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Marco Fertilizer Ban Shows Good Results

On March 7, 2016, Marco Island adopted a fertilizer ordinance. Phosphorus in fertilizer was banned altogether. A fertilizer “black-out” period of June 1 to September 30 was established. Did this work? Let’s look at the data.

A 5-year database was constructed to examine the impact of the fertilizer ban on the water quality on Marco Island. This database has the complete record of the monthly water quality samples taken in 14 locations administered by Marco city staff. Included in the database were several days that fertilizer is applied each month.

As fertilizer is not applied from June to September, these months are assigned zero fertilizer days. The rest of the months that fertilizer is applied are given the number of days in that month, either 29, 30, or 31 days. Over the last five years, 2017-2021, 60 months, fertilizer was applied for 40 months and banned for 20 months. This gives us the “before vs. after” comparison for the analysis.

It was found that when the fertilizer days were zero, the Nitrate (NO3) in the waterbody dropped significantly. Nitrate is a form of nitrogen that is a food source for algae. When the algae in the Marco waterbody is overfed, Marco experiences algal blooms. The blooms tend to occur in the summer months with warmer temperatures.

Algal blooms that occur on Marco in the summer months are now most closely correlated with the reuse of water (purple pipes) from the Wastewater Treatment Plant (WWTP). Had Marco not restricted fertilizer on the island during the summer months, the algal blooms that Marco now experiences would be that much worse.

Marco City Councilors banned fertilizer during the summer months and have saved the island from much worse blooms than we see now. These councilors dared to take the first step. They did the right thing. It was also found that during the months that fertilizer is banned, oxygen levels in the Marco waterbody increased compared to the months when fertilizer is applied.

Questions always arise about landscaping contractors’ compliance with the Marco fertilizer ordinance. Bottom line – the ban on fertilizer in the summer months is working! Food for algal blooms is down, and the oxygen levels are up! Enough contractors must be complying to see these positive results.

Broward County is getting serious about water quality in Biscayne Bay and has implemented an 8-month ban on fertilizer. Marco should do the same. Marco could take a leadership position if we banned fertilizer altogether and made our island community a “Nutrient Free Zone.” That’s right – let's drop our nutrient “footprint” to ZERO.


Nanette Rivera

Candidate for Marco Island City Council

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