Rivers are slow to recover from nutrient overload
In recent years, strict legislation was introduced to control the amount of nitrate and phosphate that runs into the sea from European rivers. However, new research reveals that water quality has not improved as much as expected. Policymakers need to take into account a time lag in the system that could be up to 40 years, say the researchers.
Excess nutrients can cause an unnatural algae ‘bloom’, stripping oxygen from water and reducing populations of fish and other animals. Controlling discharge of nutrients from human sources, including agricultural fertilisers and 1-3 wastewater, has been a key aspect of EU environmental legislation . However, very few long-term studies exist at the European level to assess how effective these regulations have been in improving the quality of freshwater discharged into the sea. In the new study, scientists used several global databases to estimate nutrient input to all river basins that drain into European seas. To investigate the connection between nutrient input and water quality, the scientists compared the total change in nutrient input from 1990 to 2005 with measurements of nitrate and phosphate from 39 European river outlets (data reported annually by member states of the OECD). The results revealed that nitrate pressure for the EU-15 Member States has fallen by 32% since 1990, thanks mainly to a reduction of 13% in fertiliser use. Wastewater input has remained fairly stable overall, although differences exist between countries. Phosphate input has also declined, but this is because over the years it has accumulated in soils meaning that farmers apply less phosphate fertiliser, rather than the result of environmental legislation. In total, 30% of the OECD monitoring stations demonstrated a decrease in nitrate concentration and there was an increase for 10%.
