Sediment Size Distribution Research Articles

The response of organic carbon fractions in sediment to rainfall characteristics and slope lengths: Based on four-years on-site monitoring data

The effect of soil erosion processes on the properties of sediment and organic carbon fractions is not well understood under complex erosion environments, such as various rainfall characteristics and transport distances, which leads to a gap in knowledge regarding the role of soil erosion in the global carbon cycle. This study investigated the impact of different rainfall characteristics (patterns and parameters) and slope lengths (5 m ∼ 20 m) on the sediment yield, particle size distribution (PSD) and properties of organic carbon fractions on China’s Loess Plateau. The results show that runoff was highest under rainfall pattern A (extreme rainfall), while the sediment concentration peaked under rainfall pattern B (heavy rainfall), with significant correlation with slope length, rainfall intensity, kinetic energy, rainfall erosivity and precipitation (p less than 0.05). Silt- and clay-sized fractions were transported as primary particles and enriched under rainfall patterns B and C with no differences between slope lengths. The enrichment ratio (ER) of sediment, effective and ultimate particles were primarily influenced by rainfall intensity-related parameters. In contrast, the aggregation ratio (AR) tended to be influenced by rainfall kinetic energy. The content and loss of organic carbon fractions correlated to rainfall parameters and slope length, although no significant difference was observed between different rainfall patterns and slope lengths. Lost organic carbon fractions were predominantly Mineral-associated organic carbon (MOC), with great enrichment under rainfall pattern C and rapid depletion as the slope length increased. Structural equation models (SEM) indicated the effect of rainfall characteristics and slope length on organic carbon loss was mainly due to the regulation of soil loss and particle size distribution of sediment in selective transport erosion processes. We highlighted the need to consider the effect of soil erosion and particle size distribution comprehensively on the carbon cycle from the perspective of organic carbon fractions to describe the potential effects of soil erosion on the carbon budget quantitatively, especially in complex environmental conditions with consideration of scale effect.

Particle-based nutrients and metal contaminants in the habitat of Unionidae mussels in the Tisza River (Hungary)

Introduction:Unioniade is a species-rich family of freshwater mussels with an almost worldwide distribution. In Central European rivers Unio crassus, Unio tumidus and Unio pictorum have relatively high populations. In order to characterize the habitats of these suspension feeders, their nutrient supply and potential metal contaminants were investigated in near-bottom suspended (NBS) sediments and bottom sediments (BS) collected at four sampling locations along the Tisza River.Methods: The grain size distribution of sediments was determined by laser-diffraction technique. The total organic carbon (TOC) and the total Kjeldahl nitrogen (TN) were measured by a TOC analyzer and automated colorimetry, respectively. The phosphorous and metal concentrations were determined by inductively coupled plasma mass spectrometry following a microwave assisted acidic extraction of sediments with aqua regia.Results: The NBS sediments contained smaller grains than the BS samples, with roughly 85%–90% of the particles being less than 60 μm, allowing these mussels to catch them. Contrarily, only 2.47%–51.8% of BS samples were less than 60 μm. The NBS sediments contained 30, 23, and 15% more organic carbon, nitrogen, and phosphorous, respectively, than the BS samples. The rounded C:N:P molar ratios in the NBS sediments were 60:4:1, whereas they were 45:3:1 in the bottom sediments. The concentration of metals was also greater in the NBS sediments with the exception of Zn at Tokaj and Fe, Al, Mn, and Cr at Szeged, where prior contaminations transported by the tributaries Bodrog and Maros are stored in the top 10 cm of BS.Discussion: On basis of the measured C:N:P molar ratios it can be stated that soil-derived organic materials are the main sources of the nutrient elements in the habitats of suspension feeders in the Tisza River. The finer NBS sediments have higher specific surface area than the BS and thereby contain more biofilms on the grains resulting in higher proportion of organic nutrients and metal ions bounded as complexes or chelates. Comparing the measured metal concentrations of sediments with the concentration limits summarized in the Consensus-Based Sediment Quality Guidelines developed for evaluation of potential risk of metal contaminants in sediments for the benthic-dwelling organisms, it can be established that only the Hg concentration exceeded the probable effect concentration.

