Control of Cyanobacterial Blooms

Leaders: Petra Visser (University of Amsterdam) & Dedmer van de Waal (Netherlands Institute of Ecology)


In this session, we will focus on the variety of methods to prevent, control, or mitigate cyanobacteria. This will start at the basis: performing a lake system analysis to assess the ecological key factors. This can consist of a water balance and nutrient budgets, information regarding water level management, hydraulic residence time, and other lake specific properties. As eutrophication is one of the main drivers of cyanobacterial blooms, decreasing nutrient input from the catchment is crucial for long-term prevention or reduction of blooms. Eutrophication is mainly caused by diffuse nitrogen and phosphorus loads from agriculture, industry and domestic effluents and solutions need to address the entire catchment area. Although these measures can be very effective in reducing nutrient inputs to a lake, the response, in terms of reduced cyanobacteria, can be delayed and limited due to internal loading from legacy nutrients in the sediment.


To enhance recovery, or address lakes where external nutrient reduction is not feasible, there are a suite of in-lake methods, for example including sediment dredging, hypolimnetic aeration, hypolimnetic withdrawal or artificial mixing, or chemical lake restoration such as addition of modified clays where metal ions bind the phosphate, and addition of hydrogen peroxide to inhibit cyanobacterial growth. Ecosystem structure can also be manipulated (biomanipulation), by enhancing macrophytes, increasing predatory fish and reducing planktivorous fish.


In this session, we will address a selection of the available methods from lake system analyses regarding nutrient sources to in-lake mitigation of cyanobacterial blooms, highlighting the effects on cyanobacteria and other biota and the various pros and cons of the methods. Importantly, our aim is to discuss with the participants and a selection of invited speakers what science can contribute to increase our knowledge on the effects of various mitigation methods, how we can learn from mitigation of harmful algal blooms across systems (freshwater, marine), and how we can effectively share knowledge with water management and learn from each-others experiences, both within and across countries.

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