Seawater desalination facilities continuously discharge hyper-saline brine into the coastal environment which often flows as a concentrated plume over the seafloor, hence possibly impacting benthic ...microorganisms. Yet, the effects of brine discharge from desalination plants on benthic bacteria, key players in biodegradation of organic material and nutrient recycling is unknown. In this study, we tested the chronic (years) effects of brine discharge from three large-scale desalination facilities on the abundance, metabolic activity and community composition of benthic bacteria. To this end, four sampling campaigns were carried at the outfall areas of the Ashkelon, Sorek and Hadera desalination facilities. The effects of the brine were compared to corresponding reference stations which were not influenced by the brine (i.e., water temperature and salinity). Our sampling data indicate that bacterial abundance and activity that includes bacterial growth efficiency were 1.3–2.6-fold higher at the outfall area than the reference station. Concomitant analysis pointed out that the bacterial community structure at the brine discharge area was also different than the reference station, yet varied between each desalination facility. Our results demonstrate that the impact of brine effluent from desalination facilities on benthic bacteria are site-specific and localized (<1.4 Km2) around the discharge point. Namely, that the effects on benthic bacteria are prominent at the brine mixing zone and change according to the discharge method used to disperse the brine as well as local stressors (e.g., eutrophication and elevated water temperature). Our results contribute new insights on the effects of desalination-brine to benthic microbes, while providing scientifically-based aspects on the ecological impacts of brine dispersion for decision makers.
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•Abundance and activity of benthic bacteria are often affected by SWRO brine.•The impact of desalination brine on benthic bacteria is local and site-specific.•The diffuser method affects benthic microbial community composition.
Benthic microbes are key organisms in the oligotrophic Southeastern Mediterranean Sea (SEMS), yet their abundance, activity, and diversity in this rapidly changing basin are not fully understood. We ...investigated the prokaryotic and microfungal communities throughout years 2018-2020 at 27 stations (6-1900 m water depths, down to 20 cm below the sediment surface), in two transects with distinct downslope transport regimes, and along the eutrophic coastline. We estimated microbial abundance with flow cytometry, secondary production as leucine assimilation, and sequenced marker genes (the 16S rRNA and internal transcribed spacer) to assess diversity indices. The highest abundance (0.21 * 10.sup.8 cells gr.sup.-1 sediment) was estimated at slope stations where we assumed substantial transport rates and found an accumulation of organic carbon. Secondary production was the highest nearshore (12 + or 4 ng C gr.sup.-1 h.sup.-1), and markedly declined offishore (0.5 + or 0.9 ng C gr.sup.-1 h.sup.-1). Populations of archaea (dominant Nitrososphaeria and Nanoarchaeia) and diverse bacteria were stable over three years, and taxonomic composition was dictated mainly by depth gradients. Saprotrophic and pathotrophic microfungi Ascomycota (70% + or 23%) and Basidiomycota (16% + or 18%) were prevalent, whereas parasitic chytrids were abundant nearshore. Our results highlight the role of downslope transport, which enriched the typical deep-sea communities with anaerobic lineages, in shaping microbial populations near the continental slope. Keywords: marine sediment, archaea, bacteria, fungi, Mediterranean Sea, biomonitoring
Unicellular photoautotrophic diazotrophs such as Crocosphaera spp. are ubiquitous in many oligotrophic and N‐limited oceans, as they can reduce N2 into bioavailable ammonia. The Mediterranean Sea is ...potentially an ideal environment for photoautotrophic diazotrophic activity, and yet N2‐fixation rates measured in the last two decades are typically very low and no diazotrophic blooms have been recorded in its offshore waters. Previous studies suggest that diazotrophs, as well as nondiazotrophic phytoplankton and heterotrophic bacteria, may be P‐limited, hence their low biomass and activity. Here, we amended surface seawater from six stations across a nutrient gradient in the Mediterranean Sea (east to west transect) with dissolved inorganic phosphorus (DIP), and with seawater‐acclimated inocula of Crocosphaera watsonii, a unicellular cyanobacterial diazotroph, to examine if DIP can stimulate diazotrophy. Our results demonstrate that C. watsonii are poor competitors for DIP relative to native nondiazotrophic heterotrophic microbial populations, especially in the ultraoligotrophic eastern Mediterranean basin, resulting in low N2‐fixation rates. Moreover, the results indicate that when the ambient DIP concentrations are < 35 nmol L−1, unicellular photoautotrophic diazotrophs such as C. watsonii will likely be outcompeted for this macronutrient in the Mediterranean Sea, whereas above 35 nmol L−1 diazotrophy can be stimulated. Our findings support the “bypass theory” stating that photoautotrophs may be outcompeted by heterotrophic bacteria for DIP in nutrient‐poor regions such as the Mediterranean Sea.
