Riparian vegetated buffer strips in water‐quality restoration and stream management

Abstract

SUMMARY: A review is presented of the literature on riparian vegetated buffer strips (VBS) for use in stream‐water‐quality restoration and limitations associated with their use are discussed. The results are also presented of recent investigations on the effectiveness of a forested and a grass vegetated buffer strip for reducing shallow subsurface inputs of nutrients from agriculture to a stream in central Illinois, U.S.A. Because riparian zones link the stream with its terrestrial catchment, they can modify, incorporate, dilute, or concentrate substances before they enter a lotic system. In small to mid‐size streams forested riparian zones can moderate temperatures, reduce sediment inputs, provide important sources of organic matter, and stabilize stream banks. Several questions on the utility and efficiency of vegetated buffer strips for stream restoration still remain unanswered, including: what types (grass v forest) are most efficient; do they become nutrient saturated; are they only temporary sinks; how does species composition influence effectiveness; and, what is the optimal width of buffer to facilitate nutrient reduction under different conditions? Water samples were collected (1989–90) from lysimeters located at three depths (60, 120, and > 120cm) in an upland area planted in conventional row crops (corn and soybean) and in three adjacent riparian buffer treatments, a 39m wide grass buffer. a 16 m wide mature forested buffer, and a buffer planted in row‐crops to the stream bank. Concentrations of dissolved and total phosphorus and nitrate‐N in each sample were determined following major precipitation events over a seventeen month period. Both the forested and grass VBS reduced nitrate‐N concentrations in shallow groundwater (up to 90% reduction). On an annual basis the forested VBS was more effective at reducing concentrations of nitrate‐N than was the grass VBS, but was less efficient at retaining total and dissolved P. During the dormant season, both grass and forested buffer strips released dissolved and total P to the groundwater. The VBS apparently acted as a nutrient sink for much of the year, but also released accumulated nutrients during the remaining portion of the year. Periodic harvesting of plant biomass may reduce the amount of P released during the dormant season. VBSs are not as effective in agriculture areas with tile drained fields. Alternative restoration practices such as discharging drain tiles into wetlands constructed parallel to the stream channel may prove to be a more effective means of controlling non‐point‐source agricultural inputs of nutrients in such areas.