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Sea grasses in Tampa Bay bouncing back, partly thanks to drought

Scientists Kris Kaufman, foreground, and B.J. Grant check on sea grass growth in Tampa Bay as part of a study for Swiftmud.

Southwest Florida Water Management District

Scientists Kris Kaufman, foreground, and B.J. Grant check on sea grass growth in Tampa Bay as part of a study for Swiftmud.

Turns out the drought that's been turning lawns brown all over Tampa Bay is actually beneficial for one type of plant:

Sea grass.

The grasses are the leading indicator of the health of Tampa Bay, and the latest figures released Monday show that sea grass beds have now expanded to cover more of the bay than at any time since the 1950s.

A big reason for that is the drought that has been going on for the past three years, which has led to the tightest lawn-sprinkling restrictions in history. The reduction in rainfall and lawn-watering means there's less polluted runoff flowing into the bay and killing the sea grass, explained Kris Kaufman, the state scientist in charge of the sea grass study.

"Less runoff is great for the bay," said Kaufman, who works for the Southwest Florida Water Management District.

Scientists are hopeful that once the rainy season begins next month, the new sea grass will stick around. They are pinning those hopes on the fact that since 2000 the region has cut by 400 tons the amount of nitrogen pollution flowing into the bay even in normally rainy times — even as the population boomed.

Tampa Bay now has about 29,647 acres of sea grass, which is 1,300 acres more than the last time the scientists checked two years ago.

Hillsborough Bay, traditionally the most polluted area of Tampa Bay, nearly doubled its sea grass coverage, from 415 to 810 acres in the two-year period. The biggest increases were documented in Middle Tampa Bay, which extends from the Gandy Bridge to the Manatee County line, where sea grasses expanded by 31 percent.

Tampa Bay is Florida's largest open-water estuary, covering about 398 square miles at high tide.

Sea grasses are crucial to the bay's health because they provide food and shelter for a wide variety of fish and other marine species. They filter impurities in the water and stabilize the bay bottom's shifting sands. To thrive, sea grass needs water clear enough to admit a lot of light.

In the 1950s and '60s, dredging created land for development around the bay but wiped out much of its sea grass, hurting commercial and recreational fishing. Polluted runoff killed even more sea grass. By the early '90s, the bay had lost 80 percent of its sea grass, more than anywhere else in Florida.

The Tampa Bay Estuary Program, created by Congress in 1991, wants to build the bay back up to its 1950s level of 38,000 acres of sea grass. The latest findings by the agency commonly known as Swiftmud mark the highest amount so far.

In addition to the drought, estuary program director Holly Greening attributed the sea grass increase to efforts to cut the amount of nitrogen pollution flowing into area waterways.

She pointed out that the region's utilities have cut the amount of nitrogen oxide pollution pouring out of their power plant smokestacks to settle into the bay.

And as more and more homeowners use reclaimed water for their lawns, sewer plants dump less treated sewage directly into the bay, which also cuts the amount of nitrogen, she said.

A few places in the bay still showed declines in sea grass coverage during the past two years — Boca Ciega Bay, Terra Ceia Bay and the Manatee River. But all three are places where sea grass had been on the rebound previously, so scientists are not all that worried about them at this point.

Both Kaufman and Greening said they hope that, once rainfall returns to a more normal level, the gains the bay has seen in sea grass will not be wiped out.

"I think we'll continue to map increases," Kaufman said.

Craig Pittman can be reached at (727) 893-8530 or craig@sptimes.com.

Tampa Bay sea grass beds
1982 22,000 acres
2006 28,300 acres
2008 29,647 acres
Goal 38,000 acres (matches 1950s levels)

Sea grasses in Tampa Bay bouncing back, partly thanks to drought 05/11/09 [Last modified: Tuesday, May 12, 2009 9:35am]
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