Plume Area Research Articles

Seasonal and Spatial Variability of Absorption Properties in Cartagena Bay’s Complex Waters

Characterizing inherent optical properties (IOPs) of water constituents is crucial for remote sensing applications. Remote sensing in Cartagena Bay is particularly challenging due to significant variations in constituent concentrations caused by the seasonal and annual variability of discharges from the Canal del Dique. This article presents the variability in absorption coefficients of phytoplankton, chromophoric dissolved organic matter (aCDOM), and non-algal particles (aNAP) in Cartagena Bay. Absorption coefficients were measured in the laboratory across multiple monitoring campaigns, with seasonal analyses conducted to establish relationships between absorption properties and biogeochemical parameters such as chlorophyll-a, salinity, and turbidity. Results indicate that at 440 nm, aCDOM and aNAP primarily dominate absorption during the rainy season, while aNAP dominates during the dry season. This variation is influenced by inflows from the Canal del Dique. Lower CDOM absorption in 440 nm (aCDOM440), and higher CDOM absorption slope (SCDOM275–295) and higher salinity values were observed during the dry season, which is consistent with the reduced fluvial influx. Spatial variability shows that higher CDOM values prevail in the river plume area during both seasons, with particularly higher values in the rainy season. Median values of aNAP were similar in both seasons, with a strong relationship found between all aNAP data and turbidity (rp = 0.785). Compared to other estuaries, Cartagena Bay exhibits optical characteristics typical of a coastal water body subjected to river discharges, including the elevated turbidity and the high dissolved organic matter influenced by significant inflow from the Canal del Dique. These features highlight the bay’s dynamic interactions with terrestrial inputs. This study provides invaluable information on the optical characteristics of Cartagena Bay, which is crucial for improving the accuracy and effectiveness of remote sensing models for optically active parameters such as turbidity, suspended solids, CDOM, and chlorophyll-a.

Investigation of anomalous lightning activity during the January 15, 2022 Tonga volcano eruption based on measurements of the VLF and ELF electromagnetic fields

An anomalous increase in the level of Very Low Frequency (VLF, 3–30 kHz) and Extremely Low Frequency (ELF, 3–3000 Hz) radio noise and the rate of VLF atmospherics was registered during the explosive eruption of the Tonga volcano on January 15, 2022 at the Akademik Vernadsky station (65.246°S; 64.257°W) about 8870 km from the volcano. At the peak activity around 5 UT, the number of atmospherics in 2-min intervals increased by almost 15 times compared to the period preceding the eruption. At this point, the estimated rate reached 360 VLF atmospherics per second. At the same time, an increase in the power spectral density of the magnetic field by 5–9 times was observed in both the ELF and VLF ranges. After 40 min, only on ELF an increased peak lasting ∼10 min was observed, comparable in magnitude to the main peak. According to the Worldwide Lightning Location Network (WWLLN), increased thunderstorm activity was concentrated very close to the volcano during this period. This discrepancy between the intensities of ELF and VLF radiation suggests a significant difference in the parameters of currents in lightning discharges occurring in the area of the volcano vent and in the area of the volcanic ash plume.

Interacting Influences of Diurnal Tides, Winds, and River Discharge on a Large Coastal Plume

AbstractThe dispersal of large river plumes in the coastal ocean depends on multiple factors, and in some cases, can be categorized into distinct dynamical regimes: a tidally dominated near‐field, a rotational mid‐field, and a coastal current far‐field. In this study, observations and modeling are used to evaluate the factors controlling the variability in the buoyant plume from Mobile Bay. Rather than distinct dynamical regimes, the Mobile Bay plume depends on forcings that act at overlapping temporal and spatial scales: diurnal tides, river discharge events, and winds. Satellite synthetic aperture radar images along with shipboard in‐situ sampling and marine radar are used to observe plume fronts in spring 2021. Hydrodynamic model simulations are compared with observations and used to characterize a large coastal plume at consistent tidal phase across a range of forcing conditions. The along‐shore position of the plume depends primarily on advection by wind‐driven surface currents. The cross‐shore extent and plume area depend primarily on the tidal amplitude and river discharge, and secondarily on northerly (seaward) winds. Along‐shore winds influence the buoyancy anomaly by altering salinity in the estuary and offshore. Upwelling winds increase the buoyancy anomaly and advect previous plumes away from the mouth. Downwelling winds reduce the buoyancy anomaly by trapping previous plumes near the coast and directing freshwater discharge toward a secondary outlet. Thus, the combined, overlapping influences of the tide, wind, and discharge dominate the variability in freshwater delivery to the shelf at time scales of days and distances of tens of km.

