A Stable Isotope Tracer Study of the Influences of Adjacent Land Use and Riparian Condition on Fates of Nitrate in Streams

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  • The influence of land use on potential fates of nitrate (NO3-) in stream ecosystems, ranging from denitrification to storage in organic matter, has not been documented extensively. Here, we describe the Pacific Northwest component of Lotic Intersite Nitrogen eXperiment, phase II (LINX II) to examine how land-use setting influences fates of NO3- in streams. We used 24 h releases of a stable isotope tracer ((NO3)-N-15-N) in nine streams flowing through forest, agricultural, and urban land uses to quantify NO3- uptake processes. NO3- uptake lengths varied two orders of magnitude (24-4247 m), with uptake rates (6.5-158.1 mg NO3-N m(-2) day(-1)) and uptake velocities (0.1-2.3 mm min(-1)) falling within the ranges measured in other LINX II regions. Denitrification removed 0-7% of added tracer from our streams. In forest streams, 60.4 to 77.0% of the isotope tracer was exported downstream as NO3-, with 8.0 to 14.8% stored in wood biofilms, epilithon, fine benthic organic matter, and bryophytes. Agricultural and urban streams with streamside forest buffers displayed hydrologic export and organic matter storage of tracer similar to those measured in forest streams. In agricultural and urban streams with a partial or no riparian buffer, less than 1 to 75% of the tracer was exported downstream; much of the remainder was taken up and stored in autotrophic organic matter components with short N turnover times. Our findings suggest restoration and maintenance of riparian forests can help re-establish the natural range of NO3- uptake processes in human-altered streams.
  • Keywords: Oregon, Organic matter storage, Streams, Spiraling, Land use, N-15, Isotope tracer, Denitrification, Nitrogen
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  • Sobota, D. J., Johnson, S. L., Gregory, S. V., & Ashkenas, L. R. (2012). A stable isotope tracer study of the influences of adjacent land use and riparian condition on fates of nitrate in streams. Ecosystems, 15(1), 1-17. doi: 10.1007/s10021-011-9489-8
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  • 15
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  • 1
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  • LINX II was supported by a grant from the NSF Ecosystems Program to Oak Ridge National Laboratory (NSFDEB #0111410). The H.J. Andrews Experimental Forest research program, funded by the National Science Foundation’s Long-Term Ecological Research Program (DEB 08-23380), the US Forest Service Pacific Northwest Research Station, and Oregon State University provided additional support. A graduate fellowship was provided to DJS through the NSF Ecosystem Informatics IGERT program (NSF award #0333257) at Oregon State University.
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