for normal concrete (NC) may not be suitable for compression cast concrete (CCC) due to the high compression pressure involved during casting. This study addresses the lack of research on CCC mix design and examines the influence of different parameters, including aggregate gradations, maximum particle size, sand ratios, and water-to-cement (w/c) ratios, on the performance of NC and CCC. Fourteen groups of concrete samples were prepared with varying aggregate grading, particle sizes, sand content, and w/c ratios. The density, compressive strength, elastic modulus, peak strain, and stress-strain behavior were analyzed. CCC specimens exhibited superior stress-strain relationships compared to NC specimens. CCC can be produced with different aggregate gradings and particle sizes. Notably, CCC specimens with a maximum aggregate size of 25 mm and no particles between sizes 5 mm and 9.5 mm (grading - 4) demonstrated the highest compressive strength and elastic modulus. CCC specimens with a sand ratio of 38% outperformed those with ratios of 28% and 48%. Increasing the w/c ratio showed similar stress-strain behavior for both NC and CCC specimens. This study proposes relationships between the properties of NC and CCC based on the findings. The results provide valuable theoretical and experimental insights for engineering applications involving CCC, considering different aggregate grading, particle size, sand ratio, and w/c ratio combinations.

Effect of SiO2 surface modification on the filler‐reinforced interfaces in SiO2‐filled functional styrene butadiene rubber composites

AbstractSilicon dioxide (SiO2), commonly known as silica, the surface is modified using bis(3‐triethoxysilylpropyl) tetrasulfide, also known as (Si69) and polyethylene glycol (PEG). A series of composites are prepared by mixing general solution styrene butadiene rubber (GSSBR) and polyethylene oxide‐functionalized solution styrene butadiene rubber (FSSBR) with unmodified and modified SiO2. A comparative analysis is conducted using various characterization techniques to evaluate the performance of different composites regarding rubber‐filler dispersion, thermal and dynamic mechanical properties. Field emission scanning electron microscopy demonstrates that FSSBR/SiO2@Si69 facilitates a more uniform and well‐dispersed distribution of silica particles, improving the compatibility between the rubber‐filler matrix and reducing the size of particle aggregates. Thermogravimetric analysis shows that composites GSSBR/SiO2@PEG and GSSBR/SiO2@Si69 + PEG and FSSBR/SiO2@Si69 possess superior thermal stability with minimal weight loss. According to the rubber process analyzer (RPA) analysis, FSSBR/SiO2@Si69 results in significantly reduced Payne effect values, indicating improved dispersion of the rubber‐filler mixture. These findings suggest that the simultaneous functionalization of SSBR and surface modification of SiO2 effectively enhance the interaction between filler and rubber.

Mechanism of nanoparticle aggregation in gas-liquid microfluidic mixing

Using gas-liquid segmented micromixers to prepare nanoparticles that have a homogeneous particle size, controllable shape, and monodispersity advantages. Although nanoparticle aggregation within a microfluid has been shown to be affected by the shear effect, the shear effect triggering conditions in gas-liquid two-phase flow is unclear and the aggregation behavior of nanoparticles under the shear effect is difficult to predict, resulting in uncontrollable physical and chemical properties of nanoparticle aggregates. In this study, a numerical simulation of nanoparticle aggregation in gas-liquid two-phase flow under the shear effect is performed using the CFD-DEM method. Then, the effects of total flow rate, gas-liquid two-phase flow ratio, and particle volume fraction on particle aggregation were analyzed to achieve control of particle aggregation shape and size. Meanwhile, the triggering mechanism of the shear effect and the mechanism of the shear effect on the aggregation of nanoparticles were clarified. The results show that increasing the total flow rate or decreasing the gas-liquid two-phase flow rate ratio can induce the shear effect, which reduces the particle aggregation size and makes the morphology tend to be spherical. Moreover, increasing the particle volume fraction, and total flow rate or decreasing the gas-liquid two-phase flow rate ratio also increases the number of particle collisions and induce interparticle adhesion. Hence, particle adhesion and the shear effect compete with each other and together affect particle aggregation.

Afforestation Influences Soil Aggregate Stability by Regulating Aggregate Transformation in Karst Rocky Desertification Areas

Surface vegetation has a substantial impact on soil aggregate stability, which is an important indicator of soil quality. However, there is still limited research on the response of soil aggregate stability indicators and the organic carbon, total nitrogen, and total phosphorus content in soil aggregates for different vegetation patterns in rocky desertification fragile ecological areas. Therefore, in order to study the effects of different vegetation restoration models on soil aggregate stability and aggregate related nutrient content and their promoting relationships in the karst rocky desertification areas in southwest China, soil samples under three artificial restoration vegetation measures (Juglans regia L.-Rosa roxburghii Tratt., Rosa roxburghii Tratt.-Lolium perenne L., Juglans regia L.-Lolium perenne L.) were collected in 0–10 cm and 10–20 cm soil, and the traditional farmland (Zea mays L.) was used as the control, combined with dry and wet sieving experiments for the research and analysis. The results showed that there were significant differences in the distribution of aggregates and soil nutrients among the four types of plots. Compared with traditional agricultural land, artificial afforestation increased the content of soil large macroaggregates (LMAs) and decreased the proportion of microaggregates (MIAs) and silt+clay (SCA), which enhanced the soil aggregate stability and reduced the soil fragmentation and erodibility. The afforestation restoration increased the content of soil aggregate-related SOC, TN, and TP, and increased with the decrease in the aggregate particle size. Research has found that soil aggregate stability indicators are significantly influenced by the particle size distribution of soil aggregates. In the positive succession process of vegetation types, soil nutrient accumulation is controlled by changes in the soil aggregate particle size, which affects the soil aggregate stability and reduces soil erodibility, thereby protecting the soil nutrient loss. The composite management of forest and irrigation in degraded ecological areas has certain reference and indicative significance for ecological restoration in rocky desertification areas.

