River pendulum swings to salinity
Once too fresh, Caloosahatchee too salty

By Kevin Lollar
klollar@news-press.com
December 11, 2007

http://www.news-press.com/apps/pbcs.dll/article?AID=/20071211/NEWS01/712110377/1075

 

As the sun took the chill off the early morning air recently, Roger Byrd ran upstream to drop his crab traps between the Caloosahatchee and Edison bridges.

He'd just about filled a crate with blue crabs farther downstream.

"It's been pretty good, but the water's a little bit dirty," Byrd said. "The river's not like anything I've ever seen. It's really salty. There's more snook upstream than I've ever seen."

 

Some people who've lived and worked on the Caloosahatchee River for much of their lives say the river has changed for the better over the past couple of years. But scientists say the change is merely a shift to high salinity following a long period during which salinity in the river was extremely low.

 

In either case, it's all about rainfall and salinity.

From the mouth of the river to the W.P. Franklin Lock and Dam, the Caloosahatchee is an estuary, a body of water where salt water from the sea mixes with fresh water from the land.

 

During the summer rainy season, salinity drops because fresh water runs into the system; during the dry season, salinity increases.

Southwest Florida's rainy season recently ended, but, because of the ongoing drought, little fresh water has run into the river, and salinity is up: At the lock, salinity is 14 parts per thousand.

"In the
Gulf of Mexico, it's 36 parts per thousand, so we're a little under half strength Gulf water all the way to the structure," said Peter Doering, a scientist with the South Florida Water Management District's Coastal Ecosystems Division. "That's not normally the case.

"During the typical wet season, it's zero up there. During the typical dry season, it's 5 to 7, so we're way above due to the lack of flow into the system."

Such a salty river has brought noticeable changes to the flora and fauna.

"From the fishing standpoint, it's probably the best it's been in 20 years," said Dave Westra, owner of Lehr's Economy Tackle in
North Fort Myers. "We're getting big schools of thredfins all the way up to Fort Myers, and redfish, snook, spotted sea trout, whiting, silver trout, mangrove snapper and baby goliath grouper up to the I-75 bridge.

"We've got two reports of undersize gag grouper at the Edison and Caloosahatchee bridges. That puts juvenile gag in the city of Fort Myers."

Westra has also seen frigate birds, a marine species, near the
Caloosahatchee Bridge.

"I can't remember ever seeing frigate birds coming up river: They're following the bait," he said.

On the day Byrd was setting traps, Steve Olive, 55, who has lived and worked on the river sporadically for 43 years, saw dolphin feeding between the Caloosahatchee and Edison bridges.

"Dolphin are not unusual in the river," Olive said. "But it's usually a late winter thing. We saw them all summer."

The two extremes

Drought has changed the Caloosahatchee dramatically over the past couple of years.

Extremely wet rainy seasons in 2004 and 2005 raised Lake Okeechobee to record levels, prompting water managers to release huge amounts of nutrient-laden fresh water down the river.

That water and nutrient-laden runoff between the lake and the mouth of the Caloosahatchee combined to cause severe environmental problems in the river and the estuary, including:

Excess nutrients triggered massive macroalgal blooms in the river, estuary and Gulf of Mexico. These algae smothered seagrass beds and artificial reefs.

Nutrients also caused blooms of microscopic blue-green algae in the river and canals, which blocked light to aquatic vegetation and depleted oxygen in the water.

Excess fresh water upset the balance of fresh and salt water on which an estuary depends.

In short, the river was an opaque mess.

But with the drought, the lake is at record low levels, so no water is being released, and downstream runoff is virtually non-existent. Instead of being very fresh, therefore, the river is very salty.

Much of the algae has cleared up, said Rick Bartleson, a research scientist at the Sanibel-Captiva Conservation Foundation Marine Laboratory, though Byrd reported algae that looked like "green wool" on his traps below the Caloosahatchee Bridge and like "black fungus" above the bridge.

"There is less algae now than at the beginning of the year," Bartleson said. "The nutrients that came in the previous year are probably hanging around in the sediments and feeding the benthic algae. But they may be running out of that source. Some of the algae has been drifting away, out into the Gulf, and taking nutrients with them."

Still a price to pay

While the salty river seems to be an improvement over the low-salinity, nutrient-rich river of the past couple of years, some parts of the Caloosahatchee are suffering, particularly benthic organisms bottom-dwelling plants and animals that live upstream where the salinity is usually low, even during the dry season.

"The upstream sites are not used to that high salinity," Bartleson said. "So communities are getting knocked way back. Grasses are gone. Mollusks such as rangia clams are getting knocked out."

A major loss in the river is tape grass, a freshwater species also known as eel grass and Vallisneria, which is an important habitat for many animals, including small fish, clams, shrimp and juvenile blue crab, and food for fish, freshwater turtles, manatees and birds.

"The upper part of the system really has lost one of its major habitat features," Doering said. "That's not good. It's going to take a while for those plants to come back."

High salinity in the river might be a problem for the many organisms that reproduce during the spring.

"The early stages of many of these organisms require low salinity," Doering said. "When it's not there, the thought is that recruitment, the passage of young stages to older fish and crabs, is retarded."

Looking for balance

During the overly fresh, nutrient-laced, algae-packed days of the Caloosahatchee, nobody said the river was a healthy environment.

The salinity pendulum has swung the other way, and many people like the river that way.

As an estuary, however, the Caloosahatchee is like Goldilocks, looking for water that's not too salty and not too fresh, but just right.

"Aesthetically, the river looks nicer than when the fresh water was coming in," Doering said. "But let's not forget that estuaries are among the most productive ecosystems in the world.

"One reason for that production the abundance of fish, shellfish, crabs is nutrients coming in, carried by freshwater inflow. When you have too much inflow, bad things start to happen. When you don't have enough, bad things happen. It's like everything else: Everything in moderation."