Scientists work together to
conduct a rainfall-simulation
test to measure bacteria
levels in runoff water. From
left to right are Reza Roodsari,
Ali Sadeghi, Kerry Sefton, Adel
Shirmohammadi, and Dan Shelton.
Pass by any dairy or cattle farm and the odor of manure will certainly
leave an impression. But that's not all manure can leave behind. Pathogens
in it can find their way into food and water supplies. Fecal bacteriaabout
1 million of which are found in each gram of manureinclude a range
of beneficial and harmful microorganisms. Since many farmers use manure
to fertilize their fields and pastures, they need an effective way to
prevent harmful bacteria, like Escherichia coli O157:H7 and Salmonella,
from reaching the water supply.
ARS microbiologist Daniel R.
Shelton, of the Animal Waste Pathogen Laboratory (AWPL) in Beltsville,
Maryland, led a study of how such organisms are spread in the environment
and whether grass buffer strips can filter them out. Shelton's collaborators
included fellow AWPL researcher Yakov Pachepsky; Ali Sadeghi and James
Starr, from the Environmental Quality Laboratory; former ARS researcher
Asad Rouhi; and University of Maryland professor Adel Shirmohammadi
and doctoral student Reza Roodsari.
In 1999, Shelton and colleagues began studying how the protozoan Cryptosporidium
parvum and the bacterium E. coli O157:H7 move through soil
and in runoff water. Then they turned their sights on ways to slow that
migration down. They planted grass strips on two 20-foot-long, 20-percent
slopes of a wedge-shaped mound called a lysimeter.
"The lysimeter is the smallest observation unit in which pathogen
transport occurs in the same way as it does in the real world,"
explains Shelton. One slope of the mound had clay loam soil and another
had sandy loam. Various indigenous grasses were grown on each soil type
to test their filtering effects. Bare parts of the slopes were used
Fresh manure from the Beltsville Agricultural Research Center's (BARC)
dairy cows was applied along the top of the slopes. Through overhead
sprinklers, designed and built by retired BARC machinist Paul Balsley,
water was applied to the slopes, simulating rainfall. Runoff was sampled
through tubes at various locations from the top of the hill to the bottom.
The samples were analyzed for bacteria content, and the results were
"Grass buffer strips were far more effective at filtering out
manure-borne parasites than expected," says Shelton. "They
stopped at least 90 percent of all rain runoff, so almost no bacteria
moved down the mound. But most of the rain ran off both bare sides of
the mound, carrying the bacteria with it."
Runoff from the bare clay loam slope contained virtually all the pathogens
present in the manure, but runoff from vegetated clay loam slope had
only 0.6 percent pathogens. Bare sandy loam soil runoff contained 25
percent of the pathogens, but vegetated sandy loam soil runoff had none.
Pathogens that remain in the soil either become food for other organisms
or settle into an area between soil particles that doesn't support life,
Shelton says. In either case, they'll die before they can infect food
or water supplies.By Sharon
Durham, Agricultural Research Service Information Staff.
This research is part of Water Quality and Management (#201) and
Manure and Byproduct Utilization (#206), two ARS National Programs described
on the World Wide Web at http://www.nps.ars.usda.gov.
Daniel R. Shelton
is with the USDA-ARS Animal
Waste Pathogen Laboratory, 10300 Baltimore Blvd., Bldg. 173, Room
101, Beltsville, MD 20705; phone (301) 504-6582, fax (301) 504-6608.