Seawater reverse osmosis (SWRO) desalination facilities produce freshwater and, at the same time, discharge hypersaline brine that often includes various chemical additives such as antiscalants and ...coagulants. This dense brine can sink to the sea bottom and creep over the seabed, reaching up to 5 km from the discharge point. Previous reviews have discussed the effects of SWRO desalination brine on various marine ecosystems, yet little attention has been paid to the impacts on benthic habitats. This review comprehensibly discusses the effects of SWRO brine discharge on marine benthic fauna and flora. We review previous studies that indicated a suite of impacts by SWRO brine on benthic organisms, including bacteria, seagrasses, polychaetes, and corals. The effects within the discharge mixing zones range from impaired activities and morphological deformations to changes in the community composition. Recent modeling work demonstrated that brine could spread over the seabed, beyond the mixing zone, for up to several tens of kilometers and impair nutrient fluxes from the sediment to the water column. We also provide a possible perspective on brine’s impact on the biogeochemical process within the mixing zone subsurface. Desalination brine can infiltrate into the sandy bottom around the discharge area due to gravity currents. Accumulation of brine and associated chemical additives, such as polyphosphonate-based antiscalants and ferric-based coagulants in the porewater, may change the redox zones and, hence, impact biogeochemical processes in sediments. With the demand for drinking water escalating worldwide, the volumes of brine discharge are predicted to triple during the current century. Future efforts should focus on the development and operation of viable technologies to minimize the volumes of brine discharged into marine environments, along with a change to environmentally friendly additives. However, the application of these technologies should be partly subsidized by governmental stakeholders to safeguard coastal ecosystems around desalination facilities.
1. Fire retardants are composed of fertilising salts that are commonly used for fighting wildfires. These chemicals have various effects on individual arthropod species and aquatic communities.
2. ...This study investigated the effects of four treatments of a prevalent fire retardant FR CROS 134 (FR), applied at concentrations of 0, 3.8 × 102, 7.6 × 102 and 11.4 × 102 mg litre−1 on oviposition habitat selection (OHS) by Culiseta longiareolata and Culex laticinctus mosquitoes in an outdoor mesocosm. Additionally, larval development of C. longiareolata was examined in response to this fire retardant.
3. The results demonstrate that OHS increased in both species, whereas survivorship (0–86.7%) and time to metamorphosis (5.4–23.1 days) of C. longiareolata were not affected by any of the treatments. However, cyanobacterial biomass increased and heterotrophic bacteria decreased in response to the addition of FR.
4. It was found that FR applications can have unintended consequences which can increase OHS by female mosquitoes. The growing use of fire retardants worldwide, and especially in Israel, justify evidence‐based assessment and environmental management of their use. This study is a first critical step in filling the knowledge gap with respect to the impact of FR on aquatic ecosystems.
This study investigated the effects of the fire retardant FR CROS 134 (FR) on oviposition habitat selection (OHS) of the mosquitoes Culiseta longiareolata and Culex laticinctus in an outdoor mesocosm experiment.
The results demonstrate OHS increasing in both species, while the survivorship (0–86.7%) and time to metamorphosis (5.4–23.1 days) of C. longiareolata were unaffected by the FR treatments.
The lowest trophic level, cyanobacteria, heterotrophic bacteria and algae, showed variable responses to FR addition. These results show direct and indirect consequences of FR application on OHS by female mosquitoes.
The progressive establishment of gas platforms and increasing petroleum accidents pose a threat to zooplankton communities and thus to pelagic ecosystems. This study is the first to compare the ...impacts of gas-condensate and crude oil on copepod assemblages. We conducted microcosm experiments simulating slick scenarios at five different concentrations of gas-condensate and crude oil to determine and compare their lethal effects and the bioconcentration of low molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs) in eastern Mediterranean coastal copepod assemblages. We found that gas-condensate had a two-times higher toxic effect than crude oil, significantly reducing copepod survival with increased exposure levels. The LMW-PAHs bioconcentration factor was 1–2 orders of magnitude higher in copepods exposed to gas-condensate than in those exposed to crude oil. The median lethal concentration (LC50) was significantly lower in calanoids vs. cyclopoid copepods, suggesting that calanoids are more susceptible to gas-condensate and crude oil pollution, with potential trophic implications.
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•Copepods are more vulnerable to gas-condensate exposure than to crude oil.•Low-weight hydrocarbon concentrations in seawater with condensate were higher than with oil.•Bioconcentration of gas-condensate in copepods was greater than with crude oil.•Cyclopoid copepods are more tolerant to hydrocarbons than calanoid copepods.
