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Abstract #21, IAH 2019 Congress, 27 Sept. 2019

Abstract #21, IAH 2019 Congress, 27 Sept. 2019.

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Abstract #21, IAH 2019 Congress, 27 Sept. 2019

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  1. Abstract #21, IAH 2019 Congress, 27 Sept. 2019 Progressive release of nitrate from agricultural vadose zone delays groundwater quality improvement response to remediationYefang Jiang1, Judith Nyiraneza1 and Xiaoyuan Geng21Charlottetown Research and Development Centre2Ottawa Research and Development CentreAgriculture and Agri-Food Canada

  2. Assessing responses of groundwater nitrate level to taking potato land out of production After removing surface nitrate source, will matrix diffusion or/and vadose zone storage control the breakthrough of nitrate in the underlying fractured bedrock aquifer? Zones A–B: Potato (2011)–Barley(2012)–Forages (2013)–Potato (2014)–Barley (2015)–Forages (2016) ZoneD: Potato (2011)–uncultivated (2012–2016)

  3. PEI geology Till (5-10 m) “Red bed” (C-P) fractured-porous sandstone (1200-1600 m)

  4. Rock coring for testing nitrate levels in overburden/bedrock (12-15 Dec. 2012)

  5. Hybrid multilevel system (MLS) P2S P2M Installing removable FLUTe liner Installing MLS MLS

  6. MLS Clustered holes Open hole P1D (Einarson 2006) • Open-hole with a large sampling interval can fail to detect the improvement response in groundwater quality to BMPs/remediation.

  7. Hydraulic head and tile drainage data • Drainage/recharge occurred primarily during the fall-winter-spring seasons. • Seasonal variations of hydraulic head were highly synchronized in all piezometers/wells, and correlated closely with tile-drain discharge.

  8. Soil and tile-drain nitrate data (uncultivated) Zone D Zone B • Significant nitrate leaching occurred after potato harvest. • Elevated post-potato harvest nitrate leaching was correlated with elevated post-potato harvest soil nitrate contents.

  9. Rock core nitrate content data Rock coring in Dec. 2012 detected the nitrate leached below the soil profile in fall 2011 in Zone D (uncultivated).

  10. Upgradient groundwater nitrate concentrations Zone C (cultivated) Zone D (uncultivated) Increasing depth Groundwater nitrate concentrations in the upgradient piezometers/wells were constantly <1 mg N/L, indicating forestry origin.

  11. Zone D (uncultivated/P2) Downgradient groundwater nitrate concentrations • Groundwater nitrate concentration decreased with increasing depth. • Groundwater nitrate concentration increased for ~2.5 years after taking overlying potato land out of production. • Groundwater nitrate concentrations under uncultivated and cultivated zones followed a similar trend until fall 2015. • Progressive release of legacy nitrate from the vadosezone delayed groundwater nitrate reduction. Zone D (uncultivated/P3) Increasing depth Increasing depth Zone C (cultivated/S3DW)

  12. Nitrate transport from vadose zone to aquifer content content Nitrate travel time in vadose zone = (vadose zone thickness X field capacity)/recharge=5.6 X 0.2/0.42=2.7 yrs.

  13. Groundwater level vs. nitrate concentrations • Groundwater nitrate concentration breakthrough was mainly driven by seasonal leaching/recharge and associated nitrate release from the vadose zone rather than by matrix diffusion. • Pressure-driven uniform flow processes created an instant water table rising but a delayed groundwater quality response to nitrate leaching events.

  14. Aquifer flow pattern and 2014 nitrate plume Potato land (Zone D) out of production since 2011 Forestry Forestry 2014 The aquifer has significant fracture permeability dominated by sub-horizontal bedding plane fractures (kh>>kv, transverse anisotropy & upward hydraulic gradient).

  15. Take-home messages • Progressive release of legacy nitrate from overlying vadose zone delayed underlying groundwater nitrate reduction to taking potato land out of production. • The effects of matrix diffusion on nitrate transport appear to be limitedat the study site. • Multilevel/clustered, long-term and high-frequencysampling is required to accurately measure the responses of groundwater quality to BMP adoption/remediation.

  16. Acknowledgements • S. Chapman, A. Malenica, B. Parker, and J. Cherry. • Funding sources: Agriculture & Agri-Food Canada (AAFC) Projects J-000252, J-000038, J-000916, J-000994 , J-000991, AAFC WEBs project, Canadian Water Network (CWN) and PEI Environment. • Land owners, the Souris and Area Branch of the PEI Wildlife Federation, Harry Rohde, Brian Murray, Danielle Murnaghan, Mark Grimmett, Sandy Jenkins, Vernon Rodd, Erica MacDonald, Qing Li, and all the students involved in the projects. For more information: Jiang et al. 2017. J. Hydrol. 555:760–776. Chapman et al. 2015. Groundwater Monit. R. 35:55–67. yefang.jiang@canada.ca

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