4 Agricultural Research/December 2003

egetative, or conservation, buffers can serve many

different purposes all aimed at the same goal—cleaner

soil and water. Clean waterways and healthy soil are

goals shared by many, including environmental regulatory

agencies. In rural areas, farmers play an integral part in getting

to that goal.

Since the beginning of U.S. Department of Agriculturesponsored agricultural conservation in the 1930s, farmers have

focused on how to preserve the environment while raising crops

and livestock. Most times, the farmers changed the things they

did in their fields to be better conservationists. Now, use of

streamside and field-edge buffers gives farmers a set of

conservation tools to use outside their fields in the less

productive parts of their farms.

Agricultural Research Service scientists in Tifton, Georgia,

and scientists at the University of Georgia have conducted studies that examine several different scenarios farmers encounter.

Ecologist Richard Lowrance, of the ARS Southeast Watershed

Research Unit, and engineer George Vellidis, of the University

of Georgia, recently conducted a 9-year study to determine

Designing the Best

Possible

Conservation Buffers

V

Restored riparian forest buffers like the one ecologist Richard

Lowrance is standing next to provide protection from manure

nutrients running off into ponds and the downstream watershed.

PEGGY GREB (K10847-1)
Agricultural Research/December 2003 5

whether restored conservation buffer zones in wetlands next to

agricultural fields can reduce the amounts of phosphorus and

nitrogen that reach streams that eventually lead to larger surface waters like lakes and rivers. They have found a restored

three-zone conservation buffer to be quite effective in removing excess nutrients from water that runs off agricultural fields

that have manure applied as a fertilizer.

Buffers, it seems, may well offer assistance to the agricultural

community in improving water and soil quality. “Riparian buffer

zones are areas of vegetation that act like sponges that take up

water and nutrients from the soil,” explains Lowrance. “Buffer

zones also help reduce soil erosion along downward slopes that

is due to rain events or irrigation and can cause surface runoff.”

Long-Term Conservation Buffer Research

The buffer system used in the long-term study has three

zones. “Zone 3 is a grassy edge that sits next to the field, zone

2 is a managed forest buffer that is situated farther from the

field, and zone 1 is a permanent forest along the stream,” says

Lowrance. To obtain a baseline of runoff amount and content

without riparian buffers, before planting, researchers monitored

both nutrient levels put on the field as well as nutrient levels

leaving the field. In the permanent forest, they planted tulip

poplars, green ash, and swamp black gum; then they let native

plant species establish among the trees over time. The scientists allowed natural succession to produce the final mix of

plants.

For the next 9 years, they monitored amounts of water and

concentrations of nutrients (nitrogen and phosphorus) in water

entering and leaving the riparian wetland. The streamflow concentrations of nitrogen and phosphorus leaving the conservation wetland buffer were about one-half and one-quarter,

respectively, of the incoming concentrations in surface runoff

from adjacent fields.

Even though 9 years may seem like a long time for a scientific study, it is a relatively short time compared to a forest’s

lifespan. “This is a young forest at 9 years old. It would take

about 40 years to produce a mature forest,” says Lowrance.

Generally, young forests have higher nutrient uptake rates

because the plants within them are growing more, while mature forests have prepared the way to create forest soils through

leaf litter and shallow roots, which increase biomass on the

forest floor. All these factors are keys to reducing the movement of nutrients to surface waters.

“It’s important to understand how buffers can be used to

help reduce nutrient transport to streams, because of the potential for high loading of nutrients from manure application sites,”

says Vellidis. “These studies showed that the restored riparian

wetland buffer retained or removed at least 60 percent of the

nitrogen and 65 percent of the phosphorus that entered from

the adjacent manure application site. This is the first time that

a study of a restored riparian buffer has shown that the retention

of phosphorus was as high or higher than nitrogen retention.”

Surface runoff and subsurface flow of water from farmland

on which animal waste has been applied can contribute to

significant loading of nutrients to receiving waters unless

appropriate management techniques are used. Grass buffer

zones or vegetative filter strips have been investigated as a

means of reducing nutrient loads in streams.

Though conservation buffers are being used to improve water

quality through USDA cost-share programs such as the

Conservation Reserve Program, few studies have looked at the

effects restored conservation buffers have on water quality.

“Most of our management recommendations have been based

on mature forest buffers and have focused on nitrogen. Now

we know that a restored riparian forest buffer can be just as

effective for phosphorus removal,” says Lowrance.

The 9-year study was in response to a request made in the

late 1980s and early 1990s by USDA’s Natural Resources Conservation Service and Forest Service to suggest riparian buffer

specifications. At that time, the general recommendation was

that natural mature buffers should be used, but USDA needed

national specifications based on the best science. The study of

restored conservation buffers conducted by Lowrance and

Vellidis put the general principles into practice and was the

first detailed test of a restored riparian buffer. But Lowrance

and Vellidis are not alone—other ARS projects have also been

conducted around the country to test buffer zones. And there

are other pressures on farmers and their states to reduce nutrients

coming from fields and entering streams.

