Trace metals and polycyclic aromatic hydrocarbons in the Eastern Mediterranean sediments: Concentration ranges as a tool for quality control of large data collections.

Assessing the status of marine pollution at regional and sub-regional scales requires the use of comparable and harmonized data provided by multiple institutions, located in several countries. Standardized data management and quality control are crucial for supporting a coherent evaluation of marine pollution. Taking the Eastern Mediterranean Sea as a case study, we propose an approach to improve the quality control procedures used for sediment pollution data, thus supporting a harmonized environmental assessment. The regional ranges of contaminant concentrations in sediments were identified based on an in-depth literature review, and the lowest measured concentrations were evaluated to determine the "background concentrations" of chemical substances not yet targeted in the Mediterranean Sea. In addition, to verify the suitability of the approach for validating large data collections provided by multiple sources, the determined ranges were used to validate a regional dataset available through EMODnet data infrastructure.

Mercury and methylmercury in the Gulf of Trieste (northern Adriatic Sea).

The distribution, sources and fate of mercury (Hg) in the water column of the Gulf of Trieste (northern Adriatic Sea), affected by the Hg polluted river Soca/Isonzo for centuries draining the cinnabar-rich deposits of the Idrija mining district (NW Slovenia), were studied in terms of total and dissolved Hg, reactive Hg, total and dissolved methylmercury (MeHg), mesozooplankton Hg and MeHg, and sedimentation rates of particulate Hg. Higher total Hg concentrations in the surface layer were restricted to the area of the Gulf in front of the river plume expanding in a westerly direction. Higher concentrations in bottom water layers were the consequence of sediment resuspension. Dissolved Hg exhibited higher concentrations in the surface layer in the area in front of the river plume. Higher bottom concentrations of dissolved Hg observed at some stations were probably due to remobilization from sediments, including resuspension and benthic recycling. The relationship between dissolved Hg in the surface layer and salinity showed nonconservative mixing in June 1995 during higher riverine inflow and nearly conservative mixing in September 1995 during lower riverine inflow. Both mixing curves confirm the river Soca/Isonzo to be the most important source of total and dissolved Hg, which are significantly correlated, in the Gulf. Reactive Hg is significantly correlated with dissolved Hg, indicating that the majority of dissolved Hg is reactive and potentially involved in biogeochemical transformations. The higher total MeHg in the bottom layer is the result of remobilization of MeHg from sediments including benthic fluxes. Strong seasonal variation of sedimentation rates of particulate Hg was found during a 2-year study in the central part of the Gulf. These variations followed those of total sedimented matter, indicating that sedimented Hg is mostly associated with inorganic matter. About a 2.5-fold higher fluxes of particulate Hg were observed at the depth of 20 m relative to 10 m which is attributed to bottom sediment resuspension. Temporal variability of mesozooplankton Hg and MeHg is the consequence of biomass and species variations, and grazing behaviour. From the preliminary Hg mass balance it appears that the Gulf is an efficient trap for total Hg and a net source of MeHg.

Black carbon in Slovenian alpine lacustrine sediments.

Black carbon (BC) contents were measured in recent sediments in five high altitude remote alpine lakes, i.e. Lake Krisko Sup., Lake Ledvica, Lake Planina, Lake Krn and Lovrensko Lake, and the eutrophic subalpine Lake Bled in Slovenia to follow the history of atmospheric pollution of fossil fuel and local biomass burning in Alps. Organic carbon (OC), its 13C values, total nitrogen and sedimentation rates using 210Pb activity data were also measured. The highest BC contents, reaching 20 mg/gdw, were noted in remote alpine lakes while in the subalpine Lake Bled sediment the concentrations were lower reaching 5 mg/gdw. Lower BC/OC ratios, ranging between 4% and 8%, were typical for remote alpine lakes and increased to about 10% in subalpine Lake Bled. The latter clearly shows the marked importance of local direct pollution sources in comparison to remote atmospheric input which decreases in a W-E direction in parallel with decreasing amounts of precipitation. Based on 210Pb sedimentation data, the minimal BC accumulation rates in sediment cores were detected in the pre-industrialisation period. In the last decades of 20th century the BC contents decreased probably due to reduced emission of pollutants.

Anoxic mineralization of biogenic debris in near-shore marine sediments (Gulf of Trieste, northern Adriatic).

Anoxic degradation of sedimentary biogenic debris using closed incubation experiments was studied at two sampling stations in the Gulf of Trieste (northern Adriatic). Production rates of dissolved inorganic carbon (DIC), NH4+, PO(4)3- and dissolved Si (dSi), and reduction rates of SO(4)2- were measured and anoxic mineralization rates were modeled using a first order G-model and multi-G approach. The depth profiles of these rates revealed an exponential decrease indicating that the largest fraction of mineralization of biogenic debris and SO(4)2- reduction occurs in the surficial sediment layer and on the sediment surface. Comparing the depth-integrated anoxic mineralization rates at both stations with benthic fluxes of DIC, NH4+, PO(4)3- and dSi measured at the in situ temperature in the dark, it appears that the DIC and PO(4)3- fluxes are higher because the mineralization mostly occurs at the sediment-water interface, and that besides SO(4)2- reduction, other electron acceptors are involved in the organic matter decomposition pathway in these surficial sediments. The NH4+ production was higher than the benthic fluxes because of NH4+ oxidation. The production of dSi was in good agreement with benthic fluxes implying that temperature is the main factor of dSi production and benthic fluxes in these sediments.