April 23, 2002

LINCOLN, Neb. — Most Nebraska livestock waste lagoons are not polluting groundwater, a two-year University of Nebraska study indicates.

Researchers monitored 26 swine, dairy and beef cattle waste lagoons at 13 sites in central and eastern Nebraska. They tested nearby groundwater and lagoon water to assess the lagoons' potential threat to groundwater quality.

"The majority of the waste lagoons in the study have not adversely impacted groundwater," said Roy Spalding, a research hydrochemist and director of the university's Water Sciences Laboratory who headed this research.

"This is particularly significant because of agriculture's importance to our state and to the public, considering roughly 85 percent of Nebraskans drink groundwater," he added.

Water lab scientists and Mariappan Sadayappan, a UNL agronomy and horticulture graduate student, recently completed the study that was designed to identify indicators of waste lagoon seepage and to evaluate these lagoons' effect on groundwater quality.

The size of lagoons and their environmental settings varied greatly; 12 of the 13 sites were in use, Spalding said. Livestock producers who operated the lagoons volunteered for the monitoring project that ran from 1999 through 2001.

Ten of the 12 active sites sampled did not appear to pollute nearby groundwater, Spalding said.

Three of the lagoons "probably contributed to a reduction of high nitrate levels in the area around them," he said. That's because beneath these lagoons, naturally occurring bacteria fed on the nitrates thereby reducing the nitrates in the sampling wells down gradient from the lagoons, Spalding said.

"This process tends to reduce the amount of nitrates flowing beneath the lagoons," he said.

Groundwater beneath two of the sampled lagoons contained higher levels of ammonia and nitrate. Both these lagoons are in areas vulnerable to pollution because groundwater is less than 35 feet below the surface and the soils are course textured and easily permeable.

The Institute of Agriculture and Natural Resources team sampled each of the lagoons and the surrounding groundwater four times over the two-year study in both the spring and fall. Researchers took samples at different depths in the lagoons to help determine variations in sample content that might occur either vertically or laterally in lagoons or groundwater.

Samples were analyzed for levels of nitrate-nitrogen, ammonia-nitrogen, chloride, dissolved organic carbon and total organic carbon.

High concentrations of chloride and ammonia are prime indicators of groundwater pollution from livestock waste lagoons, Spalding said.

Scientists also analyzed samples for nitrogen isotopes, which help distinguish the source of nitrogen, such as fertilizer, animal waste or naturally occurring in soils.

Spalding said that, overall, these findings show that most livestock lagoons don't harm groundwater quality. However, an individual lagoon's impact on groundwater quality depends on site conditions including depth to groundwater, geology, construction, soil type, extent of groundwater use in the immediate vicinity and how the lagoon is operated, such as how often and when it is pumped out.

"Though it appears a majority of the examined lagoons have not contributed to groundwater pollution, we can't be complacent since there are still documented cases where these facilities can have negative impacts on groundwater quality," he said. "That makes it important to carefully review each facility in order to better understand the possible effect it might have on groundwater pollution."

Researchers also sampled 11 of the 13 waste lagoon sites for antibiotics commonly added to livestock feed or water. These included oxytetracycline, tetracycline and chlortetracycline.

Groundwater samples collected at these sites showed no detectable levels of these antibiotics even though traces of at least one of the three antibiotics were found in the lagoon water in 23 of the 26 samples they collected.

"Although traces of antibiotics were measured in 23 of the 26 lagoon water samples, they were not detected in the groundwater beneath or near them," Spalding said.

The water lab studied the lagoons in cooperation with the Nebraska Department of Environmental Quality, which is responsible for developing and implementing programs to manage storage, handling and application of animal wastes associated with livestock operations.

The U.S. Environmental Protection Agency helped fund this research, which was conducted in cooperation with IANR's Agricultural Research Division.

04/23/02-SRr

Roy Spalding - Ph.D.
Water Sciences Laboratory
Director
(402)472-7558

Steve Ress
UNL Water Center - Communications Coordinator
(402) 472-3305

Department: NU Water Center