Suspended Particulate Matter Dynamics Research Articles

Satellite observations of suspended particulate matter concentration in Lake Gaoyou in the past four decades

Suspended Particulate Matter (SPM) concentration stands as a pivotal determinant of water quality within lake ecosystems. However, comprehension of the enduring dynamics of SPM within lakes is severely hindered due to a shortage of long-term records. Our research has developed a robust remote sensing algorithm to retrieve the SPM concentration in Lake Gaoyou, situated in the lower reaches of the Huai River basin in China. The algorithm demonstrates commendable performance, with an uncertainty of 28.68 %. Leveraging Landsat series sensors imagery, our investigation yields high spatial resolution SPM concentration maps, which first provide a four-decades record of the SPM distribution within Lake Gaoyou. Our findings unveil a significant annual reduction of 1.35 mg L−1 in SPM concentration over the past four decades. This notable decline is probably attributable to a series of ecological initiatives to enhancing the management of the eco-friendly within the basin. Furthermore, our research delineated the influence of environmental factors on the intra-annual SPM dynamics across distinct spatial domains, encompassing the natural inlet region, semi-obstructed inlet region and outlet areas within the lake The SPM concentration in the natural inlet region exhibits a conspicuous correlation with precipitation. Increased precipitation induces runoff within the basin, facilitating the transport of suspended solids and sediment into the lake, consequently augmenting SPM levels. Conversely, the semi-obstructed inlet and outlet areas are predominantly influenced by the wind field, with variations in SPM attributed to sediment resuspension caused by water mixing driven by wind forcing. Our research can be considered an important reference to the evaluation of the management of the lake over long periods.

Confounding effects of seasonality and anthropogenic river regulation on suspended particulate matter-driven mercury transport to coastal seas

Riverine mercury (Hg) is mainly transported to coastal areas in suspended particulate matter (SPM)-bound form, posing a potential threat to human health. Water discharge and SPM characteristics in rivers vary naturally with seasonality and can also be arbitrarily disrupted by anthropogenic regulation events, but their effects on Hg transport remain unresolved. Aiming to understand the confounding effects of seasonality and anthropogenic river regulation on Hg and SPM transport, this study selected the highly sediment-laden Yellow River as a representative conduit. Significant variations in SPM concentrations (108 − 7097 mg/L) resulted in fluctuations in total mercury (THg, 3.79 − 111 ng/L) in river water corresponding to seasonality and anthropogenic water/sediment regulation. Principal component analysis and structural equation model revealed that SPM was the essential factor controlling THg and particulate Hg (PHg) in river water. While SPM exhibited equilibrium state in the dry season, a net resuspension during the anthropogenic regulation and net deposition in the wet season demonstrated the impact of SPM dynamics on Hg distribution and transport to coastal regions. Combining water discharge, SPM, and Hg concentrations, a modified model was developed to quantify Hg flux (2256 kg), over 98% of which was in particulate phase.

MODIS observations reveal decrease in lake suspended particulate matter across China over the past two decades

Variations in the concentrations and distribution of suspended particulate matter (SPM) of lakes can be used to show the responses of lake environment to climate and landscape change. However, the shifts and trends of SPM and potential drivers have not been well investigated across large spatial and temporal dimensions. This study developed a robust machine learning model to generate SPM time series in 269 lakes across China larger than 30 km2 from 2002 to 2021 using MODIS/Aqua imagery. The support vector regression model showed satisfactory performance on SPM retrievals over four orders of magnitude (0.1–1000 mg L−1) (mean absolute percentage error = 26%). The model performance was shown to be insensitive to changes in environmental and observing conditions (e.g., aerosol type and thickness, viewing geometry), based on a radiative transfer simulation model. The long-term MODIS record showed a spatial pattern of lower SPM in the western lakes compared to the shallow lakes of east China. Importantly, the SPM showed a significant decrease in the 21st century (average rate of change of −0.2 mg L−1/decade). The interannual variations in SPM were aggregated into five categories, ranging from lakes with continuous changing patterns to those with reversed changing patterns. The driving factors behind the changing patterns vary between different climate zones and ecoregions. A warmer and wetter climate was associated with decreasing SPM in western lakes, while the decrease in wind speed and reduced possibility of soil erosion were the primary drivers of progressively lower SPM in the eastern shallow lakes. These results not only show a comprehensive picture of the SPM dynamics of lakes in China but also provide new insights into the complex mechanisms that drive SPM spatiotemporal dynamics.

