Coastal Ocean Research Articles

High-resolution mapping of sea surface currents in the Iroise sea from MSG/SEVIRI satellite observations: validation with HF radar and model data

ABSTRACT Sea surface currents are crucial for regulating ocean circulation, global climate, and marine ecosystem. This study uses the robust optical flow technique to map surface tidal and flow currents in the Iroise Sea and adjacent waters (ISAS) by analysing sequential sea surface temperature images from SEVIRI (Spinning Enhanced Visible and Infrared Imager) satellite. Comparisons with high-frequency (HF) radar show good agreement in total surface currents, with a mean bias of 0.15 m/s and a root mean square error (RMSE) of 0.50 m/s. Additionally, SEVIRI-derived M2 tidal currents agree well with both the Oregon State University regional tidal model and radar observations. The detided daily mean currents reveal strong concordance with the radar and Cooperative Marine Environment Monitoring Service daily (CMEMS) model, which exhibits high sensitivity to rapid wind changes. This study highlights the potential of SEVIRI satellite in expanding coastal current monitoring and forecasts and understanding coastal ocean dynamics, particularly in regions with limited in-situ measurements.

Intercomparison of In Situ and Satellite Sea Surface Salinity Products for Global Coastal Ocean Studies

Abstract Observing coastal ocean salinity is crucial for understanding the physical and biological processes impacting ocean circulation, ecosystems, and the hydrological cycle. We perform a thorough comparison between in situ and satellite sea surface salinity (SSS) products with a focus on global coastal ocean. Between 40 and 500 km from the coastline, we intercompare SSS from more than two million World Ocean Database (WOD) salinity profiles, gridded Argo data, and satellite products: NASA Multimission Optimally Interpolated Sea Surface Salinity (OISSS), 40- and 70-km Remote Sensing Systems (REMSS) Soil Moisture Active Passive (SMAP), Jet Propulsion Laboratory (JPL) SMAP, Laboratory of Oceanography and Climate: Experiments and Numerical Approaches (LOCEAN) Soil Moisture Ocean Salinity (SMOS), and European Space Agency (ESA) Climate Change Initiative (CCI) salinity. We find good agreement between the satellite products and in situ data with satellite-in situ mean differences (0.5–1.7 pss, where pss is the Practical Salinity Scale), root-mean-square differences (0.5–2.4 pss), and signal-to-noise ratios (1–3.8) generally decreasing at a faster rate from 40- to 100-km distance to the coast and remaining constant past 100 km. NASA OISSS, ESA CCI, 70-km REMSS SMAP, and LOCEAN SMOS have minimum differences with in situ observations. Empirical orthogonal function (EOF) analysis shows that all the satellite and in situ SSS compare well in capturing mode-1 and mode-2 seasonal variability but have notable differences in the amplitude of the mode-3 semiannual variability in coastal SSS. This study has implications for validation and improvement of satellite SSS and emphasizes the need for designing future satellite missions to better resolve the coastal salinity.

Physics‐Informed Estimation of Tidal and Subtidal Flow Fields From ADCP Repeat Transect Data

AbstractAcoustic Doppler current profilers (ADCPs) are a global standard in observing flow fields in rivers, estuaries and the coastal ocean. To date, it remains a labor intensive challenge to isolate mean flow fields governed by river discharge, tides and atmospheric forcing on the one hand, from small‐scale turbulence, positioning imprecision, Doppler noise and erroneous backscatter, on the other hand. Here, we introduce a generic, new method of combining raw shipborne ADCP transect data with continuity and smoothness constraints to obtain better estimates of turbulence‐averaged three‐dimensional flow velocities in any type of open water body. The physical constraints are enforced with variable relative importance via generalized Tikhonov regularization. We demonstrate that in complex estuarine flow, this procedure allows for more reliable estimates of tidal amplitudes, phases and their gradients than what is possible with a purely data‐based approach, by testing the method's generalization capabilities and robustness to turbulence and measurement noise on a data set retrieved at a tidal channel junction. The increased adherence to mass conservation and robustness to noise of various kinds allows for more reliable and verifiable estimates of Reynolds‐averaged flow components, and subsequently, of terms in the Navier‐Stokes equations.