Weathered oil, that is, tar, forms hotspots of hydrocarbon degradation by complex biota in marine environment. Here, we used marker gene sequencing and metagenomics to characterize the communities of ...bacteria, archaea and eukaryotes that colonized tar patties and control samples (wood, plastic), collected in the littoral following an offshore spill in the warm, oligotrophic southeastern Mediterranean Sea (SEMS). We show potential aerobic and anaerobic hydrocarbon catabolism niches on tar interior and exterior, linking carbon, sulfur and nitrogen cycles. Alongside aromatics and larger alkanes, short-chain alkanes appear to fuel dominant populations, both the aerobic clade UBA5335 (Macondimonas), anaerobic Syntropharchaeales, and facultative Mycobacteriales. Most key organisms, including the hydrocarbon degraders and cyanobacteria, have the potential to fix dinitrogen, potentially alleviating the nitrogen limitation of hydrocarbon degradation in the SEMS. We highlight the complexity of these tar-associated communities, where bacteria, archaea and eukaryotes co-exist, likely exchanging metabolites and competing for resources and space.
Reverse osmosis (RO) seawater desalination is currently a widespread means of closing the gap between supply and demand for potable water in arid regions. Currently, one of the main setbacks of RO ...operation is fouling, which hinders membrane performance and induces pressure loss, thereby reducing system efficiency. An alternative water source is saline groundwater with salinity close to seawater, pumped from beach wells in coastal aquifers which penetrate beneath the freshwater-seawater interface. In this research, we studied the potential use of saline groundwater of the coastal aquifer as feedwater for desalination in comparison to seawater using fieldwork and laboratory approaches. The chemistry, microbiology and physical properties of saline groundwater were characterized and compared with seawater. Additionally, reverse osmosis desalination experiments in a cross-flow system were performed, evaluating the permeate flux, salt rejection and fouling propensities of the different water types. Our results indicated that saline groundwater was significantly favored over seawater as a feed source in terms of chemical composition, microorganism content, silt density, and fouling potential, and exhibited better desalination performance with less flux decline. Saline groundwater may be a better water source for desalination by RO due to lower fouling potential, and reduced pretreatment costs.
Summary
Marine bacteria rely on phytoplankton exudates as carbon sources (DOCp). Yet, it is unclear to what extent phytoplankton exudates also provide nutrients such as phytoplankton‐derived N and P ...(DONp, DOPp). We address these questions by mesocosm exudate addition experiments with spent media from the ubiquitous pico‐cyanobacterium Prochlorococcus to bacterial communities in contrasting ecosystems in the Eastern Mediterranean – a coastal and an open‐ocean, oligotrophic station with and without on‐top additions of inorganic nutrients. Inorganic nutrient addition did not lower the incorporation of exudate DONp, nor did it reduce alkaline phosphatase activity, suggesting that bacterial communities are able to exclusively cover their nitrogen and phosphorus demands with organic forms provided by phytoplankton exudates. Approximately half of the cells in each ecosystem took up detectable amounts of Prochlorococcus‐derived C and N, yet based on 16S rRNA sequencing different bacterial genera were responsible for the observed exudate utilization patterns. In the coastal community, several phylotypes of Aureimarina, Psychrosphaera and Glaciecola responded positively to the addition of phytoplankton exudates, whereas phylotypes of Pseudoalteromonas increased and dominated the open‐ocean communities. Together, our results strongly indicate that phytoplankton exudates provide coastal and open‐ocean bacterial communities with organic carbon, nitrogen and phosphorus, and that phytoplankton exudate serve a full‐fledged meal for the accompanying bacterial community in the nutrient‐poor eastern Mediterranean.
Anthropogenically-induced oil spills release large amounts of organic pollutants into the marine environment. To date, little is known about the response of microbial populations (biomass, activity ...and diversity) to crude oil pollution in Low Nutrients Low Chlorophyll and warm systems. Here, we investigated the daily dynamics of phytoplankton and heterotrophic bacteria in response to an oil spill (500 μm thick layer) in the coastal waters of the SE Mediterranean Sea (SEMS), using mesocosms during winter and summer. Crude oil addition caused a marked decrease in phytoplankton biomass (40–76%) and production rates (22–96%), whereas heterotrophic bacterial abundance and production increased (4–68% and 17–165%, respectively). Concurrently, amplicon sequencing of the 16S rRNA gene revealed that oil-degrading bacteria became abundant 48–96 h post-oil addition, while the cosmopolitan Synechococcus and SAR11 lineages were significantly reduced (by 78–98% and 59–98%, respectively). Fertilization with inorganic nutrients (NO3 and PO4) reduced the deleterious effects of the oil, resulting in a less distinct reduction in phytoplankton biomass/abundance. Our results highlight the potential of intrinsic microbial communities to degrade oil-derived pollutants in oligotrophic coastal waters.
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•Ramifications of oil spills were studied in the SE Mediterranean Sea coastal water.•Crude-oil addition resulted in decreased abundances of Synechococcus and SAR11.•Hydrocarbon degraders became abundant following crude oil amendment.•N+P addition reduced the inhibitory effects of oil pollution to phytoplankton.
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