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1,000-Year Rainfall Event Leaves Ecological Impact

Written by on Saturday, July 6, 2024

Changing climate and unchanging human behavior combine to produce fish kills in Sarasota Bay.

By Florence Fahringer

Original Air Date: July 5, 2024

Host: Last June, one extreme weather event was followed by another, as a months-long unprecedented drought was ended by an evening of unprecedented rainfall. The sudden storm caused flash flooding across Sarasota, overwhelming county drainage systems, with runoff sweeping pollutants into the bay. Florence Fahringer talked to Abbey Tyrna of the Suncoast Waterkeeper to assess the damage.

Florence Fahringer: The flash floods on June 11 were a gut-punch to drainage systems across Sarasota, but it’s the bay which bears the bruise. The floods which inundated neighborhoods in the evening successfully drained their way to Sarasota Bay by the morning, bringing all sorts of debris with them.

Abbey Tyrna: It was actually just a bunch of things sitting around during the dry season that was piled up on the landscape: grass clippings, tree leaves, twigs, soil that was bare, to the bay. Pesticides, fertilizer … anything that hadn’t been taken up into the ground, that was just sitting on top, was all pushed into the bay. 

FF: This rapid injection of natural and artificial matter into the bay triggers a biochemical process which can be deadly for sea life.

Abbey Tyrna

AT: And when that happens, when grass clippings and tree leaves and twigs go into the bay, bacteria work on them just like they do on land to break them down. But in the water,  when bacteria’s working on them to break them down, they take up the oxygen from the water column. And for species that move or need high levels of oxygen, those species that can’t move like crabs —  they can move, but they don’t move very quickly, and they can’t get away from the low or no oxygen zone. And then juvenile fish, which actually need a lot more oxygen than their adult selves do, they can move, but they just need a high amount and they don’t move as quickly as they would if they were larger. They can’t escape low oxygen zones, so they end up dying. 

And not only that, but we also found high bacteria throughout the region. So this is a different bacteria. These are bacteria from warm blooded mammals which would make you sick, so they’re from the intestines of warm blooded mammals. That’s something that we monitor each week. And the weeks after the storm, even just up through Monday, we’ve seen high levels of these bacteria that can make people sick when they’re swimming.

FF: The Sarasota County Public Utilities department has generally patted itself on the back in the aftermath of the flash floods, describing county infrastructure as having performed “reasonably well.” Tyrna describes their performance more as a matter of perspective.

AT: I mean, I guess “reasonably well” is definitely something that could be said depending on what you are assessing. So if you’re assessing the amount of flood damage caused to individual homes, then potentially we’ve done reasonably well. And I think that’s the level of service that the county is trying to provide. When you’re looking at it through a standpoint of ecological systems and whether or not they would be able to survive repeated high intensity rainfall events like the one that was experienced on June 11th, I would say no, we did not perform reasonably well.

FF: In the weeks following the rain event, low levels of oxygen and the fish kills which followed were reported at multiple sites across Sarasota Bay, with the epicenter happening just off the coast of a recently destroyed nature preserve.

AT: So we saw thousands of dead juvenile fish and crab due to low and no oxygen conditions in the area of Sarasota Bay right off of the Crosley Estate. That was like ground zero. I don’t know if the Estate is, but I know that the Uplands area right there is owned by New College. So there was a vegetative buffer there before all of the landscape renovation, and what they have told us is that the vegetation that was removed was all exotic and invasive tree species. And certainly what does remain there are mangroves, which is great. There’s also a gap and there’s also bare soil as a result of their removal of vegetation. 

FF: The Uplands Preserve was gifted to the New College of Florida in the nineteen sixties, with the understanding that the preserve would remain vegetated and undeveloped. New College stuck to their promise until recently, their new master plan envisioning the largest building on campus being built on the preserve. In the weeks before the thousand-year-rain event, construction crews appeared without notice and removed most of the vegetation. In the weeks following the rain event, the waters off the Uplands shores fared the worst of any area within the bay, its oxygen levels reaching historic lows.

FF: Did we see similar aftermath, when we kinda just dodged Hurricane Ian?  In terms of the drainage system?

AT: Yes. I’m not really sure if there was a fish kill in the bay after Hurricane Ian, but I know that there were low oxygen conditions. I know that they were not as bad as what we found at the Crosley Estate area where there was really zero oxygen in the water from top to bottom. And that is something that is pretty severe and would cause death to anything around. 

FF: WSLR reached out to New College for comment, but did not hear back before deadline.

While the removal of vegetation is one potent source of ecological damage to the bay, another exacerbating factor is the state of drainage infrastructure in certain parts of the city.

AT: But it should be understood that most of the City of Sarasota doesn’t have  stormwater management systems in place, because the city was developed before the rules for stormwater management. So there’s a lot of ability to add systems that would help to take up water, to clean up water before it moves into the bay. But otherwise, we have a situation where the water from our streets and our yards goes directly into the bay through pipes. And that’s not a good system, especially as we continue to develop in these older areas without stormwater management systems.

FF: So how does this bode for the remainder of hurricane season? As it turns out, it wasn’t just the sheer amount of rainfall, but the one-two punch of drought & storm which exacerbated the severity and ecological impact of the rain event.

AT: Instead of having periodic flushes of our landscape, where the bay can assimilate what’s going in, we had it all flush out at once, where it just overwhelmed the assimilative capacity of the bay. So, I would imagine that as it continues to rain, and the landscape continues to be flushed, that if a hurricane were to come … for the bay, it would be probably okay and better off than what happened during June 11th.  

FF: While the drought may be over, this year’s extreme weather patterns will likely serve as a portent for Sarasota’s changing climate.

AT: The high rain event is something that we’re probably going to see more of due to changes in climate, and it’s something that we’re definitely not prepared for. 

FF: This is Florence Fahringer, reporting for WSLR News.


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