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Indicator Assessment
The decrease was less than for phosphorus because of limited success with measures to reduce agricultural inputs of nitrate.
Nitrate and phosphorus concentrations in European freshwater bodies between 1992/1993 and 2002
Note: Concentrations are expressed as annual median concentrations for groundwater, and median of annual average concentrations for rivers and lakes
Waterbase (Version 4)
Mean nitrate concentrations in groundwaters in Europe are above background levels (<10 mg/l as NO3) but do not exceed 50 mg/l as NO3. At the European level, annual mean nitrate concentrations in groundwaters have remained relatively stable since the early 1990s but show different levels regionally. Due to a very low level of mean nitrate concentrations (<2 mg/l as NO3) in the Nordic countries, the European mean nitrate concentration shows an unbalanced view of nitrate distribution. The presentation above is therefore separated in the following sub-indicators into western, eastern and Nordic countries.
On average, groundwaters in western Europe have the highest nitrate concentration, due to the most intensive agricultural practices, twice as high as in eastern Europe, where agriculture is less intense. Groundwaters in Norway and Finland generally have low nitrate concentrations.
At the European level there is some evidence of a small decrease in concentrations of nitrate in rivers. The decrease has been slower than for phosphorus because measures to reduce agricultural inputs of nitrate have not been adequately implemented across EU countries and because of the time lags between the reduction of agricultural nitrogen inputs and soil surpluses, and resulting reductions in surface and ground water concentrations of nitrate.
Concentrations of orthophosphate in European rivers have in general been decreasing steadily over the past 10 years. In the old EU Member States this is because of the measures introduced by national and European legislation, in particular the Urban Waste Water Treatment Directive, which has increased levels of wastewater treatment with, in many cases, tertiary treatment that involves the removal of nutrients. There has also been an improvement in the level of wastewater treatment in the new EU Member States, though not to the same levels as in the old Member States. In addition, the transition recession in the economies of the new Member States may have played a part in the decreasing phosphorus trends because of the closure of polluting industries and a decrease in agricultural production leading to less use of fertilisers. The economic recession in many of the new EU Member States ended by the end of the 1990s. Since then many new industrial plants with better effluent treatment technologies have been opened. Fertiliser applications have also started to increase to some extent.
During the past few decades there has also been a gradual reduction in phosphorus concentrations in many European lakes. However the rate of decrease appears to have slowed or even stopped during the 1990s. As with rivers, discharges of urban wastewater have been a major source of pollution by phosphorus, but as treatment has improved and many outlets have been diverted away from lakes, this source of pollution is gradually becoming less important. Agricultural sources of phosphorus, from animal manure and from diffuse pollution by erosion and leaching, are both important and need increased attention to achieve good status in lakes and rivers.
The improvements in some lakes have generally been relatively slow despite the pollution abatement measures taken. This is at least partly because of internal loading and because the ecosystems can be resistant to improvement and thereby remain in a bad state. Such problems may call for restoration measures, particularly in shallow lakes.
Agriculture is the largest contributor of nitrogen pollution to groundwater, and also to many surface water bodies, since nitrogen fertilisers and manure are used on arable crops to increase yields and productivity. In the EU, mineral fertilisers account for almost 50 % of nitrogen inputs into agricultural soils and manure for 40 % (other inputs are biological fixation and atmospheric deposition). Consumption of nitrogen fertiliser (mineral fertilisers and animal manure) increased until the late 1980s and then started to decline, but in recent years it has increased again in some EU countries. Consumption of nitrogen fertiliser per hectare of arable land is higher in the old than in the new EU Member States and Accession countries. Nitrogen from excess fertiliser percolates through the soil and is detectable as elevated nitrate levels under aerobic conditions and as elevated ammonium levels under anaerobic conditions. The rate of percolation is often slow and excess nitrogen levels may be the effects of pollution on the surface up to 40 years ago, depending on the hydrogeological conditions. There are also other sources of nitrate, including treated sewage effluents, which may also contribute to nitrate pollution in some rivers.
Reference
COM (2002) 407 final. Implementation of Council Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources. Synthesis from year 2000 Member States reports. Report from the Commission. COM, Brussels.
Nitrate concentrations in groundwater bodies between 1993 and 2002 in different regions of Europe
Note: Western Europe: Austria, Belgium, Denmark, Germany, Netherlands; 27 GW-bodies
Waterbase (Version 4)
Trends in nitrate concentrations in groundwater bodies (1980s to early 2000s) in European countries
Note: Number of groundwater bodies for each country given in brackets following the country abbreviation
Waterbase (Version 4)
Present concentration of nitrate in groundwater bodies in European countries, 2002
Note: The number of groundwater monitoring stations in each country is given in brackets
Waterbase
Nitrate concentrations in groundwater in different regions of Europe
Nitrate concentrations in groundwaters have remained relatively stable since the early 1990s. They vary between the different regions of Europe.
