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High amounts of mercury (Hg) can be released into the atmosphere from soil surfaces of legacy contaminated areas as gaseous elemental mercury (Hg0). The alluvial plain of the Isonzo River (NE Italy) suffered widespread Hg contamination due to the re-distribution of Hg-enriched material discharged by historical cinnabar mining at the Idrija mine (Slovenia), but an assessment of Hg0 releases from the soils of this area is still lacking. In this work, Hg0 fluxes at the soil-air interface were evaluated using a non-steady state flux chamber coupled with a real-time Hg0 analyser at 6 sites within the Isonzo River plain. Measurements were performed in summer, autumn, and winter both on bare and grass-covered soil plots at regular intervals during the diurnal period. Moreover, topsoils were analysed for organic matter content and Hg total concentration and speciation. Overall, Hg0 fluxes tracked the incident UV radiation during the sampling periods with daily averages significantly higher in summer (62.4 ± 14.5-800.2 ± 178.8 ng m-2 h-1) than autumn (15.2 ± 4.7-280.8 ± 75.6 ng m-2 h-1) and winter (16.9 ± 7.9-187.8 ± 62.7 ng m-2 h-1) due to higher irradiation and temperature, which favoured Hg reduction reactions. In summer and autumn significant correlations were observed between Hg0 fluxes and soil Hg content in soils (78-95% cinnabar), whereas this relationship was not observed in winter likely due to relatively low emissions found in morning measurements coupled with low temperatures. Finally, vegetation cover effectively reduced Hg0 releases in summer (∼9-68%) and autumn (∼41-78%), whereas the difference between fluxes from vegetated and bare soils was not evident during winter dormancy due to scarce soil shading. These results suggest the opportunity of more extended spatial monitoring of Hg0 fluxes particularly in the croplands covering most of the Isonzo River alluvial plain and where bare soils are frequently disturbed by agricultural practices and directly exposed to radiation.

Since arsenic (As) exposure is largely due to geochemical contamination, this study focused on the remediated area of Santana do Morro, a district of Santa Barbara, Minas Gerais, Brazil, which was previously contaminated with As due to gold mining. Total As concentrations in sediment, soil and plants were determined, next to As species, anionic arsenic compounds As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), in plants samples. Total As concentrations in soil and sediments were slightly elevated (16-18 µg g -1 ) and most of the plants contained low levels of As (< 1 µg g -1 ). The exception was a native plant Eleocharis geniculata (L.) which contained elevated levels of As (4 µg g -1 ). The exposure of this plant to As under controlled conditions (hydroponics) indicated its possible tolerance to elevated As levels and suggesting its potential use in phytomonitoring of As-contaminated sites. This plant is able to metabolize arsenate to arsenite and contained MMA and DMA, both in its natural habitat and under controlled conditions.

Gaseous exchanges of mercury (Hg) at the water–air interface in contaminated sites strongly influence its fate in the environment. In this study, diurnal gaseous Hg exchanges were seasonally evaluated by means of a floating flux chamber in two freshwater environments impacted by anthropogenic sources of Hg, specifically historical mining activity (Solkan Reservoir, Slovenia) and the chlor-alkali industry (Torviscosa dockyard, Italy), and in a pristine site, Cavazzo Lake (Italy). The highest fluxes (21.88 ± 11.55 ng m−2 h−1) were observed at Solkan, coupled with high dissolved gaseous mercury (DGM) and dissolved Hg (THgD) concentrations. Conversely, low vertical mixing and saltwater intrusion at Torviscosa limited Hg mobility through the water column, with higher Hg concentrations in the deep layer near the contaminated sediments. Consequently, both DGM and THgD in surface water were generally lower at Torviscosa than at Solkan, resulting in lower fluxes (19.01 ± 12.65 ng m−2 h−1). However, at this site, evasion may also be limited by high atmospheric Hg levels related to dispersion of emissions from the nearby chlor-alkali plant. Surprisingly, comparable fluxes (15.56 ± 12.78 ng m−2 h−1) and Hg levels in water were observed at Cavazzo, suggesting a previously unidentified Hg input (atmospheric depositions or local geology). Overall, at all sites the fluxes were higher in the summer and correlated to incident UV radiation and water temperature due to enhanced photo production and diffusivity of DGM, the concentrations of which roughly followed the same seasonal trend.

Estuaries can be thought as a sedimentary trap leading to the accumulation of potentially toxic trace elements (PTEs) in sediments. However, biogeochemical processes at the sediment-water interface (SWI) may also be responsible for the release of dissolved PTEs and nutrients in the overlying water column affecting the water quality. The estuarine system of the Timavo River (Gulf of Trieste, northern Adriatic Sea) is a semi-closed aquatic environment where a long-lasting oxic-hypoxic interface along the water column occurred due to the scarce water circulation in the innermost sector. To prevent bloom-forming and potential production of toxins and off-flavours, artificial mixing has been provided with a bubble plume installation connected to pressurised air and built on the sediment surface aiming at reoxygenating the water column. The aim of this research was to evaluate the behaviour of PTEs (As, Cr, Hg, Fe, Mn, Ni, Pb, V) and nutrients (NO3, NO2, NH4 and SRP) along the water column and at the SWI before (June) and during (September) the activation of the forced aeration system. Water samples were collected at different depths along the water column, in situ benthic chamber experiments were performed at the SWI and short sediment cores were sampled to investigate both the sediment and porewater. Dissolved oxygen decreased along the water column, especially in June when hypoxia (2.29 mg/L) and reductive conditions (58 mV) were observed at the bottom resulting in increasing dissolved PTE and nutrient concentrations. Accordingly, a gradual oxygen depletion was observed in the benthic chamber testifying to intense organic matter remineralisation processes. Moreover, the highest concentrations of dissolved PTEs in porewater were restricted to the top of the sedimentary sequence, especially in June when hypoxic conditions may promote PTE and nutrient effluxes from the sediment to the water column.

