To Dredge or Not to Dredge?

The famous 490-page Harper report is overshadowed by one overwhelming recommendation: Dredge Marco Island Waterways & Canals at a cost of $200 Million!

All the dredging projects I have read have common issues: 

• Runoff: The body of water has significant mainland runoff discharging into them.
• Contamination: Active septic tank leakage contamination or discharge from inland-licensed Wastewater Treatment Plants (WWTP) contribute above acceptable levels of TN & TP pollutants.
• Invasive: The presence of invasive (exotic) vegetation and/or unprecedented growth of Algal SUPER-BLOOM events! The Indian River Lagoon has Lake Okeechobee’s east discharge running into that estuary. Massive algal super-blooms have lasted up to eight months, denying adequate sun penetration to the waterbody, and killing submerged aquatic vegetation (seagrasses) and aquatic habitats (fish kills). 
• Muck: When massive bloom (and/or invasive vegetation) events die-off, the dead organic material drops to the bottom of these shallow water bodies creating a bed of “muck” which continues to decompose, consuming oxygen and releasing the nitrogen (TN) and phosphorus (TP) it had consumed as nutrients.

The waterbody is then in a state of ‘cultural eutrophication.’ The thick muck matts are not removable any other way than by dredging. These water bodies for the most part are not “flushing” tidal basins which remove much of these sediments over time through tidal exchange. 

Marco’s canals will flush with the tides, and bottom sediment deposits will reduce over time, as it has in Tampa Bay.

The Marco waterbody Dissolved Oxygen (DO) is now deteriorating. Marco is currently experiencing weekly spurts of algal blooms, but our waterways have not had super-bloom events nor does the Rookery Bay Estuary or Marco waterways have massive mainland polluting runoff discharging at the scale and volumes of the Indian River Lagoon Estuary or Tampa Bay.

We know our Marco source of phosphorus and nitrogen pollution. The partially treated sewage that is called ‘reuse water’and distributed by the Marco WWTP for irrigation of public and communal properties and golf courses, contains excessive amounts of these pollutants.

If we take the first common sense step that Indian River Lagoon and Tampa Bay took, we may dodge the dredging bullet! These estuaries’ WWTP plants reduced the nutrient levels as a FIRST STEP! They did not go directly to dredging.

These estuaries removed the excess pollutants by implementing nutrient removal at the WWTPs with Advanced Wastewater Treatment (AWT); they achieved nutrient reductions of up to 90% – THEY REDUCED THE NUTRIENTS! in the wastewater effluents.

That is the first step Marco must take!

The Tampa Bay AWT wastewater point-source reduction combined with a focus on restoration of their seagrass beds & mangroves have resulted in a present-day Tampa Bay that “looks and functions much like it did in the 1950’s”(Greening et al., 2014).Perhaps Marco waters can become ‘gin clear’ again?

The South Florida Water Management District (SFWMD) has awarded a demonstration project to the Phosphorus Free Water Solution, LLC (PFWS) company of Lakeland FL to use their proprietary technology which reduces phosphorus by 99% and nitrogen by 95% (https://phosphorusfree.com, 2021). This project will treat waters entering Lake Okeechobee from the north. If this technology is as good as the 2017 demonstration project PFWS did in Lake Apopka, sign us up!

Clean our Reuse Water! Apply AWT to Marco’s WWTP. REMOVE THE NUTRIENTS BEFORE THE REUSE WATER MAKES ITS WAY INTO THE MARCO WATERWAYS. Don’t let those dredging machines anywhere near Marco.

As the Harper report does not recommend any reduction in the nutrients being poured into the Marco waterbody, the impairments will continue - and might sedimentation (turbidity) worsen if we dredge?

The question to Dr. Harper is “what are the economic impacts of dredging to Marco’s NUMBER ONE ASSET – Our Pristine Beaches?”

Nanette Rivera

Resident, Smokehouse Bay 

Marco Island, Fl