Grain size distribution of modern beach sediments in Sri Lanka

Grain size distributions are widely used to describe sedimentary geochemistry, depositional environment, and sediment transportation. The objective of this study is to analyze grain size distributions of modern sandy beach sediments in Sri Lanka. Sediment samples (n = 90) were collected from beach berm, representing the entire coastline of Sri Lanka. Grain sizes were determined by the dry-sieving method. Statistical parameters such as mean size, sorting, skewness, and kurtosis were calculated using GRADISTATV9.1 software for all the sieved sediment samples. Grain size variations (108.2 – 609.8 µm) show that Sri Lanka mainly consists of medium sand, whereas the northeast part of the country mixes with fine sand due to the influence of Bengal fan sediments. The variations of skewness (-0.229 – 0.446) and sorting (1.305 – 2.436) indicate symmetrical distributed moderately sorted samples. These variations specify a moderate energy depositional environment/wave action around the coastline of Sri Lanka. In addition, grain size analysis confirmed relatively high and low energy deposition environments on the west and east coasts, respectively. Accordingly, the west coast is more vulnerable to coastal erosion compared to the east coast of Sri Lanka. Therefore, this study provides the baseline grain size distribution data that can be used in decision-making for coastal zone management by mitigating beach erosion.

Modeling uncertainties of reservoir flushing simulations

Every dam or barrage construction affects the watercourse and the retention of sediment that previously was carried by the river, which can lead to siltation of the reservoir and obstruction of water intakes over time, reducing their capacities. However, the information available regarding the effect of sediment and drawdown parameters, sediment management at reservoirs, as well as different equational approaches, is scarce. The current research aims to evaluate the effect of parameters associated with numerical modeling of sediment management in reservoirs considering scenarios with different drawdowns, transport equations, sediment size distributions, and thickness of the initial sediment layer. The case study of the Aimorés Hydropower Plant (HPP) is used, applying the Delft3D-FLOW model for two-dimensional modeling. All parameters influenced the volume of mobilized sediment, among which the initial layer thickness was the parameter that resulted in the greatest changes in simulated results. In general, the results show that the uncertainties in the input parameters outweigh the uncertainties between the techniques, which found large variations in results when evaluating the use of different transport equations. These results indicate the importance of proper estimation of model parameters for predicting effects with accuracy and the need for such studies before planning and management operations are evaluated to avoid environmental harm and energy waste.

Non-linear response of sediment size characteristics and associated transport patterns to soil structural stability in sheet erosion under field rainfall simulation

Sediment transport patterns (suspension, saltation and rolling) not only depend on flow hydrodynamic characteristics, but also on sediment properties, both of which are largely influenced by soil structural stability. However, how sediment sizes and transport patterns response to original soils over a wide range of structural stability remains unclear. Herein, field plot rainfall simulation experiments on five soils along an increased gradient of structural stability were conducted at two rainfall intensities of 45 and 90 mm h−1 to investigate effective sediment size characteristics and associated transport patterns in sheet erosion. Differing from runoff and sediment yield, sediment sizes were most influenced by soil structural stability (F = 386.9) rather than rainfall intensity (F = 246.7, p < 0.001). Mean weight diameter of sediment (0.16–0.84 mm) and the proportion of coarse particles (>0.25 mm) exhibited a unimodal variation with increased soil structural stability. The effective sediment size distribution shifted from unimodal with the peak at < 0.10 mm for low and high stable soils to bimodal with two peaks at < 0.10 mm and 0.5–1 mm for medium stable soils. Correspondingly, suspension-saltation (>74 %) dominated sediment transport for low and high stable soils, which was determined by fine sized fragments from aggregate breakdown and small flow transport capacity, respectively; while both suspension-saltation (<0.10 mm) and rolling (>0.25 mm) jointly contributed to sediment transport for medium stable soils, which was controlled by the interaction between fragment size and flow transport capacity. Moreover, the positive effect of rainfall intensity on sediment sizes was more remarkable for the medium than for the low and high stable soils. A conceptual model of sediment transport mechanisms in response to soil structural stability is firstly proposed, which merits consideration in the future development of erosion modeling and soil conservation techniques.

