Sediment Particle Size Research Articles

Response of nephelometric turbidity to hydrodynamic particle size of fine suspended sediment

Turbidity is used as a surrogate for suspended sediment concentration (SSC), and as a regulatory tool for indicating land use disturbance and environmental protection. Turbidity relates linearly to suspended material, however, can show non-linear responses to particulate organic matter (POM), concomitant with changes in particle size distribution (PSD). In the paper the influence of ultra-fine particulate matter (UFPM) on specific turbidity and its association with POM in suspended sediment are shown for alpine rivers in the Southern Alps of New Zealand. The approach was two-fold: a field-based investigation of the relations between SSC, POM, and turbidity sampled during event flow; and experimental work on hydrodynamic particle size effects on SSC, POM, PSD, and turbidity. Specific turbidity changes over event flow and are sensitive to increasing proportional amounts of sand, UFPM, and POM in suspension. Furthermore, the UFPM is the size fraction (<6 μm) where POM increases. The implications of the current study are that the slopes of turbidity-SSC relations are undesirable in locations that may be dominated by cyclic release of POM or distinct pulses of fine-grained material. At locations where the turbidity-SSC slopes approximate 2, the POM proportion is usually <10% of the total suspended load. However, when turbidity-SSC slopes are <1 this is likely caused by high amounts of side-scatter from UFPM concomitant with higher proportions of POM. Thus, the use of turbidity as a proxy for determining SSC may have serious consequences for the measurement of representative suspended sediment data, particularly in locations where POM may be a significant contributor to overall suspended load.

Pozolanicidade do resíduo cerâmico

&lt;p&gt;The construction industry is still responsible for generating a significant volume of waste from mortars, concrete and ceramic materials. We underline in this scenario the residue of ceramic bricks that can be used in the production of new materials, such as laying and coating mortars, concrete and ecological bricks. This usage allows the reduction of the percentage of binders in these compositions and, consequently, the reduction of costs, less consumption of non-renewable natural resources and the reduction of carbon dioxide emissions from clinker manufacture. In order to do so, it is necessary to make the scientific verification of the process of pozzolanic activity through the following experiments: X-ray Diffraction (XRD) mineralogical analysis, sieving and sedimentation particle size analysis, X-ray Fluorescence (FRX) chemical analysis and the verification of Ca(OH)2 consumption by the modified Chapelle experiment. The results showed that the ceramic residue from non-structural masonry has high levels of silica (SiO2 ), aluminum oxide (Al2 O3 ) and iron oxide (Fe2 O3 ). Secondary pozzolanic additive.&lt;/p&gt;

Hydrodynamic characteristics and channel morphodynamics at a large asymmetrical confluence with a high sediment-load main channel

Previous studies of confluences have concentrated mainly on confluences of small streams, confluences with simple geometric configurations, and confluences of curving rivers. However, the confluences of natural rivers, especially large confluences of high sediment-load rivers, generally have complex geometric confluent boundaries and various incoming flow and sedimentation conditions. In this study, several field measurements of the three-dimensional velocity components, water surface elevation, bed topography, and suspended sediment particle sizes reveal the complex hydrodynamic characteristics and bed morphology of the asymmetrical confluence of the high sediment-load Yellow River and its clear tributary, the Fen River. The results show that the water surface morphology of this confluence is elevated in the stagnation zone, mixing interface, and the opposite side of the tributary, whereas the converse is true at the downstream junction corner. The geomorphologic features of the bed show a small scour hole and a long narrow scour belt under conventional hydrological conditions, or a larger scour hole under hydraulic conditions when the value of the momentum flux ratio is much greater than one. In contrast to the confluences of small streams and curving rivers, this confluence does not exhibit continuous flow separation or helical motion, but has pronounced regions such as a stagnation zone, flow acceleration and deflection areas, a shear layer/mixing interface, and a flow recovery zone. The position and size of these regions vary with the momentum flux ratio. The particle size of suspended sediment at the confluence is normally distributed, and the changing sedimentation process corresponds to the scour and siltation state of the bed. In general, the particle size of the suspended sediment is small in the stagnation zone and the downstream channel near the tributary, but large in the acceleration zone and shear layer. These results are helpful to better understand the hydrodynamic and morphodynamics characteristics of confluences with complex geometric configurations and junction conditions.

