HR3DHG version 1: modeling the spatiotemporal dynamics of mercury in the Augusta Bay (southern Italy)

Abstract

Abstract. The biogeochemical dynamics of Hg, and specifically of its three species Hg0, HgII, and MeHg (elemental, inorganic, and organic, respectively), in the marine coastal area of Augusta Bay (southern Italy) have been explored by the high-resolution 3D Hg (HR3DHG) model, namely an advection–diffusion–reaction model for dissolved mercury in the seawater compartment coupled with a diffusion–reaction model for dissolved mercury in the pore water of sediments in which the desorption process for the sediment total mercury is taken into account. The spatiotemporal variability of the mercury concentration in both seawater ([HgD]) and the first layers of bottom sediments ([HgDsed] and [HgTsed]), as well as the Hg fluxes at the boundaries of the 3D model domain, have been theoretically reproduced, showing acceptable agreement with the experimental data collected in multiple field observations during six different oceanographic cruises. Also, the spatiotemporal dynamics of the total mercury concentration in seawater have been obtained by using both model results and field observations. The mass balance of the total Hg species in seawater has been calculated for the Augusta Harbour, improving previous estimations. The HR3DHG model could be used as an effective tool to predict the spatiotemporal distributions of dissolved and total mercury concentrations, while contributing to better assessing hazards for the environment and therefore for human health in highly polluted areas.

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

“…In that study, the data obtained by the hydrodynamic model run were adopted as inputs by an off-line advection–diffusion and biogeochemical model based on a regular mesh that was implemented to simulate the fate of Hg in the Augusta Bay. The surface current fields obtained using the hydrodynamic model application were validated throughout the comparison with the results obtained by previous similar numerical applications carried out in the same area by Denaro et al [ 19 ]. Furthermore, in Canu et al [ 47 ], SHYFEM was applied to reproduce at high resolution the 3D water circulation and the fate of an oil spill at sea in the Sicilian coastal waters, including Augusta Bay.…”

“…In previous studies by Denaro et al [ 19 ], SHYFEM has been applied to reproduce the 3D current fields in the Augusta Bay and harbor as induced by the main meteorological and oceanographic forcing, including atmospheric pressure gradients and heat fluxes, winds, and tides, during a ten-year period between 2007 and 2017. In that study, the data obtained by the hydrodynamic model run were adopted as inputs by an off-line advection–diffusion and biogeochemical model based on a regular mesh that was implemented to simulate the fate of Hg in the Augusta Bay.…”

“…Given the small extent of the continental shelf in the study area ( Figure 1 b; see Firetto Carlino et al [ 17 ]), this current directly influences the transport dynamics in coastal waters [ 18 ]. The Mistral from the NW, Greek from the NE, and Sirocco from the SW are the dominant winds in the area, with intensities up to 10 m/s during the late autumn and winter [ 19 ]. The tidal component is semidiurnal, lunar component M2 alone, with an amplitude of less than 20 cm [ 20 ].…”

“…High Hg concentrations, up to three orders of magnitude higher than the background value estimated for the Mediterranean seawater (0.1–0–8 ng L −1 ; [ 43 , 44 , 45 , 46 ]), have been measured in seawater in Augusta Bay [ 40 ]. The biogeochemical dynamics of the three Hg species, Hg 0 , Hg II , and Methyl-Hg (MeHg) as well as total Hg (Hg T ) in Augusta Bay were recently explored by a high-resolution 3D model (HR3DHG) which combined (i) diffusion–reaction equations for estimating dissolved mercury in sediment pore water and (ii) a sorption/de-sorption process for measuring total mercury in the sediments [ 19 ]. Specifically, the spatial–temporal variability of dissolved and total mercury concentration in both seawater and upper sediment layers (0–5 cm beneath sea floor) as well as the Hg fluxes at the boundaries of the 3D model domain were theoretically reproduced and compared to the experimental data reported in the literature [ 36 , 42 ] from the same area.…”

“…Synthetically, the experimental and theoretical results indicate that the amount of total Hg- bound to the particulate matter represents ~47% of Hg T in seawater. The dissolved Hg (Hg D ) covers about 35% of the total budget of Hg T in seawater, while Hg D in pore water represents a minor fraction of total Hg in the sediments [ 19 ]. The estimated Hg II /Hg T , Hg 0 /Hg T , and MeHg/Hg T ratios are ~79%, 18%, and 2.5%, respectively, which is in good agreement with values reported from other contaminated sites (e.g., Canu et al [ 47 ]).…”