Introduction

Cyanobacteria are single-celled aquatic, photosynthetic organisms that are thought to be older than 3.5 billion years2. These organisms originally helped oxygenate the atmosphere and led to the origin of plants billions of years ago. Cyanobacteria often grow in large colonies, which gives them the more common name 'blue-green algae', due to their growth pattern and common colouration. They are aquatic organisms that produce their own food but are bacteria that look similar to algae and are common in many freshwater systems2. Cyanobacteria thrive in nutrient-rich, warm-temperature waters with minimal mixing and can multiply quickly when these conditions arise3,4. Many different species of cyanobacteria form blooms, with Microcystis, Anabaena, and Planktothrix being common genera that are found in Alberta that produce cyanotoxins4,5. When these blooms happen, there are impacts to water quality by increasing turbidity, the creation of anoxic conditions increasing the death of fish and plants, and the production of naturally occurring cyanotoxins, some of which are harmful to humans and other organisms4,6. Contact with the cyanotoxins produced can lead to liver damage5, neurological damage4,7, and other fatal occurrences in humans, other mammals, fish, birds, and plants, making cyanobacteria a species of concern when produced in higher than normal amounts8. They also play essential roles in ecological communities.

As stated above, the occurrence of cyanobacteria in Alberta's waters is natural. Given the eutrophic conditions of many Alberta lakes, they are a common occurrence9; however, rising global temperatures, more extreme precipitation events, eutrophication from agriculture, and prolonged drought periods are leading to conditions more favourable for extreme blooms to arise10,11,12. These blooms are happening more and more frequently, are lasting longer, and are spreading their geographic range across Alberta and the rest of the world. This is concerning, as the mean annual temperature in Canada is increasing at double the global mean rate, with extreme warm temperatures becoming hotter and extreme cold temperatures becoming less cold. There are may projections for climate change done with Representative Concentration Pathways (RCP), which are used to predict future climate trends given different levels of carbon dioxide equivalent released into the atmosphere. All RCP projected changes in Canada have increases in temperature13. Similar trends can be seen in precipitation, with increased precipitation in the form of increased daily extreme precipitation and prolonged periods of drought13. In Alberta, climate change has been found to have increases in the annual mean daily minimum temperatures14, with warming trends, and the changing of timing and amount of precipitation and extreme events15. With the impact of climate change leading to more favourable conditions for cyanobacteria growth, it is important to understand how climate change has and will continue to impact the occurrence and spread of blue-green algae growth, along with how this impact is predicted to change the climate and further change the occurrence of blue-green algae blooms across Alberta.