The increases in nitrogen concentrations in stream water are observed throughout the world, and that leads to various environmental implications. Researches have reported the associations between levels of nitrogenous compounds in streams and land use/land cover, and indicated significant contributions by agriculture and urban land uses in a catchment. The mitigation abilities of nitrogen loads in riparian zone and vegetation coverage in a catchment have been presented in various studies, while the relative influence of riparian zone versus the whole watershed on stream water are mixed. We conducted a research on the upper Han River basin, a mountainous region of the Qinling and Daba Mts of China. NO3-N and NH4+-N in streams were determined and land use and land cover in the basin were derived using Landsat TM and +ETM. Correlation analysis and stepwise multiple regression for nitrogen in streams and landscape within the whole watershed and 100 m buffer in the different hydrological regime were conducted.
The results indicate that nitrogenous compounds in rivers are better predicted by land uses in the entire catchment than those close to stream network. The significant associations between nitrogen and vegetation demonstrate the overall influence of dominant coverage of vegetated land use in the basin on stream water nitrogen concentrations. Meanwhile, the results also demonstrate that Nitrate-N is predicted by bareland in low follow period, yet by forest cover in high flow period in the riparian zone. Ammonium-N, the main pollutant in the basin, is poorly correlated with land use in the riparian zone, while significantly linked to bareland and vegetated land cover within the watershed in high flow period. Our results suggest the remarkable interaction among water flow seasonality, landscape setting and nitrogenous concentrations in streams.