Summary prepared by: Gabriel Johnson, Department of Natural Resources Ecology and Management, Iowa State University
Johnson, G., Christianson, L., Christianson, R., Davis, M., Díaz-García, C., Groh, T., … & Rogovska, N. (2023). Effectiveness of saturated buffers on water pollutant reduction from agricultural drainage. Journal of Natural Resources and Agricultural Ecosystems, 1(1), 49-62. https://doi.org/10.13031/jnrae.15516
Major Findings:
This paper reviewed published studies (2014-2022) on the performance and cost-effectiveness of saturated buffers in tile-drained landscapes. Results of this review documented:
- Saturated buffers reduced annual nitrate losses by an average of 46% ± 24% at the edge of the field, corresponding to a rate of 8.4 ± 5.3 lb N/ac/y. Recent research shows that their performance may be even greater (Ghane 2025).
- Within drainage diverted through the saturated buffer, 82% ± 22% of nitrate was removed on average.
- Nitrogen reductions occur primarily through the process of denitrification, but plant uptake and microbial immobilization also play a role in the nitrogen dynamics within saturated buffers. In limited study, nitrous oxide losses were found to be nearly equal to traditional (unsaturated) buffers (8.4 lb N) and much less than adjacent cropland (32.4 lb N).
- Cost-effectiveness for nitrate removal averaged $2.13 ± $1.27/lb N (ranging from $0.54 to $4.17/lb N), corresponding to $10 to $27/ac treated per year.
Figure 1. Saturated buffer operation diagram. Tile flows are routed through the control structure, with the diverted flow saturating buffer soils. Interactions between nitrate (red diamonds) and microbes contribute to denitrification and conversion to nitrogen gas (purple circles).
Contributions to the conservation drainage community
This review clearly demonstrates the value of saturated buffers as an effective practice in reducing nitrate-nitrogen loads from subsurface drainage discharge. A summary analysis of nitrogen removal performance as well as cost-effectiveness is provided.
An outline of future opportunities to advance saturated buffer research, performance and adoption is also provided. Key research areas include further exploring buffer nutrient and carbon cycling across varying contexts, sensitivity of performance to site suitability factors, and the influence of vegetation management in terms of nutrient budgets. Key areas for practice implementation and adoption include potential strategies to optimize designs and management for enhanced performance (e.g., alternative distribution pipe arrangements, optimized buffer widths, automated control structure management), as well as improved and streamlined processes to identify suitable sites for implementation. Future results from siting and design efforts should help inform existing conservation program standards (NRCS Conservation Practice Standards), while also identifying new, alternative saturated buffer applications (e.g., grass waterways, contour buffer strips). Also, innovative implementation models, such as the Batch and Build concept, can capitalize on efficiencies of scale, reducing implementation costs and improving cost-effectiveness.
Finally, to further support saturated buffer research, monitoring recommendations are outlined. These recommendations included recommending the use of 4-chamber control structures when monitoring flow rates across weir stoplogs, more intensive water sampling frequencies (particularly for phosphorus) to better understand concentration and load reductions, and the development of more robust methods to determine nutrient concentrations as discharge moves through the buffer to the adjacent stream.
