Surface Suspended Particulate Matter Research Articles

Three Gorges Reservoir: metal pollution in surface water and suspended particulate matter on different reservoir operation periods

Heavy metals in surface water and suspended particulate matter (SPM) from the Yangtze River, the Jialingjiang River, the Wujiang River and the Three Gorges Reservoir (TGR) were detected to clarify the effects of water input on water quality of the TGR during the water impoundment period (October 2014) and water releasing period (January 2015), respectively. The results showed that metals concentrations in surface water were in the low range and showed different trends. Metals concentrations in SPM also presented various tendencies. In October 2014, significant or highly significant correlations were found between all the elements except for Ni, Cu and Zn. In January 2015, highly significant correlations were detected between Al, As, Cd, Sn, Sb and Ba, suggesting that these elements may share the same source in SPM. Heavy metal pollution evaluation of surface water and SPM showed that water samples sampled from water impoundment period (October 2014) of TGR suffered more heavy metal pollution than that from water releasing period (January 2015) and waters in the three most important input rivers of TGR were more polluted than waters in TGR, while it showed the opposite trend in SPM. We also found that SPM in January 2015 was more polluted by heavy metals than that in October 2014. As the water quality of TGR is most affected by the three input rivers (the Yangtze River, Jialingjiang River and Wujiang River), some of pollutants especially elements of Cd, Pb and Zn embedded in SPM showed accumulation during the two sampling campaigns and may cause adverse effect to water quality of TGR.

Surface suspended particulate matter concentration in the Taiwan Strait during summer and winter monsoons

The Taiwan Strait (TS), situated between Taiwan and China, is shallow, relatively turbid, and characterized by strong tidal currents and winter and summer monsoon seasons. The aim of this study was to use images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Aqua satellite to investigate how local sediment sources in addition to the seasonality in wind, oceanographic currents, and waves influence the suspended particulate matter (SPM) dynamics in the TS. In winter, northeast (NE) winds drive the China Coastal Current southward. Cold water with a high SPM concentration is transported southward into the Strait. After the highest SPM concentration reaches its peak in December and January, the winds weaken and the SPM concentration decreases. During summer, winds are less strong and SPM concentration is lower. Although typhoons typically occur in summer, they generate only a weak signal in the surface SPM concentration data from MODIS because of the low number of cloud-free images during these periods. Typhoons result in a short-term increase in the SPM concentration but do not strongly influence the seasonal values in the satellite-derived SPM concentration maps.

Occurrence, distribution, and risk assessment of alkylphenols, bisphenol A, and tetrabromobisphenol A in surface water, suspended particulate matter, and sediment in Taihu Lake and its tributaries

The occurrence and distribution of nine selected compounds were investigated in surface water, suspended particulate matter (SPM), and sediment in Taihu Lake and its tributaries. With the exception of 4-Butylphenol, all compounds were detected in at least two phases, and nonylphenol (NP) and 4-tert-Octylphenol (4-OP) were the predominant alkylphenols (APs) in the lake. A significant correlation was observed between NP and 4-OP, indicating that they may share the same source. Moreover, surface water phase was the dominant sink of Bisphenol A (BPA) in the aquatic environment. The concentrations of BPA between the surface water and SPM phases were closely related to each other. In addition, Tetrabromobisphenol A (TBBPA) exhibited relatively higher concentrations and detection frequencies in the SPM. Risk assessment revealed greater risk associated with the surface water than the sediment, indicating that the discharge of industrial wastewater and domestic sewage poses a serious threat to aquatic ecosystems.

