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Oxygen consuming substances in rivers (CSI 019/WAT 002) - Assessment DRAFT created Sep 2013

Indicator Assessmentexpired Created 17 Sep 2013 Published 17 Sep 2013 Last modified 23 Feb 2015, 10:13 AM

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This indicator is updated by 2012 data reported by countries in autumn 2013. The next update will be based on 2013 and 2014 data to be reported by countries in autumn 2015.

 
Contents
 

Indicator definition

This indicator illustrates the current situation and trends regarding biochemical oxygen demand (BOD) and concentrations of total ammonium (NH4) in rivers. The key indicator for the oxygenation status of water bodies is BOD, which is the demand for oxygen resulting from organisms in water that consume oxidisable organic matter.

Units

Annual average BOD after 5 or 7 days incubation (BOD5/BOD7) is expressed in mg O2/l and annual average total ammonium concentrations in micrograms N/l.


Key policy question: Is organic matter and ammonium pollution of rivers decreasing?

Key messages

Concentrations of BOD and total ammonium have decreased in European rivers in the period 1992 to 2011 (Fig. 1), mainly due to general improvement in wastewater treatment.

See also WISE interactive maps: Mean annual BOD in rivers and Mean annual Total Ammonium in rivers

Biochemical Oxygen Demand (BOD5) and total ammonium concentrations in rivers between 1992 and 2011

Note: Concentrations are expressed as annual mean concentrations. Only complete series after inter/extrapolation are included (see indicator specification). The number of river monitoring stations included per country is given in metadata (see downloads and more info). BOD7 data has been recalculated into BOD5 data. If data on total ammonium are not available, data on ammonium are included into the data series.

Data source:
Downloads and more info

BOD5 concentrations in rivers between 1992 and 2011 in different geographical regions of Europe

Note: The data series per region are calculated as the average of the annual mean for river monitoring stations in the region. Only complete series after inter/extrapolation are included (see indicator specification). The number of river monitoring stations included per geographical region is given in parentheses. BOD7 data has been recalculated into BOD5 data.

Data source:
Downloads and more info

Total ammonium concentrations in rivers between 1992 and 2011 in different geographical regions of Europe

Note: The data series per region are calculated as the average of the annual mean for river monitoring stations in the region. Only complete series after inter/extrapolation are included (see indicator specification). The number of river monitoring stations included per geographical region is given in parentheses. If data on total ammonium are not available, data on ammonium are included into the data series.

Data source:
Downloads and more info

BOD5 concentrations in rivers between 1992 and 2011 draining to different sea regions of Europe

Note: The sea region data series are calculated as the average of annual mean data from river monitoring stations in each sea region. The data thus represents rivers or river basins draining into that particular sea. Only complete series after inter/extrapolation are included (see indicator specification). The number of river monitoring stations included per sea region is given in parentheses. There were no stations with consistent data series on BOD7 in rivers draining to the Arctic Ocean. BOD7 data has been recalculated into BOD5 data.

Data source:
Downloads and more info

Total ammonium concentrations in rivers between 1992 and 2011 draining to different sea regions of Europe

Note: The sea region data series are calculated as the average of annual mean data from river monitoring stations in each sea region. The data thus represents rivers or river basins draining into that particular sea. Only complete series after inter/extrapolation are included (see indicator specification). The number of river monitoring stations included per sea region is given in parentheses. If data on total ammonium are not available, data on ammonium are included into the data series.

Data source:
Downloads and more info

Key assessment

Introduction

Biochemical Oxygen Demand (BOD) and total ammonium, are key indicators of organic pollution in water. BOD shows how much dissolved oxygen is needed for decomposition of organic matter present in water. Concentrations of these parameters normally increase as a result of organic pollution caused by discharges from waste water treatment plants, industrial effluents and agricultural run-off. Severe organic pollution may lead to rapid de-oxygenation of river water, a high concentration of ammonia and the disappearance of fish and aquatic invertebrates.

