Ratio Of Silt Research Articles

Loess chronology and composition as interpreted through the lens of fossiliferous lake sediments in central Illinois, USA

Silty lacustrine and paludal records spanning from the penultimate deglaciation (late Illinois Episode) to the present are preserved in kettles formed during marine isotope stage (MIS) 6 that lie adjacent to the MIS 2 Manito terrace along the valleys of the Sangamon and Illinois Rivers. Geochemical, mineralogical, particle-size, and chronological records from two basins, Smith Lake and Lake Ben, provide a unique opportunity to assess loess age and provenance of the south-central Laurentide ice sheet. Here, I focused on deposits of redeposited loess of the last glaciation (Wisconsin Episode). Other than subtle laminations and fossils of emergent and aquatic plants and animals, the silty texture, chemical composition, and mineralogy of the lake sediment closely resemble Peoria Silt (loess). Sediment-core records sampled from Smith Lake and Lake Ben in Mason County, Illinois, confirm rapid deposition of proximal loess derived from the nearby outwash plain of the Illinois River from ca. 30.9−18.0 calibrated (cal) k.y. B.P. From 18.0−14.7 cal k.y. B.P., deposition of proximal loess was gradually replaced by far-traveled (distal) loess chiefly derived from Superior lobe provenance and global dust. The succession is capped by a cumulic gleysol that was truncated by recent plowing. Proximal loess deposits in lakes Smith and Ben are composed primarily of very fine sand, coarse silt, and medium silt (125−16 µm) compared to the distal facies (fine silt and finer sediment: <16 µm). Proximal loess that originated from outwash of the Lake Michigan lobe contains abundant Ca, Zr, Sr, illite, and magnetic minerals. The distal facies contains relatively abundant Rb, Al, K, Si, Cu, and Pb, and it is enriched in smectite (relative to illite) and depleted in magnetic minerals. Radiocarbon ages on terrestrial gastropod aragonite in loess from the nearby New Cottonwood School and Thomas Quarry sites indicate that Peoria Silt deposition ended between 18 cal k.y. B.P. and 16 cal k.y. B.P. At these localities, the upper part of the record is complicated by the modern soil, which has altered soil organic matter and leached carbonate. At Lake Ben, the radiocarbon record of emergent aquatic vegetation indicates that sediment accumulation rates and the ratio of proximal to distal loess decreased at the correlative interval that yielded the youngest snail shell ages at Cottonwood School. The upward increase in element concentrations such as Al and decrease in coarse/fine silt ratios in the modern soil are prominent features in the Lake Ben record dating from 18−14 cal k.y. B.P. This correlation strongly suggests that many of the features of the modern soil were not developed into uniform parent material but, rather, were inherited from incremental addition of distal loess to proximal loess, collectively identified as Peoria Silt. The paucity of key elements (Cd, Hg, Se, Ag, Au) in this transition zone suggests limited contributions from western lobes (i.e., Des Moines and James lobes), but abundant Ti and Cu suggest a contribution from the Superior lobe. A new wrinkle in this interpretation is that the rise in elements such as Al, Rb, and Si suggests significant additions from generic dust from unknown sources.

Comprehensive Effect of Soil Particle Size Composition and Wind Speed on Dust Emission Efficiency

AbstractRecent studies have shown that the dust emission efficiency (Ed) of some soil surfaces undergoes changes with wind speed and that such changes are related to soil properties. Through wind tunnel experiments, we investigate the comprehensive effect of soil particle size composition (PSC) (both minimally and fully dispersed) and friction wind speed (u*) on Ed. Results show that Ed initially increases and then decreases as soil texture changes from fine to coarse, with intermediate‐textured soils having the highest Ed and the strongest dust emission ability. The ratio of silt to sand in soil is an index suitable for reflecting the influence of soil texture on Ed. The PSC of soil dry aggregate is a factor that directly determines Ed. With increasing u*, Ed tends to increase for coarse‐ and intermediate‐textured soils but not for fine‐textured soil, supporting the view that Ed is influenced by u* and that the influence is related to soil PSC. Despite the fitting power function equations between Ed and u* for some soils failing to pass the significance test in this study, the substantial influence of soil texture on the power exponents implies potential for establishing an equation capable of expressing the comprehensive effect of soil texture and u* on Ed.

