Addressing Water Quality

On May 6th former Marco Island City Councilor Charlette Roman, serving as Chair of the governing board of the Big Cypress Basin of the South Florida Water Management District, joined the Marco Island City Council in proclaiming “Florida Water Reuse Week”.  In part this proclamation states: 

“Water reuse provides a means for conserving and augmenting Florida's precious water resources; Florida has risen to be a national leader in water reuse, reusing approximately 900 million gallons of reclaimed water per day, more than 50% of the wastewater treated to conserve freshwater supplies and recharge our freshwater resources; and The City of Marco Island has joined with WateReuse Florida, the Florida Department of Environmental Protection, and the South Florida Water Management District in encouraging and promoting water reuse and conservation.”

Both agencies responsible for water in Florida promote the necessity and utility of using treated wastewater effluent, or “reuse water” for irrigation purposes.  This use is also highly regulated by them.

A small group of Marco Island residents asks us to believe this very same water is a source, perhaps even the primary cause of water quality issues in Marco Island waterways.  To be more specific, that levels of “nutrients”, in particular phosphorus in this water are the cause of low levels of oxygen in our canals.  Like these residents, I’m not a scientist so I’ll stick to basics here. Certain elements (phosphorus, nitrogen in particular) serve as “nutrients” in that they promote growth of aquatic plants and algae, just as they help fertilize your lawn (read the label on your fertilizer). These relationships are complicated, but what is indisputable is the Florida Department of Environmental Protection (DEP) sets limits on these elements, and in the late 2010’s the City was notified by DEP that certain test sites on Marco Island showed results exceeding those limits – these were declared “Impaired Waters.”

To get a handle on cause-and-effect regarding water quality and develop action plans, in late 2019 City Council, at the urging of the City’s Waterways Advisory Committee, hired the firm Environmental Research and Design (ERD) to gather and analyze water quality data and write such a plan. It’s worth noting that the selection of ERD garnered a level of unanimous support rarely seen anywhere on any subject, much less on Marco Island on such a critically important issue.

The ERD report is long, as are its recommendations. It did not however call out reuse water or phosphorus as a priority in addressing canal water quality.  There was enough debate over some of these findings that the City hired another scientist to provide a second opinion on what had been presented by ERD. In July 2022 the Jacobs Engineering Group reported that, “Jacobs’ review of the ERD Report shows there is little direct evidence to claim that applying reuse water for irrigation purposes results in a significant impact in waterway water quality degradation.” The Jacobs report also pointed to a reduction in the level of nutrients (nitrogen and phosphorous) in the City’s waterways.

The proponents of more aggressive removal of phosphorus from the City’s reuse water have invested considerable effort at to show correlation between low levels of oxygen in canal waters and elements in reuse water.  This analysis falls prey to a common logical fallacy, so common in fact it has a Latin name: cum hoc ergo propter hoc(meaning “with this, therefore because of this”).  Correlation is not causation, period. Both ERD and Jacobs addressed causation as quoted above. In addition, if one overlays the maps presented illustrating oxygen levels with where reuse irrigation water is actually applied, there isn’t even simple correlation.

City Council has made having all waterways removed from the DEP’s impairment list its #1 priority. In September 2023, FDEP approved the City’s “4e Plan”, recognizing the City’s work to improve water quality. Significant improvements have been made in the data, in partnership with the DEP, and an updated report is expected this year removing Marco Island from the impaired list.

Being “unimpaired” is only one step – we can set a higher bar.  No doubt the conversation about phosphorus will continue. Continue to do your part; keep your grass clippings and direct stormwater discharge out of our canals and follow proper practices for fertilizer application for example. We all agree there is more to be done.