Benthic cyanobacteria in lakes and rivers: distribution, abundance, implications

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Both the scientific community and the media have recently focused on planktonic cyanobacteria because they greatly affect the use of lakes and rivers for the purposes of recreation and water consumption. Benthic species and stages are mostly ignored because they are only visible when they rise to the water surface. Nevertheless, there is increasing evidence that benthic cyanobacteria play an important role in carbon and nitrogen fixation. Moreover, they may affect the trophic chain and the water supply by interacting with invertebrates, initiating harmful planktonic blooms and releasing toxins and odour-producing metabolites. In this research, I propose to 1) quantify the still poorly understood role of physical and chemical water characteristics on the distribution and abundance of benthic cyanobacteria and 2) examine the implications of their presence for water resources. I will pursue these objectives in two environments where benthic cyanobacteria are especially relevant: A) We recently reported the presence of a significant amount of the noxious filamentous cyanobacterium Lyngbya wollei in the fluvial lakes of the St. Lawrence River, where it covers roughly 50 km2 of the river bottom. This research aims to model the temporal and spatial dynamics of L. wollei proliferation. This knowledge will be important in the management of the St. Lawrence River, as the commercial and recreational fishery may already be affected by the reduction in aquatic vascular plants and associated invertebrates linked to the spread of L. wollei. The release of toxins and taste and odour compounds may increase treatment costs for water filtration plants serving a population of several million. B) Cyanobacterial blooms are increasingly observed in several lakes of the Laurentian region north of Montréal, despite low nutrient concentrations. We will test whether these blooms initiate in the littoral zone, where benthic stages may start their growth by taking advantage of the increased nutrient supply at the sediment-water interface resulting from land development around the lakes. An understanding of the mechanisms underlying harmful blooms in recreational lakes will help preserve the quality of these important elements of Canada's heritage and water resources.