The relatively high nitrate concentration in groundwater in western European countries can be seen as consequence of the intensive agriculture and the usage of nitrogen fertilisers. The temporal development of the total nitrogen fertiliser consumption within these regions and the regional differentiation in concentration levels is very similar. Data on nitrogenous fertiliser use show in all countries with consistent time series except for Germany and Lithuania a decline with a range from 5 % to 57 % in 2002 compared to 10 years before. For the Slovak Republic no data are available [2].
Not only are consumption figures high in western European countries, but also the usage per hectare of agricultural land. In 1994, the Netherlands, Denmark, Belgium and Germany were amongst the countries with the highest nitrogen fertiliser use related to the agricultural area. In Finland (11.) and Norway (4.) the nitrogen fertiliser usage is also high but the agricultural area represents only 9 % and 3 % respectively of the total land area [1]. Although the agricultural area in the new EU Member States ranges between 15 % (Cyprus) and 60 % (Hungary) of the total land area, agriculture is less intense than in western Europe. The nitrate fertiliser use per hectar of agricultural land is about the half of that in former EU 15 [3].
Fertiliser consumption and nitrate concentrations in groundwater do not show a direct relationship at this level. However, fertiliser consumption is an indicator for agricultural intensity and should give an estimate of the nitrogen load of the environment [1].
In Malta, analysis of nitrate values in groundwater measured at pumping stations over the 25 year period 1976-2001 indicates a steady increase. Generally the highest values are observed to occur in the north western part of Malta [6]. In Estonia quaternary aquifers used by small or individual settlements are subject to agricultural pollution (nitrates and pesticides) as well as military pollution from the Soviet period [7].
Furthermore, low nitrate concentration levels can occur due to reducing conditions. Therefore the indicator on ammonium and dissolved oxygen has been introduced to provide complementary information.
65 % of the demand for drinking water in Europe is covered by groundwater. The rate in Austria and Denmark is 99 % . In Finland approximately 60 % of the total water supply distributed by Finland's waterworks consists of groundwater [8]. In Germany, more than 70 % of the drinking water supply comes from groundwater and springs. Often groundwater is used untreated, particularly from private wells. It has been shown that drinking water in excess of the nitrate limit can result in adverse health effects, especially in infants less than two months of age. Decentralised drinking water supplies in some western European countries have been linked to water-related outbreaks. Contaminated drinking-water is one of the five major environmental risks perceived by citizens in the new Member States and the accession countries as affecting their own health [9].
Trends in nitrate concentrations in groundwater
Between 1993 and 2002, there was a significant decreasing trend or trend reversal in 32 % of groundwater bodies for which there were available data. However, 20 % of groundwater bodies also showed increasing trends of nitrate over the same period, reflecting that emissions of nitrate in the catchments of these groundwater bodies may not yet have been reduced or indicating that the effects of reducing emissions have not yet become evident because, for example, of high nitrogen surpluses in agricultural soils and/or long time lags before the effects of measures become apparent.
There have been significant decreases in nitrate concentrations in some groundwater bodies in some European countries. Finland (with other Nordic countries) generally has the lowest nitrate concentrations in its groundwater. However, about 22 % of Finnish groundwater bodies showed an increasing concentration between 1993 to 2002, perhaps indicating increasing pressures from agriculture and other sectors emitting nitrate. Also varying hydrological conditions may at least partly explain the upward trends.
There is often a significant time lag (up to 40 years) between changes in agricultural practices and changes in groundwater quality. The actual time lag for an individual groundwater body depends on its hydrogeological conditions. Therefore, some of the indicated upward trends in groundwater bodies might, for example, be caused by intensification of agricultural practice some 20 years ago. The actual cause effect relationship has to be assessed individually for each groundwater body. Nevertheless, it is an indication that remediation and improvement measures have to be implemented over medium or rather long term in order to reverse upward trends.
Present concentrations of nitrate in groundwater
Nitrate drinking water guide levels are exceeded in around one-third of the groundwater bodies for which information is currently available.
The concentrations of nitrate in groundwater in the different European countries generally reflect the relative importance and intensity of the driving forces affecting water quality. Those countries with low intensity driving forces perhaps coupled with effective measures to reduce nutrient emissions (pressures) (particularly the Nordic countries) generally have relatively low concentrations of these determinands. In contrast those countries with high intensity driving forces, perhaps coupled with ineffective measures to reduce emissions, have relatively high concentrations (for example some new EU countries).