Distribution and behavior of zinc in estuarine environments: an overview on Bahía Blanca estuary (Argentina)

Zinc concentrations and distribution have been fully studied within Bahia Blanca estuary, an area which is strongly influenced by urban and industrial stress. Not only metal dissolved in estuarine water were measured but also measured were sediments and suspended particulate matter (SPM), as well as associated with estuarine organisms. In all cases, internationally standardized protocols were applied to metal measurements, including analytical quality check test through analysis of certified reference materials. Total metal contents from surface sediments and SPM were compared with those from a historical database of the area, as well as with values representing the natural geochemical baseline within the system. Results showed that heavy metal pollution is mainly localized in the areas close to both industrial effluents discharge system and urban sewage outfall discharge. Data from sequential extractions indicate that metals from anthropogenic sources are potentially more mobile than those inherited from geological parent material. The influences of other potential sources of metals (i.e., streams, runoff) were also considered. SPM was clearly identified as the main carrier of the studied heavy metals within the system, and its significance to metals input into sediments and/or biota was verified. Zinc has been accumulated within the different biological species from Bahia Blanca estuary, and their kinetics of accumulation have also been considered. Finally, the combination of the obtained results allowed suggesting the maintenance of a surveillance program to assess the environmental quality of this environment.

Detection of shipwrecks in ocean colour satellite imagery

Waterborne swath acoustic and airborne laser systems are the main methods used to detect and investigate fully submerged shipwreck sites. In the nearshore, waterborne techniques are compromised as search tools as their effective swath is a function of water depth, necessitating very close survey line spacing in shallow water, increasing cost accordingly. Additionally, in turbid coastal waters bathymetric LiDAR is ineffective as it relies on clear non-turbid water. Therefore, the nearshore turbid zone represents a challenging area for archaeologists in the search for fully submerged archaeological sites. In this study, we describe a new methodology to detect the presence of submerged shipwrecks using ocean colour satellite imagery in turbid waters. We demonstrate that wrecks generate Suspended Particulate Matter (SPM) concentration signals that can be detected by high-resolution ocean colour satellite data such as Landsat-8. Surface SPM plumes extend downstream for up to 4 km from wrecks, with measured concentrations ranging between 15 and 95 mg/l. The overall ratio between the plume and background SPM concentrations is about 1.4. During slack tidal phases sediments in suspension settle to create fluffy mud deposits near the seabed. Scour pits developed around wrecks act as sinks where fine-grained suspended material is preferentially deposited at slacks. The scour pits subsequently act as sources for suspended material when the bottom current increases after slacks. SPM plumes develop immediately before maximum ebb or flood current is reached, during maximum current and immediately after. Particulate matter is suspended in sufficient concentrations to be detected in ocean colour data. The ability to detect submerged shipwrecks from satellite remote sensors is of benefit to archaeological scientists and resource managers interesting in locating wrecks and investigating processes driving their evolution.

Features of the physical environment associated with green tide in the southwestern Yellow Sea during spring

Massive green tides caused by Ulva prolifera in the Yellow Sea have occurred every summer since 2007 and have caused huge economic losses for local governments. The Subei (North Jiangsu Province, China) Shoal, with its large-scale Porphyra aquaculture, has been regarded as the most important source of U. prolifera for green tides. To reveal the physical mechanisms of floating and drifting algae in this area, the characteristics of the current, the temperature, the salinity and suspended particulate matter (SPM) in the southwestern Yellow Sea, especially in the Subei Shoal, were studied. The topography of the radial sand ridges in the Subei Shoal constrains the features of the currents and causes net longitudinal and latitudinal movements. The longitudinal net movement is a dominant dynamic factor that can bring U. prolifera into offshore waters. The amount of gas that is produced by algae during photosynthesis determines whether U. prolifera can float well on the sea surface after it is disposed into the water from Porphyra aquacultural apparatus. The Subei Shoal is characterized by a high turbidity, which can result in significant light attenuation and affect the photosynthesis together with the buoyancy of a U. prolifera in the water. According to satellite remote sensing data from 2012, the three-month-averaged surface SPM (April, May and June) in the Subei Shoal was 140 mg/dm3, and the north of the Subei Shoal (the north of 34.5°N), it was 11 mg/dm3. According to the monthly averaged surface SPM in April, the transparency in the Subei Shoal was only 0.1 m, but it often exceeded 2.0 m outside of the Subei Shoal. The results explain why the floating ability of U. prolifera increases significantly once the green algae drifted outside the Subei Shoal.