Effects of vegetation restoration on soil aggregates, organic carbon, and nitrogen in the Loess Plateau of China

Understanding the responses of soil aggregate stability and nutrient stoichiometry to vegetation restoration is essential for the ecosystem in the Loess Plateau, China. To explore the influence of vegetation restoration on soil aggregate stability and nutrient stoichiometry, we established a series of sample plots across five vegetation restoration types [sloping farmland (SFL), woodland (WL), grassland (GL), shrub land (SL), and terraced fields (TCE)], and measured the particle size distribution, stability, and organic carbon (OC) and total nitrogen (TN) content of soil aggregates. Vegetation restoration significantly affected particle size, stability, and OC and TN stocks of soil aggregates at depths of 0–40 cm. Compared with that in SFL, the quality fraction of macro-aggregates in WL, GL, SL, and TCE was 215.47%, 245.82%, 189.83%, and 95.06% greater, respectively, whereas the aggregate stability (indicated by the mean weight diameter) was 109.71%, 22.83%, 71.84%, and 77.67% greater, respectively. Vegetation restoration in WL, GL, and TCE significantly increased the OC content at 0–40 cm depth and the TN content at 0–60 cm depth. Aggregates > 0.25 mm dominated the particle size distribution in all vegetation restoration types, and had the highest OC and TN stocks; minor aggregates were the main source of OC and TN accumulation. A simulated rainfall experiment confirmed that an increase in soil aggregates (>0.25 mm) was associated with greater aggregate stability. Our findings suggested that soil aggregates > 0.25 mm are optimal for stabilizing soil aggregates, and increasing OC and TN stocks, in the Loess Plateau.

Effect of pore structure on compressive strength and permeability of planting recycled concrete

The relationship between strength, permeability, and pore structure of planting recycled concrete (PRC) was investigated using industrial computed tomography non-destructive testing technology and image analysis methods. An increase in the aggregate particle size and porosity increased the pore size and fractal dimension, and the relationship between the compressive strength and porosity conformed to the Ryshkewitch model. The fractal dimension had a weaker influence on compressive strength and permeability than did aperture size and porosity. Although vegetation growth reduced the compressive strength and permeability coefficient of PRC, the rainwater infiltration and vegetation compatibility of PRC was confirmed.

The seasonal movement of sediment-associated marine-derived nutrients in a morphologically diverse riverbed: the influence of salmon in an Interior British Columbia river

PurposeThis study (1) investigated the extent to which flocculation and the hydrological and morphological attributes of an interior salmon-bearing river regulate the seasonal storage of marine-derived nutrients (MDN) and (2) compared the contribution of MDN to the fine bed sediment relative to other nutrient sources to the river.MethodsPrevious research has determined that the co-existence of re-suspended fine sediment, generated by salmon redd construction, with salmonid excretion and decay products in the water column creates ideal conditions for the flocculation of these inorganic and organic particles. Stored and suspended fine bed sediment was sampled from seven sites with varying morphologies and bed substrate down the length of a large spawning river in the interior of British Columbia over a 12-month period. MDN contributions to the sediment was tracked using aggregated versus dispersed particle size, carbon-to-nitrogen ratios, stable carbon and nitrogen isotopes, and MixSIAR modeling.Results and discussion(1) There was a significant longitudinal spatial distinction of nutrient retention between sites upstream and downstream of a large seasonally inundated floodplain; (2) the MDN isotopic signal in the surficial stored bed sediment in this sample year was short term; and (3) upstream spawner numbers, substrate size, stream morphology, and discharge were relevant to both the magnitude and retention time of sediment-associated MDN.ConclusionA cumulative magnification of MDN was correlated with the distance from the headwaters and the number of upstream spawners. The relationship between MDN retention in interior rivers, and possible multi-year accumulation, was influenced by variability in channel morphology, substrate size, and the presence of an inundated floodplain halfway down the river.

Distribution and biodegradation of nonextractable polycyclic aromatic hydrocarbons in particle-size aggregates of field-contaminated soils

Distribution and biodegradation of nonextractable polycyclic aromatic hydrocarbons in particle-size aggregates of field-contaminated soils

Performance of atrazine adsorption behavior and microbial community structure in Mollisol aggregate fraction

Owing to complex pore systems and chemical substances, soil aggregates provide a spatially heterogeneous microenvironment for adsorption capacity and microbial survival. As the widely used pesticide in farmlands, atrazine environmental behavior is not well known at the aggregate scale. In this study, Mollisol soil samples were sieved into four aggregate-size classes: large macroaggregates (>2 mm, LMa), small macroaggregates (1–2 mm, SMa), microaggregates (0.25–1 mm, Mia) and primary particles (<0.25 mm, P). The pore characteristics of each aggregate fraction was visualized by non-invasive X-ray three-dimensional microscopic computed tomography (3D-CT) combined with pore network extraction. The adsorption kinetics of atrazine in each aggregate-size fraction can be described well by a pseudo-second-order kinetic model. The adsorption isothermal process of atrazine can be better fitted by the Langmuir isotherm model than Freundlich isotherm model. There was an obvious linear correlation between the maximum atrazine adsorption capacity and aggregate SOC content as well as TN. In addition, the abundance of bacteria, actinomycetes and anaerobic bacteria in P was totally higher than those in SMa and Mia. Although pH is strongly linked to the bacterial community in the aggregate fraction, aggregate particle size explained 18 % for shaping the microbial community. Therefore, chemical properties and pore characteristics of each soil aggregate fraction both contributed to performance of atrazine adsorption behavior and microbial community.