20 of the 27 countries with available information had groundwater bodies exceeding the drinking water directive guide concentration for nitrate of 25 mg NO3/l, and 17 of these also had groundwater bodies exceeding the maximum allowable concentration of 50 mg NO3/l. Countries with the greatest agricultural land use and highest population densities (such as Denmark, Germany, Hungary and the UK), generally had higher nitrate concentrations than those with the lowest (such as Estonia, Norway, Finland and Sweden) reflecting the impact of emissions of nitrate from agriculture.
Nitrate concentrations in rivers between 1992 and 2002 in different regions of Europe
Note: Western Europe: Austria (152), Denmark (32), France (235), Germany (121), Luxembourg (3), UK (113)
Waterbase (Version 4)
Phosphorus concentrations in rivers (orthophosphate) between 1992 and 2002 in different regions of Europe
Note: Number of monitoring stations in brackets Western Europe: Austria (103), Denmark (32), France (204), Germany (109), United Kingdom (30)
Waterbase (Version 4)
Trends in nitrate concentrations in rivers (1990s and early 2000s) in European countries
Note: Number of river stations for each country given in brackets
Waterbase (Version 4)
Trends in phosphorus concentrations in rivers (orthophosphate) in European countries during the 1990s and 2000s
Note: Number of river stations for each country given in brackets
Waterbase (Version 4)
Present concentration of nitrate in rivers in European countries, 2002
Note: The number of river monitoring stations in each country is given in brackets
Waterbase (Version 4)
Present concentration of phosphorus in rivers (orthophosphate) in European countries, 2002
Note: The number of river monitoring stations in each country is given in brackets
Waterbase (Version 4)
Nitrate concentrations in lakes between 1992 and 2002 in different regions of Europe
Note: Western Europe: Germany (5), UK (2)
Waterbase (Version 4)
Phosphorus concentrations in lakes (total phosphorus) between 1992 and 2002 in different regions of Europe
Note: Number of monitoring stations in brackets Western Europe: Austria (2), Germany (5), Denmark (23), Ireland (1)
Waterbase (Version 4)
Trends in nitrate concentrations in lakes in European countries during the 1990s and 2000s
Note: Number of lake stations for each country given in brackets
Waterbase (Version 4)
Trends in phosphorus concentrations in lakes (total phosphorus) in European countries during the 1990s and early 2000s
Note: Number of lake stations for each country given in brackets
Waterbase (Version 4)
Present concentration of nitrate in lakes in European countries, 2002
Note: The number of lake monitoring stations in each country is given in brackets
Waterbase (Version 4)
Present concentration of phosphorus in lakes (total phosphorus) in European countries, 2002
Note: The number of lake monitoring stations in each country is given in brackets
Waterbase (Version 4)
Nitrate concentrations in lakes have remained relatively stable since the early 1990s. There is some evidence that nitrate concentrations are decreasing in some rivers. Nitrate concentrations vary between the different regions of Europe particularly in rivers.
There is a close relationship between use of fertilisers and nitrate concentrations in surface waters in European regions. Concentration of nitrate in western European countries still remains relatively high as well as the nitrogenous fertiliser use. In the new member states, surface water concentrations of nitrate are lower due to lower application of nitrate in agriculture. Nordic countries generally have the lowest nitrate concentrations in its rivers and lakes.
The observed decrease in nitrate concentrations in some rivers and lakes of some EU countries can be seen as a result of national and international measures to control nitrogen pollution, in particular, from agricultural sources. However the decreases in concentrations have been relatively slow because of inadequate implementation of the Nitrate Directive by EU countries and because of the sometimes long delays between measures being applied and concentrations decreasing. The latter could be due, for example, to large nitrogen surpluses in agricultural soil which potentially may take years to decrease. Any decreases in the new member countries are likely to be due to the decrease in agricultural productivity during the economic transition period, for example the decrease in use of nitrogenous fertilisers.
Around 40 % and 9 % of monitoring stations on Europe's rivers and lakes, respectively, showed a decreasing trend of nitrate concentrations between 1992 and 2002 reflecting the success of legislative measures to reduce nitrate pollution.
However, 14 % of the river stations and 15 % of lake stations showed increasing trends of nitrate over the same period, reflecting that emissions of nitrate in the catchments of these rivers and lakes may have not yet been reduced or indicating that the effects of reducing emissions have not yet become evident because, for example, of high nitrogen surpluses in agricultural soils.
