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Predicting Nitrate Concentrations in Northern Ireland Rivers Using Time Series Analysis

Biometrics Div., Dep. of Agric. for Northern Ireland, Newforge Lane, Belfast BT9 5PX, Northern Ireland;
Agric. and Environ. Science Div., Dep. of Agric. for Northern Ireland, Newforge Lane, Belfast BT9 5PX, Northern Ireland;
Dep. of Biom., The Queen's Univ. of Belfast;
Dep. of Agric. and Environ. Science, The Queen's Univ. of Belfast.

^* Corresponding author (David.Lennox{at}dani.gov.uk).

ABSTRACT

Lough Neagh is an important natural resource, being the largest single source of potable water for Belfast. Its catchment area covers about one-third of the land area of Northern Ireland. Six inflow rivers drain 88% of the total catchment, which has a land usage of grassland and rough grazing that is similar to Northern Ireland as a whole. This report examines the causes of the year-to-year variation in river NO^–₃ concentrations that have been the focus of European Community (EC) legislation. A multiple regression model has been developed which explains 74% of the variation in NO^–₃ concentrations for the time period 1974 to 1994. Based on a knowledge of the Northern Ireland annual utilized metabolizable energy (UME) for grazing livestock and N fertilizer sales, the model employs the efficiency of fertilizer usage as an independent variable. Additional independent variables are climatic: previous summer rainfall, sun hours in the winter and rainfall for the period January to June. Based on a worst case scenario, employing the extreme values for these climatic variables and the least fertilizer efficiency ratio, the predicted NO^–₃ concentration is only 4.4 mg N L^–1, which is well below the EC maximum admissible level of 11.3 mg N L^–1 for drinking water.