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How Will Dredging Impact Algal Blooms?

How Will Dredging Impact Algal Blooms?

This post is by Robert Storm Burks.  Robert is an aquatic biologist/ecologist who formerly led scientific investigations on the St Johns River for the State of Florida for the last decade.

How will dredging the St Johns River impact algal blooms?

Algal blooms are not new to the St Johns River. In 2005, a spectacular bloom that became known as the “Green Monster” was experienced locally and created such a stunning visual, that scientists I worked with in remote sections of Bolivia were aware of it. Many of you have seen the bright green blooms on the surface of the water since that time, and they continue to appear along our shorelines in NE Florida. Recent blooms in south Florida shut down businesses, creating adverse health and economic impacts.

While many people call them blue-green algal blooms, scientists have learned that the organisms are more closely related to bacteria, classifying them as cyanobacteria. These cyanobacteria have been around for millions of years, and are considered one of the first oxygen producing species on earth. However, in recent times, frequencies and intensities of the blooms have increased around the world, including NE Florida. Given the right combination of nutrients in the water, sunlight, and optimal weather conditions, these blooms can cover large portions of our river. Worldwide increases temperatures are projected to cause more blooms, as many species of this bacteria thrive in warmer waters.

Over the years, we have collected and identified many species of cyanobacteria that live in the St Johns River. Many of these species are capable of producing toxins that can impact wildlife, pets, and people who work, recreate, and live along the river. One group of these toxins, known as hepatotoxins, target the liver and other vital organs. Another group, the neurotoxins, will attack the nervous system, and can impact breathing. Yet a third type of toxin produced by cyanobacteria can pass through the blood brain barrier of mammals and has recently been shown to impact brain cells creating symptoms similar to degenerative brain conditions like ALS, Alzheimer’s, and Parkinson’s disease.

Primary routes of exposure include ingestion from drinking contaminated water. While most people aren’t going to pour a glass of St Johns River water, much of this comes from incidental swallowing during recreational water activities such as skiing, swimming, tubing, etc. Also, we do know that some species of aquatic life can concentrate these toxins, and are then eaten either by mammals such as dolphins or people. Boiling water will only concentrate these toxins.

An often overlooked form of exposure is inhalation. Toxins at the surface can become airborne, or aerosolized by wind, wave action, boat traffic, and helicopter maneuvers. Exposure can be acute (higher concentrations at once) or chronic (lower concentrations over time).

This field is rapidly expanding, and we are gaining insight into the conditions in which certain species of cyanobacteria produce and release toxins. We do know that the death of cells containing toxins will release (lyse) them into the surrounding waters. This means that toxin containing fresh water species that cannot live in salt water will release them upon exposure to higher salinities . Since the St Johns river is much wider west and south of Jacksonville (Riverside, Ortega, San Marco, Orange Park, Mandarin), a much larger surface area may increase toxin exposure to the public in this area from both water and airborne toxins.

There have been numerous projections of adverse impacts due to increased salinity upstream from dredging to native trees, aquatic vegetation, habitat, and fisheries in the river. No studies have been performed for impacts to wildlife or public exposure to potential toxins from cyanobacteria blooms in the river.

Because dredging the St Johns River will permanently alter the environment in significant ways, my sincere hope is that local leaders will take the time to consider all the potential impacts to the health of Jacksonville residents and their natural resources before setting a project of this magnitude into motion. 

Click here for more information about the proposed dredging of the St. Johns River. 

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