There have been significant decreases in nitrate concentrations at some river and lake stations in some European countries. In the old EU countries assessed, Denmark had the highest proportion of river stations with decreasing trends indicating that national and EU measures introduced to reduce nitrate pollution, such as those in the nitrates directive, are having some effect. Finland has the lowest nitrate concentrations in its rivers and lakes. However, about 20% of Finnish river stations and 28 % (2 out of 7) of lake stations showed an increasing concentration between 1992 to 2002, perhaps indicating increasing pressures from agriculture and other sectors emitting nitrate. Also the varying hydrological conditions may at least partly explain the upward trends. The other EU countries had different proportions of river stations with decreasing, no and increasing trends. In the new EU countries, the Czech Republic had the highest proportion of river stations (74 %) with decreasing nitrate concentrations and no stations with increasing trends. The eight other new EU countries with available data had varying proportions of river stations with decreasing, no and increasing trends. Poland had the highest proportion of river stations (34 %) with increasing concentrations. The decreasing trends are probably because of the decrease in agricultural productivity and activity in these countries during the transition of their economies to become more market orientated. This has led to, for example, decreases in nitrogenous fertiliser use and in numbers of livestock (and hence manure production), both potential sources of nitrate pollution.
Nitrate drinking water guide levels are exceeded at around 10 % of river stations and at around 1 % of lake stations for which information is currently available.
The concentrations of nitrate in rivers and lakes in the different European countries generally reflect the relative importance and intensity of the driving forces affecting water quality. Those countries with low intensity driving forces perhaps coupled with effective measures to reduce nutrient emissions (pressures) (particularly the Nordic countries) generally have relatively low concentrations of these determinands. In contrast those countries with high intensity driving forces, perhaps coupled with ineffective measures to reduce emissions, have relatively high concentrations (for example some new EU countries).
In terms of nitrate, 15 of the 25 countries with available information had a number of river stations where the drinking water directive guide concentration for nitrate of 25 mg NO3/l was exceeded, and three of these countries had stations where the maximum allowable concentration of 50 mg NO3/l was also exceeded. Countries with the greatest agricultural land use and highest population densities (such as Denmark, Germany, Hungary and the UK), generally had higher nitrate concentrations than those with the lowest (such as Estonia, Norway, Finland, and Sweden). This reflects the impact of emissions of nitrate from agriculture in the former and wastewater treatment plants in the latter group of countries.
Total phosphorus concentrations in lakes have remained relatively stable since the early 1990s.
There have been significant decreases in orthophosphate concentrations in eastern and western European rivers during the 1990s. In both rivers and lakes, however, phosphorus concentrations remain above background levels increasing the risk of eutrophication in some water bodies. The Nordic countries have relatively low concentrations reflecting the high level of wastewater treatment in those countries.
Concentrations of phosphorus in Nordic rivers and lakes are much lower than in other parts of Europe and are around what are considered to be background concentrations. This reflects the relatively low population densities in these countries and the high level of treatment of sewage effluents including the removal of phosphorus.
The concentrations of total phosphorus in lakes in eastern and western Europe are similar and show no clear trends between 1992 and 2002. Concentrations are however still above what is considered to be the general background levels: the ecological significance of these elevated levels are not known.
Concentrations of orthophosphate have steadily decreased over the last 10 years in western European rivers reflecting improvements in wastewater treatment including increasing proportions of sewage effluent subject to phosphorus removal. There were also relatively large decreases in orthophosphate concentrations in eastern European rivers during the 1990's but since 2000 there is some evidence of increases in concentrations again. The extent and levels of sewage treatment have generally been lower in eastern than in western European countries. The more recent increases could reflect that more sewage treatment is being introduced in eastern European countries as socio-economic conditions improved in preparation of accession to the EU. However, without nutrient removal in the new plants, increased extent of sewage treatment may increase the emissions/loads of orthophosphate entering eastern European rivers. In 2002, concentrations of orthophosphate in eastern European rivers were much higher than in western. In both cases the concentrations are many times background concentrations: the ecological significance of these elevated concentrations is not known but it is probable that they contribute to the eutrophication of these rivers.
Around 40 % and 20 % of monitoring stations on Europe's rivers and lakes, respectively, showed a decreasing trend of orthophosphate and total phosphorus concentrations between 1992 and 2002 reflecting the success of legislative measures to reduce emissions of phosphorus such as those required by the urban waste water treatment directive.
However, 12 % of river stations and 9 % of lake stations also showed increasing trends of orthophosphate and total phosphorus, respectively, over the same period, reflecting that emissions of phosphate in the catchments of these rivers and lakes may not yet have been reduced or indicating that in some catchments there might be increasing phosphorus surpluses in agricultural soils.
Sixteen of the 19 countries assessed had a higher proportion of river stations with decreasing orthophosphate concentration than those with increasing trends. Two (Bulgaria and Slovenia) had more river stations with increasing concentrations than decreasing. Estonia and Italy were the only countries with no river stations showing increasing trends. The total phosphorus data on lakes is limited in many cases to only a few lakes in each country (e.g. Ireland, Estonia and Latvia), and therefore information from these countries must be treated with some caution. Denmark, Finland, Hungary and the Netherlands had a higher proportion of lakes with decreasing total phosphorus concentrations than those with increasing concentrations. Austria and Germany had no lake stations showing increasing trends.
