Phosphorus – It’s everyone’s legacy

OKEECHOBEE — Any discussion of the water quality issues in the Everglades and Lake Okeechobee must include the issue of legacy phosphorus.

Legacy phosphorus, quite simply, is phosphorus already in the system. It’s in the muck at the bottom of the lakes, rivers and canals. It’s in the soils of the watershed north of the Big O in areas that drain into the lake.

And that legacy keeps growing.

In 2000, the Florida Department of Environmental Protection (FDEP) set the target maximum phosphorus load entering Lake Okeechobee at 140 metric tons per year, including 35 metric tons of atmospheric phosphorus (rain contains some phosphorus).

The Lake Okeechobee Sediment Management Feasibility Study prepared by Blasland, Bouck & Lee, Tetra-Tech Inc., Environmental Quality Inc. and Haymar Inc. was published in 2003. The 3-year study found that although the high concentration of phosphorus in the water entering Lake Okeechobee is the primary driver of the high phosphorus level in the lake, the phosphorus level in the water in Lake Okeechobee can also be exacerbated by phosphorus in the lake bottom sediment.

The Florida Department of Environmental Protection has set the target level for phosphorus in the lake at 40 parts per billion (ppb). To put that in perspective, the target for the Everglades is 10 ppb. Rainwater may contain up to 8 ppb. The phosphorus level in the lake water varies in different parts of the lake, and at different lake levels, but usually averages around 120 ppb according to SFWMD reports. This past year, it has averaged higher in phosphorus due to the tremendous nutrient load flushed into the lake from Hurricane Irma in 2017.

Per the data, no consistent reduction in phosphorus loading has been achieved since FDEP set the target limit.

The 2003 study speculated that once the phosphorus loading into the lake had been reduced to the FDEP target, the phosphorus level in the lake would drop, and the lake’s marshes could start to clean up the phosphorus already in the lake sediment. At the time of the 2003 study, there was an expectation that the target load could be achieved by 2015. Based on that prediction, they estimated it would take an additional 35 years for the lake to recover.

So far, no progress has been made. The phosphorus is still there, in the muck at the bottom of the lake.

According to FDEP studies presented at Lake Okeechobee Bain Management Plan meetings, the lake can’t start to recover until the annual phosphorus load into the lake is reduced.

In 2003, the phosphorus load in that muck was estimated at 51,600 metric tons. In the past 15 years, there was no chance for the lake to reduce the tonnage because of the high levels of phosphorus continuing to enter the lake.

In water year 1986, the phosphorus load into Lake Okeechobee was 421 metric tons, according to SFWMD records. In water year 2017, the phosphorus load was 484 metric tons.

In water year 2018 (May 1, 2017 through April 30, 2018), thanks to Hurricane Irma, the phosphorus load into the lake was 1,046 metric tons.

Whose legacy is it?

Agriculture, urban development and Mother Nature all played a part in building up phosphorus in the soil as well as in the waterways of South Florida.

A legacy of dairies …

LaMartin’s History of Okeechobee County, noted in 1945, Okeechobee County had only a single 109-cow dairy farm. By the late 1950s dairy-men had discovered that the area offered productive land at reasonable prices. By 1972 there were 26 dairies in operation with about 25,000 cows.

By 1972, Okeechobee County was the leading dairy production county in the southeastern United States and accounted for 45 percent of Florida’s milk production.

In the 1950s, it was an accepted practice to clean the milking barns by washing waste into nearby canals or waterways. The heyday of dairy farming left a legacy of nutrient load from manure. That nutrient load from dairies was addressed decades ago.

In the 1980s when algal blooms in Lake Okeechobee led FDEP to seek the source of the excess nutrients entering the lake, it was quickly blamed on the 50 dairies in the basin watershed. Dairy farming concentrates cattle, increasing the amount of waste per acre. Dairy cows are fed grain, rather than just grazing in the pasture, so the nutrient load in their manure was expected to be higher than that of beef cattle. FDEP was so sure of the dairy-phosphorus link that in 1986, a law was passed, the FDEP Dairy Rule, which put strict limits on the phosphorus content of runoff from dairies. The rules were so strict that many dairies simply could not meet them. More than half of the dairies moved out of the watershed, taking advantage of a dairy buyout program. The dairies that stayed found ways to recycle the waste and keep it out of the runoff and/or use berms and retention ponds to keep the water on the property.

In 1986, when the FDEP dairy rule was passed, scientists warned that even after the cows left the watershed, it could take 20 years for the “legacy” residual phosphorus in the soil to be washed away. That was 30 years ago.

A legacy of sewage dumping …

Some of the phosphorus attributed to “agriculture” comes from urban areas. Land spreading of biosolids is still a common practice in Florida, and it is commonly done in remote, rural areas zoned for agriculture. But the nutrient load in the materials dumped are many times — sometimes hundreds of times — the amount needed for use as fertilizer. The primary purpose of land spreading of biosolids is to get rid of the waste as cheaply as possible.

Biosolids is another name for human waste that has been treated to eliminate pathogens.

While other methods of disposal of sewage such as incineration and bioenergy are available, according to FDEP most Florida utilities dispose of biosolids by land application, dumping the treated waste in a landfill or processing it to a marketable standard and distributing it as fertilizer. Municipalities usually choose the least expensive method available.

Until 2010, the State of Florida allowed land spreading of biosolids without requiring a state permit for all land application sites. That means we don’t know exactly how much human waste was spread on the land, or where that nutrient load was dumped prior to 2010. Also, while the FDEP Dairy Rule stopped runoff from dairies in the Lake Okeechobee watershed in 1989, land spreading of human waste was allowed, even in sensitive watersheds, until 2013.

