16 | 2017 LAKE STEWARDS NEWSLETTER Cyanobacterial blooms (also known as blue-green algal blooms) are on the rise, globally. In Ontario, there has been a significant increase in the number of confirmed cyanobacterial bloom reports by the Ontario Ministry of the Environment and Climate Change (OMOECC) since the 1990s. Algal blooms are concerning to property owners and lake users because of their adverse effects on water clarity and potential taste and odour issues. Additionally, some species including Cyanobacteria may produce toxins that may pose a risk to human and pet health. Indirectly, bloom events can also reduce the amount of suitable fish habitat, and have overall negative effects on lake ecosystem health. Algal blooms in lakes experiencing cultural eutrophication (nutrients added as a result of human activities) have been relatively well-studied, and it is no surprise that such lakes can experience cyanobacterial blooms. Although rare, cyanobacterial blooms in low- nutrient lakes are becoming more common: about 1 in 4 bloom reports to the OMOECC between 1994 and 2009 were from low-nutrient lakes. (see above) However, environmental triggers for cyanobacterial blooms in low-nutrient lakes are not well understood. What’s Causing These Blooms? One important reason is the pronounced effects of climate changeonfundamentallakeprocessessuchasthelengthofthe ice-free season, as well as the duration and strength of thermal stratification. Thermal stratification is the layering of water in a lake into distinct temperature and density zones, with warmer lessdensewateratthesurfaceandcolder,denserwaterdeeper in the lake. Climate warming can enhance thermal stratification and reduce the strength of water column mixing. Warmer temperatures, combined with stronger and longer thermal stratification, provide distinct advantages for cyanobacterial growth. Relative to other types of algae, cyanobacteria have higher temperature requirements and can regulate their buoyancy. This means they are less dependent on vertical mixing to maintain their position in the upper parts of the water column, where there is adequate light for photosynthesis. InOntario,meanannualairtemperaturehasincreasedbyabout 1.5˚C since 1948, and many lakes now experience a longer ice- freeperiod,aswellasstrongerthermalstratification.Compared to a few decades ago, algal blooms are being reported significantly later into the fall, suggesting that a lengthening of the open water season is changing algal bloom dynamics. Although there is much we need to understand, it is now clear thatclimatechangeshouldbeinvestigatedasapotentialtrigger for recent increases in cyanobacterial blooms in Ontario lakes. Nuisance Algal Blooms in Ontario Lakes: What We Can Learn From the Past by Elizabeth Favot Cyanobacterial bloom on remote and low-nutrient Dickson Lake in Algonquin Provincial Park, August 2015. We can each manage our own waterfront properties, through regular septic system maintenance, and promoting naturalized shorelines, to reduce phosphorus inputs, and mitigate the impacts of climate change on the waterfront. Get tips and best practices for your own property in FOCA’s publications: the Shoreline Owner’s Guide to Healthy Waterfronts, and Managing Your Waterfront Property in a Changing Climate. Member Associations can contact FOCA to enquire about getting multiple copies of these guides. Tips for Property Owners ts 3rd Edition g