Remote estimates of suspended particulate matter in global lakes using machine learning models

Suspended particulate matter (SPM) in lakes exerts strong impact on light propagation, aquatic ecosystem productivity, which co-varies with nutrients, heavy metal and micro-pollutant in waters. In lakes, SPM exerts strong absorption and backscattering, ultimately affects water leaving signals that can be detected by satellite sensors. Simple regression models based on specific band or hand ratios have been widely used for SPM estimate in the past with moderate accuracy. There are still rooms for model accuracy improvements, and machine learning models may solve the non-linear relationships between spectral variable and SPM in waters. We assembled more than 16,400 in situ measured SPM in lakes from six continents (excluding the Antarctica continent), of which 9640 samples were matched with Landsat overpasses within ±7 days. Seven machine learning algorithms and two simple regression methods (linear and partial least squares models) were used to estimate SPM in lakes and the performance were compared. To overcome the problem of imbalance datasets in regression, a Synthetic Minority Over-Sampling technique for regression with Gaussian Noise (SMOGN) was adopted in this study. Through comparison, we found that gradient boosting decision tree (GBDT), random forest (RF), and extreme gradient boosting (XGBoost) models demonstrated good spatiotemporal transferability with SMOGN processed dataset, and has potential to map SPM at different year with good quality of Landsat land surface reflectance images. In all the tested modeling approaches, the GBDT model has accurate calibration (n = 6428, R2 = 0.95, MAPE = 29.8%) from SPM collected in 2235 lakes across the world, and the validation (n = 3214, R2 = 0.84, MAPE = 38.8%) also exhibited stable performance. Further, the good performances were also exhibited by RF model with calibration (R2 = 0.93) and validation (R2 = 0.86, MAPE = 24.2%) datasets. We applied GBDT and RF models to map SPM of typical lakes, and satisfactory result was obtained. In addition, the GBDT model was evaluated by historical SPM measurements coincident with different Landsat sensors (L5-TM, L7-ETM+, and L8-OLI), thus the model has the potential to map SPM of lakes for monitoring temporal variations, and tracks lake water SPM dynamics in approximately the past four decades (1984–2021) since Landsat-5/TM was launched in 1984.

Dynamics of Suspended Particulate Matter in an Impounded River Under Dry and Wet Weather Conditions

AbstractThe dynamics of suspended particulate matter (SPM) and SPM‐associated biological and physicochemical processes in a river vary under dry and wet weather conditions and hydraulic structures, which moves a free‐flowing river to a semi‐lacustrine environment. This study investigated the response of SPM dynamics and riverbed morphodynamics to climate and anthropogenic stressors based on in‐situ observations and biogeochemical analyses of river water and riverbed sediment. The biochemical analyses and flocculation tests demonstrate abundant biopolymers and high flocculation potential of the river water during the pre‐flood period with algal bloom. This might promote SPM deposition and high‐concentration sediment layer (HCSL) formation on the riverbed. The high fractions of clay minerals and organic carbon in the riverbed sediment indicate the deposition of organic‐rich biomineral flocs. Vertical turbidity profiles with “long tails” of high turbidity near the riverbed also confirmed SPM deposition and HCSL formation. However, the highly turbulent flow conditions during the post‐flood period disturbed the tails of high turbidity and homogenized the vertical profiles of turbidity, temperature, and dissolved oxygen. Additionally, terrestrial humic substances were discharged from the watershed during this period, increasing the deflocculation and stabilization of SPM but decreasing deposition on the riverbed, thereby reducing the fractions of clay minerals and organic carbon in the sediment. This study demonstrated the interaction mechanism of SPM dynamics and riverbed morphodynamics with hydrological and biogeochemical processes in an impounded river under dry and wet weather conditions. The findings provide insights into water resource management to deal with climate change and anthropogenic stressors.

Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary

Riverine mercury (Hg) is the largest global source of Hg in coastal oceans. The Yellow River delivers the majority of Hg to the semi-enclosed Bohai Sea, where Hg contamination adversely affects the surrounding heavily populated provinces in northern China. Mercury distribution patterns in the river-estuary interacting area provides essential information to understand the riverine Hg transport and biogeochemical cycling of Hg in the estuary. Analyzing the spatial distributions of total- (THg) and methyl-Hg (MeHg) in the lower end of Yellow River (∼105 km) and adjacent estuary, we found the dominant role of suspended particulate matter (SPM) in Hg transport, with 99.1% and 86.3% of THg and MeHg being in particulate phase. The SPM dynamics, such as transport, retention, sorting and sedimentation, governs Hg transport with water flow and particle-water partition of Hg. While THg decreased along the water flow to the river mouth with the settlement of particulate THg (about 27.5% onto the riverbed and the rest entering the sea), MeHg and particulate MeHg increased by 110% and 117%, respectively. This study highlights the distinct patterns in THg and MeHg distribution and transport and suggests potential Hg methylation and external MeHg input in the river-estuary mixed zone.

HY-1C/D CZI Image Atmospheric Correction and Quantifying Suspended Particulate Matter

HY-1C/D both carry a coastal zone imager (CZI) with a spatial resolution of 50 m and a swath width of 950 km, two observations can be achieved in three days when two satellites operating in a network. Accurate atmospheric correction is the basis for quantitative inversion of ocean color parameters using CZI However, atmospheric correction in estuarine and coastal waters with complex optical properties is a challenge due to the band setting of CZI. This paper proposed a novel atmospheric correction algorithm for CZI images applicable to turbid waters in estuarine and coastal zone. The Rayleigh scattering reflectance of CZI was calculated based on a vector radiative transfer model. Next, a semi-empirical radiative transfer model with suspended particle concentration as the parameter is used to model the water-atmosphere coupling. Finally, the parameters of the coupling model are solved by combining a global optimization method based on a genetic algorithm. The results indicate that the CZI-derived remote-sensing reflectance (Rrs) are in good agreement with the quasi-synchronous Landsat-8/9 operational land imager (OLI) derived Rrs in the green and red bands (R2 > 0.96). Validation using in situ data revealed that the RMSE of the CZI-derived Rrs in the green and red bands was 0.0036 sr−1 and 0.0035 sr−1. More importantly, the values and spatial distributions of suspended particulate matter (SPM) estimated by CZI and those estimated by OLI in the Subei Shoal and the Yangtze River Estuary are basically consistent, and the validation using in situ data revealed that the inversion of SPM concentration by CZI was effective (R2 = 0.86, RMSE = 0.0362 g/L), indicating that CZI has great potential and broad application prospects for monitoring the spatial and temporal dynamics of SPM in estuarine and coastal waters. The study results will lay the foundation for further estimating suspended sediment fluxes and carbon fluxes, thus providing data support and scientific basis for promoting resource development, utilization and conservation strategies in estuarine and coastal areas.

In-situ long-period monitoring of suspended particulate matter dynamics in deep sea with digital video images

Suspended particulate matter (SPM) plays an important role in material transport, deposition, resuspension and the function of benthic communities’ processes in deep sea. SPM concentration data is usually indirectly measured by optical/acoustic sensors. However, converting these sensors’ signal to SPM concentration is associated with a number of uncertainties, which will lead to mis-estimation of the results. Some researchers recommend combining several optical/acoustic sensors to determine SPM concentration. However, due to the lack of corresponding video images, the interpretation of significant mismatch signals recorded by different sensors is subjective. Consequently, a better understanding of long-period SPM dynamics, especially in deep sea, is still a challenge. In this study, we seek to monitor the dynamics of SPM in deep sea, by firstly obtaining in-situ digital video images at a water depth of 1450 m on the northern slope of South China Sea in 2020, and secondly developing a digital image processing method to process the in-situ monitoring data. In this method, we defined an image signal which was the ratio between the area of the SPM and that of the total image, to characterize the SPM concentration. A linear regression model of the image signal and SPM concentration was established (R2 = 0.72). K-fold cross-validation showed that the performance of the model was well. We calculated the SPM concentration derived from image signal, and manually classified SPM into three distinct morphological groups. The long-period observation revealed that numerous aggregates existed in deep sea. The change of SPM concentration and morphology under hydrodynamics was synchronous. When current speed equaled to or exceeded 0.15 m/s, there was a significantly increase in SPM concentration and size. However, such increase was episodic. When current speed decreased, they will also decrease. In addition, we compared the image signal with the optical/acoustic backscattering signal, analyzed the mismatch period among these three signals. We found that the optical backscatter signal can’t accurately reflect the SPM concentration during the mismatch period. To our best knowledge, this is the first time that the in-situ digital video images were used to analyze the dynamics of SPM in deep sea.

Flocculation of suspended particles during estuarine mixing in the Changjiang estuary-East China Sea

Flocculation, triggered during estuarine mixing plays an important role in land-to-sea interactions and is a fundamental topic in near-shore oceanographic studies. Identifying in situ flocculation in large-river estuaries can be challenging due to the complex seawater circulation and heterogeneous suspended particulate matter (SPM) composition in these areas. In this study, three cruises were conducted in the Changjiang (Yangtze) River Estuary and the adjacent area in March, May, and July 2016. Vertical profiles of SPM total volume, mean size, and size spectra were determined using laser in situ scattering and transmissometry (LISST) measurements at 66–89 stations during the three cruises. Stable isotopic ratios of δ 13 C were also measured in the organic carbon contents of SPM collected at the surface, middle, and bottom layers of the sampling stations. LISST data were used to successfully identify the flocculation occurring in the field as well as to trace SPM size spectrum changes before and after the flocculation process. The δ 13 C values were utilized to study the response of biogeochemical parameters to the flocculation. Phytoplankton blooms occurring in May largely resulted in discontinuous variations in LISST parameters and δ 13 C from March to July. Although the pattern of SPM size spectra involved in flocculation differed among seasons, flocculation processes were always contributed by smaller particles with sizes of several tens of μm aggregating into larger ones >300 μm. Using LISST and δ 13 C measurements combined greatly improved our understanding of SPM dynamics in estuarine and coastal areas where estuarine flocculation was a critical component. • The SPM in the Changjiang Estuary could be classified into three sources. • Three sources were terrestrial sediments, biological particles, and flocculation. • LISST and OBS data could identify flocculation occurring in large-river estuaries. • The δ 13 C variations were more controlled by seasonal or spatial factors. • A combination of LISST and δ 13 C measurements could elucidate SPM dynamics.

Spatiotemporal dynamics of suspended particulate matter in the Bohai Sea, China over the past decade from the space perspective

Suspended particulate matter (SPM) concentration is an important biogeochemical parameter for water quality assessment and morphodynamic studies. In this study, the four recent SPM retrieval models developed for Bohai Sea were evaluated using in situ datasets, and the best performing model was selected to investigate the spatiotemporal dynamics of SPM in Bohai Sea from 2011 to 2021 based on 1164 satellite imageries. The results indicated that the satellite-derived SPM concentrations had a high accuracy (R2 = 0.86, relative percentage difference = 33.71 %). The SPM concentrations in the Bohai Sea demonstrated a significant decadal decreasing trend (0.503 mg/L/yr), and the distribution area with low SPM (<30 mg/L) increased by 3.29 % annually. The southern Bohai Sea declined observably, involving the Bohai Bay (2.07 mg/L/yr), Laizhou Bay (1.916 mg/L/yr), and central Bohai Sea (−0.661 mg/L/yr). Monthly SPM was characterized by significant seasonality. The SPM circulation pattern in the Bohai Strait was generally northerly inflow and southerly outflow. Significant wave heights (Hs) dominated the SPM variations and explained 58.9 % of monthly SPM changes in the Bohai Sea. The strong waves reduction was the main reason for the decadal decline of SPM concentrations. Wind waves associated with monsoons controlled seasonal variations of SPM and promoted the output in winter through the southern Bohai Strait. Storms could cause a sharp increase in SPM concentrations, especially in Bohai Bay and Laizhou Bay which were highly sensitive to northerly winds and strong waves. After the storm ended, the effects of short-duration storm might fade away within a few hours, while that of long-duration storm could last for 2–3 days. High sediment transport from Yellow River (>500 × 104 t/M) controlled 74.8 % of monthly SPM variations within 3-km area off the estuary, 45 % of that within 5-km area, and 28.4 % of that within 10-km area.

