Regulation of Nitrate‐N Release from Temperate Forests: A Test of the N Flushing Hypothesis

Regulation of Nitrate‐N Release from Temperate Forests: A Test of the N Flushing Hypothesis During the past decade, significant spatial and temporal variability in the release of nitrate‐nitrogen (N) from catchments in a sugar maple forest in central Ontario was observed. To explain this variability, we tested the flushing hypothesis (Hornberger et al., 1994), where, when the soil saturation deficit is high, N accumulates in the upper layers of the soil and, as the soil saturation deficit decreases, the formation of a saturated subsurface layer flushes N from the upper layers of the soil into the stream. We used the Regional Hydro‐Ecological Simulation System to simulate water, carbon, and N dynamics. A N flushing index was modeled as S/S30, the ratio of the current day saturation deficit to the previous 30‐day average saturation deficit. A N source index was modeled as the ratio of N supply/demand. The relationship between the simulated N indices and the observed release of N indicated two mechanisms for the release of N from catchments: (1) a N flushing mechanism, where the N‐enriched upper layer of the soil is flushed, after a period of low demand for N by the forest (e.g., during spring snowmelt and autumn stormflow, the water table rising into previously unsaturated parts of a N‐enriched soil profile) or after a period of high demand for N by the forest (e.g., during summer droughts, the water table rising into previously saturated parts of a N‐impoverished soil profile following a period of enhanced rates of nitrification); and (2) a N draining mechanism, where spring snowmelt recharge of the groundwater translocates N from the upper layer of the soil into deeper hydrological flow pathways that are released slowly over the year. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Water Resources Research Wiley

Regulation of Nitrate‐N Release from Temperate Forests: A Test of the N Flushing Hypothesis

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Publisher
Wiley
Copyright
Copyright © 1996 by the American Geophysical Union.
ISSN
0043-1397
eISSN
1944-7973
D.O.I.
10.1029/96WR02399
Publisher site
See Article on Publisher Site

Abstract

During the past decade, significant spatial and temporal variability in the release of nitrate‐nitrogen (N) from catchments in a sugar maple forest in central Ontario was observed. To explain this variability, we tested the flushing hypothesis (Hornberger et al., 1994), where, when the soil saturation deficit is high, N accumulates in the upper layers of the soil and, as the soil saturation deficit decreases, the formation of a saturated subsurface layer flushes N from the upper layers of the soil into the stream. We used the Regional Hydro‐Ecological Simulation System to simulate water, carbon, and N dynamics. A N flushing index was modeled as S/S30, the ratio of the current day saturation deficit to the previous 30‐day average saturation deficit. A N source index was modeled as the ratio of N supply/demand. The relationship between the simulated N indices and the observed release of N indicated two mechanisms for the release of N from catchments: (1) a N flushing mechanism, where the N‐enriched upper layer of the soil is flushed, after a period of low demand for N by the forest (e.g., during spring snowmelt and autumn stormflow, the water table rising into previously unsaturated parts of a N‐enriched soil profile) or after a period of high demand for N by the forest (e.g., during summer droughts, the water table rising into previously saturated parts of a N‐impoverished soil profile following a period of enhanced rates of nitrification); and (2) a N draining mechanism, where spring snowmelt recharge of the groundwater translocates N from the upper layer of the soil into deeper hydrological flow pathways that are released slowly over the year.

Journal

Water Resources ResearchWiley

Published: Nov 1, 1996

References

  • Overview of a simple model describing variation of dissolved organic carbon in an upland catchment
    Boyer, Boyer; Hornberger, Hornberger; Bencala, Bencala; McKnight, McKnight
  • Short term fluctuations in dissolved organic matter concentrations in streamflow draining a forested watershed and their relation to the catchment budget
    Foster, Foster; Grieve, Grieve
  • Nitrogen fixation: Anthropogenic enhancement‐environmental response
    Galloway, Galloway; Schlesinger, Schlesinger; Levy, Levy; Michaels, Michaels; Schnoor, Schnoor
  • Shenandoah Watershed Study: Calibration of a topography‐based, variable contributing area hydrological model to a small forested catchment
    Hornberger, Hornberger; Beven, Beven; Cosby, Cosby; Sappington, Sappington
  • Maximum conductances for evaporation from global vegetation types
    Kelliher, Kelliher; Leuning, Leuning; Raupach, Raupach; Schulze, Schulze
  • A rationale for old water discharge through macropores in a steep, humid catchment
    McDonnell, McDonnell
  • The role of nitrate in the acidification of streams in the Catskill Mountains of New York
    Murdoch, Murdoch; Stoddard, Stoddard
  • Runoff production in a forested, shallow soil, Canadian Shield basin
    Peters, Peters; Buttle, Buttle; Taylor, Taylor; LaZerte, LaZerte

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