Get access

Nitrogen Sources and Sinks Within the Middle Rio Grande, New Mexico1

Authors

  • Gretchen P. Oelsner,

    1. Respectively, Doctoral Candidate and Research Assistant, Associate Professor, and Adjunct Assistant Professor and Assistant Director of Science, Department of Hydrology and Water Resources, 1133 E. James E. Rogers Way, University of Arizona, Tucson, Arizona 85721
    Search for more papers by this author
  • Paul D. Brooks,

    1. Respectively, Doctoral Candidate and Research Assistant, Associate Professor, and Adjunct Assistant Professor and Assistant Director of Science, Department of Hydrology and Water Resources, 1133 E. James E. Rogers Way, University of Arizona, Tucson, Arizona 85721
    Search for more papers by this author
  • James F. Hogan

    1. SAHRA, Sustainability of Semi-Arid Hydrology and Riparian Areas, P.O. Box 210158-B, University of Arizona, Tucson, Arizona 85721-0158 (E-Mail/Oelsner: goelsner@hwr.arizona.edu).
    Search for more papers by this author

  • 1

    Paper No. J05215 of the Journal of the American Water Resources Association (JAWRA). Discussions are open until February 1, 2008.

Abstract

Abstract:  Relationships between discharge, land use, and nitrogen sources and sinks were developed using 5 years of synoptic sampling along a 300 km reach of the Rio Grande in central New Mexico. Average river discharge was higher during 2001 and 2005 “wet years” (15 m3/s) than during the drought years of 2002-04 “dry years” (8.9 m3/s), but there were no differences in nitrogen loading from wastewater treatment plants (WWTPs) which were the largest and most consistent source of nitrogen to the river (1,330 kg/day). Average total dissolved nitrogen (TDN) concentrations remained elevated for 180 km downstream of the Albuquerque WWTP averaging 1.2 mg/l in wet years and 0.52 mg/l in dry years. Possible explanations for the constant elevated TDN concentrations downstream of the major point source include reduced nitrogen retention capacity, minimal contact with riparian or channel vegetation, large suspended sediment loads, and low algal biomass. Somewhat surprisingly, agricultural return flows had lower average nitrogen concentrations than river water originally diverted to agriculture in both wet (0.81 mg/l) and dry years (0.19 mg/l), indicating that the agricultural system is a sink for nitrogen. Lower average nitrogen concentrations in the river during the dry years can be explained by the input of agricultural returns which comprise the majority of river flow in dry years.

Ancillary