We synthesized our present understanding of pelagic–benthic (P–B) interactions in the northern Adriatic Sea (NAS) and Chesapeake Bay (CB) in a comparative analysis that builds on a prior comparison. We focus on primary production (PP) in the water column and benthos, the sedimentation and horizontal transport of particlulate organic matter (POM), and biogeochemical responses of the benthic community to sedimentation. Phytoplankton net PP (NPP) remains higher in CB (five times that in NAS) and rates of benthic respiration appear greater in CB (three times that in NAS). A lower fraction of phytoplankton NPP plus riverine inputs of POM is deposited to sediments in the NAS (23%) compared to CB (83%). A high percentage of organic matter inputs are respired by plankton and exported in the NAS and CB, and benthic communities respired a similar percentage of POM (86% in the NAS, 92% in CB). Net release of regenerated N from the benthos (0.2–0.3 mol N m−2 year−1) is also similar in both systems. At 0.53 mol N m−2 year−1, rates of benthic denitrification are higher in CB than in the NAS (0.3 mol N m−2 year−1), and the NAS appears to bury similar fractions of deposited N and P (N: 23% in NAS, 19% in CB; P: 50% in NAS, 45% in CB). To address the impacts of future climate‐driven warming and acceleration of the water cycle, we recommend a return to sustained monitoring combined with numerical simulations to allow improved understanding and predictions of changes in P–B interactions.

The accumulation of contaminants and their potential mobility represent two of the main environmental issues facing coastal environments. Sediments often act as “reservoirs” of contaminants, including potentially toxic trace elements, but they can also be considered a secondary source of contamination due to remobilisation processes at the sediment-water interface which may affect the quality of the coastal water and aquatic biota. This research aims to provide a geochemical characterisation of the estuarine system of the Timavo/Reka River, focusing on the occurrence of trace elements in different environmental matrices with the purpose of highlighting potential critical conditions in terms of environmental quality. The surface sediments were found to be enriched in several trace elements especially in the innermost sector of the area. There, sulphate-reductive conditions in the bottom saltwater testify to potential anoxia at the sediment-water interface, driving trace element accumulation in the residual fraction of the sediments. However, Fe and Mn redox behaviour appears to play a crucial role in the recycling of dissolved trace elements in the water column. With the lone exception of the saltwater in the innermost sector, trace elements were found to be mainly associated with suspended particles due to oxidation and precipitation processes, whereas a common lithogenic origin was identified for Cr, Ni, and Co, which are significantly correlated both in the surface sediments and in the suspended particles.

Butyltin compound (BTC) contamination was evaluated in two north Adriatic marinas, San Rocco (Italy) and Lucija (Slovenia). BTC sedimentary concentrations (121 ± 46 and 352 ± 30 ng Sn g-1 in San Rocco and Lucija, respectively) evidenced the past use of antifouling paints, confirmed by the reduced tributyltin content (~ 46%) with respect to the sum of BTC. Elemental and organic carbon isotopic (δ13C) analyses of bulk sediments and its lipid and humic substances were performed in order to evaluate their role in BTC partitioning and preservation. The δ13C of sedimentary bulk and refractory organic matter suggested that diagenetic processes could play a role in the preservation or release of pollutants. No contamination was found in water collected from the benthic chamber and thus, fluxes at the sediment-water interface were not assessed, except for MBT efflux at Lucija (28.9 ng Sn m-2 day-1). Nevertheless, BTC concentrations in porewaters (up to 75 ng Sn l-1) and rather low sediment-porewater partitioning coefficients (Kd) with respect to the data reported in the literature would suggest a potential risk of the reintroduction of BTC into the water column at both sites: at Lucija, sedimentary contamination is high despite the greater Log Kd, whilst at San Rocco, the low BTC concentration is associated with a reduced sediment affinity.

Estuaries are unique water systems and represent a vital link between land and sea. River transported contaminants, among which trace elements are of major concern, are subjected to a variety of physical, chemical and biogeochemical processes in the estuarine mixing zone. The Isonzo/Soča River is the main source of freshwater into the Gulf of Trieste (northern Adriatic Sea) and is known as the primary source of Hg due to long-term cinnabar (HgS) extraction from the Idrija mining district (Slovenia). Mercury distribution, cycling and speciation have been intensively studied at the Isonzo/Soča River mouth. Still, little information is currently available regarding other trace elements (As, Co, Cu, Cs, Cr, Fe, Ni, Mn, Pb and Zn). Indeed, this research aims to evaluate trace element occurrence and partitioning behaviour among suspended particulate matter (> 0.45 μm), colloidal material (0.45 μm – 10 kDa) and the truly dissolved fraction (< 10 kDa) at the mouth of the Isonzo/Soča River. Generally, trace elements are mainly associated with suspended particulate matter, which represents their main effective vehicle to coastal environments. In addition, dilution effects between riverine and marine particles are responsible for the decrease in particulate trace element concentrations along the water column. Mercury was notably present in winter in the freshwater, as expected under conditions of high river discharge. As opposed to other trace elements, particulate Mn was found to be high in the marine water, particularly in summer when high water temperatures could promote oxidation and precipitation processes. The Isonzo/Soča River mouth is characterised by a strong salinity gradient and geochemical processes appear to affect trace element partitioning behaviour. In this context, Fe, Mn and Cu were found to be mainly associated with the suspended particles and displayed the highest concentration in the colloidal material. Conversely, the truly dissolved fraction prevailed for As and Cs, which are often present in ionic dissolved forms in natural water systems.

Estuaries are transitional water systems where the hydrodynamic processes governing water circulation actively influence suspended particle transport and deposition. In the estuarine mixing zone, the strong physico-chemical gradients resulting from the interaction between river freshwater and seawater may affect the distribution, mobility and fate of several potentially toxic compounds, among which trace elements are of major concern. Knowledge regarding the partitioning behaviour of trace elements would provide essential scientific support for the environmental management of estuaries. In this study, trace element occurrence and phase partitioning among suspended particulate matter, colloidal material and the truly dissolved fraction were investigated in the main Italian and Slovenian estuarine environments of the Gulf of Trieste (northern Adriatic Sea). Further information about the water quality at the river mouths was provided and, in addition to the traditional evaluation of single chemical parameters, a multi-way principal component analysis was employed in order to depict disparities among sampling sites, water layers and seasonal conditions with the final aim of evaluating trace element phase partitioning. Results indicated that the suspended particulate matter acts as the main effective vehicle for Cu, Cr, Fe, Ni and Pb, and enhanced adsorption processes resulted in elevated partitioning coefficients, especially for Fe and Pb. Although disparities occurred between sampling sites and seasons, trace elements showing affinity for the solid phase appeared to be partially bound to the colloidal material. Conversely, As and Cs prevailed in the truly dissolved fraction, especially in seawater and showed scarce affinity for both the suspended particles and colloids.