Long-term trajectory of the macroinvertebrate community in the downstream channel of a hydropower dam after the operation of a sediment bypass tunnel

A sediment bypass tunnel (SBT) is a dam facility used to mitigate reservoir sedimentation and is expected to contribute to river ecosystem restoration by delivering sediment to the degraded downstream channel. We analyzed past monitoring data of benthic invertebrates sampled downstream of the Asahi Dam in Nara Prefecture Japan to understand the long-term changes in the invertebrate community after the installation of the SBT. Before the SBT installation, the reaches upstream of the dam (one Up site) and downstream of the dam (two Down sites) showed different invertebrate communities, dominated by invertebrates that preferred clean cobble beds, sand and gravel layers, or run habitats in the former and invertebrates that preferred stable or porous beds or pool habitats in the latter. A significant increase in the Up–Down site community similarity within a few years after the SBT installation indicated a rapid recovery of the invertebrate community at the Down sites. During the 16 years of the after-SBT period, the total density and taxon richness at the Down sites increased in the early half, while they decreased in the latter half due to bed changes associated with the continuous accumulation of sediments. The change in dominant invertebrates from taxa of the large sizes to those of the small sizes and the increase in the interhabitat community similarity suggest that the bed of the Down sites became finer and flatter by sand and gravel that filled interstitial spaces of cobbles in the late stage. While the invertebrate community at the Down sites recovered dramatically by the sediment supply through the SBT, additional actions (e.g., cobble augmentation, installation of flow guiding structures) to maintain a balanced sediment size distribution and developed pool-riffle structures would be necessary to maintain the potential habitat heterogeneity and biodiversity in the long term. Our study also demonstrated that invertebrates responded to the sediment supply according to their habitat preferences, which suggests that the classifications of invertebrates by habitat-related traits (e.g., bed-residence types and pool-riffle types in this study) would help to properly understand the sediment and bed status of river reaches under channel degradation or aggradation.

The nature and controls on downstream change of channel sediment along the Shiyang River, Northwest China

The grain size composition and distribution of river sediments are important for understanding regional geomorphological evolution, source-sink processes and drainage ecology. The Shiyang River basin, an inland river system in northwestern China, provides an environmental context within which to investigate the relationship between sediment particle size and environmental factors. Based on the analysis of the grain size characteristics of modern riverbed sediments, basin geomorphological parameters and lithology, it is found that the median grain size (Md) of river sediments shows a decrease trend from upstream to downstream in the basin. One of the tributaries named the Jinta River shows an obvious downstream fining trend (exponentially decreasing) of Md, which is related to the old geomorphological development stages and relatively homogeneous lithology in the basin. The downstream fining trend of Md along the Xiying River, another tributary, shows complex fluctuations, which might be affected by the tectonically active, young geomorphic development stage, complex lithology of the basin, and the sediment confluence of tributaries. The gravel-sand transition zone occurs in the plain section of the river about 28 km out of the mountain, which is related to the combination of regional geomorphological features, river morphology and hydraulic sorting.

Regime of fluvial phosphorus constituted by sediment

Phosphorus (P) is a crucial macronutrient, and recently a venture agent of pollutant, in aquatic systems worldwide. Most of P circulates with sediment through rivers, and the relationship between P and sediment is the basis for understanding the biogeochemical processes in rivers. Although studies of fluvial P have been carried out at specific sites and for particular problems, the general regime by which sediment affects P recirculation still warrants attention. In this study, a series of water samples were collected from six different rivers in China whose sediment concentration and size distribution vary widely and their P properties were analyzed in the laboratory. From this analysis of field samples, a highly consistent comet shaped pattern of sediment effects on P is revealed, i.e., generally the range of the concentration of total P has a diverge-converge trend as the sediment concentration increases. It is further supported by examining the strictly composed samples from P adsorption experiments. Furthermore, case analyses were performed on the basis of the above relationships to illustrate the impact of sediment on P cycling in rivers. The results can infer the following: 1) There is a strong positive correlation between total P and sediment concentration, indicating that sediment is a crucial agent in the movement and fate of P. 2) The negative correlation between dissolved P and sediment concentration indicates a buffering effect of sediment, especially fine sediment, on dissolved P, interpreting the intricate phenomena of increased dissolved P concentration caused by sediment reduction. Hence, natural sediment has the prevailing advantage in moderating the water quality of rivers, which is directly relevant to mitigating the present pollution and eutrophication of waters. 3) River damming causes a P blockage tendency, altering the fluvial nourishment to contamination in the river.

