Spatiotemporal distribution of seabed litter in the SE Levantine Basin during 2012-2021

This study explores the first record of spatiotemporal distributions of macro and micro-litter on the seafloor in the Southeastern (SE) Levantine Basin (LB) during 2012-2021. Macro-litter was surveyed by bottom trawls in water depths of 20-1600 m and micro-litter by sediment box corer/grab at a depths range of 4-1950 m. Maximal macro-litter concentrations were recorded at the upper continental slope (200 m), averaging 4700 ± 3000 items/km². Plastic bags and packages were the most abundant items (77 ± 9 %) with a maximum of 89 % at 200 m depth, and their size decreased with increasing water depth. Micro-litter debris were found mainly in shelf sediments (≤30 m water depth) with an average concentration of 40 ± 50 items/kg, while shit particles transferred to the deep sea. These findings suggest an extensive distribution of plastic bags and packages in the SE LB, predominantly accumulating in the upper continental slope and deeper, based on their size.

Community dynamics and ecological shifts on Mediterranean vermetid reefs

Mediterranean coastal ecosystems experience many local and global stressors and require long-term monitoring to detect and follow trends in community structure. Between 2009 and 2017, we seasonally and annually monitored the spatiotemporal community dynamics at 11 sites on the rocky shores of the southeastern Mediterranean, focusing on the understudied intertidal vermetid reef ecosystem. Marked seasonal trends were found in biodiversity, with the highest diversity in winter and spring. Canopy-forming brown algae, dominating the northwestern Mediterranean intertidal reefs, were generally scarce on the reef platform and almost only found in tidepools. Interannual shifts in community structure were driven mostly by sharp fluctuations in a few dominant native and alien species and the regional mass mortality of an Indo-Pacific mussel in summer 2016. Compared to an older macroalgae dataset, dating back to 1973-1995, we found that some warm-affinity (summer) taxa became more dominant and cold-affinity (winter) species less dominant, while one once conspicuous species, Halimeda tuna, completely disappeared. The observed community shifts are probably driven mostly by stressors related to climate change. We encourage forming a network of long-term, multi-site ecological monitoring programs in the Mediterranean to improve our understanding of ecosystem change and to enable making better predictions at the basin scale.

Legacy groundwater pollution as a source of mercury enrichment in marine food web, Haifa Bay, Israel

Haifa Bay (HB), located along the northern Mediterranean shore of Israel was polluted with Hg from a chlor-alkali plant (ECI) and from the Qishon River industries, for decades. From the mid-1980s industrial Hg loads into HB decreased dramatically until their complete cessation in 2000. Consequently, concentrations in marine biota and sediments decreased almost to reference levels. However, during 2006-2014, an unexpected increase of total Hg (THg) concentrations was observed in three commercial fish species collected at northern HB (N.HB). To determine the cause of this increase, THg and methyl Hg (MeHg) were measured in seawater, coastal groundwater, suspended particulate matter, plankton, macroalgae, benthic fauna, and in marine and beach sediments. THg in groundwater and sediments from the vicinity of ECI were extremely high (up to 251 μg L^-1 and 2200 ng g^-1, respectively). MeHg concentrations in groundwater were low and constituted <0.1% of THg, except in the surf zone opposite the ECI, where MeHg constituted 0.2% of the THg. THg and MeHg concentrations were consistently higher in benthic biota and plankton from N.HB and northwards, compared to corresponding samples from southern HB (S.HB) and the reference site (RS). MeHg in bivalves and sponges from N.HB and SZ was higher than from S.HB and RS, despite having similar THg concentrations, which suggests a stronger source of MeHg in N.HB. Our findings suggest that the discharge into N.HB of Hg polluted groundwater under the ECI increased during the period 2006-2014. The Hg was assimilated by plankton or adsorbed onto inorganic particles, which were further ingested by benthic and pelagic consumers, as well as transported northward with the alongshore current. These findings demonstrate for the first time the potential of relic pollution in groundwater to increase heavy metal burdens in local marine food webs.