The Gulf of Trieste and adjacent Grado and Marano Lagoon (northern Adriatic Sea) are considered as an important “natural bioreactor” that can increase sedimentary methylmercury (MeHg) production by mobilizing the extensive mercury (Hg) pool as a result of historical (500 years) Hg mining and smelting activities in Idrija (NW Slovenia), the world’s second largest Hg mine. Even though the mine was definitely closed in 1995 the Soča/Isonzo River system still delivers about 1.5 t of Hg to the gulf annually and the MeHg is elevated in this marine environment. Research conducted by late M.E. Hines showed that Hg is readily methylated and demethylated in marine, lagoonary and freshwater sediments but the relative activities varied greatly with locality. Methylation activity increased from freshwater to the marine sites, conversely the highest demethylation was found in estuarine and lagoon sites. The methylation/demethylation ratios were consequently low in coastal sites but increased ib the gulf. Subsequent investigations in the southern, less contaminated (“pristine”) sediments of the gulf revealed that MeHg is also continuously produced especially in autumn in parallel with higher bottom water temperature and lower oxygen content. Sulphate reduction was found to control both processes. Hg methylation in sediments of coastal lagoon was controlled by rapid demethylation and the Hg bioavailability was affected by Hg adsorption and precipitation, In offshore marine sites, the sulphide produced by sulphate reduction lowers Hg methylation. Methylation of dissolved Hg, nearly 100% colloidally bonded, in the seawater column of the gulf was not detected (showing a pronounced Hg reduction potential) suggesting that sediments are the principal methylation site and the source of MeHg to the water column. It is likely that demethylation and reduction prevent the excessive accumulation of MeHg in the food webs of the Gulf of Trieste.

Estuaries represent a crucial link between land and sea where river fluxes of trace elements are subjected to a variety of physical and biogeochemical processes. The boundary conditions are extremely variable in the estuarine mixing zone affecting trace element speciation and their partitioning among different phases. The Isonzo/Soča River represents the main source of Hg in the Gulf of Trieste due to past mining activity at the Idrija mercury mine (Slovenia). The aim of this work is to evaluate trace element occurrence, size partitioning and mixing behaviour at the mouth of the Isonzo/Soča River. For this purpose, large volume water samples were collected from surface, mixing and bottom layers under various seasonal conditions. Size fractionation was performed using vacuum filtration and cross-flow ultrafiltration to isolate the suspended particulate matter (SPM) and the colloidal retentate solution, respectively, from the truly dissolved. Trace elements appear to be mainly associated with the SPM and dilution effects between riverine and marine particles are responsible for the decrease in their concentration along the water column. As expected, Hg was notably present during winter in the surface freshwater, in particular under conditions of elevated river discharge. On the contrary, Mn was found to be higher at the bottom, particularly during summer, as a consequence of oxidation processes followed by the precipitation of Mn oxy-hydroxides promoted by high water temperature. The strong physico-chemical gradients, especially in terms of salinity, are often responsible for the non-conservative behaviour of several trace elements. Iron, Mn and Cu displayed a non-conservative behaviour during mixing and simultaneously showed the highest content of colloidal material. On the contrary, conservative behaviour was found for As and Cs which are often present under ionic dissolved forms in natural water systems

Since the environmental levels of selenium (Se) can moderate the bioaccumulation and toxicity of mercury (Hg) in marine organisms, their interactions were studied in seawater, sediments, plankton and the benthic (Bull ray Pteromylaeus bovinus, Eagle ray Myliobatis aquila) and the pelagic (Pelagic stingray Dasyiatis violacea) rays, as apex predators in the Gulf of Trieste (Northern Adriatic Sea). Male and female rays showed no difference in the Se contents in muscle tissue. Pelagic species contained higher Se levels in muscle but slightly lower levels in the livers of both genders. The Hg/Se ratios in seawater dissolved and colloidal fractions, plankton and sediment were

Metabolism and carbon, oxygen, and nutrient fluxes (DIC, DOC, DO2, NO2−, NO3−, NH4+, PO43− and SiO44−) were studied during three surveys at two sites (VN1 and VN3) located at a fish farm at the Marano and Grado Lagoon (northern Adriatic Sea), using an in situ benthic chamber. Field experiments were conducted in July and October 2015 and March 2016 at a depth of approximately 2 m along the main channels of the fish farm. Water samples were collected by a scuba diver every 2 h in order to investigate daily fluxes of solutes across the sediment-water interface (SWI). Regarding the solid phase, Corg/Ntot and Corg/Porg molar ratios suggested an autochthonous marine origin of the organic matter and a minor preservation of P in the sediments, respectively; high values of sulphur (Stot) were also encountered (0.8–2%). The conditions at VN3 were mostly anoxic with high NH4+ levels (30–1027 μM) and the absence of NO3−. Substantial daily patterns of all solutes occurred especially in autumn and winter. On the contrary, fluxes at VN1 were less pronounced. Usually, inverse correlations appeared between dissolved O2 and DIC trends, but in our system this was observed only at VN3 in autumn and accomplished by a parallel increase in NH4+, PO43− and SiO44− during intense nutrient regeneration. These results are significantly different than those reported for open lagoon environments, where nutrient regeneration at the SWI and in surface sediments is the primary source of nutrients available for assimilation processes, especially during the warmer period of the year when the natural nutrient input by fresh water inflows is limited. Due to the importance of this site for aquaculture, biodiversity and ecosystem services, useful suggestions have been provided from this study in order to improve the quality of this unique aquatic system.

