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Post-hurricane water quality update from the Sarasota Bay Estuary Program

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From SBEP Director Dave Tomasko:

On Wednesday, October 12th, Jay [Leverone] and I were joined by staff from the Southwest Florida Water Management District (SWFWMD) for our second sampling effort for Sarasota Bay. This effort is meant to enhance, not substitute for, existing monitoring efforts. It also focuses on the lower bay, since that is the area hit hardest by the winds and rainfall from Ian. We are also sampling additional parameters – the amount of bacteria in the water, and the amount of organic material washing into the bay that can cause oxygen levels to drop and bring about fish kills.

To save time – with all the slow speed zones in the lower bay – we start off at the 10th Street boat ramp and then head out of New Pass and shoot southward 16 miles until we re-enter the bay via Venice Inlet. The shoreline drops off to the east in that area, and so once you clear the shoals on the south side of New Pass you are up to 1.8 miles offshore if you shoot straight for Venice Inlet. At a point more than 1 ½ miles offshore, about halfway down, I shot the below video. It shows rafts of water hyacinths and duckweed floating in the Gulf of Mexico. They were large enough that they fouled our prop and caused cavitation. But think of that – freshwater plants – likely from Cow Pen Slough – shot out into the Gulf more than a mile and a half. That is how much freshwater influence we’ve had in our region, from the tens of billions of gallons or rainfall that fell on our watershed.

Our second round of sampling found that the salinity is starting to recover in the lower bay, but the oxygen problem is actually getting a bit worse. Last week, the only time we had low oxygen was in the bottom of the bay when there was a very strong gradient between fresh to mostly fresh surface waters and the saltier waters trapped below that lens of freshwater. This week, our low oxygen values were still restricted to the bottom, but the salinity gradient between top and bottom was much weaker. A slight increase in the amount of samples with hypoxia (oxygen levels stressful to marine life) was found as well. And, in comparison to last week, we noticed a few dead fish this time, and not nearly as many dolphins. Plus, the water smelled not that good in several areas, mostly in central and northern Little Sarasota Bay. This was anticipated, as Little Sarasota Bay has the longest residence time – only about 30% of its water is exchanged after 10 days, the slowest rate of any part of Sarasota Bay.