August 31 - 1053 - Gabriel Johnson
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This document summarizes research on the performance of four saturated riparian buffers in Iowa over sixteen site years from 2018-2021. The key findings are: 1) The buffers consistently removed nitrate from subsurface agricultural drainage, with an average removal rate of 1.88 g/m2/day and removing 45% of the total nitrate load on average. 2) Buffers with larger widths relative to their drainage areas had higher nitrate removal fractions. 3) Despite high bypass flows, the site treating the most flow (BC-2) removed the highest total nitrate mass. 4) Sixteen new site years of data showed continued consistent nitrate removal by these buffers.
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August 31 - 1053 - Gabriel Johnson
- 1. Performance of Saturated Riparian Buffers in Iowa Across Sixteen Site Years Gabe Johnson Iowa State University Co-Authors: Tom Isenhart and Dan Jaynes International Drainage Symposium | August 31, 2022 Water Quality and Drainage – Saturated Buffers and Hybrid Projects NRCS/SWCS photo by Lynn Betts
- 2. Background • Extensive subsurface drainage in U.S. Midwest NRCS/SWCS Lynn Betts 2
- 3. Background • Extensive subsurface drainage in U.S. Midwest • Nitrate-nitrogen (NO3-N) transported directly from field to stream • Eutrophication, hypoxia, drinking water contamination 3 Drainage benefits: Field access Soil warming Yield increases Drainage drawbacks: Nutrients transported directly to streams Bypass natural areas for nitrate removal • e.g., stream buffers, natural wetlands
- 4. Edge of Field Practices Capture and treat drainage water before discharging into stream 4 Iowa Learning Farms Wetlands Denitrifying Bioreactors Saturated Buffers
- 5. Saturated Buffers Divert subsurface drainage from crop fields through a vegetated stream buffer Removal of nitrate nitrogen (NO3-N) via denitrification and plant uptake 5
- 6. Objectives • Analyze nitrate removal performance of four saturated buffers from 2018-2021 • Compare results with prior studies and earlier years of data at these sites • Prior Work: Jaynes and Isenhart, 2019 6
- 7. Study Sites BC-1 BC-2 IA-1 SH BC-1 IA-1 BC-2 SH Installation Date Oct. 2010 June 2013 Oct. 2015 May 2016 Drainage Area (ha) (estimated) 5.9 4.7 40.5 3.4 Buffer Width (m) 21 24 22 19 Distribution Pipe Length (m) 335 308 168 266 Jaynes and Isenhart, 2019: Data from installation through 2017 7
- 8. Methods • Flow monitored in control structures using v-notch weirs and pressure transducers • Approximately bi-weekly sampling for nitrate • Control structure • Monitoring wells • Creek • Nitrate mass loads determined by multiplying concentrations by flow volumes • Nitrate load removed determined from difference in concentration of field tile and wells nearest stream 8
- 10. Flow Totals Site Year Annual Precipitation Days with tile flow Total tile flow Tile flow diverted to buffer Fraction of tile flow diverted to buffer Fraction of total precipitation drained mm mm yr-1 % BC-1 2018 1208.4 194 367 195 53% 30% BC-1 2019 1007.1 240 215 63 29% 21% BC-1 2020 788.6 138 140 41 29% 18% BC-1 2021 707.3 45 28.5 21.6 76% 4% BC-2 2018 1208.4 356 551 201 36% 46% BC-2 2019 1007.1 320 242 44.9 19% 24% BC-2 2020 788.6 205 101 15.9 16% 13% BC-2 2021 707.3 182 113 45 40% 16% IA-1 2018 1208.4 191 412 399 97% 34% IA-1 2019 1007.1 228 480 420 88% 48% IA-1 2020 788.6 79 87.9 58.6 67% 11% IA-1 2021 707.3 5 0.16 0.16 100% 0.023% SH 2018 1401.6 310 1388 593 43% 99% SH 2019 999.6 288 601 264 44% 60% SH 2020 645.3 190 224 148 66% 35% SH 2021 740.8 163 160 138 86% 22% 10
