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Tuesday, Sep 19, 2017
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Report: Excessive summer rain damaged health of Tampa Bay

A report released by the Tampa Bay Estuary Program that rates the quality of water in Tampa Bay last year shows a decrease in clarity due to algae blooms mainly caused by the heavy rains that fell on the region in July, August and September.

The areas where water quality declined and algae blooms spiked were near storm-water and sewage-treatment plants that overflowed during the rain that dumped, in some areas, more than 20 inches over a two-week period. Treatment plants that were over capacity were forced to release untreated water into the bay and the nutrients contained in that discharge caused algae to bloom.

It’s the first time in three years that water quality goals were missed, estuary program officials say.

What remains unknown is the fate of the bay’s seagrass beds which, prior to the rainfall last summer, had continued to grow beyond expectations providing an ecosystem that remains vibrant throughout most of the bay.

“What the assessment says is that we have slight declines overall in water quality in two major segments of the bay,” said estuary program spokeswoman Nanette Holland O’Hara. “But the good news is we now have sufficient light penetrating to the bottom of the bay to maintain seagrass growth and promote the seagrass recovery.”

The 2015 Tampa Bay Water Quality Assessment, which used data collected from 45 stations all across the bay, is the fourth of an overall plan implemented in 2012 to gauge the progress of water quality in Old Tampa Bay, Hillsborough Bay, Middle Tampa Bay and Lower Tampa Bay.

The largest spike in algae, referred to as chlorophyll-a in the report, was in Old Tampa Bay, which lies north of the Gandy Bridge. There, chlorophyll-a levels observed were well above the annual averages dating back to 1974, the report said.

“Old Tampa Bay always has been a priority for us because it has typically lagged behind the other areas in seagrass recovery,” O’Hara said. “A lot of it has to do with the upper end of the bay which doesn’t have the tidal flows that the other parts of the bay have.”

A spike also occurred in Middle Tampa Bay, which stretches from the southern end of Tampa to the tip of St. Petersburg. Together, Old Tampa Bay and Middle Tampa Bay make up about 50 percent of the overall water body.

Except for those three months of heavy rain, O’Hara said, all the targeted water clarity levels were met. But the summer rains caused enough algae to skew the results.

Algae blooms block sunlight from reaching the bay’s bottom and can have a negative effect on seagrass beds, which rely on clear water and sunlight to flourish.

The nuisance algae, Pyrodinium bahamense, was reported in Old Tampa Bay throughout the summer and fall.

In the months since the heavy rains, the bay has flushed itself out, O’Hara said.

“Our bay is pretty resilient,” she said. “We were hoping this was a short-lived response to those extraordinary months.”

Aerial surveys and photographs were recently completed, but the report on seagrass bed health for 2015 won’t be completed for another year, O’Hara said.

“It’s just too early to tell,” how seagrass in the bay fared, she said.

Scientists at the end of the summer predicted vast swaths of seagrass beds, which had been growing steadily since the 1980s, would die off because of all the nutrient rich rain water draining into the bay.

Sea grass beds are considered one of the key building blocks of a healthy estuarine system, environmental experts say. They flourish in less than 6 feet of clear water and are important nurseries and feeding grounds for numerous species in Tampa Bay, including shrimp, spotted sea trout, red drum and snook.

In the winter of 1997-98, parts of Tampa received about 10 inches of rain in two days, and the resulting algae bloom killed off about 1,200 acres of seagrass in the bay.

A study released in May said Tampa Bay’s seagrass beds have rebounded to such a remarkable degree that their health is as robust as it was 60 years ago. The acreage of beds had not only met the goal of 38,000 acres set in the 1990s, but exceeded it by more than 2,000 acres.

The Southwest Florida Water Management District seagrass mapping survey last year counted 40,295 acres of healthy seagrass, the most in the system since 1950, before dredging and pollution began carving away at the seagrass plains.

In the 1970s, Tampa Bay coastal development and pollution along with dredging cut deep into seagrass beds, water resource scientists say, and in the 1980s, seagrass acreage was the lowest it ever was.

In Old Tampa Bay, the expanse between the Gandy Bridge to Oldsmar, seagrass bed resurgence has lagged behind because of pollution, poor current circulation, sewage treatment plants and nutrient-rich runoff from Lake Tarpon. Still, the water management district’s survey last summer had encouraging news: There was a 47 percent increase in seagrass in that region, or about 3,273 additional acres, since 2012.

While the fate of the sea-grass beds remains murky, some certainly will be lost.

“One would expect when water quality is degraded from heavy rainfall over the summer and this winter, that we undoubtedly will see widespread decline of seagrass beds in areas that up until recently were recovering,” said Peter Clark, president of Tampa Bay Watch, an environmental group that monitors water quality in the bay and often uses volunteers to plant seagrass beds in dead zones. “Those recovering beds are the most sensitive to water quality impacts and that’s where we will see changes occur.”

The next water management district survey of seagrass beds in Tampa Bay is scheduled to be released in the spring of 2017, though the aerial survey and photography, typically done over the winter months because that’s when the water clarity is best, is completed, O’Hara said.

“The bay looks pretty good right now,” said O’Hara. “I’ve been out kayaking and fishing this past week and it’s pretty clear right now,”

kmorelli@tampatrib.com

(813) 259-7760

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