Sediment Water Content Research Articles

Study on the influence parameters and anti‐abrasion performance of steam‐cured hydraulic concrete for prefabricated water conveyance channel

AbstractExcessive sediment concentration in water can cause damage to prefabricated concrete channels. This study evaluates the impact of sediment‐laden water flow on the mass loss of concrete after abrasion, incorporating scanning electron microscope‐energy dispersive spectrometer (SEM‐EDS) and X‐ray diffraction (XRD) analyses to assess the effects of four steam‐curing parameters—delay time, heating rate, constant temperature duration, and steam curing temperature—on the abrasion resistance of concrete used in enterprise prefabricated water conveyance channels. The results indicate that the abrasion resistance of concrete for prefabricated channels improves gradually with increases in delay time and constant temperature duration. When the delay time exceeds 3 h and the constant temperature time exceeds 4 h, the concrete's abrasion resistance can reach more than 5 h(g/cm2)−1. Rapid heating rates and excessively high steam curing temperatures adversely affect the concrete's abrasion resistance. However, when the heating rate is controlled within 20°C/h and the steam curing temperature does not exceed 70°C, the concrete's abrasion resistance can achieve more than 5 h(g/cm2)−1. In compliance with the standard DL/T5201‐2021 requirements, it is recommended that concrete with high demands for abrasion resistance should preferentially select steam‐curing parameters within these ranges.

Nitrogen oxides emissions from coastal wetland sediments: Experimental assessment of the influence of vegetation and nitrogen input

Nitrogen oxides (NOx = NO + NO2) have essential impacts on global climate and the environment, making it essential to study the contribution of wetland-generated NOx to environmental problems. With exogenous nitrogen input from anthropogenic activities, wetland sediments become active emission hotspots for NOx. In this study, we conducted field experiments in a typical salt marsh wetland to measure nitric oxide (NO, the primary component of NOx from sediments) exchange fluxes in both mudflat and vegetated sediments. We found that NO fluxes in vegetated sediments (0.40 ± 0.15 × 10−12 kg N m−2 s−1) were relatively higher than in mudflat sediments (−1.31 ± 1.39 × 10−12 kg N m−2 s−1), with this difference occurring only during the vegetation-dying season (autumn). Correlations between sediment NO fluxes and environmental parameters revealed that NO flux variation during the observation period was primarily influenced by sediment respiration, temperature, water content, and substrate availability. However, the influence of these factors on NO fluxes differed between mudflat and vegetated sediments. In-situ data analysis also suggested that tidal horizontal migration, which affects sediment substrate and salinity, may regulate sediment NO emissions. Furthermore, in-situ incubations with nitrogen addition (ammonia, nitrite, and nitrate) were conducted to study the response of sediment NO emissions to exogenous nitrogen. We observed that nitrogen addition caused a 259.7 % increase in NO emissions from vegetated sediments compared to the control during the effective period of nitrogen addition (days 1–3). However, although nitrogen addition markedly stimulated sediment NO emissions, the overall NO production capacity constrained the extent of this increase.

Consequences of intense drought on CO2 and CH4 fluxes of the reed ecosystem at Lake Neusiedl

Reed (Phragmites australis) dominated wetlands are commonly known as strong carbon (C) sinks due to the high productivity of the reed plant and C fixation in the wetland soil. However, little is known about the effects of drought on reed-dominated wetlands and the possibility of Pannonian reed ecosystems being a source of greenhouse gases (GHG). The drought at Lake Neusiedl had a particular impact on the water level, but also had consequences for the reed belt. Therefore, we investigated the drought-influenced C fluxes and their drivers in the reed ecosystem of this subsaline lake over a period of 4.5 years (mid-2018 to 2022). We applied eddy covariance technique to continuously quantify the vertical turbulent GHG exchange between reed belt & atmosphere and used vegetation indices to account for reed growth. Methane emissions decreased by 76% from 9.2 g CH4-C m-2a-1 (2019) to 2.2 g CH4-C m-2 a-1 (2022), which can be explained by the falling water level, the associated drying out of the reed belt and its consequences. Carbon dioxide emissions initially decreased by 85% from 181 g CO2-C m-2 a-1 (2019) to 27 g CO2-C m-2 a-1 (2021), but then increased to twice the 2019 level in 2022 (391 g CO2-C m-2 a-1). Due to the drying reed belt, the reed initially grew into formerly water-covered areas within the reed belt, especially in 2021, leading to higher photosynthesis through 2021. This development stopped and even reversed in 2022 as a consequence of the sharp decrease in sediment water content from about 65 to 32 Vol-% in mid-2022. Overall, drought led to a decoupling of the reed ecosystem from the open lake area and developed the wetland into a strong C source.

