Ocean Outfall Research Articles

Concentrations and Characteristics of Polybrominated Diphenyl Ethers (PBDEs) in Marine Zooplankton from the Gaoping Waters of Southwestern Taiwan

Bioaccumulation by zooplankton is the outset for persistent organic pollutants that enter the marine food chain. Owing to a full spectrum of anthropogenic activities, the Gaoping waters of southwestern Taiwan are exposed to large quantities of polybrominated diphenyl ethers (PBDEs). However, information on these contaminants in zooplankton in this study area is lacking. In this study, we analyzed 19 PBDE congeners concentrations in 36 zooplankton samples from the Gaoping waters. A high variation in the total PBDE concentrations in zooplankton (from not detected to 1415 ng g−1 dry weight) was found, with the highest PBDE levels being recorded near the entrance of the Kaohsiung Harbor (KH). Significantly higher levels were noted for the KH transect than for the Gaoping River estuary (GR) and Fengshan Township (FS) transects, indicating that PBDE inputs originate from the ocean sewage outfalls. BDE-15 (43%) and BDE-209 (16%) were the predominant PBDE congeners in the zooplankton. Our results suggest that anthropogenic activities might predominantly contribute to significantly high PBDE concentrations. The traditional food web may easily transport these higher levels of PBDEs in zooplankton to higher trophic levels of marine organisms, since the Gaoping waters serve as essential nursery and spawning grounds for invertebrates and fishes.

Non-proportional distribution and bioaccumulation of metals between phytoplankton and zooplankton in coastal waters.

Metal concentrations were concurrently quantified in seawater, phytoplankton, and zooplankton from a heavily impacted coast of southern Taiwan. Combined size and density fractionation were used to accurately quantify metal concentrations in phytoplankton. Cr, Co, Ni, Cu, As, and Pb were analyzed using an inductively coupled plasma mass spectrometer (ICP-MS). As expected, metals significantly increased with an order of seawater<phytoplankton<zooplankton (p<0.05); but did not differ between estuarine, nearshore, and offshore sites (p>0.05). Metals were higher along Kaohsiung Harbor and marine outfall diffusion sites, highlighting their major impacts on plankton metal contamination. Notably, phytoplankton (Cr BCF>100; half of the sites) significantly accumulated more metals contrary to zooplankton (BAF<10). Metal concentrations and bioaccumulation factors between phytoplankton and zooplankton showed significant negative correlations. This demonstrates a non-proportional distribution and bioaccumulation of metals in phytoplankton and zooplankton-corroborating laboratory findings on zooplankton ability to control metals, irrespective of significantly high bioaccumulation in phytoplankton.

Modelling and simulation of a hydropower system using wastewater discharged from Marine outfalls

Municipal or industrial wastewater from the treatment plant is discharge by marine outfalls through the use of a pressurized pipeline scheme. The wastewater is discharged deep under the sea surface at a distance from the coast. During discharging of the wastewater, the excess pressure is applied to push the wastewater deep under the sea. The operation of allowing the wastewater to be discharge far away from the coast, takes the environmental perspective into consideration. However, from engineering perspective, significant amount of energy is wasted during discharging of wastewater and can be recovered. Hence, the aim of this paper is to model and simulate an energy recovery system able recover some of the energy wasted, using a hydro-turbine and generator in a hydropower scheme. The simulation results, for the South African Green Point outfall, have demonstrated that the marine outfalls have the potential to generate electrical energy during discharging of the wastewater. Using a 16-kW permanent magnet synchronous generator, the load demand of a 16 kW resistive load was met at a nominal voltage of 313 Vrms. Given the constant discharge flowrate of 28.4 × 106 litres of wastewater per day at Green Point outfall site, a significant amount of electrical energy can be generated.

