Are Lake Alum Application Strategies Set Up For Failure?
Distribution methods may be ignoring up to half the potential phosphorus loading in your lake.
Since 2012, we have been working with stakeholders at a high value 300-acre lake in the US. They have been considering putting in SolarBee® Lake Circulators to control toxic blue-green algae (cyanobacteria) blooms. So far however, they have opted to apply aluminum sulfate (alum) in an effort to tie up phosphorus at the sediment (thus preventing "internal loading” or recycling of phosphorus).
This summer we received another call from them. Despite repeated applications of alum during the past 3 years, the lake has been "continuously inundated” with cyanobacteria. So we made yet another presentation to their Board. By now they could have bought SolarBees and likely had much better results... plus saved a ton of money... plus be all set for the next 25 years.
Why here but not there?
In discussing their alum applications, we learned it was only applied in deeper water (deeper than the thermocline which in this case is about 6 feet deep) and none into the littoral zone (the near-shore shallow areas). Apparently they thought fish & wind mixing would disturb the existing phosphorus anyway even if alum was applied.
My thoughts right away went to “lateral mixing” which was studied well by two USACE engineers Barko and James over 20 years ago. Every day lateral mixing pulls interstitial water and phosphorus out of the near-shore lake sediment spreading it out across the upper waters of the lake at the depth of the thermocline (also known as the epilimnion). This process is well known and as predictable as ocean winds on shore. Wind mixing then makes that phosphorus available to cyanobacteria throughout the epilimnion. Research has shown lateral mixing can contribute 50% of the epilimnetic phosphorus loading in most lakes.
No Benefit, No Surpise...
It is not surprising to me the above stakeholders have continuously applied alum in the deep waters for three years with no benefit to the lake at all.
If the alum folks ever hope to defeat phosphorus loading caused by lateral mixing, they need to figure out how to apply alum to the shallow areas too. Their chances of success will be a little better but based on our experience, results from alum applications will still be pretty marginal.
Posted By: Joel Bleth, CEO & Co-Owner of Medora Corporation, GridBee® SolarBee®
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