Balticsea 2020

Sedimentation ponds with limestone filters and a wetland area

One of the measures implemented within the program Living coast is to reduce the leaching of nutrients from agriculture. Effective measures on land are necessary to reduce eutrophication in the water. Sam Ekstrand, from WEREC, has led a sub-project to reduce nutrient leaching from the fields at Säbyviken in Stockholm archipelago by constructing settling ponds with lime filter closes to the farm.

Limestone filters and ponds
Säby farm currently grows cereals and previously kept livestock and fertilised the fields with manure. These fields account for much of the leaching into Säbyviken. To reduce the release of nutrients two small ponds with limestone filters has been installed.

The agricultural land at Säby farm is drained into ditches that flow into Säbyviken. In 2012 and 2013 WEREC Water Ecoystem Recovery AB built two phosphorus ponds with lime filter beds to separate phosphorus leaching from the under drains in the farm land. The ponds have been designed according to the policy for phosphorus pond at the Swedish Board of Agriculture, with a depth, a ground work and flat edges.

According to calculations the ponds will separate between 20 and 30% of the phosphorus transported from respective drainage to Säbyviken. The ponds also separate nitrogen. The water retention will be about two days at high flows and approximately 25 days at low flows. This means that at least 10% of the nitrogen in the water passing the facilities is separated. The estimates are based on measurements from other facilities in Sweden and from the project “VASTRA” (Mistra). During 2014-2016, the project will evaluate the effectiveness of the facilities at Saby farm.