Catchment-fueled cyanobacteria blooms

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The highest rates of global change are occurring in northern ecosystems. Climate warming, hydrological intensification, and acidification recovery are linked to increased inputs of terrestrial dissolved organic matter (DOM) into northern lakes (i.e., browning) - which in turn have consequences to the productivity and diversity of algae that form a major pathway of energy transfer to food webs in lakes. Cyanobacterial blooms (cyanoblooms) threaten freshwater resources worldwide. Formerly pristine clear water lakes in the north are unexpectantly experiencing cyanoblooms, perhaps an early warning of more frequent, intense cyanoblooms in the future. Heightened public concern for cyanoblooms has been observed with a significant increase in the number of cyanobloom reports to governments by people living on the shores of northern lakes. The commonly accepted conceptual model is that cyanoblooms are associated with phosphorus (P) and/or nitrogen (N) mismanagement. However, we are now receiving "new" reports in northern rural and remote lakes with no known history of cyanoblooms. A new conceptual model of what forms cyanoblooms is needed. I hypothesize that the climate-induced browning of northern lakes creates light and nutrient conditions for exceptional cyanobacterial growth. While the effects of DOM on lake light and nutrient (e.g., N, P, and iron (Fe)) conditions is known, further knowledge is needed to understand algae species-specific adaptations to browning. DOM functions as a nutrient vector transporting P, N, and Fe from the surrounding catchment, and as a nutrient sponge preventing the precipitation of P and Fe and keeping them in the water column. To test this hypothesis, I will (1) Characterize climate changes at northern latitudes, focusing on those changes that lead to lake browning and the associated alterations to lake light and nutrient conditions; (2) Link browning to changes in algal biomass and the enrichment of cyanobacteria over other algae; and (3) Explore consequences of an increase in cyanobacteria dominance on the transfer of essential fatty acids (predicted to decrease) and cyanotoxins (to increase) in lake food webs. From a human perspective, there is nothing positive about cyanoblooms. The close association between freshwater resources and human activities place humans in the cyanotoxin exposure path. Direct effects include human exposure to cyanotoxins through drinking water or aerosols that can cause neurological and hepatological disorders. Indirect effects include cyanobacteria initiating a cascade of altered biological outcomes, as cyanobacteria may reduce the essential fatty acid composition and increase the toxin content in dietary fish or lead to lake hypoxia and the loss of fish or fish breeding grounds. My research program will create knowledge that will form the basis of essential "early warning" systems that can lead to the prevention and mitigation of cyanoblooms in northern lakes.