Influence of redox gradients on nitrate transport from the landscape to groundwater and streams

Science of the Total Environment
By: , and 



Increases in nitrogen applications to the land surface since the 1950s have led to a cascade of negative environmental impacts, including degradation of drinking water supplies, nutrient enrichment of aquatic ecosystems and contributions to global climate change. In this study, groundwater, streambed porewater, and stream sampling were used to establish trends in nitrate concentrations and how redox gradients influence nitrate transport across diverse glacial terranes. Decadal sampling has found that elevated nitrate concentrations in shallow groundwater beneath cropland have been sustained for decades. Redox gradients established in the saturated zone using dissolved O2, iron, nitrate and excess N2 from denitrification suggest that nitrate-bearing zones are thin in glacial terranes dominated by fine materials. These thin nitrate-bearing zones lead to suboxic, low nitrate streambed porewater and limit the contributions of nitrate to streams from slow-flow groundwater. In contrast, thick oxic zones in more coarse-grained glacial terranes allow nitrate to reach deeper groundwater, resulting in streambed porewater with elevated nitrate concentrations and causing a large portion of stream nitrate to be derived from slow-flow groundwater. Groundwater age tracer data indicate that denitrification occurs more quickly in the terrane dominated by fine material than in the more coarse-grained terrane. The quicker depletion of nitrate in the more fine-grained terrane suggests that the thinner oxic zone in this terrane is due, in part, to the greater availability and reactivity of electron donors in this terrane than in the more coarse-grained terrane. Groundwater age tracer data and hydrograph separation analysis suggest that saturated zone lag times between when changes in land use practices occur and when changes in stream water are fully observed may vary widely across hydrogeologic settings.

Study Area

Publication type Article
Publication Subtype Journal Article
Title Influence of redox gradients on nitrate transport from the landscape to groundwater and streams
Series title Science of the Total Environment
DOI 10.1016/j.scitotenv.2021.150200
Volume 800
Year Published 2021
Language English
Publisher Elsevier
Contributing office(s) Colorado Water Science Center, Oregon Water Science Center
Description 150200, 12 p.
First page 1
Last page 12
Country United States
State Illinois, Indiana, Iowa, Michigan, Minnesota, Wisconsin
Other Geospatial Lake Michigan
Google Analytic Metrics Metrics page
Additional publication details