The “new normal” high rainfall tropical cyclones: Linkage to harmful cyanobacterial bloom expansion into estuarine and coastal waters

Hurricane Ecosystem Response Synthesis – Research Coordination Network Webinar

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Dr. Hans Paerl presenting “The “new normal” high rainfall tropical cyclones: Linkage to eutrophication and cyanobacterial bloom expansion into estuarine and coastal waters”
Global warming is generating more intense, elevated rainfall from tropical and extra-tropical storms, which have led to record flooding along the storm tracks, extending from the coast to inland watersheds. In addition to delivering elevated nutrient (N and P) and other contaminant loads to receiving riverine, estuarine, and coastal waters, floodwater also tend to reduce salinity in these waters. The combined effect of elevated nutrient loads and “freshening” of downstream waters is promoting eutrophication (“new production” from a carbon perspective) and expanding the window of opportunity for harmful cyanobacterial blooms, or CyanoHABs, to proliferate. Elevated stormwater runoff events followed by periods of protracted droughts are the perfect “storm scenario” for downstream proliferation of CyanoHABs, which will benefit from elevated nutrient supplies, depressed salinity levels and increases in water residence times. This, combined with warming is a potent combination of changing environmental conditions favoring expansion of CyanoHABs along the entire freshwater to marine continuum. Examples of this scenario are now evident in numerous estuarine and coastal ecosystems, including the Mississippi-Atchafalaya drainage into the northern Gulf of Mexico, Florida’s coastal lagoons and estuaries draining Lake Okeechobee, the Albemarle-Pamlico estuarine complex in North Carolina, the San Francisco Bay Delta, as well as the Yangtze River Delta in China. This scenario presents multiple CyanoHAB mitigation challenges, in that both watershed nutrient loading will need to be reduced to new threshold levels and water retention strategies need to be optimized to retain and process nutrients in the watershed upstream from CyanoHAB sensitive receiving waters.

Hans Paerl, PhD | Distinguished Professor | Institute of Marine Sciences, University of North Carolina at Chapel Hill | https://paerllab.web.unc.edu/research/