Feb 16, 2007

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OVERTON – "Few people get to see a bass this big – ever," said Duel Glass, East Texas lake owner.

The bass Glass holds as he speaks is nearly 2 feet in length and weighs about 12 pounds. Though trophy size, the bass not a trophy "catch," but a "casualty."

Glass has just netted the huge bass and another one just like it off the bottom on a chilly February afternoon. It is one of thousands of large and small bass, perch and other species of fish recently killed by a drastic drop in the pH of his large-acreage lake near Joinerville in Rusk County.

Glass is not alone in his loss. Pond owners in many areas of East Texas may be experiencing similar losses. Glass' bass were a casualty of a combination of factors: drought, acidic East Texas soils, and heavy rain in January, said Billy Higginbotham, Texas Cooperative Extension fisheries and wildlife specialist.

"Each of the last two winters, we've had scenarios occur with our drought conditions that have led to extensive fish kills in private ponds throughout East Texas," Higginbotham said. "The common denominators of these kills have been ponds or reservoirs that have been extremely low due to the drought conditions. Then during January, some heavy rainfall runoff events filled ponds to capacity where they may have had only a half or a third of their total volume present, prior to the rainfall."

In many areas of the state, these run-off events would not cause problems, he said. But most counties in East Texas have highly acidic soils. And this causes the run-off water from the watershed to be highly acidic too.

The result is "either a drop in pH to a level that meets the acid-death point – around a pH of 4 to 4.5 for most of our freshwater species – or, the pH changed so dramatically in a short period of time it put the fish into pH shock," Higginbotham said.

A way to prevent pH shock of rain following an extended drought– or at least lessen it – is to maintain the pH of the drainage areas into ponds, said Dr. Vincent Haby, soil scientist with the Texas Agricultural Experiment Station.

"It's important for pond catchment areas that these soils be adequately limed in order to keep the pH of the water in the ponds up or you can lime the pond water according to procedures that Dr. Higginbotham and the wildlife science people have developed for this region," Haby said.

Many areas in East Texas have acidic soils for a combination of reasons, Haby said, all related to the sandy nature of the surface soils, which have a "low resistance to chemical change."

"These soils are naturally acidic because they lack the limestone that is in the alkaline higher clay-content soils such as in the Blackland areas," he said. "Acidity in East Texas soils increases because of organic matter decomposition that forms low concentrations of mineral acids such as sulfuric, nitric and carbonic acids."

Another factor arises when erosion or deep tillage exposes iron pyrite to the air. The sulfur component of the pyrite then oxidizes to form sulfuric acid. The loss of basic elements such as calcium, magnesium, potassium and sodium by leaching out of the soil or because of plant uptake also contributes to soil acidity.

Also, soil acidity is increased as ammonium-based fertilizers are converted to nitrate by naturally occurring soil bacterial processes.

"Finely ground limestone must be applied to these sandy East Texas soils in order to maintain pH in a favorable range for crop growth and pH in runoff waters," Haby said.

Currently, overcoming soil acidity in East Texas has been made harder by the expense of liming , Haby said.

"It's becoming more difficult for producers to maintain their soils in an adequately limed state because of the increased transportation costs for limestone and the increased spreading costs due to the high fuel costs that we receive," he said. "So producers may be putting off liming (watershed areas) for these ponds."

Tests of soil samples from the exposed bottom of Glass' lake showed it had a pH of 3.0, which could also be a factor in the increased acidity of the lake, Haby said.

Soils of lake and pond bottoms are apt to contain lots of organic matter, which in turn has a high concentration of sulphur compounds. When lake waters recede and the sulphur in the pond bottom is exposed to air, it can quickly oxidize to form sulphuric acid, he said.

In the case his lake, Glass said, the pH was already low. Moreover, much of the catchment area is composed of pine and hardwood forest, making spreading lime difficult. Before the heavy January rainfalls, his lake's pH measured about 5.5 to 6.0, which is fairly acidic.

Before the January rains, Glass estimated his lake was 12- to 14-feet low. The rains raised the water level about 5 or 6 feet, he said, but dropped the pH to about 4.4. according to lab tests. This drastic drop likely threw large and small bass alike into shock, Higginbotham said.

"To our knowledge – based on our reports – this is pretty much a phenomenon based in East Texas where we have extremely acidic soils," he said.

But just because some East Texas pond owners haven't experienced fish kills already doesn't mean they're out of hot water, Higginbotham said. Many may have seen loss of fish populations because of the drought of the last two years. Now that their ponds are mostly filled again, they may be considering restocking. But if they do so without first testing the water, they could get a surprise.

"In the absence of a water test, they run a real risk of killing every fish they stock," he said.

All of the Extension offices in East Texas counties that have acidic soils and therefore likely acidic pond water have water testing kits. However, before pond owners call their Extension office, they should be aware that the problem is confined to East of Interstate 35 – and only in those counties with soils that are prone to be acidic, Higginbotham said.

How do East Texas pond owners know if the soils in their county are acidic?

"A good way to check on that is that if you've got liming service that routinely applies agriculture limestone to pastures and hay meadows, then that's a pretty good indication that there acid soils present in that county," Higginbotham said.