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Indicator Assessment
Concentrations of biochemical oxygen demand (BOD) and ammonium have markedly decreased in European rivers in the period 1992 to 2012, mainly due to a general improvement in waste water treatment.
Similarly, concentrations of phosphate in European rivers more than halved over the period 1992 to 2012. The decrease in river orthophosphate is due to the measures introduced by national and European legislation, in particular the Urban Waste Water Treatment Directive, which involves the removal of nutrients. Also the change to the use of phosphate-free detergents has contributed to lower phosphorus concentrations.
River nitrate concentrations have declined steadily from 2.7 to 2.1 mg N/l over the period 1992 to 2012. Agriculture is the largest contributor of nitrogen pollution, and due to the EU Nitrate Directive and national measures, the nitrogen pollution from agriculture has been reduced and this is reflected in lower river nitrate concentrations.
More than half of the river and lake water bodies in Europe are reported to be in less than good ecological status or potential, and will need mitigation and/or restoration measures to meet the Water Framework Directive objective of all water bodies having good status by 2015.
Biochemical oxygen demand (BOD) and ammonium are key indicators of organic pollution in water. BOD shows how much dissolved oxygen is needed for the 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, high concentrations of ammonia and the disappearance of fish and aquatic invertebrates. Some of the year-to-year variation can be explained by variations in precipitation and runoff.
The most important sources of organic waste load are: household wastewater; industries such as the paper or food processing industry; and silage effluents and manure from agriculture. Increased industrial and agricultural production in most European countries after the 1940s, coupled with a greater share of population being connected to sewerage systems, initially resulted in increases in the discharge of organic waste into surface water. Over the past 20 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.
In European rivers, the concentrations of oxygen demanding substances (BOD) have been decreasing throughout the period 1992 to 2012, in total, BOD concentration decreased by 1.6 mg/l from 1992 to 2012 (reduction of 2.9% per year). A significant decrease is evident at 62% of the more than 500 river stations, with an additional 6% of stations showing a marginally decreasing trend. On the other hand, a significantly increasing BOD trend has been recorded at just 3% of stations, with marginally increasing BOD at an additional 1% of stations.
Over the 21 years from 1992 to 2012, the average ammonium concentration in European rivers decreased by 231 µg N/l. The average yearly decrease is 11.6 µg N/l (-3.5% per year). A significantly decreasing concentration trend has been observed at 59% of the stations, with an additional 5% of stations showing a marginally decreasing trend, and only a few river stations showing an increasing ammonium concentration over the period 1992 to 2012.
The decrease is mainly due to improved sewage treatment resulting from the implementation of the Urban Waste Water Treatment Directive and national legislation. 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.
Further information is available in the Oxygen consuming substances in rivers (CSI 019/WAT 002) indicator.
Large inputs of nitrogen and phosphorus to water bodies from urban areas, industry and agricultural areas can lead to eutrophication. This causes ecological changes that can result in a loss of plant and animal species (reduction in ecological status) and have negative impacts on the use of water for human consumption and other purposes.
Average concentrations of orthophosphate in European rivers have decreased markedly since 1992. At 52% of the river stations there has been a decline in orthophosphate concentration since 1992, while there has been an increase at only 9% of the stations. For lakes there has been a decline in total phosphorus concentrations since 1992 at 40% of the stations, while there has been an increase at 14% of the stations. This decrease reflects the success of legislative measures to reduce emissions of phosphorus such as those required by the Urban Waste Water Treatment Directive (UWWTD) and a reduction in the phosphate content of detergents.
At European level, river nitrate concentrations have declined steadily over the period 1992 to 2012. The trend is the same for the time period 2000 to 2012. Overall, there has been a decrease in river nitrate concentrations at 44% of the stations, while there has been an increase at 13% of the stations. Agriculture is the largest contributor of nitrogen pollution and, as a result of the EU Nitrate Directive and national measures, nitrogen pollution from agriculture has been reduced. This is reflected in lower river nitrate concentrations.
Further information is available in the Nutrients in freshwater (CSI 020/WAT 003) indicator.
Ecological status or potential is an expression of the quality of the structure and functioning of surface water ecosystems. The main objective of the Water Framework Directive (WFD) states that all surface waters should be in good or high ecological status by 2015. The current status classification is the baseline from which the improvements objective of the WFD is measured. Overall, more than half of the total number of classified river and lake water bodies in Europe are reported to have less than good ecological status/potential. All these water bodies, therefore, need management measures to restore their ecological status or potential to fulfil the WFD objective. The number and percentage of water bodies in less than good ecological status or potential in different water categories is as follows (see also Fig. 2) rivers: 51 300 (56%) and lakes: 6 500 (44%).
The main reason that lakes are in a better condition than rivers is that about two thirds of the reported lake water bodies are in Sweden and Finland, where the population density and agricultural pressure is relatively low. However, lakes are also generally reported to have better status than rivers within EU Member States. The worst ecological status or potential in river and lake water bodies are reported in north-western Europe such as River Basin Districts (RBDs) in Northern Germany, the Netherlands and Belgium (Flanders), where more than 90% are reported to be in less than good ecological status or potential. Other problem areas are in Poland, southern Germany, Czech Republic, southern England, northern France and Hungary, as well as several single RBDs in other Member States, where 70-90% of freshwater bodies are reported to be in less than good status or potential.