The most important sources of organic waste load are: household wastewater; industries such as paper industries or food processing industries; and silage effluents and manure from agriculture. Increased industrial and agricultural production, coupled with a greater percentage of the population being connected to sewerage systems, initially resulted in increases in the discharge of organic waste into surface water in most European countries after the 1940s. Over the past 15 to 30 years, however, the biological treatment (secondary treatment) of waste water has increased, and organic discharges have consequently decreased throughout Europe. See also CSI 024: Urban waste water treatment.

Overall trend in BOD and total ammonium (Fig. 1)

In European rivers, the oxygen demanding substances measured as BOD and total ammonium have decreased by 53 % (from 4.0 mg/l to 1.9 mg O2/l) and 75 % (from 473 to 119 µg N/l), respectively, from 1992 to 2011 (Fig. 1). The decrease is due mainly to improved sewage treatment resulting from the implementation of the Urban Wastewater Treatment Directive and national legislations. The economic downturn of the 1990s in central and eastern European countries also contributed to this fall, as there is an ongoing decline in pollution from manufacturing industries. This suggests that either further improvement in wastewater treatment is required or that other sources of organic pollution, for example from agriculture, require greater attention, or both.

Overall there has been a significant decrease in BOD concentrations at 60.1 % of the river stations (an additional 5.6 % marginally significant) between 1992 and 2011, while there has been a significant increase at only 3.3 % of the stations (an additional 0.7 % marginally significant). Similarly, there has been a significant decrease in total ammonium concentrations at 55.0 % of the stations (an additional 6.8 % marginally significant), while there has been a significant increase at only 2.3 % of the stations (an additional 1.1 % marginally significant).

BOD and total ammonium time series and trends per geographical regions (Fig. 2 and Fig. 3)

The largest proportion of monitoring stations with significant or marginally significant negative trend in BOD is found for the western and the southern European rivers, while the lowest proportion is found for the northern European rivers. Based on the sum of significant and marginally significant trends, the trends for the rivers in different geographic regions are:

  • West: 74.7 % negative, 0.9 % positive, and 1.52 mg O2/l average decrease;
  • South: 76.1 % negative, 0 % positive, and 3.99 mg O2/l average decrease;
  • East: 55.5 % negative, 9.5 % positive, and 1.14 mg O2/l average decrease;
  • Southeast: 52.1 % negative, 5.2 % positive, and 2.28 mg O2/l average decrease;
  • North: 46.7 % negative, 6.7 % positive, and 0.19 mg O2/l average decrease.


Countries with more than 60 % of the stations with negative trend in BOD are Austria, Bulgaria, the Czech Republic, Denmark, France, Ireland, Luxembourg, Slovakia, Slovenia, Spain and the United Kingdom.

The decrease of total ammonium from 1992 to 2011 is the largest in the southern (82 %) and eastern European rivers (78 %), closely followed by the decrease in the western European (75 %) and southeastern European rivers (74 %) (Fig. 3).

The concentrations in Eastern European rivers, as assessed for the period 1992-2011 (around 80 µg N/l), are significantly lower than those in the previous assessment (made in 2012, for the period 1992-2010: around 200 µg N/l). The reason is that in 1992-2010 assessment data for 96 monitoring stations in Poland were included, whereas in 1992-2011 assessment, only four stations in Poland are included. Monitoring stations in Poland had an important impact on the assessment of indicator for the Eastern European geographical region as a whole. The same difference can be observed for the South European region due to larger number of river monitoring stations in Spain included in the assessment, which are at the same time the only stations representing South European region (82 % decrease in 1992-2011 period, compared to 20 % decrease in 1992-2010 period). Southeastern and western European rivers also saw significant decrease in total ammonium concentrations (both around 75 %), however southeastern European rivers still have the highest total ammonium concentrations in Europe (around 300 µg N/l).