Sediment deformation and strain evaluation during methane hydrate dissociation in a novel experimental apparatus

Natural gas hydrate is an efficient alternative future energy source because huge reserves of methane gas are caged in hydrate-bearing sediments. The research on the deformation of sediments during hydrate dissociation is important for safe hydrate production. In this work, a novel experimental apparatus was designed and built to investigate sediment deformation and strain evaluation during methane hydrate dissociation by depressurization. Experimental results are compared for methane hydrate dissociation for various hydrate saturations, porosities, and particle sizes of sediments. Experimental results illustrate that gas hydrate dissociation by depressurization experienced three main stages. The phenomenon secondary hydrate formation was found during hydrate dissociation by depressurization, which leads to the decrease of sediment permeability. The strain of the sediment is proportional to the volume of methane gas production. Higher hydrate saturation leads to larger sediment deformation by hydrate decomposition. Higher sediment porosity leads to looser sediment particles and larger sediment deformation during hydrate dissociation by depressurization. Larger sediment particle sizes lead to smaller interface areas between hydrate and sediment particles, and larger sediment deformation during hydrate dissociation by depressurization.

Influence of flow on phosphorus-dynamics and particle size in agricultural drainage ditch sediments.

Particle size is one factor affecting phosphorus (P) dynamics in soils and sediments. This study investigated how flow facilitated by hydraulic pumps and aquatic vegetation species water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes) affected particle size and P-dynamics in organic sediments in agricultural drainage ditches. Sediments with finer particle size (>0.002 mm) were hypothesized to contain greater total P (TP) and less labile P than sediments with coarser particle size. Particle size was determined using a LS 13 320 Laser Diffraction Particle Size Analyzer. Sediments were tested for pH, TP, and organic matter. Fractions of P were determined using a sequential fractionation experiment and 31P Nuclear Magnetic Resonance (NMR) Spectroscopy. Larger average particle size and lower average total P concentrations were found in the inflows of the field ditches compared to the outflows. Presence of flow and aquatic vegetation did not have a significant impact on particle size, TP, or labile P fractions. Median (p = 0.10) particle size was not significantly correlated to TP. Overall, there was an average trend of coarser particle size and lower P concentrations in the inflow compared to the outflow. The presence of inorganic limerock could have affected results due to increased P adsorption capacity and larger average particle size compared to the organic fraction of the sediment.

Impact of Formulation and Suspension Properties on Redispersion of Aluminum-Adjuvanted Vaccines

The adsorption of antigens to the surface of 2 commonly used insoluble adjuvants, aluminum phosphate and aluminum hydroxide, has been well characterized. In spite of the pharmaceutical benefits, alum-based vaccine formulations can present challenges in redispersion of the final product after storage. Inability to resuspend alum-based vaccines during administration results in inadequate dosing, thus rendering the product unusable. Here, the influence of formulation conditions on the resuspendability of aluminum adjuvant–containing vaccines was investigated. Particle size analysis by Micro-Flow Imaging (MFI™), zeta potential measurement, and sedimentation analysis by Turbiscan® were used to characterize suspension properties. Ionic strength, pH, and antigen concentration were found to significantly influence sedimentation behavior, particle size, and redispersion. Increasing ionic strength increased the sedimentation rate of adjuvants favoring resuspendability. The addition of bovine serum albumin to aluminum phosphate reduced resuspendability more significantly than the addition of lysozyme. Decreased resuspendability correlated with an increase in fine-to-large particle ratio and decrease in sedimentation rate. In summary, resuspendability of adjuvant drug product is favored by increased flocculation, decrease in fine-to-large particle ratio, and reduction in surface charge of antigen and adjuvant. A careful balance of these formulation conditions can therefore be an effective means to mitigate challenges of alum adjuvant redispersion.