Sediment water content drives movement of intertidal crab Helice tientsinensis more strongly than salinity variations

Intertidal wetlands undergo dynamic water and salinity variations, creating both promising and challenging habitats for diverse organisms. Crabs respond strongly to these variations by means such as altering their movements, thereby restructuring their spatial distribution and influencing coastal ecosystem resilience. However, the movements of crabs under varying environmental conditions require further elucidation. We conducted a systematic mesocosm experiment using the ubiquitous intertidal crab species Helice tientsinensis with four amount levels and six salinity levels of sprayed water applied through a custom apparatus, with a primary focus on crab movement. Crab movement from the experimental side of the apparatus (with altered conditions) to the control side (resembling field conditions of the intertidal wetlands of China's Yellow River Delta) and vice versa was recorded. The results revealed significant differences in moving out of the experimental side and moving in among the different water and salinity conditions, both separately for the two factors and simultaneously. Decreases in water content had a more pronounced effect on crab movement, leading to an increased number of crabs moving out of the experimental side of the apparatus. Conversely, as the experimental side became wetter, crabs tended to move towards it, and this movement was intensified by increases or decreases in water salinity. A structural equation model revealed that the moving-out and moving-in played fundamental roles in determining the number of resident crabs at the end of each experiment. While crabs preferred moist sediment with lower salinity, changes in salinity alone had minimal direct effect compared to sediment water contents. Our results clarify crab movements under varying water and salinity conditions, offering valuable insights to support adaptive interventions for crab populations and inform adaptive conservation and management strategies in intertidal wetlands.

Water Content and Pb Concentrations in the Bottom Sediments Of The Gdansk Deep (South-Eastern Baltic Sea) According to the Portable X-Ray Fluorescence Analyzer Olympus Vanta C

Water Content and Pb Concentrations in the Bottom Sediments Of The Gdansk Deep (South-Eastern Baltic Sea) According to the Portable X-Ray Fluorescence Analyzer Olympus Vanta C

Effect of temperature on surface fluid sediment properties with cyanobacterial bloom biomass accumulation

In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then settle into sediment, leading the formation of fluid sediment. Several factors including temperature can influence surface sediment properties. In this study, the influence of temperatures on surface sediment properties was determined in microcosm experiments through monitoring sediment physicochemical and rheological properties. During one-month incubation, it was found that surface sediment density and water content varied exponentially with increase in temperatures from 10 to 35 ℃. The results of particle size distribution indicated that cyanobacterial blooms biomass (CBB) degradation in sediment led to sediment flocculation and agglomeration. In the meantime, there were high ratios polysaccharide/protein in extracellular polymeric substances (EPSs), which enhanced the sediment particle agglomeration. Further, the yield stress in rheological test for sediment with (R2 = 0.97) and without (R2 = 0.85) CBB presented an exponential decay with increase in temperatures. And a threshold value at 20 ℃ for sediment critical shear stress (τcr) indicated that sediment could be resuspended easier when temperature was more than 20 ℃. Altogether, this study showed that the increase in temperatures with a threshold at 20 ℃, can cause sediment particle flocculation, resulting in a loose and fragile structure. And the results would be helpful to sediment management considering environmental effects of sediment suspension for eutrophication shallow lakes.

