The aims of this work are: (i) To understand potential transformations and dynamics within the broad chromophoric dissolved organic matter (CDOM) pool in the sea surface microlayer (SML) and the underlying water (ULW) at a Mediterranean coastal site using high-resolution (biweekly, one-year) temporal data and by applying established absorbance indices across multiple spectral regions along with the novel fluorescent dissolved organic matter (FDOM) to CDOM, FDOM/CDOM index. (ii) To evaluate the relative contributions of in situ processes, upward flux from the ULW, and atmospheric (rainwater) inputs in the shaping of the dissolved organic matter (DOM) and CDOM pools in the SML. Twenty-two paired SML–ULW samples and fourteen rainwater samples were analyzed for dissolved organic carbon (DOC), UV–visible (250–700 nm) absorption spectra, and 3D fluorescence excitation emission matrices (EEMs). The SML was consistently enriched in DOC, CDOM, and FDOM relative to the ULW throughout the study. Enrichment factors (EFs) for long-wavelength absorption coefficients (a300, a370) exceeded 5 indicating a preferential accumulation of high molecular, aromatic absorbing DOM. Relationships between DOC, a300 and the spectral slope (S275−295) indicated that specific processes in the SML modulate the abundance and optical quality of DOM beyond bulk DOC quantity. Photodegradation was apparent in both layers, though more pronounced in the ULW. In the SML, photodegradation effects appeared to be partially counterbalanced by in situ production or aggregation of hydrophobic, optically active, higher-molecular-weight material. Parallel Factor Analysis (PARAFAC) identified four FDOM components: two humic-like (A–C, A–M) and two protein-like (T, B). Terrestrial humic-like (A–C) and tryptophan-like (T) fluorophores were dominant and strongly enriched in the SML (EF >4). However, humic-like and tryptophan-like components exhibited SML enrichment linked to both a300 absorption and layer, while tyrosine – like component was enriched independently of layer effects and mainly reflected a300 fluctuations. By introducing a new FDOM/CDOM index, a decoupling between fluorescent and non-fluorescent chromophoric organic fractions was revealed: the SML exhibited higher fluorescence in the UV-C/UV-B excitation regions (A, B, T peaks) but lower fluorescence in the UV-A/near-visible excitation region (C peak), suggesting selective accumulation of absorbing but non-fluorescent CDOM in longer wavelengths. Potential drivers of this decoupling include biological transformations, rapid microlayer reorganization, and atmospheric inputs. Rainwater showed DOC concentrations and absorption features comparable to the SML but distinct fluorescence characteristics. PARAFAC modeling of rainwater did not resolve the tryptophan-like fluorophore and revealed blue-shifted humic-like components, consistent with photochemically aged, low molecular weight DOM of mixed marine–terrestrial origin. Overall, the results indicate that wavelength-dependent enrichment of CDOM and FDOM in the SML is primarily driven by photodegradation, biological activity, rapid molecular reorganization, and atmospheric deposition, rather than upward DOM flux from the ULW.

Herein, we aim to provide a baseline assessment of the pollution status of the water column in coastal areas of Saudi Arabia (Red Sea and the Gulf of Aqaba), using trace metals (Cd, Co, Cr, Cu, Ni, Pb and Zn), total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs), in seawater samples obtained from 71 sampling stations in June-July 2021. Concerning trace metals, the maximum concentrations for Co, Cu and Ni were detected in Al-Shuqaiq, whereas the highest Pb and Zn concentrations were found in the Jeddah lagoon waters. Elevated concentrations of TPHs and the highest sum of PAHs were recorded in surface waters of Al Lith, Jeddah lagoon and Jeddah Mena. Overall, the concentrations of all trace metals, TPHs and individual PAHs for which environmental standards have been stipulated for the Kingdom of Saudi Arabia fall well below the threshold values.

