mathematical modelling of erosion, mercury transport and transformations from idrija to the gulf of...
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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 Idrijaregion and the Gulf of
Trieste
•ELOISE 2004
Mercury mine in Idrija:
•127.000 tons of Hg extracted in 500 years
•37.000 tons of Hg “lost”
•over 12.000 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 2004
1 4 6 7 9 11 12 13 14 17 D6 AA CZ
MeHg in Fish
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6 7
Location
MeH
g [
ng
/g]
WHO limit
Gulf of Trieste: Annual mass balance
of total Hg and MMHg
Gulf of Trieste: Annual mass balance
of total Hg and MMHg
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Modelling approach
Hydrodynamics (flow / circulation)
Transport and dispersion of pollutants
Biogeochemistry (sources, sinks, reactions - transformations)
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Interaction between the models
Local scale models
Meso-scale aquatic models•Mediterranean
-
Regional scale aquatic models• Idrijca and Soča River
• Gulf of Trieste
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Input data
Boundary conditions
• sources• erosion
Models
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Erosion model (Idrija region): Hg
release 2.500 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
A i
junction(J)
Idrij
ca R
iver
GIS-layer based model
Data – layers: topography, geology, pedology, land cover, land use, slope, precipitation, runoff.
Measurements: Hg
•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
W ASP5
RIVMOD MERC4
- hydrodynam ics- sedim ent transport
- ve locities- depth- shear stress
- m ass balance equations(advective and d iffusive
transport)
- concentrations of various po llu tants- bed load concentrations- suspended load conc.
- m ercury speciation andkinetic transform ation
- concentrations of inorganic m ercury (H gII)- concentrations of m ono- m ethyl m ercury (M M H g)
•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…)
Calibration poin t 1
Calibration poin t 2
Autumn – winter conditions, high discharge (flood events)
Simulation of an observed flood event
MeRiMod - Calibration Q100
050
100150200250300350
400450500550600650700750
0 12 24 36 48 60 72 84 96
Time [h]
Flow [m3/s] Suspended sed. (statistics) [g/m3] Susp. sed. (model) [g/m3]
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Transformation processes (HgT)
summer conditions (low discharge 10 - 25 m /s)
comparison to measurements (Hines et al., 2000)
agreement mostly within a factor of 5
qualitatively questionable
Total Hg in water
0
10
20
30
40
50
0 20000 40000 60000 80000 100000 120000
Distance from Idrija [m]
ng
/l
HgT HgT(diss) Measurements HgT
322 ng/l
3
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Transformation processes (MMHg)
MeHg in water
0.00
0.20
0.40
0.60
0.80
1.00
0 20000 40000 60000 80000 100000 120000
Distance from Idrija [m]
ng
/l
MeHg(T) MeHg(Diss) Measured MeHg(T)
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 forcingwindtidal forcingriver inflow momentum
HYDRODYNAMIC MODEL
PCFLOW3D-HD
river loads sea currentssea bottom processesPCFLOW3D-ST
SEDIMENTATION MODEL
• air-water exchange• methylation demethylation• reduction• oxydation• exchange with the bottom sediment
ADVECTION-DISPERSION MODEL FORMERCURY with transformations
Hg MODULEPCFLOW3D
•ELOISE 2004
CONCEPT OF THE WATER MODEL (MERCYMS)
demethylation
methylationMMHgHgII
Hg0
deposition deposition
dry wet dry wet
reduction
oxydation
bottom layer release
decay & settling
decay & settling
air-water exchange
settling & resuspension
settling & resuspension
dissolved
particulate
plankton
gaseous
diff
usi
on
diff
usi
on
METH = Kmeth * Hg2DiDEMETH = Kdemeth * MHgDiRED = Kred * Hg2DiOXY = Koxy * Hg0
Equations:
•ELOISE 2004
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
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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…
ConclusionsDifferent 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