Estimating Surfzone Currents with Near-Field Optical Remote Sensing

Abstract Currents transport sediment, larvae, pollutants, and people across and along the surfzone, creating a dynamic interface between the coastal ocean and shore. Previous field studies of nearshore flows primarily have relied on relatively low spatial resolution deployments of in situ sensors, but the development of remote sensing techniques using optical imagery and naturally occurring foam as a flow tracer has allowed for high spatial resolution observations (on the order of a few meters) across the surfzone. Here, algorithms optical current meter (OCM) and particle image velocimetry (PIV) are extended from previous surfzone applications and used to estimate both cross-shore and alongshore 2-, 10-, and 60-min mean surface currents in the nearshore using imagery from both oblique and nadir viewing angles. Results are compared with in situ current meters throughout the surfzone for a wide range of incident wave heights, directions, and directional spreads. Differences between remotely sensed flows and in situ current meters are smallest for nadir viewing angles, where georectification is simplified. Comparisons of 10-min mean flow estimates from a nadir viewing angle with in situ estimates of alongshore and cross-shore currents had correlations r2 = 0.94 and 0.51 with root-mean-square differences (RMSDs) = 0.07 and 0.16 m s−1 for PIV and r2 = 0.88 and 0.44 with RMSDs = 0.08 and 0.22 m s−1 for OCM. Differences between remotely sensed and in situ cross-shore current estimates are at least partially owing to the difference between onshore-directed mass flux on the surface and offshore-directed undertow in the mid–water column.

Predicting and analyzing the three-dimensional spatiotemporal evolution process of tidal currents by using a brand new machine learning algorithm

A machine learning algorithm was developed for efficiently predicting the 3D (three-dimensional) spatiotemporal evolution process of tidal currents and analyzing their spatial distribution characteristics. In the algorithm, an extremely simplified multi-layer perceptron architecture, an embedded spatial information learning method, and a splicing-sharing method for tidal currents at different water depths were used to achieve a high-coverage, comprehensive, and systematic 3D tidal current prediction of the study area. The developed algorithm can efficiently predict the future time series of three-dimensional tidal current movement and solves the problem that existing algorithms are unable to analyze the similarity of the three-dimensional spatiotemporal distribution of tidal currents over many years. In this study, 3D tidal current evolutions in the southern waters of Liaoning Province, China, were analyzed. The Finite-Volume Coastal Ocean Model ocean model was used to simulate tidal currents in the study zone, generating a dataset to train the developed machine learning model. The trained model was then used to predict and analyze tidal currents. The prediction results show that the developed machine learning model has high prediction accuracy for tidal currents over a future period of 12 h, with R2 (R-Square) of 0.871, mean absolute error of 0.047 m/s and root mean square error of 0.152 m/s. Additionally, the developed machine learning model could effectively analyze the correlation of spatial distribution characteristics of tidal currents at different water depths, and tidal currents with similar evolution processes at different zones could also be classified.

Uncertainties About the Role of River and Mangrove Dissolved Inorganic Carbon and Alkalinity Loads in Buffering the Great Barrier Reef Lagoon

AbstractTerrestrial dissolved inorganic carbon (DIC) and total alkalinity (TAlk) loads have contrasting effects on the pH and carbonate chemistry of the coastal ocean. While TAlk can buffer against ocean acidification, elevated exports of free CO2 can further exacerbate ocean acidification. In this study, we quantify terrestrial DIC and TAlk loads from rivers and mangrove floodplains across six bioregions and varying flow conditions to assess their impact on the buffering capacity of the Great Barrier Reef (GBR) lagoon in Australia. For a mid‐flow year, median terrestrial DIC and TAlk loads ranged from 0.72 to 0.89 Tg C yr−1 and 0.26 to 1.03 Tg C yr−1, respectively. We find that mangrove‐dominated terrestrial inputs only have a small influence on the whole GBR but contribute 12.5% (range: 1.9%–45.7%) of the DIC and 18.7% (range: 2.8%–68.2%) of the TAlk inner shelf inventory. Depending on the approach used to estimate TAlk loads, mangroves have a potential short‐term buffering effect on near‐shore coastal waters due to higher TAlk loads. However, long‐term mangrove TAlk production via pyrite formation complicates this interpretation, highlighting the need for ongoing monitoring to understand the complex interplay between terrestrial inputs and their effect on the GBR carbonate chemistry.