The increasing trends might be because of ineffective control of phosphorus in some river catchments, particularly those with relatively small (in terms of load) sources of phosphorus that might fall outside legislative requirements. Dishwasher detergents containing phosphorus are also becoming increasingly important as dishwashers are increasingly used in more affluent societies. There are also cases where agricultural sources of phosphorus are becoming more important in catchments as point sources are progressively reduced. Phosphorus surpluses may also be increasing in some agricultural soils.
All the new EU countries, except Slovenia, had some river stations with decreasing phosphate concentrations. The decreasing trends reflect a general improvement of sewage treatment in these countries (though they have not yet fully implemented the urban waste water treatment directive) and/or the closure of polluting industries that has occurred during the restructuring of their economies as part of the process of transition into the EU.
The concentrations of phosphorus in rivers and lakes in the different European countries generally reflect the relative importance and intensity of the driving forces affecting water quality. Those countries with low intensity driving forces (e.g. low population density) perhaps coupled with effective measures to reduce nutrient emissions (pressures) (particularly the removal of phosphorus from waste water effluents in the Nordic countries) generally have relatively low concentrations of these determinands. In contrast those countries with high intensity driving forces, perhaps coupled with ineffective measures to reduce emissions, have relatively high concentrations (for example some new EU countries).
Those countries with high proportions of nutrient removal in their sewage treatment works (such as Sweden, Finland and the Netherlands) have relatively low orthophosphate concentrations whereas those countries with relatively low nutrient removal, high population densities and high phosphorus fertiliser usage (such as France, Italy and UK) tend to have relatively high orthophosphate concentrations.
As already described the ecological significance of the elevated concentrations of phosphorus in rivers and lakes is not known. The water framework directive requires the achievement of good ecological status in surface water bodies. Where nutrient emissions are identified as a pressure impacting/decreasing ecological status then target concentrations equating to good ecological status will have to be set for each type of river and lake water body. It is anticipated, therefore, that in the longer term concentrations of phosphorus in European rivers and lakes will continue to decrease and as a result eutrophication to decrease and ecological quality increase.
[1] EEA (2000). Groundwater quality and quantity in Europe. Environmental assessment report No 3. Copenhagen. http://reports.eea.eu.int/groundwater07012000/en
[2] EEA Dataservice. Fertiliser consumption - Raw data and trend. http://dataservice.eea.eu.int/dataservice/viewdata/viewpvt.asp?id=184
[3] EEA (2004). Agriculture and the environment in the EU accession countries. Implications of applying the EU common agricultural policy. Environmental issue report No 37. EEA, Copenhagen. http://www.eea.eu.int/
[4] German Environmental Report 2002. http://www.bmu.de/english/download/files/umweltbericht_engl_2002.pdf
[5] COM (2002) 407 final. Implementation of Council Directive 91/676/EEC concerning the protection of waters against pollution caused by nitrates from agricultural sources. Synthesis from year 2000 Member States reports. Report from the Commission. COM, Brussels.
[6] State of the Environment Report for Malta. 2002. http://www.mepa.org.mt/environment/publications/soer2002/SOER02.PDF
[7] State of Environment in Estonia. 2002. http://nfp-ee.eionet.eu.int/SoE/index_en.htm
[8] Finnish State of the Environment. Environmental administration. http://www.environment.fi/default.asp?node=6085&lan=en
[9] WHO (2004). Health and the Environment in the WHO European Region: Situation and policy at the beginning of the 21st century. Part I. The environment health situation in the WHO European region. Executive summary. Fourth Intergovernmental Preparatory Meeting. WHO, Copenhagen. http://www.euro.who.int/EEHC
[10] Working database groundwater: Umweltbundesamt Vienna. No online access.
[11] Waterbase - Groundwater quality - Information and pressures on groundwater bodies. http://dataservice.eea.eu.int/dataservice/viewdata/viewpvt.asp?id=265
[12] Indicator fact sheet 05 - Nitrogen balance in agricultural soils
[13] Indicator fact sheet 02 - Numbers of livestock
IEEP (2002): Background study on the link between agriculture and environment in accession countries. National reports. IEEP, London. http://www.ieep.org.uk
This indicator shows concentrations of phosphate and nitrate in rivers, total phosphorus in lakes and nitrate in groundwater bodies. The indicator can be used to illustrate geographical variations in current nutrient concentrations and temporal trends.
The concentration of nitrate is expressed as milligrams of nitrate per litre (mg NO3/l) for groundwater and milligrams of nitrate-nitrogen per litre (mg NO3-N/l) for rivers.
The concentration of phosphate and total phosphorus are expressed as milligrams of phosphorous per litre (mg P/l).
