Search

The Baltic Sea, a semi-enclosed marginal sea with a catchment area four times its size, acts as a sink and continues to show detectable levels of persistent organic pollutants (POPs) in its sediments. This is attributed to the synthesis and industrial use of commercial polychlorinated biphenyls (PCB) products, as well as the widespread use and discharge of certain chlorinated pesticides into the natural environment during the last century. Our study investigates chlorinated hydrocarbon pollutants, the polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and its metabolites as well as hexachlorobenzene (HCB) in sediments based on several short sediment cores from different basins covering almost the entire Baltic Sea. In this study, we document the decline of PCB, HCB and DDT metabolites in Baltic Sea sediments, visible in a sevenfold reduction of pollution levels over a period of 50 years since their maximum production in the mid-eighties of the last century. We reflect the pollution levels against the global regulations, especially the worldwide ban of the POPs at the beginning of the 21st century. Based on our results, we are now able, for the first time, to evaluate the fate of POPs in Baltic Sea sediments and to provide further explanation for the detection of POPs in previous and future studies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 The Authors. Published by Elsevier B.V. All rights reserved.)

Sharm El-Sheikh, located at the southern entrance of the Gulf of Aqaba, is a key tourist destination known for its mild climate and commitment to environmental initiatives, notably hosting COP27 in 2022. This study evaluates heavy metal contamination in beach sediments to assess environmental and human risks. Sampling was conducted at Sharm Port and El-Maya Bay, both popular tourist areas. Sediment samples revealed varying concentrations of Fe, Mn, Zn, Pb, Cu, and Co, all within safe levels. Non-carcinogenic and carcinogenic risks were evaluated through chronic daily intake and hazard indices, revealing that ingestion poses the highest risk among exposure pathways. However, the beach sediments of the study area are generally safe for recreational use by both adults and children according to international standards. Statistical analyses identified low-level natural and anthropogenic sources of contamination, underscoring the need for ongoing environmental monitoring to preserve environmental quality in this vital tourist area and to ensure public health and safety by implementing sustainable waste management practices, regulating tourism activities, and protecting marine ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Ltd. All rights reserved.)

Marine sediments are major sources of legacy pollution, capable of releasing toxic mercury (Hg) into the water column when disturbed. This study evaluated Hg remobilization from surface sediments during resuspension events by examining sediment properties, Hg concentrations, and speciation. Research was conducted in the southern Baltic Sea, representing diverse environmental conditions and human impacts. The findings showed that sediment resuspension was the primary driver of Hg remobilization, with diffusion flux playing a minimal role. Both dissolved and particulate Hg were released almost immediately after resuspension, with elevated concentrations persisting long enough to be transported beyond the disturbed area. The diffusion of dissolved Hg was enhanced by labile Hg fractions in the sediment, with reducing conditions and high organic matter content further promoting this process. Particulate Hg remobilization was influenced by sediment characteristics, particularly bulk density, which affected resuspension susceptibility and dispersion of suspended matter. The total Hg concentration and labile organic-bound Hg fractions also significantly influenced particulate Hg release. These results highlight the importance of sediment properties in managing Hg-contaminated sites and have implications for environmental protection and marine operations planning., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier B.V. All rights reserved.)

Investigations of the spatial-temporal variations of nutrients within mangrove coastal zones are essential for assessing the environmental status of an aquatic ecosystems. However, major processes controlling nitrate cycle along the submarine groundwater discharge (SGD) pathway from the mangrove areas to adjacent tidal creek remain underexplored. A time series measurement over a 25 h tidal cycle was conducted in Qinglan Bay tidal creek (Hainan Island, China). Samples of the creek seawater, nearby terrestrial groundwater and sediment porewater were collected for analysis of nutrient concentrations and dual nitrate isotopic compositions (δ 15 N-NO 3 - and δ 18 O-NO 3 - ). We observed high concentrations of nutrients in terrestrial groundwater, and their concentrations decreased with distance towards the coastal area. Using dual nitrate isotopes and a MixSIAR model, we concluded that ammonia nitrogen fertilizer (Amm-NF) is the primary nitrate sources for groundwater, while creek water nitrate originates from various sources, including manure and sewage, soil organic nitrogen, and chemical fertilizer. The isotopic ratios (δ 18 O: δ 15 N) suggest active nitrification occurs in low tide creek water, whereas assimilation and limited denitrification occurs in high tide creek water and groundwater. Based on previous report of SGD rate in the region, we calculated the flux of SGD-derived nutrient export to coastal water, and the result indicates low N: P ratio and N limitation in the tidal creek. This study highlights the complexity of different sources and biogeochemical processes that impact the nutrient distribution and nitrate dynamics in the nearshore mangrove ecosystem. Understanding these processes is essential for effectively protecting and managing of the mangrove aquatic ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Ltd. All rights reserved.)

The hydrodynamics, water temperature, and water quality model for the Dan River and Renzhuang Reservoir continuum were developed using field monitoring data and the Environmental Fluid Dynamics Code (EFDC). An in-situ water discharge experiment enabled the calculation of water propagation time using a simulated flood progression method and the hydrodynamics module of EFDC. Based on these model results, degradation coefficients for chemical oxygen demand, biochemical oxygen demand, nitrogen (N), phosphorus (P), fluoride, arsenic were determined, revealing significantly higher values when the wetland barrage was opening. According to field monitoring and EFDC model outputs, the water environment capacity (WEC) of total nitrogen (TN) in Dan River was even negative, with the WEC of TN and total phosphorus (TP) in Renzhuang Reservoir being very low at 147 kg/d and 1490 kg/d, respective. Furthermore, the water environment carrying capacity (WECC) was found to be extremely low (~0.2 %) and limited by TN and TP. The results demonstrated that the spatiotemporal variations of water quality presented by the EFDC model facilitate an intuitive and comprehensive observation of water quality compliance rates over time and space, providing valuable references for decision-makers. The WEC and WECC of the study area underscored the urgency of N and P coordination control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

With years of green tide outbreaks in the Southern Yellow Sea (SYS) and climate change, early findings over multiple years suggest that the green tide may originate from various pathways. Previous studies have identified attached outbreak species of U. prolifera in the intertidal zone along the SYS coast. However, there has been limited research tracking and monitoring their succession processes or conducting comparative genetic analyses with floating U. prolifera in corresponding years. Therefore, this study continuously monitors the succession process of attached outbreak species of U. prolifera along the SYS coast, utilizing morphological and molecular biological methods to investigate their phylogenetic relationship with floating U. prolifera. The findings suggest that the distribution of the attached outbreak species of U. prolifera occurred in the intertidal zone along the coast of Rudong, Jiangsu Province from February to April 2023. However, subsequent surveys up to March 2024 did not observe their presence again. Apart from May and June 2023, other months consistently exhibited a long-term presence of various species of attached macroalgae, including Ulva flexuosa, Ulva meridionalis, and Ulva linza. The morphological characteristics of the attached outbreak species closely resemble those of the floating U. prolifera. Genetic diversity analysis using ITS and 5S rDNA sequences revealed that all attached outbreak species and floating U. prolifera in the same year belong to the same haplotype with high conservation and consistency in their ITS and 5S rDNA sequences. This study also identified natural shedding among the attached outbreak species, confirming their potential as supplementary sources contributing to Yellow Sea green tide outbreaks along the SYS coast., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025 Elsevier Ltd. All rights reserved.)