The Coastal Ocean Environment Summer School In Nigeria and Ghana: The Value of Long-Term, Sustained Capacity Sharing

The Coastal Ocean Environment Summer School In Nigeria and Ghana (COESSING; https://coessing.org) has been run for one week every year since 2015. The school, an endorsed project of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030), has provided a platform for approximately 1,000 scientists from Africa, the United States, and Europe to exchange scientific knowledge, to network, to learn, and to collaborate. Our interdisciplinary, multicultural, and multi-institutional approach offers a model for knowledge exchange across the globe and across different educational levels.

Comparing surface currents near the mouth of three bays along the U.S. East Coast: Chesapeake Bay, Delaware Bay, and New York Bay

Monthly surface currents at 2 km resolution near the mouths of three U.S. east coast bays were obtained from high-frequency radars (Coastal Ocean Dynamics Application Radar, CODAR) during 2012–2024. The currents near these bays, the Chesapeake Bay (CB), the Delaware Bay (DB) and the New York Bay (NB) were analyzed to infer similarity and differences, as well as potential common forcing from regional and basin-scale factors. The contribution to flow variability from local and remote forcing is evaluated by comparing surface currents with (a) river discharges into each bay, (b) with local and regional winds, and (c) with the North Atlantic Oscillation (NAO). The results show that surface flow variability near the mouth of the bays is linked with all three driving factors. The three bays often show similar flow patterns not only of the seasonal cycle, but also during extreme weather events. For example, increased surface flow into the bays from the Atlantic Ocean is seen when hurricanes are observed offshore in the fall, and increased surface flow from the bays is seen during winter storms. During positive NAO phases, eastward flow from all three bays increased due to intensified westerly winds, while during negative NAO phases flow decreased with weakening winds in the region. River discharges into the bays increased during 2012–2019 but decreased during 2019–2024. This change in river discharge trend was especially large in the CB, resulting in a change in trends of the surface currents. Monthly currents of each bay are only weakly correlated with the monthly river flow (R ~ 0.2–0.3; P < 0.05), while the seasonal cycles of rivers and currents have higher correlations (R ~ 0.6–0.7). Local winds show high correlations with the monthly currents (R ~ 0.75) with the current direction ~ 45° to the right of the wind, as expected from Ekman theory. However, contributions to current variability from regional and remote factors cannot be ignored. The results demonstrate the complex nature of the currents near the mouth of bays since multiple drivers, including estuarine, coastal and open ocean dynamics contribute to the observed variability.

Persistent organic pollutants and fatty acids in humpback whales: Antarctic and Chilean feeding and Brazilian breeding sites.

This study investigated the fatty acid composition and persistent organic pollutant (POP) levels in humpback whales across the Southern Ocean, Chilean and Brazilian coast. We found significant regional variations in both fatty acids and POPs. Whales from the Strait of Magellan exhibited a distinct fatty acid profile, indicative of a specialized diet rich in higher trophic level prey. In contrast, whales from the Antarctic Peninsula and Brazilian coast displayed fatty acid compositions typical of humpback whales with krill-based diets. Additionally, pollutant concentrations, particularly PCBs, were significantly elevated in whales from the Strait of Magellan. This suggests a strong link between dietary habits and pollutant exposure.

