High Suspended Particulate Matter Concentrations Research Articles

Analysis of oceanic suspended particulate matter in the western North Pacific using the complex amplitude sensor

Oceanic suspended particulate matter (SPM) plays important roles in the coupling of climate and biogeochemical cycles via ocean–atmosphere interactions. However, methods for quantifying the properties of SPM in seawater have not yet been well established. Here we present the application of the recently developed complex amplitude sensor (CAS) for analyzing the complex forward-scattering amplitude of individual SPM (0.2–5.0 µm in diameter) obtained at depths of 0–100 m during a research cruise in the western North Pacific. The measured distribution of the complex amplitude indicated that the CAS-derived SPM data could be roughly classified into five major types. Comparison with reference sample’s complex amplitude data and scanning electron microscopy analysis suggested that these types could be attributed mainly to diatom fragments, carbonaceous materials (likely organic matter), mineral dusts, iron oxides, or black carbon. Depth profiles revealed that relatively high concentrations of SPM, presumably dominated by diatom fragments and carbonaceous materials with peak diameters of 0.7–1.0 µm, were typically associated with elevated turbidities and chlorophyll a concentrations. Based on this case study, we discuss the practical advantages and limitations of using the CAS to measure size-resolved concentrations of SPM in seawater and to characterize its composition.

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.

Composition and sources of suspended particles in the Pacific Arctic region

During the 6th (2014) and 7th (2016) Chinese Arctic Expedition (CHINARE), samples of suspended particulate matter (SPM) were collected from both surface (depth: <1.0 m) and subsurface (depth: approximately between 10 and 150 m) waters over the northern shelf of the Bering Sea and in the western Arctic Ocean. To investigate the distribution and sources of organic matter in both the surface water and the vertical profile, the concentration and stable carbon isotopic composition of SPM, particulate organic carbon (POC), and particulate nitrogen (only in surface water samples) were determined, and some particle samples were selected for examination using scanning electron microscopy. Results showed apparent geographical partitioning and temporal variation in both the concentration and the composition of SPM. Higher SPM concentrations were observed in nearshore, shelf break, and sea ice edge areas; the distribution of POC concentration displayed a similar pattern, with higher values found from the northern part of the Bering Shelf to southern parts of the Chukchi Shelf. In surface water, SPM mainly comprised clay and detrital minerals with higher POC contents, lighter δ13C values, and higher POC/PN ratios, indicating organic matter predominantly derived from terrestrial sources in areas south of St. Lawrence Island and north of 73°N. The downward trend of heavier δ13C values, together with reduction in clay and detrital minerals, suggests that vertical transport of SPM is hindered by stratification, resulting in transport of terrestrial materials toward northern basin areas. In the Chukchi Slope and Canada Basin areas, extremely light δ13C values (as low as −33.41‰ PDB) were mainly observed at depths of 20–60 m, where the Polar Mixed Layer (PML) intersects with the Upper Halocline Layer (UHL). Under the condition of low sea ice extent in 2016, the POC-δ13C values were heavier in the PML than in the UHL in the Chukchi Slope and Canada Basin areas. These findings provide insights into the sources, transport, and fate of organic matter in the Pacific Arctic region, which have important implications for understanding the biogeochemical cycles and ecosystem dynamics in this remote and rapidly changing environment.

210Po and 210Pb as tracers for particle cycling in a shallow semi-enclosed bay of Taiwan Strait

