APPENDIX E
PARAMETERISATION OF FATE IN
SURFACE WATER
1
1. Background
TOXSWA (TOXic substances in Surface WAters, Adriaanse, 1996; Beltman and Adriaanse, 1999) has
been parameterised to simulate pesticide fate in the FOCUS defined surface water bodies, based on
input from spray drift and either runoff or drainage. TOXSWA in FOCUS uses input from MACRO
and PRZM to simulate the behaviour of substances that enter the water system by drainage through the
soil or run-off at the soil surface, respectively.
The input for the TOXSWA model is organised in three input files. Three output files are always
created: the ECH file, echoing all input, the ERR file, containing all run warnings and, if the run was
stopped, a run error, and the SUM file, giving a summary of the main input and output of the run. In
addition to these three standard output files, the user can ask for in total 13 more files, containing water
or mass balances for specified subsystems and periods, distribution patterns and concentration profiles.
The TOXSWA User Interface is developed as a user-friendly environment for running TOXSWA and
the FOCUS scenarios. It is coupled to the SWASH tool that helps the user to define the needed runs
and to prepare input for the various FOCUS models. TOXSWA and SWASH make use of the same
database and that is why the user only needs to check the TOXSWA input in its GUI, to ask for the
wished output files and to execute the runs, prepared by SWASH. SWASH also takes care that the
correct spray drift deposition values are entered into TOXSWA and that the correct output files from
MACRO or PRZM are coupled to TOXSWA. All model input is echoed in the ECH file, while an
overview of the main input, including the water and pesticide entries by spray drift, drainage and
runoff, is given in the SUM file.
2. General description of TOXSWA input
Simulated system
The water body system simulated by TOXSWA consists of a water and a sediment layer. The water layer
permanently carries water. In the FOCUS scenarios it contains suspended solids, but no macrophytes. The
sediment layer is characterised by the properties bulk density, porosity and organic matter content, that
may vary with depth, but have been set to constant values in the FOCUS scenarios. In the water layer the
pesticide concentration varies in the horizontal direction, but is assumed to be constant throughout depth
and width. In the sediment layer, the pesticide concentration is a function in both the horizontal and
vertical directions.
For the numerical solutions of the mass balance equations, the water layer is divided into a number of
nodes in the horizontal direction. Below each node, a number of nodes are defined for the sediment layer.
For the FOCUS scenarios distances between the nodes in the water layer vary from 5 m (streams) to 30 m
(pond), while for the distances between the nodes in the sediment vary from 1 to 30 mm (all compounds,
except pyrethroids).
Water body type, adjacent area and catchment
The FOCUS Surface Water Scenarios distinguishes three water body types: a pond of 30 x 30 x 1 m (l x
w x d), a ditch of 100 x 1 x ≥ 0.3 m and a stream of 100 x 1 x ≥ 0.3 m. In the TOXSWA model however,
only two types of water bodies can be specified: a pond or a watercourse. A set of other parameters,
defining the water flow dynamics, determines whether the watercourse behaves more like a ditch or a
small stream water type. In the FOCUS scenarios parameterisation of TOXSWA is such that two types of
watercourses are simulated: a slowly moving ditch and a more dynamic stream, both with a minimum
water depth of 0.3 m, that is maintained by a weir at 10 to 900 m below the downstream end of the
watercourse. In the pond the water level is maintained by a weir at the outlet with a crest height of 1 m.
The pond is fed by a small, constant base flow plus water drained or run off a surrounding, contributing
area of 4500 m2. The ditch is fed by a constant base flow originating from 2 ha ‘catchment’, as well as by
drainage water fluxes from a 1 ha adjacent field plus the 2 ha catchment. The stream flow is composed of
a constant base flow from 100 ha catchment plus two or three other components. Drainage or runoff water
fluxes from the adjacent 1 ha field as well as from the 100 ha catchment located upstream, feed the
stream. Next to these, a small recession flow, accounting for subsurface inflow, is added to the streams of
the four Runoff scenarios.
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Not all water body types figure in all scenarios. A selection has been made of those water bodies, that are
characteristic for the scenario concerned.
