Evaluating the sources and fate of anthropogenic dissolved inorganic nitrogen (DIN) in two contrasting North Sea estuaries

Sci Total Environ. 2006 Dec 15;372(1):317-33. doi: 10.1016/j.scitotenv.2006.09.018. Epub 2006 Nov 13.


Nitrogen isotope ratios (delta(15)N) were used to help elucidate the sources and fate of ammonium (NH(4)(+)) and nitrate (NO(3)(-)) in two northeastern English estuaries. The dominant feature of NH(4)(+) in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH(4)(+) concentrations (ranging from 30-150 microM) near the sewage outfall varied considerably between surveys, the sewage-derived delta(15)N-NH(4)(+) signature was remarkably constant (+10.6+/-0.5 per thousand) and could be tracked across the estuary. As indirectly supported by (15)N-depleted delta(15)N-NO(3)(-) values observed close to the mouth of the Tyne, this sewage-derived NH(4)(+) was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH(4)(+) concentrations were low (<7 microM) compared to those in the Tyne and delta(15)N-NH(4)(+) values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO(3)(-). A decrease in riverine NO(3)(-) flux during the summer coinciding with an increase in delta(15)N-NO(3)(-) values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light delta(15)N-NO(3)(-) (ca. 0 per thousand) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO(3)(-) during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and delta(15)N values was explained by simple end-member mixing models, implying very little estuarine processing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agriculture
  • Environmental Monitoring
  • Nitrates / analysis
  • Nitrogen / analysis*
  • Nitrogen Isotopes
  • North Sea
  • Quaternary Ammonium Compounds / analysis
  • Rivers
  • United Kingdom
  • Waste Disposal, Fluid
  • Water Pollutants, Chemical / analysis*


  • Nitrates
  • Nitrogen Isotopes
  • Quaternary Ammonium Compounds
  • Water Pollutants, Chemical
  • Nitrogen