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This article in JEQ

  1. Vol. 35 No. 6, p. 2425-2432
    Received: Apr 25, 2006

    * Corresponding author(s): rhale01@gmail.com
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Chloride Effects on Nitrogen Dynamics in Forested and Suburban Stream Debris Dams

  1. Rebecca L. Hale *a and
  2. Peter M. Groffmanb
  1. a Hampshire College, 895 West St., Amherst, MA 01002-5001
    b Inst. of Ecosystem Studies, 65 Sharon Turnpike, P.O. Box AB, Millbrook, NY 12545


Organic debris dams (accumulations of organic material) can function as “hotspots” of nitrogen (N) processing in streams. Suburban streams are often characterized by high flows that prevent the accumulation of organic debris and by elevated concentrations of solutes, especially nitrate (NO3 ) and chloride (Cl). In this study we (1) studied the effects of urbanization on the extent and characteristics of debris dams in large and small streams and (2) evaluated the effects of NO3 and Cl on rates of N cycle processes in these debris dams. In some suburban streams debris dams were small and rare, but in others factors that reduce the effects of high stream flows fostered the maintenance of debris dams. Ambient denitrification enzyme activity (DEA) in these suburban and forested streams was positively correlated with stream NO3 concentrations. In laboratory microcosms, DEA in debris dam material from a forested reference stream was increased by NO3 additions. Chloride additions constrained the response of DEA to NO3 additions in material from the forested stream, but had no effect on DEA in material from streams with a history of high Cl levels. Chloride additions changed the sign of net N mineralization from negative (consumption of inorganic N) to positive in debris dam material from the forested reference stream, but had no effect on net mineralization in material from streams with a history of exposure to Cl Understanding the factors regulating the maintenance and N cycling activity of organic debris, and incorporating them into urban stream management plans could have important effects on N dynamics in suburban watersheds.

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