Optical Backscatter Sensors Research Articles

Near-surface particulate backscattering observations with bio-optical Lagrangian drifters

Abstract Particulate matter concentration is an essential ocean variable (EOV) useful for understanding biogeochemical processes, improving ocean productivity estimates, and constraining coupled physical and biogeochemical numerical models. While direct observations of this parameter are difficult to obtain, the optical backscattering coefficient of marine particles (bbp) can be used as a reliable proxy. However, most in-situ multi-spectral bbp measurements are ship-borne or obtained from moored systems, thus with a limited spatial and temporal coverage. Utilizing Surface Velocity Programme (SVP) drifting buoys with self-contained backscatter sensors designed for extended deployment periods offers a promising solution for collecting data in challenging marine environments. In this study, we presented for the first time the integration of a commercially available, high-frequency and multispectral optical backscatter sensor into an SVP drifter, the so-called BO-SVP drifter designed to collect bbp measurements near the ocean surface. bbp measurements obtained by the BO-SVP drifter were reliable over a wide range of environmental conditions, showing a good agreement with independent datasets (relative bias < 10%; relative standard deviation < 36%). The BO-SVP drifter captures the satellite sub- and pixel scale variability by combining the Lagrangian approach and a high frequency sampling. This configuration enables the acquisition of measurements across numerous pixels in a single day, enhancing validation activities for ongoing and future satellite products and the quantification of associated uncertainties. The measurements acquired by these platforms can offer valuable insights into particle distribution at fine spatial scales, daily variability, and its relationship with water masses type and ocean dynamics.

Measurements of dune erosion processes during the RealDune/REFLEX experiments

Nearshore hydro- and morphodynamic data were collected during a field experiment under calm conditions, moderate conditions, and storm conditions with dune erosion in the collision regime. The experiment was conducted on the Sand Engine near Kijkduin, the Netherlands, from October 18, 2021, to January 7, 2022. Two artificial unvegetated dunes were constructed just above the high water line to measure storm erosion and dune impacts from higher water levels and waves. During the experiment, three storms occurred that resulted in significant erosion of both dunes. The collected hydrodynamic data include pressure sensor and velocimeter data along two cross-shore transects. The collected morphodynamic data include bathymetry and topography surveys, optical backscatter sensor data in the inner surf zone, and a continuous cross-shore line-scanning lidar data set of the dune face. This comprehensive data set can be used to (1) study relevant nearshore hydrodynamic and morphodynamic processes that occur during calm conditions, moderate conditions, and storm conditions with dune erosion in the collision regime, and (2) validate existing dune erosion models.

Modeling sediment concentrations and loads for two small agricultural watersheds in Prince-Edward-Island (Canada): present conditions and a future scenario

The degradation of soils and its detrimental consequences on aquatic environments is an important research topic in agricultural regions such as Prince Edward Island (PEI, Canada). Enhanced information related to suspended sediments in watercourses can serve as an effective decision-making tool in agricultural land management. This study aims to compare flow, suspended sediment concentrations (SSC), and loads using the Soil and Water Assessment Tool (SWAT) in two watersheds in Prince Edward Island (PEI). The final investigations will focus on the potential variations in hydrological and sedimentary values in the future using a relatively pessimistic climate change scenario. Finally, the projected sediment concentrations and loads will be analyzed, considering their potential impacts on ecosystems. Water level and turbidity were recorded using two water level loggers and two optical backscatter sensors (OBS) deployed in the Tuplin Creek and Spring Valley watersheds. These instruments continuously recorded suspended sediments and flow data from June 2021 to September 2022. The data were used to manually calibrate the hydrological and suspended sediment models. The understanding of sediment loads and the benefits of proposed changes to agricultural practices can be tested with the SWAT model, as it incorporates a land use index that varies spatially and temporally. Calibration and validation of both the hydrological and sediment models were satisfactory, with Kling-Gupta Efficiency coefficients varying between 0.51 and 0.73 and Nash-Sutcliffe coefficients varying between 0.61 and 0.73 respectively, indicating successful simulation of both variables in an agricultural context in spite of relatively short calibration and validation periods. Under the selected climate change scenario (RCP 8.5), daily flows and suspended sediment concentrations were simulated until 2,100, showing a slight increase in the average suspended sediment concentration (CSS). For Tuplin Creek, extremely high sediment peaks (>1,500 mg/L) could become significantly more frequent, potentially causing more frequent and severe ecosystem disturbances according to the simulations.

