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 and lack of coverage across the landscape. To accurately characterize annual maximum pesticide concentrations in streams, daily sampling may be necessary during active pesticide runoff periods. The cost of daily sample collection and analysis prohibits this high sampling frequency for most monitoring programs. In this context, a common question raised in assessments is how likely peak concentrations (i.e., annual maximums) may be missed if sampling intervals are greater than daily. The US Geological Survey (USGS) developed the statistical model SEAWAVE-QEX to address the need to estimate infrequently occurring pesticide concentrations, such as annual maximum daily concentrations, for sites with non-daily monitoring data. This study evaluates the capability of SEAWAVE-QEX to estimate annual maximum concentrations of commonly used herbicides in the Grote Kemmelbeek (GKb) catchment in Belgium. High temporal resolution sampling of flow and multiple pesticides occurred for a period of 3.5 years at this predominantly agricultural catchment. This study used several subsamples of the daily monitoring data to test the impact of sampling frequency on SEAWAVE-QEX estimated annual maximum concentrations. Also, original data without previously identified point source pesticide emission events was subsampled to evaluate the sensitivity of SEAWAVE-QEX to point source driven events. Annual 1-day maximum concentration estimates from SEAWAVE-QEX were compared to the observed values as well as those from a previously calibrated SWAT model of the catchment. The study concludes that SEAWAVE-QEX can be particularly sensitive to non-flow correlated exposure events (e.g., point source contributions or drift), as well as sampling regimes used as input to the model.

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

ACS Fall 2021

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