High Silt Research Articles

Sahilkent (Bafra, Samsun) yöresindeki alüvyal zeminlerin sıvılaşma potansiyelinin CPT verileri kullanılarak araştırılması

In this study, liquefaction potential of the alluvial soils consisting of clay, silt, and sand sized materials in Sahilkent (Bafra, Samsun) area was investigated using CPT data. Within the scope of the study, 20 boreholes each having a depth of 15 meters were drilled throughout Bafra district, and one undisturbed soil sample were obtained per meter from 5 of these boreholes located in Sahilkent area. Wet sieve, hydrometer, plastic limit, liquid limit, and natural water content determinations were conducted on 20 samples with high silt and sand content. In the preliminary evaluation, it was determined that there is a liquefaction potential in some regions at different depths, and in order to perform detailed liquefaction analyses, 15-meter-deep CPTu were carried out in 1 meter distance from those 5 borehole locations. In CPTu tests, data including cone tip resistance, sleeve friction, effective stress, relative stiffness, etc. were recorded every 5 cm, and average values of these data for each meter depth were used in the liquefaction analysis. Liquefaction analyses was conducted for an earthquake scenario of Mw = 7.2 and the liquefaction potential of the 15-meter soil layer in the study area was determined. As a result of the analyses, it was determined that no liquefaction will occur for an earthquake scenario of Mw = 7.2 in Sahilkent region. It is thought that high fine-grained content of the alluvium, and the fact that existing clean sand levels are located between fine-grained soil layers increase the resistance of the soil against liquefaction.

Study on Volume Reduction of Cesium Contaminated Soil by High Gradient Magnetic Separation: Design of Magnetic Filters

The superconducting magnetic separation was examined to reduce the volume of cesium contaminated soil by the Fukushima Daiichi nuclear power plant accident. By using superconducting high gradient magnetic separation, silt and clay with high radioactive concentration due to the large particle surface area per unit mass can be further separated into high-dose 2:1 type and low-dose 1:1 type clay minerals selectively. Here, we examined filter conditions to improve the magnetic separation performance in farmland soil that is rich in organic matter. The results of magnetic separation of uncontaminated soil suggested that the separation selectivity of 1:1 and 2:1 type clay minerals was larger with the filters with smaller wire diameter. On the other hand, it was found that it was difficult to magnetically separate 0-20 μm particles even with the filters with small wire diameter and high selectivity. To solve this problem, magnetic separation was performed under the same conditions on actual contaminated soil that was highly classified into 0-20 μm and 20-75 μm particles. As the result, it was found that the radioactivity can be further reduced by removed high-dose 0-20 μm particles and targeting the 20-75 μm particles.

Impact of no-tillage on water purification and retention functions of soil

There are still uncertainties regarding the long-term impact of no-tillage farming practices on separate soil functions in the United Kingdom. This paper aimed to evaluate the chemical and physical processes in two different agricultural soils under no-tillage and conventional management practices to determine their impact on water related soil functions at field scale in the United Kingdom. The field-scale monitoring compares two neighboring farms with similar soil and topographic characteristics—one of the farms implemented no-tillage practices in 2013, while the second farm is under conventional soil management with moldboard plowing. Two soil types were evaluated under each farming practice: (1) a free-draining porous limestone, and (2) a lime-rich loamy soil with high silt and clay content. Field monitoring was undertaken over a two-year period and included nutrient analysis of surface and subsurface soil samples, bulk density, soil moisture, infiltration capacity, surface runoff, and analysis of phosphorus (P) and suspended solids in watercourses in close proximity to the test fields. The conversion to no-tillage changed the soil structure, leading to a higher bulk density and soil organic matter content and thereby increasing the soil moisture levels. These changes impacted the denitrification rates, reducing the soil nitrate (NO₃) levels. The increased plant material cover under no-tillage increased the levels of soil phosphate (PO₄^3–) and PO₄^3– leaching. The extent to which soil functions were altered by farming practice was influenced by the soil type, with the free-draining porous limestone providing greater benefits under no-tillage in this study. The importance of including soils of different characteristics, texture, and mineralogy in the assessment and monitoring of farming practice is emphasized, and additionally the between field and in-field spatial variability (both across the field and with depth) highlighted the importance of a robust sampling strategy that encompasses a large enough sample to effectively reveal the impact of the farming practice.

