『Summary
The effects of land use and land use change on stream nitrate
are poorly understood. While case studies have been presented,
most process work has been done in areas with one land use (minimally
distributed or agricultural) and areas with substantial atmospheric
deposition. In this paper we present results from three neighboring
headwater catchments in western Oregon with similar (low) atmospheric
deposition, size, and geology but with different, spatially consistent
land use expressions: forest, agriculture, and residential. The
climate in western Oregon has a distinct pattern of a three-month
rainless period in the summer, a wetting up with many storms in
the fall and winter, and a decrease of storms in the spring. We
investigate how human activity alters the export of nitrate, whether
the input of nitrate changes throughout the year which may affect
storm response (i.e., depletion of soil water nitrate, addition
of fertilizer, etc.), and how the changing contribution of source
waters throughout the year affects streamflow concentrations.
Our results showed marked differences in export rates between
the three catchments. The forested catchment showed minimal export
for three monitored storms (fall, winter, spring) through the
seasonal wetting up of the catchments, and the residential catchment
showed high export for all three storms. While the agricultural
catchment displayed elevated export in the fall (similar to the
residential catchment), exports decreased progressively throughout
the rainy period (following late summer manure and green bean
application). Overall, our results of storm event nitrate concentrations
suggest that varying nitrate inputs have a large affect on nitrate
dynamics. While within-storm nitrate concentration response patterns
in the residential catchment were the same as the patterns in
the reference forested catchment (a “concentration” pattern throughout
the year), a “dilution” pattern was observed in the fall and winter
and a “concentration” pattern was observed in the spring in the
agricultural catchment.
Keywords: Catchment hydrology; Nitrate; Runoff generation; Stream
chemistry; Land use』
Introduction
Site description
Forested catchment
Agricultural catchment
Residential catchment
Methods
Results
Hydrologic response to storm events
Nitrate response to storm events
Discussion
Seasonal trends
Sources of streamflow
Hydrology vs. land use
Flushing of nitrate
Implications for watershed development
Conclusions
Acknowledgements
References