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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
F01010,
doi:10.1029/2004JF000124,
2005
Nitrogen and carbon flow from rock to water: Regulation through soil biogeochemical processes, Mokelumne River watershed,
California, and Grand Valley, Colorado
JoAnn M. Holloway
U.S. Geological Survey, Boulder, Colorado, USA
Richard L. Smith
U.S. Geological Survey, Boulder, Colorado, USA
Abstract
Soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse
gas N2O, an intermediate product from the reduction of NO3
− to N2. In this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock
acting as a nonpoint source of nitrogen, testing the hypothesis that nitrate leaching to stream water is in part regulated
by denitrification. Two sites, one in a Mediterranean climate and the other in an arid climate, were investigated to understand
the interplay between carbon and denitrification potential. Both sites included carbonaceous bedrock with relatively high
nitrogen concentrations (>1,000 mg N kg−1) and had low background nitrogen concentrations in surface and groundwater. There was a net accumulation of carbon and nitrogen
in soil relative to the corresponding bedrock, with the exception of carbonaceous shale from the arid site. There the concentration
of carbon in the soil (15,620 mg C kg−1) was less than the shale parent (22,460 mg C kg−1), consistent with the bedrock being a source of soil carbon. Rates of denitrification potential (0.5–83 μg N kg−1 hr−1) derived from laboratory incubations appeared to be related to the ratio of dissolved organic carbon and nitrate extracted
from soils. These data indicate that microbial processes such as denitrification can help maintain background nitrogen concentrations
to tens of μM N in relatively undisturbed ecosystems when nitrogen inputs from weathering bedrock are accompanied by sufficient
organic carbon concentrations to promote microbial nitrogen transformations.
Received 21
January
2004;
accepted 3
January
2005;
published 22
February
2005.
Keywords: weathering;
soil;
denitrification;
carbon.
Index Terms: 0469 Biogeosciences: Nitrogen cycling; 0486 Biogeosciences: Soils/pedology (1865); 0496 Biogeosciences: Water quality; 1858 Hydrology: Rocks: chemical properties; 1886 Hydrology: Weathering (0790, 1625).
Read Full Article (file size: 642391 bytes) Cited by
Citation: Holloway, J. M., and R. L. Smith
(2005),
Nitrogen and carbon flow from rock to water: Regulation through soil biogeochemical processes, Mokelumne River watershed,
California, and Grand Valley, Colorado,
J. Geophys. Res.,
110,
F01010,
doi:10.1029/2004JF000124.
This paper is not subject to U.S. copyright. Published in 2005 by the
American Geophysical Union.
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