Sediment Density Research Articles

Inversion of ocean acoustic modal-dispersion and amplitude data for seabed geoacoustic models including attenuation

The long-range acoustic field due to an initial sound source in a shallow-water waveguide can be expressed as the sum of a number of dispersive, propagating modes. Modal-dispersion data (arrival time as a function of frequency), as extracted with warping time-frequency analysis, have been inverted to estimate seabed sediment sound-speed and density profiles. In this work, measurements of modal amplitudes as a function of frequency are combined with modal-dispersion data in a joint (simultaneous) inversion which also provides sensitivity to frequency-dependent sound attenuation coefficients in the sediment layers. Since the source signature (spectrum) is often unknown in practice, the relative amplitudes between modes can be considered as data, or the source spectrum can itself be included as additional unknowns in the inversion. Here, trans-dimensional Bayesian inversion is applied to modal-dispersion and amplitude data to estimate marginal probability profiles for sediment geoacoustic properties, including attenuation. The signal processing and inversion methods are demonstrated using modal-dispersion and amplitude data extracted from acoustic measurements made by a hydrophone-equipped underwater glider during the 2017 Seabed Characterization Experiment (Work supported by the Office of Naval Research).

Assessment of Stormwater Infiltration Basins Models Developed in Gaza Strip

Stormwater remains the sole source of aquifer recharge in the Gaza strip, which should be utilized properly through artificial infiltration. The study objective is to investigate and analyze the infiltration efficiency of three large exiting infiltration basins in the Gaza strip (Alamal, Asadaqa, and Waqf) using different infiltration techniques. The technique applied in Ala-mal basin is the natural surface spreading of stormwater while Asadaqa basin used the surface spreading combined with graveled boreholes. Waqf basin used non-graveled boreholes (empty shafts cased with UPVC pipes). The infiltration rate and efficiency were recorded and estimated for each basin during the 2021-2022 wet season and compared to a past 2017-2018 wet season at a water depth of 1.70 m. The study revealed that, the actual infiltration capacity of Waqf basin was estimated as 2,000 m3/day in the 2021-2022 wet season, twice that in the 2017-2018 wet season, with an infiltration efficiency of 57.47 %, that was attributed to the 18 drilled non-graveled boreholes, which enhanced the seepage of stormwater into the underlying soil. Asadaqa basin has the lowest infiltration efficiency of 3.90 % due to the continuous accumulation of thick and dense sediment layer on the basin floor, with nonchanged actual infiltration capacity (around 2,800 m3/day) between the two studied wet seasons. On the oth-er hand, Alamal basin infiltration efficiency was only 4.60 %, with actual infiltration capacity of 629 and 105.4 m3/day dur-ing the two wet seasons, respectively where some repair and upgrade works were performed at Alamal basin which enhanced the actual infiltration capacity but still far from the design infiltration capacity. For future studies, Waqf basin technique should be thoroughly studied and investigated as a novel artificial infiltration method, with deep study on the factors af-fecting the infiltration process.

Application of High-Precision Filters on Airborne Magnetic Data: A Case Study of the Ogoja Region, Southeast Nigeria

Aeromagnetic data from the Ogoja region, Southeast Nigeria, were enhanced using high-precision methods including the tilt angle of total horizontal gradient (TAHG), the softsign function (SF), and the improved logistic function (IL) with the aim of creating a new structural map. This new map can help improve the understanding of the trend, spatial distribution, and pattern of the lineaments. The TAHG, SF, and IL methods generated geologic structures with correlating trends, distributions, and patterns. However, the SF and IL techniques mapped the borders of geologic structures more precisely. The lineaments extracted from the SF and IL maps were reduced to equator (RTE) magnetic data, and a GIS was used to create structural maps with NE–SW, NW–SE, NNE–SSW, and NNW–SSE orientations. Furthermore, the depths (0–2100 m) of these geologic structures were estimated using the tilt depth technique (TDT). The high lineament density and thin sedimentation observed in the study area were triggered by the widespread Santonian igneous intrusions associated with the Abakaliki Anticlinorium. The techniques applied in our study can be employed in areas with the same conditions around the world for the precise delineation of geologic structures from magnetic and gravity data.