SWEMniCS: a software toolbox for modeling coastal ocean circulation, storm surges, inland, and compound flooding

Flooding from storm surges, rainfall-runoff, and their interaction into compounding events are major natural hazards in coastal regions. To assess risks of damages to life and properties alike, numerical models are needed to guide emergency responses and future assessments. Numerical models, such as ADCIRC have over many decades shown their usefulness in such assessments. However, these models have a high threshold in terms of new user engagement as development and compilation is not trivial for users trained in compiled programming languages. Here, we develop a new open-source finite element solver for the numerical simulation of flooding. The numerical solution of the underlying PDEs is developed using the finite element framework FEniCSx. The goal is a framework where new methods can be rapidly tested before time-consuming development into codes like ADCIRC. We validate the framework on several test cases, including large-scale computations in the Gulf of Mexico for Hurricane Ike (2008).

Turbidity Currents Carrying Shallow Heat Invading Stable Deep-Water Areas May Be an Unrecognized Source of “Pollution” in the Ocean

When turbidity currents carrying shallow heat enter stable stratified lakes or oceans, they can trigger changes in temperature, dissolved chemicals, oxygen concentrations, and nutrient mixing through the stable stratified environmental water. Although it is common for warm turbidity currents to invade stable regions, the impact of turbidity current characteristics on environmental entrainment and the impact of temperature changes caused by the mixing of warm turbidity currents with the environment remains poorly understood. In this study, systematic experiments on warm turbidity currents were conducted to understand how sediment-driven turbidity currents lead to mixing in stable stratification using existing environmental entrainment numbers. The experimental results show that the dimensionless numbers Rs (the ratio of the change in environmental water concentration caused by salinity to sediment load), RT (the ratio of the change in environmental water concentration caused by temperature difference to sediment load), and R0 (non-dimensional density ratio) control the flow process of warm turbid plumes, and corresponding functional relationships are summarized. The frequent occurrence of warm turbidity currents events caused by increasingly prominent environmental problems cannot be ignored, as it directly affects the deep-water environment of lakes or coastal oceans, which may be an important contribution to heat transfer that has not been evaluated in previous ocean events.

Dispersal of the Changjiang River Water in East Asian Shelf Seas

AbstractRiver plumes are crucial in transporting terrestrial materials from rivers to oceans. Knowledge gaps, however, still exist in understanding the transport pathway and the ultimate fate of riverine water in coastal oceans. This study conducted a 50‐year climatological numerical simulation to investigate the long‐term transport processes of Changjiang River water in the East Asian shelf seas. The Changjiang River water exhibits distinct seasonal patterns near the estuary mouth and in the coastal area south of the estuary, and it tends to be retained within the shelf seas, which influences its far‐field transport. The Changjiang River water takes less than 1 year to reach the eastern shelf edge of the East China Sea and over 12 years to enter the Bohai Sea. The Kuroshio current impedes the cross‐shelf transport of Changjiang water, with water in the Kuroshio region over 6 years old. The Taiwan Warm Current not only acts as a barrier that regulates the pathways of Changjiang River water but also serves as an important conduit for water exiting the East China Sea. The Changjiang River water leaves the estuary through four branches, forming eight major transport pathways in the Yellow and East China Seas. Approximately 85% of Changjiang River water flows through the Tsushima/Korea Straits, about 14% exits from the shelf edge of the East China Sea, and less than 1% passes through the Taiwan Strait. The results underscore the importance of water renewal and shelf circulation in the long‐term transport of river water within coastal oceans.

A dataset on environmental DNA, bacterio-, phyto- and zooplankton from an emerging periglacial lagoon in Svalbard, Arctic.