Sensitivity analysis of magnetic susceptibility under different climatic conditions during the late Pleistocene-Holocene period

Understanding the climate change experienced by the Loess Plateau in China from the end of the late Pleistocene to the Holocene is helpful for exploring global palaeoclimate change and predicting future climate change. However, sensitivity studies on palaeoclimate proxies under different geological periods and different climatic conditions are still lacking, which affects the accurate identification of palaeoclimate changes and the precision with which future climate change predictions can be made. Three soil profiles in Luochuan County were sampled, and the magnetic susceptibility (χlf), frequency-dependent susceptibility (χfd%), clay content (<0.005 mm), clay/coarse silt ratio, calcium carbonate content (CaCO3), and total content of organic carbon (TOC) of the profiles were analysed. The results showed that the climate changed from dry and cold to warm and wet to dry and cool since the end of the late Pleistocene. The precipitation (MAP) and temperature (MAT) since the end of the late Pleistocene were reconstructed by using the magnetic susceptibility of different soil particle size fractions (>2 mm, 2–1 mm, 1–0.5 mm, 0.5–0.25 mm, <0.25 mm), and the results were compared with those from other researchers. The results showed that the magnetic susceptibility of the fine fraction (<0.25 mm) was more sensitive at 0–3200 cal. yr. BP, 8500–13,000 cal. yr. BP, and 15,000–25,000 cal. yr. BP, while that of the coarse fraction (>0.25 mm) was more sensitive at 3200–8500 cal. yr. BP. Based on this finding, the precipitation and temperature of this period were reconstructed. This study provides a research method for selecting suitable climate proxies to describe climate changes in different geological periods to accurately conduct quantitative or semiquantitative assessments of climate change.

Shear Modulus of a Carbonate Sand–Silt Mixture with THF Hydrate

The maximum shear modulus (Gmax) is an important factor determining soil deformation, and it is closely related to engineering safety and seafloor stability. In this study, a series of bender element tests was carried out to investigate the Gmax of a hydrate-bearing carbonate sand (CS)–silt mixture. The soil mixture adopted a CS:silt ratio of 1:4 by weight to mimic the fine-grained deposit of the South China Sea (SCS). Tetrahydrofuran (THF) was used to form the hydrate. Special specimen preparation procedures were adopted to form THF hydrate inside the intraparticle voids of the CS. The test results indicate that hydrate contributed to a significant part of the skeletal stiffness of the hydrate-bearing CS–silt mixture, and its Gmax at 5% hydrate saturation (Sh) was 4–6 times that of the host soil mixture. Such stiffness enhancement at a low Sh may be related to the cementation hydrate morphology. However, the Gmax of the hydrate-bearing CS–silt mixture was also sensitive to the effective stress for an Sh ranging between 5% and 31%, implying that the frame-supporting hydrate morphology also plays a key role in the skeletal stiffness of the soil mixture. Neither the existing cementation models nor the theoretical frame-supporting (i.e., Biot–Gassmann theory by Lee (BGTL)), could alone provide a satisfactory prediction of the test results. Thus, further theoretical study involving a combination of cementation and frame-supporting models is essential to understand the effects of complicated hydrate morphologies on the stiffness of soil with a substantial amount of intraparticle voids.

Experimental study of subgrade soil stabilised with geopolymer based on glass powder and calcium carbide

Considering cement environmental sustainability issues, geopolymer materials composed of glass powder and calcium carbide could be a suitable alternative to the cement. In order to improve the mechanical properties of the subgrade soil, an experimental study, on three series of natural soil, Cement-Stabilized Subgrade (CSS), and Geopolymer-Stabilized Subgrade (GSS) soils have been presented. All soil specimens made up with various silt ratios, and studied under UCS test. Various mix design of geopolymer materials were prepared for UCS test and the optimal ratio of mix design, in which the resulting geopolymer contains the highest soil compressive strength. The results indicates that soil mechanical properties are a function of additives and fines contents. GSS soil could be used as an effective stabilizer compared to CSS one. Furthermore, SEM analysis proved that GSS soil tends to have a uniform and dense microstructure, and the geopolymerization reaction between the soil particles, was appropriate.

