UF Research: Underground Rivers, Springs Not The “Pipes” They Appear

November 23, 1999

GAINESVILLE — Rivers and streams in north Florida have a curious habit of disappearing into the ground, only to reemerge elsewhere, a result of the porous rock formations that lie not far beneath the ground.

But ongoing studies by a University of Florida geologist offer new evidence that much of the water that feeds the springs in the region flows through tiny pores in the rocks, not large underwater conduits. The research has a couple of important implications, said Jon Martin, a UF assistant professor of geology. One is that much of the water may come from a large area around the springs, meaning it could carry pollution that had been in the groundwater for some time or originated from another region, he said. The findings apply not only in Florida, but also in other states in the Southeast, he said.

“The real problem is how long does the water and associated pollutants remain below the surface, and then where does it go?” Martin said. “The pollution can get in the groundwater and be there for tens of years or hundreds of years.”

The other important implication of the research, Martin said, is that it calls into question one of the terms of a recent settlement between the state and a cement company that plans to build a plant near the Ichetucknee Springs State Park, a popular recreational destination in Suwannee County. The Florida Department of Environmental Protection last week agreed to allow the company, Anderson Columbia Co. of Lake City, to build the plant in part on condition it sell a lime rock mine north of the springs. State officials feared the mine could impede or cut off the springs’ water source, but Martin said his research shows the mine may not impact the springs one way or the other.

The results suggest “the water coming out of those springs is not fed by an extensive conduit system. Much of the water discharging from the springs comes from the micro pore systems,” Martin said.

Martin’s research contrasts the results of most other scientific studies of karst aquifers showing the wall rock of underwater conduits to be far less permeable, Martin said. Those studies focused on the western Appalachians, which have far older karst systems, he said. “Those places have much older rocks, so much of the porosity has been filled up,” he said. “In Florida and other parts of the Southeast such as South Carolina and Georgia, the karst systems are much younger, so that hasn’t happened yet.”

For part of the research, Martin used automated equipment to make repeated temperature readings at the Santa Fe River’s sink and rise along the Alachua-Columbia county line, as well as at lake a between the two. Pumping out more than 100 cubic feet of water per second, Santa Fe’s rise is considered one of Florida’s 38 largest, or first-magnitude, springs.

The researchers matched the temperature data with samples of the chemical composition of the water at private water wells near the sink and rise, taking measurements when the river was flowing normally, when it was flooding and when a flood was ebbing. Although the readings began in January 1998 and ended a year later, Martin said he is just now completing an analysis of the data, which contained more than 15 million temperature readings alone. His conclusion: The underground “pipe” between the Santa Fe’s sink and rise — actually a series of connections in the porous limestone — may lose or gain a significant amount of water when the river is flowing normally. “The water can leak into the conduits, and it can leak out of the conduits,” he said.

During floods, the conduit loses water, which corresponds with anecdotal evidence pointing to an influx of water in wells during floods. “People in this area say that when it rains, their well water gets muddy,” he said.

Brian Katz, a research hydrologist at the U.S. Geological Survey in Tallahassee, said Martin’s findings bolster the case for keeping pollution away from a wide geographical area around springs. “His research and other research clearly demonstrates that you need to look beyond the sink or the spring and protect the entire source area,” he said.