NITROGEN AND PHOSPHORUS IN SURFACE WATERS OF THE UPPER COLORADO RWER BASIN¹

Abstract

As part of a basinwide water-quality study, nitrogen and phosphorus data for the Upper Colorado River Basin from the Colorado-Utah State line to the Continental Divide were analyzed for spatial distributions, concentrations associated with various land uses, and temporal trends. Nitrogen and phosphorus concentrations generally increased in a downstream direction. Some nutrient concentrations were elevated at some sites in the upper parts of the basin in areas influenced by increasing urbanization. Sites were grouped according to land use and site type, and median nutrient concentrations were compared among groups. Sites within the agricultural areas of the basin generally had the highest concentrations of nitrogen and phosphorus; concentrations for mainstem, tributary, and urbanization sites were slightly lower than for the agricultural sites. Background sites, or sites with minimal land-use impacts, had very low median nutrient concentrations. Several sites with long-term data were analyzed for temporal trends in concentrations. Several statistically significant downward trends of low and moderate magnitude were observed for nitrogen and phosphorus species. No upward trends were observed in the data at any site.(KEY TERMS: water quality; nutrients; nitrogen; phosphorus; Colorado River.)

Nitrogen and carbon flow from rock to water: Regulation through soil biogeochemical processes, Mokelumne River watershed, California, and Grand Valley, Colorado

“…The geology of Grand Valley is dominated by nitrogen‐rich Mancos Shale, which has the potential to contribute to natural background nitrogen concentrations in surface and groundwater. The highest nutrient (nitrogen and phosphorus) concentrations in the Upper Colorado River Basin, which extends from the Continental Divide in Colorado to the Utah‐Colorado border, are generally in agricultural areas, including the Grand Valley [ Spahr and Wynn , 1997]. The flux of N‐NO 3 in the Colorado River at the Utah‐Colorado border (UC (Figure 2)), calculated from data compiled through the U.S. Geological Survey National Water‐Quality Assessment Program [ Butler et al , 1996] is 0.049 kg N ha −1 yr −1 , with 0.046 kg N ha −1 yr −1 estimated for Salt Creek (SC (Figure 2)).…”

HYDROLOGICAL AND GEOCHEMICAL TRENDS AND PATTERNS IN THE UPPER RIO GRANDE, 1975 TO 19991

“…When no data in a month were available, no monthly median was recorded. Monthly medians across each calendar year were then used to identify an annual median (Spahr and Wynn, 1997). The number of months throughout the 25-year sampling period in which a monthly median was available was fairly consistent across all parameters at each station, but there was some variation among stations (Table 2).…”

“…Numerous studies of trend and/or spatial patterns in river water quality using dissolved and suspended components (rather than sediment cores) appear in the literature. They include studies ranging from temporal scales of one to five years and spatial scales smaller than a few dozen square kilometers (Aulenbach et al, 1996;Bolstad and Swank, 1997;Mallin et al, 2000) to temporal scales up to 20 years and ranging in spatial scale up to hundreds of thousands of square kilometers (Hay and Campbell, 1990;Zampella, 1994;Robinson et al, 1996;Trench, 1996;Edmonds and Blew, 1997;Lurry and Dunn, 1997;Spahr and Wynn, 1997;Peters et al, 1999;Glasgow and Burkholder, 2000).…”

Nitrogen and phosphorus data for surface water in the Upper Colorado River basin, Colorado, 1980-94

“…This report documents, summarizes, and provides on 3.5-m diskette the surface-water nutrient data that were collected from January 1980 through August 1994. Interpretive analyses of the data are in Spahr and Wynn (1997). Ancillary data for parameters, such as water temperature, streamflow, specific conductance, dissolved oxygen, pH, and alkalinity, also are included on the data diskette, if available, but are not summarized in this report.…”