Problem: Marco Island Waterways Are Deficient In Oxygen

Attachments

Submitted (illustration)

Marco Island Water Quality Status Report September 2021.

Marco Island waterways have been deficient for Dissolved Oxygen (DO) regularly starting October 2020. In 2017, 4% of all of the Marco water quality samples were deficient in oxygen. So far in 2021, 68% of all of the Marco water quality samples are deficient in oxygen. The trend is decisively negative and shows no signs of slowing down.

A Hypoxia Investigation was finalized at the Marco Island Waterways Advisory Committee (WAC) meeting on September 16, 2021. This report links nutrients (nitrogen and phosphorus) contained in the reuse water from the Marco Wastewater Treatment Plant (WWTP) to oxygen depletion in the Marco waterways. A direct statistical linkage has been established.

Science supports this linkage: “In some estuaries, large nutrient inputs, typically from sewage, stimulate algal blooms. When the algae die, they begin to decompose. The process of decomposition depletes the surrounding water of oxygen and, in severe cases, leads to hypoxic (very low oxygen) conditions that kill aquatic animals” (NOAA)

When DO levels drop below 3.0 mg/L, the water is considered hypoxic. Oxygen depletion is a phenomenon that occurs in aquatic environments as dissolved oxygen becomes reduced in concentration to a point where it becomes detrimental to aquatic organisms living in the system, such as fish, grasses, and oysters.

As we can see in the attached map, Basin Five gets NO reuse water from the WWTP and is the only completely healthy basin on the island. We can see the connection between the reuse nutrients and the oxygen deficiency just by looking at this map. The red areas are condos and golf courses where reuse water is distributed.

Let’s be clear, reuse water is treated sewage. “Reuse” is the politically correct term. Sounds like a good thing. What the state forgot when they promoted this program is the massive amounts of nutrients that come with this “water” that we use to fertilize the lush green grass in our public spaces. We are recirculating our own sewage.

Phosphorus is the reuse pollutant most directly related to the oxygen deficiency on the island. The Marco WWTP operates a process that does not remove phosphorus. It removes only nitrogen. The existing WWTP process, no matter how hard they try, can’t do any better in phosphorus removal. The Marco WWTP was not designed to remove phosphorus.

Marco Island needs to upgrade the sewage treatment facility to produce reuse water that does not damage our waterways. The new process is called Advanced Wastewater Treatment (AWT). Everglades City will install an AWT system in 2022 that will remove BOTH nitrogen and phosphorus from their reuse water. Marco should do the same.

Solution: Upgrade the Marco WWTP to an Advanced Wastewater Treatment (AWT) system

Eugene Wordehoff, Marco Island

Member, Waterways Advisory Committee to City Council