The accuracy of acoustic measurement for seabed detection and the appraisal of density criteria associated with the nautical bottom in the Patimban port development area, north of West Java, Indonesia

The implementation of nautical bottom in port areas characterised by muddy seabed has been discussed within the past tens of years. The nautical bottom is defined as a critical depth limit beyond which contact with a ship's keel causes either damage or unacceptable effects on controllability and manoeuvrability. In many cases, it is described in terms of sediment density criteria representing a specific area, obtained from either on-site physical measurement using mechanical instruments or laboratory tests of sampled sediments. However, the definition of nautical bottom still lacks comparison with the widely used acoustic measurement through echo-sounding. In this paper, we discuss results from geotechnical drilling and free-fall cone penetrometer probing to estimate the nautical bottom and its density criteria, as well as a hydrographic survey by means of echo-sounding. The study area is a low gradient, shallow, and mud-dominated seabed in the Patimban port development area, north of West Java, Indonesia. Samples of seabed from geotechnical drilling facilitate the development of a calibration curve to empirically relate the sampled sediments' undrained shear strength and density obtained from laboratory tests. The calibration curve is used to estimate density profiles from undrained shear strength profiles obtained from the free-fall cone penetrometer. Undrained shear strength profiles from 46 stations are converted into density profiles and their vertical gradient to detect the boundary between the water and the top-most seabed layer, i.e., the nautical bottom. Along with the deployment of the free-fall cone penetrometer, a dual-frequency echosounder survey is launched. The detected nautical bottom in each station is compared to the depths obtained from the dual-frequency echo-sounding. It is advised that the nautical bottom in our study area shall be associated with sediment density criteria of 1.29–1.33 t/m3. The nautical bottom typically lies at about the upper one-fourth of the approximately 0.4 m separation of acoustic depths observed from the high- and low-frequency returns from the dual-frequency echosounder. This finding confirms that high-frequency echo-sounding tend to underestimate the nautical bottom in muddy areas, while the low-frequency tend to overestimate it. The agreement between acoustic and nautical depth seems to be influenced by seabed sediment density. In an area with higher sediment density (1.31–1.33 t/m3), the coefficients of determination, r2, between nautical and acoustic depths are 0.94 and 0.87 for the high- and low-frequency returns, respectively. On the other hand, in an area with lower sediment density (1.29–1.31 t/m3), the coefficients are reduced to 0.15 and 0.12 for the high- and low-frequency returns, respectively. The work presented in this paper offers a supporting procedure to cope with the uncertainty of seabed detection performed by hydrographic surveys across a muddy and shallow coastal environment. Seabed surveys through echo-sounding in areas equivalent to where this study is carried out should be accompanied by physical seabed probing to assure the accuracy of bottom detection.

Sediment density flow distribution on wave‐influenced deltas

ABSTRACTDeltas are at the transition between fluvial and marine sedimentary environments where sediment density flows are often triggered during high river discharge events, forming submarine channels and sediment waves. On wave‐influenced deltas, longshore currents are particularly efficient at transporting sediment alongshore, reducing the likelihood of sediment density flows from occurring at river mouths. This study describes four deltaic sedimentary systems at different stages of their evolution on a formerly glaciated continental inner shelf of eastern Canada in order to better understand the distribution of sediment density flows on wave‐influenced deltas. Three types of settings are recognized as being prone to sediment density flows: (i) in the early stages of wave‐influence and on large deltas, converging longshore currents can lead to offshelf sediment transport; (ii) on wave‐influenced to wave‐dominated deltas, a sandy spit can re‐route the river mouth and sediment density flows form where the spit intersects the delta lip; (iii) in advanced stages of wave‐dominated deltas and during their demise, rocky headlands are exposed and can intersect the slope, where off‐shelf sediment transport occurs. These types of sediment density flows were all characterized by debris flows or surge‐type turbidity currents which have limited offshore run‐out. More rarely, hyperpycnal flows form at the river mouths, especially where the river incises glaciomarine clays prone to landsliding in the river, which increases fine‐grained fluvial suspended sediment concentration. Overall, these results highlight the predominance of fluvial‐dominated deltas during a phase of relative sea‐level fall combined with high sediment supply. However, as soon as sediment supply diminishes, wave action remobilizes sediment alongshore modifying the distribution and types of sediment density flows occurring on wave‐influenced deltas.