The largest proportion of monitoring stations with significant or marginally significant negative trend in total ammoniumis found for the western and southeastern European rivers, while the lowest proportion is found for the northern European rivers as follows (sum of significant and marginally significant trends):

  • West: 76.3 % negative, 2.4 % positive, 296 µg N/l average decrease through the whole period;
  • East: 64.2 % negative, 0.8 % positive, 201 µg N/l average decrease; 
  • Southeast: 74.2 % negative, 3.4 % positive, 785 µg N/l average decrease; 
  • South: 52.1 % negative, 0 % positive, 384 µg N/l average decrease; 
  • North: 30.5 % negative, 8.4 % positive, 10 µg N/l average decrease.


Countries with more than 60 % of the stations with negative trend in total ammonium are the former Yugoslav Republic of Macedonia, Slovenia, the United Kingdom, Germany, Lithuania, Ireland, Poland, Bulgaria, France, Austria, Luxembourg, Belgium and Norway.

BOD and total ammonium time series and trends per sea regions (Fig. 4 and Fig. 5)

The largest decrease of BOD from 1992 to 2011 has occurred in the rivers draining to the  Mediterranean Sea (63 %), resulting in the lowest concentrations in Europe  The lowest concentrations (about 1.6 mg O2/l) were found in the Mediterranean sea and Celtic Seas, Bay of Biscay and Iberian Coast sea region (Fig. 4). Due to ongoing decrease, the concentrations in these rivers have become lower than the concentrations in the Baltic Sea region, which remain fairly stable (about 1.8 mg O2/l). The second highest decrease of BOD has occurred in the rivers draining to the Black Sea (60 %). Even though still the highest among all sea regions, their concentrations (about 2.3 mg O2/l) have approached the average European concentrations . Similarly high, but also decreasing are the rivers of Greater North Sea (about 2.2 mg O2/l).. The decrease of BOD is 40 % for the rivers draining to the Greater North Sea and 58 % for the rivers draining to the Celtic Seas, the Bay of Biscay and the Iberian Coast.

The trend analysis also shows that the largest proportion of monitoring stations with significant or marginally significant negative trend in BOD is found for the rivers draining to the Mediterranean and the Black sea, while the lowest proportion is found for the rivers draining to the Celtic Seas, the Bay of Biscay and the Iberian Coast, and the Baltic Sea. The sums of significant and marginally significant trends are as follows:

  • Mediterranean Sea: 75.4 % negative, 2.9 % positive, 2.66 mg O2/l average decrease;
  • Black Sea: 78.2 % negative, 0 % positive, 2.46 mg O2/l average ;
  • Greater North Sea: 66.9 % negative, 3.7 % positive, 1.5 mg O2/l average decrease;
  • Celtic Seas, Bay of Biscay, Iberian Coast: 63.6 % negative, 0.8 % positive, 1.62 mg O2/l average decrease;
  • Baltic Sea: 43.2 % negative, 12.2 % positive, 0.48 mg O2/l average decrease.


Concentrations in rivers draining to different sea are the largest in the Greater North Sea (158 µg N/l) and the Black Sea regions (158 µg N/l). Somewhat smaller are concentrations in Mediterranean Sea (122 µg N/l) and Celtic Seas, Bay of Biscay and Iberian Coast regions (109 µg N/l). The Baltic Sea region has a lower record of 59 µg N/l. The lowest decrease has occurred in the rivers draining to the Arctic Ocean (45 %) with very low concentrations (about 5 µg N/l).

The decrease of total ammonium from 1992 to 2011 has been similar (70-80 %) in all sea regions except for Arctic Ocean (45 %). The largest proportion of monitoring stations with significant or marginally significant negative trend in total ammonium is found for the rivers draining to the Black Sea, Celtic Seas, Bay of Biscay and Iberian Coast, Greater North Sea, while the lowest proportion is found for the rivers draining to the Arctic Ocean (Black Sea: 80.6 % negative, 1 % positive; Celtic Seas, Bay of Biscay, Iberian Coast: 74.8 % negative, 0.8 % positive; Greater North Sea: 68.8 % negative, 2.8 % positive; Mediterranean Sea: 57.7 % negative, 4.2 % positive; Baltic Sea: 45.6 % negative, 5.3 % positive; Arctic Ocean: 38.5 % negative, 7.7 % positive; sum of significant and marginally significant trends).

