Oxygen consuming substances in rivers
Concentrations of biochemical oxygen demand (BOD) and total ammonium have decreased in European rivers in the period 1992 to 2012 (Fig. 1), mainly due to general improvement in waste water treatment.
Is organic matter and ammonium pollution of rivers decreasing?
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 concentration of ammonia and disappearance of fish and aquatic invertebrates. Some of the year-to-year variation can be explained by variation in precipitation and runoff.
The most important sources of organic waste load are: household wastewater; industries, such as paper or food processing; 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 the population connected to sewerage systems, initially resulted in increases in the discharge of organic waste into surface water. 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.
Present concentrations per country
See the WISE interactive maps for information displayed by countries on BOD in rivers and ammonium in rivers
In 2012 (or the latest reported year), countries with an average BOD concentration in the lowest category (less than 1.4 mg/l) are Slovenia (1.0 mg/l), the United Kingdom (1.2 mg/l), France (1.3 mg/l) and Ireland (1.4 mg/l).
In 2012 (or the latest reported year), countries with an average ammonium concentration in the lowest category (less than 40 µg/l) are Norway (11 µg/l), Finland (26 µg/l), the United Kingdom (32 µg/l), Sweden (39 µg/l), Slovenia (40 µg/l) and Ireland (40 µg/l).
Overall trend in BOD and total ammonium
In European rivers, oxygen demanding substances have been decreasing throughout the period 1992 to 2012 (Figure 2). Total BOD concentration decreased by 1.6 mg/l from 1992 to 2012. By using the filter in figure 2 the river BOD trends for the individual co