Cyril Garneau1, Sauvage S. 1, Probst A.1, Lofts S.2, Tipping E.2, Brito D.3, Neves R.3, Sanchez-Perez J-M. 1
1 Université de Toulouse, CNRS, France2 Centre for Ecology and Hydrology, Lancaster Environment Center, Bailrigg, Lancaster, U.K.
3 Maretec, Instituto Superior Técnico, University of Lisbon, Portugal
Trace metals transfer in rivers: a semi-empirical formulation to describe a complex sorption – desorption process to be
implemented in SWAT model.
SWAT 2014, Pernambuco, Brazil
River = integrator of pollution
Atmospheric deposition
Urban release andindustries
Mining activities
Geological background
Trace Metal problematic in natural waters
• Exhibits a wide range of behaviour in natural waters
• Controlled by variousenvironmental factors
• difficult to model
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SWAT 2014, Pernambuco, Brazil
Transfer of trace metals in rivers
• Advection• Dispersion• Transient storage
• Sédimentation• Érosion
𝐾𝑑 =𝑇𝑀𝑝𝑎𝑟𝑡
𝑇𝑀𝑑𝑖𝑠𝑠
µ𝑔𝑘𝑔µ𝑔𝐿
Dissolved phaseParticulated phase
Physico-chemistry
[Metal]
Nature of SSSWAT 2014, Pernambuco, Brazil
Modelling approaches : Sorption models
MINTEQA2 (Allison et al., 1991)
WASP (Ambrose et al., 1993)
WHAM (Tipping, 1993)
Trace elementFree adsorption site
Occupied adsorption site
SWAT 2014, Pernambuco, Brazil
• Different levels of modelling simplicity
– SWAT: the TM are fully dissolved and transported from the inlet to the outlet.
– Two phases separation of TM: The TM exist either in a dissolved form or in a particulate one.
– Two phases separation with dynamic equilibrium: The two TM phases can interact to maintain an equilibrium based on the physico-chemistry.
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Modelling approach
𝑇𝑀𝑑𝑖𝑠𝑠𝑜𝑢𝑡 = 𝑇𝑀𝑑𝑖𝑠𝑠𝑐ℎ ×𝑉𝑜𝑢𝑡𝑉𝑐ℎ
𝑇𝑀𝑝𝑎𝑟𝑡𝑐ℎ = 𝑇𝑀𝑝𝑎𝑟𝑡𝑐ℎ,𝑖 + 𝑇𝑀𝑝𝑎𝑟𝑡𝑒𝑟𝑜𝑑𝑒𝑑 − 𝑇𝑀𝑝𝑎𝑟𝑡𝑑𝑒𝑝𝑜𝑠𝑖𝑡𝑒𝑑
𝑇𝑀𝑝𝑎𝑟𝑡𝑜𝑢𝑡 = 𝑇𝑀𝑝𝑎𝑟𝑡𝑐ℎ ×𝑉𝑜𝑢𝑡𝑉𝑐ℎ
𝐾𝑑 = 𝑓 𝑝ℎ𝑦𝑠𝑖𝑐𝑜 − 𝑐ℎ𝑒𝑚𝑖𝑡𝑟𝑦 =𝑇𝑀𝑝𝑎𝑟𝑡
𝑇𝑀𝑑𝑖𝑠𝑠
µ𝑔𝑘𝑔µ𝑔𝐿
𝑇𝑀𝑑𝑖𝑠𝑠𝑐ℎ =𝑇𝑀𝑡𝑜𝑡𝑎𝑙𝑐ℎ
1 + 𝐾𝑑 × 𝑆𝑃𝑀
𝑇𝑀𝑝𝑎𝑟𝑡𝑐ℎ = 𝑇𝑀𝑡𝑜𝑡𝑎𝑙𝑐ℎ − 𝑇𝑀𝑑𝑖𝑠𝑠
SWAT 2014, Pernambuco, Brazil
Objectives
• Propose an alternative modelling option for trace metal
– Use two TM phases: dissolved and particulate
– Use a dynamic Kd formulation based on available variables and quantities in SWAT
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First step : we have to identify key parameters involved in Kd formulation
SWAT 2014, Pernambuco, Brazil
Complex modelling
MOHID- Full St-Venant equations- Advection – diffusion equations- Transient storage- Erosion – deposition equations
WHAM
- Simulates upstream river and tributaries
- Watershed dynamic outputs
- SPM concentration
- Chemical speciation of TM
- Specific reaction with organic matter
SWAT 2014, Pernambuco, Brazil
Study case
• The Garonne River sector– Reach of 80 km (watershed 13800 km²)
– Monthly average discharge 75 to 341 m3/s
• 4 campaigns in 2005 (13 sites)• Nutrients
• Major ions
• Physico-chemistry
• 15 Trace metals
SWAT 2014, Pernambuco, Brazil
Study caseChoise of two trace elements- Lead (Pb)- Arsenic (As)- Copper (Cu)
Low
wat
ers
Hig
h w
ater
s
𝑓𝐶𝑂𝑃 = min0,60
𝑆𝑃𝑀 − 1.0+ 0.021; 0.24
+
SWAT 2014, Pernambuco, Brazil
TM temporal concentration evolution
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TM c
on
cen
trat
ion
(µ
g/l
)
Date Date
SWAT 2014, Pernambuco, Brazil
TM spatial concentration evolution
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Low waters High waters
SWAT 2014, Pernambuco, Brazil
Key results
• The particulate phase is important to describe sources and sinks of trace metals
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41% of copper trapped on the riverbed
76% of lead trapped on the riverbed
SWAT 2014, Pernambuco, Brazil
Key results
• Physico-chemistry influence
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Log1
0(K
d)
and
pH F
low
(m3.s
-1)
pH
𝐾𝑑ld
𝐾𝑑𝐶𝑜
Flow
SWAT 2014, Pernambuco, Brazil
Key results
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5.4
5.6
5.8
6
6.2
6.4
6.6
6.8
7 7.5 8 8.5 9 9.5
log1
0(K
d)
pH
Lead
Verdun
5.4
5.6
5.8
6
6.2
6.4
6.6
6.8
0 50 100 150
log1
0(K
d)
SPM
Verdun
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
5.1
7 7.5 8 8.5 9 9.5
log1
0(K
d)
pH
Copper
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
5.1
0 50 100 150
log1
0(K
d)
SPM
SPM controlled Kd
SWAT 2014, Pernambuco, Brazil
Key results
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5.4
5.6
5.8
6
6.2
6.4
6.6
6.8
0 1 2 3 4
log1
0(K
d)
POC
Lead
Verdun
4.3
4.4
4.5
4.6
4.7
4.8
4.9
5
5.1
0 1 2 3 4
log1
0(K
d)
POC
Copper
SWAT 2014, Pernambuco, Brazil
Proposition
• Metal input generation– Anthropic sources: point-sources, atmospheric
deposition, diffuse sources (fertilizers application)– Geogenic source: Based on soil maps, residence time
and mixing models (Wade et al. 1999)
• Modelling requirements– Fixed Kd model: efficient for high Kd trace metal – Variable Kd model: efficient for low Kd– A simple empirical variable Kd model can be built on
limited inputs variables (pH, SPM and POC concentrations)
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SWAT 2014, Pernambuco, Brazil
Thank you for your attention
SWAT 2014, Pernambuco, Brazil