Partitioning of potentially harmful elements (PHEs) and their speciation in estuarine environments strongly depends on the physico-chemical boundary conditions, especially in terms of salinity gradient. Due to their high abundance in aquatic environments, colloidal fraction is known to play a central role in the regulation of PHEs occurrence, mobility and speciation. Aquatic colloids represent important intermediaries in the removal processes, such as coagulation, of PHEs and, consequently, they are one of the most important factors able to regulate the fate of PHEs in the environment. The present work aims to report the results of PHEs partitioning between particulate (> 0.45 µm), colloidal (10 kDa - 0.45 µm) and dissolved (< 10 kDa) fractions in different estuarine waters of the Gulf of Trieste (Northern Adriatic Sea). In order to achieve these objectives, water samples from surficial and bottom layers of the water column were collected along Italian and Slovenian river mouths. Several CTD (Hydrolab H2O Multiprobe with a 0.10 dbar pressure step) vertical profiles of salinity, temperature and turbidity were performed in order to identify the water masses before sampling. Generally, the surficial water samples were collected at variable depths, according to the salinity trend and along the salinity gradient, whereas the bottom water samples were representative of the marine water intrusion. In addition, the main physico-chemical parameters (temperature, pH, redox potential (Eh), dissolved oxygen and electrical conductivity (EC)) were measured in situ through portable probes (pH-meter PH25 and Conductivity-meter CM35+ by Crison Instruments) submersed in a bucket. Samples for PHEs detection were filtered through 0.45 µm filters (Millipore HA, Ø 47 mm) in order to isolate the particulate fraction which was acid-digested through a total dissolution in a closed microwave system (Multiwave PRO, Anton Paar). Subsequently, the filtrate samples were ultrafiltered through 10 kDa membranes (Vivaflow 200, Sartorius). The ultrafiltration was performed in recirculation mode using a concentration factor equal to about 60 in order to collect large amounts of colloids. All sample aliquots were analysed for PHEs determination by means of Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Nexion 350x Perkin Elmer), with the only exception of Hg analyses which was also performed through Cold Vapor Atomic Fluorescence Spectrometry (CV-AFS, Mercur Analytic Jena).

One of the main environmental issues affecting coastal marine environments is the accumulation of contaminants in sediments and their potential mobility. In situ benthic chamber experiments were conducted at two tourist ports (marinas) located in the Gulf of Trieste, one in Slovenia and one in Italy. The aim was to understand if and where recycling at the sediment-water interface (SWI) may affect metal(loid)s. Short sediment cores were also collected near the chamber to investigate the solid (sediments) and dissolved phases (porewaters). Both diffusive and benthic fluxes were estimated to elucidate the release of metal(loid)s at the SWI. Total element concentrations and their labile fractions were determined in sediments to quantify their potential mobility. The total element contents were found to be two orders of magnitude higher in the Italian marina than in the Slovenian one, especially for Hg (up to 1000 mg kg−1), whereas the labile fraction was scarce or null. The opposite occurred in the Slovenian marina. Metal(loid)s in porewaters showed a clear diagenetic sequence and a close dependence upon the suboxic/anoxic conditions of sediments. The results suggest that although the sediments of the Italian marina exhibit the highest total metal(loid) concentration, these elements are scarcely remobilisable. Conversely, in the Slovenian marina, sediments seem to be comparatively more prone to release metal(loid)s at the SWI.

Purpose Concentrations and transformations of mercury were measured in river, estuarine, and marine sediments to determine factors affecting the fate of mercury entering the northern Adriatic Sea. Materials and methods Radiotracer methodology was used to compare rates of mercury methylation (203Hg), MeHg demethylation (14C), and sulfate reduction (35S) in sediment depth profiles to concentrations of total and dissolved mercury species in the lower freshwater region of the Isonzo River, the coastal lagoons, and in the Gulf of Trieste, northern Adriatic Sea. Results and discussion Mercury was readily methylated and demethylated in all sediments, but the relative activity of these processes varied greatly with location. Methylation activity increased greatly from freshwater to the marine regions; however, demethylation was extremely high in the estuarine and lagoon sites. Ratios of methylation to demethylation were low in these coastal sites but increased further offshore in the gulf, which agreed with increased ratios of MeHg to total Hg (%MeHg) in gulf sediments. Comparisons of microbial activities indicated that sulfate reduction strongly controlled both methylation and demethylation. However, Hg methylation in coastal lagoon sediments was controlled by rapid demethylation and the bioavailability of Hg that was affected by Hg adsorption and precipitation. Methylation in offshore marine sites correlated with sulfate reduction but not the partitioning of Hg between pore water and solid phases. The decrease in sulfide production offshore exacerbated Hg methylation. Conclusions The freshwater to marine gradient in the Idrija/Soča/Isonzo/Adriatic region is dynamic, exhibiting horizontally variable rates of microbial activities and Hg transformations that create Bhot spots^ of MeHg accumulation that are controlled differently in each region.

One of the main environmental issues affecting the coastal marine environments is the accumulation of contaminants in sediments and their potential mobility. The sediment acts as a sink for many chemical species (metal(oid)s, PAHs, PCBs etc.). However, this situation can be only temporary since early diagenesis biogeochemical processes can recycle these contaminants which may subsequently accumulate along the aquatic trophic chain. In this work, in situ experiments were conducted at two tourist ports (marinas) located in the Gulf of Trieste (northern Adriatic Sea), one in Slovenia and one in Italy. The latter is well known to be a site contaminated by long-term shipbuilding activities. The main aim was to understand if and where recycling at the sediment-water interface (SWI) may affect trace metal(oid)s. A benthic chamber, successfully used in other works in the same Gulf 1,2, was employed. Water sampling was performed during a 8-hour period to measure trace metal(oid) concentrations with time. Short sediment cores were collected near the chamber to investigate the solid (sediments) and dissolved phases (porewaters). Both diffusive and benthic fluxes were estimated to elucidate the release of trace metal(oid)s at the SWI. Total trace element concentrations were determined following a complete mineralization of the sediment (aqua regia + HF), whereas a weak extraction with diluted HCl (0.5 M) was carried out to quantify their potential “bioavailable fraction”. Quantitative analyses were performed by ICP–OES on sediment mineralized solutions and by ICP–MS on porewater and benthic water samples. Total element contents in sediments, resulted up to two orders of magnitude higher in the Italian marina (0.4 %Pb, 0.15% As and Cu, 0.25% Zn) than in the Slovenian one, confirming the high contamination level of this site. Despite this heavy contamination, the “bioavailable fraction” of metal(oid)s extracted was scarce or null. Conversely, sediments from the Slovenian site showed high percentages of the extractable fraction from 4% (Cr) to 82% (Cu) of the total content. Trace metal vertical profiles in porewaters showed a clear diagenetic sequence. The suboxic/anoxic conditions of sediments allowed the dissolution of Fe and Mn oxy-hydroxides, thus enhancing the concentrations in porewaters of Fe, Mn and other associated trace metal(oid)s. However, the diagenetic sequence and the suboxic/anoxic transition were highly dependent on the characteristics of each site. Maximum concentrations of dissolved Fe, Mn, Pb and Zn were found in the first centimeters of one site of the Italian marina where sediments became quickly anoxic with depth. Conversely, in the Slovenian marina and in the second Italian site, the highest concentrations were recovered from the deepest porewater layers, especially for Fe (up to 2.5 and 7.7 mg L-1, respectively). Positive effluxes were observed for Mn, Pb, Zn and V in the Italian marina whereas for Cu and Ni were most notably in the Slovenian marina and for as at both sites. Hg fluxes were low in spite of its high concentrations (up to 1000 mg kg-1) in sediments of the Italian site. In general, benthic fluxes of metal(oid)s at the SWI can be partially explained by considering the dissolution of Fe/Mn oxy-hydroxides and metal speciation in bottom sediments. The results suggest that although the bottom sediments of the Italian marina exhibit the highest trace metal(oid) concentrations, they are scarcely remobilizable. On the contrary, in the Slovenian marina, sediments seem to be comparatively a significant source of trace elements (except for Fe, Pb and V) in the water column as consequence of diagenetic processes at the related interface.

