‘Slow the flow’ to reduce algae blooms, harmful discharges and invasive plants

Posted 2/27/19

OKEECHOBEE -- Want to stop harmful algae blooms in Lake Okeechobee?

Want to reduce the growth of nonnative invasive plants — and the need to use chemical herbicides to control …

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‘Slow the flow’ to reduce algae blooms, harmful discharges and invasive plants

OKEECHOBEE -- Want to stop harmful algae blooms in Lake Okeechobee?

Want to reduce the growth of nonnative invasive plants — and the need to use chemical herbicides to control invasive plants — in the lake?

Want to control the lake level to reduce the need for harmful freshwater releases to the coastal estuaries?

Lake area residents urge: “Slow the flow: Protect Lake O.”

At recent meetings to discuss a new plan for the management of Lake Okeechobee, Big Lake area officials urged the U.S. Army Corps of Engineers to rise above the politics and follow the science. Scientists who have studied the watershed for decades say a critical part of the answer to Lake Okeechobee’s water quality and quantity problems lies in controlling the flow into the lake from the north, and cleaning the water before it enters Lake Okeechobee.

The Comprehensive Everglades Restoration Plan (CERP) cites the need for water storage north, south east, west of the lake. The University of Florida Water Institute, published in 2015, also calls for more storage and treatment north, south east and west of the lake.

Flow drives nutrient load

At the April 2013 Lake Okeechobee Basin Management Plan (BMAP) meeting, Frank Nearhoof, of the Florida Department of Environmental Protection, explained that “the flow drives the (nutrient) load” to Lake Okeechobee.

He said 90 percent of the water flowing into Lake Okeechobee comes in during a very short period of time. Most of the time there is very little flow into the lake, he said but 10 percent of the time there are rapid flows. That 10 percent of the time is also responsible for 60-70 percent of the total phosphorus going into Lake Okeechobee.

This is the key to restoring the lake, Mr. Nearhoof said. “If we can’t detain this flow, we are doomed to failure,” he said.

Nutrient load feeds algae

The excess nutrient load into Lake Okeechobee has also been blamed for harmful “blooms” of cyanobacteria. About a dozen types of cyanobacteria, commonly referred to as “blue green algae” (although it is not actually algae) are naturally present in Lake Okeechobee.

Some are capable of producing toxins, some are not. Even those capable of producing toxins do not always do so. Although cyanobacteria and algae are found naturally in all freshwater, the excess nutrient load, combined with hot weather, can cause the microscopic cyanobacteria to reproduce so rapidly that it becomes a visible “bloom.”

During the summer of 2018, when a massive cyanobacterial bloom was documented in Lake Okeechobee, Dr. Karl Havens, director of Florida Sea Grant, explained in his blog: “The solution to the algal bloom problem is to clean up the nutrient sources north of Lake Okeechobee and in the land around the two estuaries.”

Nutrient load feeds invasive plants

In the 1980s, when the Southern Everglades was overwhelmed and overgrown by vegetation that did not belong there, excess nutrient load was rightfully blamed. Following a federal lawsuit, a strict limit of no more than 10 parts per billion (ppb) phosphorus was set for water entering Everglades National Park. Thanks to strict water quality controls and the construction of water treatment areas, that limit has been met, allowing the natural Everglades vegetation to recover.

In 2000, following harmful algae blooms and an explosion of nonnative aquatic plants on Lake Okeechobee, the liquid heart of the Everglades, the Florida Legislature passed the Lake Okeechobee Protection Plan, setting a limit on phosphorus entering Lake Okeechobee at 105 metric tons per year (plus 35 metric tons from the atmosphere via rainfall). The state law called for the Florida Department of Environmental phosphorus target to be met by 2015.

However, without federal oversight, and with only a fraction of the promised state funding, the phosphorus reduction target has not been met. In 2017, due in part to hurricane Irma, phosphorus load into the Lake was 10 times the target load.

Failing to cut the nutrient load feeding the harmful aquatic plants, the state uses chemical herbicides to kill the unwanted vegetation. In recent months anglers from all over the state have complained about the Florida Wildlife Conservation Commission (FWC) spraying program, and have alleged that the spraying also destroys the native vegetation critical to the habitat for fish and wildlife. Anglers also claim the chemical herbicides add to the nutrient load in the waterways.

The connection between excess nutrient load and growth of harmful aquatic plants is well documented, according to Dr. Paul Gray of Florida Audubon. Excess nutrient load also causes overgrowth of some native Florida plants, such as cattails, squeezing out other native plants.

Hydrilla. Courtesy, IFAS, K.A. Langeland.

Man made changes mean water moves faster

In 1917, Taylor Creek, which was then known as the Onoshohatchee River, was deepened and straightened for navigation and to create a liquid highway from the fish houses on Taylor Creek to a railway connection north of the newly established City of Okeechobee.

Before the Kissimmee River was channelized, water that fell in the upper Kissimmee Valley slowly sheet flowed south to Lake Okeechobee. That hydrological trip took 6 to 8 months.

Now water that falls south of Orlando winds up in Lake Okeechobee in a matter of weeks.

Also north of the lake, straight deep canals — Harney Pond and Indian Prairie — also funnel water quickly into the lake.

Water is moving into the lake faster than Mother Nature intended. That means there is less time for water to evaporate into the air or percolate into the earth to recharge the aquifer along the way. With the current system, water may flow into the lake six times faster than it can be released - and six months of the year the flow south is limited by the federal government to protect the nesting grounds of an endangered bird.

The speed at which water can flow into the lake makes it physically impossible for the U.S. Army Corps of Engineers to control the lake level; they do their best to manage it. When the rising lake level threatens public safety, the corps relieves the pressure on the earthen Herbert Hoover dike by sending water east and west. The excess freshwater from the lake disrupts the salinity levels in the coastal estuaries, resulting in ecological harm. In addition, these harmful discharges are also limited by the capacity of the water control structures and, at best, can only slow the rise of the lake.

Additional water storage facilities are under construction east and west of the lake. Thanks to Senate Bill 10, preparations are underway for the Everglades Agriculture Area Reservoir south of the lake.