High levels of nutrients, such as nitrogen and phosphorus, and subsequent eutrophication in coastal waters is a major concern of the Baltic Sea Action plan1, which has set reduction targets in nutrients to be met by 2021. In the last 15-20 years Estonia has experienced a number of changes which affect nutrient levels in rivers that feed into the Baltic Sea. A fall in agricultural production has reduced fertiliser use, the amount of arable land and the amount of livestock. Wastewater treatment plants have also become more effective.
The study, partly supported by the EU under the SCENES2 project, analysed the effects of these large-scale changes on nutrient concentrations in Estonian rivers that feed into the Baltic Sea to help identify possible options for controlling pollution. These could be useful in implementing river basin plans within the Water Framework Directive3.
Using data from the last 15-20 years, the study identified trends in the concentrations of nitrogen and phosphorus for 53 sampling sites on 40 rivers and streams. The results indicated that the concentration of nitrogen had decreased significantly at 18 of the sites, which included locations with a high share of agricultural land as well as locations with forests and wetlands. These reductions are thought to be due to decreases in agricultural land and fertilisers, increases in abandoned land and better farm management practices. Four sites experienced an increase in nitrogen which was thought to be due to a general increase in winter runoff, causing more nitrogen to be washed into the rivers.
There was a slightly different picture for phosphorus concentrations with a decrease at 13 sites and an increase at seven sites, but similarly, there was no clear pattern of land type. The researchers suggested the decrease could be explained by improvements in wastewater treatment in the larger cities, but also a decline in rural populations and better handling of manure and fertilisers. However, ineffective water treatment in smaller settlements could be the cause of phosphorous increases at the seven sites, along with the higher number of households and industries connected to the sewerage systems and insufficient maintenance of drainage systems.
The study indicated that the impacts of nutrients on water quality varied widely. The researchers suggest there is still a need for 'eco-engineering' solutions to improve the retention and removal of nutrients in the soil and groundwater. For example, the natural processes of removing nitrogen and phosphorus could be improved using artificial wetlands and detention ponds to prevent the nutrients from reaching the rivers.
- See: http://www.helcom.fi/BSAP/en_GB/intro/
- SCENES: Water Scenarios for Europe and for Neighbouring States was supported by the European Commission under the Sixth Framework Programme. See: www.environment.fi/syke/scenes
- See: http://ec.europa.eu/environment/water/water-framework/index_en.html
Source: Iital, A., Pachel, K., Loigu, E. et al. (2009). Recent trends in nutrient concentrations in Estonian rivers as a response to large-scale changes in land-use intensity and life-styles. Journal of Environmental Monitoring. 12:178-188.