Estuaries of southwest England: Salinity, suspended particulate matter, loss-on-ignition and morphology

Analyses of consistently measured survey data and published hydrological data for the estuaries of southwest England show that: (1) freshwater runoff and estuary length are strongly related to catchment area; (2) salt intrusion length is always greater than 74% of the estuary length during low runoff, spring-tide summer conditions and, on average, is more than 90% – there is a statistically significant relationship between salt intrusion length and tidal range (increased intrusion) and freshwater runoff (decreased intrusion); (3) salinity stratification is strongly, positively correlated with the Simmons’ Ratio – a measure of the relative balance of freshwater- and tidally-induced current speeds; (4) residence times are strongly correlated with tidal range and tidal length and somewhat less strongly correlated with tidal prism – longer estuaries with smaller tides have longer residence times than shorter estuaries with stronger tides; (5) maximum surface suspended particulate matter (SPM) concentrations vary from 2 to 20,000mgl−1; (6) maximum surface SPM concentrations are strongly related both to tidal range and tidal length and less strongly correlated with tidal prism – long, strongly tidal estuaries have greater concentrations; (7) loss-on-ignition (LOI) of SPM is strongly related to SPM concentration – low concentrations (less than a few mgl−1) typically have LOI>50% and high concentrations (greater than a few hundred mgl−1) typically have LOI∼10%; (8) LOI of the freshwater SPM is greater than that in the area of maximum estuarine SPM concentration, so that SPM within the high-turbidity reaches of southwest estuaries is significantly different from that entering the estuaries in their freshwater inflows; (9) an observed scaling relationship between estuary tidal length and a prescribed function both of depth at the mouth and tidal range is similar to that given by theoretical work (Prandle, 2004; Prandle et al., 2006), as is an observed scaling relationship between depth at the mouth and mean annual runoff. To our knowledge, the measurements and results presented here for the estuaries of southwest England are, in many cases, the first that quantify their important in-water physical characteristics and behaviour. Apart from presenting new information, the synthesis has some important implications for estuarine management, and may aid the straightforward estimation of some key physical variables for these systems.

Influence of deep-water derived isoprenoid tetraether lipids on the [formula omitted] paleothermometer in the Mediterranean Sea

The TEX86H paleothermometer based on isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) has widely been applied in various marine settings to reconstruct past sea surface temperatures (SSTs). However, it still remains uncertain how well this proxy reconstructs annual mean SSTs. Here, we assess environmental factors governing the TEX86H paleothermometer in the Mediterranean Sea, by studying the distribution of isoGDGTs in surface sediments, suspended particulate matter (SPM), and two sediment cores. A redundancy analysis using the fractional abundance of the six major isoGDGTs indicates that the sedimentary isoGDGTs are mostly influenced by three environmental factors explaining a large part (74%) of the variance in isoGDGT distribution. In order of decreasing significance, these factors are annual mean SST, continental organic matter input as indicated by the BIT index, and water depth. However, when considering only the four isoGDGTs that are used for the TEX86H proxy, water depth is the most significant parameter, explaining 63% of the variance. Indeed, a strong positive relationship between water depth and TEX86H is observed in both surface sediments and SPM from the Mediterranean Sea. This is driven by an increase in fractional abundances of GDGT-2 and crenarchaeol regio-isomer and a decrease in the fractional abundances of GDGT-1 and GDGT-3 with increasing water depth, leading to a bias to higher temperatures of TEX86H in deep-water surface sediments. The fact that the water-depth trend is also apparent in SPM suggests that this change might be due to a change in thaumarchaeotal community thriving below surface mixed-layer waters and that this signal is, at least partly, incorporated into sedimentary isoGDGTs. Interestingly, surface-sediment TEX86H values from >1000m water depth do not show a correlation with water depth anymore and instead are correlated to annual mean SSTs. A composite deep-water TEX86H dataset of surface sediments from both the Mediterranean Sea and the Red Sea, interconnected regional restricted basins with relatively high bottom-water temperatures and high salinity, forms a distinctive correlation line, statistically distinct from that of the general global correlation. Application of this correlation on two sedimentary records from the western Mediterranean Sea covering the last deglaciation yields SSTs nearly identical to those obtained with the U37K′ paleothermometer, whereas the global calibration substantially overestimates SSTs. Our results show that the warm bias of the TEX86H proxy in the Mediterranean Sea is not due to seasonality, as previously suggested. Further research is needed to elucidate the mechanism behind the strong water depth trend of TEX86H in the Mediterranean Sea which is not apparent in open ocean settings.