Loadings
Pesticides may enter the water body by various routes. Spray drift deposition can occur at specified times
and onto specified stretches of the watercourse. For the FOCUS scenarios a drift calculator has been
developed, that calculates drift entries as a function of crop, water body type and number of applications.
Pesticide fluxes may enter by either drainage or by runoff plus eroded soil from the adjacent field. In the
FOCUS scenarios the contributing margin for drainage and runoff fluxes is 100 m, while eroded soil
originates from a 20-m margin only. The fluxes have been specified on an hourly basis for the FOCUS
Surface Water Scenarios and enter specified stretches of the watercourse. Finally pesticides may enter
from the catchment located upstream of the TOXSWA watercourse by drainage or runoff. For ditches the
catchment does not deliver pesticides into the ditch, while for streams 20% of the 100 ha catchment
contributes pesticides to the stream. To allow for the 20% spray drift contribution from the upstream
catchment in the case of streams, the drift values of the calculator have been multiplied with a factor 1.2.
For ponds the contributing area is 4500 m2. In the FOCUS scenarios the drainage and runoff/ erosion
entries are calculated by the MACRO and PRZM model, respectively.
Substance
The input data on the substance comprise data on the physico-chemical properties (molecular weight,
diffusion coefficients, vapour pressure and water solubility), the transformation data (half-life) and the
sorption data for both sediment and suspended solids (Freundlich coefficient and exponent), but not for
macrophytes as the FOCUS scenarios do not consider these. If data are available the user can consider
using different transformation rates for the water layer and the sediment.
Pyrethroids
Compounds with a high sorption capacity (Koc > 10 000 L/kg ) require a specific parameterisation of
the sediment layer in TOXSWA model in order to obtain a converging numerical solution of the mass
conservation equation for the sediment. This parameterisation has been explained in detail in an
appendix of the TOXSWA in FOCUS User Manual (Ter Horst, et al., 2003).
Weather
TOXSWA uses monthly averaged water temperatures. The averages are based on the daily minimum and
maximum values from the MARS dataset for the 10 FOCUS Surface Water Scenarios.
3. TOXSWA input
The procedure is to prepare FOCUS input files for TOXSWA in a sequence of steps using files that are
already available. For each run, the necessary input files for TOXSWA are:
1. The TXW file; containing:
- the paths and the names of the other input files, time control parameters and output parameters
- input on the watercourse, incl. sediment system
- input on the hydrology of the system
- input data on the loadings of the surface water with substance
- all substance parameters;
2. The MET file; containing meteorological input (with the filename denoting the location)
3. Either the M2T file; containing drained water fluxes and substance loads, or the P2T file;
containing runoff water fluxes, erosion mass fluxes and substance loads.
The TXW file is named xxxxxw_pm.txw, in which ‘xxxxx’ is used for the run identification number,
‘w’ for the water body type (p for Pond, d for Ditch, and s for Stream systems) and ‘pm’ to indicate
whether a parent or metabolite is concerned. Accordingly, the ECH, ERR and SUM files (and optional
TOXSWA output files) are named xxxxxw_pm.ext.
