A recent scientific study published in Ecological Engineering, titled “Long-term water quality responses to sediment removal in a small, shallow, urban lake” provides new evidence that sediment removal can deliver long-lasting improvements in lake water quality. The research, led by Laura H. Härkönen together with Antti Taskinen, Olga Tammeorg and Anna-Lena Granlund-Blomfelt (University of Helsinki), examines the long-term ecological effects of sediment removal in Lake Gallträsk, offering valuable insights for lake restoration initiatives.

Eutrophication caused by excess nutrients, particularly phosphorus, remains one of the most pressing challenges for lakes across Europe. Phosphorus stored in lake sediments can continue to fuel algal blooms even after external nutrient inputs are reduced. Sediment removal, often carried out through dredging, is considered a promising restoration measure because it directly removes this internal nutrient source. However, evidence on the long-term effectiveness of such interventions has been limited.

The study focused on a restoration project carried out between 2009 and 2011 in Lake Gallträsk, a small and shallow urban lake in southern Finland. During this intervention, suction dredging was used to remove the upper 50-100 centimetres of sediment from approximately 18 percent of the lake’s surface area. The primary aim was to increase water depth for recreational purposes, but the operation also provided an opportunity to evaluate its ecological benefits.

Using long-term monitoring data collected both before and after the intervention, the researchers applied structural break and interrupted time series analyses to assess how the lake responded over time. The results showed a clear and significant reduction in phosphorus concentrations in the water column following sediment removal. This decline indicates that removing nutrient-rich sediments can effectively reduce internal phosphorus loading and support the recovery of lakes that have experienced long-term nutrient pollution.

The findings provide important evidence that sediment removal can act as an effective long-term restoration measure, particularly in small, shallow lakes where legacy phosphorus stored in sediments continues to drive eutrophication. For projects such as FERRO, which aim to support innovative approaches to lake restoration and nutrient management, these results contribute to a growing body of knowledge on how targeted interventions can accelerate ecological recovery and improve freshwater ecosystem health.