Initial soil aggregate formation and stabilisation in soils developed from calcareous loess

In soil, carbonates are important inorganic binding agents, controlling aggregate formation and soil structural stability. Until today, a clear understanding of the aggregate forming mechanisms in calcareous soil is missing. The objective of this study was to elucidate the initial aggregate formation in calcareous loess from the point when soil organic matter content was low and soil properties were mostly controlled by the parent material. We used a space-for-time chronosequence approach on agriculturally reclaimed loess soils in an open-cast lignite mining area in Garzweiler, Germany. We selected six time points from 0 to 24 years after reclamation in order to investigate the early processes of soil aggregate formation. Samples from two sampling depths (1–5 cm and 16–20 cm) were wet sieved into four size classes: silt- and clay-sized fraction (<63 µm), large microaggregates (63–200 µm), small macroaggregates (200–630 µm), and large macroaggregates (>630 µm). Each aggregate size class was characterized for soil organic carbon, total nitrogen and CaCO3 content. Organic matter amendment induced the formation of large macroaggregates (>630 µm), but we did not detect an accumulation of soil organic carbon neither in microaggregates nor in the silt- and clay-sized fraction. The silt- and clay-sized fraction contained large amounts of CaCO3 throughout the whole space-for-time chronosequence. This finding shows that in undeveloped loess material, microaggregation is controlled by cementation by carbonates inherited from the loess. These carbonates were likely easily dissolved during contact with water, therefore, aggregates in the early stage of soil development were not water-stable. Soil aggregate formation on young calcareous soils consists of two main mechanisms, 1. fresh soil organic matter predominantly contributes to macroaggregate formation, and 2. intrinsic cementing of loess through carbonates affects microaggregate stability. Therefore, the early stages of soil development in loess material do not show an aggregate hierarchy as we would expect in soils with high silt and clay content, such as Cambisols and Luvisols.

Physical and Mechanical Study of Palm Oil Fuel Ash (POFA) based Geopolymer as a Stabilizer for Soft Soil

Construction of structures on soft soil is a challenging task and considered as one of the biggest concerns in geotechnical engineering. Binders that are environmentally friendly such as fly ash based geopolymer have been explored widely. In this study, the agro-waste material, Palm Oil Fuel Ash (POFA) was used to produce an environmentally friendly geopolymer binder to be used in soft soil stabilization. POFA was used in three ratios; 10%, 20% and 30% of dry weight of soil to produce geopolymer. Sodium hydroxide (NaOH) was used as an alkali activator at 12 molarity along with sodium silicate (Na2SiO3). Physical properties of soil (Atterberg Limits, Plasticity Index, and Linear Shrinkage Limit) and compaction assessment; before and after mixing with the geopolymer binder were investigated. The studied soil was classified as an inorganic high plasticity silt (MH), according to the Unified Soil Classification System (USCS). From compaction results; optimum moisture content (OMC) values showed a decreased pattern from 24.7% to 17.5%; and maximum dry density (MDD) increased from 1.37 Mg/m3 to 1.73 Mg/m3 for geopolymer with POFA ranging from 0% to 30% of the dry weight of soil, respectively. The optimum dosage of POFA based geopolymer was found to be 30% according to all tests mentioned. These properties suggest the potential use of the agro-waste based geopolymer binder to stabilize the soft soil.

Assessment of Some Geotechnical Properties for Soils of Euphrates River Banks (Kufa- Mishkhab), Middle of Iraq

