Twin Cities WRS Seminar
and WRC Headwaters Lecture

Blooms Like It Hot: Combating Cyanobacterial Blooms in a World Experiencing Climate Change


Dr. Hans Paerl
University of North Carolina

March 30, 2018


Harmful (toxic, hypoxia-generating, food web altering) blue-green algal or cyanobacterial blooms (CyanoHABs) are proliferating worldwide in freshwater ecosystems, where they represent a serious threat to drinking water, recreational and fishing use and overall sustainability. Nutrient (both phosphorus and nitrogen) input reductions have been prescribed to control CyanoHABs. However, climatic changes, specifically warming, increased vertical stratification, salinization, and intensification of storms and droughts, favor CyanoHABs and thus play synergistic roles in promoting CyanoHAB frequency, intensity, geographic distribution, and duration. In particular, rising temperatures cause shifts in critical nutrient thresholds at which cyanobacterial blooms can develop. From a management perspective, nutrient input reductions aimed at controlling CyanoHABs may need to be more aggressively pursued in a warmer, hydrologically more extreme world. Additional control steps that have been taken include 1) altering the hydrology to enhance vertical mixing and/or flushing and 2) decreasing nutrient fluxes from organic-rich sediments by physically oxygenating or removing the sediments or capping sediments with clay. These efforts, however, have met with mixed results and can disrupt benthic and planktonic habitats. In most instances, long-term effective eutrophication and CyanoHAB control must consider adaptive nutrient control strategies within the context of altered thermal and hydrologic regimes associated with climate change.