Modeling static water bodies has been used for regulatory ecological pesticide exposure assessments for many years. Static water body exposure modeling continues to be important in standard FIFRA assessments and in endangered species assessments. The watershed drainage area relative to the volume of the static receiving water body, referred to as the DA/NC (drainage area to normal capacity ratio), can have a significant impact on pesticide exposure concentrations. This is particularly true in regulatory exposure modeling following the US EPA’s assumption of a constant volume static water body with no outlet, wherein large influxes of pesticide transported by runoff can enter the water body, yet water delivering the pesticide is unaccounted for. Recent approaches to determining representative watershed areas for different sized static water bodies have focused on the use of climate data and water balance approaches to determine watershed sizes across geographic regions. These approaches have shown the potential to result in extreme watershed sizes in drier climates, and potentially undersized watersheds in wetter climates, that bear no resemblance to actual watersheds. The use of high resolution hydrography and DEM spatial datasets to delineate watersheds of small ponds using GIS has the potential to provide much more physically realistic estimates of watershed areas specific to different geographic and climatic regions. A spatial analysis of small pond watersheds of two different size classes (analogous to the US EPA endangered species Bin 6 and Bin 7 water bodies) was conducted across multiple HUC2 watersheds to compare watershed size estimates using this spatial approach to those derived using purely water balance methods. The spatial approach was found to provide valuable watershed size distributions, and coupled with a varying volume static water body, offers a realistic conceptual model for static water body ecological exposure modeling. Data limitations and future improvements will be discussed.

Use of topographic and hydrographic spatial datasets in determining watershed areas in static water body exposure modeling

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.