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Liao, Lixia; Green, Christopher T.; Bekins, Barbara A.; Böhlke, J. K.

Factors controlling nitrate fluxes in groundwater in agricultural areas

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  • Medientyp: E-Artikel
  • Titel: Factors controlling nitrate fluxes in groundwater in agricultural areas
  • Beteiligte: Liao, Lixia; Green, Christopher T.; Bekins, Barbara A.; Böhlke, J. K.
  • Erschienen: American Geophysical Union (AGU), 2012
  • Erschienen in: Water Resources Research
  • Sprache: Englisch
  • DOI: 10.1029/2011wr011008
  • ISSN: 0043-1397; 1944-7973
  • Entstehung:
  • Anmerkungen:
  • Beschreibung: <jats:p>The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup>, N<jats:sub>2</jats:sub> from denitrification, O<jats:sub>2</jats:sub>, Cl<jats:sup>−</jats:sup>, and environmental tracers of groundwater age were matched to observations by adjusting the parameters for recharge rate, unsaturated zone travel time, fractions of N and Cl<jats:sup>−</jats:sup> inputs leached to groundwater, O<jats:sub>2</jats:sub> reduction rate, O<jats:sub>2</jats:sub> threshold for denitrification, and denitrification rate. Model results revealed important interactions among biogeochemical and physical factors. Chloride fluxes decreased between the land surface and water table possibly because of Cl<jats:sup>−</jats:sup> exports in harvested crops (averaging 22% of land‐surface Cl<jats:sup>−</jats:sup> inputs). Modeled zero‐order rates of O<jats:sub>2</jats:sub> reduction and denitrification were correlated. Denitrification rates at depth commonly exceeded overlying O<jats:sub>2</jats:sub> reduction rates, likely because shallow geologic sources of reactive electron donors had been depleted. Projections indicated continued downward migration of NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> fronts at sites with denitrification rates &lt;0.25 mg‐N L<jats:sup>−1</jats:sup> yr<jats:sup>−1</jats:sup>. The steady state depth of NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> depended to a similar degree on application rate, leaching fraction, recharge, and NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> and O<jats:sub>2</jats:sub> reaction rates. Steady state total mass in each aquifer depended primarily on the N application rate. In addition to managing application rates at land surface, efficient water use may reduce the depth and mass of N in groundwater because lower recharge was associated with lower N fraction leached. Management actions to reduce N leaching could be targeted over aquifers with high‐recharge and low‐denitrification rates.</jats:p>
  • Zugangsstatus: Freier Zugang