Other Conservation Buffer Research

Another study in Tifton is being conducted by soil scientist

Robert Hubbard and animal scientist G.L. Newton of the

University of Georgia to evaluate effectiveness of a grass-forest

Engineer Andy Knowlton collects water from a farm pond

downstream from the restored riparian forest buffer.

PEGGY GREB (K10843-1)
buffer (zones 3 and 1) treatment system to filter out nutrients

from swine lagoon contents sprayed onto fields. Water and soil

samples are taken and examined for the amount of phosphorus

and nitrogen removed by the system. Nutrient uptake for the

grasses is limited, with uptake of nitrogen at almost 45 percent

and phosphorus at nearly 20 percent. This research indicates

that grass buffers do not work well as a sole buffer against

nitrogen and phosphorus runoff but work better when combined

with other buffer systems such as forested buffers.

In another study headed by Lowrance and Vellidis, herbicides

were examined in a grass-forest buffer system. During this 3-

year study, they found that the three-zone riparian buffer was

effective at reducing the amounts of two herbicides, atrazine

and alachlor, that entered the shallow groundwater and surface

runoff. In contrast to the results with nitrogen and phosphorus,

the grass filter strip received higher amounts of herbicides and

provided a higher rate of removal. So the entire buffer system

(grass plus forest) is effective at reducing herbicide concentrations to below detectable levels and in substantially

reducing nutrient amounts.

Lowrance and Hubbard conducted another study to determine whether removal of mature trees in a streamside mature

forest buffer would limit the buffer’s effectiveness at removing

nutrients. Again using a three-zone system, Lowrance and

Hubbard removed trees that were estimated to be 45-50 years

old in the part of the buffer not immediately next to the stream.

They found that the buffer’s pollution (nitrogen, phosphorus,

and pesticides) control functions suffered no harm. The

harvested forest grew back quickly, and the forest soil in the

study area experienced very little disturbance. This study offers

promise that farmers will be able to gain income from the

buffers while keeping their buffering capacities at peak levels.

Future Considerations

The U.S. Environmental Protection Agency, through the

Federal Water Pollution Control Act Amendments of 1972,

mandates development of water quality management plans to

control nonpoint-source, or diffuse, pollution from agriculture,

including manure application sites. As a result, considerable

research has been devoted to this topic. Coastal plain streams

in Georgia, Florida, and other states often don’t meet water

quality standards because of low dissolved oxygen. “This may

be due to nutrient enrichment mostly from diffuse sources of

nitrogen and phosphorus in these streams,” says Lowrance.

According to Lowrance, the buffer research should help.

“Ultimately, this research should aid growers in developing a

way to lower nutrients that make it to streams and waterways.”

Accurate and precise determinations of nutrient levels in water and

soil samples are essential for evaluating buffer effectiveness. Here,

chemist Leila Hargett prepares water samples for nutrient analysis

by automated colorimetry.

PEGGY GREB (K10853-1)

6 Agricultural Research/December 2003

Technician Chris Clegg prepares samples for nitrogen gas analysis

to estimate denitrification rates. During denitrification, microbes

remove nitrate from shallow groundwater.

PEGGY GREB (K10851-1)
Agricultural Research/December 2003 7

Engineer Andy Knowlton (left) and technician Rodney Hill take a

deep soil sample from the edge of a buffer system to estimate

denitrification rates in the soil.

Paige Gay, a University of Florida Ph.D. candidate, collects a runoff

sample from a LowImpact Flow Event (LIFE) sampler. The

restored buffer she is testing removes sediment and chemicals from

surface runoff.

“Buffer zones are not a magic bullet, but a system to mitigate nutrient flow to soil and water,” says Vellidis. “The most

important aspect of this research is that the restored buffer has

been studied for a relatively long time, and the studies have

revealed that there is a large nutrient retention.”

Through the years, it became clear that trees or forests must

be part of the conservation buffer system if nitrogen and phosphorus and other pollutants are going to be removed. “For the

Southeast, we are now suggesting that restored conservation

buffers that include a managed forest buffer can actually outperform a mature forest,” says Lowrance.

The next step for Lowrance and Vellidis’s study of restored

conservation buffers is to assess an entire watershed. According

to Lowrance, such a study would require intense collaboration

between state government, farmers, and scientists. “To ideally

study a 5,000-acre watershed, scientists would have to collect

all the data about the ecosystem for 5 years, then put in a wide

range of buffers. It would then take 20 to 30 years to monitor

and analyze the relationship between the buffers and runoff,”

says Lowrance.—By Sharon Durham, ARS.

This research is part of Water Quality and Management, an

ARS National Program (#201) described on the World Wide

Web at www.nps.ars.usda.gov.

Richard Lowrance is in the USDA-ARS Southeast Watershed

Research Unit, 2379 Rainwater Road, Tifton, GA 31794; phone

(229) 386-3894, fax (229) 386- 7215, e-mail lorenz@tifton.cpes.

peachnet.edu. ★

PEGGY GREB (K10844-1) PEGGY GREB (K10850-1)