Seasonal variations of sinking velocities in Austral diatom blooms: Lessons learned from COMICS

The sinking velocity (SV) of organic particles is a critical driver of carbon transport to the deep sea. Accurate determination of marine particle SV and their influencing factors is therefore a key to better understanding of biological carbon storage in the ocean. We used two different approaches to estimate average SVs of particles during a Southern Ocean spring bloom (North of South Georgia): optical backscatter sensors on gliders (“large”, >50 μm diameter), and radioactive pairs (234Th–238U and 210Po-210Pb). Our results were complemented with time-of flight estimations of bulk SVs from deep sediment traps deployed at 1950 m.Bulk SVs increased consistently with depth from 15 ± 1 m d−1 at 10 m to 50 ± 10 m d−1 at the depth of export (Zp = 95 m) and from 96 ± 35 m d−1 at 150 m to 119 ± m d−1 at 450 m. Only the fastest particles, mainly comprised by faecal pellets (FPs) and diatom aggregates, survived remineralization and dominated carbon fluxes at deep depth.The SV variability at the base of the Euphotic Zone was studied in relation to the stage of the bloom by analysing three different moments of the spring diatom bloom in the region during the years 2012, 2013 and 2017. The export efficiency (ExpEff), defined as the ratio POC flux exported below the Euphotic Zone to the satellite derived surface NPP, was also evaluated. It was found from the temporal series that ExpEff and SV vary throughout the diatom bloom as the community structure progresses. A good correlation between both variables was observed (ExpEff = (0.023 ± 0.006) SV, r = 0.82, p = 0.04). Showing that the variability in how efficiently the carbon flux is exported out of the Euphotic Zone can be explained by the SV at which the particles sink. Further investigations are required to analyse if this is a specific model of the functioning of the BCP during the diatom bloom in North South Georgia or if it can be extrapolated to other scenarios.

REAL-TIME MONITORING OF HYDRODYNAMICS AND SUSPENDED SEDIMENT CONCENTRATIONS IN A COASTAL REEF

The algal reef ecosystem in Taoyuan coast, Taiwan, is considered a unique endemic species population, but the coastal constructions might cause the sensitive ecological area problems (Kuo et al., 2020). Several studies have confirmed that suspended sediment concentration (c) is a major detrimental factor affecting reef health. In recent years, there has been a focus on long-term monitoring of the c, but without continuous data. Most of study used an optical backscatter sensor (OBS) for long-term monitoring of the c because of its small size, low power, highly linear response and insensitivity to bubbles or organic matter. By contrast, few studies focus on testing how frequency the OBS should be calibrated because of other factor such as sediment size also affect the sensor response. Furthermore, although the long-term monitoring was demonstrated over the years ago, little attention has been paid to the real-time monitoring of c, especially since this method is achieved in the sensitive algal reef. For this reason, the real-time and long-term monitoring of waves and c (started in 2019 and lasts for 7 years) are necessarily performed in this algal reef conservation.

INVESTIGATION INTO HOUSTON SHIP CHANNEL SHOALING AT THE BAYPORT FLARE IN GALVESTON BAY

Sedimentation at the confluence of the Houston and Bayport Ship Channels (Bayport Flare) in the Upper Galveston Bay, along the Gulf Coast of Texas, USA, is a costly issue requiring frequent dredging. Hydrodynamic and sediment dynamic processes in the Upper Galveston Bay, particularly around the Bayport Flare, are being explored using measurements from vessel mounted and fixed Acoustic Doppler Current Profilers (ADCP), Optical Backscatter Sensors (OBS), Tilt Current Meters (TCM), as well as densely spaced sediment surface grab samples, core samples, and salinity profiles. These field measurements are used to assess the causes of the extremely high sedimentation rates (approximately 30 cm per year based on dredging records between 2013 and 2017) seen in the Bayport Flare. The effect of salinity on the flocculation and sedimentation of particles near the ship channels is also being explored through laboratory experimentation.