Naturally-occurring 210Po and 210Pb are good tracers for particle cycling in the estuarine and coastal environment. Activities of 210Po and 210Pb were measured in samples of bulk (wet + dry) atmospheric deposition, river water and surface seawater collected in the Zhangjiang Estuary-Dongshan Bay to investigate the geochemical scavenging rates (or residence times) of these particle-reactive nuclides. The spatial distribution of 210Po and 210Pb were strongly influenced by suspended particulate matter (SPM) concentrations and in almost all stations, 210Po and 210Pb were mainly in particulate form (51.7%–92.2% of the total for 210Po and from 44.3% to 90.3% for 210Pb). Due to the very high SPM concentration, enhanced scavenging of 210Po and 210Pb was observed in the maximum turbidity zone of Zhangjiang River, with a marked decrease of dissolved nuclides’ activities. We built a mass balance model and we found out that atmospheric inputs are the major source of these radionuclides comparing with other sources (e.g., river inputs or ingrowth production) in the study area. Residence times of 210Pb were calculated to be 2.2–9.8 and 0.5–8.9 days for dissolved and particulate 210Pb, respectively. And residence times of dissolved and particulate 210Po were 6.3–31.7 and 2.2–13.9 days, respectively. In the turbidity zone, we found an unexpected result that particulate 210Po and 210Pb had the longest residence times (about two weeks), suggesting that SPMs in the turbidity zone would not be easy to sink to the sea floor. We also found that different SPMs showed significantly different 210Po/210Pb activity ratios, which increased in the following order: atmospheric deposition in dry season < SPMs in river < SPMs in the Zhangjiang Eastuary-Dongshan Bay < biogenic particles (including detritus, fecal pellets, cells of phytoplankton and zooplankton). This phenomenon implied that 210Po/210Pb activity ratio in the particles has the potential application in distinguishing SPM sources in the coastal seas.

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.

Dynamics of trace metals with different size species in the Pearl River Estuary, Southern China

The Pearl River Estuary (PRE), the largest estuary in Southern China, regulates the fluxes of riverine trace metals into the South China Sea. However, the geochemical behavior of trace metals in this estuary is still ambiguous. In this study, we investigated the dynamics of trace metals in different phases (i.e., particulate, colloidal and truly dissolved) in the PRE in both wet and dry seasons characteristic of the region. Transformations of trace metals between particulate (>0.45 μm), colloidal (1 kDa to 0.45 μm) and truly dissolved (<1 kDa) phases were observed during the estuarine mixing. Colloidal metals (except for Pb) showed non-conservative ‘removal’ behavior in the low-salinity zone (S < 10‰), suggesting the coagulation of colloidal metals and subsequent deposition to bed sediments being an important sink of dissolved trace metals. By contrast, truly dissolved metals exhibited a mid-salinity maximum distribution (i.e., Mn, Ni, Cu and Cd) or little variation along the salinity gradient (i.e., Fe). The increase of truly dissolved metal concentration was accompanied by the decrease of particulate metal concentration, indicating that the desorption of suspended particles was an important source of dissolved Mn and Cd in the PRE. Metal released from the suspended particles increased in the dry season due to the high suspended particulate matter concentration. Dissolved Mn concentration in the bottom water in wet season was higher than that in dry season, implying that benthic Mn input increased as the bottom water became hypoxic. Abnormally high concentrations of particulate and dissolved Pb were observed at the lower PRE, implying the presence of a potential point source pollution. A flux model predicted that total dissolved Fe, Ni, Cu and Zn underwent net removal while dissolved Mn and Cd had net inputs during the estuarine mixing. This study raveled contrasting geochemical behaviors of trace metals with different size phases and the different sources and sinks of dissolved metals in the PRE.

Optical Classification of Lower Amazon Waters Based on In Situ Data and Sentinel-3 Ocean and Land Color Instrument Imagery

Optical water types (OWTs) were identified from an in situ dataset of concomitant biogeochemical and optical parameters acquired in the Amazon River and its tributaries, in the Lower Amazon region, at different hydrological conditions from 2014 to 2017. A seasonal bio-optical characterization was performed. The k-means classification was applied to the in situ normalized reflectance spectra (rn(λ)), allowing the identification of four OWTs. An optical index method was also applied to the rn(λ) defining the thresholds of the OWTs. Next, level-3 Sentinel-3 Ocean and Land Color Instrument images representative of the seasonal discharge conditions were classified using the identified in situ OWTs as reference. The differences between Amazon River and clearwater tributary OWTs were dependent on the hydrological dynamics of the Amazon River, also showing a strong seasonal variability. Each OWT was associated with a specific bio-optical and biogeochemical environment assessed from the corresponding absorption coefficient values of colored dissolved organic matter (aCDOM) and particulate matter (ap), chlorophyll-a and suspended particulate matter (SPM) concentrations, and aCDOM/ap ratio. The rising water season presented a unique OWT with high SPM concentration and high relative contribution of ap to total absorption compared to the other OWTs. This bio-optical characterization of Lower Amazon River waters represents a first step for developing remote sensing inversion models adjusted to the optical complexity of this region.