Variations in GDGT distributions through the water column in the South East Atlantic Ocean

The TetraEther indeX of 86 carbon atoms (TEX86) temperature proxy is widely used in reconstructions of past sea surface temperature. Most current calibrations are based on surface sediment distributions of the glycerol dialkyl glycerol tetraether lipids (GDGTs) that comprise TEX86 and assume that these GDGTs are exported from the upper mixed layer. However, GDGT export from deeper waters could impact sedimentary GDGT distributions and therefore TEX86 paleothermometry. Here we examine GDGT distributions in suspended particulate matter (SPM) and underlying sediments collected from the Southeast Atlantic Ocean. Our results reveal different GDGT distributions – specifically the ratio between GDGTs bearing 2 vs. 3 cyclopentyl moieties, [2/3] ratios – between surface, subsurface (>50–200m) and deep water (>200m) SPM, which suggests the occurrence of in situ (deep) production that is not apparent when considering TEX86. The GDGT distributions in sediments match those of subsurface waters rather than surface waters, suggesting that they have not been preferentially derived from the upper mixed layer; this is consistent with GDGT abundances being highest in shallow subsurface SPM (∼100 to 200m). It remains unclear what governs the different [2/3] ratios throughout the water column, but it is likely related to a combination of temperature and thaumarchaeotal community structure.

Estuarine suspended particulate matter concentrations from sun-synchronous satellite remote sensing: Tidal and meteorological effects and biases

Optical data from a sun-synchronous satellite were used to investigate how large-scale estuarine suspended particulate matter (SPM) concentrations were affected by tidal and bulk meteorological drivers, and how retrieved SPM is biased by tidal aliasing and sampling under clear sky conditions. Local absorption and scattering properties were used to derive surface SPM maps from 84 cloud-free ENVISAT MERIS FR reflectance images of the Westerschelde estuary (51° 30′ N, 3° 30′ E) for the period 2006–2008, and validated with in situ SPM at fixed stations (r=0.89 for geometric means). The distinctly different SPM maps were categorized for different tidal and seasonal conditions. Resulting composites reveal spatial patterns in SPM as a function of semi-diurnal tidal phase, fortnightly tidal phase, or season. For the estuary proper, tidal and seasonal effects on the variation of SPM are similar in magnitude. Observed controls for surface SPM are distance to shallow source area, tidal current velocity, and advection of North Sea and estuarine surface waters. Turbidity maxima appear only during favourable tidal and meteorological conditions. For the Westerschelde, the bias introduced by sun-synchronous sampling causes low water image acquisitions to uniquely coincide with spring tides, and high water images with neap tides. Cloud-free images were associated with low wind velocities. Simulations from a mud transport model confirmed the overestimation of geometric mean SPM from the tidal aliasing, and underestimation from fair weather. This resulted in a net relative error of −8% at the wave-exposed mouth, but biases cancelled out in the upper estuary. We argue that local biases should be considered when interpreting water quality products for estuaries and coasts around the world.