The Saronikos Gulf and the small emBayment of Elefsis Bay (Eastern Mediterranean, Greece) represent the seaward boundary of the metropolitan areas of Athens and Piraeus Port, hosting 1/3 of the current Greek population. It constitutes a complex ecosystem due to the topographical and hydrological differentiation of the area, as well as its trophic character. Maintenance of the good environmental status of the Saronikos Gulf marine ecosystem is very important due to the cumulating impacts coming from multiple human activities. In order to protect and improve the marine environment and implement effective policies to sustain its quality, it is necessary to monitor the spatial and temporal variation of the major ecosystem elements, the pollutant levels, and their effects on the ecosystem and marine organisms. Thus, in this chapter, we provide an overview of ecosystem elements, hazardous substances, and alien species that have undergone changes over the last 25 years because of the various pressures, emphasizing mainly the sewage treatment plant of Athens in Psittalia Island. The environmental status of the inner Saronikos Gulf is also examined. Summarizing, we highlight the gradual improvement of many parameters of the ecosystem. This trend of improvement has started since 2004, as a result of the secondary treatment of the wastewater and the decrease of the industrial activities following the economic crisis in Greece. Nevertheless, it is essential the maintenance of the monitoring of the Saronikos Gulf and Elefsis Bay in order to investigate any expected change due to cumulative impacts from multiple human activities which in combination with climate change may provoke new ecological balances. Possible changes and impacts on the Saronikos Gulf ecosystem must be recorded to optimize the protection and the management of the marine environment in the context of the implementation of the European Directives in our country.

Mercury (Hg) is an environmentally hazardous metal and a priority element in Mediterranean environmental monitoring. Hg is a priority pollutant in the main pieces of European legislation pertaining to the marine environment (the Marine Strategy Framework Directive - MSFD and the Water Framework Directive WFD). Despite the environmental importance of Hg there is limited knowledge on levels in Greek waters. The Laboratory of Environmental Chemistry (LEC) analyses very low Hg concentrations (above 0.5ng/L) using state of the art equipment in clean room facilities and participates in the national WFD coastal zone monitoring since 2012 in collaboration with the Hellenic Centre for Marine Research (HCMR). This paper presents the first attempt to evaluate Hg levels in the coastal waters of Greece in the last 8 years (2012-2020) and identify trends and spatial patterns. The Hg levels measured in all areas were well below the European Legislation threshold of 70ng/L (EC 2013/39). Increased levels of Hg were found, as expected, near the major cities of Greece (Athens, Thessaloniki) and the major rivers of Northern Greece as well as in some of smaller ports.

An intercalibration exercise on the characterisation of microplastics in marine sediment and water samples was carried out among five laboratories involved in the implementation of the Marine Strategy Framework Directive (MSFD) in their country. The samples were prepared by mixing cleaned natural sediment and sea water with microplastics sets made of particles of various polymers, shapes and colours. Overall, the errors on total counts were under 25% in absolute value. The risk of non-detection and loss of particles is greater than the risk of contamination during sample analysis. Significant differences are observed among particle types. It appears difficult to obtain reliable and comparable data on the colour of microplastics. A comparison of the errors with regards to the protocols used led to recommend NaCl [1.2 g/cm3] density separation for sediment and one filtering step (200 μm). The operators' experience appears as a key factor for the quality of the results.

The mining operation and tailing deposits in Stratoni region, Northern part of Greece, make monitoring activities necessary both in the terrestrial and coastal areas. As a part of a preliminary monitoring action, in summer of 2012, surface sediment samples in the coastal area of Stratoni (in Ierissos Gulf) were collected and measured aiming a) to obtain concentration levels of (Natural Occurring Radioactive Materials) NORM and heavy metals (e.g. As, Zn, Cu, Pb and Mn,), b) to identify minerals composition and c) to determine the distribution of the grain size. The activity concentrations of 238U, 232Th daughters and 40K were found between (20-100) Bq/kg, (20-35) Bq/kg and (420-700) Bq/kg, respectively. The concentrations of the most toxic heavy metals were found, (8-4100) ppm for As, (30-4000) ppm for Zn, (7-200) ppm for Cu, (40-1700) ppm for Pb and (400-26000) ppm for Mn. In addition, granulometric analysis reveals mostly sandy and sandy-mud sediments (97 – 53% content of sand). In general, enhanced levels of heavy metals and radionuclides were located near the load-out pier area of the coastal region. So, the input mechanisms of them (via local streams, rainfall, floods or others) into the sea and their levels has to be periodically investigated through more concerted monitoring actions.