Modelling suspended particulate matter dynamics at an Antarctic fjord impacted by glacier melt

When Antarctic glaciers retreat, high sediment loads from geomorphological and glaciological sources can disturb the biota, especially filtering organisms, and thereby significantly alter the ecology of the Antarctic coast. We applied the Finite volumE Sea-ice Ocean-Coastal Model (FESOM-C), a numerical tool equipped with a sediment module, to simulate for the first time the suspended particulate matter (SPM) dynamics in a fjordic environment at the northern West Antarctic Peninsula, Potter Cove as a case study. Depth-averaged SPM dynamics during a meteorologically representative austral summer (120 days from December to March) considered tidal and atmospheric forcing. Additionally, idealised experiments with passive particles based on post-processing Lagrangian module identified and followed possible material trajectories in Potter Cove. Particle dynamics in the area show them to be primarily tidal and wind-driven, sensitive to bathymetry, with the higher SPM concentrations in the inner cove and the highest hydrographical complexity in the transitional area between the fjordic and marine habitat. The SPM plume covers 5.5 km2 of the total inlet of 9 km2, with monthly mean values between 15 and 330 mg/l. The maximum SPM concentrations are during January (790 mg/l), and the maximum plume expansion during February. The model was validated with available in situ measurements. With this study, we can identify areas in Potter Cove (and similar coastal fjordic environments, prospectively) of increasing physical stress by longer SPM residence time and high accumulation rates induced by glacial meltwater. These factors are crucial for pelagic and benthic assemblages dependent on light and food availability, as well sediment deposition.

Spatio-temporal dynamics of suspended particulate matter in the middle Niger River using in-situ and satellite radiometric measurements

Study Region: Middle Niger River Basin (MNRB), Ansongo to Niamey, Sahel, West Africa.Study Focus: Although MNRB hydrology and the red flood phenomena have been addressed in the past literature, water quality parameters and suspended particulate matter (SPM) dynamics remain poorly known. SPM impacts dam silting, exacerbating flooding, and microbial water quality. This study couples in-situ SPM measurements to radiometric measurements by in-situ and satellite sensors to analyse the temporal and spatial evolution of SPM in the MNRB and assess the contribution of the local flood (red flood) to SPM in Niamey.New Hydrological Insights for the Region: SPM is composed of very fine kaolinites with a major mode around 200–300 nanometers which results in high reflectance in the visible and infrared bands. Radiometric measurements by both radiometer and Sentinel-2 MSI sensors are well correlated to in-situ SPM, allowing efficient spatio-temporal monitoring of SPM concentration. SPM increases very rapidly at the beginning of the rainy season, reaching a peak, characterized by very high SPM values, about one month before the red flood. Satellite data highlight the significant contribution of the right bank tributaries to SPM in the MNRB during this period. SPM then decreases and remains low despite the second runoff increase (black flood) arriving in Niamey after the end of the rainy season from the upper basin.

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.

Observations of Suspended Particulate Matter Concentrations and Particle Size Distributions within a Macrotidal Estuary (Port Curtis Estuary, Australia)

An understanding of suspended particulate matter (SPM) dynamics is of great importance to design awareness and management strategies of estuaries. Using a Laser In Situ Scattering and Transmissiometry (LISST) instrument, variations in suspended particle size volumetric concentrations (VC) and particle size distributions (PSD) were measured at six sites within Port Curtis estuary (Australia). The port is a macrotidal estuary with significant economic and environmental importance. Observed VC and SPM sizes demonstrated spatial and temporal trends strongly controlled by the variable energy conditions operating on the neap and spring cycle timescale, with a clear trend towards increasing concentrations and decreasing SPM sizes with increasing tidal ranges. Mid-estuary sites were characterized by the greatest depth-averaged VC under transitional and spring conditions. Estuary-wide mean spring tide total water profile concentrations revealed a near 300% increase in comparison to neap tide condition concentrations. In the upper-estuary sites the mean contribution of the combined 2.5–35 µm size classes to the total profile PSDs was greatest during all tidal conditions, whilst within the lower-estuary site the combined 35–130 µm size classes were greatest. Mean contributions of the largest size class (300–500 µm) dominated surface-waters throughout the estuary during the neap tide period, which when compared with the transitional and spring tide conditions, demonstrated changes of −82% to −48% and −82% to −40%, respectively. Overall, the results from this case study provides further evidence of the important influence of neap and spring tidal regimes on SPM dynamics within estuarine settings and the need to observe parameter dynamics on such timescales.