LITHOLOGICAL AND MINERALOGICAL COMPOSITION OF ACCUMULATIVE BEACH SEDIMENTS OF THE DNIESTER-DNIPRO SEGMENT OF THE BLACK SEA

The article presents the results of studies of modern beach sediments of the northwestern Black Sea coast from the village of KarolinoBuhaz (Odesa oblast) to the village of Rybakivka (Mykolaiv oblast). The length of the coastal zone is about 110 km. Most of the beaches here are sloping beaches of various morphologies and widths. Using a uniform methodology, 64 samples were collected and processed along the entire profile. The sampling was carried out from the middle part of the beach strip between the water's edge and the shore in the summer in the absence of storms from a depth of 30 cm. The area of the sweep was 30×30 cm. Each sampling point was accompanied by a description of the geological structure, condition of the coastal zone and characteristics of the beach area. The sampling points were georeferenced using a GPS system. Grain size and mineralogical analyses were carried out, and the main patterns of lithological composition and distribution of mineral fractions along the entire profile were established. Several contrasting areas were identified: 1) Karolino-Buhaz-Chornomorsk, where the medium-grained (0.5–0.25 mm) fraction significantly prevails (67 %). In the sediments of this area, the main mineral of all fractions is quartz (90 %). The dominant heavy minerals are garnet, ilmenite, and magnetite; 2) Chornomorsk – Cape Velykyi Fontan and Lanzheron (Odesa oblast) – Kobleve (Mykolaiv oblast) with a significant content of coarse-grained psamite (2–1 mm) – 29 % and gravel (2–5 mm) – 16 % fractions. The main minerals here in all fractions are quartz and calcite; 3) Cape Velykyi Fontan -Lanzheron is characterised by a variable particle size distribution, with the bulk represented by fractions of 0.25–0.5 mm and 0.25–0.1 mm, which have different proportions on different beaches. The dominant mineral in all fractions is quartz, with calcite detritus present in subordinate amounts. Heavy minerals are represented by single grains of garnet, ilmenite, magnetite, staurolite; 4) Kobleve – Rybakivka (Mykolaiv oblast) with an increase in the content of fractions of 0.25–0.1 mm (up to 42 %). The main mineral in all fractions is quartz (up to 87 %). The secondary component is calcite detritus. Biotite, muscovite and tourmaline are notable impurities in fine-grained fractions. On some beaches located near the seaport of Odesa, numerous glassy spheroidal aggregates of various compositions and ferruginous spheroids have been found in fractions of less than 0.5 mm. In places of concentration of such formations, the colour of the beach sediments becomes grey. The total content of anthropogenic material in the beach sediments of the studied segment is on average 0.1–0.12 %. It increases significantly (up to 0.23 %) in the vicinity of the port of Odesa and adjacent areas. In addition, in contrast to the Danube-Dniester segment, there is a noticeable increase in the amount of large-sized material of man-made origin (plastic, concrete, bricks, wood fragments, metal, fabric, etc.) in the beach area. The main factor in the formation of the mineral and particle size distribution of beach sediments in the Dniester-Dnipro segment of the coast is coastal abrasion. The role of terrigenous inputs from the land is minimal and is manifested only in the northern part (Berezan Bay area). The formation of the material and fractional composition is significantly influenced by periodic artificial sand alluviation (beach area of the Odesa agglomeration), strengthening of slopes with concrete blocks, piling up of blocks of igneous and metamorphic rocks, mainly granitoid, breakwaters and other structures that change the direction and influence along the coastal currents.

