Would you please forward this email to all EMA members. I would like for the EMA to discuss this item at the next meeting.
The News-Press story referred to below was good, but in my opinion missed the most important aspect of the story. All of the dead marine life in Matlacha is just outside, and only just outside, the recently removed Ceitus Boat Lift/Berm. I agree that the cause of the destruction was excess fresh water, but it should be noted that the reason the excess fresh water is concentrated on the northwest side of Matlacha is that removal of the berm causes most of the fresh water from a 120 square mile drainage basin to dump in one place (which is northwest Matlacha).
When the Cape
Northwest Spreader System was properly maintained, the rainy season waters
flowed through the mangroves and distributed somwhat
from Fay toxic to fish, sponges
By Kevin Lollar
Last week, researchers
from the Sanibel-Captiva Conservation Foundation
Marine Laboratory found dead fish in
At about the same time, hundreds of stinking gray blobs showed up in Matlacha canals — scientists identified the blobs as sponges and tunicates (sack-like filter feeders).
“I’ve never seen anything like these things,” Leo Amos, a Matlacha resident since 1974, said of the blobs. “They’re piling up under my dock. They’re just sitting there, rotting and smelling.”
The unusual suspects in the case of the dead fish and gray blobs: Hypoxia (extremely low dissolved oxygen) and fresh water, specifically, fresh water dumped on the Caloosahatchee watershed by Tropical Storm Fay.
Matlacha’s sponges and tunicates, which like relatively high salinity, might have died simply from too much fresh water.
Fish in Tarpon Bay and the Caloosahatchee, however, might have been done in by stratification — layers of salt and fresh water that cause low-oxygen conditions.
Here’s what happens: In a tidal river such as the lower Caloosahatchee, the tide pushes salt water upstream — in times of drought, salt water goes farther up the river.
During and after heavy rains, freshwater runs into the river and flows downstream.
Saltwater is heavier
than freshwater, so the salt water moving upstream creates a wedge under the
fresh water flowing downstream. In other words, the river becomes stratified
with the fresh water lying on top of instead of mixing with the salt water.
“There’s a freshwater lens that keeps oxygen from getting to the lower, saltier layer,” marine laboratory research scientist Rick Bartleson said. “Organic matter and bacteria in the sediment use up oxygen, which gets really low. We were seeing 1 to 2 milligrams per liter. Anything below 3 is hypoxic.”
Often after big rain events, runoff and releases from
“After Fay, the fresh water was not causing algal blooms,” Bartleson said. “It was just bringing in organic matter and bacteria, washing terrestrial vegetation into the river — it could even be lawn clippings. Then it starts to decompose and sucks up the oxygen.”
What a hypoxic river laboring under a freshwater lens needs is a good mixing, which is what the Caloosahatchee got with the high winds of Hurricane Gustav — dissolved oxygen Friday afternoon at Shell Point was 4.61 milligrams/l and 5.78 at the
But with likelihood of more rain from Hurricane Ike along with the U.S. Army Corps of Engineers’ decision Wednesday to release water from Lake Okeechobee over 11 days beginning Thursday, more problems are possible, said Aswani Volety, chairman of Florida Gulf Coast University's Department of Marine and Ecological Sciences.
“I am not sure about the levels of freshwater that the Army Corps is releasing,” Volety wrote in an e-mail. “If the levels are very high, we could see some negative impacts, especially since the past year or so has been very dry and salinities were high.
“Since the Corps of Engineers did not release water till now, I suspect the bulk of the freshwater in the
Of course, fresh water isn’t the only threat from runoff and Okeechobee releases, said Rae Ann Wessel, the marine laboratory’s natural resources policy director.
“We’ll be getting nutrients in the discharges that will decrease dissolved oxygen and increase turbidity,” she said. “Anything coming out of the lake is going to add to the impact of what’s coming from off the land.”