Characteristics Of Surface Sediments Research Articles

Mapping surface sediment characteristics in enclosed shallow‐marine environments using spatially balanced designs and the random forest algorithm

AbstractMapping the sedimentary character of the seafloor in large water‐filled basins is fundamental for understanding landform dynamics to inform research, management, intervention and conservation actions. Seabed mapping methods have undergone considerable development in the last two decades, including the uptake of machine learning approaches for sediment size prediction and classification. However, predictions of surficial sediment characteristics are often hindered by the availability of ground truthing data, their arrangement in space and the modelling approach chosen. Spatially informed sampling designs provide an opportunity to significantly improve the accuracy and uncertainty of predicted sediment distributions. In this study, we apply a machine learning algorithm to predict sediment distributions across Port Phillip Bay, a large (1930 km2) structurally controlled estuary on the southeast coast of Victoria, Australia. Surface sediment samples (n = 252) were collected using a spatially balanced design, ensuring that sampling effort was spread evenly within the embayment with increased sampling intensity placed in more heterogeneous areas. Surficial textural metrics were modelled using the random forest algorithm with bathymetric and hydrodynamic predictor variables. Models highlighted trends in sediment grain size, sorting and composition consistent with predicted wave‐ and current‐induced sediment mobilisation. Model predictions were accurate (normalised‐root mean squared error [NRMSE]: 0.14–0.16); however, standard error was not homogeneous across the study area. Uncertainty maps highlighted areas where additional sampling effort may be needed, including areas where transitional bathymetry impacted surficial sediment character and areas of anthropogenic modifications to the seabed. This study shows the benefits of undertaking spatially informed sample design, block cross‐validation during model fitting and quantifying spatial uncertainty in predictive maps to accurately quantify the fundamental boundary conditions of sediment size. The results of this study are intended to inform local coastal management, including beach renourishment activities. However, approaches outlined are applicable to any study where the seafloor grain size is a fundamental variable in understanding landscape change.

Challenges in the measurement of cross-shore geotechnical characteristics of sandy beach surface sediments

Geotechnical properties of surficial beach sediments affect beach erosion and shoreline changes. This study sets out to measure relative density, moisture content, friction angle, and shear strength of sandy beach surface sediments from dune to swash zone towards the goal of assessing their importance in sandy beach morphodynamics. Methods of sediment sampling, a conductivity based moisture probe, field penetrometers, and a field vane shear were deployed to collect data at the sandy Atlantic-side beach in Duck, North Carolina. The tools used were assessed based on their operability in the beach environment and data quality, and results are discussed in the context of beach morphodynamics. A digital field vane shear provided an efficient and direct method of measuring shear strength, but the difficulty of computing stresses on the failure plane, which is necessary to validate the results, ultimately reduced the usability of this instrument. The results from three penetrometers were compared to a partially-saturated bearing capacity model, where a portable free-fall penetrometer yielded the best fit. However, a modified velocity-dependent strain rate correction factor (K=0.31vi) was required to convert dynamic sediment resistance to a quasi-static resistance for the partially saturated sands. A small-scale digital push in penetrometer also achieved a positive correlation when compared to moisture content, but the small tip diameter (5 mm) coupled with the grain size at the beach (0.35 mm) raised concerns about the ability to derive an accurate measure of strength. It was determined that estimating strength parameter using a partially saturated bearing capacity model was appropriate for water contents less than 25% by volume, or anywhere in the crosshore above the swash to the dune. Relative density and moisture content were found to be closely linked, with partial saturation resulting in samples that featured negative relative densities up to −40%.

Assessment of heavy metal contamination and sediment characteristics in Ozomu lake, southern Nigeria: Implications for environmental health