СОВРЕМЕННОЕ СОСТОЯНИЕ ДОННЫХ БИОЦЕНОЗОВ ГЕЛЕНДЖИКСКОЙ БУХТЫ ЧЕРНОГО МОРЯ

The state of macrozoobenthos and meiobenthos of the Gelendzhik Bay of the Black Sea was assessed in 2020–2021 based on three bottom grab surveys. Five types of biotopes were identified based on the particle size distribution of the bottom sediments, the redox potential of pore water, the content of organic carbon, and the type and presence of macrophytobenthos. A study of the oxygen content in the water column did not reveal hypoxia. Four types of macrozoobenthos communities were noted in the bay. The main dominants were bivalves and gastropods. In the central part of the bay, the communities were similar to typical Black Sea communities from the venus sand belt. The spatial structure of macrozoobenthos was associated with the type of biotope identified on the basis of abiotic characteristics and benthic vegetation. Macrozoobenthos was represented mainly by mobile burrowing infauna, belonging to the type of food filter feeders with a bivalve shell (bivalves). The meiobenthos of the bay was represented mainly by nematodes, which dominated both coastal areas and deeper waters. The spatial structure of the meiobenthos was determined by the granulometric composition of the bottom sediments, and the dependence on the type of vegetation and the redox potential of pore water was unreliable. In the coastal area, the reducing conditions were found in the surface layer of the bottom sediments, and also the low abundance and biomass of macrozoobenthos. The station with reducing conditions was distinguished by the dominance of larger (up to 5 cm) worm-like segmented polyphages and predators and the absence of juvenile forms of macrozoobenthos. At the station with reducing conditions, the lowest species diversity of meiobenthos was noted, and the nematode-copepod index reached 620:1, which is an order of magnitude higher than at other stations in the bay. A comparison of the current state of communities with historical data (1979, 1990) was made. It is shown that at the present stage the biodiversity of the bay has increased, while the abundance of macrozoobenthos has decreased. There were no stable areas of hypoxia or freezes in the bottom layer of waters.

Regularities of distribution of particulation types of modern bottom sediments and organic carbon by depth in the western part of the Barents sea

In this article, the possibilities of statistical analysis methods were demonstrated on the example of studying modern bottom sediments in the western part of the Barents Sea. As a result of cluster and dispersion analyses, regularities in the distribution of granulometric types of modern bottom sediments and organic carbon dissolved in them with depth within the sublittoral and bathyal zones of the sea were established. Based on the results obtained, it was concluded that the size distribution of sediments was due to the mechanical differentiation of sedimentary material as it was transported by sea currents, as well as the distance from the main sources of drift — Novaya Zemlya, the Kola Peninsula and Svalbard. At the same time, the accumulation of organic carbon in bottom sediments was associated with the peculiarities of the distribution of communities of marine organisms within the considered facies zones. The high content of organic carbon in the bathyal zone of the sea was associated with an increase in primary productivity here, as well as with the transfer by sea currents of the accumulated biogenic material of the littoral and sublittoral zones towards the bathyal.

Size, shape and orientation matter: fast and semi-automatic measurement of grain geometries from 3D point clouds

Abstract. The grain-scale morphology and size distribution of sediments are important factors controlling the erosion efficiency, sediment transport and the aquatic ecosystem quality. In turn, characterizing the spatial evolution of grain size and shape can help understand the dynamics of erosion and sediment transport in coastal, hillslope and fluvial environments. However, the size distribution of sediments is generally assessed using insufficiently representative field measurements, and determining the grain-scale shape of sediments remains a real challenge in geomorphology. Here we determine the size distribution and grain-scale shape of sediments located in coastal and river environments with a new methodology based on the segmentation and geometric fitting of 3D point clouds. Point cloud segmentation of individual grains is performed using a watershed algorithm applied here to 3D point clouds. Once the grains are segmented into several sub-clouds, each grain-scale morphology is determined by fitting a 3D geometrical model applied to each sub-cloud. If different geometrical models can be tested, this study focuses mostly on ellipsoids to describe the geometry of grains. G3Point is a semi-automatic approach that requires a trial-and-error approach to determine the best combination of parameter values. Validation of the results is performed either by comparing the obtained size distribution to independent measurements (e.g., hand measurements) or by visually inspecting the quality of the segmented grains. The main benefits of this semi-automatic and non-destructive method are that it provides access to (1) an un-biased estimate of surface grain-size distribution on a large range of scales, from centimeters to meters; (2) a very large number of data, mostly limited by the number of grains in the point cloud data set; (3) the 3D morphology of grains, in turn allowing the development of new metrics that characterize the size and shape of grains; and (4) the in situ orientation and organization of grains. The main limit of this method is that it is only able to detect grains with a characteristic size significantly greater than the resolution of the point cloud.