Distribution Patterns of Sediment Organic Carbon Stocks in Shallow Lakes and the Significance for Sustainable Lake Management: Chaohu Lake in Eastern China as a Case Study

Shallow lake sediments have huge potential for carbon storage, but they are vulnerable to various environmental changes and are highly susceptible to becoming a source of carbon emissions. Understanding the amount of sediment carbon storage can provide information about the potential of shallow lakes in mitigating climate change. In this study, sediment sampling was conducted at 12 study sites in Chaohu Lake, China, and sediment water content, grain size, bulk density, and sediments organic carbon (SOC) content were examined in five layers along the vertical direction, respectively, and the distribution and storage of SOC were estimated. The results showed that the surface sediments in the west lake area of Chaohu Lake would release 66,300 t of SOC to the overlying water body in the future. The sediments in the middle lake area and the east lake area will absorb another 15,900 t and 17,300 t of TOC from the water body in the future, respectively. Overall, the lake-wide sediments will release 33,100 t of SOC into the water body in the future. In addition, the results of the study also indicate that human activities are another major influence on the change in organic carbon stocks in lake sediments, and therefore, proactive measures for the restoration and protection of lake sediments are essential because increasing the SOC stocks in the sediments and maintaining the lakes in a sustainable manner can contribute to the crucial role they play in mitigating climate change.

Driving effects of dissolved organic carbon on cadmium release of the sediments by cyanobacterial decomposition

The driving effects of dissolved organic carbon (DOC) on cadmium (Cd) release of the sediments by cyanobacterial decomposition were investigated, and the great shallow lakes (Taihu Lake, China) with the algae-type, grass-type, and grass-algal alternation areas were chosen as the study area. The results showed that DOC concentration in the overlying water and Cd content in sediments were the highest in the algae-type areas, amounting to 6.4 mg L−1 and 2.4 mg kg−1, respectively, while the DOC contents in the surface sediments showed higher in the algae-type and grass-type areas. The sediments from the grass-type and algal-type areas showed the strong Cd source state, and only the sediments from Zhushan Bay had the sink state. Most of the sediments had the low Cd release risk, and the values of the degree of Cd saturation (DCdS) and Cd release risk index (CdRI) showed a significant correlation with the DOC content in the sediments (P < 0.05). The Cd release contribution originated from the surface sediments, and F1 (the extractable state of Cd form) was the main Cd release form (the maximum value of 51 % from grass-type areas). Due to the algal decomposition and the complex external environment, the contribution values of F2 (the reducible state of Cd form) and F1 was similar (40 %–47 %) in the process of Cd release from the surface and bottom sediments in grass-algae alternation areas, as well as in some algae-type areas. This study provides theoretical foundation for Cd release control at the ecosystems level.

Sedimentation Behavior of Flocculant-Treated Dredged Slurry under Filtration of Woven Geotextiles

Geotextile tubes have offered a cost-effective and convenient solution for the treatment of dredged slurry in recent years. Despite their benefits, the dewatering process of this method remains cumbersome and time-consuming. The incorporation of flocculants into dredged slurries has been shown to mitigate the clogging of geotextile tubes, thereby enhancing the efficiency of the dewatering process. To quantify the impact of flocculant addition on the dewatering performance, a series of laboratory tests were conducted to investigate the sedimentation behavior of flocculant-treated river-dredged slurries under filtration of woven geotextiles. The impact of different flocculants is evaluated with the sedimentation rates of dredged slurries, specifically nonionic polyacrylamide (NPAM) and cationic polyacrylamide (CPAM). Results demonstrated that both NPAM and CPAM, at an optimal concentration of around 250 mg/L, could substantially increase the settling rates of slurries when filtered through geotextiles. At equivalent flocculant concentration, NPAM outperforms CPAM in accelerating sedimentation rates. It is also evidenced that adding flocculants can significantly augment the particle size and permeability of slurries. After adding flocculants, the water content and dry density of the final sediments exhibit a more uniform distribution in the vertical direction compared to the original slurry. Furthermore, scanning electron microscopy was employed to analyze the micromorphology of the final sediments treated with different NPAM concentrations. The results showed that the slurries exhibited significant void structure under treatment with the optimal concentration of NPAM, demonstrating the flocculants’ effectiveness in enhancing the dewatering process of river-dredged slurries when filtered with geotextiles.

