Water Clears in Southeast's Largest Lake

Lake Okeechobee, covering 730 square miles with more than 100,000 acres of wetland habitats, is located in the center of the Everglades ecosystem, a link between lakes and rivers to the north and wetlands and bays to the south.

Aided by two relatively inactive hurricane seasons and resulting low phosphorus inflows, the lake is experiencing environmentally favorable conditions not seen in more than three years, the district says.

Phosphorus levels in Lake Okeechobee recently registered an average of 77 parts per billion, ppb, across 27 monitoring sites, with near-shore areas at an average of 33 ppb showing the greatest improvement. One monitoring site registered a low 11 ppb phosphorus.

After hurricanes Frances and Jeanne in 2004, phosphorus levels in the lake reached more than 400 ppb; after gigantic Hurricane Wilma in 2005, levels averaged more than 300 ppb.

A portion of Lake Okeechobee's shoreline. (Photo courtesy SFWMD)

Despite winds and rainfall that swept along the coast recently due to Tropical Storm Noel, South Florida has experienced minimal storm activity during the past two hurricane seasons. This has vastly improved Lake Okeechobee's water clarity in near-shore areas, benefiting submerged aquatic vegetation.

One year ago, less than 3,000 acres of submerged aquatic vegetation dotted the lake bottom; today, improved water clarity is allowing more sunlight to penetrate to the lake floor, helping these plants to proliferate.

District scientists have just documented the recovery of submerged aquatic vegetation across more than 30,000 acres throughout the lake.

The current record drought affecting the southeastern states has not been all bad for the lake. Low water levels have created mud flats around the perimeter of the lake, attracting birds not normally seen in the Lake Okeechobee area to feed on insects and other invertebrates. More than 10,000 shorebirds, including gulls, terns and sandpipers, were observed during a monitoring mission earlier this year.

At the same time, low water levels threaten apple snails, the primary food source for the endangered snail kite. The district, in partnership with the Harbor Branch Oceanographic Institute, is exploring ways to grow apple snails and return them to the lake when water levels rise.

The Audubon Society of Florida in a report last year warned that the environmental health of the lake "has been degraded from decades of management that has placed the wants of some humans above the needs of wildlife and the environment."

"The most important action that can be taken is to stop the importation of additional phosphorus into the watershed," Audubon says in its report. "At the same time that Comprehensive Everglades Restoration Plan and the Lake Okeechobee Protection Plan are being designed to reduce phosphorus inflows to Lake Okeechobee by about 400 tons per year, at a cost nearing a billion dollars or more, an additional 5,000 tons of phosphorus are imported to the watershed each year."

Most of the phosphorus loads to Lake Okeechobee come from truck and field crops, pasture, and dairy operations. Pasture has a relatively low load of phosphorus per acre, but is the largest land use in the watershed, thus its large contribution to the lake. Dairies and row crops, occupy only about four percent of the watershed yet bring in more than half the annual phosphorus to Okeechobee’s lower watershed.

Decades of phosphorus loading have resulted in the accumulation of a thick layer of organic muck over 300 square miles of the lake’s bottom, which contains an estimated 51,000 tons of phosphorus.

Now, taking advantage of the low water levels, crews are scraping away excess sediments. Earlier this year, more than 1.9 million cubic yards of phosphorus-rich muck were scraped and trucked off Lake Okeechobee's dried-out shoreline, exposed by this year's drought.

In addition, 1,000 native pond apple and cypress trees were planted on the rim canal and spoil islands near Clewiston, and 1,725 trees were planted near Moore Haven.

Adding native trees where they once grew in abundance and re-exposing the lake's naturally sandy bottom are expected to further improve critical aquatic habitats when water levels return to normal.

"Lake Okeechobee is going to be healthier as a result of this work," said district executive director Carol Ann Wehle. "Although the drought and current water shortage have brought many difficult challenges, they also provide a real opportunity for environmental restoration in Lake Okeechobee and other sensitive areas."

Copyright Environment News Service (ENS) 2007. All rights reserved.