Inhibition of sediment erosion and phosphorus release by remediation strategy of contaminated sediment backfilling

The management of sediment-water interfaces, especially bed stability, is essential for controlling accumulated contaminants in the sediment. In this study, the relationship between sediment erosion and phosphorus (P) release under the remediation strategy of contaminated sediment backfilling (CSBT) was explored through a flume experiment, i.e. the dredged sediment was calcined into ceramsite after dewatering and detoxification and then backfilled to the dredged area for sediment capping, thus avoiding the introduction of foreign materials via in-situ remediation and the large-scale land occupation associated with ex-situ remediation. Acoustic Doppler velocimeter (ADV) and optical backscatter sensor (OBS) were used to measure the vertical distributions of flow velocity and sediment concentration in the overlying water, respectively, and diffusive gradients in thin films (DGT) was used to measure the P distribution in the sediment. The results revealed that improving bed stability from CSBT can considerably improve the robustness of sediment-water interface and reduce sediment erosion by more than 70%. The corresponding P release from the contaminated sediment could be inhibited with an inhibition efficiency as high as 80%. CSBT is a potent strategy for managing contaminated sediment. This study provides a theoretical reference for controlling sediment pollution, further supporting river and lake ecological management and environmental restoration.

Real-time and long-term monitoring of waves and suspended sediment concentrations over an intertidal algal reef

Suspended sediment concentration (c) has been considered a critical environmental factor in reef habitats; however, the values and variations of c are not evident in a unique reef mainly created by crustose coralline algal concretions compared to abundant studies in coral reefs. The results of real-time and long-term monitoring of waves and c over the intertidal algal reef are reported because of the construction of an offshore industrial harbor near the reef. The real-time monitoring systems were based on techniques, including optical backscatter sensors (OBSs) for measuring c, pressure sensors for measuring waves, data loggers, and wireless networks for data transmission. The instruments sampled every hour and ran continuously and automatically for years. The OBS measurement was compared and validated with biweekly water sampling. A good correlation between the results of the two methods was observed. Nevertheless, more calibrations of OBSs in different seasons reduced the variance between the two methods over a year-long timescale. The year-long data showed a remarkable seasonal variation in c. The average c was approximately 140 mg/l during the winter season, while it was only approximately 70 mg/l during the summer season. The observed c was higher than that in other coral reef environments; the elevated and highly variable c, ranging from approximately 0 to 500 mg/l, may be one factor that creates the unique algae reef environment. The year-long measurement of waves and c showed that the variation in c was mainly due to the variation in waves in different seasons and was well correlated with the wave-induced bed shear stress. The real-time and long-term data measured by the system will aid in better understanding and providing useful environmental data for accessing future environmental changes and protecting reef habitats.

Developing an optical backscatter method for determining casein micelle particle size in heated milk

A plethora of different factors, such as heat treatment, pH, soluble calcium and phosphate concentrations, colloidal calcium phosphate, ionic strength, redox potential, etc., affect functionally of critical milk components such as casein micelles, fat globules and whey proteins. These physicochemical changes induce fat- or protein-protein interactions that would be associated to changes in particle size that might be revealed using light backscatter measurements. We hypothesized that inline, simple, low-cost light backscatter measurements might have the potential to provide functionally related information, representing an interesting opportunity for process control. Casein micelle particle size and near infrared light backscatter spectra were measured in milks heat treated at 80 and 90 °C and pH 6.3, 6.7 and 7.1 in order to obtain prediction models for estimating changes in casein micelle particle size during milk heat treatment. Light intensity was measured over a spectral range of 200–1100 nm using a simple optical backscatter sensor and was implemented into models for particle size predictions as a function of heat treatment temperature and pH. Models which included an exponential factor containing a ratio of two specific wavebands were found to improve R2 when compared to single wavelength models. The best model exhibited an R2 of 0.993 and SEP of 2.36 nm. The developed prediction models show promise for in-line monitoring of whey protein denaturation and casein micelle particle size.

