Wednesday, June 28, 2006

ENV: Karst Badwater

via Mike Quinn . . .

Subterranean life thrives deep in water system
Researchers find that 'badwater' in Edwards Aquifer is home to an array of life-forms
By MICHAEL RAY TAYLOR, Houston Chronicle, June 19, 2006, 10:37PM

Suppose you discovered the following in your drinking water: Long spaghetti-like strands of bacteria, flaky yellow mats that smell of rotten eggs, a stubby white fish named Satan, blind salamanders, snails.

What would you do?

Answer: Grow them in the lab and publish a paper. At least, that's what you do if you're Annette Summers Engel, geomicrobiologist who loves caves and slimy creatures.

Engel and a team of geologists from Louisiana State University have found a bacteria-based ecosystem thriving 1,000 feet below San Antonio, where the fresh water of the Edwards Aquifer intersects with a lesser-known body of salty water.

Called "the badwater" by local ranchers and well-drillers, this reservoir provides a chemical food source for bacteria that, in turn, support an array of underground life, including blind fish and salamanders, according to a study to be published in the journal Geomicrobiology.

"Most people ignore the badwater, because you can't drink it and you can't give it to cows," said Engel, who, with graduate student Kelli Wilson Randall, initiated the year-long research project in cooperation with the science arm of the Edwards Aquifer Authority. "But, intellectually, it is very interesting."

Engel compared the strings and mats of sulfur-eating microorganisms to bizarre life discovered in deep-sea hydrothermal vents. "Many of these microbes have genetic 'cousins' in the deep-sea vents," she said.

Two types of rare blind catfish, salamanders, snails and tiny creatures called isopods had been known to live in total darkness within the Edwards Aquifer, which provides drinking water to San Antonio and dozens of surrounding communities. Some of these organisms depend on nutrients carried underground via caves and sinkholes that feed rainwater — and pollutants — into the system.

Food for larger creatures
Engel believes many of the larger subterranean creatures have evolved to feed off "this incredible mass of gooey stuff" that grows where the badwater, which is about a third as salty as seawater, meets fresh water. The interface lies 600 to 1,000 feet below the surface.

The total extent of the badwater is unknown. The source of the salts likely is a gypsum layer deposited 65 million years ago, when Texas was underwater. The badwater dissolves these salts of an ancient sea.

The toothless blind catfish, Trogloglanis pattersoni, has unusual mouth parts adapted to graze spaghetti-like strands of microbes that thrive in the chemical mixing zone. But the widemouth blindcat, a finger-sized, white catfish with the diabolical scientific name Satan eurystomas, is a predator.

''When you look in the belly of Satan, you find it loaded with isopods and other animals (from the mixing zone)," Engel said.

Beyond the scientific significance of these species, protecting them adds another wrinkle to already contentious water regulation.

"Water is extremely political in Texas," Geary Schindel, chief technical officer of the Edwards Aquifer Authority, told a group of municipal water supply managers gathered last week from around the country for a San Antonio convention. "It's like Mark Twain said. 'Whiskey is for drinking. Water is for fighting over.' "

When the water level drops, the flow to area springs slows down, affecting cities that depend on the Comal, San Marcos and Guadalupe rivers, as well as the creatures living in them.

"If the spring flow at Comal drops to 200 cubic feet per second, we're in danger of impacting species covered by the Endangered Species Act," said Roland Ruiz, an EAA public affairs officer. "If it drops to 150 cfs, some species may be in danger of extinction."

Protecting own water levels
Some water experts have called the Endangered Species Act a "hammer" downstream cities and industries use to preserve their own water levels. The fishing and shellfish industries of the coastal estuaries, among others, are highly dependent on freshwater outflow from the Edwards Aquifer.

While Schindel does not expect the unusual microbes Engel's team discovered to affect current regulations, he said it indicates that there are two very different ecosystems in the aquifer: one in the recharge zone, fairly close to inflowing caves and sinkholes, and another hundreds or thousands of feet down.

More interesting to Schindel is the study's implications for the aquifer structure itself.

The Edwards Aquifer comprises three main zones: The drainage area, a basin of some 5,450 miles that channels rainfall into streams and rivers; the recharge zone, where the water of some drainage sources enters the limestone bedrock through caves and sinkholes; and the artesian zone, where water is stored until removed through wells and natural springs.

While existing literature describes the artesian layer as a "giant sponge" of limestone, Schindel prefers to call it a tangle of "complex plumbing."

The plumbers may be microbes.

Schindel has conducted extensive dye traces trying to chart the path of water through the recharge and artesian zones.

"In rare cases, water that enters at one point travels two miles per day," he said. "In other cases, dye that is injected in a well that's right beside a spring never reaches it — but shows up at a spring nearly a mile away 36 hours later."

In the standard "meteoric" model of the aquifer, rainwater coursing through caves and sinkholes in the recharge zone enters a homogenous, porous layer. "We have a dynamic Karst system," Schindel said, that instead follows what he calls a "hypogenic" model.

"Karst," named after a region in Slovenia, is a landscape characterized by limestone hills, underground rivers and large springs. In the hypogenic model, these rivers are carved not by rainfall from above, but by strong acid from below, eating tunnels into the rock.

Under a hypogenic model, microbes consume sulfur in the form of sulfides. They then excrete sulfate as sulfuric acid, which dissolves limestone; other bacteria use the sulfate to make more sulfide, creating a self-perpetuating cave excavation system.

Bacteria like those Engel found have been seen elsewhere in the world in acid-filled caves, usually in oil-producing regions, where sulfides are released by oil deposits.

Thirty miles east of San Antonio, the badwater gets warmer and saltier. Eventually the Edwards Aquifer itself becomes a rich petroleum brine, the Stewart City Reef Trend.

What does this mean to the average person, drinking a glass of water that has traveled through 50 miles of plumbing excreted by acid-dripping bacteria en route to water treatment and the home?

"I wouldn't worry about the bacteria, or the saline water mixing with the fresh water," Schindel said. "That's not something that keeps me up at night."

Instead, computer models created by for the EAA by the U.S. Geological Survey show that the speed and pressure with which freshwater flows through the upper artesian layer keep it from mixing with the underlying salt water.

While this means that residents are not likely to draw spaghetti-like strands through their taps, it also means that any foreign matter introduced in the recharge zone can travel to water wells much quicker than anyone previously thought.

"What I worry about is some unknown pathogen flowing into the recharge zone," Schindel said. "That's what keeps me up at night."

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