Evaluation of SEAWAVE–QEX in a high agricultural intensity catchment in Belgium

Abstract

Pesticide surface water monitoring data have rarely been used as the only quantitative measure of exposure because the available monitoring data for most pesticides has not been considered robust enough for direct use in pesticide exposure assessments due to infrequent sampling. The cost of daily sample collection and analysis prohibits frequent sampling for most monitoring programs. In this context, a common question raised in assessments is how likely peak concentrations (i.e., annual maxima) may be missed if sampling intervals are longer than daily. The US Geological Survey developed the statistical model "seasonal wave with streamflow adjustment and extended capability" (SEAWAVE-QEX) to address the need to estimate infrequently occurring pesticide concentrations, such as annual maximum daily concentrations, for sites with nondaily monitoring data. This study compares the results of two postprocessing methods and evaluates the capability of SEAWAVE-QEX to estimate annual maximum concentrations of three commonly used herbicides and one metabolite in a catchment in Belgium. The study concludes that the appropriateness of using SEAWAVE-QEX to estimate annual maximum concentrations depends on pesticide characteristics and use and that the model can be particularly sensitive to nonflow correlated exposure events (e.g., point source contributions or drift).

Evaluation of streamflow as a covariate in models for predicting daily pesticide concentrations

“…The conclusions of this study are specific to the monitoring data that were analyzed but are expected to generalize for atrazine to sampling designs with similar frequencies and other extreme target quantities (e.g., upper percentiles) due to the impact of any excess skew of transformed flow covariates. For other compounds and monitoring data in different surface water systems the relationship between covariate skewness and that of the response variable may differ and should be evaluated separately (see Rathjens et al (2022) for an evaluation of SEAWAVE-QEX on flufenacet, flufenacet sulfonic acid, diflufenican, and isoproturon).…”