Microbiome profiling and characterization of virulent and vancomycin-resistant Enterococcus faecium from treated and untreated wastewater, beach water and clinical sources

Vancomycin-resistant Enterococcus faecium (VREfm) is an opportunistic pathogen among the highest global priorities regarding public and environmental health. Following One Health approach, we determined for the first time the antibiotic resistance and virulence genes, and sequence types (STs) affiliation of VREfm recovered simultaneously from marine beach waters, submarine outfall of a wastewater treatment plant and an offshore discharge of untreated sewage, and compared them with the surveillance VREfm from regional university hospital in Croatia to assess the hazard of their transmission and routes of introduction into the natural environment. Importantly, VREfm recovered from wastewater, coastal bathing waters and hospital shared similar virulence, multidrug resistance, and ST profiles, posing a major public health threat. All isolates carried the vanA gene, while one clinical isolate also possessed the vanC2/C3 gene. The hospital strains largely carried the aminoglycoside-resistance genes aac(6′)-Ie-aph(2″)-Ia, and aph(2″)-Ib and aph(2″)-Id, which were also predominant in the environmental isolates. The hyl gene was the most prevalent virulence gene. The isolates belonged to 10 STs of the clonal complex CC17, a major epidemic lineage associated with hospital infections and outbreaks, with ST117 and ST889 common to waterborne and hospital isolates, pointing to their sewage-driven dissemination.To gain better insight into the diversity of accompanying taxons in the surveyed water matrices, microbiome taxonomic profiling was carried out using Illumina-based 16S rDNA sequencing and their resistome features predicted using the PICRUSt2 bioinformatics tool. An additional 60 pathogenic bacterial genera were identified, among which Arcobacter, Acinetobacter, Escherichia-Shigella, Bacteroides and Pseudomonas were the most abundant and associated with a plethora of antibiotic resistance genes and modules, providing further evidence of the hazardous effects of wastewater discharges, including the treated ones, on the natural aquatic environment that should be adequately addressed from a sanitary and technological perspective.

Effect of secondary treatment at the South Bay Ocean Outfall (SBOO) on microbial ocean water quality near the US-Mexico border.

In this study, density plume visualizations and statistical comparisons were made of enterococci bacteria (the main marine recreational microbial water quality indicator) densities, both before and after the upgrade of the discharge from the South Bay Ocean Outfall (SBOO) to secondary treatment level, so that the effect of this upgrade on ocean microbial water quality could be assessed. During the dry weather (bathing) season, reduction in enterococci densities was rather limited with only 2 shore stations and one kelp station showing significant reductions, and none showing increased compliance frequency. During the wet weather season, although the signature of land-based sources of bacterial pollution were evident, a majority of both shore (7 of the 11 stations) and kelp (4 of the 7 stations) stations showed statistically significant (p≤0.05) reductions enterococci densities pointing to the role of the upgrade to secondary treatment in improving microbial water quality.

Dilution characteristics of dual buoyant jets in wavy cross-flow environment

Due to the difference in density between the discharge effluent and coastal water, partially treated wastewater is often discharged into the marine environment as a buoyant jet via submarine outfalls with multiport diffusers. The dilution characteristics of effluent discharge (dual buoyant jets) in a wavy cross-flow environment were studied in a laboratory. The planar laser-induced fluorescence technique was used to obtain the concentration data of the jets. The effects of different environmental variables on the diffusion and dilution characteristics of the jets were examined through physical experiments, dimensional analysis, and empirical formulations. It was found that the dilution process of the dual jets could be divided into two components: the original jet component and the effluent cloud component. The jet-to-current velocity ratio was the main parameter affecting the concentration levels of the effluent cloud. The merging of the two jets increased the jet concentration in the flow field. When the jets traveled further downstream, the axial dilution increased gradually and then increased significantly along the axis. Under the effects of strong waves, the concentration contours branched into two peaks, and the mean dilution became more significant than under the effects of weak waves. Therefore, the dilution of the effluent discharge was expected to be significant under strong wave effects because the hydrodynamic force increased. A dilution equation was derived to improve our understanding of the dilution process of buoyant jets in a wavy cross-flow environment. This equation was used to determine the influences of the jet-to-current velocity ratio, wave-to-current velocity ratio, and Strouhal number on the minimum jet dilution. It revealed that the wave and buoyancy effects in effluent discharges were significant.

