St. Lucie Algae Bloom Blamed on Watershed

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Observation Networks Reveal Data

Last Friday afternoon, members of the Sanibel Captiva Conservation Foundation (SCCF) listened to public presentations from Dr. Eric Milbrandt, director of the SCCF Marine Laboratory and Dr. Ian Walsh, director of Science and Senior Oceanographer, Sea-Bird Scientific/WET Labs, Inc. Both men reported on what they had discovered after studying data from water quality monitoring systems on both the east and west coasts of the state and – for Dr. Walsh, who concentrated on the blue-green algae plagued east coast – the results were rather surprising.

 

Dr. Eric Milbrandt – West Coast Estuary

Milbrandt’s findings were based on SCCF’s state-of-the-art water-monitoring system, the River Estuary and Ocean Observing Network [RECON], which has for the past 10 years been recording detailed, real-time data on water quality.

“Basically, when it rains in Florida, all that water comes down, trickles over roads, agricultural areas, lawns, et cetera and ends up in the estuaries – where it can drive the production of tiny photoplankton and microscopic algae that grows in the water column. However, when you get excess amounts of nutrients that leads to blooms and conditions like hypoxia.”

Milbrandt said that there is a lot more nitrogen in the environment now as compared to the 1950’s.

“We’ve had a very exceptional year this year in that we’ve had an El Nino since last fall,” he said. “This means that warm water flows upward and changes the jet-stream to one that dips down low. This year, we had 10 inches in rain in January when we normally have only 2 inches. South Florida is pretty much flat, and has a flood control component with Lake Okeechobee as the center-point. When the lake fills faster than it can be drained, this leads to excessive discharges to protect the people living near the lake from being flooded.”

Eric explained that the sensors used in the RECON system are attached to pilings, collecting data hourly.St. Lucie Algae Bloom Blamed on Watershed Image

“We collect a variety of parameters including salinities, dissolved oxygen and chlorophyll – which means dissolved algae in the water,” he said. “In January and February, salinities in the Gulf were much lower than normal due to the high flows from Franklin Lock – which includes both the lake and runoff from the watershed.”

Dr. Milbrandt looked at when the amounts of chlorophyll spiked, and found a distinct relation to when discharges were made.

“We see about a 2-week lag from the two data points, which makes sense because that’s how long it takes for the water to get downstream,” he said. “This data shows a really good relationship between nutrient loading and chlorophyll buildup.”

“Blue-green algae tends to out-compete other diatoms when phosphate is abundant, it thrives in warm waters and it tends to float in clumps – making detection more difficult,” Dr. Milbrandt continued. “We also know it can produce toxins but we’re not sure when and where it produces them. Mycrocystis (blue-green algae) can regulate its own buoyancy in that it comes to the surface and takes all the light for itself, excluding other light plants from growing. For being a primordial organism, its really quite smart.”

Finally, Milbrandt pointed out the green macroalgae seen on the beach lately is Ulva – a species tolerant of low salinities that loves nutrients and is being studied as an indicator of nutrient pollution.

“We think what’s happening is that the boundary of the estuary has been extended,” he said. “I do want to mention the brown water that’s causing a lot of angst – they are a tea-like compound that’s a visual indicator of freshwater. It’s not harmful to people but it will block light needed by plants on the bottom.”

 

Dr. Walsh – St. Lucie and Martin County

Dr. Welsh uses a comparable system to RECON, one that was actually modeled after it called the Indian River Lagoon Observatory Network (IRLON). When he first took a look at the data on July 5, it didn’t quite jibe with what he was reading in the local newspapers.

“The headlines were saying that the Lake Okeechobee releases were driving the blue-green algae bloom, but that’s not true – the nutrients were already there and they were coming from runoff,” he said. “What the discharges were doing is dramatically changing the estuary to the point where a ‘secondary lake’ was being created in an area between the ‘north fork’ and the ‘south fork’ of the St. Lucie River.”

To understand what he’s talking about, take a look at a map of the St. Lucie. Unlike our Caloosahatchee River, the south fork extends from Port Mayaca on Lake O and is a narrow canal known as C-44 until it reaches the community of Palm City. From there it opens up into a wide area extending upwards to the north fork and east past the city of Stuart out to Jensen Beach. It is in this area that tidal mixing naturally occurs.

“The (monitoring) systems are much more nutrient oriented on the east side so we’ve got nitrate and phosphate sensors over there along with chlorophyll and salinity censors,” he said. “The great thing about having the data is you can just follow it.”

Walsh pointed to charts that showed much higher phosphate levels coming in from the north fork – which is runoff – than from the south fork, which is releases from the lake.

“Lake O releases have one 1mg/L of phosphate, where runoff has more than 6,” he said. “This is data that we get as we look at it – updated hourly.”

Walsh noted that June 27 marked the end of the high discharge period for the St. Lucie.

“What led to the bloom is the fact that the source of water to the south fork was actually the north fork,” he said. “It’s not that Lake O is adding more nutrients to the system, it’s changing the circulation – essentially creating a lake there and the water is flowing out slower. This means that the nutrient-rich water is there longer, leading to the algae bloom.”

Walsh concluded by recommending more monitoring to determine whether the runoff is mostly coming from the agricultural areas to the north or the septic systems already in the area; adding microcystis barometers to the monitoring system and a request that discharges from the lake be modulated so that a bunch of water isn’t sent downriver at once.

He also praised SCCF’s efforts with their RECON system.

“SCCF’s effort is remarkable,” he said. “We must replicate it around the world, because the seas are rising!”

 

Keri Hendry Weeg