Riječni upliv na termohalina svojstva, zamućenost i suspendirane tvari u plitkom zaljevu (Koparski zaljev, sjeverni Jadran)

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

Behaviour of Metal(loid)s at the Sediment-Water Interface in an Aquaculture Lagoon Environment (Grado Lagoon, Northern Adriatic Sea, Italy)

The cycling of metal(loid)s at the sediment\u2013water interface (SWI) was evaluated at two selected sites (VN1 and VN3) in an active fish farm in the Grado Lagoon (Northern Adriatic, Italy). In situ experiments using a transparent benthic chamber and the collection of short sediment cores were performed, to investigate the behavior of metal(loid)s in the solid (sediments) and dissolved (porewaters) phases. Total and labile concentration of metal(loid)s were also determined in sediments, to quantify their potential mobility. Comparable total concentrations were found at both sites, excluding As, Mn, Pb and V, which were higher at VN3. Metal(loid) porewater profiles showed a diagenetic sequence and a close dependence with redox (suboxic/anoxic) conditions in the surface sediments. Positive diffusive fluxes along with benthic fluxes, particularly at the more oxic site, VN1, were found for almost all metal(loid)s, indicating their tendency to migrate towards the overlying water column. Despite sediments at two sites exhibiting high total metal(loid) concentrations and moderate effluxes at the SWI, the results suggest that they are hardly remobilized from the sediments. Recycling of metal(loid)s from the SWI would not constitute a threat for the aquatic trophic chain in the fish farm

Dissolved gaseous mercury production and sea-air gaseous exchange in impacted coastal environments of the northern Adriatic Sea

The northern Adriatic Sea is well known for mercury (Hg) contamination mainly due to historical Hg mining which took place in Idrija (Slovenia). The formation of dissolved gaseous mercury (DGM) and its subsequent volatilisation can reduce the amount of Hg available in the water column. In this work, the diurnal patterns of both DGM production and gaseous elemental Hg (Hg0) fluxes at the water-air interface were seasonally evaluated in two selected environments within this area, a highly Hg-impacted, confined fish farm (VN: Val Noghera, Italy) and an open coastal zone less impacted by Hg inputs (PR: Bay of Piran, Slovenia). A floating flux chamber coupled with a real-time Hg0 analyser was used for flux estimation in parallel with DGM concentrations determination through in-field incubations. Substantial DGM production was observed at VN (range = 126.0–711.3 pg L−1) driven by both strong photoreduction and possibly dark biotic reduction, resulting in higher values in spring and summer and comparable concentrations throughout both day and night. Significantly lower DGM was observed at PR (range = 21.8–183.4 pg L−1). Surprisingly, comparable Hg0 fluxes were found at the two sites (range VN = 7.43–41.17 ng m−2 h−1, PR = 0–81.49 ng m−2 h−1), likely due to enhanced gaseous exchanges at PR thanks to high water turbulence and to the strong limitation of evasion at VN by water stagnation and expected high DGM oxidation in saltwater. Slight differences between the temporal variation of DGM and fluxes indicate that Hg evasion is more controlled by factors such as water temperature and mixing conditions than DGM concentrations alone. The relative low Hg losses through volatilisation at VN (2.4–4.6% of total Hg) further confirm that static conditions in saltwater environments negatively affect the ability of this process in reducing the amount of Hg retained in the water column, therefore potentially leading to a greater availability for methylation and trophic transfer

Elemental composition of plankton exometabolites (mucous macroaggregates): Control by biogenic and lithogenic components

Among the various exometabolitic effects of marine microorganisms, massive mucilage events in the coastal zones of temperate and tropical seas are the most spectacular and environmentally important. Abundant mucilage material in the form of aggregates appears in late spring/early summer in the water column of the Adriatic Sea. These macroaggregate biopolymers originate mainly from plankton exometabolites, with both autochthonous and allochthonous components, and strongly impact the tourism, fisheries, and economy of coastal countries. In contrast to extensive studies on the structural and chemical nature of macroaggregates performed over past decades, the full elemental composition of these substances remains poorly known, which does not allow for a complete understanding of their origin, evolution, and necessary remediation measures. Here, we report the results of comprehensive analyses of 55 major and trace elements in the composition of macro aggregates collected at the surface and in the water column during massive mucilage events. Through normalization of the elemental chemical composition of the upper earth crust (UCC), river suspended material (RSM), mean oceanic plankton, and mean oceanic particulate suspended material, we demonstrate that the water column macroaggregates reflect a superposition of the signal from plankton and marine particulate matter. The surface macroaggregates were preferentially enriched in lithogenic component, and carried the signature of planktonic material. The rare earth element (REE) signal was strongly dominated by plankton and, to a lesser degree, by oceanic particulate matter, while at the same time being strongly (>80 times) impoverished compared with UCC and RSM. Taken together, the elemental composition of macroaggregates allows for distinguishing the lithogenic and biogenic impacts on the occurrence of these unique large-scale mucilage events, linked to the exometabolism of marine plankton combined with the input of allochthonous inorganic material

River Sources of Dissolved Inorganic Carbon in the Gulf of Trieste (N Adriatic): Stable Carbon Isotope Evidence

River inputs can significantly affect carbon dynamics in the costal ocean. Here, we investigate the influence of four rivers (Isonzo/Soča, Timavo/Reka, Rižana, and Dragonja) on inorganic carbon (C) in the Gulf of Trieste in the northern Adriatic Sea using stable isotope signatures of dissolved inorganic carbon (δ¹³CDIC). In 2007, rivers exported 1.03 × 10¹¹ g C in the form of dissolved inorganic carbon (DIC) to the Gulf of Trieste with the lowest export observed in the Dragonja and the highest in the Isonzo/Soča. River plumes were associated with higher total alkalinity (TA) and pCO2 values compared with Gulf of Trieste waters, but their inputs showed high spatial variability. The δ¹³CDIC values and the isotopic mass balance suggested that river input during the spring of 2007 represented about 16 % of DIC at our study site VIDA, located in the southeastern part of the Gulf of Trieste. During autumn of 2007, the riverine contribution of DIC was less pronounced (3 %) although the river export of C was higher relative to the spring season. Convective mixing with the Gulf of Trieste waters and bora wind events appear to reduce the riverine contribution to the DIC system. Our results suggest that river plumes play an important role in C cycling in the Gulf of Trieste by direct inputs of higher riverine DIC and by increased biological uptake of DIC promoted by the supply of riverine nutrients

Gaseous Mercury Exchange from Water-Air Interface in Differently Impacted Freshwater Environments

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

Benthic nutrient cycling at the sediment-water interface in a lagoon fish farming system (northern Adriatic Sea, Italy)

Metabolism and carbon, oxygen, and nutrient fluxes (DIC, DOC, DO2, NO2 12, NO3 12, NH4+, PO4 3 12 and SiO4 4 12) were studied during three surveys at two sites (VN1 and VN3) located at a fish farm at theMarano and Grado Lagoon (northern Adriatic Sea), using an in situ benthic chamber. Field experimentswere 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\u20132%). The conditions at VN3 were mostly anoxic with high NH4 + levels (30\u20131027 \u3bcM) and the absence of NO3 12. Substantial daily patterns of all solutes occurred especially in autumn andwinter. On the contrary, fluxes at VN1were less pronounced. Usually, inverse correlations appeared between dissolved O2 and DIC trends, but in our systemthis was observed only at VN3 in autumn and accomplished by a parallel increase in NH4+, PO4 3 12 and SiO4 4 12 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

Effects of hypoxia on biogeochemical cycling of nutrients and trace elements in a stratified estuarine system (Gulf of Trieste, northern Adriatic Sea)

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

Methylmercury in the Gulf of Trieste (Northern Adriatic Sea): From Microbial Sources to Seafood Consumers

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

Nature and Lability of Northern Adriatic Macroaggregates

The key organic constituents of marine macroaggregates (macrogels) of prevalently phytoplankton origin, periodically occurring in the northern Adriatic Sea, are proteins, lipids and especially polysaccharides. In this article, the reactivity of various macroaggregate fractions in relation to their composition in order to decode the potentially »bioavailable« fractions is summarized and discussed. The enzymatic hydrolysis of the macroaggregate matrix, using α-amylase, β-glucosidase, protease, proteinase and lipase, revealed the simultaneous degradation of polysaccharides and proteins, while lipids seem largely preserved. In the fresh surface macroaggregate samples, a pronounced degradation of the α-glycosidic bond compared to β-linkages. Degradation of the colloidal fraction proceeded faster in the higher molecular weight (MW) fractions. N-containing polysaccharides can be important constituents of the higher MW fraction while the lower MW constituents can mostly be composed of poly- and oligosaccharides. Since the polysaccharide component in the higher MW fraction is more degradable compared to N-containing polysaccharides, the higher MW fraction represents a possible path of organic nitrogen preservation. Enzymatic hydrolysis, using α-amylase and β-glucosidase, revealed the presence of α- and β-glycosidic linkages in all fractions with similar decomposition kinetics. Our results indicate that different fractions of macroaggregates are subjected to compositional selective reactivity with important implications for macroaggregate persistence in the seawater column and deposition