Mixing zone delimitation for submarine outfall in tropical marine water using the uranine dilution measurement approach

Submarine outfalls are standard wastewater management systems implemented in coastal areas. This manuscript presents a methodology for mixing zone delimitation of wastewater plume discharged through a submarine outfall in tropical marine waters. Sodium fluorescein (Uranine) was used as a tracer to track wastewater mixing and dilution factor in the coastal water of Cartagena de Indias (Colombia). Historical marine water quality, marine currents, and meteorology data were obtained, and analyzed. Two field campaigns were carried out to monitor coliforms, enterococci, and uranine concentrations in the studied area. The results showed that the water column was well mixed, and stratification was negligible due to the low vertical variations in temperature (29.0–29.35 °C), salinity (35.8–36.2), and density (1022.6–1023.0 kg ⋅ m−3). The initial dilution during the dry to the rainy (April) and from the rainy to the dry (December) seasons reached similar dilution factors up to 1:43000 in less than 150 m. The regulatory mixing zone was delimited to an area of 6.6 km2. Uranine is suitable for delimiting the wastewater mixing zone in tropical marine waters.

Primary analysis of the phytoplanktonic community of the water capture channel of a thermal electric plant in Northeast Brazil

In the environmental policy of the Pernambuco Thermoelectric Power Plant, there are plans for monitoring the environmental quality. This study is about the marine phytoplankton community, in the area of ​​influence it has followed a regularity of studies in its catchment channel and in the area of ​​disposal of the submarine outfall. Collections were made every three months, between March 2020 and October 2021. Collections were carried out by trawling 20 µm nets in the area of the submarine outfall and using a Van Dorn oceanographic bottle, inside the catchment channel. from the plant. The taxonomic analyzes showed that in the water catchment channel the genera Chaetoceros and Navicula stood out for their abundance, being represented by 956 and 283 individuals, respectively. At the collection point, the most abundant genera were Pinnularia and Oscillatoria, with 1978 and 559 representatives, respectively.

Driving factors of phytoplankton trace metal concentrations and distribution along anthropogenically-impacted estuaries of southern Taiwan

Phytoplankton are key marine components in global primary productivity and ocean biogeochemistry. However, anthropogenic activities impact phytoplankton through toxic metal dispersion—threatening the food web with increased metal bioaccumulation. This study assessed the phytoplankton trace metal concentrations, distribution, and relationship with community structure. Environmental parameters (temperature, salinity, pH, dissolved oxygen, biological oxygen demand, suspended solids, chlorophyll-a, ammonium, nitrate, nitrite, phosphate, silicate, total phosphorus) and phytoplankton were collected in southern Taiwan; from five transects (estuaries; T1–T5), composed of estuarine (Es) and offshore (Os) sites. This study respectively used size and density fractionation to accurately measure phytoplankton trace metals. Results showed that anthropogenically-impacted rivers and marine outfall discharges drive community structure and phytoplankton trace metal distribution. Among sites, T3–T5Es differed in its environmental characteristics. Significant differences on environmental characteristics and trace metals in phytoplankton were found between transects—indicating higher anthropogenic impacts in T3 (Dianbao–Houjin estuary) and T4 (Kaohsiung Harbor estuary). Phytoplankton trace metals follows an order of Fe >> Mn > Cr > Cu > Ni > Co > As > Pb > Hg. Metals in estuarine phytoplankton were higher compared offshore, but not significantly different (p > 0.05), highlighting the role of marine outfalls in offshore pollutant diffusion. Phytoplankton metal distribution showed a distinct spatial gradient between agriculture- and industry-associated areas. Significantly high Cr bioaccumulation factor (BCF > 100) were also found in transects T2 and T4. Overall, this study presents an accurate trace metal data and BCF in phytoplankton of southern Taiwan. Further, insights on the potential relationship between phytoplankton community structure and trace metal concentrations are presented – with nutrients mainly impacting phytoplankton community, initiating a ripple effect which likely favored blooming of metal-tolerant species (high dominance) – increasing the trace metal bioaccumulation.

