Managing Eutrophic Waters in Artificial Recharge Plants : Cyanotoxin risk in Swedish freshwaters

Sammanfattning: In the last decades, the frequency and intensity of cyanobacterial blooms have been of increasing concern. They have become a direct threat to the drinking water supply by clogging filters, bringing odour and unpleasant taste to the treated water and worst of all, causing elevated cyanotoxins, which can be difficult to remove, yet lead to severe health issues. This thesis aims to present a comprehensive knowledge base and tools for water managers and operators to understand cyanobacterial risk in their water so that bloom problems can be prevented or mitigated. Firstly, an adaptive approach for cyanobacteria management in drinking water supply is proposed, starting with an overview of this problem and resulting in a conceptual management tool design, a Cyanobacteria Management Tool (CMT) by which multi-indicators for actions are provided. Secondly, the magnitude of this problem in Swedish freshwaters was studied both on a national and local scale, including their geographical distribution, species dynamics, bloom seasonal pattern and their connection with eutrophication status, land use, and other factors. Thirdly, the studyhighlights impact of nutrients on cyanobacteria formation, including testing twohypothesizes, 1) if Total Phosphorus (TP) can be used to predict cyanobacteria risk and 2) if the Dissolved Inorganic Nitrogen and Phosphorus ratio (DIN/TP) is a better indicator for cyanobacteria risk than TN/TP. The results were also verified by a fullscale on-site experiment study of pre-treating eutrophic water at a local water treatment plant. Lastly, cyanotoxin detection challenges and strategies are presented. The key findings are:• Local target levels for TP for preventing cyanobacterial blooms are possible to be assessed by applying quantile regression analysis;• DIN/TP is a better indicator than TN/TP in predicting high levels of cyanobacteria; high levels of cyanobacteria coincide with DIN/TP <10;• Most problematic lakes that experience intensive cyanobacterial blooms arelocated in southern Sweden; and the lakes are eutrophic or hypereutrophic due to intensive land use;• Clear seasonal patterns of cyanobacteria biomass and percentage in phytoplankton community can be derived by applying long-term series analysis. Analysis results show that regarding cyanobacteria risk, special attention should be paid in the months of May through November;• Cyanotoxin screening tools such as enzyme-linked immunosorbent assay (ELISA) or lateral flow immunoassay (LFA) are useful for early screening of certain toxins such as microcystins and saxitoxins; advanced analytical tools such as LC–MS/MS are required for the confirmation of toxin profiles.Research findings presented in this thesis can be used to update a locally based CMT and applied as a workflow for water operators to improve their monitoring routines and develop their strategies. Measures to control nutrients in freshwaters are necessary to protect our drinking waters from intensive cyanobacterial blooms.