Formation of Turbidity Maximum in the Modaomen Estuary of the Pearl River, China: The Roles of Mouth Bar

AbstractAn estuarine turbidity maximum (ETM) functions as a filter and plays a key role in transporting suspended sediment. The features of ETM and their formation mechanisms vary with different types of estuaries. Their responses to morphological factors require further study. In this study, the Modaomen Estuary of the Pearl River was selected to examine the formation mechanisms of the ETM and roles of the mouth bar. Hydrodynamics, suspended sediment concentration, and sediment size distribution were measured via cruise shipboard in the mouth bar zone during the dry season of 2020, which indicated that the ETM occurred in the central and western bars. Furthermore, numerical modeling of an idealized estuary based on Delft3D was performed to explore the effects of the existence of a mouth bar on the dynamic structures causing the ETM, including saltwater intrusion, residual longitudinal circulation, and bed sediment resuspension. The results indicated that the existence of a mouth bar contributed to the occurrence of double residual circulations and enhanced bed shear stress on the mouth bar, which favor the ETM formation. In general, two different dynamic regimes were responsible for the ETM formation, that is, sediment trapping by saltwater intrusion and sediment resuspension induced by tidal currents. The mouth bar played a key role in these two mechanisms, including altering the estuarine circulation and bed shear stress. The results contribute to a better elucidation of the ETM formation in estuaries and provide scientific guidelines for estuarine management and engineering.

Flow-driven soil erosion processes in a calcareous semiarid soil: Rill length and flow rate impacts

Understanding the dynamic mechanisms of rill erosion is vital for accurately modeling of soil erosion. In this research, rill erosion was experimentally studied using different rill lengths. A flume, 11 m long and 0.2 m wide adjusted to 3% slope, was used for constructing rectangular rills of 0.05 m width and six different lengths (1 to 12 m). The experiments were carried out on a clayey calcareous soil from a semiarid region under two flow rates of QL = 0.025 and QH = 0.045 L s−1. Temporal sediment concentrations (C) were measured at the rill outlet for 40 min and the sediment size distribution (PSD) was recorded twice during each test. The common decreasing trend of C was affected by both flow rate and rill length. The formation of head-cuts along the bed of long rills was an important erosion process affecting C and PSD. The compiled data were used to determine the exponential models' parameters of both C and soil detachment rate based on the steady, unsteady, and event-average values. While, the equilibrium sediment transport occurred by increasing rill length beyond 7 m under QL, the tested rills under QH were not sufficiently long for the flow to reach its maximum transport capacity at the gentle slope used and for the calcareous soil tested. Based on the sediment PSD, the selective transport of coarse particles was evidenced. Selectivity transport was affected by rill length reached its maximum at the rill length of 7 m.The findings provides better understanding of rill erosion processes for calcareous soils on gentle slopes in semiarid regions. Further research is needed for better understanding of the rill erosion processes on short gentle slopes to provide experimentally supports for the existing theoretical concepts of rill erosion models.

