May 12, 2009

Seagrasses in Tampa Bay bouncing back, partly thanks to drought

Craig Pittman, St. Petersburgh Times 11 May 09;

The leading indicator of Tampa Bay's health is the size of its sea grass beds — and the latest figures, released Monday, show they are now covering more of the bay than any time since the 1950s.

One big reason: the drought that's been going on for the past three years, which has led to the tightest lawn-sprinkling restrictions in history.

Less rainfall and less lawn-watering means less polluted stormwater runoff flowing into the bay and killing sea grass beds, explained Kris Kaufman, the state scientist in charge of the seagrass study.

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

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 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 back on fertilizer use among homeowners, thus curtailing the amount of nitrogen pollution flowing into area waterways.

Greening also 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.

All told, the estuary program estimates that over the past decade Tampa Bay businesses and residents have reduced the nitrogen flowing into the bay by more than 400 tons, even as the region's population grew by nearly a million people.

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.

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