Source apportionment and loads (riverine and direct) of nutrients to coastal waters
Assessment made on 01 May 2004
ClassificationWater (Primary theme)
Coasts and seas
- WEU 007
Policy issue: Are discharges of organic substances and nutrients decreasing?
Discharges of both phosphorus and nitrogen from all quantified sources to the North Sea and Baltic Sea have decreased since the 1980s.
Agriculture is now the major source of nitrogen and phosphorus discharges into the North Sea, whereas for the Baltic Sea agriculture is the main source of nitrogen pollution and urban wastewater the main source of phosphorus pollution.
Data for the Black Sea are less comprehensive than for the Baltic and North Sea, but indicate that riverine discharges are the largest sources of nitrogen and phosphorus.
Comprehensive data is also not available for the Mediterranean but all coastal cities discharge their (treated or untreated) sewage to the sea and only 4 % have tertiary treatment, indicating that the nutrient input from this source maybe high. Agriculture is also intensive in the region and 80 rivers have been identified as contributing significantly to the pollution of the Mediterranean (EEA 1999).
There were significant reductions in phosphorus discharges to the North Sea from urban wastewater treatment works (UWWT), industry and other sources between 1985 and 2000. The reduction from agriculture has been less marked and this was also the largest source of discharges in 2000. Nitrogen discharges to the North Sea have decreased significantly from all four sources between 1985 and 2000 with agriculture being the major source in 2000. However, some countries, such as Norway, Sweden and UK, reported increases in riverine discharges (and direct discharges for the UK) of nitrogen to the North Sea between 1985 and 2000 whereas the other states reported reductions (North Sea Progress report 2002). Even though the data for the Baltic Sea are less recent (late 1980s to 1995) they give a similar picture for the North Sea with significant reductions in discharges of nitrogen and phosphorus from agriculture, UWWT, industry and aquaculture. In 1995, the major source of phosphorus and nitrogen to the Baltic Sea was UWWT and agriculture, respectively. Regarding point sources, the 50 % HELCOM reduction target was achieved for phosphorus by almost all the Baltic Sea countries, while most countries did not reach the target for nitrogen (HELCOM 2000, http://www.vyh.fi/eng/orginfo/publica/electro/fe524/fe524.htm ). Information relating to the Black Sea is less comprehensive in terms of source apportionment and how loads have changed with time. In 1996, the most significant sources of phosphorus and nitrogen to the Black Sea were riverine inputs. The major rivers in the Black Sea catchment are the Danube, Dnieper, Don, Southern Bug, and Kuban covering an area of around 2 million km2 and receiving wastewater from more than 100 million people, heavy industries and agriculture areas. The Danube contributes about 65 % of the total nitrogen and phosphorus discharges from all sources.
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