This study examines the inter‐ and intra‐annual variability of different forms of N [total nitrogen (TN), nitrate‐nitrogen (N‐NO3) and total Kjeldahl nitrogen (TKN)] in stream waters of a rural headwater catchment in Galicia (NW Spain) during a 5‐year period, covering 2004–2009 water years (October–September). Daily time series were used to verify the temporal variability and to characterize the nitrogen pollution. The TN concentrations were low, although the values constantly exceeded the critical range (0.5–1.0 mg L−1) over which potential risk of eutrophication of water systems exists. Nitrate was the predominant form of nitrogen in the river throughout the study period, accounting for 82–85% of the TN. Significant differences were found for different forms of N between water years and seasons, indicative of wide inter‐ and intra‐annual variability of nitrogen concentrations, mainly related to rainfall and flow oscillations. The seasonal pattern in the concentrations of TN, N‐NO3 and TKN in stream water was similar to many humid and temperate catchments, with higher concentrations in winter, when variability was also the highest in the period, and lower values in summer.
Part of the book: Nitrogen in Agriculture