Over the last few decades, climate change in Svalbard (European Arctic) has led to the emergence and growth of periglacial coastal lagoons in the place of retreating glaciers. In these emerging water bodies, new ecosystems are formed, consisting of elements presumably entering the lagoon from the melting glacier, the surrounding tundra water bodies and the coastal ocean. The data presented here were collected from an emerging lagoon in the western region of Spitsbergen, Svalbard, situated between the retreating Eidembreen Glacier and Eidembukta Bay in 2022-2023. The current size of the lagoon area is approximately 6 square kilometers. The sampling was carried out at 26 sites across various sections of the lagoon, spanning from close proximity to the glacier to the furthest point away. The dataset contains the results of bacterioplankton (total cell concentration and carbon biomass), phytoplankton (taxonomic composition, cell size for selected taxa, abundance, biomass and carbon biomass), zooplankton (taxonomic composition, abundance), and environmental DNA (eDNA) metabarcoding. The dataset will be utilized to provide a comprehensive description of the structure of the lagoon ecosystem. It will also facilitate a comparison of its various parts, which vary in terms of their age of origin, i.e., release from the glacier. Additionally, the dataset will aid in the understanding of the intricate interactions between the freshwater and marine elements of the ecosystem. It can be used for comparative analysis of biodiversity assessment using eDNA and traditional microscopy methods in the identification of phyto- and zooplankton. Furthermore, these data can be utilized for environmental monitoring, tracing the temporal shifts and conducting comparative analysis of periglacial lagoons that are emerging in various regions of Svalbard as a result of climate change.

Seasonal Cycle in Sea Level Across the Coastal Zone

AbstractData from tide gauges and satellite altimeters are used to provide an up‐to‐date assessment of the mean seasonal cycle in sea level () over most of the global coastal ocean. The tide gauge records, where available, depict a seasonal cycle with complex spatial structure along and across continental boundaries, and an annual oscillation dominating over semiannual variability, except in a few regions (e.g., the northwestern Gulf of Mexico). Comparisons between tide gauge and altimeter data reveal substantial root‐mean‐square differences and only slight improvements in agreement when using along‐track data optimized for coastal applications. Quantification of the uncertainty in the altimeter products, inferred from comparing gridded and along‐track estimates, indicate that differences to tide gauges partly reflect short‐scale features of the seasonal cycle in proximity to the coasts. We additionally probe the seasonal budget using satellite gravimetry‐based manometric estimates and steric terms calculated from the World Ocean Atlas 2023. Focusing on global median values, the sum of the estimated steric and manometric harmonics can explain 65% (respectively 40%) of the annual (semiannual) variance in the coastal observations. We identify several regions, for example, the Australian seaboard, where the seasonal budget is not closed and illustrate that such analysis is mainly limited by the coarse spatial resolution of present satellite‐derived mass change products. For most regions with a sufficiently tight budget closure, we find that although the importance of the manometric term generally increases with decreasing water depth, steric contributions are non‐negligible near coastlines, especially at the annual frequency.

BOATSv2: new ecological and economic features improve simulations of high seas catch and effort

Abstract. Climate change and industrial fishing are having profound effects on marine ecosystems. Numerical models of fish communities and their interaction with fishing can help assess the biogeochemical and socioeconomic dynamics of this coupled human–natural system and how it is changing. However, existing models have significant biases and do not include many processes known to be relevant. Here we describe an updated version of the BiOeconomic mArine Trophic Size-spectrum (BOATS) model for global fish and fishery studies. The model incorporates new ecological and economic features designed to ameliorate prior biases. Recent improvements include reduction of fish growth rates in iron-limited high-nutrient low-chlorophyll regions and the ability to simulate fishery management. Features added to BOATS here for the first time include (1) a separation of pelagic and demersal fish communities to provide an expanded representation of ecological diversity and (2) spatial variation of fishing costs and catchability for more realistic fishing effort dynamics. We also introduce a new set of observational diagnostics designed to evaluate the model beyond the boundary of large marine ecosystems (66 commonly adopted coastal ocean ecoregions). Following a multi-step parameter selection procedure, the updated BOATSv2 model shows comparable performance to the original model in coastal ecosystems, accurately simulating catch, biomass, and fishing effort, and markedly improves the representation of fisheries in the high seas, correcting for excessive high seas and deep-sea catches in the previous version. Improvements mainly stem from separating pelagic and demersal energy pathways, complemented by spatially variable catchability of pelagic fish and depth- and distance-dependent fishing costs. The updated model code is available for simulating both historical and future scenarios.