While the state has banned the practice in the Lake Okeechobee watershed, the Florida Audubon has called for the state to ban all land spreading of biosolids throughout the state.

The Florida Legislature also left a loophole in the law which allows unregulated distribution Class AA biosolids – which are the most highly processed type of human waste – throughout the state.

A legacy of golf courses and “vanity” lawns …

Fertilizers used to keep the non-native grasses used for golf courses and urban lawns green year round can also contribute to the problem. Some homeowners associations require property owners to use and maintain St. Augustine grass. A Florida law passed in 2009 sought to support homeowners’ efforts to use “Florida friendly” plants has not stopped the HMOs from filing lawsuits against property owners who challenge their rules, and most residents don’t have the resources to fight the HMOs in court.

A legacy of naturally-occurring phosphorus …

Florida soil contains a lot of natural phosphorus, as evidenced by the phosphate mines in Polk County. According to the Florida Industrial and Phosphate Research Institute website, “A blanket of phosphate deposits covers much of peninsular Florida. In the areas that are considered economical to mine, the matrix layer, which consists of approximately equal parts phosphate rock, clay, and sand, averages 12 to 15 feet in thickness. The matrix is buried beneath a soil overburden that is typically 15-30 feet deep.”

Much of the watershed that feeds into Lake Okeechobee is naturally high in phosphorus, and when it was dredged for navigation and flood control, water started to flow more quickly, changing the way that phosphorus moves from the soil into the waterways.

A legacy of backpumping and backflow

The legacy of backpumping water from canals south of Lake Okeechobee back into the lake started with concerns about water supply. In 1968 the U.S. Army Corps of Engineers proposed using pumps to send water the wrong direction – from the EAA back into Lake Okeechobee – to prevent water shortages. While farmers use little fertilizer in the Everglades Agricultural Area because the “black gold” soil is high in natural fertilizer, nitrogen and phosphorus from the muck itself came with that backpumped water, In 2006, a federal district judge in Miami ruled that the district must comply with the Clean Water Act. And on Jun 15, 2007, a federal court issued an injunction requiring the South Florida Water Management District to apply for pollution permits to engage in pumping dirty water into the lake. Today, backpumping is still allowed but only to prevent flooding in the cities on the lake’s south shore.

Similar to backpumping, backflow means the water is going the wrong direction, from the south or from the east into the lake. When the lake level is lower than the water level in the canals on the south and eastern shores, water can flow back into the lake, bringing with it excess nutrient loads. The C-44 canal which connects with the lake at Port Mayaca averages about 300 ppb phosphorus, due to the runoff directly into that canal.

During Water Years 2014-2018, on average, water from south of Lake Okeechobee contributed about 5 percent of the total phosphorus load per year; water from the east contributed about 3 percent of the total phosphorus load.

A legacy of commercial farming …

While much of the blame for phosphorus load has been placed on cows and sugar cane, other agricultural sources also contribute to the load. Runoff from row crops, sod farms, chicken farms and other agriculture throughout the watershed – which starts at Orlando – contributes to the phosphorus load. (When it comes to phosphorus, sugar cane gets a bad rap – it’s actually a “nutrient sink” which removes phosphorus from the watershed.)

A legacy of development .,..

According to the U.S. Census, Florida is the fourth-fastest growing state in the country with more than 21 million residents. The South Florida Water Management District is home to more than 8 million people. When the current flood control system was designed, the population of South Florida was about 2 million. In addition to full time residents, millions more live in South Florida in the winter or vacation here. In 2017, about 72 million people visited at the top of the watershed that flows into Lake Okeechobee. Every building roof, street and parking lot means more runoff and less green space available to allow rain to soak back into the earth, That runoff carries with it fertilizer and pesticides from urban landscapes, oils and coolant spilled on roadways, trash and debris.

A legacy of invasive aquatic plants

Environmental reporter Twila Valentine, who studied and wrote about the Kissimmee River and Lake Okeechobee for more than 25 years, had a theory about the muck at the bottom of Lake Okeechobee. She explained that before the lake was diked, it had seasonal highs and lows. During the high water periods, it had a much larger footprint than it does today. Even then, the lake had contained a lot of floating vegetation, much of it nonnative. The floating plants take in nutrients from the water. Before it was diked, when the water was high, the water would flow south, carrying with it large mats of aquatic vegetation. When the lake level receded in the dry season, these large mats of vegetation would be deposited south of the big lake. In addition, during high wind events such as hurricanes, the floating aquatic vegetation would be carried out of the lake with the storm surge, and left on the shore. As the plants decayed, they contributed to the muck soil, building up the “black gold” soil of the Everglades.

Since the lake was diked, the water flows south only through canals. The floating vegetation is now trapped in the lake. When it dies, it falls to the lake bottom, turning into muck. In addition, to keep the vegetation from blocking navigation, the Florida Wildlife Commission uses chemical spraying to kill the vegetation, causing it to fall to the bottom of the lake, where it adds to the muck.

If the vegetation could be removed mechanically it would reduce the nutrient load in the lake and also prevent build up of more muck on the lake bottom, Mrs. Valentine theorized.

Sources for this article included: the University of Florida Water Institute study of Lake Okeechobee; data from the South Florida Water Management District, the Florida Department of Environmental Protection and the U.S. Army Corps of Engineers, “Land into Water – Water Into Land” by Nelson Manfred Black; “A Brief History of Lake Okeechobee Ecosystem Responses to Water Level Management,” by Dr. Paul Gray, Florida Audubon; “The Swamp,” by Michael Grunwald; “Lake Okeechobee, Lady of Mystery,” by Twila Valentine; and the writer’s own research for the “Search for the Truth about Lake Okeechobee” series.

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