Implications of turbulence in a macrotidal estuary in northeastern Brazil — The São Marcos Estuarine Complex

Pollution, hypoxia, and salinization are frequent occurrences in estuarine environments. The management of these issues requires the understanding of estuarine dynamics, which are governed by both freshwater and tidal inputs. The aim of the present study was to investigate the dynamics of the São Marcos Estuarine Complex (SMEC) in northeastern Brazil under different rainfall regimes. Two moorings were deployed in the SMEC in 2017 (one downstream [M-I] and one upstream [M-II]) for the collection of data during a complete tidal cycle in three sampling campaigns representative of the rainy, transition, and dry periods. Circulation had an asymmetrical, bidirectional flow, with ebb currents (V > 0) predominating over flood currents (V < 0). The thermohaline indices indicated the presence of two water masses in the SMEC: coastal water in the rainy and dry seasons and river water in the transition period. High concentrations of suspended particulate matter (SPM) (>1,000 mg l−1) were found in the SMEC, with mean values close to 230 mg l−1. The highest concentrations were found near the bottom in the dry season. High concentrations of dissolved oxygen (>190μmol kg −1) were also found, despite the high concentrations of SPM. The Richardson number indicated vertical instability throughout the SMEC, which explains the occurrence of a potential energy anomaly in the range of 7.0 × 10−6 to 1.1 × 10−5 J m−3 s−1. The SMEC was well mixed and poorly stratified most of the time, except at M-I in the dry season, when it was partially mixed with weak vertical stratification. River discharge and the Stokes drift were the main salt exporting and importing mechanisms in the SMEC, respectively. The present results broaden knowledge on macrotidal estuarine dynamics in the Amazon/semiarid interface that can assist in water quality management.

Limited capacity of suspended particulate matter in the Yangtze River Estuary and Hangzhou Bay to carry phosphorus into coastal seas

The Yangtze River carries high fluxes of suspended particulate matter (SPM) and associated particulate phosphorus into the Yangtze River Estuary (YRE), but primary production in coastal seas is phosphorus-limited. Understanding the kinetics of exchangeable inorganic phosphorus (Ex-iP) released from SPM in response to different salinities and SPM concentrations is the key to demonstrating their capacity to carry bioavailable phosphorus into coastal seas. We conducted field investigations and set up a series of incubation experiments with SPM collected from marine and freshwater settings under controlled conditions, with biotic activities inhibited.Our incubation experiments showed that initial rise in salinity substantially increases the efficiency and rates of Ex-iP release, leading to an early release of majority of Ex-iP from riverine SPM when encountering saline waters, but high salinity may result in desorption. Concentrations of released DIP are linearly related to SPM concentrations, but concentrations of DIP in micromoles per gram of SPM are negatively logarithmically related to SPM concentrations, which help prevent SPM from full release of Ex-iP at the river mouth. Release of Ex-iP is insufficient to buffer DIP in the YRE. The contribution of Ex-iP from SPM decline rapidly with the attenuation of SPM concentration, and becomes negligible offshore. Extremely high loads of SPM in Hangzhou Bay allows it to retain some capacity to carry Ex-iP offshore. High concentrations of SPM in a turbid estuary are more important in reducing the removal of DIP by phytoplankton uptake through restriction of light penetration, as the SPM possesses a very limited capacity to carry Ex-iP to coastal seas. However, such high concentrations might be a key contributor to the regeneration of remineralization of organic phosphorus in an estuary.

El-Niño Southern Oscillation (ENSO) effects on the variability of Patos Lagoon Suspended Particulate Matter