Mesoscale dynamics and its interaction with coastal upwelling in the northern Gulf of Guinea

Mesoscale dynamics is essential to understanding the physical and biological processes of the coastal ocean regions due to its ability to modulate water properties. However, on the shelf, interactions between eddies, coastal currents, and topography involve complex processes whose observation, understanding, and accurate simulation still pose a major challenge. The purpose of our work is to quantify the mesoscale eddies in the northern Gulf of Guinea, off West Africa (10°W–10°E, 2°N–7°N), and their dynamical interaction with the near-surface ocean particularly in the coastal upwelling that occurs in summer between 2°W and 2°E. We used a regional NEMO model simulation at 1/36° resolution over the 2007–2017 period with daily outputs. A total of 38 cyclonic and 35 anticyclonic eddy trajectories were detected over the 2007–2017 period in July–August–September (JAS), with a mean radius along their trajectories of 95 km and 125 km, respectively. The mean lifetime for cyclones and anticyclones is approximately 1 month with an associated sea-level amplitude between 1 and 2 cm. We then focused on the JAS upwelling period of the year 2016 and found a 73 km radius cyclonic eddy east of Cape Three Points (Ghana) with a lifetime of 1 month which interacted with the coastal upwelling. Indeed, the quasi-stationary eddy dwelled within the coastal upwelling region from mid-July to mid-August 2016. A Lagrangian study shows that the eddy waters come from the coastal upwelling, then mix with warmer offshore waters, and later are transported eastward by the Guinea Current. Using a heat budget analysis, we show that this eddy–coastal upwelling interaction has an impact on sea surface temperature (SST) with a double effect: i) the eddy expands offshore the cold and salty waters (23°C and 35.6) of the coastal upwelling from 14 to 26 July; and ii) from 27 July until its dissipation, the eddy weakens this upwelling by an easterly inflow of warm offshore waters. This study highlights how the eddy–upwelling interaction can modulate the coastal upwelling in the northern Gulf of Guinea.

Development of a daily coastal ocean model for Mississippi Sound and Bight

The Mississippi Sound and Bight is a complex coastal system with shallow estuarine waters that are highly vulnerable to the effects of climate change and anthropogenic influences. In order to further our understanding of the system and provide natural resource managers and decision-makers with science-based guidance, a pre-operational coastal ocean forecast system has been developed using the Coupled Ocean Atmosphere Wave Sediment Transport Modeling System (COAWST). The COAWST application for Mississippi Bight (msbCOAWST) can be run in hindcast mode, pre-operational near real-time mode, or forecast mode and relies on other operational models including the National Water Model (NWM) for river forcing, the High Resolution Rapid Refresh model (HRRR) for atmospheric forcing, and the Navy Coastal Ocean Model (NCOM) for open ocean boundary forcing. msbCOAWST is being validated using data from a variety of in situ measurements that quantify coastal processes, including tides and water quality parameters (i.e. temperature and salinity). The highest model skill is obtained for temperature followed by water levels and salinity. msbCOAWST has been used to provide guidance for quantifying how freshwater influences derived from river diversion operations impact water quality in estuarine waters. While the model is initially developed to study water quality and circulation in pre-operational near real-time and forecast modes, it is currently being extended to include waves, sediment transport, and biogeochemistry and also linked with habitat suitability models and ecological models in hindcast mode so as to comprehensively reveal consequential environmental concerns due to the onset and persistence of hypoxia, seasonal and storm-induced waves with their associated impacts on the region’s fisheries and shellfisheries.

