Microbial communities in subterranean estuaries play important roles in the biogeochemical cycle. However, the microorganisms associated with biogeochemical behaviors in subterranean estuaries have received little attention. Here, the bacterial communities were compared between the fresh and saline groundwater in a subterranean estuary. Correlation analysis between bacterial groups and salinity indicated that different species represented different groundwater types. The key bacterial groups found along the subterranean estuaries have been shown to influence organic pollutant degradation and nitrate utilization. These species may be potential candidates for the in situ bioremediation of subterranean estuaries that are contaminated with pollutants. The utilization of nitrate and organic pollutants by bacteria in subterranean estuaries serves as a nitrate sink and inorganic carbon source. Our results show the role of bacteria in remediating pollutants through submarine groundwater discharge (SGD) to the coastal ocean, and specific species may be helpful in selecting reasonable groundwater end-members and reducing SGD uncertainties.

Prior studies indicated salt marsh periwinkles (Littoraria irrorata) were strongly impacted in heavily oiled marshes for at least 5 years following the Deepwater Horizon oil spill. Here, we detail longer-term effects and recovery over nine years. Our analysis found that neither density nor population size structure recovered at heavily oiled sites where snails were smaller and variability in size structure and density was increased. Total aboveground live plant biomass and stem density remained lower over time in heavily oiled marshes, and we speculate that the resulting more open canopy stimulated benthic microalgal production contributing to high spring periwinkle densities or that the lower stem density reduced the ability of subadults and small adults to escape predation. Our data indicate that periwinkle population recovery may take one to two decades after the oil spill at moderately oiled and heavily oiled sites, respectively.

The daily accumulation rates, composition, sizes and potential sources of marine litter collected on a remote island within the Western Indian Ocean were investigated. In total, 9119 items of marine litter were collected during 40 surveys, which equated to 0.0082 items·m⁻¹·d⁻¹. Between 2003 and 2019 there was a significant increase in the amount of litter deposited, with the highest daily accumulation rate recorded in 2019 (0.0255 items·m⁻¹·year⁻¹). All specific litter types increased over time and also differed significantly in their accumulation rates, with polystyrene fragments/pieces (0.00249 items·m⁻¹·d⁻¹), plastic items (0.00135 items·m⁻¹·d⁻¹) and plastic bottles (0.0011 items·m⁻¹·d⁻¹) being the most commonly encountered during this study. The majority of the litter found was ≤5 cm in size. Nearly all (>80%) litter collected was made of or contained some form of plastic. Recommendations for improved management of litter and the importance of establishing regular beach clean-ups within the Seychelles are briefly discussed.

Microplastics are an emerging concern for the health of marine ecosystems. In the southeastern US, the filter-feeding Eastern oyster, Crassostrea virginica, is susceptible to microplastic ingestion. We quantified the distribution of microplastics within adult oysters (harvestable size >7.5 cm) from 28 reefs throughout a rural estuary with limited riverine inputs (St. Catherines Sound, Georgia). To determine which variables best predict microplastic concentration in oysters, we also quantified oyster recruitment, distance to ocean, fetch, and water body width. Oysters averaged 0.72 microplastic particles per individual (0.18 particles per gram wet mass); microfragments and microplastics were equally abundant. Although microplastic concentrations were low, multivariate models identified a positive effect of water body width on the site-level concentration of plastic microfibers; average microfragment length was affected by fetch. Our work informs a growing understanding of microplastic distribution in coastal estuaries, providing an important rural contrast to the urbanized estuaries that have been examined.

The temporal–spatial distribution of marine autotrophic picoplankton (APP) in the central Bohai Sea was investigated in April (spring), June (early summer), August (summer), and October (autumn) in 2015 through a combination of HPLC-pigment method and flow cytometry. Flow cytometry results showed that APP was composed of Synechococcus (Syn) and pico-eukaryotes (PEUKs). The lowest average abundances of Syn and PEUKs was obtained in April. Afterward, the average APP density substantially increased, and Syn dominated the total cell abundances. Although generally outnumbered by Syn, PEUKs were the larger contributor to total APP carbon biomass (>52%) in all the cruises, except in August, when Syn bloomed. Compared with the cytometric method, HPLC-pigment CHEMTAX revealed a more sophisticated diversity of APP community. In April, diatoms were the main contributor to pico-Chl a, whereas prasinophytes became the main contributor in June and October. Syn bloom was evidenced by CHEMTAX, which revealed that it contributed 69.3% of Chl a in August. Redundancy analysis suggested that temperature was the main factor influencing the distribution of APP. Moreover, nutrients and their structures had some effects, which depended on different APP groups in the area. The accordance between CHEMTAX and cytometric method was evaluated through correlation analysis. A significantly positive correlation between cell abundance and CHEMTAX-derived Chl a was observed for Syn in August and PEUKs in June. Nevertheless, further study is needed owing to the observed discrepancies between the methods.