Mangrove wetlands are strategic locations for mitigating climate changes. In order to address the harm of rapid climate change to mangrove ecosystems, it is necessary to scientifically predict the fate of mangrove ecosystems, which can be achieved by reconstructing the development history of mangrove forests. This study analyzes the contribution of mangrove-derived organic matter (CMOM) from sediment core F in Phang Nga Province, Thailand by using the endmember mixing model based on stable organic carbon isotopes (δ 13 C org ) and C/N (molar) ratio. The variations of CMOM over the past ∼3195 cal yr BP indicate that mangrove forests underwent three periods of flourishing: ∼3195-2620 cal yr BP, ∼2030-1130 cal yr BP, and ∼410-0 cal yr BP, and two periods of deterioration: ∼2620-2030 cal yr BP and ∼1130-410 cal yr BP. Among the potential factors that might affect the development of mangrove forests, relative sea level (RSL), regional hydrodynamics, and human activities do not have notable effects on mangrove flourishment/deteriorating. However, climate factors, particularly air temperature, rainfall, and sea surface salinity are the main factors influencing the flourishing/deterioration of mangrove forests. In the Andaman Sea, these climatic factors are mainly driven by the Indian summer monsoon (ISM)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2025. Published by Elsevier Ltd.)

Microplastic (MP) pollution has reached the remotest areas of the globe, including the polar regions. In the Arctic Ocean, MPs have been detected in ice, snow, water, sediment, and biota, but their temporal dynamics remain poorly understood. To better understand the transport pathways and drivers of MP pollution in this fragile environment, this study aims to assess MPs (≥ 11 μm) in sediment trap samples collected at the HAUSGARTEN observatory (Fram Strait) from September 2019 to July 2021. MP fluxes determined by μ-Fourier transform infrared (FTIR) imaging ranged from 0 to 2.9 MP m -2 d -1 , peaking in April 2020 and April 2021, with all detected MPs being <300 μm in size. There was no strong correlation between MPs and any of the recorded biogeochemical and physical variables, as each MP flux event was associated with different variables such as biogenic matter, sea ice concentration, or origin. By providing time series data over 21 months, this study provides a baseline for future MP flux assessments in Fram Strait, Arctic., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The Jiaozhou Bay (JZB) intertidal zone is a significant carbon reservoir that plays a crucial role in transporting and accumulating organic matter; however, quantitative studies of organic matter sources are scarce. In this study, we present bulk parameters of total organic carbon (TOC), TOC/TN, δ 13 C, and biomarker contents in 36 surface sediment samples from the JZB intertidal zones to quantify the contribution of organic carbon (OC) derived from terrestrial/marine sources, such as C 3 plants, C 4 plants, estuarine productivity, sewage outlets, and marine productivity. The results demonstrated that a two-end-member model based on the traditional indicators of TOC/TN or δ 13 C is not appropriate for quantifying the OC source. The presence of C 3 plants, C 4 plants, and sewage outlets in the JZB intertidal zone could lead to errors in determining OC contribution when solely using TOC/TN or δ 13 C. A classical mixing diagram (three-end-member model) utilizing TOC/TN and δ 13 C values revealed that OC contribution was dominated by marine productivity throughout the intertidal zone. In the west, the average OC contribution from marine productivity, estuarine productivity, and C 4 plants was 73.8 %, 14.2 %, and 12.0 %, respectively. In the east, the average OC contribution from marine productivity, estuarine productivity, and sewage outlets was 57.6 %, 24.9 %, and 17.4 %, respectively. The higher OC contribution from marine productivity in the west was attributed to the occurrence of Spartina alterniflora, while the OC contribution from estuarine productivity in the east was primarily due to the presence of more rivers flowing into the JZB compared to the west. By combining biomarkers and OC contents, a significant positive relationship verified the suitability of the end-member values selected for the three-end-member mixing model in the west and east intertidal zones of JZB. This finding was further supported by principal component analysis (PCA) analyses of these proxies. This study demonstrated that OC sources in intertidal zones varied among contrasting coastal environmental conditions and addressed the knowledge gap regarding biogeochemical cycles and ecological protection in the JZB intertidal zones., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Marine oil spills lead to intertidal sediment pollution, causing benthic bioaccumulation and toxicity. However, relatively few studies have been conducted on the effects of crude oil sediment pollution on benthos. In this study, Sinonovacula constricta was used as the research object in a sediment environment to study the accumulation and elimination effects of S. constricta on long-term exposure to crude oil pollution as well as the toxicity effects at the biochemical and tissue levels through laboratory exposure tests. The objective of this study was to provide theoretical support for monitoring the biological toxicity of intertidal crude oil pollution. The results showed that S. constricta accumulated petroleum hydrocarbons in the sediment, which were positively correlated with pollution concentration and time. The fitting results of the two-compartment kinetic model were good and could be applied to the accumulation and elimination of sediment crude oil pollution. The activity of antioxidant enzymes and the content of malondialdehyde in the gills were mainly induced, and there was a dose- and time-dependent relationship. Crude oil pollution can cause digestive tube ablation, lumen swelling, and blood cell infiltration in the viscera of S. constricta. S. constricta can be used as an indicator organism for oil pollution in the intertidal zone, and its gills and visceral mass can be used as target tissues., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Glaciers play key roles in capturing, storing, and transforming global carbon and nitrogen, thereby contributing markedly to their cycles. However, an integrated mechanistic approach is still lacking regarding glacier's primary producers (PP), in terms of stable dissolved inorganic carbon isotope (δ 13 C-DIC) and its relationship with dissolved carbon and nitrogen transformation d ynamic changes/cycling. Here, we sampled waters from glaciers, streams, tributaries, and the Indus River (IR) mainstream in the Upper IR Basin, Western Himalaya. Dissolved organic matter (DOM) appears to increase, on average, by ∼2.5-23.4% with fluctuations when passing from glaciers to streams-tributaries-IR mainstream (the upper and lower parts, respectively) continuum, implying that DOM originates from glaciers PP and is subsequently degraded. The corresponding fluctuations are observed for fluorescent DOM (FDOM), dissolved organic nitrogen (8.0-106.8%), NO 3 - -N (-13.5/+16.6%), NH 4 + -N (-8.8/+13.0%), and NO 2 - -N (70.7-217.5%). These variations are associated with overall DOM/FDOM transformations, with the production of ending byproducts (e.g. CO 2 /DIC). The δ 13 C-DIC values fluctuated from glaciers (-5.3 ± 2.5‰) to streams (-4.4 ± 2.1‰), tributaries (-4.3 ± 1.6‰), and IR mainstream (-4.2 ± 1.3‰). The δ 13 C-DIC data are consistent with C transformations that involve lighter CO 2 emission into the atmosphere, whereas highly depleted DIC/CO 2 is the signature of DOM degradation after its fresh production from glaciers PP which originated by photosynthetic activities (e.g. uptake/sink of atmospheric CO 2 : -8.4‰). Finally, glacier-fed meltwaters would simultaneously contribute to the biogeochemical characteristics of downward margins and specific ecosystems (lake/pond/groundwater/hot springs) via transformation dynamics/cycling of dissolved C and N with high photo/microbial lability. Our results highlight the substantial contribution of western Himalayan glaciers-derived DOM to the global C and N cycles., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