- 11. Results: Nitrate Removal Site Year Total NO3 in field tile Total NO3 diverted to buffer Total NO3 removed in buffer Nitrate removal rate Nitrate removal per area drained Fraction of total NO3 load removed kg g m-1 d-1 kg ha-1 % BC-1 2018 219 117 108 1.66 18.3 49 BC-1 2019 260 78.3 75.3 0.94 12.8 29 BC-1 2020 94.5 26.5 26.2 0.57 4.4 28 BC-1 2021 18.0 13.8 12.8 0.85 2.2 71 BC-2 2018 1560 601 503 8.40 12.4 32 BC-2 2019 1230 178 155 2.88 3.8 13 BC-2 2020 410 63.6 45.7 1.33 1.1 11 BC-2 2021 383 171 159 5.22 3.9 42 IA-1 2018 150 145 138 2.35 29.4 92 IA-1 2019 116 98.8 87.9 1.25 18.7 76 IA-1 2020 47.5 31.5 28.0 1.15 6.0 59 IA-1 2021 ND ND ND ND ND ND SH 2018 499 207 137 1.66 40.3 27 SH 2019 165 70.1 41.5 0.54 12.2 25 SH 2020 72 47.9 31.1 0.62 9.1 43 SH 2021 44.3 38.2 35.5 0.82 10.4 80 Average 351 126 106 2.02 12.3 45 Green: Wet Year Red: Dry Year 11
- 14. Nitrate Removal Summary Site NO3 removal rate NO3 removal per drainage area Fraction of total NO3 load removed Number of Site Years g m-1 d-1 kg ha-1 % BC-1 1.73 11.4 42 11 IA-1 1.41 14.0 81 8 BC-2 3.84 4.52 19 6 SH 0.74 14.2 35 6 Average 1.88 11.2 45 Total Standard Deviation 1.66 8.30 26 31 14 All site years from 2011 to 2021 Data from 2011 to 2017 from Jaynes and Isenhart, 2019
- 15. Conclusions • 16 new site years of data showed continued consistent nitrate removal • Fraction of total NO3 load removal highest in sites with large buffer lengths relative to drainage areas • Despite high bypass flows, total NO3 mass removal highest in site treating most flow (BC-2) 15
- 16. Future Work • Statistically significant differences in site performance? • Summary metrics – is kg/ha (mass load per drainage area) adequate? • Add additional site-years and analyze long term trends • Improved design guidelines to optimize performance 16
- 17. Acknowledgements USDA-ARS National Lab for Agriculture and the Environment Kent Heikens Natalia Rogovska Dan Jaynes, retired USDA NRCS Conservation Innovation Grant NR213A750013G038 Questions? Contact: gjohnson@iastate.edu 17
- 19. Load removed vs % of total load removed 19 y = -0.0757x + 12.032 R² = 0.0067 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 0 5 10 15 20 25 30 35 NO 3 -N Load Removal per drainge area (kg/ha) Fraction of Total NO3-N Load Removed (%)
Editor's Notes
- 4 study sites that have been previously monitored Hamilton and Boone counties, IA BC1 18 Wells IA 1 16 wells BC2 9 wells SH 6 wells BC2 is outlier with much larger drainage area relative to buffer length IA-1 has small drainage area relative to buffer length Coland soils at most sites, some more well drained clarion soils at SH
- FLOW TO BUFFER 2018 and 2019 wetter than average 2020 and 2021 drier than average 2018 had higher summer rains, lower spring rains 2019 had higher spring rains and lower summer rains Both 2018 and 2019 had higher fall rains than spring rains 2020: higher spring rains than summer and fall 2021: higher summer rains, then fall, then spring
- 2018 had higher summer rains, lower spring rains 2019 had higher spring rains and lower summer rains Both 2018 and 2019 had higher fall rains than spring rains 2020: higher spring rains than summer and fall 2021: higher summer rains, then fall, then spring
- Timing, intensity, duration of precip events meant than even in wet years there could still be relatively similar removal based on flow diverted
- Consistent performance at sites with similar ratio of drainage area to buffer length (BC-1, IA-1, SH) Higher removal rate per length of buffer at BC-2 due to high loads diverted to buffer, even though on average it removed a lower fraction of the total load Design considerations: ensuring adequate buffer length for the expected flow volumes (drainage area) We’re working on updating our estimates of drainage area How can we improve design to optimize performance?
- Design considerations: ensuring adequate buffer length for the expected flow volumes (drainage area) We’re working on updating our estimates of drainage area How can we improve design to optimize performance?
- Design considerations: ensuring adequate buffer length for the expected flow volumes (drainage area) We’re working on updating our estimates of drainage area How can we improve design to optimize performance?