This study investigates heavy metal concentrations and surface sediment characteristics in the Ozomu Lake, located in southern region of Nigeria. Sediment samples were systematically collected across three stations, over six months, spanning from March to August. This period encompasses the transition from the late dry season to the early wet season, offering valuable insights into the seasonal variations of heavy metal distribution and sediment properties. The concentrations of heavy metals in the sediment were determined using standard methods, along with the analysis of particle size distribution and organic content (% organic carbon and % organic matter). Essential findings reveal significant values. Iron (Fe) averaged 1194.86 mg/kg, zinc (Zn) 30.71 mg/kg, copper (Cu) 14.80 mg/kg, manganese (Mn) 17.43 mg/kg, lead (Pb) 1.17 mg/kg, and cadmium (Cd) 0.18 mg/kg. Enrichment factor (EF) assessments indicate notable enrichment in Fe, Zn, Cu, Mn, and Cd. Key sediment properties include total organic carbon (%TOC) at 4.46%, total organic matter (%TOM) at 7.72%, and particle size distribution with clay at 8.99%, silt at 6.24%, and sand at 84.77%. Principal component analysis (PCA) uncovers intricate relationships among heavy metals, shedding light on their sources and distribution. Geo-accumulation indices (Igeo) reveal moderate pollution levels in Fe and Cd, suggesting potential ecological risks. Conversely, Zn, Cu, Mn, and Pb remain within unpolluted ranges. The study enhances our understanding of heavy metal contamination in Ozomu Lake, emphasizing the need for tailored management and conservation strategies. Future research should explore seasonal variations and specific pollution sources in the lake's catchment area. This study contributes valuable insights into Ozomu Lake's environmental dynamics and underscores the importance of sustainable management for its long-term health and ecological integrity.

Study on the geomorphological changes of deep troughs under the influence of reclamation in the Caofeidian

Reclamation projects generally change the hydrodynamics and thus affect the topography of the seabed, which is the main threat to the safety of marine engineering. The Caofeidian Reclamation Project, the largest reclamation project in China to date, involved the reclamation of coastal regions of the Hebei Province. However, the project also created several issues and flaws due to the size of the reclaimed area. Through the comparative analysis in the Caofeidian sea area of multi-phase bathymetric topography, shallow stratigraphic changes, and numerical simulation of sediment dynamics, the characteristics of surface sediments and spatial distribution of erodibility were summarized. New marine geological hazards were discovered, such as submarine landslides and erosion depressions. It was concluded that after the reclamation of the Caofeidian, the south of the deep trough was still in an erosion state, and the erosion rate increased slightly. The shear stress formed by strong tidal currents in the deep trough was greater than the critical erosion shear stress of surface sediments, which caused the erosion transport of sediments. It was the primary dynamic mechanism leading to the long-term erosion state of the deep trough.

Characteristics of Surface Sediments and Accumulation before and after the Typhoon Kompasu and Soulik in the Gochang Donghori Sandy Intertidal Flat, Korea

Characteristics of Surface Sediments and Accumulation before and after the Typhoon Kompasu and Soulik in the Gochang Donghori Sandy Intertidal Flat, Korea

Grain size characteristics of surface sediment in the Jilantai Salt Lake Protection System after long‐term wind‐sand activities

AbstractIn order to explore the influence of vegetation on homogeneity of surface particle size distribution (PSD) and heterogeneity of soil structure, observations, theory, and multifractal results were synthesized to highlight the evolution of the soil particle composition in the Jilantai Salt Lake Protection System (Jilantai system) after long‐term wind‐sand activities and its soil structure characteristics. From flowing sand dune to saline‐alkali wasteland areas, the mean grain size and surface particle sorting degree gradually increased and decreased, respectively, whereas the shape of the particle frequency curve gradually changed from extremely positive deviation to negative deviation, and the peak shape of the curve gradually changed from narrow to wide. Furthermore, the inhomogeneity of the soil particle composition gradually decreased, whereas the range of the soil PSD gradually increased, and the soil increasingly became fine‐grained. Therefore, the contents of clay and silt in shelterbelt soil increased by 16% and 18.36%, respectively, over 1986 levels. Additionally, clay and silt play a vital role in determining soil particle parameters such as standard deviation (SD), skewness (SKI), and monofractal (D), while vegetation factors are the main controlling factors of clay and silt. In conclusion, the Jilantai system could increase heterogeneity and homogeneity and decrease the concentration of soil PSD by changing the sedimentary environment, while this affect depends largely on the fractional vegetation cover, vegetation height, and light penetrating porosity. Moreover, the multifractal and particle parameters could describe the soil structure characteristics and sedimentary process, respectively, after long‐term wind‐sand activities.