Surface dense discharge from rectangular and trapezoidal channels

In this paper, the effect of channel geometry on the characteristics of surface dense jets was experimentally investigated. Their geometric properties for various densimetric Froude numbers were studied for rectangular and trapezoidal channels. A simple innovative image processing technique was implemented to study flow trajectory, jet width, plunge point location, impact point, and location of ultimate discharge mixing zone. For small Froude numbers, Frd≤20, it was observed that the channel geometry was an important parameter influencing the dense flow behavior. The plunge point and impact point for the trapezoidal section were 1.37 and 1.53 times more than the rectangular section, linearly proportional to densimetric Froude number. Longer trajectory in trapezoidal channels leads to better dilution at the impact point. The comparisons showed when the objective was to achieve higher mixing, the trapezoidal section was preferable. However, in terms of the ultimate mixing location, both sections were the same. The closer the shape of the channel to the best hydraulic section (semi-circle section), the geometrical parameters and mixing characteristics would be more appropriate. The non-dimensional equations were determined based on dimensional analysis and regression with R2 > 0.9 in the rectangular section and R2 > 0.8 in the trapezoidal section, which are beneficial to design and optimization of marine outfalls on large scales.

Predicting and Scoring Estuary Ecological Health Using a Bayesian Belief Network

Excessive nutrient and sediment inputs threaten ecological condition in many estuaries. We describe a Bayesian Belief Network (BBN) that calculates an Estuary Trophic Index (ETI) score ranging between 0 (no symptoms of eutrophication) to 1 (grossly eutrophic) for estuaries in Aotearoa New Zealand (NZ). The ETI BBN includes estuary physiographic characteristics (estuary type, flushing time, intertidal area, estuary closure state, water column stratification) and nutrient and sediment loads available from existing geospatial tools and databases, that drive responses of ‘primary’ indicators (macroalgae and phytoplankton biomass) and ‘secondary’ indicators (or symptoms) of estuary ecological impairment (sediment carbon, sediment apparent redox potential discontinuity depth, water column oxygen, macrobenthos and seagrass condition). Relationships between the BBN nodes are based primarily on observational and model-based information from NZ and international studies rather than expert opinion. The model can be used in a purely predictive manner under knowledge-poor situations, using only the physiographic drivers and nutrient/sediment loads, or refined using field-derived observations of indicator values to reduce the uncertainty associated with the probabilistic BBN score. It is designed for shallow tidal lagoons, tidal river estuaries and coastal lakes; systems which are sensitive to eutrophication and sedimentation pressure and are common in NZ and globally. Modelled ETI BBN scores agreed well with ETI scores calculated from observed indicator values for 11 well-studied NZ estuaries. We predict ecological condition of 291 NZ estuaries, most of which have no monitored information on trophic state. We illustrate capabilities of the ETI BBN with two case studies: to evaluate improvements in estuary health arising from diversion of wastewater from an estuary via an ocean outfall, and to estimate catchment diffuse nutrient load reductions required to meet estuary health objectives. The ETI BBN may serve as a template for other agencies wishing to develop similar tools.

Probing the outfall-related anomalous Hg levels in the Danshuei Estuarine Coastal, Taiwan

Seasonal and spatial distributions of total mercury (THg) in the Danshuei Estuary and adjacent coastal areas near the ocean outfall of Taipei, Taiwan, have been successfully investigated from May 2003 to January 2005. We found spatio-temporal variation in THg levels in the Danshuei coastal area was the result of sources and supplies of Hg. High THg concentrations in sediments and seawater were particularly found near the effluent outfall. Average THg levels (avg.: 9–22 ng L−1) were much higher than those in surrounding coastal seawaters (avg.:1–2 ng L−1). Organic carbon contents then played vital roles in controlling water and sedimentary Hg concentrations and occurrences. Hg enrichment factor (EF) as an index of contamination status in surface sediments of the Danshuei coastal area averaged 2.0 ± 0.8 (EFs > 1), indicating an extra non-crustal source from anthropogenic loadings. It implies the Dansheui coastal environment nearby the sewer outfall is facing Hg pollution.