Twelve stations in the cities of Kufa and Mishkhab were selected for studying the geotechnical, including physical, engineering, chemical and mineralogical, properties of soils in the river banks along the Euphrates River. Grain size distribution of the bank soils showed higher silt than clay and sand percentages. Soil samples from the 12 stations were classified according to the USCS standards. Silt with low plasticity constituted 91% of the silt fraction, whereas that with high plasticity composed 9%. The saturated density values ranged between 1.75-2.073 g/cm3 with an average of 1.953 g/cm3, while the dry density values ranged between 1.307-1.740 g/cm3 with an average of 1.553 g/cm3. The values of the dry and saturated density are within the permissible limits. Direct shear test showed cohesion values (C) that ranged between 15-55 kN/m2 with an average value of 34.8 kN/m2. The values of the internal friction angle (Ø°) of the clay type of soil with low plasticity ranged between 8.5°-17° with an average of 9.91°. The Ø° values of the other soil types ranged between 9°-17° with an average of 25°. Therefore, clay with high plasticity had higher Ø° values than the permissible limits. The results of unconfined compression test showed a range of 22.802-58.587 kN/m2 with an average of 38.173 kN/m2, with water percentage of 30%. The mineralogical tests of the bank soil performed using XRD analysis showed that the analyzed soil samples are composed mainly of quartz, calcite, chlorite, palygorskite, and montmorillonites. The pH value ranged between 6.4-7.55 with an average of 7.10, indicating low basicity. Gypsum concentrations ranged between 0.049-12.75 % with an average of 3.99 %, while that for carbonate ranged between 5-45 % with an average of 26.16%. Sulphates concentration ranged between 0.23-5.93 % with an average of 1.85%. Several treatment measures are proposed to stabilize the soil of the studied area.

Experimental Study of the Dynamic Permeability in Two-Stage Gravel Packs Considering Particle Blockage and Remigration

Abstract The two-stage gravel-packing technique has been widely adopted in the development of unconsolidated sandstone reservoirs with high sanding rates and silt contents. Compared with the traditional gravel-packing operation, the lifespan and long-term conductivity of the two-stage gravel pack improve significantly. In the present study, an experimental study was undertaken to determine the dynamic permeability change of two-stage gravel packs during sand production. Thirty-nine groups of flooding tests were carried out with various experimental settings, and the pressure drop of each section (i.e., the sanding section, gravel bed I, and gravel bed II) was monitored dynamically during flooding. The permeability characteristics of each section were used to determine the mechanisms of sanding, pore blockage, and particle remigration under different packing arrangements. Using the proposed experimental setup, a sensitivity analysis was carried out to study the parameters that may affect the permeability of the sand pack, such as the two-stage gravel size, packing length, flooding rate, and silty sand content. Based on the observed permeability recovery phenomena in gravel bed I during the experiments, a dynamic permeability prediction model considering the remigration of deposited particles was proposed. Compared with the traditional deep-bed filtration model and the experimental results, the verification showed that the new model is more suitable for predicting the dynamic permeability of two-stage gravel packs.

Spatio-Temporal Characteristics of Drought Events and Their Effects on Vegetation: A Case Study in Southern Tibet, China

Frequent droughts in a warming climate tend to induce the degeneration of vegetation. Quantifying the response of vegetation to variations in drought events is therefore crucial for evaluating the potential impacts of climate change on ecosystems. In this study, the standardized precipitation index (SPI) was calculated using the precipitation data sourced from the China Meteorological Forcing Dataset (CMFD), and then the drought events in southern Tibet from 1982 to 2015 were identified based on the SPI index. The results showed that the frequency, severity, and intensity of drought events in southern Tibet decreased from 1982 to 2015, and the highest frequency of drought was found between 1993 and 2000. To evaluate the impact of drought events on vegetation, the vegetation characteristic indexes were developed based on the normalized difference vegetation index (NDVI) and the drought characteristics. The assessment of two drought events showed that the alpine grasslands and alpine meadows had high vegetation vulnerability (AI). The assessment of multiple drought events showed that responses of vegetation to drought were spatially heterogeneous, and the total explain rate of environmental factors to the variations in AI accounted for 40%. Among the many environmental factors investigated, the AI were higher at middle altitudes (2000–3000 m) than low altitudes (&lt;2000 m) and high altitudes (3000–4500 m). Meanwhile, the silt soil fraction in the upper soil layer (0–30 cm) had the greatest positive correlation with AI, suggesting that areas with a high silt soil fraction were more sensitive to drought. The relative contribution rates of environmental factors were predicted by a multivariate linear regression (MLR) model. The silt soil fraction was found to make the greatest relative contribution (23.3%) to the changes in AI.