Geochemical and mineral composition characteristics of hydrothermal-related clay-sized surface sediments from southern Mid-Atlantic Ridge: Implications for hydrothermal depositional environment

Numerous hydrothermal activities were observed along the southern Mid-Atlantic Ridge (SMAR) in recent years. In this study, six clay-sized surface sediments collected from three hydrothermal fields (Caifan, Xunmei and Taiji) and one sample from Kaifeng seamount were analyzed for mineralogical and geochemical compositions. X-ray diffraction (XRD) results reveal that samples are mainly composed of fine-grained goethite, chlorite, and occasionally with jarosite and smectite. Interestingly, smectite not observed under XRD patterns are determined with the application of transmission electron microscope (TEM). Smectite is probably formed by interaction between Fe-oxyhydroxides (goethite) and detrital/hydrothermal silicates. Major and minor elements geochemical data indicate samples from Caifan and Xunmei are highly influenced by hydrothermal activities, and alteration of sulfides was prominent. However, it is not true for the sample from Kaifeng seamount and Taiji hydrothermal field, where are dominant by Mg-rich chlorite of volcanic rocks origin rather than aeolian. Rare earth element (REE) concentrations of both clay-sized and bulk sediment were compared to illustrate the REE characteristics and the degree of hydrothermal contribution. In the Taiji hydrothermal field and Kaifeng seamount, REE were mainly present in clay-sized fraction and chlorite may act as an efficient carrier of REE in these samples. On the other hand, in the Caifan and Xunmei hydrothermal fields, only goethite (or Fe-oxyhydroxides) plays an important role on carry of REE rather than smectite due to low abundance and poor crystallinity.

Contrasting sources and fates of sedimentary organic carbon in subtropical estuary-marginal sea systems

Sediments deposited in subtropical deltas and continental shelves are the “recorders” of sources, transport processes, and accumulation of organic carbon (OC) at the land-ocean interface, but their role in the global carbon cycle remains poorly constrained. In this study, we determined the abundance and carbon isotopic composition (δ13C and Δ14C) of bulk OC, as well as characteristics of specific biomarker compounds (plant wax n-alkanes, n-fatty acids, and phytoplankton sterols) in surface sediments from the Pearl River estuary (PRE) and adjacent continental shelf of the northern South China Sea (SCS) in order to examine the sources and fates of OC delivered to a large subtropical river-marginal sea system. We observed marked spatial variability in the sources, hydrodynamic processes and accumulation of sedimentary OC in PRE and northern SCS shelf, with the emergence of two distinct regimes reflected in the bulk OC isotopic characteristics of surface sediments. In Pearl River impacted regions, relatively fresh terrestrial OC (OCterr) was subject to substantial degradation and aging during transport within the estuary and from the estuary to the shelf. In contrast, sedimentary OC in the Taiwanese river impacted region comprised a mixture of fluvially-derived refractory OCterr from the Choshui River and modern marine OC. Burial efficiencies of OCterr are also spatially heterogeneous as a result of these different OC sources and hydrodynamic processes. The overall OCterr burial efficiencies are relatively low in the Pearl River influenced region, with an average value of 27 ± 10% in the PRE and an average value of 17 ± 6% in the western shelf, in contrast to the higher values in the region impacted by Taiwanese rivers (55% ± 39%).These findings suggest both sources and hydrodynamic processes during transport exert strong influence on the fate of OC, with important implications for the role of river-dominated marginal seas in the global carbon cycle.

Changes in the spatial distribution of total phosphorus in sediment and water column of a shallow subtropical lake

