The nitrogen content of rivers in upland Britain: the significance of organic nitrogen

The influence of catchment characteristics on the form and concentration of nitrogen (N) in upland rivers is currently being assessed. Since April 199 7, river water from 61 catchments located throughout the uplands of Britain have been regularly sampled and analysed for total dissolved nitrogen (TDN ), nitrate (NO3-N), ammonium (NH4-N) acid dissolved organic nitrogen (DON). Concentrations of TDN were small, generally less than 1.2 mg l(-1), and va ried significantly among upland regions. The relative contribution of NO3-N , NH4-N and DON to mean TDN also varied among regions. The proportion of NO 3-N ranged from 25% to 84%, while the proportion of DON ranged from 14% to 69%. Ammonium contributed less than 7% to TDN in each region. Results show that DON can contribute significantly to TDN. Thus, assessment of anthropog enic impacts on TDN losses from upland ecosystems need to consider not only the dissolved inorganic species but also DON.