Experimental and computational assessment of wetting pattern for two-layered soil profiles in pulse drip irrigation: Designing a novel optimized bidirectional deep learning paradigm

One of the most important parameters in the design and implementation of drip irrigation systems is the accurate prediction of the wetting dimensions pattern around the emitters, which leads to the precise determination of the distance between the emitters and the drippers. This search provides a comprehensive experimental and computational investigation to predict accurate wetting patterns (dimensions and area) in the layered-textural soil profiles under pulse drip irrigation. To achieve this first 1217 sets of experiments, including the physical and hydrometric properties of two-layered soil profiles under plus drip irrigation, were carried out at Kurdistan University, Iran. Then, a new hybrid deep learning (DL) approach comprised of Boruta extreme gradient boosting (Boruta-XGB) feature selection incorporated with the bidirectional gated recurrent unit (Bi-GRU) scheme was designed to predict the diameter of horizontal distribution (D), downward vertical distribution (V), and wetting area below the emitter (A). For each scenario, the most influential predictors in terms of input combinations (C1, C2, and C3) were extracted among nine available inputs using Boruta-XGB, employed in the Bi-GRU model. The multilayer perceptron neural network (MLP) and adaptive boosting tree (Aadaboost) were also developed as benchmark comparing models based on several metrics (e.g., correlation coefficient (R), root mean square error (RMSE), and Kling-Gupta efficiency (KGE) and various infographic analyses. The outcomes demonstrate that the C3 combination includes the elapsed time, emitter outflow rate (Q), initial soil moisture rate (θ1/θ2), saturated hydraulic conductivity ratio (Ks1/Ks2), the ratio of irrigation time in a cycle to the entire cycle time (Tirr/Ttot), and the ratio of silt (Silt1/Silt2) with Bi-GRU yielded better accuracy in terms of (R = 0.994, RMSE = 1.295 cm, and KGE = 0.989) for D-scenario, (R = 0.995, RMSE = 1.489 cm, and KGE = 0.992) for V-scenario, and for A-scenario (R = 0.996, RMSE = 76.624 cm2, and KGE = 0.976) than MLP and Adaboost models.

수중음향을 이용한 해저 저질 분석

Seabed sediments are becoming a significant information for marine development and understanding the fishing environment. In this study, the backscattering strength according to the particle size of the seabed sediment was analyzed. The soil sample collection of this study was conducted with a gravity corer, and sound data collection at the station was performed using a 38kHz a scientific echosounder. Eco-view (8 versions) was used as the collected sound data. At the station where the Sand ratio was high, a high reflection strength was observed, and at the station where the Silt ratio and Clay ratio were high, a low reflection strength was found. Based on the reflection intensity results, it can be seen that the acoustic reflection intensity is high in the order of Gravel, Sand, Silt, and Clay.

Spatial distribution of halophytes and environment factors in salt marshes along the eastern Yellow Sea

BackgroundSalt marshes provide a variety of ecosystem services; however, they are vulnerable to human activity, water level fluctuations, and climate change. Analyses of the relationships between plant communities and environmental conditions in salt marshes are expected to provide useful information for the prediction of changes during climate change. In this study, relationships between the current vegetation structure and environmental factors were evaluated in the tidal flat at the southern tip of Ganghwa, Korea, where salt marshes are well-developed.ResultsThe vegetation structure in Ganghwa salt marshes was divided into three groups by cluster analysis: group A, dominated by Phragmites communis; group B, dominated by Suaeda japonica; and group C, dominated by other taxa. As determined by PERMANOVA, the groups showed significant differences with respect to altitude, soil moisture, soil organic matter, salinity, sand, clay, and silt ratios. A canonical correspondence analysis based on the percent cover of each species in the quadrats showed that the proportion of sand increased as the altitude increased and S. japonica appeared in soil with a relatively high silt proportion, while P. communis was distributed in soil with low salinity.ConclusionsThe distributions of three halophyte groups differed depending on the altitude, soil moisture, salinity, and soil organic matter, sand, silt, and clay contents. Pioneer species, such as S. japonica, appeared in soil with a relatively high silt content. The P. communis community survived under a wider range of soil textures than previously reported in the literature; the species was distributed in soils with relatively low salinity, with a range expansion toward the sea in areas with freshwater influx. The observed spatial distribution patterns may provide a basis for conservation under declining salt marshes.