Polybrominated diphenyl ethers (PBDEs) in the surface sediments and suspended particulate matter (SPM) from Lake Chaohu, a large shallow Chinese lake

Suspended particulate matter (SPM) and surface sediment samples were collected from Lake Chaohu to investigate the residues, congener profile, and spatial distribution of polybrominated diphenyl ethers (PBDEs) in a large shadow lake in the middle of the Yangtze River Basin. The concentration of Σ13BDEs (defined as the sum of 13 target congeners excluding BDE 209) and the concentration of BDE 209 ranged from 236.7 to 1373.4pg/g dry weight (dw) and from 4.2 to 691.2pg/g dw in the surface sediments, respectively, which were 2–3 orders of magnitude smaller than those found in the SPM. The congener composition was dominated by BDE 47 (50.8%) and BDE 209 (21.3%) in the sediment, while the proportion of BDE 47 to Σ14BDEs in the SPM was slightly higher than that in the sediment. The concentration of Σ14BDEs in the sediment from the drinking water source (WR) area in the eastern part of the lake was very low, with a mean value of 514.8pg/g, whereas the mean concentration was 102.4ng/g in the SPM. A cluster analysis (CA) was conducted to further illustrate the dominance of each congener and the similarity of each sampling site. Many factors, including resuspension, photodecomposition, microbial oxidation, local discharge, and dredging, influenced the distribution in the sediment and SPM for the PBDE congeners as well as the spatial distribution of PBDEs. A formula for the PBDE concentrations in the surface sediment and SPM was constructed to understand the potential relationship between sediment and SPM concentrations. Although the formula did not accurately predict specific PBDE congener concentrations in the sediment, it remains a practical and useful way to assess the overall pollution of PBDE in sediment in Lake Chaohu, as it depends only on the concentrations of PBDEs in the SPM.

Interannual variability of surface and bottom sediment transport on the Laptev Sea shelf during summer

Abstract. Sediment transport dynamics were studied during ice-free conditions under different atmospheric circulation regimes on the Laptev Sea shelf (Siberian Arctic). To study the interannual variability of suspended particulate matter (SPM) dynamics and their coupling with the variability in surface river water distribution on the Laptev Sea shelf, detailed oceanographic, optical (turbidity and Ocean Color satellite data), and hydrochemical (nutrients, SPM, stable oxygen isotopes) process studies were carried out continuously during the summers of 2007 and 2008. Thus, for the first time SPM and nutrient variations on the Laptev Sea shelf under different atmospheric forcing and the implications for the turbidity and transparency of the water column can be presented. The data indicate a clear link between different surface distributions of riverine waters and the SPM transport dynamics within the entire water column. The summer of 2007 was dominated by shoreward winds and an eastward transport of riverine surface waters. The surface SPM concentration on the southeastern inner shelf was elevated, which led to decreased transmissivity and increased light absorption. Surface SPM concentrations in the central and northern Laptev Sea were comparatively low. However, the SPM transport and concentration within the bottom nepheloid layer increased considerably on the entire eastern shelf. The summer of 2008 was dominated by offshore winds and northward transport of the river plume. The surface SPM transport was enhanced and extended onto the mid-shelf, whereas the bottom SPM transport and concentration was diminished. This study suggests that the SPM concentration and transport, in both the surface and bottom nepheloid layers, are associated with the distribution of riverine surface waters which are linked to the atmospheric circulation patterns over the Laptev Sea and the adjacent Arctic Ocean during the open water season. A continuing trend toward shoreward winds, weaker stratification and higher SPM concentration throughout the water column might have severe consequences for the ecosystem on the Laptev Sea shelf.