Physical analysis of building materials with soil

Industrialization in construction has allowed the use of materials such as concrete and steel, these being essential for the construction of large buildings and structures, however, in some vulnerable areas, using this type of techniques and materials represents a high cost, due to which the traditional or vernacular architecture is a sustainable alternative. This research carries out a physical analysis of the materials used in the constructions on land that are developed in the municipality of Ocana, Norte de Santander, Colombia. The results obtained indicate that the soil used in the analyzed structures has a maximum density of 1.41 g/cm3 with a humidity percentage of 32.55%; likewise, in natural condition these soils have a liquid limit of 67.85 a limit plastic of 45.72 and a plasticity index of 22.13. In other words, the soil has characteristic plastic characteristics of a fine soil. This corresponds to the granulometric classification of the soil, which corresponds to a high plasticity Silt, which has sands with diameters between 395 μm and 76.1 μm. It also has a specific gravity of 2.65 g/cm3.

Fractal dimension of particle-size distribution and their relationships with alkalinity properties of soils in the western Songnen Plain, China

The purpose of this study was to identify the fractal dimension and their relationships with alkalinity properties of soils, and to evaluate the potential of fractal dimension as an indicator of alkalinity properties of soil. Six soils with an increasing salinity (electrical conductivity was 0.09, 0.18, 0.62, 0.78, 1.57 and 1.99 dS m−1, respectively) were selected from the western part of the Songnen Plain (China). Salt content, exchangeable sodium percentage, sodium adsorption ratio and other properties of the soils were determined and the soil particle-size distribution (0–2000 μm) was measured using a laser diffraction particle size analyser. Our results show that the overall fractal dimension of the selected soils ranged from 2.35 to 2.60. A linear regression analysis showed a significant negative correlation between fractal dimension and the amount of coarse sand and fine sand (r = − 0.5452, P < 0.05 and r = − 0.8641, P < 0.01, respectively), and a significant positive correlation with silt and clay (r = 0.9726, P < 0.01 and r = 0.9526, P < 0.01, respectively). Thus, soils with higher silt and clay content have higher fractal dimension values. Strong linear relationships between fractal dimension and salt content (P < 0.05), in particular a very significant positive relationship with HCO3− (P < 0.01), also exist. It is therefore possible to conclude that a soil’s fractal dimension could serve as a potential indicator of soil alkalization and the variability in alkaline soil texture.

Adsorption – Desorption Behavior of Penoxsulam Herbicide on Soils with Different Characteristics

ABSTRACT A safe use of herbicide in the environment can be assessed by it’s adsorption – desorption behavior in soil. In the present work laboratory studies were performed to examine adsorption-desorption behavior of penoxsulam herbicide on six soils having widely different properties. Adsorption kinetics of penoxsulam was best accounted by pseudo-first order model. Among acidic soils, soil having the lowest pH (5.36) showed highest partition coefficient (kd) whereas, in case of alkaline soils, soil of relatively less alkaline pH (7.88) and higher silt and organic content had higher kd value. The kd of penoxulam showed a highly significant and negative correlation with soil pH (r = −0.987, significant at p ≤ 0.01). Adsorption-desorption data fitted well to Freundlich isotherm model. Percent desorption of penoxsulam showed a highly significant and positive correlation with soil pH (r = 0.973, significant at p ≤ 0.01). Step-wise multiple regression analysis revealed that kd, Freundlich adsorption-desorption isotherm constants and hysteresis of penoxulam in soils could be successfully predicted by soil properties. The fourier transformed infrared spectral comparisons showed that adsorption of penoxsulam on soil occurred through H-bonding of several polar moieties with soil constituents besides a likely complex reaction of triazole group with some transition metals present on soil exchange complex.

Effect Analysis of Soil Type and Silt Content on Silt-Based Foamed Concrete with Different Density.

This paper investigates the influence of silt content and coarse particle content on the mechanical and physical properties of foamed concrete, including compressive and flexural strength, modulus of elasticity, water absorption, drying shrinkage, and air-void structure. Four types of silt with different coarse particle contents were obtained by soil mixing. The results showed that high density, low silt content, and high coarse particle content can provide better mechanical properties. High silt content and high coarse particle content would lead to lower drying shrinkage. Silt content was the main factor affecting the pore distribution of foamed concrete, and higher coarse particle content could optimize the air-void structure. Meanwhile, the change in air-void structure can accordingly affect the water absorption of foamed concrete. Results showed that, at the same density and silt content, higher coarse particle content can optimize the physical and mechanical properties of foamed concrete.