Determination of Erodiblity (USLE-K) Status of Suruc Plain Soils Before Transition to Irrigated Agriculture within the Scope of Southeastern Anatolia Project

Erosion is a major problem that limits vegetative production, adversely affects the ecosystem and causes soil losses that are difficult to recover. This study was carried out with the aim of determining the erosion status and some soil properties of the soils of Suruc plain in Sanlıurfa province. Soil properties; It has been determined that the pH is slightly high, the soils are non-saline, the organic matter is medium and the soil is clayey. Expresses the change of data by the coefficient of variance (CV). The lowest variability (CV = 2.45) in the soils of Suruç plain is the other parameters, respectively, the clay ratio (CV = 19.27) medium level, silt ratio (CV = 20.64) medium level, organic matter (CV = 27.14) medium level and sand ratio. (CV = 27.34) varies moderately. It was determined that the soil properties showing the highest variability were lime (CV = 37.06), EC (CV = 38.89) hydraulic conductivity (CV = 695.41). According to the correlation coefficient of soil erosion (USLE-K) parameter (r=0.99**) and P &amp;lt;0.01 level, it was determined that there is a very important relationship. The high coefficient of variation of some soil properties revealed the need for more sampling in the area. According to the frequency table, the erosive degrees of the soils are determined to be 10% very little, 26% less, 56% medium and 8% strongly erodable soils. In the Suruc plain, which will be opened to irrigation within the scope of the Southeastern Anatolia project, instead of traditional irrigation methods, more suitable irrigation systems should be chosen according to the soil characteristics and the slope of the land.

The Role of Abiotic Environmental Factors in the Vertical Distribution of Macrozoobenthos at the Northeastern Black Sea Coast

In this study, an attempt is made to evaluate the impact of environmental factors on the vertical distribution of the macrozoobenthos at the northeastern shelf of the Black Sea. The samples of macrozoobenthos were taken by an Ocean grab at the depths of 10–70 m in 2014–2017 along four transects between the Abrau Peninsula and the settlement of Shepsi. The particle size distributions of the bottom sediments and the near–bottom water temperature were also measured. Two major groups of stations were distinguished according to the quantitative structure and composition of the macrozoobenthos—shallow (10–40 m), corresponding to variable temperature conditions, and deep (50–70 m), corresponding to constant temperature conditions. Two subgroups were distinguished in the shallow zone coinciding with the upper mixed layer (10–15 m) and thermocline (20–40 m). The first subgroup was characterized by sandy sediments inhabited by the community of the suspension feeder bivalve, Chamelea gallina; silty sands at the stations of the second subgroup contained a community dominated by several Veneridae species. Silty sediments were spread all over the deep-water zone; the pelophylic bivalves Parvicardium simile and Modiolula phaseolina were dominant. The ratio of silt to sand fractions in the bottom sediments and the near-bottom water temperature were critical factors in distinguishing between the groups of stations. The subgroups were distinguished according to the percentage of aleurite and pebble. The coefficient of sediment sortedness, which reflects the stability of the hydrodynamics and the rates of sedimentation, also influences the differences (mostly due to Bivalvia). The total variation explained by depth almost overlapped with the variation accounted for by other factors. The major role in distinguishing between the groups belonged to the two taxa constituting most of the biomass (Bivalvia) and the density and species diversity (Polychaeta).

Diversity and peculiarities of soil formation in eolian landscapes – Insights from the mineral magnetic records

Magnetic properties of loess-paleosol sequences are widely utilized as sensitive, easily-obtained and reliable proxy archives of past climate change in continental settings. However, soil formation in aeolian landscapes may occur under different and changing conditions of dust sedimentation, which will affect the growth and development of the pedogenic magnetic component. This phenomenon is explored in our study by analyzing depth variations of the following magnetic characteristics: frequency dependent magnetic susceptibility, anhysteretic magnetic susceptibility and the ratio between anhysteretic susceptibility and isothermal remanent magnetization acquired in a 100 mT back field (χarm/IRM-100 mT), along three loess-paleosol profiles from NE Bulgaria. A conceptual model for the time evolution of the grain size of the pedogenic magnetic fraction with soil depth is proposed, which is build upon the mechanism of soil formation – accretional or in stable land surfaces, or a combination of the two. Another magnetic ratio – isothermal remanence acquired in a 300 mT back field divided by low field magnetic susceptibility (IRM-300 mT/χ) is utilized as a proxy for the changes in the ratio of silt to clay fractions, indicative of changes in dust sedimentation regimes during glacial-interglacial transitions. According to the proposed conceptual model, verified by the magnetic signature of three Holocene soils from NE Bulgaria, discrimination between accretional soils and soils developed without dust additions during soil forming period can be done. Accretional soils are characterized by parallel changes in grain size sensitive magnetic proxies. Soils, developed at stable landscape conditions show gradation of the depths at which maximum enhancement of various proxies occurs with deepest occurrence of the maximum in χfd, followed by depth of maximum χarm and χarm/IRM-100 mT. Another implication of the new conceptual model is that the mean coercivity of the pedogenic component of accretional soils will be higher than that of soils developed without eolian input at equal temperature conditions because of the soils' thermal gradient and different depths, at which pedogenic minerals form in the two settings. The results revealed that the Holocene soils (So) has developed under different soil-forming conditions than paleosols from the same sites.

