SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Simulation of stream nitrate-nitrogen export using the Soil and Water Assessment Tool model in a dairy farming watershed with an external water source 
Authors:Jiang, R., C. Y. Wang, R. Hatano, A. Hayakawa, K.P. Woli and K. Kuramochi 
Journal:Journal of Soil and Water Conservation 
Volume (Issue):69(1) 
Article ID: 
URL (non-DOI journals): 
Broad Application Category:hydrologic and pollutant 
Primary Application Category:nitrogen cycling/loss and transport 
Secondary Application Category:hydrologic assessment 
Watershed Description:672 km^2 Shibetsu River, located in the eastern part of Hokkaido Island in northern Japan. 
Calibration Summary: 
Validation Summary: 
General Comments: 
Abstract:Quantitative assessment of stream nitrate-nitrogen (NO3-N) export in a watershed with an external underground water source is complex because the underground flux for both the water discharge and NO3-N cannot be directly measured. A modeling approach, using the Soil and Water Assessment Tool (SWAT), was tested to simulate the NO3-N export in the 672 km2 (417 mi2) Shibetsu Watershed with external water source (EXT) in eastern Hokkaido, Japan. The EXT and its NO3-N loading contents were added as the assumed point source discharge and loading in the SWAT model. The results yielded high Nash-Suttcliffe coefficient (Ens) values for daily streamflow (over 0.5) and monthly NO3-N loading (over 0.7) for the simulation during the calibration and validation periods. The simulated seasonal patterns of discharge and NO3-N loading were also well matched with the measured data during 2004 to 2008. However, the spatial patterns of NO3-N concentrations showed a poor r2 correlation (r2 = 0.34) with the measured data in 2004. These results showed that, although the model had limitations for the simulation of spatial patterns, the method of adding EXT and NO3-N loading as assumed points in SWAT was reasonable for the assessment of the stream NO3-N export. Therefore, the calibrated model was repeated without adding EXT and NO3-N loading as assumed points. Approximately 66% of the NO3-N export was from the watershed itself, and the NO3-N export was high in the grasslands. These results indicated that most of the NO3-N export was related to dairy farming in the Shibetsu Watershed, and the best management practices for controlling nonpoint source pollution should focus on manure applications on grasslands in the future. Meanwhile, the EXT (47% of streamflow) contributed to 34% of the annual NO3-N loading, which may cause the overestimation of the stream NO3-N export when using only the measured data. Therefore, the EXT should not be ignored when estimating the annual NO3-N loading. 
Keywords:external water source, nitrate, nitrogen, nonpoint source pollution, Soil and Water Assessment Tool