Atmospheric impact of nitrous oxide uptake by boreal forest soils can be comparable to that of methane uptake

AimsEnvironmental factors controlling nitrous oxide (N2O) uptake in forest soils are poorly known, and the atmospheric impact of the forest N2O sink is not well constrained compared to that of methane (CH4).MethodsWe compared nitrous oxide (N2O) and CH4 fluxes over two growing seasons in boreal forest soils located in Eastern Finland. Within a spruce forest, we compared plots with long-term nitrogen (N) fertilization history and non-fertilized plots, and additionally pine forest plots without a fertilization history. The flux data was complemented with measurements of climatic conditions and soil physical and chemical characteristics, in order to identify factors affecting N2O and CH4 fluxes.ResultsNon-fertilized spruce forest soils showed the highest cumulative N2O uptake among the sites, whereas the pine forest site displayed low cumulative N2O emission. Nitrous oxide uptake was favored by high soil silt and water content. The low temperature seasons, spring and autumn, had the highest N2O uptake, likely associated with high soil water content typical for these seasons. In the spruce forest the N2O uptake was seasonally decoupled from the CH4 uptake.ConclusionsApplying the Global Warming Potential (GWP) approach, the cooling effect of N2O uptake in the spruce forest was on average 35% of that of CH4 uptake showing that N2O uptake should be considered when evaluating the atmospheric impact of boreal forests.

Cyclic lipopeptide-producing Pseudomonas koreensis group strains dominate the cocoyam rhizosphere of a Pythium root rot suppressive soil contrasting with P. putida prominence in conducive soils.

Pseudomonas isolates from tropical environments have been underexplored and may form an untapped reservoir of interesting secondary metabolites. In this study, we compared Pseudomonas and cyclic lipopeptide (CLP) diversity in the rhizosphere of a cocoyam root rot disease (CRRD) suppressive soil in Boteva, Cameroon with those from four conducive soils in Cameroon and Nigeria. Compared with other soils, Boteva andosols were characterized by high silt, organic matter, nitrogen and calcium. Besides, the cocoyam rhizosphere at Boteva was characterized by strains belonging mainly to the P. koreensis and P. putida (sub)groups, with representations in the P. fluorescens, P. chlororaphis, P. jessenii and P. asplenii (sub)groups. In contrast, P. putida isolates were prominent in conducive soils. Regarding CLP diversity, Boteva was characterized by strains producing 11 different CLP types with cocoyamide A producers, belonging to the P. koreensis group, being the most abundant. However, putisolvin III-V producers were the most dominant in the rhizosphere of conducive soils in both Cameroon and Nigeria. Furthermore, we elucidated the chemical structure of putisolvin derivatives-putisolvin III-V, and described its biosynthetic gene cluster. We show that high Pseudomonas and metabolic diversity may be driven by microbial competition, which likely contributes to soil suppressiveness to CRRD.

Effects of heathland management on seedling recruitment of common juniper (Juniperus communis)

Background and aims – Common juniper (Juniperus communis L.) is one of the most widespread woody species on the planet. Over recent decades, however, common juniper populations are decreasing in size and number in different regions. Lack of recruitment, caused by extremely low seed viability and the absence of suitable microsites for recruitment, is the key reason for this decline. For successful germination, the seeds need gaps in the existing vegetation and a soil with a relatively high base saturation. The aim of this study was therefore to assess how management actions such as sod cutting, rotavation and liming (alone or in various combinations) influence soil characteristics, seed germination and seedling survival of common juniper.Methods – We installed a sowing experiment across 104 1-m2 plots in four different sites in Belgium and the Netherlands using treatments with different combinations of fencing, sod cutting, rotavation, litter addition and liming. We determined how these treatments affected soil characteristics and how they influenced seed germination and seedling survival.Key results and conclusions – Across the whole experiment, germination rates of juniper seeds were very low (almost always &lt; 1%). Our results confirm that bare ground promotes the germination of juniper seeds. Secondly, higher silt and lutum (clay) proportions in the soil and higher soil organic matter content seemed to have a positive impact on recruitment, possibly due to drought reduction. Management actions that negatively affect those soil characteristics, such as deep sod cutting, should thus be avoided in heathlands on sandy soils. Our results reveal a complex relationship between seedling recruitment success, soil conditions and management of common juniper populations. Overall, combinations of fencing, (superficial) sod cutting and liming or rotavation were most successful.

