Large-Scale Mercury Dispersion at Sea: Modelling a Multi-Hazard Case Study from Augusta Bay (Central Mediterranean Sea)

Abstract

This contribution discusses an example of potential multi-hazard effects resulting from an earthquake in a highly seismogenic area of the Mediterranean Sea, the Augusta Bay, which presents high levels of contamination in sediments and seawater, due particularly to high-concentrations of mercury as a result of a long-term industrial exploitation. In particular, a high-resolution hydrodynamic and transport model is used to calculate the effects of enhanced mercury spreading in the open sea after significant damage and collapse of the artificial damming system confining the embayment where a very high concentration of Hg occurs in seafloor sediments and seawater. Coupling high-resolution 3D dynamic circulation modelling and sediment-seawater Hg fluxes calculated using the HR3DHG diffusion-reaction model for both inorganic and organic Hg species offers a valuable approach to simulating and estimating the effects of spatial dispersion of this contaminant due to unpredictable hazard events in coastal systems, with the potential attendant enhanced effects on the marine ecosystem. The simulated scenario definitely suggests that a combination of natural and anthropogenic multi-hazards calls for a thorough re-thinking of risk management in marine areas characterised by significant levels of contamination and where a deep understanding of the biogeochemical dynamics of pollutants does not cover all the aspects of danger for the environment.

Keywords: earthquake damages; hazard chain; marine-coastal area; mercury contamination; numerical modelling.

Figure 1

(a) Location map of Augusta Bay; (b) coastal toponyms of Augusta Bay and of the Rada di Augusta. Bathymetry in B modified after Firetto Carlino et al. [17].

Figure 2

The area of Eastern Sicily with the background of main geological features (a), redrawn after [23] and historical instrumental epicenters (Seismic Magnitude) of Eastern Sicily, extracted by the CPTI04 INGV seismic catalogue (b).

Figure 3

Distribution map of Hg in the surface (0–10 cm) sediments of Augusta Bay.

Figure 4

Model domain and bathymetric details. Part of the finite element mesh adopted to reproduce the geometry of Augusta Bay and the surrounding coastal areas (panel (a)). Domain geometry and bathymetric details for Augusta Harbour as adopted for the Scenario 1 (panel (b)).

Figure 5

Domain geometry and bathymetric details for Augusta Harbour (a) and the collapsed seawall areas. Panel (b) depicts the northern seawall, panel (c) the central seawall, and panel (d) the southern seawall after the earthquake event adopted for Scenario 2.

Figure 6

Yearly average distributions of tracer concentration values (mg L⁻¹), computed for both scenarios for the surface layer (surface, panels (a,b)), the bottom layer (bottom, panels (d,e)), and the averages along the water column (vert. avg, panels (g,h)). The differences between the tracer concentration in Scenario 2 and Scenario 1 are reported in the left panels for the surface (panel (c)) and bottom layers (panel (f)) and for the vertical averages (panel (i)).

Figure 7

Spatial distribution of the maximum tracer concentration values (mg L⁻¹) computed during the whole simulation run for each element of the model domain for both scenarios at the surface (panels (a,b)) and bottom layers (panels (d,e)). The differences between the maximum tracer concentration in Scenario 2 and Scenario 1 are reported in the left panels for surface (panel (c)) and bottom layers (panel (f)).