Nutrients in freshwater (CSI 020/WAT 003) - Assessment published Feb 2015
- Since 2005, average nitrate concentrations in European groundwater have declined and in 2011, the mean concentration had almost returned to the 1992 level.
- The average nitrate concentration in European rivers declined by 0.03 milligrams per liter of nitrogen (mg N/l) (0.8%) per year over the period 1992 to 2012.
- The decline in nitrate concentration reflects the effect of measures to reduce agricultural inputs of nitrate, as well as improvements in wastewater treatment.
- Average orthophosphate concentration in European rivers has decreased markedly over the last two decades (0.003 milligrams per liter of phosphorous (mg P/l) or 2.1% per year).
- Also, average lake phosphorus concentration decreased over the period 1992-2012 (0.0004 mg P/l, or 0.8% per year).
- The decrease in phosphorus concentration reflects both improvements in wastewater treatment and the reduction of phosphorus in detergents.
Are concentrations of nutrients in our freshwaters decreasing?
Nitrate in groundwater: There was a slight increase in average annual mean nitrate concentration in European groundwater from 1992-1998. Since 2005, the concentrations have declined again, and in 2011 the mean concentration had almost returned to the 1992 level. The shorter time series shows the same pattern, giving hardly any trend overall. However, this larger selection of groundwater bodies shows a somewhat higher average European concentration level.
Nitrate in rivers: At European level, river nitrate concentrations have declined steadily over the period 1992-2012. The trend is the same for the time period 2000-2012, and the larger selection of stations shows a lower average concentration. Agriculture is the largest contributor of nitrogen pollution and, due to the EU Nitrate Directive and national measures, the nitrogen pollution from agriculture has been reduced in some regions over the last 10-15 years. This reduced pressure is reflected in lower river nitrate concentrations.
Phosphorus in rivers. The average concentrations of orthophosphate in European rivers more than halved over the period 1992-2012. In many rivers the reduction started in the 1980s. The marked decline is evident also for the time period 2000-2012, but the average concentration is somewhat higher when including more river stations.
The decrease in river orthophosphate is due to the measures introduced by national and European legislation, in particular the Urban Waste Water Treatment Directive , which involves the removal of nutrients. Also, the switch to phosphate-free detergents has contributed to lower phosphorus concentrations.
Phosphorus in lakes. During the past few decades, there has also been a gradual reduction in phosphorus concentrations in many European lakes. As treatment of urban waste water has improved, phosphorus in detergents is reduced, many waste water outlets have been diverted away from lakes and phosphorus pollution from point sources is gradually becoming less significant. However, diffuse runoff from agricultural land continues to be an important source of phosphorus in many European lakes. Moreover, phosphorus stored in sediment can keep lake concentrations high and prevent improvement of water quality despite a reduction in inputs.
Are nitrate concentrations in our groundwater decreasing?
Present concentrations per country
Groundwater nitrate concentrations primarily reflect the relative proportion and intensity of agricultural activity. In 2012, 23 out of 32 countries had groundwater monitoring stations with an average concentration above the threshold Groundwater Quality Standard of 50 milligrammes of nitrate per litre (mg NO3/l) as laid down in the Groundwater Directive (2006/118/EC) . Belgium and Spain had the highest proportion (more than 20%) of groundwater stations with an average concentration above the standard, but there was also a high proportion (10-20%) of groundwater stations above the standard in Austria, Cyprus, Czech Republic, Denmark, Germany, Italy, Montenegro, Netherlands and Portugal. Groundwater nitrate concentrations were generally low (most or all groundwater stations less than 10 mg NO3/l) in Albania, Bosnia and Herzegovina, Croatia, Finland, Iceland, Lithuania, Norway, Serbia, Sweden and the UK.
Trends in groundwater nitrate concentration (see Fig. 2)
There was a slight increase in average the annual mean nitrate concentration in European groundwater from 1992 to 1998. Since 2005, concentrations have declined again and in 2011, the mean concentration had almost returned to the 1992 level. By using the filter in figure 2, the groundwater nitrate trends for the individual countries are illustrated.
Looking at individual groundwater bodies (GWBs) there is a wide variation in trends (see Groundwater - nitrate - statistical analysis), with 32% of the GWBs showing decreasing nitrate concentrations since 1992, while 28% of the GWBs showed increasing concentrations. The countries with the highest proportions of GWBs with significant decreasing trends were Netherlands, Portugal and Slovakia. These countries also had the largest annual decrease in concentrations.
Geographical region time series and trends
There is marked variation in groundwater nitrate concentrations between different geographical regions of Europe. In Western Europe, the concentrations are high, and the levels have been fairly stable over the whole period, with similar proportions of decreasing and increasing trends, and about half the GWBs with no significant trend. The other regions are represented by far fewer GWBs. Results show that Northern Europe is at the other end of the scale, with low concentrations, but as for Western Europe, levels have been fairly stable over time. In Eastern Europe, the average concentration started declining after 1996, but increased again after 2003. However, since 2008, concentrations have declined, and have, since 2010, been at about the same level as at the start of the time series, and about 10 mg NO3/l lower than in Western and Southeastern Europe. In Southeastern Europe (only represented by Bulgaria), the concentration levels were high in the period 1997-2000. Disregarding this peak, there is still an overall increasing trend, with levels now higher than in Western Europe. However, as for Western Europe, the proportions of significantly increasing and decreasing trends were similar.