The influence of river discharge on the spatial and temporal variability of thermohaline and turbidity conditions at the sea surface (0.5 m) was studied in the shallow Bay of Koper (Gulf of Trieste, northern Adriatic Sea) which is influenced mainly by the polluted Rižana River. Conductivity, temperature and turbidity were measured monthly at 36 sampling sites between June 2011 and June 2013. Empirical orthogonal function analysis (EOF) was applied to investigate the data and to study the spatial distribution of variability and their temporal variations of temperature, salinity, density and turbidity. The EOF results showed an area of high variance in the proximity of the Rižana River mouth for all variables. The high variations in the time series for all variables were shown to be related mainly to high variations in the time series of the river discharges. Coupled field analysis showed the area of low salinity and high turbidity. A strong relationship was found between turbidity and suspended solid (TSS) concentration data collected in the local rivers and near shore zone suggesting that turbidity can be used as a satisfactory surrogate of TSS estimation., Utjecaj riječnog upliva na prostorne i vremenske varijabilnosti, termohalina svojstva i mutnoće na morskoj površini (0,5 m) je istraživano u plitkom Koparskom zaljevu (Tršćanski zaljev, sjeverni Jadran), koji je pod utjecajem uglavnom zagađene rijeke Rižana. Vodljivost, temperatura i mutnoća su mjereni mjesečno na 36 postaja između lipnja 2011. i lipnja 2013. Primijenjena je analiza empirijske ortogonalne funkcije (EOF) kako bi se istražili podaci i utvrdio prostorni raspored varijabilnosti, te vremenske promjene temperature, slanosti, gustoće i zamućenosti. Rezultati dobiveni EOF metodom su pokazali visoka odstupanja za sve varijable u području blizu ušća rijeke Rižana. Visoke varijacije u vremenskoj seriji za sve varijable su pokazala da se uglavnom odnose na visoke varijacije u vremenskom nizu riječnog dotoka. Združena analiza terenskih istraživanja pokazala je da se radi o području niske slanosti i visoke zamućenosti. Jaka veza je pronađena između zamućenosti i koncentracije suspendiranih krutih tvari (TSS), dok podaci prikupljeni u lokalnim rijekama i u neposrednoj blizini obale upućuju na to da se zamućenost može koristiti kao zadovoljavajući surogat za TSS procjene .

Tršćanski je zaljev (sjeverni Jadran) jedno od živom najonečišćenijih područja u Sredozemlju, a i u svijetu, zbog nekadašnje rudarske aktivnosti u Idriji (zapadna Slovenija). Veza je između mikrobnog nastanka metilirane žive i njezine bioakumulacije i biomagnifikacije u hranidbenim lancima voda zaljeva još slabo poznata, iako ključna za razumijevanje poveznica između izvora i organizama na višem stupnju hranidbenog lanca, npr. riba, koje su vektori prijenosa onečišćenja na ljude i druge organizme. Ovaj pregledni članak obuhvaća mikrobno biogeokemijsko kruženje žive u zaljevu, prijenos i bioakumulaciju metilirane žive u pelagičkim i bentičkim hranidbenim lancima, te izloženost ljudskog organizma živi nakon konzumacije ribe i školjaka. Svi su ti podaci važni zbog velikog gospodarskog značaja Tršćanskog zaljeva., The Gulf of Trieste (northern Adriatic Sea) is one of the most mercury-polluted areas in the Mediterranean and in the world due to the past mining activity in the Idrija region (western Slovenia). The link between microbial production of toxic methylmercury (MeHg), and its bioaccumulation and biomagnification in marine food webs of the gulf is at present rather poorly characterized but is critical to understanding the links between sources and higher trophic levels, such as fish, that are ultimately vectors of human and wildlife exposure. This overview explores three major topics: (i) the microbial biogeochemical cycling of Hg in the area, (ii) the trophic transfer and bioaccumulation of MeHg in pelagic and benthic marine food webs, and (iii) human exposure to Hg through marine fish and shellfish consumption. These are important goals since the Gulf of Trieste is an area of great economical importance.

International audience; Long-term experimental studies suggest that, under transient anoxic conditions, redox fronts within the sediment shift upwards, causing sequential rise and fall of ben-thic fluxes of reduced species (Mn(II), Fe(II) and S(-II)). In-faunal benthic organisms are associated with different re-dox fronts as micro-habitats and must be affected by such changes during natural hypoxia events. In order to document the geochemical evolution of the sediment during prolonged anoxia in the framework of an in situ experiment designed to mimic natural conditions, benthic chambers were deployed on the seafloor of the Northern Adriatic and sampled after 9, 30 and 315 days of incubation. Oxygen and sulfide were measured continuously in the early stages (9 days) of the experiment. High-resolution pore water profiles were sampled by DET probes and redox-sensitive species (S(VI), Mn(II) and Fe(II)) and alkalinity were measured. Starting oxygen saturation was about 80 % within the chamber. After 7 days, anoxia was established in the bottom waters within the chambers. Mn(II) and Fe(II) started diffusing towards the anoxic water column until they reached the surficial sediment. Being reoxidized there, Mn and Fe re-precipitated, giving a rusty coloration to the seafloor. Infau-nal species appeared at the sediment surface. After 20 days, all macro-organisms were dead. Decomposition of macro-organisms at the sediment-water interface generated S(-II) within the entire height of the chamber, leading to a downward flux of sulfides into the sediment, where they were quickly oxidized by metallic oxides or precipitated as FeS. S(-II) was below detection in the water column and pore waters at the end of the experiment. Our results suggest that S(-II) enrichment in the water column of coastal systems, which are episodically anoxic, is strongly controlled by the biomass of benthic macrofauna and its decay during anoxia, whereas its residence time in the water column is controlled by iron availability (as solid oxides or as dissolved reduced cations) within the sediment, even without water circulation.

