Agricultural Nitrates in Surface and Ground Waters

The fact sheet "Agricultural Nitrates in Surface and Ground Waters" measures the quality of surface water and groundwater with regard to nitrates from agricultural sources.

The Nitrates Directive, on the protection of water against pollution caused by agricultural nitrates, was transposed into the national legal system by the Decree-Law No. 235/97, as amended by Decree-Law No. 68/99.

In farming, the application of fertilisers onto the soil, in the form of compost or animal manure or slurry, containing nitrogenous compounds, is intended to favour crop growth. Excessive fertiliser application leads to water pollution, affecting both surface water and groundwater.

The identification of polluted water and water at risk of being polluted by nitrates of agricultural origin (if appropriate measures are not taken) considers, inter alia, the following criteria:

  • Groundwater containing or at risk of containing a nitrate concentration above 50 mg/L;
  • Inland surface waters (rivers or reservoirs), particularly those used or intended for the production of water for human consumption that contain or may contain a nitrate concentration in excess of 50 mg/L;
  • Inland surface waters (rivers or reservoirs), estuaries, coastal and marine waters with eutrophication or that may become eutrophic in the short term.

Areas that drain into waters identified as polluted or at risk of being polluted by nitrates from agricultural sources are designated vulnerable zones.

The first zones considered vulnerable to agricultural nitrates were identified in 1997 (Decree No. 1037/97), and included the following three vulnerable zones: Esposende - Vila do Conde, Aveiro and Faro.

Under the Nitrates Directive, the Member States of the European Union are required to draw up a four-year report, pursuant to Article 10, on the evolution of water quality, covering its various forms – surface water, groundwater, transitional and coastal waters.

This fact sheet concerns mainland Portugal and shall be updated every four years.

Objectives and targets: 
  • Reduce water pollution caused or induced by nitrates from agricultural sources and prevent its spreading.
Progress analysis:

The last identification of zones vulnerable to nitrates from agricultural sources occurred in 2010 under Decree No. 164/2010, with the following nine zones being currently considered vulnerable: Esposende – Vila do Conde, Estarreja – Murtosa, Litoral Centro, Tejo, Beja, Elvas, Estremoz – Cano, Faro and Luz de Tavira.

Last update: 
Monday, 7 August, 2017