Turbidity Zone Research Articles

Characterization and source apportionment of pharmaceuticals in surface water of the Yangtze Estuary and adjacent sea.

Pharmaceuticals, which are closely linked to human activities, have attracted global attention. This study investigated the occurrence characteristics of 20 pharmaceuticals in surface water of the Yangtze Estuary and adjacent sea. A total of 14 targeted pharmaceuticals were detected in both spring and summer sampling campaigns. The mean concentrations of sulfonamides and non-sulfonamides were 36.60 ± 19.43ng·L-1 and 50.02 ± 41.07ng·L-1, respectively. As for non-antibiotics, their concentrations were in the range of 24.34 ± 916.8ng·L-1 with caffeine accounting for 6.17 ~ 86.70% (average percentage of 42.22%). Meanwhile, spatial distribution patterns showed similarities between antibiotics and non-antibiotics, with high levels occurring near the upper estuary, aquaculture areas, wastewater treatment plants, and the maximum turbidity zone. This phenomenon could be related to the sources of pharmaceuticals and the physicochemical properties of water bodies. Obviously, the first three areas are highly impacted by human activities or serve as important sources of terrestrial contaminants entering the East China Sea. The last area retains high amounts of suspended particles which may exert strong trapping effects on hydrophobic chemicals. Principal component analysis revealed the presence of three potential sources for pharmaceuticals in the Yangtze Estuary, with a relatively high percentage originating from incompletely treated municipal sewage. As for the temporal trend, pharmaceutical contamination was found to be higher in spring compared to summer, potentially due to variations in pharmaceutical consumption patterns, local rainfalls, and water temperatures. These findings provide fundamental data support for implementing appropriate local management strategies for pharmaceutical usages.

Contribution of high turbidity to tidal dynamics in a curved channel in Zhoushan Islands, China

The curved tidal channel, Luotou Deep-water Navigational Channel, is the main channel of the Ningbo Zhoushan Port, which is ranked first in the world. Tidal dynamics in the channel are spatially and temporally asymmetric. In this study, the three-dimensional tidal dynamics in the channel were analyzed using field data and simulated using FVCOM. The results show that the tides in the channel flood/ebb along the northern/southern bank near the bottom/surface layer and these asymmetries are due to the imbalanced Coriolis force, centrifugal force, sea-level gradient, and density gradient. Residual current velocity peaks (0.7 m/s) in the middle of the channel as the same distribution as sediment flux. There are two high turbidity zones (>4 kg/m3) which are northern at flood than at an ebb in the channel. The drag reduction effect of fluid mud enhances the lateral circulation, which is strong near the Chuanshan Peninsula and frictional dissipation plays an important role in it. The presence of suspended sediment changes the contribution of acceleration terms through impacting density and bottom friction, and the centrifugal force term has the largest increases. This study provides the foundation for the morphology evolution and harbor management of macro-tidal turbid coastal zones. Highlights A baroclinic model was built to study the tidal dynamics in macro-tidal turbid Zhoushan Islands. Asymmetric tides and lateral circulation occur in the Luotou Deep-water Navigational Channel (DNC). Mechanism of lateral circulation depends on tidal phases and locations in the DNC. Sediment impacts water density and drag coefficient, and then changes currents and sediment fluxes in the DNC.

Spatiotemporal variability of suspended sediment concentration in the coastal waters of Yellow River Delta: Driving mechanism and geomorphic implications

Satellite images have revealed a significant decline in the suspended sediment concentration (SSC) near surface in the coastal waters of Yellow River Delta (YRD) in recent years. However, there is limited information on the spatial disparity in SSC distributions and its dynamic mechanism. In this study, we utilize a well-calibrated SSC retrieval algorithm and a depth-averaged numerical modeling approach to investigate the delta and sub-delta scale variation trends and driving mechanisms of SSC in the coastal waters of YRD over the past few decades. The results of this study demonstrate the existence of high turbidity zones in coastal waters of the northern abandoned delta and the active lobe of the YRD. These zones have experienced general decreasing trends of SSC at the interannual timescale. Additionally, the distribution of SSC is significantly higher in dry seasons compared to that in wet seasons. The magnitude and varying trends of SSC are strongly influenced by the total bottom shear stress (BSS) caused by combined effects of waves and currents, although the wave-induced BSS is found to be less significant that the current-induced one, but vary more significantly due to wind forcing in the Bohai Sea. Furthermore, the grain size of seabed sediments plays a dominant role in the sediment mobilization and resuspension processes over interannual and longer timescales. The distribution of high BSS and sediment mobility zones align with the active areas for morphological changes with the YRD exhibiting net accretion in the active river mouth and erosion in the abandoned delta lobes. These findings highlight the multiscale variations and the close relationship between SSC and BSS, providing valuable insights into sediment dynamics with geomorphic evolution in highly human-interfered deltaic systems.

