thumbnail

Whole-stream response to nitrate loading in three streams draining agricultural landscapes

Journal of Environmental Quality

By:
, , , , and
DOI:10.2134/jeq2007.0187

Links

Abstract

Physical, chemical, hydrologic, and biologic factors affecting nitrate (NO3 ) removal were evaluated in three agricultural streams draining orchard/dairy and row crop settings. Using 3-d “snapshots” during biotically active periods, we estimated reach-level NO3  sources, NO3  mass balance, in-stream processing (nitrification, denitrification, and NO3  uptake), and NO3  retention potential associated with surface water transport and ground water discharge. Ground water contributed 5 to 11% to stream discharge along the study reaches and 8 to 42% of gross NO3  input. Streambed processes potentially reduced 45 to 75% of ground water NO3  before discharge to surface water. In all streams, transient storage was of little importance for surface water NO3  retention. Estimated nitrification (1.6–4.4 mg N m−2 h−1) and unamended denitrification rates (2.0–16.3 mg N m−2 h−1) in sediment slurries were high relative to pristine streams. Denitrification of NO3  was largely independent of nitrification because both stream and ground water were sources of NO3  Unamended denitrification rates extrapolated to the reach-scale accounted for <5% of NO3  exported from the reaches minimally reducing downstream loads. Nitrate retention as a percentage of gross NO3  inputs was >30% in an organic-poor, autotrophic stream with the lowest denitrification potentials and highest benthic chlorophyll a, photosynthesis/respiration ratio, pH, dissolved oxygen, and diurnal NO3  variation. Biotic processing potentially removed 75% of ground water NO3  at this site, suggesting an important role for photosynthetic assimilation of ground water NO3  relative to subsurface denitrification as water passed directly through benthic diatom beds.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Whole-stream response to nitrate loading in three streams draining agricultural landscapes
Series title:
Journal of Environmental Quality
DOI:
10.2134/jeq2007.0187
Volume:
37
Issue:
3
Year Published:
2008
Language:
English
Publisher:
ACSESS
Contributing office(s):
Washington Water Science Center
Description:
12 p.
First page:
1133
Last page:
1144
Online Only (Y/N):
N
Additional Online Files (Y/N):
N