CH 4 is among the most potent greenhouse gases. In this study, we investigated one of the important CH 4 production hotspots, the continental margins. We examined the spatiotemporal distributions of CH 4 in sediment cores from the Bohai and South Yellow Seas, China. Using real-time PCR and metagenomic sequencing, we analyzed the microbial communities related to CH 4 production. Our results indicated that concentrations of CH 4 generally increased with depth gradually, minimal seasonal variation observed between spring and summer. Notably, spatial heterogeneity, rather than temporal variation, was the predominant factor affecting CH 4 distribution and methanogen community differences in sediments. Furthermore, the structure of microbial communities, in conjunction with environmental factors, significantly impacts potential CH 4 production. These findings provide valuable insights into the mechanisms underlying methane production and its environmental controls in marine sediments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationship that could have appeared to influence the work reporter in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study conducts an in-depth assessment of the spatial distribution, ecological risks, and correlations among 12 antibiotics, antibiotic resistance genes (ARGs), and dominant microorganisms in a representative river-estuary system, classified by land use and hydrodynamic conditions. Sulfonamides and quinolones were identified as the major contaminants in surface waters, with aquaculture and healthcare wastewater responsible for over 80 % of the antibiotic load. Contrasting seasonal patterns were observed between freshwater (wet season: 215 ng/L, dry season: 99.9 ng/L) and tidal estuaries (wet season: 45.9 ng/L, dry season: 121 ng/L), attributed to antibiotic transport from terrestrial sources or coastal aquaculture areas. The estimated annual antibiotic influx into Jiaozhou Bay was 70.4 kg/year, posing a considerable threat to aquatic algae and disrupting the stability of aquatic food chain. BugBase predictions suggested that antibiotics in the environment suppressed bacteria characterized by biofilm formation (FB) and the presence of mobile elements (CME). However, ARG transmission was likely to drive the spread of CME, FB, and stress-tolerant (OST) bacteria within microbial communities. The significant positive correlations observed between sulfamethoxazole and 63 microbial genera indicate a broad distribution of microbial resistance, which exacerbates the potential for ARG accumulation and dissemination across both the bay and the Yellow Sea., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Seawater-groundwater interactions can enhance the migration process of microplastics to coastal aquifers, posing increased associated environmental risks. Here, we aim to analyze the relationship between seawater intrusion (SWI) and groundwater microplastic pollution in Laizhou Bay (LZB), which is a typical area of sea-land interactions. The results showed that modern seawater intrusion was the main process controlling the migration of microplastics. The detected microplastics in the study area showed a migration pattern from nearshore marine areas to groundwater aquifers along the SWI direction. In addition, the microplastics also reached the brine formed by palaeo-saltwater intrusion through hydraulic exchange between aquifers. By comparing the spatial distributions of different microplastic parameters, we found that nearshore fisheries, commercial, tourism, textile, and agricultural activities were the main sources of microplastics in groundwater in the study area. A risk assessment model of microplastics associated with SWI was further optimized in this study using a three-level classification system by assigning appropriate weights to different potential influencing factors. The results showed moderate comprehensive ecological risks associated with microplastics from seawater intrusion in the study area, with high microplastic enrichment risks. This study provides a scientific basis for future research on seawater-groundwater interactions and microplastic pollution in coastal regions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The demand of lithium (Li) has increased rapidly in recent decades under carbon neutrality strategies, but the environmental fate and potential risks of Li in aquatic ecosystem are barely known. This study conducted a comprehensive field survey in the Yangtze River Estuary (YRE) and the adjacent East China Sea (ECS), to investigate the spatial distribution of dissolved Li and bioaccumulation of Li in the coastal food web. The dissolved Li increased with salinity (from 7.39 to 189 μg L -1 ), controlled by the conservative mixing of Li-enriched seawater and Li-poor riverine water. Negative correlation was observed between Li content and stable nitrogen isotope in the coastal biota, indicating bio-diminish of Li in the food web. Furthermore, the Li contents in muscle tissues were significantly higher in bivalves (as filter-feeders; mean: 0.75 ± 0.41 μg g -1 ) than in fish (as predator; mean: 0.10 ± 0.05 μg g -1 ) and other biota species, indicating that dissolved uptake might be the major exposure pathway for Li. Importantly, it was noticed that the bioaccumulation factors (BAFs) in fish muscle varied greatly (from 0.17 to 5.82), showing lower BAFs for fish inhabiting in marine and benthic regions (with higher salinity and higher dissolved Li concentration). Such inhibition effects of salinity on Li bioaccumulation could not be explained by the modulation of salinity on Li speciation, but highly attributed to the inhibition of high salinity on the dissolved uptake of Li, which was associated with the co-transportation of Li and Na. Our results illuminate the importance of salinity on regulation the spatial variations of dissolved Li and Li bioaccumulation in the YRE and the adjacent ECS, which could help the understanding of Li biogeochemical cycling and potential risks in estuarine and coastal regions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Mercury is a potent neurotoxin. The toxicity of Hg depends on the form in which it occurs, which consequently determines its bioavailability to the organism. The processes of distribution and elimination of Hg in organisms from lower trophic levels are still poorly understood. Therefore, in the present study, great point was paid separately to the soft tissues and hard tissues, which may play an important role in the detoxification of the crab's body from neurotoxicant. The study was conducted on the non-native species: Harris mud crab, collected in 2020. Concentrations of total mercury and its forms were carried out using a Direct Mercury Analyzer, DMA-80 (Milestone, Italy). Sex did not determine the Hg concentration of its forms in R. harrisii. Organism size influenced on crab body processes: biodilution of Hg during growth in summer and bioaccumulation of Hg before stagnation in autumn. The distribution of Hg in the crab's soft tissues and walking legs was related to the trophic origin of the mercury, while halide-bound mercury and semilabile forms and HgS were redistributed into the crab's carapace. This protects the soft tissue of crabs against the toxic effect of Hg. Consequently, a smaller load of Hg in the crabs can be introduced to the circulation or biomagnified in the food web in the region where R. harrisii is an important link of the trophic chain., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

