De Zoetermeerse Plas (Noord Aa) is a recreational area in Zoetermeer, The Netherlands. In addition to being utilized for recreation, the lake retains water from nearby reclaimed land. As a result, the lake would see blue-green algal blooms in the summer, resulting in the lake’s closure to swimming during the busy season.
In efforts to reduce blue-green algae blooms, the Zoetermeer Municipality, in partnership with the Rijnland Waterboard, deployed five MPC-Buoy units in Spring 2016 to monitor, predict and prevent excessive algae growth. Key water quality and algae metrics are monitored by the units, enabling a water body’s unique circumstances to be used to emit ultrasound at precise frequencies.
Steep reductions in algae concentrations
The initial 2-year pilot project at the Noord Aa concluded in 2018. Treatment activities were resumed in 2020 following an evaluation of the LG Sonic MPC-Buoys by the Zoetermeer Municipality. The buoys kept an eye on the lake’s water quality and algal growth. Algal concentrations were dramatically reduced in 2021, according to data from the water quality monitoring program MPC-Buoy. Summertime phycocyanin (a pigment found in blue-green algae) concentrations were 90% lower than in 2020.
The Rijnland Waterboard hired the research organization Ecofide to do fieldwork in the Noord Aa in 2021 to look at the impact of ultrasonography on zooplankton. Researchers found no evidence of the potentially harmful effects of the ultrasonic soundwaves emitted on the zooplankton due to the study. This conclusion is consistent with the outcomes of a related field study conducted in 2017 at the Noord Aa.