Determination of favourable biotechnological conditions for Chironomus larva cultivation and development

The cultivation of Chironomus larva under artificial conditions needs necessary conditions in the vivarium to provide the biological characteristics of its reproduction, growth and development. Chironomus larva is biologically valuable feed and source of protein for many young species of fish. Being the natural feed it is of great demand now days. The article presents the research results connected with the optimal water mass ratio and the nutrient medium for Chironomus larva. It has been prouved that the auxiliary agents have positive influence on Chironomus mosquitoes egg laying. The study has been conducted in the vivarium of Bila Tserkva NAU Research Institute of Food and Animal Products Processing Technologies. The observation methods and statistical techniques have been used to establish the optimal technological parameters. It has been scoped that Chironomus larva survives better in the nutrient medium, where the water mass ratio of silt is 1:5 and 1:6. There is a bigger amount of larva survival in these examples (in 5.6% times) in comparison with the control group (the ratio of water to silt is 1:2). There is the biggest amount of Chironomus larva deathratein the medium with the water mass ratio of silt 1:1. The use of auxiliary agents in the nutrient medium has a positive effect on Chironomus egg laying. After washing the nutrient medium, it was found that the optimal amount of auxiliary agents was 40 items bigger (20 floating and 20 immersed in sludge), but their use allows to increase the number of eggs laid in 1.2 times. Key words: silt, cultivation biotechnology, Chironomus, larvae, auxiliary agents, water to silt ratio, the survival of Chironomus larvae, water.

Sand and silty-sand soil stabilization using bacterial enzyme–induced calcite precipitation (BEICP)

This paper examines the bio-derived stabilization of sand-only or sand-plus-silt soils using an extracted bacterial enzyme application to achieve induced calcite precipitation (ICP). As compared to conventional microbial induced calcite precipitation (MICP) methods, which use intact bacterial cells, this strategy that uses free urease catalysts to secure bacterial enzyme–induced calcite precipitation (BEICP) appears to offer an improved means of bio-stabilizing silty-sand soils as compared to that of MICP processing. Several benefits may possibly be achieved with this BEICP approach, including bio-safety, environmental, and geotechnical improvements. Notably, the BEICP bio-stabilization results presented in this paper demonstrate (i) higher rates of catalytic urease activity, (ii) a wider range of application with sand-plus-silt soil applications bearing low-plasticity properties, and (iii) the ability to retain higher levels of soil permeability after BEICP processing. Comparative BEICP versus MICP results for sand-only systems are presented, along with BEICP-based results for stabilized soil mixtures at 90:10 and 80:20 percentile sand:silt ratios. This BEICP method’s ability to obtain unconfined compressive strength results in excess of 1000 kPa with sand-plus-silt soil mixtures is particularly noteworthy.

Shear modulus and damping ratio of a nonplastic silt at large shear strains

Site response analyses and solution of dynamic soil-structure interaction problems need determination of variation of shear modulus and damping ratio with shear strain. Since many studies in literature concern evaluation of behavior of sands and silty sands, a series of cyclic triaxial tests were performed to determine the variation of shear modulus and damping ratio of a nonplastic silt with shear strain. Stress controlled cyclic triaxial tests on silt specimens of initial relative densities ranging among 30%, 50% and 70% were performed. Tests were carried out on identical samples under different CSR levels, and the confining pressure was selected as 100 kPa. Variation of shear modulus and damping ratio of silts with cyclic stress ratio amplitude, relative density and number of cycles were investigated. It was understood that soil relative density and cyclic stress ratio amplitude has a significant influence on shear modulus and damping ratio of silts. It was also observed that, as the cyclic stress ratio amplitude is increased, greater shear modulus and lower damping ratio values were obtained.

