Effects of Urbanization on Salinity and Selenium Loading in Montrose Arroyo, Western Colorado

Science Center Objects

Salinity and dissolved selenium are known water-quality impairments in the lower Gunnison River watershed of western Colorado. Salinity is a concern because of its adverse effects on agricultural land and equipment, and on municipal and industrial users. The Montrose Arroyo watershed in Montrose, Colorado, contains agricultural and residential areas as well as undeveloped land and has undergone substantial land-use change since the early 1990s. Previous sampling efforts indicated salinity concentrations and loads have remained constant since land-use change began in the early 1990s; however, recent sampling also indicated that dissolved-selenium concentrations and loads have begun to increase.

This project resampled three sites on Montrose Arroyo to determine, on a watershed level, the effects of urbanization on salinity loading. The results of this investigation will quantify how land-use change is affecting salinity loading. These results will be used to calibrate the existing Upper Colorado Detailed Salinity Model (USDSM) for the estimation of the effects of land-use change on salinity loading in areas where agricultural land is being converted to urban land use for the estimation of the effects of land-use change on salinity loading in areas where agricultural land is being converted to urban land use.

During 1988 through 2000 pre and post remediation data were collected at three sites on Montrose Arroyo in western Colorado.  The remediation activity being evaluated was the piping of 8.5 miles of irrigation laterals for the purpose of reducing salinity and selenium loading resulting from the delivery of irrigation water. The effect of the piping of irrigation laterals was to reduce salinity loading about 11 percent. Since 1993, an estimated 75 percent of agricultural land has transitioned to urban land in the lower portion of Montrose Arroyo subbasin, with most of the transition occurring after 2000. The USGS has documented, on a site-specific basis, a decrease in water use and deep percolation associated with the conversion of agricultural lands to urban land use.

The investigation was done in Montrose Arroyo over a three-year period, including 24 months for collecting the streamflow and water-quality data required to quantify the effects of land-use change on salinity loading.

OBJECTIVES:

  1. Determine the effects of urbanization on salinity loading in Montrose Arroyo.
  2. Apply results to estimates of future salinity loading in the Uncompahgre River Basin
  3. Use the information from this study to update the land-use portion of the Upper Colorado Detailed Salinity Model (USDSM).