Roles of raindrop impact in detachment and transport processes of interrill soil erosion

To date the roles of raindrop impact in sediment entrainment and transport processes of interrill soil erosion are not yet fully quantified. The objectives are to 1) evaluate the effects of raindrop impact on sediment entrainment, 2) systematically quantify the relative importance of raindrop-driven and flow-driven transport, and 3) characterize sediment size distributions in different sediment transport regimes. A loam soil with 48.4% sand and 23% clay was packed into flumes (L × W × H: 1.8 × 0.5 × 0.1 m) and subjected to intensities of 60, 90, 120 mm h−1 at gradients of 5, 10, and 16°. Air filter and tarp covers were used to vary impact energy and flow length. Results show that sediment is largely entrained by raindrop impact and transported by raindrop-impacted flow. Interrill erosion consists of two composite processes: raindrop-induced detachment/entrainment and raindrop-impacted flow transport. The former includes direct detachment by raindrop impact and ‘flow detachment’. The latter includes raindrop-driven and flow-driven transports. The proportions between the two transports vary with slope steepness, slope length, flow depth (or flow discharge), rainfall intensity, and sediment characteristics. Raindrop-driven transport is competent but inefficient, while the opposite is true for flow-driven transport. Because raindrop impact plays dual roles in detaching soil (and/or entraining sediment) and enhancing sediment transport, a drop energy factor must be included in interrill erosion models to adequately simulate the dual roles. More studies are required to derive a drop energy function that takes into consideration the rainfall energy dissipation by canopies of various plants under natural conditions.

Quantifying the effects of sediment transport on river channel geometry and flood level – a case study of the December 2014 flood

ABSTRACT Rapid urbanization has an accelerated impact on catchment hydrology and geomorphology due to land use and land cover changes as a result of anthropogenic development activities in river catchment areas that cause increased surface runoff and higher sediment yield. The present study investigates the channel changes and sediment transport phenomena, including bed material movement from the upstream to the estuaries of the Pahang River Basin, Peninsula Malaysia. The river geometry survey associated with the spatial variation in sediment transport has confirmed that changes in river bed profile occur due to the erosion and sediment deposition along the Pahang River. The sediment size distribution for the Pahang River was very coarse sand and gravel after the December 2014 flood . The river geometry survey showed a gentle slope that can induce lower discharge typical of alluvial rivers relating to flood events. Quantitative assessment of sediment load is, therefore, of critical importance for future river basin management.

Geochemical implications for gas hydrate occurrence and seepage at Sites GMGS5-W07 and W09 in Qiongdongnan Basin, South China Sea

The compositions and morphological characteristics of minerals and the cycle of trace elements in sedimentary environments are considered to be powerful indicators for the occurrence and evolution of gas hydrates. In this article, total organic carbon (TOC) content, particle size distribution, mineral composition, element distribution, and iron speciation of sediments from sites GMGS5-W07 and GMGS5-W09 of the South China Sea are studied. The high content of TOC and the occurrence of authigenic mineral assemblages suggest the accumulation potential of gas hydrate at the two sites. In the methane-rich layers, redox-sensitive trace elements, such as Co, Ni, Cu, Zn, As, Sb, Fe, and Mn, are enriched while reducing conditions lead to the accumulation of Fe and the increase of Fe(II) species proportion in sediments. Enrichment factors and Pearson correlation analysis of trace elements show that the circulation of trace elements at site W07 is more strongly affected by methane-rich fluids than at site W09. Fe-oxyhydroxides play a critical role in the development of As and Sb enrichments, and in particular, seep fluids may be a pivotal extra input of Mo, As, and Sb at site W07. Therefore, more intense methane seepage might have happened at site W07, and this conjecture has been further confirmed by higher Sr/Ca in sediments. Based on these results, the change in seepage intensity is not associated with the occurrence of gas hydrate.

Grain size distribution and fluvial environmental implications of Sebou estuary (Morocco)

The hydrodynamics and grain size distributions of sediment in estuarine and coastal environments provide important information on the material source, environmental events, and so forth. According to our knowledge, there is no research on the sediment characteristics of the entire Sebou estuary (Morocco), particularly, on the correlation between hydrodynamics and sediment properties. Grain-size analysis of estuary sediments along Sebou estuary (Morocco) has been carried out to reveal the depositional environment condition, energy and hydrodynamic conditions, as well as the mode of transportation along the study area. Linear discriminate analysis technique and bivariate plotting of grain size parameters are used to explain and understand the environment of sediment deposition. Hydrodynamic processes working during the deposition of sediments have been identified by CM plotting. As the mean grain size increased, sorting improved, and skewness became more positive and leptokurtic to very leptokurtic nature was observed in both periods. The spatial distribution indicates majority of sample fall in silt and clay category in both periods (i.e., spring and neap). Based on the CM pattern it was inferred that the sediment fall in rolling and suspension field. The sediments may be derived from offshore and catchment area deposits of the clay and silt, and evidence was found to suggest that these deposits are being eroded by tidal currents.