Cyclic resistance and liquefaction behavior of silt and sandy silt soils

The liquefaction behavior and cyclic resistance ratio (CRR) of reconstituted samples of non-plastic silt and sandy silts with 50% and 75% silt content are examined using constant-volume cyclic and monotonic ring shear tests along with bender element shear wave velocity (Vs) measurements. Liquefaction occurred at excess pore water pressure ratios (ru) between 0.6 and 0.7 associated with cumulative cyclic shear strains (γ) of 4% to 7%, after which cyclic liquefaction ensued with very large shear strains and excess pore water pressure ratio (ru>0.8). The cyclic ring shear tests demonstrate that cyclic resistance ratio of silt and sandy silts decreases with increasing void ratio, or with decreasing silt content at a certain void ratio. The results also show good agreement with those from cyclic direct simple shear tests on silts and sandy silts. A unique correlation is developed for estimating CRR of silts and sandy silts (with more than 50% silt content) from stress-normalized shear wave velocity measurements (Vs1) with negligible effect of silt content. The results indicate that the existing CRR–Vs1 correlations would underestimate the liquefaction resistance of silts and sandy silt soils.

Comparing Potential Unstable Sites and Stable Sites on Revegetated Cut-Slopes of Mountainous Terrain in Korea

This study employs a diverse set of variables to explain slope stabilization on stable versus failure-prone revegetated cut-slopes in Korea. A field survey was conducted at potential unstable sites and stable sites using 23 variables. Through a non-parametric test of the field survey results, 15 variables were identified as primary determinants of slope failure. Of these variables, one described physical characteristics (elapsed year); four variables described vegetation properties (plant community, vegetation coverage rate, number of trees, and number of herbs); and 10 variables represented soil properties (porosity, soil hardness, water content, sand ratio and silt ratio of soil texture, tensile strength, permeability coefficient, soil depth, soil acidity, salt concentration, and organic matter). Slope angle, which was mainly considered in previous studies, of variables in physical characteristics was not statistically selected as one of the 15 variables because most of sites were located on steep slopes. The vegetation community, vegetation coverage, and number of trees influence slope stabilization. Vegetation coverage is highly correlated with other soil and vegetation variables, making it a major indicator of slope stabilization. All soil variables were related to slope failure such that subsequent slope failure was related to the method of slope revegetation rather than the environmental condition of the slope. Slope failure did not occur in revegetated slopes that matched the characteristics of the surrounding landscape and contained a large number of native trees. Most soil and vegetation variables showed differing values for whether a revegetated slope is potentially unstable or stable.

Climate vs. parent material — Which is the key of Stagnosol diversity in Croatia?

Stagnosols are the most widespread soils in the Pannonian region of Croatia. In Croatia they are referred to as Pseudogleys and considered to form primarily by normal (top–down) pedogenesis. However, the formation of their non-calcareous loess parent materials probably involved different sources, transports, and depositional environments. We aimed to determine the courses of soil formation and the characteristics of three Stagnosol profiles studied along the mean annual precipitation (MAP) gradient (700–1100mm) in the Pannonian region of Croatia. We found that soil redoximorphic features formed in situ by ongoing pseudogleization. Vertical trends for the clay/silt and coarse/fine silt ratios pointed to top–down pedogenesis. However, high organic C content at the bottom of one soil profile is the result of erosion/sedimentation processes, whereas high clay content in the subsoil of another profile was largely the result of sedimentation in a shallow paleo-lake. Therefore, some Croatian Stagnosols should be considered polygenetic. Each soil profile was classified using the WRB system, and the new WRB-2014 version proved more suitable than the previous one (WRB-2006). However, suggestions for improvements are given. In line with the MAP gradient were several morphological and only two chemical (pH and base saturation) soil characteristics. Organic C content did not correspond to MAP due to variability of forest topsoils. Clay content and CEC did not agree with MAP due to variability of loess parent materials across the Pannonian region of Croatia. The existence of more than one source of loess material (confirmed by the modal analysis) and the differences in depositional paleo-environments resulted in slightly different mechanical compositions of the investigated parent materials. We concluded that both climate and parent material must be regarded as key factors for the formation and characteristics of Stagnosols in the Pannonian region of Croatia (and the wider southwestern Pannonian Basin).