Below we specify the input in the three input files. The scenario and parameter definitions are based
on:
1) FOCUS DEFINITION = Definitions made by the FOCUS working group
2) FOCUS SCENARIO SPECIFIC = Definitions made by the FOCUS group for a specific scenario
3) DEVELOPMENT DEFINITION = Definitions made during the TOXSWA FOCUS development
4) USER INPUT = Input to be specified by the user in the TOXSWA FOCUS input files
3
1) TXW file
Parameter and description
Value, source & comments
Section 1: Run characteristics
prname
Name of project
USER INPUT
locname
Name of location
USER INPUT
runcom
Comments for run
USER INPUT
op_hyd
Simulation control option
USER INPUT
met
Path and/or name of input file for
meteorological data
FOCUS SCENARIO SPECIFIC
rodr
Path and name of input file on drainage
or runoff loading
FOCUS SCENARIO SPECIFIC
stdate
Starting date of simulation
FOCUS SCENARIO SPECIFIC
endate
End date of simulation
FOCUS SCENARIO SPECIFIC
chastdatemet
Year-month of first entry of average
Temperature
FOCUS SCENARIO SPECIFIC
chaendatemet
Year-month of last entry of average
temperature
FOCUS SCENARIO SPECIFIC
deltwb
Calculation time step for sediment (s)
FOCUS SCENARIO SPECIFIC
deltouth
Time step for output (h)
Set to 12.0 h. DEVELOPMENT DEFINITION
nwbsy
Number of selected sediment segments
Set to 1. DEVELOPMENT DEFINITION
iwbsy
Sediment segment number
Last sediment segment at the downstream end of loaded
stretch of watercourse. FOCUS DEFINITION
ktop
Number of segments forming the top
layer of the sediment
Set to 12 (50 mm thickness by FOCUS DEFINITION)
ntcurve
Selected times for additional output
Not used in FOCUS scenarios. DEVELOPMENT
DEFINITION
tcurvedate
Date and hour for additional output
Not used in FOCUS scenarios. DEVELOPMENT
DEFINITION
op_hyb
Water balance
Set to 1. DEVELOPMENT DEFINITION
op_mfl
Drainage or runoff entries
Set to 1. DEVELOPMENT DEFINITION
op_rc1
Basic characteristics of representative
channel
Set to 1. DEVELOPMENT DEFINITION
op_rc2
Additional characteristics of
representative channel
Set to 1. DEVELOPMENT DEFINITION
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op_cwa
Concentrations in all segments of the
water layer
Set to 1. DEVELOPMENT DEFINITION
op_csx
Concentrations in sediment subsystem
selected for output (x = 1)
Set to 1. DEVELOPMENT DEFINITION
op_mwa
Mass balance of the entire water layer
Set to 1. DEVELOPMENT DEFINITION
op_mwx
Mass balance of the water layer above
the sediment subsystem selected for
output (x = 1)
Set to 1. DEVELOPMENT DEFINITION
op_msa
Mass balance of the entire sediment
subsystem
Set to 1. DEVELOPMENT DEFINITION
op_msx
Mass balance of sediment subsystem
selected for output (x = 1)
Set to 1. DEVELOPMENT DEFINITION
op_dba
Distribution of substance in the entire
water body
Set to 1. DEVELOPMENT DEFINITION
op_dbx
Distribution of substance in the water
layer above the sediment subsystem
selected for output (x = 1)
Set to 1. DEVELOPMENT DEFINITION
op_mob
Mass balance of the water layer, with
lumped terms, on a monthly basis.
Set to 1. DEVELOPMENT DEFINITION
Section 2: Definition of water layer and sediment
xdit
Total length of water body
Set to 30.0 m for Pond, 100.0 m for Ditch, and 100.0 m
for Stream systems. FOCUS DEFINITION.
xfb
Length of front buffer
Set to 0.0 m. DEVELOPMENT DEFINITION
xeb
Length of end buffer
Set to 0.0 m. DEVELOPMENT DEFINITION
nxnodit
Number of segments in water body
Set to 1 for Pond, 10 for Ditch, and 20 for Stream
systems. DEVELOPMENT DEFINITION
nxnofb
Number of segments in front buffer
Set to 0. DEVELOPMENT DEFINITION
nxnoeb
Number of segments in end buffer
Set to 0. DEVELOPMENT DEFINITION
lesefb
Length of segments in front buffer
Set to 0.0 m. DEVELOPMENT DEFINITION
lesedit
Length of segments in water body