Juvenile downstream migration patterns of an anadromous fish, allis shad (Alosa alosa), before and after the population collapse in the Gironde system, France.

Diadromous fish have exhibited a dramatic decline since the end of the 20th century. The allis shad (Alosa alosa) population in the Gironde-Garonne-Dordogne (GGD) system, once considered as a reference in Europe, remains low despite a fishing ban in 2008. One hypothesis to explain this decline is that the downstream migration and growth dynamics of young stages have changed due to environmental modifications in the rivers and estuary. We retrospectively analysed juvenile growth and migration patterns using otoliths from adults caught in the GGD system 30 years apart during their spawning migration, in 1987 and 2016. We coupled otolith daily growth increments and laser ablation inductively-coupled plasma mass spectrometry measurements of Sr:Ca, Ba:Ca, and Mn:Ca ratios along the longest growth axis from hatching to an age of 100 days (i.e., during the juvenile stage). A back-calculation allowed us to estimate the size of juveniles at the entrance into the brackish estuary. Based on the geochemistry data, we distinguished four different zones that juveniles encountered during their downstream migration: freshwater, fluvial estuary, brackish estuary, and lower estuary. We identified three migration patterns during the first 100 days of their life: (a) Individuals that reached the lower estuary zone, (b) individuals that reached the brackish estuary zone, and (c) individuals that reached the fluvial estuary zone. On average, juveniles from the 1987 subsample stayed slightly longer in freshwaterthan juveniles from the 2016 subsample. In addition, juveniles from the 2016 subsample entered the brackish estuary at a smaller size. This result suggests that juveniles from the 2016 subsample might have encountered more difficult conditions during their downstream migration, which we attribute to a longer exposure to the turbid maximum zone. This assumption is supported by the microchemical analyses of the otoliths, which suggests based on wider Mn:Ca peaks that juveniles in 2010s experienced a longer period of physiological stress during their downstream migration than juveniles in 1980s. Finally, juveniles from the 2016 subsample took longer than 100 days to exit the lower estuary than we would have expected from previous studies. Adding a new marker (i.e., Ba:Ca) helped us refine the interpretation of the downstream migration for each individual.

Assessment and Characterization of Woji Creek Riverbed in Port Harcourt, Rivers State, Nigeria, Utilizing Side Scan Sonar Technology

Woji Creek plays a crucial role in vessel navigation, supports diverse flora and fauna habitats, and sustains local livelihoods. However, human activities and natural events have led to changes in its riverbed over time. Given its significance for coastal stability and geomorphology, there is a pressing need to classify, evaluate, and ensure its environmental sustainability. The primary objective of this study is to employ side scan sonar technology to classify and assess the riverbed of Woji Creek in Port Harcourt, Nigeria. The study aims to classify the riverbed, analyze water depth variations, evaluate navigational suitability, and determine turbidity levels within the creek. To achieve these objectives, the methodology involved acquiring Side-Scan Sonar (SSS) and Sub-bottom profile data. These datasets underwent backscatter processing to create geocoded backscatter images. Feature points were extracted and matched from these images to derive riverbed classification, depth categories, water volume distribution, and river turbidity analysis. The riverbed classification revealed the presence of three primary sediment types: Clayey Silty Sand, Silty Clay, and Silty Sand, each with distinct implications for navigation. Shallow, Moderate, Deep, and Very Deep areas were identified within Woji Creek, each influencing navigational conditions. Additionally, the water volume distribution analysis provided essential insights into depth limitations and route planning.
 Moreover, the assessment of river turbidity identified low, moderate, and high turbidity zones, reflecting water clarity and suspended particle levels. These findings serve as invaluable decision support tools for navigation planning and management in Woji Creek, offering comprehensive insights into the riverbed, depth suitability, volume distribution, and water quality. Leveraging this data can enhance strategic decision-making processes and contribute to the sustainable management of this vital waterway.

