Modelling biocide and herbicide concentrations in catchments of the Rhine basin

Abstract

Abstract. Impairment of water quality by organic micropollutants such as pesticides, pharmaceuticals or household chemicals is a problem in many catchments worldwide. These chemicals originate from different urban and agricultural usages and are transferred to surface waters from point or diffuse sources by a number of transport pathways. The quantification of this form of pollution in streams is challenging and especially demanding for diffuse pollution due to the high spatio-temporal concentration dynamics, which require large sampling and analytical efforts to obtain representative data on the actual water quality.Models can also be used to predict to what degree streams are affected by these pollutants. However, spatially distributed modelling of water quality is challenging for a number of reasons. Key issues are the lack of such models that incorporate both urban and agricultural sources of organic micropollutants, the large number of parameters to be estimated for many available water quality models, and the difficulty to transfer parameter estimates from calibration sites to areas where predictions are needed.To overcome these difficulties, we used the parsimonious iWaQa model that simulates herbicide transport from agricultural fields and diffuse biocide losses from urban areas (mainly façades and roof materials) and tested its predictive capabilities in the Rhine River basin. The model only requires between one and eight global model parameters per compound that need to be calibrated. Most of the data requirements relate to spatially distributed land use and comprehensive time series of precipitation, air temperature and spatial data on discharge. For larger catchments, routing was explicitly considered by coupling the iWaQa to the AQUASIM model.The model was calibrated with datasets from three different small catchments (0.5-24.6 km 2 ) for three agricultural herbicides (isoproturon, S-metolachlor, terbuthylazine) and two urban biocides (carbendazim, diuron). Subsequently, it was validated for herbicides and biocides in Switzerland for different years on 12 catchments of much larger size (31-35 899 km 2 ) and for herbicides for the entire Rhine basin upstream of the Dutch-German border (160 000 km 2 ) without any modification. For most compound-catchment combinations, the model predictions revealed a satisfactory correlation (median r 2 : 0.5) with the observations. The peak concentrations were mostly predicted within a factor of 2 to 4 (median: 2.1 fold difference for herbicides and 3.2 for biocides respectively). The seasonality of the peak concentration was also well simulated; the predictions of the actual timing of peak concentrations, however, was generally poor.Limited spatio-temporal data, first on the use of the selected pesticides and second on their concentrations in the river network, restrict the possibilities to scrutinize model performance. Nevertheless, the results strongly suggest that input data and model structure are major sources of predictive uncertainty. The latter is for exampl...

Relating Degradation of Pharmaceutical Active Ingredients in a Stream Network to Degradation in Water‐Sediment Simulation Tests

“…For conservative APIs we found that the emissions calculated from consumption data from Moser et al (2018) and the consumer excretion rates plus WWTP removal rates from Singer et al (2016) nicely matched the observed flux data of Ruff et al (2015) for almost each measurement point. This fact makes the same likely for the degrading compounds, thereby indirectly supporting our statements on the extent and place of degradation.…”

“…The stream network is built up from reaches, and basic physical properties were assigned based on the CCM2 river and catchment database (EU JRC, http://ccm.jrc.ec.europa.eu/). The model is calibrated for seven active pharmaceutical ingredients (APIs) using emission data from the CrossWater project (Ingold et al, 2018;Moser et al, 2018), estimated excretion and wastewater treatment plant (WWTP) removal data from Singer et al (2016), and pharmaceutical flux measurements by Ruff et al (2015). Model results are analyzed both in terms of parameter values and spatial distribution.…”

Herbicide Exposure and Toxicity to Aquatic Primary Producers

“…Modelling expected concentrations of herbicides in catchments can provide essential insights into the exposure of aquatic primary producers to herbicides. Moser et al (2018) showed that key drivers and processes are reasonably well approximated by a simple model that includes land use as a proxy for herbicide use, weather data for the timing of herbicide applications and discharge or precipitation as drivers for transport. They could predict the timing and level of peak concentrations within a factor of 2 to 3 in a spatially distributed manner at the scale of large river basins.…”

“…Herbicides originate from different urban and agricultural usages and are transferred to surface waters from point and diffuse sources by several transport pathways (Moser et al 2018). Exposure of aquatic primary producers to herbicides can occur through water for all algae and aquatic plants, through air for emergent and floating plants and through sediment for rooting plants and benthic algae ( Fig.…”

“…They could predict the timing and level of peak concentrations within a factor of 2 to 3 in a spatially distributed manner at the scale of large river basins. Better quantification of episodic pesticide pollution events would result in more comprehensive assessments of variations in herbicide exposure (Munz et al 2017), and coupled progress in modelling, such as the FOCUS modelling approach, and in measuring herbicide concentrations in the field remain necessary to improve exposure assessments in aquatic ecosystems (Moser et al 2018).…”