Combining Landsat-8 and Sentinel-2 to investigate seasonal changes of suspended particulate matter off the abandoned distributary mouths of Yellow River Delta

Suspended particulate matter (SPM) is the primary component of coastal waters. The spatiotemporal dynamics of SPM has an important influence on water bio-optical properties, pollutant diffusion, landform evolution, and carbon, oxygen, and nutrient cycles. This study presents the spatial distribution of monthly average SPM concentrations from 2017 to 2020 in the abandoned Diaokouhe and Shenxiangou distributary mouths of the Yellow River Delta (YRD). The SPM concentrations were derived based on 161 Landsat-8 OLI and Sentinel-2A/B MSI satellite images. Accuracy assessment using the synchronous in-situ measurements (R2 = 0.91, root mean square error (RMSE) = 38.79 mg/L, and relative percentage difference (RPD) = 23.45%) and cross comparison between SPM concentrations derived from the two sensors (R2 = 0.97, RPD = 8.77%) showed convincing performances. Our results show that the monthly average SPM is characterized by significant seasonality, with a higher concentration and wider range in dry seasons compared to that in wet seasons. The spatial distributions of SPM are closely associated with coastal water depths. The SPM concentration in the Shenxiangou mouth is always lower than that of the shallower Diaokouhe mouth. The long-term seabed erosion provides a continuous supply of sediment. Wind-wave forces explain the seasonal variations of SPM by inducing the resuspension of bottom sediments. The residual currents control the transportation of SPM to the offshore and to the east. The artificial groins located between the two river mouths show obvious sediment trapping effects. Moreover, the interception capability of impermeable groins is considerably better than that of permeable groins.

Seasonal and tidal variations in suspended particulate matter dynamics of two microtidal rivers of Karnataka, central west-coast of India

Seasonal and tidal variations in suspended particulate matter dynamics of two microtidal rivers of Karnataka, central west-coast of India

A Study on Seasonal Dynamics of Suspended Particulate Matter in Korean Coastal Waters Using GOCI

Lee, Y.-K.; Choi, J.-K., and Lee, H.-J., 2020. A study on seasonal dynamics of suspended particulate matter in Korea coastal waters using GOCI. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Geospatial Research of Coastal Environments. Journal of Coastal Research, Special Issue No. 102, pp. 232-245. Coconut Creek (Florida), ISSN 0749-0208.Analysis of suspended particulate matter (SPM) is a key to understanding the turbulent sediment flow in the Heuksan mud belt (HMB), located along the southwestern coast of the Korean Peninsula. The purpose of this study was to investigate intra-annual variability in remotely sensed SPM data derived from the Geostationary Ocean Color Imager (GOCI) around the HMB over a period of 1 year (2013). Monthly averaged SPM images obtained by the GOCI showed pronounced seasonal changes in turbid water. Dominant environmental factors for intra-annual and diurnal variability of SPM, including river discharge, winds, and tides, were assessed. Monsoon wind dominated seasonal variation in SPM dispersion; the extent of turbid water increased during the winter and decreased during the summer months. Diurnal variation observed from 1-day composite images showed clearly that tidal current was the dominant factor affecting the short-term dispersal pattern of SPM. The gate-controlled river discharge showed the reverse seasonal pattern compared with SPM concentration. However, a turbid plume from the Geum River observed in GOCI data could support the identification of this river as the major source of the HMB. In conclusion, this study demonstrated that the spatial and temporal dynamics of the HMB, including intra-annual and diurnal variability, can be successfully detected using the GOCI.

