Estimation of dynamic load of mercury in a river with BASINS-HSPF model

Mercury (Hg) is a naturally occurring element and a pervasive toxic pollutant. This study investigated the dynamic loads of Hg from the Cedar-Ortega Rivers watershed into the Lower St. Johns River (LSJR), Florida, USA, using the better assessment science integrating point and nonpoint sources (BASINS)-hydrologic simulation program-FORTRAN (HSPF) model. The site-specific BASINS-HSPF model was developed for dynamic loads of Hg based on watershed, meteorological, and hydrological conditions. The model was calibrated and validated with existing field data. It was then applied to predict the daily and annual loads of Hg from the watershed outlet into the LSJR in response to rainfall events and water fluxes. In general, the predicted average daily total Hg flux during the 10-year simulation period was about 0.69 g ha(-1) year(-1). This finding was within the range of 0.22-1.41 g ha(-1) year(-1) reported in the Florida Everglades area. Simulations further revealed that the effects of rainfall events on Hg loading were significant, particularly in a very wet period. A maximum total Hg flux was predicted during this wet period at a rate of 122.59 g ha(-1) year(-1). Results from this study provide a useful case study on estimating Hg contamination in watersheds. The approaches used in this study could be transferred to estimate the dynamic loads of Hg in watersheds from other regions.