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The Tampa Bay Estuary Program has selected seagrass restoration target depths for each major bay segment at which adequate light conditions (20.5% of subsurface irradiance) shall be maintained to ensure seagrass growth and the long-term Tampa Bay seagrass goal of 15,400ha.
To evaluate the progress of the seagrass restoration effort, field investigations of accurate water depths at the deep edges of Tampa Bay seagrass meadows are now underway using differential GPS carrier-phase processing.
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| Dr. Roger Johansson (City of Tampa) presents poster at USGS Tampa Bay Pilot Study Science Conference. |
One GPS instrument serves as a base station at a surveyed benchmark with a known altitude above the mean sea level and a second instrument is towed across the seagrass meadows. The technique yields accurate depth measurements of approximately +/- 5cm of survey sites located up to 10km from bench mark sites. The depth of the measured deep edges ranged from about -0.30mMTL for Halodule wrightii meadows in the upper section of Hillsborough Bay to near -2.0mMTL for Syringodium filiforme meadows on the southwestern side of Middle Tampa Bay.
The estimated average percent of subsurface incident light available at the deep edges of the surveyed seagrass meadow ranged from 59.8 to 28.9% for H. wrightii, from 31.4 to 16.0% for S. filiforme and from 20.9 to 16.9% for Thalassia testudinum. The differential GPS carrier-phase processing technique was field practicable and measured seagrass elevations with acceptable accuracy.
The field measurements provided an important first-step in understanding the current depth distribution of the major Tampa Bay seagrass species.
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