BOD and total ammonium present concentrations by countries
See WISE interactive maps for information displayed for countries, for river basin districts (BOD) and for individual stations: Mean annual BOD in rivers and Mean annual Total Ammonium in rivers

Countries with more than 50 % of all river stations within the category of the lowest BOD concentrations (class 1: < 1.4 mg O2/l) for 2011 or the latest reported year are Slovenia, Spain, Cyprus, Ireland, France, the United Kingdom and Finland.  Countries with more than 20 % of the stations within the category of the highest BOD concentrations (class 5: >= 4 mg O2/l) are Turkey, Montenegro, Albania, the Former Yugoslav Republic of Macedonia, Greece, Kosovo under UNSCR 1244/99, Hungary and Romania.

Countries with more than 50 % of all river stations within the category of the lowest total ammonium concentrations (class 1: < 0.04 mg N/l) for 2011 or the latest reported year are Iceland, Norway, Finland, Ireland, Austria, Slovenia, Sweden, Latvia, Spain, France, the United Kingdom, Lichtenstein and Croatia. Countries with more than 20 % of the stations within the category of the highest total ammonium concentrations (class 5: >= 0.4 mg N/l) are Kosovo under UNSCR 1244/99, the Netherlands, Montenegro, Belgium, Albania, Luxembourg, Greece, Romania, the Former Yugoslav Republic of Macedonia and Bulgaria.

Data sources

Policy context and targets

Context description

There are a number of EU directives that aim to improve water quality and reduce the loads and impacts of organic matter. First, the Water Framework Directive requires the achievement of good ecological status or good ecological potential of rivers across the EU by 2015 and repeals, step-by-step, several older water related directives. Alongside this, the following directives stay in place: the Nitrates Directive (91/676/EEC), aimed at reducing nitrate and organic matter pollution from agricultural land, the Urban Waste Water Treatment Directive (91/271/EEC), aimed at reducing pollution from sewage treatment works and certain industries (see also CSI24 Urban waste water treatment) and the Integrated Pollution Prevention and Control Directive (96/61/EEC) aimed at controlling and preventing the pollution of water by industry.

Targets

The indicator is not directly related to a specific policy target but shows the efficiency of wastewater treatment (see CSI024). The environmental quality of surface waters with respect to organic pollution and ammonium and the reduction of the loads and impacts of these pollutants are, however, objectives of several directives, including the Surface Water for Drinking Directive (75/440/EEC), which sets standards for the BOD and ammonium content of drinking water, as well as other directives mentioned in the previous chapter.

Related policy documents

Methodology

Methodology for indicator calculation

Data source: Data on rivers is collected annually through the WISE-SoE data collection process. WISE SoE was previously known as EUROWATERNET (EWN) and EIONET-Water. Biological quality elements in rivers have been integrated into the reporting of river water quality, starting from the 2012 reporting period. A formal request is sent to NFPs and NRCs every year with reference to templates to use and guidelines.

The data requested on rivers includes the physical characteristics of the river monitoring stations, proxy pressures on the upstream catchment areas, as well as chemical quality data on nutrients and organic matter, and hazardous substances in rivers. It also includes the biological data (primarily calculated as national Ecological Quality Ratios), as well as information on the national classification systems for each Biological Quality Element and waterbody type. This reporting obligation is an EIONET Priority Data flow.

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 BOD5, BOD7, total ammonium and ammonium.

Most countries monitor BOD5. Finland monitors BOD7. Lithuania monitored BOD5 up to 1995 and started monitoring BOD7 in 1996. Latvia monitored BOD7 from 1996 to 2001. Estonia monitored BOD5 in 2010, while it monitored BOD7 up to 2009. BOD is commonly used for BOD5. For countries reporting BOD7, these values have been converted to BOD5 (BOD7 = 1.16 BOD5) for reasons of comparability.

