Mitigating a global expansion of toxic cyanobacterial blooms: confounding effects and challenges posed by climate change

Abstract

Managing and mitigating the global expansion of toxic cyanobacterial harmful algal blooms (CyanoHABs) is a major challenge facing researchers and water resource managers. Various approaches, including nutrient load reduction, artificial mixing and flushing, omnivorous fish removal, algaecide applications and sediment dredging, have been used to reduce bloom occurrences. However, managers now face the additional challenge of having to address the effects of climate change on watershed hydrological and nutrient load dynamics, water temperature, mixing regime and internal nutrient cycling. Rising temperatures and increasing frequencies and magnitudes of extreme weather events, including tropical cyclones, extratropical storms, floods and droughts, all promote CyanoHABs and affect the efficacy of ecosystem remediation measures. These climatic changes will likely require setting stricter nutrient (including both nitrogen and phosphorus) reduction targets for bloom control in affected waters. In addition, the efficacy of currently used methods to reduce CyanoHABs will need to be re-evaluated in light of the synergistic effects of climate change with nutrient enrichment.