Spatiotemporal Evolutions of the Suspended Particulate Matter in the Yellow River Estuary, Bohai Sea and Characterized by Gaofen Imagery

Suspended particulate matter is a crucial component in estuaries and coastal oceans, and a key parameter for evaluating their water quality. The Bohai Sea, a huge marginal sea covering an expanse of 77,000 km² and constantly fed by numerous sediment-laden rivers, has maintained a high level of total suspended particulate matter (TSM). Despite the widespread development and application of TSM retrieval algorithms using commonly available satellite data like Landsat, Sentinel, and MODIS, developing TSM retrieval algorithms for China’s Gaofen (GF) series (GF-6 and GF-1) in the Bohai Sea is still a great challenge, mainly due to the limited applicability of empirical algorithms. In this study, 259 in situ measured-TSM samples were collected for algorithm development. The remote sensing reflectance (Rrs) curve demonstrates prominent peaks between 550 and 580 nm. Through conversion to remote sensing reflectance, it was found that single-band data had a weak correlation with TSM, reaching a maximum correlation of 0.44. However, by combining bands of band ratio calculations, the correlation was enhanced. Particularly, the blue and green band equivalent Rrs ratio had a correlation coefficient of 0.81 with TSM, and the proposed TSM inversion exponential algorithm developed based on this factor obtained an R-squared (R²) value of 0.76 and a mean relative error (MRE) of 32.24%. Analysis results indicated that: (1) there are spatial variations in the TSM within the Bohai Sea, Laizhou Bay, and the Yellow River estuary, with higher levels near the coast and lower levels in open waters. The Yellow River estuary experiences seasonal fluctuations higher TSM during spring and winter, and lower variations during summer and autumn, and (2) the dynamics of TSM are affected by Yellow River runoff, with increased runoff leads to higher TSM levels and expanded turbid zones. This study proposes a new algorithm to quantify TSM evolutions and distributions in the Bohai Sea and adjacent regions using China’s Gaofen imageries.

Characteristics of suspended sediment concentration and distribution of maximum coastal turbidity of the Mekong river

This paper presents the results of applying a 3D mathematical model to study the in the Mekong riverside area’s maximum turbidity zone (MTZ). This study has established and calibrated a three-dimensional system model with a combination of hydraulics-waves and suspended sediment transport with measured data in the study area. Based on the calculated scenarios for the flood and the dry seasons, the results show the occurrence of MTZs in the riparian zone of the Mekong river with typical suspended sediment concentrations ranging from 0.04–1.0 kg/m3 dry season and 0.2–1.1 kg/m3 flood season. The location and size of the MTZs change seasonally with the interaction between freshwater and tidal oscillations. They appear more in the dry season. At high tide, seawater with high salinity intrudes into estuaries with a range of up to 50 km, causing disturbance and flocculation. While in the flood season, the distribution of the largest turbidity has moved the floodplain with a range of about 20 km.

Spatial assessment of triazole organic compounds in surface water from the coastal estuaries to the East China sea

Triazole is widely used in the synthesis of pharmaceuticals, pesticides, and fungicides. However, triazole organic compounds are often a source of toxicity in the water environment due to the presence of chlorobenzene. This study reported on the occurrence and distribution of 15 TrOCs in the surface waters of estuaries and the East China sea, and identified the influences of TrOCs originating from the estuarine environment on the ocean. The results showed that the total concentrations of ∑TrOCs in the surface water of estuaries along the coasts of Jiangsu (JS), Zhejiang (ZJ), and Shanghai (SH), China ranged from 0.020 to 104 ng L−1 (7.49 ± 18.2 ng L−1), whereas they ranged from 0.235 to 1.25 ng L−1 (mean 0.711 ± 0.235 ng L−1) in the East China sea. Difenoconazole and tebuconazole were the dominant TrOCs in the estuaries, whereas fenbuconazole and hexaconazole dominated in the ocean. TrOCs in surface water of estuaries showed a continuous spatial distribution and presented regional characteristics mainly related to agricultural activities. In contrast, TrOCs in the East China Sea showed a low spatial variation and dispersion, which may be related to complex disturbance by currents and dilution. The low levels of estuarine TrOCs measured in SH estuaries (<0.5 ng L−1) indicates that the Yangtze River may only pose a low-level TrOC contamination risk to the East China Sea. Moreover, estuary transport in the estuaries of ZJ may have influenced the occurrence of TrOCs in the offshore East China Sea area, although they may have also undergone a filter process in the estuary turbid zone; whereas it had little influence on the open sea. This study can act as a critical reference for the presence of TrOCs in surface water both estuaries and the ocean.

