Humans: The most ‘harmful invasive’ of all? Human waste adds millions of pounds of phosphorus and nitrogen to Florida’s ecosystems

OKEECHOBEE — For decades, South Florida has been plagued by harmful invasive plants and animals that wreak havoc on the native ecosystems. Waterways are choked with hydrilla, originally imported from Asia for aquariums. Melaleuca, imported from Australia in a misguided plan to “drain the swamp,” grows so thick it squeezes out native vegetation and animals.

This chart speaks to population density.

Burmese pythons, released by owners tired of their pets, grow large enough to compete with alligators for prey, and sometimes even target gators AS prey. The list of harmful invasives in Florida is long … and it keeps growing.

The most harmful invasive of all could well be humans.

Dr. Dan Canfield, a professor of Limnology in the University of Florida, explains that once a human enters an ecosystem, that ecosystem is changed forever.

It’s human nature to make changes, to build shelter from the weather, to plant crops and raise animals to eat, to build roads to make it easier to travel.

Early Florida pioneers changed the ecosystem. They dug canals to create liquid highways for their boats. Later, state and federal government agencies expanded the canals to drain land for development and agriculture.

The more humans move into the ecosystem, the more it changes. Florida’s population is growing at around 1,000 persons per day.

Humans continue to change the ecosystem by importing other things into it … things like invasive plants that look pretty in an aquarium but somehow wind up in a waterway or a pet snake that gets too big to keep in the house … and things like foods from all over the world.

Much has been studied and written about the impact of farm animals and other agriculture on the ecosystem, how much phosphorus is used to fertilize grass, how much grass a cow eats, how much phosphorus leaves the system when a calf goes to market, and how much phosphorus is in the manure that might wind up in runoff after a heavy rain. Today’s ranchers do a lot of math trying to keep that phosphorus load in balance to prevent excess nutrient load from winding up in the waterways.

Farmers may fertilize their fields, but they also take away nutrient load when they harvest a crop. In some cases, as with sugar cane, the harvest actually reduces the total nutrient load in the watershed.

Little, however, has been written about the nutrient load from human waste.

Humans are complicated. We aren’t content to graze on the fruits and vegetables available in our ecosystem, plentiful though they may be in South Florida. We don’t limit our numbers to those who can survive on the naturally-available food supply. Gone are the pioneer days when Floridians grew their own food or harvested native swamp cabbage and sour oranges. Grocery stores are well stocked with processed foods, canned foods and dried foods as well as fruits, vegetables and meats shipped in from other states and other countries. All of these imports mean increase in the nutrient load entering the ecosystem.

There is no delicate way to put this: Human waste, and in particular, urine, is a major factor in the nutrient load entering the ecosystem.

Let’s do the math …

The average human produces about 3.1 pounds of urine per day, according to One gallon weighs about 8 pounds.

Urine is mostly water, but it also contains minerals such as nitrogen and phosphorus. According to the National Center for Biotechnology Information, U.S. National Library of Medicine, about 80 percent of the nitrogen and about 60 percent of the phosphorus in human waste is contained in the urine.

How much phosphorus and nitrogen are in human waste? A lot depends on the group of humans you test. Humans who consume more protein have more nitrogen in their waste.

Those whose diet is lower in protein have a lower concentration of nitrogen.

“Nitrogen and Phosphorus Harvesting from Human Waste” by S.K. Pradhan, a. Mikota and R. Vahata, published in 2017 on the U.S. National Institute of Health website, reported 1.5 percent phosphorus and 13 percent nitrogen in urine.

Urine produced by a human with a protein rich diet can contain 10 percent nitrogen or more, according to “The Characterization of Feces and Urine” by C. Rose, A. Parker, B. Jefferson and E. Cartmell published in in “Critical Reviews in Environmental Science and Technology, in May 2015. The researchers found human urine averages about 1 percent phosphorus.