Modelling the distributions of desalination brines from multiple sources along the Mediterranean coast of Israel

We use numerical simulations to study the possible spatiotemporal effects of brine release from five desalination plants, located along the Israeli Mediterranean coastline. It is commonly believed that salinity anomalies, associated with brine discharge from desalination plants, causes effects which are confined to an area of several hundreds of meters from the discharge outfall. We show that discharging brine using diffusers produces small but robust salinity anomalies that propagate tens of kilometers as density currents (DCs). In contrast, premixing the brine with power plant cooling water compensates the negative buoyancy and prevents their generation. The propagating DCs can impact coastal water dynamics by increasing the velocities and transports in alongshore and downslope directions. The spreading and trajectories of the DCs was strongly influenced by seasonal stratification. In winter, due to a mixed water column, the DCs were relatively focused and propagate downslope. While in the summer they are confined to a narrow band along the coastline. Our model results highlight the possibility that brine discharge might have a large scale, non-negligible effect on shelf circulation than previously considered. Further studies are needed to assess the environmental, dynamical and ecological effects of desalination brine propagation, especially in the far field.

Seawater quality at the brine discharge site from two mega size seawater reverse osmosis desalination plants in Israel (Eastern Mediterranean)

Two mega-size seawater desalination plants, producing 240 Mm³/y freshwater, discharge brine into the Mediterranean coast of Israel through two marine outfalls, located 0.8 km apart. Six years monitoring brine discharge have shown almost no impact on seawater quality. The brine dispersed near the bottom following its initial mixing, and was not detected near the surface. Maximal excess salinity at the salty layer ranged from 4.3 to 9.1% over the reference and the affected area was highly variable (2 km² - >13 km²), with maximal plume size from 1.75 to more than 4.4 km. Brine increased seawater temperature by up to 0.7 °C near the outfalls. It had no impact on oxygen saturation, turbidity, pH, nutrients (except for total organic phosphorus (TOP)), chlorophyll-a and metal concentrations. TOP, from the polyphosphonate-based antiscalant discharged with the brine, was correlated with excess salinity. It is unknown if the results of this short term study represent a steady state, with temporal variability, or the beginning of a slow incremental impact. Israel is planning to more than double desalination along its 190 km Mediterranean coast by 2050. A long term, adaptable, program, in conjunction with specific research and modeling, should be able to assess and predict the impact of large scale brine discharge on the marine environment.

Chronic effects of brine discharge form large-scale seawater reverse osmosis desalination facilities on benthic bacteria

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.

Message in a bottle - The story of floating plastic in the eastern Mediterranean sea

The Mediterranean Sea is a closed basin with limited water exchange through the Strait of Gibraltar, and sites along its shores show the greatest densities of marine debris in the world. Plastic bottles, which are a growing concern due to high consumption of soft drinks and bottled water, constitute most of the floating marine debris. In this paper we present the transport mechanisms of floating marine debris to and from the Israeli coast using an experimental offshore release and recovery of plastic bottles, with the participation of citizens. Many bottles released near the beach in the south part of Israel, returned to the beach at a short distance and time from the release point. Some release locations had no bottle returns. Ten bottles, released from three locations, were recovered many dozens to hundreds of kilometers from the release point. Since most of the westward water flow in the eastern Mediterranean is subsurface, it was not surprising to find our floating debris only in the east. That makes the Levant basin in the eastern Mediterranean a collection area for floating debris.

Spatial distribution and sources of organic matter and pollutants in the SE Mediterranean (Levantine basin) deep water sediments

A study of deep sea sediment quality was conducted at 52 stations off the Mediterranean coast of Israel (50-1900m depth). Total Organic Carbon (TOC), Polycyclic Aromatic Hydrocarbons (∑PAHs), Poly Chlorinated Biphenyls (∑PCBs) ranged between 0.58 and 1.44%, 12-190 and <0.3-7.7μgkg^-1, respectively. The TOC distribution indicated the Nile delta as an important source of organic matter and the important effect of topography on deposition patterns in this region. PCBs and PAHs quantitative levels were associated with nearby gas well drilling (well below environmental criteria) and dredge-material dumping sites. A significant correlation between these pollutants and TOC was found in the southernmost stations suggesting a common source. PAHs isomer ratios in most of the stations indicated a petrogenic source, while the contribution of pyrogenic sources appears to be very small. These findings form a sound baseline for assessing the potential impact of future deep sea drilling activities that are expected to increase significantly in the Eastern Mediterranean basin.

