Abstract. This study describes and implements an integrated, multimedia,
process-based system-level approach to estimating nitrogen (N) fate and
transport in large river basins. The modeling system includes the following
components: (1) Community Multiscale Air Quality (CMAQ), (2) Weather Research
and Forecasting Model (WRF), (3) Environmental Policy Integrated Climate
(EPIC), and (4) Soil and Water Assessment Tool (SWAT). The previously developed
Fertilizer Emission Scenario Tool for CMAQ (FEST-C), an advanced user
interface, integrated EPIC with the WRF model and CMAQ. The FEST-C system,
driven by process-based WRF weather simulations, includes atmospheric N
additions to agricultural cropland and agricultural cropland contributions
to ammonia emissions. This study focuses on integrating the watershed
hydrology and water quality model with FEST-C system so that a full
multimedia assessment on water quality in large river basins to address
impacts of fertilization, meteorology, and atmospheric N deposition on water
quality can be achieved. Objectives of this paper are to describe how to
expand the previous effort by integrating the SWAT model with the FEST-C
(CMAQ/WRF/EPIC) modeling system, as well as to demonstrate application of the
Integrated Modeling System (IMS) to the Mississippi River basin (MRB) to
simulate streamflow and dissolved N loadings to the Gulf of Mexico (GOM). IMS
simulation results generally agree with US Geological Survey (USGS) observations/estimations; the
annual simulated streamflow is 218.9 mm and USGS observation is 211.1 mm
and the annual simulated dissolved N is 2.1 kg ha−1 and the USGS estimation is 2.8 kg ha−1. Integrating SWAT
with the CMAQ/WRF/EPIC modeling system allows for its use within large river
basins without losing EPIC's more detailed biogeochemistry processes, which
will strengthen the assessment of impacts of future climate scenarios, regulatory
and voluntary programs for N oxide air emissions, and land use and land
management on N transport and transformation in large river basins.