Experimental investigation of the effects of shrub filter strips on debris flow trapping and interception

Ecological engineering plays an increasingly significant role in mountain hazard control, but the effect of species selection and arrangement (e.g., row spacing and stem spacing) on debris flow suppression is still unclear. To further understand the interception efficiency of shrub arrangement parameters on debris flow and explore the difference with slow hydraulic erosion, sixteen sets of small-scale flume experiments with different stem and row spacings were done to study the effects of shrubs on debris flow severity, flow rate, velocity, and particle size. The results suggest that, for a dilute debris flow, sediment interception effectiveness (27.4%–60.9%) decreases gradually as stem spacing increases. Moreover, as row spacing increases, flow velocity reduction (34.4%–44.9%) and flow reduction (18.5%–47.4%) gradually decrease; and the bulk density reduction (0.5%–5.3%) and sediment interception increase initially and then decrease. In contrast, for a viscous debris flow, the flow reduction, flow velocity reduction, and sedimentation interception decrease gradually as the stem spacing increases. As row spacing increases, the flow velocity reduction, flow reduction, and sediment interception all increase initially and then decrease. A formula for the flow velocity of dilute debris flow after the filter strip was derived based on the energy conservation law and Bernoulli's equation, confirming that debris flow movement is closely related to the degree of vegetation cover. This research strengthens the current understanding of the effectiveness of vegetation in debris flow disaster prevention and control and can guide practical applications.

Volume Contraction in Shallow Sediments: Discrete Element Simulation

Displacements induced by mineral dissolution and subsurface volume contraction affect overlying soils. In this study, we examine the consequences of mass loss or volume contraction at shallow depths using a discrete element method. The goal of the study is to identify particle-scale and global effects as a function of the relative depth of a dissolving inclusion, initial soil density, and granular interlocking. There are successive arch formation and collapse events, and a porosity front propagates upwards as grains slide down to refill the space. Grains around and within the refilled cavity are loosely packed and have small contact forces that are sufficient to avert the buckling of granular arches that form around the dissolving zone. Denser packings and interlocking combine to exacerbate rotational frustration and lead to more pronounced force chains along granular arches, looser fill, and reduced surface settlement. In fact, surface settlement vanishes, and the sediment hides the localized dissolution when deep inclusions z/D ≥ 5 dissolve within dense sediments. While scaling relations limit the extrapolation of these numerical results to tunneling and mining applications, macroscale trends observed in the field resemble results gathered in this study.

Spatial and Temporal Variability of Bed Exchange Characteristics of Fine Sediments From the Weser Estuary

Sedimentation of fine-grained sediments in estuaries is a natural physical phenomenon influenced by biogeochemical processes. In the estuarine turbidity maximum (ETM), enhanced net deposition of sediments is observed even in areas with higher hydrodynamic exposure, such as the navigational channel. Maintenance dredging is a common method to maintain the navigational channel, which requires large financial effort and has potential negative impacts on the environment. Research at the Institute for River and Coastal Engineering addresses the challenge of understanding the processes leading to net sedimentation and accumulation in estuarine navigational channels in reach of the ETM. In this contribution, investigations of bed exchange properties of estuarine cohesive sediments conducted in field and laboratory studies are presented. The results provide rarely available and estuary-specific parameters characterizing sediment transport, mainly related to erosion processes. By performing field campaigns within the ETM of the Weser estuary, cores of freshly deposited sediments have been sampled from two sites (Blexer Bogen and Nordenham) along the center of the navigational channel. Sediment characteristics (grain size distribution, water content, loss on ignition, density profiles) have been derived, and the erodibility of the deposits is investigated both quasi in situ and in the laboratory using an erosion microcosm system. Erodibility experiments are run in a closed system so sediment concentration above the lutocline increases during the experiment. This is a unique feature of this study, and it is expected to produce more natural characteristics of net erosion. By proving the reproducibility of the natural structure of the deposited sediments (stratification and density profiles) in the laboratory, systematic studies for analyzing the sensitivity of determined parameters (shear stresses and erosion rates) to varying environmental conditions (settling conditions and density) could be performed. Temporal development of suspended sediment concentration and erosion rates is the main result of the erodibility experiments, from which we derive bandwidths for erosion parameters, like floc erosion rate, critical shear for floc erosion, and critical shear for mass erosion.

