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

Abstract

In this study the temporal variability of nitrogen (N) transport in a small rural agroforestry catchment (16 km²) 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.

Keywords:

• Agroforestry catchment
• Kjeldahl nitrogen
• nitrate
• NW Spain
• runoff events
• temporal variability

Acknowledgments

This research is part of a project funded by the Spanish Ministry of Education and Science (REN2003-08143) and by Xunta of Galicia (PGIDIT05RAG10303PR, 10MDS103031PR). The first author has benefited from a research contract (Ángeles Alvariño Program) funded by the Xunta of Galicia.