Submerged aquatic vegetation in lake shows signs of recovery

OKEECHOBEE — Lake Okeechobee’s submerged aquatic vegetation (SAV) is showing signs of recovery, according to information shared at the Aug. 8 meeting of the Lake Okeechobee Aquatic Plant Management Interagency Task Force, representatives from the Florida Wildlife Conservation Commission, the U.S. Army Corps of Engineers and the South Florida Water Management District. The meeting was held at the SFWMD office in Okeechobee.

The SAV is the lake’s natural filter system. It also provides spawning areas for fish, cover for young fish and habitat for birds and wildlife.

The lake’s SAV suffered during recent high water years, dropping from 40,000 acres to less than 20,000 acres. Water levels above 16 feet (above sea level) drown out the marshes around the lake’s edges.

In 2017 Hurricane Irma churned Lake Okeechobee, destroying about 11,000 acres SAV, according to SFWMD reports. The storm also dumped enough rain in the watershed north of the lake to raise the lake level three feet in a matter of weeks as the Kissimmee River valley drained into Lake O. The high water levels in the lake and turbidity in the water meant the light did not reach the lake bottom, making it difficult for submerged plants to grow. The SAV dropped to about 5,000 acres.

According to the meeting presentation, it takes about two years for the big lake to recover from a hurricane, and the recovery cannot start until the lake level drops low enough for sunlight to reach the plant seeds on the lake bottom. The SAV is the natural competitor for the nutrients that feed blooms of algae and cyanobacteria. The loss of SAV results in increases in algal blooms.

The ecological changes in the lake following hurricane damage are not preventable but are predictable, the task force members were told. After a hurricane, the lake will have a couple years of algae blooms and loss of fisheries.
Don Fox of FWC said while some lake area residents and visitors are concerned that the lake level is too low, the lake can come up very quickly if there is a storm. He said changes in the watershed north of the lake have a big impact on the Big O.

“The upper Kissimmee basin has lost its dynamics,” said Mr. Fox. “There is a lot of unpredictability.”

The plants have been growing a lot faster since July, said Brendon Hession of FWC.

He said that also means the invasive non-native plants are growing faster.

“The majority of plants are in less than 2 feet of water. People using the lake are not seeing these plants,” he said.

Mr. Fox said years ago, “when water was low, crews were out on 4 wheelers treating water hyacinth when they were 4 inches tall.” He said the current plant management plan uses a different strategy.

Prior to 2008, the lake was managed on a schedule that allowed the water level to get to 17 feet. Mr. Fox said this meant there was no littoral edge — the SAV was crammed up against the dike.

The Lake Okeechobee Regulation Schedule (LORS 2008) tries to keep the lake between a low level of 12.5 feet and a high of 15.5 feet. The lake has a much better mix of native plants since LORS 2008 was adopted, but it makes the non-native invasive vegetation more difficult to treat, he said.

“LORS 2008 was designed to enhance plant growth, to enhance the ecology of the lake,” he said. Exotic plants are just taking advantage of the situation.

According to the meeting report, this year’s lower lake levels have helped more of the SAV to recover. Chara is growing in the lake near Clewiston and eel grass is growing near Kings Bar. The report estimated 3,500 acres eel grass, 1,500 acres of hydrilla and 1,000 acres of Chara (also called muckgrass) with densities ranging from 5 to 85 percent coverage in the lake.

According to the report, the reason the Harney Pond area has not recovered is that the bullrush line was taken out by Hurricane Irma. Without that protective bullrush line, there is too much turbidity in the water there for SAV to grow.

Mr. Hession said Chara is considered a “pioneer species.” It is usually the first plant to come back. It’s a good sign for the lake, he said. Other SAV plants usually follow the Chara.

Dr. Gray said SFWMD usually goes out in August to survey all of the SAV in Lake Okeechobee.

He said while this year’s lower lake level has benefited the SAV, in general it is best for the lake’s ecology that it go no lower than 12 feet. Occasional low water years are a part of the natural cycle.

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