A coupled physical-biogeochemical model is used with numerical experiments to investigate the dynamics controlling the spatiotemporal variability of dissolved oxygen (DO) distribution in the Bohai Sea. The model reproduces distinct seasonal variability of DO concentration in the Bohai Sea as characterized by low in summer with large vertical gradient and high in winter with enhanced ventilation. The evolution of bottom DO-depleted zones at northern and southern depressions is primarily controlled by water stratification and topography but also modulated by lateral transport. High bottom turbulence kinetic energy and weak stratification above the Central Bank of the Bohai Sea induce relatively high DO concentration. A comparison between the model and no-resuspension experiment suggests a slight (<5 %) impact of resuspension on DO concentration variation in the Bohai Sea. The input of terrestrial materials from the Yellow River may provide additional nutrients and phytoplankton, sustaining a relatively weak but stable oxygen production along the transport pathway., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Soil acts as storage for many toxic substances, including mercury and its compounds. However, in addition to its storage function, soil can also be a source of many substances to the aquatic environment. Methylmercury (MeHg) is one of the most toxic form of mercury (Hg) present in the environment. Some studies consider Poland to be one of the major emitters of Hg into both the atmosphere and the Baltic Sea. The purpose of the study was to identify factors affecting the formation and retention of MeHg in the soil as well as it remobilization to the river. Fifteen soil core samples with a length of 200 cm were collected during the fall/winter of 2021-2022. The factors responsible for the inflow and formation of MeHg were precipitation, distance from the riverbank, soil moisture and age of organic matter. MeHg can be transported to topsoil with precipitation. An increase in MeHg concentration was also observed in moist soils located in the vicinity of riverbank. MeHg concentration was lower in soils with degraded organic matter than with fresh organic matter., Competing Interests: Declaration of Competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Ulva prolifera is a dominant species in green tides and has been affecting marine ecosystem for many years. Due to the low availability of CO 2 in the environment, U. prolifera utilizes the CO 2 concentrating mechanisms (CCMs) to increase intracellular inorganic carbon concentration. However, the transcriptional response mechanism and temporal changes of U. prolifera CCMs based on transcriptomics have not been thoroughly described. Therefore, we induced U. prolifera CCMs in a low CO 2 environment to explore the dynamic regulation of CCMs expression under inadequate inorganic carbon supply. The results showed that inorganic carbon limitation increased the inorganic carbon affinity of U. prolifera, upregulating CCMs. The first 24 h of inorganic carbon environmental changes were the most active period for U. prolifera's expression regulation. U. prolifera gradually achieved a new steady state by regulating metabolic processes such as nucleic acids, energy, and ethylene-activated signaling pathways. In the carbon fixation system of U. prolifera, there are characteristics of both biophysical and biochemical CCMs. After 24 h of inorganic carbon limitation, the biophysical CCMs becomes more effective under conditions of inorganic carbon depletion. This study aids in exploring the CCMs of U. prolifera and their evolution in response to environmental changes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Coastal hypoxia, exacerbated by the combined influence of eutrophication and global warming, presents a significant environmental challenge. However, the lag correlation between organic matter (OM) export from the upper layers and bottom dissolved oxygen (DO BOT ) reduction still lack clear elucidation. This study investigated the coupling between net ecosystem production (NEP, representing the maximum OM export) and DO BOT in the Changjiang River plume (CRP), using a wave-driven profiler system. The high-resolution profiles revealed rhythmic fluctuations in water column NEP, with sediment-water exchange (-74.6%) and NEP (-4.0%) dominating DO BOT reduction. Notably, surface NEP impacts DO BOT with a lag time of 25.65 h, indicating an OM sinking speed of 1.32 mm s -1 . NEP at a depth of 3.4 m exerted the most significant influence on DO BOT , explaining a 12% reduction. These findings elucidate the response mechanism of DO BOT reduction to upper OM export and provide insights for hypoxia prediction in coastal and estuarine areas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Over the past 18 years, green tides have persistently occurred in the Yellow Sea. Micropropagules of these algae are key to bloom formation, yet their species composition and succession during dissipation remain underexplored. During the dissipation process of accumulated green tide algae, a large number of micropropagules are released. This study monitored the dissipation of green tide algae at a coastal site, tracking micropropagules in water and sediment using an internal transcribed spacer (ITS) and 5S rDNA primers. Results showed that the dissipation lasted about one month, with significant micropropagule release. Initially, micropropagules matched 5S-II Ulva prolifera, but later species like Ulva torta, Ulva simplex, Ulva flexuosa, and Ulva meridionalis emerged. Ulva meridionalis dominated sediment in July and August, while U. torta was prevalent in water, and U. flexuosa was dominant in other months. Accumulated U. prolifera in the intertidal zone may not contribute to the seeding of the next year's bloom. This study sheds light on the dissipation process and succession patterns of micropropagules in coastal environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study aimed to understand the sources and transport mechanism of organic matter (OM) in the Ganges-Brahmaputra-Meghna (GBM) river system in Bangladesh. We conducted analyses of total organic carbon (TOC), total nitrogen (TN), their stable isotopes (δ 13 C and δ 15 N), and sediment grain size. The results reveal a heterogeneous mixture of OM derived from terrestrial plants, aquatic environments, and anthropogenic sources. The Brahmaputra River exhibited higher concentrations of TOC and TN, with δ 13 C and δ 15 N values indicating that the OM is primarily sourced from C 3 plants. Conversely, the Ganges River demonstrated lower TOC levels and higher isotopic values, reflecting significant anthropogenic inputs. The Lower Meghna showed a mixture of terrestrial and marine sources. Variations in the TOC/TN ratios across the river system underscore the complex interplay between natural and anthropogenic factors. Additionally, sediment grain size plays a crucial role, with finer sediments in the Brahmaputra River associated with increased OM concentrations, while coarser sediments in the Ganges River correlate with lower TOC and TN levels., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The behavior of gases within subsurface pores determines the oil and gas recovery and CO 2 storage in the region. In this study, we report a novel method based on Raman spectroscopy for observing the distributions of CH 4 and CO 2 gases in the pores of sandstone reservoirs. First, we designed a pressure-cell to inject gases into a sample. Then, CH 4 and CO 2 gases were injected into the sample using the pressure-cell placed on the Raman spectroscopy system sample stage. Quartz and feldspar were the predominant minerals in the sample. The CH 4 -occupied pores exhibited a Raman peak at 2917 cm -1 . Two-dimensional (2D) and three-dimensional (3D) mapping of the pores depicted the geometry of the CH 4 gas-filled pores. After injecting CO 2 gas, we observed an intensity peak at 1388 cm -1 ; we obtained 2D and 3D maps of the CO 2 gas-filled pores based on this peak value. This study demonstrates the potential use of Raman spectroscopy as a visualization tool to reveal the pore geometry of sandstone reservoirs and determine the distribution of gases within such reservoirs. Our study can serve as a foundation for understanding the behavior of gases in subsurface reservoirs, improving oil and gas prospecting and exploration, and assessing CO 2 storage. ., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

Redox conditions play a crucial role in determining the fate of many contaminants in groundwater, impacting ecosystem services vital for both the aquatic environment and human water supply. Geospatial machine learning has previously successfully modelled large-scale redox conditions. This study is the first to consolidate the complementary information provided by sediment color and water chemistry to enhance our understanding of redox conditions in Denmark. In the first step, the depth to the first redox interface is modelled using sediment color from 27,042 boreholes. In the second step, the depth of the first redox interface is compared against water chemistry data at 22,198 wells to classify redox complexity. The absence of nitrate containing water below the first redox interface is referred to as continuous redox conditions. In contrast, discontinuous redox conditions are identified by the presence of nitrate below the first redox interface. Both models are built using 20 covariate maps, encompassing diverse hydrologically relevant information. The first redox interface is modelled with a mean error of 0.0 m and a root-mean-squared error of 8.0 m. The redox complexity model attains an accuracy of 69.8 %. Results indicate a mean depth to the first redox interface of 8.6 m and a standard deviation of 6.5 m. 60 % of Denmark is classified as discontinuous, indicating complex redox conditions, predominantly collocated in clay rich glacial landscapes. Both maps, i.e., first redox interface and redox complexity are largely driven by the water table and hydrogeology. The developed maps contribute to our understanding of subsurface redox processes, supporting national-scale land-use and water management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

