『Abstract
Headwater streams have a demonstrated ability to denitrify a
portion of their nitrate (NO3-)
load but there has not been an extensive consideration of where
in a stream this process is occurring and how various habitats
contribute to total denitrification capability. As part of the
Lotic Intersite Nitrogen Experiment II (LINX II) we measured denitrification
potential in 65 streams spanning eight regions of the US and draining
three land-use types. In each stream, potential denitrification
rates were measured in common substrate types found across many
streams as well as locations unique to particular streams. Overall,
habitats from streams draining urban and agricultural land-uses
showed higher potential rates of denitrification than reference
streams draining native vegetation. This difference among streams
was probably driven by higher ambient nitrate concentrations found
in urban or agricultural streams. Within streams, sandy habitats
and accumulations of fine benthic organic matter contributed more
than half of the total denitrification capacity (mg N removed
m-2 h-1). A particular rate of potential
denitrification per unit area could be achieved either by high
activity per unit organic matter or lower activities associated
with larger standing stocks of organic matter. We found that both
small patches with high rates (hot spots) or more widespread but
less active areas (cool matrix) contributed significantly to whole
stream denitrification capacity. Denitrification estimated from
scaled-up denitrification enzyme assay (DEA) potentials were not
always dramatically higher than in situ rates of denitrification
measured as 15N gas generation following 24-h 15N-NO3 tracer additions. In general, headwater streams
draining varying land-use types have significant potential to
remove nitrate via denitrification and some appear to be functioning
near their maximal capacity.
Keywords: Stream; Denitrification; DEA; Comparative; Substrate-specific;
Comparison of potential with realized denitrification』
Introduction
Methods
Site selection and description
Results
Discussion
Capacity of streams to denitrify
Contribution of particular substrate types
Nitrate influence on DEA
Appendix
References