Transport inventories and exchanges of organic matter throughout the St. Lawrence Estuary continuum (Canada)

Hypoxia (O2 &amp;lt; 2 mg/L) driven by eutrophication in estuaries and shelves is a worldwide expanding problem. The role of organic matter (OM) inputs is emerging as an important contributor to this issue, beside the well-known implication of inorganic nutrients. The St. Lawrence Estuary, one of the largest and deepest estuarine system in the world is facing strong persistent and increasing hypoxia. In this context, transport and exchange of particulate and dissolved organic matter (POM and DOM, respectively) were investigated as a first step to understand their implication in hypoxia. Tributaries and Gulf contributions were compared to St. Lawrence Estuary inventories for the spring freshet (May), the summer low-flow (August), and the fall-mixing (October). Furthermore, changes in OM ratios were examined along the estuarine gradient from the upper St. Lawrence Estuary (USLE), downstream of the maximum turbidity zone, to the lower estuary (LSLE). For the USLE, net transport was always positive and net export/loading ratios suggested that 64–90% of POM and 30–63% of DOM were either retained or transformed during its course from tributaries to LSLE. Net transport from the USLE toward the LSLE was 3–13 fold more important in May than in August or October. For the LSLE, net transport to the Gulf was generally negative meaning that OM production was the dominating proces. The extremely high net export/loading ratios in August indicate that POM production was 28.8 to 41.4 times the combined inputs of tributaries and Gulf. Net export/loading ratios remained superior to one during May and October (1.7–9.4) for the LSLE. Changes along the upstream–downstream continuum were seen for POM, with a steady increase relative to total suspended matter from 7.3% to 50.2%, but they were not observed for DOM, for which no obvious trends were detected. Our results highlight the importance of explicitly considering OM in eutrophication monitoring programs of the St. Lawrence Estuary, as the mineralisation of a portion of the large OM pool size could influence our understanding of hypoxia and acidification of the deep waters of LSLE.

Numerical modeling of microplastic interaction with fine sediment under estuarine conditions

Microplastic (MP) pollution is an important challenge for human life which has consequently affected the natural system of other organisms. Mismanagement and also careless handling of plastics in daily life has led to an accelerating contamination of air, water and soil compartments with MP. Under estuarine conditions, interactions with suspended particulate matter (SPM) like fine sediment in the water column play an important role on the fate of MP. Further studies to better understand the corresponding transport and accumulation mechanisms are required. This paper aims at providing a new modeling approach improving the MP settling velocity formulation based on higher suspended fine sediment concentrations, as i.e. existent in estuarine turbidity zones (ETZ). The capability of the suggested approach is examined through the modeling of released MP transport in water and their interactions with fine sediment (cohesive sediment/fluid mud). The model results suggest higher concentrations of MP in ETZ, both in the water column as well as the bed sediment, which is also supported by measurements. The key process in the modeling approach is the integration of small MP particles into estuarine fine sediment aggregates. This is realized by means of a threshold sediment concentration, above which the effective MP settling velocity increasingly approaches that of the sediment aggregates. The model results are in good agreement with measured MP mass concentrations. Moreover, the model results also show that lighter small MP particles can easier escape the ETZ towards the open sea.

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.

Typhoon triggers estuarine heavy metal risk by regulating the multifractal grainsize of resuspended sediment

The turbulent boundary layer generated by wind in the estuarine surface water serves as a main factor affecting the distribution of suspended particulate matter (SPM) and suspended sediment concentration (SSC). In this study, representative typhoon-induced variation of surface fine SPM (<63 μm) was simulated in the Yangtze River Estuary (YRE) under two time scenarios. Each scenario contained four grainsize SPM fractions named Fraction 1 (<8 μm), Fraction 2 (8–16 μm), Fraction 3 (16–32 μm), Fraction 4 (32–63 μm). The typhoon-induced resuspended multifractal SSC quantification (TRMSQ) based on the relationship between SPM grainsize and heavy metal adsorption capacity was proposed to assess the variation in the resuspended threat of heavy metal to 6 key estuarine protected objects (three reservoirs & three national reserves) between Scenarios 1 and 2. The results presented that Fraction 3 exhibited the maximum increment in SSC resuspension mass and longest regression time from typhoon. Combined with TRMSQ, chromium (Cr) was calculated to be the riskiest typhoon-induced factor. The integrated resuspended risk of heavy metals for each protected object tends to increase from the northwest of Chongming Island (1.2) towards the maximum turbidity zone (>9) downstream, with an estuary-wide mean of 3.3.