South America is particularly subject to El-Niño Southern Oscillation (ENSO)-triggered phenomena, with above-average precipitation during ENSO warm events (El Niño) and below-average precipitation during cold events (La Niña). Seventeen years (2003–2019) of reflectance data from the Moderate Resolution Imaging Spectroradiometer (MODIS) - Aqua sensor were used to quantify the Suspended Particulate Matter (SPM) distribution and variability in Patos Lagoon, southern Brazil, based on three semi-analytical algorithms. An atmospheric correction suitable for extremely turbid coastal waters was applied. Occasional negative retrievals of remote sensing reflectance (Rrs) products were filtered and removed. SPM concentrations were modeled from filtered Rrs values by applying the chosen semi-analytical algorithms: a single band algorithm, a weighted algorithm, and a multi-band algorithm (referred here as NECHAD10, HAN16, and NOVOA17, respectively). After those steps, the daily modeled SPM data were averaged into eight-day, monthly, and yearly composites. SPM time series were then compared to the ENSO index and environmental parameters. As a result of substantial interannual variability, the highest SPM concentrations were found to match El-Niño events (in 2009 and 2012) while the lowest corresponded to a strong La Niña (2010) and a neutral year (2014). The modeled SPM was compared to in-situ SPM data to ensure the applicability to/in Patos Lagoon. Our main results suggest that while the three tested algorithms allow the analysis of temporal and spatial SPM variability, HAN16 and NOVOA17 seem to provide the best results for the Patos Lagoon region. On the other hand, NECHAD10 yields more satisfactory results considering the yearly and eight-day composites. Therefore, we call attention to the methods of handling data as each approach might lead to a different interpretation of the same phenomena.

Human impact on suspended particulate matter in the Yellow River Estuary, China: Evidence from remote sensing data fusion using an improved spatiotemporal fusion method

Transport of suspended particulate matter (SPM) in estuarine waters plays an important role in regulating erosion-accretion and biogeochemical processes. In the Yellow River Estuary (YRE), artificial water and sediment regulation scheme (WSRS) and coastal engineering structures are the 2 typical anthropogenic activities affecting the spatiotemporal dynamics of estuarine SPM. The monitoring of SPM transport affected by such human activities requires SPM mapping at both high spatial and high temporal resolutions. In this study, we presented an improved Flexible Spatiotemporal Data Fusion (FSDAF) strategy with consideration of highly dynamic SPM variations in estuarine waters, and generated 30-m hourly SPM concentrations based on Landsat 8 OLI and GOCI datasets. The new strategy produced higher SPM estimation accuracy than the original FSDAF, with the relative percentage difference (RPD) decreasing from 29.75% to 5.31% using GOCI-derived hourly SPM as reference. With in situ SPM measurements as reference, the fused SPM concentrations had an RMSE of 12.09 mg/L and an RPD of 27.17%. Investigation of interday SPM variations before, during, and after the WSRS in 2018 revealed that the first WSRS significantly increased the SPM concentration and plume extent; new wetland with an area of 12.56 km2 was formed due to sediment accretion near the river mouth. The two groins offshore from the coastlines on the north and south sides of YRE exhibited obvious sediment trapping effects in that higher SPM concentrations on one side of each groin were found regardless of the turbidity modes and diurnal SPM variations; the trapping effects were associated with the number of groins and groin length. Intraday variations of SPM were influenced by tidal currents, with plume direction following the ebb and flooding tidal current direction. The inter- and intraday characteristics of the 30-m hourly SPM dynamics facilitate the detailed analysis of the sediment transport associated with human activities.

Hydrodynamics and suspended particulate matter retention in macrotidal estuaries located in Amazonia-semiarid interface (Northeastern-Brazil)

The aim of the current study was to determine the nature of the seasonal variability of the Suspended Particulate Matter (SPM) fluxes from the drainage basin to the estuary in a macrotidal region (Northeastern Brazil), and the estuarine response to a seawater intrusion regarding sediment deposition, which will support the understanding of the global transport of materials at the continent-ocean interface. Thermohaline structure data was acquired using a Conductivity, Temperature, and Depth (CTD) probe with a sampling frequency of 4 Hz. Suspended particulate material was measured by gravimetric measurements applied to exact filtered volume samples. The outflows were measured through the use of an Acoustic Doppler Current Profiler (ADCP) with frequency of 1.5 MHz. The horizontal thermal and saline gradients varied from warmer and less saline waters (2014) to cooler and saline waters (2015). The gradient behavior when linked to volume transport and SPM flows, suggests a minimization of the fluvial flows in 2015, easing the advance of coastal water (CW) towards the inner estuary, leading to an inversion of the baroclinic pressure gradient. The bottom saline front, generated by the entrance of coastal water masses, caused an increase in SPM concentrations due to increased fluid density, resuspension of previously deposited sediment, and erosion of banks. High concentrations of SPM indicate higher volume transport suggesting a hydraulic barrier due to the change/inversion of the baroclinic pressure gradient, resulting in water and material retention. Material deposition was observed during neap tide, while during spring tide the material is resuspended, increasing the concentration, generating cycles of deposition and erosion during the neap-spring tides. The sediment in suspension that reach the estuary, even with low fluvial volume, stay in this environment forming new islands because of deposition. High deposition rates or sediment cycling, if generated by the hydraulic barrier, may indicate that the flows of SPM from the continental drainage to the estuary and adjacent continental shelf are interrupted and the residence time is increased.