The environmental quality of freshwater with respect to eutrophication and nutrient concentrations is an objective of several directives. These include: the Nitrates Directive (91/676/EEC), aimed at reducing nitrate pollution from agricultural land; the Urban Waste Water Treatment Directive (91/271/EEC), aimed at reducing pollution from sewage treatment works and certain industries; the Industrial Emissions Directive (2010/75/EU), aimed at reducing emissions from industry to air, water and land; the Convention on Long-range Transboundary Air Pollution and the National Emission Ceilings Directive, aimed at reducing air pollution to, inter alia, avoid eutrophication of surface waters from air pollution; and the Water Framework Directive, which requires the achievement of good ecological status or good ecological potential of surface waters by 2015, unless exemptions are applied. The Water Framework Directive also requires the achievement of good chemical and good quantitative groundwater status by 2015 as well as the reversal of any significant and sustained upward trend in the concentration of any pollutant. In addition, the Drinking Water Directive (98/83/EC) sets the maximum allowable concentration for nitrate of 50 mg NO3/l. It has been shown that drinking water in excess of the nitrate limit can result in adverse health effects, especially in infants less than two months old. Groundwater is a very important source of drinking water in many countries and is often used untreated, particularly from private wells.
Among the key principles of The Seventh Environment Action Programme of the European Community 2014-2020 are the 'full integration of environmental requirements and considerations into other policies', 'better implementation of legislation' and 'more and wiser investment for environment and climate policy'. This could result in a more intense application of agri-environmental measures to reduce nutrient pollution of the aquatic environment, e.g. in the Common Agricultural Policy, which after the reform in 2013 has an even stronger focus on sustainable farming and innovation. Reducing nutrient pollution from agriculture is also an important aspect of the European Green Deal and the ‘Farm to Fork’ Strategy. Other action points in the European Green Deal are also related to reducing nutrient pollution, e.g. ‘Zero pollution action plan for water, air and soil’ and ‘Measures to address the main drivers of biodiversity loss’.
This indicator is not directly related to a specific policy target. The environmental quality of surface waters with respect to eutrophication and nutrient concentrations is, however, an objective of several directives:
Source of data
The data on water quality of rivers, lakes and groundwater in Waterbase are collected annually through the WISE SoE - Water Quality (WISE-6) data collection process. It includes data on nutrients, organic matter, hazardous substances and general physico-chemical parameters as well as for biological data for rivers and lakes. The WISE-6 data flow was new as of 2019, and has from 2020 replaced WISE-4. This reporting obligation is an Eionet core data flow. A request is sent to National Focal Points and National Reference Centres every year with reference to templates to use and guidelines. As of 2015, WISE SoE - Water Quality (WISE-6)supersedes Eurowaternet reporting.
The data in Waterbase is a sub-sample of national data assembled for the purpose of providing comparable indicators of the pressures, state and impact of waters on a European-wide scale. The data sets are not intended for assessing compliance with any European directive or any other legal instrument. Information on the sub-national scales should be sought from other sources.
Site selection
Data from all reported monitoring sites are extracted for the indicator assessment. Some data are excluded following the QC process (see the QC section below). The time series analysis is based on complete time series only (see Inter/extrapolation and consistent time series below). For groundwater, the time series are based on data for groundwater bodies, not individual monitoring sites.
Determinands
The determinands selected for the indicator and extracted from Waterbase are:
For rivers, total oxidised nitrogen is used instead of nitrate when nitrate data are missing. If both are monitored at the same site and at the same time, nitrate values are given precedence. All values are labelled as nitrate in the graphs, but it is indicated in the graph notes for which countries' total oxidised nitrogen data are used.
Mean
Annual mean concentrations are used as a basis in the indicator analyses. Unless the country reports aggregated data, the aggregation to annual mean concentrations is done by the EEA. Countries are asked to substitute any sample results below the limit of quantification (LOQ) by a value equivalent to half of the LOQ before calculating the site annual mean values. The same principle is applied by the EEA.
The annual data in most cases represent the whole year, but data are used also if they represent shorter periods. Up until 2012, data could be reported at different temporal aggregation levels. Here, annual data have been selected, but if this was not available, seasonal data were selected according to a specific order of preference.
Quality control (QC)
An automatic QC procedure is applied when data are reported, including checking that the values are within a certain range defined for each determinand. Automatic outlier tests based on z scores are also applied, both to the disaggregated and aggregated data, excluding data failing the tests from further analysis. In addition, a semi-manual procedure is applied, to identify issues that are not identified in the automatic outlier tests. The focus is particularly on suspicious values having a major impact on the country time series and on the most recently reported data. This comprises e.g.:
• values not so different from values in other parts of the time series, but deviating strongly from the values closer in time;
• consecutive values deviating strongly from the rest of the time series (including step changes);
• whole time series deviating strongly in level compared to other time series for that country and determinand;
• where values for a specific year are consistently far higher or lower than the remaining values for that country and determinand.