Environmental pollution of industrial areas and especially of areas which contain industries that involve processing of NORM (Naturally Occurring Radioactive Materials), requires monitoring radionuclide activ- ities and trace metal concentration. In the gold mine facility of Stratoni region in Ierissos Gulf, surface sediment samples were analysed regarding TENORM (Technologically Enhanced NORM) and toxic metals (e.g. As, Pb, Cu, Cr and Ni). Radionuclide activity concentrations (226Ra, 214Pb, 214Bi, 210Pb, 228Ac, 212Pb, 212Bi, 208Tl, 40K) were measured by means of gamma-ray spectrometry using a high-purity ger- manium (HPGe) detector, while the trace metals concentrations were determined using the XRF (X-Ray Fluorescence) technique. The results indicate that the surface sediments of the Ierissos Gulf are significantly polluted with As, Pb and Cu. Surface distribution analysis of the studied radionuclides and toxic metals (e.g. TENORM, As, Pb, and Cu) indicates maximum contamination levels close to the factory area, which decrease gradually with increasing distance from the shore. The interpretation of the increased levels is under investigation since the load-out facility of the mining operations in the town of Stratoni affects the whole ecosystem.

Macro- and microplastics abundances were determined in the Adriatic Sea following the MSFD TG10 protocol. The studied areas included populated gulfs, river outlets and offshore waters in five Adriatic countries. The use of small ships enabled us to detect small sized plastics (2.5-5 cm) and record average macroplastics densities of 251 +/- 601 items km(-2), one order of magnitude higher than previously considered. Results from manta net tows for microplastics revealed an average abundance of 315,009 +/- 568,578 items km(-2) (217 +/- 575 g km(-2)). We found significantly higher microplastics abundances in nearshore (<= 4 km) than in offshore waters (> 4 km) and this trend seems to affect also the small sized macro plastic fragments (2.5-5 cm). The dominant polymers were polyethylene and polypropylene while the presence of some rare polymers and waxes used in food and dentistry indicated waste water treatment plants as potential sources of microplastics.

The dominance and persistence of plastic debris in the marine environment are well documented. No information exists in respect to their lifespan in the marine environment. Nevertheless, the degradation potential of plastic litter items remains a critical issue for marine litter research. In the present study, polyethylene terephthalate bottles (PETs) collected from the submarine environment were characterized using ATR-FTIR in respect to their degradation potential attributed to environmental conditions. A temporal indication was used as indicative to the years of presence of the PETs in the environment as debris. PETs seem to remain robust for approximately fifteen years. Afterwards, a significant decrease of the native functional groups was recorded; some even disappear; or new-not typical for PETs-are created. At a later stage, using the PET time series collected from the Saronikos Gulf (Aegean Sea–E. Mediterranean), it was possible to date bottles that were collected from the bottom of the Ionian Sea (W. Greece). It is the first time that such a study has been conducted with samples that were actually degraded in the marine environment.

A methodology is presented to assess the environmental status sensu the Marine Strategy Water Framework Directive (MSFD) based on data obtained from the monitoring of water quality in the Hellenic coastal waters within the Water Framework Directive (WFD). An adapted decision tree used for integrating the results of the WFD in the Basque country was applied. Modifications lie to the evaluation of the physicochemical status based on a eutrophication index developed for Eastern Mediterranean waters. Results on hydromorphological, physicochemical and biological elements are presented. The chemical status was evaluated based on measurements of heavy metals in water. The evaluation of the biological quality was based on the use of metrics developed for phytoplankton biomass, benthic macroinvertebrates and macroalgae updated to accommodate MSFD needs. Results on the integrative status of the water bodies were validated by correlating classification results with a pressure index and environmental indicators in water column and sediment. Following this decision tree the majority of stations expected to be at risk of achieving the good status were found in moderate status. Benthos was found to be the element with the closest agreement with the integrated final status having an increased weighting in the decision tree. The quality of benthos and in some limited cases the eutrophication index determined largely the final status. The highest disagreement with the integrative classification was produced by macroalgae. All indicators used correlated with water and sediment parameters but benthos correlated better with sediment factors while phytoplankton and eutrophication index with water column parameters.

