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Florida Keys News - Islamorada/KL Free Press
Wednesday, January 30, 2013
Tracking water quality through algae

EVERGLADES -- Florida International University biologist Tom Frankovich pulls on his wetsuit and jumps into the water of Seven Palm Lake.

Wearing a mask, snorkel and fins, and carrying a square tool called a quadrat, he gets quickly to work. Frankovich dives down to the bottom of the shallow estuary -- just five feet deep at this first spot of the day -- sets the quadrat on the lake floor, and then by looking at how much vegetation shows up in its 20 subdivided sectors, estimates the total percentage of algae and seagrass cover there.

"Less than 5 percent ruppia," he calls out upon surfacing, referencing a type of seagrass.

Frankovich dives to the bottom again, surfaces a moment later and yells "zero" back to the boat, where an assistant stands ready with pencil and paper to record the data.

He circles the boat, making 15 such dives and calling out the result each time. Then he's back in the boat, motoring to the next site, to do it all over again.

Every three months for the past six years, Frankovich has been making these 15 dives at 44 sites scattered in the brackish lake system that borders north central Florida Bay, on the southern edge of the Everglades National Park mainland. He augments that data with water quality samples that he takes monthly at the same 44 sites -- all in an effort to learn more about the processes that are acting upon this Everglades estuary system.

He hopes that scientists and policy makers will one day be informed by what he discovers when making decisions about how to implement Everglades restoration projects.

"One of the prerequisites of aquatic system health is water quality," Frankovich said. "And getting that water quality right and interpreting the relationship between the water quality and the aquatic community is vital."

The areas that Frankovich studies are divided into two lake systems. The easterly one, which has greater connectivity between the lakes themselves and between the lake and Florida Bay, includes Terrapin Bay, Monroe Lake and Middle Lake, in addition to Seven Palm.

The westerly system includes West Lake, Cuthbert Lake, Long Lake and a lake known as The Lungs.

Both areas were chosen because anecdotal accounts suggest they contained substantial populations of a leafy green algae species called chara prior to the construction of major water diversion canals en masse in the Everglades starting in the 1950s. Those healthy chara beds used to support large populations of wading birds, as well a migratory winter ducks, such as the coot, with its black body and white beak, and the scaup, a black-headed duck with a gray and white body.

But chara cover on the lake bottoms has gotten much thinner in recent decades, scientists believe, and with it have gone the birds and ducks, as well as the juvenile shrimp, small crabs and small fish that the chara algae supports.

In general, scientists blame the precipitous decline in the water quality of the Florida Bay region over the past several decades on overly salty conditions caused by the canal system, which diverts Everglades freshwater east, sending it out to the Atlantic Ocean rather than into the bay.

Since chara typically thrives in fresh and brackish water, increased salinity was also assumed to be the reason for its decline in the lakes of the southern Everglades.

But during his monitoring efforts, Frankovich learned that a persistent bloom of the surface algae phytoplankton was teaming up with excess salt to take a toll on chara.

Frankovich laid out his findings in a peer-reviewed 2012 paper published in the journal Marine and Freshwater Research. In it, he wrote that diminished light conditions, brought about by phytoplankton blooms, are especially prevalent in the westerly system he studies, which he has dubbed Alligator Creek for one of the water bodies that connects those lakes.

The easterly system, which he calls McCormick Creek after one of its connecting flowways, had similar salinity to the Alligator Creek area, but much better water clarity. It also had twice the amount of chara cover.

As usual, the main ingredient in the algae bloom is excess phosphorus. Frankovich's readings show that the Alligator Creek area has more than three times as much of the nutrient as the McCormick Creek basin. So bringing back the Alligator Creek chara, and all the fish, crabs, wading birds and ducks that it supports, might be as dependent upon a reduction in phosphorus as it is on an increase of freshwater flow.

The good thing is that the two might be interrelated.

Frankovich isn't yet sure what has brought phosphorus levels up in the Alligator Creek basin. That's part of what he's trying to tease out as he gathers more data from the two lake systems. But he has some educated guesses.

It's partially because the western Florida Bay region is known to be more loaded with phosphorus than the eastern part of the estuary. Another factor could be the excrement generated by woodstorks that nest at the large Cuthbert Lake rookery.

But Frankovich hypothesizes that the biggest factor is the geography of the Alligator Creek system. In brackish water transition zones of the southern Everglades, most of the phosphorus pushes in with seawater from the south, while fresh water tends to flush out phosphorus loads.

When the South Florida canal system began diverting large quantities of fresh water a half century ago, it allowed more seawater to push into the Everglades brackish zones, including the Alligator and McCormick creek areas. But, Frankovich believes, because the lakes in the McCormick Creek area have more connectivity and better water flow than those in Alligator Creek, the phosphorus there flushes out more easily.

However, if more fresh water were to reach Alligator Creek, it too would flush better, while also seeing a decrease in its salt levels.

While the data is still too raw to draw a conclusion, Frankovich said he's hopeful that is already happening.

Starting with the wet season of last summer, the South Florida Water Management District began operating a $26 million pump, canal and water retention system designed to get more fresh water flowing into Florida Bay.

Since then, Frankovich has seen a slight improvement in the water clarity of Alligator Creek, as well as an increase in chara cover. In fact, during his quarterly visit to the basin last week, the chara was so thick in Long Lake that he couldn't use his propeller.

He's also encountering far more ducks than he has seen during his previous six years of water monitoring.

"The ducks do seem to be there because the vegetation is there," Frankovich said. "And the vegetation is there because the water quality is better."

rsilk@keysnews.com

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