Understanding Sources of Phosphorus and Trophic State in the Forbes Lake Water Supply

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The occurrence of cyanobacteria blooms in several lakes and reservoirs in Atlantic Canada in recent years has generated significant public awareness and concern. The apparent increasing frequency in cyanobacteria blooms could be due to a number of factors, including climate change and decreased levels of acid deposition. However, increased nutrient loading is still recognized as a central factor influencing potential for blooms. Phosphorus is typically the limiting nutrient in freshwater systems, and identification and control of phosphorus sources within the lake watershed is a critical first step in preventing cyanobacteria blooms. The Town of New Glasgow Water Utility sources their drinking water from a 72 ha reservoir called Forbes Lake. The lake has never experienced an algal bloom but recent changes to water treatment plant operations have resulted in the recycling of phosphorus-based corrosion control agents back into the lake. The Utility and Dalhousie University are undertaking this research project to better understand the risk associated with this extra phosphorus addition to the lake, and if mitigative steps need to be taken to remove this source of phosphorus. The research will involve a field sampling program aimed at characterizing current phosphorus levels and trophic state of Forbes Lake, and the development of a watershed model to understand the various sources of phosphorus to the lake. Outcomes from this research will guide the utility in making critical decisions related to management of both the source water lake and water treatment process.