Hybrid engineering incorporating salt marsh terraces into sea wall repair maintains their defence function and creates new habitats

Sea walls are widely-used engineered structures designed to protect low lying land from flooding. Rising sea levels and coastal erosion threatens sea wall integrity and requires maintenance and repair. As an alternative to conventional repairs, a hybrid engineering design incorporating sediment-filled terraces to allow the development of salt marsh has been trialled to protect sea walls in the Colne-Blackwater Estuary complex, Essex. U.K. Over a 10 year period, three different trajectories of development were measured. Salt marsh halophytes colonised 7 out of 15 terraces, with % plant cover ranging between 5% and 170%. Halophyte species richness on terraces ranged from 1 to 8 species (average = 1.7 per 4 m2), compared to existing salt marsh adjacent to the repairs (max. species richness 9, average 6.85), with positive significant relationships between % halophyte cover and halophyte richness and between % halophyte cover and sediment water content (19–51% on terraces). Organic carbon content was significantly lower on the terraces compared to existing salt marsh (7–19 % AFDW on terraces, 17–24% in marsh sediments). A sediment shear strength of 30 kPa was optimal for % plant cover on terraces. The height of the terraces relative to tidal inundation was a key determinant of successful halophyte colonisation. A second trajectory (3 of 15 terraces) resulted in development of macro- and microalgal mats, up to 100 % cover. Both these trajectories resulted in up to 25 cm of vertical sediment accretion. Shell banks formed on 2 terraces. Seven terraces were subject to erosion, associated with desiccation and absence, or loss, of halophyte cover. Eroding terraces showed both surface lowering (20–30 cm) and massive sediment failure (blocks >50 cm deep falling away). After a decade, protection of the sea wall was still provided by 14 of the 15 terraces, with only one having to be rebuilt. Utilising a nature-based approach incorporating sea wall terraces resulted in the formation of three types of linear habitat (salt marsh, microbial mats, shell banks) providing some ecosystem services that would not have existed if a conventional hard-engineered repair had been used.

Loss of POC and DOC on seagrass sediments by hydrodynamics

Coastal development and climate change are sparking growing concern about the vulnerability of the organic carbon (OC) stocks in marine sediments to remineralization, especially in high threaten coastal ecosystems like seagrass meadows. Uncertainties still exist regarding the role played by hydrodynamics, seagrass canopies and sediment properties in OC resuspension and remineralization. A set of laboratory experiments were conducted to assess, for the first time, the mechanisms by which the particulate and dissolved organic carbon (POC and DOC) may be released and remineralized under hydrodynamic conditions (i.e., unidirectional and oscillatory flows) in two eelgrass densities and sediments properties (i.e., grain size and OC content). After a gradually increase in hydrodynamic forces, our results demonstrated that the presence of eelgrass reduced sediment erosion and OC loss in high-density canopies, while low-density canopies promote OC resuspension (on average, 1.8-fold higher than high-density canopies). We also demonstrated that unidirectional and oscillatory flows released similar DOC from surface sediments (on average, 15.5 ± 1.4 and 18.4 ± 1.8 g m−2, respectively), whereas oscillatory flow released significantly more POC than unidirectional flows (from 10.8 ± 1.1 to 32.1 ± 5.6 g m−2 for unidirectional and oscillatory flows, respectively). POC and DOC released was strongly influenced by both seagrass meadow structure (i.e., lower eelgrass density and shoot area) and sediment properties (i.e., lower mud and higher sediment water content). We found that, although >74 % of OC in upper sediments was remineralized within 30 days, a relatively high amount of OC in high-density canopies is recalcitrant, highlighting its potential for the formation of blue carbon deposits. This study highlights the vulnerability of OC deposits in seagrass sediments to resuspension if the meadow is degraded and/or the climate change yield stronger storms, which could potentially weaken the seagrass meadows' service as blue carbon ecosystem in the future.

Mapping depth-integrated microphytobenthic biomass on an estuarine tidal flat using Sentinel satellite data

