Inorganic and Organic Losses of Nitrogen from Upland Regions of Britain: Concentrations and Fluxes

摘要

The nitrogen (N) composition of streams draining eight upland regions of Britain was compared using monthly samples collected between April 1997 and April 1998. Stream samples were analysed for total N (TN), particulate N (PN), nitrate (NO_3), ammonium (NH_4), and dissolved organic nitrogen (DON). Concentrations of TN were small, generally less than 1.5 mg N l~(-1), were dominated by dissolved forms of N, and varied significantly between regions. NO_3 accounted for the majority of variability. Concentrations of DON also varied between regions but to a smaller extent than those of NO_3. There were considerable variations in TN fluxes between upland regions, which ranged between 3.8 and 16.1 kg N ha~(-1) year~(-1). The majority of the variation was due to NO_3 fluxes, which were largest in regions receiving largest inputs of atmospheric N deposition and ranged between 1.4 and 13.5 kg N ha~(-1) year~(-1). Fluxes of DON ranged between 1 and 3.5 kg N ha~(-1) year~(-1), while fluxes of PN were generally less than 0.5 kg N ha~(-1) year~(-1), and NH_4 fluxes ranged between 0.1 and 0.4 kg N ha~(-1) year~(-1). NO_3 was the dominant fraction (47-84%) of N exported from all upland regions except the Highlands, where DON accounted for 52% of the TN flux. This study has shown that the DON fraction is an important com-ponent of the total N transported by upland streams in Britain.