Distribution of silty mantles in soils of the Northcentral Appalachians, USA

Across the northcentral Appalachians, USA, high silt content soils are found as silty mantles or deep, high silt content pedons. The origin of such soils can be attributed to additions of wind-blown dust deposits (WBD) or local parent materials (i.e. shales or siltstone lithology). Previous research on silt soils originating specifically from WBD attributed to late marine isotope stage (MIS) 2 loess has often been isolated to drainageways receiving outwash from deglaciation. We hypothesize that thin (<25–50 cm) silty mantles, and some deep silt soils occurring farther from outwash systems, are also indicative of post MIS 2 WBD and their extent is widespread. To test this hypothesis, we evaluated over 900 pedons from an ~119,280 km2 area of the northcentral Appalachians, USA to: (i) develop a particle size signature indicative of soils largely derived from WBD versus local parent materials, (ii) determine the potential depth of WBD additions to soils, and (iii) document the spatial extent of WBD versus deep, high-silt content soils across part of the region. Results suggest that silty mantles are prevalent across the study area and have a particle size signature indicative of loess and the mean depth of WBD additions to soils is ~50 cm. Below 50 cm, local lithology or pedogenesis more influences particle size trends. Pedon results were applied in a spatial modeling effort using the USA Soil Survey Geographic Database (SSURGO) to document the extent of silty mantles (over non-silt sourced parent materials) and deep, high silt content soils. Model results indicate silty mantles are common on stable landscape positions or positions that accumulate sediments (depressions or valleys). Our finding of silty mantles, or deep high silt content profiles, over lithologies high in sand infers a source other than the underlying lithology. In addition, the presence of such silty mantles on summits and upper slopes suggests the importance of these landforms as stable positions preserving WBD. Our results suggest that stable landforms preserve WBD deposits and where topography is of lesser relief, broader deposition across several aspects is common. Aspect dependent deposition is tied to glaciofluvial sources of WBD, and modeled silty mantles correspond strongly to regional studies of loess.

Edaphic factors determining the colonization of semiarid mine tailings by a ruderal shrub and two tree plant species: Implications for phytomanagement

Phytomanagement has been considered a feasible technique to decrease the environmental risks associated to mine tailings and its implementation relies on a suitable plant species selection. The goal of this study was to identify the edaphic factors, including microbiology, affecting the establishment of plant species with contrasting growth patterns during the phytomanagement of mine tailings. For this purpose, a comprehensive rhizosphere characterization was performed in an early ruderal colonizer, Zygophyllum fabago and two late successional tree species, Pinus halepensis and Tetraclinis articulata, growing at a mine tailings pile in southeast Spain. The neutral pH of the tailings determined low 0.01 M CaCl2 metal extractable concentrations (e.g. <10 μg kg−1 Pb and Cd). Thus, other soil properties different from metal concentrations resulted more determining to explain plant establishment. Results revealed that Z. fabago selectively colonized tailings patches characterized by high salinity (3.5 dS m−1) and high silt percentages (42%), showing a specific halotolerant rhizospheric microbial composition, such as the bacterial Sphingomonadales and Cytophagales orders and the fungal Pleosporales and Hyprocreales orders. The two tree species grew at moderate salinity areas of the tailings pile (1.7 dS m−1) with high sand percentages (85%), where Actinomycetales was the most abundant bacterial order (>10% abundance). The contrasting mycorrhizal behaviour of both tree species (ectomycorrhizal for P. halepensis and endomycorrhizal for T. articulata) could explain the differences found between their fungal rhizospheric composition. In terms of phytomanagement, the selective plant species colonization following specific soil patches at mine tailings would increase their biodiversity and resilience against environmental stressors.