Tidal Sediment Supply Maintains Marsh Accretion on the Yangtze Delta despite Rising Sea Levels and Falling Fluvial Sediment Input

Tidal marshes are among the world’s most valuable ecosystems; however, they are increasingly threatened by rising sea levels and a decline in fluvial sediment supply. The survival of a tidal marsh under these twin threats depends upon the net input of tidal sediments, because this will determine the deposition rate. The rate of relative sea level rise currently affecting the Yangtze Delta is rapid (~4 mm/a), and the sediment discharge from the Yangtze River has decreased by &gt;70% over recent decades. In order to improve our understanding of the response of the marshes in the turbid zone of the Yangtze Estuary to these changing environmental conditions, we measured sediment transport in and out of a tidal basin and calculated the deposition rate over eight tidal cycles covering different tidal ranges during the summer and winter seasons. The suspended sediment concentration (SSC) during the flood phase of the tidal cycle (average = 0.395 kg/m3) was markedly higher than that during the ebb (average = 0.164 kg/m3), although water transport during the flood tide was almost equivalent to that during the ebb. As a result, ~40% of the sediment inflow during the flood phase was retained within the marsh. This reason is mainly attributable to the dense marsh vegetation, which attenuates waves and currents and to which the sediments adhere. The annual deposition rate in the marsh was approximately 6.7 mm/a. These findings indicate that under the combined influence of sea level rise and river sediment supply reduction, the sediment transport through the turbidity maximum zone of the Yangtze River estuary could maintain the relative stability of the marsh area to a certain extent.

End-member modeling and sediment trend analysis as tools for sedimentary processes inference in a subtropical estuary

Mathematical models based on grain size data enable identifying sediment transport sources and processes in coastal regions, helping to understand the relationship between hydrodynamic and sedimentary processes. This study applied End-Member Analysis and Grain Size Trend Analysis to a grain size database from the Paranaguá Estuarine Complex (PEC), a subtropical estuary in southern Brazil. The end-member analysis allowed identifying three grain size populations, whose spatial distribution is influenced by the dynamics between river discharge and tidal currents acting in the Paranaguá Estuarine Complex. The end-member 1 — formed by finer sediments — is mainly distributed over Antonina Bay and extends into the maximum turbidity zone. The Grain Sized Trend Analysis revealed that these sediments — derived from the weathering of rocks from the Serra do Mar mountain range system — are transported in the west-east direction by river discharge, mainly from the Cachoeira and Nhundiaquara rivers. Furthermore, our results indicate that sediments from end-members 2 and 3 — which are coarser — are distributed in the Paranaguá and Laranjeiras Bays. The transport of these sediments happens towards the center of the estuary due to wave- and tidal-generated currents.

Rapid and simple determination of iron-porphyrin-like complexes (Fe-Py) in estuarine and marine waters

This work presents a new method for determining iron-porphyrin-like complexes (Fe-Py) based on Continuous Flow Analysis (CFA) with chemiluminescence detection and its application to natural waters in an estuarine environment. The involved reaction is founded on luminol oxidation by hydrogen peroxide in the presence of Fe-Py complexes at pH 13. The detection limit is 7.2 pM hemin equivalent, the linear range extends to 150 nM and precision of the method is 6.4% at 0.25 nM (n = 8). This new method's detection limit is 15 times lower than the previous analytical procedure of Vong et al. (2007), based on Flow Injection Analysis (FIA) and using different chemical conditions. Moreover, the presented method is fast (90s/analysis), involves a low consumption of reagents, a small sample volume, and simplified sample handling. The method was applied to natural samples collected along the temperate macrotidal Aulne estuary (Bay of Brest, France). Here, we report for the first time on the spatial distribution of the Fe-Py complex concentration (dissolved, reactive particulate) over the entire salinity gradient of a macrotidal temperate estuary. The Fe-Py concentrations in the riverine and marine end-members were 0.873 ± 0.007 nM (S = 0.92) and 0.010 ± 0.004 nM (S = 34.86), respectively. Between these two salinities, non-conservative behaviour was observed, with an increase in Fe-Py concentrations to 1.142 ± 0.031 nM at S = 5.2 corresponding to the Maximum Turbidity Zone (MTZ), followed by a strong removal of Fe-Py in the salinity range 5–20. Then, the Fe-Py concentrations decreased linearly during mixing processes, reaching picomolar levels towards the coastal waters. The estimated entering flux from the river equaled 240 ± 2 g.d−1 whereas the net flux to coastal sea waters was 95 ± 10 g.d−1 leading to a loss of ~60%. The estuarine system globally acts as a sink for Fe-Py complexes, probably due to the aggregation of Fe-Py complexes on particles, to flocculation and/or sedimentation.

