Modeling diffuse soil contamination from agriculture.
introduction
SUMMARY:
•Soil contamination, as defined in the
Soil Thematic Strategy.
•Local soil contamination and Diffuse
soil contamination
•Modeling Tools of Diffuse soil
contamination.
•SWAT Description
•SWAT application, two cases
•Leaching Modeling. Pesticide soil
contamination.
•PRZM and PEARL description
•PRZM and PEARL application
•Conclusion
introduction
Soil contamination, as defined in the
Soil Thematic Strategy.
The introduction of contaminants in the soil may result in damage to or loss of
some or several functions of soils and possible cross contamination of water.
The occurrence of contaminants in soils above certain levels entails multiple
negative consequences for the food chain and thus for human health, and for
all types of ecosystems and other natural resources.
introduction
Local and Diffuse Soil contamination,
Sources.
Local Soil contamination, Sources.
Local (or point source) contamination is generally associated with
mining, industrial facilities, waste landfills and other facilities both
in operation and after closure.
These activities can pose risks to both soil and water.
Diffuse Soil contamination, Sources.
Diffuse pollution is generally associated with atmospheric deposition,
certain farming practices and inadequate waste and wastewater
recycling and treatment.
introduction
Diffuse Soil contamination, Sources.
•Atmospheric deposition is due to emissions from industry, traffic and agriculture. Deposition of
airborne pollutants releases into soils acidifying contaminants (e.g. SO2, NOx), heavy metals (e.g.
cadmium, lead arsenic, mercury), and several organic compounds (e.g. dioxins, PCBs, PAHs).
•Production systems where a balance between farm inputs and outputs is not achieved in relation
to soil and land availability, leads to nutrient imbalances in soil, which frequently result in the
contamination of ground- and surface water.
•Pesticides are toxic compounds deliberately released into the environment to fight plant pests and
diseases. They can accumulate in the soil, leach to the groundwater and evaporate into the air from
which further deposition onto soil can take place.They also may affect soil biodiversity and enter
the food chain.
•With regard to waste, sewage sludge, the final product of the treatment of wastewater, is also
raising concern. A whole range of pollutants, such as heavy metals and poorly biodegradable trace
organic compounds, potentially contaminates it what can result in an increase of the soil
concentrations of these compounds.
introduction
Diffuse Soil contamination, Sources.
Production systems where a balance between farm inputs and outputs
is not achieved in relation to soil and land availability, leads to nutrient
imbalances in soil, which frequently result in the contamination of
ground- and surface water.
Modeling the fate of contaminants requires an understanding of the
soil-water-air continuum.
The modeling tool should be able to simulated physical, chemical and
biological processes occurring in these different compartments.
The modelling approach ...
Simulation of soil processes: organic matter turnover, crop growth, nitrogen uptake, water
infiltration, evaporation from crop and soil surface, nitrification, denitrification, interception of
precipitation and emissions to the atmosphere.
Atmospheric
deposition
N fixation
Fertilizer
applications
Plants
consumption
SOIL
N Leaching
AIR
Atmospheric
emissions
Plants consumption
Surface and subsurface runoff
NITRIFICATION/
DENITRIFICATION
STORAGE
RIVER
GROUNDWATER
Point
discharges
… a nested approach
• Vertical flow in the unsaturated
zone links the soil processes to
the 2-D overland flow and to
the 3-D groundwater flow.
• A fully distributed physically based
model representing variations in
catchment characteristics and driving
variables by a network of uniform grids
or sub-basins.
 Estimation of loads at representative sites, aggregation at
landscape scale, and upscaling to regions .
 Calculation of the impacts of the agricultural sector under
selected land use scenarios.
An Observational Network of European Watersheds
• Scenario analyses (socioeconomic, climate,
environmental) to improve
resource management and
provide information that
will aid for the sustainable
management of the
watershed.
• Impact assessment of waste
management strategies,
tourism, urban areas,
mining activities, land use
changes.
Modeling tools
Modeling of Diffuse soil contamination.
Modeling Tools: able to considering processes occurring in the soilwater-air compartments in the studied area, mainly used for
Nitrogen and Phosphorus modeling.
•SWAT (Soil Water Assessment Tool, Blackland Research Centre,
Texas US-Arnold et al., 1992)
SWAT description
swat
main
characteristics
basin-scale
continuous time
daily time step
physically based
computationally efficient
long-term simulations
water, sediments, nutrients, pesticides
SWAT description
Hydrology
model
SWAT
hydrology
Physical model
precipitation
surface
runoff
evapo
transpiration
lateral flow
infiltration
Physical model
SWAT
hydrology
Surface runoff
use of SCS curve number method to estimate surface runoff
Evapotranspiration
Three methods included in SWAT
Penman-Monteith
Hargreaves
Priestley-Taylor
ET is evaluated from
soils and plants as well
Snow melt
melting if the second soil layer temperature exceeds 0 C
and proportional to the snow pack temperature
SWAT
Soil module
Physical model
Water that enters the soil may move along one of several different
pathways. The water may be removed from the soil by plant uptake or
evaporation. It can percolate past the bottom of the soil profile and ultimately
become aquifer recharge. A final option is that water may move laterally in the
profile and contribute to streamflow. Of these different pathways, plant uptake of
water removes the majority of water that enters the soil profile.
