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Nitrogen chemistry of subsurface storm runoff on forested Canadian Shield hillslopes
Author(s) -
Hill A. R.,
Kemp W. A.,
Buttle J. M.,
Goodyear D.
Publication year - 1999
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/1998wr900083
Subject(s) - throughfall , surface runoff , macropore , hydrology (agriculture) , subsurface flow , soil water , environmental science , storm , nitrate , biogeochemistry , infiltration (hvac) , environmental chemistry , soil science , geology , groundwater , chemistry , ecology , mesoporous material , biochemistry , oceanography , geotechnical engineering , biology , catalysis , thermodynamics , organic chemistry , physics
The nitrogen dynamics of storm runoff was studied using throughfall trenches on slopes with thin soils in a white pine forest catchment near Dorset, Ontario. Hydrologic data were combined with analysis of isotopic signatures and nitrogen chemistry in throughfall, soil water, and hillslope runoff. Two hypotheses were tested: (1) macropore preferential flow pathways are a source of nitrate flushing in storm runoff, and (2) the nitrogen chemistry of subsurface storm flow is controlled by the mixing of event water fluxes via macropores with preevent soil water. Most flow occurred at the soil‐bedrock interface on the slopes, and the use of 18 O indicated that a considerable fraction of event water moved vertically to bedrock via preferential flow paths. Despite high levels of inorganic N in throughfall, subsurface runoff N losses during autumn storms were dominated by dissolved organic nitrogen, and little nitrate flushing occurred via preferential flow paths. Comparisons of observed NO 3 ‐ and NH 4 + concentrations versus concentrations predicted from the mixture of event and preevent water in subsurface flow did not support hypothesis 2 and instead indicated depletion of inorganic N. Low rates of N mineralization and negligible nitrification in surface 0–0.1 m soil during June–October suggested high biological utilization of a limited soil N supply. Laboratory experiments in which soil cores were leached with solutions containing NO 3 ‐ and bromide confirmed that the organic Ae horizon was a sink for NO 3 ‐ . These data suggest that the biogeochemistry of the organic horizon can regulate patterns of inorganic N loss in subsurface runoff moving by preferential flow pathways in forest soils.