Since the detection of the toxin microcystin left nearly half a million Ohio and Michigan residents without drinking water for several days in early August, discussions of ways to prevent a recurrence have largely focused on the need to reduce the amount of phosphorus fertilizer that washes off croplands and flows into western Lake Erie to trigger harmful cyanobacteria blooms.
In a study published online Oct. 8 in the journal Water Resources Research, scientists from U-M and the National Oceanic and Atmospheric Administration conclude that microcystin-producing cyanobacteria in Lake Erie are becoming more sensitive to phosphorus and that reductions may have to cut far deeper than recently proposed targets.
"Our results suggest that current phosphorus loading targets will be insufficient for reducing the intensity of cyanobacteria blooms to desired levels, so long as the lake remains in a heightened state of bloom susceptibility," said lead author Daniel Obenour, formerly of the U-M Water Center and now at North Carolina State University. Other authors are Don Scavia of U-M and Andrew Gronewold and Craig Stow of the National Oceanic and Atmospheric Administration.
...Though the total amount of phosphorus entering the lake seems to be the best predictor of bloom size, that variable alone doesn't fully explain the observed size increase during the study period examined by the team, 2002 to 2013....