Performance of saturated riparian buffers in Iowa, USA

Authors: Jaynes, Dan; ISENHART, THOMAS - Iowa State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2018
Publication Date: 9/6/2018
Citation: Jaynes, D.B., Isenhart, T.M. 2018. Performance of saturated riparian buffers in Iowa, USA. Journal of Environmental Quality. 48(2):289-296. https://doi.org/10.2134/jeq2018.03.0115.
DOI: https://doi.org/10.2134/jeq2018.03.0115

Interpretive Summary: Nitrate in our Nation's surface waters can be detrimental for its use as a drinking water source and can cause excessive algal growth and "dead zones" in coastal waters such as the Gulf of Mexico. Much of this nitrate comes from agricultural production on seasonally wet soils where farmers have installed subsurface pipes or tiles to remove the excess water. Edge-of-field practices have been developed to remove nitrate contained in these tiles before it enters streams and rivers. One of the newest practices, saturated riparian buffers can remove much of the nitrate that would otherwise leave a farmer's field. While promising, there is little data available on the performance of this practice. In the this research we showed that saturated buffers can be very effective in removing nitrate from tile drainage before it can enter streams. Annual nitrate removal ranged from 13 to 179 lbs of N per year. This is nitrate that would have otherwise entered directly into the adjacent stream. The impact of this finding will be greater use of the practice and ultimately to less nitrate in our Nation's stream and rivers.

Technical Abstract: Nitrate from artificial drainage pipes (tiles) underlying agricultural fields is a major source of reactive N in surface waters, especially NO3. A novel approach for reducing NO3 loss is to intercept a field tile where it crosses a riparian buffer and divert a fraction of the flow as shallow groundwater within the buffer. This practice is called a saturated buffer, and while promising, little data on the performance of the practice is available. This research investigated the effectiveness of saturated buffers in removing NO3 at six sites installed across Iowa, resulting in a total of 17 site-years. Water flow and NO3 in the tile outlets, diverted into the buffer, and NO3 concentration changes within the buffer were monitored throughout the year at each site. Results showed that all the saturated buffers were effective in removing NO3 from the tile outlet, with the average annual NO3 load removal ranging from 13 to 179 kg-N. This is NO3 that would have otherwise discharged directly into the adjoining streams. The removal effectiveness, which is the total NO3 removed in the saturated buffer divided by the total NO3 delivered to the tile outlet, ranged from 8% to 84% when averaged by year at each installation. This corresponds to an average removal rate of 0.0041 kg-N m-3 d-1 with a range of 0.0043–0.1637 g-N m-3 d-1. Assuming a 40-yr life expectancy for the structure and a 4% discount rate, we computed a mean Equal Annual Cost for saturated buffers of $213.83. Given the average annual removal of 72.8 kg for all site-years, this cost equates to $2.94 (kg-N)-1 removed, which if very competitive with other field-edge practices such as denitrification bioreactors and constructed wetlands. Thus, saturated buffers continue to be a promising practice for NO3 removal in tile drained landscapes.