Evaluation of tetrachloroethylene (PCE) and its degradation products in human exhaled breath and indoor air in a community setting

Tetrachloroethylene (PCE) is a widely utilized volatile chemical in industrial applications, including dry cleaning and metal degreasing. Exposure to PCE potentially presents a significant health risk to workers as well as communities near contamination sites. Adverse health effects arise not only from PCE, but also from PCE degradation products, such as trichloroethylene (TCE) and vinyl chloride (VC). PCE, TCE, and VC can contaminate water, soil, and air, leading to exposure through multiple pathways, including inhalation, ingestion, and dermal contact. This study focused on a community setting in Martinsville, Indiana, a working-class Midwestern community in the United States, where extensive PCE contamination has occurred due to multiple contamination sites (referring to 'plumes'), including a Superfund site. Utilizing proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), PCE, TCE, and VC concentrations were measured in the exhaled breath of 73 residents from both within and outside the plume areas. PCE was detected in 66 samples, TCE in 26 samples, and VC in 68 samples. Our results revealed a significant positive correlation between the concentrations of these compounds in exhaled breath and indoor air (Pearson correlation coefficients: PCE = 0.75, TCE = 0.71, and VC = 0.89). This study confirms the presence of PCE and its degradation products in exhaled breath in a community exposure investigation, demonstrating the potential of using exhaled breath analysis in monitoring exposure to environmental contaminants. This study showed the feasibility of utilizing PTR-TOF-MS in community investigations to assess exposure to PCE and its degradation products by measuring these compounds in exhaled breath and indoor air.

Correlation Between Dynamic Spray Plume and Drug Deposition of Solution-Based Pressurized Metered-Dose Inhalers.

Background: The lack of visual dynamic spray characterization has made the understanding of the physical processes governing atomization and drug particle formation difficult. This study aimed to investigate the changes in the spray plume morphology and aerodynamic particle size of solution-based pressurized metered-dose inhalers (pMDIs) under different conditions to achieve better drug deposition. Methods: Solution-based pMDIs were studied, and the effects of various factors, such as propellant concentration, orifice diameters, and atomization chamber volume, on drug deposition were examined by analyzing the characteristics of spray plume and aerodynamic particle size. Results: Reducing the actuator orifice and spray area led to a concentrated spray plume and increased duration and speed. Moreover, the aerodynamic particle sizes D50 and D90 decreased, whereas D10 remained relatively unchanged. Decreasing the atomization chamber volume of the actuator led to reduced spray area and an increased duration but a decreased plume velocity. D90 exhibited a decreasing trend, whereas D10 and D50 remained relatively unchanged. Reducing the propellant concentration in the prescription, the spray area and the plume velocity first decreased and then increased. The duration initially increased and then decreased. The values of D50 and D90 showed an initial decreasing followed by an increasing trend, whereas D10 remained relatively unchanged. Conclusions: During the development process, attention should be paid to the changes in the spray area, spray angle, duration, and speed of the spray plume. This study recommended analyzing the characteristics of the spray plume and combining the data of two or more aerodynamic particle size detection methods to verify the deposition in vitro to achieve rapid screening and obtain high lung deposition invivo.

