Preliminary Assessment of the Riverine Nitrogen Concentration and Load in an Agroforestry Basin in NW Spain

In this study, the concentrations and loads of different forms of nitrogen [nitrate nitrogen (NO3-N), total Kjeldahl nitrogen (TKN), and total nitrogen (TN)] in the headwater catchment of the Mero River (NW Spain) were analyzed. The TN concentrations were relatively low (mean: 2.57 mg L−1). Nitrate was the predominant form of N in the Mero catchment, accounting for 76.65 percent of the TN concentration. Measured NO3-N concentrations were always lower than the maximum allowed drinking water concentration. An annual TN load of 61.2 Mg was computed, representing an export of 0.94 Mg km−2 y−1, whereas annual exports NO3-N and TKN were of 0.79 and 0.15 Mg km−2 y−1, respectively.