The occurrence of antibiotic resistance genes (ARGs) and their associated environmental factors in estuaries are poorly understood. In this study, we comprehensively analyzed ARGs in both water and sediments from inlet to outlet of the Yangtze Estuary, China. The relative abundances of ARGs were higher in the turbidity maximum zone (TMZ) than other sites, implying that suspended particulate matter (SPM) was the major reservoir for ARGs in water. ARGs showed an increasing trend from inlet to outlet in sediments. Positively correlation between intI1 and sul1 in both water and sediments indicated that sul1 may be regulated by intI1. Correlation analysis and redundancy analysis showed that the spatial variations of estuarine ARGs were positively correlated with sample properties (e.g., temperature, SPM, pH) and chemical pollutants (e.g., heavy metals and antibiotic residues), among which chemical pollutants were the major drivers for the ARG distribution in both water and sediments.

In this present paper, the distribution of toxic metals and sediment quality were evaluated in five sampling points of the Itapicuru-Mirim River located in the city of Jacobina, Bahia, Brazil. The concentration of the elements arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) were determined from sediment samples collected from the superficial layer (0–10 cm) in November 2013. After the samples' total decomposition, the total concentration of metals was determined by inductively coupled plasma optical emission spectrometry (ICP OES), except for Hg, which was measured by inductively coupled plasma atomic emission spectrometry (ICP AES). A geochemical evaluation of sediment quality was performed using enrichment factor (EF), geoaccumulation index (Igₑₒ), and pollution load index (PLIThe results of the total concentrations in the analyzed sediment samples were compared with the threshold effect levels (TELs) and probable (PELs) effect levels (PELs) in sediment quality guidelines (SQGs). For the fraction <75 μm, the decreasing order for the metal concentrations was (ppm): Fe (10.86%) > Mn (120.8) > Cr (122) > Zn (76.5) > Pb (49.6) > Cu (32.6) > Ni (28.6) > Hg (0.31) > Cd (0.13). Igₑₒ suggested a moderate to seriously polluted category for Hg and moderately polluted for Cu. Generally, the results indicated probable risks to the biota caused by Cr, Ni, Pb, and Hg metals. However, only Hg, Cd, and Cu were of anthropogenic origin. Although the sediments are relatively preserved from pollution by these metals, there is a progressive deterioration of this compartment downstream of the Itapicuru-Mirim River in the city of Jacobina.

Pollution in aquatic ecosystems is rapidly becoming one of the world's greatest ecological challenges. Given their intermediate position between terrestrial and marine environments, estuarine systems are especially vulnerable to human pollution. Amazonian estuaries have unique characteristics, such as heterogeneous landscape intercalating tracts of vegetation with sandbanks and beaches. In the present study, we provide the first qualitative and quantitative data on litter retention in an Amazonian estuary, comparing vegetated and bare substrate areas. Overall, 12,003 items were recovered, with a mean ± SD density and weight of 1.69 ± 2.16 items/m² and 78.08 ± 93.11 g/m², respectively. Plastic was the principal material (80.97%) found. The highest number of items was found in the vegetated habitats (73.11%), indicating these areas as the most affected by plastic pollution. Our findings provide important insights for future research planning and implementation of effective public policies for conservation and management of these important ecosystems.

The abundance and distribution of microplastics in estuaries have been barely documented, and generally without accounting for the vertical structure in the water column. This study presents the very first data on the occurrence and distribution of microplastics in the Adour Estuary, SW France. The experimental data set was complemented by numerical simulations to gain understanding of the behaviour of suspended microplastics. Microplastics were found throughout the water column with a mean abundance of 1.13 part/m³. Films and fragments were the most abundant types of particles collected. Numerical simulations demonstrated that vertical distribution of microplastics in the water column is highly dependent on particle characteristics and on the local hydrodynamics. The main trend is that neutrally-buoyant microplastics are easily flushed out while heavier microplastics are prone to entrapment in the estuary, in particular under low discharge conditions. The present study suggest that estuaries could be a sink of microplastics.

Microplastics (<5 mm) are present in marine ecosystems worldwide where they can be ingested by a wide range of organisms from different trophic levels. In this study we analyzed the gastrointestinal tract of 443 specimens of Stellifer brasiliensis (124 juveniles, 254 subadults, and 65 adults) sampled in tropical beaches adjacent to the Paraíba River estuary. We found 1–3 microplastics in 42 fishes (9.48%), averaging 1.31 ± 0.52 microplastics per fish. The number of ingested microplastics by the different ontogenetic stages was statistically similar, but the adults had a higher ingestion frequency (13.8%). Among subadults, the condition factor of fishes that ingested microplastics was significantly smaller (p < 0.05) than those that had not ingested them. The ingestion of microplastics by the different ontogenetic stages of S. brasiliensis reflects the availability of this pollutant in the studied environment and highlights the vulnerability of fishes and other organisms through food webs.