Florida, USA, 7 July 2006: A patch of water that resembles chocolate milk is lingering in Pine Island Sound is boggling scientists. Area hydrologist Greg Rawl first noticed the plume from a satellite image a few weeks ago. From the north end of Pine Island Sound to Redfish Pass the muddy water extends across the bulk of the sound, but no one knows where it came from, why it’s lingering or what it is.
For the past several years, Rawl has been keeping track of how fresh water from the Caloosahatchee and Peace rivers spills into the Gulf of Mexico. The fresh water usually takes on a black or tea-colored hue from decaying plant matter in the river, but this plume is opaque and muddy. Scientists with Lee County Environmental Lab, Sanibel Captiva Conservation Foundation and the DEP are all equally baffled.
Rawl and Steve Bortone, biologist with Sanibel- Captiva Conservation Foundation said it’s in an interesting location because nitrogen-rich water from the Caloosahatchee and phosphorus-rich water from the Peace intermingle in Pine Island Sound. Nitrogen in the Caloosahatchee comes primarily from fertilizers and organic matter that wash into the river from the watershed and Lake Okeechobee. The Peace is naturally high in phosphorus, but phosphate mining along the river exacerbates the conditions.
Keith Kibbey, manager of Lee County Environmental Lab, also speculated that the two rivers could be contributing to the odd water. He said the county’s staff is stretched too thin to check the water. Instead, the county will rely on the DEP’s data.
Low dissolved oxygen levels are a tell-tale signs of an algae bloom that has come and gone, but Nelson also found dissolved oxygen to be normal and about the same inside the plume as on the outside. She also said salinity is about the same inside and outside the plume, indicating that it’s not an isolated pocket of fresh water.
“It’s not coming from the Caloosahatchee or out of Charlotte Harbor. It’s just sitting in the middle of Pine Island Sound,” said Jennifer Nelson, environmental consultant for the Florida Department for Environmental Protection. Rather than algae, she said, water samples showed high levels of mineral granules within the discolored water. But the turbidity isn’t coming from the rivers either. “That’s why there’s not an obvious source of this,” Nelson said.