In the present work, abundance, spatial distribution and qualitative composition, of benthic marine litter, were investigated in five study areas from the Eastern Mediterranean and Black Seas (Saronikos, Patras and Echinades Gulfs; Limassol Gulf; Constanta Bay). Surveys were performed using the monitoring protocol proposed by the Technical Group for Marine Litter. Densities ranged from 24items/km(2) to 1211items/km(2), with the Saronikos Gulf being the most affected area. Plastics were predominant in all study areas ranging from 45.2% to 95%. Metals and Glass/Ceramics reached maximum values of 21.9% and of 22.4%. The size distribution of litter items showed that ⩾50% fall into medium size categories (10×10cm, 20×20cm) along with an elevated percentage of small-sized (<5×5cm) plastic litter items. The comparative analysis of the data highlighted the dependence of the marine litter problem on many local factors (human sources and oceanographic conditions) and the urgent need for specific actions.

The objective of our study was to provide a comprehensive evaluation on C, N, P cycling in medium sized Mediterranean rivers, such as the Evros, experiencing multiple pressures (intensive agriculture, industrial activities, population density). Our work aims also to contribute to the development of integrated management policies. Dissolved organic matter (DOM) cycling were investigated, during a one-year study. It was shown that the organic component of N and P was comparable to those of large Mediterranean rivers (Rhone, Po). In the lower parts of the river where all point and non-point inputs converge, the high inorganic N input favour elevated assimilation rates by phytoplankton and result in increased chl-a concentrations and autochthonous dissolved organic matter (DOM) production during the dry season with limited water flow. Moreover, carbohydrate distribution revealed that there is a constant background of soil derived mono-saccharides on top of which are superimposed impulses of poly-saccharides during blooms. During the dry season, inorganic nutrients and DOM are trapped in the lower parts of the river, whereas during high flow conditions DOM is flushed towards the sea and organic nitrogen forms can become an important TDN constituent (at least 40%) transported to shelf waters. The co-existence of terrigenous material with autochthonous and some anthropogenic is supported by the relatively low DOC:DON and DOC:DOP ratios, the positive correlation of DOC vs chl-a and the decoupling between DOC and DON. Overall, this study showed that in medium size Mediterranean rivers, such as the Evros, intensive agriculture and pollution sources in combination with water management practices and climatic variability are important factors determining C, N, P dynamics and export to coastal seas. Also, it highlights the importance of the organic fraction of N and P when considering management practices.

The dynamics of dissolved organic matter (DOM) in the Marmara Sea–Dardanelles Straits–North Aegean Sea were investigated using measurements of dissolved organic carbon and nitrogen (DOC, DON), PARAFAC modeling of 3-D excitation–emission fluorescence spectra and bacterial production (BP) and respiration (BR) rates. In the surface brackish waters, chemical parameters showed an increase from the Aegean to the Marmara (DOC: 65–217μmolL−1; DON: 3.08–9.34μmolL−1; Dissolved Inorganic Nitrogen (DIN): 0.044–1.38), followed by an increase in BP rates (7.2–195nmolL−1d−1). In the subsurface waters, DIN also showed an increase in the Marmara basin (0.085–9.79μmolL−1) followed by an increase in BP rates (3.3–17.4nmolL−1d−1). PARAFAC modeling revealed three fluorescent components: λex/λem: <260(330)/464nm, humic-like; λex/λem: <(260) 285/364nm, quinone-like; λex/λem: 270/308nm, tyrosine-like. DOC:DON ratios were found similar for the Marmara (21±3) and the N. Aegean Sea (19±2). The slopes ΔDOC:ΔDON suggested that in the Marmara Sea mineralization processes require more carbon relative to nitrogen (22.3), whereas in the N. Aegean there is preferential removal of nitrogen over carbon (5.66). The lack of significant correlation between DOC and AOU (apparent oxygen utilization) in the deep Marmara waters indicates that particulate organic matter is important in deep mineralization processes.