Occurrence Relationship Between Microplastics and Heavy Metals Pollutants in the Estuarine Sediments of Poyang Lake and the Yangtze River

Heavy metals are typical pollutants in the environment and microplastics are relatively newly recognized environmental pollutants, with their coexistence potentially compounding pollution and ecological risks. In this study, we investigate the contents and morphological characteristics of microplastics and heavy metals (Cu, Cd, Pb, Zn, and Cr) in the estuarine sediments of Poyang Lake and the Yangtze River as a means of exploring the relationship between them. The results showed that the abundance of microplastics ranged from 356 n·kg-1 to 1452 n·kg-1, with an average abundance of 982.33 n·kg-1 in the dry sediments. Microplastics were identified as being of three main types:fragments, fibers, and films, whereby fragments were the most dominant type found and accounted for 48.23% of the total microplastics in the sediments. The main color of microplastics in the sediments was chromatic, and the particle size of most microplastics was<1 mm. The major polymer components were polyethylene (PE), low density polyethylene (LDPE), and polyethylene (PP). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) results indicated that the surfaces of microplastics were rough, porous, cracked, and torn, and that the five heavy metals were found on the surfaces of different microplastics. These heavy metals accumulated to different degrees in the estuarine sediments, and redundancy analysis indicated that environmental factors[including the total organic carbon (TOC), pH, electrical conductivity (EC), and sediment particle size] and the occurrence of microplastics all had significant (P<0.05) effects on the distribution of heavy metal concentrations in sediments. Variation partitioning analysis (VPA) showed that the contribution rates of environmental factors and microplastics to the bioavailability of heavy metals were 37.70% and 0.70% respectively, but the combined effect was 49.60%. We conclude that microplastics in sediments may act as carriers of heavy metals and activate their bioavailability, hence posing a potential threat to the ecological security of estuaries and wetlands.

Effect of sediment concentration and particle size on erosion behavior of forged stainless steel

Erosion due to slurry is a main impediment in a number of industrial applications like hydraulic machinery components, slurry pipe lines, valves, thermal power plants, etc. Forged stainless steel alloy 13Cr-4Ni-(Mo) is extensively used in many hydraulic machinery components owing to its good corrosion and wear resistance. In the light of above current study is an investigation of the effect of sediment concentration and particle size on the slurry erosion of forged 13Cr-4Ni-(Mo). Experiments were performed in an erosive wear tester using sand and water slurry to evaluate the erosive wear. Wear rate was calculated using mass loss measurement. The tests were carried out at four levels of sediment concentration (10–25 wt%) and at varied particle size (125–425 µm). It is found that the increase in the sediment concentration of the slurry results in increase of wear loss of material due to increased probability of sediment particles attacking the surface. Increased particle size increases the area of contact between sand particles and target material and resulted in higher material loss. SEM and optical confocal studies were carried out on worn surfaces and it also shows that increased sediment concentration and higher sized particles caused more degradation on target surfaces.

Correlation Analysis between Sediment Particle Size and Number of Macromia daimoji (Endangered Species II) Nymphs in Naeseong Stream, Korea

Correlation Analysis between Sediment Particle Size and Number of Macromia daimoji (Endangered Species II) Nymphs in Naeseong Stream, Korea

Spatio-temporal variation of sediment properties reveals missing trophic links for deposit-feeding crabs in sandy shore food webs

