A riparian forest buffer is an area of trees and/or shrubs that is adjacent to a river or stream. Its purpose is to prevent sediments and pollutants from directly discharging into aquatic ecosystems. A riparian forest buffer is a edge-of-ﬁeld practice.
Figure 19. Riparian forest buﬀers. Credit: Xiaoqiang Liu, Food, Agricultural and Biological Engineering, The Ohio State University
A riparian forest buffer can be used on ﬁelds bordering water channels and bodies, with the trees/shrubs being adjacent or up-gradient to the bodies of water.
A riparian forest buffer reduces erosion, nutrient runoff and pesticide runoff It also improves habitats for aquatic organisms by lowering water temperatures via shade. A buffer also helps stabilize banks and ditches.
- The effectiveness of nutrient removal varies depending on the site’s hydrology, lithology, and topography.
- In a 1984 experiment (Peterjohn and Correll, 1984) found that a 19-meterlong riparian forest buﬀer reduced suspended particles by 89 percent, nitrate-N by 60 percent, total phosphorus by 74 percent, dissolved phosphorus by 58 percent, and organic-carbon by 60 percent.
- For nontile drained lands, riparian forest buffers can achieve up to 90 percent of nitrate removal (Osborne and Kovacic, 1993).
- Nitrate effectiveness can be more than 90 percent but varies signiﬁcantly depending on the buﬀer width and the hydrogeomorphological settings, such as hydrology, soil type, upland aquifer depth and connectivity, and nutrient input from upland (Vidon and Hill, 2004).
- Nitrate removal varies with seasonal hydrology. The removal rate for a forest buﬀer is 93 percent during a low water table period, but it drops to 50 percent during a high water table period (Liu et al., 2014).
- Phosphate removal is site-speciﬁc, especially for the dissolved reactive phosphate where a site could be either a sink or a source.
- Sediments and debris are trapped from overland ﬂow.
- During the dormant season, riparian forest buffers can release dissolved and total phosphorus to adjoining water or groundwater.
- Riparian forest buffers might not be effective for the removal of nitrogen and phosphorus from agricultural areas with tile drainages (Osborne and Kovacic, 1993), and the removal efficiency is decreased signiﬁcantly during high-ﬂow periods in the Midwest region of the United States (Liu et al., 2014).
- On an annual basis, forested vegetated buﬀers are more effective at reducing concentrations of nitrate-N than are grassed vegetated buffers. However, forested vegetated buffers are less efficient at retaining total and dissolved phosphorus.
- A wood chip bioreactor, phosphate ﬁlter, or constructed wetland might be needed as a supplemental measure to effectively curtail nutrient problems.
- Periodic harvesting of plant biomass might reduce the amount of phosphorus released during the dormant season.
- Costs are site-speciﬁc and will depend on the length/width of the buffer and the vegetation species used. If the riparian zone is vegetated and hydrologically connected between the upland and stream, there may be no cost at all, other than the cost and effort of negotiating an easement with the landowner to ensure continued integrity of the buffer (Passeport et al., 2013).
- If riparian buffers do not exist and/or must be revegetated or rebuilt (e.g., by way of stream bank reengineering), costs can increase quickly. In general, a forest buffer costs between $218–$729 per acre to plant and maintain. Costs include site preparation, plants, planting, maintenance, and replanting (Lynch and Tjaden, 2000).
- Riparian forest buffers qualify for the Conservation Reserve Program, which helps with the cost of establishment and provides an annual payment. Forest buﬀers might also result in a bonus for trees planted and a per-acre incentive.
- The location of the planting and the number of acres—as well as the amount and types of trees planted—contribute to variances in costs.
- Planting can be by hand or machine. It is worth noting that machineplanted trees tend to survive at a higher rate.
- Land taken out of production should be considered in the cost analysis.
- For more details, please contact your local SWCD.
- Above-ground stems from bushes or trees dissipate the erosive energy of overland water ﬂow, while the root mass improves soil cohesion and armors the embankment against the erosive aﬀect of the water (Carlson, 1992).
- Establishment of vegetation provides ﬁltration and deposition, removing sediment, pesticides, and nutrients from runoﬀ.
- Below-ground roots uptake nutrients and water, aﬀecting water table ﬂuctuations. Roots provide organic carbon to microbes to conduct anaerobic denitriﬁcation, resulting in nitrate removal.
- Tree shade reduces streamwater temperatures, but loss of shade can increase water temperatures by 3.6–18 degrees Fahrenheit, creating an environment less suitable for aquatic wildlife.