Julian PJ II, Schafer T, Cohen MJ, Jones P, Osborne TZ. 2023. Changes in the spatial distribution of total phosphorus in sediment and water column of a shallow subtropical lake. Lake Reserv Manage. 39:213–230. In shallow lakes, interactions between bed sediment and the water column strongly influence the availability and transport of nutrients. Lake Okeechobee, in South Florida, is a eutrophic, shallow, polymictic lake that exhibits frequent mixing of the water column and resuspension of unconsolidated sediments. The objective of this study was to evaluate the temporal and spatial patterns of water and sediment characteristics and evaluate the linkage of sediment and water column total phosphorus (TP) concentrations. Spatiotemporal generalized additive models identified key periods during which both surface water total suspended solids (TSS) and TP increased, corresponding to hurricane and tropical storm activity. Our models identified regions with persistently greater water column concentrations than the lake average, indicating potential hot spots in resuspension processes and/or internal loading. Sediment bulk density (BD) and TP were inversely correlated, indicating that light, less dense sediments have greater TP concentrations, potentially contributing to the redistribution of sediments and P. An integrated evaluation of surface water and sediment characteristics using a generalized additive model revealed that sediment TP strongly influences water column TP concentrations, potentially explaining the spatial distribution of surface water TP concentrations. The area of the lake with sediment TP concentration ≤500 mg/kg is increasing while the low bulk density sediments area is decreasing, marking a potential improvement in sediment conditions. If this trend persists, it indicates that the lake is increasingly storing P in sediments that can resist entrainment, with significant implications for assessing the trajectory of lake restoration.

Impacts of a beaver dam analogue complex on streambed vertical hydraulic gradients in a 1.2‐km stream reach in Wyoming, USA

AbstractBeaver dam analogues (BDAs) have seen growing use as restoration structures across the western United States. This study investigates the patterns in streambed upwelling and downwelling along a 1.2‐km stream reach in Red Canyon Creek (RCC), Wyoming before and after the installation of 31 new BDAs and the upgrade of four existing BDAs in July 2021. Over 100 mini‐piezometers were used to measure upwelling and downwelling in low‐flow, summer periods as quantified by vertical hydraulic gradient (VHG). Both before and after BDA installation, the stream reach was dominated by downwelling patterns, suggesting that RCC was a net losing stream during this summer period, with and without BDAs. While there were spatial variations in VHG before BDA installation, this variation was not dependent on stream depth, water surface concavity, sediment characteristics, and position relative to meanders, suggesting that unobservable subsurface properties may be a control on VHG or that there are attributes that were not captured due to the 10‐m spacing of mini‐piezometers. After BDA installation, VHGs were primarily related to the magnitude of the elevation gradient across the BDA. VHGs were highest near the BDAs and diminished once moving more than a few metres from the BDAs. When VHGs were averaged over the full reach length, BDAs appeared to slightly enhance net stream loss, albeit we could not control for possible seasonal differences in water table gradient during the observtion period.

Clay mineral distribution characteristics of surface sediments in the South Mid-Atlantic Ridge

Clay mineral distribution characteristics of surface sediments in the South Mid-Atlantic Ridge

Stratified vertical sediment profiles increase burrowing crab effects on salt marsh edaphic conditions

AbstractBurrowing animals can profoundly affect the biological structure and ecosystem functions of their environments. For instance, burrowing crabs increase sediment deposition and facilitate sediment homogenization and turnover, with potential impacts to sediment biogeochemistry. However, the relative importance of burrowing crabs on sediment dynamics can vary considerably between, and within, habitats. Sediment properties influence how burrowing crabs will affect edaphic conditions, but these studies often assume homogenous sediment conditions and fail to consider how sediment properties change with depth. Thus, understanding how burrowing crab effects on sediment properties are influenced by the vertical sediment profile should inform where burrowing crabs structure edaphic conditions. Here, we conducted an intensive field survey across three tidal salt marshes with variable sediment properties to understand if marsh vertical sediment profiles can help predict the nature of burrowing crab–sediment relationships. We found that burrowing crabs homogenize sediments in all marshes, but their effects on sediment homogenization and edaphic conditions were greater in marshes with highly stratified vertical sediment profiles. Our study suggests that understanding the vertical sediment profile of a salt marsh may provide critical insights into how crab burrowing may influence the edaphic conditions and physical characteristics of marsh surface sediments—especially in restored, created, and managed salt marshes.

