Application of watershed deposition tool to estimate from CMAQ simulations the atmospheric deposition of nitrogen to Tampa Bay and its watershed

Abstract

The U.S. Environmental Protection Agency (EPA) has developed the Watershed Deposition Tool (WDT) to calculate from the Community Multiscale Air Quality (CMAQ) model output the nitrogen, sulfur, and mercury deposition rates to watersheds and their sub-basins. The CMAQ model simulates from first principles the transport, transformation, and removal of atmospheric pollutants. We applied WDT to estimate the atmospheric deposition of reactive nitrogen (N) to Tampa Bay and its watershed. Implications: Air quality modeling reveals that atmospheric deposition of reactive nitrogen (N) contributes a significant fraction to Tampa Bay's total N loading from external sources. Regulatory drivers that lower nitrogen oxide emissions from power plants and motor vehicles are important to bay management strategies, which seek to improve water quality through N load reduction.

Relative Importance of Landscape Versus Local Wetland Characteristics for Estimating Wetland Denitrification Potential

“…Non-point sources account for the majority of nitrogen loads from the Tampa Bay watershed and will present a particular challenge to managing its effects in the bay. Atmospheric deposition is considered the dominant source of nitrogen (46%) delivered to the coastal areas of the Tampa Bay watershed, according to a recent SPARROW (SPAtially-References Regression On Watershed attributes) modeling paper (Hoos and McMahon 2009) and more recent CMAQ (Community Multi-scale Air Quality) model output which estimates the direct and indirect delivery from atmospheric nitrogen at 71% of the total nitrogen loads reaching the estuary (Poor et al 2013). Atmospheric nitrogen contributions will likely become more significant in the future because of increased emissions of combustion exhausts often associated with expanding transportation needs resulting from the spread of urbanization, although increasing motor vehicle efficiencies may offset this.…”