Pilot program re-creates low-salinity habitat

Once upon a time, when Florida panthers and black bears still freely roamed the Tampa Bay watershed, more than 300 creeks and rivers supplied the estuary with fresh water, creating low-salinity habitats that supported the vast majority of fish species as well as a multitude of birds and other wildlife.

As the region developed though, the value of that critical habitat was not recognized. Ditches were dug to drain “useless swamplands” for agriculture, then dammed to hold freshwater for crops (see baysoundings.com/central-pinellas-a-century-ago-lowering-lakes-to-raise-agriculture/). Even more ditches — some dug by hand — crisscrossed mangrove forests to minimize deadly diseases carried by mosquitoes.

A half-century later, researchers and scientists are looking at ways to reverse that damage and reconnect Tampa Bay with low-salinity habitats that fish and other wildlife can use. “Nearly 100% of the tributaries that once drained to Tampa Bay have been affected,” reports Ed Sherwood, senior scientist for the Tampa Bay Estuary Program.

A pilot program in partnership with the Southwest Florida Water Management District is looking at two channels that drain into Old Tampa Bay to see what impact opening them will have on water quality and fisheries.

Channels A and G, located near Rocky Creek in northwest Tampa, are basically long skinny lakes with weir structures that allow them to overflow into Tampa Bay during periods of high rain. They block bay organisms from using the waters, particularly juvenile fish — including snook and redfish — that require low-salinity habitat for part of their lives.

From a water-quality perspective, allowing the channels to drain naturally will minimize “flashy” increases in fresh water carrying high levels of nutrients from the largely urbanized watershed. The channels also are expected to be colonized by oysters that filter nutrients, and the tidal fluctuations that expose channel sediments and inundate vegetated shorelines will reduce nutrient levels.

Opening the weirs to allow salt water in the canals has also reduced the aquatic weeds that created floating mats, adds Nancy Norton, program engineer at SWFWMD’s Surface Water Improvement Program. “Our aquatic maintenance team reports that they have been able to really cut back on the herbicides because the species that formed the mats don’t like salty water.”

Residents were first informed about the pilot program at a public meeting and saw results almost immediately after the weirs were opened. Water in the channels and Rocky Creek dropped one to two feet in the first 48 hours as the fresh water that had been dammed up was released into Tampa Bay.

Although initially alarmed by the dramatic drop off, most residents are delighted to see the return of wildlife — including manatees and dolphin ­— in what had been freshwater channels. “Fishermen, in particular, should see the benefits of reconnected habitats for juvenile fish as well as healthier seagrasses in Old Tampa Bay,” Sherwood said.

Once final data has been collected, results will be shared with residents and their input sought on plans to develop long-term options for the channels. “We’re thinking about extending the pilot program for another year,” Norton said. “We had planned on one year so we’d get both dry and wet season data, but sometimes weather can fluctuate to such a degree that we’d like to get another year of data.”

But even if the pilot program is deemed very successful, opening additional tidal tributaries may be limited by land uses around them, she said. “The tidal fluctuations may or may not be acceptable to the development that has occurred — there are a lot of reasons why the structures are there and it may not be feasible to remove them.”

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