Analysis of the water quality dynamics of Lake Vomb; Interactions between water quality profile and cyanobacterial bloom in a eutrophic lake in Sweden

Sammanfattning: Lake Vomb, located in Sk˚ane, Sweden, provides water for groundwater infiltration, used for the drinking water supply of several municipalities, including Malm¨o. The lake is in a bad ecological condition with intense algae blooms during summer. Cyanobacteria dominate mentioned blooms in 2021 posing the threat of releasing cyanotoxins. The goal of this work is to asses the water quality dynamics to support the lake management. An approach to predict algae blooms and oxygen depletion to return the lake into a good ecological state and secure a long-term drinking water supply is investigated. To assess the water quality, the profiles of the parameters pH, dissolved oxygen, and the water temperature was analysed for possible correlations with the abundance of algae represented by the chlorophyll-a concentration. Meteorological effects on the water quality dynamics were assessed. The availability of essential nutrients was evaluated by inspecting the phosphorous and nitrogen concentrations in the in- and outflow of the lake. The pH value at the water surface showed the strongest correlation with the chlorophyll-a concentration during the summer. Besides seasonal patterns, wind and temperature fluctuations indicate a correlation with oxygen depletion. The possibility of phosphorous release supporting the algae bloom was found, but more measurements are needed to find the cause and possible preventative measures. Random forest was used to predict the risk of high chlorophyll-a concentrations and oxygen depletion. The model shows potential, but more input data is needed to make significant predictions. Future research could focus on the regulation of phosphorous release and implementation of the phosphorous dynamic into the prediction model.