Suspended Matter Distribution in the Surface Layer of the East Equatorial Atlantic

Abstract—The research is dedicated to the suspended particulate matter (SPM) distribution and the hydrological–hydrochemical conditions within the oceanic upwelling of the so-called Guinea Dome. This dome is a 500 km diameter stable cyclonic eddy, the center of which is located at 10° N and 22° W. It was formed owing to northern branch of Equatorial Counter Current activity. A cruise in November 2016 made it possible to observe the rising of isotherms and isohalines up to 50 m in the northern part of the dome, as well as a high SPM concentration (up to 0.7 mg/L) in the ocean surface layer south of 8° N.

The influence of river discharge and wind on Patos Lagoon, Brazil, Suspended Particulate Matter

ABSTRACTEight years (2008–2015) of reflectance data from the Moderate Resolution Imaging Spectroradiometer (MODIS) – Aqua sensor are used to quantify Suspended Particulate Matter (SPM) distribution and variability in Brazil’s Patos Lagoon. After application of an atmospheric correction suitable for extremely turbid coastal water and calculation of SPM concentrations from the reflectance values using an established algorithm, the daily remote sensing data were averaged into eight-day and monthly composites. The climatological patterns show a gradient from higher concentrations in the north to lower concentration in the south, with highest concentrations in austral spring and summer and lowest in autumn and winter. Strong interannual variability shows 2009 and 2012 to have the highest SPM concentrations and 2010 and 2014 to have the lowest. Time series of SPM were then compared with the main forces to the lagoon circulation (wind and river discharge). Peaks in SPM are associated with peaks in river discharge. Maximum SPM occurred following peaks in river discharge combined with strong northeast (NE) winds, suggesting that freshwater input and direction-specific winds are the major mechanisms of sediment transport in Patos Lagoon.

An estuarine-tuned quasi-analytical algorithm (QAA-V): assessment and application to satellite estimates of SPM in Galveston Bay following Hurricane Harvey

Abstract. The standard quasi-analytical algorithm (Lee et al., 2002) was tuned as QAA-V using a suite of synthetic data and in situ measurements to improve its performance in optically complex and shallow estuarine waters. Two modifications were applied to the standard QAA: (1) the semi-analytical relationship for obtaining remote sensing reflectance just below the water surface as a function of absorption and backscattering coefficients was updated using Hydrolight® simulations, and (2) an empirical model of the total non-water absorption coefficient was proposed using a ratio of green to red bands of an ocean color sensor, which is known to work well in various inland and estuarine environments. The QAA-V-derived total absorption and backscattering coefficients, which were evaluated in a variety of waters ranging from highly absorbing and turbid to relatively clear shelf waters, showed satisfactory performance on a Hydrolight-simulated synthetic dataset (R2 &gt; 0.87, MRE &lt; 17 %), an in situ estuarine and nearshore dataset (R2 &gt; 0.70, MRE &lt; 35 %), and the NOMAD (R2 &gt; 0.90, MRE &lt; 30 %). When compared to the standard QAA (QAA-v6), the QAA-V showed an obvious improvement with ∼ 30–40 % reduction in absolute mean relative error for the Hydrolight-simulated synthetic and in situ estuarine and nearshore datasets, respectively. The methodology of tuning QAA was applied to the VIIRS ocean color sensor and validation results suggest that the proposed methodology can also be applied to other ocean color and land-observing sensors. The QAA-V was also assessed on VIIRS imagery using a regional relationship between suspended particulate matter (SPM) and particulate backscattering coefficient at 532 nm (bbtnw532; R2 = 0.89, N = 33). As a case study, the QAA-V processing chain and VIIRS imagery were used to generate a sequence of SPM maps of Galveston Bay, Texas following the unprecedented flooding of Houston and the surrounding regions due to Hurricane Harvey in August 2017. The record discharge of floodwaters through two major rivers into the bay resulted in very high SPM concentrations over several days throughout the bay, with wind forcing additionally influencing its distribution into the coastal waters of the northern Gulf of Mexico. The promising results of this study suggest that the application of QAA-V to various ocean color and land-observing satellite imagery could be used to assess the bio-optical state and water quality dynamics in a variety of coastal systems around the world.