Microphytobenthos (MPB) are central to benthic tidal flat ecological networks. Large-scale information on total MPB biomass is difficult to obtain from traditional in-situ measurements. Here, we assessed the effectiveness of using surface sediment properties as proxies for predicting the total (depth-integrated) MPB biomass with Sentinel satellite data. First, the best subset regression was applied to the in-situ data to determine the properties that best predict the biomass decay rate with depth (sampling every cm up to 10 cm depth). Then, data from a controlled laboratory experiment were used to analyse the spectral response to different sediment properties (i.e., variations in sediment grain size, organic matter and water content). Subsequently, an algorithm was developed to obtain the spatial distribution of the sediment properties and the depth-integrated total MPB biomass from remote sensing data. Finally, we presented a case study in which the seasonal dynamics of total (depth-integrated) MPB biomass were obtained from Sentinel-2 Multispectral Instrument (MSI) satellite data using the Google Earth Engine (GEE) platform. The results showed that (1) the vertical distribution of MPB biomass on a tidal flat could be predicted by the surface MPB biomass, median grain-size (D50) and water content (W0) of the sediment (top 1 cm); (2) the near infrared (NIR) band absorption depth was a key feature in estimating D50 and W0; and (3) the seasonal variation in the total (depth-integrated) MPB biomass was prominent in Chongming Dongtan, Changjiang Estuary. We concluded that the depth-integrated exponential decay algorithm was useful for estimating total MPB biomass and, combined with mappable sediment-surface data, could help map the total MPB biomass in estuarine tidal flats at a large scale.

Statistical approach to identify variables predicting sulphide clay occurrence in southern Finland

Acid sulphate soil and sulphide-bearing sediments cause various challenges in construction projects and land use planning, as well as harmful environmental effects. Fine-grained sulphide sediments were mainly formed in coastal areas during the Litorina Sea water phase at approximately 7000 BP in the capital region of Finland, but not all these sediments contain sulphide clay. In this study, environmental and material property variables related to the depositional conditions of sulphide clay were selected for statistical analyses to find their association with the occurrence of sulphide. The datasets consisted of sulphide investigations by the City of Espoo, the City of Helsinki, and the Geological Survey of Finland. Statistically significant associations were found in the study area between the occurrence of sulphide and enumerative variables (i.e., sediment organic content, total clay depth, topographic class in the Litorina Sea phase, and water depth) in the Litorina Sea phase. Locations where sulphide clay is especially likely to occur consist of organic-rich (≥ 2%) thick clay (≥ 15 m) deposits in a topographically narrow depression with deep Litorina water (≥ 30 m), or where there is a moderate depth clay (3–5 m) in a local depression with shallow Litorina water (10–20 m). The best individual predictor for sulphide clay occurrence in the study area was found to be the sediment organic content, and, together with sediment water content, these variables very accurately predicted the occurrence of sulphide clay. In addition, clay depth is a very good predictor and, together with the topographic class narrow depression and the Litorina water depth or current elevation, can be used to predict sulphide occurrence.

Study on the Relationship between Resistivity and the Physical Properties of Seafloor Sediments Based on the Deep Neural Learning Algorithm

The occurrence of deep-sea geohazards is accompanied by dynamic changes in the physical properties of seafloor sediments. Therefore, studying the physical properties is helpful for monitoring and early warnings of deep-sea geohazards. Existing physical property inversion methods have problems regarding the poor inversion accuracy and limited application scope. To address these issues, we establish a deep learning model between the resistivity of seafloor sediment and its density, water content, and porosity. Compared with empirical formulas, the deep learning model has the advantages of a more concentrated prediction range and a higher prediction accuracy. This algorithm was applied to invert the spatial distribution characteristics and temporal variation of the seafloor sediment density, water content, and porosity in the South China Sea hydrate test area for 12 days. The study reveals that the dynamic changes in the physical properties of seafloor sediments in the South China Sea hydrate zone exhibit obvious stratification characteristics. The dynamic changes in the physical properties of seafloor sediments are mainly observed at depths of 0–0.9 m below the seafloor, and the sediment properties remain stable at depths of 0.9–1.8 m below the seafloor. This study achieves the monitoring and early warning of dynamic changes in the physical properties of seafloor sediments and provides a guarantee for the safe construction of marine engineering.

