I’ve heard from a lot of people in the past few days, asking about the tropical system and the algal bloom. So I reached out to some folks to try and get some answers. It turns out the answer is probably not one you want to read.
“This is unfortunately a novel problem from several ways,” Richard Stumpf a NOAA oceanographer with the NOAA National Centers for Coastal Ocean Science said. “A ‘freshwater’ cyanobacteria bloom is unusual on the Mississippi coast, and such blooms are not typically found in coastal areas where tropical storms hit. So there is not a good case study to evaluate hypotheses.”
Two different scenarios
Despite what you may have heard, the Mississippi harmful algal bloom is likely here to stay. Three different oceanographers from three different parts of the field have suggested there is no way to predict if a storm could wipe out the problem, but the answer is likely no. While a tropical system could offer short-lived relief, it isn’t a long-term fix.
“It would be a guess,” Stumpf said. “As to whether the storm would increase or disperse the bloom. “
Stumpf offered two simplistic scenarios:
- Strong winds could cause currents that could disperse the bloom, or the winds could promote resuspension that make more nutrients available to develop the bloom.
- Heavy rain could lead to flushing (which has been observed in estuaries), or simply bring in more nutrients to enhance the bloom (also observed in estuaries).
How do these form?
These blooms exploit physics to thrive – a calm, stratified body of water.
“These blooms can be triggered by different factors,” Ricardo M Letelier, marine biologist and oceanographer at Oregon State University said. “The input of fresh water [is] one of them. Algae and cyanobacteria require light and nutrients to grow fast. Fresh water input into the coastal ocean through river discharge brings nutrients and helps stratify the upper water column”
And the stratified water column is what allows these blooms of freshwater algae to thrive in a salt water environment.
“These are freshwater organisms coming down the river with fresh water nutrients,” Donald Redalje, a professor at the University of Southern Mississippi and biological oceanographer said. “If there is enough mixing, it could kill some of the organisms.”
How much mixing is needed?
If there is enough, though, is the key phrase. While a tropical system – be it a Tropical Storm or Hurricane – could stir up the water, because there would be an increase in runoff from the inland areas from rainfall, the problem would either persist through the storm, or reform shortly after the storm left.
“If there was enough wind,” Redalje said. “[the storm] may be able to push some of the fresh water offshore.”
But Redalje noted that just as soon as the wind stopped and the freshwater continued to pour out of the Mississippi, the problem would continue. And depending on conditions, a feedback loop could commence.
“Stratification also helps the surface water to become warmer,” Letelier said. “Increasing metabolic rates and generating a positive feedback that further stratifies the water-column (warm water being less dense and as light is absorbed by phytoplankton it also increases the water temperature)”
And the waters would be right back in the same boat (no pun intended) they are in right now.
Drier weather will help disperse the bloom
The main message is that the constant flow of fresh water into the Gulf of Mexico is causing the Harmful Algal Bloom along the Mississippi coast and until the injection of freshwater slows down, the algal bloom will persist. And since the Mississippi River is running high due to flooding in the Upper Midwest, Ohio River Valley, and the Mississippi Delta… the relief from the freshwater injection into the Gulf may take a while.
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