The geochemical gas field in surface sediments in the Southwest sub-basin of East Vietnam Sea: distribution, origin, and comparative features with other regions of Western East Vietnam Sea

We analyzed 39 gas samples, including carbon dioxide, hydrocarbon gases C1–C4, hydrogen, and helium, in surface sediment from 19 gravity cores collected from the SW sub-basin of the East Vietnam Sea (EVS) using the headspace and vacuum degassing methods. Based on the result, we discussed the distribution and origin of gases in the southwest sub-basin EVS surface sediments. The sediments are mostly clay and silty clay containing methane ranging from 0.5–440 ppm. The anomalous concentrations of methane, helium, and hydrogen occur along the continental slope in the Nam Con Son basin of Southwest EVS. Methane is the dominant gas compared to other detected hydrocarbon gases, including ethylene, propane, and butane. Based on comparative results, the background methane concentrations in surface sediments decrease from South to North, from the southwestern sub-basin of the East Vietnam Sea to the Phu Khanh and the Red river basins. We propose the presence of a large-scale degassing zone of hydrocarbon gases and discuss the gases’ origin in surface sediments based on hydrocarbon gas ratios, carbon isotope compositions of carbon dioxide and methane, and the relationship between geochemical characteristics of surface sediments and fault system, and surface sediment gases.

Spatiotemporal dynamics of surface sediment characteristics and benthic macrofauna compositions in a temperate high-energy River-dominated Ocean Margin

The benthic compartment of River-dominated Ocean Margins (RiOMar) is largely affected by sedimentary processes, as well as by natural and anthropogenic disturbances. Recent studies have confirmed the major importance of riverine inputs and local hydrodynamics in the spatial structuration of low- and high-energy temperate RiOMar, respectively. Differences in the nature of these structuring factors could also affect the temporal dynamics of these two types of systems. The present study is aiming at: (1) quantifying spatiotemporal changes in surface sediment and benthic macrofauna within the West Gironde Mud Patch (WGMP; high-energy system) over both short (2016–2018) and longer (2010/2016–2018) time scales, (2) identifying the main environmental factors explaining those changes, and (3) achieving a comparison with the Rhône River Prodelta (RRP; low-energy system) in view of further characterizing the functioning of the benthic components of these two temperate RiOMar. Surface sediment characteristics (grain size, quantitative and qualitative descriptors of particulate organic matter) and benthic macrofauna compositions were assessed based on 4 seasonal sampling of 5 stations located along a depth gradient within the WGMP. Results highlighted the existence of spatial patterns for both surface sediment and benthic macrofauna, which are both better explained by local hydrodynamics. Most variables presented seasonal changes. Benthic macrofauna compositions also showed pluri-annual changes, which were attributed to a cicatrization process following a major disturbance caused by the 2013–2014 series of severe winter storms, and suggests the major role of local hydrodynamics in explaining 2010/2016–2018 temporal changes in WGMP benthic macrofauna compositions. The comparison with the RRP further highlighted major discrepancies between the two systems in the main processes (i.e., hydrodynamics versus river hydrological regime) explaining surface sediment characteristics and benthic macrofauna compositions, which supports current RiOMar typologies.

Pollution Characteristics of Surface Sediments in Luhun Drinking Water Reservoir in the Middle China

The pollution status of surface sediments in the Luhun drinking water reservoir in the central of China was analyzed and evaluated, and three sampling points were selected for this study. The results showed that the organic matter content of the Luhun reservoir was as high as 5.2%, which was at a high level. The analysis of nitrogen, phosphorus, and their components showed that the total nitrogen (TN) and total phosphorus (TP) pollution in Luhun reservoir was in the medium pollution level, among which the ion-exchange state of nitrogen component and the strong-alkali extraction state of phosphorus component accounted for a relatively high risk of release into the overlying water. The results showed that the bioavailability index of Pb and Cr was as high as 0.73 and 0.62, which was of big pollution risk. Generally speaking, the sediment of Luhun reservoir had a high risk of pollution to the overlying water. The results of this study can provide a theoretical basis for urban safe water supply and provide support for water quality improvement.

