Cross-stream comparison of substrate-specific denitrification potential

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 h). 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 S. E. G. Findlay (&) A. J. Burgin Cary Institute of Ecosystem Studies, Millbrook, NY 12545, USA e-mail: [email protected] P. J. Mulholland Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA S. K. Hamilton Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060, USA J. L. Tank Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA M. J. Bernot Department of Biology, Ball State University, Muncie, IN 47306, USA C. L. Crenshaw Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA W. K. Dodds Division of Biology, Kansas State University, Manhattan, KS 66506, USA N. B. Grimm School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA W. H. McDowell J. D. Potter Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH 03824, USA D. J. Sobota Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331, USA 123 Biogeochemistry (2011) 104:381–392 DOI 10.1007/s10533-010-9512-8