Set to 30.0 m for Pond, 10.0 m for Ditch and 5.0 m for
Stream systems. DEVELOPMENT DEFINITION
leseeb
Length of segments in end buffer
Set to 0.0 m. DEVELOPMENT DEFINITION
wibot
Bottom width of water body
Set to 30.0 m for Pond, 1.0 m for Ditch, and 1.0 m for
Stream systems. FOCUS DEFINITION
sisl
Side slope, horizontal/vertical
Set to 1.E-05. DEVELOPMENT DEFINITION
wdhfl
Water depth defining perimeter for
exchange water layer – sediment
Set to 0.01 m. DEVELOPMENT DEFINITION
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Parameter and description
Value, source & comments
coss
Concentration of suspended solids
Set to 15.0 g.m-3. FOCUS DEFINITION
raomss
Mass ratio of organic matter
Set to 0.09. FOCUS DEFINITION
dwmp
Dry weight of macrophyte biomass
Set to 0.0 g.m-2. FOCUS DEFINITION
castwl
Initial (start) mass concentration in
segments of the water layer
Set to 0.0 g.m-3. DEVELOPMENT DEFINITION
coair
Background concentration of pesticide
in air
Set to 0.0 g.m-3. DEVELOPMENT DEFINITION
zwb
Thickness of sediment layer
Set to 0.1 m. DEVELOPMENT DEFINITION
zebb
Thickness of end buffer in sediment
layer
Set to 0.0 m. DEVELOPMENT DEFINITION
nznowb
Number of segments in sediment layer
Set to 14. DEVELOPMENT DEFINITION
nznoebb
Number of segments in end buffer
Set to 0. DEVELOPMENT DEFINITION
lesewb
Thickness of segments in sediment layer
Set to 1 mm for the first 4 segments at the top, 2 mm
for the next 3 segments, 5 mm for the 8th and 9th
segment, 10 mm for the 10th, 11th and 12th segment, 20
mm for the 13th segment, and 30 mm for the 14th
segment at the bottom. DEVELOPMENT
DEFINITION
leseebb
Thickness of segments in end buffer
Set to 0.0. DEVELOPMENT DEFINITION
bdwb
Bulk density of dry sediment at each
segment
Set to 800 kg m-3. FOCUS DEFINITION
por
Porosity at each segment
Set to 0.6. FOCUS DEFINITION
tor
Tortuosity at each segment
Set to 0.6. DEVELOPMENT DEFINITION
raomwb
Mass ratio of organic matter in dry
sediment at each segment
Set to 0.09. FOCUS DEFINITION
ldis
Dispersion length
Set to 0.015 m. DEVELOPMENT DEFINITION
castwb
Initial (start) mass concentration at each
segment
Set to 0.0 g m-3. DEVELOPMENT DEFINITION
Section 3: Hydrology of water bodies
qseif
Seepage rate
Set to 0.0 m3 m-2 d-1. DEVELOPMENT
DEFINITION
colot
Concentration in seepage water
Set to 0.0 g m-3. DEVELOPMENT DEFINITION
op_vafl
Switch for: constant flow of water
Set to 1, so variable flow selected. FOCUS
DEFINITION
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op_hd
Switch for hourly or daily data on
drainage/runoff
Set to 0, so hourly values are used. FOCUS
DEFINITION
delthy
Time step for water balance
Set to 600 s. DEVELOPMENT DEFINITION
wdh
Constant water depth
Set to 0.5 m. Not used in FOCUS scenarios.
DEVELOPMENT DEFINITION
u
Constant flow velocity
Set to 10 m d-1. Not used in FOCUS scenarios.
DEVELOPMENT DEFINITION
op_powc
Switch for: pond (one segment) or
watercourse (more segments)
Set to 0 for Pond systems and set to 1 for Ditch and
Stream systems. DEVELOPMENT DEFINITION
For Pond only (next 5 parameters):
arpo
Size of area surrounding the pond,
contributing runoff or drained fluxes
Set to 0.45 ha. FOCUS DEFINITION
arerpo
Size of area surrounding the pond,
contributing eroded sediment with
sorbed substance
Set to 0.06 ha. FOCUS DEFINITION
Qbasepo
Minimal inflow into pond
In m3 d-1. FOCUS SCENARIO SPECIFIC
crestbodypo
Height of the body up to the crest of the
weir in the pond
Set to 1.0 m. FOCUS DEFINITION
wicrestpo
Crest width of weir, located at the
outflow of the pond
Set to 0.5 m. DEVELOPMENT DEFINITION
For Watercourse only (next 14 parameters):
lerc
Length of representative channel
Set to 200.0 m for Stream systems of D1, D2 and D4,
110.0 m for Stream systems of D5, R1, R2, R3, and
R4. Set to 1000.0 m for all Ditch systems.
