Effects of groundwater-flow paths on nitrate concentrations across two riparian forest corridors

Journal of the American Water Resources Association
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Abstract

Groundwater levels, apparent age, and chemistry from field sites and groundwater-flow modeling of hypothetical aquifers collectively indicate that groundwater-flow paths contribute to differences in nitrate concentrations across riparian corridors. At sites in Virginia (one coastal and one Piedmont), lowland forested wetlands separate upland fields from nearby surface waters (an estuary and a stream). At the coastal site, nitrate concentrations near the water table decreased from more than 10 mg/L beneath fields to 2 mg/L beneath a riparian forest buffer because recharge through the buffer forced water with concentrations greater than 5 mg/L to flow deeper beneath the buffer. Diurnal changes in groundwater levels up to 0.25 meters at the coastal site reflect flow from the water table into unsaturated soil where roots remove water and nitrate dissolved in it. Decreases in aquifer thickness caused by declines in the water table and decreases in horizontal hydraulic gradients from the uplands to the wetlands indicate that more than 95% of the groundwater discharged to the wetlands. Such discharge through organic soil can reduce nitrate concentrations by denitrification. Model simulations are consistent with field results, showing downward flow approaching toe slopes and surface waters to which groundwater discharges. These effects show the importance of buffer placement over use of fixed-width, streamside buffers to control nitrate concentrations.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Effects of groundwater-flow paths on nitrate concentrations across two riparian forest corridors
Series title Journal of the American Water Resources Association
DOI 10.1111/j.1752-1688.2010.00427.x
Volume 46
Issue 2
Year Published 2010
Language English
Publisher Wiley
Contributing office(s) Virginia Water Science Center
Description 15 p.
First page 246
Last page 260
Country United States
State Virginia