Coastal dynamics on equatorial beaches of amazonian coast during extreme tide events

This paper describes the influence of tidal currents on sediment transport on Amazonian equatorial beaches during extreme events. The study area (Salinópolis city) was divided into two sectors: western (Sampaio tidal channel) and eastern (Atalaia Island). Field surveys were conducted in 2013 during two periods of highest tides: April (the rainy season) and October (the less rainy season and Spring Equinox). The optical backscatter sensors (tide, turbidity, and wave data) and current meter sensors (velocity field data) were programmed to collect data every 0.1 and 60 seconds, respectively. They operated together for 24/12 hours on the upper shoreface (surf zone). Wave heights were higher in the Atalaia Island (up to 1 meter during the less rainy season). The currents were stronger, reaching 1.2 m.s-1, during ebb tide in the rainy season (Sampaio tidal channel). Higher turbidity values (maximum 1,200 FTU) occurred at the Atalaia Island during the less rainy season. The coastal dynamics in the area derives mostly from the Amazonian continental shelf, where intense tidal currents interact with a high volume of particulate debris, especially fine sand in Salinópolis. Nevertheless, estuaries and tidal channels are also largely responsible for sediment supply and play a key role in shoreline stability and coastal transport, especially during extreme tide events.

Use of a Scattered Light Sensor for Monitoring the Dispersed Surface in Crystallization

AbstractThe specific surface area of the dispersed phase in suspensions, emulsions, bubble columns and aerosols plays a decisive role in the increasement of heat and mass transfer processes. This has a direct effect on the space‐time yield in large‐scale chemical/process engineering production plants. Initial investigations show that an easy‐to‐install optical backscatter sensor outputs the dispersed surface area as a direct primary signal under certain boundary conditions. The article describes the construction, the mode of operation and first investigations applying of this new sensor. The sensor works even in high concentrated suspensions and emulsions, where conventional nephelometry already fails. Trends and limitations found so far for the sensor, which can be used in‐line in batch and continuously operated crystallizers, even in harsh production environments and in potentially explosive zones, are shown.

In‐Situ Observation of Storm‐Induced Wave‐Supported Fluid Mud Occurrence in the Subaqueous Yellow River Delta

AbstractTwo relatively comprehensive and long‐term observation campaigns of bottom sediment dynamics have been conducted at the subaqueous Yellow River delta in the winters of 2016 and 2018. High suspended sediment concentration (SSC) up to 10 g/L were observed in 2016 and active events of wave‐supported fluid mud (WSFM) were found to exist at the abandoned river delta during storms in 2018. A set of calibrated optical backscatter sensors measured the near‐bed SSC >30 g/L with a maximum WSFM thickness >60 cm. WSFMs emerging at the abandoned river delta were classified into three types: single‐peak, multi‐peak, and hybrid according to the time‐varying characteristics of WSFMs. The dominant factors triggering the WSFM generation and dissipation are storm‐wave actions and tidal effects, with limited contribution from current‐induced turbulence. In this study, several lines of evidence were put forward to prove the presence of seabed liquefaction to a depth of 10–16 cm, and thus we can infer that another significant factor enhancing the WSFM thickness scale may be wave‐induced liquefaction. Observations showed obvious signs of WSFM motion, or in other words, wave‐supported gravity flow (WSGF) moved downslope. The downslope velocity (around 1.9 cm/s) was estimated by solving a buoyancy‐friction force balance. This study observed frequent WSFM events at the abandoned Yellow River delta for the first time and demonstrates the need to attach more concerns about its roles in sediment transport and offshore engineering in the future.

Acoustic based assessment of cross-sectional concentration inhomogeneity at a suspended sediment monitoring station in a large river

