Distribution patterns of organic pollutants and microbial processes in marine sediments across a gradient of anthropogenic impact.

Marine sediments are part of the hydrological cycle and the ultimate storage compartment of land-derived organic matter, including pollutants. Since relevant microbially-driven processes occurring at benthic level may affect the quality of the overall aquatic system, the necessity for incorporating information about microbial communities functioning for ecosystem modelling is arising. The aim of this field study was to explore the links occurring between sediment contamination patterns by three selected class of organic pollutants (Polycyclic Aromatic Hydrocarbons, PAHs, Nonylphenols, NPs, Bisphenol A, BPA) and major microbial properties (Prokaryotic Biomass, PB; total living biomass, C-ATP; Prokaryotic C Production rate, PCP; Community Respiration rate, CR) across a gradient of anthropogenic pollution. Sediments were sampled from 34 sites selected along 700 km of the western coastline of the Adriatic Sea. Organic contamination was moderate (PAHs <830 ng g-1; NPs <350  ng g-1; BPA <38  ng g-1) and decreased southward. The amount of PAHs-associated carbon (C-PAHs) increased significantly with sediment organic carbon (OC), along with microbial functional rates. The negative relation between PCP/CR ratio and OC indicated the shift toward oxidative processes in response to organic pollution and potential toxicity, estimated as Toxic Equivalents (TEQs). Our outcomes showed that sediment organic contamination and benthic microbial processes can be intimately linked, with potential repercussions on CO2 emission rates and C-cycling within the detritus-based trophic web.

Sediment reworking rates in deep sediments of the Mediterranean Sea.

Different pelagic areas of the Mediterranean Sea have been investigated in order to quantify physical and biological mixing processes in deep sea sediments. Herein, results of eleven sediment cores sampled at different deep areas (> 2000 m) of the Western and Eastern Mediterranean Sea are presented. ²¹°Pb(xs) and ¹³7Cs vertical profiles, together with ¹4C dating, are used to identify the main processes characterising the different areas and, finally, controlling mixing depths (SML) and bioturbation coefficients (D(b)). Radionuclide vertical profiles and inventories indicate that bioturbation processes are the dominant processes responsible for sediment reworking in deep sea environments. Results show significant differences in sediment mixing depths and bioturbation coefficients among areas of the Mediterranean Sea characterised by different trophic regimes. In particular, in the Oran Rise area, where the Almeria-Oran Front induces frequent phytoplankton blooms, we calculate the highest values of sediment mixing layers (13 cm) and bioturbation coefficients (0.187 cm² yr⁻¹), and the highest values of ²¹°Pb(xs) and ¹³7Cs inventories. Intermediate values of SML and D(b) (~6 cm and ~0.040 cm² yr⁻¹, respectively) characterise the mesothrophic Algero-Balearic basin, while in the Southern Tyrrhenian Sea mixing parameters (SML of 3 cm and D(b) of 0.011 cm² yr⁻¹ are similar to those calculated for the oligotrophic Eastern Mediterranean (SML of 2 cm and D(b) of ~0.005 cm² yr⁻¹).

Anthropogenically derived mercury in sediments of Pialassa Baiona, Ravenna, Italy.

Pialassa Baiona, a coastal wetland near the city of Ravenna, has been impacted for two decades (1958-1978) by industrial discharges containing mercury and floating agglomerates of residues of polymerization processes. Although the industrial use of mercury completely ceased in the early 90's, surface sediments are still highly contaminated, mercury concentrations decreasing from the southern sub-basin, close to the discharge point, to the farthest northern border. Concentrations of total mercury, synthetic polymers (determined by pyrolysis-GC/MS), total organic carbon, C/N ratio, total sulfur and 210Pb dating, were determined in sediment cores collected in the southern and northern sub-basins. Mercury and polymers exhibited parallel profiles with a peak corresponding to the historic emission record in the southern core, while in northern cores peaks of maximum concentration display a delay reflecting the time required for the pollutants to migrate. A recently developed mercury sequential extraction procedure was applied to the most polluted layers to study inorganic mercury speciation. Results indicate differences between the southern and northern areas, suggesting a more efficient binding of mercury to sediments in the southern sub-basin.