Assessing the impacts of anthropogenic and hydro-climatic drivers on estrogen legacies and trajectories

Intensification of concentrated animal feeding operations combined with the use of tile drains in agricultural fields has resulted in land-applied manure being a significant source of hormones to the environment. Currently, no model exists to simulate hormone fluxes from tile drains under field conditions. Therefore, we developed the Hormone Export and Recovery Dynamics (HERD) model, which incorporates hydro-climatic, biogeochemical, and anthropogenic drivers that affect hormone fate and transport. We validated HERD using known input (rainfall; lagoon effluent irrigation) and response data (tile drain flow; 17β-estradiol and estrone fluxes) from the 2009 growing season, 18 years after land-application activities began at a tile-drained field in Indiana. We used HERD to better understand the: (1) decision-making process underlying effluent irrigation activities; (2) contribution of macropore flow to estrogen transport; (3) potential for long-term applications to result in the development of legacy estrogen sources within the soil profile; and (4) potential recovery trajectory of estrogen transport following the cessation of animal waste applications. HERD adequately predicted irrigation events based on lagoon storage limits. Simple threshold exceedance logic for macropore flow activation accounted for ~87% of the observed estrogen loads. Application history was found to be important, as not accounting for 18 years of application led to a severe underestimation of the observed estrogen loads; however, accounting for application history led to a much closer match between modeled and observed fluxes. Simulated trajectories after cessation of applications indicated that estrogens may continue to leach for several decades, which has important implications for mitigating hormone concentrations in receiving water bodies.