Groundwater nitrate reductions within upstream and downstream sections of a riparian buffer

Tiffany L. Messer, Michael R. Burchell, Garry L. Grabow, Deanna L. Osmond

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

The objective of this study was to evaluate the water quality benefits provided by a buffer enrolled in the North Carolina Conservation Reserve Enhancement Program (NC CREP). A 5-year study was conducted on two distinct buffer sections along the same stream to evaluate the hydrology and attenuation of groundwater nitrate (NO 3 --N) entering from nearby agricultural fields. The average buffer widths were 60m (Section 1, upstream) and 45m (Section 2, downstream). Three transects of groundwater monitoring well nests within each buffer zone were installed to monitor water quality and water table depths for 5years. Mean groundwater NO 3 --N concentrations at the 1.5m depth decreased from 4.5mgL -1 to 1.7mgL -1 and from 12.9mgL -1 to 1.4mgL -1 in buffer Sections 1 and 2 respectively. These differences were significant in both buffer sections (α=0.05), but the wider Section 1 received significantly less NO 3 --N than did Section 2 (P<0.0001). Groundwater NO 3 --N loads were reduced by 0.003kgm -2yr -1 (76% reduction) at the 1.5m depth, while in Section 2 these loads were reduced by 0.02kgm -2yr -1 (94% reduction) and 0.04kgm -2yr -1 (86% reduction) at the 1.5m and 3m depths, respectively. Topography, water table and redox measurements, nitrate to chloride ratios, and deep groundwater cation analyses, indicated both sections were suitable for denitrification to proceed. However, the position of the wider Section 1 buffer in the landscape limited the amount of NO 3 --N contaminated groundwater that entered from the agricultural fields, and thus could have been designed to be narrower. The effectiveness of NO 3 --N reduction in riparian buffer systems is dependent on multiple landscape and biogeochemical factors and not buffer width alone. Findings provide design guidance for conservation buffer program managers as related to the influence of buffer landscape position on groundwater nitrate reduction.

Original languageEnglish
Pages (from-to)297-307
Number of pages11
JournalEcological Engineering
Volume47
DOIs
StatePublished - Oct 2012

Bibliographical note

Funding Information:
This grant was supported by the NC Department of Environment and Natural Resources – Division of Soil and Water Conservation and the NC Clean Water Management Program to improve the impact of the NC Conservation Reserve Enhancement Program (NC CREP). Special thanks to the staff from these agencies, in particular Natalie Woolard, David Williams, and Charles Bowden. Many thanks to the NCDENR Aquifer Protection Section (Rick Bolich, Evan Kane, and Ray Milosh) who coordinated installation of deep aquifer wells at the site. NCSU staff, undergraduate and graduate students, from the Department of Bio&Ag Engineering provided support for well installation, data collection, and site maintenance, particularly, L.T. Woodlief, Craig Baird, Dale Hyatt, Mike Shaffer, Jamie Blackwell, Jacob Wiseman, and Randall Etheridge. Dan Line was pivotal in his contributions to stream flow and water quality monitoring, and Karen Hall provided assistance in vegetation surveys. We also received advice from Dr. Wendell Gilliam and Dr. Robert Evans on experimental setup. We would also like to thank Dr. Jason Osborne for his assistance with the statistical analysis used in this study.

Keywords

  • Groundwater
  • Hydrology
  • NO -N
  • Nitrate
  • Riparian buffer

ASJC Scopus subject areas

  • Environmental Engineering
  • Nature and Landscape Conservation
  • Management, Monitoring, Policy and Law

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