Competing effects of vegetation density on sedimentation in deltaic marshes

Marsh vegetation, a definitive component of delta ecosystems, has a strong effect on sediment retention and land-building, controlling both how much sediment can be delivered to and how much is retained by the marsh. An understanding of how vegetation influences these processes would improve the restoration and management of marshes. We use a random displacement model to simulate sediment transport, deposition, and resuspension within a marsh. As vegetation density increases, velocity declines, which reduces sediment supply to the marsh, but also reduces resuspension, which enhances sediment retention within the marsh. The competing trends of supply and retention produce a nonlinear relationship between sedimentation and vegetation density, such that an intermediate density yields the maximum sedimentation. Two patterns of sedimentation spatial distribution emerge in the simulation, and the exponential distribution only occurs when resuspension is absent. With resuspension, sediment is delivered farther into the marsh and in a uniform distribution. The model was validated with field observations of sedimentation response to seasonal variation in vegetation density observed in a marsh within the Mississippi River Delta.

Stratigraphic record reveals contrasting roles of overflows and underflows over glacial cycles in a hypersaline lake (Dead Sea)

In lakes and oceans, links between modern sediment density flow processes and deposits preserved in long-term geological records are poorly understood. Consequently, it is unclear whether, and if so how, long-term climate changes affect the magnitude/frequency of sediment density flows. One approach to answering this question is to analyze a comprehensive geological record that comprises deposits that can be reliably linked to modern sediment flow processes. To address this question, we investigated the unique ICDP Core 5017-1 from the Dead Sea (the largest and deepest hypersaline lake on the Earth) depocenter covering MIS 7-1. Based on an understanding of modern sediment density flow processes in the lake, we link homogeneous muds in the core to overflows (surface flood plumes, ρflow<ρwater), and link graded turbidites and debrites to underflows (ρflow>ρwater). Our dataset reveals (1) overflows are more prominent during interglacials, while underflows are more prominent during glacials; (2) orbital-scale climate changes affected the flow magnitude/frequency via changing salinity and density profile of lake brine, lake-level, and source materials.

Organic matter pools in sediments of the tidal Elbe river

Anaerobic sediment organic matter decay generates methane, delays sediment consolidation, reduces sediment density, viscosity and shear strength, all impacting the sediment rheological parameters and the navigable depth. This study quantifies the share of anaerobically and aerobically degradable sediment organic matter (SOM) in a depth profile and along a transect through the tidal river Elbe in the section of the Port of Hamburg. From exponential organic matter decay functions, organic matter decay rates (mg C gTOC−1 d−1) were derived and clustered with a k-Means Cluster Analysis. The reactivity of different (kinetic) organic matter pools along the river transect were characterized based on their biodegradation rates. A fast, medium, slowly and non-degradable pool (pools 1–4) were identified based on the measured organic matter lability. SOM lability decreased from upstream to downstream, evidenced by the decreasing amount of the easily degradable pool 1 material from upstream to downstream. The size of the slowly degradable pool 3, assumed to be associated with SOM bound to the mineral particles, did not show any spatial gradient and is therefore suggested to represent a baseline share of hardly accessible SOM in the investigation area (about 12%−16% of TOC). Total degradability thus appears to be governed by the amount of SOM present in addition to this basis (pool 3), which in turn follows a source gradient and an age gradient from upstream to downstream. The recalcitrant pool 4 was the largest at any part of the harbour, for any depth, and for both, anaerobic and aerobic conditions (about 75%−85% of TOC). This indicates that the sediment in the investigation area, including the uppermost fluidic and freshly settled layers, mostly comprises stabilised organic matter and contributes largely to storage of organic carbon. Differently sized anaerobic SOM pools with depth were observed as well as seasonal changes of the easily degradable SOM pool 1. The degradability was larger in upper sediment layers, it was also larger under aerobic conditions (by about 10% of TOC) but the differences between aerobic and anaerobic decay decreased from upstream to downstream.

