Design and Efficacy of Saturated Riparian Buffer Zones in Central Illinois

Author

Emma Eldridge, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2022

Degree Name

Master of Science

Department

Forestry

First Advisor

Schoonover, Jon

Abstract

Saturated buffers are a newly developed agricultural best management practice (BMP) used to redirect tile flow away from waterways, thereby mitigating nutrient losses and downstream eutrophication. As of 2021, the Illinois Nutrient Loss Reduction Strategy has included saturated buffers as a means to minimize nutrient losses from agriculture. Although saturated buffers are promising and have been shown to remove up to 98% of incoming nitrate-N, other research indicates instances of backflow, where water from the buffer is drained via the distribution lines, which is problematic for a practice intended to reduce out flows. Moreover, saturated buffers have not been approved for phosphorus abatement, as there is a dearth of research on saturated buffers as a means of phosphorus loss reduction. As a result, an experimentally designed saturated buffer (PF), which included pitchfork-shaped dispersion lines and a backflow check valve, was installed alongside a traditional or standard (ST) buffer on a privately owned farm in Moultrie County, Illinois to directly compare design efficacy. Routine and event-wise water samples were used to calculate nitrate-N and DRP loads, as well as monitor the movement of nutrients through both the ST and PF buffers. In terms of design efficacy, the added dispersion lines and check valve were successful additions to the saturated buffer design, as there was an overall significant difference in days of dispersion and days of backflow between the PF and ST buffers. Furthermore, the PF buffer diverted 35% and 1.9 % of tile flow in 2020 and 2021, respectively, while the ST buffer added 116% and 137% of tile influent to the stream in 2020 and 2021, respectively. The PF buffer was also more successful in retaining the nitrate-N load in 2020, diverting 18% of influent nitrate-N from the stream while the ST buffer had an effluent nitrate-N load 94% higher than the influent load due to backflow events. However, in 2021, both the PF and ST buffers intensified nitrate-N loading by 180% and 151%, respectively. The PF buffer redirected 52% and 90% of influent DRP to the riparian buffer in 2020 and 2021, respectively. Whereas the ST buffer increased DRP loading in 2020 by 97% and in 2021 by 126%. Ultimately, the efficacy of saturated buffer could be improved with minimal, low-cost additions to their designs. Check valves, for example, are a simple supplement to the standard saturated buffer that can only enhance efficacy. Added dispersion lines, while providing more opportunity for diversion of tile flow, does require more land be removed from agricultural production, so the costs and benefits should be weighed.