Nitrogen deposition :: Rivers and Streams

Impact Type: Deposition of pollutant

Key Concerns:

Deposition of ammonia, nitrate and other forms of nitrogen from the atmosphere could be an important source of nitrogen in some upland catchments where intensive agricultural activity is absent. Detailed nitrogen budgets, however, do not exist, so the relative inputs from atmospheric deposition are unknown. In such cases, increasing nitrogen inputs from atmospheric sources are likely to have ecological impacts. In most lowland rivers and burns, nitrogen inputs from catchment land-use, not deposition from the atmosphere, are likely to be much more significant (Strong et al. 1997, Smith & Stewart 1989, Foy et al. 1982).

Additional Comments:

A critical load cannot be given for nitrogen, as quantitative relationships between biology and nitrogen concentrations are poorly understood. The nitrogen to phosphorus ratio can be important, with a molar ratio of around 16:1 (7:1 by weight) being the threshold between N- and P-limitation (Wetzel 2001). Impacts could be assessed by deviation from a 'natural' ratio for an individual site. The nitrogen concentration and load in rivers, particularly those in agricultural catchments, have been rising for a few decades (Zhou et al 2000, Gibson et al. 1992). The main source of this nitrogen is inorganic fertilisers (Strong et al. 1997, Smith & Stewart 1989).

Critical Load/Level: 

Critical Load/ Level

No comparable habitat with established critical load estimate available


Foy, R.; Smith, R.V.; Stevens, R.J. 1982 Identification of factors affecting nitrogen and phosphorus loadings to Lough Neagh Journal of Environmental Management 15 109-129
Gibson, C.E.; Smith, R.V.; Stewart, D.A. 1992 nitrogen cycle in Lough Neagh, N. Ireland, 1975 to 1987 Int. Revue ges. Hydrobiol 77 73-83
Smith, R.V.; Stewart, D.A. 1989 A regression model for nitrate leaching in Northern Ireland. Soil Use and Management 5 71-76
Strong, K.M.; Lennox, S.D.; Smith, R.V. 1997 Predicting nitrate concentrations in Northern Ireland rivers using time series analysis Journal of Environmental Quality 26 1599-1604
Zhou, Q.; Foy, R.H.; Gibson, C.E. 2000 2000Long-term changes of nitrogen and phosphorus loadings to a large lake in North-west Ireland Water Research 34 922-926