Modeling the effects of near-surface plumes of suspended particulate matter on remote-sensing reflectance of coastal waters

A radiative transfer model was applied to examine the effects of vertically stratified inherent optical properties of the water column associated with near-surface plumes of suspended particulate matter on spectral remote-sensing reflectance, R(rs)(λ), of coastal marine environments. The simulations for nonuniform ocean consisting of two layers with different concentrations of suspended particulate matter (SPM) are compared with simulations for a reference homogeneous ocean whose SPM is identical to the surface SPM of the two-layer cases. The near-surface plumes of particles are shown to exert significant influence on R(rs)(λ). The sensitivity of R(rs)(λ) to vertical profile of SPM is dependent on the optical beam attenuation coefficient within the top layer, c(1)(λ), thickness of the top layer, z(1), and the ratio of SPM in the underlying layer to that in the top layer, SPM(2)/SPM(1), as well as the wavelength of light, λ. We defined a dimensionless spectral parameter, P(λ)=c(1)(λ)×z(1)×(SPM(2)/SPM(1)), to quantify and examine the effects of these characteristics of the two-layer profile of SPM on the magnitude and spectral shape of R(rs)(λ). In general, the difference of R(rs)(λ) between the two-layer and uniform ocean decreases to zero with an increase in P(λ). For the interpretation of ocean color measurements of water column influenced by near-surface plumes of particles, another dimensionless parameter P'(λ) was introduced, which is a product of terms representing homogenous ocean and a change caused by the two-layer structure of SPM. Based on the analysis of this parameter, we found that for the two-layer ocean there is a good relationship between R(rs)(λ) in the red and near-infrared spectral regions and the parameters describing the SPM(z) profile, i.e., SPM(1), SPM(2), and z(1).

Weather and climate induced spatial variability of surface suspended particulate matter concentration in the North Sea and the English Channel

Images from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite have been used to investigate the meteorological and climate induced variability of suspended particulate matter (SPM) concentration in the North Sea. The meteorology has been characterized by the 11 weather types deduced from a refined system of Lamb’s classification of synoptic weather charts. Climatological effects have been related to the North Atlantic Oscillation index. The surface SPM concentration maps from MODIS have been ensemble averaged according to these weather types or climatological conditions. The data show that each type has a distinct distribution of surface SPM concentration in the North Sea. The differences are explained by different hydrodynamic and wave conditions. The occurrence of storms will impact the shallow regions by increasing the resuspension of bottom material. Prevailing winds will, on the other hand, change the residual transport of SPM in the North Sea. The more protected Southern Bight exhibits relatively stronger influences of advection, whereas in the central North Sea and the German Bight resuspension is more pronounced. This patterns result in an alternation of relatively high SPM concentration in the Southern Bight and in the rest of the southern North Sea during certain weather conditions. Limitations in satellite images have been assigned to stratification effects due to the occurrence of highly concentrated mud suspensions during certain weather types. The approach provides a tool to improve our understanding of coastal and shelf sea processes, especially with respect to variations of SPM concentration distribution according to weather, climate and climate change.

Daily and seasonal dynamics of suspended particles in the Rhône River plume based on remote sensing and field optical measurements

Satellite ocean colour remote sensing can serve as a powerful tool to assess river plume characteristics because it provides daily mapping of surface suspended particulate matter (SPM) concentration at high spatial resolution. This study’s ultimate objective was to better understand daily and seasonal particle dynamics in a coastal area strongly influenced by freshwater discharge and wind—the Rhone River (France), this being the major source of terrestrial input to the Mediterranean Sea. SPM concentrations and biogenic composition (chlorophyll a, organic carbon) were investigated during several bio-optical field campaigns conducted in spring–autumn of 2010 both from aboard a research vessel and by means of an autonomous profiling float. Freshwater discharge and wind velocities varied significantly during the year, associated with marked fluctuations in surface SPM (upper 1 m), even within hours and not restricted to any specific season. Thus, the range was ca. 12–25 g m–3 (dry mass basis) on 9 April (spring), and ca. 3–39 g m–3 on 4–5 November (late autumn). Short-term variations were observed also in SPM composition in terms of POC (albeit not chl a), with POC/SPM ratios ranging between ca. 3 and 11% over ca. 3 weeks in spring. Nevertheless, the particulate backscattering coefficient (b bp) proved to be a robust proxy of SPM concentration in the river plume (b bp(770) = 0.0076 × SPM, R2 = 0.80, N = 56). It has recently been demonstrated that 80% of the Rhone’s terrestrial discharge occurs during flood events. The results of the present study revealed that, under these conditions, SPM is constrained largely within surface waters (i.e. at depths <5 m), with only weak daily vertical variability. By implication, ocean colour satellite data are highly suitable in meaningfully estimating the overall SPM load exported by the Rhone River to the Mediterranean. These findings make a solid contribution to future improvements of three-dimensional sediment transport models for the region and similar settings.