The aim of this work is to assess trace metal pollution status (Cd, Cu, Ni, Pb, Zn) in the waters of Saronikos Gulf, Greece, in line with the WFD and MSFD European Directives, based on data collected over a decade (2000–2010). Dissolved metal background levels are estimated for the first time for Greek marine waters and the upper limits are: Cd: 0.574nmolL−1; Cu: 8.26nmolL−1; Ni: 7.94nmolL−1; Pb: 2.60nmolL−1; Zn: 115nmolL−1. The variability of dissolved and particulate metals reflected the presence of several point sources and revealed the importance of natural mechanisms acting as non-point sources. The status of Saronikos Gulf is classified as ‘High’ for most metals studied. An exception to this is the enclosed Elefsis Bay where Cu, Ni and Zn concentrations are found above background. Our work will assist the implementation of WFD and MSFD directives in Greece.

Chronic ulcerative dermatopathy (CUD) also known as chronic erosive dermatopathy, hole-in-the-head, head and lateral line erosion syndrome (HLLE) and lateral line depigmentation (LLD) is a chronic disease of unknown aetiology that affects the lateral line canals of the head and the trunk of various fish species. It has been described only in freshwater species although there are reports that it also affects marine fish. Here, we describe the disease in cultured sharpsnout sea bream using histology and scanning electron microscopy and identify several marine species as CUD sensitive. The results of this study correlate the development of the disease with the use of borehole water, indicating that the aetiology is probably associated with water quality rather than nutritional imbalance or infectious agents.

Saronikos Gulf (Greece) practically constitutes the sea border of the metropolitan city of Athens and the alongshore outskirts, and it receives the treated wastes of ∼4 million people from a point source that discharges on the sea bottom at ∼65m water depth. Total organic carbon (TOC) was measured in 477 seawater samples collected in the Saronikos Gulf, during 10 cruises, from August 2001 to May 2004 and analyzed with the High Temperature Catalytic Oxidation method (HTCO). TOC concentrations ranged from 49 to 198μmolCL−1 in agreement with other Mediterranean coastal waters. The highest TOC concentrations were found in the upper waters (0–75m), whereas in the deeper parts of the Gulf (between 100 and 400m) TOC concentrations were kept constantly low (49–70μmolCL−1). A general pattern towards higher TOC concentrations during summer was also observed. Calculations of non-refractory (labile+semi-labile) organic material based on a one-dimensional (1D) conceptual model showed that it corresponds to 33% of the bulk TOC during summer and to 27% during winter. Bacterial production (BP) was measured at selected stations of ∼70–80m depth using the [3H] leucine method. Depth integrated BP values varied from 2.8 to 10.9mmolm−2d−1, whereas extraordinary high integrated BP values (126 and 140mmolm−2d−1) were observed at the station over the treated sewage outflow. From the turnover time, τ, of the non-refractory TOC by bacteria it was implied that organic matter in the effluents is extremely labile (2–58 days). Moreover, τ values at the other sites showed that during summer non-refractory organic material resisted bacterial degradation (1–8 months), whereas during early spring it was easily degradable (20–50 days). The balance of TOC fluxes for the Inner Gulf for June and September 2003 showed that the Inner Gulf acts as a net producer of TOC during summer. Our results suggest that the presence of the Athens treated sewage outfall does not contribute to the observed summer accumulation of TOC in the Inner Gulf and other causes such as increased bacteria predation and/or nutrient limitation must be responsible.

