Nutrients in freshwater (CSI 020) - Assessment published Dec 2010

Indicator definition

Concentrations of orthophosphate 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.

Units

The concentration of nitrate is expressed as mg nitrate (NO₃)/l for groundwater and mg nitrate-nitrogen(mg NO3-N)/l for rivers and orthophosphate and total phosphorus as mg P/l.

Policy context and targets

Context description

The indicator is not directly related to a specific policy target. The environmental quality of freshwaters with respect to eutrophication and nutrient concentrations is however 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 Integrated Pollution Prevention and Control Directive (96/61/EEC) aimed at controlling and preventing pollution of water from industry, and the Water Framework Directive which requires the achievement of good ecological status or good ecological potential of rivers across the EU by 2015. The Water Framework Directive also requires the achievement of good groundwater status by 2015 and also 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/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 of age. Groundwater is a very important source of drinking water in many countries and is often used untreated, particularly from private wells.

One key approach of the Sixth Environment Action Programme of the European Community 2001-2010 is to 'integrate environmental concerns into all relevant policy areas' which could result in a more intense consideration of applying agri-environmental measures to reduce nutrient pollution of the aquatic environment (e.g. in the Common Agricultural Policy).

Targets

The 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:

-         Drinking Water Directive (98/ 83/EC) maximum allowable concentration for nitrate of 50 mg/l.

-         Surface Water for Drinking Directive (75/440/EEC). guideline concentration for nitrate of 25 mg/l

-         Nitrates Directive (91/676/EEC) requires the identification of groundwater sites/bodies where annual average nitrate concentrations exceed or could exceed 50 mg NO₃/l.

-         Urban Waste Water Treatment Directive (91/71/EEC) aims to decrease organic pollution

Related policy documents

• COM (2001) 31 final. Environment 2010.
  Environment 2010: Our future, our choice, 6th Environmental Action Programme, Communication from the Commission to the Council, the European Parliament, the Economic and Social Committee and the Committee of the Regions. COM (2001) 31 final.
• Council Directive (91/271/EEC) of 21 May 1991
  Council Directive of 21 May 1991 concerning urban waste water treatment (91/271/EEC)
• Council Directive (91/676/EEC) 12 December 1991
  Council Directive of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources (91/676/EEC).
• Council Directive 75/440/EEC
  Council Directive 75/440/EEC of 16 June 1975 concerning the quality required of surface water intended for the abstraction of drinking water in the Member States
• Council Directive 96/61/EC (IPPC)
  Council Directive 96/61/EC of 24 September 1996 concerning Integrated Pollution Prevention and Control (IPPC). Official Journal L 257.
• Council Directive 98/83/EC
  Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption
• Environmental Health Action Plan for Europe (EHAPE)
  WHO/Europe programme on environmental health policy.
• Water Framework Directive (WFD) 2000/60/EC
  Water Framework Directive (WFD) 2000/60/EC: Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy.

Methodology

Methodology for indicator calculation

Source of data (data handling part): The data in Waterbase are collected through the Eurowaternet process and are therefore sub-samples of national data assembled for the purpose of providing comparable indicators of pressures, state and impact of waters on a Europe-wide scale and 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.

Station selection: No criteria are used for station selection (except for time series and trend analysis; see below)

Determinants: The determinants selected for the indicator and extracted from Waterbase are:

• for groundwater, nitrate,
• for rivers, nitrate, total oxidised nitrogen and orthophosphate,
• for lakes, total phosphorus.

Mean: Annual mean concentrations are used in the present concentration and time series presentations. Countries are asked to substitute any sample results below the limit of detection (LOD) or limit of quantification (LOQ) by a value equivalent to half of the LOD or LOQ before calculating the station annual mean values. Average mean concentration values of zero or null are discarded from the calculations. 

For rivers where nitrate and total oxidised nitrogen (TON) are monitored at the same station and at the same time, nitrate values are given precedence. For stations where only TON is reported, these data are used instead of nitrate. Also, in cases where more years of data are available for TON than nitrate for a single station, the TON data are used. All values are labeled as nitrate in the graphs, but it is indicated in the graph notes for which countries TON data are used.  

Inter/extrapolation and consistent time series 

For time series and trend analyses, only series that are complete after inter/extrapolation (i.e. no missing values in the station data series) are used. This is to ensure that the aggregated data series are consistent, i.e. including the same stations throughout the time series. In this way assessments are based on actual changes in concentration, and not changes in the number of stations. For rivers and lakes “stations” in this context means individual monitoring stations. 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 stations, and in some cases the number of monitoring stations 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. 