Source, transport, and fate of nitrate in shallow groundwater in the eastern Niger Delta

The eastern Niger Delta region in Nigeria is a hotspot for reactive nitrogen pollution due to extensive animal husbandry, pit latrine usage, and agricultural practices. Despite the high level of human activity, the sources and processes affecting nitrogen in groundwater remain understudied. Groundwater nitrate (NO3−) concentrations are highly variable, with some areas recording values well above the safe drinking water threshold of 50 mg/L. This is particularly true near municipal sewage systems. Elevated nitrite (NO2−) and ammonium (NH4+) concentrations were also detected in the study area. Sewage analysis revealed NO3− concentrations ranging from 1 to 145 mg/L, NO2− from 0.2 to 2 mg/L, and notably high NH4+ concentrations. A comparison of major ions indicated that 71%, 90%, 87%, and 92% of groundwater samples surpassed reference site levels for calcium (Ca2+), sodium (Na+), potassium (K+), and chloride (Cl−), respectively, pointing to sewage as a likely source of contamination. The NO3−/Cl− ratios at several sites suggested that most groundwater NO3− originates from human waste. Stable isotope analysis of NO3− showed a general enrichment in 15N and, in some cases, a depletion in 18O, indicating that the NO3− originates from sewage-derived NH4+ nitrification. Although denitrification, a process that reduces NO3−, is present, the high dissolved oxygen (DO) and NO3− levels in the groundwater suggest that denitrification is insufficient to fully mitigate NO3− pollution. Consequently, there is a risk of NO3− leaching from shallow aquifers into the Niger Delta’s surface waters and ultimately into the coastal ocean.

The efficacy of wastewater treatment plant on removal of perfluoroalkyl substances and their impacts on the coastal environment of False Bay, South Africa

Per- and polyfluoroalkyl substances (PFASs), which have their origins in both industrial processes and consumer products, can be detected at all treatment stages in wastewater treatment plants (WWTPs). Quantifying the emissions of PFAS from WWTPs into the marine environment is crucial because of their potential impacts on receiving aquatic ecosystems. In this study, the levels of five PFAS were measured in both influent and effluent sewage water samples obtained from a municipal WWTP, the discharges of which flow into False Bay, on the Indian Ocean coast of Cape Town, South Africa. Additionally, seawater, sediment, and biota samples from eight sites along the False Bay coast were also analysed. Results showed high prevalence of PFAS in the different environmental matrices. Perfluorononanoic acid was most dominant in all these matrices with maximum concentration in wastewater, 10.50 ng/L; seawater, 18.76 ng/L; marine sediment, 239.65 ng/g dry weight (dw); invertebrates, 0.72–2.45 µg/g dw; seaweed, 0.36–2.01 µg/g dw. The study used the chemical fingerprint of five PFASs detected in WWTP effluents to track their dispersion across a large, previously pristine marine environment and examined how each chemical accumulated in different marine organisms. The study also demonstrates that primary and secondary wastewater treatment processes cannot fully remove such compounds. There is thus a need to improve effluent quality before its release into the environment and promote continuous monitoring focusing on the sources of PFAS, including their potential transformation products, their environmental fate and ecological risks, particularly in areas receiving effluents from WWTP.

Field and numerical investigation of groundwater flow and dissolved inorganic nitrogen (DIN) dynamics in a sandy nearshore aquifer

Nutrients delivered to the coastal ocean via submarine groundwater discharge (SGD) can have a major impact on marine ecosystems. The flux of nutrients delivered via this pathway can be modified by biogeochemical processes occurring in coastal nearshore aquifers. This study combines field investigations with numerical simulations to characterize patterns of groundwater flow, salinity and dissolved inorganic nitrogen (DIN) in a permeable nearshore aquifer and to quantify SGD and associated DIN fluxes to the ocean. At the field study site, an upper saline plume (USP) and saltwater wedge with low DIN concentrations were observed together with a fresh groundwater zone with high DIN concentrations. Seawater infiltration predominantly occurred in the intertidal zone, contributing 85% of the total infiltration, with the greatest infiltration occurring in the upper-middle intertidal zone. The simulations indicate that the USP expanded and contracted through the tidal cycle, and the width of the high-DIN freshwater discharge zone also varying. The freshwater discharge zone was narrower around the high tide period due to expansion of the overlying low-DIN zone associated with the USP. Over the simulated period, only approximately 30% of the DIN entering the nearshore aquifer ultimately discharged to the ocean. The findings of this combined field and numerical study are needed to inform future field and numerical investigations examining the fate of DIN in nearshore aquifers.