Supplementary material to "HR3DHG version 1: modelling the spatio-temporal dynamics of mercury in the Augusta Bay (southern Italy)"

Abstract

1 65 -M T C water−atm is the gas phase overall mass transfer coefficient [m/h]; -H is the Henry's law constant [dimensionless].The temporal behaviour of Hg gas−atm is reproduced for one year by using the experimental data collected by IAS-CNR in 2011, and reported in a previous work (Bagnato et al., 2013). The dynamics of precipitations is obtained by using the remote sensing data on the average monthly precipitations in Augusta Bay (see the NASA web site http://eosweb.larc.nasa.gov/sse/RETScreen/). 70The M T C water−atm is calculated according to the River model (Ciffroy, 2015) as follows:Here, the water film mass transfer coefficient (M T C water−atm,w ) and the gas film mass transfer coefficient (M T C water−atm,g ) are given by:where u wind is the wind speed [m/s];-P M CO2 is the molar mass of carbon dioxide [g/mol]; 80 4 -P M molar is the molar mass of elemental mercury [g/mol];-P M H2O is the molar mass of water [g/mol].The wind speed is obtained by averaging the values of annual mean wind speed of the last 15 years for the studied area (see the NASA web site http://eosweb.larc.nasa.gov).The annual mercury evasion flux at the seawater-atmosphere interface (V) is obtained by integrating the φ GEM for the whole 85 horizontal surface of the basin, and for the whole year. The annual atmospheric deposition of the elemental mercury is calculated by integrating the φ dep for the whole horizontal surface of the basin, and for the whole year. S1.1.2 Boundary conditions (lateral fluxes) -Dissolved elemental mercury concentration The lateral fluxes for all variables are set up equal to zero at the boundaries of Augusta basin (Valenti et al., 2017) except where inlets, rivers and sewerage are localized. Moreover, we can neglect the elemental mercury flux at the water-sediment interface 90(z = z b ). Therefore, we fix the following fluxes at the basin boundaries: