The hybrid mechanistic-statistical watershed model SPARROW (Spatially Referenced Regression on Watershed Attributes) was applied to estimate the sources and transport of total nitrogen (TN) in surface waters of Ishikari River Basin (14,330 km(2)), the largest watershed on the Hokkaido Island of Japan. The loads from atmospheric deposition, point sources and erosion are routed through the drainage network (900 streams) with first-order stream decay. Then we calibrated the model using measurements of TN from 31 monitoring sites of mixed spatial data on topography, soils and stream hydrography. The R-2 and MSE are 0.82 and 0.62 separately. On this basis, the predication of TN distribution was evaluated, and the mean incremental annual TN yield was 11.61kg/ha/yr.