Parameterisation of Fate in Surface Water

APPENDIX E

PARAMETERISATION OF FATE IN SURFACE WATER

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.

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

1) TXW file

Parameter and description

/

Value, source & comments

Section 1: Run characteristics
prnameName of project
locnameName of location
runcomComments for run
op_hydSimulation control option
met Path and/or name of input file for meteorological data
rodr Path and name of input file on drainage or runoff loading
stdateStarting date of simulation
endateEnd date of simulation
chastdatemetYear-month of first entry of average Temperature
chaendatemetYear-month of last entry of average temperature
deltwbCalculation time step for sediment (s)
deltouthTime step for output (h)
nwbsyNumber of selected sediment segments
iwbsySediment segment number
ktopNumber of segments forming the top layer of the sediment
ntcurveSelected times for additional output
tcurvedateDate and hour for additional output
op_hybWater balance
op_mflDrainage or runoff entries
op_rc1Basic characteristics of representative channel
op_rc2Additional characteristics of representative channel
op_cwa Concentrations in all segments of the water layer
op_csx Concentrations in sediment subsystem selected for output (x = 1)
op_mwaMass balance of the entire water layer
op_mwxMass balance of the water layer above the sediment subsystem selected for output (x = 1)
op_msa Mass balance of the entire sediment subsystem
op_msxMass balance of sediment subsystem selected for output (x = 1)
op_dbaDistribution of substance in the entire water body
op_dbxDistribution of substance in the water layer above the sediment subsystem selected for output (x = 1)
op_mobMass balance of the water layer, with lumped terms, on a monthly basis.
Section 2: Definition of water layer and sediment
xditTotal length of water body
xfbLength of front buffer
xebLength of end buffer
nxnoditNumber of segments in water body
nxnofbNumber of segments in front buffer
nxnoebNumber of segments in end buffer
lesefbLength of segments in front buffer
leseditLength of segments in water body
leseebLength of segments in end buffer
wibotBottom width of water body
sislSide slope, horizontal/vertical
wdhflWater depth defining perimeter for exchange water layer – sediment / USER INPUT
USER INPUT
USER INPUT
USER INPUT
FOCUS SCENARIO SPECIFIC
FOCUS SCENARIO SPECIFIC
FOCUS SCENARIO SPECIFIC
FOCUS SCENARIO SPECIFIC
FOCUS SCENARIO SPECIFIC
FOCUS SCENARIO SPECIFIC
FOCUS SCENARIO SPECIFIC
Set to 12.0 h. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Last sediment segment at the downstream end of loaded stretch of watercourse. FOCUS DEFINITION
Set to 12 (50 mm thickness by FOCUS DEFINITION)
Not used in FOCUS scenarios. DEVELOPMENT DEFINITION
Not used in FOCUS scenarios. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 1. DEVELOPMENT DEFINITION
Set to 30.0 m for Pond, 100.0 m for Ditch, and 100.0 m for Stream systems. FOCUS DEFINITION.
Set to 0.0 m. DEVELOPMENT DEFINITION
Set to 0.0 m. DEVELOPMENT DEFINITION
Set to 1 for Pond, 10 for Ditch, and 20 for Stream systems. DEVELOPMENT DEFINITION
Set to 0. DEVELOPMENT DEFINITION
Set to 0. DEVELOPMENT DEFINITION
Set to 0.0 m. DEVELOPMENT DEFINITION
Set to 30.0 m for Pond, 10.0 m for Ditch and 5.0 m for Stream systems. DEVELOPMENT DEFINITION
Set to 0.0 m. DEVELOPMENT DEFINITION
Set to 30.0 m for Pond, 1.0 m for Ditch, and 1.0 m for Stream systems. FOCUS DEFINITION
Set to 1.E-05. DEVELOPMENT DEFINITION
Set to 0.01 m. DEVELOPMENT DEFINITION