In this study, seasonal changes of mercury (Hg) species in the highly variable estuary of Soča/Isonzo River (northern Adriatic Sea) were investigated. Samplings were performed on a seasonal basis (September 2009, May, August and October 2010) and Hg species (total Hg, methylmercury (MeHg), dissolved gaseous Hg (DGM)) in waters, sediments and pore waters were determined. In addition, a range of ancillary parameters were measured (salinity, nutrients, organic carbon (OC), nitrogen species). Hg values were interpreted using these parameters and hydrological conditions (river flow, wave height) around the time of sampling. There were no significant changes in Hg load from river to the gulf, compared to previous studies. The load was temporarily higher in May 2010 due to higher river flow. Wave height, through changing hydrostatic pressure, was most likely to cause resuspension of already deposited Hg from the bottom (August 2010). The estuary is a net source of DGM to the atmosphere as suggested by DGM profiles, with salinity, redox potential and organic matter as the most probable controls over its production. MeHg is produced in situ in sediment or in water column, rather than transported by river, as indicated by its correlation with OC of the marine origin. Calculated fluxes for THg and MeHg showed sediment as a source for both the water column. In pore waters, OC in part affects partitioning of both THg and MeHg; however other factors (e.g. sulphide and/or oxyhydroxides precipitation and dissolution) are also probably important.

Sequential nutrient regeneration and organic matter (OM) degradation in surface sediments of the Gulf of Trieste (northern Adriatic Sea) were examined using in situ benthic chambers under normoxic, anoxic and reoxic conditions. Intensive NH4&plus; and PO4− anoxic regeneration was subsequently slower in prolonged anoxia. NH4&plus; production was probably also a consequence of dissimilatory nitrate reduction to NH4&plus;. The presence of anammox and laterally pumping of oxygenated water by benthic infauna explained the presence of NO3− in anoxia. Anoxic phases were characterized by enhanced dissolution of Sibiog, decreasing pore water Ca and Mg concentrations indicating carbonate precipitation and higher Fe and Mn concentrations as a result of reduction/respiration. Reoxygenation was characterized by enhanced bioturbation. Nitrification caused NH4&plus; decrease and P precipitated quickly as carbonate fluorapatite and FePO4. In addition adsorption of P onto Fe-hydroxides could also occur since Fe (and Mn) reoxidized quickly. Increased Ca levels suggested enhanced carbonate dissolution. Diffusive fluxes at the sediment–water interface (SWI), calculated from pore water modelling using diffusion-reaction model, revealed high anoxic NH4&plus; effluxes and Ca (and Mg) influxes. PO4− fluxes were very low and high NH4&plus;/PO4− flux ratios in anoxic and reoxic phases suggested an excess of benthic inorganic N. Nutrient budgets at the SWI showed intensive anoxic recycling of inorganic N but low P and Si cycling in all redox phases.

A series of relatively simple incubation experiments to assess and evaluate microbial mercury (Hg) transformations in water column and sediments were performed monthly or bimonthly in a period from March 2011 to December 2011. Sampling campaigns were performed at station F in the southeastern part of Gulf of Trieste, northern Adriatic Sea. Gulf of Trieste has been for the last 500 year continuously impacted with inflow of Hg, originating from the Idrija Hg mine. The microbial mercury transformations were assessed using a short-lived (t1/2=64.12 h) radioisotope 197 Hg. Calculated activities of microbial Hg reduction and methylation were correlated with other environmental factors, such as temperature, nutrient availability, oxygenation, organic matter, substrate (Hg in bioavailable chemical form) availability, structure of microbial community and presence of mer operon. Preliminary results show that in water column a substantial Hg reduction occurs, whereas methylation was not observed. On the other hand, long-term incubation experiments with sediments show that methylation process is active however preliminary results also suggest a significant MeHg degradation.

As part of the “MIRACLE” project, the biogeochemical cycling of mercury (Hg) at the sediment–water interface was studied in the field in the Marano and Grado Lagoon (Northern Adriatic Sea). Seasonal investigations were conducted at selected experimental sites, where Manila Clams (Tapes philippinarum) were previously seeded. Measurements were performed seasonally during three campaigns, using two benthic chambers, one transparent and one dark, to evaluate the effect of light on Hg cycling. Total dissolved Hg (THg), methylmercury (MeHg), and dissolved gaseous Hg (DGM) species were considered. Diurnal benthic fluxes were found to significantly exceed the diffusive fluxes at all stations. The assessment of the annual recycling of Hg species from sediments to the water column showed that up to 99% of MeHg is recycled annually to the water column, while Hg recycling ranges from 30 to 60%. MeHg poses the higher risk for potential bioaccumulation in clams, but it is partially mitigated by Hg reduction, which seems to be an important process leading to evasion losses of Hg from these environments. Estimated benthic fluxes suggest that Hg recycling at the sediment–water interface is more active in the Grado sector. Hence, based on the estimated release of MeHg from sediments, it is suggested that the western sector seems to be more suitable for clam farming and the extension of rearing activities.

