Effectiveness of Saturated Buffers on Water Pollutant Reduction from Agricultural Drainage

Highlights Saturated buffers redistribute tile drainage water below riparian buffers to reduce nitrate-nitrogen loading. NRCS Conservation Practice Standard 604 guides saturated buffer design in the USA. Annual edge-of-field nitrate-nitrogen loss reductions averaged 46 ± 24% and 9.4 ± 5.9 kg N/ha/y. Further research on design, siting, and mechanisms will enhance performance. Abstract. It is a pivotal time in the development of saturated buffers as a conservation drainage practice. Field data have demonstrated that this practice can effectively reduce nitrate loads in subsurface drainage. The compilation and assessment of current knowledge for this relatively new practice is timely to help identify future opportunities. This review summarizes the state of the science for saturated buffers in the US within the context of this special collection’s emphasis on performance and cost. Suggested research areas are identified to improve understanding of saturated buffer function and performance and to refine design processes and criteria to accelerate adoption. As currently designed, saturated buffers removed an average of 46 ± 24% (mean ± sd) of the N load that would have otherwise entered receiving waters (9.4 ± 5.9 kg N removed/ha-y; n = 30 site-years). Cost efficiencies, which generally trended around $3 to $5/kg N removed per year, were considered relatively efficient compared to similar nitrate removal practices (range: $1.20 to $9.20/kg N/y), with planning level costs between $25 and $66/ha treated/y. As adoption is scaled, engineering design costs need to be considered unless the design model can be simplified. Future research should refine design processes, management, and siting criteria to facilitate scaled adoption for water quality goals. Additional studies on nutrient cycling within saturated buffers are needed to fill gaps about nitrogen and phosphorus dynamics and the role of buffer vegetation. Saturated buffers have significant nitrate reduction potential for tile-drained landscapes, but design adaptations may be needed to facilitate adoption in varied landscapes. Keywords: Denitrification, Edge-of-Field, Nitrate, Nonpoint-source pollution, Saturated riparian buffer, Subsurface drainage, Tile drainage, Water quality.