Temperature in water and sediment in the pesticide model TOXSWA : implementation report

Abstract

• Acquisition, duplication and transmission of this publication is permitted with clear acknowledgement of the source.• Acquisition, duplication and transmission is not permitted for commercial purposes and/or monetary gain.• Acquisition, duplication and transmission is not permitted of any parts of this publication for which the copyrights clearly rest with other parties and/or are reserved.Wageningen Environmental Research assumes no liability for any losses resulting from the use of the research results or recommendations in this report. such as transformation in water and in sediment, volatilization from the water layer and transport in the water layer and in sediment by advection, dispersion and diffusion. Several processes describing the fate of the active ingredient depend on the temperature. Until now the change of temperature was described in a simple way by using monthly averaged temperatures. The temperature of the sediment equated the temperature of the water layer. This description of the temperature does not consider the daily change of the temperature in the water layer, and neither the change in daily average during the month. The concepts for describing the temperature in the water layer and in the sediment were improved, enabling enhanced incorporation of the effect of temperature on exposure concentrations.The improved description of the temperature in the water layer is based on quantification of contributions of all relevant terms of the energy budget of the water system. These terms are incoming and outgoing shortwave and longwave radiation, sensible and latent heat exchange between air and water, precipitation, potential heat exchange between water and sediment and external sources, such as incoming drainage water. In this improved temperature concept it is assumed that the water layer is perfectly mixed, hence the temperature is constant for each time horizontally and vertically in the entire water layer. The temperature of sediment is assumed equal to the water temperature. The improved temperature model then comprises a 1D bulk model.The improved concept for temperature in TOXSWA was tested using an existing model implementation of the 1D bulk model. De temperatures calculated by TOXSWA agreed well with temperatures determined with the 1D bulk model.The effect of use of the improved temperature module was evaluated by executing calculations of the TOXSWA model using the two options, i.e. the option of the 1-D bulk model as well as the option of the monthly averaged temperatures. Notable differences were calculated for the impact on transformation and volatilization. Depending on the change of temperature in the month using the improved concept of temperature can result in higher or lower exposure concentrations.The improved description of the effect of temperature on diffusion not only considered the improved description of the temperature as a function of time, but also the introduction of dependency of the diffusion coefficient on temperature. Test calculations showed that introduct...

Hydrolysis and biotic transformation in water in the pesticide model : Implementation report

“…In deze nieuwe versie van TOXSWA, kernversie 3.4, kan de gebruiker nu kiezen uit de opties om afbraak als een overall proces te simuleren, of als een enkel proces of als combinatie van de enkele processen fotolyse (Beltman et al, 2015), hydrolyse en biotische omzetting. De laatstgenoemde processen zijn gemodelleerd als functie van de concentratie in alleen de waterfase, terwijl de overall afbraak een functie is van de totale concentratie in de waterlaag, d.w.z.…”

“…The explanation of Beltman et al (2015) on the change in the transformation concept of lumped transformation, presuming transformation to occur in the water phase as well in the sorbed phase (TOXSWA kernel version 3.3) to transformation occurring in the water phase only (TOXSWA kernel version 3.4), is repeated in Annex 1.…”

“…The following equation is used to calculate the rate coefficient for photolysis, k ph (Beltman et al, 2015):…”

“…The concepts used have been reported for each process separately in Deneer et al (2010) and for photolysis more in detail in Beltman et al (2015). This report only treats the hydrolysis and biotic transformation processes.…”

“…This report only treats the hydrolysis and biotic transformation processes. The photolysis transformation process has been implemented in the TOXSWA model as described by Beltman et al (2015).…”