Tens of thousands of leaking septic systems are contributing to Southwest Florida’s water-quality woes, sending nutrient-rich fecal matter throughout the region’s shallow water table and porous soils to pollute groundwater, feed outbreaks of blue-green algae, and fuel more intense fish-killing red tides.
Researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute traced nutrients that are specific to “human waste containment sources” in the Caloosahatchee River watershed miles downstream, where they contribute to the strength and length of algae blooms and overload fresh and salt water environs with bacteria and nutrient pollution.
“These water quality issues in North Fort Myers are caused by aging septic systems installed in high densities in areas with shallow water tables,” said Brian Lapointe, a senior author of the study and a research professor at the oceanographic institute. “In addition, the presence of canals in these residential areas with septic systems may increase the rate of pollutant transfer from groundwater to surface water via" tides.
The actual number of septic systems in Lee County is unknown. After working for three years in the region, the researchers believe there are least 100,000, which is a staggering number considering their purpose. Perhaps more remarkable is nobody knows the location of nearly two-thirds of those septic systems.
The Florida Atlantic researchers published their findings this month in the journal Science of The Total Environment.
The septic system was invented in the mid-1800s to solve a problem for rural residents during the winter: the need to leave the warmth and safety of a home to walk through wind, rain or snow to an outhouse.
The cheap, simple, and effective systems grew rapidly in popularity.
The heart of the system is the tank, often made of concrete, into which pipes carry sewage flow. Solids in the waste settle in the tank, which usually has one or two chambers, and microbes get to work digesting the material. Water is cleansed through the process, too, and drains out the other end of the tank into a series of buried pipes with holes for the water to drip out and sink into the soil, where it is purified further through natural processes.
The Harbor Branch researchers spent three years studying septic systems in the greater North Fort Myers area and discovered many are adversely affecting water quality. Some were installed prior to current septic system design standards and are ineffective at removing nitrogen. During the rainy season, in places, the water table rises enough to mingle with septic systems, which mixes untreated sewage and surface water creating highly polluted runoff.
Testing found a specific type of nitrogen in coastal red tides closely matched that found at an inland septic system, pointing to human waste as a driver of worsening harmful algal blooms.
Florida Atlantic’s study is the second from a state university this summer to connect algal blooms with human activity, something that has long been suspected.
A University of Florida study proved human-caused nutrient pollution moving from agricultural regions north of Lake Okeechobee down the Caloosahatchee River made algae blooms in the Gulf of Mexico stronger and last longer.
Environmental researchers, led by the University of Florida’s Center for Coastal Solutions, documented the link after studying a decade of red tide data from the Caloosahatchee River, Charlotte Harbor, and the surrounding watersheds including the coasts of Charlotte and Lee counties.
The economic costs of algae blooms are often wide-reaching and hard to peg. A different University of Florida study, published in the journal Tourism Economics, found the financial impact of the massive red tide outbreak of 2018 included at least $184 million in tourism revenue alone.
Most of those dollars were lost among Southwest Florida’s resorts, restaurants, and attractions plagued by the bloom. But due to the interconnectedness of economic factors in Florida more than 15 percent of the losses from the harmful algae bloom occurred in other parts of the state.
The researchers from Florida Atlantic University suggest governments like Lee County’s switch septic system users to central sewer lines, an expensive proposition that has proven to be something neither municipalities or individual homeowners want to pay for.
“It would be beneficial for coastal areas with high densities of septic systems and canals to be prioritized for septic-to-sewer conversions or other advanced wastewater treatment options,” said Brian Lapointe, the senior author. “As other recent research has noted, the scale of the red tide issue demands watershed-scale solutions and nitrogen management based on a holistic view.”
Environmental reporting for WGCU is funded in part by VoLo Foundation, a non-profit with a mission to accelerate change and global impact by supporting science-based climate solutions, enhancing education, and improving health.
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