Riverine Influences and Seasonal Dynamics: Exploring Carbonate System Variations and Air‐Sea CO2 Fluxes in the Southern Yellow Sea and East China Sea

AbstractIn this work, the seasonal variations of the carbonate system and air‐sea CO2 fluxes were investigated by two cruises in the southern Yellow Sea (SYS) and the East China Sea (ECS), which were significantly influenced by the Changjiang riverine inputs across seasons. Biological‐mediated change of dissolved inorganic carbon (DIC) was first quantitated through a three end‐member mixing model from winter to spring. Our modeling results suggested that DIC addition through biological remineralization persisted in the SYS during winter and spring, while DIC removal was evident in the Changjiang River Plume and the offshore ECS triggered by river inputs in spring. Horizontal and vertical mixing together constituted the largest contribution to the interseasonal variability of partial pressure of CO2 (pCO2) in the SYS (−69.5%), the river plume (−59.3%), and the ECS offshore (−43.8%), followed by temperature effects in the plume area (29.4%), and biological processes in the ECS offshore (24.1%) and the SYS (−7.7%), with air‐sea CO2 exchange contributing the least in both three subregions. The SYS, the river plume, and the ECS offshore all acted as atmospheric CO2 sinks in both winter and spring. Furthermore, their ability to absorb atmospheric CO2 increased from winter to spring, as reflected in a ∼1.8‐fold increase in the overall spring air‐sea CO2 flux compared to winter estimation.

Experimental investigation on the impact of fuel injection schemes on the fuel/air mixing characteristics in alternating wedge struts

To enhance the performance of scramjet engines, it is essential to understand the fuel/air mixing characteristics downstream of alternating wedge struts and the dynamics of streamwise vortices. Two optical measurement techniques, Mie scattering and acetone-particle laser-induced fluorescence, were employed to study the impact of fuel injection location and different injection gases on the fuel/air mixing characteristics downstream of alternating wedge struts at total temperature of 300 K and total pressure of 800 kPa. The results indicated that the particle laser-induced fluorescence measurements provided superior results compared to Mie scattering, due to the more uniform distribution and better following characteristics of acetone molecules as seeding particles. Different fuel injection locations resulted in varying fuel distributions and plume morphologies downstream. The plume sizes obtained from the three types of fuel orifices were generally consistent, but the mixing effect of the orifices on the first strut was better, whose injection locations being at the trailing edge intersections, with a larger plume area and more uniform fuel distribution. The fuel/air mixing process downstream of the alternating wedge struts was primarily dominated by streamwise vortices. Despite certain differences in the physical properties of nitrogen and hydrogen molecules, the measurement results showed that the plume morphologies obtained with both gases were quite similar. Additionally, a streamwise vortex model was developed to predict the dynamics of streamwise vortices and the evolution of fuel plume morphology, and it was compared with experimental results.

Factors influencing the variation of the Sepik-Ramu River system's sediment plume off the north coast of New Guinea

The Sepik-Ramu River system (SRRs) is a principal contributor of terrestrial materials to the pelagic waters of the tropical Western Pacific, boasting the highest sediment discharge in New Guinea. However, this system's sediment outflow and dispersal patterns are not well-documented. This study seeks to address this gap by analyzing the estuarine sediment plumes, which are the key indicators of the marine dispersion of terrestrial materials. Utilizing Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2010 to 2020 and applying the Novoa17 algorithm, we examined the distribution and temporal evolution of the sediment plume of the SRRs estuary. The sediment plume was categorized into two distinct zones: core and diffuse, based on suspended sediment concentration (SSC) levels. Our findings reveal significant seasonal variations of these sediment plumes in the nearshore. The plume area expands during the wet season and contracts during the dry season, respectively, with core and diffuse plumes sharing similar change characteristics. The diffuse plume primarily extends northeast in the wet season and subsequently shifts northwest in the dry season, and the core plume consistently points to the northeast. The study further explores the driving factors and mechanisms behind these patterns, identifying river discharge as the primary influence on the core plume and sea surface winds and coastal currents as determinants of the diffuse plume's behavior. Interannual variations in the plume characteristics were found to be influenced by the El Niño-Southern Oscillation (ENSO), which indirectly affects plume dynamics through its impact on regional precipitation. During El Niño events, characterized by drier conditions and reduced discharge, the plume SSC and area typically decrease. During La Niña events, the plume's SSC and area typically increase, except for the 2011 super La Niña's negative anomaly, caused by the rain belt's excessive westward shift.

