Transient water flow in the TOXSWA model (FOCUS) versions): concepts and mathematical description

The TOXSWA model is used in the pesticide registration procedures in the Netherlands and the EU. This report documents the transient water flow module of TOXSWA, which simulates variable discharges and water depths in the edge-of-field ponds, ditches and streams of the EU FOCUS Surface Water Scenarios at an hourly resolution. It combines water conservation equations with water depth-discharge relations based upon weirs located downstream. In watercourses, backwater curves describe water depths as a function of distance to the weir. The water conservation equations consist of a base flow, excess water fluxes from drainage or runoff and an outflow. The conservation equations have been solved numerically using the finite difference method. A limited verification of the numerical solution has been undertaken. Example runs present model input and outpu

Spatial moment analysis of transport of nonlinearly absorbing pesticides using analytical approximations

Analytical approximations were derived for solute transport of pesticides subject to Freundlich sorption, and first-order degradation restricted to the liquid phase. Solute transport was based on the convection-dispersion equation (CDE) assuming steady flow. The center of mass (first spatial moment) was approximated both for a non-degraded solute pulse and for a pulse degraded in the liquid phase. The remaining mass (zeroth spatial moment) of a linearly sorbing solute degraded in the liquid phase was found to be a function of only the center of mass (first spatial moment) and the Damköhler number (i.e., the product of degradation rate coefficient and dispersivity divided by flow velocity). This relationship between the zeroth and first spatial moments was shown to apply to nonlinearly sorbing pulses as well. The mass fraction leached of a pesticide subject to Freundlich sorption and first-order degradation in the solution phase only was found to be a function of the Damköhler number and of the dispersivity, so independent of sorption. Hence perceptions of the effects of sorption on pesticide leaching should be reconsidered. These conclusions equally hold for other micropollutants that degrade in the solution phase onl

Simulatie van de stikstofhuishouding van beregend grasland

Met het waterhuishoudingsmodel WATBAL is de waterhuishouding gesimuleerd van een beregeningsproef welke gedurende drie jaren is uitgevoerd. De stikstofhuishouding van vier beregenings- en bemestingsobjecten van deze proef is gesimuleerd. De proef was uitgevoerd op een droogtegevoelige zandgrond met dik humuspakket en diep gelegen grondwaterspiege

Nalevering van carbendazim uit slootbodems in bollenteeltgebieden : de rol van nalevering uit slootbodems bij het ontstaan van normoverschrijdingen in oppervlaktewater

In discussie tussen de waterschappen, onderzoekers en bollentelers werd geopperd dat de overschrijdingen van carbendazim in het oppervlaktewater mogelijk niet alleen worden veroorzaakt door recente emissieroutes op het erf en het veld, maar dat nalevering van carbendazim uit sediment dat door vroegere emissies verontreinigd is geraakt ook een rol kan spelen. Die invloed vanuit het sediment kan er wel zijn maar zal maar een beperkte rol spelen bij verontreiniginge

Identification and quantification of point sources of surface water contamination in fruit culture in the Netherlands

Measurements of pesticide concentrations in surface water by the water boards show that they have decreased less than was expected from model calculations. Possibly, the implementation of spray drift reducing techniques is overestimated in the model calculation. The impact of point sources is probably underestimated. A project was initiated for the quantification and qualification of possible point sources in Dutch fruit culture. From a survey it was concluded that the majority of fruit growers do not posses the mandatory equipment regarding filling and cleaning of sprayers. This creates a potential environmental risk for surface water contamination. Further research is focused on: internal and external cleaning of sprayers, environmental impact of the washings, discharge of transport water from fruit sorting installations, and bioremediation systems for processing contaminated water

Emissies van bestrijdingsmiddelen bij het spoelen van bloembollen

De emissies van bestrijdingsmiddelen naar grondwater en via af te voeren spoelslib uit de bloembollenteelt is geschat met eenvoudige modellen. In spoelslib zullen vooral middelen worden aangetroffen die sterk adsorberen aan organische stof of in hoge dosering worden toegepast, zoals tolclofosmethyl en prochloraz. De gemeten verzadigde doorlatendheid van bassinbodems bedroeg 0,2 tot 0,5 cm/d, wat resulteerde in berekende waterfluxen door de bassinbodem van 4 tot 5 cm/d. Bij zulke hoge fluxen zal de concentratie van carbendazim maar weinig dalen tijdens het transport vanuit bassins naar het grondwate

Comparison of pesticide concentrations at drinking water abstraction points in The Netherlands simulated by DROPLET version 1.2 and 1.3.2 model suites

The user-friendly software tool DROPLET (acronym for DRinkwater uit OPpervlaktewater-Landbouwkundig gebruik Evaluatie Tool) assists the Dutch Board for the Authorization of Plant Protection Products and Biocides (Ctgb) in evaluating whether pesticides may exceed the 0.1 μg/L standard in one of the Dutch surface water abstraction points for drinking water production. Based upon Good Agricultural Practice DROPLET uses the peak concentration in the FOCUS D3 ditch (with spray drift deposition according to Dutch numbers) as starting point for the final, expected concentration at the abstraction pointssituated in the larger waterbodies downstream. This report compares concentrations in the abstraction points calculated by the old model suite (FOCUS-SWASH 3.1, FOCUS-MACRO 4.4.2, FOCUS-TOXSWA 3.3.1 and DROPLET 1.2) with those calculated by the more recently released model suite (FOCUS-SWASH 5.3, including the substance database SPIN 3.3, FOCUS-MACRO 5.5.4, FOCUS-TOXSWA 4.4.3 and DROPLET 1.3.2). The concentrations in the drinking water abstraction points calculated by the new model suite may be up to a factor of approximately 2.5 higher than the ones calculated by the old model suite. This is practically entirely due to the increased pesticide mass in the drainage fluxes calculated by the new version of the MACRO model. The calculations by the TOXSWA and DROPLET models have not been changed. Because nomeasured water and mass fluxes for drainage are available for the D3 scenario, it is not possible to indicate whether the fluxes calculated by MACRO 4.4.2 or those by MACRO 5.5.4 reflect better reality. Thus no recommendation can be made on the model suite to be used in the Dutch exposure assessment for drinking water production from surface waters

Afspoeling van amitrol, atrazion en glyfosaat vanaf een betonklinkerverharding; veldproeven en modelsimulaties

In vier veldproeven op 100 mr betonklinkerbestrating is de afspoeling van amitrol, atrazin en glyfosaat naar het regenwaterriool gemeten. De totaal afgespoelde hoeveelheid is 6 tot 44␟an de dosering. Het grootste deel spoelde af met de eerste millimeters neerslag. Infiltratie naar de ondergrond en de oplosbaarheid van de herbiciden bleken de belangrijkste afspoelingsbepalende processen. Adsorptie van de gebruikte middelen aan het steenoppervlak had nauwelijks invloed op de afspoeling. Door toevoegen van de processen infiltratie en opname van herbicide in de steen aan het model kon de afspoeling beter worden gesimuleerd

Potentiele puntemissies van gewasbeschermingsmiddelen naar oppervlaktewater berekend met POSSUM

Activiteiten met gewasbeschermingsmiddelen kunnen leiden tot puntemissies naar oppervlaktewater met als gevolg overschrijdingen van normen. Voor drie voorbeeld bedrijven is de potentiële emissie van gewasbeschermingsmiddelen naar oppervlaktewater berekend met het POSSUM model (POint Sources SUrface water Model