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Establishment of a basis for administrative use of PestSurf

Annex 14

14 Corrections to earlier documentation

In connection with the calculation of 56 scenarios in PestSurf, some errors/inconsistencies were identified in the stream model and in the setup of the stream model. These are listed in the following, together with the suggested changes to the relevant reports. At the same time questions arose that may be considered if the model is to be updated.

14.1 Model errors

  1. It was discovered that the wind drift contribution (in mg/m²) was multiplied with the cross section of the water body and not the surface area of the water body. This error was corrected during the project.

14.2 Errors in the model setup

  1. Sediment in streams and ponds. The sediment thickness is the streams is stated in the documentation to be 2 cm. No sediment thickness is reported for the ponds in the documentation. In the model, the sediment thickness was implemented as 10 cm in the stream and 10 cm in the pond. The sediment thickness in the streams has been changed to 2 cm. The sediment thickness in the pond is still 10 cm, but the concentration in sediment in the ponds is calculated over the top 2 cm.

14.3 Errors in the translation of data between the user interface and the model

  1. With respect to calculation of Kd for the water bodies, an error was identified. The translation of data between the user interface and the model followed the description in the technical report. However, the described equations were not correct when the amount of organic C is specified for the scenarios and not the amount of organic matter. The correct equations written below. The error was corrected.

    If the input is Koc
    Kd_Water = Kd_sediment = (Koc*LOI_Scen/ 1*106), where
    LOI_Scen =NVOC, weight % for the specific scenario.

    If the input is Kom
    Kd_Water = Kd_sediment = (Kom*LOI_Scen*1.724)/1*106, where
    LOI_SCEN =NVOC, weight% for the specific scenario.

    If the input is Kclay
    Kd_Water = Kd_sediment = (Kclay*(Clay_content))/1*106

    where
    Clay_content = Clay content for the specific scenario (5 % for sediment in stream, 20 % for sediment in pond).

14.4 Other changes implemented

  1. The minimum storage frequency for pesticide concentrations in the stream has been changed from 3 days to one day.

14.5 D. Changes required to the documentation

Re. 1.3.1. Required corrections regarding Kd-calculations

Corrections to ”Scenarios and Model describing fate and transport of pesticides in surface water for Danish conditions

Table 4.4 requires updating. The table shows the ignition loss of the sediments, but not the non-volatile organic carbon (NVOC) which is actually implemented in the model. The figures implemented in the model stem from Helweg et al. (2003) and are the experimentally derived values. It seems, however, that the all implications of the change from Loss of ignition to NVOC were not taken into account. The formulation used at present multiplies the Koc-value with 1.724, resulting in a sorption that is too high by this factor.

New table 4.4:

Scenario Loss of ignition NVOC Porosity
  g/kg D.W. g/kg D.W.  
Lillebæk pond- macrophyt dom. 82 33 0.75
Lillebæk pond, phytoplan.dom. 600 348** 0.95
Lillebæk stream 25 29 0.75
Odderbæk pond- macrophyt dom. 82 33* 0.75
Odderbæk pond, phytoplan.dom. 600 348** 0.95
Odderbæk stream 197 100 0.75

Explanatory note, not to be included in the scenario-report:
* 29 was implemented in the model but this appears to be an error.
** The value “600” was implemented in the model. The value “348” is 600/1.724 and thus the estimated carbon content of the specified material.

Additional text concerning clay content in the scenarios to be added in section 4.7:

“The clay content of the sediment in the scenarios is specified as 20 % for the ponds and 5 % for the streams. The values have not been measured but 20 % is the value found in the experimental ponds used in the project. Due to flow conditions in the stream, the clay content in the stream is likely to be much lower than .the conditions in the ponds, and 5 % is considered a high estimate”.

Correction to “Technical report” page 63

“If the input is Koc
    Kd_Water = Kd_sediment = (Koc*LOI_Scen/ 1*106), where
    LOI_Scen =NVOC, weight % for the specific scenario.

If the input is Kom
    Kd_Water = Kd_sediment = (Kom*LOI_Scen*1.724)/1*106, where
    LOI_SCEN =NVOC, weight% for the specific scenario.

If the input is Kclay
    Kd_Water = Kd_sediment = (Kclay*(Clay_content))/1*106

where
Clay_content = Clay content for the specific scenario (5 % for sediment in stream, 20 % for sediment in pond)”.

Re. 1.4.1.Storage frequency

Corrections to ”Scenarios and Model describing fate and transport of pesticides in surface water for Danish conditions

Page 60, 3. para from the bottom, 5th line: “The rest of the period, data are stored daily.

 

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Version 1.0 December 2006, © Danish Environmental Protection Agency