Effect of Temperature on the Acoustic Reflection Characteristics of Seafloor Surface Sediments

Effect of Temperature on the Acoustic Reflection Characteristics of Seafloor Surface Sediments

Grain size characteristics of surface sediment and its response to the dynamic sedimentary environment in Qiantang Estuary, China

The composition and grain size characteristics of sediment in estuarine and coastal environments provide important information on the material source, hydrodynamic environment, environmental events, etc. However, few studies have focused on the sediment characteristics of the entire Qiantang Estuary, particularly, on the correlation between hydrodynamics and sediment properties. Through systematic sampling of the surface sediment in a large area of the Qiantang Estuary, the spatial distribution characteristics of the surface sediment of the Qiantang Estuary, such as the grain size composition and particle size parameters, in different sections of the estuary area are analyzed. By comparing the particle size data of different estuaries, the similarities and differences of the particle size parameters of the Qiantang Estuary and other estuaries are compared and analyzed. According to the differences in the sediment composition, the distribution status of the particle size frequency curves and the morphological characteristics of the probability curves in the entire study area, the Qiantang Estuary is divided into 7 dynamic depositional areas: Fuchunjiang Hydropower Station–Fuyang, Fuyang–Qibao, Qibao–Cao'e River, Cao'e River–Zhapu, North Shore of Hangzhou Bay, middle part of Hangzhou Bay, and South Shore of Hangzhou Bay, which are different from the previous estuary segmentation system. The study area is divided into 13 dynamic depositional sub-regions using the Pejrup M triangle diagram. Combining the calculation results of the mathematical model and the Pejrup M triangle diagram, the relation between the dynamic deposition environment and the bottom shear stress is discussed. It is found that the spatial distribution of the bottom shear stress in the study area is in good agreement with the zoning of the dynamic sedimentary environment.

Stoichiometric characteristics of carbon, nitrogen and phosphorus in surface sediments of different plant communities in Lake Baiyangdian wetland

白洋淀是雄安新区的核心生态功能区.为探究白洋淀不同植物群落区表层沉积物碳（C）氮（N）磷（P）化学计量特征，采集了96组表层沉积物样品开展对比分析.研究表明：白洋淀湿地表层沉积物总有机碳（TOC）含量均值为39.64 g/kg，范围为14.4~136.82 g/kg，总氮（TN）和总磷（TP）均值分别为2.62和0.75 g/kg，范围分别为0.72~10.57和0.46~1.38 g/kg；不同植物群落区表层沉积物C、N、P化学计量特征存在显著差异，挺水植物分布区表层沉积物TOC和TN含量高于其他区，水田区沉积物TP含量最高；表层沉积物C：N：P比例平均值为141：8：1，C：N比值相对稳定，C：P和N：P比值空间分异性较大；不同水生植物群落区沉积物C、N、P化学计量特征存在差异，挺水植物区沉积物C：P和N：P比值显著高于其他各分区，沉水植物区表层沉积物C：N最大，挺水植物区和沉水植物区C：N：P比例平均值分别为222：13：1和129：6.5：1；白洋淀表层沉积物C、N、P化学计量特征受植物群落生物量、磷氮磷化学计量特征、枯落物分解速率以及人类活动等多个因素影响；与我国东部主要湖泊相比，白洋淀表层沉积物C、N、P含量均处于较高水平，建议在水生植物生长末期收割打捞运出淀外，减少淀内N、P营养盐累积，减缓白洋淀富营养化和沼泽化进程.;Lake Baiyangdian is the main ecological function area of Xiong'an New Area. To explore the stoichiometric characteristics of carbon, nitrogen and phosphorus in surface sediments of different plant communities in Lake Baiyangdian, 96 samples of surface sediment were collected for comparative analysis. Results showed that the average total organic carbon (TOC) contents of the surface sediments were 39.64 g/kg, ranging from 14.4 to 136.82 g/kg, while the average total nitrogen (TN) and total phosphorus (TP) contents were 2.62 and 0.75 g/kg, ranging from 0.72 to 10.57 and 0.46 to 1.38 g/kg, respectively. There were significant differences in carbon and phosphorus stoichiometric characteristics of surface sediments in different plant community regions. TOC and TN contents in surface sediment of emerged aquatic plant areas were higher than those in other areas, and TP contents in surface sediment of paddy fields were the highest. The mean value of the C:N:P ratio in surface sediments was 141:8:1, the C:N ratio was relatively stable, and the C:P and N:P ratios were highly variable. There were significant differences in carbon, nitrogen and phosphorus stoichiometry in sediments of different aquatic plant communities. The ratios of C:P and N:P in surface sediments of emerged aquatic plant areas were significantly higher than those of other regions. The mean C:N:P ratios of emerged aquatic plant area and submerged plants area were 222:13:1 and 129:6.5:1, respectively. The stoichiometric characteristics of carbon, nitrogen and phosphorus in surface sediments of Lake Baiyangdian were affected by many factors, such as plant community biomass, stoichiometric characteristics, decomposition rate and human activities. Compared with the main lakes in eastern China, the contents of carbon, nitrogen and phosphorus in the surface sediments of Lake Baiyangdian were at a higher level. It is suggested to harvest, salvage and transport the aquatic plants out of the lake at the end of the growth period to reduce the accumulation of nitrogen and phosphorus nutrients in the lake and slow down the process of eutrophication and swamping of Lake Baiyangdian.

