Mathematical modelling of erosion, mercury transport and transformations from Idrija to the Gulf of Trieste Dušan Žagar, Ana Knap, Rudi Rajar, Gregor Petkovšek, Milena Horvat, Branko Kontić, Jože Kotnik, Nives Ogrinc, Matjaž Četina University of Ljubljana, Slovenia Jožef Stefan Institute, Slovenia ELOISE 2004 EUROCAT & MERCYMS

Mercury cycle in the wider Idrija region and the Gulf of Trieste ELOISE 2004 Mercury mine in Idrija: tons of Hg extracted in 500 years tons of Hg “lost” over tons entered the river system about 2500 kg/yr enters the river system about 1500 kg/yr transported to the Gulf of Trieste ELOISE 2004

Hg in the river system and fish ELOISE 2004 From: Hines et al.2000; Horvat 2002; Horvat D6 AA CZ WHO limit

Gulf of Trieste: Annual mass balance of total Hg and MMHg Gulf of Trieste: Annual mass balance of total Hg and MMHg ELOISE 2004

Modelling approach Hydrodynamics (flow / circulation) Transport and dispersion of pollutants Biogeochemistry (sources, sinks, reactions - transformations) ELOISE 2004

Interaction between the models Local scale models Meso-scale aquatic models Mediterranean - Regional scale aquatic models Idrijca and Soča River Gulf of Trieste ELOISE 2004 Input data Boundary conditions sources erosion

Models ELOISE 2004 Erosion model (Idrija region): Hg release kg/year River model (Idrijca and Soča): transport and transformations Marine model (Gulf of Trieste): Hg input 1500 kg/year

EROSION MODEL and Hg release Results: input data for the river model possible remediation measures GIS-layer based model Data – layers: topography, geology, pedology, land cover, land use, slope, precipitation, runoff. Measurements: Hg ELOISE 2004

Modelling results for PT scenario ELOISE 2004

Results and findings from EROSION MODEL Present situation: annual Hg release to Idrijca River: 2500 kg PT scenario: change in land use and elimination of hot spots: decrease of annual Hg release to 1445 kg Possible reduction: 42 % Cost: 28 mil. € ELOISE 2004

1-D model MeRiMod structure already used for the Carson River (NV, USA) adapted for Idrijca and Soča Rivers (parameters – measurements) real time unsteady-state simulations ELOISE 2004

MeRiMod modelling cases: Case 1 : Flood waves – transport (autumn, spring) overbank deposition in flood-plains bank erosion historical mass balance of the catchment improvement of input data for PCFLOW3D Case 2 : methylation in the river system (summer) ELOISE 2004

Calibration & validation – transport Point 1: within ± 30 % Point 2: within a factor of 4 (15 t model, 4.7 t estimated) scenarios for historical Hg mass balance of the catchment (Q500, Q200…) Autumn – winter conditions, high discharge (flood events) Simulation of an observed flood event ELOISE 2004

tons

Transformation processes (HgT) summer conditions (low discharge m /s) comparison to measurements (Hines et al., 2000) agreement mostly within a factor of 5 qualitatively questionable 322 ng/l 3 ELOISE 2004

Transformation processes (MMHg) K = f (water temp., Ph) many BGC parameters still missing comparison to measurements (Hines et al., 2000) agreement within a factor of 3, qualitatively good. met/dem ELOISE 2004

CONCEPT OF THE 3D WATER MODELING SYSTEM (MARINE ENVIRONMENT) thermohaline forcing wind tidal forcing river inflow momentum HYDRODYNAMIC MODEL PCFLOW3D-HD river loads sea currents sea bottom processes PCFLOW3D-ST SEDIMENTATION MODEL air-water exchange methylation demethylation reduction oxydation exchange with the bottom sediment ADVECTION-DISPERSION MODEL FOR MERCURY with transformations Hg MODULE PCFLOW3D ELOISE 2004

CONCEPT OF THE WATER MODEL (MERCYMS) demethylation methylation MMHgHgII Hg0 deposition drywetdrywet reduction oxydation bottom layer release decay & settling air-water exchange settling & resuspension dissolved particulate plankton gaseous diffusion METH = Kmeth * Hg2Di DEMETH = Kdemeth * MHgDi RED = Kred * Hg2Di OXY = Koxy * Hg0 Equations: ELOISE 2004

Reactions & evasion simulations HgT, MMHG, Hg0 Preliminary results Surface layer; ng/l ELOISE 2004

Evasion rate ng/m2/h ng/m2 ELOISE 2004 Preliminary results Surface layer

ATMOSPH.- OUT = 60 t Gibraltar OUT = 10.1 t IN = 7.5 t IN = 10 t (?) Bosporus IN = 0.3 t Point sources 2.3 t Rivers 13.7 t To sediment = 14t MEDITERRANEAN 2040t = IN Surface: 2.51*10**6 km2 Volume: 3.60*10**6 km3 Average concentr. of Hg in MED.SEA: 0.57 ng/l or 2.84 pM Total IN: 33.8 t Total OUT: 70.1 t (- Sediment 14 t) MASS BALANCE OF Hg IN THE MEDITERRANEAN ELOISE 2004

Calibration - validation Connecting reaction coefficients and environmental parameters (data from measurements – deep sea and coastal) artificial intelligence (machine learning) “simple” statistical methods T, DO, ChlA, NOx, TSM, wind, radiation…. ELOISE 2004 Hg(2+), Hg0, MMHg, DMHg…

Conclusions Different processes are important in different compartments and scales Understanding and modelling of complete Hg cycling is needed Erosion: remediation measures were determined River system: transport in agreement with measurements, BGC processes somewhat worse Marine: verification done, calibration in progress Coupled models are useful tool in analysing Hg cycling processes in the environment ELOISE 2004

POSSIBLE MEASURES to reduce toxic effect of MMHg in the area Reducing Hg transport within the river system: diminish erosion near Idrija (forestation, elimination of hot spots) dredging of sediments along both rivers construction of new reservoirs (?) – or elimination (?) Reducing methylation (conditions): to improve water quality in the river sytem and the Gulf – WW treatment, reducing mariculture, aeration (?) dredging of bottom sediment to reduce the source of MMHg - technically possible, very expensive, where to put Hg contaminated sediment (?) Administrative measures – prohibition of fishing, mariculture… ELOISE 2004