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Holocene stratigraphic sequence and anthropogenic markers in the coastal sediments of the Gulf of Trieste (north-eastern Adriatic sea).
No full textSediment resuspension during vessel manoeuvres in port areas: evidence from field observations
Full text linkPurpose: The increase in maritime traffic in the Bay of Koper (Gulf of Trieste, northern Adriatic Sea) has been made possible given the increase in the local port capacity and logistics, which, in turn, means an increase in the number of arrivals of larger vessels (which were the original motive for port expansion); this poses a potential risk for coastal environments due to the impact of the resuspension of bottom sediment which affects the physical and chemical characteristics of the water column. The aim of this work was to assess the magnitude of these perturbative events.Materials and methodsTurbidity (NTU) measurements were made using a CTD multiprobe during a vessel manoeuvre in the port navigational canal and in the entire Bay of Koper. In the highest turbidity zone, samples were collected from the surface water layer (0.5 m), at a depth of 6.0 m and 12.0 m. Total suspended solids (TSS) and suspended organic matter (SOM) were measured gravimetrically. TSS grain-size distribution was determined using a laser granulometer.Results and discussionThe effect of the vessel manoeuvre was evident on turbidity with a maximum value of 137 NTU (TSS = similar to 139 mg l(-1)) and a sampled concentration of TSS of 37 mg l(-1) (bottom layer) in the water column immediately after the ship manoeuvre. Grain-size analysis shows a spectrum of particles with a mode size between 22 and 88 mu m (medium silt and very fine sand, respectively). The estimated resuspension mass of total suspended solids (TSS) was similar to 109 t in the restricted manoeuvre area extending about similar to 736 x 493 m and with an average depth of 15 m.ConclusionsThe results demonstrated the significant impact of vessel manoeuvres on the measured parameters, the impact of which cannot be underestimated in terms of marine environmental protection and maritime traffic safety. Moreover, this impact is expected to increase in the near future
Benthic fluxes of mercury species in a lagoon environment (Grado lagoon, Northern Adriatic Sea, Italy)
No full textThe 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 lg g1, showed slight variability with depth and time. Conversely, MeHg contents were highest (up to 21.9 ng g1) 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 L1, 0.15–15% of THg) varied seasonally; higher contents were observed in the warmer period. The MeHg diffusive fluxes (up to 17 ng m2 day1) 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 m2 day1) 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 m2 day1 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 O2 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 thelaboratory 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 O2 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
Anthropogenic markers in the Holocene stratigraphic sequence of the Gulf of Trieste (northern Adriatic Sea).
No full textThe Gulf of Trieste is a shallow semi-enclosed marine basin in the northernmost part of the Adriatic Sea that has been affected by the relative rise in sea-level during the Holocene. The sedimentary sequences in three cores, ranging in length from 130 to 320 cm, were investigated through the variability in grain-size parameters, major (Al, Fe, S, N, Ca and Mg) and trace (Ti, Mn, Cr,
Ni, Cu, Zn and Hg) elements, organic and inorganic C, δ13C and 14C dating in order to obtain information on paleoenvironmental
evolution and the historical development of heavy metal contamination. The potential sources of pollution are: urban sewage from nearly 400,000 inhabitants, industrial effluents, and 500 yr of Hg mining activity in the Idrija region (western Slovenia), located in the upper basin of the Isonzo river, the main freshwater input to the coastal zone. The conventional 14C ages of bulk sedimentary OC in the basal part of the three cores were 9030±70 (GT1), 8270±50 (GT2) and 9160±120 (GT3) yr BP. An upward increase in highly negative δ13Corg values from the core bottoms indicates that lacustrine-swamp conditions in the study area were rapidly followed by a typical marine depositional environment. Cluster analysis performed on the geochemical data for all subsamples of the three cores identifies several groups with a clear stratigraphic meaning. Factor analysis of the data shows related element groups that can be interpreted as being related to, for instance, the natural contribution from aluminosilicates and carbonates, from organic matter (peat) and the more recent anthropogenic “impact”. Predicted natural linear relationships for metal-Al were obtained from the core subsamples and they can be used as a baseline to evaluate metal enrichments on a regional scale. Results show that more recent sediments in the central sector of the Gulf of Trieste are slightly enriched in Cu (max Enrichment Factor EF=2.1) and Zn (max EF=1.6), and noticeably contaminated by Hg (up to 23.32 μg g−1) to a maximum depth of 90 cm and up to 60 times above the estimated regional background (0.13 μg g−1). The Hg historical trend is well correlated with extraction activity at the Idrija mine, thus allowing indicative sedimentation rate estimation and tentative assessment of the rate of Hg accumulation in bottom
sediments (from 1.77 to 31.49 mg m−2 yr−1 at the surface). The large inventory of Hg in the core GT2 appeared to be the result of
proximity to the fluvial source, which is still active in supplying Hg to the coastal areas and makes the Gulf of Trieste one of the most Hg contaminated area in the whole Mediterranean basin
Transport and dispersion of particulate mercury associated to a river plume in the Northern Adriatic lagoonary environment.
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MIXING AND SEDIMENTATION PROCESSES IN A RIVER-DOMINATED DELTA: THE CASE OF THE ISONZO RIVER (NORTHERN ADRIATIC SEA).
No full textTransport and dispersion of particulate mercury associated to a river plume in coastal Northern Adriatic environments.
No full textThe 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 Lÿ1) 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
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