Organically complexed and total dissolved copper and nickel were measured in the Thermaikos Gulf waters during winter 1998. Total concentrations ranged from 1.13 nmol/L to 7.02 nmol/L for copper and from 3.04 nmol/L to 9.50 nmol/L for nickel. The C18 Sep-Pak solid phase extraction technique was used in order to determine the amount of copper and nickel complexed with the hydrophobic component of the dissolved organic matter (DOM). Up to 32.4% of total copper and 4.57% of total nickel were complexed with the DOM extracted by C18. By applying HPLC analysis it was shown that the majority of the organic compounds retained by C18 had intermediate to low polarity. Using the absorbance ratio a254/a436 it was possible to unravel that humic substances of both terrestrial and marine origin were present in the Thermaikos Gulf and their distribution followed the dilution of riverine waters. Moreover our results indicated that organic binding of both Cu and Ni was stronger with the hydrophobic compounds of terrestrial origin than with those of marine origin.

The objectives of this study were to examine both spatial and temporal changes of particulate major elements and minor metals, as well as dissolved Mn and Cd, in the waters of Thermaikos Gulf. Collections of water and suspended particulate matter (SPM), as depth profiles (5–8 depths), were undertaken at 10 principal stations, essentially on a N–S traverse of the western side of the Gulf.One of the principal aims of the study was to observe if there was any change in the patterning of the elements between the three occupations of the stations: (a) in September 2001, immediately before the commencement of trawling; (b) in October 2001, whilst fishing was active; and (c) in winter/early spring conditions (February 2002), when fishing was still active, but after a change of river/atmospheric conditions.Bottom (∼20m) waters were dominated by sediment resuspension; this was identified by concentration changes in the aluminosilicate elements (e.g. Al, Ti, K, Fe) of the SPM. A two- to three-fold increase occurred between September and October, caused probably by trawling; this was sustained at the offshore stations, in February. During February, the western inshore stations showed little sediment resuspension, caused by extreme winter cooling and the sinking of water. Consequently, a N–S density discontinuity existed at all water depths, which prevented the thermohaline cyclonic circulation from penetrating into the western seaboard of the Gulf. The distribution of dissolved and particulate Mn in the lower waters was due to redox cycling of the element at the benthic boundary; this was more intense in the north, where the organic supply was higher.Biogenic element concentrations and Ca/Al, Si/Al ratios showed no evidence that trawling activity promoted higher biological production. Strong correlations of Co, Cr, Ni and V, with Al and K, showed that these elements were associated strongly with detrital aluminosilicates. However, the variable association of Cd, Pb and Zn, with K (and Al), especially in the upper waters, implied an anthropogenic source derived from the rivers and the city of Thessaloniki. Examination of the Kd's of Cd showed a two-order of magnitude decrease with depth, caused by resuspension and possible advection of relatively unpolluted sediments, into the western Gulf.

One hundred-twelve seawater samples collected from 15 stations during two oceanographic cruises in '97 and '98 in the North Aegean Sea were analysed for dissolved Zn and concentrations ranged from 0.73 to 17.16 nM (mean value 4.96 nM) for the May '97 cruise and from 1.31 to 9.88 nM (mean value 3.41 nM) for the February '98 one. The concentrations found in this study are in good agreement with those reported for the western Mediterranean (2.7 - 4.7 nM) and the Adriatic (2.71-3.93 nM). From the analysis of the data it is clear that there are no differences between the nearshore and the open sea samples. No seasonal differentiations were observed. In contrast to the general vertical distribution pattern of Zn in the ocean, the vertical distribution pattern in the samples analysed is quite different. There is a general trend of elevated surface layer concentrations and also a second maximum for certain stations in the bottom layers. From the above we can suggest that the reason of the relatively enhanced surface Zn concentrations may be sources of different origin, such as atmospheric inputs, riverine/coastal runoff, Black Sea Water influence, etc. As far as the bottom layer maximum is concerned, it may be due to the remobilization of Zn from sediments.