1300-m-High gas plume from pockmarks in the north Nansha waters, South China sea

The northeastern region of Nansha Waters, located in the southern margin of the South China Sea, is abundant in gas resources. However, it remains unclear if the central and northern areas of Nansha Waters possess gas resources and if there are any associated leaks. The Jiuzhang Basin is located in the northern Nansha Waters. Pre-stack depth migration, analysis of seismic attributes and multibeam data processing were conducted to image the seabed topography and backscatter intensity, as well as the seismic structure of the water and sedimentary layers in the Jiuzhang Basin. The result reveals a presence of large plumes, approximately 1500 m in width and up to 1300 m in height, from a pockmark. The plume is characterized by a strong seismic amplitude featuring chaotic reflections, a high instantaneous frequency (100–150 Hz), and a strong instantaneous amplitude. These seismic features commonly appear in hydrocarbon-bearing seawater, indicating that the plume is composed of gas. The relationship between the volume fraction of bubbles in the gas plumes and the amplitude of multi-channel seismic waves suggests that the volume fraction of bubbles within the gas plume can reach up to 5.0 × 10−3. Meanwhile, a new pockmark with a length of 248 m, a width of 90 m, and a depth of 20.4 m, and an abrupt 22 m drop in water depth of an existing pockmark are observed in the gas plume area. These observations, combined with the gas plume revealed by the multi-channel seismic collected in 2013 and multibeam collected in 2020, suggest a very strong and recently active gas leaks in the pockmark area of the northern Jiuzhang Basin. Furthermore, in the pockmark area, there are gas-bearing formations with weak reflections, and mud diapirs charactered by low seismic velocity, low amplitude chaotic reflections, and pulled up reflections on both sides, and faults extend to the seabed. These observations suggest that gas plume originate from deep strata of the northern Jiuzhang Basin. Large gas plumes and mud diapirs are often indicative of the existence of deep gas reservoirs. Therefore, the presence of such active gas plumes and mud diapirs in the northern region of the Jiuzhang Basin signifies the presence of abundant gas resources.

Sustained increase in suspended sediments near global river deltas over the past two decades

River sediments play a critical role in sustaining deltaic wetlands. Therefore, concerns are raised about wetlands’ fate due to the decline of river sediment supply to many deltas. However, the dynamics and drivers of suspended sediment near deltaic coasts are not comprehensively assessed, and its response to river sediment supply changes remains unclear. Here we examine patterns of coastal suspended sediment concentration (SSC) and river sediment plume area (RPA) for 349 deltas worldwide using satellite images from 2000 to 2020. We find a global increase in SSC and RPA, averaging +0.46% and +0.48% yr−1, respectively, with over 59.0% of deltas exhibiting an increase in both SSC and RPA. SSC and RPA increases are prevalent across all continents, except for Asia. The relationship between river sediment supply and coastal SSCs varies between deltas, with as much as 45.2% of the deltas showing opposing trends between river sediments and coastal SSCs. This is likely because of the impacts of tides, waves, salinity, and delta morphology. Our observed increase in SSCs near river delta paints a rare promising picture for wetland resilience against sea-level rise, yet whether this increase will persist remains uncertain.

Nitrate fate in coastal unconfined aquifers influenced by preferential flows

This study examined the influence of preferential flow on pore water flows and marine nitrogen transport reaction in variable saturation and variable density coastal aquifers. The 2-D unconfined aquifer model established was based on the software COMSOL by coupling the dynamic and chemical processes together. The results showed that preferential flow affects groundwater flow and salinity distribution, leading to a more complicated mixing process. The preferential flow resulted in an increase in mixing zone area and the upper saline plume area of 10.33 and 2.62 m2, respectively, a decrease in saltwater wedge area of 7.22 m2, and an increase in nitrate (NO3-) removal efficiency from 7.9% to 8.97%. The NO3- removal efficiency increases progressively with the depth (h) and quantity (n) of preferential flows; however, it decreases after a certain quantity. Further quantitative analysis revealed an increase in the intensity of nitrification and dissolved oxygen inflow flux with preferential flow depth and quantity increase. This phenomenon usually occurs on coasts where biological caves are abundant. The results also offer significant implications for designing engineering measures to mitigate saltwater intrusion and are significant to prevent groundwater quality deterioration in coastal zones.

