Open AccessSpatial patterns of soil nitrification and nitrate export from forested headwaters in the northeastern United States
Author(s) -
Ross Donald S.,
Shanley James B.,
Campbell John L.,
Lawrence Gregory B.,
Bailey Scott W.,
Likens Gene E.,
Wemple Beverley C.,
Fredriksen Guinevere,
Jamison Austin E.
Publication year - 2012
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2011jg001740
Subject(s) - nitrification , watershed , transect , environmental science , hydrology (agriculture) , nitrate , deposition (geology) , streams , nitrogen , ecology , geology , sediment , chemistry , biology , geomorphology , computer network , geotechnical engineering , organic chemistry , machine learning , computer science
Nitrogen export from small forested watersheds is known to be affected by N deposition but with high regional variability. We studied 10 headwater catchments in the northeastern United States across a gradient of N deposition (5.4 − 9.4 kg ha −1 yr −1 ) to determine if soil nitrification rates could explain differences in stream water NO 3 − export. Average annual export of two years (October 2002 through September 2004) varied from 0.1 kg NO 3 − ‐N ha −1 yr −1 at Cone Pond watershed in New Hampshire to 5.1 kg ha −1 yr −1 at Buck Creek South in the western Adirondack Mountains of New York. Potential net nitrification rates and relative nitrification (fraction of inorganic N as NO 3 − ) were measured in Oa or A soil horizons at 21–130 sampling points throughout each watershed. Stream NO 3 − export was positively related to nitrification rates ( r 2 = 0.34, p = 0.04) and the relative nitrification ( r 2 = 0.37, p = 0.04). These relationships were much improved by restricting consideration to the 6 watersheds with a higher number of rate measurements (59–130) taken in transects parallel to the streams ( r 2 of 0.84 and 0.70 for the nitrification rate and relative nitrification, respectively). Potential nitrification rates were also a better predictor of NO 3 − export when data were limited to either the 6 sampling points closest to the watershed outlet ( r 2 = 0.75) or sampling points <250 m from the watershed outlet ( r 2 = 0.68). The basal area of conifer species at the sampling plots was negatively related to NO 3 − export. These spatial relationships found here suggest a strong influence of near‐stream and near‐watershed‐outlet soils on measured stream NO 3 − export.