Quantifying trophic relationships among basal food sources and primary consumers is essential to our understanding of food web structure and dynamics, but is challenging in soft shore systems where the variety of potential food sources often masks the actual pathways of energy flow. To elucidate trophic relationships among basal food sources and primary consumers, we assessed the diet composition of a deposit-feeding crab,Scopimera intermedia, an abundant primary consumer inhabiting tropical shores, using direct enumeration and stable isotope techniques. Stable isotope analyses revealed that meiofauna accounted for the majority of the crab’s diet (nematodes reaching 43% in median proportion) compared to, at most, 11% contributed by microphytobenthos (MPB). Although the abundances of MPB and meiofauna varied, meiofauna dominated over MPB in the crab’s diet at different sites and seasons. Such an important role of meiofauna in consumer diets contrasts with previous studies on sediment food webs, where MPB has often been proposed as the most plausible primary food source. The relative roles of meiofauna and MPB as food sources are, however, likely to be mediated by local physical environments. Sediment particle size, for example, is more coarse higher on the shore, where the larger interstitial spaces enable colonization of meiofauna but will limit large, motile MPB due to increased photostress. The trophic importance of commonly assumed primary food sources may thus be modified by environmental physical stress and, as a result, the role of intermediate trophic links in modulating food web dynamics should not be neglected.

Prediction of the Suspended Transport Rate of River Reach

A new suspended transport rate equation using field measurements that apply to the Euphrates River’s reach in the upstream direction from the Ramadi barrage in Iraq was developed via multiple linear regression. The governing parameters were carefully chosen based on dimensional analysis and grouped into four parameters: shields, transport, mobility, and particles. The ability of the suspended transport rate equations of Karim-Kennedy and van Rijn were tested. A total of 25 series of field data for which the concentration of suspended load, average flow depth, sediment particle size, flow velocity, and the width of the water surface were applied. A comparison of the suspended transfer rates in the river reach and the calculated transport rates in the modified equation showed good coincidence. The evaluation results showed that the new equation performed better than the three equations used. The performance of the new equation was determined utilizing three statistical criteria (the coefficient of determination, discrepancy ratio and relative error). The computed suspended transport rates were found within a discrepancy ratio of 1.02 for the measured values and a relative error of 13.4%. The performance of the Van Rijn formula performed better, with a discrepancy ratio of 1.26 for the measured values and a relative error 39%, than the other two equations. The percentage of data that ranged between 0.5–2.0 of the discrepancy ratio varied between 72–100% for the three equations and the new equation.

Benthic Macroinvertebrates Diversity and Physical-Chemical Parameters as Indicators of the Water Qualities of Ntawogba Creek Port Harcourt Nigeria

The study evaluated the water qualities of Ntawogba creek by utilizing the benthic macroinvertebrates diversity as well as physical-chemical parameters data, to give us an indication of the biochemical condition and health of the river. The research was carried out for twelve (12) months, firstly by establishing three (3) main sampling stations and their co-ordinates along the stretch of the creek based on ecological niche of the stream and human activities on the study area. The physical-chemical parameters measured and analysed include, Temperature, pH, Electrical Conductivity, Salinity, Turbidity, Total Dissolved Solids, Dissolved Oxygen and Biochemical Oxygen Demand, according to APHA 1998 standard methods. Sediment particle size was determined by hydrometer method. Replicate samples of benthic macroinvertebrates were collected from each station randomly with Eckmann’s grab. The results of the physical-chemical data were subjected to 2-way analysis of variance and differences among means where separated by Turkey-Honest significant difference at 95% probability. Percentage occurrence and relative numerical abundance of macroinvertebrates were calculated using excel descriptive statistical tool. Diversity of the benthos was determined using Shannon Wiener index hequitability of species. The results showed that pH values ranged from mild acidic to alkalinity (6.42 to 7.63). The values of turbidity, TDS, BOD and DO exceeded limits of World Health Organization in most of the sampling stations. The sediment particles of the stream were significantly dominated by sand fractions with the highest mean recorded in station three (74.08±0.71). The total number of benthic macroinvertebrates individuals in the sampled stations was 28,730 and total number of species was 40. The diversity, taxa richness and evenness recorded at station one were 0.823, 1.934 and 0.683, while station two had 0.605, 1.163 and 0.605 and station three had 0.301, 3.085 and 0.206. The results show that the human activities grossly polluted the stream, and constant monitoring is required to safeguard the waterbody and aquatic ecosystem in the study area.