The Dynamics of Suspended Particulate Matter in the Oued Nachef (Tafna Basin, Algeria): Typology of Flood Events and Contribution to Sediment Transport

This article focuses on the study of sediment transport during flood events in the Oued Nachef watershed that feeds the Mefrouche dam. To understand the sediment dynamics in this watershed, ANRH data on instantaneous water discharges and the respective concentrations of suspended particulate matter were used. This enabled the selection of some of the largest flood events over a 24-year period in order to establish the log-log relationships between sediment load (concentration and flux) and water discharge. However, the discharge-concentration relationships revealed hysteresis phenomena that enabled a flood typology to be established and classified into seven categories, thus showing very different transfer dynamics in relation to flood events. The results showed that Category 6 floods presenting hysteresis in the form of a figure of eight exported almost 44% of the suspended particulate matter load while representing just 29% of the flow discharge.

Glider-Based Active Acoustic Monitoring of Currents and Turbidity in the Coastal Zone

The recent integration of Acoustic Doppler Current Profilers (ADCPs) onto underwater gliders changes the way current and sediment dynamics in the coastal zone can be monitored. Their endurance and ability to measure in all weather conditions increases the probability of capturing sporadic meteorological events, such as storms and floods, which are key elements of sediment dynamics. We used a Slocum glider equipped with a CTD (Conductivity, Temperature, Depth), an optical payload, and an RDI 600 kHz phased array ADCP. Two deployments were carried out during two contrasting periods of the year in the Rhone River region of freshwater influence (ROFI). Coastal absolute currents were reconstructed using the shear method and bottom tracking measurements, and generally appear to be in geostrophic balance. The responses of the acoustic backscatter index and optical turbidity signals appear to be linked to changes of the particle size distribution in the water column. Significantly, this study shows the interest of using a glider-ADCP for coastal zone monitoring. However, the comparison between suspended particulate matter dynamics from satellites and gliders also suggests that a synoptic view of the processes involved requires a multiplatform approach, especially in systems with high spatial and temporal variability, such as the Rhone ROFI area.

High-frequency and tidal period observations of suspended particulate matter in coastal waters by AHI/Himawari-8.

Driven by tidal forcing and terrestrial inputs, suspended particulate matter (SPM) in shallow coastal waters usually shows high-frequency dynamics. Although specific geostationary satellite ocean color sensors such as the geostationary ocean color imager (GOCI) can observe SPM hourly eight times in a day from morning to afternoon, it cannot cover the whole semi-diurnal tidal period (∼12 h), and an hourly frequency may be insufficient to witness rapid changes in SPM in highly dynamic coastal waters. In this study, taking the Yangtze River Estuary as an example, we examined the ability of the geostationary meteorological satellite sensor AHI/Himawari-8 to monitor tidal period SPM dynamics with 10-min frequency. Results showed that the normalized water-leaving radiance (Lwn) retrieved by the AHI was consistent with the in-situ data from both cruise- and tower-based measurements. Specifically, AHI-retrieved Lwn was consistent with the in-situ cruise values, with mean relative errors (MREs) of 19.58%, 16.43%, 18.74%, and 26.64% for the 460, 510, 640, and 860 nm bands, respectively, and determination coefficients (R2) larger than 0.89. Both AHI-retrieved and tower-measured Lwn also showed good agreement, with R2 values larger than 0.75 and MERs of 14.38%, 12.42%, 18.16%, and 18.89% for 460, 510, 640, and 860 nm, respectively. Moreover, AHI-retrieved Lwn values were consistent with the GOCI hourly results in both magnitude and spatial distribution patterns, indicating that the AHI can monitor ocean color in coastal waters, despite not being a dedicated ocean color sensor. Compared to the 8 h of SPM observations by the GOCI, the AHI was able to monitor SPM dynamics for up to 12 h from early morning to late afternoon covering the whole semi-diurnal tidal period. In addition, the high-frequency 10-min monitoring by the AHI revealed the minute-level dynamics of SPM in the Yangtze River Estuary (with SPM variation amplitude found to double over 1 h), which were impossible to capture based on the hourly GOCI observations.