Submarine Outfalls of Treated Wastewater Effluents are Sources of Extensively- and Multidrug-Resistant KPC- and OXA-48-Producing Enterobacteriaceae in Coastal Marine Environment.

The rapid and ongoing spread of carbapenemase-producing Enterobacteriaceae has led to a global health threat. However, a limited number of studies have addressed this problem in the marine environment. We investigated their emergence in the coastal waters of the central Adriatic Sea (Croatia), which are recipients of submarine effluents from two wastewater treatment plants. Fifteen KPC-producing Enterobacteriaceae (nine Escherichia coli, four Klebsiella pneumoniae and two Citrobacter freundii) were recovered, and susceptibility testing to 14 antimicrobials from 10 classes showed that four isolates were extensively drug resistant (XDR) and two were resistant to colistin. After ERIC and BOX-PCR typing, eight isolates were selected for whole genome sequencing. The E. coli isolates belonged to serotype O21:H27 and sequence type (ST) 2795, while K. pneumoniae isolates were assigned to STs 37 and 534. Large-scale genome analysis revealed an arsenal of 137 genes conferring resistance to 19 antimicrobial drug classes, 35 genes associated with virulence, and 20 plasmid replicons. The isolates simultaneously carried 43–90 genes encoding for antibiotic resistance, while four isolates co-harbored carbapenemase genes blaKPC-2 and blaOXA-48. The blaOXA-48 was associated with IncL-type plasmids in E. coli and K. pneumoniae. Importantly, the blaKPC-2 in four E. coli isolates was located on ~40 kb IncP6 broad-host-range plasmids which recently emerged as blaKPC-2 vesicles, providing first report of these blaKPC-2-bearing resistance plasmids circulating in E. coli in Europe. This study also represents the first evidence of XDR and potentially virulent strains of KPC-producing E. coli in coastal waters and the co-occurrence of blaKPC-2 and blaOXA-48 carbapenemase genes in this species. The leakage of these strains through submarine effluents into coastal waters is of concern, indicating a reservoir of this infectious threat in the marine environment.

Distribution patterns and transportation behavior of alkylphenol polyethoxylate degradation metabolites among river, port area, and coastal water bodies of Kaohsiung City, Taiwan

In this study, we conducted a comprehensive study of the distribution, transportation behavior and potential ecological risk of alkylphenol polyethoxylates (APnEOs) in the aquatic environments of Kaohsiung City, Taiwan because little information is available regarding the fate of APnEOs in the water bodies of a total environment. At Love River, APnEOs concentrations were much higher at upstream of interception stations L15 (27.33 ± 1.22 μg/L) and L16 (6.31 ± 0.14 μg/L) than at downstream of interception stations L1–L14 (0.69–2.54 μg/L). Additionally, the average ethoxy (EO) chain lengths of APnEOs at L15 and L16 were longer than at L1–L14. These observations were attributed to the sluice between L14 and L15 that intercepts and accumulates untreated sewage from upstream areas and to the infrastructure of the sewage system that prevents domestic sewage from flowing downstream in the river and to the Kaohsiung Port Area. At Kaohsiung Port Area, APnEO concentrations ranging from 0.63 to 6.50 μg/L were measured. The concentration range and average EO chain length of these APnEOs were similar to those of the downstream stretch of the river, which was attributed to the mixing efficiency of the Kaohsiung Port Area and Love River through tidal exchange. At Cijin Coastal Area, APnEO concentrations ranged from 0.14 to 18.77 μg/L. Notably, the APnEO concentration of surface waters was much higher than that of bottom waters. This observation was attributed to the sewage discharged from the ocean outfall buoying up to the surface instead of mixing with surrounding bottom waters. In potential ecological risk, 19 of 39 sampling points exceeded toxic equivalency of 1 μg/L, and approximately 48.7% of the sampling points would exceed the threshold. The result provides insight into the environmental implications of APnEOs contamination in aquatic environments and useful information for environmental policy and ecological risk assessments.