Such values are removed from the analysis (both time series/trend and present state analysis) and checked with the countries. Depending on the response from the countries, the values are corrected, flagged as outliers or flagged as confirmed valid. Any response affecting the indicator analysis is corrected in the next update of the indicator.
Inter/extrapolation and consistent time series
For time series analyses, only series that are complete after inter/extrapolation (i.e. no missing values in the site data series) are used. This is to ensure that the aggregated time series are consistent, i.e. including the same sites throughout the time series. In this way, assessments are based on actual changes in concentration, and not changes in the number of sites. For the trend analysis, it is essential that the same time period is used for the different sites, so that the results are comparable. However, the statistical approach chosen can handle gaps in the data series, so inter/extrapolation is not applied here. For rivers and lakes, 'sites' in this context means individual monitoring sites. For groundwater it means groundwater bodies, i.e. the basis for inter/extrapolation and selection of complete data series is groundwater body data series. Each groundwater body may have several monitoring sites, and in some cases the number of monitoring sites has changed over the years. This means that some of the complete data series for groundwater (after inter/extrapolation) are not truly consistent and must hence be regarded as more uncertain than the complete series for lakes and rivers. The purpose of choosing this approach is to increase the number of groundwater time series in the analyses.
Changes in methodology: Site selection and inter/extrapolation
Until 2006, only complete time series (values for all years from 1992 to 2004) were included in the assessment. However, a large proportion of sites were excluded by this criterion. To allow the use of a considerably larger share of the available data, it was decided in 2007 (i.e. when analysing data up until 2005) to include all time series with at least 7 years of data. This was a trade-off between the need for statistical rigidity and the need to include as much data as possible in the assessment. However, the shorter series included might represent different parts of the whole time interval and the overall picture may therefore not be reliable.
In 2009, it was decided to inter/extrapolate all gaps of missing values of 1-2 years for each site. At the beginning or end of the data series, one missing value was replaced by the first or last value of the original data series, respectively. In the middle of the data series, missing values were replaced by the values next to them for gaps of 2 years and by the average of the 2 neighboring values for gaps of 1 year.
In 2010, this approach was modified, allowing for gaps of up to 3 years, both at the ends and in the middle of the data series. At the beginning or end of the data series, up to 3 years of missing values are replaced by the first or last value of the original data series, respectively. In the middle of the data series, missing values are replaced by the values next to them, except for gaps of 1 year and for the middle year in gaps of 3 years, where missing values were replaced by the average of the 2 neighboring values.
In 2018, this approach was slightly modified using linear interpolation for gap filling in the middle of the time series. Moreover, if data were available from 1989-1991 these were applied in the gap filling procedure, making it possible to interpolate instead of extrapolating at the beginning of the time series.
Only time series with no missing years for the whole period from 1992 or 2000 after such inter/extrapolation are included in the assessment. Even if the gap filling is not applied in the trend analyses, the same time series are used, for easier comparison of the time series and trend analysis results. The gap filling procedure increases the number of sites that can be included in the time series/trend analysis. Using also the shorter time period from 2000 allows the inclusion of more sites, making the data more representative. Still, the number of sites in the time series/trend analysis is markedly lower compared with the analysis of the present state, where all available data can be used.
Aggregation of time series
The selected time series (see above) are aggregated to country and European level by averaging across all sites for each year.
Trend analyses
Trends are analysed by the Mann-Kendall method (Jassby et al., 2020) in the free software R (R Core Team 2020), using the wql package. This is a non-parametric test suggested by Mann (1945) and has been extensively used for environmental time series (Hipel and McLeod, 2005). Mann-Kendall is a test for a monotonic trend in a time series y(x), which in this analysis is nutrient concentration (y) as a function of year (x). The test is based on Kendall's rank correlation, which measures the strength of monotonic association between the vectors x and y. In the case of no ties in the x and y variables, Kendall's rank correlation coefficient, tau, may be expressed as tau=S/D where S=sum_{i<j} (sign(x[j]-x[i])*sign(y[j]-y[i])) and D = n(n-1)/2. S is called the score and D, the denominator, is the maximum possible value of S. The p-value of tau is computed by an algorithm given by Best and Gipps (1974). The tests reported here are two-sided (testing for both increasing and decreasing trends). Data series with p-value <0.05 are reported as significantly increasing or decreasing, while data series with p-value >= 0.05 and <0.10 are reported as marginally increasing or decreasing. The results are summarised by calculating the percentage of sites (groundwater body/river site/lake site) within each category relative to all sites within the specific aggregation (Europe or country). The test analyses only the direction and significance of the change, not the size of the change.