Assessment of sediment profiles applying nuclear techniques: use of a nucleonic gauge in Panama Canal watershed

An industrial nuclear technique based on the use of an X-ray profiler was implemented to estimate the densities or concentrations of sediments present in an Atlantic maritime zone in the areas subjected to dredging under the governance of the Panama Canal Authority (ACP).The sediment profiles show in most areas there is a concentration of between 1.00-1.15 g/cm³ except for one area in particular, the density starts at 1.20 g/cm³ and even reaches values greater than 1.50 g/cm³; therefore, an already consolidated sediment is present, which, depending on the depth found. Values of 1.265 g/cm³, 1.297 g/cm³, 1.185 g/cm³ obtained by ACP previous studies are within the range of 1.20–1.30 g/cm³ measured with the nucleonic gauge. However, it should be noted that during the tests with the X ray profiler, sediment densities values greater than the aforementioned limit were also obtained that varying according at depths close to 12 m and 18 m with values reached up to 1.513 g/cm³ and 1.60 g/cm³, respectively. This demonstrates that sediment accumulation depends on depth. This nucleonic gauge is feasible technique for the study of the sedimentation phenomenon in channel basins and even in other projects nationwide.

The Mass Distribution of Soputan Volcano Based on Gravity Data

The gravity method is a passive method based on the density measurement among sediment. This method is usually applied to identify the condition of the earth’s subsurface. Soputan Volcano is located in District Minahasa Tenggara. Soputan Volcano is included in type A Volcano or stratovolcano and it stands at 1783.7 MSL. This research aims to identify the distribution of subsurface mass (sediment density) of Soputan. The data used was Data from satellite GGmPlus and elevation data of ERTM which was corrected to ellipsoid reference. 3D inversion modeling applied Grablox software. The complete value of the Bouguer anomaly obtained was 110 – 162 mGal. The density result obtained from the inversion model was 2.3 g/cm3 to 2.95 g/cm3. The sediment that could be identified was andesite sediment and basalt sediment. Based on that result, the layer arranging Soputan Volcano consists of many variations of mass in each depth grouped into andesite, breccia, basalt, andesite-basaltic, lava, breccia, and tuff.

Development of a Density Gauge for Measuring Water and Mud Density based on a Radioactive Technique

The density or concentration of mud is one of the key variables in studying cohesive sediments, due to being accumulated through settlement and consolidation, as well as resuspended through erosion. This indicates that the proper measurement of sediment density is important. Therefore, this study aims to evaluate the accuracy of density measurement by using the gamma-ray attenuation method as a non-intrusive technique. For Compton Scattering, gamma-ray attenuation was effectively independent of mineralogy, subsequently depending on only the electron density of the material, which is directly related to the bulk density of the mixture. Based on the results, the advantages of utilizing the nucleonic density gauge indicated that the technique was non-intrusive and very flexible for many experimental arrangements, as well as the high accuracy of measurements with errors less than 1%.