Substantial submarine groundwater discharge in the estuaries of the east coast of India and its impact on marine strontium budget

The concentration and isotopic compositions of dissolved Sr (87Sr/86Sr) were measured in four major estuaries of the east coast of India, including those of the Ganga (Hooghly), Mahanadi, Godavari, and the Krishna during their peak discharge period, July-September 2013, along with particulate matters in some of them. Dissolved Sr displays strong conservative behaviour in all four estuaries within the analytical uncertainties, emphasizing simple mixing between river water and seawater. Sr isotopic composition, however, behaved non-conservatively in all four estuaries. Dissolved 87Sr/86Sr of many samples in these estuaries deviate significantly from the theoretical mixing line defined by seawater and river water, indicating some additional sources of radiogenic Sr in all four estuaries. Such deviation in the Ganga estuary could result from a minor dissolution of suspended material with very radiogenic Sr in the turbid zone of the estuary. However, several lines of evidence support submarine groundwater discharge as an important source of Sr in these estuaries. We used an inverse modelling approach to characterize the significance of submarine groundwater discharge and quantified its fluxes from the four estuaries based on 87Sr/86Sr in this study, highlighting its potential to estimate groundwater contribution to the water budget in estuaries. The fluxes of submarine groundwater discharge from the estuaries of the east coast of India is estimated to be ∼ 11000 ± 900 m3s−1, dominated by the Ganga-Brahmaputra system, and delivers ∼ 1.1 ± 0.06 × 109 moles of Sr annually with quite radiogenic 87Sr/86Sr, 0.7228, comparable to their riverine fluxes. These estuaries contribute 0.3 – 0.7% to the global submarine groundwater discharge derived Sr. This study reveals a large supply of radiogenic Sr from submarine groundwater discharge which further increases the requirement of less radiogenic Sr to balance the continental radiogenic Sr in the global marine Sr budget.

Coastal Bathymetry Estimation from Sentinel-2 Satellite Imagery: Comparing Deep Learning and Physics-Based Approaches

The ability to monitor the evolution of the coastal zone over time is an important factor in coastal knowledge, development, planning, risk mitigation, and overall coastal zone management. While traditional bathymetry surveys using echo-sounding techniques are expensive and time consuming, remote sensing tools have recently emerged as reliable and inexpensive data sources that can be used to estimate bathymetry using depth inversion models. Deep learning is a growing field of artificial intelligence that allows for the automatic construction of models from data and has been successfully used for various Earth observation and model inversion applications. In this work, we make use of publicly available Sentinel-2 satellite imagery and multiple bathymetry surveys to train a deep learning-based bathymetry estimation model. We explore for the first time two complementary approaches, based on color information but also wave kinematics, as inputs to the deep learning model. This offers the possibility to derive bathymetry not only in clear waters as previously done with deep learning models but also at common turbid coastal zones. We show competitive results with a state-of-the-art physical inversion method for satellite-derived bathymetry, Satellite to Shores (S2Shores), demonstrating a promising direction for worldwide applicability of deep learning models to inverse bathymetry from satellite imagery and a novel use of deep learning models in Earth observation.

O2O: An Underwater VLC Approach in Baltic and North Sea

Recently, underwater visible light communication (UVLC) has become a potential wireless carrier candidate in the acrimonious mingled ocean straits. The combined strait of the North and Baltic ocean is a harsh and strongly turbid aqueous zone that contributes signal fading at a large scale. Due to this, we are proposing a UVLC system within the Baltic–North ocean mingled water under strong turbulence channel conditions. In this study, the Gamma–Gamma distribution is used to model UVLC link under an OOK modulation scheme. Subsequently, the reason for the unavailability of the latest North–Baltic oceanographic data within this bayou, we investigate the BER and outage probability performance of the proposed system within the mingled strait for the whole year during 1996s. Throughout, this work, the performance is obtained individually in both of the oceans and then compared with the heterogeneous state. It is noteworthy that the analytical work has been considered of the following distinct physio-chemical properties and the data provided for each ocean. Additionally, the simulation results are verified the analytical work of the proposed system model.

