Agricultural Riparian Areas in Southern Appalachia

By Tammy Barnes, NCAT Agriculture Specialist

Contents

Introduction
Benefits of a Riparian Zone
Function of a Riparian Area
Riparian Forest Buffer Zones
Creating a Forested Riparian Buffer
References
Resources

Introduction

Have you ever walked along a beautiful stream bank that has lots of trees and plants? Did you notice the abundance of insects, birds, and frogs in this area? There’s a special name for this vegetated zone by a creek, stream, river, wetland or pond: riparian area or buffer. In agricultural settings, riparian zones can look very different; some can be buffered by trees, shrubs, grass, or a combination of these vegetative covers.  How these buffers look depends on the stream size and order, topography, and whether the riparian areas have been impacted by agricultural activities such as grazing or tree harvesting. In the mountainous areas of southern Appalachia, most of the riparian areas are forested, and they are often headwaters for ephemeral, steep, fast-flowing streams that drain to valley floors. The streams in the valley are usually bordered by a mix of trees, shrubs, forbs, and grasses. A highly functioning riparian area has species richness, which consists mostly of native species.

Benefits of a Riparian Zone

There are many benefits of establishing or improving riparian areas. First, they buffer surface water, such as wetlands (lentic systems) and streams, creeks, and rivers (lotic systems) from the possible negative impact of nearby land use. In general, they protect and stabilize stream and wetland environments. Riparian areas and their associated stream edge are where groundwater and surface water mix, a place sometimes called a hyporheic area. Hyporheic areas are where nutrients are exchanged in the stream and where stream base flow is maintained.

Healthy riparian buffers can provide the following benefits:

• Protect the stream banks from eroding and preserve the stream’s winding characteristics
• Protect surface water from nonpoint pollutants such as sediment, livestock and wildlife feces, as well as nutrients (nitrogen and phosphorus) from upslope land use
• Help maintain acceptable water temperature through shading and groundwater recharge
• Provide habitat for animals, fish, insects, native plants, and trees

Function of a Riparian Area

Runoff from agricultural production can contain pollutants such as phosphorus, pesticides, and bacteria. The roles of riparian vegetation are the uptake and long-term storage of nutrients, sediment capture from runoff, and stream bank stabilization.  Many factors determine the effectiveness of riparian buffers. In agricultural areas, the most important factor is the type and amount of native vegetation. Think of woody tree roots as the rebar of the bank and grass/ forb roots as the cement.

Roots from woody species can remove nutrients from surface and sub-surface water. The water-borne nutrients that the woody species uptake are turned into new plant material (wood and leaves). The roots of the woodies protect the stream bank from excessively eroding by providing bank stabilization. However, trees are less effective than grasses in capturing runoff sediment before it enters the stream. Grasses and forbs in riparian systems trap sediment from field erosion, slow runoff that carries nutrients with the sediment, and take nutrients into their leaves and fibrous roots. A well-functioning riparian buffer system has grasses integrated. Often, the grass zone is found at the field edge and adjacent to the woody riparian zone.

Buffer width influences the effectiveness of a riparian area. Grassed areas of 20 feet or more  are more efficient in removing surface runoff nutrients than smaller widths (Mayer et al., 2005). Interestingly, grasses and trees are highly efficient in removing nitrates in subsurface water. Because the most effective riparian buffers have both trees and grasses, riparian areas that contain both these types of vegetation don’t need to be as wide as grass-only buffers. For example, grass buffers are 75% effective in removing nitrates at 154 feet in width, while grass/tree buffers have the same efficiency at just 66 feet (Mayer et al., 2005). Most agricultural riparian buffer systems are designed to be 20 to 35 feet wide and have both trees and grass zones.