Observed vs. predicted variability in non-algal suspended particulate matter concentration in the English Channel in relation to tides and waves

The study of water clarity is essential to understand variability in biological production, particularly in coastal seas. The spatial and temporal variability of non-algal suspended particulate matter (SPM) in surface waters of the English Channel was investigated and related to local forcing by means of a large satellite dataset covering the study area with a spatial resolution of 1.2 km and a daily temporal resolution. This analysed dataset is a time series of non-algal SPM images derived from MODIS and MERIS remote-sensing reflectance by application of an IFREMER semi-analytical algorithm over the period 2003–2009. In a first step, the variability of time series of MODIS images was analysed through temporal autocorrelation functions. Then, non-algal SPM concentrations were assessed in terms of site-specific explanatory variables such as tides, wind-generated surface-gravity wave amplitudes and chlorophyll-a (Chl-a), based on three statistical models with fitting parameters calibrated on a dataset of merged MERIS/MODIS images gathered from 2007 to 2009 over the whole English Channel. Correlogram analysis and the first model highlight the local patterns of the influence of the tide, especially the neap–spring cycle, on non-algal surface SPM. Its effect is particularly strong in the central and eastern English Channel and in the western coastal areas. The second model shows that waves prevail as driver at the entrance of the English Channel. The most sophisticated of the three statistical models, although involving only three explanatory variables—the tide, waves and Chl-a—is able to estimate non-algal surface SPM with a coefficient of determination reaching 70% at many locations.

Improving the description of the suspended particulate matter concentrations in the southern North Sea through assimilating remotely sensed data

The integration of remote sensing data of suspended particulate matter (SPM) into numerical models is useful to improve the understanding of the temporal and spatial behaviour of SPM in dynamic shelf seas. In this paper a generic method based on the Ensemble Kalman Filtering (EnKF) for assimilating remote sensing SPM data into a transport model is presented. The EnKF technique is used to assimilate SPM data of the North Sea retrieved from the MERIS sensor, into the computational water quality and sediment transport model, Delft3D-WAQ. The satellite data were processed with the HYDROPT algorithm that provides SPM concentrations and error information per pixel, which enables their use in data assimilation. The uncertainty of the transport model, expressed in the system noise covariance matrix, was quantified by means of a Monte Carlo approach. From a case study covering the first half of 2003, it is demonstrated that the MERIS observations and transport model application are sufficiently robust for a successful generic assimilation. The assimilation results provide a consistent description of the spatial-temporal variability of SPM in the southern North Sea and show a clear decrease of the model bias with respect to independent in-situ observations. This study also identifies some shortcomings in the assimilated results, such as over prediction of surface SPM concentrations in regions experiencing periods of rapid stratification/de-stratification. Overall this feasibility study leads to a range of suggestions for improving and enhancing the model, the observations and the assimilation scheme.