Detection of organochlorine pesticides in estuarine sediments of protected wetlands in Taiwan using high‐resolution gas chromatography/high‐resolution mass spectrometry and gas chromatography‐electron capture detector

AbstractTrace residues of organochlorine pesticides (OCPs) in estuarine surface sediments were investigated at three protected wetlands in southern Taiwan using high‐resolution gas chromatography/high‐resolution mass spectrometry (HRGC/HRMS) and gas chromatography‐electron capture detector (GC‐ECD). This study facilitates the development of new strategies for investigating OCPs, particularly at background levels. Linear relationships were obtained between total OCP concentrations (∑OCP), as analyzed by HRGC/HRMS, and the sediment's total organic carbon (TOC) and water content. It contrasted with the results acquired by GC‐ECD, where no significant relationship was found. GC‐ECD is a rugged option for daily routine practice, particularly in cases of patterns yielded by GC‐ECD is clear; the HRGC/HRMS method provides more reliable qualitative and quantitative capabilities and is highly recommended for studying the fate of OCPs and carrying out risk assessments. The average ∑OCP of these three wetlands by HRGC/HRMS was found in a range of 0.214 to 1.049 ng/g dry weight. The highest OCP level might be attributed to associated irrigation systems receiving massive discharges of domestic sewage from an urban area upstream of the wetland. The ratio of dichlorodiphenyltrichloroethane (DDT) to its metabolites indicated that the DDT residue in these areas was from aged input. According to sediment quality guidelines, adverse ecotoxicological effects of OCPs upon sediments were not expected in these protected wetlands.

The Influence of the Internal Properties of River Ice on Ground Penetrating Radar Propagation

Ground penetrating radar (GPR) has proven to be a very effective method for examining ice thickness. However, two preconditions must be met for this approach to be useful; the round-trip travel time of electromagnetic (EM) waves and radar transmission speed in the ice must be known. These issues are problematic because many factors affect radar transmission speed in ice, including impurities, physical properties such as porosity and density, and temperature. Results show that if these factors are not taken into account and a signal velocity of 0.17 m/ns in pure ice is used to estimate thickness, overestimates will result. We carried out a series of GPR surveys using dual channel host 200 MHz shielded antennas at the Toudaoguai Hydrological Station on the Yellow River, China, and collected samples to analyze ice impurities and physical properties. The results show that the ice crystal types include frazil, granular, and column at the Toudaoguai Hydrologic Station section. Our analysis of ice gas bubble and sediment content showed that the gas bubble volume content is between 11.95 and 13.0% in the frazil ice and between 7.9% and 8.6% in granular and columnar ice. At the same time, the ice sediment content ranged between 0.11‰ and 0.57‰, and the average was 0.24‰ in granular and columnar ice, which was about one-tenth that of the suspended sediment concentration in water. Additionally, a combination of GPR data as well as ice impurities, porosity, density, and temperature enabled us to provide insights on the variability of radar transmission speed and the equivalent dielectric permittivity in river ice. Our extensive observations reveal that radar transmission speed falls between 0.141 m/ns and 0.164 m/ns and that the equivalent dielectric permittivity of river ice increases in concert with ice temperature.

The Effect of Environmental Dredging of Muck on an Assemblage of Benthic Amphipods

To yield environmental benefits, fine sediments with ~10% organic matter, termed muck, were dredged from a tributary to the Indian River Lagoon. Key changes were documented by sampling amphipods, sediments, and the water column near the bottom before dredging, and approximately one month and one year after dredging. Overall, muck yielded the fewest taxa, muck or sediments in creeks that were dredged yielded a moderate number of taxa, and undisturbed sediments in the lagoon yielded the highest number of taxa. Amphipods did not appear in areas with muck until one month and one year after dredging. In contrast, amphipods in sediments that were not muck decreased after dredging. Increases in the occurrence of amphipods paralleled increases in concentrations of dissolved oxygen and decreases in the water, silt/clay, and organic content of sediments. Overall, results indicated that conditions for amphipods were improved by removing muck, and that dredging sandier sediment led to decreased taxonomic richness and numbers of amphipods, which resembled the effects of navigational dredging. Thus, this study suggested that managers should consider the type of sediment to be dredged when permitting projects.

