Key Scottish Environment Statistics 2013

Nitrate Concentrations in Rivers⁹: 1993-2012

Distribution of mean nitrate concentrations, percentage of sites¹⁰ within each band

The enrichment of waters by nutrients, such as nitrates and phosphates, may lead to damage to the aquatic environment through the accelerated growth of algae and other plant life. The rapid growth and subsequent decay of plant organisms depletes oxygen levels, and this can have harmful effects upon fish and other aquatic life. This process is termed eutrophication.

High nitrate levels tend to have a greater impact on marine and coastal waters than on freshwater; a substantial part of the nitrates in freshwater will eventually reach the sea. The main source of nitrates in freshwater is agriculture.

Concentrations of nitrate below 0.3 mg N/l are considered to be natural or background levels¹¹; since 2007, over 40% of the sites have met this classification. In 2011, 41.0% of sites had a mean nitrate concentration < 0.3 mg N/l. The percentage of sites with average nitrate concentrations ≥2.5 mg N/l peaked at 25.5% in 1997, but has since fallen to its lowest level of 15.6% in 2011.

The 2012 figures are not directly comparable to previous figures as a smaller sample of sites (176, down from 200) has been used to calculate the percentages. This resulted in a change of the distribution of the nitrate concentrations in the sites. In 2012, 35.8% of sites had a mean nitrate concentration of < 0.3 mg N/l.

Regulations have been made designating 14% of the area of Scotland¹² as Nitrate Vulnerable Zones (NVZs).¹³ In NVZs, mandatory rules on farming practices aim to reduce nitrate water pollution from agricultural sources.

Source: Scottish Environment Protection Agency / Metadata