Experimental study for visualizing CO2-dissolved water plume migration under hydraulic gradient conditions and implication for field monitoring data

Investigating the possible direction of a CO2-dissolved water plume migration near the potential CO2 leakage area is a significant task because it helps estimate the spatial and temporal monitoring scale to detect the signal of released CO2 from the storage. Accordingly, the Korea CO2 Storage Environmental Management (K-COSEM) research center tried to develop an intensive monitoring system and applied it to the artificial CO2 release test in the actual field. Monitoring data from the field tests depicted the horizontal movement of the CO2-dissolved water plume along the direction of the groundwater flow. However, it remains unclear how the CO2-dissolved water plume migrates vertically and how gas accumulation occurs near the capillary zone. The present study simulated the CO2 release test with a visual expression method utilizing a Hele-Shaw cell with hydraulic gradient conditions (i = 0, 0.1, and 0.01) and tried to estimate the significant influences on a diffusive-advective transport of the dissolved gas plume with the shallow aquifer condition. The visualization experiment results were intuitively verified to determine whether the theoretical principles of action related to plume flow applied in this context. The results suggest that a CO2-dissolved water plume is distributed by hydraulic gradients and density-driven CO2 convective flow. The plume shape, center, and area were analyzed using an image analyzer program; the results demonstrated that the plume characteristic evolved depending on the significant effects on the plume. When the plume was mainly affected by the hydraulic gradient, it rapidly moved from the injection point to the last boundary; in contrast, when it was influenced primarily by density-driven CO2 convective flow, it flowed diagonally downward in the shape of varied branches. The numerical model calculated the migration of the CO2-dissolved water plume affected by both factors. The laboratory experiment and numerical simulation results suggest that the migration of a CO2-dissolved water plume may be affected by the hydraulic gradient and density-driven CO2 convective transport. As such, these factors should be considered when designing and analyzing CO2 monitoring signals to detect CO2 leaks from shallow aquifer systems.

The roles of river discharge and sea ice melting in formation of freshened surface layers in the Kara, Laptev, and East Siberian seas

Wide areas of the Siberian Arctic shelf are covered by freshened surface water layers, which are among the largest in the World Ocean. River discharge is the main freshwater source for formation of these layers; therefore, they are commonly referred to as river plumes (the Ob-Yenisei plume in the Kara Sea and the Lena plume in the Laptev and East Siberian seas). The contribution of sea ice meltwater (SIM) to the Ob-Yenisei and Lena plumes is pointed out to be small, albeit its actual volume remains unknown. In this study, we use a novel dataset of satellite-derived sea ice thickness in the Arctic Ocean during the melt period to quantify the annual volume of SIM, which was received by the Ob-Yenisei and Lena plumes during 2012–2020. We reveal that SIM is a significant source for the Lena plume providing, on average, 20% of total annual freshwater content. Moreover, the share of SIM in the Lena plume shows large inter-annual (14%–29%) variability, i.e., during certain years, SIM provides almost one-third of freshwater volume of the Lena plume. This variability is governed by inter-annual variability of ice thickness, as well as seasonal variability of sea ice melting conditions. Conversely, the contribution of SIM to the Ob-Yenisei plume is relatively low (8% on average), and its total annual share varies from 6% to 11% during the study period. This difference is mainly caused by significantly smaller area of the Ob-Yenisei plume as compared with the Lena plume. The forecasted earlier onset of ice melting in the Arctic Ocean in future decades due to climate change could decrease the contribution of SIM to the Ob-Yenisei plume, whereas its influence on the Lena plume remains unclear.

