Influences of catchment characteristics on nitrogen concentration in largely forested streams during the base flow period

Based on measured stream nitrogen concentrations at outlets of 12 small sub-areas (1.3-54.7 km²) in a largely forested catchment during the base flow period, we investigated the influences of discharges and different catchment characteristics on stream nitrogen concentration. Our field surveys were carried out during the 11-month's period from April 2001 to February 2002 and the correlations between nitrogen concentrations and catchment characteristics were studied. The results showed that the vegetation cover was strongly correlated to total nitrogen (TN) and nitrate + nitrite - nitrogen (NO_x-N) concentrations. That is, the TN and NO_x-N concentrations had positive correlations with mean normalized difference vegetation cover index (NDVI) of each sub-area during dormant seasons (mean NDVI < 0.70) and had negative correlations during the growing season (mean NDVI≥ 0.70). The significance of catchment characteristics to TN and NO_x-N concentrations was ranked as vegetation cover > soil > topography > land use, and the best models can account for 55-64% of the variance of TN and NO_x.-N concentrations.