Benthic metabolism and carbon and nutrient cycling at the sediment–water interface were studied seasonally in the Marano (sites MB and MC) and Grado Lagoon (sites ART and BAR), northern Adriatic Italy, using porewater vertical profiles and daily fluxes of O2, DIC, DOC, NO3−, NH4+, PO43− and SiO44− measured in situ deployed transparent and dark benthic chambers. Diffusive and benthic fluxes of solutes were evaluated on a seasonal basis. Sites MC and ART were characterized by higher Corg. contents due to input of riverine organic matter and mariculture, respectively. The Corg., Ntot., Ptot., Porg. and Sibiog. contents decreased along the sediment cores while porewater concentrations of DIC, DOC, NO3−, NH4+, PO43− and SiO44− increased along the sediment cores at all study sites due to the degradation of labile sedimentary matter. Higher concentrations of all porewater solutes and higher diffusive fluxes were observed in warmer periods. Benthic fluxes of O2, DIC, NO3−, NH4+, PO43− and SiO44− showed intensive seasonal variations. Based on O2 and DIC metabolism, the lagoon sediments were highly heterotrophic except at BAR being in trophic balance or weakly heterotrophic. NO3− and SiO44− exhibited influxes due to intense microphytobenthic assimilation, mostly by diatoms, and denitrification while extremely low PO43− fluxes suggest P as a limiting factor. The great difference observed between the diffusive and the in situ benthic fluxes suggests the importance of bioturbation and that the pertinent processes occur at the sediment–water interface. Tentative annual budgets of carbon and nutrients in surface sediments of studied sites indicate that their cycling, compared to burial flux, is more intensive at the sediment–water interface. These basic benthic biogeochemical processes can be important to better understand the trace metal cycling, especially Hg mobilization and sequestration, in the lagoon environment.

Mercury (Hg) transformation activities and sulfate (SO 4 2 − ) reduction were studied in sediments of the Marano and Grado Lagoons in the Northern Adriatic Sea region as part of the “MIRACLE” project. The lagoons, which are sites of clam ( Tapes philippinarum ) farming, have been receiving excess Hg from the Isonzo River for centuries. Marano Lagoon is also contaminated from a chlor-alkali plant. Radiotracer methods were used to measure mercury methylation ( 230 Hg, 197 Hg), methylmercury (MeHg) demethylation ( 14 C-MeHg) and SO 4 2 − reduction ( 35 S) in sediment cores collected in autumn, winter and summer. Mercury methylation rate constants ranged from near zero to 0.054 day −1 , generally decreased with depth, and were highest in summer. Demethylation rate constants were much higher than methylation reaching values of ∼0.6 day −1 in summer. Demethylation occurred via the oxidative pathway, except in winter when the reductive pathway increased in importance in surficial sediments. Sulfate reduction was also most active in summer (up to 1600 nmol mL −1 day −1 ) and depth profiles reflected seasonally changing redox conditions near the surface. Methylation and demethylation rate constants correlated positively with SO 4 2 − reduction and pore-water Hg concentrations, and inversely with Hg sediment–water partition coefficients indicating the importance of SO 4 2 − reduction and Hg dissolution on Hg cycling. Hg transformation rates were calculated using rate constants and concentrations of Hg species. In laboratory experiments, methylation was inhibited by amendments of the SO 4 2 − -reduction inhibitor molybdate and by nitrate. Lagoon sediments displayed a dynamic seasonal cycle in which Hg dissolution in spring/summer stimulated Hg methylation, which was followed by a net loss of MeHg in autumn from demethylation. Sulfate-reducing bacteria (SRB) tended to be responsible for methylation of Hg and the oxidative demethylation of MeHg. However, during winter in surficial sediments, iron-reducing bacteria seemed to contribute to methylation and Hg-resistant bacteria increased in importance in the reductive demethylation of MeHg. The high rates of MeHg demethylation in lagoon sediments may diminish the accumulation of MeHg.

Previous research recognized most of the Northern Adriatic coastal lagoon environments as contaminated by mercury (Hg) from multiple anthropogenic sources. Among them, the Pialassa Baiona (P.B.) Lagoon, located near the city of Ravenna (Italy), received between 100 and 200 tons of Hg, generated by an acetaldehyde factory in the period 1957–1977. Further east, the Grado Lagoon has been mainly affected by a long-term Hg input from the Idrija mine (western Slovenia) through the Isonzo River since the 16th century. Hg cycling at the sediment–water interface (SWI) of the two lagoons was investigated and compared by means of an in situ benthic chamber, estimating diffusive Hg and Methyl-Hg fluxes in the summer season. Major chemical features in porewaters (Fe, Mn, H 2 S, dissolved inorganic (DIC) and organic carbon (DOC), nutrients) and in the solid phase (C org , N and S) were also explored to understand the general biogeochemical conditions of the system in response to benthic respiration. The daily integrated flux for the methylated Hg form was extremely low in P.B. Lagoon, accounting for only 7% of the corresponding flux calculated for the Grado Lagoon. Despite a higher sedimentary Hg content in the P.B. Lagoon (14.4–79.0 μg g −1 ) compared to the Grado Lagoon (10.7–12.5 μg g −1 ), the in situ fluxes of Hg in the two experimental sites appeared similar. A selective sequential extraction procedure was applied to the solid phase, showing that the stable crystalline mineral phase cinnabar (HgS) is the predominant Hg fraction (about 50%) in the Grado Lagoon surface sediments. Conversely, Hg mobilization and sequestration in the P.B. Lagoon is related to the extremely anoxic redox conditions of the system where the intense sulfate reduction, by the release of sulfur and the formation of sulfides, limits the metal recycling at the SWI and its availability for methylation processes. Thus, the environmental conditions at the SWI in the P.B. Lagoon seem to represent a natural “barrier” for the potential risk of Hg transfer to the aquatic trophic chain.

Coastal areas in the northernmost part of the Adriatic Sea (Gulf of Trieste and the adjacent Grado Lagoon) are characterized by high levels of Hg, both in sediments and in the water column, mainly originating from the suspended material inflowing through the Isonzo/Soca River system, draining the Idrija (NW Slovenia) mining district, into the Gulf of Trieste. Hypoxic and anoxic conditions at the sediment–water interface (SWI) are frequently observed in the Gulf of Trieste and in the lagoon, due to strong late summer water stratification and high organic matter input. Mercury mobility at the SWI was investigated at three sampling points located in the Gulf of Trieste (AA1, CZ) and in the Grado Lagoon (BAR). Experiments were conducted under laboratory conditions at in situ temperature, using a dark flux chamber simulating an oxic–anoxic transition. Temporal variations of dissolved Hg and methylmercury (MeHg) as well as O2, NH 4 + , NO 3 - + NO 2 - , PO 4 3 - , H2S, dissolved Fe and Mn, dissolved inorganic C (DIC) and dissolved organic C (DOC) were monitored simultaneously. Benthic Hg fluxes were higher under anoxic conditions than in the oxic phase of the experiment. Methyl Hg release was less noticeable (low or absent) in the oxic phase, probably due to similar methylation and demethylation rates, but high in the anoxic phase of the experiment. The MeHg flux was linked to SO4 reduction and dissolution of Fe (and Mn) oxyhydroxides, and formation of sulphides. Re-oxygenation was studied at sampling point CZ, where concentrations of MeHg and Hg dropped rapidly probably due to re-adsorption onto Fe (Mn) oxyhydroxides and enhanced demethylation. Sediments, especially during anoxic events, should be, hence, considered as a primary source of MeHg for the water column in the northern Adriatic coastal areas.