Spatial and seasonal pattern of microbial nitrate reduction in coastal sediments in the Vistula River plume area, Gulf of Gdańsk

Estuaries can remove and/or retain land-derived nitrogen (N) and act as filters buffering N loads to the open sea. The N coastal filter can be seasonally variable depending on water temperature and transported loads, two factors acting in synergy and strongly influenced by climate change. The capacity of sediments to mitigate riverine N loads was investigated at four sites in the Vistula River plume area (Gulf of Gdańsk, Southern Baltic Sea). Samplings were carried out in two contrasting seasons: spring and summer, characterized by different water temperatures and nitrate (NO3-) levels. Inorganic N fluxes, and rates of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were measured in intact sediment cores by means of dark incubations and 15N-nitrate concentration-series experiments. Sampling sites were selected along a gradient of depth (5 to 24 m), that was also a gradient of sediment organic matter content. In both seasons, denitrification rates increased along with depth and from spring (6.5 ± 7.0 µmol m-2 h-1) to summer (20.4 ± 15.4 µmol m-2 h-1), despite lower NO3- concentrations in summer. In spring, at higher NO3- loading, denitrification was likely limited by low water temperature, and elevated sediment oxygen penetration. Coupled denitrification-nitrification prevailed over denitrification of water column NO3- across all sites and seasons, contributing to over 80% of the total denitrification. Notably, no anammox was detected at the sampling sites. DNRA exhibited low to undetectable rates in spring, especially at the shallowest sites. However, during summer, N recycling via DNRA increased and ranged from 0.7 to 14.9 µmol m-2 h-1. The denitrification efficiency (DE), calculated as the ratio between molecular nitrogen (N2) flux and dissolved inorganic N effluxes from sediments, ranged from 0 to 37% in spring, whereas in summer DE did not exceed 16%. Despite the dominance of denitrification over DNRA, the analyzed sediments acted as weak N buffers under in situ dark conditions. However, concentration-series experiments suggested high potential denitrification capacity, exceeding 400 µmol m-2 h-1, in response to short-term, large riverine inputs of NO3-.

Observations of river-wave interactions at a small-scale river mouth

Small coastal rivers often discharge directly into the surfzone, where the fate of freshwater and river-borne materials (e.g., sediment, nutrients and contaminants) is primarily determined by interactions between buoyant plume processes and the nearshore wave forcing. Understanding river-wave interactions in the surfzone is essential to assess coastal water quality and impacts on ecosystem health along adjacent shorelines. These interactions are modulated by the variability in river discharge, offshore wave climate, tidal forcing, and surfzone dynamics, and therefore occur over a wide range of timescales. However, the different timescales at which river-wave interactions occur have not been fully investigated. Here we use in-situ and remote (drone-based) observations collected at the mouth of the Maipo River, a small-scale river system in central Chile, to investigate interactions between the river outflow and the incident wave forcing that may influence the distribution of freshwater along the coast. We focus on interactions occurring at infragravity (wave groups), tidal, and synoptic (offshore wave climate) timescales. The observations included inlet and surfzone deployments, and documented low river discharge conditions (QR∼ 20–27 m3s−1) with variable wave forcing (Hs∼ 1–3 m). We observed that the salinity signal at the river mouth is strongly modulated by the tide, with a freshwater plume forming solely during the ebb. Large oscillations associated to infragravity (IG) motions are continuously observed on top of the tidal variability. These oscillations are evidenced in surfzone salinity, inlet water levels, and inlet velocity during the early ebb when the freshwater plume starts to develop. As the plume evolves into a strong outflow jet during the late ebb, they are not observed in the inlet and become restricted to the surfzone. The combined analysis of drone imagery and in-situ observations suggests that the observed variability in surfzone salinity at IG frequencies is associated with the arrival of wave groups and the propagation of wave fronts in the plume area. In particular, during the late ebb, the large oscillations in surfzone salinity (amplitude of 15–20 psu) are explained by a contraction and expansion of the outflow plume in response to the variability in the onshore wave forcing at the timescale of wave groups. On synoptic timescales (hours to days), the surfzone salinity responded to the intensity of the offshore wave forcing (∼ 20 m depth), with higher waves promoting lower salinity as freshwater is mostly retained near the coast. A wave-river momentum comparison confirms that the wave forcing had the potential to trap freshwater in the surfzone. This study shows that nearshore waves may influence the dynamics of small river plumes and the fate of freshwater (and associated terrestrial materials) on a wide range of timescales, from infragravity (1–5 min) to hours and days.