The pressures reported to affect most surface water bodies are pollution from diffuse sources, in particular agriculture, causing nutrient enrichment. Hydromorphological pressures also affect many surface water bodies resulting in altered habitats.
Further information on the state of Europe's freshwater can be found in SOER2015 Freshwater quality and SOER2015 Hydrological systems and sustainable water management.
This indicator shows:
1. Annual median concentrations in rivers of Biological Oxygen Demand (BOD) and ammonium (NH4).
2. Trends in concentrations of orthophosphate and nitrate in rivers.
3. Ecological status of river and lake water bodies.
The concentration of nitrate is expressed as mg nitrate-nitrogen (mg NO3-N/l) for rivers and orthophosphate as mg P/l.
The annual average BOD after five or seven days incubation (BOD5/BOD7) is expressed in mg O2/l and the annual average total ammonium concentration is expressed in micrograms N/l.
The ecological status or potential is presented as a percentage of the total classified water bodies by count.
Ammonium concentrations are normally raised as a result of organic pollution, caused by discharges from waste water treatment plants, industrial effluents and agricultural runoff. Ammonium exerts a demand on oxygen in water since it is transformed to oxidised forms of nitrogen. In addition, it is toxic to aquatic life at certain concentrations dependent on water temperature, salinity and pH. Background concentrations of ammonium are around 15 μg/l (as N) (Meybeck, 1982, quoted in EEA, 1999).
BOD is a key indicator of the oxygenation status of water bodies. BOD is the oxygen demand brought about by organisms in water and sediment acting on oxidisable organic matter. In most European countries, the BOD5 test is used where oxygen consumption is measured after five days incubation under controlled conditions. In other, mainly northern Europe countries, the BOD7 test is used where samples are incubated for seven days. High BOD is usually a result of organic pollution, caused by discharges from wastewater treatment plants, industrial effluents and agricultural runoff. A high BOD has several effects on the aquatic environment including reducing river water chemical and biological quality, reducing the biodiversity of aquatic communities and reducing the microbiological quality of waters. Background levels are difficult to quantify and are likely to be at or below the detection limit of the analytical method used, i.e. between 1 and 2 mg O2/l.
Large inputs of nitrogen and phosphorus to water bodies can lead to eutrophication causing ecological changes that result in a loss of plant and animal species (reduction in biodiversity and ecological status), and have negative impacts on the use of water for human consumption and other purposes.
There are a number of EU Directives aimed at reducing the loads and impacts of organic matter. These include:
Ecological status and potential, as reported in the first river basin management plans, are related to the Water Framework Directive (WFD). The WFD came into force on 22 December 2000, and according to the directive, the first river basin management plans should be published, at the latest, nine years after the directive entered into force. There are, however, serious delays in some parts of the EU and in some Member States consultations are still on-going.
The indicator is directly linked to the objective of the WFD. The main objective of the WFD states that all surface waters should be in good or high ecological status or potential by 2015, or 15 years after entry into force of the directive. The indicator shows the number of water bodies where management measures are needed, and for which water categories and in which regions the need for measures is highest.
Ammonium, BOD, N and P concentrations indicate water quality. If concentrations are high, quality goes down, threatening aquatic biodiversity and reducing the integrity of the ecosystem and its capacity to deliver ecosystem services.
Enrichment of water bodies with organic matter can lead to oxygen depletion and changes in the trophic structure and functioning of aquatic ecosystems. Until the WFD establishes reference conditions and good status for water bodies - including for water bodies impacted by organic matter discharges, type-specific concentrations equivalent to good ecological status - it will not be possible to relate the indicator to specific impacts on ecological status or biodiversity. However, with decreasing concentrations of oxygen consuming substances and nutrient concentrations it can be assumed in general that the water quality of water bodies is improving and by association aquatic life will benefit.
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.
The data in Waterbase is collected through the Eionet-Water process and is therefore a sub-sample of the national data assembled for the purpose of providing comparable indicators of pressures, state and impact of waters on a Europe-wide scale. The data sets are not intended for assessing compliance with any European Directive or any other legal instrument.
A detailed description of the methodology can be found in the specification sheets for EEA core set indicators 019 'Oxygen consuming substances in Rivers' (http://ims.eionet.europa.eu/IMS/ISpecs/ISpecification20041007131940/full_spec) and 020 'Nutrients in freshwater' (http://ims.eionet.europa.eu/IMS/ISpecs/ISpecification20041007131957/full_spec), as well as in: http://www.eea.europa.eu/data-and-maps/indicators/freshwater-quality/freshwater-quality-assessment-published-may-2
see 'Methodology for indicator calculation'
No methodology references available.
No uncertainty has been specified
No uncertainty has been specified
MAIN DISADVANTAGES IN THE INDICATOR
ANALYSIS OF OPTIONS
This indicator has been adopted as an EEA core set indicator. The information basis for the indicator and the assessments possible will improve in time as the WFD assessments are implemented by Member States.
This indicator was selected for the Headline Indicator instead of other globally available indicators (e.g. as used in UNEP GEMS/water), because the EEA core set indicators contain detailed data for a substantial number of European countries.
For references, please go to https://www.eea.europa.eu/data-and-maps/indicators/freshwater-quality/freshwater-quality-assessment-published-may-2 or scan the QR code.
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