Stream flow dynamics influences agrochemical exposure timing, duration, and frequency. Tracer studies were conducted in headwater watersheds in Iowa and Missouri to characterize stream hydrological properties to better understand drivers behind the magnitude and duration of crop protection chemical concentrations in stream water and watershed model parameterization. We used chemical tracer chemographs to calculate travel time and stream volume for stream reaches under low-flow conditions. Florescent dye was injected at strategic stream locations and continuously monitored with in-situ fluorometers. Accurate travel times of the chemical tracer were calculated from injection points to corresponding, downstream monitoring points along stream reaches, and were then combined with stream discharge data to estimate stream reach flow volume. Assessing tracer data with observed runoff events indicated that the ratio of rainfall-driven stream flow to initial stream flow volume influenced duration of chemical exposure at the headwater outlet. Results also illustrate that flow in small headwater streams is significantly different from that predicted by NHD+ indicating stream characteristics at this scale require higher resolution data. Finally, tracer study results are being used to inform stream flow numerical simulations toward a better representation of stream hydrodynamic properties at the headwater watershed scale.<br/>

Tracer studies in headwater watersheds in the Midwestern U.S. to characterize stream flow dynamics

254th National Meeting (2017)

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