Analysis of colloidal activated carbon alternatives for in situ remediation of a large PFAS plume and source area

AbstractThis study evaluated optimal locations for in situ remediation of per‐ and poly‐fluoroalkyl substances (PFAS) in groundwater with colloidal activated carbon (CAC). New Freundlich isotherms for PFAS adsorption to CAC were estimated to illustrate the effect of competitive adsorption with dissolved organic carbon and other PFAS in a groundwater sample. A hypothetical model scenario was constructed based on source area characteristics similar to a site impacted by aqueous film forming foam in South Dakota. Modeling indicates that, even with high PFAS concentrations, CAC would still be capable of maintaining concentrations below proposed maximum contaminant levels in the adsorption zone for at least 30–40 years. Two‐dimensional areal modeling indicates that the future breakthrough of PFAS is likely to occur in the localized core of the plume, and that the corresponding future reinjection of CAC will only need to be conducted over a smaller portion of the original injection footprint. The benefits of implementing a phased remedial approach at PFAS sites are discussed. Source area and mid‐plume CAC treatments are shown to be ineffective at attenuating PFAS concentrations at the downgradient property boundary within a reasonable timeframe when PFAS travel time is relatively slow. Among the CAC alternatives evaluated here, a downgradient CAC permeable reactive barrier has the best performance with respect to protecting downgradient receptors.

Past, Present, and Future Anatomy of an Oil Brine Plume Remediation near Poplar, Montana: A Case Study

AbstractThe Biere #1‐22 oil production well near Poplar, Montana leaked brine and light nonaqueous phase liquid (LNAPL) to the shallow alluvial aquifer for several years before final closure in 2002. Since 2008, 2.5 billion L of brine have been removed (~90% of the original Cl mass). However, Cl will not reach the original background levels due to the reservoir of solutes entrained in the Bearpaw bedrock remnant from the lateral dense aqueous phase liquid flow across the alluvial/bedrock interface. After removal of ~100,000 L of product since 2006, residual LNAPL is now confined to 2.2 ha (5.5 acres) a decrease from the original 2.7 ha (6.6 acres) areal extent by 17%. The initial ~7.5 m thick product in 2002 is stable at a maximum of ~1 m. However, LNAPL has infiltrated into fine‐grained clay/silt units forming a smear zone in lenses 10 to 20 m bgs. Ongoing remediation has successfully mitigated benzene groundwater impacts over the last 14 years, with the benzene plume area having decreased by >99% (at the 5 μg/L) level from the maximum ~140 ha in 2002. This appears to be the first study evaluating the challenges to remediate a mixed LNAPL/dissolved organic/inorganic plume. Based on the mass removal to date, the asymptotic trends in solute concentrations, unpotable background groundwater quality, absence of a source/receptor pathway, lack of beneficial groundwater use, duration of mitigation with no obvious future accrual in benefit and the availability of institutional controls, it seems that the remedial strategies employed since 2006 have met their cost/benefit goals.

A first ecological coherent assessment of eutrophication across the North-East Atlantic waters (2015–2020)

This paper presents the outcomes of the fourth application of the Common Procedure for the Identification of the Eutrophication Status of the OSPAR Maritime Area (the “Common Procedure”), conducted for the period 2015–2020 for the North East Atlantic. Previously, OSPAR has assessed eutrophication based on national assessment areas and disparate approaches lacking a transparent and comparable basis. A more harmonized approach has now been achieved through development of ecologically relevant assessment areas defined by oceanographic criteria rather than international boundaries, allowing for consistent assessments across exclusive economic zones and acknowledging that eutrophication is a transboundary problem. Thresholds that were specific for those harmonized assessment areas and eutrophication parameters have been derived primarily from an ensemble modeling approach to determine pre-eutrophic conditions. Common assessment areas and harmonized thresholds have enabled, for the first time, an objective and comparable assessment of the eutrophication status of the whole OSPAR Maritime Area. This establishes a level playing field for managing eutrophication and a solid basis for deriving OSPAR nutrient reduction targets as a prerequisite for targeted and successful regional eutrophication management. This assessment shows that eutrophication problem areas persist, in particular along the continental coasts from France to Denmark/Sweden and in the Greater North Sea and the Bay of Biscay and Iberian coast. The main areas affected by eutrophication are the plumes and adjacent coastal areas in the Greater North Sea and Bay of Biscay/Iberian Coast, with riverine nutrient inputs remaining the major source of nutrient pollution. Approximately 6% (152,904 km2) of the OSPAR Maritime Area is eutrophic, with the impacted area supporting many important ecosystem services. Fifty-eight percent of river plume areas (eight assessment areas out of 14), 22% (five of 27) of the coastal areas and 10% (three of 17) of the shelf areas were classified as problem areas. Application of the current assessment process to historical data from the previous three OSPAR assessment periods shows a gradual improvement since 2000. However, the OSPAR 2010 objective “to combat eutrophication, with the ultimate aim of achieving and maintaining a healthy marine environment where anthropogenic eutrophication does not occur” has not yet been fully achieved. Further measures to reduce nutrient loads are needed to ensure long-term sustainability of our coastal waters.