All countries reported total ammonium until 2006. In 2007, Greece and Liechtenstein started reporting ammonium instead of total ammonium. Instead of total ammonium, Cyprus, Lichtenstein and Slovenia began reporting ammonium in 2008, Austria and Netherlands in 2009, Bulgaria and Latvia in 2010, and Estonia, Norway and Poland in 2011.  Besides total ammonium, Slovakia also started to report ammonium for some stations in 2008. Belgium, Germany, Italy, Luxembourg, Slovakia and the United Kingdom report either ammonium or total ammonium for an individual station in a selected year from 2008 on. Data of either of the two determinants was included in the assessment. For those stations in Slovakia where both were reported, total ammonium data was included in the assessment.

All values are labeled as BOD5/total ammonium in the graphs, but it is indicated in the graph notes for which countries BOD7/ammonium data are used.

An automatic QA/QC procedure excludes data (stations*year) from further analysis. This is based on flagging in Waterbase, deriving from QA/QC tests. In addition a semi-manual QA procedure is applied, to identify outliers that are not identified in the QA/QC tests. This comprises e.g. values deviating strongly from the whole time series, values not so different from values in other parts of the time series, but deviating strongly from the values closest in time, consecutive values deviating strongly from the rest of the time series or whole data series deviating strongly in level compared to other data series in the country. If not explicitly confirmed valid by reporting countries, such values are flagged in Waterbase, but only excluded from the following year’s assessment due to timing issues. More details on the QA/QC procedure can be found here:

    • groundwater QA/QC description
    • rivers QA/QC description
    • lakes QA/QC description


Quality checked data: In the table on nutrients ("Waterbase_rivers_v12_Nutrients"), QA-fields are treated as follows:

      • Field "QA_MVissues": all flagged values are excluded from the indicator calculation, except for zero values (flag 103).
      • Field "QA_LRviolation": all flagged values are allowed, except for flagged values that break the rule “Mean >= Minimum” (flag 201) and “Mean <= Maximum” (flag 202). 
      • Field "QA_outlier": all flagged values are excluded from the indicator calculation, except for outliers confirmed by country (flags 491, 493).  
      • Field "QA_station_issues: all flagged values are allowed (including wrong coordinates or missing coordinates), except for "Water Category value is incompatible with this particular dataset” (flag 511) and “station is not defined in the station table" (flag 599).
      • Field "QA_CR violation": all flagged values are allowed.

Mean: Annual mean concentrations are used in the time series and present concentration graphics. Countries are asked to substitute any sample results below the limit of detection/determination by a value equivalent to half of the limit of detection/determination before calculating the station annual mean values. Mean concentration values of zero are included in the indicator calculation as zero (0).


Inter/extrapolation and consistent time series

For time series (Fig. 1-5) 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.

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, in 2007 (i.e. when analysing data up until 2005), it was 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 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 two years and by the average of the two neighbouring values for gaps of one year.

In 2010 this approach was modified, allowing for gaps of up to three years, both at the ends and in the middle of the data series. At the beginning or end of the data series up to three 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 one year and for the middle year in gaps of three 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 1992-2011 after such inter/extrapolation are included in the assessment. The number of gaps is unlimited, only gap length (size) of three years is defined. 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. In Figure 1, the two time series are used: 1992–2012 and 2000–2012.

Aggregation of time series

The selected time series (see above) must be aggregated in to a smaller number of groups and averaged, before the aggregated series can be displayed in a time series plot. Determinants are grouped into five geographical regions of Europe, which contain the following countries: 

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

Northern: FI, IS, NO, SE. 

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

(List of country codes can be found here )

Not all countries listed per region are included in the figures due to no data being reported or no stations with complete time series after inter/extrapolation. Due to changes in the monitoring network (adapting to monitoring networks under Water Directives) the time series are broken and limited number of time series is available for some countries. 

