Nutrient Control to Prevent the Occurrence of Cyanobacterial Blooms in a Eutrophic Lake in Southern Sweden, Used for Drinking Water Supply

Control of nutrients, mainly nitrogen (N) and phosphorus (P), plays a significant role in preventing cyanobacterial blooms (harmful algal blooms (HABs)). This study aims at evaluating changes in the risk of the occurrence of cyanobacterial blooms and advancing the understanding of how nitrogen and phosphorus affect the growth of cyanobacteria in a eutrophic lake, Lake Vombsjön, in southern Sweden. Our results show that TP (total phosphorus) has stronger positive correlation with cyanobacteria biomass than DIP (dissolved inorganic phosphorus); DIN (dissolved inorganic nitrogen) has a stronger negative correlation with cyanobacteria biomass than TN (total nitrogen); and DIN:TP has a stronger negative correlation with cyanobacteria biomass than TN:TP. The highest amount of cyanobacteria biomass, above WHO (World Health Organization) Alert Level 2 (10 mm3/L) for drinking water correspond to the DIP/TP ratio below 10. To diminish the growth of cyanobacteria in Lake Vombsjön, TP and DIN control should be in focus, preferably a TP below 20 µg/L, and the DIN:TP ratio should be maintained at a level of at least above 10, but preferably above 50, thereby reducing the likelihood for a nitrogen limiting situation which may favor cyanobacteria dominating blooms