Partitioning of polychlorinated biphenyls onto porewater–surface sediment systems collected along Umgeni River, KwaZulu-Natal, South Africa

This study focuses on the sorption efficiency of porewater–sediment of eight selected polychlorinated biphenyls (PCBs) most monitored in the environment as recommended by the Environmental Protection Agency. Five river sediment samples were collected along the Umgeni River of KwaZulu-Natal province of South Africa that contained different soil contents. The Walkley–Black method was employed for the determination of soil organic matter in the sediments, while sediment mineralogy and morphology, as well as elemental composition, were evaluated using powder X-ray diffraction and scanning electron microscopy equipped with energy-disperse X-ray, respectively. The sorption studies between porewater and sediment systems were carried out using batch adsorption experiments. The results showed that sediment samples containing high clay and silt content (13.90%, 30.43% and 18.58%, 19.93%) (site AWW and IDI) have the highest sorption percentage between 65.86–89.81% and 61.39–70.43%, respectively, for all the PCBs, while sites IDO and BL with high sand content (86.29% and 85.20%) sorbed the least amount of PCBs (32.32–53.06% and 43.23–59.77%, respectively). Among the sediment physicochemical parameters, soil organic matter was observed to correlate positively and play an important role in the sorption of PCBs. Also, a decrease in the ratio of Si:(Al + Fe) was noticed to have a positive impact on the sorption of PCBs. This is the first study done on this river to critically evaluate the porewater–sediment distribution and transportation of PCBs. Sorption efficiency of sediments of known physicochemical properties similar to this study area can be predicted by the sorption results of the present study.

Single Trees Litter Contribution to Soil Physiochemical Properties in Sudan Savanna Ecosystem, North-Western Nigeria

Litter contribution of single trees to soil properties in Nigeria’s Sudan Savanna was investigated. The tree species are Sclerocarya birrea, Balanites aegyptiaca, Acacia nilotica, Azadirachta indica, Mangifera indica and Piliostigma reticulatum. Total of 54 soil samples were collected at 15 cm depth and 5, 10 and 15 m away from the tree’s trunks. Soil was analysed using standard laboratory procedures. Physical properties indicated high sand, low silt, clay and moisture which differed significantly (P 0.05) between tree species. Chemical properties indicated slight acidic pH in vicinity of the trees from 5.10 at 15 m under A. nilotica to 6.30 at 5 m and 15 m under S. birrea and A. indica. Organic carbon ranged from 0.04 cmolkg at 15 m under M. indica to 2.30 cmolkg at 5 m and 15 m under A. indica. Nitrogen (0.077 g/kg) and phosphorus (0.49 g/kg) were higher at 5 m under A. nilotica and low (N=0.003 g/kg; P=0.01 g/kg) at 15 m under B.aegyptiaca, which in turn had higher Ca++ (1.06 cmol/kg) than the other species. Higher Mg++ (0.85 cmol/kg) was obtained at 5 m under A. nilotica while higher K+ (1.08), Na+ (0.65) and CEC (6.80) (cmolkg) were obtained at 5 m under M. indica. The soil closer to trees generally had better nutrients and pH statuses and the soil under A. nilotica, A. indica, S. birrea, M. indica and B. aegyptiaca had better properties than under P. reticulatum.

Spatiotemporal variations of benthic macrofaunal community in the Xiamen Amphioxus Nature Reserve, eastern South China Sea

In order to realize the spatiotemporal variations of benthic macrofaunal communities at the “Amphioxus Sand” habitat, six surveys including four seasons and three consecutive summers (i.e., 2014, 2015 and 2016) were conducted in two core sites, i.e., Huangcuo (HC) and Nanxian-Shibaxian (NX), in the Xiamen Amphioxus Nature Reserve in China. A total of 155 species of macrofauna were recorded, therein, polychaetes were dominant in terms of species number and density. Significant spatiotemporal variations of macrofaunal communities were observed. The density of polychaetes and the biomass of molluscs in the HC site were higher than those in the NX site. Macrofauna were more diverse and abundant in the cold seasons (winter and spring) than that in the warm seasons (summer and autumn). The annual variations of macrofaunal communities may be attributed to the changes in sediment texture among the three years of the survey. The variations in macrofaunal communities were mainly related to the proportion of polychaetes within the community. In addition, the density of amphioxus (include Branchiostoma japonicum and B. belcheri) was negatively correlated to that of polychaetes, bivalves, and crustaceans. Amphioxus was less likely to be found in the sediments with higher silt and clay content. Five biotic indices including Margaref’s richness index (d), Peilou’s evenness index (J’), Shannon-Wiener diversity index (H’), AMBI and M-AMBI were calculated in the present study. AMBI seems suitable in assessing benthic health at the “Amphioxus Sand” habitat, and a potential risk of ecological health in Xiamen Amphioxus Nature Reserve should be aware.