Predictable failure of Grand Lake St Mary’s alum treatment

15 October 2012

A 2-year, $8.5 million project to stop toxic algae in Ohio’s largest inland lake isn’t working.

This is not a case of 20:20 hindsight.  The use of alum as a primary control for nutrients in lakes is fraught with more difficulties that many will realize.  Quite apart from the need for a really solid understanding of the water chemistry issues and challenges, which few applicators seem to have, the sheer scale of this venture pretty much doomed it from the outset.  The applicators in this case must have been extremely bold and confident.  Shredding 8.5 million individual dollar bills and throwing them into the lake could have achieved the same outcome.

Even if it had worked to a degree, the problem would have resurged.  This time around, wind-induced mixing of lake sediments is considered to be the reason why the application did not work.  If this risk was known up front, why was sediment injection with alum not preferred over on-lake spraying?  Blaming the wind may have merit, but its going to need to be backed up by solid hydrodynamic data linking windspeeds and fetches to lake and wave depth, and so on, to convince the critics.

Bottom line:  you need to do a lot of homework before throwing money at this option to manage eutrophication.  The option has merit in a small percentage of site-specific cases, most often for mopping up residual nutrient enrichment after other interventions have been applied.

There are so many factors that influence algal blooms – its not just about phosphorus – although managing phosphorus plays a big role.  Its also often impossible to link intervention to response – simply spraying alum onto a lake becomes a vast, uncontrolled experiment – if the apparent outcome is less algae, whose to say what brought this about??

Bill Harding, PhD,  is a lake biologist with thirty years of experience and graduate/post-graduate qualifications in chemistry, microbiology and zoology.  He specializes in the ecological associations of biota in lakes impacted by eutrophication.

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