Arctic–alpine blockfields in the northern Swedish Scandes: late Quaternary – not Neogene

Abstract. Autochthonous blockfield mantles may indicate alpine surfaces that have not been glacially eroded. These surfaces may therefore serve as markers against which to determine Quaternary erosion volumes in adjacent glacially eroded sectors. To explore these potential utilities, chemical weathering features, erosion rates, and regolith residence durations of mountain blockfields are investigated in the northern Swedish Scandes. This is done, firstly, by assessing the intensity of regolith chemical weathering along altitudinal transects descending from three blockfield-mantled summits. Clay / silt ratios, secondary mineral assemblages, and imaging of chemical etching of primary mineral grains in fine matrix are each used for this purpose. Secondly, erosion rates and regolith residence durations of two of the summits are inferred from concentrations of in situ-produced cosmogenic 10Be and 26Al in quartz at the blockfield surfaces. An interpretative model is adopted that includes temporal variations in nuclide production rates through surface burial by glacial ice and glacial isostasy-induced elevation changes of the blockfield surfaces. Together, our data indicate that these blockfields are not derived from remnants of intensely weathered Neogene weathering profiles, as is commonly considered. Evidence for this interpretation includes minor chemical weathering in each of the three examined blockfields, despite consistent variability according to slope position. In addition, average erosion rates of ~16.2 and ~6.7 mm ka−1, calculated for the two blockfield-mantled summits, are low but of sufficient magnitude to remove present blockfield mantles, of up to a few metres in thickness, within a late Quaternary time frame. Hence, blockfield mantles appear to be replenished by regolith formation through, primarily physical, weathering processes that have operated during the Quaternary. The persistence of autochthonous blockfields over multiple glacial–interglacial cycles confirms their importance as key markers of surfaces that were not glacially eroded through, at least, the late Quaternary. However, presently blockfield-mantled surfaces may potentially be subjected to large spatial variations in erosion rates, and their Neogene regolith mantles may have been comprehensively eroded during the late Pliocene and early Pleistocene. Their role as markers by which to estimate glacial erosion volumes in surrounding landscape elements therefore remains uncertain.

Age and Origin of Blockfields on Scottish Mountains

Numerous researchers have proposed that blockfields on mid-latitude plateaux are frost-modified relicts formed initially by chemical weathering under warm, humid pre-Quaternary (Neogene) conditions. Others contend that they formed mainly by frost action during the Quaternary. We test these competing hypotheses for blockfields on three mountains in NW Scotland: a matrix-supported diamict blockfield (sandstone), clast-supported diamict blockfield (quartzite) and an openwork blockfield (schist). Clay concentrations in the fine fraction are low (0–6.8%) and both clay:silt ratios and secondary clay minerals (illite, kaolinite and gibbsite) are consistent with prolonged chemical weathering under periglacial conditions. There is negligible depletion of labile elements in the fine fraction relative to the parent rock. Conversely, evidence for surface and near-surface granular disaggregation, an increase in clast angularity with depth, dominantly angular sand grains, in situ detached clasts and fractured clasts above rockhead favour formation by frost weathering under Pleistocene stadial conditions. There is no convincing evidence for blockfield inheritance from Neogene regolith. As the blockfields were buried under cold-based glacier ice during the last glacial maximum, they pre-date ice-sheet build-up at ∼35–30 ka. Measured rates of plateau surface lowering suggest that present blockfield regolith is probably of Late Pleistocene (<135 ka) age.