Asymmetric abundances of submarine sediment waves around the Azores volcanic islands

Sediment waves are common on the submarine flanks of volcanic islands, but the processes that form them are difficult to decipher from geophysical data alone. Here, we identify downslope-trending trains of sediment waves in multibeam sonar data from five islands of the Azores. Train abundances are derived by counting the train intersections with depth contours around each island, revealing that they are typically twice as common on the north slopes of the islands compared with their south slopes. To provide context, we also characterise the Holocene mobility of sediments on the shelves, ocean density structure (for evaluating internal wave critical gradients) and sediment lithologies in four cores from beneath the slopes, which contain shelf carbonates in some volcaniclastic turbidites. Holocene mobility is assessed using sidescan sonar data, which reveal shelf-crossing sand streams. Using results of a high-resolution wave model, wave-imposed shear stresses are found to have exceeded the stresses at threshold of motion for most of the modern shelf sediments during recent extreme wave conditions.Sediment waves could potentially arise from sedimentary flows, gravity mass movements (shallow slumping) or ocean internal waves. Sedimentary flow origins are favoured by streamwise changes of wavelengths and upslope bedform migrations suggested by seismic reflections. The asymmetry of abundances north and south of each island is also an important clue. For example, it is unlikely that systematically different sediment geotechnical properties occur on the two sides of the islands, hence no reason to expect greater mass movements on northern slopes. Internal waves originate mainly from the south and hence also do not explain the asymmetry. Primary volcaniclastic flows are likely to be equally important on both sides. Sedimentary flows originating from shelf sediment agitated during storms or from failed slope sediment appear to explain best the asymmetry. In that case, prevailing wind and waves approaching the islands from the northwest lead to more frequent sediment gravity flows because they lead to greater flux of sediment from coastal erosion towards northerly outer shelves and upper slopes, where it is prone to slope failure. Offshore-directed near-bed currents originating from northwesterly wind-driven surface currents also transport shelf sediment efficiently to the north, further aided by greater wave agitation on that side. The high abundances of wave trains on the north sides of the islands therefore favours origins involving sedimentary gravity flows associated with wind and wave effects.

First source-to-sink monitoring shows dense head controls sediment flux and runout in turbidity currents.

Until recently, despite being one of the most important sediment transport phenomena on Earth, few direct measurements of turbidity currents existed. Consequently, their structure and evolution were poorly understood, particularly whether they are dense or dilute. Here, we analyze the largest number of turbidity currents monitored to date from source to sink. We show sediment transport and internal flow characteristic evolution as they runout. Observed frontal regions (heads) are fast (>1.5 m/s), thin (<10 m), dense (depth averaged concentrations up to 38%vol), strongly stratified, and dominated by grain-to-grain interactions, or slower (<1 m/s), dilute (<0.01%vol), and well mixed with turbulence supporting sediment. Between these end-members, a transitional flow head exists. Flow bodies are typically thick, slow, dilute, and well mixed. Flows with dense heads stretch and bulk up with dense heads transporting up to 1000 times more sediment than the dilute body. Dense heads can therefore control turbidity current sediment transport and runout into the deep sea.

The ProkaBioDen database, a global database of benthic prokaryotic biomasses and densities in the marine realm

Benthic prokaryotes include Bacteria and Archaea and dominate densities of marine benthos. They play major roles in element cycles and heterotrophic, chemoautotrophic, and phototrophic carbon production. To understand how anthropogenic disturbances and climate change might affect these processes, better estimates of prokaryotic biomasses and densities are required. Hence, I developed the ProkaBioDen database, the largest open-access database of benthic prokaryotic biomasses and densities in marine surface sediments. In total, the database comprises 1,089 georeferenced benthic prokaryotic biomass and 1,875 density records extracted from 85 and 112 studies, respectively. I identified all references applying the procedures for systematic reviews and meta analyses and report prokaryotic biomasses as g C cm−3 sediment, g C g−1 sediment, and g C m−2. Density records are presented as cell cm−3 sediment, cell g−1 sediment/ sulfide/ vent precipitate, and cell m−2. This database should serve as reference to close sampling gaps in the future.