DEVELOPMENT DEFINITION
botslrc
Bottom slope of representative channel
Set to 0.001 for Stream systems of D1, D2, D4, R1 and
R4, 0.002 for Stream systems of D5, R2 and R3. Set to
0.0001 for all Ditch systems. DEVELOPMENT
DEFINITION
wibotrc
Bottom width of representative channel
Set to 1.0 m. DEVELOPMENT DEFINITION
sislrc
Side slope (hor/ vert) of representative
channel
Set to 1.0 E-5. DEVELOPMENT DEFINITION
Qbaserc
Minimal inflow into representative
channel
In m3 d-1. FOCUS SCENARIO SPECIFIC
arrc
Size of the area located upstream
Set to 100.0 ha for Stream systems, and 2.0 ha for
Ditch systems. FOCUS DEFINITION
crestbodyrc
Height of the crest above the channel
bottom of the weir
Set to 0.5 m for Stream systems, and 0.4 m for Ditch
systems. DEVELOPMENT DEFINITION
wicrestrc
Crest width of weir
Set to 0.5 m. DEVELOPMENT DEFINITION
kMan1m
Value of the Manning coefficient for
bottom roughness at 1 m water depth
Set to 11 m1/3 s-1 for Stream systems, and 25 m1/3 s-1 for
Ditch systems. DEVELOPMENT DEFINITION
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alphaen
Energy coefficient resulting from the
non-uniform distribution of flow
velocities
Set to 1.2. DEVELOPMENT DEFINITION
Qbasewc
Minimal inflow into watercourse
In m3 d-1. FOCUS SCENARIO SPECIFIC
arupwc
Size of the area located upstream of the
watercourse
Set to 100.0 ha for Stream systems and 2.0 ha for Ditch
systems. FOCUS DEFINITION
leplot
Margin of treated plot, contributing
runoff or drained fluxes
Set to 100.0 m for Drainage and Runoff scenarios.
FOCUS DEFINITION
leerwc
Margin of treated plot, contributing
eroded sediment with sorbed substances
Set to 20.0 m for Runoff scenarios (dummy for
Drainage scenarios). FOCUS DEFINITION
Parameter and description
Value, source & comments
Section 4: Pesticides loadings
op_ldsd
Option for spray drift
Set to 1. FOCUS DEFINITION
op_lddr
Option for drainage, model output
Set to 1 for drainage scenarios. FOCUS DEFINITION
op_ldro
Option for runoff, model output
Set to 1 for run-off scenarios. FOCUS DEFINITION
ntldsd
Number of loadings
USER INPUT
chatldsd
Time of loading
Not used in FOCUS scenarios; read from MACRO or
PRZM output file (M2T or P2T, respectively).
applot
Mass applied at plot (g/ha)
Not used in FOCUS scenarios; read from MACRO or
PRZM output file.
mldsd
Mass per square metre deposited onto
the water surface
In mg m-2, calculated by drift calculator in SWASH.
FOCUS SCENARIO SPECIFIC
stxldsd
Start of loaded stretch of water body
Set to 0.0 m for Pond, Ditch, and Stream systems.
DEVELOPMENT DEFINITION
enxldsd
End of loaded stretch of water body
Set to 30.0 m for Pond, 100.0 m for Ditch, and 100.0 m
for Stream systems. DEVELOPMENT DEFINITION
op1_lddr or
op1_ldro
Output from which model
Set to 1 or 2, depending on whether output of the
hydrological model MACRO (dr) or PRZM (ro) is
used. DEVELOPMENT DEFINITION
op_lddrhd or
op_ldrohd
Switch for hourly or daily input data
for drainage (dr) or runoff (ro) entries
Set to 0, so hourly data are used. FOCUS
DEFINITION
stxlddr or
stxldro
Start of stretch of watercourse in which
drainage or runoff water enters
Set to 0.0 m DEVELOPMENT DEFINITION
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enxlddr or
enxldro
Start of stretch of watercourse in which
drainage or runoff water enters
For Runoff scenarios only (next 2 parameters):
raindr
Ratio of infiltration draining directly to
water body
Set to 30.0 m for Pond, 100.0 m for Ditch and 100.0 m
for Stream systems. DEVELOPMENT DEFINITION
Set to 0.03 for R2 and R3, and 0.1 for R1 and R4
scenarios (-). FOCUS DEFINITION
nsewbldro
Number of upper sediment segments in
sediment into which the pesticide sorbed
onto the eroded soil will be evenly
distributed
Set to 7 (upper 10 mm). DEVELOPMENT
DEFINITION
op_ldupbound
Switch for inflow across the upstream
end
Set to 1, so inflow from the upstream end is considered.