SWAT considers:
•Soil Structure
•Percolation
•Lateral Flow
physical model
Soil Structure
SWAT
hydrology
Swat considers three phases in the soil:solid, liquid and gas.
The solid phase consists of minerals and/or organic matter that forms
the matrix or skeleton.Between the solid particles, soil pores are formed
that hold the liquid and gas phases. The soil solution may saturate the
soil completely or partially. Swat calculates the balance in every layer
and once (..and if ) this layer reach the saturation moves the water to
the next one.
Soil Name: s1Db
Soil Hydrologic Group: C
Maximum rooting depth(m) : 900.00
Porosity fraction from which anions are excluded: 1.000
Crack volume potential of soil: 0.000
Texture 1
: LFS-LFS-S
Depth
[mm]:
300.00 600.00 900.00
Bulk Density Moist [g/cc]:
1.46
1.46
1.41
Ave. AW Incl. Rock Frag :
0.17
0.28
0.35
Ksat. (est.) [mm/hr]:
1.00
2.40 200.00
Organic Carbon [weight %]: 1.50
0.86
0.52
Clay
[weight %]:
22.00
5.00
3.00
Silt
[weight %]:
59.00
76.00
7.00
Sand
[weight %]:
19.00
19.00
90.00
Rock Fragments [vol. %]:
0.00
0.00
0.00
Soil Albedo (Moist) :
0.06
0.06
0.06
Erosion K
:
0 .23
0.23
0.23
Salinity (EC, Form 5) :
1.00
0.00
0.00
physical model
SWAT
hydrology
Percolation is calculated for each soil layer in the profile. Water is allowed to
percolate if the water content exceeds the field capacity water content for that
layer. When the soil layer is frozen, no water flow out of the layer is calculated.
The volume of water available for percolation in the soil layer is calculated:
percolation
SW ly excess= FC ly – sSW ly if FC ly > SW ly
SW ly excess = 0 , = excess ly if FC ly < or = SW ly
where SWly,excess is the drainable volume of water in the soil layer on a given
day (mm H2O), SWly is the water content of the soil layer on a given day (mm
H2O) and FCly is the water content of the soil layer at field capacity (mm
H2O).
Percolation
physical model
SWAT
hydrology
Lateral Flow
Lateral flow will be significant in areas with soils having high hydraulic
conductivities in surface layers and an impermeable or semipermeable
layer at a shallow depth. In such a system, rainfall will percolate
vertically until it encounters the impermeable layer. The water then
ponds above the impermeable layer forming a saturated zone of water,
i.e. a perched water table. This saturated zone is the source of water
for lateral subsurface flow.
lateral flow
SWAT
weather
Physical model
driving variables
• precipitation
• temperature
• solar radiation
• wind speed
• relative humidity
daily measurements
Monthly measurements
In case of missed values, a weather
generator is included in the code
Physical model
swat
sediments
sediment yield
MUSLE: Modified Universal Soil Loss Equation
(USDA, Williams et al. 1977)
Physical model
swat
crop growth
solar radiation
leaf area
index
heat
units
harvest
index
crop
yield
energy
interception
crop
parameter
biomass
production
Physical model
swat
nutrients
NITROGEN model in SWAT
Residue
Stable organic N
harvest
Plant uptake
Decay
Active organic N
Organic fertilizer
Mineralization
NO3
Inorganic fertilizer
Physical model
swat
nutrients
PHOSPHORUS model in SWAT
Organic fertilizer
Mineralization
Lumped Active/Stable
organic P
Residue
Plant uptake
Sediment-bound labile
P
Dissolved labile P
Sediment-bound
fixed P
Inorganic fertilizer
Models application
TWO EXAMPLES DEVELOPED USING
SWAT COUPLED WITH GIS (ArcInfo and ArcView, ESRI)
OUSE Catchment (UK)
BURANA PO di VOLANO Catchment (IT)
MAIN ISSUES OF THE MODEL APPLICATIONS
Allowing the quantification of the total load of pollutant affecting a
watershed. This model should be used to understand how the soil
quality and water quantity/quality are affected by agricultural
activities.