Seasonal Dynamics of Biogeochemical Processes in the Water Column of the Northeastern Black Sea

Integrated studies on the hydrochemistry and water column rates of microbial processes in the eastern sector of the Black Sea along a standard 100-miles transect off Gelendzhik from the coast to the central part of the sea at water depths of 100–2170 m show that a series of warm winters and the absence of intense convective winter mixing resulted in a relatively low content of suspended particulate matter (SPM), particulate organic carbon (POC), and nutrients in the water column in March 2009. The relatively high SPM concentrations and the presence of isotopically light POC at the offshore station are indicative of the supply of terrigenous material from land and low contributions of phytoplanktonic organic matter to the composition of SPM. This may explain the low rates of biogeochemical processes in the water column near the coast. The surface layer at deep-water stations is dominated by isotopically heavy phytoplanktonic organic matter. This suggests that the supply of terrigenous material from land was insufficient in offshore deep-water areas. Therefore, warm winters and insufficient nutrient supply do not prevent photosynthesis in the photic layer of the deep-water zone, which generates organic substrates for heterotrophic aquatic communities. The results of isotopic analysis of POC, measurements of the rates biogeochemical processes, and the hydrochemical characteristics of the water column can be used to determine the nature and seasonal variability of the POC composition.

Do the plants in functional green walls contribute to their ability to filter particulate matter?

Indoor air quality has become a growing concern as people are spending more time indoors, combined with the construction of highly sealed buildings that promote thermal efficiency. Particulate matter (PM) is a common indoor air pollutant, with exposure to high concentrations associated with several detrimental health outcomes. Active botanical biofilters or functional green walls are becoming increasingly efficient and have the potential to mitigate high suspended PM concentrations. These systems, however, require further development before they become competitive with industry standard in-room air filters. Whilst the plant growth substrate in active biofilters can act as a filter medium, it was previously not known whether the plant component of these systems played a function in PM filtration. This study thus examines the influence of the botanical component on active green wall PM single pass removal efficiency (SPRE), with a focus on evaluating the air filtration features of different plant species in green wall modules. All tested botanical biofilters outperformed biofilters that consisted only of substrate. Green walls using different plant species had different single pass removal efficiencies, with fern species recording the highest removal efficiencies across all measured particle sizes (Nephrolepis exaltata bostoniensis SPRE for PM0.3-0.5 and PM5-10 = 45.78% and 92.46% respectively). Higher removal efficiencies were associated with increased pressure drop across the biofilter. An assessment of plant morphological data suggested that the root structure of the plants strongly influenced removal efficiency. These findings demonstrate the potential to enhance active botanical biofiltration technology with appropriate plant species selection.

Shellfish Aquaculture from Space: Potential of Sentinel2 to Monitor Tide-Driven Changes in Turbidity, Chlorophyll Concentration and Oyster Physiological Response at the Scale of an Oyster Farm

The algorithms of Novoa et al. (2017) and Gons et al. (2005) were recalibrated and applied to Sentinel2 data to respectively retrieve suspended particulate matter (SPM) and chlorophyll a (chl a) concentration in the environmentally and economically important intertidal zones. Sentinel2-derived chl a and SPM concentration distributions were analyzed at the scale of an oyster farm over a variety of tidal conditions. Sentinel2 imagery was then coupled with ecophysiological modeling to analyze the influence of tide-driven chl a and SPM dynamics on oyster clearance and chl consumption rates. Within the studied oyster farming site (Bourgneuf Bay along the French Atlantic coast), chl consumption rate mirrored the changes in chl a concentration during neap tides, whereas oyster clearance and chl consumption rates were both negatively impacted by high SPM concentration during spring tides.