태안 남해포 갯벌 패류양식해역의 환경특성

남해포 갯벌은 반폐쇄적인 만형 갯벌로 퇴적지형은 단조로운 사질 위주의 퇴적상과 조위에 따른 군집분포 특성을 가지고 있는 비교적 자연성을 유지하고 있는 지역이다. 갯벌어장의 노출시간은 상부에서 380분-430분, 중부에서 390분-450분, 하부에서 290분-340분으로 동일 지점에서는 주간에 비해 야간 노출시간이 50분-1시간이 더 길었고, 정점별로는 St. 1과 St. 2는 10분-20분의 차이밖에 없었으나, St. 3은 St. 1과 St. 2에 비해 노출시간이 각각 90분, 100분-110분이 더 적게 나타났다. 갯벌어장의 영양염류는 아질산성 질소, 인산인의 변동이 적고 강우량이 많았던 7월에 비하여 8월에 암모니아성 질소와 질산성 질소의 변동이 나타나고, 저질에서 COD는 3개 정점에서 양식장 오염니 기준을 초과하지 않았으나, AVS는 3개 정점 모두에서 기준을 초과하였다. 저질의 입도는 니질사 또는 사질로 분급이 양호하여 바지락이 서식하기에는 적절하지 않았으며, 동죽과 백합이 적절한 것으로 나타났다. 갯벌어장 표층퇴적물의 COD, AVS, IL의 지화학적특성은 다소 오염된 지역이 나타나지만 패류의 성장에 영향이 적은 것으로 생각된다. C/N 비는 St. 1, St. 2에서 10이상의 값을 나타내어 외부에 의한 오염이 진행된 것으로 조사 되었으며 C/S 비는 조사정점 세 지역에서 2.8 이하로 정상적인 해양환경으로 조사 되었다. 중금속에 대한 농축비 (Ef) 는 조사정점에서 1 보다 크게 나타나 대기나 하천을 통하여 유입되어 중금속이 퇴적물에 농축되어 있음을 의미한다. 또한 농집지수 (Igeo) 의 결과는 연구지역이 Igeo class가 1에 집중되어 있어 약간 오염되었거나 오염되지 않은 수준으로 나타났지만 Cd, AS, Hg는 Igeo class가 2로 오염되어 있는 수준으로 나타났다. 갯벌 미세조류의 정규식생지수는 월 평균 0.06이었으며, 엽록소 a 농도는 월 평균 <TEX>$91.42mg/m^2$</TEX>로 10월에 최대이고 8월에 최소로 조위별로는 St. 2 (중부), St. 1 (상부), St. 3 (하부) 순으로 나타났다. 그리고 조사기간 동안 출현한 규조류는 총 152종이었으며 동죽의 먹이생물은 전 조사기간 동안 출현 하였다. 유용패류의 출현량은 동죽 성패의 서식밀도는 St. 2 (중부)에서 가장 높았으며, 치패는 St. 3 (하부) 에서 가장 높았고 말백합 성패와 치패는 St. 2 (중부) 지점에서 많은 것으로 나타났다. 그리고 5월에 남해포 갯벌 11개 정점에서 유용패류 서식실태를 조사결과 동죽 성패는 St. 1, St. 5 지점에서만 20마리/<TEX>$m^2$</TEX> 이상의 밀도로 서식하였다. 동죽이 대부분을 차지한 이매 패류의 치패는 St. 6, St. 7, St. 10 지점에서 128-288마리/<TEX>$m^2$</TEX> 의 비교적 높은 밀도로 서식하였다. 조위가 다른 세 정점에서 2010년 가을에 늦게 가입한 것으로 추정되는 동죽 치패들은 2월 (평균각장 2.16-3.84 mm) 부터 7월 (7.21-14.41 mm) 까지 정상적인 성장 특성을 보였으며, 2011년 7-8월에 착저했던 동죽 치패들은 9월에 어떤 원인으로 서식밀도가 급격히 감소하는 특성이 관찰되고 있어, 9월경 늦게 산란 착저한 그룹의 치패들이 이듬해 남해포 동죽 자원으로 성장하는 것으로 추정되었다. 7월부터 8월 사이에 단기간 집중 강우 현상과 무더위는 태안 남해포 갯벌에서 동죽, 말백합, 가무락 등 유용패류의 안정적 생산을 치명적으로 위협하는 요인이 될 수 있기 때문에 하절기 어장관리 및 자연산 모패 자원 관리에 많은 관심이 필요할 것으로 판단된다. To assess the effect of environmental factors on the sustainability of cultured production shellfish, we investigated the habitat characteristics of tidal flat (Namhae-po in Taean). We measured the physiochemical parameters (temperature, salanity, pH, dissolved oxygen and nutrients) and the geochemical characteristics (chemical oxygen demand, ignition loss, C/N ratio and C/S ratio). Surface sediments were collected from several site of tidal flat to examine the geochemical characteristics of both the benthic environment and heavy metal pollution. The grain size for research area of tidal flat were similar at the ratio of silt and clay in comparison with the other site of it. The C/N ratio was more than 5.0, reflecting the range arising from the mix of marine organism and organic matter. The C/S ratio (about 2.8) showed that survey area had anoxic or sub-anoxic bottom conditions. The enrichment factor (Ef) and index of accumulation rate (Igeo) of the metals showed that those research areas can be classified as heavily polluted, heavily to moderately polluted, or more or less unpolluted, respectively. Adult surf clam (Mactra veneriformis) density was highest at St. 2 (middle part of the Namhae-po), on the other hand, surf clam spat density was highest at St. 3 (lower part of the Namhae-po). Heavy rain, terrigenous suspended clay with fresh water from neighboring agricultural land, and severe high air temperature during summer could be thought as detrimental causes of spat and adult mortality in Namhae-po tidal flat. We suggested that the growth of shellfish in the tidal flat was effected by the various environmental conditions, so an improvement in the cultured method was needed.