Establishing and operating a harmonized sediment monitoring system along large rivers such as the Danube River is a challenging international task. As an element of such a system, a new monitoring site with state-of-the-art instrumentation is currently under development in the Upper-Hungarian section of the Danube River. The monitoring station will consist of a near-bank optical backscatter sensor and a horizontal acoustic Doppler current profiler (H-ADCP). As previous studies showed, the suspended sediment concentration (SSC) that is continuously measured with near-bank sensors can significantly enhance the temporal resolution of sediment transport monitoring. However, sediment plumes from tributary inflows upstream of the monitoring station can alter the detected near-bank concentrations, eventually biasing the sediment load estimation. Such an influence is likely in the cross-section of the planned monitoring station, therefore, a thorough preliminary analysis of the cross-sectional variation of the SSC was performed, based on expeditionary sediment measurement campaigns. Between 2018 and 2021 24 campaigns were carried out at different hydrological regimes, where physical sediment samplings together with fixed and moving boat ADCP measurements were performed. The cross-sectional variability of SSC and its influence on the sediment load estimations were assessed based on the moving boat ADCP measurements, after calibrating the backscatter signal with more than 500 physical samples. Based on the results, we identified different cross-sectional patterns of the SSC which is apparently governed by: (i) the actual hydrological situation considering both the main river and the tributary, and (ii) the local river morphology. Based on our findings, we suggested a correction method that accounts for the above effects, using which the near-bank SSC can be reliably converted into total suspended sediment load.

Sediment dynamics on a tidal flat in macro-tidal Hangzhou Bay during Typhoon Mitag

The hydrodynamics and sediment characteristics of tidal flats during typhoons are of great significance for coastal geomorphology and ecosystems. In this study, field records of waves, currents, and suspended sediment concentration (SSC) in the southern tidal flat (Andong) in the macro-tidal turbid Hangzhou Bay, China, were collected during Typhoon Mitag. The field data showed that there was little variance in the magnitude of the tidal currents during the typhoon. The directions were disordered with the peak ebbing currents changing from the southeast to the east, presumably due to the winds and northerly currents from the tidal creeks during the precipitation period. The significant wave heights (Hs) and turbulence kinetic energy (TKE) significantly increased during Typhoon Mitag. The SSC obtained by the optical backscatter sensor (OBS) near the bottom level rose rapidly to 6–7 kg/m3 during the initial stage of tidal cycles during calm conditions but decreased to 4–6 kg/m3 during Typhoon Mitag, probably due of the enhanced upward sediment transport by turbulent mixing. During normal weather conditions, the bed shear stresses induced by currents (τc) were mostly larger than those induced by waves (τw), while the τw exceeded the τc during the storm. The instantaneous bed shear stresses induced by currents and waves were mostly lower than the critical shear stress. Extracting turbulence from waves effectively diminishes the overestimation of turbulence. In calm conditions, the small-scale features (>0.5 Hz) of the scalograms exhibited some degree of disorder owing to the random nature of turbulence. Small-scale characteristics were embedded in relatively large-scale motions during extreme conditions, and a small quantity of plume-like streaks appeared between the frequency bands of 1/16 and 1 Hz. The temporal distributions of the high wavelet power regions of U'W' and c'W' coincided with each other, indicating the critical role of intermittent turbulence in sediment dynamics. The results of this study shed light on the study of coastal morphology and marine disasters.

Sources and dynamics of suspended particulate matter in a large-river dominated marine system: Contributions from terrestrial sediments, biological particles, and flocculation

Elucidating the sources and dynamics of suspended particulate matter (SPM) in large-river dominated estuarine and coastal areas is challenging, because these areas are characterized not only by high turbidity with complex terrestrial sediment transportation and deposition processes, but also by high primary production and plankton biomass. In addition, flocculation occurring near the river mouth can also markedly modify SPM dynamics, and its roles in affecting SPM concentrations, variations, and inherent properties remain inadequately addressed. In July 2016, an exceptional flood event occurred in the Changjiang (Yangtze) River basin, and a cruise on the Changjiang River Estuary and the adjacent shelf area was conducted. During this cruise, we deployed instrument of OBS (optical backscatter sensor) and LISST (laser in situ scattering and transmissometry) at 87 stations to study the SPM variations in 32 size classes (2.5–500 μm) and to elucidate the contributions of terrestrial sediments, biological particles, and flocculation to SPM sources and dynamics. The entire water columns at inner stations and the seawaters in the lower-depth waters at outer stations were found to be generally dominated by terrestrial SPM with smaller sizes. The waters in the upper depths at the outer stations were generally occupied by autochthonous and biological SPM with larger sizes, which mostly showed maximum values in the subsurface layers and were closely associated with fluorescence. In two stations near the river mouth and estuarine salinity front, the SPM, also with larger sizes, probably experienced flocculation. The findings from this study may greatly improve our understanding of SPM sources and dynamics under the multiple influences of physical and biogeochemical processes in large-river dominated estuarine and coastal areas.

