Contrasting Dynamics of Nitrate and Kjeldahl Nitrogen in a Stream Draining a Rural Catchment in Galicia (NW Spain)

In this study the temporal variability of nitrogen (N) transport in a small rural agroforestry catchment (16 km(2)) located in NW Spain is analyzed. Total annual N loss was 20.34 t, and the specific N yield was 8.16 kg ha(-1) y(-1). This rate is low in relation to rural catchments in other regions with similar size and distribution of land use. Nitrate (N-NO3), which represents about 78% of the N transported, was mainly mobilized during baseflow (59%), whereas most of the total Kjeldahl nitrogen (TKN) export occurred during runoff events (54%). A significant difference in the transport of N-NO3 and TKN within the catchment was observed. The relationship between N-NO3 concentrations and discharge within runoff events was mainly dominated by anticlockwise hysteresis loops, whereas in the case of TKN clockwise hysteresis loops predominated.