Ditch dams and filters to trap phosphorus in agriculture

Part of the nutrients in manure and fertilisers for plant production run off with rain water and leach through the soil to ditches and rivers and end up in lakes and seas. This so-called "diffuse leakage" is the largest source of algal blooms, oxygen depletion and dead zones in the Baltic Sea. This project seeks to bind phosphorus leaching from agricultural land in the ditch close to the source, thereby reducing the discharge of phosphorus to the sea.

The project is divided into two phases. Phase I concluded that up to 60 percent of phosphorus leaching from agricultural land and transported in the ditches can be caught in ditch filters and ditch dams. Lime-based filters were evaluated in full-scale experiments at three field stations in southern Sweden. The measurements have been going on far over two years. The results show that the filter takes up about 40-45 percent of the phosphorus and that they still work well after this time. An additional 15-20 percent of the phosphorus can be captured if the filters are combined with dams. The filter captures phosphate-phosphorus which otherwise would be readily available to plants and algae.

Furthermore, the study conclude that the technology is cost effective compared to other measures in Sweden, for example, constructed wetlands and buffer zones. These measures require more farm land and mainly capture particulate phosphorus which is less available to plants and algae.

During Phase II, which began in late 2011, the technology will be evaluated and demonstrated in Poland and the Baltic States, where soils and growing conditions are different compared to the Swedish situation. The filters from Phase I will also be studied further to test their endurance to bind phosphorus.

The objective of this project is to clarify the large-scale applicability of the technology in the Baltic Sea region, and the overall potential impact on emissions of phosphorus to the Baltic Sea. The knowledge will be disseminated to farmers and authorities in the region.

 

dikesdammar

Project status

Start: 2009-03-01
End: 2013-12-31

sam-ekstrand

Project manager

Sam Ekstrand, IVL