Working On A Chain Gang

Jacksonville fights algae with 'floating gardens'

0 Comments | Florida Times Union, Jul 10, 2010 | by JAMES CANNON

Hoping to stem harmful algae blooms in the St. Johns River, Jacksonville is experimenting with a natural way of filtering out contaminants.

The answer may lie in floating gardens of specially selected grasses and weeds that serve as high-powered water scrubbers.

Initial testing by a company is being done at a retention pond near Talleyrand Avenue, and so far Jacksonville city officials are optimistic.

The problem is an overload of nitrogen and phosphorous, much of it the result of stormwater runoff from over-fertilized lawns and failing septic tanks. High nitrogen levels lead to algae blooms, which kill fish and raise an unmistakable stench. Jacksonville residents witnessed the adverse effects of nutrient pollution in May and June, when clouds of algae wreaked havoc on the river's ecosystem.

The city has built hundreds of retention ponds over the years to control flooding and help remove pollutants before they hit the river, and launched an advertising campaign to inform the public about the dangers of over-fertilizing. But the problem remains.

"And this is only the beginning. Conditions are right for an even more severe problem," said St. Johns Riverkeeper Neil Armingeon.

A typical retention pond removes about 35 percent of the nitrogen and phosphorous in the water before it enters the river. Natural degradation and absorption by plants are the primary tools for eliminating excess nutrients, said Dana Morton, an aquatic biologist with the city's Environmental Quality Division.

The vegetation mats involved in the Talleyrand experiment aim to double the filtration rate - and save the city a lot of money.

"This has the potential to revolutionize how water is filtered in cities with high nutrient levels," said Steve Beeman, co-owner of Beemats, the company that designed and built the garden floats.

There are currently four sections in the middle of the retention pond and a U-shaped grouping of mats around the outtake valves to give the water a final screening.

The octagonal mats are made of closed-cell foam rubber dotted with holes housing six varieties of nutrient-eating plants: Redtop, Soft Rush, Canna, Pickerel, Bur-Marigold and Arrowhead. Most of the plants can be found growing wild in Northeast Florida.

When the plants reach maturity, their root systems extend up to 2 feet under water, greatly increasing their efficiency as water cleaners.

Beemats, a New Smyrna Beach-based company, has installed enough mats to cover 12,000 square-feet, or 5 percent of the 5 1/2-acre pond's surface area. Although Canna and Soft Rush absorb the most nitrogen and phosphorous, Beeman believes diversity is key.

"We need to find out which types of plants work well in different seasons and climates," he said. "We are trying to find the least labor-intensive, most efficient and most cost-effective way to do this."

The mats' 30,000 plants must be replanted every year to ensure damaging nutrients are being effectively removed from future river water, he said. Once the plants are removed, they're composted and used to fertilize top soil in the area.

A STUDY OF NUTRIENT LEVELS

Nutrient levels at the retention pond have been studied for the past two years so that comparisons can be made after the experiment, which began last month, runs its course.

Although Beeman's mats have been used in other cities - Naples, Fort Myers and Tallahassee - Jacksonville is the first to have them installed as part of a statewide pollution-control experiment. To qualify, a city must study nutrient levels in its reservoirs for a specified time period
water filtration