Intrusions of sediment laden rivers into density stratified water columns could be an unrecognized source of mixing in many lakes and coastal oceans

AbstractWhen a sediment laden river flows into a stratified water body, the water mass can either intrude as an overflow, interflow or underflow, depending upon the density contrast. Different modes of sediment driven convection occur in each case. For the case of overflows, convective sedimentation occurs beneath the plume, whereby sediment rich plumes rapidly transport fine materials to depth. If underflow of dense sediment laden waters initially occurs, then after sediment has been deposited, the light interstitial material can subsequently loft and potentially mixes the entire water column. For an interflow, both lofting and sediment driven convection can occur above and below the pycnocline. All of these different regimes can be described in terms of two dimensionless parameters: namely RS = ΔρS/ΔρC and RA = ΔρA/ΔρC, where ΔρA is the density contrast between the upper layer and the river inflow (due to just salinity or temperature differences), ΔρC is the density contrast due to sediment between river and upper‐layer, and ΔρS is the density contrast between upper and lower layers (due to just salinity or temperature differences). Laboratory experiments were used to describe the vigour of convection in terms of these dimensionless parameters, which then allows behaviour of various inflows to be predicted. In most cases the convective velocities observed were an order of magnitude faster than Stokes settling velocities. These observations are also applied to predict how a turbidity current could lead to lofting and possible overturn of the stratification of Lake Kivu, a large meromictic lake between Rwanda and the Democratic Republic of the Congo.

Beyond habitat boundaries: Organic matter cycling requires a system‐wide approach for accurate blue carbon accounting

AbstractAs coastal ecosystems become widely recognized for their capacity to sequester carbon (blue carbon), standard accounting methodologies for the generation of carbon credits are being developed. To ensure the applicability of these standards across blue carbon ecosystems, we investigated organic carbon provenance and burial in salt marshes and seagrass meadows of an arid, upwelling‐dominated Eastern Pacific lagoon. We found low carbon density in benthic sediments of Bahía de San Quintín (5.9 ± 0.5 mg C cm−3), only marginally higher in Zostera marina beds (6.9 ± 0.5 mg C cm−3), likely due to remineralization and hydrodynamically driven export of seagrass material, resulting in low carbon burial rates (4.5 ± 2.5 g C m−2 yr−1). Sediment organic carbon is mainly controlled by the fraction of fine sediment and its source is largely allochthonous, although sources differ spatially. Salt marshes at San Quintín derive 40% of their organic matter from autochthonous material and exhibit higher carbon burial rates (up to 414.7 ± 28.6 g C m−2 yr−1) and sediment carbon densities (32.0 ± 0.7 mg C cm−3) compared to benthic sediments. This study emphasizes the connectivity of blue carbon habitats with marsh plant detritus supplementing benthic carbon burial and incorporation of detrital eelgrass in marsh sediments. Our findings highlight the importance of allochthonous organic matter for carbon sequestration in blue carbon habitats, suggesting standard accounting practices that deduct allochthonous organic matter would miss the full potential for carbon burial.

An empirical formula development to predict suspended sediment load for Khour Al-Zubair port, South of Iraq

AbstractA new formula for determining the suspended sediment load in Khour Al-Zubair port has been proposed using dimensional analysis. Six cross-sections have been identified in Khour Al-Zubair port at Basrah province, South of Iraq for the purpose of conducting field measurements during the two tidal periods (Neap and Spring). The study involved taking field measurements of the hydraulic and fluid properties, and sediment sampling by section every 2 h to get effective parameters used for developing empirical formula. These parameters include the density of sediment (ρs), mean velocity (V), hydraulic radius (Rh), fall velocity of the particle (Ws), median grain size (d50), the salinity of water (S), water level (WL), the width of the estuary (B), specific gravity (Gs), maximum flow depth (Dmax), and kinematics viscosity (ν). The formula was developed using the statistical analysis using the SPSS program and dimensional analysis method. A good agreement between the loads computed by the suggested formula and the observed data has been attained based on the correlation coefficient value (R= 0.97). The results showed that the average total suspended sediment loads by using the proposed formula is 1288285.464 tons/year.