How much phosphorus comes from flood control ditches?

Posted 11/14/19

OKEECHOBEE — For more than 20 years, those who live and work in Lake Okeechobee’s northern watershed have wondered just how much of the phosphorus entering the big lake is a direct effect of the …

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How much phosphorus comes from flood control ditches?


OKEECHOBEE — For more than 20 years, those who live and work in Lake Okeechobee’s northern watershed have wondered just how much of the phosphorus entering the big lake is a direct effect of the Central and South Florida Flood Control Project (C&SF).

In the 1960s, the C&SF Project modified the native Kissimmee-Okeechobee-Everglades system extensively throughout South Florida, including digging canals to achieve flood control in the Upper and Lower Kissimmee basins.

In 1998, Pat Hogue of the Okeechobee County Extension Office was among those who took soil samples from the spoil along the Kissimmee River channel — the dirt dug out of the riverbed to create a straight, deep channel to speed the flow of water from the Kissimmee River basin south to Lake Okeechobee.

Taking soil samples is a routine part of an extension agent’s job. When the samples were sent to the University of Florida for testing, the phosphorus readings spiked “off the chart,” as high as 448+ parts per million. The + indicates that at this point there is so much phosphorus, further testing is irrelevant, he explained.

How does that compare with other soil? According to Mr. Hogue, for Bahia grass pastures, anything below 15 parts per million might need additional phosphorus in fertilizer. However, under the Best Management Practices (BMP) program, before ranchers can apply fertilizer to a pasture, they must also conduct plant tissue tests to make sure the grass needs the additional phosphorus, since Bahia has long roots and phosphorus levels deeper in the ground could be higher than phosphorus levels in the soil close to the surface.

In the average backyard garden, phosphorus levels of 30-50 parts per million are desired, depending on what you are growing, Mr. Hogue explained.

Mr. Hogue said he and his colleagues took their findings to the South Florida Water Management District, but the governing board was not interested. “They accused us of not knowing how to take a soil sample,” he recalled. The board ridiculed extension agents with decades of experience taking soil samples, accusing them of not knowing how to do one of the most basic parts of their job.

Over the past 30 years, others have tried to get SFWMD to consider the phosphorus loading that could be coming from the flood control channels and from the spoil left on the canal banks, with no success.

Why wouldn’t previous SFWMD water management boards consider this possible source of the excess phosphorus flowing into Lake Okeechobee? Okeechobee News reporter Twila Valentine, who won the Florida Press Association’s top award for environmental reporting for her coverage of the Kissimmee River restoration project, had a theory: “Nobody messes with the Mouse,” a reference to the Orlando theme parks and the tourism dollars they generate. Admitting the phosphorus could be coming from the river channel, and finding a way to address that problem, could jeopardize the flood control system that has allowed rapid development in the Orlando/Kissimmee area she theorized.

Mr. Hogue tried the soil tests again in 2009. The results were the same — with the phosphorus readings “off the scale.” He published his findings in December 2010 in an article titled “Impact of Cattle Grazing in South Florida.”

Not only did digging the channel leave soil high in phosphorus on the banks, but the Kissimmee River restoration project pushes the soil back into the channel, said Mr. Hogue. Multiple times since the restoration work started, storm events have caused that phosphorus-rich fill to be washed out of the channel and into Lake Okeechobee. Most recently, Hurricane Irma damaged a section of the restoration in an area that had just been filled prior to the storm.

Others have brought the issue to the attention of other SFWMD governing boards over the past 20 years.

At the Aug. 14 SFWMD meeting, the question came from Matt Pearce, president of the Florida Cattlemen’s Association. Mr. Pearce said the high levels of phosphorus in the water flowing into the lake is legacy phosphorus, much of it unleashed by the channelization of the Kissimmee River for flood control. One of the largest pockets of phosphorus wasn’t mined by industrial industry, Mr. Pearce said. It was unintentionally mined by the U.S. Army Corps of Engineers when they dug the Kissimmee River channel. The phosphorus-rich material was placed on the spoil bank, and when it rains that phosphorus goes into the river, he said. Then when the corps decided to “restore” the river, they started putting that phosphorus-rich spoil, now in loose form, back into the river, he continued. When a big storm sends massive flows of water down the Kissimmee River, it blows the soil out of the channel, sending it into Lake Okeechobee.

“That is why we have phosphorus spikes,” when there is heavy rainfall, he said. “I don’t know anybody in here who can fix that.”

Most recently, at the Nov. 5 meeting in Okeechobee to discuss changes to the Works of the District rules for the northern watershed, Gary Ritter of Florida Farm Bureau urged water managers to examine the nutrient dynamics going on in the flood control canals.

“Agriculture has been in the watershed for many decades. The real problems started when the flood control system was put into this watershed,” he said.

Canals dug for development might also contribute to the problem. Mr. Hogue recalled running a soil test for a homeowner who was having difficulty with his lawn in the Treasure Island development in Okeechobee County. As with the riverbank spoil, the phosphorus tests spiked. Mr. Hogue said an examination of the property found that when the canals were dug to provide homeowners with waterfront property and lake access (via the Rim Canal), the phosphorus-rich spoil was spread out over the adjoining lots.

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