Changes in methodology: Station 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 the stations was excluded by this criterion. To allow the use of a considerably larger part of the available data, it was in 2007 (i.e. when analysing data up until 2005) decided to include all time series with at least seven 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 rather to inter/extrapolate all gaps of missing values of 1-2 year for each station. At the beginning or end of the data series 1 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 two neighbouring 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 are replaced by the average of the two neighbouring values. Only time series with no missing years for the whole period 1992 after such inter/extrapolation are included in the assessment. This procedure increases the number of stations that can be included in the time series/trend analysis. Still, the number of stations is markedly reduced compared to the analysis of the present situation, where all available data can be used.

Aggregation of time series 

The selected time series (see above) must be aggregated into a smaller number of groups and averaged before the aggregated series can be displayed in a time series plot. Data for all determinands are grouped into five geographic regions of Europe, containing the following countries:

Eastern: CZ, EE, HU, LT, LV, PL, SI, SK. 

Northern: FI, IS, NO, SE. 

Southern: CY, ES, GR, IT, PT.

South-Eastern: AL, BA, BG, HR, ME, MK, RO, RS, TR, XK.

Western: AT, BE, CH, DE, DK, FR, IE, LI, LU, NL, UK.

Country codes

Some of the listed countries are not included in the figures because there were no stations with complete time series after inter/extrapolation.

Data for river determinants are in addition grouped into six sea region catchments, which are defined not by countries but by river basin districts. The data thus represents rivers or river basins draining into that particular sea. The sea regions are defined as Arctic Ocean, Greater North Sea, Celtic Seas, Bay of Biscay and the Iberian Coast, Baltic Sea, Black Sea and Mediterranean Sea. The sea region delineation is according to the Marine Strategy Framework Directive (MSFD) Article 4, with the Arctic Ocean added as a separate region. As the catchment area draining into what is defined as the North-East Atlantic region of the MSFD is very big, it was decided rather to use the sub-region level here, but merging the Celtic Seas and the Bay of Biscay and the Iberian Coast.

Determinants are also aggregated for the whole of Europe. 

Trend analyses

Trends are analysed by the Mann-Kendall method (McLeod 2005) in the free software R (R Development Core Team 2006). 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 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 ("strong trends"), while data series with p-value >= 0.05 and <0.10 are reported as marginally significant ("weak trends"). The test analyses only the direction and significance of the change, not the size of the change.

Present concentration distributions:

The latest year for which there are concentration data for the river and lake stations and groundwater bodies is selected for each country separately. The number of stations with annual mean concentrations occurring in the selected concentration classes are then calculated and presented. The allocation of a station to a particular class is based only on the face value concentration and not on the likely statistical distribution around the mean values.

• The class defining values for nitrate are based on typical background concentrations in the different water categories and the legislative standards (50 mg/l NO3) and guide values (25 mg/l NO3). 
• The class defining values for orthophosphate (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 concentrations of phosphorus in each country.

More information is given in the WISE maps, in the page http://www.eea.europa.eu/themes/water/interactive/water-live-maps/status-of-water-quality

Methodology for gap filling

No methodology for gap filling has been specified. Probably this info has been added together with indicator calculation.

Methodology references

• Hipel, K.W. and McLeod, A.I., (2005). Time Series Modelling of Water Resources and Environmental Systems Electronic reprint of our book orginally published in 1994.
• Mann, H.B. (1945), Nonparametric tests against trend Econometrica, 13, 245-259.
• McLeod, A.I. (2005). Kendall: Kendall rank correlation and Mann-Kendall trend test. R package version 2.0.
• R Development Core Team (2006). R: A language and environment for statistical computing.
• R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0

Uncertainties

Methodology uncertainty

Nitrate concentrations in groundwaters 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 evaluate the nitrate concentration in groundwater and its development, closely-related parameters such as ammonium and dissolved oxygen have to be taken into account. 

Data sets uncertainty

The data sets 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. Countries are asked to provide data on rivers and lakes and on important groundwater bodies according to specified criteria. These rivers, lakes and groundwater bodies are expected to be able to provide a general overview, based on truly comparable data, of river, lakes and groundwater quality at the European level. 

Rationale uncertainty

No uncertainty has been specified