The role of the major biogeochemical processes in Hg cycling at the sediment–water interface was investigated in the Grado Lagoon (Northern Adriatic Sea). This wetland system has been extensively contaminated from the Idrija Hg Mine (Slovenia) through the Isonzo River suspended load carried by tidal fluxes. Three approaches were used to study the sediment–water exchange of total Hg (THg), methylmercury (MeHg), reactive Hg (RHg) and dissolved gaseous Hg (DGHg): (1) estimation of diffusive fluxes from porewater and overlying water concentrations, (2) measurements of benthic fluxes using a deployed light benthic chamber in situ and (3) measurements of benthic fluxes during oxic–anoxic transition with a laboratory incubation experiment. The THg solid phase, ranging between 9.5 and 14.4 μg g −1 , showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g −1 ) at the surface; they tended to decrease to nearly zero concentration with depth, thus suggesting that MeHg production and accumulation occur predominantly just below the sediment–water interface. Porewater MeHg concentrations (0.9–7.9 ng L −1 , 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive fluxes (up to 17 ng m −2 day −1 ) were similar to those in the nearby Gulf of Trieste [Covelli, S., Horvat, M., Faganeli, J., Brambati, A., 1999. Porewater distribution and benthic flux of mercury and methylmercury in the Gulf of Trieste (Northern Adriatic Sea). Estuar. Coast. Shelf Sci. 48, 415–428], although the lagoon sediments contained four-fold higher THg concentrations. Conversely, the THg diffusive fluxes in the lagoon (up to 110 ng m −2 day −1 ) were one- to two-fold higher than those previously estimated for the Gulf of Trieste. The diurnal MeHg benthic fluxes were highest in summer at both sites (41,000 and 33,000 ng m −2 day −1 at the fishfarm and in the open lagoon, respectively), thus indicating the influence of temperature on microbial processes. The diurnal variations of dissolved THg and especially MeHg were positively correlated with O 2 and inversely with DIC, suggesting an important influence of benthic photosynthetic activities on lagoon benthic Hg cycling, possibly through the production of organic matter promptly available for methylation. The results from the dark chamber incubated in the laboratory showed that the regeneration of dissolved THg was slightly affected by the oxic–anoxic transition. Conversely, the benthic flux of MeHg was up to 15-fold higher in sediments overlain by O 2 depleted waters. In the anoxic phase, the MeHg fluxes proceeded in parallel with Fe fluxes and the methylated form reached approximately 100% of dissolved THg. The MeHg is mostly released into overlying water (mean recycling efficiency of 89%) until the occurrence of sulphide inhibition, due to scavenging of the available Hg substrate for methylation. The results suggest that sediments in the Grado Lagoon, especially during anoxic events, should be considered as a primary source of MeHg for the water column.

The role of suspended particulate matter (SPM) as an important carrier of mercury (Hg) dispersed into the Gulf of Trieste and in the adjacent Grado lagoon (Northern Adriatic Sea) was studied during a high Isonzo River inflow and the resulting river plume formation. Despite the fact that extreme flood events are rare during the year, they account for most of the PHg influx (37–112 ng L−1) into the Gulf of Trieste. When the river plume is diverted to the SW under the influence of an E–NE wind, the tidal flux acts as a “transport belt” carrying the PHg, mostly inorganic, into the Grado lagoon. A preliminary estimation indicates that the amount of PHg entrapped in the lagoon basin following a tidal semi-cycle accounts for 1.4 kg/12 h, which corresponds to about 49% of the total Hg carried by the tidal flow. These findings should be considered in future remediation strategies in the lagoon environment.

To reconstruct a history of polycyclic aromatic hydrocarbon (PAH) pollution in the Gulf of Trieste, one of the largest urbanized areas in the Adriatic Sea, we analyzed three long sediment cores collected between 1996 and 1997. Concentrations of total PAHs, the sum of 16 PAH compounds and six of their methylated analogues, in all three cores show a decrease from 600–800 ng g−1, at the surface, to levels below 250 ng g−1 in deepest layers (down to 3 m). The same trend was shown with separate representative pyrogenic PAHs (pyrene, benzofluoranthene and phenanthrene). Using Hg as a recent geochronological tracer, we observe an increasing input of PAHs since the beginning of the 20th Century and, especially, after the Second World War coinciding with increasing industrialization and urbanization of the region. This correlation is supported by PAH ratios that are indication of combustion processes and represent a marker for anthropogenic inputs. No correlation exists between PAHs and black carbon within the core profiles, indicating two different fractions of the ‘black carbon continuum’.

The 10th International Symposium on Interactions Between Sediment and Water was held in Lake Bled, Slovenia from August 28 to September 3, 2005. Approximately 155 delegates, attended the symposium where talks and posters addressed five themes incorporating the physical, chemical, biological, and/or management aspects of lacustrine, riverine, estuarine, and/or marine sediment were presented. A review of the symposium themes and plenary talks was provided. As well, this symposiums' focus is put into context with respect to historical changes noted over the 29 years that the International Association for Sediment Water Science (IASWS) has been meeting.

Mercury species in the highly stratified water column of the Isonzo River mouth (northern Adriatic Sea) were investigated in February, May and August 2002 (low-normal fluvial discharge). Total, dissolved and particulate mercury (Hg) and methylmercury (MeHg) were measured and their concentrations were related to physico-chemical parameters in terms of temperature, salinity, turbidity, O2 concentrations and total suspended matter (TSM) as well as particulate organic carbon (POC) content. Particulate Hg and MeHg are well correlated to medium-fine silty suspended sediment and organic matter, respectively. Desorption of Hg from particles in the brackish layer was observed. Due to the presence of a saltwedge, the lower river course seems to be a trap for Hg carried by fluvial waters. MeHg normally decreases approaching the sea but the local increase in the inner zone of the saltwedge could be related to methylation processes in the bottom water layer. Hg export is effective only during medium and high riverine flows acting as an important source of Hg into the northern Adriatic and the adjacent lagoon system.