Field investigation of flow and bed erosion/deposition at the confluence of the Yellow River and Fen River

In order to study the characteristics of flow structure and bed erosion/deposition at the confluence of the Yellow River and the Fen River, the three-dimensional velocity components, water depth, water level, and suspended sediment particle sizes of the typical sections were measured in field to analyze the bed morphology, the flow field structure, suspended sediment distribution, and the variation of the bed erosion or deposition. The results showed that the pattern of the flow field at the confluence essentially conforms to the conceptual model, but represented a relatively complex structure, owing to the dual influence of the convergent flows and the tanglesome bed topography. The spatial distribution of suspended sediment was affected by the flow velocity and eddy turbulence. The particle size of suspended sediment was approximately normal distribution. The median particle size ranged from 17.19μm to 140μm. The suspended sediment at the confluence center was mainly composed of upstream transfer sediment and resuspended local sediment near the bed surface. The riverbed morphology was highly complex with frequent changes in erosion and deposition. And there was a strip-shaped sand ridges at the center of the channel and a long-narrow scouring belt near the tributary side. In addition, the bed configuration was similar in the dry and normal season. Due to the sediment deposition, the bed elevation was higher in dry season than that in normal season. During the flood season, the washed bed was stated in a dynamic flattening period, as well as the sand ridge disappeared and the scour belt became shallow.

Influence of Suspended Sediment Concentration and Particle Sizes on the Sound Attenuation of the Fluvial Acoustic Tomography Technique

Fluvial Acoustic Tomography System (FATS) as an advanced technology acquires continuous streamflow data in rivers and estuaries even during floods. However, the acoustic signals are dramatically attenuated by suspending sediments which this problem is a new field of study. In this study, we propose a new equation to estimate the maximum applicable measurement distances (MAMDs). It is based on the cross-sectional suspended sediment concentration (<SSC>) and the particle sizes on the 30-kHz FATS. Our study results show that MAMD might be 2,380 m in the clear water. Moreover, the streamflow monitoring can be perfectly done while <SSC> is less than 12.67 kg/m3 with the particle radii of 3 μm, when the horizontal distance between two acoustic stations is 100 m. Also, the acoustic signals are not decayed if the particle radii equal to 20 mm and the maximum <SSC> is 6.6 kg/m3. This study highlights the performance of FATS in the presence of high <SSC> and provides a better perspective of applying FATS in different rivers with high variability of <SSC>.

Bend-induced sediment redistribution regulates deterministic processes and stimulates microbial nitrogen removal in coarse sediment regions of river

Understanding the differences of biogeochemical processes between straight and bent channel is important for weighting them in urban river planning and reconstruction. Shifts in the assembly of the sediment microbial community of bent channels are key, but understudied, component of bend-induced increases in biogeochemical reaction rates. Here, the assembly of microbial community and its feedback to nitrogen transformation in urban river bends were firstly studied by coupling ecological theory, aqueous biogeochemistry, DNA sequencing, and hydrodynamic profiling. It was found that the sediment particle size was the main driving force for producing the significant difference of microbial community structure in river bends. Homogeneous selection, quantified by β-nearest taxon index (βNTI), emerged in the urban river bends and accounted for 79.2% of all ecological processes. Moreover, a significant positive relationship between βNTI and the sediment particle size indicated that shifts in particle size were associated with shifts in deterministic selective pressures, which govern the composition of the microbial community. The significant correlation between the βNTI and changes in nitrate concentration also indicated that nitrate leads to deterministic processes, which select microbial taxa. These microbial taxa which are governed by deterministic processes show specific nitrogen transformation traits, and react on the nitrate concentration. A multiphase transport model allowed the separation of the effects of deterministic processes on nitrogen concentration from measured concentration influenced by complex biogeochemical processes. The results indicated that both the ammonia transformation and microbial nitrogen removal were stimulated in coarse sediment regions of the river bends, and were confirmed by abundant differences of microbial taxa that could promote ammoxidation and denitrification. The coarse sediment benefits microbial nitrogen removal in urban river bends, a discovery that should inform urban river reconstruction designs and the efforts to assess the environmental water capacity of urban rivers.

