The potential of assessing harmful algal bloom risks in Swedish raw water sources - A study of four Swedish drinking water sources

Abstract

Higher temperatures and extreme weather due to climate change are expected to increase algae growth in Swedish surface waters, potentially disrupting drinking water production through algal toxins or clogged filters. This project aimed to assess the risks associated with high algal biomass in Swedish surface waters, identify critical conditions that trigger harmful algal blooms, and explore effective strategies for how these risks can be managed. Four case studies (Lerum, Tjörn, Sotenäs, and Sandviken) and a literature review were conducted. The analysis found no correlation between selected parameters and algal blooms in the studied waters, although weather data indicated trends consistent with climate change. The limited raw water data likely influenced the results. It was concluded that municipal risk management for algal growth is inadequate. Improved monitoring, systematic sampling, and the use of daily measurements of pH, turbidity, and water temperature are recommended as indicators of algae growth. If changes in these indicators are detected, they should be followed by visual inspections. Additionally, more extensive measures, such as sampling total biomass or chlorophyll-a, can be used as more precise indicators of algae growth.