Spatial variability of the physicochemical characteristics of surface sediments in the “Three Rivers and One Dune” Region in the Kuye River Basin, Mu Us Sandy Land, China

Eolian-fluvial interactions are a common geomorphic phenomenon and Earth surface process in arid regions. We selected the “Three Rivers and One Dune” region, in the Kuye River Basin, in the northeastern Mu Us Sandy Land in Northern China, for a study of eolian-fluvial interactions, based on a geomorphological survey and analysis of the grain size and chemical element contents of surface sediments. The results showed that the interactions of wind and water flow enhanced have caused the mixing of the surface sediments, which is reflected by the spatial heterogeneity of their physicochemical properties, which are different from those of the local parent rock and local sandy environments. In detail, the variations of the chemical weathering-related indicators, including the CIA, CIW, CPA, Na/K and Rb/Sr, along four transects all indicated that the degree of chemical weathering was generally low in the region (CIA < 50), implying that the materials are unweathered or in an incipient chemical weathering state. Combined with the grain size results, in the upper reaches (transect KYH-1) the mean grain size was coarser, the degree of sorting was lower, and there was a lower degree of chemical weathering. Transect KYH-4, located in the most southeasterly part of the study area, has the lowest mean grain size and is relatively well sorted; hence, it has undergone a greater degree of chemical weathering. Transects KYH-2, KYH-3 and KYH-4 span the “Three Rivers”, and their sediments are relatively well mixed and heavily influenced by locally-derived materials. The differences in physicochemical properties between the transects can be attributed to the diversity of slope directions and of the angles between the wind direction and the river flow. Overall, our results, combined with regional comparisons, indicate that the sand sources of the dunes in the study area are mainly locally derived.

A multiproxy study of intertidal surface sediments from two macrotidal estuarine systems (Canche, Authie) in northern France: Insights into environmental processes

Estuaries are considered one of the most dynamic ecosystems in the world, ensuring high production and transfer of large quantities of organic matter (OM) from continents to the ocean. Despite the large influence of estuaries in the functioning of coastal ecosystems, our understanding of OM dynamics in these buffering coastal environments remains fragmented. In this frame, our study was carried out to describe and understand the main drivers of OM distribution in two estuaries (Canche, Authie) of the eastern English Channel, based on descriptive and quantitative approaches. For this purpose, in February and March 2018, surface sediments were sampled at low tide along cross-shore transects in the intertidal zone of each estuary. Analysis of sediment grain size, porosity, proportion of aggregated particles, total carbonate content and organic geochemical characteristics (total OM content, atomic TOC/TN ratio, δ13C value) of surface sediments allowed identifying four biosedimentary facies: sand flat, mud flat, low and high salt marshes. In parallel, the elemental and isotopic characterization of the suspended particulate OM inputs by the rivers, the surface biofilms and the halophytic vegetation was performed to trace the three major sources contributing to sedimentary OM in both estuaries. Spatial distribution of OM in surface sediments (ranging between 0.6 and 26.9% dry weight) evidenced higher contents along marsh platforms than in sand and mud flats. and the OM pool was mainly constituted of a mixing of C3 terrestrial vascular plants, marine and riverine phytoplankton. The comparison between both estuaries highlighted that the geomorphology impacted by natural and anthropic factors plays a preponderant role in the distribution and the sources of sedimentary OM by influencing vegetation communities and hydrodynamic processes. In the context of sea level rise, an improved understanding of the OM dynamics within each biosedimentary facies is crucial to better constrain and assess the role of macrotidal estuaries in carbon cycle.