Influence of silver nanoparticles on settling of suspended sediments

Silver nanoparticles (AgNPs) are one of the main nano-contaminants and their entry into the environment may pose a threat to the aquatic ecosystems. Meanwhile, AgNPs have an important impact on geological processes. In this paper, we studied the influence of AgNPs on the sedimentation of suspended sediments. Results showed the settling rate of sediments increased from 13.06 to 20.08 h−1 in the presence of 0.2 mg/L AgNPs. The morphology characterization indicated the average particle size of sediments increased from 34.74 to 42.87 μm after interacting with AgNPs, resulting in the acceleration of settlement on the basis of Stokes' law. The chemical analysis detected 43–57% of AgNPs were incorporated onto sediments, which was the dominant reason for the increased sediments size and settling rate. The influences of various water quality parameters, e.g., pH, ionic strength, temperature, humic acid and surfactant, on the sediments settlement and interaction with AgNPs were comprehensively studied. Elevating the solution pH, ionic strength, temperature, contents of humic acid and anionic/nonionic surfactants would suppress the settling of suspended sediments, whereas cationic surfactant showed a promoting effect on sediments settlement. In addition, the settling experiments were conducted in collected lake water and seawater, and results showed the real water matrices hindered the sediments settlement and interaction with AgNPs.

Drought effects on tropical estuarine benthic assemblages in Eastern Brazil

Climate change will increase the frequency and intensity of extreme weather events with potential effects in coastal and estuarine ecosystems. During drought periods, higher salinity and temperature can directly impact estuarine benthic assemblages through physiological stress and alteration of sedimentary habitats, but these effects are poorly evaluated to date. Here we report a 14-month monitoring of benthic assemblages in a tropical estuary in the Eastern Brazil Marine Ecoregion during the severe drought period of 2015/2016. The drought in Eastern Brazil resulted in a decrease of estuarine mean sediment particle size and concurrent changes in macrofaunal benthic assemblages during the driest months. We also observed a 3-fold reduction on macrofaunal abundance with dominance of surface-dwelling Magelonid, Sternaspid, Capitellid and Oligochaeta annelids. The changes in macrofaunal structure during the severe drought also decreased the community bioturbation potential (BPc) by 5-fold, if compared to pre-drought periods. We argue that the projected increases in the frequency and severity of climatic events, such as observed during severe droughts worldwide, will greatly change the benthic fauna and their ecological functions in tropical estuarine ecosystems.

An integrated optic and acoustic (IOA) approach for measuring suspended sediment concentration in highly turbid environments