OpenOBS: Open‐source, low‐cost optical backscatter sensors for water quality and sediment‐transport research

AbstractOptical backscatter sensors (OBSs) are commonly used to measure the turbidity, or light obscuration, of water in fresh and marine environments and various industrial applications. These turbidity data are commonly calibrated to yield total suspended solids (TSS) or suspended sediment concentration (SSC) measurements for water quality, sediment transport, and diverse other research and environmental management applications. Commercial sensors generally cost > $1000–3000. Here we leveraged simple, low‐cost microprocessors, electronics, and housing components to design and construct open‐source OBSs for < $150 per unit. The circuit relies on a photodiode to sense backscattered light, two stages of signal amplification, and a high‐resolution analog‐to‐digital converter to read the detected signal. The instrument and logger utilize inexpensive, custom‐printed circuit boards with through‐hole soldering mounts; micro‐SD card reader and real‐time clock modules; and PVC housings with commercial end caps and epoxy‐potted diode emitter and receiver. All parts are readily and publicly available, and minimal experience in soldering and coding is required to build and deploy the sensor. In lab and field tests, standard deviations were comparable to those measured by commercial sensors (~ 2–3% of the mean for suspended muds and 20–30% for suspended sands). These open‐source sensors represent a useful advance in inexpensive sensing technology with broad applications across scientific and environmental management disciplines.

ADV-Based Investigation on Bed Level Changes Over a Meso-Macro Tidal Beach

Beach intra-tidal bed level changes are of significance to coastal protection amid global climate changes. However, due to the limitation of instruments and the disturbance induced by wave motions superimposed on water levels, it was difficult to detect the high-frequency oscillation of the submerged beach bed level. In this study, an observation, lasting for 12 days and covering the middle tide to the following spring tide, was conducted on a meso-macro tidal beach, Yintan Beach, to simultaneously detect the characteristics and influence mechanism of bed level changes at intra-tidal and tidal cycle scales. The collected data included water depth, suspended sediment concentration (SSC), waves, high-frequency three-dimensional (3-D) velocity, and the distance of the seabed to the acoustic Doppler velocimeter (ADV) probe, which were measured by an optical backscatter sensor, two Tide & Wave Recorder-2050s, and an ADV, respectively. The results showed that the tidal cycle-averaged bed level decreased by 58.8 mm, increased by 12.6 mm, and increased by 28.9 mm during neap, middle, and spring tides in succession, respectively, compared with the preceding tidal regimes. The net erosion mainly resulted from large incident wave heights and the consequent strong offshore-directed sediment transport induced by undertows. Moreover, the variations in the bed level were more prominent during a neap to middle tides than during middle to spring tides, which were jointly caused by the wave-breaking probability regulated by water depth and the relative residence times of shoaling wave, breaker, and surf zones that were determined by relative tidal range. In terms of the intra-tidal bed level, it displayed an intra-tidal tendency of increase during floods and decrease during ebb tides, i.e., the intra-tidal bed level changes were controlled by water depth, which modulated the effects of waves on sediment resuspension and vertical sediment exchange. To be specific, waves and SSC were responsible for the intra-tidal bed level changes under low-energy wave conditions, while mean current and bedform exerted important influences on the variations of the intra-tidal bed level under moderate wave conditions, which broke the foregoing interrelation between bed level, waves, and SSC. This study, therefore, emphasizes the usage of ADV measurement to investigate bed level changes in sandy coasts.

The effect of concentration on particle settling in the Minas Basin, Nova Scotia

In the hyper-tidal Minas Basin located in the upper Bay of Fundy, Canada, the concentration of total suspended matter increases by an order of magnitude in winter as material from the expansive tidal flats is remobilized and storms increase cliff erosion. Tripods with a digital floc camera, LISST 100X Type B, optical backscatter sensors, settling velocity camera, ADCP and an in-situ water filtration system were deployed during winter and summer conditions to examine how this variation in concentration affects particle packaging and settling. In winter, the higher concentration leads to rapid formation of large, low density flocs with lower settling velocities during the brief periods of low stress between ebb and flood. In summer, the material in suspension is dominated by small aggregates with higher excess densities and higher settling velocities. After a 70 mm rainfall event, flocs with lower density, and lower settling velocities appear again. Flocculation rate increases with concentration leading to the rapid formation of flocs in winter. However, stresses are high, so sediment remains mobile in winter. In the transition from winter to summer concentration is initially high, floc formation and settling is rapid, and wave energy is reduced allowing material to accumulate on the flats. In summer, the concentration of the sediment remaining in suspension is too low for flocs to form and aggregates dominate the population of particles suspended by the tide. Only when an input of new sediment occurs do new flocs form.