The transportation of silicon (Si) by rivers to the sea plays a vital role as an external source of Si budget for coastal environments, impacting the carbon cycle in the ocean. Nevertheless, the transport of reactive silica (RSi) from small rivers to the coastal sea has been frequently disregarded in scientific investigations. This research focused on 24 rivers situated along the Bohai Sea (BS) Rim, encompassing small rivers (SR) and the largest river in the region, the Yellow River (YR), to analyze their concentrations and fluxes of dissolved silicate (DSi), biogenic silica (BSi) and other amorphous forms of Si. The findings indicated seasonal variations in DSi concentrations, with higher levels observed during the flood season. Annually, approximately 105 × 10 3  t DSi and 200 × 10 3  t BSi were transported to the BS, with SR and YR contributing equally to the total riverine BSi flux. The smaller rivers were found to increase the BSi fraction of RSi due to elevated biological fixation. The ratios of average DSi and BSi fluxes to the river watershed area of SR were 3.5 and 6 times higher, respectively, compared to those of YR. SR play a critical role in the terrestrial Si export in the BS Rim. Human activities have led to significant deviations in the Si ratios to nitrogen and phosphorus in these rivers from the Redfield-Brzezinski ratio. This discrepancy could impact the phytoplankton community, primary production, and the environment of the BS. The study highlights the substantial contribution of SR to coastal environments, particularly in semi-closed marine environments like the BS., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Dawsonite, as a natural CO 2 tracing mineral, is intimately associated with CO 2 injection and serves as a crucial mineral for geological carbon sequestration. The massive and stable presence of dawsonite in the geological background is a key consideration for CO 2 mineralization capture and plays a significant role in identifying CO 2 geological burial sites. To investigate the optimal conditions for the rapid synthesis of dawsonite using CO 2 , we conducted comparative experiments to examine the three primary influencing factors: temperature (100 °C, 120 °C, 140 °C, 160 °C, 180 °C, and 200 °C), pH (8.5, 9, 9.5, 10, and 10.5), and reaction time (6 and 12 h). Through scanning electron microscopy and X-ray diffraction analysis, the optimal conditions for dawsonite synthesis were determined. The experiments revealed that within the pH range of 8.5-10.5 and at temperatures of 100-180 °C, the dawsonite products obtained are consistently pure, which indicates that CO 2 can be effectively mineralized and sequestered as dawsonite within these temperature and pH ranges. The synthesis yield increased and then decreased with increasing pH and temperature. At 200 °C, the crystallinity of dawsonite decreased and the content of pseudo-boehmite increased. This suggests that higher temperature conditions are not conducive to the mineralization and sequestration of CO 2 . Extending the reaction time did not have a significant promoting effect on the quality of the product. The maximum amount of dawsonite synthesis, good dispersion and homogeneity of crystals, and maximum ratio of mineralization of CO 2 by dawsonite were achieved at a temperature of 140 °C and a pH of 9.5, indicating that these are the optimal conditions for the hydrothermal synthesis of dawsonite using CO 2 . Moreover, these are the optimal geological conditions for the mineralization sequestration of CO 2 in the form of dawsonite., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Scientific research confirms the harmful effects of airborne cyanobacteria and microalgae. However, determining human exposure to these microorganisms remains a challenge. The six-stage Tisch impactor was used to collect bioaerosols from April to September 2020 in the coastal zone of the southern Baltic. The MPPD model was used for estimation of regional, lobar, and generation deposition of microorganisms in human respiratory tract. The mass deposition fraction of cyanobacteria and microalgae in the head region gradually increased with the aerosol size. The maximum deposition fractions in the trachea, bronchial, and the pulmonary region were found for particles between 2.1 and 3.3 μm. The contribution of cyanobacteria and microalgae was the highest in the head region. The majority of microorganisms found in pulmonary region dominated in particles smaller than 2.1 μm. Exposure to the ambient bioaerosols may have an adverse impact on the human health in the region of southern Baltic Sea., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The northwestern shelf of the Black Sea has been affected by eutrophication and bottom hypoxia since the sixties. Consequently, the macrozoobenthos has suffered a well-established decline in biodiversity. However, the nature of the current benthic communities remains questionable. From 1995 to 2017, we compiled species and abiotic data for 138 sites over the shelf. Through an appropriate multivariate analytical approach, we identified benthic community changes solely due to organic pollution variations. Our results show signs of recovery with an increase in biodiversity and proportion of species vulnerable to organic enrichment. These changes were related to a decrease in riverine loads and subsequent eutrophication. However, some long-lived species typical of the area still did not exhibit noticeable recovery, which suggests that either the recovery process has not yet been achieved or some environmental conditions are still not met to warrant a sea floor ecosystem state substantially healthy., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Severine Chevalier reports financial support was provided by Fund for Scientific Research. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study conducted a comprehensive analysis of trace element concentrations in the Upper Indus River Basin (UIRB), a glacier-fed region in the Western Himalayas (WH), aiming to discern their environmental and anthropogenic sources and implications. Despite limited prior data, 69 samples were collected in 2019 from diverse sources within the UIRB, including mainstream, tributaries, and groundwater, to assess trace element concentrations. Enrichment factor (EF) results and comparisons with regional and global averages suggest that rising levels of Zn, Cd, and As may pose safety concerns for drinking water quality. Advanced multivariate statistical techniques such as principal component analysis (PCA), absolute principal component scores (APCS-MLR), Monte Carlo simulation (MCS), etc were applied to estimate the associated human health hazards and also identified key sources of trace elements. The 95th percentile of the MCS results indicates that the estimated total cancer risk for children is significantly greater than (>1000 times) the USEPA's acceptable risk threshold of 1.0 × 10 -6 . The results classified most of the trace elements into two distinct groups: Group A (Li, Rb, Sr, U, Cs, V, Ni, TI, Sb, Mo, Ge), linked to geogenic sources, showed lower concentrations in the lower-middle river reaches, including tributaries and downstream regions. Group B (Pb, Nb, Cr, Zn, Be, Al, Th, Ga, Cu, Co), influenced by both geogenic and anthropogenic activities, exhibited higher concentrations near urban centers and midstream areas, aligning with increased municipal waste and agricultural activities. Furthermore, APCS-MLR source apportionment indicated that trace elements originated from natural geogenic processes, including rock-water interactions and mineral dissolution, as well as anthropogenic activities. These findings underscore the need for targeted measures to mitigate anthropogenic impacts and safeguard water resources for communities along the IRB and WH., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