Factors controlling 137Cs distribution in bottom sediments of Koronowo Reservoir (Poland)

PurposeThe main aim of this study was to investigate factors influencing the long-term distribution of 137Cs activity concentrations in the bottom sediments of the dam lake, Koronowo Reservoir, 32 years after the Chernobyl nuclear power plant accident. For this purpose, selected properties of the collected sediment samples, such as grain size, mineralogical composition, and organic matter (OM) content, were investigated.Materials and methodsThe samples of lake sediments were collected with a Kayak-type gravity corer. The spatial and vertical distributions of 137Cs and 40K activity concentrations in the bottom sediments were investigated based on gamma spectrometry measurements. The particle size distribution of surface lake sediments was determined using a laser particle size analyzer. SEM and XRD were used for the mineralogical analysis of the collected sediment samples. Additionally, the content of organic matter was examined in all samples using an elemental analyzer.ResultsThe 137Cs content was significantly elevated in the case of fine-grained (< 63 µm) surface lake sediments (classified as silts, which are deposited in the profundal zone of Koronowo Lake) and ranged from 12.5 ± 4.1 to 29.2 ± 4.0 Bq kg−1. It was found that the increased concentration of 137Cs activity is more closely related to the content of the silt fraction (2–63 µm) than to the clay fraction (< 2 µm) in the collected surface lake sediments. The content of clay minerals also showed a significant positive correlation with 137Cs activity concentration in the surface lake sediments of Koronowo Lake. A similar relationship was noticed for the OM content, but it may be suspected that it is the result of radiocesium-bearing particle accumulation in OM-rich sediments.ConclusionThe most important factor influencing the spatial distribution of 137Cs activity concentrations in the surface lake sediments of Koronowo Lake, apart from the bottom morphology and grain size of sediments, is the content of clay minerals. Moreover, the increased detrital inflow to the lake after the construction of the dam could have probably affected the vertical distribution of 137Cs activity concentrations in the bottom sediments, as evidenced by, e.g., the measurements of 40K activity concentration.

Modeling dust emission in alpine regions with low air temperature and low air pressure – A case study on the Qinghai-Tibetan Plateau (QTP)

• Variations of temperature and pressure could impact dust emission process. • Air density is an important parameter in dust emission modeling. • The improved model could simulate precisely the dust emission in the QTP. • The dust emission in the QTP mainly occurred in winter and early spring. Dust emission is one of the important segments of the circulation of materials between lithosphere, atmosphere, and ocean systems. However, studies on dust emission have mainly concentrated on arid and semiarid regions with few studies focused on dust emission in alpine areas, where having lower air temperatures and lower air pressure environments. The lower air temperature and lower air pressure could significantly impact the air density and make the entrainment and transport of dust different from those at lower altitudes. The lack of accurate studies on dust emission in alpine regions has resulted in large uncertainties in the global dust budget and brought large challenges in controlling aeolian hazards in alpine regions. To bridge this gap, we took the air density as an important parameter to simulate dust emission in the Qinghai-Tibetan Plateau (QTP), where has typical low air-temperature and low air-pressure environments. The measured data showed that the lower air temperature and low air pressure affect the particle size distributions (PSDs) of aeolian sediment, the threshold velocity (TFV) as well as the dust emission rate. Herein, we introduced air density as an important factor to improve a dust emission model, and the validated results showed that the deviations of the simulated horizontal sand flux and vertical dust flux were less than 30% and 35%, respectively. Using the improved model, we could exactly depict the spatial and temporal distribution of dust emission in the QTP. The results shown, our model could exactly depict the spatial and temporal distribution of dust emission in the QTP. We believe that the improvement of the model could offer a new perspective on dust emission in environments with lower air temperature and lower air pressure, and the simulated results could provide valuable data for global dust budget estimation.