Determinants are in addition grouped into six sea region catchments, which are defined not by countries but by river basin districts or river basin district subunits if consistent with catchment areas of seas. 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 Ocean 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). The test was suggested by Mann (1945) and has been extensively used with 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 under the null hypothesis of no association is computed by in the case of no ties using an exact 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"). Data series with p-value >0.10 have no significant trend. The test is non-parametric which means that the amount of change from year to year is not considered, only the direction 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 unit (groundwater body/river station/lake station). This is summarised by calculating the average slope (regardless of the significance of the trend) for all units in Europe or a selected region. Multiplying this by the number of years of the time series gives an estimate of the absolute change over time. This can be related to the mean value of the aggregated time series to give a measure of relative change. 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.

Present concentration distributions

The latest year for which there are concentration data for the selected river stations are extracted from Waterbase. The number of stations with annual mean concentrations occurring in the selected concentration bands or 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 new/revised class defining values for BOD5 concentrations (mg O2/l): <1.4, 1.4 to 1.99, 2 to 2.99, 3 to 3.99, 4 to 4.99, >5. The two highest classes are merged to >4.
      • The new/revised class defining values for total ammonium concentrations (mg N/l): <0.04, 0.04 to 0.09, 0.1 to 0.19, 0.2 to 0.39, 0.4 to 0.99, >1. The two highest classes are merged to >0.4.

More information is given in the WISE maps on Water quality in rivers and lakes under section "Help": http://www.eea.europa.eu/themes/water/interactive/soe-rl (BOD in rivers, Total ammonium in rivers).

Methodology for gap filling

Methodology for gap filling is described under Inter/extrapolation and consistent time series

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 Core Team (2013). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.
  • Sen, Pranab Kumar (1968). "Estimates of the regression coefficient based on Kendall's tau", Journal of the American Statistical Association 63: 1379–1389
  • Theil, H. (1950). "A rank-invariant method of linear and polynomial regression analysis. I, II, III", Nederl. Akad. Wetensch., Proc. 53: 386–392, 521–525, 1397–1412

Uncertainties

Methodology uncertainty

The methodologies used for aggregating and testing trends in concentration are relatively robust and illustrate the overall European and regional trends. However, uncertainty may be included in evaluating single countries or river basins.

Data sets uncertainty

The data sets for rivers include almost all countries in the EEA area, but the time coverage varies from country to country. The data set provides a general overview of concentration levels and trends of organic matter and ammonia in European rivers. Most countries measure organic matter as BOD over five days but a few countries measure BOD over seven days, which may introduce a small uncertainty in comparisons between countries.

The river monitoring stations included in the assessment vary yearly due to availability of time series for the whole period starting from 1992. In the 2013 assessment, data for a significant number of stations was not reported. Conversely, some new stations were added, if the QA/QC procedure showed that stations reported under different names or codes could be treated as identical. This optimisation needs further quality checking. In the end, 702 stations were assessed in 2013 (compared to 849 stations in 2012) for BOD5 and 921 stations were assessed in 2013 (compared to 952 stations in 2012) for total ammonium.

Rationale uncertainty

Biochemical oxygen demand and total ammonium are well suited for illustrating water pollution with oxygen consumption. However, using annual average values may not fully illustrate the severity of low oxygen conditions.

More information about this indicator

See this indicator specification for more details.

Generic metadata

Topics:

Water Water (Primary topic)

Tags:
soer2010 | freshwater | csi | freshwater quality | bod5 | ammonium | water | thematic assessments | rivers
DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 019
  • WAT 002
Geographic coverage:

Contacts and ownership

EEA Contact Info

Peter Kristensen

Ownership

EEA Management Plan

2013 1.4.2 (note: EEA internal system)

Dates

Frequency of updates

Updates are scheduled once per year
European Environment Agency (EEA)
Kongens Nytorv 6
1050 Copenhagen K
Denmark
Phone: +45 3336 7100