The Effect of a Step Increase in Depth and Decay upon Dispersion of Coastal Effluent Discharges

Coastal wastewater-discharged effluents contain a mixture of pollutants with decay rates that vary with water depth. Analytical models using a two-dimensional advection-diffusion equation are presented to study the effects of a cross-stream sudden depth change and decay on mixing and dispersing steady discharge of effluents through a sea outfall. The solutions are illustrated graphically by plotting contours of concentration, resembling snapshots of discharged effluent plumes in the far-field. Different shapes of effluent plumes are observed due to the variability of length of the step seabed, and the concentration at the step seabed is formulated to measure how much has discharged effluents dispersed into or out of the shallow coastal waters.

Design of marine outfalls for reducing environmental impact of brine

Design of marine outfalls for reducing environmental impact of brine

Benthic infaunal assemblages adjacent to an ocean outfall in Australian marine waters: Impact assessment and identification of indicator taxa

An impact assessment of oceanic effluent releases from Belmont wastewater treatment works (WWTW) in Newcastle, Australia, was undertaken. Benthic infaunal assemblages in sandy sediments of ~25 m water depth were examined, at sites adjacent to the release point, and at increasing distances up to 2 km in both a NE and SW direction over five consecutive years (2016–2020). Localised impacts were evident for infaunal assemblages, with sites within 20 m of the outfall (“Impact” site types) exhibiting lower taxa richness and Shannon diversity, higher abundances of polychaetes and/or nematodes, higher polychaete ratios, and shifts in assemblage composition in comparison to sites at greater distances during some years. Taxa with increased localised abundances at the outfall were identified as indicators for monitoring impacts, including deposit-feeding polychaetes (Families Polygordiidae, Paraonidae and Dorvilleidae) and Phylum Nematoda. Future infaunal monitoring could include molecular tools and paired sediment analyses.

Current status of recycled water for agricultural irrigation in Australia, potential opportunities and areas of emerging concern

Three per cent of Australian agricultural irrigation comes from recycled water. The 1990s establishment of states' Environment Protection Authorities and their regulatory standards and effluent disposal charges led to effluents from Wastewater Treatment Plants (WWTPs) being used for agricultural irrigation. Adelaide and Melbourne, with agricultural land close to plants, expanded intensive vegetable industries. Sydney has limited land available and discharges 90% of its sewage through deep ocean outfalls after primary treatment. Brisbane with more distant farms, found pumping effluent hard to justify economically. Some larger regional cities/towns purchased farms to manage discharges as commercial businesses. Others market recycled water to nearby growers. Uses depend on treatment standards. Water with secondary treatment and pathogen reduction is suitable for processed crops, grazed or cut pastures, sugar cane, cotton and wine grapes, and is widely used for amenity horticulture, but requires careful salinity management. Water with tertiary treatment meeting log reduction pathogen standards may be used on food crops eaten raw (e.g. lettuce). Commonwealth government subsidies during the millennium drought (2001–2009) supported WWTP upgrades and irrigation infrastructure expansion. However, seasonal water demand and unwillingness of growers to pay full cost recovery prices led to some recycled waters still being discharged to water bodies. Some schemes over-estimated likely irrigation demand. Currently, there is scope for further developing recycled water agricultural irrigation by submitting business cases for subsidies from the new National Water Grid Authority. But there is increasing interest in the potential use of recycled water for drinking water augmentation, for which Australia has had guidelines since 2008. Perth has capacity for 28 hm3/yr recycled water to replenish its groundwater drinking sources while Brisbane has three plants totalling 84 hm3/yr for indirect potable supply, but not yet operating. Recycled water for critical human needs could eventually out-compete agricultural irrigation.