Distribution of Coomassie Blue Stainable Particles in the Pearl River Estuary, China, Insight Into the Nitrogen Cycling in Estuarine System

Distributions of Coomassie Blue stainable particles (CSP), the sources and transports, as well as their implications for nitrogen biogeochemical cycles in the Pearl River estuary (PRE) were investigated during two cruises in August 2016 and January 2017. CSPcolor concentrations (CSP concentration determined spectrophotometrically) were 73.7–685.3 μg BSA eq L–1 [μg Bovine serum albumin (BSA) equivalent liter–1] in August 2016 and 100.6–396.4 μg BSA eq L–1 in January 2017, respectively. CSP concentrations were high in low-salinity waters (&amp;lt;5), and declined from the river to the middle estuary by 80% in the wet season and 55.6% in the dry season, respectively, then increased again in the lower estuary due to high primary production. CSP concentrations were mainly associated with chlorophyll a (Chl a) concentration except for the turbid mixing zone, suggesting that autochthonous phytoplankton production served as the primary source of CSP in the PRE. The concentrations of nitrogen (N) as CSP in the PRE were comparable to the nitrogen content of particulate hydrolysable amino acids (PHAA). Pictures of CSP taken by microscopy and the correlation between composition of PHAA and the ratio of Chl a/CSPcolor showed that CSP were relatively degraded due to delivery of old terrestrial protein to river section and extensive microbial degradation during mixing at the upper and middle parts of the estuary, whereas CSP in lower estuary appeared to be more labile due to higher fresh algal production. The contribution of CSP nitrogen (CSP-N) to the particulate nitrogen (PN) pool was 34.98% in summer and 30.8% in winter. The conservative estimate of CSP-N input flux in the Pearl River Delta was about 6 × 106 mol N d–1. These results suggested that CSP was a significant pool of organic nitrogen in the PRE. The study of CSP composition in terms of nitrogen provides new insight into the roles of CSP on nitrogen biogeochemical processes in the turbid and productive estuarine system.

Underwater Light Characteristics of Turbid Coral Reefs of the Inner Central Great Barrier Reef

Hyper-spectral and multi-spectral light sensors were used to examine the effects of elevated suspended sediment concentration (SSC) on the quantity and quality (spectral changes) of underwater downwelling irradiance in the turbid-zone coral reef communities of the inner, central Great Barrier Reef (GBR). Under elevated SSCs the shorter blue wavelengths were preferentially attenuated which together with attenuation of longer red wavelengths by pure water shifted the peak in the underwater irradiance spectrum ~100 nm to the less photosynthetically useful green-yellow waveband (peaking at ~575 nm). The spectral changes were attributed to mineral and detrital content of the terrestrially-derived coastal sediments as opposed to chromophoric (coloured) dissolved organic matter (CDOM). A simple blue to green (B/G, λ455:555 nm) ratio was shown to be useful in detecting sediment (turbidity) related decreases in underwater light as opposed to those associated with clouds which acted as neutral density filters. From a series of vertical profiles through turbid water, a simple, multiple component empirical optical model was developed that could accurately predict the light reduction and associated spectral changes as a function of SSC and water depth for a turbid-zone coral reef community of the inner GBR. The relationship was used to assess the response of a light sensitive coral,Pocillopora verrucosain a 28-d exposure laboratory-based exposure study to a daily light integral of 1 or 6 mol quanta m2. PAR with either a broad spectrum or a green-yellow shifted spectrum. Light reduction resulted in a loss of the algal symbionts (zooxanthellae) of the corals (bleaching) and significant reduction in growth and lipid content. The 6 mol quanta m2d−1PAR treatment with a green-yellow spectrum also resulted in a reduction in the algal density, Chl a content per cm2, lipids and growth compared to the same PAR daily light integral under a broad spectrum. Turbid zone coral reef communities are naturally light limited and given the frequency of sediment resuspension events that occur, spectral shifts are a common and previously unrecognised circumstance. Dedicated underwater light monitoring programs and further assessment of the spectral shifts by suspended sediments are essential for contextualising and further understanding the risk of enhanced sediment run-off to the inshore turbid water communities.