27 Oct, 2020

Eleven Years On and Highly Desirable Aquatic Plant Species Have Returned to Behlendorfer See, Germany

Nearly 11 years after being treated, the Behlendorfer See near the city of Lübeck in Northern Germany is still reaping the benefits of Phoslock.

The 63ha, 15m deep lake, which received a single treatment in 2009, had suffered from nutrient enrichment for many years from its predominantly agricultural catchment. As a result, the lake experienced regular blue-green algal blooms which led to a reduced aquatic plant community. Consequently, the lake was not meeting European legislation for ‘good ecological status’ outlined by the Water Framework Directive (WFD).

Several catchment management measures were initiated to help improve its water quality. However, the impact of years’ worth of nutrients entering the lake had taken its toll and the lake failed to recover due to ongoing release of phosphorus from the lake sediments, a process called internal loading. A Phoslock application of 214 tonnes was applied in in December 2009 to an area of approximately 40ha which was deeper than 7m.

“Highly desirable aquatic plant species have returned to the lake indicating “a very positive sign […] that the lake is improving ecologically.”

Since the application, the lake has been regularly monitored by the region’s State Office for Agriculture, Environment and Rural Areas (Landesamt für Landwirtschaft, Umwelt und ländliche Räume (LLUR)). Results from the official website for the lake show total phosphorus and phosphate concentrations have significantly declined since the application and remain low nearly 11 years later.

Indirect effects from the treatment have also been positive. For example, water transparency has increased and the algal community has shifted away from blue-green species. So much so, that Behlendorfer See’s WFD status for phytoplankton in 2019 was stated as “good” by the LLUR.

According to a recent report by lanaplan (2020) who assessed the Behlendorfer See’s WFD compliance in 2019 against previous years for aquatic plants, “a total of twelve species occurred, of which three are classified as endangered”. This is an increase of 3 new species since the application. Although the lake remains dominated by eutrophic plant species, charophyte species have been returned to the lake since the treatment. Charophytes are a highly desirable plant species and their return to the lake is a positive sign, showing that the lake is improving ecologically.

Source of information: Landesamt für Landwirtschaft, Umwelt und ländliche Räume (https://www.schleswig-holstein.de/)

lanaplan 2020. Monitoring the quality component of macrophytes for the WFD and Habitats Directive in Schleswig-Holstein lakes: vegetation of the Behelndorfer See, the Bültsee, the Garrensee, the Great Plöner See, Great Pönitzer See, Great Segeberger See, of the Ihlsee (Krs. Segeberd), the Kollsee, the Langsee (Kosel), the Pinnsee, of Schluensee, Suhrer See and Wittensee on behalf of the Landesamt für Landwirtschaft, Umwelt und ländliche Räume. P278.