The size of the change is estimated by calculating the Sen slope (or the Theil or Theil-Sen slope) (Theil 1950; Sen 1968) using the R software. The Sen slope is a non-parametric method where the slope m is determined as the median of all slopes (yj−yi)/(xj−xi) when joining all pairs of observations (xi, yi). Here the slope is calculated as the change per year for each site. This is summarised by calculating the average slope (regardless of the significance of the trend) for all sites in Europe or a country. For the relative Sen slope (Sen slope %), the slope joining each pair of observations is divided by the first of the pair before the overall median is taken and multiplied by 100. Again, this is summarised for Europe or individual countries by averaging across sites. The Sen slope was introduced for this indicator in 2013.
The Mann-Kendall method or the Sen slope will only reveal monotonic trends and will not identify changes in the direction of the time series over time. Hence a combination of approaches is used to describe the time series: a visual inspection of the time series, describing whether the general impression is a monotonic trend, no apparent trend, clear shifts in direction of the trend or high variability with no clear direction; an evaluation of significant versus non-significant and decreasing versus increasing monotonic trends using the Mann-Kendall results; an evaluation of the average size of the monotonic trends using the Sen slope results.
Current concentration distributions:
For analysis of the present state, average concentrations are calculated over the last 3 years. Outliers and suspicious values are removed before averaging. In this case all groundwater bodies and lake and river sites can be used, which is a far higher number than those that have complete time series after inter/extrapolation. The 3-year average is used to remove some inter-annual variability. Also, since data are not available for all sites each year, selecting data from 3 years will give more sites. The average value thus represents 1, 2 or 3 years. The sites are assigned to different concentration classes and summarised per country (count of sites per concentration class).
• The classes defining values for nitrate are based on typical background concentrations in the different water categories and the legislative standard (11.3 mg N/l) and guide value (5.6 mg N/l).
• The classes defining values for phosphate (rivers) and total phosphorus (lakes) concentrations are based on typical background concentrations in the different water categories and on the range of concentrations found in Waterbase, and only give an indication of the relative distribution of concentrations of phosphorus in each country.
Methodology for gap filling is described above (under inter/extrapolation and consistent time series).
Nutrient conditions vary throughout the year depending on, for example, season and flow conditions. Hence, the annual average concentrations should ideally be based on samples collected throughout the year. Using annual averages representing only part of the year introduces some uncertainty, but it also makes it possible to include more sites, which reduces the uncertainty in spatial coverage. Moreover, the majority of the annual averages represent the whole year.
Nitrate concentrations in groundwater originate mainly from anthropogenic influence caused by agricultural land-use. Concentrations in water are the effect of a multidimensional and time-related process, which varies from groundwater body to groundwater body and is, as yet, less quantified. To properly evaluate the nitrate concentration in groundwater and its development, closely-related parameters such as ammonium and dissolved oxygen should be taken into account.
This indicator is meant to give a representative overview of nutrient conditions in European rivers, lakes and groundwater. This means it should reflect variability in nutrient conditions over space and time. Countries are asked to provide data on rivers, lakes and important groundwater bodies according to specified criteria.
The datasets for groundwater and rivers include almost all countries within the EEA, but the time coverage varies from country to country. The coverage of lakes is less good. It is assumed that the data from each country represents the variability in space in their country. Likewise, it is assumed that the sampling frequency is sufficiently high to reflect variability in time. In practice, the representativeness will vary between countries.
Each annual update of the indicator is based on the updated set of monitoring sites. This also means that due to changes in the database, including changes in the QC procedure that excludes or re-includes individual sites or samples and retroactive reporting of data for the past periods, which may re-introduce lost time series that were not used in the recent indicator assessments, the derived results of the assessment vary in comparison to previous assessments.
Waterbase contains a large amount of data collected throughout many years. Ensuring the quality of the data has always been a high priority. A revision of Waterbase reporting and the database-composition process took place in the period 2015–2017. This included restructuring of the data model and corresponding reporting templates; transformation of the legacy data (i.e. data reported in the past, for the period up until and including 2012); re-definition of specific data fields, such as aggregation period defining the length of aggregation in a year; update of the datasets according to correspondence with national reporters; recodification of monitoring site codes across EIONET dataflows; and connection of the legacy data time series with the newly-reported data in restructured reporting templates. Still, suspicious values or time series are sometimes detected and the automatic QC routines exclude some of the data. Through the communication with the reporting countries, the quality of the database can be further improved.
Using annual average values provides an overview of general trends and geographical patterns in line with the aim of the indicator. However, the severity of shorter-term, high-nutrient periods will not be reflected.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/nutrients-in-freshwater/nutrients-in-freshwater-assessment-published or scan the QR code.
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