Parameter and description

/

Value, source & comments

cossConcentration of suspended solids
raomssMass ratio of organic matter
dwmpDry weight of macrophyte biomass
castwlInitial (start) mass concentration in segments of the water layer
coairBackground concentration of pesticide in air
zwbThickness of sediment layer
zebbThickness of end buffer in sediment layer
nznowbNumber of segments in sediment layer
nznoebbNumber of segments in end buffer
lesewbThickness of segments in sediment layer
leseebbThickness of segments in end buffer
bdwbBulk density of dry sediment at each segment
porPorosity at each segment
torTortuosity at each segment
raomwbMass ratio of organic matter in dry sediment at each segment
ldisDispersion length
castwbInitial (start) mass concentration at each segment
Section 3: Hydrology of water bodies
qseifSeepage rate
colot Concentration in seepage water
op_vaflSwitch for: constant flow of water
op_hdSwitch for hourly or daily data on drainage/runoff
delthyTime step for water balance
wdhConstant water depth
uConstant flow velocity
op_powcSwitch for: pond (one segment) or watercourse (more segments)
For Pond only (next 5 parameters):
arpoSize of area surrounding the pond, contributing runoff or drained fluxes
arerpoSize of area surrounding the pond, contributing eroded sediment with sorbed substance
QbasepoMinimal inflow into pond
crestbodypoHeight of the body up to the crest of the weir in the pond
wicrestpoCrest width of weir, located at the outflow of the pond
For Watercourse only (next 14 parameters):
lercLength of representative channel
botslrcBottom slope of representative channel
wibotrcBottom width of representative channel
sislrc Side slope (hor/ vert) of representative channel
QbasercMinimal inflow into representative channel
arrcSize of the area located upstream
crestbodyrcHeight of the crest above the channel bottom of the weir
wicrestrcCrest width of weir
kMan1mValue of the Manning coefficient for bottom roughness at 1 m water depth
alphaenEnergy coefficient resulting from the non-uniform distribution of flow velocities
QbasewcMinimal inflow into watercourse
arupwcSize of the area located upstream of the watercourse
leplotMargin of treated plot, contributing runoff or drained fluxes
leerwcMargin of treated plot, contributing eroded sediment with sorbed substances / Set to 15.0 g.m-3. FOCUS DEFINITION
Set to 0.09. FOCUS DEFINITION
Set to 0.0 g.m-2. FOCUS DEFINITION
Set to 0.0 g.m-3. DEVELOPMENT DEFINITION
Set to 0.0 g.m-3. DEVELOPMENT DEFINITION
Set to 0.1 m. DEVELOPMENT DEFINITION
Set to 0.0 m. DEVELOPMENT DEFINITION
Set to 14. DEVELOPMENT DEFINITION
Set to 0. DEVELOPMENT DEFINITION
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
Set to 0.0. DEVELOPMENT DEFINITION
Set to 800 kg m-3. FOCUS DEFINITION
Set to 0.6. FOCUS DEFINITION
Set to 0.6. DEVELOPMENT DEFINITION
Set to 0.09. FOCUS DEFINITION
Set to 0.015 m. DEVELOPMENT DEFINITION
Set to 0.0 g m-3. DEVELOPMENT DEFINITION
Set to 0.0 m3 m-2 d-1. DEVELOPMENT DEFINITION
Set to 0.0 g m-3. DEVELOPMENT DEFINITION
Set to 1, so variable flow selected. FOCUS DEFINITION
Set to 0, so hourly values are used. FOCUS DEFINITION
Set to 600 s. DEVELOPMENT DEFINITION
Set to 0.5 m. Not used in FOCUS scenarios. DEVELOPMENT DEFINITION
Set to 10 m d-1. Not used in FOCUS scenarios. DEVELOPMENT DEFINITION
Set to 0 for Pond systems and set to 1 for Ditch and Stream systems. DEVELOPMENT DEFINITION
Set to 0.45 ha. FOCUS DEFINITION
Set to 0.06 ha. FOCUS DEFINITION
In m3 d-1. FOCUS SCENARIO SPECIFIC
Set to 1.0 m. FOCUS DEFINITION
Set to 0.5 m. DEVELOPMENT DEFINITION
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
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
Set to 1.0 m. DEVELOPMENT DEFINITION
Set to 1.0 E-5. DEVELOPMENT DEFINITION
In m3 d-1. FOCUS SCENARIO SPECIFIC
Set to 100.0 ha for Stream systems, and 2.0 ha for Ditch systems. FOCUS DEFINITION
Set to 0.5 m for Stream systems, and 0.4 m for Ditch systems. DEVELOPMENT DEFINITION
Set to 0.5 m. DEVELOPMENT DEFINITION
Set to 11 m1/3 s-1 for Stream systems, and 25 m1/3 s-1 for Ditch systems. DEVELOPMENT DEFINITION
Set to 1.2. DEVELOPMENT DEFINITION
In m3 d-1. FOCUS SCENARIO SPECIFIC
Set to 100.0 ha for Stream systems and 2.0 ha for Ditch systems. FOCUS DEFINITION
Set to 100.0 m for Drainage and Runoff scenarios. FOCUS DEFINITION
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_ldsdOption for spray drift
op_lddrOption for drainage, model output
op_ldroOption for runoff, model output
ntldsdNumber of loadings
chatldsdTime of loading
applotMass applied at plot (g/ha)
mldsdMass per square metre deposited onto the water surface
stxldsdStart of loaded stretch of water body
enxldsdEnd of loaded stretch of water body
op1_lddr orOutput from which model
op1_ldro
op_lddrhd orSwitch for hourly or daily input data
op_ldrohdfor drainage (dr) or runoff (ro) entries
stxlddr orStart of stretch of watercourse in which
stxldrodrainage or runoff water enters
enxlddr orStart of stretch of watercourse in which
enxldrodrainage or runoff water enters
For Runoff scenarios only (next 2 parameters):
raindrRatio of infiltration draining directly to water body
nsewbldro Number of upper sediment segments in sediment into which the pesticide sorbed onto the eroded soil will be evenly distributed
op_ldupboundSwitch for inflow across the upstream end
rasuupboundRatio of upstream area where substance is applied and the total upstream area / Set to 1. FOCUS DEFINITION
Set to 1 for drainage scenarios. FOCUS DEFINITION
Set to 1 for run-off scenarios. FOCUS DEFINITION
USER INPUT
Not used in FOCUS scenarios; read from MACRO or PRZM output file (M2T or P2T, respectively).
Not used in FOCUS scenarios; read from MACRO or PRZM output file.
In mg m-2, calculated by drift calculator in SWASH. FOCUS SCENARIO SPECIFIC
Set to 0.0 m for Pond, Ditch, and Stream systems. DEVELOPMENT DEFINITION
Set to 30.0 m for Pond, 100.0 m for Ditch, and 100.0 m for Stream systems. DEVELOPMENT DEFINITION
Set to 1 or 2, depending on whether output of the hydrological model MACRO (dr) or PRZM (ro) is used. DEVELOPMENT DEFINITION
Set to 0, so hourly data are used. FOCUS DEFINITION
Set to 0.0 m DEVELOPMENT DEFINITION
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
Set to 7 (upper 10 mm). DEVELOPMENT DEFINITION
Set to 1, so inflow from the upstream end is considered.
FOCUS DEFINITION
Set to 0.0 for Ditch systems and set to 0.2 for Stream systems. FOCUS DEFINITION

Parameter and description