Lake still suffering from Hurricane Irma damage

OKEECHOBEE — In September 2017, Hurricane Irma churned the waters of the big lake, ripped up aquatic vegetation and left the shoreline littered with uprooted plants. After the storm, drainage from the north caused the lake to rise rapidly, drowning the nearshore vegetation with high water.

The lake’s ecosystem recovery can’t start until the water recedes.

The lake dropped down below 13 ft. in May, but unfortunately it did not stay low enough, long enough for the lake marshes to recover. May brought four times the average rainfall for that month, pushing the lake level back up, and pushing any chance for marsh recovery to the next dry season.

According to Zach Welch, of the South Florida Water Management District Lake and River Ecosystems division, there are three parts of the lake in play. The pelagic zone is the deep water near the center. This is where the muck build up is, and it tends to be muddier than the other parts of the lake. The nearshore zone has clear or turbid water, depending on how high the lake is. The littoral zone (the marshes around the edge of the lake) has shallow water, dense vegetation and clearer water.

In the nearshore zone, higher lake stages tends to increase the ability for the turbid water to be transported into the grassline. As the lake level increases, so does the phosphorus level in the nearshore zone.

With lower lake stages, more plants can grow in the nearshore zone.

According to SFWMD, the lake lost about 11,000 acres of submerged aquatic plants due to Irma. Those plants cannot recover until the lake drops down below 13 ft. and stays down long enough for the plants to grow.

During the hurricane, Irma’s winds pushed the water up higher than 20 feet at Fisheating Creek. At the same time, the east side of the lake dropped down below 10 feet. The storm winds resulted in an 11 ft. difference in lake level from one side to the other. The water sloshing around stirred up the mud.

The hurricane debris also created a barrier at the edge of the marsh, further disrupting the natural ecosystem.

“We have hit 16 feet or deeper for 6 years in a row,” said Dr. Paul Gray of Florida Audubon.

“The SAV (submerged aquatic vegetation) have been declining.

“Once the SAV is gone, or reduced to a patchy existence, the nutrient-rich water from the middle can wash into the emergent plant zone and spur cattail increases. That is going on now and we won’t know how much that will amount to until the SAVs can grow back and stop the trend – which won’t happen until the next major drought.”

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