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This article in JEQ

  1. Vol. 37 No. 3, p. 1034-1050
     
    Received: Dec 20, 2006


    * Corresponding author(s): lpuckett@usgs.gov
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doi:10.2134/jeq2006.0550

Transport and Fate of Nitrate at the Ground-Water/Surface-Water Interface

  1. Larry J. Puckett *a,
  2. Celia Zamorab,
  3. Hedeff Essaidc,
  4. John T. Wilsond,
  5. Henry M. Johnsone,
  6. Michael J. Braytonf and
  7. Jason R. Vogelg
  1. a USGS, 413 National Center, Reston, VA 20192
    b USGS, 6000 J Street, Sacramento, CA 95819
    c Hedeff Essaid, USGS, 345 Middlefield Road, Menlo Park, CA 94205
    d USGS, 5957 Lakeside Boulevard, Indianapolis, IN 46278
    e USGS, 10615 SE Cherry Blossom Drive, Portland, OR 97216
    f USGS, 8987 Yellow Brick Road, Baltimore, MD 21237
    g USGS, 5231 S. 19th Street, Lincoln, NE 68512

Abstract

Although numerous studies of hyporheic exchange and denitrification have been conducted in pristine, high-gradient streams, few studies of this type have been conducted in nutrient-rich, low-gradient streams. This is a particularly important subject given the interest in nitrogen (N) inputs to the Gulf of Mexico and other eutrophic aquatic systems. A combination of hydrologic, mineralogical, chemical, dissolved gas, and isotopic data were used to determine the processes controlling transport and fate of NO3 in streambeds at five sites across the USA. Water samples were collected from streambeds at depths ranging from 0.3 to 3 m at three to five points across the stream and in two to five separate transects. Residence times of water ranging from 0.28 to 34.7 d m−1 in the streambeds of N-rich watersheds played an important role in allowing denitrification to decrease NO3 concentrations. Where potential electron donors were limited and residence times were short, denitrification was limited. Consequently, in spite of reducing conditions at some sites, NO3 was transported into the stream. At two of the five study sites, NO3 in surface water infiltrated the streambeds and concentrations decreased, supporting current models that NO3 would be retained in N-rich streams. At the other three study sites, hydrogeologic controls limited or prevented infiltration of surface water into the streambed, and ground-water discharge contributed to NO3 loads. Our results also show that in these low hydrologic-gradient systems, storm and other high-flow events can be important factors for increasing surface-water movement into streambeds.

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