Distribution and geochemical composition of suspended particulate material in the shallow embayment of northern Thermaikos Gulf, Greece

The distribution and the chemical composition of Suspended Particulate Matter (SPM), in the northern Thermaikos Gulf, were studied during an annual experiment, carried out from June 2004 to June 2005. Water samples were collected at three depths (1m below surface, 10m depth, and 2m above bottom) and filtered to obtain SPM, particulate organic carbon (POC), total particulate nitrogen (PNtot) and particulate phosphorus (PP) concentrations. SPM and POC concentrations exhibited strong spatial and temporal variations, related to the different environmental characteristics in the study area such as river network, biological productivity, anthropogenic interferences, wind regime, and resuspension of the bottom sediments. The highest SPM concentrations were recorded at the surface (mean = 1.45 ± 0.75mg/l, maximum value = 11.60mg/l) and close to the bottom (mean = 1.49 ± 0.67mg/l, maximum value = 11.72mg/l), creating surface and bottom nepheloid layers (SNL and BNL), respectively. The maximum values were recorded close to the river mouths; the rivers are identified as the major sources of SPM. The Axios and Aliakmon rivers supplied the gulf with particulate matter, during the entire sampling period.Chemical analysis has revealed the significant correlation among the elements Al, Si, Fe, Ti, K, V, Mg and Ba suggesting the presence of terrigenous aluminosilicate minerals. Silica and Ca have terrigenous origin, but also come from autochthonous biogenic fraction. Chromium, Ni and Co, are of natural origin and derived from mafic and ultramafic rocks of the Axios and Aliakmon watersheds. Copper and Zn are correlated with each other and their distributions follow that of POC; these two metals are derived from partially treated domestic and industrial effluents. The vertical distribution of organic matter implies increased primary production within the upper layer of the water column. Phosphorus is present mainly in an organic form.During the sampling period, the water column was well-oxygenated. Early diagenesis only affected the concentrations of Mn and to a lesser extent Fe in the recently deposited seabed sediment.

Atmospheric Corrections and Multi-Conditional Algorithm for Multi-Sensor Remote Sensing of Suspended Particulate Matter in Low-to-High Turbidity Levels Coastal Waters

The accurate measurement of suspended particulate matter (SPM) concentrations in coastal waters is of crucial importance for ecosystem studies, sediment transport monitoring, and assessment of anthropogenic impacts in the coastal ocean. Ocean color remote sensing is an efficient tool to monitor SPM spatio-temporal variability in coastal waters. However, near-shore satellite images are complex to correct for atmospheric effects due to the proximity of land and to the high level of reflectance caused by high SPM concentrations in the visible and near-infrared spectral regions. The water reflectance signal (ρw) tends to saturate at short visible wavelengths when the SPM concentration increases. Using a comprehensive dataset of high-resolution satellite imagery and in situ SPM and water reflectance data, this study presents (i) an assessment of existing atmospheric correction (AC) algorithms developed for turbid coastal waters; and (ii) a switching method that automatically selects the most sensitive SPM vs. ρw relationship, to avoid saturation effects when computing the SPM concentration. The approach is applied to satellite data acquired by three medium-high spatial resolution sensors (Landsat-8/Operational Land Imager, National Polar-Orbiting Partnership/Visible Infrared Imaging Radiometer Suite and Aqua/Moderate Resolution Imaging Spectrometer) to map the SPM concentration in some of the most turbid areas of the European coastal ocean, namely the Gironde and Loire estuaries as well as Bourgneuf Bay on the French Atlantic coast. For all three sensors, AC methods based on the use of short-wave infrared (SWIR) spectral bands were tested, and the consistency of the retrieved water reflectance was examined along transects from low- to high-turbidity waters. For OLI data, we also compared a SWIR-based AC (ACOLITE) with a method based on multi-temporal analyses of atmospheric constituents (MACCS). For the selected scenes, the ACOLITE-MACCS difference was lower than 7%. Despite some inaccuracies in ρw retrieval, we demonstrate that the SPM concentration can be reliably estimated using OLI, MODIS and VIIRS, regardless of their differences in spatial and spectral resolutions. Match-ups between the OLI-derived SPM concentration and autonomous field measurements from the Loire and Gironde estuaries’ monitoring networks provided satisfactory results. The multi-sensor approach together with the multi-conditional algorithm presented here can be applied to the latest generation of ocean color sensors (namely Sentinel2/MSI and Sentinel3/OLCI) to study SPM dynamics in the coastal ocean at higher spatial and temporal resolutions.