Pore pressure evolution in bed sediment overridden by debris flow: A general formulation

AbstractDebris flows can grow dramatically in volume and mobility as they override bed sediment due to the reduction in bed friction resistance caused by high pore fluid pressure (PP). However, the mechanisms that control PP evolution in overridden bed sediment are still unclear. Here, a new mathematical model clarifies how diverse styles and magnitudes of PP evolution can result from regulation of the flow diffusion and shear contraction of bed sediment. Normalization of the model equations shows that the propensity for PP generation depends on timescales of PP diffusion and deformation of the bed grains. The PP of saturated bed sediment under immobile conditions is equal to the fluid pressure at the bottom of the flow due to a non‐flux basal boundary. However, the PP of unsaturated bed sediment is lower than that of the overlying flow. PP diffusion from a debris flow into an unsaturated bed increases with the bed’s permeability and water content. The shear deformation behavior changes from undrained to drained with increasing permeability or decreasing shear velocity of the saturated bed sediment, leading to a reduced magnitude of pore pressure. By contrast, the shear deformation transitions from drained to undrained behavior with increasing permeability and water content of unsaturated bed sediment. The entrainment rate and erosion pattern of bed sediment are closely related to the PP evolution and liquefaction ratio of the bed sediment due to Coulomb‐friction shear tractions. Our models can be used to interpret the feedback of PP on the flow momentum during debris flow entrainment.

Nitrogen loss from anaerobic ammonium oxidation coupled to Iron(III) reduction activity across estuarine and coastal wetlands of China: Spatial variations, controlling factors, and environmental implications

Anaerobic ammonium oxidation coupled with ferric iron reduction (Feammox) is a newly identified microbial nitrogen (N) removal process in natural ecosystems. However, little is known about the distributions of Feammox activity and their environmental drivers across estuarine and coastal wetlands at a continental scale. In this study, we determined the potential Feammox rates and related microbial diversities and abundances along the estuarine and coastal wetlands of China encompassing subtropical to temperate climate zones. Measured potential Feammox activity ranged from 0.05 to 0.23 mg N kg−1 d-1, and the process rates at the subtropical sites were generally higher than at the temperate sites. Partial least squares path model (PLS-PM) showed that the abundance of Fe reducing bacteria significantly and directly affected the potential Feammox rates, while sediment characteristics (mainly including sediment water content, Fe(III), TOC and NO3–) and geographical factors (longitude and latitude) had an indirect effect on the process rates. The N loss via the Feammox was approximately 1.72–7.89 kg N ha−1 year−1, accounting for 0.41–1.91 % of multi-annual average land-based inorganic N transported into the estuarine and coastal wetlands of China. Overall, this study reveals the distribution patterns and controlling factors of the Feammox process in estuarine and coastal wetlands of China, and provides a valuable database for N management in estuarine and coastal ecosystems.

The Suitable Sites for Seagrass Transplantation in Lae-Lae Island and Sandbar According to Sediment Characteristics

The success of a seagrass transplantation effort depends on identifying locations with optimal sediment characteristics for seagrass growth and survival. This study analyzed sediment characteristics of seagrass bed sediment and adjacent unvegetated sediment on Lae-Lae Island and Lae-Lae sandbar (Makassar, South Sulawesi) to determine the suitable sites for seagrass transplantation. Seagrass bed sediments and adjacent unvegetated sediments were collected from four locations to measure sediment particle size, redox potential, organic matter, water content, nitrate, and phosphate concentrations. Analysis of similarities (ANOSIM) was performed using PAST (Paleontological Statistics) software to determine a suitable site for seagrass planting (transplantation). The results show that surface sediments in the Lae-Lae island are composed of medium sand and coarse sand with grain sizes varying from 0.290 to 0.768 mm, whereas in the Lae-Lae sandbar, the sediment is composed of medium sands (0.371 – 0.460 mm). Redox potential (Eh) varied from -34.1 to -65.7mV, water contents were 1.3 to 1.8%, organic contents were 19.85 to 38.53%, nitrate content varied from 0.60 to 3.47, and phosphate content varied from 7.42 to 14.19 ppm. The percentage of mud (clay and silt) and organic matter were slightly higher in seagrass bed sediments compared to unvegetated area sediments. No differences in nutrient contents (nitrate and phosphate) between seagrass sediments and unvegetated were observed in this study. ANOSIM results show no difference in the sediment characteristics between a seagrass bed and unvegetated sand at the north and south sides of Lae-Lae Island and Lae-Lae sandbar, which means that these three sites are suitable for seagrass transplantation.Keywords: sediment, seagrass, transplantation, site selection, ANOSIM, Lae-Lae