A cyclone formation, eastward plume drag, ion-hydration process, and the consequent ionospheric changes following the 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption

In this paper, we investigate the possible mechanism behind the volcanic plume drag and the massive expansion of the ionospheric Total Electron Content (TEC) along the eastern longitudes by using near-field observations of the 15 January 2022 Hunga Tong-Hunga Ha'apai volcanic eruption. The meteorological omega parameter shows a dominant upward/downward movement of the air parcels along the eastern and southern sides of the volcanic eruption. This dominant air convection under the presence of the heavy moisture of volcanic plume and vector winds indicated the formation of a cyclone over and around the Tonga volcano. This cyclone dragged the heavy volcanic plume towards the eastern longitudes (150oE – 180oE). Moreover, we observe that the volcanic plume injected about 5 DU of Sulfur Dioxide (SO2) and 30 kgm−2 of the water content along the total atmospheric column. The chain reactions of Hunga Tonga volcanic trace gases with the gases present in the neutral atmosphere instigated an air ionization process, while under the presence of the heavy water content, these ions underwent an ion-hydration process that contributed to the electrodynamical changes in the region. These electrodynamical changes can be regarded as Atmospheric Chemical Potential (ACP) in the lower atmosphere. We observe a sharp increase in the ACP of ∼0.26 eV along the eastern longitudes (160–180°E) exactly above the dragged volcanic plume area. The long-term TEC changes that have been observed towards the eastern longitudes are the result of the ion-hydration process at the lower atmosphere. The statistical analysis showed a critical change during the day of the event up to ∼48 TECU with an increasing value of 28 and 18 TECU from the lowest and highest ranges before the event over the crater, respectively. Our main findings showed ionospheric anomalies in the near field started from 6:00 to 16:00 UTC. Based on Swarm satellites, the S4 values have significant changes around 0.3–0.6 lasting for tens of minutes.

Modeling the interannual variability in Maipo and Rapel river plumes off central Chile

Abstract. River plumes have a direct influence on coastal environments, impacting coastal planktonic and benthic communities, including fishery resources. In general, the main drivers of river plume dynamics are the river discharge and the alongshore wind stress, whereas the tides and topography play a secondary role. In central Chile, rivers flowing into the eastern Pacific have a relatively short path on land, with a high slope and a mixed snow–rain regime. This study aims to understand the interannual variability in the plumes of the Maipo and Rapel rivers in the coastal/shelf area off central Chile and their influence on local ocean dynamics. We used the Coastal and Regional Ocean Community (CROCO) model, with 1 km horizontal resolution and 20 sigma levels, to simulate the ocean dynamics for the period 2003–2011. The results show that the plume's area coverage and coastal ocean salinity are strongly correlated with the river discharges. The predominant northeastward winds control the plumes' orientation toward the northwest. However, episodes of southeastward winds in winter can reverse the plumes' direction, promoting their attachment to the coast and southward transport. Results also show a salification trend linked to the severe droughts hitting central Chile during the studied period. This salification determines a change in local dynamics which could be more frequent in future scenarios of climate change with a significant lack of rain and river discharges along central Chile.