Twenty two years of sewage sludge marine disposal monitoring in the Eastern Mediterranean Sea: Impact on sediment quality and infauna and the response to load reduction

Effects of sewage sludge disposal on sediments and infauna are presented in a unique long-term (22years) data set from the Eastern Mediterranean. While organic carbon (Corg) and metals affected sediment quality in an area which size varied seasonally, the infauna exhibited seasonal "boom and bust" cycle. Metal concentrations declined following load reduction. However, Corg did not decrease and infaunal abundance, closely related to Corg, varied with changes in environmental forcing. Mild winters affected the infaunal populations at the heavily impacted stations, due to anoxic conditions. Planned cessation of disposal is estimated to reduce Corg and metal concentrations to pre-discharge levels. Yet the resettling biota is expected to differ significantly from the pre-discharge one and consist in large part of Erythraean non indigenous species.

Ecological quality assessment in the Eastern Mediterranean combining live and dead molluscan assemblages

The EU directive to quantify ecological quality by deviation from pre-impacted conditions often fails to be implemented because past information is usually incomplete or missing. Molluscan death assemblages, representing long-term accumulation of shells on the sea floor, average out short-term variability and can serve as a baseline for quality assessment. AMBI, Bentix and Shannon-Wiener indices were calculated for live and dead assemblages from polluted and control stations on the highly oligotrophic Levantine shallow shelf of Israel. Bentix successfully tracked deterioration over time, from moderate EcoQS in the dead to poor in the live assemblage. Additional modification of the ecological classification of species by scoring the naturally abundant Corbula gibba as pollution-sensitive improved the utility of the Bentix index in monitoring in this part of the Mediterranean. This adjustment of Bentix, and use of death assemblages for an ecological baseline, should therefore be incorporated in monitoring for compliance with EU directives.

Seawater quality and microbial communities at a desalination plant marine outfall. A field study at the Israeli Mediterranean coast

Global desalination quadrupled in the last 15 years and the relative importance of seawater desalination by reverse osmosis (SWRO) increased as well. While the technological aspects of SWRO plants are extensively described, studies on the environmental impact of brine discharge are lacking, in particular in situ marine environmental studies. The Ashqelon SWRO plant (333,000 m(3) d(-1) freshwater) discharges brine and backwash of the pre-treatment filters (containing ferric hydroxide coagulant) at the seashore, next to the cooling waters of a power plant. At the time of this study brine and cooling waters were discharged continuously and the backwash discharge was pulsed, with a frequency dependent on water quality at the intake. The effects of the discharges on water quality and neritic microbial community were identified, quantified and attributed to the different discharges. The mixed brine-cooling waters discharge increased salinity and temperature at the outfall, were positively buoyant, and dispersed at the surface up to 1340 m south of the outfall. Nutrient concentrations were higher at the outfall while phytoplankton densities were lower. Chlorophyll-a and picophytoplankton cell numbers were negatively correlated with salinity, but more significantly with temperature probably as a result of thermal pollution. The discharge of the pulsed backwash increased turbidity, suspended particulate matter and particulate iron and decreased phytoplankton growth efficiency at the outfall, effects that declined with distance from the outfall. The discharges clearly reduced primary production but we could not attribute the effect to a specific component of the discharge. Bacterial production was also affected but differently in the three surveys. The combined and possible synergistic effects of SWRO desalination along the Israeli shoreline should be taken into account when the three existing plants and additional ones are expected to produce 2 Mm(3) d(-1) freshwater by 2020.

Natural oligotrophy vs. pollution-induced eutrophy on the SE Mediterranean shallow shelf (Israel): environmental parameters and benthic foraminifera

The eastern Mediterranean is naturally highly oligotrophic, but urbanization along the Levant coast has led to raised organic and nutrient loads. This study tracks living foraminiferal assemblages at two sites near an activated sewage sludge outfall from 11/2003 to 5/2004. Oligotrophic site PL29 shows seasonal variations in O(2), chlorophyll a, and organic carbon, and has an abundant, diverse benthic foraminiferal assemblage living at various in-sediment depths. At eutrophic site PL3, approximately 16 years of sludge injection favor a depleted assemblage primarily of opportunist foraminifera. This site shows less seasonality, is subjected to organic matter overload, O(2)-stress, and periodic anoxia, foraminifera are less abundant and diverse, and live at shallower depths. The assemblages at both sites represent a common pool of species, with Ammonia tepida highly dominant. Benthic foraminifera were therefore found to be sensitive to trophic trajectories, respond on sub-seasonal time-scales, and track injection and dispersal of organic loads on the shelf.