FOCUS DEFINITION
rasuupbound
Ratio of upstream area where substance
is applied and the total upstream area
Set to 0.0 for Ditch systems and set to 0.2 for Stream
systems. FOCUS DEFINITION
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Parameter and description
Value, source & comments
Section 5: Substance properties
suname
Substance name
USER INPUT
mamol
Molar mass of substance
In g mol-1. USER INPUT
psat
Saturated vapour pressure pesticide
In Pa. USER INPUT
tepsat
Temperature at which saturated vapour
pressure measured
In K. USER INPUT
mepsat
Molar enthalpy of vaporisation
In J mol-1. USER INPUT
cosol
Solubility pesticide in water
In g m-3. USER INPUT
tesol
Temperature at which solubility is
measured
In K. USER INPUT
mesol
Molar enthalpy of dissolution
In J mol-1. USER INPUT
kdmpdit
Slope sorption isotherm macrophytes
Set to 0.0 m3 kg-1. Dummy in FOCUS scenarios.
FOCUS DEFINITION
kdomssdit
Slope sorption isotherm suspended
Solids
In m3 kg-1. USER INPUT
coobkomss
Reference concentration for sorption on
suspended solids
In kg m-3. USER INPUT
exfrss
Freundlich exponent for sorption to
suspended solids
Dimensionless. USER INPUT
kdomwb1
Slope sorption isotherm sediment
In m3 kg-1. USER INPUT
coobkomwb
Reference concentration for sorption on
sediment
In kg m-3. USER INPUT
exfrwb
Freundlich exponent for sorption to
sediment
Dimensionless. USER INPUT
dt50wl
Half-life in water layer
In d. USER INPUT
tedt50wl
Temperature at which transformation in
water is measured
In K. USER INPUT
aetf
Molar Arrhenius activation energy
In J mol-1. USER INPUT
dt50wb
Half-life in sediment
In d. USER INPUT
tedt50wb
Temperature at which transformation in
water is measured
In K. USER INPUT
kdfw
diffusion coefficient of pesticide in
water
In mm2 d-1. USER INPUT
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2) MET file
Parameter and description
Meteo table
Value, source & comments
Table with meteorological data
The meteo data are based on air temperature data
extracted from the MARS dataset for all locations. The
meteo data file contains average, monthly data on
estimated water temperature (°C). FOCUS
SCENARIO SPECIFIC
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3) M2T file, or P2T file
The M2T file is generated with the model MACRO. The output file header contains the SWASH run
ID and creation date, the model version and parameter file used, the compound name and a
specification of the FOCUS scenario, including spray drift application parameters. The results are listed
in a data table with:
1. date and time,
2. drainage water flux (mm h-1), and,
3. pesticide flux to drains (mg a.i. m-2 h-1).
The P2T file is generated with the model PRZM. The output file header contains the SWASH run ID
and creation date, the model version and input files used, the compound name and a specification of the
FOCUS scenario, including spray drift application parameters. The results are listed in a data table
with:
1. date and time,
2. runoff water flux (mm h-1),
3. runoff pesticide flux (mg a.i. m-2 h-1),
4. erosion mass flux (kg h-1),
5. erosion pesticide flux (mg a.i. m-2 h-1), and
6. infiltration (mm h-1).
References
Adriaanse, P.I., (1996). Fate of pesticides in field ditches: the TOXSWA simulation model, Report 90,
DLO Winand Staring Centre, Wageningen, The Netherlands.
Adriaanse, P.I., W.H.J. Beltman and F. Van den Berg, in prep. Behaviour of pesticides in small surface
waters: the TOXSWA model, version 2.0. Alterra, Wageningen, The Netherlands.
Beltman, W.H.J. & P.I. Adriaanse., (1999). User’s Manual TOXSWA 1.2, Technical Document 54.
DLO Winand Staring Centre, Wageningen, The Netherlands.
Ter Horst, M.M.S., P.I. Adriaanse, W.H.J. Beltman and F. Van den Berg, (2003). User’s guide for the
TOXSWA User Interface. Manual of TOXSWA in FOCUS, version 1.1.1. Alterra report 586.
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