Tracing suspended matter in Tiab estuary applying ANN and Remote sensing

Knowledge about deposition and sedimentation in estuaries is important since these environments are favorable domain for human activity. Variety of hydrodynamic parameters causes sedimentation/deposition in an estuary among them tidal current. It is therefore necessary to monitor these processes in estuaries and provide strategies to control the rate of sedimentation/deposition. Several methods are available to measure total suspended solids (TSS). Using combined methods of direct and indirect suspended sediment measurements in this research, we achieved a reliable method to study the suspended sediment status in an estuary located northern of the Persian Gulf, known as Tiab estuary. Field measurements were performed as two scheduled cruises one in October and one in November 2015. Current velocity and turbidity were recorded using RCM9 device and optical backscatter sensor. Water samples were collected using Niskin Bottle. Measurements were carried out both along the estuary and stationery. Artificial Neural Network (ANN) in combination with Linearity method has been applied to reproduce sufficient SS data. The ANN feed-forward back-propagation provides reliable TSS values with the RMSE and correlation coefficient of 0.137 and 0.943, respectively. Results show that the estuary is flood dominated, thus in general the estuary is under constant sedimentation. Applicability of satellite imagery of Sentinel to trace TSS in this estuary is investigated and improved. The difference between the SST rate in the four tidal phases, including high and low tide and flood and ebb phase, was examined using the NSMI-index. We found the average NSMI index in high tide is 0.216, in the low tide is 0.278, in flood phase is 0.302, and in ebb phase is 0.295. Both field and satellite data show that the concentration of TSS in the ebb phase increases, and in the low and high tide decreases. Both results also revealed that the accumulation of TSS in the meandered area is relatively high.

Suspended particulate matter in a submarine canyon (Whittard Canyon, Bay of Biscay, NE Atlantic Ocean): Assessment of commonly used instruments to record turbidity

Nepheloid layers with elevated concentrations of suspended particulate matter (SPM) are found throughout the world's oceans. They are generated by both natural processes, involving resuspension of seabed sediment by bottom currents, and anthropogenic sediment resuspension due to bottom trawling, dredging and in the future potentially due to deep-sea mining. These nepheloid layers represent pathways of lateral SPM transport, including lithogenic and biogenic sediment, organic matter, (trace) metals, organic pollutants and plastics. For assessment of the dispersion of these materials, it is essential that SPM mass concentrations can be accurately quantified. However, this is not straightforward as the detected turbidity signal, which is used as a proxy for SPM mass concentration, not only depends on the concentration of particles, but also on physical characteristics of these particles, such as particle size, substance and shape. Here we present a comparative study of turbidity data to assess the potential implications different sensors have on the estimates of SPM mass concentration. Optical backscatter sensors (OBSs), transmissometers and both low- and high-frequency ADCPs were deployed simultaneously in the Whittard Canyon (North Atlantic Ocean), and water samples were collected for quantification of SPM mass concentration and ex-situ particle size analysis. We found that SPM mass concentrations inferred from the transmissometer are easily overestimated in the biologically productive surface layer due to higher light absorption by chlorophyll-bearing phytoplankton, compared to suspended detritic particles. Furthermore, we observed that depending on sensor type some particles are not, or less well, detected. This is due to differences in particle size sensitivities of these sensors towards the diverse range of particle sizes found in the Whittard Canyon, whereby the low-frequency ADCP was most sensitive for coarse-grained material and the high-frequency ADCP and OBSs most sensitive for fine-grained material. In future studies, we suggest to use a combination of different sensors as the use of only one type of sensor could potentially lead to misinterpretation and mis-quantification of particle transport processes and fluxes.