We investigated the microplastics (MP) abundance, characteristics and pollution severity in the six coral reef ecosystems along the southern and western coasts of Sri Lanka during the southwest monsoon. The small blue-coloured fibres dominated within coral reefs and reef environments. The average coral, surface water and surface sediment MP concentration were 806.64 ± 93.72 particles kg -1 ww, 23.42 ± 5.01 particles m -3 , and 54.11 ± 8.04 particles kg -1 dw, respectively. Coral MP concentration was significantly correlated with surface water (r = 0.65) and surface sediments (r = 0.59) indicating that the reef environment was the source of coral MP enrichment. Coral MP concentration was spatially different (p < 0.05) which may likely be due to the changes in winds, waves, coral biology and plastic sources. MP Pollution Load Index indicated that low MP contamination hazard. Since the presence of MP often deteriorates coral's health, further investigations are necessary to understand the MP's effects on the health of coral reef ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The residual air saturation plays a crucial role in modeling hydrological processes of groundwater and the migration and distribution of contaminants in subsurface environments. However, the influence of factors such as media properties, displacement history, and hydrodynamic conditions on the residual air saturation is not consistent across different displacement scenarios. We conducted consecutive drainage-imbibition cycles in sand-packed columns under hydraulic conditions resembling natural subsurface environments, to investigate the impact of wetting flow rate, initial fluid state, and number of imbibition rounds (NIR) on residual air saturation. The results indicate that residual air saturation changes throughout the imbibition process, with variations separated into three distinct stages, namely, unstable residual air saturation (S gr-u ), momentary residual air saturation (S gr-m ), and stable residual air saturation (S gr ). The results also suggest that the transition from S gr-u to S gr is driven by changes in hydraulic pressure and gradient; the calculated values followed the following trend: S gr  > S gr-u  > S gr-m . An increase in capillary number, which ranged from 1.46 × 10 -7 to 3.07 × 10 -6 , increased S gr-u and S gr-m in some columns. The increase in S gr ranged from 0.034 to 0.117 across all the experimental columns; this consistent increase can be explained by water film expansion at the primary wetting front along with a strengthening of the hydraulic gradient during water injection. Both the pre-covered water film on the sand grain surface and a pore-to-throat aspect ratio of up to 4.42 were identified as important factors for the increased residual air saturation observed during the imbibition process. Initial air saturation (S ai ) positively influenced all three types of residual air saturation, while initial capillary pressure (P ci ) exhibited a more pronounced inhibitory effect on residual air saturation, as it can partly characterized the initial connectivity of the air phase generated under different drying flow rates. Under identical wetting flow rate conditions, S gr was higher during the second imbibition than during the first imbibition due to variations in initial fluid state, involving both fluid distribution and the concentration of dissolved air in the pore water. In contrast, NIR did not have an obvious effect on the three types of residual air saturation. This work aims to provide empirical evidences and offer further insights into the capture of non-wetting phases in groundwater environments, as well as to put forward some potential suggestion for future investigations on the retention and migration of contaminants that involves multiphase interface interactions in subsurface environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A total of 222 surface sediments were collected in the Ulleung Basin, southwestern East/Japan Sea, from the coast to the basin and analyzed for grain size, total organic carbon, biogenic silica and major and trace elements. The metal concentrations of the surface sediments were highly spatially variable, and their distributions were grouped into four types by factor analysis: waste dumping materials (Cr, Cu, Zn, Sn, Sb, and Pb); detrital materials (Al, Fe, and Cs); suboxic diagenetic materials (Mn, Mo, Co, and Ni); and anoxic diagenetic materials (Cd and U). From core samples collected near the dumping site, approximately the top 10 cm was well mixed in the 210 Pb ex profiles and highly enriched in the above metals related to dumping materials. The enrichment factor of Sn indicates dumping materials well, and its distribution can be used to estimate the dispersion range of the dumped material in this basin., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Since plastic waste has become a worldwide pollution problem, studying the ability of marine microorganisms to degrade plastic waste is important. However, conventional methods are unable to in situ real-time study the ability of microorganisms to biodegrade plastics. In recent years, Raman spectroscopy has been widely used in the characterization of plastics as well as in the study of biological metabolism due to its low cost, rapidity, label-free, non-destructive, and water-independent features, which provides us with new ideas to address the above limitations. Here, we have established a method to study the degradation ability of microorganisms on plastics using confocal Raman imaging. Alternaria alternata FB1, a recently reported polyethylene (PE) degrading marine fungus, is used as a model to perform a long-term (up to 274 days) in situ real-time nondestructive inspection of its degradation process. We can prove the degradation of PE plastics from the following two aspects, visualization and analysis of the degradation process based on depth imaging and quantification of the degradation rate by crystallinity calculations. The findings also reveal unprecedented degradation details. The method is important for realizing high-throughput screening of microorganisms with potential to degrade plastics and studying the degradation process of plastics in the future., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

The concentrations, spatial distributions, pollution level, and health risks of heavy metals in sediments of the Sharm Obhur, Northern Jeddah, Saudi Arabia were evaluated. Average concentrations were found to be: Cr > Zn > Ni > Cu > As>Pb with the highest concentrations found near the head of the sharm, and decreasing towards the mouth. Environmental indices, together with the statistical analyses, showed that the sharm experiences a low to moderate degree of pollution. Sampling sites with heavy metal contamination are concentrated near the head and the southern coast of the sharm, where intensive human activities associated with a boat dock, construction, and recreation are common. The mean carcinogenic risk (CR) values of As, Cr and Ni are at permissible level suggesting unlikely adverse impacts of heavy metals on human health. Despite acceptable CR values; however, serious non-carcinogenic and carcinogenic health threats from metals may yet be an issue particularly for sensitive populations such as children., Competing Interests: Declaration of competing interest The authors contributed in this work declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