Turbulent Mixing due to Surface Waves Indicated by Remote Sensing of Suspended Particulate Matter and Its Implementation into Coupled Modeling of Waves, Turbulence, and Circulation

Abstract This paper studies the impact of the surface waves on the turbulent mixing. The satellite observations of suspended particulate matter (SPM) at the ocean surface as an indicator of turbulent quantities of the flow are used. In a water column, SPM builds a vertical profile depending on settling velocities of the particles and on vertical mixing processes; thus, SPM is a perfect marker to study the turbulent quantities of the flow. Satellite observations in the North Sea show that surface SPM concentrations, in locations of its deposition, grow rapidly and build plume-shaped, long (many kilometers) uninterrupted and consistent structures during a storm. Also, satellites reveal that SPM rapidly sinks to the seabed after the storm peak has passed and wave height decreases (i.e., in the absence of strong turbulence). The nonbreaking wave-induced turbulence has been discussed, parameterized, and implemented into an equation of evolution of turbulent kinetic energy (TKE) in the frame of mean-flow concept, which can be used in existing circulation models. The ratio between dissipated and total wave energy is used to describe the influence of wave damping on the mean flow. The numerical tests reproduce experiments in a wave tank very well and are supported by observations of SPM in the North Sea. Their results show that the motion of an individual nonbreaking wave includes turbulent fluctuations if the critical Reynolds number for wave motion is exceeded, independent of the presence of currents due to wind or tides. These fluctuations can produce high diffusivity and strongly influence mixing in the upper water layer of the ocean.

Mechanisms controlling the intra-annual mesoscale variability of SST and SPM in the southern North Sea

Thermal and optical remote sensing data were used to investigate the spatial and temporal distribution of sea surface temperature (SST) and of suspended particulate matter (SPM) in the southern North Sea. Monthly SST composites showed pronounced seasonal warming of the southern North Sea and delineated the English coastal and continental coastal waters. The East-Anglia Plume is the dominant feature of the English coastal waters in the winter and autumn SPM composites, and the Rhine region of freshwater influence (ROFI), including the Flemish Banks, is the dominant feature of the continental waters. These mesoscale spatial structures are also influenced by the evolution of fronts, such as the seasonal front separating well-mixed water in the southern Bight, from the seasonally stratified central North Sea waters. A harmonic analysis of the SST and SPM images showed pronounced seasonal variability, as well as spring–neap variations in the level of tidal mixing in the East Anglia Plume, the Rhine ROFI and central North Sea. The harmonic analysis indicates the important role played by the local meteorology and tides in governing the SST and near-surface SPM concentrations in the southern North Sea. In the summer, thermal stratification affects the visibility of SPM to satellite sensors in the waters to the north of the Flamborough and Frisian Fronts. Haline stratification plays an important role in the visibility of SPM in the Rhine ROFI throughout the year. When stratified, both regions typically exhibit low surface SPM values. A numerical model study, together with the harmonic analysis, highlights the importance of tides and waves in controlling the stratification in the southern North Sea and hence the visibility of SPM.

Estimating sediment and caesium-137 fluxes in the Ribble Estuary through time-series airborne remote sensing

High spatial and temporal resolution airborne imagery were acquired for the Ribble Estuary, North West England in 1997 and 2003, to assess the application of time-series airborne remote sensing to quantify total suspended sediment and radionuclide fluxes during a flood and ebb tide sequence. Concomitant measurements of suspended particulate matter (SPM) and water column turbidity were obtained during the time-series image acquisition for the flood and ebb tide sequence on the 17th July 2003 to verify the assumption of a vertically well mixed estuary and thus justifying the vertical extrapolation of spatially integrated estimate of surface SPM. The 137Cs activity concentrations were calculated from a relatively stable relationship between SPM and 137Cs for the Ribble Estuary. Total estuary wide budgets of sediment and 137Cs were obtained by combining the image-derived estimates of surface SPM and 137Cs with estimates of water volume from a two-dimensional hydrodynamic model (VERSE) developed for the Ribble Estuary. These indicate that around 10,000 tonnes of sediment and 2.72 GBq of 137Cs were deposited over the tidal sequence monitored in July 2003. This compared favourably with bed height elevation change estimated from field work. An uncertainty analysis on the total sediment and 137Cs flux yielded a total budget of the order of 40% on the final estimate. The results represent a novel approach to providing a spatially integrated estimate of the total net sediment and radionuclide flux in an intertidal environment over a flood and ebb tide sequence.