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Salinity levels in Matlacha Pass dropping

July 25, 2012
By MEGHAN McCOY (mmccoy@breezenewspapers.com) , Pine Island Eagle

Due to the heavy rainfall that has doused the area recently, the salinity levels of the estuary in Matlacha Pass have dropped to low levels, which are affecting the marine life that lives within the waters.

The low levels of salinity are being caused due to the removal of the Cape Coral North Spreader Ceitus Barrier and the heavy rainfalls that have taken place.

Greg Rawl, chairman of the Southwest Florida Watershed Council, said the heavy rainfalls are traveling downstream because of the removal of the Ceitus structure. He said the removal has allowed most of the stormwater to come out towards the south end of Matlacha.

"Historically it was forced to have more even distribution," he said of when the spreader was in place.

Rae Ann Wessel, natural resource policy director for the Sanibel, Captiva Conservation Foundation, said the Ceitus Canal, which was dredged and had a boat lift barrier to separate the stormwater from Cape Coral, played an important role in preserving the rich marine habitat that is a part of the aquatic preserve on the Matlacha Pass side.

Stormwater, Wessel said, is full of all the stuff that washes off of roads, driveways and lawns, which is why it is classified as one of the biggest forms of pollution.

"When the water would come into the spreader waterway, the barrier would cause it to be retained to get residence time - water sitting for a period of time," she said, which would settle out the nutrients, along with coming into contact with plants that would further clean the water.

Wessel said when the water became high behind the barrier, it would get funneled out through the mangroves on the western side, which again would further clean the water.

"It was seen as a multi-layered treatment approach to clean the dirty stormwater," she said.

With the barrier removed, Wessel said the very dirty stormwater is now coming out through the canal and going down into the Matlacha Pass area.

"Without the barrier, it is just a free for all," she said. "As a consequence to that, the heavy rains without the barrier the water is getting no treatment."

Phil Buchanan said although the rainy season has just begun in Southwest Florida, the level of excess freshwater flowing out of the hole that was created by removing the Cape Coral North Spreader Ceitus Barrier has already reached lethal levels.

"The salinity level necessary to sustain much estuary marine life such as oysters is around 20 parts per thousand (ppt)," he said.

Rawl said if you dump so much saltwater in, it is no longer saltwater, due to the water becoming fresh.

"A lot of critters like oysters, they are fixed, they can't move when the salinity drops," he said. "Those are the ones in greatest risk, they can't pick up and leave their home, if the water level falls to low they will die."

With freshwater being delivered into the waters, the salinity decreases, which affects the marine organisms that cannot move like oysters, grasses, sponges, corals, mussels and clams.

"They will run out of oxygen because the freshwater that sits on the saltwater creates a barrier," Wessel said. "It is changing the chemistry of the water quality and that can affect different species and life cycles in different ways."

Aaron Adams, senior scientist with Mote Marine Lab, said the salt content of the water is an extremely important factor to all the organisms that are in an estuary. He said although a lot of species can tolerate full ocean salinity, a lot of species can only tolerate certain ranges of salinity.

"If they can tolerate large changes to salinity, it has to happen slowly," Adams said.

The large amounts of stormwater that has been dumped, Adams said, is known as the facet affect, due to freshwater being turned on and off when it rains and runs into the Matlacha Pass. One day, he said you could have a salinity of 20 ppt in Matlacha Pass and then the next it can drop to almost zero.

"The large portion of the estuary organisms cannot tolerate that change," Adams said.

He said they have found that the alteration of freshwater flow in the estuary creeks negatively affect the number of species of fish and their abundance.

"Alteration of freshwater flow causes ecological damage and thus causes decline in the over health of the estuary," Adams said.

Adams said the Caloosahatchee River experienced the same kind of fall in its salinity level, which affected the saltwater sea grass. He said a large portion of the river does not have sea grass anymore because of the salinity level.

"When the salinity gets too low, all the saltwater sea grass dies," he said.

A reading that Buchanan took Wednesday, July 18, at 11:20 a.m., at the former Ceitus Barrier location, was 1.5 ppt, which he said is not much above the salinity of tap water.

"Only three weeks ago, before the rains, the reading at the same site was a respectful 20.8 ppt," Buchanan said.

He also did a reading along Shoreview Drive in Matlacha, which is downstream from where the barrier was located, which was 1.8 ppt at 11:10 a.m. Wednesday.

Comparison readings were done by Buchanan at the Matlacha Park Pier, which read 15.2 ppt last Wednesday and Galt Island that read 28 ppt.

"In other words, salinity readings all around Pine Island are good everywhere except where the concentrated excess poor quality freshwater (storm water) dumps from North Cape Coral," he said. "Don't expect any saltwater marine life survival in that area of Matlacha until well after the rainy season ends. You should also expect the continued buildup of siltation to threaten to block the only waterway channel out of that entire area."

Pollutants come in a lot of different forms when dealing with water, according to Wessel, and when you add volume, place and time of freshwater to saltwater it can be damaging. She said freshwater sits on top of saltwater and when it comes down the narrow canal and opens up into an aquatic preserve it carries sediments with it and deposits it where the water flow stops.

"It causes problems with navigation and makes it very hazardous," Wessel said.

 
 

 

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