Accurate measurement of suspended sediment concentration (SSC) in highly turbid environments has been a problem due to optical or acoustic signal saturation and attenuation. The saturation returns a limited measurement range, and the attenuation raises an ambiguity problem that a low optical or acoustic output could mean a low or a high SSC. In this study, an integrated optic and acoustic (IOA) approach is proposed to (i) overcome the ambiguity problem; (ii) increase the measurement range to high SSC values; and (iii) obtain high-resolution SSC profiles. The IOA approach is a combination of Argus Suspension Meter (ASM), Optical Backscatter Sensor (OBS) and Acoustic Doppler Velocimeter (ADV). In this approach, the ASM-derived SSC is preferred because of its lowest relative error, followed by OBS and ADV. The ASM can produce high-resolution (1 cm interval) SSC profiles when it is not saturated (usually SSC < 9 g/L). When ASM is saturated, the SSC is recovered by OBS. Since the ambiguity problem is solved, the measurement range of OBS and ADV can be extended up to 300 g/L. The best way to use an ADV, however, is to have a rough estimation first and assist in the OBS conversion, because its estimates contain large uncertainty. To further mitigate the impact of sediment particle size on SSC retrieval, we suggest the usage of in-situ sediment samples for sensor calibration. The IOA approach was verified in the Yangtze Estuary which is a highly turbid system. Comparison of the IOA approach outputs against water sampling results demonstrates the reliability of the IOA approach with a relative error of 17–34%. The observed high SSCs were up to 63 g/L. The field data show that high SSCs were confined in the benthic layer (within 2 m above the bed) in the wet season under a high river discharge, whereas the suspension was better mixed throughout the water column in the dry season. • A combination of ASM, OBS and ADV resolves the ambiguity problem of two possible SSC values for an OBS or ADV output. • The integrated optic and acoustic (IOA) approach enlarges the measurement range of OBS and ADV to 300 g/L. • The IOA approach provides high-resolution (1 cm) SSC profiles by ASM. • The IOA approach was successfully applied in the Yangtze Estuary with SSC > 10 g/L.

After Hurricanes Irma and Matthew: Living Shorelines Stabilize Sediments

Constructed intertidal oyster reefs, an example of a “living shoreline”, can protect against erosion and loss of habitat, but can they prevent erosion during high-energy storm events such as hurricanes? Oyster reefs were constructed in 2012 within the Guana Tolomato Matanzas National Estuarine Research Reserve in Northeast Florida to stabilize the shoreline sediment and prevent erosion of an archeological site. Sediment cores were collected behind constructed oyster reefs before and after hurricanes Matthew (2016) and Irma (2017) to study changes in sediment particle size due to these high-energy storms. Pre-hurricane data were collected in 2016 from three different constructed reefs, as well as three control sites where no reef was present. Pre-hurricane sediment profiles behind the constructed reefs consisted of finer sediments, ~36% silt and clay, in the surface ~10-12 cm, with decreasing silt and clay and increasing sand content as depth increased. This was different than the sediment from the control sites with ~4% silt and clay in all depths sampled. Like the sediment profiles before the high energy storms, the post-hurricane sediment data showed a clear layer of finer sediment ~10-12 cm over coarser sediment. Although they were high-energy storms, the storms did not appear to significantly affect the sediment behind the constructed oyster reefs. Sediment profiles remained consistent after these storms but may not remain undisturbed during the next storm without some intervention because the oyster reefs have been degrading. KEYWORDS: Oyster Restoration; Living Shorelines; Hurricanes; Coastal Erosion; Sedimentation; Salt Marsh

Sources of stream bed sediment in an urbanized watershed

Excessive delivery of fine-grained sediment and sediment-bound nutrients to surface waters results in water quality impairment. Information on the relative contribution of different sources contributing sediment to river systems is a prerequisite to target management practices. The overall goal of this study was to determine the sources of stream bed sediment at a subwatershed scale using sediment fingerprinting approach in an urbanized, 31 km2 Moore's Mill Creek watershed in Southern Piedmont region in Alabama, USA. The relative source contribution from construction sites and stream banks was quantified for two different particle size fractions, 63–212 μm (fine sand) and <63 μm (silt and clay). Results of this study showed that both construction sites and stream banks were important sources of stream bed sediment. The stream bed sediment in the upstream reaches originated largely from channel bank sources, and in the lower reach (watershed outlet), construction sites were the dominant sources of stream bed sediment. The results of this study showed that the relative source contribution from different sources is dependent on the particle size of the sediment, time and location of sampling within a watershed, riparian buffers, and areas of construction activities in proximity to the sampling sites. Conservation practices in this watershed should be targeted to stream banks or construction sites depending upon the dominant source of stream bed sediment within a subwatershed. Overall, this study underscores the importance of considering the spatial and temporal variability of sediment sources as a function of sediment particle size for targeted implementation of best management practices.