Study shows 12-15 feet range best for lake’s ecology

What will the new Lake Okeechobee Systems Operations Manual (LOSOM) look like? In meetings around Lake Okeechobee, area residents encouraged the U.S. Army Corps of Engineers to follow the science.

Special to the Lake Okeechobee News/Zach Welch/SFWMD
Submerged aquatic vegetation in Lake Okeechobee has increased over the past year. Occasional but rare, extreme low water levels can benefit the SAV. The RECOVER Lake Stage measures put the lake level at 12 to 15 feet with deviations no more often than once a decade.

If the corps follows the recommendations of their own scientists, the new lake schedule will vary only slightly from the current plan, which strives to keep the lake between a low of 12.5 feet above sea level and a high of 15.5 feet.

The draft RECOVER Lake Okeechobee Stage Envelope Performance Measure, published online on Dec. 5, sets the preferred lake level at 12-to-15 feet.

The target is for the lake to remain within in the desired envelope and avoid extreme stages.

“A wide body of published research documents the benefits of seasonally variable water levels within the range of 12.0 feet as a June-July low and 15.0 feet as a November-January high, on the plant and animal communities of Lake Okeechobee,” the documentation states.

Keeping the lake in the healthy 12-to-15 feet range has many benefits, the report continues:

• Falling water levels from late winter to spring concentrates prey resources in the littoral zone for improved wading bird foraging and nesting.

• Water levels near 12 feet benefit submerged plants and bulrush at the outer edges of the marsh by reducing light attenuation in the summer months and promoting growth of underground biomass for survival during turbid, high-water events.

• A natural rocky reef in the southern portion of the lake isolates turbid water from large areas of the near-shore zone at a lake stage around 14 feet. This helps improve water clarity, promotes submerged aquatic vegetation (SAV) and reduces phosphorus levels.

• Seasonal variation within the 12-to-15 feet envelope results in annual flooding and drying of the majority of the marsh, which favors development of a diverse emergent plant community and reduces muck accumulation.

• Extreme high stages allows wind-driven waves to uproot SAV.

• High stages allow deposition of mud into the near-shore regions, covering sand and peat sediments and reducing their suitability for SAV.

Levels above the target range are harmful to the lake, the report continues.

• High stages transport nutrient-rich water from the mid-lake region into the littoral zone where the higher nutrient levels encourage the growth of invasive aquatic vegetation which crowds out the native SAV.

While rare, occasional low lake stages can benefit the lake’s marshes, extreme low lake levels — more often than once a decade — can also be harmful, the report continues.

• Low lake stages result in direct losses of habitat and can severely limit or even eliminate entire breeding seasons for many species of fish and wildlife.

• Exposing peak in the southern portions of the lake can degrade habitat for the endangered Okeechobee gourd and increase risk of peak fires, leading to a permanent loss of marsh elevation.

• Ecological recovery from extreme low lake stages can take multiple years.

Ideally, the lake should slowly rise during the wet season and slowly fall during the dry season.

The report notes:
• High lake stages (above 14.5 feet) at the end of the wet season maximize the wetlands and aquatic habitat for the breeding season for many species of fish and wildlife.
• A moderate recession (less than 0.2 feet per week), throughout the majority of the spring avoids stranding breeding fish.
• Moderate ascension rates (less than 0.25 feet per week) throughout the majority of the wet season reduce the flooding of alligator nests, snail kite nests and apple snail eggs, while allowing SAV growth to keep up with the light reducing penetration.

The evaluation was based on 52 years of data (1965 through 2016). The 15-page report includes two pages just to reference the studies referred to, and to acknowledge the scientists and researchers who contributed to the studies.

Comments on the 15-page Draft Lake Okeechobee Stage Envelope Performance Measure will be accepted through Dec. 20. Please submit comments via email to Gretchen.S.Ehlinger@usace.army.mil, if possible, (recommended subject RECOVER Lake O Stage Envelope PM Comments) and reference the line and/or page numbers to expedite the review process.

Comments may also be mailed to: Dr. Gretchen Ehlinger, U.S. Army Corps of Engineers Jacksonville District, P.O. Box 4970, Jacksonville, FL 32232‐0019.

Additional information on RECOVER is available online at saj.usace.army.mil/RECOVER/.

Publisher/Editor Katrina Elsken can be reached at kelsken@newszap.com

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