“Urine Composition: What’s Normal?” by Dr. Liji Thomas, on the website estimated the average human produces 11 grams per day of nitrogen in urine, or about 8.85 pounds per year. A diet high in protein will increase (possibly double) the nitrogen levels in urine, Dr. Thomas noted.

Even using the lowest estimate, the nitrogen and phosphorus in human waste adds up.

A 1995 study conducted in Sweden found that an adult’s urine contains enough nutrients to provide 50 percent or more of the fertilizer to grow the crops needed to feed one adult.
According to the U.S. Census, in 2017, the population of Florida was 20,984,400. In addition to the residents, Florida is also popular with tourists. According to the Florida Governor’s Office, in 2017, approximately 116,500,000 tourists visited the Sunshine State.
What happens to the urine? If you have septic tank, it mixes with water from the house (used for washing and flushing) in the septic tank. In the septic tank, bacteria consume ammonium (a form of nitrogen) and convert it to nitrate, according to the U.S. Department of Health. Liquid from the tank flows into the drain field. If the drain field is not functioning properly, it could wind up in nearby waterways. Even if the septic system is functioning properly, that nutrient load is going back into the ecosystem.

Randy Edwards, who holds a Ph.D. in Marine Science explains: “The reality is that septic tanks are a major problem with regard to nutrient pollution of coastal waters. Such nutrient pollution can be a major reason that red tides are more frequent, more persistent, more extensive in area, and more intensive and devastating. However, science has found that most nutrient pollution from septic tank systems comes from normally functioning systems — not just from malfunctioning systems. Even properly functioning septic systems release large quantities of nutrients to surrounding sandy soils, where rainfall quickly percolates them into near-surface water tables that ultimately flow into coastal water bodies.”

According to the U.S. Department of Health: “Wastewater treated by a properly functioning on-site sewage system generally contains significant amounts of nitrate. After leaving a properly functioning drain field, nitrified effluent flows through soil. What happens to nitrates in soil is highly variable. It may be used by plants, flow to ground or surface water, or be consumed by bacteria. The amount of nitrate removed after leaving the drain field varies between 0 and 90 percent depending on site conditions. An improperly functioning OSS can result in excessive ammonium/ ammonia or nitrates discharged to the soil, where it can flow to groundwater or surface water and cause problems.”

If your home is on a sewer system, the wastewater is treated to remove pathogens (harmful bacteria). Sewage systems remove nitrogen through a process which converts ammonia to nitrate followed by the reduction of nitrate to nitrogen gas, which is released into the atmosphere. Phosphorus can be removed biologically, using specific bacteria. The biomass of the bacteria, enriched with phosphorus, can be used in fertilizer. Another method of removing phosphorus from wastewater involves using chemicals to cause it to precipitate into a sludge which may be dumped in a landfill or used as fertilizer.

The treated wastewater might be used to irrigate orange groves or golf courses, or it could be distributed on spray fields or pumped about 3,000 feet into the earth into the Boulder Zone via deep well injection.

If you live near the coast, some of the wastewater could wind up in the ocean, or in a river.

In crowded coastal areas, that nutrient load could be significant.

The City of Fort Myers dumps treated wastewater into the Caloosahatchee River. According to the City of Fort Myers’ own website: “The City of Fort Myers Wastewater Treatment Division consists of 2 regional Advanced Wastewater Treatment Facilities. The Central AWWT Facility is located at 1501 Raleigh St. and is designed to treat 11 million gallons of wastewater per day. The South AWWT Facility, located at 1618 Matthew Drive, is designed to treat 12 million gallons per day. The existing Bardenpho treatment systems were put on line in 1985, replacing the old sewer plants at both facilities. These waste water treatment plants treat wastewater from all of the City of Fort Myers and much of Lee County. The majority of the treated effluent from the two plants is discharged to the Caloosahatchee River,” the website states.

Publisher/Editor Katrina Elsken can be reached at

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