This study developed a novel approach to compare the runoff+erosion mass flux potential of a hydrophobic chemical using 36 ecological regulatory scenarios with national‐scale distributions of modeled mass flux from over 750,000 NHD+ agricultural catchments.
In the real world, the actual delivery of mass to flowing waterbodies depends on the extent to which each catchment contains co‐occurrence of soil and weather and crop. Mass flux results from PRZM were aggregated to each catchment based on the proportions of locally relevant modeling inputs in each catchment. For interpretation, the USEPA scenario can be considered analogous to a single catchment that is composed of a single soil (specified in the scenario) that is 100% cropped and completely treated.
The figure displays the plotting position of each catchment based on the cumulative percent of total national catchment area containing cotton (y‐axis) with the corresponding average annual total runoff + erosion mass flux per unit area (x‐axis). For example, of the 138,707 catchments containing cotton in the US, the MS cotton scenario produces greater runoff+erosion mass flux per unit area of the catchment than all but 8 catchments (i.e., it ranks 99.99th percentile).
Read the journal article via our Publications page or directly from IEAM.