Analysis of micropollutants in a marine outfall using network analysis and decision tree

The presence of micropollutants (MPs), including pharmaceutical, industrial, and pesticidal compounds, threatens both human health and the aquatic ecosystem. The development and extensive use of new chemicals have also inevitably led to the accumulation of MPs in aquatic environments. Recreational beaches are especially vulnerable to contamination, affecting humans and aquatic animals via the absorption of MPs in water during marine activities (e.g., swimming, sailing, and windsurfing). Additionally, marine outfalls in an urbanized coastal city can cause serious chemical and microbial pollution on recreational beaches, leading to an increase in adverse effects on public health and the ecological system. Therefore, the aim of this study was to, with the use of network and decision tree analyses, identify the features and factors that influence the change in MP concentrations in a marine outfall. These analyses were conducted to inspect the relationship between each MP and its hierarchical structure as well as hydrometeorological variables. Additionally, a risk analysis was conducted in this study in which the MPs were prioritized based on their optimized risk quotient values. During our monitoring of MP concentrations over time at the marine outfall, high concentrations of pharmaceutical and industrial compounds were detected when the tide level was low after rainfall. Furthermore, results of the risk analysis and the prioritization revealed that a total of 18 substances identified in our study posed a risk to the ecosystem; these include major ecotoxicologically hazardous substances such as telmisartan, mevinphos, and methiocarb. Results of the network analysis demonstrated distinct trends for pharmaceutical and industrial substances, whilst those for pesticide compounds were irregular. Additionally, the hierarchical structures for most MPs consisted of rainfall, tide level, and antecedent dry hours; this implies that these factors influence MP dynamics. These findings will be helpful for establishing chemical contamination management plans for recreational beaches in the future.

Microbiome and antibiotic resistance profiling in submarine effluent-receiving coastal waters in Croatia

Wastewater treatment plant (WWTP) effluents are pointed as hotspots for the introduction of both commensal and pathogenic bacteria as well as their antibiotic resistance genes (ARGs) in receiving water bodies. For the first time, the effect of partially treated submarine effluents was explored at the bottom and surface of the water column to provide a comprehensive overview of the structure of the microbiome and associated AR, and to assess environmental factors leading to their alteration. Seawater samples were collected over a 5-month period from submarine outfalls in central Adriatic Sea, Croatia. 16S rRNA amplicon sequencing was used to establish taxonomic and resistome profiles of the bacterial communities. The community differences observed between the two discharge areas, especially in the abundance of Proteobacteria and Firmicutes, could be due to the origin of wastewaters treated in WWTPs and the limiting environmental conditions such as temperature and nutrients. PICRUSt2 analysis inferred the total content of ARGs in the studied microbiomes and showed the highest abundance of resistance genes encoding multidrug efflux pumps, such as MexAB-OprM, AcrEF-TolC and MdtEF-TolC, followed by the modified peptidoglycan precursors, transporter genes encoding tetracycline, macrolide and phenicol resistance, and the bla operon conferring β-lactam resistance. A number of pathogenic genera introduced by effluents, including Acinetobacter, Arcobacter, Bacteroides, Escherichia-Shigella, Klebsiella, Pseudomonas, and Salmonella, were predicted to account for the majority of efflux pump-driven multidrug resistance, while Acinetobacter, Salmonella, Bacteroides and Pseudomonas were also shown to be the predominant carriers of non-efflux ARGs conferring resistance to most of nine antibiotic classes. Taken together, we evidenced the negative impact of submarine discharges of treated effluents via alteration of physico-chemical characteristics of the water column and enrichment of bacterial community with nonindigenous taxa carrying an arsenal of ARGs, which could contribute to the further propagation of the AR in the natural environment.