ARCHIVE: Observatory monitoring framework – indicator data sheet
Environmental impact: Water
Indicator DA3: Nitrate and phosphate levels in rivers
This indicator shows the levels of phosphate (as phosphorus, P) and nitrate (NO3), from all sources, in river water in England. 59% of nitrates and 26% of phosphates in English waters are of agricultural origin. Changes in cropping practices or livestock types, numbers or management as a result of CAP reform could impact on nutrients leaching to water although the impact of other initiatives (eg Nitrate Vulnerable Zones, Water Framework Directive) also needs to be taken into account.
Chart DA3 shows the lengths of rivers with nitrate levels over 30 mg NO3 per litre, and phosphate (as phosphorus) levels
over 0.1 mg P per litre. The nitrate limit very roughly corresponds with a 95 percentile limit of 50mg/l used in the EC Nitrates Directive and the EC Drinking Water Directive. Government guidance recommends that rivers should not exceed annual mean phosphate concentrations of 0.1mg per litre.
Please note that the General Quality Assessment (GQA) reporting for river water quality has been revised because of the changes to the monitoring programme in the move towards Water Framework Directive (WFD) reporting. Figures for some years have been revised by the Environment Agency. Further details can be found in the accompanying fact sheet.
- Since 2000 nitrate levels have gradually fallen from 39% of river lengths exceeding 30 mg NO3 per litre to 29% in 2009.
- Since 2000 phosphate levels have gradually fallen from 62% of river lengths exceeded 0.1 mg P per litre to 50% in 2009.
The proportions of rivers exceeding aforementioned levels in rivers within English Environment Agency regions can be seen in Charts DA3a and DA3b. Different natural conditions exist in different parts of England. For example, nutrient concentrations are naturally greater in East Anglia than in the uplands.
Since 2000, there have been overall reductions in most regions. However, in the Southern region the proportion of river length exceeding 30mg/l of nitrates increased somewhat between 2000 and 2005. Although this has since reduced the proportion remains above the 2000 levels. The Anglian region continues to have the greatest proportion of river length exceeding 30mg/l of nitrates.
The proportion of rivers exceeding 0.1mg/l of phosphorus has declined in all regions between 2000 and 2009. The greatest reductions have been in the North East, Midland, Anglian and Thames regions.
The picture changes very slightly if we consider the lower limit of 0.06 mg/l.
The charts below show average concentrations of N and P in watercourses flowing through different landscape types.
Data for lowland arable and pastural landscapes are available for England but are only available for upland landscapes for Great Britain. Values
for lowland England were considerably higher than for Great Britain as a whole for both types of landscape for both N and P. This data can be found
in the accompanying datasheet.
- Average nitrate levels in watercourses in English arable landscapes were around twice those in pastural landscapes.
- Levels of nitrate loss from the uplands are much lower than from the lowlands and concentrations have remained consistently at around 5mg/l.
Nitrate remaining in the soil or arising from decomposition of crop residues is lost from arable fields in autumn and winter when rainfall is high and crops are absent or growing slowly and unable to take up surplus nitrogen. In fields under grassland, more of the nitrogen is retained in organic matter, but leaching still occurs where soil N levels are high.
- Levels of phosphate in water have fluctuated much more than nitrates in lowland landscapes. However the general trend has been downwards.
- In English lowland pastural landscapes, average concentrations declined.
- In upland areas in GB average concentrations remained level.
This indicator was updated in September 2010. The next update is expected in September 2011.
Further information and contact
Background information can be found in the accompanying fact sheet.
This is also a Biodiversity Strategy Indicator.
For information on this indicator contact Defra's Observatory team on +44 (0) 1904 455229, email: firstname.lastname@example.org
Page last modified: 10 November, 2010
Page published: June, 2007