Examples: OUSE Catchment (UK)
Soil Map
Examples: OUSE Catchment (UK)
Landuse Map
OUSE Land Use: (%)
•FRSE
2.25
•PAST
27.02
•RANGE 32.88
•WWHT 29.10
•URBAN 8.75
OUSE WATERSHED MONTHLY TIME STEP SIMULATION(30 years
simulation): FLOW OUT [m3/s] and LINEAR CORRELATION
OUSE HYDROLOGY
mesurated
NEW SETUP
180
160
OUTFLOW (cm/s)
140
120
100
80
60
40
20
0
gen-86
gen-87
gen-88
gen-89
gen-90
OUSE HYDROLOGY, STATISTICAL ANALYSIS
NEW SETUP
Linear (NEW SETUP)
OUTFLOW /cm/s)
200
150
100
2
R = 0.9239
50
0
0
20
40
60
80
100
120
140
160
180
200
OUSE WATERSHED MONTHLY TIME STEP SIMULATION(30
years simulation): TOTAL NITROGEN [Kg]
2.00E+06
mesurated
NEW SETUP
TOTAL NITROGEN(Kg)
1.80E+06
1.60E+06
1.40E+06
1.20E+06
1.00E+06
8.00E+05
6.00E+05
4.00E+05
2.00E+05
0.00E+00
Jan-87
Jan-88
Jan-89
Jan-90
LANDUSE SCENARIO: COMPARISON BETWEEN N EXCESS AND N PLANT UPTAKE WITH
TWO DIFFERENT APPLICATION RATE OF ORGANIC NITROGEN IN THE OUSE WATERSHED
LANDUSE SCENARIO: COMPARISON BETWEEN NO3 TO RIVER AND NO3 LEACHING WITH
TWO DIFFERENT APPLICATION RATE OF ORGANIC NITROGEN IN THE OUSE WATERSHED
210 Kg/ha
ORGANIC NITROGEN
AVERAGE ANNUAL CHANGE:
-6.34 %
170 Kg/ha
ORGANIC NITROGEN
Examples: Burana Po di Volano (IT)
Examples: Burana Po di Volano(IT)
Influence of Climate Change on Nitrogen Percolation from Soils
to Groundwater
Present scenario
Burana-Po di Volano
watershed
Scenario I
NO3 leaching
(Kg/ha)
Scenario II
0-6
7-12
13-18
19-24
25-30
31-36
37-42
43-48
49-54
55-60
61-66
67-72
73-78
79-84
85-90
Usi non aseminativo
GCM Scenario
CGCM1 e HadCM2
year 2050
Modeling tools
Modeling of Diffuse soil contamination.
Leaching Models: applied to determine the quantity of Pesticide
leaching thought the soil profile reaching the shallow aquifer.
•PRZM2: Pesticide Root Zone Model, Environmental Protection
Agency, US - Carsel et al. 1984.
• PEARL: Pesticide Emission Assessment at Regional and Local
Scales by Alterra Green World Research.
Models application
TWO EXAMPLES DEVELOPED USING
PRZM and PEARL coupled with ARCVIEW GIS
TREVIGLIO Catchment (IT)
EUROPEAN SCALE
MAIN ISSUES OF THE MODEL APPLICATIONS
Models are run at field and regional scale to be tested (PRZM,
PELMO) then the necessary information are collected at European
level and run with a model like PEARL (able to work with big
database) to estimate the persistence of selected substances at
European scale.
Examples: TREVIGLIO catchment (IT)
Modeling of Diffuse soil contamination.
Regional scale
PRZM2 is a one-dimensional, dynamic, compartmental
model that can be used to simulate chemical movement in
unsaturated soil systems within and immediately below
the plant root zone. It has two major components:
•hydrology
•chemical transport.
The model was specifically designed to provide loading to
selected media, including air, water, groundwater. PRZM2
runs on daily time step. PRZM2 is extensively used from
the U.S. Environmental Protection Agency to simulate the
transport of field-applied pesticides in the crop root zone.
Examples: TREVIGLIO catchment(IT)
Atrazine
(app. Rate 1.5 Kg/ha)
Concentration limits applied for classification of the Maps.
Soil Vulnerability to Pesticide Leaching
Concentration (µg/l)
Very Low Vulnerability
< 0.001
Low Vulnerability
0.001 – 0.01
Medium - Low Vulnerability
0.01 – 0.1
Medium - High Vulnerability
0.1 – 1
High Vulnerability
1 – 10
Very High Vulnerability
> 10
Alachlor
(app. Rate 2.0 Kg/ha)
Use a process based model supported by the FOCUS working group that includes all
major processes involved with pesticide transformation and fate. For instance, we are
currently using the PEARL model which is used to evaluate the leaching of pesticides
to the groundwater in support to the European and Dutch pesticide registration
procedures.
0
20
Depth (cm)
40
60
80
100
120
measured
predicted
December 14 1990
140
0.0
0.1
0.2
0.3
0.4
0.5
0.6
-1
Bentazone concentration (mgl )
Bentazone soil concentration 22 and 278
days after application of 0.8 kg/ha of
bentazone on field under winter wheat (NL)
Deliverable: map of pesticides persistence in the top layer, in the root
zone, and leaching below the root zone
Collect the necessary information at European level and run the PEARL model to
estimate the persistence of selected substances
CONCLUSION:
• These kind of modeling tool could be useful to analyze and simulate
the water contamination in a medium-big scale watershed.
•They are able to determine soil limitations (topography, rooting depth,
chemical fertility, organic carbon) of European soils (using harmonised
European soil information system).
• It is also possible to derive crop suitability zones and compare the
capability maps with land use maps.
•Useful to make some general conclusion about the effect of the global
climate change could be done.
LIMITATIONS:
•The calibration of the model is time-consuming and it would need
more efficient tools
•The quality of the model simulation depends on the quality of the
data available.