As human activities become more intensive, a substantial number of heavy metals are discharged into estuarine or wetland environments. Due to the poor degradability, heavy metals are prone to adsorption and deposition on suspended particles in bottom sediments. Subsequently, under the influence of disturbances, there is a potential for their re-release, causing secondary pollution. To investigate the release process of the heavy metal Cr from sediment, laboratory experiments were conducted under both unidirectional flow and regular wave conditions. At the initial stage, the temporal trends of particulate (Cr P ) and dissolved (Cr D ) Chromium concentrations were both characterized by initial increments followed by stabilization and continuous escalation. Vertically, the stable concentrations of Cr P and Cr D increased with the presence of vegetation and the enhancement of hydrodynamics. The Elovich equation, pseudo-second-order kinetic equation, Double constant equation (Freundlich model), and parabolic diffusion equation were employed to predict the release process of Cr D from bottom sediment. The Elovich equation proved most suitable for describing the release process of Cr D , with an R 2 exceeding 0.9. In order to assess the influence of vegetation on the Cr release process, the Stem-Reynolds were introduced to modify the Elovich equation. The final maximum error was 12 % (excluding the initial stage), which was much lower than that using the original Elovich equation (maximum error of 32 %). The study findings provide practical support for estuarine and wetland managers to formulate effective heavy metal management measures, which contribute to the conservation and sustainable management of aquatic ecosystems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Manganese (Mn) is a vital micronutrient and participates in multiple biochemical reactions and enzyme catalytic activities. Its cycling is tightly connected with iron (Fe) and nitrogen (N). Although coastal sediments are recognized as an important source of dissolved Mn to marine waters, this contribution remains inadequately quantified. In the summer of 2019 and 2020, we investigated benthic fluxes of dissolved Mn, Fe and ammonia (NH 4 + ) in the Changjiang Estuary and East China Sea shelf using the 224 Ra/ 228 Th disequilibrium approach. Our results showed that the availability of reactive Mn oxides (Mn D ) played a crucial role in sedimentary Mn regeneration, as revealed by the positive correlation (r = 0.75, P < 0.05) between Mn fluxes and Mn D contents. In addition, the positive correlation (r = 0.80, P < 0.01) between the decomposition rates of sedimentary organic matter (NH 4 + flux) and Mn fluxes suggested that the reduction of Mn D was mainly driven by the organic carbon oxidation. Furthermore, NH 4 + and Mn fluxes exhibited an exponential increase against the product of dissolved oxygen concentration (DO) and the amplification factor of sediment surface area (ξ). In this context, ξ represents the rate of bottom water DO pumped into the sediment via physical reworking and bio-irrigation. In contrast to the most efficient Fe released from sediment overlain by hypoxic waters (DO <62.5 μM), the maximum Mn flux (63.5 ± 9.4 mmol m -2 d -1 ) was observed at sediment with oxygenated bottom waters (DO = 158 μM). This implies that the regeneration of Mn was associated with a more permissive redox state compared to that of Fe. We further demonstrated that Mn flux was 1-2 orders of magnitude higher than those estimated through traditional methods. Therefore, coastal sediments may contribute more Mn to ocean waters than previously thought. The precise estimation of Mn release from coastal sediments holds critical significance for research on the global Mn budget., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Marine litter poses a significant environmental challenge in the Saronikos Gulf, Greece. Employing an integrated approach, data from both beach and underwater sites were analyzed. The average litter density on beaches was 2.61 items m -2 , with plastic being the most common material, notably small polystyrene fragments and cigarette butts. The western part of the Gulf exhibited higher litter density, mainly due to surface circulation patterns. Most beaches fell short of meeting Good Environmental Status criteria for marine litter. Higher litter densities were observed in autumn. Benthic litter density decreased with depth, being 23 times higher in shallower waters, with plastic being the predominant type. This extensive study offers crucial insights into the pollution status and litter distribution in the Saronikos Gulf, contributing significantly to the global understanding of marine litter distribution on coastal ecosystems. Such information is crucial for raising awareness, informing policy decisions, and driving environmental actions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The accumulation of heavy metals from sewage and garbage dumping can seriously impact beach tourism and thus the local economy, but it is difficult to quickly and accurately determine the pollution location and source of heavy metals and clarify their diffusion range. This study investigates a new in situ magnetic testing method to address this issue. (1) The in situ method can be used to effectively and quickly evaluate heavy metal sources and diffusion ranges based on the distribution of κ values. (2) According to chemical experiments, the specific elements polluting a beach can be determined, such as the Cr, Ni, Zn, and Fe pollution of Beach No. 3. (3) Although κ values for assessing heavy metal pollution on different beaches vary, metal pollution occurs when the higher κ value is more than 50 times the lower κ value on the same beach. (4) The κ values vary in different seasons due to the influence of natural factors and urban seasonal sewage policies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study comprehensively assesses spatial distribution, pollution levels, and potential sources of heavy metal(loid)s in surface sediments across multiple river systems along the coastal area of the East China Sea. Copper in Qiantang River and Xiangshan Bay showed higher concentations and exceeded the threshold effect value, while the higher content of Lead was mainly found in the Saijiang River, Oujiang River, and Minjiang River. Heavy metal(loid)s in the alluvium of Qiantang River, Jiaojiang River, and Yangtze River showed low to moderate pollution levels, with Cd posing the highest ecological risk, followed by Hg. Meanwhile, Qiantang River, Jiaojiang River, Yangtze River, and Oujiang River exhibited considerable to moderate ecological risks and low toxic risk. PMF model analysis results reveal that concentrations of Cr, Ni, and As were closely related with natural geogenic input (36.56 %), while industrial and traffic activities (48.77 %) were primary source of Cu, Pb, Zn, and Hg, and main source of Cd was agricultural emissions (14.67 %)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Planktonic organisms, which have direct contact with water, serve as the entry point for mercury (Hg), into the marine food web, impacting its levels in higher organisms, including fish, mammals, and humans who consume seafood. This study provides insights into the distribution and behavior of Hg within the Baltic Sea, specifically the Gulf of Gdańsk, focusing on pelagic primary producers and consumers. Phytoplankton Hg levels were primarily influenced by its concentrations in water, while Hg concentrations in zooplankton resulted from dietary exposure through suspended particulate matter and phytoplankton consumption. Hg uptake by planktonic organisms, particularly phytoplankton, was highly efficient, with Hg concentrations four orders of magnitude higher than those in the surrounding water. However, unlike biomagnification of Hg between SPM and zooplankton, biomagnification between zooplankton and phytoplankton was not apparent, likely due to the low trophic position and small size of primary consumers, high Hg elimination rates, and limited absorption., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

In coastal sediments characterized by substantial terrestrial input, the Redfield ratio may not be adequate to determine whether phosphorus (P) is preferentially remineralized relative to carbon (C). Employing a two end-member δ 13 C mixing model, we observed a gradual decrease in the fraction of terrestrial organic matter as the distance from the river mouth increased. Consequently, the C/P ratio of sedimentary organic matter before early diagenetic alteration (C u /P u ) decreased from 213 ± 26 to 126 ± 4. In contrast, the C/P ratio of sedimentary organic matter after early diagenetic alteration (C org /P org ) increased from 208 ± 32 to 265 ± 23. The deviation of C org /P org ratios from C u /P u ratios suggests that P was preferentially remineralized from organic matter relative to C. Moreover, the degree of preferential remineralization (DPR) of P, represented by (C org /P org )/(C u /P u ), increased with the distance from the river mouth, suggesting a connection to cross-shelf transport. Besides preferential P remineralization, the control mechanisms for P regeneration from sediments strongly depend on the dissolved oxygen (DO) levels of bottom water. Under oxygenated bottom water (DO >120 μM), the precipitation of Fe oxides reduced benthic DIP flux, resulting in a C/P ratio in flux well above the C u /P u ratio (1813 ± 725 vs. 213 ± 26). Conversely, when bottom water DO was low (DO<100 μM), the dissolution of Fe oxides and preferential P remineralization increased DIP fluxes, but the precipitation of authigenic apatite suppressed DIP fluxes, leading to C/P ratios in flux approximating C u /P u ratios (129 ± 35 vs. 158 ± 10 and 200 ± 82 vs. 141 ± 7). In a moderate redox state (100 < DO <120 μM), preferential P remineralization and the dissolution of Fe oxides increased DIP fluxes, resulting in C/P ratios in flux below C u /P u ratios (29 ± 8 vs. 131 ± 5 and 15 ± 6 vs. 126 ± 4)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Planktonic bacteria play a crucial role in sustaining the ecological balance of aquatic ecosystems. However, their seasonal variations in different aquaculture areas within the East China Sea, along with their correlation to environmental factors, have not been extensively explored. In this study, each area with 3 sample points were set up to represent the fish aquaculture area, shellfish aquaculture area and non-aquaculture area. In 2019, we undertook four marine surveys along the Xiasanhengshan uninhabited island, during which we gathered surface seawater samples for both physicochemical analysis and high-throughput sequencing. This allowed us to obtain data about the physicochemical properties and microbial composition in each surveyed region. A short-term eutrophication phenomenon was present in the sea, and the spatial and temporal distribution of planktonic bacteria differed based on the mariculture area. At the phylum level, Proteobacteria accounted for >50 % of the community abundance in winter, spring, and autumn, while Cyanobacteria accounted for >30 % of the community abundance in summer. Because Cyanobacteria blooms are likely in summer, the relationship between Cyanobacteria and environmental factors was studied. Redundancy analysis showed that Cyanobacteria were consistently positively correlated with phosphate. Eutrophication and abnormal proliferation of Cyanobacteria in the study area necessitate ameliorations in the mariculture structure. The variation of genus in Proteobacteria is consistent with that of eutrophication, so some genera in Proteobacteria have the potential to become biological indicator species., Competing Interests: Declaration of competing interest The authors declare that this study contains no conflict of interests., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study investigated the sources of sedimentary organic matter (OM) in the Yangtze River estuary (YRE), using multiple biomarkers. The results of stable carbon isotope (δ 13 C) and total organic carbon to nitrogen ratio (TOC/TN) suggests the contribution of marine-derived OM significantly increased seawards, while fatty acid (FA) composition provides more specific information on OM sources. In total, 30 components of FAs were identified at the studied 17 sites, which mainly composed of phytoplankton FA, followed by ubiquitous FA and bacterial FA, while terrestrial FA contributed less to the total FAs. Under the strong impacts of the large physicochemical gradients in the YRE, TOC, TN and FA components showed higher concentrations in the estuary mixing zone (especially within the turbidity maximum zone), attributing to their strong binding with OM-enriched fine particles. The spatial heterogeneity of sedimentary OM sources was highly impacted by salinity and Chl-a, as well as bacteria-mediated OM degradation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The transport of microplastics (MPs) is susceptible to being influenced by catchment hydrology; however, there is a notable lack of research on their retention and responses to flood events in estuarine sedimentary records. Herein, we collected two cores in the Yangtze Estuary to explore their microplastic pollution, influencing factors and linkage to flood events. MP abundance exhibited a decreasing trend from the top to the bottom in both cores. Both plastic production and sediment mean grain size showed a significant positive correlation with MP abundance. The sedimentary record displayed a marked surge in MP abundance during the extreme flood period, suggesting a direct influence of flooding on MP deposition. The resuspension of upstream MPs and erosion of land-based MPs by heavy rain might be responsible for this increase. Furthermore, our study identified significant periodicities in MP abundance, closely aligned with the hydrological patterns of the Yangtze River. This study highlights the role of floods in fluvial MP distribution and proposes MPs as a proxy of extreme floods from the 20th century in estuarine environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Magnetic spherules originate from anthropogenic and natural sources and can be differentiated based on morphology and composition. Using magnetic measurement, diameter measurement, scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) analysis of a 10 m sediment core in the mud area of the South Yellow Sea, we found that magnetic spherules occur at all observed depths of the core. The magnetic spherule concentrations vary from 10 spherules/0.5 g to 62 spherules/0.5 g. Here, concentrations generally less than 10 spherules/0.5 g are considered as the background value in the core. The peak value of magnetic spherules appeared at the 0.02, 0.3, 2 and 8 m, and their concentrations are 62, 52, 36, 48 spherules/0.5 g, respectively. According to the deposition age, concentration, diameter, morphology and chemical characteristics of the spherules, it is found that the spherules at 0.02 m are produced by industrial coal burning. A volcanic eruption event was the main responsible for the accumulation of spherules at 0.3 and 8 m, while the spherules located at 2 m are related to a wildfire event. Magnetic spherules are common in continental shelf regions and can well document the human activities and natural environment events., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Lakes, as vital components of the Earth's ecosystem with crucial roles in global biogeochemical cycles, are experiencing pervasive and irreparable worldwide losses due to natural factors and intensive anthropogenic interferences. In this study, we investigated the long-term dynamic patterns of the Tonle Sap Lake, the largest freshwater lake in the Mekong River Basin, using a series of hydrological data and remote sensing images between 2000 and 2020. Our findings revealed a significant decline in the annual average water level of the lake by approximately 2.1 m over 20 years, accompanied by an annual average reduction in surface area of about 1400 km 2 . The Tonle Sap Lake exhibited episodic declines in water level and surface area, characterized by the absence of flooding during the flood season and increasing aridity during the dry season. Furthermore, the shoreline of the lake has significantly advanced towards the lake in the northwestern and southern regions during the dry season, primarily due to sedimentation-induced shallowing of the lake edge depth and decreased water levels. In contrast, lake shorelines in the eastern region remained relatively stable due to the constructed embankments for the protection of the cultivated farmland. While the seasonal fluctuations of the Tonle Sap Lake are regulated by regional precipitation in the Mekong River Basin, the prolonged shrinking of the lake can be mainly ascribed to intensive anthropogenic activities. The interception of dams along the upper Mekong River has resulted in a decrease in the inflow to Tonle Sap Lake, exacerbating its shrinkage. Moreover, there are minor impacts from agricultural land expansion and irrigation on the lake. This study highlights the driving forces behind the evolution of Tonle Sap Lake, providing valuable information for lake managers to develop strategies aimed at conserving and restoring the ecological integrity of the Tonle Sap Lake., Competing Interests: Declaration of competing interest The authors declare that there are no conflicts of interest regarding the submitted paper of “Profiling dynamics of the Southeast Asia's largest lake, Tonle Sap Lake”., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Coastal subsidence is a geological disaster that has devastating consequences. However, an accurate understanding of its risks involves more than simply assessing the amount or rate of land subsidence. The existing methods used to evaluate geological disaster risks depend on extensive data collection, entail substantial workloads, suffer from error estimation challenges, and lack regional adaptability. These limitations prevent us from fully understanding coastal subsidence risks in estuarine deltas. Therefore, in this study, we propose a new subsidence risk assessment method that addresses the challenges of traditional geological risk assessments in terms of spatial coverage, spatiotemporal resolution, and data collection difficulty. First, Sentinel-1 multitemporal interferometric synthetic aperture radar (MT-InSAR) and cluster analysis were used to estimate the subsidence hazards. Subsequently, Landsat-8 imagery and a random forest (RF) classifier were used to obtain land use and land cover (LULC), and the analytic hierarchy process (AHP) was used to obtain settlement vulnerability. Thereafter, subsidence susceptibility was derived from the sediment layer thickness. By combining subsidence hazard, vulnerability, and susceptibility, the first subsidence risk map with a 30 m resolution was generated. The results showed that 4.54 % of the Yellow River Delta (YRD) area was high-risk, 8.75 % was medium-risk, and 10.14 % was low-risk. Notably, the risk map shows a clear overlap between high-risk and saltwater mining areas in the YRD. The proposed method is expected to improve our understanding of the coastal subsidence risk in estuarine deltas. Considering that the risk in high-value economic areas in the YRD is increasing, whereas the risk in low-value economic areas may change owing to human activity, early preventive measures are required., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Mangrove forests can help to mitigate climate change by storing a significant amount of carbon (C) in soils. Planted mangrove forests have been established to combat anthropogenic threats posed by climate change. However, the efficiency of planted forests in terms of soil organic carbon (SOC) storage and dynamics relative to that of natural forests is unclear. We assessed SOC and nutrient storage, SOC sources and drivers in a natural and a planted forest in southern Thailand. Although the planted forest stored more C and nutrients than the natural forest, the early-stage planted forest was not a strong sink relative to mudflat. Both forests were predominated by allochthonous organic C and nitrogen limited, with total nitrogen being a major driver of SOC in both cases. SOC showed a significant decline along land-to-sea and depth gradients as a result of soil texture, nutrient availability, and pH in the natural forest., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: PEI SUN LOH reports financial support was provided by Asia-pacific Network for Global Change Research. CHOON WENG LEE, CHUI WEI BONG reports financial support was provided by Ministry of Higher Education Malaysia for the HICoE Phase II fund (HICoE IOES-2023C). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)